Tin [1st ed.] 978-3-540-08234-7;978-3-662-10559-7

Table of contents :
Front Matter ....Pages I-XV
Introduction (J. W. Price)....Pages 1-2
Detection (J. W. Price)....Pages 3-7
Gravimetric Methods (J. W. Price)....Pages 8-11
Volumetric Analysis (R. Smith)....Pages 12-42
Photometric Methods (J. W. Price)....Pages 43-60
Electrochemical Methods (J. W. Price)....Pages 61-65
Solvent Extraction (R. Smith)....Pages 66-79
Atomic Absorption Spectroscopy (R. Smith)....Pages 80-95
Emission Spectroscopy (R. Smith)....Pages 96-125
X-ray Fluorescence (R. Smith)....Pages 126-144
Radiochemical & Mossbauer Methods (J. W. Price)....Pages 145-148
Analysis of Tin Ores & Concentrates (R. Smith)....Pages 149-172
Analysis of Secondary Materials and Intermediates (R. Smith)....Pages 173-179
Analysis of Tin Alloys and Solders (R. Smith)....Pages 180-191
Analysis of Ingot Tin (R. Smith)....Pages 192-198
Tin in Copper-Base Alloys (R. Smith)....Pages 199-204
Tin in Ferrous Alloys (J. W. Price)....Pages 205-208
Tinplate (J. W. Price)....Pages 209-213
Organotin Compounds (J. W. Price)....Pages 214-247
Tin and Tin Alloy Plating Solutions (J. W. Price)....Pages 248-252
Tin Chemicals (J. W. Price)....Pages 253-255
Back Matter ....Pages 257-264

Citation preview

Handbuch der analytischen Chemie

John W. Price · R. Smith

Tin

HANDBUCH DER

ANALYTISCH EN CHEMIE HERAUSGEGEBEN VON

W. FRESENIUS WIESBADEN

DRITTER TEIL

HANDBOOK OF

ANALYTICAL CHEMISTRY EDITED BY

W. FRESENIUS WIESBADEN

PARTIII

VOLUME 4ay

TIN

SPRINGER-VERLAG BERLIN HEIDELBERG GMBH 1978

TIN BY

J. W. PRICE

AND R. SMITH

WITH 31 FIGURES

SPRINGER-VERLAG BERLIN HEIDELBERG GMBH 1978

]. W. PRICE and R. SMITH 51 Tudor Gardens London W3 ODU, Great Britain

ISBN 978-3-662-10559-7 (eBook) ISBN 978-3-662-10561-0 DOI 10.1007/978-3-662-10559-7 Library of Congress Cataloging in Publicarion Daca (Revised). Main entry und~ eitle: Handbuch der analytischen Chemie. Bach volume has also speciaJ t p. 195o- ed. by Wilhdm Fresenius and Gerhart Jande. Indudc:s bibliographics. CONTENTS: 2. T. Qualitative Nachweisverf.thren. Bd. 1 a.

Elemente der asten Hauptgruppe (einschl. Ammonium) Wasserstoff, Lithium, Natrium, Kalium, Ammonium, Rubidium, Eacsium, bc:ub. von H.

Schilling, H. Spandau und 0. Tomkok. 1944. Bd. I b. Elemente der ecsten Nebengruppe, Kupfer, Silber, Gold, bearb. von H. Bode. 1955 (etc.]. I. O,emisrry, An•lyric. I. Fresenius, Remigius, 187S- ed. I!. J•nder, Gerhan, 1892- 1961, ed. III. Fresenius, Wilhelm, 1913- ed. QD75.H25 543 41-36317 '""·

Das Werk ist urhdxrrechclich geschützt. Die dadurch begründeten Rechte:, insbesondere die der Übersetzung, des Nachdrucks, der Enmahme von Abbildungen, der Funksendung, der Wiederg.be auf phoromechmischem oder ähnlichem Wege und der Speicherung in Darenverarbeirungsanhgen bleiben, auch bei nur auszugsweiser Verwertung vorbehalten. Bei Vervielfliltigungen fiir gewerbliche Zwecke ist gemäߧ 54 UrhG eine Vergütung an

den Verlag zu z:ahlen, deren Höhe mit dem Verlag zu vereinbaren ist. Die Wiedergabe von Gebrauchsnamen, Handdsnamcn, Warenbezeichnungen

usw. in diesem Buche berechtigt auch ohne besondere Kennzeichnung nicht zu der Annahme, daß solche Namen im Sinne der Warenzeichen· und Markenschucz·Geseczgebung als fn:i zu betr.t.Chten wären und daher von jedermann benutzt werden dürften. © by Springer-Verlag Berlin Heidelberg 1978 Ursprünglich erschienen bei Springer-Verlag Berlin Heidelberg New York 1978

Sacz: V:uia-Compnsecsacz, Hcidelberg

Druck. und Buchbindead>c:icen: K. Triltsch, Würzburg 2ll2/3120-l43210

PREFACE

Tin, one of the very few metals known in antiquity, owed its importance in early times to its ability to harden copper, the usefulness of the resulting alloy for the production of weapons and tools being so great that historians now refer to a 'Bronze Age'. Since those times, tin has continued tobe in demand, mainly in the metallic form for the production of alloys or as a coating on steel. In the early stages of tin production, small parcels of ore would be smel ted and the product retumed to the miner for sale. As the scale of refming became larger, the smelting of single parcels became impracticable and the smelter developed assaying methods, usually based on a miniature smelting operation on a representative sample, carried out in a crucible with carbon or, later, cyanide as reducing agent. Today rapid and accurate methods of analysis have been developed and tin analysis is no longer the sole province of the tin miner and smelter but is an essential service in many of today's industries. It is mainly to industrial analysts concemed with tin in one form or another that this book is directed. In addition to the metallurgical uses of tin, accounts have been· included of the analysis of electroplating solutions and of organotin compounds and it is hoped that the latter will be of help to those working in this new field. No attempt has been made to catalogue all published work but rather to reflect as far as possible current methods. lt is inevitable in any work of this nature that the authors' own experience must influence and perhaps bias the selection of material. This is particularly so in those areas where there are few relevant publications, and here the authors have relied on previously unpublished work. An aspect of analysis in general that has hitherto been somewhat neglected is that of sampling and sample preparation, and there is little doubt that, with many of the materialsdealt with here, sampling requires more attention than does the analysis itself. The authors have therefore included sampling methods as part of the work. The sampling methods given here have in large part been drawn from accepted practice within the authors' experience.

ACKNOWLEDGEMENT

The Authors wish to express their thanks to all those who have assisted in the preparation of this book. One ofus (J.W.P.) would like to thank Dr. D.A. Robins, Director of the Tin Research Institute, for library facilities at the Institute and also Miss A.H. Chapman, who has carried out the experimental work in the Analytical Dept. of the Institute over a period years, for helpful discussions. One ofus (R.S.) wishes to thank the Directors of Capper Pass Ltd. for permission to publish some of the work referred to in the text and for their personal interest during the preparation of the manuscript. In addition, he thanks his colleagues past and present at Capper Pass whose experience has been a steady foundation upon which to write, and especially Messrs. P. Fishand J. Harding for their helpful comrnents. Finally, the authors offer their grateful thanks to their wives Doris Price and Beryl Smith for typing the manuscript, and for their help and encouragement during the course of this work. J.W. Price R.Smith

CONTENTS

Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 2 Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. 2. 3. 4. 5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ores and Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slags and Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aqueous Salutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metals and Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 .1. Chernical Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2. Tin-base and Lead-base Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3. Iron and Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4. Aluminium and Magnesium Alloys. . . . . . . . . . . . . . . . . . . . . . . . . 6. Surface Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. Organic Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. .. .. .. .. .. .. .. .. .. .. _.

Chapter 3 Gravimetrie Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Precipitation of Hydrous tin(IV) Oxide . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2. Precipitation of Metastarrnie Acid . -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Precipitation as Sulphide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Reducing Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 .1. Precipitation of Hg 2 Cl 2 , . • . • • . • • . • • . • • • • • • • • • • • . • • • • • • • • . 4.2. Preeipitation of Se . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Precipitation ofTin(IV) Selenite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Precipitation with Organic Reagents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Cupferron and Neo-cupferron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 .2. N-benzylphenylhydroxylarnine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3. Ammonium Benzoate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4. Arsonic Acid Derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5. Tannin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6. 8-Hydroxyquinoline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 3 3 4 4 5 5 6 6 6 6 7 7 8 8 8 9 9 9 9 10 10 10 10 10 10 11 11 11

Chapter 4 Volumetrie Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1. Iodometrie Titrati:ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1.1. 1.2. 1.3. 1.4. 1.5.

Introduction and Basic Method . . . . . . . Removal of Impurities with Iron Powder Wet Reduction. . . . . . . . . . . . . . . . . . Effect of Air on Stannous Salutions. . . . Iodirre and Iodate Titrants . . . . . . . . . .

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12 14 15 19 21

X

1.6. End-Point Delection .................................... 23 1. 7. Standardisation ....................................... 24 1.8. Interferences ......................................... 26 2. Other Redox Titrants ....................................... 31 2.1. Potassium Bromate and Related Compounds .................... 31 2.2. Potassium Ferricyanide .................................. 32 2.3. Ferric Chloride ....................................... 32 2.4. Other Titrants ........................................ 33 2.5. Iodine Monochloride Titrations ............................. 34 3. Complexometric Titrations .................................... 35 3.1. Direct Titrations ...................................... 35 3 .2. Back Titrations .................................. - .... 37 3.3. Indirect Titrations ..................................... 38 3.4. Displacement Titrations ............•..................... 39 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Chapter 5 Photometrie Methods . . . . . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . 43 1. Introduction ............................................. 43 2. Methods of Separation of Small Amounts of Tin ..................... 44 2.1. Distillation .......................................... 44 2.2. Extraction into an Organic Solvent .......................... 45 2.3. Precipitation, Classical Methods ............................ 45 2.4. Ion-exchange ......................................... 46 3 . Reagents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.1. Introduction ......................................... 46 3.2. Dithiol ............................................. 48 3.3. Phenylfluorone ....................................... 49 3.4. Catechol Violet ....................................... 51 3.5. Gallein ............................................. 53 3.6. Quercetin ........................................... 54 3.7. Haematoxylin and Haematin .............................. 54 3.8. 4-Hydroxy-3-nitrophenyl Arsonic Acid ........................ 55 4. Fluorimetric Methods ....................................... 56 References .............................................. .. 57 Chapter 6 Electrochemical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

1. Introduction ............................................. 61 2. E1ectrodeposition .......................................... 61 3. Controlled Potential Electrolysis;Cou1ometric Analysis ................. 61 4. Po1arography ............................................. 62 5. Amperometry ............................................ 63 6. Anodic Stripping Voltammetry ................................. 64 References .............................................. .. 65 Chapter 7 Solvent Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

1 . Ion Association Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 1.1. Fluoride Extractions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 1.2. Chloride Extractions .................................... 67 1.3. Bromide Extractions .................................... 67 1.4. Iodide Extractions ..................................... 69 1.5. Thiocyanate Extractions ................................. 70 1.6. High Molecular Weight Amines ............................. 71

XI

2. Phosphorus Containing Extractants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Alkylphosphoric Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Alkylthiophosphoric Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Alkyldithiophosphoric Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Trialkylphosphine Oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Chelate Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 .1. Acetylacetone and Related Compounds . . . . . . . . . . . . . . . . . . . . . . . 3.2. 8 Hydroxyquinoline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Cupferron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4. Hydroxamic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5. Dithizone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 .6. Dithiocarbamates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7. Xanthates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8. Toluene 3, 4 Dithiol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9. Other Extractants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7I 7I 72 72 73 73 73 74 74 75 75 76. 77 77 78 78

Chapter 8 Atomic Absorption Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 80

I. Atomic Absorption Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1. Absorption Wavelengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I.2. Choice of Flarnes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3. Interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Atomic Flame Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Molecular Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Chemiluminescence Atomic Emission . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Thermally Excited Atomic Emission . . . . . . . . . . . . . . . . . . . . . . . . . 3. Atomic Fluorescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Electrotherrnal Atomisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

80 80 80 82 83 83 84 85 86 87

5. Separation Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Solvent Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 .2. Coprecipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3. Sublimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 .4. Other Separations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

87 87 89 90 9I 92 94

Chapter 9 Emission Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

I. Spectral Characteristics of Tin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 I .I. Molecular Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 I.2. Atomic Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 1.3. Atomic Line Interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 2. Types of Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 03 3. Behaviour of Tin in Are Discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 04 3.1. Ionisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I04 3 .2. Volatilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 3 .3. Interna! Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 4. Metallurgical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 4 .1. Aluminium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 4.2. Antimony . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 4 .3. Arsenic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 08 4.4. Bismuth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

XII

4.5. Cadmium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6. Copper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7. Gallium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8. Hafnium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9. Irons, Steels, Ferroalloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10. Lead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11. Manganese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12. Nickel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13. Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14. Selenium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.15. Silver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.16. Tantalum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.17. Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.18. Thallium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.19. Tungsten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.20. Yttrium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.21. Zinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Geochernical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Miscellaneous Inorganic Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. Organic Materials, Foodstuffs, Biological Specimens . . . . . . . . . . . . . . . . . . 8. Environmental Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

109 109 111 111 111 113' 114 114 115 115 115 115 116 116 116 116 116 117 119 121 122 122

Chapter 10 X-Ray Fluorescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1. Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2. Spectral Characteristics of Tin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Ores and Concentrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Direct Analysis of Powders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Fusion Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Non-Dispersive Instruments . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . 3. Solders and Whitemetals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Structure ofSolders, Segregation, Ageing . . . . . . . . . . . . . . . . . . . . . 3.2. SampiePreparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 .3. Standards Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 .4. Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Copper Base Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Other Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ' . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

126 126 126 126 128 128 131 132 134 134 136 13 7 138 141 142 143

Chapter ll Radiochemical and Mössbauer Methods . . . . . . . . . . . . . . . . . . . . . 1. Radiochernical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Mössbauer Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . · . · · ·

145 145 147 148

Chapter 12 Analysis of Tin Ores and Concentrates . . . . . . . . . . . . . . . . . . . . . 1. Tin Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Sampling ofTirr Ores and Concentrates . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Size of Bat eh or Consignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Prirnary Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

-149 149 150 15 0 150

XIII Crushing and Dividing Practical Aspects Maisture Determination Pretreatment of Sampie Roasting Nitric Acid Treatment Hydrofluoric Acid Treatment Decomposition Procedures Fusion Methods Reduction Methods Sublimation with Ammonium Iodide Decomposition by Acids 50 Analytical Methods DeterminationofTin Determination of Impurity Elements References 2.30

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Chapter 13 Analysis of Secondary Materialsand Intermediates Drosses and Ashes Slags Fume, Flue Dusts Turnings, Borings 50 Muds, Slimes, Detinning Residues Hardhead and Irony Intermediates 10

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Chapter 14 Analysis of Tin Alloys and Solders Sampling Standard Methods Solders Antimonial Alloys Chemical Analysis Tin Lead Antimony Copper Other Elements Density Methods References 10

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XIV Chapter 17 Tin in F errous Alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Volumetrie Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. General Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Rapid Method for Cast Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Photometrie Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Phenylfluoraue Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 .2. Pyrocatechol Violet Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 .3. 4-Hydroxy-3-nitro-phenylarsonic Acid Method ................. 4. Atomic Absorption Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Cast Iran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Sintered Iran Compacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

205 205 206 206 206 206 207 207 207 208 208 208 208

Chapter 18 Tinplate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Determination of Tin Coating Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 .1. Coulometric Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. X-ray Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. BendixMethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. 'Strip and Weigh' Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5. Volumetrie Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Determination ofOil Film Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. DeterminationofOxideFilm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Performance Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

209 209 210 210 210 210 211 211 212 212 213 213

Chapter 19 Organotin Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Eiemental Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 .1. Determination of Tin . . . . . . . . . . . . . . . . . . . ·. . . . . . . . . . . . . . . 2.2. Determination ofCarbon and Hydrogen . . . . . . . . . . . . . . . . . . . . . . 2.3. Determination of Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Determination of Sulphur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5. Determination of Halogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Determination of Functional Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Carboxylates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 .2. Hydrides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Oxidesand Hydroxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Determination of Organatin Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Volumetrie Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Photometrie Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Electrochemical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 .1. Polarography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2. Amperometry and Voltarnmetry . . . . . . . . . . . . . . . . . . . . . . . 4.3.3. Anodic Stripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4. Fluorimetric Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5. Atomic Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6. Miscellaneous Physical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Separations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

214 214 215 215 216 216 216 217 217 217 218 218 218 218 219 222 222 224 224 225 225 226 226

XV 5 .1.

Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1. Gas-Liquid Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.2. Paper Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.3. Thin Layer Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . 5.2. Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3. Solvent Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4. Steam Distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Radiometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1. PVC Stabilisers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1.1. Determination of Stabilisers . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1.2. Migration From PVC into Foods and Food Simulants ......... 8.2. Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1. Crop Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.2. Residues in Solls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3. Wood and Anti-fouling Paints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4. Environmental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.1. Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.2. Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

226 227 228 230 232 232 233 233 234 235 235 235 236 237 237 240 241 242 242 242 243

Chapter 20 Tin and Tin-Alloy Electroplating Solutions . . . . . . . . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Tin Plating Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Tin-Lead Plating Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Tin-Copper Plating Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Tin-Nickel Plating Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Tin-Zinc Plating Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. Other Tin Alloy Plating Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. Atomic Absorption Methods of Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 9. Coating Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 .1. Destructive Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1.1. Strip and Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1.2. Jet Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1.3. Coulometric Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2. Non-destructive Methods ........... _ .................... References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

248 248 249 249 250 250 250 250 251 251 251 251 252 252 252 252

Chapter 21 Tin Chemieals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Tin(II) Chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Tin(IV) Chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Tin(II) Sulphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Sodium and Potassium Stannates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. Tin(II) Fluoroborate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. Tin(II) Octoate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

253 253 253 254 254 · 254 254 254 255

Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256

CHAPTER 1

INTRODUCTION By J.W. Price

Tin does not occur naturally as metal, but is found associated with granitic rock as the mineral cassiterite, Sn0 2 , most of the tin now being found in unconsolidated deposits censisting of gravels, sands and clay resulting from the denudation of tin-bearing rocks. Mining of these deposite is carried out by dredging or hydraulically with high-pressure water jets. Hard rock deposits occur in Bolivia, Australia, South Africa and Cornwall, the cassiterite being present as lodes or veins in the rock and these are worked by sinking vertical shafts and driving tunnels at different levels; in mountainous terrain vertical shafts may be unnecessary, tunnels being driven·in from the hillsides. Cassiterite having a high density of about 7 g/cm 3 can be concentrated from the mined ore by gravity methods, usually on shaking tables or jigs, and separation from other accompanying heavy minerals is effected by froth flotation and magnetic Separation. The resulting concentrates are smelted into metal by heating with carbon, usually in the form of anthracite, in reverberatory furnaces; in the case of high grade material the resulting metal is of high purity, while that produced from lower grade concentrates is likely to contain a high level of impurities which are usually removed by electrolysis. Tin in slags and in 10\v-grade material is increasingly being recovered in volatilisation plants. Details of these processes are given in the publications cited in References [1, 2, 3]. Aceurate analysis of ores, concentrates, mill products etc. presents the analyst with some difficulty because of the insolubility of cassiterite in acid and the sample must be brought into solution by e.g. alkaline fusion or hydrogen reduction. Tin, except in small amounts, is traditionally determined volumetrically and this method is still the most accurate and most widely used in the industry; though now well understood it still presents pitfalls to the inexperienced. Tin metal is marketed in the form of ingots, typically weighing 1OOlb., each ingot being stamped with the producers brand name; these brand names are almost universally accepted as a guarantee of purity so that analysis of such ingots is rarely, if ever, necessary. National standard specifi.cations exist for ingot tin and examples of these are given in Chapter 15. The principal standard on the continent of Europe and in the U.S.A. for pure tin is now 99.9 %, while in the U.K. 'standard tin' T.2, 99.75% is accepted for many uses. In general, the impurity contents of commercial tin metal are weil within acceptable lirnits and it is only for special uses that very high purity metal is essential. For example, a case where impurity levels are important is the manufacture of tin oxide for ceramic use, where as little as 0.05% of antimony or lead can produce as slightly yellow instead of a pure white product. Annual world consumption of metallic tin is of the order of 200,000 tonnes. This amount is seen in perspective when compared with 30 times as much copper and 20 times as much lead or zinc, but the relatively high price of tin makes its total value

2

Introduction

[Ref.p. 2

comparable with that of the other 'base' metals. Ofthis total consumption figure of 200,000 tonnes nearly half is used in the production of tinplate - tin-coated steel sheet- with 25% being used for solders and 15% for white meta! alloys including pewter and for copper-base alloys such as bronze. The remaining 10% is taken up by a variety of uses, among which tin chemicals, both inorganic and organic, occupy an increasing share. Annual world production of tinplate is of the order of 12 - 15 x 106 tonnes, more than 90% of it being produced by electrodeposition of the tin in a continuous strip process. A wide range of tin coating thicknesses is available and the general analyst may be called upon to check that the thickness of the coating is suitable for the particular purpose for which the tinplate is to be used. Detailed testing of tinplate is somewhat specialised and is usually carried out only by the !arge users, the can makers and their customers, traditionally the food and beverage industries, accounting for perhaps 80% of the tinplate used. F ood in cans, if stored for long periods at elevated temperatures, may dissolve some of the tin coating from the interior of the cans, and although this dissolved tin is harmless if ingested, regulationsexist in many countries which'specify maximum permitted Ievels, typically 100ppm in solid foods. Tin at these Ievels is best determined photometrically or by atomic absorption after wet-oxidation of the organic matter. Solder composition is the subject of numerous national standards for a wide variety of uses e.g. B.S.219; A.S.T .M. B.32; D.l.N. 1707, tin content being the most important consideration, though impurities which affect fluidity and wetting during the soldering operation have become of increasing significance, particularly because of the growth of high-speed mass soldering in the electronics industries, and the analyst must also be prepared to determine such impurities as aluminium, zinc and cadmium at very low concentrations in solder baths. The metallurgical uses of tin date from ancient times, bronze and pewter having both been in use for more than 3,000 years. Both tin-base and copper-base alloys are today of considerable commercial importance - world production of copper-tin alloys is about 600,000 tonnes annually - and in addition tin is fmding increasing use in zirconium and titanium alloys, in powder metallurgy and, in small amounts, as an additive to cast iron. National and international specifications exist for many alloys containing tin and referee methods for their analysis have been published. The metallurgical analyst must use rapid methods for production control and here in particular automated instrumental methods are important; strictly chemical methods of analysis are less used except for standardisation purposes. lt is, however, in the new field of organotin compounds that the analyst is likely to meet the most challenging problems. These compounds are used, broadly speaking, in two separate fields - as plastics stabilisers, particularly for PVC, and as biocides in a variety of applications such as crop protection, timher preservation, anti-fouling paints etc. In these uses the organotin compounds can come into contact with foods and residues from agricultural applications can pose ecological questions. Much work has been published during the last few years and satisfactory analytical methods are beginning to emerge, particulary for the determination of very low concentrations of these compounds. References 1. Mantell, C.L.: Tin, A.C.S. Monograph 51. Reinhold (1949) 2. Wright, ·P.A.: The Extractive Metallurgy of Tin, Elsevier (1967) 3. Mackey, T.S.: The Electrolytic Tin Refining Plantat Texas City, J. Metals, 22, 32 (1969)

CHAPTER 2 DETECTION By J .W. Price

1. Introduction With the establishment of instrumental methods, classical qualitative analysis has become of less importance, particularly as such methods as e.g. spectrochemical, X-ray fluorescence (for the examination of solid samples) and atomic absorption (for samples in solution) are generally specific for the element concemed, thus avoiding the need for Separations. Accordingly group separations and general reactions of tin compounds in solution are dealt with here only briefly, as they are covered in most analytical texts. In particular, a very full account of methods for the detection of tin published before 1956 is given in the book edited by Fresenius andJander [1). Tin, a group IV element, can form compounds in both the IV+ and II+ oxidation states. Both tin(II) and tin(IV) compounds are amphoteric, in the latter the acidic properties being more prominent than the basic, so that tin(IV) compounds in aqueous solution exist almost exclusively as complex anions, this being much less marked in tin(II) compounds. Both types of compound are very readily hydrolised in solution, with precipitation of basic salts or hydrated oxides, no true tin hydroxides being known. Tin(II) compounds are strong reducing agents, both the solid compounds and their aqueous solutions being readily oxidised in the air, and most of the reactions used for the detection of tin depend on the reducing properties of tin(II) on both organic and inorganic compounds. Classical group separations are based on the insolubility of tin sulphides in dilute acid (0.5 M hydrochloric acid) and their solubility in alkali sulphide or hydroxide; in this procedure tin is accompanied by arsenic and antimony and also by Au, Pt, Ir, Mo, Ge, Se, Te andRe, if present. Numerous schemes have been put forward for the separation oftin from these elements [1], some examples of which are given in Table 1. In addition, separations are possible by paper- and column-chromatography, details of which are also given i~ Reference [ 1).

2. Ores and minerals Tin concentrations down to 0.001% have been detected by direct spectrographic examination of powdered samples, while higher detection Iimits have been reported for the use of Mössbauer spectrometry in geological surveying (Chapter 11). Portable X-ray fluorescence equipment is also available for use in surveying. Chernical tests based on acid attack on the sample are of doubtful value owing to the insolubility of cassiterite and alkaline fusion should be used whenever possible, the melt being dissolved in acid and tin looked for in the solution. By the reaction of Sn0 2 with hydriadie acid to form red Snl 4 it has been found possible to detect as little as 0.1 mg Sn. This test

4

Detection

[Ref.p. 7

is better carried out by heating the sample with ammonium iodide; mix 0.2g of the powdered sample with 2g ammonium iodide and heat to 450 - 500° in a test tube. A yellow to red Sublimate condenses on the wall of the tube if tin is present. This can be confirmed by dissolving in 2M hydrochloric acid and testing with dithiol. In a sirnilar test [2] the sample is heated with arnmonium chloride and a little granulated magnesium meta!. The colourless sublimate in this case contains some tin(II) chloride, which can be detected by placing in contact with cotton wool moistened with a solution of arnmonium phosphomolybdate. A blue colour is produced with a minirnum of 1mg Sn0 2 .

Chemical Separations of the Sulphides of the Tin Group Elements Present Sb, As 1. Add excess oxalic acid to a solution of the sulphides in HCI and pass H 2 S. Sb and As (also Se, Te and Mo if present) are precipitated, Sn remains in solution. (Se, Te, Mo) 2. Dissalve sulphides in conc. H 2 S0 4 , dilute, add HF and pass H 2 S. Sb and As are precipitated, Sn remains in solution. To the solution add excess boric acid, neutralise free acid with ammonia. Sn precipitated as sulphide. 1. Dissalve sulphides in HCl, reduce with metallic Fe or Ni. Sb metal precipitated, Sn Sb remains in solution. 2. Pass H 2 S into a solution which is 2 N in HCI. Sb is precipitated, Sn remains in solution. Heat sulphide precipitate in 5 M HCI. As is insoluble, Sn (+ Sb) goes into soluAs tion. Heat sulphide precipitate in conc. HCI. Only Sb and Sn are dissolved. Mo, Se, Te, Au, Pt

3. Slags and residues These should be separated into 'meta!' and 'fines' by grinding and sieving and the two fractions examined separately. The metallic portion is dissolved in hydrochloric acid with the addition of a few drops of hydrogen peroxide and tin looked for in the solution. The 'fines' are fused with sodium hydroxide/peroxide, the cooled melt dissolved in water, the solution acidified with hydrochloric acid and tested in the same way.

4. Aqueous solutions Dilute acid solutions containing Sn(II) or Sn(IV) are unstable, precipitating hydrated oxides at pH values above 2.5; alkaline solutions of Sn(IV) e.g. sodium stannate, are stable in the presence of excess alkali but alkaline stannites decompose, especially on heating, with disproportionation to metallic tin and stannate. For the detection of Sn(II) in the presence of Sn(IV) there arenot many suitable tests available. The classical formation of 'purple of Cassius' by the reducing action of Sn(II) on solutions of gold chloride is very sensitive; other reducing agents, particularly Fe 2 •, must be absent. Salts of the platinum metals give similar colour reactions, the formation of a deep red with a platinaus salt being clairned [3] tobe specific for

Ref.p. 7]

5.1 Chemical Reactions

Sn(II). Addition of oxalic acid to a solution of a tin salt in ethanol gives a precipitate ofthe Sn(II) oxalate, the Sn(IV) compound being soluble [4], but the test is not very sensitive. Other reactions stated to be specific for Sn(II) in the presence of Sn(IV) are the decolorisation of solutions of methylene blue [5], Bordeaux Red and Brilliant Vialet [6] in hydrochloric acid solution, but other reducing agents must be absent. In alkaline solution stannite can be detected in the presence of a !arge excess of stannate as follows: precipitate bismuth hydroxide from an acid solution of a bismuth salt by makingjust alkaline with sodium hydroxide, fllter, and pour the hat alkaline solution to be tested over the precipitate on the filter paper. A black deposit of bismuth meta! is obtained if stannite is present, the surface of the bismuth hydroxide being coloured brown if only traces of Sn(II) are present. Mixtures of the two tin oxides can be separated by heating to boiling in a solution containing 4% oxalic acid and 4% ammonium oxalate. The tin(II) oxide dissolves but Sn0 2 is insoluble. Metallic tin, if also present, is removed by first dissolving in neutral 5% ferric sulphate solution [7]. As already stated, tin(II) compounds are strong reducing agents and almost any compound that produces a colour change or a precipitate with a reducing agent can be used as a test for tin. Tin(IV) compounds are readily reduced to tin(II) in hydrochloric acid solution by metals such as iron, Iead, nicke!, aluminium or zinc and the resulting solution can be used for the test. Very few of the reagents that have been proposed are specific for tin and most of them are of historical interest only; details of more than 100 of them are given in Reference [ 1]. The reagents that have been found satisfactory for the photometric determination of tin (Chapter 5) can of course be used for qualitative tests and the elimination of possible interferences can be carried out as described there. Perhaps the most useful test for tin in solution is the production of a red colour with dithiol (zinc derivative), while the equally sensitive test with cacothelene - the formation of a violet colour is not interfered with by bismuth as is dithiol. Cacothelene test: to the hydrochloric acid solution add hydroxylammonium chloride, dilute with water so that the acid concentration is 1 - 2 M, and add a few drops of a saturated aqueous solution of the reagent. A red-violet colour is produced with as little as 10 jJ.g/ml Sn(II). Dithiol test: to the hydrochloric acid solution ('"'2N) add a few drops of thioglycollic acid and a little solid zinc dithiol and warm gently. A red colour is produced by 1 jJ.g/ml Sn and a red precipitate by !arge amounts. Many other metals react to give coloured precipitates but in the presence of an excess of the reagent on!y bismuth gives a red colour. Both these reagents can be used as 'spot' tests: a drop of the test solution is placed on filter paper followed by a drop of the reagent solution.

5. Metals and alloys Spectrographic methods of test are given in Chapter 9 and arenot referred to here. 5 .1 Chemical Reactions Chemically a reaction that is specific in the absence of Ti and Zr depends on the formation of a turbidity with 4-hydroxy-3-nitrophenyl arsonic acid (Chapter 5.3.8). The sample is dissolved in nitric acid, the solution evaporated to dryness and the residue dissolved in hydrochloric acid. On addition of an aqueous solution of the reagent (0.8%) !arge amounts of tin give an immediate white precipitate while as little as 50jJ.g in a volume of 30m! give a visible turbidity on warming or allowing to stand.

5

6

Detection

[Ref.p. 7

The same test has been used to detect down to 0.2% Sn in lead-antimony alloys. With these the hydrochloric acid solution is diluted with an equal volume of water and cooled, the solution decanted from the precipitated Iead chloride and heated to boiling after addition of the reagent. 5.2 Tin-base and Lead-base alloys Tin-rich samples can be dissolved in hydrochloric acid with formation of Sn(II) chloride which can be tested for directly with cacothelene or dithiol. Lead-rich material should be dissolved in nitric acid and the solution evaporated to dryness. Large amounts of tin are precipitated as metastaunie acid, which can be isolated by flltration and dissolved in hydrochloric acid; with small amounts the whole residue should be heated with hydrochloric acid, the solution diluted with an equal volume of water and the precipitated Iead chloride separated by decantation. Tin is then present in the clear solution as Sn(IV) and must be reduced to Sn(II) before testing with these reagents. 5.3 Iron and Steel Direct chemical methods of test are not very satisfactory and it is usually necessary to dissolve a sample in dilute sulphuric acid and to precipitate the tin as sulphide, adding a copper salt as collector. The sulphide precipitate is then dissolved in acid and the solution tested with dithiol as above. 5.4 Aluminium and magnesium alloys A simple chemical test has been described [8] in which the sample is dissolved in 5 M hydrochloric acid and a drop of the solution treated with a drop of dilute starchiodine (1 rnl of 0.1 N iodine + 5 ml of 5% starch solution diluted to 100ml). Immediate decolorisation indicates the presence of tin. A test proposed for the detection of down to 0.02% Sn in a number of alloys [9] relies on the green fluorescence of a tin-morin complex under UV light. The sample is heated with a few drops of concentrated sulphuric acid and, after diluting with water, solid potassium iodide is added and the tin extracted into a 5% solution of iodine in benzene. A drop ofthe benzene solution is placed on fllter paper and treated successively with arnmonia vapour, a drop of sodium sulphite solution to remove iodine, and a drop of a 0.05% solution of morin in acetone. Excess reagent is removed by dipping the paper in acetic acid and the spot viewed under UV light. A green fluorescence can be seen with as little as 0.05J.tg Sn.

6. Surface coatings Tin coatings, both electroplated and hot-dipped, are readily identified by placing a drop of 5 M hydrochloric acid on the degreased surface and after 2 - 3 min transferring the drop to fllter paper and testing with dithiol or cacothelene. This procedure can also be used for the testing of tin-lead and tin-zinc coatings but is not suitable for tincopper or tin-nicke! alloys, which may be identified as follows: place 1 - 2 drops of bromine water on the degreased surface and allow to react for 5 min. Transfer the drop to fllter paper, add 1 drop of 10% thioglycollic acid and 1 drop of a methanolic solution of zinc dithiol. A red colour indicates the presence of tin. Copper and nicke! may

Ref.p. 7]

7. Organic matter

be detected in a similar way, a blue colour produced on making the spot on the fllter paper alkaline with ammonia indicating copper and a red colour formed on adding dimethylglyoxime to the alkaline spot indicating. nicke I.

7. Organic matter Methods of test involving preliminary ignition of the sample to remove organic matter are to be avoided if possible as there is in some cases a danger of loss of tin by volatilisation and generally the tin in the ash is more or less insoluble in acid, requiring an alkaline fusion to take it into solution. Wet oxidation with sulphuric acid and an oxidising agent, usually nitric acid, can be carried out rapidly provided that the nitric acid is added in small amounts and the water forrned in the reaction evaporated before the addition of more acid. Canned foods should be wet-oxidised with the exception of some fruits and vegetables, from which tin can be extracted by heating with 5 M hydrochloric acid. Tin is separated from the sulphuric acid solution obtained after wet-ashing by precipitation as sulphide, adding a coppersalt as collector, or as hydrated oxide by making alkaline with arnmonia after the addition of a ferric or an aluminium salt. The resulting precipitate is ftltered, dissolved in acid, and tested with dithiol as above.

Re[erences 1. Fresenius, W., Jander, G.: Handbuch der analytischen Chemie Part li, Vol. 4(1I) SpringerVerlag 1956 2. Ben-Dor, L., Markovitz, G.: Mikrochim.Acta, 1967, 957 3. Chotulew, Y.P.: Chem. Abstr., 32, 8978 (1938) 4. Meyer, E.G., Kahn,M.: J. Amer. Chem. Soc., 73,4950 (1951) 5. Wohlmann, E.: Z.Anal.Chem., 122, 161 (1941) 6. Smith, J. W., Rogers, H.E.: J.Chem.Educat., 16, 143 (1939) 7. Gauzzi, R.: Ann.Chim.Ital., 47, 1316 (1957); (C.A., 52,7017 (1958)) 8. Clark, J., Stross, W.: Metallurgia, 46,212 (1952) 9. Feig!, F., Gentil, V.: Mikrochim. Acta, 93 (1954)

7

CHAPTER 3 GRA VIMETRIC METHODS By J.W. Price

Classical gravimetric procedures for the determination of tin are based mainly on the dehydration of hydrous tin(IV) oxide at 800°C and the thermal stability of the oxide Sn0 2 on heating in air at temperature up to 950°C [1 ]. The hydrous oxide can be obtained by neutralising an acid solution of a tin(IV) salt, usually the chloride, or a complex with an organic reagent can be precipitated from acid solution and ignited to destroy organic matter and leave a residue of Sn0 2 , but the most important method is that of nitric acid attack on a tin-containing alloy with formation of 'metastannic acid'.

1. Precipitation of Hydrous Tin(IV) Oxide Precipitation of hydrous tin(IV) oxide is not much used except as a means of Separation from e.g. Cu, Ni and Mo, as the precipitate is difficult to filter and wash. Precipitation is carried out (i) by making the solution alkaline with arnmonia (ii) by boiling the faintly acid solution with excess of arnmonium nitrate:

(iii) by adding a 20% aqueous solution of pyridine to the hot solution containing 5 - 10% NH4 Cl until it is alkaline to methyl orange. In all cases the precipitate is washed with 1% NH 4 N0 3 solution to remove chlorides which may cause loss of tin during ignition.

2. Precipitation of Metastannic Acid Precipitation by nitric acid attack on a metal sample: 3Sn + 4HN0 3 + H 2 0

-+

3Sn0 2 .H 2 0 + 4NO

has long been used for control purposes, particularly for copper alloys. It is important to bear in mind the limitations of this method: (i) if the sarnple is dissolved in dilute (5 - 10 %) acid it is necessary to evaparate the solution to dryness to ensure complete precipitation of the tin. This evaporation can be avoided by dissolving in SO% acid, boiling to expel oxides ofnitrogen, diluting with an equal volume of water and digesting for 30 min near the boiling point before filtering. (ii) Copper alloys containing large amounts of phosphorus (1 - 2 %) dissolve very slowly in nitric acid and for these the method is not suitable. Both phosphorus and antimony are precipitated with the tin, quantitatively if there is a ten-fold excess of tin present. (iii) Iron in

Ref.p. 11]

4.2 Precipitation of Se

!arge amounts (> 0.5 %) can peptise some of the hydrated tin mtide causing low results: smaller amounts are partly adsorbed on the precipitate, causing high results. (iv) Cantamination of the precipitate is tobe expected by silica, tungsten, tantalum and niobium and, to a lesser extent, by copper and zinc. Correction for this can be made by heating the ignited and weighed precipitate with ammonium iodide at 450°C, volatilising the tin as Snl 4 . The residue is treated with nitric acid and again ignited and its weight deducted from the original. (v) Precipitation of small amounts (< 0.1 %) of. tin is incomplete, and for these the use of Mn0 2 as a 'collector' by boiling the nitric acid solution of the sample with permanganate/manganous nitrate allows complete recovery but of course involves a further step in the determination [ 13].

3. Precipitation as Sulphide While forming the basis of a number of classical methods of separation [ 14] precipitation as sulphide is not much used as a method of determination owing to the difficulty of flltering a somewhat slimy precipitate. The sulphide is obtained by the passage of H 2 S into dilute acid solutions or by formation of the soluble thiostannate in alkaline solution and then acidifying with acetic acid. Tin(IV) sulphide may also be precipitated with thioacetamide from homogenaus solution which is 0.8 M in HCl, [ 15] with thioformamide [ 16] or with thiourea dioximide (17]. The addition of a small amount of HgCl 2 has been recommended in order to obtain complete precipitation of the tin; any mercury in the precipitate is removed during ignition of the precipitate to Sn0 2 .

4. Reducing Reactions Methods based on the reducing power of Sn(II) solutions suffer from the disadvantages of the difficulty of ensuring complete reduction of tin-containing solutions and of the relative ease with which reoxidation can take place. 4.1 Precipitation of Hg 2 Cl 2 In one such method, which is stated to give good results in the ana1ysis of tin-base alloys [ 18], tin is first reduced to the meta! in hydrochloric acid solution by means of metallic zinc, the tin re-dissolved by heating the solution with the exclusion of air, and the cooled solution quickly poured into an excess of mercuric chloride solution. The precipitated Hg 2 Cl 2 is filtered ar,d dried at 105°C before weighing; it has a favourable conversion facter of 0.2514. 4.2 Precipitation of Se A sirnilar procedure involves the addition of selenous acid to the reduced tin solution, with precipitation of elementary Se, which can be dried at 110° C and weighed. H 2 Se0 3 + 2 SnC1 2 + 4 HCl--+ 2 SnCl4 + 3 H 2 0 +Se

9

10

Gravimetrie Methods

[Ref.p. 11

4.3 Precipitation of Tin(IV) Selenite An alternative procedure [ 19] which does not require prior reduction of the tin, precipitates Sn(IV) selenite by the addition of H 2 Se0 3 to the oxidised· solution cantairring 2% v/v of hydrochloric acid. In this case the precipitate is ignited and weighed as Sn0 2 .

5. Precipitation with Organic Reagents 5.1 Cupferron and neo cupferron Cupferron and neo cupferron ( the ammonium salts of nitrosophenyl- and nitrosonaphthyl-hydroxylarnine) form bulky white precipitates by replacement of the hydrogen of the oxime group, giving complexes with Sn(II) and Sn(IV). Precipitation is carried out in acid solution (-6% HCl) in the cold ( < 10°); the precipitate filters well but the reagents are not specific, so that prior separation from e.g. Cu and Pb is necessary. Antimony does not interfere if oxidised to Sb(V) with permanganate, while Cu and Pb may be eliminated by precipitation with H2 S from a solution cantairring 3- 5% HF, the tin in the filtrate being precipitated with cupferron after the addition of boric acid and boiling to expel H2 S. Cupferron has been recommended for the precipitation of tin after it has been isolated by distillation as the brornide (2]. In all cases the precipitate is dried and ignited to Sn0 2 at 800- 850°C. 5.2 N-benzoylphenylhydroxylamine A related compound N-benzoylphenylhydroxylamine behaves rather differently in that in acid solution it frrst reduces Sn(IV) to Sn(II) and then forms an addition compound which is stable up to 170°C and so can be dried at ll0°C and weighed, or can be ignited to Sn0 2 . No interference is caused in 6% HCl solution by Cu or Pb, so that a direct determination of tin in copper alloys is possible by dissolving the sample in HCl (3). 5.3 Ammonium benzoate Ammonium benzoate added to an acid solution (pH3) precipitates tin(IV) benzoate which can be ignited to Sn0 2 [ 4] .The reagent is not specific, but some interferences can be avoided by adding suitable complexing agents. 5.4 Arsonic Acid Derivatives Several arsonic acid derivatives give precipitates in acid solution which can be ignited to Sn0 2 e.g. phenylarsonic acid in 5% HCl allows separation from Cu, Pb, Sb and Ni, but Zr and Th interfere. A micromethod using this reagent has been described [5]. Similar precipitates are abtairred with anthraquinone-arsonic acid [6], tetraphenylarsonium chloride [7] and 4-hydroxyl-3-nitrophenyl arsonic acid [8], the last of these being a useful reagent for the turbidimetric determination of small amounts of tin [9). Benzene arsonic acid has recently been used for the precipitation of tin from dilute acid solutions containing Pb. A saturated aqueous solution of the reagent is added to the hot sample solution, the precipitate fJ.ltered, washed with 4% NH4N0 3 solution and ignited to Sn0 2 [10].

Ref.p. 11]

5.6 8-Hydroxyquinoline

11

5.5Tannin Tannin added in slightly acid solution ( -Q.OS N) produces a bulky white precipitate by flocculation of the disperse positively charged hydrous tin(N) mtide by the negative tannin sol, and in chloride solutions this affords a separation of tin from Cu, Pb, Fe, Al, Be, As and V, but Sb is co-precipitated [ 11]. The interference of Zr can be prevented by the addition of oxalate. The precipitate is ignited to Sn0 2 • 5.6 8-Hydroxyquinoline 8-Hydroxyquinoline added to a solution of Sn(IV) in 0.2 M HO forms the complex SnC1 2 -(C 9 H 6 NOh which may be dried at 110° C and weighed as such. Citrate, phosphate and tartrate as weil as Bi, Sb and Mo interfere [12].

References

1. Dupuis, T., Duval, C.: Anal. Chim. Acta, 4, 201 (1950) 2. Mogerman, W.D.: J.Res.Nat.Bureau Stds., 33, 307 (1944) 3. Ryan, D.E., Lutwick, G.D.: Canad.J.Chem., 31, 9 (1953) 4. Jewsbury, A., Osborn, C.H.: Anal. Chim. Acta, 3, 642 (1949) 5. von Mach, N., Hecht, F.: Mikrochim. Acta, 2, 227 (1937) 6. Kuznetsov, V.!.: Zavod. Lab., 11, 263 (1945) 7. Willard, H.H., Smith, G.M.: Ind. Eng. Chem. (Anal. Ed.), 11, 186, 269 (1939) 8. Tougarinoff, B.: Bull. Soc. Chim. Beige, 45,542 (1936) 9. Karsten, P., Kiess, H.L., Walraven, J.: Anal. Chim. Acta, 7, 355 (1952) 9a. Dozinel, C.M., Gill, H.: Chemist. Analyst., 45, 105 (1956) 9b. Pohl, H.: Metall, 12, 103 (1958) 10. Fano, V., Zanotti, L.: Microchem. J, 18, (1973), (A.A., 26, 2606) (1974) 11. Holness, H., Schoeller, W.R.: Analyst 71,217 (1946) 12. Hamaguchi, H., Jkeda, N., Ogawa, K.: Buli. Chem. Soc. Japan, 32, 656 (1959) 13. Luke, C.L.: Ind. Eng. Chem. (Anal. Ed.), 15,626 (1943) 14. Hillebrand, W.F., Lundell, G.E.F., Bright, HA., Hoffmann, J.I.: Applied Inorganic Analysis 1953 New York, Wiley and Sons 15. Martinez Lope, M.J., Maccira Vidan, A., Vidan, Marti-Burriel, F.: An Quim. 71, 84 (Anal. Abstr., 29, 313100) (1975) 16. Musil, A., Gagliardi, H., Reischl, K.: z. Anal. Chem., 140, 342 (1953) 17. Nieuwenburg, C.J., van Lighten, J. W. .L.: Chem. Anal., 36,41 (1954) 18. Fairchild, J.G.: Ind. Eng. Chem. (Anal., Ed.), 15,625 (1943) 19. De Carvalho, R.G.: Rev. Quim. Pura e appl., 1, 24 (1950)

CHAPTER 4

VOLUMETRIC ANALYSIS By R. Smith

The early development of volumetrie methods was largely a result of the need of rnining assayers during the nineteenth eentury to irnprove their unseleetive and variable dry assay proeedures. Lenssen [ 1] in 1859 titrated stannous solutions against iodine in an alkaline tartrate solution, Benas [2] found that aeeurate results with the iodirnetrie titration eould only be obtained in the absenee of air, while Borgmann [3] claimed that iodides present in the assay solution eatalysed the oxidation of stannous ehloride by dissolved oxygen. The aeeeptanee of the wet assay was by no means universal. Crookes [4] in his 'Seleet Methods in Chemical Analysis' published in 1871 offers no volumetrie methods for tin, whereas Parry [5] writing in 1906 reeommended the wet assay as being more reliable than dry methods for the valuation of tin ores. Pa"y gave six titrants for the tin assay: FeC1 3 , Acid I 2 , alkaline I 2 , KMn0 4 , K2 Cr 2 0 7 and ~Fe(CN)6. Potassium iodate eame into use as a titrant following the work of Andrews [6].and was applied to the determination of tin by Jamieson [7]. During the first half of the twentieth eentury there were many investigations into the ehoiee of titrant, redueing agent and deeomposition proeedure, as weil as into the effeets of other elements. As the tin determination is now known to be a very eomplex system, many of the eonclusions made during this period should be eritieally examined. In more reeent years, Wright [8] has rationalised many of the apparently eontradietory results of earlier authors. He has treated the redox equilibria involved on a quantitative theoretical basis. Despite this, the iodometrie tin assay remains a topie of eontinual investigation and speeulation. The determination is based on an empirieal standardisation which beeomes inereasingly justified as the eomplexity of the method beeomes understood. Complexometrie titrations involving EDTA ( ethylenediarnine tetra aeetie aeid) have been restrieted, hitherto, to the determination of tin in alloys and simple matriees.

1. Iodometrie Titrations 1.1 Introduetion and Basie Method Iodometrie titration is the most widely used teehnique for the deterrnination of tin in amounts greater than 1 %, and may easily be extended down to 0.1 %. The assay has a number of irnportant variations, all eapable of giving poor results if applied without eonsideration of the nature of the sample. Thesevariations in proeedure are embodied in the main stages of the determination: (i) Prelirninary treatment-In the ease of some ores and minerals it may be neeessary to remove irnpurities by a prelirninary

Ref.p. 40]

1.1 Introduction and Basic Method

acid leach or by roasting. (ii) Decomposition and complete dissolution of the sample. (iii) Separation of major quantities of interfering elements. (iv) Separation of minor and trace impurities by cementation on iron powder. (v) Reduction of tin to the stannous form, in acid solution and usually by means of a dissolving metal. (vi) Titration of tin (II) against a solution of iodine or potassium iodate, usually with a large excess of potassium iodide in the absence of air. Items (i) - (iii) will be treated in conjunction with specific applications in later chapters. As a practical introduction we give below a method suitable for the determination of tin above 1 % following a sodium peroxide fusion.

C0 2 INLET

SOOml

FLASK

Fig. 1 Flask (500 ml) for Nickel Reduction

Nickel Reduction Method Fuse 1 g of sample with 1.5 g of sodium Carbonate and 5 g of sodium peroxide in a zirconium crucible under a cover of 1 g of sodium peroxide. Cool, and leach with 100m! water in a 400ml beaker. Wash out the crucible and acidify carefully with 70ml of concentrated hydrochloric acid. Finally wash the crucible with water and inspect for complete dissolution. Add a few crystals of potassium iodide and 3g of iron powder, heat at approximately 70°C to dissolve the iron powder but do not boil. When the iron has almost dissolved, filter into a 500ml round flask through a small cotton wool plug. Wash twice with hot 2% hydrochloric acid and reserve the filtrate. Transfer the plug to the original beaker and dissolve the residue with 30 ml of concentrated hydrochloric acid and 0.5 g potassium chlorate. Heat until the precipitate is dissolved and excess chlorine has been removed. Cool, add 3 g of iron powder and heat at 70°C until the iron is nearly dissolved. Filter through a cotton wool plug into the 500ml flask containing the first filtrate. Wash six times with hot 2% hydrochloric acid and dilute to 300m! with water. Insert a bung carrying a tube and glass rod with a nicke! coil as shown in Fig. 1. (The coil is made from 30 cm of 2 mm diameter nicke! rod). Boil for 60 min, and connect irnmediately to a supply of carbon dioxide and p lace in a cooling tank. When cold remove the coil, wash with the minimum of water, add two or three marble chips and starch indicator. Titrate with N/6 potassium iodate solution to a permanent blue colour. Standardise by dissolving 0.4g of pure tin foil in 30m! of warm concentrated hydrochloric acid and 2m! of 0.1% antimony trichloride solution. Add a fusionblank obtained by carrying out the

13

14

Volumetrie Analysis

[Ref.p. 40

fusion of sodium carbonate and peroxide above in a zirconium crucible. Leach the blank with 100 ml of water then with 70ml of concentrated hydrochloric acid, and proceed through the method above. Weight of Tin Standard Iodate factor (g. of Sn/rn!) Titre on Standard Titre x Factor x 100 Weight of Sampie N/6 Potassium Iodate: Dissolve 5.998 g of dried potassium iodate and 100 g of potassiurn iodidein water. Add 2 g of sodiurn hydroxide and dilute to 1 litre. (1 g of tin is equivalent to approxirnately 100 ml of titrant). Tin%

1.2 Removal of Impurities With Iron Powder Iron powder removes certain impurities by cementation as metals. These include Ag, As, Bi,Cu, Hg, Se, Sb and Te. The Separation is carried out in acid solution using 1 - 5 g of iron powder and filtering before the iron is completely dissolved. Failure to do this results in dissolution of impurities. Heavy deposits of cementate occlude tin and complete dissolution in hydrochloric acid and potassium chlorate, followed by re-precipitation with more iron is necessary. Iron treatment is usually carried out after the removal of major impurities and before the reduction stage. It is common practice to use a mixture of equal weights of hydrogen reduced (ferrum reductum) and electrolytic iron powders. The object of mixing is to give a wide range of particle sizes, allowing high initial activity followed by a more prolonged action. The rate of dissolution depends on the level of impurities present; copper coats the iron surface and slows the reaction, antimony accelerates the rate of solution. Other authors have reported the use ofiron wire [5] and iron nails [20]. This author has encountered several poor batches of iron powder, these were contaminated with traces of grease which caused severe foaming and also had a high carbon content. Surprisingly, the assays were not affected and this has led us to the conclusion that the choice of iron powder is not a critical feature of the determination. Sulphur is often present as an impurity in iron powder and under extreme circurnstances may precipitate tin as sulphide. Coprecipitation of tin with cementates of copper and antimony is well-known [ 15, 26, 33, 64] and several studies have been carried out. Traces of tinarealso precipitated by iron as Table 1 shows [61]. The results of Table 1 were obtained using the Nickel Reduction procedure given earlier. The solution from the second iron powder treatmentwas assayed separately; titrations were carried out using N/ 12 potassium iodate with 50g/l potassium iodide. It can be seen that appreciable coprecipitation occurs with Ag, As, Bi, Cu and Sb. The amounts of copper tested were small yet had a marked effect. Evans and Higgs [ 15 J showed that up to one tenth of the tin content of an assay could be removed by coprecipitation with an equal weight of copper during reduction with iron. The behaviour of mi;x.tures of impurity elements during cementation is complex; copper is removed by iron only with difficulty in "clean" solutions. This has been attributed [61] to masking of iron by smooth deposits of copper. When antimony and copper are present together, cementation is improved and a non-adherent deposit is produced. Furthermore, in the presence of both elements, the occlusion of tin is very much reduced [35]. This behaviour has been attributed to the precipitation of the compound Cu 2 Sb and for this reason, several procedures call for the addition of an antimony solution before cementation. Attempts to calculate the concentration of impurities remaining in solution using the oxidationpotential of iron in contact with a ferrous solution have been unsuccessful. The Fe 2 +/Fe couple generates a potential of- 0.46v relative to the stan-

Ref.p. 40]

1.3 Wet Reduction

15

Table 1. Precipitation of Tin During Iron Cementation [61] lmpurity added (mg)

lmpurity% 0.5 g sample Nil

Nil

Sn Retained (mg) 1.07 0.53 0.80 0.80

Ag

7.5 15

As

25 75

5 15

1.07 1.60

Bi 100 200

20 40

1.34 1.60

1.5 3

1.60 1.60

Cu

5 10 15

1 2 3

1.07 1.27 1.67

Sb

50 100 200 300

10 20 40 60

1.01 2.27 4.54 6.38

Table 1 showing amount of tin precipitated in first cementation with iron powder, results were obtained by dissolving the cementate as described in the Ni reduction method, treating with more iron powder and analysing the second flltrate for tin (0.2g tin used)

dard hydrogen electrode when dissolution of 3 g·of iron powder in 200 · 250ml of solution is nearly complete. This potential would be sufficient to remove nearly all the tin from the assay solution and it is more reasonable to suppose that under the conditions of the reaction, the iron surface is occluded with cementate and gaseous hydrogen. As a result the activity of the iron surface is considerably less than unity. 1.3 Wet Reduction The most commonly used reductants for the tin assay are aluminium and nicke!. Other reducing agents include: antimony, cadmium, cobalt, hypophosphite, iron, Iead and zinc. The ideal choice should be capable of quantitatively reducing tin only to the stannous form; stronger reducing agents affect the selectivity of the procedure by converting foreign elements to interfering lower valence states. Very powerful reductants, such as sodium borohydride [63] cause Iosses of tin by volatilisation [10] as the gaseous hydride, stannane. In a survey of metallic reducing agents (Table 2). Evans and Higgs [ 15] found that only nicke! did not precipitate tin as the metal. In the case of zinc and aluminium reductions, the precipitation of tin is an accepted feature of the method. Tin is redissolved after addition of more acid. (i)Aluminumis widely used as a reducing agent, although it is not mentioned in the earlier classical works on tin assaying [5, 11, 12] presumably because of its very high cost. Aluminium reduces tin to spongy metal; should the acid strength be too great the solution froths and tin is easily lost by 'creeping'. The spongy tin is then dissolved before titration by boiling with more acid. Tin precipitated in the cold is reported [13, 14] to di~solve rhore rapidly than if precipitated from hot solution. Aluminium reduction has the advantages of leaving a colourless solution for titration; there is no pas-

16

[Ref.p. 40

Volumetrie Analysis Table 2. Precipitation of Tin by Common Reductants [15] Reductant Lead

HCl (% of conc.acid)

Added Elements (mg) Sn Sb Cu 200 200

10 10 20 50

200 200 200 200

Iran

20 20 20

100 200 200

200

Nickel

20 20 50

100 200 200

200 200

Zinc

10 10

200 200

200

Aluminium

10 10

200 200

200

200

200 100 200

Coprecipitated Sn(mg) 2 2 27 13

3 7 2 nil nil nil

100

100

141 21

100

125 162

sivation (as with iron) and the deposit does not adhere to the reductant causing erratic action (as with zinc). Complete reduction is easily achieved and vigoraus prolonged boiling (as with nicke!) is unnecessary. Aluminium is a powerful reducing agent, however, and many common elements which could interfere in the subsequent titration are precipitated as metals (eg Sb, Cu) or are reduced to lower valence states. Losses by coprecipitation are, therefore, easily possible. Under suitable conditions, aluminium will return assays which are comparable with those obtained using nicke! [16, 17, 18] or iron [16, 17] reduction. For the reasons given above, aluminium is preferable to nicke! for the determination of tin in concentrations greater than 50% andin the presence of few impurities.

Aluminium Reduction Method Carry out the sodium peroxide fusion on 0.5 g of sample as outlined in the Nickel Reduction method. Carry out double iron powder treatmentalso and filter into a SOOml round flask. Add 20 ml of concentrated hydrochloric add and 3 g of alumini um meta!. Fit a Göckel trap containing saturated sodium bicarbonate solution. When the reaction ceases, add 0.5 g of aluminium and 40 ml of concentrated hydrochloric acid. When no further reaction takes place, boil to dissolve precipitated tin. Cool, ensuring some bicarbonate is drawn into the flask, remove the trap and titrate immediately using a starch indicator as described in the Nickel Reduction procedure.

(ii) Nickel is recommended as a reducing agent in the early literature, [5, 11, 12,31] and is the author's personal preference for low grade or complex materia1s. The advantages of nicke! are its mild reducing action, and consistent performance. The disadvantages are the prolonged and vigoraus boiling required to achieve reduction, the green colour of the resultant solution and the diminished activity of the meta! if it is not properly cleaned and etched between assays. Nickel has been used as sheet [ 17, 19, 20, 23, 24], shot [ 15], coiled wire [ 16] or powder [21, 25] although the last mentioned is not recommended (see below). Before use nicke! must be activated by etching. This is done by boiling the coil or sheet in 1 :3 hydrochloric acid: water containing 5% sodium chloride until the lustre of the surface is dulled. Coils or strips of nicke! sheet should be cleaned by boiling in the above solution. Because of its mild reducing action, nicke! would be expected to give rise to fewer interferences than stronger reducing agents. Although nicke! does not normally reduce

1.3 Wet Reduction

Ref.p. 40]

17

stannous solutions to metallic tin, workers in Bolivia [16, 22] have noted the precipitation of small quantities of tin under rather special conditions. At the high altitudes encountered in that country, the boiling point of the assay solution is considerably lowered. To achieve complete reduction, of stannic tin, therefore, unusually prolonged boiling times must be used [22]. Any metallic tin precipitated must be redissolved by boiling the solution with the nickel coil removed before titration.

Table 3. Reduction of 0.1g Tin on Boiling with Nickel [61] Tin Found (rng) Time (rnin)

Ni Sheet

NiCoil

5 10 15 20 25 30

75 91 96 99 97 101

79 89 93 99 99 101

Evans andHiggs [15] recommended nickel reduction in that no deposition ofmetallic tinwas encountered. Holness [26] found that with the greater surface area of nickel powder amounts of 0.1 - 0.2mg tin were lost from solutions containing 10-20mg tin. In the presence of 0.1 -.I g antimony, the loss increased to 1 - 1.5mg tin. Only very slight retention of tinwas found [26] when nickel sheet was used. This may explain the fmdings ofSteger[157] who obtained assays of 2.44, 2.42, 2.40and 2.39% Sn on Canadian Mineral Seiences MP-1 Zn/Sn/Cu ore using Al foil, Fe granules, Ni powder or Pb shot respectively. The differences were said tobe statistically significant.

The time required for complete reduction using a nickel coil is recommended, in the method given, as 60 min after boiling commences. Some laboratories prefer to count the boiling time from the disappearance of yellow ferric ions. Results on solutions containing tin only, suggest that the recommended boiling time of 60 rnin is excessive (Table 3). In practice, we have found [61] this tobe necessary. (iii) Zinc is somewhat sirnilar to aluminium in its reducing action and deposits metallic tin from solution. Beringerand Stephens [27] assayed tin ores by a preliminary decomposition procedure involving reduction of cassiterite by zinc dust at red heat [5, 11]. The excess zinc remaining after fusion was used as the reducing agent during acid attack of the residue. Other groups have used: 20 mesh zinc [28], zinc rods [14], zinc amalgam [29] and zinc tumings [30]. Zinc appears to suffer from the disadvantage that the surface becomes covered with tin sponge which prevents further reduction [14, 30]. In modern practice, aluminium has largely replaced zinc as a reducing agent, except in those instance where a dry reduction of cassiterite is frrst carried out using zinc powder. (iv) Lead was used by Powell [32] as a reductant and has proved popular with other writers [18, 33- 36]. Theoretically, lead is the mildest of the common effective agents.

18

Volumetrie Analysis

[Ref.p. 40

The standard oxidation potentials [37] of several metals in contact with normal solutions are: Eo volts - 0.126 -0.250 -0.440 -0.763 - 1.66

Lead causes no reduction to spongy tin, nevertheless in the presence of antimony or copper severe coprecitipation of tin is said to occur [15]. Soviet workers [36] have suggested that tin is volatilised as the chloride during reduction with lead and recommend the use of alumini um. The precipitation of lead chloride on cooling has not been mentioned by the advocates ofthe method.Evans [34] and Clarke [35] found that the theoretical factor could be obtained if air was excluded from both the reduction and the titrant. Usually the theoretical factor (i.e. that obtained by standardisation against a titrant such as arsenious oxide) is not obtained and tin is used as a standard; granular or strip (30 cm x 2.5 cm) lead may be used. Lead Reduction Method Carry out the sodium peroxide fusion on 0.5 - 1 g of sample as outlined in the Nickel Reduction. Cool the crucible, leach with 20m! of water, then wash out with 125 ml of concentrated hydrochloric acid. Carry out the iron powder treatment as described previously, fJ.lter into a 500ml round flask and dilute to approxirnately 250m!. Add 15 g of granulated Iead or a strip of foil (30cm x 2.5cm), heat to boiling and continue for a period of 45 min after the disappearance of the yellow chloroferrate ion. Cool under an atmosphere of carbon dioxide. When cold, add starch indicator solution and titrate immediately and rapidly as described before.

( v)Iron is reported to give quantitative reduction oftin, quiet liberation ofhydrogen and does not precipitate tin from solution [38 - 40]. In practice, small quantities of tin can be precipitated by iron powder [61], and appreciable quantities are coprecipitated in the presence of copper [ 15]. lron is easily passivated and is not easily cleaned. ( vi)Antimony is not commonly used as a reductant despite the many accounts in the literatme [15, 25, 41 - 44, 72]. lt is a milder reducing agent than lead as the oxidation potentials [37] show: Sn 2+/Sn4 + Pb/Pb 2 + Sb/SbO+

E =+ 0.151 + 0.0295log (Sn4 +/Sn 2 +) E =- 0.126 + 0.295log (Pb 2 +) E =+ 0.212- 0.0394pH + 0.0197log (SbO+)

From these equations it can be seen that antimony will act as a reducing agent for tin only under suitable conditions. Millerand Currie [42] found that sticks of antimony were satisfactory but required cleaning and recasting between determinations. Evans and Higgs [ 15] found that the reducing power of antimony varied with particle size and that accurate results could only be obtained with particles of 0.02- 0.04mm diameter. Sieving gave incorrect particle sizing and water elutriation was used to separate size fractions. ( vii) Cobalt has also been suggested [ 15] as a metallic reductant, but appears to offer no advantages. Bismuth amalgam [78] reduction requires a temperature of 45°C in 5 - 12M hydrochloric acid with shaking. Under these conditions, reduction is complete in .only 10 min. ( viii)Evans [45,46] found Sodium Hypophosphitetobe a convenient reducing agent for tin. Complete reduction is obtained on boiling a 50% hydrochloric acid solution in the presence of a mercuric chloride catalyst. When the solution is diluted with five times its own volume of air-free water, the acid strength diminishes to a point where

1.4 Effect of Air on Stannous Salutions

Ref.p. 40]

19

the excess hypophosphite does not interfere with the titration. Iron and copper have tobe separated and nitric acid must be absent. The interference of antimony is eliminated by addition of potassium iodide just before titration. Interference from fluoride [47] could be avoided by. the addition of either sodium tetraborate or boric acid. Tungstate and iodide were also reported [47] as interfering anions. Applications of the hypophosphite reduction have been published for the analysis of non-ferrous alloys [48, 51, 52, 55]; steels, irons and iron ore [54] and tin ores [49, 50]. Determinations have been carried out [55] of as little as 0.002% Sn, titrating against 0.005N KI0 3 . Hypophosphite reduction has been suggested [56] as a satisfactory way of overcoming copper interference in the conventional tin assay. In all the procedures ·mentioned mercuric chloride has been used as a catalyst; the titration is usually carried out after the addition of both potassium iodide and pcitassium thiocyanate. Pourbaix [37] claims that Cu, Ni, Pd and powdered graphite also act as catalysts for the oxidation of hypophosphite. The use of orthophosphite as a reducing agent has also been reported [57]. Hypophosphite Reduction Method Carry out a fusion on 0.5 g of sample as described in the Nickel Reduction method. Leach the sample with 50ml of water and wash the crucible with 70ml of concentrated hydrochloric acid and carry out the iron powder treatment described. To the round flask containing the flltrate add 1 ml of saturated mercuric chloride solution, 5 g of sodium hypophosphite and 2 g of tartaric acid. Boi!, then simmer gently for 5-6 min, fit a Gockeltrap and cool. Add lg of potassium iodide, starch indicator and titrate with 0.1 N iodine solution. The end-point is quite clear but the blue colour of the starch solution may fade after a few seconds.

(ix) The necessity for wet reduction may be avoided if a metal sample is being analysed Hourigan [57] andNechamkin [128] dissolved tin/lead alloys in boiling concentrated hydi:ochloric acid under carbon dioxide and titrated directly with potassium iodate. 1.4 Effect of Air on Stannous Solutions In 1884, Benas [2] discovered that dissolved air oxidises stannous solutions and seriously affects the accuracy of the tin titration. lt is now accepted practice, that immediately after reduction with a metal, the assay solution should be allowed to cool under an inert atmosphere (usually carbon dioxide). The inert atmosphere may be maintained during the titration by the addition of marble chips:

Rubber -" Seal

\

I NaHC0 3

Soln.

Fig. 2 Göckel-Contat traps

The atmosphere of carbon dioxide is provided in a nurober ofways. A cylinder, reduction valve and lute allowing about 30cm water pressure is convenient for a batch of up to 40 assays. The gas may be used to occupy the headspace of the reduction

20

(Ref.p. 40

Volumetrie Analysis

flask (see Fig. 1) or can be bubbled through the solution. Solid carbon dioxide (9] (approximately 8cm3) is a suitable alternative to gaseaus co2. Provision of an inert atmosphere during cooling by the addition of sodium bicarbonate or marble chips is cautioned as these reduce the acid strength and may allow tin to precipitate. The presence of ferric iron impurities in marble chips may cause significant errors, particularly if added to a hot solution. A popular and convenient alternative to gaseaus carbon dioxide is the Göckel trap [76] shown in Fig. 2. This is filled with saturated sodium bicarbonate solution. During reduction, steam is expelled through the trapo On cooling, bicarbonate solution is drawn into the reduction flask, co2 is generated and maintains a positive pressureo

Okell and Lumsden [59] have contributed the mostdefinitive work on the subject of air interference and Iist the following measures as being effective in overcoming this: (i) Reduction of the acid concentrations [28]0 (ii) Reduction of the iodide concentration as iodide was thought to catalyse the reaction between oxygen and stannous chloride [3]0 (iii) Addition of a catalytic inhibitor, usually antimony [60] o(iv) Prevention of air ingress to the titration flasko (v) Addition of excess titrant and back-titrationo

Most of these measures advocated in the early Iiterature are undesirableo Acid concentrations should be kept at 2 - 4 M hydrochloric acid for nickel and aluminium reductions to prevent tin hydrolysis and to maintain an active reductiono Low iodide concentrations are to be avoided at all costs as under these conditions iodate and iodine titrants are strongly oxidising and may titrate impurity elementso Backtitration is also undesirable in that traces of precipitated metals such as arsenic or antimony may dissolve in the excess titrant and score as tin, alternatively thesemetals can be slowly oxidised by stannic salts and will again give high results [57] 0

3SnC14 + 2Sb ~ 3SnC12 + 2SbC1 3 A rapid conventional titration is, therefore, commonly used to minimise the dissolution of precipitated metals.

Table 40 Nickel Reduction Method-Showing Effect of Air on Stannous Solutions [61] Theoreticala Titre (ml)

Cooled inair (ml)

Cooled inC02 (ml)

39090

38o90

39079

0.4 g tin meta! standard

Cooled in b co2 +CaC03 (ml) 39o91

a Obtained by calculation b CaC0 3 added as Marble Chips before titration All results are the average of three titrations

The only successful way to eliminate the effect of air on the tin assay is by cooling and titrating under an atmosphere of carbon dioxideo Same analysts obtain good results by cooling under air, however, this approach relies on proportionate oxidation of both standards and unknownso Titrations obtained on pure tin Standards, reduced by nickel, are listed above (Table 4) and indicate the importance of a C0 2 purge [61] 0

1.5 lodine and Iodate Titrants

Ref.p. 40]

21

Okell and Lumsden [59] took note of the oxygen dissolved in the titrant. Titrating 0.1 g of tin against iodirre of different strengths they found appreciable differences from the theoretical titre with dilute iodirre solutions. When dissolved oxygen was removed from the most dilute titrant, theoretical titres were found. (see Table 5)

Table 5. Effect of Dissolved Air in Titrant Solution [59] lodine Titrant

Theoretical Titre (ml)

Actual Titre (ml)

Error %

N/5 N/10 N/20 N/40

8.42 16.85 33.70 67.40

8.41 16.81 33.28 65.04

-0.1 -0.2 - 1.3 - 3.6

1.5 Iodirre and Iodate Titrants Both iodine and potassium iodate are widely used as titrants for the oxidation of stannous solutions: 3SnC1 2 + K10 3 + 6HC1

+ 2HC1

3SnC14 + K1 + 3H 2 0

(i)

+ 2HI

(ii)

+ 6KC1 + 3H 2 0

(iii)

SnC1 4

and at the end point: K10 3

+ SKI

+ 6HC1 = 31 2

With both titrants the end-point is the appearance of free iodine and is easily detected with a starch indicator. The use of iodine is traditional and dates from the nineteenth century [1 - 3, 5, 11] whereas the use of ioda te has followed from the later work of Andrews [6] and Jamieson [7]. It is very important that the titrant or assay solution should contain a !arge excess of iodide. If this precaution is not taken, the oxidising power of the titrant becomes so great that interfering substances are titrated. Formost work, iodirre or iodate strengths of N/5 or N/10 are commonly used. Routine assay laboratories frequently use N/6 titrants for which 1 gram of tin is approximately equivalent to 100m!. Successful titrations with N/100 iodirre or iodate have been reported [45, 59]; this author has found N/60 iodatetobe satisfactory for the determination of 1 - 20mg of tin. Fig. 3 shows the stability domains of iodine in aqueous solution at 25°C, calculated [37] from electrochemical oxidation potentials. The solid lines indicate the potential of equimolar solutions, the broken lines indicate the potentials for decomposition of water to hydrogen or oxygen. For example, a solution of O.SM K1 and O.SM K.l0 3 at pH 12 will be represented by point a in Fig. 3 and will have a potential of approximately + 0.4 volt (relative to the standardhydrogen electrode). lt can be seen from Fig. 3 that in alkaline solutions, iodate and iodide ions are stable in the presence of one an-

22

(Ref.p. 40

Volumetrie Analysis

E (volts)

HI04

1.0

1-

0

-1.0

-2

0

2

4

6

8

10

12

pH

Fig. 3 Potential - pH equilibrium diagram for the system iodine waterat 25° C for solutions containing 1 g atom 1/litre. Dotted Jines show potentials for evolution of gaseaus oxygen and hydrogen. (FromM. Pourbaix, Ref. (37] p. 621)

other. Alkaline iodine solutions are unstable and disproportionate to iodate and iodide ions: 31 2 + 6KOH

=KI0 3 + SKI + 3H 2 0

(iv)

Conversely, in acid solutions, Fig. 3 shows that the reaction in equation (iii) takes place and that iodine is the stable species. Titrants based on iodine are, therefore, equivalent to standard iodate solutions provided both contain a large excess of iodide. The two titrants differ only in their acidity. The advantage of iodate titrants is their superior stability. Kolb [80] found that potassium iodate solutions could be stored for periods of over one year without a change in normality. Our experience [61] is that iodate/iodide solutions in constant use decrease steadily in normality and must be standardised daily. Other iodine species are present in the acid assay solution particularly the tri-iodide ion 13. The equilibria involved in the titration are: E = + 0.621 + 0.0295log {hl_

(v)

E = + 0.536 + 0.0295log (13)

(vi)

(02

(03

Under the conditions of the tin titration, the reaction with both titrants may be looked upon as: (vii)

1.6 End-Point Detection

Ref.p. 40]

23

1.6 End-Point Detection The use of starch as an indicator is almost universal for the tin(II) titration. Kalthoff and Beleher [67] state that concentrations of iodine of 2-10 x 10-s N are sufficient to give a blue colour with starch in 0.002N potassiurn iodide. In a 200rnl solution this is equivalent to an end-point error of 0.04rnl with a 0.1 N iodine titrant. The indicator sensitivity is reduced with iodide contents lower than 0.002N but is not increased substantially on increasing the arnount of iodide. Sirnilarly, ions which form strong cornplexes or insoluble cornpounds with iodide ( e.g. rnercury or copper) reduce the sensitivity of the indicator. The sensitivity of the end-point is further decreased if warm solutions are used [67] and with solutions of over 70°C the end-point is a dirty green. Under these conditions the end-point error with 0.1 N iodirre solution is greater than 1rnl. In acid solutions, starch will detect [67] 2 x 10-s N free iodine. This, therefore, allows us to calculate the potential of the I 2 Jr couple for the endpoirrt conditions [8] using equation (v) and hence calculate the equilibriurn concentrations of stannic and stannous ions. Furthermore, it is also possible to rnake calculations of the equilibriurn concentrations of interfering species (see Table 6). This clearly shows the irnportance of iodide in determining the selectivity of the titration. Iron is present in rnany assays frorn the crucible, sarnple and frorn the iron powder cernentation. In the exarnple given in Table 6, in 0.01 M iodide solution, log 10 (Fe 3 •;Fe 2 ) = · 2.89 or Fe 3 •;Fe 2 • = 1.3 x 10- 3 . Therefore, if lOg of iron are present, 13rng Fe will be titrated to Fe 3 • and will score as tin. This calculation is approxirnate in that no allowance is made for stabilisation of the ferric state by complex formation of the type FeC1 4 -,Fe CI~-. The stabilisation of the upper valence state increases the iron interference beyond that calculated in Table 6. Where very low titres are involved, it is obviously not sufficient, to incorporate an excess of iodide in the titrant. Potassiurn iodide should be added to the assay solution before reduction. Starch has sorne disadvantages as an indicator for iodornetric titrations; its insolubility in cold water, the instability of aqueous dispersions, and the insolubility of the starch iodine cornplex. The last necessitates the addition of starch solutions irnrnediately before the end-point. Kalthoffand Beleher [67] have authoritatively reviewed the use of starch as an indicator and recornrnend the following preparation: Prepare a paste by rubbing 2g of starch with lOmg of mercuric iodidein 30m! of water. Add the paste to 1 litre of boiling water and continue heating until a clear solution is obtained. The mercuric iodide acts as a preservative, and should remain stable for long periods if stored in a stoppered bottle. The production of a reddish colour with iodine is an indication that the starch solution has deteriorated and needs replacing.

Table 6. Equilibrium Concentrations of Va!ence States at End Point of the Tin Titration Iodide Concentration IRedox Potential E volts

1M +0.482

O.lM +0.541

O.OlM +0.600

O.OOlM +0.659

O.OOOlM +0.715

Jogi o(Sn4+/Sn2+) log 1 o 10%) in organotin compounds after wet-ashing a 5 mg sample. 3.8 4-Hydroxy -3-nitrophenylarsonic acid

~As0(0H) 2

Ho-y

N0 1

Arsonic acidderivatives form insoluble precipitates with Sn(IV) in acid solution (Chapter 3, Section 4) and of these the 4-hydroxy-3-nitrophenyl derivative was first suggested by Karsten, Kies and Walraven [ 119] for the turbidimetric determination of small amounts (0.1 - 0.2mg) of tin in antimony sulphide. They found that !arge amounts of chloride prevented precipitation, but that, apart from titanium and zirconium, there was little interference from other metals. Iran in up to 100-fold excess could be tolerated but delayed complete precipitation for several hours, so that it was preferable to allow the solution to stand overnight, the precipitate which settled out being readily and reproduciby re-dispersed by shaking. In the presence of a large excess of iron some contamination of the precipitate takes place and in such cases it was suggested that the precipitate should be filtered off, wet-ashed and re-precipitated. These authors measured the turbidity at 424nm, but there is no sharp absorption maximum and measurement can be made at any point between 420 and 470nm. The absence of interferences makes it possible to determine tin directly by this method in a number of metals and alloys. Thus Dozinell and Gill [120] determined tin in refmed copper, and Challis andJones [121] determined 0.001-0.4% tin in a series of copper-base alloys, while Pohl [122] determined 0.0001 - 0.1% tin in zincbase alloys, and a standard procedure has been published [ 123] for the determination of the same range of tin content in aluminium alloys. The reagent is suitable for the determination of tin in organic matter such as foods after wet-ashing. To an aliquot of the resulting sulphuric acid solution containing 0.10.2mg Sn in 5 ml H2 S0 4 are added 1Oml of 30% tartaric acid solution and after mixing, 4ml of reagent solution (2g dissolved in 50ml of methanol and diluted to lOOml with water) and the solution diluted to 20ml. After standing for two to three hours or preferably overnight to allow complete precipitation the solution is shaken and its turbidity measured in a 2cm cellatabout 450nm.

56

Photometrie methods

[Ref.p. 57

4. Fluorimetric Methods Compounds which are reduced to fluorescent products by Sn(II), particularly various naphthol sulphonic acids have been used for the detection and determination of tin as described in a series of publications by Anderson et al [ 124], but it is only since the fairly recent availability of commercial spectrofluorimeters that the increased sensitivity of fluorimetric methods as compared with photometric procedures has become of interest for the determination of trace amounts of tin. Although Anderson ( 1956) was able to determine 0.1 J.(g/ml of tin by its reaction with 6-nitro-2-naphthylamine-8-sulphonic acid, the reacting species is Sn(II) and as already mentioned in the case of the molybdenum blue method, one is then faced with the problems of oxidation of the tin and of positive interferences by other reducing ions present, so that it is essential when possible to use reactions based on tin(IV). It was found by Coyle and White [125] that flavonal (3-hydroxyflavone) produces a bright blue fluorescence with tin(IV) in dilute acid solution, with a sensitivity of about 0.1 J.(g Sn/mi. Quantitative results were obtained in a 33% dimethylformamide solution that was 0.06M with sulphuric acid and fluorescence was measured at 405/450nm. with a calibration range of 0.2- 0.6J.(g Sn/25 ml. It was found that zirconium, chloride, fluoride and phosphate interfered and that close control of the dimethylformamide concentration was necessary. This reagent has recently been used for the fluorimetric determination of triphenyltin compounds (see Chapter 9). 8-Hydroxyquinoline has been suggested [ 126] as a fluorescent reagent for tin, but produces only a weak fluorescence (2 J.Lg/ml Sn) but Pa! and Ryan [ 127] found that the 5-sulphonic acid derivative is much more sensitive and that fluorescence intensities are independent of the valence state of the meta!. Although F e(III), Cu( II) and Hg(II) quench the fluorescence, 300ppm ofFe(III), 75J.Lg/ml ofCu(II) and 100ppm of Hg(II) do not interfere in the determination of 0.1 ppm of tin in the presence of hydroxylamine or thioglycollic acid (iron), thiosulphate (copper) or chloride (mercury). Small amounts of fluoride and EDTA quench the fluorescence, large amounts of organic acids (citrate, tartrate, oxalate) reduce the intensity by 50% while traces of Al, Zn and Zr increase it considerably and nicke! reduces it. The neutral sample solution (0.05- 2.5J.Lg Sn) (1 ml) is treated with 3ml of acetic acid/acetate buffer (pH 4.0- 5.2) and with a 250 molar excess of reagent solution (10" 3 M in water) diluted to 1Omland the fluorescence measured at 360/512nm. Improved sensitivity and good tolerance to other elements have been reported by Filer [128] for 3,4,7-trihydroxyflavone. Here alse a nurober of elements interfere in the direct determination of the tin and a preliminary separation by extraction of the iodide into toluene is suggested. Any iron present must be reduced to Fe(II) and complexed with sulphamic acid in sulphate buffer to prevent serious interference. Fluorescence is measured at 427/473nm and calibration curves arelinear up to 6J.(g Sn/ 25 ml and the detection Iimit is stated to be 0.007 J.(g Sn. Other reagents that have been put forward are Rhodamine B (range up to lOJ.(g Sn/Sml;measurement at 555/580nm) and morin [130] (range 0.1- SOJ.(g Sn;measurement at 420/SOOnm). Although all these reagents have some disadvantages the high sensitivity of fluorimetric methods and the increasing need for methods of determining smaller and smaller amounts of tin make this an interesting field for further study.

References

References

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 47a. 47b. 4 7c. 48. 49. 50. 51. 52. 53, 54. 55.

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z.

=

57

58 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 66a. 67. 68. 69. 70. 71. 72. 73. 73a. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. 88. 89. 89a. 90. 90a. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113. 114.

Photometrie methods

Luke, C.L.: Anal. Chem. Acta, 37, 97 (1967); 39, 404 (1967) /shibashi, M., et al.: Japan Analyst, 7, 473 (1958) Nagamura, H., et al.: Japan Analyst, 13, 264 (1964) Yamazaki, M., et al.: Japan Analyst, 22, 112 (1973) Kanna, S., Ogura, H.: Shokalin Eiseigaku Zasshi 5, 116 (1964); Chem. Abstr. 61, 7619 (1964) Ackermann, G., Heegn, H.: Talanta 21,431 (1974) Nakamura, Y., Kamiwida, S.: Shokalin Eiseigaku Zasshi 14, 352 (1973) Nazarenko, V.A., Berijuk, E.A.: Zhur. Anal. Khim. 15, 306 (1960) Nazarenko, V.A., Lebedeva, N. V.: Zavod. Lab. 28, 268 (1962) Asmus, E., Kraetch, J.: Z. Anal. Chem. 223,401 (1966) Asmus, E., Kossmann, U.: Z. Anal. Chem. 245, 137 (1969) Asmus, E., Weinert, H.: Z. Anal. Chem. 249, 179 (1970) Asmus, E., Jahny, J.: Z. Anal. Chem. 255,186 (1971) Asmus, E., Krapp, B., Moczko, F.M.: Z. Anal. Chem. 256, 276 (1971) Sagakova, V.P., Lyubivaya, A.I.: Trudy Urk. Nauch. Inst. Konserv. Prom. 1, 118 (1959) Suk, V., Malat, M.: Chemist Analyst 45 40 (1956) Ross, W.J., White, J.C.: Anal. Chem. 33,421,424 (1961) Wakeley, W.D., Varga, L.P.: Anal. Chem. 44, 169 (1972) Tanaka, K.: Japan Analyst 11, 332 (1962) Tanaka, K., Yamayoshi, K.: Japan Analyst 13,540 (1964) Tanaka, K.: Japan Analyst 13, 725 (1964) Newman, E.J., Jones, P.D.: Analyst 91,406 (1966) Analytical Methods Committee: Analyst 92, 320 (1967) Malat, M.: Z. Anal. Chem. 187,404 (1962) Dagnall, R.M., West, T.S., Young, P.: Analyst 92, 27 (1967) Corbin,H.B.: Analyt. Chem. 45,534 (1973) Karnaukhova, N.N.: Zavod. Lab. 36,1047 (1970) Adcock, L.H., Hope, W.G.: Analyst 95, 868 (1970) Kodama, Y., Tsubota, H.: Japan Analyst 20, 1554 (1971) Sedova, V.A.: Soversh. Tekhnol. Praszvod. Olova 61 (1972); Chem. Abstr. 80, 148897 (1974) Lowry, R.R., Tinsley, I.J.: J. Amer. Oil Chem. Soc. 49,508 (1972) Wood, G.A.: Geochem. Res. Centre. Imperial College London Tech. Comm. 11, 1957 Stanton, R.E., McDonald, A.J.: Trans. Inst. Min.Met. 71, 27 (1961); Analyst 87, 600 (1962) Mah, D.C., Tupper, W.M.: Carleton Univ., Dept. Geol., Geol. Paper, 66-2, 1 (1966) Hutchin, F., Fiander, S.J.: Trans. Inst. Min. Metall. 76, C69 (1967) Heegn, H.: Freiberg Forsch. A, 455, 47 (1969) Ackermann, G., Heegn, H.: Talanta 21,431 (1974) Murano, M., Mijazaki, S.: Bunseki Kagaku 15, 657 (1966) Murano, M., Mijazaki, S.: Kanagawa-Ken Kogyo Shikensho Kenyo Hokuku 21,51 (1968); Chem.Abstr. 70, 73986 (1969) Jones, J.C.H.: Analyst 93, 214 (1968) Timofeeva, O.A., Podolenko, A.A.: Sadovod. Vinograd. Vinodel. Mold. 24, 27 (1969) Stanton, R.E.: Food Tech. Australia 22, 236 (1970) Yamahata, E., Kusuyama, T., Konishi, K.: Bunseki Kagaku 20, 223 (1971) Liska, K.: Chem. Listy 49, 1656 (1955) Janousek, /., Studlar, K.: Hutn. Listy, 15, 889 (1960) Lyaskovskaya, T., Krasil'nikova, T.: Myas. Ind. SSSR, 32, 44 (1961); Trudy Vses. Nauchno-Issled. Inst. Myas. Prom. 128 (1962) Karvanek, M., Curda, D., Mi/er, V.: Prumysl Potravin 16, 369 (1965) Kirk, R.S., Pocklington, W.D .. : Analyst 94,71 (1969) Eyrich, W.: Deut. Lebensm. Rundsch. 68, 280 (1972) Fitak, F.,Pilkowska, B.: Rocz. Panstw. Zakl. Hig. 24,331 (1973) Raik, Y.S., Timopeeva, O.A.: Isobret Prom. Obraztsy Tovarnye Znaki 45, 10 (1969) Bondarev, M. V., Gandel'man, Kh.K.: Vinodel Vinograd SSSR, 29, 28 (1969) Chetkowski, W.: Prace Inst. Hutn. 18, 109 (1966) Sakaki, T.: Nippon Kinzoku Gakkaishi 35, 1082 (1971); A.A. 23, 280 (1972) Ponosov, V.!., et al.: Anal. Abstr. 23, 280 (1972) Wunderlich, E., Bosse, G.: Erzmetall, 24, 537 (1971) Charlot, G.: Anal. Chim. Acta, 1, 233 (1947) Ginzburg, L.B., Shkrobot, E.P.: Zavod. Lab. 23,527 (1957) Patrovsky, V.: Chem. Listy, 48, 1694 (1954) Stolyarov, K.P., Pogodaeva, V.G., Kuz'minova, N.E.: Vestn. Leningrad Univ. Fiz. Khim. 23, 133 (1969) Engberg; A.: Analyst 98, 137 (1973) Teicher, H., Gordon, L.: Anal. Chem. 25, 1182 (1953) Norwitz, G.: Analyst 86, 835 (1961)

References

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115. Asmus, E., Altman, H.J., Thomasz, E.: Z. Anal. Chem. 216, 3 (1966) 116. Spelker, H., Graffmann, G.: Z. Anal. Chern. 228, 401 (1967) 117. Shirodker, R., Schibilla, E.: Z. Anal. Chern. 248, 173 (1969) 118. Genda, S., Morikawa, T.: Kagaku.To Kogyo (Osaka) 43, 265 (1969); Chern. Abstr. 71, 108908 (1969) 119. Karsten, P., Kies, H.L., Walraven, J.J.: Anal. Chim. Acta 7, 355 (1952) 121. Challis, H.J.G., Jones, J.T.: Anal. Chirn. Acta, 21,58 (1959) 122. Pohl, H.: Metall, 12, 103 (1958) 123. Association Francaise de Normalisation: N.F.A. 06-578 (1956) 124. Anderson, J.R.A., et al.: Anal. Chim. Acta 8, 393 (1953); 15, 246 (1956); 17,453 (1957); 19,257 (1958); 22,1 (1960) 125. Coyle, C.F., White, C.E.: Anal. Chern. 29, 1486 (1957) 126. Shkrobot, E.P., Ginzberg, L.B.: Zavod. Lab. 23,527 (1957) 127. Pa/, B.K., Ryan, E.D.: Anal. Chim. Acta 48, 227 (1969) 128. Filer, T.D.: Anal. Chern. 43,1753 (1971) 129. Nishikawa, Y., eta/.: Japan Analyst 19,1224 (1970) 130. Shcherbov, D.P., et a/.: Zavod. Lab. 39,546 (1973); Chern. Abstr. 79,73291 (1973) 131. Hirokawa, K.: Sei. Rep. Tokio Univ. A, 13,426 (1961) 132. Zhivopistesev, V.P., etal.: Zhur. Anal. Khim. 26,761 (1971);Anal. Abstr. 23,1368 (1972) 133. Bosch Sessat, F.: Inform. Quirn. Anal. 22, 227 (1968); Chern. Abstr. 70, 111308 (1969) 134. Alimarin, I.P., et al.: Zhur. Anal. Khim. 25, 2287 (1970) 135. Barinowski, R., etal.: Chernia Anal. (Poland) 19,997 (1974) 136. Busev,A.I., etal.: Tr. Korn. Anal. Khirn. Akad. Nauk. SSSR 17,218 (1969); Chern. Abstr. 72, 128316 (1970) 137. Busev, A.l., et al.. : Zhur. Khim. 26, 1517 (1971) 138. Thierig, D., Umland, F.: Z. Anal. Chern. 221, 229 (1966) 139. Shumova, T.l., Blyum, I.A.: Zavod. Lab. 34, 659 (1968) 140. Köthe, J.: Chernia Anal. (Poland) 17,445 (1972); Anal. Abstr. 24, 2765 (1973) 141. Zhivopistev, V.P., Minima, U.S.: Vch. Zap. Rerrn. Gas. Univ. 178,196 (1968); Chern. Abstr. 73, 136996 (1970) 142. Zhivopister, V.P., Minima, U.S.: Vch. Zap. Rerrn. Gas. Univ. 141, 213 (1966); Chern .. Abstr. 69, 15909 (1968) 143. Usatenko, Yu. I., et al.: Zhur. Anal. Khirn. 22, 1823 (1967); Chern. Abstr. 68, 65430 (1968) 144. Dey, Arun K.: Chirn. Anal. 40, 202 (1958); Anal. Abstr. 6, 1180 (1959) 145. Elinson, V.A., Tsvetkova, V.T.: Zavod Lab. 37, 662 (1971) 146. Nazarenko, V.A., et al.: Zhur. Anal. Khim. 28, 1100; Chern. Abstr. 79, 87158 (1973) 147. Zaidi, S.A.A., et al.: Ind. J. Chern. 9, 374 (1971); Chern .. Abstr. 74, 146969 (1971) 148. Be/eher, R., et al.: Anales Real. Soc. Espan. Fis. Quim. 59, 281 (1963) 149. Yoshinga Oka etal.: Japan Analyst 83,699 (1962);Chern. Abstr. 59,10761 (1963) 150. Okac, A., Urchlabsky, M.: Z. Anal. Chern. 182,425 (1961);Anal. Abstr. 9,1406 (1962) 151. Bagdasarov, K.N., et al.: Elektrochirn. Optichn. Metody Analiza Sb. 176 (1963); Chern. Abstr. 61, 3 (1964) 152. Tataev, O.A., Shakhabudinov, A.Sh.: Chern. Abstr. 80, 10343 (1974) 153. Uhlemann, E., Pohl, V.: Anal. Chirn. Acta 65,319 (1973);Chern. Abstr. 79,100116 (1973) 154. Ting, H.H., Ch'en, K. Y.: K'o Hsueh T'ung Pao, 3, 93 (1959) 155. Obolonchik, N. V.: Trudy Korn. Analyt. Khim. 16, 41 (1968); Anal. Abstr. 16, 2388 (1969) 156. Ackermann, G., Köthe, J.: Chernia Analit. (Poland) 17, 445 (1972); Chern. Abstr. 78, 37533 (1973) 157. Skakov-Trybula, Z., Polanska, J.: Chernia Analyt. (Poland) 15,635 (1970); Anal. Abstr. 20, 3712 (1971) 158. Meditsch, J. de 0.: Rev. Qzirn. lnd. (Rio de Janeiro) 39, 14 (1970) Chern. Abstr. 74, 150703 (1971) 159. Tataev, O.A., Shakhabudinov, A. Sh.: Novey Metody Khirn. Anal. Mater 1, 49 (1971) Chern. Abstr. 77,121755 (1972) 160. Popov, M.A.: Anal. Abstr. 12, 602 (1965) 161. Lopez, Ramon, A., Lachica, M.: An. Quim. 67, 751; Chern. Abstr. 76, 121170 (1972) 162. Hiiro, K., Tanaka, K., et al.: Chern. Abstr. 72, 74383 (1970) 163. Aleksandrov, A.N., Vasilieva-Aleksandrova, P.: Zhur. Analit. Khim. 18, 905 (1963) 164. Kasiura, K., Oelsiak, K.: Chernia. Analit. (Poland) 14, 139 (1969) Anal. Abstr. 18, 3871 (1970) 165. Wakamatsu, S.: Nippon Kinzoku Gakkaishi, 21,450 (1957); Chern. Abstr. 55, 8173(1961) 166. Lukin, A.M., et al.: Vest. Mosk. gos. Univ. 247 (1972); Chern .. Abstr. 74, 71420 (1971); Anal. Abstr. 23, 3689 (1972) 167. Gregory, G.R.E.C., Jeffery, P.G.: Analyst 92, 293 (1967)

60 168.

Photometrie methods

Kobayashi, T., Yado, M.: Shokulin Eiseigaku Zasshi 9, 465 (1968) Chem. Abstr. 70, 76506 (1969) 169. Mori, /.: Yakaguku Zasshi 90, 778 (1970); Chem. Abstr. 73, 94274 (1970) 170. Garg, B.S., Singh, R.P.: Microchem. J. 18,509 (1973);Chem. Abstr. 79,132599 (1973) 171. Purmalis, V.: Latv. P.S.R. Zinat Akad. Vestis Kim. Ser. 2, 234 (1972); Chem. Abstr. 77, 42682 (1972) 172. Aleksandrov, A., Vasilieva-Aleksandrova, P.: Mikrochim. Acta 6, 1189 (1968); Chem. Abstr. 70, 43682 (1969) 173. Ackermann, G., Köthe, J.: Proc. Anal. Chem. Conf. (3rd), 2, 55 (1970)

CHAPTER 6 ELECTROCHEMICAL METHODS By JoWo Price

1. lntroduction Electrochemical methods have been relatively little used in the analysis of tin, apart from the use of controlled potential electrolysis for the analysis of some alloy systems and the use of conventional polarography for the determination of moderate amounts of tin in eogo organic matter. However, improved instrumentration, giving increased sensitivity, particularly in aoco polarography, has made it possible to determine tin at very low concentrations; the work so far donein this field seems highly promising, though difficulties with eogo reagent blanks, may prove a limiting factor.

20 Electrodeposition Tin, present either as Sn(II) or Sn(IV) can be electrodeposited from acid chloride solutions [ 1] Low results can be caused by partial re-dissolution of the tin by electrolytic action during washing; this error is reduced by using a copper-plated platinum cathode and by neutralisation of the electrolyte just before termination of the electrolysiso A depolariser such as hydroxylammonium chloride must be presento Other metals present are co-deposited so that preliminary Separation of eogo copper and antimony is necessaryo Lead and tin, co-deposited from chloride solution, can be separated by dissolution of the deposit in a mixture of nitric and hydrofluoric acids, followed by deposition of the lead as Pb0 2 Oxalate solutions were once used for the electrodeposition of tin following Separation of copper and antimony as sulphides, whiie slightly acid tartrate solutions can be used to separate copper and lead from tin by electrolysis, the tin being subsequently deposited after the addition ofhydrochloric acid [2]0 Phosphoric acid can be used instead of tartaric acid to complex the tin, the same Separations being possible, tin again being deposited after the addition of hydrochloric acid 0

0

[3]

0

30 Controlled potential electrolysis; coulometric analysis Electrodeposition of tin without voltage control is now of little importance but the use of controlled potential electrolysis is of value in the analysis of a number of alloys containing tino Thus, in the analysis of copper-base alloys copper, bismuth and antimony can be deposited from chloride solution by maintaining the cathode potential at about- 0.35Vo vso Socoeo, leaving tin, lead, nicke!, and zinc in solution [4]0 lf desired tin and lead can be removed with the copper by increasing the potential to- Oo7Vo

62

Electrochemical methods

[Ref.p. 65

after deposition of the copper. The separation of copper, Iead, tin and antirnony by this method has been studied by Al[onsi [5] and used by him for the analysis of copper-base [6], Iead [7] and tin- [8] base alloys. However, perhaps the most important form of controlled potential electrolysis is the mercury pool cathode, flrst described by Lingane [9 ], particularly for the separation of the copper group elements. Thus in weakly acid tartrate solution (pH 4.5) copper can be removed by electrolysis at a potential of- 0.15V. vs. s.c.e., copperplus bismuthat- 0.4 V. and copperplus bismuth plus most of the Iead at- O.SSV., leaving cadmiurn in solution. Lead and tin cannot be separated in this way but the method has been used for the determination of impurities such as zinc and aluminiurn in tin-base alloys. In electrolysis with a mercury cathode, the weight of meta! deposited cannot be determined directly but coulometric methods can be used and, with modern instrumentation, using current integrators etc., are capable ofhigh accuracy. The work done by Bard and Lingane [ 10] showed that the electrolytic reduction of tin can be carried out in acid chloride solutions at constant current and constant potential. When using a mercury pool electrode in constant potential electrolysis it was shown by Meites [ 11] that reduction of an ion to the meta! proceeds rather slowly, while during oxidation, fewer side reactions exist, resulting in lower background currents and better accuracy and precision. These findings were applied by Wise and Williams [ 12] to the determination of tin by coulometric oxidation in glasses, copper alloys and tin concentrates. Using a supporting electrolyte of 3M KBr + 0.2M HBr and a mercury pool cathode, they carried out the reduction step at- 0.7V. vs. Ag/AgCl until only a small constant background current (< 0.01 ma) persisted. The polarity of the electrodes was then reversed and the tin oxidised at- 0.3V. until the background current was again less than 0.01 ma. Interference due to cadmium can be avoided by carrying out the tin reduction at- O.SSV. and antimony can be removed by flrst electrolysing at - 0.3V. and then reducing the tin at- 0.7V. using a fresh portion ofmercury. Theinterference of Iead cannot be avoided in this way but, tagether with cadmium, it can be removed by reduction at- 0.9V. from an ammoniacal tartrate solution, the solution then neutralised with hydrobromic acid and the tin determined as above after addition of the same supporting electrolyte [ 13].

4. Polarography The conventional d.c. polarography of tin solutions was described in detail in a series of papers by Lingane et al. and the earlier work in this fleld has been summarised by KolthoffandLingane [14]. In most media Sn(II) gives two waves, an anodic step, Sn(II) ""' Sn(IV) + 2e, and a cathodic step Sn(II) ""' Sn( o), which is usually reversible and well-defmed and which has been used in a number of cases for analytical purposes. Unfortunately there are difflculties in being certain of obtaining all the tin in a solution in the Sn(II) form and further uncertainty exists in maintaining the sample in this state in view of the ease with which air-oxidation can take place. For these reasons it is generally preferable to work with solutions in which the tin is present as the stable Sn(IV), which in a base electrolyte consisting of 1M hy-

Ref.p. 65]

5. Amperometry

63

drochloric acid cantairring 4M ammonium chloride gives two steps, the first resulting from the reduction of the SnCWcomplex to the SnClfcomplex and the second from the reduction of SnCl~-to the metal. The second of these steps was used successfully by Lingane [15] to determine tin in copper-base alloys and by Godar andAlexander [ 16] for the determination of tin in foods; it was subsequently found [ 17] that betterdefined steps are obtained in SM hydrochloric acid solution and linear calibration curves are obtained in this medium over the concentration range 10" 3 - 10" 5 M (E 112 ~ 0.5V). A serious disadvantage of this method lies in the interference caused by copper, antimony, bismuth and Iead, all of which have E 1; 2 values morepositive than- 0.6V in acid chloride solutions. The interference oflead is likely tobe the most important as it frequently accompanies tin and various methods of separation have been put forward: no step is given by Sn(II) in sodium hydroxide or arnmonical tartrate solution, while Iead gives well-defmed steps in both media, so that a correction can be made to the combined tin-lead wave found in acid solution. Alternatively tin may be removed from the sample solution by volatilisation as the bromide after measurement of the combined wave, the residual step being due to Iead alone. None of these methods is entirely satisfactory and they are now largely of historical interest. The development of more sensitive polarographic methods such as square-wave [ 18] or cathode ray oscillography [ 19], while allowing the direct determination of small amounts oftin in e.g. iron and steel, did not altogether solve the problern of Iead in terference and many workers prefer to make a preliminary separation of the tin before polarography e.g. by distillation of the bromide [20] or by co-precipitation with manganese dioxide [21, 22]. More recently a.c. methods of polarography have been found in general to offer advantages in increased sensitivity and freedom from interferences and application of these methods to the determination of tin has confirmed their superiority over d.c. methods. A comparison of available methods has been made by Bond [23] who concluded that for tin concentrations within the range 10-3 - 10-6 M in hydrochloric acid supporting electrolytes, conventional a.c. polarography with a dropping mercury electrode of natural drop frequency is superior to other methods of conventional and inverse d.c. polarography and to both a.c. and d.c. rapid polarography. For lower concentrations of tin, down to 1o-s M, anodic stripping polarography ( see Section 6) is recommended. A.c. polarography has been used successfully for the direct determination of tin down to 0.005% in a variety of geochemical materials, using a 1 g sample, no interference from overlapping waves of other elements being observed [24]. The peak potential of the a.c. Sn(II) wave vs. Ag/ AgCl was observed between - 0.4 and- 0.7V, depending on the nature of the supporting electrolyte. Sampies were taken into solution by fusion with peroxide or with a mixture of 2 g boric acid and 3 g sodium fluoride, the latter being preferred for most rock samples. For the polarography of organotin compounds see Chapter 19.

5. Amperometry The first amperometric titration of tin using the dropping mercury electrode was suggested by Lingane [25] who determined Sn(II) in amounts up to 10mg/50ml by titration with Cu(II) solutions in an acidtartratemedium of pH 4.3, using an applied potential of- 0.2V vs. s.c.e. In this way the anodic diffusion current due to the tin is compensated by the cathodic current of the copper tartrate complex, the end-point

64

Electrochernical methods

[Ref.p. 65

of the titration being where the net current becomes zero after correcting for the residual current. The more usual from of amperometric titration in which the element to be determined is precipitated by addition of a suitable reagent is exemplified by the work of Kalthoffand Johnson on the determination of Sn(IV) with m-nitrophenylarsonic acid [26] and tetraphenylarsonium chloride [27]. The former was used to determine 60 - 120mg Sn/ lOOml in 0.2M hydrochloric acid, but equilibrium conditions are reached only slowly and better results were obtained with the second reagent, working in 2-4M hydrochloric acid and 3 - 4M chloride, with an applied valtage of- 0.3 V vs. s. c. e. Methods of this kind are subject to numerous interferences, both by elements producing steps at the applied valtage and by those forming precipitates with the titrating reagent, the need for Separations thus making them less attractive. Other examples of precipitation reagents that have been used in this way are tannin [28] and cupferron [29], the latter being made interference-free in the analysis of Zircaloy samples by a preliminary distillation of the tin as the bromide. The solubility of the tin-cupferron complex is kept low by addition of 3M ammonium sulphate and the titration carried out with 0.05 M cupferron at - 0.84 V vs. Ag/ Agf:_l. Amperometric methods for the determination of tin(II) suffer from the uncertainty of complete reduction of small amounts of tin and ease of oxidation by air. Satisfactory results have been reported by the use of bromate [30], dichromate in formate solution at pH 3 (31] and permanganate [32]. For the application of amperometry to the determination of organotin compounds see Chapter 19.

6. Anodic Stripping Voltammetry In this method a sufficiently negative potential is applied to a hanging mercury drop electrode system to reduce Sn(IV) to Sn(o) and by controlled electrolysis at this potential the tin can be concentrated into the mercury drop. The amalgam can then be stripped of its tin by changing the potential of the drop in a positive direction so that the tindiffuses back into the solution, the peak height of the current-voltage curve being proportional to the tin concentration. The method was used by DeMars [33] for the analysis of binary tin-indium alloys (0.0 1 - 20% In) and was investigated by Phillips and Shain [34] for the direct determination of tin (~ 0.001 %) in steel, using a 0.1g sample. Interference by molybdenum, tungsten and copperwas mitigated by the use of a standard addition technique. Detailed studies by Bond et al. [35, 36] have shown that while the inverse method is not generally as accurate, rapid or reproducible as conventional a.c. polarography, in the tin concentration range of 1o- 3 - 10-6M it is superior in sensitivity and is recommended by them for analysis of tin in the range 1o-6 - 1o-s M. These workers used a supporting electrolyte of SM hydrochloric acid and electrolysed for 3 min at a potential of- l.OV vs. Ag/AgCI. The strippingwas then carried out by scanning over the range of- 1.0- OV at a scan rate of 1 V per minute. Anodic Stripping has recently been used [37] for the determination of traces (0.3ppb) oftin in copper, the tin being first isolated from a 2g sample by distillation of the bromide, while traces of tin, down to 1o-6 % have been determined without separation in 0.1 g samples of galliumarsenidein hydrochloric acid solution [38].

Ref.p. 65]

6. Anodic Stripping Voltammetry

Tin and lead have been determined in the presence of each other by means of a carbon paste electrode (39]. For the application of anodic stripping to the deterrnination of organotin compounds see Chapter 19.

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39.

Lindsey, A.J.: Analyst 75, 104 (1950) Lingane, J.J., Jones, S.L.: Anal. Chem. 23, 1798 (1951) Aylward, G.H., Brison, A.: Analyst 78, 651 (1953) Lingqne, J.J.: Ind. Eng. Chem. (Anal. Ed.) 18,429 (1946) Alfonsi, B.: Anal. Chim. Acta 19, 276, 289, 569 (1958) Alfonsi, B.: Anal. Chim. Acta 20, 277 (1958) Alfonsi, B.: Anal. Chim. Acta 25, 374 (1961) Alfonsi, B.: Anal. Chim. Acta 26, 316 (1962) Lingane, J.J.: lnd. Eng. Chem. (Anal. Ed.) 16, 147 (1944) Bard, A.J., Lingane, J.J.: Anal. Chim. Acta 20,463 (1959); 22, 577 (1960) Meites, L.: Anal. Chim. Acta 18,364 (1958) Wise, W.M., Williams,J.P.: Anal. Chem. 37, 1292 (1965) Wise, W.M., Campbell, D.E.: Anal. Chem. 38, 1079 (1966) Kolthoff, I.M., Lingane, J.J.: 'Polarography' Vol. II Interscience 1952 Lingane, J.J.: lnd. Eng. Chem. (Anal. Ed.) 18,429 (1946) Godar, E.M., Alexander, O.R.: Ind. Eng. Chem. (Anal. Ed.) 18,681 (1946) Fe"ett, D.J., Milner, G. V.C.: Analyst 81, 193 (1956) Barker, G.C., Jenkins, l.L.: Analyst 77, 685 (1952) Rooney, R.C.: Analyst 88,959 (1963) Kai/mann, S., Liu, R., Oberthin, H.: Anal. Chem. 30, 485 (1958) Goto, H., Ikeda, S., Watanabe, S.: Japan Analyst 3, 320 (1954) Schofes, P..H.: Analyst 86, 392 (1961) Bond, A.M.: Anal. Chem. 42, 1165 (1970) Bond, A.M., O'Donell, T.A., Waugh, A.B.: Anal. Chem. 42, 1168 (1970) Lingane, J.J.: J. Amer. Chem. Soc. 65, 866 (1943) Kolthoff, I.M., Johnson, R.A.: J. Electrochem. Soc. 98, 138 (1951) Kolthoff, I.M., Johnson, R.A.: J. Electrochem. Soc. 98, 231 (1951) Subramanian, N.: J. Sei. lnd. Res. 16, 518 (1957) Yamamura, S.S., Rein, J.E., Booman, G.L.: Anal. Chem. 31, 1868 (1959) Subramanian,N.: J. Sei. Ind. Res.16, 516 (1957) Deshmukh, G.S., Murty, S. V.S.S.: Z. Anal. Chem. 198, 328 (1963) Singh, D., Sharma, S.: Indian J. Chem. 8, 192 (1970) DeMars, R.D.: Anal. Chem. 34, 259 (1962) Phillips, S.L., Shain, /.:Anal. Chem. 34, 262 (1962) Bond,A.M.: Anal. Chem. 42,1165 (1970) Bond,A.M., O'Donnell, T.A.: Anal. Chem. 42,1168 (1970) Van Dyck, C., Verbeek, F.: Anal. Chim. Acta 66, 251 (1973) Troshima, G.M.: Tr. Tomsk. Gos. Univ. 237,69 (1973); Chem. Abstr. 80,90828 (1974) Monien, H., Zinke, K.: Z. Anal. Chem. 250, 178 (1970)

65

CHAPTER 7 SOLVENT EXTRACTION By R. Smith

Salutions of stannous and stannic salts precipitate hydroxides of tin at pH 1 - 2 and therefore solvent extraction procedures are best carried out in strong acid solutions to avoid this complication. Solvent extraction processes and associated theory aredealt with in detail in books on the subject (1 - 4), furthermore recent developments are reviewed biannually in the journal, Analytical Chemistry. Several convenient and quantitative extraction procedures are available for tin and in view of the universal application of such procedures in all branches of analytical chemistry it is quite impossible to review them completely here. Forthis reason, the authors have included here only those solvent extraction prodedures which have been used either as concentration or separation techniques. Extractive reagents which are likely to be used only in colorimetric analysis have been included in the relevant chapter.

1. Ion Association Systems In acid solutions containing halide or thiocyanate tin exists as complex ions of the type Sn X ~-; where the associated cation may be the hydrogen ion H+ or a protonated solvent molecule, suchasthat formed by diethyl ether, H(OEt 2 f. Strongly basic, high molecular weight aminessuch as the so-called liquid anion exchangers (e.g. tri-octylarnine) exist as the protonated form in acid solutions and may also serve as the counter ion. In addition to the extraction of anionic complexes, tin may also be extracted as simple molecules of the type SnX 4 . Tin has a maxirnum Co-ordination nurober of six and the remaining co-ordination sites are occupied by electron donor molecules such as dibutylphosphoric acid, diethylether or trioctylphosphine oxide. 1.1 Fluoride Extractions Both Sn(II) and Sn(IV) are quantitatively extracted (99.9%) by diethylether from aqueous solution containing 4.6M HF [5]. No extraction was noted for Ag, Bi, Cd, Co, Cr, Ga, K, Mn, Ni, Os, Te, Ti, U or Zr. Partial extraction was noted for As(III), Mo(IV), Sb(III) and Se(IV), while other elements extracting appreciably with Sn were Ta(V) and Nb(V). Other workers [6] have found the fluoride system for tintobe less satisfactory and give only partial extraction (5%) when working with 20M HF solutions and diethylether. Tin is not extracted from either 6M HC1/0.4M HF or 6M H2 S0 4 /0.4M HF into di-isopropyl ketone (7). In the former system, appreciable extraction of As(III), Fe(III), Ga, Nb, Sb(V), Se(VI), Ta and Te(VI) occurs, whilst in the latter system only

1.3 Bromide Extractions

Ref. p. 78]

67

Se, Ta and Te extract. Similarly, no extraction of tin takes place into methyl isobutyl ketone from 6M H 2 S04 /10M HF/2.2 M NH 4 F [8]. 1.2 Chloride Extraction Fig. 1 shows the extractability of Sn(IV) into diethylether from HCl solutions [ 1). At best this approaches 30% extraction with 4.5M HCL Similar observations have been made by Swift [9], who found 15% extraction from Sn(II) solutions of 6M HCl, and by Mylius and Huttner {10] who reported 17% extraction of Sn(IV) from 6M HCL

~or-----~r-------r-------r-------r-------~------r-----~

2

Fig.l

3

4

5

6

HCI MOLARITY

Methyl isobutyl ketone (MIBK), however, is a better extractant [ 11] and with greater than 5.5M HCl both Sn(II) and Sn(N) are quantitatively extracted. The presence of other acids (H 2 S0 4 or HC10 4 ) facilitates the extraction. F e(II) is not extracted under these conditions, but Sb(III), Sb(V), Se(IV) and Fe(III) are extracted if acid strengths greater than 8M HCl are used. In 8M HCI other ions extracted are: As(III) 90%, As(V) 25%, Ge(IV) 98% and Te(IV) 96%. Other elements extracting [12] from 8M HCI into MIBK were Cr(III) 82%, Mo(VI) 95%, V(V) 10%. Similar results were obtained by Waidich and P[annhauser [13]. Extraction of Sn(IV) from 7M HCI into iso amyl acetate [ 14] or ethyl acetate is said to be negligible and may be used to separate tin from antimony as extraction of Sb(V) is quantitative.

1.3 Bromide Extractions Both tin(II) and (IV) are extracted (Table 1) from 4M HBr into diethylether [15]. The extraction is not quantitative (84%) but is nevertheless significantly better than

[Ref. p. 78

Solvent Extraction

68

that obtained from a chloride solution. Other elements extracting weil under these conditions include: Au, Fe(III), Ga, In, Sb{IV) and Te{III). Less than 25% extraction was encountered with: As{III), Hg{II), Mo(VI) and Sb(III).

O(o

100

z ;:

0

~

..... Ui

z

....UJ ~

z 0

Ui

"'

~

UJ

..; "'

N N

..,

"'~

"' "'

225

..;

N

N

N

230

235

240

"' ;:::

..,

..,

"'

N

."'

r-

Cl)

Cl)

"'"'

N

245

250

255

WAVELENGTH nm

Fig. 4 Chemiluminescence atomic emission spectrum of 100J..Ig/ml Sn in a turbulent air/H 2 flame using iso-propanol as solvent [26]

86

Atomic Absorption Spectroscopy

[Ref. p. 94

Alkemade and Zeegers [27] have summarised excitation processes involved in chemiluminescence flame spectroscopy and suggest the reactions below as being responsible for excitation: CH+O CH+OH C2 + o CO*+ Sn CO*+ SnO

-)-)-)-)-)-

CO* + CO* + CO* + Sn* + Sn*+ C02

6H = -7.6eV 6H =- 7.7eV 6H =- 8.85 eV

H H2 CO CO

Most of the interest in chemiluminescence flame spectroscopy was shown before atomic absorption developed as an accepted analytical technique. Recent studies [25] have received little further support and it is unlikely that research of practical value to the analyst will be carried out in the near future.

3. Atomic Fluorescence Spectroscopy Initial studies [80] of the atomic fluorescence of tin using an air/H 2 flame and highintensity hollow cathode lamps as excitation sources were rather disappointing and a detection lirnit of 1OOpg/ml Sn was reported. This au thor [81] abtairred similar results with organotin compounds in air/hydrogen and argon/hydrogen flames using a microwave-excited electrodeless discharge tube as the exci tation source. Subsequently, Browner, Dagnall and West [12], using electronically modulated electrodeless,discharge tubes were able to observe atomic fluorescence at several wavelengths from tin in Ar/02/H2, Ar/H2 and air/acetylene flames. The relative fluorescence intensities abtairred from 1OOpg/ml Sn in these flames is given in Table 4. As in atomic absorption, the best Iimits of detection were found in a very fuel-rich Ar/0 2/H 2 flame (0.11 pg/ml Sn). Under these conditions interferences were found tobe prohibitive and a lean air/H2 or Ar/02/H 2 flame was recommended ( detection limit 0.3 pg/ml Sn in Ar/02/H2 and 2pg/ml Sn in air/H 2). In atomic fluorescence, the presence of Ar in place of N 2reduces collisional quenching of excited atoms and usually results in considerably enhanced fluorescence intensities. Calibration curves were linear up to 250pg/ m1 Sn. Table 4. Atomic Fluorescence Relative Intensities for Tin in Different Flames [12] Wavelength (nm)

Re!. Source Intensity

224.61 235.48 242.95 254.66 326.23 270.65 284.00 333.06 286.33 300.91 . 303.41 317.51 380.10

1.00 32.1 54.3 46.0 570 380 500 725 330 420 620 780 718

Relative Fluorescence Intensity Ar/02 /H2 3.70 3.61 7.42 5.92 8.14 81.5 215.0 37.0 237 200 519 482 66.7

Ar/H2

Air/C2 H2

6.30 4.75 35.5 58.5 58.5 4.74 122 94.0 130 213 39.6

2.15 3.00 3.54 2.55 17.0 27.0 72.0 8.06 36.5 31.4 91.2 64.4 12.1

Ref. p. 94]

5.1 Solvent Exttaction

87

4. Electrothermal Atomisation Replacement of the atomic absorption flame by an electrically heated carbon tube or filament is now part of accepted analytical practice and a number of authoritative articles on this aspect of atomic absorption have been published [2, 83 · 87, 97]. The technique is finding applications where extreme sensitivity is required and where relatively poor precision ( coefficients of variation of 10 - 20%) is acceptable. In some very early work, L 'vov [86] obtained 1% absorption at 286.3nm with 2 x 10-1 2 g Sn using a heated tube atomizer with arc volatilisation. Fora 1OOt-tl sample

this corresponds to a concentration of 2 x 1o-s ,ug/ml Sn and is by far the lowest concentration of tin measured using electrothermal atomisers. Everett, West and Williams [58] obtained a 1% absorption signal with 9 x 10- 11 g Sn at 286.3nm and 7 x 1o-ll g Sn at 224.6nm, using a carbon filament. Pub1ications [88, 89] from the University of Floridareport detection limits of the order of 1o-ll g Sn or 0.02,ug/ml Sn with graphite filaments and atomic fluorescence detection. A detection limit of 10- 10 g Sn was reported [90] using a heated tantalum filament atomizer. The use of an Ar/H 2 or H 2 sheathing gas in conjunction with graphite filament and rod atomisers gives improved detection limits, precision and freedom from interference for a number of elements. Tin is one element where this practice is almostessential [58, 88, 89, 91, 92, 93] to achieve complete reduction and gives enhancemen ts of ten-fold over a nitrogen sheathed fJJ.ament [58]. Typical flow rates are 2.81/min N2 and 1.31/min H 2 ; with open fllaments the glowing carbon automatically ignites the hydrogen sheathing gas and the resultant flame must be extinguished before the next sample can be introduced. Electrothermal atomisers have been used mainly for the analysis of oils, where the presence of tin may indicate impending bearing failures [58, 92, 93]. There appear tobe many interfering elements [58] at least with fllament atomisers, although the consequences of interference may be unimportant at the low levels for which the technique is used. Tin has also been determined in steel samples [55] using an induction heated graphite furnace of a rather unique design. The determination is of interest in that direct analysis of solid drillings samples was carried out in this particular instance.

5. Separation Procedures Separation procedures are used in atomic absorption either to increase the concentration of an elementtobe determined or toseparate the element from !arge quantities of matrix constituents which might interfere or cause burner blockage. Because of the inherent selectivity of atomic absorption, many more concomitants may be tolerated than would be the case in solution spectrophotometry, for example. Many of the concentration procedures used for other techniques would be applicable to atomic absorption, however, only the siruplest are usually necessary. 5.1 Solvent Extraction Solvent extractions used in the determination of tin by atomic absorption usually employ either a sulphur ligandsuch as ammonium pyrrolidine dithiocarbamate or an ion-association systemsuch as the extraction from acidic solutions. In both instances, the organic extract may be nebulised directly (preferably into a nitrous oxide/ acetylene flame) or tin may be stripped into an aqueous phase which is then nebulised.

88

Atomic Absorption Spectroscopy

[Ref. p. 94

The most suitable solvents for atornic absorption include methyl isobutyl ketone, ethyl acetate and saturated hydrocarbons. Solvents such as benzene or toluene produce excessively fuel-rich flames; carbon tetrachloride or chloroform produce large quantities of hydrochloric acid and other noxious products which may even extinguish the flame with some types of instrument. Extremely volatile solvents, such as diethyl ether, should be avoided on the grounds of safety; viscous solvents interfere with phase separation during extraction and have low uptake rates on nebulisation. Although organic and aqueous phases should be allowed to settle out after shaking, it is rarely necessary to remove the unwanted phase; the nebuliser capillary may be dipHed directly into the appropriate phase. Ammonium pyrrolidine dithiocarbamate (APDC) - This has been used extensively as a non selective extractant for many metals for atomic absorption [29], and has found some applications in the deterrnination of tin. lt may be used almost interchangeably with sodium diethyl-dithiocarbamate (NaDDC), both being storedas 1% aqueous solutions. Atmospheric oxidation of both reagents is rapid, particularly in acid solutions and stocks should be made up daily. APDC is more resistant to oxidation in acid solution than NaDDC. Extractions may be carried out into either ethyl acetate or methyl isobutyl ketone. The rnain disadvantage with APDC or NaDDC is that they are stable only above pH 4, under which conditions tin is readily precipitated as the hydroxide. Tin is extracted quantitatively with NaDDC only as Sn(IV) [31] at pH 5.6. Table 5 gives a summary of the pH ranges over which several elements may be extracted into MIBK using APDC [30].

Table 5. Ranges of pH for Complete Extraction of Meta!/ APDC complexes [30] pH

Elements Extracted

2 -14 Ag, Au, Cu, Ir, Rh, Tl(III) 2 -10 Bi, Co, Fe, Hg, In, Ni, Os, Pb, Pd, Pt, Re, Ru, Zn 3- 8 Ga 3- 7 Cr(VI) not Cr(III) 2- 6 Se, Sn(IV) 4- 6 Mn, Th, V 3- 5 .Sb, Te 2- 4" As(III), Nb, U 2- 3 Mo,W

APDC Extraction Procedure for Tin in Lead Alloys [32] Heat 0.5 g of Iead alloy sawings with 20 ml concentrated sulphuric acid and 4 g of potassium sulphate until no further reaction occurs and strong fumes are evolved. Cool and treat with 250 ml of water, fllter and dilute to 500ml with 10% hydrochloric acid. To a 50ml aliquot add 5ml of 2% aqueous APDC and extract immediately with lOml of MIBK. Nebulise the organic extract into a nitrous oxide/acetylene flame and measure the tin absorbance at 286.3nm.

Ion association systems are widely used for the extraction of tin and successfully overcome the disadvantages of chelating extractions. The extraction is carried out in strong acid solutions using simpleandinexpensive reagents. Excellent selectivity may be obtain~d for tin and, if necessary, comparatively large amounts may be

Ref. p. 94]

5.2 Coprecipitation

89

extracted. The various extraction systems used rely on the formation of complexes such as Snl~- or Sn(SCN)~-: The positive ion accompanying the tin complex into the organic phase may be the hydrogen ion or a Iong-ehain amine. The solvent used for extraction is important and quantitative separations which are successful with toluene or benzerre are often unsuccessful with MIBK. Two procedures given below have been used for the atomic absorption determination of tin in foodstuffs [33] and antimony, bismuth, Iead and tin in aluminium, iron and nicke! base alloys [34]. Details of the chemistry of solvent extraction systems will be found in the chapter on Solvent Extraction.

Solvent Extraction for Tin in Foodstuffs [33] lOg of eanned food were ashed with 10m! of eoneentrated sulphuric acidplus suffieient 30% hydrogen peroxide to give eomplete ashing. Vegetables and materials eontaining organotin compounds should be wet ashed with nitrie acid instead of hydrogen peroxide. Transfer the digest to a 50 ml volumetrie flask, add suffieient sulphurie aeid to give 12 ml in all, then dilute to volume with water. Transfer a 25 ml aliquot (or less) into a separating funnel and add 2.5 ml of 83% potassium iodide solution (or 2g of solid potassium iodide). Add 10m! of toluene and shake vigorously for 2 min, separate the phases and diseard the aqueous phase. Clean the toluene layer by shaking with 5 rnl of 1 : 4 sulphurie aeid and 0.4g potassium iodide, diseard the aqueous layer. Add 5 ml of water and 0.5 ml of 5 M potassium hydroxide solution and shake for 30 sec. Colleet the aqueous layer in a 25 ml volumetrie flask, aeidify with 5 ml of 1 : 1 hydrochloric aeid and 1ml of 5% aseorbic aeid so!ution to reduce free iodine. Dilute to volume and nebulise into an air/hydrogen flame measuring at 224.6nm. Aqueous standards eontaining the same amounts of potassium hydroxide, hydrochlorie acid and aseorbic aeid should be used and should be in the range 0.2- 100,Ug/rnl Sn. Alternatively an air/aeetylene flame may be used with standards in the range of 2 - 360 pg/rnl Sn.

Solvent Extraction Procedure for Tin in Metals [34] Dissalve 1- 5g of alloy in 60ml of eoneentrated hydrochloric acid with 60ml of water (nicke! base alloys), or with 20m! of eoneentrated nitrie aeid (iron base and Fe-Ni-er alloys), and dropwise addition of 30% hydrogen peroxide (Al alloys). Evaparate to 5 ml, add 10m! of hydrochloric acid and add formic aeid dropwise to remove nitrie acid. Add 5 ml of hydrochlorie acid, wash down with 5ml of water and add 4g of aseorbie acid to samples eontaining iron. Add 15m! of 30% potassium iodide solution and transfer to a 150m! separating funnel, rinsing with water to give a final volume of about 50ml. Pipette 10m! of 5% trioetylphosphine oxidein MIBK, shake for 30 sec and separate the phases. Discard the aqueous layer. If an emulsion forms it may be broken by centrifuging or flltration. Some phase separation papers contain tin eompounds soluble in MIBK, so take eare. Nebulise the extraet into a nitrous oxidefacetylene flame measuring at 286.3 nm. Prepare standards in the range 1 - 50 ,Ug/ml Sn by taking aqueous standards through the same proeedure. Antirnony, bismuth and Iead may be ineorporated in the standards; the use of organo metallic standards is not recommended [94]. 5.2 Coprecipitation Coprecipitation is a relatively easy technique for the removal of traces of tin from solutions containing !arge amounts of matrix elements. The few reported applications of coprecipitation have been modifications of standard procedures used with other techniques.

Kono [35] separated tin by coprecipitated with manganese dioxide from solutions of zinc base alloys and with beryllium hydroxide from solutions of ferrous alloys. The precipitates were then dissolved in hydrochloric acid and the solutions sprayed into a nitrous oxide/acetylene flame, measuring at 286.3nrn. Another application ofmanganese dioxide as a carrier has been in the determination of antimony, bismuth lead and tin in nicke! [36]. Manganese dioxide is formed by the reaction of manganaus sulphate and potassium permanganate in a solution of the sample at 70 - 100°C in the presence of 0.001 - 0.1 M nitric or perchloric acid. The precipitate is dissolved in concentrated

90

Atomic Absorption Spectroscopy

(Ref. p. 94

hydrochloric acid with addition of 30% hydrogen peroxide. The manganese concentration in the final solution is less than 0.3% and very little nickel is coprecipitated. Tin in the range 1 - lOO~g/g can be determined using an argon/hydrogen diffusion flame in the presence of up to 1 g of nickel, iron or copper. Traces of antirnony, arsenic, bismuth, iron, Iead, selenium, tellurium and tin may be recovered from up to 20g of copper by coprecipitation with lanthanum hydroxide (37]. This also acts as a releasing agent for subsequent atomic absorption. Coprecipitation of Tin from Copper by Lanthanum Hydroxide (37] Dissalve 20g of copper in nitric acid and boil to expel nitrous fumes. Add water to dissolve the residue and add 20 ml of 5 % lanthanum nitrate solution. Add slowly 200 ml of concentrated ammonia solution, [Jlter and wash with 1 : 10 ammonia solution then with water to remove copper. Dissalve the precipitate in 10m! of concentrated hydrochloric acid and 40ml of 1 : 1 nitric acid and dilute to 200m! for atomic absorption. Standards should incorporate 10ml of a "matrix" solution containing 1g/l copper, 50g/llanthanum nitrate (La(N0 3 h.6H 2 0) and 1: 10 nitric acid. Other elements: As, Bi, Fe, Pb, Se, Sb and Te may be incorporated in the standards and determined. The rangeswill depend on the source of the copper.

Coprecipitation of Tin from Copper. Zinc or Aluminium with Manganese Dioxide Dissalve 5g of alloy or meta! in 35m! of 1 : 1 nitric acid, dilute to approximately 200m! and add Sm! of 10% manganese nitrate solution and 5ml of 1% potassium permanganate solution. Boil for a few minutes, filter, rejecting the filtrate then dissolve the manganese dioxidein 20rnlof 1: 3 hydrochloric acid and 30% hydrogen peroxide added as required to complete the dissolution. Dilute to 100m! for atomic absorption using an air/hydrogen flame at 286.3 nm comparing against standards of 2- 200~g/ml containing 5g/l manganese nitrate and 5% hydrochloric acid.

5.3 Sublimation The classical distillation procedures for separating tin as the volatile bromide or chloride have not been employed in atomic absorption analysis as they are relatively time consuming and do not permit the treatment of large of numbers of samples. Bromide volatilisation can be used for the removal of Iarge amounts of antirnony, arsenic and tin if these are matrix elements and must be removed for the determination of other constituents. Sublimation oftin iodide, however, has been used by Bowman [38] for the separation of down to 0.02% Sn from ores and concentrates for atomic absorption. The procedure is simple and can be carried out in a test tube according to the procedure below. Furthermore, an automatic sublirnation apparatus has been devised (39] to treat up to 30 samples at any one time. The apparatus consists of two concentric rings, slotted to carry 30 test tubes radially. The tubes are inclined at .20° to the horizontal, their ends extending 4 cm beyond the outer ring and 2 cm beyond the inner one. They are rotated at 22 revs/min for 12 min then at 8 revs/min for 8 min. Heat is supplied by two bumers beneath the bottoms of the tubes and a flXed arm with a rubber shoe causes the tubes to rotate about their axes for a quarter turn as they pass the arm. Guimont (95] described an apparatus in which a rack containing forty 25 rnl test tubes was placed in a fumace so that the lower ends of the tubes were at 550°C while the upper ends were kept cool in a water-bath. A combination of iodide sublimation and solvent extraction has recently been used by Welsch and Chao (96] for the analysis of tin ores. Sublimation Method for Ores and Concentrates [38] Mix 0.2 g of fi!lely ground ore with 1 g of ammonium iodide in a test tube. Heat gently so that the sublimate condenses on the walls gradually and does not escape from the tube. Dissalve the sublimatein 10 ml of 2M hydrochloric acid at 75°C and dilute to 50ml with 2M hydrochloric acid

91

5.4 Other Separations

Ref. p. 94]

after filtering. Determine tin by atomic absorption in an air/hydrogen or nitrogenfhydrogen diffusion flame at 224.6nm against Standards of 2- 200pg/ml containing 2% ammoniumiodidein 2M hydrochloric acid.

5.4 Other Separations Few other practicable separation techniques have been reported in conjunction with the atomic absorption determination of tin. Direct extractions of feedstuffs with chloroform [40] have been carried out to determine organotin compounds, such as dibutyltin dilaurate. The extract was evaporated to low bulk then diluted with methanol before spraying. Similar exploitations of the solubility of organotin compounds in non-aqueous solvents have been made for the determination of tin in organametallic biocides on woollen fabrics [41] andin paint and vinyladditives [42]. Tin in tinplate has been determined by anodic dissolution of the sample between two carbon cathodes in 1 : 8 hydrochloric acid [43]. The nebuliser capillary tubewas dipped into the electrolyte and tinwas determined in an air/acetylene flame. The effects of iron were overcome by addition of 1000 - 2000,ug/ml iron to both electrolyte and standards. Forthedetermination of down to 2,ug/g tin in geological materials [44] a peroxidefusionwas carried out followed by electrolysis at 60- 80°C, 1.5- 2V and 0.7 - 1.0amp in the presence of a hydrochloric acid solution containing copper and lead with hydroxylammonium chloride added as a depolariser. Copper-coated electrodes were used and the deposit was dissolved in hydrochloric acid for the determination of tininan air/hydrogen flame at 224.6nm. Tin may be volatilised from 0.5M hydrochloric acid solutions as the hydride stannane: Thompson and Thomerson [82] found that addition of 2ml of 1% sodium borohydride solution to 1ml ofthe sample in 0.5M hydrochloric acid generated volatile SnH 4 as a single pulse. This was taken up in a stream of nitrogen or argon carrier gas and passed into a heated silica tube aligned with the optical axis of the atomic absorption spectrophotometer. The silica tube was mounted above the grid of a widepath air/acetylene burner and was heated in the air/acetylene flame. An auxiliary nitragen stream was used to cool the carrier gas input and was also injected into transverse tubes near the ends of the silica tubein order to prevent ignition of hydrogen produced during the vigoraus decomposition of sodium borohydride. A schematic diagram of the generator cell an silica atomisation tube is given (Fig. 5). Because of

-

N in

2

path

Fig. 5. Schematic of (a) hydride generator cell and (b) silica atomisation tube for the separation of tin as stannane

Table 6. Determination of Tin by Atomic Absorption Spectroscopy - Applications Matrix

Concen tration

Sampie Treatment

Ref.

Al Alloys

0.0002-0.1%

[35]

Al Alloys

0.0002-0.1%

Cu Metal Cu Alloys

J.lg/g Ievels 0.1 -10%

Cu Alloys

0.1 -10%

Cu Alloys

0.6-4.5%

Diss. Al alloys in HN03/HCI/H 2 S04 and extract with MIBK from 3.5M H2S0 4 /3.5 M HCJ:N20/C2H 2 flame 286.3nm See extraction with HCI/KI/TOPO MIBK, this Chapter See coprec. with La(OHh, this Chapter Diss. in 1:1:2 HCI/HN03!H 2 0, add HCJ for Sn and dilute. Add Cu to standards N2 O/C2H2 flame Diss. in 1:1 HCI/H 2 0 with min HN0 3 Air/H 2 flame 2 24 .6 nm Diss. in HCI with min HN03. Ar/H 2 or N 2/H 2 flame. Add FeCJ 3 releasing agent

Cu Alloys Iron Ferrosilicon Ferromanganese Steel

0.1 -10% 0.0002-0.1%

... >0.002%

Steel

...

Coprec. with Be(OH) 2 and redissolve Diss. in HF in PTFE bomb Diss. in 1:1 HCl, air/C 2H2

[34] [37] [14]

[69] [15] [56,70] [35] [76] [71]

...

Several methods for wide range of mild, low alloy, high alloy steels and iron

[75]

...

Diss. in HCI/HN03/HCJ04, N20/C2H2 flame, add Fe to standards See extraction with HCl/KI/TOPO MIBK, this Chapter Diss. in HCI/HN0 3 , extract from 0.5M HCI/0.5 M KSCN/ascorbic acid into MIBK. N20/C 2 H2 flame, 224.6nm

[77]

Steel

Traces

Steel

0.001-0.25%

Steel Steel Ni Alloys

0.33%

Pb Alloys

0.001 -0.005%

Pb Alloys

3-7%

Pb Alloys

[34] [48]

Diss. in HCI/HN03 Induction heated graphite furnace See extraction with HCl/KI/TOPO - MIBK, this Chapter Diss. lOg in 15 ml conc. HN0 3/15 ml 2% NH 4 F. Air/H 2 flame, 224.6nm, match standards for Pb/HN0 3 /NH4F Diss. in 1:2:10 HBF 4 /HN0 3/H 20, add. 0.2g tartaric acid. Air/C 2 H2 flame 235.8nm Standards from type metals

[15]

o.l%

Diss. under reflux with 8:2:3:5 50% tartaric acid/HF/15M HN03/H 2 0

[72]

Rapid diss. in 2:3:5 HBF 4/HN0 3 /H 20 with ultrasonic agitation in cold. Sn not determined

[62]

Coprec. with Mn0 2 , redissolve, N 20/C 2 H2 flame, 286.3 nm

[35]

Diss. in HF/HN03, add sat. H3B03, air/ C2H2 flame

[46]

Diss. by anodic electrolysis. Det. Sn in electrolyte with air/C 2H2 flame. Add 0.10.2% Fe to standards and unknown

[43]

... 0.0002 - 0.1%

Pb Alloys

...

Zn Alloys

Traces

Zr Alloys

...

Tinplate

0.1 - 1 %

[55] [34]

[13] [49]

Matrix U Fission Products Cr Plating Soln. Sn Plating Soln.

Concentra tion

Ref

. ..

[11]

.. .

...

[51]

...

H202 Slag, Soots, ZnConcentrates Ores, Concentrat es Ores,Con centrates Ores, Concentrates

>0.05JJ.g/ml 0.2-10%

Sphalerite Sulphide Ores, Silicates T.Jsed Oils

0.08% >0.0002% >0.5JJ.g/ml

Used Oils

0.2 - 2.5 JJ.g/ml

Oils, Xylenes Organa Sn

0- 20ng/ml

Organa Sn in PVC Organa Sn in Paints Organa Sn in Fabrics Organa Sn in Feeds

Sampie Treatment

...

200 - 1500 JJ.g/ml 0.02-80% 0.005-80%

0.5 -lOOJJ.g/ml 300JJ.g/g

...

... 0.03%

Organa Sn inWood

...

Polymers, Wool, Cotton Cellulose, Nylon, Polyester Juices Juices, Drinks Juices

... >ltJ.g/g 1 - lOOOjJ.g/ml 1 -lOOOJJ.g/ml >3JJ.g/ml

Foods

...

Foods

10 -lOOOJJ.g/g

Food

...

Dilute, air/C2H2 flame

[74]

Direct, 0 2 /H2 flame, 286.3nm Diss. in HN03/HF, fuse residue with Na2C03/Na2B40 7 and leach with HCI Air/C2H2 flame, 286.3nm Grind and disperse in water, nebulise suspension, air/H 2 flame, 224.6nm See Sublimation Separation- this Chapter

[63] [73]

FuselSublime with NH4I as ref. [38]. Add ascorbic acid/HCI/KI and extract with Trioctylphosphine oxide/MIBK. N20/C2H2 flame, 286.3 nm N2/H2 or Ar/H2 flame, 224.6nm Fuse with Na2 0 2 , diss. and electrolyse· with HCI/hydroxylamine/Cu/Pb. Diss. residue. Air/H 2 flame, 224.6nm Dilute 1:2 with MIBK, N20/C2H2 flame 286.3 nrn Dry at 250°C, ash to 440°C, atomise 2000°C with graphite rod, 224.6 nrn 0.5 jJ.I sample, aqueous standards Direct, carbon filament with H2 flame 224.6 or 286.3 nm Sensitivity study on MIBK solutions, air/C2H2 and N20/C2H2, 224.6 nm, 286.3nm Ash, convert Sn to acetate, air/C2H2 flame 224.6nm Either decompose with 1:1 HN03/H20 or dilute with MIBK, Air/C 2H2 flame > l2jJ.g Sn required. Diss. in ethanol

[4 7] [38] [60]

[50] [44]

[9] (57] (58] (59] [65] (42] [41]

Extract with CHCI 3 , evaparate add methanol [40] and spray, air/C2 H2 flame, 286.3 nrn DibutylSn-Dilaurate additives Extract with HCI/Ethanol, separate by ion(53] exchange, add 0.1% Li to all solutions. N20/C 2H2 flame, 224.4nrn [78] Wet ash with H2S04/H202

... Centrifuge, dilute, air/C2H2 Centrifuge, dilute, heat to remove C02 from carbonated drinks To 20ml add lOml HCI, dil. to lOOml, centrifuge. N2 0/C 2 H2 flame, 286.3nrn Ash with H2 S04/HN0 3 , extract Sn into MIBK See Extraction Method for Foods- this Chapter

...

[66] [45] [68] [67] [64] [33] [61]

94

Atomic Absorption Spectroscopy

the pulse-like nature of the absorption signal a detection lirnit of 0.0005 J.J.g/ml Sn at 224.6nm was recorded in this work [82]. At the time of writing, the work has not been applied to practical analytical problems and the effects of oxidation state and interferences are as yet unknown. Nevertheless, the technique could provide an extremely sensitive method for tin using inexpensive accessories with a conventional AAS spectrometer and is already under active investigation for the determination of elementssuch as As, Bi,Ge, Pb, Sb, Se, Te which also form volatile hydrides.

6. Applications Practical applications of atomic absorption to the deterrnination of tin are given in Table 6. Abrief reference is given to the sample treatment adopted and will suffice for most purposes. In most cases the determinations are carried out directly after dissolution of the sample. The applications listed cover the range of tin technology from alloying components, tin plating, organo tin additives, to tin catalyst residues in fibres. Tin determinations in used lubricating oils are a valuable pointer in diagnosing bearing wear and impendings failure. As a contaminant, tin is present in foods and drink, and is very harmful contaminant in the manufacture of steel. References 1. Mavrodineau, R., Boiteux, H.: Flame Spectroscopy, New York: Wi!ey 1965 2. Kirkbright, G.F., Sargent, M.: Atomic Absorption and Fluorescence Spectroscopy, London: Academic Press 1974 3. Varian Techtron Pty.: Hollow Cathode Lamp Data, 1970 4. Rubeska, I.: Spectrochim. Acta 29B, 280 (1974) 5. Capacho-Delgado, L., Manning, D.C.: Spectrochim. Acta 22, 1505 (1966) 6. Juliano, P.O., Harrison, W. W.: Anal. Chem. 41, 1016 (1969) 7. Sastri, V.S., Chakrabarti, C.L., Willis, D.E.: Can. J. Chem. 47,587 (1969) 8. Kahn, H.L., Schallis, J.E.: Perkin Eimer A.A. Newsletter 7, 5 (1968) 9. Schallis, J.E., Kahn, H.L.: Perkin Eimer A.A. Newsletter 7, 84 (1968) 10. Capacho-Delgado, L., Manning, D.C.: Perkin Eimer A.A. Newsletter 4, 317 (1965) 11. Grison; J.: Chim. Anal. 51,605 (1969) 12. Browner, R.F., Dagnall, R.M., West, T.S.: Anal. Chim. Acta 46, 207 (1969) 13. Perry, B.: Spectrovision 25, 8 (1971) ' 14. Johns, P., Price, W.J.: Metallurgia 81, 75 (1970) 15. Nakahara, T., Munemori, M., Musha, S.: Anal. Chim. Acta 62, 267 (1972) 16. Burke, K.E., Albright, C.H.: Dev. Appl. Spectros. 8, 33 (1970) 17. Pickett, E.E., Koirtyohann, S.R.: Spectrochim. Acta 24 B, 325 (1969) 18. Kahn, H.L.: Perkin Eimer A.A. Newsletter 7, 40 (1968) 19. Dagnall, RM., Thompson, K.C., West, T.S.: Analyst 93,518 (1968) 20. Meissner, H.: Z. Anal. Chem. 80, 247 (1930) 21. Tamura, Z., Kawahara, K.: Japan Analyst 5, 559 (1956) 22. Smith, R.: Spectrochemical Methods of Analysis, Winefordner, J.D., Ed. New York: Wiley Interscience ( 1971) 23. Woodward, C.: Spectros. Lett. 4, 191 (1971) 24. Buell, B.E.: Anal. Chem. 35, 372 (1963) 25. Alder, J.F., Thompson, K.C., West, T.S.: Anal. Chim. Acta 50, 383 (1970) 26. Gilbert, P.T.: Paper at 13th Pittsburgh Conf.Anal.Chem.Appl.Spectros. March (1962) 27. Alkemade, C.T.J., Zeegers, P.J.T.: Spectrochemical Methods of Analysis, Winefordner, J.D., Ed. New York Wiley: Interscience (1971) 28. Pickett, E.E., Koirtyohann, S.R.: Spectrochim. Acta 23B, 235 (1968) 29. Malissa, H., Schoffmann, E.: Mikrochim. Acta 187 (1965) 30. Watson, CA.: Monograph 74 Chadwell Heath, Essex: Hopkin & Williams Ltd. 31. Dagnall, RM., Smith, R., West, T.S.: Talanta 13, 609 (1966) 32. Matsuo, T., Shida, J., Nakamura, C.: Japan Analyst 20, 697 (1971) 33. Engberg, A.: Analyst 98, 137 (1973) 34. Burke, K.E.: Analyst 97,19 (1972)

References 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. SO. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. 88. 89. 90. 91. 92. 93. 94. 95. 96. 97.

Kono, T.: Japan Analyst 20, 552 {1971) Burke, K.E.: Anal. Chem., 42, 1536 {1970) Reiche/, W., Bleakley, B.G.: Anal. Chem. 46,59 {1974) Bowman, JA.: Anal. Chim. Acta 42, 285 {1968) Sierra, J., Leon, JM.: Trans. Inst. Min. Metall. 76B, 210 {1967) George, GM., Albrecht, MA., Frahm, L.J., McDonnell, J.P.: J .Ass.Off. Anal.Chemists 56, 1480 {1973) Freeland, G.N., Hoskinson, RM.: Analyst 95, 579 {1970) Eider, N.G.: Appl. Spectros. 25, 313 {1971) Clauss, C., Laugel, P., Hasselmann, M.: Chim. Anal. 53, 102 {1971) Moldan, B., Rubeska; /., Mikovsky, M., Huka, M.: Anal. Chim. Acta 52, 91 {1970) Roos, J.T.H.: Spectrovision 28,4 {1972) Schlewitz, J.H., Shields, M.G.: Perkin Eimer A.A. Newsletter 10, 39 {1971) Harrison, W. W., Juliano, P.O.: Anal. Chem. 43, 248 {1971) Headridge, J.B., Sowerbutts, A.: Analyst 97,442 {1972) Gouin, J.U., Holt, J.L., Miller, R.E.: Anal. Chem. 44, 1042 {1972) Rubeska, I., Mikovsky, M.: Perkin Eimer A.A. Newsletter 11, 57 {1972) Clark, R.C., Osborn, G.: Electroplating Metal Finish. 25, 18 (1972) Qua"ell, T.M., Powell, R.J. W., Cluley, H.J.: Analyst 98, 443 {1973) Williams, A.l.: Analyst 98, 233 {1973) Bell, H.F.: Anal. Chem. 45, 2296 {1973) Ashy, M.A., Headridge,J.B., Sowerbutts, A.: Talanta 21, 649 (1974) Barnett, W.B., Kerber, J.D.: Perkin Eimer A.A. Newsletter 13, 56 {1974) Chuang, F.S., Winefordner, J.D.: Appl. Spectros. 28, 215 (1974) Everett, G.L., West, T.S., Williams, R. W.: Anal. Chim. Acta 70, 291 {1974) Peetre, l.B., Smith, B.E.F.: Mikrochim. Acta, 301 (1974) Mensik, J.D., Seidemann, J.: Perkin Eimer A.A. Newsletter 13, 8 {1974) Duran, L., Soto, L.: Revta Agrquim. Technol. Aliment. 13,476 {1973) Hwang, J.Y., Sandonato, LM.: Anal. Chem. 42, 744 {1970) Agazzi, E.J.: Anal. Chem. 37, 364 (1965) Woidich, H., Pfannhauser, W.: Deut. Lebensmitt.Rdsch. 69, 224 (1973) Fassy, H., Lalet, P.: Chim. Anal. 52, Ü81 {1970) Price, J.P.: T.A.P.P.l. 54, 1497 (1971); Anal. Abstr. 22,4163 (1972) Price, W..J., Roos, J.T.H.: J. Sei. Food Agric. 20,437 {1969) Meranger, J.C.: Bull. Environ. Contam. Toxicol. 5, 271 {1970) Scott, C.C., Wallen, M.A.: Spectros. Lett. 4, 353 (1971) Toma, 0., Crisan, T.: Z. Metalkunde 25,715 {1971) Foster, P., Bozon, H., Molins, R.: Analusis 1, 205 {1972) Seco, J.L.J., Coedo, A.G., Lopez, M.T.D.: Revta. Metall. 5, 602 {1969) Mastalerz, R., Raczynska, D.: Chemia Analit. 16, 85 (1971) Levine, J.R., Moore, S.G., Levine, S.L.: Anal. Chem. 42,412 (1970) Hamson, T.S., Foster, W. W., Cobb, W.D.: Metall Meta! Form. 40, 361 (1973) Langmyhr, F.J., Paus, P.E.: Anal. Chim. Acta 45, 173 (1969) Thomerson, D.R., Price, W.J.: Analyst 96, 825 {1971) 0/ivier, M.: z. Anal. Chem. 248, 145 (1969) Amos, M.D., Willis, J .. B.: Spectrochim. Acta 22, 1325 (1966) Manning, D.C., Heneage, P.: Perkin Eimer A.A. Newsletter 7, 80 {1968) Smith, R., Stafford, C.M., Winefordner, J.D.: Canad. Spectros. 14, 2 {1969) Thompson, K.C., Thomerson, D.R.: Analyst 99, 595 {1974) Kirkbright, G.F.: Analyst 96, 609 (1971) Woodriff, R.: Appl. Spectros. 28,413 (1974) DeGalan, L.: Chem. Weekbl. 70, 38 (1974) L 'vov, B. V.: Spectrochim. Acta 24B, 53 {1969) Massman, H.: Spectrochim. Acta 23B, 215 (1968) Chuang, F.S., Winefordner, J.D.: Appl. Spectros. 29,412 (1975) Molnar, C.J., Winefordner, J.D.: Anal. Chem., 46, 1418 {1974) Hwang, J. Y., Mokeler, C.J., Ullucci, P.A.: Anal. Chem. 44, 2018 {1972) Reeves, R.D., Pate!, B.M., Molnar, C.J., Winefordner, J.D.: Anal. Chem. 45, 246 (1973) Reeves, R.D., Molnar, C.J., Glenn, M.T., Ahlstrom, J.R., Winefordner, J.D.: Anal. Chem. 44, 2205 (1972) Pate!, B.M., Reeves, R.D., Browner, R.F., Molnar, C..J., Winefordner, J.D.: Appl. Spectros. 27, 171 {1973) Thornton, K., Burke, K.E.: Analyst 99,469 (1974) Guimont, J., Bouchard, A., Pichette, M.: Talanta 23, 62 (1976) Welsch, E.D.,.Chao, T.T.: Anal. Chim. Acta 82,337 {1976) Fuller, C. W.: Electrothermal Atomization for Atomic Absorption Spectrometry, Analytical Seiences Monograph No 4, London: The Chemical Society (1977)

95

CHAPTER 9 EMISSION SPECTROSCOPY By R. Smith

A nurober of authoritative textbooks are available on the subject of emission spectroscopy and deal thoroughly with the fundamental principles of the technique. Some of the more recent books are those of Moenke [ 1], Mika and Torok [2], Grove [3], Addink [4] and Slavin [5]. In addition, a nurober of excellent reviews [6, 7) or abstracts [8] are published at regular intervals. Other useful publications are the ASTM book [9], the IUPAC recommendations on terminology [10] and several compilations of atomic wavelengths [ 11 - 14]. This chapter deals with the emission spectroscopy of tin using conventional arc/ spark emission source units. A nurober of other emission sources are available at the time of writing, including inductively-coupled plasma torches, glow discharge lamps, hollow cathode lamps, Iaser microprobes, etc. These techniques are for the most part undergoing development and evaluation, and as they are not widely used at present for strictly routine use, the authors have omitted them from this chapter. Furthermore, the emission spectroscopy of tin using a flame as the excitation source has found only limited applications and is described in the chapter on Atomic Absorption Spectroscopy. The analysis of tin meta! or alloys by emission spectroscopy is described in the appropriate chapters.

1. Spectral Characteristics of Tin 1.1 Molecular Spectra Molecular spectra, such as those emitted by SnH or SnO, may be excited in flames [ 15 J but are unimportant in arc/spark emission spectroscopy. 1.2 Atomic Spectra The emission spectroscopic determination of tin, present as minor or trace quantities, is convenient in that there are several atomic lines of varying intensity covering a wide range of wavelengths. The characteristic wavelengths [ 12, 13] are given in Table 1 together with their approximate relative intensities. Tin resonance transitions (i.e. emissions terrninating in the 3 P 0 ground state) occur at 207.31, 224.61, 254.66 and 286.33nm. In addition, a nurober of transitionsexist which terrninate in the low energy 3 P1 (0.21 e V) state: 197.08, 209.16, 211.39, 214.87, 219.93, 233.48, 235.48, 238.07, 266.12, 270.65,300.91 and 303.14nm. Both types oftransition will be subject to self-absorption and self-reversal. This will Iimit the linearity of calibrations on certain instruments and, where possible, these lines should be avoided.

1.3 Atomie Line Interferenees

Ref. p. 122]

97

Table 1. Atomie Emission Speetrum of Tin [ 12, 13] Wavelength nm

Are Intensity

Energy Levels K

197.080 198.355 204.066 207.308 209.158

2600 1500 800 480 550

1692-52416 3428-53826 3428-52416 0-48222 1692-49487

209.639 210.093 211.393 214.873 215.143

140 150 550 60 140

8613-56299 3428-51010 1692-48982 1692-48216 3428-49894

219.449 219.934 220.965 221.105 223.172

160 220 320 30 48

3428-48982 1692-47146 3428-48670 8613-53826 3428-48222

224.605 225.117 226.719 226.891 228.668

420 19 48 320 65

0-44509 8613-53021 8613-52707 3428-4 7488 3428-4 7146

231.723 233.480 235.484 235.790 238.072

220 140 550 6 20

8613-51754 1692-44509 1692-44145 8613-51010 1692-43683

240.815 242.170 242.949 243.34 7 245.52

26 360 550 4 5

8613-50126 8613-49894 3428-44576 3428-44509 3428-44145

Wavelength

Are Intensity

Energy Levels K

248.34 249.57 252.39 254.66 257.16 259.44

110 110 15 240 100 55

3428-43683 8613-48670

266.12 270.65 276.18 277.98 278.50 281.26

140 700 11 100 32 12

1692c39257 1692-38629 3428-39626 8613-44576 8613-44509 17163-52707

281.36 284.00 285.06 286.33 291.35 300.91

60 1400 170 1000 24 700

8613-44145 3428-38629 8613-43683 0-34914 17163-514 75 1692-34914

303.28 303.41 314.18 317.51 326.23 333.06

40 850 4 550 550 110

17163-50126 1692-34641 17163-48982 3428-34914 8613-39257 8613-38629

365.58 380.10 452.47 563.17 855.26

40 280 40 4 1

17163-44509 8613-34914 17163-39257 17163-34914 34914-46603

nm

0-39257 8613-47488 8613-47146

1.3 Atomic Line Interferences A more important criterion for line selection, however, is a consideration of line overlap with the spectrallines of other elements. Table 2lists some of the more useful tin lines tagether with potentially interfering lines from other elements [ 14]. The data of Table 2 were obtained by mixing a synthetic sample containing the elements of interest with a matrix of Li 2 C0 3 and graphitein the ratio (1 : 4 : 20). A graphite crater electrode was fllled with 35 mg of the mixture and completely burned in a d.c. arc for 150 sec. The spectrum was recorded photographically. From Table 2, it is possible to assess the importance of line overlap in a particular application. F or example, in the range 0.04 - 0.4% Sn, there will be a pronounced interference from Cr 303.42 nm on the Sn 303.41 nm line. The limit of detection of the former is 0.03% Cr and that of the latter 0.003% Sn. However, at the Sn 283.99 nm wavelength, Cr 284.00nm is also coincident, but the detection limits are 0.003% Sn and 1% Cr; hence interference occurs only at much higher chromium concentrations. At Sn 326.23nm there are no neighbouring chromium lines and this wavelength would be chosen if the interference from other elements permitted.

98

[Ref. p. 122

Emission Spectroscopy Table 2. Line Overlap Interference with Tin Spectral Lines [14]

Analytical Line

Sn I 3175.019

Sn I 2839.989

Sensitivity (%) 1:4:20

0.002

0.0025

Concentration Range (%) 1:4:20

0.025-0.3

0.035-0.4

Interfering LineA

!:J./1.

Sensitivity (%) 1:4:20

Th 3174.460 Mn3174.651 Mo3174.672 Ti 3174.80 Pt 3174.824 Co 3174.905 Fe 3174.96 Fe 3175.035 Fe 3175.0 Mo3175.049 Mn3175.2 u 3175.358 Fe 3175.447 Mo3175.53 Mo3175.587 Cr 3175.6

- 0.559 - 0.368 - 0.347 - 0.219 - 0.195 - 0.114 - 0.059} +0.016 - 0.019 +0.030 +0.181 +0.339 +0.428 +0.511} +0.568 +0.581

30 10 20 10 15 2

Zr 2839.330 Zr 2839.4 V 2839.437 Mo2839.585 u 2839.651 Ta 2839.778 Nb 2839.80 Ti 2839.80 u 2839.890 Mn2840.001 Cr 2840.021 Al 2840.05 w 2840.097 w 2840.220 w 2840.1 V 2840.106 Th 2840.156 Ti 2840.2 Ta 2840.39 Fe 2840.423 Cr 2840.438 u 2840.466 V 2840.599 u 2840.623

- 0.650} - 0.589 - 0.552 - 0.404 - 0.338 - 0.211 - 0.189 - 0.189 - 0.099 +0.012 +0.032 +0.061 +0.108} +0.231 +0.111 +0.117 +0.167 +0.211 +0.401 +0.434 +0.449 +0.477 +0.610 +0.634

Mn3033.563 3033.575 V 3033.822 Nb 3034.0 u 3034.049 Th 3034.069 Th 3034.1 Cr 3034.190 w 3034.195 Mo3034.2 Co 3034.433 Ni 3034.5 Fe 3034.538

50 - 0.558 - 0.546 5 0.1 - 0.299 1.5 - 0.121 20 - 0.072 0.7 - 0.052 } - 0.021 0.03 +0.069 +0.074 5 +0.079 5 0.6 +0.312 2 +0.379 +0.417 1

w

Sn I 3034.121

0.003

0.04-0.45

A

50

-

2 25 2 1 0.5 20 0.5 2 1 15 10 5 5 1 10 1 30 20 10 5 5 5 1 5 5 10 2

Atomic Line Interferences

Ref. p. 122]

99

Table 2 (continued) Analytical Line

Sn I 3262.328

Sensitivity (%) 1:4:20

0.003

Concentration Range(%) 1:4:20

0.04-0.45

Sn I 3009.147

0.005

0.07-0.8

Sn I 3330.594

0.015

0.25- 3

Sn I 2546.552

0.04

0.6 -7

Interfering LineA Pt 3261.692 Nb 3261.695 u 3261.718 Mn3261.8 Zr 3261.8 Mo3261.84 Nb 3261.879 Ba 3261.96 Fe 3262.013 V 3262.062 Mo3262.188 Ba 3262.275 Fe 3262.280 Ta 3262.3 V 3262.3 Mo3262.353 Pb 3262.353 Pb 3262.4 Mo3262.628 Th 3262.671 u 3262.7 Mn3262.9 Mn 3262.9 V 3008.505 V 3008.614 Ni 3008.8 Mn3008.822 u 3008.922 Nb 3008.964 Nb 3009.0 w 3009.076 Fe 3009.092 Ca 3009.205 Mn3009.4 u 3009.42 Fe 3009.570 V 3009.6 Th 3009.725 Sr 3329.988 Sr 3330.1 Fe 3330.313 u 3330.399 Th 3330.475 Co 3330.6 Cr 3330.60 Mo3330.663 Mn3330.668 Ta 3331.007 Ta 3331.2 Fe 2445.979 V 2545.983 V 2546.0 Cr 2546.456 Mn2546.607 Fe 2546.661 Co 2546.737 Co 2546.8 Ta 2546.803 Fe 2546.874 V 2547.075 w 2547.136

!:::.">..

A

Sensitivity (%) 1:4:20

- 0.636 - 0.633 - 0.610 - 0.528 - 0.528 - 0.488 - 0.449 - 0.368 - 0.315 - 0.266 - 0.140 - 0.053 - 0.048 - 0.028 - 0.028 + 0.025 + 0.025} + 0.072 + 0.300 + 0.343 + 0.372 + 0.572} + 0.572

10 5 0.5 30 3 3 0.2 20 15 1 30 5 10 10 1 1 10

- 0.642} - 0.533 - 0.347 - 0.325 - 0.225 - 0.183} - 0.147 - 0.071 - 0.005 + 0.058 + 0.253 + 0.273 + 0.423 + 0.453 + 0.578

0.5

0.1 0.1 15 25

1 30 2.5 10

3 5 0.5 20 0.7 0.1 2 1 - 0.606 } 0.3 - 0.494 - 0.281 50 1.5 - 0.195 - 0.119 0.1 + 0.006 7 + 0.006 5 + 0.069 10 + 0.074 0.7 1 + 0.413 } + 0.606 - 0.573 0.025 - 0.569 } 0.5 - 0.552 40 - 0.096 + 0.055 20 + 0.109 50 + 0.185 } 7 + 0.248 + 0.251 5 + 0.322 2 10 +0.523 + 0.584 1

100

[Ref. p. 122

Emission Spectroscopy

Table 2 (continued) Analytical Line

Sn I 2850.618

Sn I 2661.248

Sn I 2779.817

Sensitivity (%) 1:4:20

0.04

0.07

0.1

Concentration Range(%) 1:4:20

0.6 -7

1 -11

1.5 -16

Interfering LineA

I::::.'I\

A

Sensitivity (%) 1:4:20

u 2849.983 Co 2850.043 u 2850.487 Ta 2850.491 Cr 2850.5 V 2850.686 V 2850.768 Mo2850.787 Mo2850.898 w 2850.800 u 2850.820 Co 2850.951 Ta 2850.985 Ti 2851.102 Sb 2851.112 Mo2851.179 V 2851.254 Th 2851.261 Mg2852.129

- 0.635 - 0.575 - 0.131 - 0.127 - 0.118 + 0.068} + 0.150 + 0.169} + 0.280 + 0.182 + 0.202 + 0.333 + 0.367 + 0.484 + 0.494 + 0.561 + 0.636 + 0.643 +1.511

10 2 10 0.03 0.5 3 3 30 0.5 1

Co 2660.6 Mn2660.619 Ti 2660.640 u 2661.1 Fe 2661.196 Fe 2661.312 Ta 2661.336 Th 2661.38 V 2661.423 w 2661.557 Co 2661.715 Cr 2661.728 Nb 2661.856 Ta 2661.886

- 0.648 - 0.629 - 0.608 - 0.148 - 0.052 + 0.064 + 0.088 + 0.132 + 0.175 + 0.309 + 0.467 + 0.480 + 0.608 + 0.638

25 50 3 10 5 5 0.05 10 0.1 15 15 1 2.5 1

Fe 2779.299 Zr 2779.3 w 2779.317 Nb 2779.361 u 2779.406 Mo2779.476 Fe 2779.70 Ta 2779.704 Nb 2779.719 w 2779.724 Mg2779.834 Mn2779.998 Mn278Q.Q. Mo2780.036 u 2780.040 V 2780.097 As 2780.197 Ta 2780.208 Nb2780.245 w 2780.283 Cr 2780.703

- 0.518 - 0.517 - 0.500 - 0.456 - 0.411 - 0.341 - 0.117 - 0.113 - 0.098 - 0.093 + 0.017 + 0.181 } + 0.183 + 0.219 + 0.223 + 0.280 + 0.380 + 0.391 + 0.428 + 0.466 + 0.886

10 5 40 0.5 1.5 1 30 10 0.5 15 0.008 1

2 3 1 0.1 5 2 2

0.08 1 30 0.7 5 0.25 25 5

101

Atomic Line Interfetences

Ref. p. 122]

Table 2 (continued) Analytical Line

Sn I 2483.403

Sn I 2571.592

Sensitivity (%) 1:4:20

0.1

0.1

Concentration Range(%) 1:4:20

1.5-20

1.5- 18

Interfering Line Ä

Ä

/Sl\

Sensitivity (%) 1:4:20

V 2483.070 Fe 2483.270 Pt 2483.367 Ta 2483.4 Fe 2483.535 Co 2483.612 V 2483.648 Mn2483.7 Nb2483.717 Nb2483.882 Ta 2484.0 u 2484.008 Ni 2484.034

- 0.333 - 0.133 - 0.036 - 0.003 + 0.132 + 0.209 + 0.245 + 0.297 + 0.314 + 0.479 + 0.597 + 0.605 + 0.631

20 0.005 2 5 3 1 15 60 25 25 2 5 3

Ti 2571.034 V 2571.057 Ta 2571.192 Nb 2571.326 Zr 2571.391 Zr 2571.4 w 2571.445 Cr 2571.741 Cr 2572.1 Nb 2572.102 Cr 2572.146 Co 2572.237

- 0.558 - 0.535 - 0.400 - 0.266 - 0.201 } - 0.192 - 0.147 + 0.149} + 0.508 + 0.510 + 0.554 + 0.645

0.5 20 1 2 0.02

Ti 2812.982 2813.042 Fe 2813.288 Cr 2813.41 Cr 2813.552 Cr 2813.685 Mn2813.473 u 2813.549 u 2813.795 u 2813.982 Mn2813.992 V 2814.0 Mo2814.046

- 0.600 - 0.540 - 0.294 - 0.172} - 0.030 + 0.103 - 0.109 - 0.033 + 0.213 + 0.400 + 0.410 +0.418 + 0.464

2 2 0.05

0.5 8 10 10 2 10 5

w

- 0.455 - 0.445 - 0.428 - 0.366 - 0.168 - 0.019 + 0.051 + 0.069 + 0.081 + 0.098 + 0.144 + 0.281 + 0.381 + 0.518 + 0.590

2 30 25 8 1 25 25 10 15 1 3 15 3 15 0.3

u

Sn I 2813.582

Sn I 2495.719

0.2

0.2

2.5- 30

2.5-35

2495.264 Zr 2495.274 u 2495.291 Th 2495.353 Co 2495.551 Cr 2495.7 u 2495.77 V 2495.788 Ni 2495.8 Pt 2495.817 Fe 2495.863 Ni 2496.0 B 2496.1 Ta 2496.237 Cr 2496.309

5 0.5 5 2 2

15

102

[Ref. p. 122

Emission Spectroscopy Table 2 (continued)

Analytical Line

Sn I 3032.775

Sn I 2594.423

Sn I 2785.031

Sn I 3141.809

Sensitivity (%) 1:4:20

0.25

0.3

0.4

0.8

Concentration Range(%) 1:4:20

3-35

3.5 -40

4.5-50

> 10

Interfering LineA

ISJ\

Mn3032.3 Mo3032.545 Nb3032.768 As 3032.84 Cr 3032.927 u 3032.979 Sb 3033.0 Fe 3033.101 u 3033.193 Mo3033.234 Mo3033.33 Mo3033.3 Ta 3033.392 Nb 3033.393 Cr 3033.4

- 0.475 - 0.230 - 0.007 + 0.065 + 0.152 + 0.204 + 0.225 + 0.326 + 0.418 + 0.459} + 0.555 + 0.525 + 0.617 + 0.618 + 0.625

50 30 0.1 15 3 5 15 10 0.5

Ni Cr Fe Fe Co Ta

2593.9 2594.02 2594.Q38 2594.150 2594.158 2594.247 u 2594.275 Nb2594.338 Ta 2594.536 Ti 2594.629 Nb2594.740 u 2594.989 Th 2595.033

- 0.523 - 0.403 - 0.385} - 0.273 - 0.265 - 0.176 - 0.148 - 0.085 + 0.113 + 0.206 + 0.317 + 0.566 + 0.610

2 5

u

2784.450 Ti 2784.643 u 2784.669 Ta 2784.967 Th 2784.978 Mo2784.992 Mo2785.0 u 2785.17 Fe 2785.213 Ba 2785.264 V 2785.543 Th 2785.613

- 0.581 - 0.388 - 0.362 - 0.064 - 0.053 - 0.039} - 0.031 + 0.139 + 0.182 + 0.233 + 0.512 + 0.582

Ta 3141.380 Mo3141.415 w 3141.424 V 3141.485 Ti 3141.537 u 3141.538 Pt 3141.658 Ti 3141.670 Mo3141.730 Cr 3141.82 Th 3141.849 Th 3141.0 u 3141.953 w 3142.145 V 3142.186 Cu 3142.444 Fe 3142.453

- 0.429 - 0.394 - 0.385 - 0.324 - 0.272 - 0.271 - 0.151 - 0.139 - 0.079 + 0.011 + 0.040} + 0.091 + 0.144 + 0.336 + 0.377 + 0.635 + 0.644

A

Sensitivity (%) 1:4:20

3 10 1 5

3 2 0.5 25 3 15 10 1 15 10 0.5 3 3 1.5 3 0.3 10 10 10 3 5 10 3 5 1.5 0.05 5 15 0.5 3 5 1 0.8 10 20 5 5

103

2. Types of Discharge

Ref. p. 122] Table 2 (continued) Analytical Line

Sn 1 2812.566

Sensitivi ty

Concentration Range

(%)

(%)

1:4:20

1:4:20

2

> 20

Interfering LineA

V 2811.980 Cr 2812.006 Fe 2812.049 Fe 2812.1 Mo2812.147 V 2812.169 u 2812.235 Ni 2812.3 Mo 2812.585 Mo2812.6 V 2812.694 Mn2812.845 Ti 2812.982 u 2813.042

6A. A

Sensitivi ty (%)

1:4:20

- 0.586 10 3 - 0.560 3 - 0.517} - 0.466 3 - 0.419 - 0.397 10 15 - 0.331 - 0.266 10 3 +0.019} +0.034 +0.128 20 0.5 +0.279 2 +0.416 2 +0.4 76

2 Types of Discharge A comprehensive classification of discharge types has been given by Mika and Torok [2]. A less comprehensive, but convenient classification [9] describes the commercially available source units in current use: a) Continuous d.c. arc - a self-maintaining d.c. discharge. b) Intermittent d.c. arc- a non-capacitative discharge having a series of pu1ses of the same polarity and usually Iasting for less than 0.1 sec. c) A.C. arc - a non-capacitative discharge consisting of a series of pulses of alternating polarity. The pulses are extinguished in each half cycle when the potential across the analytical gap falls to a value that is insufficient to maintain the discharge. d) Triggered Capacitor Discharge - A series of electrical discharges from capacitors which may be oscillatory, critically damped or over damped. It is initiated by separate means and is extinguished on each half cycle. e) Spark - A series of electrical discharges from capacitors, each of which is self-initiated and oscillatory and is extinguished on each half cycle.

The spark source is differentiated from the triggered capacitor discharge in that the latter needs aseparate means for initiating the discharge. In general, a spark source produces potentials of the order of 10 - 40 kV using capacitances of 0.001 - 0.02 pF. A triggered capacitor discharge produces potentials of 0.2 - 2 kV using capacitances of 1 - 25 0 pF. Both discharges may be unidirectional ( successive discharges have similar polarity) or bipolar (successive discharges have opposite polarity). Schreiber and Joseph [ 16] have compared three of the more comrnon source units for the determination of Sn in Iead alloys. The conventional, high-valtage spark or triggered capacitor discharge source produces typically 50 sparks/sec. Comparatively recently, so-called "high-repetition rate" sources producing up to 1000 sparks/sec have become commercially available and offer considerable advantages in shorter analysis times for a given precision and better reproducibility overall.

104

[Ref. p. 122

Emission Spectroscopy

3. Behaviour of Tin in Are Discharges 3.1 Ionisation Semenova [17] demonstrated the relationship between the absolute temperature of a d.c. arc and the ionisation potential of the arc constituents. Easily ionised elements reduce the arc temperature whereas elements such as carbon (ionisation potential 11.3 eV) allow temperatures of up to 8000°K. This relationship is illustrated in Fig. 1. Elements oflow ionisation potential have a disproportionately pronounced effect on temperature [ 18] and alkali metal salts are often deliberately added to the sample to buffer the effects of the matrix constituents present.

TEMP. (OK)

8000

6000 Copper arc 1163)

2000L----L----~---L----4---~----~--~~--~--~ 7 8 9 10 II 12 6 5 IONISATION POTENTIAL (cV)

Fig. 1 Effect of arc constituent on temperature [17]

Fig. 2 shows the degree of ionisation of tin at various temperatures from calculations based on the Saha equation [ 19]. In the carbon arc at 8000°K tin is ionised by about 18%, but this becomes negligible on adding alkali metal salts. The atornic line emission intensity is, however, exponentially related to temperature and reductions in the arc temperature caused by excessive additions of alkali metal salts, may decrease sensitivity unacceptably. Forthis reason, particularly in qualitative analysis, carbon powder is often mixed with the sample to increase the arc temperature. Frequently the sample is mixed with alkali metal salts and carbon. The choice of additive is also important in that it must volatilise throughout the whole duration of the burn; from this point of view calcium salts are usually preferable to alkali metal salts.

3.2 Volatilisation

Ref. p. 122)

105

IONISATION 0

/o

10.0

1.0

O.IL-----L--....U.--'---.....1.---'--___.JL...-_--l

0

4000

8000

12000

TEMPERATURE (°K)

Fig. 2 Ionisation of tin at various temperatures [18]

3.2 Volatilisation Selective volatilisation of elements in the arc can be of considerable value; the most celebrated example is the "carrier distillation" technique of Scribner and Mullin [20]. In the d.c. arc analysis ofuranium mdde, 2% Ga 2 0 3 was added to the sample. This encouraged the volatilisation of trace elements relative to that of uranium. As a result, the spectra of tin and several other elements were observed with very little interference from the complex uranium spectrum. Gallium may be used, in this particular instance, as an internal standard. Table 3 gives the order of volatilisation of elements, oxides and sulphides in an arc [ 18]. The high vapour pressures of the sulphides and halides of tin may be exploited to reduce exposure time and, therefore, reduce background spectra. Zavorotnova [21] found alkali meta! fluorides were particularly effective as carriers for tin using carbon electrodes and [22] that NaF must be present in at least one hundredfold

Table 3. Order ofVolatilisation of Elements in the Are [18] As Elements Hg, As, Cd, Zn, Sb, Bi, TI, Mn, Ag, Sn, Cu, In, Ga, Ge, Au, Fe, Co, Ni, Pt, Zr, Mo, Re, Ta, W As Sulphides As, Hg, Sn, Ge, Cd, Sb, Pb, Bi, Zn, TI, In, Cu, Fe, Co, Ni, Mn, Ag, Mo, Re. As Oxides As, Hg, Cd, Pb, Bi, Tl, In, Ag, Zn, Cu, Ga, Sn, Li, Na, K, Rb, Cs, Mn, Cr, Mo, W, Si, Fe, Co, Ni, Mg, Al, Ca, Ba, Sr, V, Ti, Be, Ta, Nb, Sc, La, Y, Zr, Hf.

106

Emission Spectroscopy

[Ref. p. 122

excess over the tin content. Smaller additions of NaF caused systematic errors in the determination of tin in mineral specimens. Additions of 1 - 2% carbon powder with the NaF were also recommended [22]. Hanna andAbdella [23] determined tin in sand after adding BaF 2 and graphite powder and found that anodic excitation of the sample was preferable to cathode layer excitation, particularly for tin. Other fluoride carriers used for tin determinations include: AgF [25, 29] and polytetrafluoroethylene (PTFE) [26- 29]. Chloride salts are also effective carriers for tin and have found wide application. Kawaguchi, Shigematsu andMizuike [30], for example, determined 0.01- 0.02~-tg Sn by adding 20~-tl of a test solution containing 0.1% NaCl on to a graphite electrode impregnated with a solution of 1% paraffm in benzene to prevent absorption of the aqueous test solution. Excitation was in a 30 amp. d.c. arc with argon atmosphere for 0.7 sec. with a 6 mm gap. Cobalt ( 4~-tg/rnl) was used as the internal standard. Another approach is to design the lower electrode as a graphite crucible fitted with a smalllid with a hole in the centre ("boiler cap" electrode). During the burn, the crucible remains relatively cool and only the very volatile elements escape into the discharge. This technique has been used to determine tin and As, Au, Bi, Cd, Ga, Ge, In, Pb, Sb, Tl in minerals using NH 4 Cl/K 2 C0 3 as carrier [33] and in Nb 2 0 5 with an AgCl/ AgF carrier [24] .

Tennant [31] controlled the rate of evaporation of very volatile elements (As, Hg and Sn) by adding Al 2 0 3 /CaC0 3 /K 2 C0 3 . In this instance, the additive acted as a matrix buffer rather than a carrier. Sirnilarly, Yokohama [32] recommended calcium nitrate as a buffer for 0.3~-tg Sn added as a solution in M HN0 3 to a carbon electrode. The solution contained 3mg/ml Ca(N0 3 h and 0.2mg/ml Cd(N0 3 ) 2 internal standard and was evaporated to dryness before excitation in a 6 amp d.c. arc for 30 sec. Finally, it must be emphasised that in mineral specimens, tin is present as discrete particles of the sulphide or oxide widely dispersed in the base matrix. Poor precision is often encountered as a result. Care should be taken to grind these samples as fmely as possible and to use a buffer which will fuse the sample during the burn or to carry out a fusion before spectroscopic analysis. 3.3 Interna! Standards Another consequence of volatilisation and matrix effects lies in the choice of a suitable internal standard. The Standard should be pure with respect to the elements sought, it should volatilise at a similar rate, it should have atomic lines of similar excitation potential and wavelength to those of interest, and the lines should be free from self-absorption. Table 4 shows data obtained by Scott [34] using cathode layer excitation with a d.c. arc. The effects of matrix variations on line intensity are clearly demonstrated. Gallium is used frequently as an internal standard for tin, although Table 4 suggests that major changes in matrix composition would affect the two elements in rather different ways. Similarly, it is particularly important when using a carrier, that both tin and the internal standardundergo similar reactions in the arc electrode. A more detailed discussion of internal standardswill be found in the sectians dealing with specific applications.

4.1 Aluminium

Ref. p. 122]

107

Table 4. Variation of Line Intensity with Matrix for Several Elements % Changes in Intensity Relative to Al203 Matrix

Element Al203

Si02

Co Fe Ni V Mo Zr Fe Ag Cu Ga Sn

345.3 345.1 341.4 318.5 317.0 339.1 330.5 328.0 327.3 294.3 283.9

Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil

- 10

-

- 52 - 4 --

Fe Pb

283.8 283.3

Nil Nil

- 36

- 34 + 174 - 99 - 49 - 32 - 31 - 5 - 16

-

32

CaC03

-

7 24 9 + 230 + 7 + 54 - 6 - 5 - 39 + 63 + 21

--

-

21 9

Ca3(P04)2

-

9 15 7 + 185 + 10 + 50 - 21 - 44 - 34 + 6 - 17

-- 19 - 45

N~P207

- 64 - 66 - 60 - 40 +50 - 52 - 73 - 53 - 63 + 4 - 54

-- 62 - 66

NaCl

Na2C03

- 8 - 20 - 9 + 16 - 3

-57 -72 -56 -53 -55 -41 -76 -55

-- 9

--

+ 22 - 36 - 75 -72 - 43 - 36

- 44

-36 -41

-62 -49

4. Metallurgical Analysis This section is devoted specifically to the determination of tin in metals. The determination of tin in other items of metallurgical interest such as slags, mattes and refractories has more in common with the techniques used in geochemical analysis and will be found in that section. In general, when standards of an appropriate range and metallurgical state are available, metals are analysed in a sparkor tiggered capacitor discharge. The surface to be examined is usually machined to a clean finish and is supplied to the instrument as a rod or flat sample for mounting in a Petrey stand. When the sample is available only as drillings or filings it may be prepared by melting (in which case the analysis is similar tothat foramassive metal specimen), compacted into a briquette, analysed by a molten-globule technique or dissolved and analysed by arc discharge methods normally reserved for non-metals. The particular type of discharge will reflect the need for precision (spark discharges used) or sensitivity (arc discharges used). 4.1 Aluminium The spectrographic analysis of aluminium is described in ASTM E101 (photographic) and ASTM E227 (direct-reader) methods for tin and 14 or 22 elements respectively (9]. Samples for both methods are prepared as chill-cast discs finished on a lathe by removing 1.3 mm off the chilled face. Turnings and sheet should be pressed into a briquette, melted and cast into a disc. Thick sheets may be analysed directly after machining 0.8 mm from the surface to be exarnined. Samples are inserted in a Petrey stand with an ASTM C5a graphite counter electrode (6.15mm diameter with 20° rounded tip). The Sn 326.233 or 317.502nm lines are used. Results are obtained by plotting log Intensity vs log Concentration and a coefficient of variation of 2-4% should be expected for 0.05% Sn. The line Sn 317 .502nm is used for ASTM E227 in the first order (0.1 - 1.0% Sn) and in the second order (1.0- 8.0% Sn). The calibration is linear with a detection lirnit of 0.001% Sn (Spark) or 0.0002% Sn (Capacitor Discharge ). At 0.04% Sn the coefficient of Variation with the triggered capacitor discharge is 2.4 %.

108

[Ref. p. 122

Emission Spectroscopy

Conditions for Photographie Spectrography (ASTM E101) are:

Capacitance, !J.F Inductance, iJ.H Potential, V Discharges, sec-I Gap,mm Preburn, sec Exposure, sec

Fuessner Spark 0.021 400- 1400 75 120 3 5- 10 10-30

Arc-Interrupted Spark 0.009 - 0.017 300-500 250 240 3 5- 10 10-30

Rectified Spark Rotary Interrupter 0.007 300-800 230-250 240 3 5- 10 10- 30

HVSpark 0.005 - 0.025 200- 1500 60-240 3 5 -10 10-30

Conditions for Direct-Reading Spectrography (ASTM E277) are: HV Spark Capacitance, !J.F Inductance, iJ.H Voltage, kV _1 Discharges, sec Preburn, sec Exposure, sec

0.007 360 20 240 3-5 10- 15

Triggered Capacitor Discharge 60 300 0.94 60 3 10-15

Redfield and Wagoizer [35] have studied the mould-casting of aluminium for spectrography whilst Stickers, Wild and Hofmann [36] have discussed elimination of mtide band spectra using an argon and/or hydrogen atmosphere. 4.2 Antimony Tin and fifteen elements were determined in antimony (37] by grinding to a powder, mixing with one tenth of its weight of graphite and exciting 50mg in a graphite cup electrode using a 10 amp d.c. arc in an atmosphere of oxygen. A detection Iimit of 0.4!J.g/g Sn was obtained at the Sn 284.0nm line. Standards were made from spectroscopically pure antimony and oxides of the impurities. Zone refining [38] may be used to concentrate tin and fourteen impurities. More than 90% of the impurity content passes to the concentrate and offers a novel approach for the analysis of low-melting metals and alloys. 4.3 Arsenic Tin may be determined [39] in arsenic metal by heating 1 g of sample in air at 190°C to volatilise As 2 0 3 • Dissolve the residue in nitric acid, evaparate and redissolve in hydrochloric acid. Add 2!lg Pd as internal standard and add an aliquot to a 9 : 1 sodium chloride: graphite powder mixture for excitation in a 13 amp d.c. arc with graphite electrodes. The Iimit of detection is 0.005!J.g Sn. Alternatively [40], I g of sample may be dissolved in 3 : 1 HCI : HN0 3 , diluted with water and very carefully evaporated with Hßr to remove arsenic but not tin. After dilution, 6- 20mg Bi(N0 3 ) 3 is added, then KOH. The bismuth hydroxide precipitate is fllt.ered, washed, mixed with powdered graphite and examined in an 8 amp d.c. arc to give a detection Iimit of 0.02!J.g/g Sn.

Ref.p.122]

4.6 Copper

109

4.4 Bismuth Standards may be made by melting the meta! and impurities in air or under pahn oil [41] and casting into 1Omm diameter rods which are sawn in two and flled flat with a coarse file. Care should be taken not to break the rods which are very brittle. Excite in a triggered capacitor discharge using a pointed graphite counter electrode. The Bi 303.49nm line has been found tobe of similar intensity to the Sn 303.41 nm line for pure Bi and 0.14% Sn [42]. 4.5 Cadmium Standards may be prepared [44] by melting cadmium and tin in a graphite crucible at 500°C in a muffle, which is purged continuously with carbon dioxide. Alternatively the metals may be melted in a 6mm diameter glass tube attached to a vacuum pump, the glass being broken away after cooling. The sticks are machined to give a flat surface for excitation in a 3.5 amp a.c. arc with 4 mm gap, 10 sec preburn and 30 sec exposure. Controlled cooling of a 250g sample of cadmium effectively concentrated impurities in the liquid phase and allowed determinations of down to 0.2ng/g Sn[45]. Impurities may also be concentrated [46] by removal of cadmium at 380°C, 0.1 torr by vacuum sublimation of a SOg sample. Sublimation is continued until a residue of 0.2 - 0.5 g is obtained, this is dissolved in HN0 3 , evaporated and heated at 500600°C. The residue is mixed with one fifth of its weight of graphite powder and excited in a 10amp d.c. arc for 30sec. A Iimit of detection of lOng/g Sn was claimed with similar Ievels for sixteen other elements. Synthetic standards based on CdO were used. Tin may be concentrated by partial precipitation of Cd(OH) 2 by arnmonia from a nitric acid solution. The washed, dried precipitate is redissolved in 4- 5 drops of HN03, added to graphite powder and examined in an 8 amp a.c. arc. Manganese dioxide [48] or aluminium hydroxide [48] have also been used as coprecipitants and give a detection Iimit of O.lt.tg/g Sn. Yusupov and Shavrin [49] studied the spectrographic analysis of binary alloys of Cd with Sn, Pb and Zn. The intensity of impurity lines (Bi, Cu, Pb, Sb and Sn) corresponded to the degree of arc or spark erosiqn and was closely related to the thermal conductivity of the alloy. 4.6 Copper ASTM E486 describes [9] the determination of 0.9- 1.2% Sn in admiralty meta! using a chill-cast disc or 30mm x 8mm diameterrod sample. Approximately 2 mm should be machined from the chill-cast face. Excite using a 6mm diameter pointed graphite rod counter electrode (ASTM CS) and the conditions given on page 110: In all cases with direct metals analysis, samples and Standards should be in similar metallurgical states. The segregation of Iead and to a lesser extent, tin in ]arge castings is well-known. Coldworked copper and brasses are said [50] to give more intense impurity spectra than annealed metals. Brownsdon and Van Sameren [51] analysed brasses as 6mm diameter rods, cubic ingots or thick strips in a 5 amp d.c. arc with sample as cathode and a pure copper rod anode. Cathode excitation was used [51, 52] for Cu/Ni, Cu/Zn, copper and brasses. Cast discs of tin bronz es were analysed for tin [53] using a high-voltage spark and mask of insulating resin on the disc surface leaving an area for excitation of 15mm diameter. Schatz [57] used an interrupted d.c. arc for tin in copper alloys.

110

Emission Spectroscopy

[Ref. p. 122

Conditions for analysis of Admiralty Meta! (ASTM E486) AC Spark

Triggered Capacitor Discharge

lnductance, pH Capacitance, pF Current, A Voltage, V Preburn, sec Exposure, sec Gap,mm Coefficient of Variation,%

40 0.015 5-8 230 3- 20 15- 17 3 3.0

400 60 0.6 940 3-20 15- 17 3 2.5

Analytical Lines:

Sn 266.125a 317.505 286.333 238.999

Cub 302.156a 306.342 299.736 299.736

a Triggered capacitor discharge b 50% transmittance fJlter

The "globule-arc" method has been traditionally used for the determination of impurities in copper (54, 55]. A 0.2- 0.5 g sample of drilling is placed in a notch in the end of a graphite rod acting as the lower negative electrode. A copperrod is used as anode. When the arc is ignited the sample melts to give a globule; the electrodes should be manipulated to keep a steady arc incident on the globule. A copper anode is said to give considerably less CN band background than a graphite counter electrode. The "globule-arc" method gives fewer ion lines than an solid electrode arc and gives a detection Iimit (44] of Spg/g Sn in a 7 amp d.c. arc. An oxygen atmosphere may be used (56] to further reduce CN background. Leichtle (58] analysed copper base alloys compacted into pellets using a 14 amp d.c. arc with an upper graphite cathode and the sample supported in a graphite crater electrode. A similar briquetting technique was recommended in ASTM E414 for 1 - 30 pg/g Sn and eight other elements present in copper. The sample was excited as cathode in a d.c. arc with a copper counter electrode. The Sn 284.00nm and Cu 284.65nm lines were measured photographically to give a coefficient of variation of 6- 13% in the range 2- 10pg/g Sn.

When suitable standards are not available or if a !arge sample must be taken (for reasons of representative sampling), it may be preferable to dissolve the material in nitric acid. Jaycox [59] diluted the resultant solutions of copper-based alloys with nineteen parts of copper nitrate solution. The diluted solution was absorbed on to porous graphite electrodes, dried and excited in a d.c. arc. A more recent study by Elwell andPeake (60] examined the determination of 0.005- 0.2% Sn insmall samples of copper-base alloys. They found briquetting procedures introduced excessive iron contamination from the press and that the samples frequently disintegrated during excitation. They dissolved 0.3g ofsample in Sm! of 1 : 1 HN0 3 , evaporated and ignited at 400°C. The oxidewas ground in an agate mortar, transferred to a graphite cup electrode (9mm height, 12mm o.d., lOmm i.d., Smm base thickness) which was supported on a 25mm diameter graphite pillar. A 15 sec exposure was used with sample as cathode (60pH, 250pF, 10!2). Twelve other elements were determined with tin. A manganese dioxide coprecipitation was used by Park (61] to determine 0.4- 15 pg/g Sn in high purity copper, using a 100 g sample, dissolved in 11itre of 2 : 3 HN0 3 /

Ref. p. 122]

4.9 Irons, Steels, Ferroalloys

111

water. Trace elements were precipitated by adding 10m! of 20% KBr and 10ml of 3% KMn0 4 and boiling. Two precipitations were carried out, the residues were dissolved in 50m1 of hydrochloric acid, neutralised with ammonia and 1ml of concentrated hydrochloric acid added. Tin and other elements were precipitated with hydrogen sulphide, fütered, dissolved in nitric and hydrochloric acids and evaporated to 5ml. Aliquots were absorbed on graphite electrodes for excitation in the d.c. arc. 4.7 Gallium The method of reference [40] for tin in arsenic has been used for the analysis of gallium and gallium arsenide. 4.8 Hafnium Tin and twenty other elements were determined [62] by direct analysis of metal fllings or oxide powders using a graphite crater electrode and d.c. or a.c. arc. The same method was used for zirconium. 4.9 Irons, Steels, Ferroalloys Tin occurs in iron and steel as a contaminant from metal scrap where it is present as tinplate or soldered joint residues. Tin is added to some cast irons. Plain carbon and low alloys steels- may be analysed for Sn (0.005 - 0.02%) and eight other elements by ASTM E403 [9] which is applicable to chill-cast or rolled and forged specimens, 25- 64mm diameter and 10- 38mm thick. Steels with total alloy contents of less than 3% are claimed to show no metallurgical state matrix effects. Standards can be obtained commercially [63, 64] or may be chemically analysed [65]. Sampiesare prepared (ASTM E403) by machining 2mm from a flat surface, polishing wet or dry with 80 grit alumina or silicon carbide cloth and finishing with 120 grit. Mount in a Petrey stand with 6.15 mm diameter graphite counter electrode with either 120° sharp (ASTM C2) or 20° rounded (ASTM C5) points. Excite in a triggered capacitor or discharge using conditions A or B. (A: 7 - 10pF, 50pH, 2.5 - 5 n., 0.94 - l.OkV, 0.3 - 0.8amp r.f., 5 - 35 discharges/sec, 3 mm gap) (B: 40 - 60pF, 360pH, 25- 30rl., 0.94- 1.0kV, 2- 3amp r.f., 60 discharges/sec). Both methods use a 25 sec exposure and measure Sn 317.502, Sn 326.33 and Fe 271.441 nm lines with a directreading spectrograph. Note that the iron reference line is ionic whereas the tin lines originate in the atomic spectrum. Sn 317 .502nm is subject to line interference from Mo, Co, Ti and Cr; Sn 326.233nm coincides with weak lines from Fe and Mo. The coefficient of variation for 0.012% Sn is 4.8%. The mostsensitive tin lines, however, lie in the vacuum ultraviolet and may be observed with a vacuum spectrograph and argon-flushed spark chamber. Tin (0.003 0.040%) may be determined tagether with twelve other elements including carbon (193.09nm), sulphur (180.73nm) and phosphorus (178.29nm) by ASTM E415 [9]. The method is intended for control analysis of preliminary and !adle tests from basic oxygen, open hearth or electric furnaces and for finished metal. Sampies are prepared as for ASTME E403 above and are mounted in a Petrey stand with a counter electrode of 6.4 mm diameter hard-drawn silver rod or a 1.5 mm diameter thoriated tungsten rod. The rods are machined to a 90° or 120° cone and are polished with fine abrasive cloth. Replace counter electrodes after 40- 50 bums when a black deposit accumulates and intensity diminishes. Thoriated tungsten may allow over one hundred bums before replacement. Both types of counter electrode should be conditioned by 2- 6 spark-

112

Emission Spectroscopy

[Ref. p. 122

ings before use. Dischargeparameters are: 10- lSJ.tF, 50 -70Jili, 3- sn, 0.94-1.0 kV, 0.3- 0.8amp r.f., 60 discharges/sec, preburn 6- 20 sec, exposure 8- 25 sec, 3- 5 mm gap, Sn 189.99nm, Fe 271.44nm. In this procedure both Sn 189.99 and Fe 271.44 nm lines are ion spectra. The coefficient ofvariation ranges from 16% at 0.005% Sn to 4% at 0.25% Sn. Maekawa and Suzuki [66] using a 0.94kV condensed arc discharge and a direct reading spectrometer studied the line overlap of Mo 317.505 and Sn 317 .502nm in the range 0.005 - 0.15% Sn. lnterference with tin determinations was noted with molybdenum contents greater than 0.15% Mo. An empirical diagram was used to correct for 0.15- 1.2% Mo. Coefficients ofvariation were 18% (0.003% Sn) and 3.4% (0.042% Sn).

Plain carbon and low alloy steels have also been analysed [67] for tin using a lowwattage intermittent arc with graphite or silver counter electrodes. An a.c. arc or condensed spark discharge gave better sensitivity for tin than a purespark [68]. Vacuum spectrographs have been used for tin in low alloy steels by Tunney [69] and Goto [70] who used an oscillatory discharge (lOJ.tF, SOJ.Lf:l, 3Q, 0.9kV) for the carbon 193.09, 165.70, 156.14 and 172.01 nm lines but preferred an overdamped discharge (30J.LF, SOJ.Lf:l, 25n, 0.9kV) for Sn 181.13nm and As 197.26nm with Fe 210.91 nm as reference. Direct analysis of steels is only possible when standards of a sirnilar metallurgical state are available. ASTM E403 claims that steels with total alloying contents ofless than 3% do not show this type of matrix effect for tin and the particular elements examined. Nevertheless with steels which have been rolled, annealed or otherwise worked it is unlikely that suitable standards could be obtained for accurate determinations of the elements of interest. A nurober of recasting techniques have been studied to overcome this problern [71 -73]. Stamp [72] pressed drillings into a pellet after mixing with aluminium which was used as a deoxidant. The pellets were melted in a d.c.arc under a reduced pressure of 50 torr of argon. Tunney and Hughes [73] melted their samples in an argon arc before casting into moulds (38mm diameter by 3mm deep). The cast samples were lapped or linished and could be used for x-ray fluorescence or atomic emission spectroscopy. The Iosses of some elements during melting were corrected for (eg C, Mn, P, Sand Si). Chemical treatments may be employed to overcome matrix effects and to facilitate standardisation. Weisberger, Pristera and Reese [74] determined tin and thirteen other elements in iron and steels by heating 0.01 g with HN0 3 to convert to oxide, mixing the residue with graphite and exciting in a high-valtage a.c. arc. Up to 0.2% Sn could be determined with ± 10% accuracy. Iron powders were analysed [75] for tin and sixteen elements by treatment with HN0 3 and NH4 N0 3 followed by ignition at 250°C. The residue was mixed with PTFE (polytetrafluoroethylene) powder and graphite (100 : 10 : 25).The PTFE acted as a carrier for excitation in a IOamp d.c. arc using iron as an internal standard. The dissolution of ferrous alloys in nitric acid followed by ignition is typical of several reported procedures. In a study on the effects of various buffers on volatilisation curves, arc temperature and line intensities [76] a mixture of potassium nitrate and silica (1 : I) was recommended for tin and other volatile elements e.g. Ag, As, Bi, In, Sb and Te. On applying the method to iron and steels [77], the buffer incorporated 0.5% Sb 2 0 3 as internal standard. Volatilisation of the above elements in a 9 amp d.c. arc was complete in 60 sec although the buffer reduced the volatility of iron and minirnised its interference. The Iimit of detection was 3J.tg/g for Sn. A somewhat sirnilar chemical

Ref. p. 122)

4.10 Lead

113

treatment but without the addition of buffer or standardwas used [78) with a 9amp d.c. arc operating in a magnetic field. Tin has been coprecipitated (80] as the sulphide using cadmium as the collector fromM H 2 S0 4 containing 1% sodium acetate and 10% acetic acid. The precipitate was carefully ignited to avoid Iosses of tin sulphide, mixed with an equal weight of graphite powder and excited in a 4amp d.c. arc for 30 sec. The Sn 317 .5nm and Cd 308.3nm lines were used and the method was employed down to 0.0015% Sn. Other approaches involve solvent extraction of tin (81] into ether from 6.5M HCl. Afterevaporation and extraction of the residue into etherfromM HCl/2% arnmonium thiocya"hate, the organic extract was again evaporated and tin determined in a Feussner arc. Anion-exchange procedure (82] was used to concentrate traces (1 - lOOJ.Lg/g) of tin in highly alloyed steels. After dissolution of 1.5 g of sample in an appropriate acid mixture and evaporating almost to dryness, a solution of the residue in SOml of 2M HCl was passed down a column of a strong anion exchange resin (250 mm x 10 mm diameter) in the chloride form, previously equilibrated with 2M hydrochloric acid. After wet ashing of the resin with H2 S0 4 /HN0 3 , 7.5 mg of copper was added (as a copper sulphate solution) as internal standard. The mixturewas ignited at 400°C mixed with carbon powder (1 : 3) and excited in a 10amp d.c. arc between carbon electrodes. Cast irons were analysed directly [44] by chill-casting in a sand mould (50~ 25 x 25 mm). The sample was broken in half and the fractured surface polished then excited in a Samp d.c. arc for 10 sec with a 4mm gap. The Sn 335.23 and Fe 335.33nm lines were used. A 150 I.M.M.mesh gauze filterwas used as an attenuator, estimated errors were: 0.01-0.15% ± 0.01% Sn and 0.15-0.02% ± 0.02% Sn. Ferro alloys: binary alloy,s of iron, are most conveniently analysed by solution techniques in view of the difficulty of obtaining a range of suitable standards. Some alloys such as ferrosilicon may be ground in a ring mill. Svehla and Kvopkova (83] determined tin in ferrotungsten with an error of ± 12% at the 0.1% Sn Ievel using powdered samples placed in a nicke! electrode and excited in a d.c. arc. Up to 0.07% Sn in ferromanganese has been determined [79] by spark excitation of 6M HCl solutions in a porous cup electrode. Limits of detection for tin (0.02 %) and five other elements were generally poor and repeatability was of the order of 10 - 25%. The method was claimed to be superior to atomic absorption only for tin. 4.10 Lead The determination of tin in Iead alloys is relatively easy in that synthetic standards may be easily prepared. Master alloys are frrst made [41] by melting tin, Iead and any other low melting metals under palm oil, stirring with a graphiterod and burning off the oil before casting the metal into thin strips for subsequent dilution with lead. Rods (lOOmm x lOmm diameter) may be cast after melting the master alloy with more Iead in a silica crucible - oil is unnecessary at this stage. High melting elements such as iron and copperwill not be lost as a dross ifpresent in amounts less than 0.2%. The rods are cut in two and the cut surfaces flled and excited as the cathode in a triggered capacitor discharge with graphite rod anode and photographic recording. The detection Iimit is 1 - 2J.Lg/g Sn with a 3 min exposure. This method [41] is similar to ASTM E-117 [9] which use a disc sample instead of a rod. Discharge conditions [9] are for a high valtagespark (0.14J.LF, 330J.LH, 30 sec exposure) or triggered capacitor discharge (20J.LF, 200J.LH, 0.94kV, 10D, 1.2amp, 30 sec exposure). Line pairs Sn 303.41 and Pb 322.05 nm were used.

114

Emission Spectroscopy

[Ref. p. 122

Other excitation sources have been studied [84] for Iead analysis but no single source is outstandingly superior. A Iimit of detection of 2/J.g Sn was obtained [85] with an interrupted a.c. arc and 9 mm x 6 mm diameter rods. An interrupted d.c. arc (0.01 sec pulses) was used by Janda and Sehroll [118] todeterminedown to 1.2/J.g/g Sn with a Iead cathode and graphite anode. Brownsdon and Van Sameren [51] determined 0.002- 9.0% Sn in Iead and its alloys. Breckpot [86] described a method for tin and eight other elements in binary alloys of Iead and conducted a study of the Sn/Pb/Sb system [87] with Sb and Sn in the range 0.1 - 3%. Breckpot showed that a 1 amp d.c. arc could be sustained between Iead electrodes if they are sufficiently massive to avoid melting and if the opposing surfaces exceed 2 - 3 cm 2 • Tin was determined in the range 0.13- 1.8% in antimoniallead alloys [88] using a low voltage spark (4/J.F, 8 amp, 150 sparks/min). Sampies were 6 mm diameter rods with wedge shaped ends; Sn 317.5nm and Pb 322.0nm lines were measured. Standards for antimonial alloys should be prepared by first melting pure Iead and antimony without covering in an iron !adle or !arge crucible. After casting, a weighed amount of the alloy is melted with tin and other low-melting metals to give standards or master alloys. With rod electrodes, undue segregation takes place if the antimony content exceeds 20% (41) and dilution of samples with Iead is recommended before analysis. Lazebruk and Yatsenko [89] vaporised the sample and allowed the vapour to condense on a copper electrode which was excited in a 2.5 amp a.c. arc. Nausester [90] determined up to 20% Sn in type metals (containing up to 28% Sb) and also up to 60% Sn in solders using a point-to-plane spark excitation method. The importance of a chill cast sample was emphasised. Downarowicz and Zagorski [91] effected a 200-fold concentration of tin and antimony in high-purity Iead by coprecipitation with manganese dioxide. The precipitate was excited in an a.c. arc between carbon electrodes using the Sn 235.5 and Mn 247.3 nm lines. Alternatively, 1 g of Iead may be dissolved in HN0 3 , evaporated to dryness, taken up in 60- 80ml concentrated HCI and passed down a column of 100- 200 mesh Dowex 1 -X 10 strongly basic anion exchange resin equilibrated with 9M HCI. The colurnn is washed with 25 ml of 9 M HCI and Sn tagether with Bi, Cu and Fe eluted with 6M HN0 3 . Afterevaporation to dryness, 20mg of residue was excited between graphite electrodes in an 18 amp a.c. spark for 40 sec. The Iimit of detection was 38ng Sn.

4.11 Manganese Muzgin and Gladysheva [93] dissolved the sample in HN0 3 , evaporated to dryness and ignited the residue at 250°C. Volatile elements (Bi, Cd, Cu, Pb and Sn) were volatilised at 1400°C from 40mg of residue and condensed on a carbon electrode which was excited in a 6 amp a.c. arc. Further enhancements could be achieved by volatilising in the presence of 3% NaN0 3 . 4.12 Nickel ASTM E483 [9] describes the determination ofvolatile elements: Bi, Pb and Sn in nickel-base alloys using a carrier distillation technique. About 200mg of drillings are dissolved in 2m! of HF and 1Ornl of HN0 3 by warming in a PTFE beaker. An internal standard of 1rnl of 40/).g/ml indium solution is added and the solution evaporated to dryness in a platinum crucible. The residue is ignited for 20 min at 800°C, ground, weighed and 10% of AgCI:LiF mixture (11 : 1) added. Charges of SOmg are weighed into ASTM S2 graphite cup electrodes, mounted on an Sl pedestal with a 3.05 mm

Ref.p. 122]

4.16 Tantalum

115

flat-ended rod as the counter electrode. The charges are vented by pressing a conical tool into the centre to give a hole 4.57mm deep by 1.25mm diameter. The tool also acts as a ram to compact the charge. Excite in a 12amp d.c. arc with 33 sec exposure and a 50% transmission frlter. Measure the Sn 286.33 andIn 275.39nm lines photographically. Other tin lines must be used ifthe Fe 286.'25 and Fe 286.34nm interfere. Coefficients of variation are 5 - 25%. The method is described in detail by Atwell and Golden [94]. High purity nicke! has been analysed [95] for Bi, Co, Cu, Sn and Zn by dissolution in HN0 3/H 2S0 4 , evaporating to dryness, oxidising with one drop of permanganate and extracting with 4% ammonium thiocyanate and 0.3% diantipyrinylmethane into chloroform. Afterevaporation to dryness the residue is excited in a d.c. arc. Monel has been analysed by Barker [96] andArnott [97]. 4.13 Phosphorus Tin has been determined [98] by dissolving 5 g of phosphorus in 20ml of HN0 3 in a PTFE beaker. After boiling to remove HN0 3 , 8ml of HCl and cobalt chloride (40 J,Lg/ml) is added then diluted to 50ml. A 1ml aliquot is applied to a rotating graphite electrode and excited in a 10kV spark. Tin may be determined below 10pg/g. 4.14 Selenium Tin and twenty two other elements were determined [99] by dissolving 1g in 10 ml of HN03 and 2.5 ml of H2 so4 with addition of 2J,Lg of Pd internal Standard. After evaporation to dryness at 300°C to remove Se02 , the residue was dissolved in 6M HCl and transferred with 1Omg of NaCl :graphite (1 :9) to a graphite crater electrode and excited in a d.c. arc. 4.15 Silver Tin is deterrnined in silver by ASTM E378 [9] in the range 0.0001 - 0.005% Sn. 1g is dissolved in 5 ml of 1 : 3 HN0 3 :H 20, evaporated to dryness, ground and packed into an ASTM S4 graphite electrode (6.15 mm diameter with very shallow cavity and undercut). Excite in a 12 amp d.c. arc for 30 sec with a 40% transrnission frlter, measure Sn 284.0 or Sn 286.33 mm line. 4.16 Tantalum Tantalum has a complex spectrum which hinders the determination of impurities. Ifthe metal is converted to oxide [100] by heating at 600- 700°C for 2 hours, impurities may be evaporated at 1400°C and condensed on copper electrodes as in reference [93] (see analysis of manganese). An internal standard of 0.01% thallium was added before volatilisation of impurities and the line pairs Sn 259.85 and Tl 258.01 nm were measured. The detection Iimit was 3 x 10-s% Sn. Similarly 1g of tantalum or niobiumwas converted to oxide [101] as above, fused with potassium persulphate (25g for Nb, 60g for Ta) for 15 min, leached with 60ml of 10% citric acid (tartaric for Nb) and 0.15ml of copper nitrate solution (lOOmg/ml Cu) added. Insoluble sulphides were precipitated with H 2S; were frltered, washed and dried at 500°C. 20 mg of residue was placed in a graphite crater electrode (3.5 mm diameter, Smm deep) as anode and excited in a 6amp d.c. for 60 sec. Standards were prepared similarly and a detection Iimit of 0.1 pg/g Sn was obtained at Sn 317.50 nm.

116

Emission Spectroscopy

[Ref. p. 122

4.17 Titanium Titanium was analysed for tin and twenty other elements [102] by converting to oxide and subjecting the residue to d.c. arc spectrography. Synthetic standards were made by hydrolysis of TiCI 4 with addition of impurities. 4.18 Thallium Thallium may be separated from impurities by distillation under vacuum as TICI or TIN0 3 and the residue analysed by d.c. arc for tin and fifteen other elements [103]. 4.19 Tungsten Tin may be determined in tungsten or molybdenum powder by direct d.c. arc spectrography of 50mg ofmetal powder in a 7 amp arc using a 4.5 mm diameter, 5 mm deep graphite crater electrode. A detection Iimit of 10~g/g Sn at Sn 283.99 can be obtained with a 2 min burn. Lower Ievels of tin [ 101] may be determined by calcination of the meta! to oxide at 600°C for 45 min followed by dissolution of the residue by heating with 4rnl of 30% NaOH and then addition of 30% tartaric acid to pH2. After addition of 15 mg of copper as a solution of the nitrate, proceed as in reference [101] for the analysis oftantalum. 4.20 Yttrium Tin (0.3 - 1OO~g/g) was determined [ 104] by dissolving in HN0 3 , heating at 800°C to convert to oxide, adding 4% of arnmonium hydrogen fluoride and exciting a 50 mg portion in a d.c. arc. A graphite anode (6mm diameter, with crater 4.8mm diameter, 4.5 mm deep with 1.5 mm diameter central post) was used. The technique of converting metals with rich spectra to involatile oxides has been reported elsewhere [62, 100, 101, 105]. 4.21 Zinc Zinc may be analysed directly in a d.c. arc [106] or may be dissolved in HCI and impurities (i.e. As, Bi, Cd, Pb, Sb and Sn) extracted from 0.5- l.SM HCI with diethyldithiophosphate [1 07]. The extract is evaporated on to carbon powder in a porcelain crucible and a portion of residue examined in a 6 amp a.c. arc. Alternatively [ 108 ], tin may be coprecipitated at pH 8- 10 with 0.14 mM aluminium nitrate and 0.7 mM ammonium nitrate solution. The precipitate is mixed with carbon powder and sodium chloride for analysis in a 9 amp a.c. arc with graphite electrodes. In ASTM E27 [9] tin may be determined in zinc or zinc alloys by dissolution of drillings or sawings in equal volumes of 1 : 4 HCl : H 2 0 and 1 : 4 HN0 3 : H 2 0 to give a final 0.33 g/ml of the meta! sample. Approximately 0.1 ml is added to an ASTM S6 graphite cup electrode (6.16 mm diameterrod with 4.1 mm diameter, 6.4 mm deep cavity). After drying for 1 hour at 75°C the sample is examined in a 7 amp d.c. arc in a 60 sec burn using a 20- 80% transmission fii.ter. The counter electrode is an ASTM C6, 3.05 mm diameter flat-ended grapliite rod. Synthetic standards incorporate tin, zinc and major matrix elements. The method is suitable for 0.001 - 0.05% Sn. Zinc is used as internal standard; the Sn 284.00, 317.50 and Zn 267.05 nm lines are used.

117

5. Geochemical Analysis

Ref. p. 122]

5. Geochemical Analysis The determination of tin in rocks, ores and minerals is restricted exclusively to arc methods and in particular to those involving the d.c. arc. The general behaviour of tin in the arc has already been discussed in Section 3; the relevant factors insofar as geochemical analysis is concerned are: a) Addition of a flux - in the majority of methods an alkali metal salt is added in order to bring about fusion of the sample in the electrode crater; this also serves as an ionisation buffer. Compounds used include: borates, carbonates, chlorides, phosphates and sulphates of the alkali metals. b) Addition of a matrix buffer- several methods include addition of a relatively involatile compound which controls the rates of volatilisation of the elements under examination. Alumina [125], quartz [115], calcium carbonate [122, 125] and barium su1phate [119] have been used in this way. c) Addition of a ca"ier- the sulphides and halides of tin are relatively volatile and it is sometimes convenient to use a carrier of this type to give a cleaner spectrum. Involatile impurities with fairly complex spectra are not excited, but elements such as As, Bi, Cd, Cu, Sb and Sn can be effectively isolated. Carriers employed include: sodium chloride [115, 123], PTFE [26, 117],cupric chloride [26, 117], sulphur [ 119] and ammonium chloride [33]. d) Addition of carbon powder - to raise the arc temperature and to act as a matrix buffer. Its use is of more benefit in the determination of other impurity elements than in the determination of tin, which is easily excited and relatively volatile. e)Addition ofintemal Standards-these include antimony [113, 121, 126], beryllium [116], bismuth [123, 125], cadmium [115, 120], gallium [119], germanium [114, 128], indium [ 112, 124] and palladium [ 127]. Care should be taken with internal standards as complex and low grade ores may contain the above elements, particularly Bi, In and Sb. The determination of tin in specimens of geochemical interest is summarised in Table 5.

Table 5. Geochemical Analysis by Emission Spectroscopy Range

Details

Matrix Ores

> 0.02%

Mix 1:1 with flux and excite in d.c. arc with graphite electrodes. Flux: 0.2 · 5% Jn 2 0 3 in K2S04. Sn 317.51, Sn 326.23, In 325.86 nm.

[112]

Ores

0.004. 0.5%

For ores with !arge amounts of Al, Fe, Si and Be, Cu, Ga, In, Pb, Ti, Zn. Mix 1 :1 with flux: carbon powder/Na 2 C0 3 /Sb 2 0 5 (90: 10:1 ), a.c. arc with carbon electrodes. Sn 303.41, Sn 284.00, Sb 287.79 nm.

[113]

Ores

0.03-10%

[114]

Ores

...

Mix with ZnS containing Ge0 2 internal standard. 9 amp d.c. arc with carbon electrodes in Stallwood jet assembly. Grind to 200 mesh with buffer. Sample/NaCI CdS04/Si02(5:1 :1 :46), 16 amp a.c. arc with powder introduced in air stream. Sn 303,41, Cd 298.06 nm

[115]

Ref.

[Ref. p. 122

Emission Spectroscopy

118

Tab!e 5 (continued) Matrix

Range

Rocks, soils

> 10 p.g

Rocks (granites)

...

Rocks (carbonaceous)

...

Rocks (carbonaceous)

...

Rocks (gypsum)

...

Rocks

...

0.01-2%

Details

Ref.

Fume Si0 2 with HF/H 2S04 in Pt crucible. Remove Fe by extraction with HCI/NH 4 SCN from 6.5 M HCI/H 2 0 2 . Extract Sn into CHCI 3 with ammonium tetramethy!ene dithiocarbamate, evaparate to dryness, add Be internal standard

[116]

Mix sample/PTFE/CuCI 2 carrier (1 :1 :1)

[26,117]

Mix sample/Li2C03/(NH4hS04 (15:3:1) Excite 0.4 g in 7- 10 amp d.c. arc in micrographite crucible

[118]

As Ref. 109, incorporating 5% S, 7.5% BaS0 4 7.5% Ga203 in rock matrix

[119]

Precipitate with 8 - hydroxyquinoline at pH 5.9 in presence of tannic acid and thionalide with Al collector. lgnite at 600°C. Mix with graphite, Na 2P03 containing Lu 2 03 and CdO internal standards. Burn for 80 sec in 20 amp. d.c. arc

[120]

Mix sample/potassium antimony tartrate (1 :1), 12 amp. a.c. arc with carbon electrodes. Sn 242.95, Sb 242.64 nm. Same calibration for silicate, Fe silicate or sulphide minerals.

[121]

Mix 0.5 g sample/flux (3 :1). Flux: NH 4 CI/ K2C03 (1 :1). Place in graphite crucible (11 mm diameter, 28 mm deep) fitted with Iid with hole (3 mm diameter) a.c. arc.

[33]

Mix sample/CuC03/C/NaH 2P0 4 (3 :1:1 :1), d.c. carbon arc

[122]

Rocks minerals

...

Rocks (silicates)

...

Rocks (silicates)

0.003-0.1%

Mix sample/NaCI (2:1). NaCI contains 2.92% Bi 20 3 internal standard, 7 amp d.c, arc for 45 sec. Standards from basalt matrix

[123]

Rocks (silicates)

> 10p.g/g

[124]

Silicates

>1 p.g/g

Grind to 150 mesh and mix sample/K 2 S0 4 (3 :1). K2S04 contains 0.1% In 2 0 3 intemal standard. Excite 130 mg twice in superimposed bums in d.c. arc with 0 2 atmosphere. Sn 317.51, In 325.86 nm Mix 20 mg sample with 20 mg buffer. Buffer: AI203/CaC03/K2C03 (7:3:1) containing 0.1% Bi203. d.c. carbon arc. Mix sample with C powder containing 0.8% Sb 2 0 3 internal standard (for Sn, Pb, Ga) and 0.04% Pd black (for Ni, Cr, Co, V, Sc)

I

[125]

Silicates

...

Silicates

...

Mix 6 mg sample/buffer (1 :4) Buffer: synthetic silicate/graphite (1 :3). Counter electrode rod made from graphite powder containing 0.2% Pd internal standard. 5 amp d.c. arc to smooth burn then 15 amp for 70 sec. With direct reader gives ± 5 % at 1 p.g/ g Sn.

[127]

Silicates

...

Mix sample/Na 2 C0 3/Ge0 2 /graphite (2:2:3 :4) and excite in 8 amp d.c. are with graphite electrodes using Ge as internal standard

[128]

[126]

119

6. Miscel!aneous Inorganic Materials

Ref. p. 122]

6. Miscellaneous Inorganic Materials The analysis of inorganic solid materials follows the general principles discussed under Geochemical Analysis. The use of fluorinated carriers is apparently fairly widespread particularly where an involatile matrix is being examined. Sodium fluoride [130, 143], silver fluoride [24, 25) and PTFE powder [27, 29] have all been used with success. An interesting concentration technique is that of Krasilshchik et al. [ 134] who removed tin and other elements from solution by electrolysis on to a carbon cathode. The carbon rod was tightly wrapped with PTFE so that only the end was exposed to the solution. After 30 min electrolysis in a pH 2.5 citrate buffer, the rod was removed, dried, the PTFE taken off and the rod excited as an anode in a 12 amp d.c. arc discharge.

Table 6. Analysis of Miscellaneous Inorganic Materials by Emission Spectroscopy Matrix Arsenic trichloride

Range

> 1 pg/g

Details

Ref

Extract AsC1 3 from HCl into benzene and evaparate aqueous solutionon to carbon powder for excitation in 14 amp d.c. arc

[129]

Boron nitride

2. 50J1g

Mix 30 mg with graphite (1 :1). Graphite contain 4% NaF and 2% La 2 0 3 (internal std) Sn 284.0 nm

[130]

Copper sme1· ting products

0.001 . 1%

Applied to concentrates, smelting charges, residues, slags and flue dusts. Standards prepared on same base as unknown. Mix with MgO (1 :2) and arc for 1 min for Sn and 6 other volatile elements. Sn 284.0 nm

[131]

Cesium sal ts

...

In graphite cavity (4 mm dia, 10 mm deep) place 60 mg PTFE powder then sample mixed with carbon powder (5 :1). Excite with 15 amp a.c. arc. PTFE allows wide range of Cs contents

[27]

Cadmium e1ectro1ytes

...

See Ref. [ 13 9] und er Zinc electrolytes

[139]

Gallium arsenide

...

Remave epitaxial GaAs layer with methanoll bromine and remove gallium by applying the soln.to a column of PTFE/decanol. Wash with 5 M HCl to remove. Fe, In, Sn; evaparate to dryness and excite residue in arc

[28]

Gallium arsenide

...

Mix 50 mg with graphite and PTFE powder (5: 1:1 ). Excite in graphite cavity electrode with 15 amp d.c. arc

[29]

Ball mill 5 mg with carbon powder (1 :3) Excite in cavity electrode. Sn 317.5, As 311.9, 243.7 nm

[132]

Gallium arsenide

5 - 200 Jlgfg

Gold p1ating solutions

...

Evaparate to dryness, mix with graphite containing 1 % In 2 0 3 (internal standard) and sufficient potassium salts to give 30% K

[133]

Magnesium salts

...

Magnesium salt electro1ysed in 0.1 M Na citrate and 6 M citric acid at pH 2.5 for 30 min at 10 V, 0.4 amp with 1 mm dia. Pt wire anode and 6 mm dia. carbon rod cathode. Are carbon rod in 12 amp d.c. arc as anode with carbon cathode.

[134]

120

[Ref. p. 122

Emission Spectroscopy

Table 6 (continued) Matrix Niobium oxide

Niobium oxide

Range

...

0.001-3%

Details

Ref.

Pack30mgof AgCl/AgF (1:1) into carbon cup electrode followed by 20 mg graphite powder then 100 mg of a mixture of Nb 2 0 5 and graphite (7 :3 ). Place cap with hole over cup and excite in d.c. arc

[24]

Sn and Nb vaporised at sarne rate during mid portion of arc. PbO added as internal standard (0.1 %). Sn 286.33. Pb 287.33.

[135]

Rare earth Molybdates

...

Mix 86 mg with 14 g carbon powder and 9 mg Ga 2 0 3 (internal Standard) and 1 mg sodium iodide. Excite in graphite cavity electrode in 12 arnp d.c. arc for 55 sec after a 5 sec preburn

[136]

Sodium meta! or sodium chloride

...

Dissolve in ethanol, add conc. HCl, evaporate at 60°C and dry at 200°C. Mix residue (or NaCI) with graphite and an internal standard. Excite in d.c. arc

[13 7]

Sodium potassium Iithium mixed carbonates

...

Mix with Si0 2 and carbon powder (20:7:1) excite in 14 amp d.c. arc

[138]

Sodium molybdate

...

See reference [ 136] under Rare Earth Molybdates

[136]

Tantal um oxide

...

Direct in d.c. arc using Ta as internal standard

[139]

Dehydrate at 160°C for 24 hr, mix with graphite, NaCl/KCl and Ge0 2 (30:10:1 :0.1 %). Excite in 12 amp d.c. arc

[140]

Mix with carbon powder and K 2 C0 3 (10:1 :1) incorporating 100J1g/g Co and Ga internal standards. Excite in 10 amp d.c. arc with carbon cavity e!ectrode and carbon disc counter electrode

[141]

Mix with Ga 2 0 3 (100:2) and excite in 14 amp d.c. arc for 35 sec with 5 sec preburn. Sn 317.50,326.23 nm.ASTME402

[9]

Telluric acid

0.05jJg/g ...

...

Plants, soils

...

Plants

...

Dry 5 g milk in silica crucible, ash at 400°C overnight [149] and mix 40 mg residue with 260 mg of graphite/CdO/ NiO/KCl/CaC0 3 (20:1:1:2:2). Excite in d.c. arc Sn 284.0, Cd 326.1 nm Dry 2- 5g at 100° and ash at 400- 450°C. Excite 20mg ash in carbon electrode in 14 amp a.c. arc. Mixture of NaCI, KCI, Ca3 (P0 4 h and MgO used as matrix for Standards. Sn 284.0 nm

[150]

Ash 2m! serum with lml HN0 3 + 0.25ml HC10 4 at 130°C for 5-6 hr. Evaparate residue with lml HCl and dissolve in 1ml1% NH 4 C! and excite a 0.2ml aliquot in carbon crater electrode with 10 amp d.c. arc.

[151]

Ash 125 mg sample in activated 0 2 stream. Mix with Ga 2 03 and excite in graphite cup electrode

[152]

lg Soil or lOg plant ash fused with Na 2 C03 and [153] dissolved in 150m! water. Add sodium citrate and adjust to pH 8.3 with ammonia. Extract with 0.1% dithizone in CHC1 3. Evaparate to dryness on 100 mg graphite. lgnite at 450°C, mix with lOmg Li 2 C0 3 (internal standard) and excite in d.c. arc Camparisan of anodic and cathodic excitation for ashed residues

[154]

122

Emission Spectroscopy

[Ref. p. 122

8. Environmental Analysis Tin is of some considerable interest as an enviromental contaminant, although its toxic properties have yet to be studied in detail. The main source of tin in the environment is in the widespread use of organo-tin chemicals, which have attractive properties as plastics stabilizers, pesticides, fungicides, etc. Although these compounds range from highly toxic to edible, they degrade to hydrated tin oxide after a relatively short period and have no Iasting effects as pollutants. A selection of environmental applications is listed in Table 8 and, in addition, there are some analyses of relevant interest in Table 7.

Table 8. Environmental Analysis by Emission Spectroscopy Details

Matrix

Ref.

Collect on filter paper disc, fold and roll disc. Insert into a hollow Airborne Particulates cylindrical graphite electrode. A tungstenrod operated by a motordriven cam pushes the paper into the gap of an a.c. spark during a 30 sec exposure

(155]

Place 4 mm dia. portion of filter in a graphite crater electrode previously Airborne Particulates treated with liquid paraffin and packed with NaF /graphite powder (1 :4 ). Add 50pl of 30pg/g In solution in 2M HN0 3 and excite in d.c. arc. Sn 317.50, In 325.6lnm

(156]

Soils

See Ref. (153] Table 7

[15 3]

Soils

Dry at 105°C and ignite at 550°C for 1 hour. Grind, mix with Li2 C0 3 / K2 S0 4 /graphite powder and excite in d.c. arc. Detection Iimit 1 pg/g Sn. Improved reproducibility and precision are obtained by LiB02 fusion.

[157]

Waters

Evaparate to dryness at 180°C, add 8pg/g Sn in residue.

(158]

Waters

Evaparate to dryness on to Na2 S0 4 /MgS0 4 /CaS04 (52:22:26) and exci te in arc discharge

Waters

Extract 0.5- lOOpg Sn from 1-20 l. water from hot springs by extraction at pH 5 - 6 with dithizone/CCI 4 from tartrate solution. Evaporate extract to dryness and treat with HN0 3 . Add lümg NaN0 3 and heat residue to fuse. Excite residue in d.c. arc

Waters

Pass 50 litres through 200g of cation exchange resin in the H+ form. Elute with 2M HCI and extract Sn with sodium diethyldithiocarbamate at pH 4-5 into CHCJ 3 or CCI 4 . Excite aliquot in 13 amp. a.c. arc for 2min.

[161]

Waters

Shake llitre with 500mg of activated sugar carbon, thioacetamide, dithizone and diethyldithiocarbamate at pH 5-8 and settle for 15 min. Ash at 550°C, mix residue with carbon powder/K 2 S0 4 (2:1) and excite in 16 amp. d.c. arc

[162]

NaCl/Si~

/CaC0 3 . Detection Iimit

[159]

References

1. Moenke, H.: Atomic Spectroscopy in Trace Analysis, Leipzig: Akademische Verlagsgesellschaft, Geestund Porting KG., 1973 2. Mika, J., Torok, T.: Analytical Emission Spectroscopy, London: Butterworths 1973 3. Grove, E.L.: Analytical Emission Spectroscopy, Voll, Part 1, New York: Dekker 1971 4. Addink, N. W.H.: D.C. Are Analysis, London: Macmillan 1971 5. Slavin, M.: Emission Spectrochemical Analysis, (Val 36 in Chemical Analysis monographs Eds. Eiving P.J., Kolthoff, L.M.,) New York: Wiley Intersience 1971

References

123

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Emission Spectroscopy

Schatz, F. V.: Spectrochim. Acta 6, 198 (1954) Leichtle, P.A.: J. Opt. Soc. Amer. 34,454 (1944) Jaycox, E.K.: J. Opt. Soc. Amer. 35, 175 (1945) Elwell, W.T., Peake, DM.: Analyst 96,465 (1971) Park, B.: Ind. Eng. Chem., Anal. Ed. 6, 189 (1934) Gordon, N.E., Jacobs, RM.: Anal. Chem. 25, 1605 (1953) Report on Available Standard Sampiesand High Purity Materials for Spectrochemical Analysis, ASTM DS 2, Philadelphia: ASTM 1964 C. Woodward, Ed.: A. Rept.Anal. Atom. Spectros. 3, 43 (1973) ASTM Method E30 for Chemical Analysis of Steel, Cast Iran, Open-Hearth Iran and Wrought lron, The 1974 Annual Book of ASTM Standards Part 12, Philadelphia: ASTM 1974 Maekawa, S., Suzuki, T.: Japan Analyst 15,477 (1966) Spectrographic Analysis Sub-Committee, Brit. Iran Steel Res. Assoc., J. Iran Steel Inst. 181, 316 (1955) Eremenko, AM., Tverdokhlebova, S. V., Tsikora, /.L.: Zavod. Lab. 37,430 (1971) Tunney, A.A.: Brit. Steel Corp. Open Rept. GS/TECH/258/1/73/C (1973) Goto, H., Ikeda, S., Hirokawa, K., Seno, H., Kaya, A.: Japan Analyst 13,661 (1964) Smitz, L., Loose, W., Koch, K.H.: Z. Anal. Chem. 266, 186 (1973) Stamp, C., McKenzie, P., Harrison, T.S.: Metallur.e;ia Metals Form. 40, 222 (1973) Tunney, A.A., Hughes, H.: Brit. Steel Corp. Open Rept. GS/TECH/251/1/73/C (1973) Weisberger, S., Pristera, F., Reese, E.F.: Appl. Spectros. 9, 19 (1955) Morello, B., DeGregorio, P., Savastano, G.: Appl. Spectros. 28. 14 (1974) Pravcheva, K., Ganer, P., Deliiska, A.: Campt. Rend. Acad. Bulg. Sei. 24, 893 (1971) Pravcheva, K., Ganer, P., Deliiska, A., Ninova, V.: Z. Anal. Chem. 254, 16 (1971) Pravcheva, K., Ganer, P., Ninova, V., Deliiska; A.: Z. Anal. Chem. 255, 113 (1971) Poster, P., Mo/ins, R., Bozon, H.: Analusis 1, 434 (1972) Cerjan-Stefanovic, S., Turina, S., Marjanovic, V.: Croat. Chem. Acta 43, 83 (1971) Pohl, F.A.: Mikrochim. Acta 258 (1954) Komarovskii, A.G., Vasil'eva, L.A., Tikhomirova, N.N.: Zavod. Lab. 37, 179 (1971) Svehla, A., Kvopkova, 0.: Hutn. Listy 16,588 (1961) B.N.F.M.R.A., Lead Analysis Panel, Spectrochim. Acta 7, 205 (1955) Naimark, L.E.: Trudy Inst. Metall. Obogasch. Alama. Ata 31, 72 (1968) Breckpot, R.: Bull. Soc. Chim. Belg., 46,619 (1937) Breckpot, R., Creffier,J., Perlingh, 0.: Ann. Soc. Sei. Brux. 57, 295 (1937) Kochergina, T. Y., Zaitseva, V.A.: Fiz. Sb. L'vov, Univ. 4, 438 (1958) Lazebruk, D.D., Yatsenko, V./.: Nauch. Zap. Ukr. Poligr. Inst. 12, 99 (1958) Nausester, H.K.: Appl. Spectros. 11, 115 (1957) Downarowicz, J., Zagorski, Z.: Chemia Analit. 4, 445 (1959) Krasnobaeva, N., Aleksandrov, S.: Acta Chim. Hung. 64, 1 (1970) Muzgin, V.N., Gladysheva, L.A.: Zavod. Lab. 34, 1076 (1968) Atwell, M.G., Golden, G.S.. : Appl. Spectros. 24, 362 (1970) Shvartz, DM., Granfel'd, A.l.: Zavod. Lab. 25, 946 (1959) Barker, F.G.,J.: Iran Steel Inst. 139, 211 (1939) Arnott, J.: Metallurgia 30, 300 (1944) Osumi, Y., Higashi, K., Mikaye, Y.: Japan Analyst 18, 1219 (1969) Joshi, B.D., Banga, T.R., Dalvi, A.G./.: Z. Anal. Chem. 260, 107 (1972) Zakharov, E.l., Lipis, L. V., Petrov, K.l.: Zhur. Analit. Khim. 14, 135 (1959) Ryabchikov, D.l., Vainshtein, E.E., Bonsova, L. V., Volynets, M.P., Korolev, V. V., Kutsenko, Y.I.: Trudy Komiss. Anal. Khim. Akad. Nauk. SSSR 12, 82 (1960) Melamed, S.G.: Zavod. Lab. 21, 1066 (1955) Chalkov, N. Y., Yudelevich, l.G., Ustimov, A.M.: Izv. Sib. Otdel. Akad. Nauk. SSSR Ser. Khim. Nauk. 161 (1972) Kaneko, K.. Goseki. S.: Japan Analyst 18, 220 (1969) Vainshtein, E.E., Belyaev, Y.l., Akhmanova, M. V.: Trudy Komiss. Anal. Khim. Akad. Nauk. SSSR 12, 236 (1960) Alvarez-Herrero, C., Burriel-Marti, F.: Revta Meta!. 8, 200 (1972) Beloglazova, A.D., Krupnov, V.K., Safaeva, F.Z.: Zavod. Lab. 34, 1057 (1968) Tiptsova, V.G., Drostran, A.G., Golitsyna, M./.: Zhur. Analit. Khim. 23, 1684 (1968) Jacobs, R.M., Gordon, N.E.: U.S. Atom. Energy Comm. Rept. WAPD.CTA (GLA)-16212 Oct (1972) Gordon, N.E., Jacobs, RM.: Anal. Chem., 25, 1605 (1953) Wheat, J.A.: Appl. Spectros. 12, 152 (1958) Murray, K.A., Maritz, J.F.: J.S. African Inst. Min. Metall. 65, 571 (1965) Rivkina,M.A.: Zavod. Lab. 21,459 (1955) Tymchuk, P., Mykytiuk, D.S., Russell, D.S., Berman, S.S.: Canad. Spectros. 11, 129, 140 (1966)

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Gruzdeva, N.I: Obogaschchenie Rud. 1, (1960). Anal. Abstr. 9, 611 (1962) Pohl, F.A.: Z. Anal. Chem. 141, 81 (1954) Ivanova, G.F.: Zhur. Analit. Khim. 21,1307 (1966) Janda, I., Schroll, E.: Mikrochim .. Acta 389 (1959) Schroll, M., Weninger, M.: Mikrochim. Jchnoanalyt. Acta. 2, 378 (1965) Cru[t, E.F.,Husler, J.: Anal. Chem. 41,175 (1969) Shilling, M.L.: lzv. Akad. Nauk. SSSR, Ser. Piz. 19, 216 (1955) Pavlenko, L.I.,Popova, V.S.: Zavod. Lab. 30,699 (1964) Hamaguchi, H., Kuroda, R.: Japan Analyst 4, 207 (1955) Kolbe, P.: Geochim. Cosmochim. Acta 29, 153 (1965) Tennant, W.C.: Appl. Spectros. 21, 282 (1967) Hamaguchi, H., Kuroda, R., Negishi, R.: Bull. Chem. Soc. Japan 33, 901 (1960) Tennant, W.C., Sewell, J.R.: Geochim. Cosmochim. Acta 33, 640 (1969) Tanaka, T., Yamasaki, K.: Japan Analyst 18, 324 (1969) Kuz'min, N.M., Popova, G.D., Kuzovlev, l.A., Solomatin, V.S.: Zhur. Analit. Khim. 24, 899 (1969) Vengsarkar, B.R., Machado, I.J., Malhotra, S.K.: Talanta 22, 903 (1975) Krasnobaeva, N., Tashkova, A.: Campt. Rend. Acad. Bulg. Sei. 17, 917 (1964) Dittrich, K., Roessler, H.: Talanta 20, 897 (1973) LeRov. V M., Lincoln, A.J.: Plating 60, 922 (1973) K6asilshchik, V.Z., Manova, T. G., Raginskaya, L.K., Kuznetsova, O.S.: Zavod. Lab. 39, 93~ (1973) Holdt, G., Schäfer, H.: Z. Anal. Chem. 146, 4 (1955) Raginskaya, L.K., Manova, T.G., Sotrukova, V.N.: Zavod. Lab. 36, 1348 (1970) Ricard, J.: Meth. Phys. Analyse 8, 32 (1972) Moskalenko,N.J., Strekalovskii, V.N.,Muzgin, V.N.: Zavod. Lab 37,1079 (1971) Chandola, L.C., Venkatasubramanian, R.: Z. Anal. Chem. 266, 127 (1973) Zmbova, B., Teofilovski, C.: Talanta 20, 217 (1973) Degtyareva, U.F., Sinitsyna, L.G., Barikhina, T.A.: Zhur. Analit. Khim. 28,1164 (1973) Sato, M., Matsui, H., Matsurbara, T.: Japan Analyst 20, 215 (1971) Naik, R.C., Karnik, K.P.D.: Rept. Bhabha Atom. Res. Centre, BARC-621 (1972) Larina, L.K., Makartseva, V.N.. Blenkova. N.S.: Zhur. Analit. Khim. 27, 1634 (1972) Ovrutskii, M.I., Freger, S. V., Kechto, V.N., Belogub, T.N.: Ukr. Khim. Zhur. 36, 492 (1970) Anal. Abstr. 20,3071 (1971) Barr, D.R., Larson, H.J.: Appl. Speetros. 26,51 (1972) Biske, V.B., Feaster, J.F.: Proe. Amer. Soe. Brew. Chem. 189 (1964) Hudson, J.R.: J. Inst. Brew. 61, 127 (1955) Gehrke, C. W., Runyon, C. V., Pickett, E.E.: J. Dairy Sei. 37, 1401 (1954) Zore, V.A., Tikhonova, Z.l.: Gigiena i Sanit. 2, 58 (1963) Anal. Abstr. 11, 1913 (1964) Niedermeier, W., Griggs, J.H., Johnson, R.S.: Appl. Spectros. 25, 53 (1971) Haupt, P.M., Torrenga, B.J.: T.N.O. Nieuws 27,453 (1972). Anal. Abstr. 25,3212 (1973) Wark, W.J.: Anal. Chem. 26, 203 (1954) Strasheim, A., Camerer, L.: J.S. Afr. Chem. Inst. 8, 28 (1955) Lander, D. W., Steiner, R.L., Anderson, D.H., Dehm, R.L.: Appl. Spectros. 25, 270 (1971) Hasegawa, T., Sugimac, A.E.: Japan Analyst 20, 840 (1971) Ecrement, F.: Meth. Phys. Analyse 7, 128 (1971) Chesterikov, A.: Bull. Soe. Fr. Miner. Christallogr. 93, 357 (1970) Kozin, A.N., Korosteleva, N.A., Yurova, V.P.: Trudy Kuibyshevsk. Gos. Nauk, Inst. Neft. Prom. 39, 227 (1968) Ikada, N.: J. Chem. Soc. Japan, Pure Chem. Sect. 76, 1011 (1955) Miroshnikova, Z.P.: Trudy Voronezh. Gos. Univ. 82, 80 (1971) Anal. Abstr. 22, 4556 (1971) Korganova, T.S., Polyakov, V.A., Kolotov, B.A., Nechaeva, T.P.: Zavod. Lab. 39,1186 (1973) Corliss, C.H.: J. Res. Nat. Bur. Standards 66A, 1 (1962)

CHAPTER 10 X-RA Y FLUORESCENCE By R. Smith

1. General 1.1 Instrumentation A number of different X-ray fluorescence instruments are in routine use: (i) Crystal dispersion, tube excitation, sequential counting. (ii) Crystal dispersion, tt!be excitation, simultaneaus counting. (iii) Crystal dispersion, electron excitation. (iv) Non-dispersive, Ross filter, radio isotope excitation. (v) Non-dispersive, semi-conductor detector.

Types (i) and (ii) are used in laboratories throughout the world and unless otherwise stated, any reference in this chapter will assume instruments of type (i). Instruments of type (iv) arealso widely used but arerather more limited in their scope and tend to be used for well-defmed applications. Type (iv) instruments may also be obtained as portable monitors and are used in prospecting, mining and on-line mineral dressing applications. Instruments of types (üi) and (v) are available cornmercially but have found few applications in the analysis of materials containing tin. A more complete description of X-ray instrumentation will be found in standard texts [ 1, 2] or in manufacturers' literature. Biennial reviews are published in the journal, Analytical Chemistry and comprehensive bibliographies are produced by Philips N.V. [5). 1.2 Spectral Characteristics of Tin Tin absorbs X-radiation at wavelengths of 0.4247 A and less (K absorption edge) and at wavelengths of 2. 777 A or less (LI absorption edge ). In addition, weaker Ln and Lm absorption edges occur at 2.982 A and 3.156 A. The MI absorption edge occurs at 13.8 A and is unlikely tobe of irnportance other than in the determination of elements lighter than Mg. The other M absorption edges are outside the usual working range of current spectrometers. The principal fluorescence emission lines for tin are the SnKa 1 and Sn Ka 2 at 0.4906 A and 0.4951 A respectively. Resolution of these two lines is not normally attempted and a convoluted peak at 0.4921 Ais usually measured. The Sn Kß lines are usually about one third of the intensity of the Ka 1 2 line and are found at: Kß 1 0.4352, Kß 2 0.4258, Kß 3 0.4359, Kß4 0.4252 and Kß: 0.4318 A. Antimony with Sb Ka 1 2 0.4 719 A may overlap the Sn K a line at the short wavelength wing and may require 'careful resolution. The presence of Sb, however, does not hinder the determination of tin other than in limiting the coice of wavelengths for counting background radiation. The Ag Kß spectrum at 0.487 - 0.498 A also overlaps the Sn K a line. Under some circumstances ( eg the examination of photographic residues) it may be possible to confuse the Sn Ka and Sn Kß lines with the Ag Kß and I Ka lines respectively.

1.2 Spectral Characteristics of Tin

Ref.p. 143]

127

In the analysis of light matrices, such as organic materials, the magnitude of scattered background radiation is likely to be fairly high at the Sn Ka wavelength, particularly if trace analysis is being undertaken. Under these circumstances, measurement of the Sn La 1 3 .600, Sn La 2 3.609, Sn l.ß 1 3 385 or Sn Lß 2 3.175 A may be preferable. These wavelengths may also be of use if Sn Ka/Sn La ratios are to be measured in examining effects caused by particle size in the sample [3]. The most suitable crystal for the Sn L spectrum is LiF (200) (2d spacing 4.027 A); the choice for Sn Kais rather more varied; LiF (200) is by far the most popular crystal for resolving Sn Ka radiation, unfortunately the angle of diffraction (20 = 14.0°) is extremely low and although high count rates may be obtained, dispersion is poor. Considerable improvement in dispersion at the Sn Ka wavelength may be obtained using LiF (220), LiF (420) or LiF (422) crystals. This is expressed in Table 1. The improvements in resolution are accompanied by a decrease in diffracted intensity and for most purposes the LiF (220) crystal represents a reasonable compromise. Use of the LiF (420) or LiF (422) crystals may be attended with other disadvantages: both are

Table 1. Crystals Used for Dispersion of Sn Ka Radiation Crystal

2d (Ä)

2fJO

d%x

LiF (200) LiF (220) LiF (420) LiF (422) Topaz (303)

4.028 2.850 1.802 1.645 2.712

14.03 19.89 31.69 34.81 20.91

0.52 0.75 1.21 1.30 0.79

d is the interplanar spacing of the crystallattice (J is the angle of diffraction

~~ is a measure of dispersion with respect to wavelength dfJ dA.=

1 d cos2fJ

capable of resolving the Sn Ka 1 and Sn K.a 2 !ines, almost completely. In most instances it is more convenient to measure the two lines as an unresolved single peak. The topaz (303) crystal, although important historically, is rarely used in modern X-ray practice. Topaz, ho.wever, gives good dispersion at the Sn Ka wavelength, slightly better than LiF (220); the temperature coefficient has been found [4, 5) tobe less than that of LiF (220). LiF (220) exhibits "forbidden" reflections from the 110,330 and 550 planes giving rise to spurious spectrallines at the 3/2, 5/2 orders; topaz also gives rise to series of spurious reflections which differ in intensity from crystal to crystal (Fig. I). The LiF (220) crystal gives intensities which are markedly superior to those 0f the topaz (303) crystal and for this reason alone is generally favoured. The scintillation counter is always used for measurements of Sn K radiation and the proportional flow counter for Sn. L.

[Ref.p. 143

X-Ray-Fluorescence

128

COUNTS/SEC X

SnK ..

100 20

10

2nd ORDER SIV Paint Varn.Prod. 62, 27 (1972); Anal. Abstr. 24, 2269 (1973) Chamberlain, B.R., Leech, R.J.: Talanta 14, 597 (1967) Nakanishi, H., Yoshimura, M., Yoshisako, K., Itsuki, K.: Japan Analyst 13, 1131 (1964) Lachance, G.R., Traill, R.J.: Can.J. Spectros. 11,43 (1966) Rasberry, S.D., Heinrich, K.F.J.: Anal. Chem. 46, 81 (1974)

CHAPTER 11

RADIOCHEMICAL & MOSSBAUER METHODS By J.W. Price

1 . Radiochemical methods Irradiation of tin with thermal neutrons produces several radioactive isotopes, and of these 113 Sn which is a -y-emitter with a half-life of 119 days, has been used for labeHing organotin compounds in studies of animal metabolism and of agricultural residues (see Chapter 19.6). The other important use ofradiochemical methods is in the determination of trace amounts of tin by neutron activation analysis and for this the most suitable isotope is 121 Sn, which is a pure ß-emitter with a half-life of 27 hours. Irradiation is carried out in a flux of about 10 12 n.cm -2 s- 1 for periods of 6-24 hours, Cle sample being allowed to decay for 24 hours before processing. A disadvantage in the use of 121 Sn is the need to obtain a radiochemically pure compound for ß-counting, the main contaminants being arsenic, antimony, molybdenum and tellurium, and a series of Separations, usually involving one or more solvent extractions, must be carried out. The radiochemistry of tin and suggested schemes of chemical Separation, particularly from fission products, are given in detail in a monograph by Nervik [1). The determination of tindown to 0.0001% in iron and alloy steels by neutron activation has been described by Williams [2]. The irradiated sample (1 g) tagether with 20mg tincarrierwas dissolved in hydrochloric acid, the solution oxidised with bromine and sulphides precipitated after neutralisation of most of the free acid with ammonia. The precipitate was dissolved in hydrochloric acid, oxidised and sulphides re-precipitated and re-dissolved in 1ml of the acid. After addition of copper, antimony and molybdenum carriers and 0.5 ml each of sulphuric and hydrofluoric acids and dilution to 10 ml, sulphides were again precipitated, leaving the tin in solution. Traces of sulphide in suspension were removed by scavenging with lanthanum fluoride, and tin precipitated as sulphide after addition of 10m! of saturated boric acid solution. Traces of iron were removed as hydroxide by adding iron carrier to a solution of the sulphide precipitate in 1 ml of hydrochloric acid after oxidising with bromine, by making strongly alkaline with 10M sodium hydroxide. The ftltrate was acidified with hydrochloric acid and tin again precipitated as sulphide, ignited to oxide and counted. (It is preferable to ignite the sulphide precipitate to oxide before counting in order to reduce self-absorption of the low-energy ß-particles). Counting was continued at 24 hour intervals for 10 days in order to obtain the slope of the decay curve; this was extrapolated to zerotime to give the uncorrected count for 121 Sn and the tail of the decay curve was also extrapolated to determine the activity caused by long-lived tin isotopes and radiochemical impurities. Finally the corrected activity was converted to weight of tin by comparison with a standard sample of tin meta! (2 mg) irradiated and processed in the same way as the sample. A different radiochemical Separation procedure was used by Hamaguchi et al [3) to determine 50 - 300 pgj g of tin in ferro alloys. The sample, tagether with 20mg of tin carrier, was dissolved in 20ml of 6M hydrochloric acid, 4ml of 9M. sulphuric

146

Radiochemical & Mossbauer Methods

[Ref.p. 148

acid and 2ml of nitric acid, flltered, diluted to 150rnl and sulphides precipitated with H2 S after addition of 2 g of tartaric acid. The sulphide percipitate was dissolved in 5ml ofhydrochloric acid and, after addition of 2mg of iron(III), 5ml of 2.5M hydrofluoric acid and 5 ml of water, extracted with 15 rnl of methyl isopropyl ketone. Tin in the aqueous phasewas then precipitated as sulphide after addition of 10rnl of saturated boric acid solution and the precipitate dissolved in 4ml of sulphuric acid cantairring 0.2 g of hydrazine sulphate and 2mg each of Sb 3 +, As 3 • and Cu 2 • carriers. After addition of 22rnl of water, foreign activities were extracted with 20ml portians of diethylarnmonium diethyldithiocarbarnate (10gll chloroform) until no more colour was produced in the extract. Tin was then extracted as the iodide from the aqueous phase with 20rnl of methyl isopropyl ketone after addition of 5 g of potassium iodide, the organlc phase washed with 1.5M potassium iodidein l.SM sulphuric acid and the tin stripped by shaking with lOrnl of 2.5 M hydrofluoric acid. Finally tin sulphide was precipitated after adding 15 ml of saturated boric acid solution, flltered, dissolved in a mixture of 1 ml of nitric acid and 2ml of perchloric acid and the solution evaporated to fuming to precipitate Sn0 2 • After diluting with water the precipitate was filtered, ignited, weighed to determine the chemical yield and mounted for counting. The same scheme of Separation was used successfully by these workers for the determination of tin in sea-water andin biological materials, while Byme [4] determined down to 0.1 Jlglg Sn in kale, human hair and fruit juices, after irradiating and ashing, by dissolving the ash in 4.5M sulphuric acid- 0.5M potassium iodide and extracting Snl 4 into toluene. The extract was washed with 1.5M sulphuric acid IM potassium iodide to remove arsenic and antirnony and the tin back-extracted into 1.5M sulphuric acid for measurement of the 1-activity of 123 m Sn (half-life 40 min). This procedure was considered by Bowen [5] to give inadequate decontarnination from arsenic and antirnony and he included a further step involving a thiocyanate extraction ofthe tin as follows; the toluene solution cantairring the tinwas stripped with 10ml of 1M hydrochloric acid and the aqueous layer after the addition of arsenic and antirnony carriers and 5ml of 3M potassium thiocyanate was extracted with 15 ml of diethylether. Tin was back-extracted from the ethereallayer into 10ml of 2M sodium hydroxide and, after the neutralisation of the solution with hydrochloric acid, precipitated as the sulphide, filtered, weighed for chemical yield and the activity of the 121 Sn counted. No corrections were found necessary for dead time or selfabsorptio.n and a precision of ± 10% in the range 50 - 300nglg was found, with a sensitivity of 10- 20ng. A further radiochemical procedure suitable for the determination of tin in nicke! alloys has been described [6]. After precipitation of the tin as metastarrnie acid the precipitate is heated with arnmonium iodide to sublime Snl 4 which is dissolved in a mixture of 1.5M perchloric acid I 2.5M I sodium iodide and extracted into benzene. After back-extraction into 0.5M hydrochloric acid tin is precipitated with N-benzoylphenylhydroxylarnine, the precipitate dried and weighed, the activity of 121 Sn then being counted as above. Substantially the sarne procedure has been used by Tejinus and Haidar [7] for the analysis of biological and geological sarnples. F or the determination of tin ( 10-1 ,OOOppm) in geological material Johansen and Steines [8] preferred a method based on 113 Sn, the sarnples being irradiated for 14 days at a neutron flux of 10 12 n.cm- 2 s- 1 and stored for 14 days before processing. They were then fused with 2g of sodium hydroxide after addition of tin carrier and zinc holdback carrier, the melt dissolved in water, the solution acidified with sulphuric acid and the tin precipitated as sulphide by the addition of thioacetarnide. The

Ref.p. 148]

2. Mössbauer Spectroscopy

147

precipitate was dissolved in 5 ml of hydrochloric acid and 0.5 ml of nitric acid, 20ml of 5 M ammonium thiocyanate added and tin extracted by shaking three times with 30m! of diethyl ether. The combined extracts were evaporated over 50ml of 3M sulphuric acid and tin again precipitated from the filtered solution with thioacetamide, the sulphide filtered, ignited to Sn0 2 and weighed. After allowing 24 hours for the transient equilibrium 113 Sn - 113 m In to be established the 1-activity based on the 392ke V photopeak of 113 m In was recorded. A similar method was used by Obrusnik [9] for the determination of indium and tin in granite. Chemical separation of the tinwas avoided by extraction of indium into dithizone from alkahne cyanide solution, followed by substoichiometric replacement by mercury, the dithizone extract being shaken with a solution of 400ttg of mercury in tartrate buffer (pH 7 .5). The 1-activity of the 113 m In in the aqueous phase was then measured as above. Of other methods of separation that can be used in radiochemistry (see Ref. ( 1]) the most important are chromatography and ion-exchange. Chromatography. The separation of arsenic, antimony and tin by thin-layer chromatography has been described by Seiler [ 10 ], who used as developing solvent a mixture of methanol-ammonia-water-polysulphide (35: 10:5:1) and detected arsenic and antimony as their sulphides and tin with diphenylcarbazide, while Stronski [ 11] separated In-Sn-Te and Sb-Sn by extraction chromatography with Amberlite LA-2 for the production of carrier-free radioisotopes from irradiated targets. Ion-exchange. A complete separation of tin and antimony activities can be obtained by using cation-exchange resin (Dowex 50) and solutions which are 12M in hydrochloric acid, the SnC!~ -complex not being absorbed while the antimony is strongly held [ 12]. Mixtures of tellurium, antimony and tin tracer in 0.1 M oxalic acid solution have been separated on Dowex-1 columns [ 13]; using 0.1 M oxalic acid neutralised to pH 4.8 as eluent, antimony is removed from the column while tin can be eluted with 0.1 M sulphuric acid. Mixtures of Sn 4 + and Sb 5 + can be separated on Amberlite IRA-400 using ammonium malonate as eluent (14]; the tin complex is strongly held by the resin but can be stripped with 4.5M sulphuric acid. Neutron activation analysis has been used for the determination of trace impurities in samples of high-purity tin metal, and detailed separation schemes have been put forward for the simultaneaus determination of up to 15 impurities in the submicrogram range using a 1g sample [ 15, 16].

2. Mössbauer Spectroscopy The Mössbauer effect has been of considerable value in the study of the structure of tin compounds, particularly of the organotins [ 17] but its application to quantitative measurements has so far been less important. The possibility of using a relatively simple non-destructive method for the determination of Sn0 2 has led to its investigation for the analysis of ores and minerals [ 18] and in geological surveying ( 19]. A portable field apparatus has been described (20], which uses a source of 1-quanta in the form of Sn0 2 enriched in 119 Sn and a scintillation counter detector for 1-quanta of 24keV. When the source is stationary some of the quanta passing through the sample are resonance-absorbed by the 119 Sn nuclei present, while if the source is moving the

Radiochernical & Mossbauer Methods

148

energy of the quanta changes owing to the Doppler effect and no resonance-absorption takes place, the difference between the number of pulses registered being proportional to the amount of tin in the sample .. A sensitivity of about 0.1% Sn is obtained with an accuracy at the 1% level of about ± 10%. The problems involved in using Mössbauer spectroscopy for the accurate determination of tin have been examined in detail by Pe/la et aL [21] using synthetic mixtures of Sn0 2 and Al 2 0 3 with Pd 3 - 119 rn Sn as a source, and their fmdings applied to the determination of tin in copper-base alloys [22). The source used in this case was lOmCi of 119 m Sn as BaSn0 3 , a 0.05mm Pd foil being placed over the source to fiJ.ter the 25keV Sn X-rays, and using a sample thickness of O.Smm. An intemal standard was prepared by grinding a mixture of tin metal powder with Al 2 0 3 and casting the mixturein resin to form a disc O.Smm thick and 3cm 2 in area, with a tin content of 8mg/cm 2 • The alloy samples (I - 8% Sn) were dissolved in nitric acid and the precipitated metastannic acid fiJ.tered, ignited and mixed with enough Al 2 0 3 to give a total weight of 165mg. The mixturewas transferred to a cell holder and spectra accumulated until 7 x 10 5 counts per charmel were obtained. Calibration curves were obtained by dissolving known weights of tin metal in nitric acid and continuing as above, the areas of the Sn0 2 and ß-tin absorption peaks being evaluated and C1eir ratio plotted against the tin concentration. Sn0 2 is particularly suitable in Mössbauer studies because of its sensitive analytical response in terms of the change in absorption intensity per unit change in concentration, so that determination of naturally occurring cassiterite and determination of tin in alloys soluble in nitric acid would appear the most suitable applications for Mössbauer spectrometry in quantitative work. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

19. 20. 21. 22.

Nervik, W.E.: The Radiochemistry of tin NAS-NS 3023 U.S. Atomic Energy Commission 1960 Williams, A.I.: Analyst 84,433, 1959 Hamaguchi, H., Kawabuchi, N., Oniama, R., KurociJI, R.: Anal.Chirn.Acta 30, 335, 1964 Byrne,A.R.: Radiochern. Radioanalyt. Lett. 7, 287,1971 Bowen, H.JM.: Analyst 97,1003, 1972 Morris, D.F.C., Denny, JA.: Radiochem. Radioanalyt. Lett. 8, 219, 1971 Tejinus, B.M., Ha/dar, B.S.: Radiochem.Radioanalyt. Lett. 13, 25, 1973 Johansen, 0., Steines, E.: Analyst 94,976, 1969 Obrusnik, /.: Talanta 16,563, 1969 Seiler, H.: Helv.Chirn.Acta 54,533, 1971 Stronski, I.: Radiochem. Radioanalyt. Lett. 5,"113, 1970 Kraus, KA., Michelson, C.D., Nelson, F.: J.Amer.Chem.Soc. 81, 3204, 1959 Smith, G. W., Reynolds, SA.: Anal.Chim.Acta 12, 151, 1955 Dawson, J., Magee, R.J.: Mikrochim.Acta 3, 325, 1958 Lanfranco, G.: Metallurg.Ital. 63, 225, 1971 Maenhaut, W., Adams, F., Hoste, J.: J.Radioanalyt.Chem. 6, 83, 1970; 9, 27, 1971; 14, 295,1973 ~mith, P.J.: Organomet.Chem.Rev.Sect.A. 5, 373, 1970 Kalmakov. AA., Salakhutdinov, N.: Izv. Vysshikh Uchebn.Zaved, Tsvetn. Met. 8, 158 (1965). Chem. Abstr. 64, 3107 (1966) Salakhutdinov, N.: Teor. Sredstva Avtomat., 396 (1968) Chem.Abstr. 71, 27232 (1969) Salakhutdinov, N., Kalrnakov A.A.: Izv. Vyssh. Ucheb. Zaved.Tsvet.Met. 13, 17 (1970) Chern. Abstr. 73, 105200 (1970) Stuart, R.A., Donohoe, A.J., Boyle, A.J.F.: Proc.Austral.Inst.Min.Metall., 230, 69 (1969) Chem. Abstr. 71, 56356 (1969) Dolenko et al., A. V.: Vses.Nauk-Tekh.Konf, 467, 1968, Atomizdat USSR 1971 (Chem. Abstr. 77, 121696, 1972) Goldanskii, V./., et al.: Tr.Vses.Nauk.-Issled.lnst.Yad.Geoflz.Geokhim. 3, 220, 1968 (Chern. Ab~r. 72,139362) 1970 Pella, P.A., Devoe, J.R., Snediker, D.K.: Anal. Chem. 41, 46, 1969 Pe/la, PA., DeVoe,J.R.: Anal. Chem. 42, 1833, 1970

CHAPTER 12 ANALYSIS OF TIN ORES & CONCENTRATES By R. Smith

1. Tin Minerals The principal tin minerals are given in Table 1, tagether with their formulae and areas of occurrence. In addition to the elements listed in Table 1, other elements associated with tin include: As, Bi, Cd, F, In, Mo, Nb, Ta, Ti, Wand Zn.

Table 1. Principal Tin Minerals [ 1] Native Tin

Sn

Nesbitt LaBine Mine Saskatchewan

Niggliite

(PtTe)x(PtSnly

Insizwa, S.Africa

Stannopalladinite

Pd3Sn2

USSR

Cassiterite

Sn02

Widespread occurrence

Souxite (wood tin)

Sn02,xH20

Mexico; Bolivia

Cuprocassiterite

Sn02 ,2Cu(0Hh ,Sn(OHh

Hochschildite

PbSn03,4H20

Montesite, herzenbergite

SnS

Bolivia

Stannite

Cu2FeSnS4

Widespread occurrence

Hexastannite

Cu 6FeSnSs

Bolivia

Mawsonite Sakuraite

Cu7Fe2SnS10 (CuZnF eAg)J (lnSn)S4

Ikurno Mine, Japan

Teallite

PbSnS2

Bolivia

Cyiindrite

Pb6Sn6Sb2S1s or Pb3Sn4Sb2S10

Bolivia

Franckeite Canfieldite,argyrodite

PbsSn3Sb2S14 Ag 8 (SnGe)S6

Bolivia;Yukon, Canda Bolivia;Gerrnany;Tasmania

Nordenskioldinite

CaSn(B03h

Stockesite

CaSnSi(OH)407

Bolivia

Tin concentrates range from almostpure cassiterite with 78% Sn found in Central Africa to low-grade Bolivian materials with as little as 10% tin and containing !arge quantities of sulphur, lead and zinc.

150

Analysis of Tin Ores & Concentrates

[Ref.p. 170

2. Sampling of Tin Ores and Concentrates The principles of bulk sampling statistics and geochemical value assessment have recently been reviewed by Ingamells [2]; guidelines for sampling bulk materials are given in a Japanese Standard [3] and a publication by the Institute ofMining and Metallurgy [4] contains a number of articles on all aspects of the sampling of solids. The following guidelines for sampling tin concentrates refer particularly to consignments or batches of material and are based on practical experience in the European smelting industry. 2.1 Size of Batchor Consignment- the consignment may be of any size but should be subdivided into "lots" to minimise the effects of random errors. For purchasing transactions a convenient Iimit to the size of lots is 20 tonnes Sn in concentrate with a maximum of 100 tonnes of material in the Iot. A combined error of ± 0.2% Sn for assaying and sampling is, therefore, ± 200kg Sn on the largest Iot. 2.2 Primary Sampling - it is impossible to give a scheme for the drawing of a primary sample as the consigment will vary. Where possible trucks, containers, railwagons, etc., should be sampled during unloading. Tipping trucks or containers should be sampled immediately after the Ioad has been tipped - samples should be taken from all over the heap which should then be thoroughly turned over, preferably with a mechanical digger and sampled again Bags and drums should be sampled during emptying. With drums and !arge bags the sample should include increments from top, middle and bottom. Spear sampling from intact bags tends to reject material from the bottarn of the bag and also !arge lumps [82] At all stages in sampling, care should be taken to avoid loss of moisture by keeping the bulk sample in a covered container. Heaps of material should not be allowed to dry out or become wetted between weighing and sampling. Care should be taken to avoid loss of fine material in windy conditions or rejection of !arge particles which tend to roll off sampling shovels. It is common practice to draw a primary sample equal to 5% or 10% of the weight of the Iot, giving a maximum of 5 or 10 tonnes of sample.lf 1000 shovelfuls (n) of concentrate are taken for the bulk sample and the standard deviation (s) of the tin contents of individual shovelfuls is 5% Sn then:

9 5% confidence Iimit

t is Student's 't'

+~ -..rn

± 1.95

X

J 1000

5

=

± 0.31% Sn

Table 2 illustrates the errors which may be obtained in taking 5% primary samples. If a 10% sample were taken using twice the number of increments, the errors would be reduced by a factor of 1.41. 2.3 Crnshing and Dividing- primary samples are usually divided by coning and quartering or by a mechanical device to give a sample of 50- 150kg having a maximum particle diameter of about 15mm. This should be crushed to pass a 2 mm (1 /16 inch) sieve and then further divided for final sample preparation. The concentrate should be dried and 250- 1000g milled to pass a 76pm sieve (B.S. 200). The sample should be dried again before assay and at least 0.3g taken by the assayer.

Ref.p. 170]

151

2. Sampling of Tin Ores and Concentrates

Table 2. Errors (95% Confidence Limits) of Primary Sampling with 2kg Increments to give a 5% Sampie - if Standard Deviation of Increments is 5% Sn Primary Sampie Increments

LotSize tonnes

0.195 0.275 0.435 0.613

2500 1250 500 250

100 50 20 10

Sampling Error ±%Sn

Sampling Error ±kg Sn 195 138 87 61

A number of sampling models exist which enable calculations to be made of errors for varying particle sizes and sample weights. All theories assume that the sample is well mixed and that the only error is the so-called "fundamental error". This error is committed when sampling is perfect and is analagous to the error involved in estimating the number of black and white balls in a collection of a hundred by taking a random sample of ten balls. The fundamental sampling error may be calculated by the 'size/weight ratio' theory of Bailey [6, 7]. This assumes that only the largest particles contribute to the error, that the mineral is completely liberated from the gangue and that the particles are cubic. A more sophisticated theory by Gy [4, 8] overcomes these objections at the expense of introducing more variables.

(i)

Where: a 2 (FE) is fundamental error expressedas a relative variance. is the sample weight. is the lot weight. is the mineral (Sn0 2 ) content of the lot, expressedas a decimal p A ; PG are densities of the mineral and gangue respectively. is a 'shape' factor (for ores and concentrates f =0.5). f is a 'size distribution' factor (g = 0.50 for products graded between two g screens and g = 0.25 for products graded through only one screen). is the 'liberation' factor given by Table 3 is the diameter of largest particles. (Screen opening to retain 5% oversize). d is the particle diameter at which the mineral is effectively liberated from the d0 gangue Ms M a

Table 3. Calculation of Liberation Factor '1' in Gy Sampling Theory Liberation F actor 1

1

0.8

0.4

0.2

0.1

0.05

0.02

d/d 0

1

1

4

10

40

100

400

152

Analysis of Tin Ores & Concentrates

[Ref.p. 170

Equation (i) may be simplified to: a2 (FE)= Cd3

Where: Cis a constant.

(ii)

Ms

Figs 1, 2, 3 and 4 show the standard deviations involved when concentrates of Sn 75%, 63%, 30% and 10% are subdivided to sarnples of different weights and having different sizes of the largest particles. These calculations refer to the 'fundamental error' on a thoroughly mixed sarnple. Figs 1, 2, 3 and 4 also suggest that the recomrnendations of the practical sarnpling scheme given in this paragraph are probably over cautious and that the major sarnpling errors will be associated with drawing the primary sarnple.

109~--------~~~--~--L-~~----------~

0.01

0.1

10

1.0

d (cml Fig. 1 Fundamental sampling errors (Standard deviation) for concentrates with 75% Sn (95% SnQz ) and Iiberation slze 10 mm

Ref.p. 170]

2.4 Practical Aspects

153

2.4 Practical Aspects Some practical points in the sampling of tin ores are: (i) Concentrates may increase or decrease in tin content with particle size. (ii) Sampling tools or techniques which reject particular size fractions are almost certain tobe biased. Size analysis is generally a more sensitive indication of bias than tin assay. (iii) Where a few !arge trucks or containers are to be sampled as one Iot, it is good practice to treat each truckload as a separate sample and combine the dried fmes in proportion to the weight of the Ioad at the sample preparation stage. Separate moisture determinations should be carried out and a proportioned moisture calculated for the combination. (iv) Care should be taken when milling to pass a given mesh size that oversize material is not lost on returning to the mill. Because this is more difficult to mill, it is almost certain to be of a different composition from the fines. (v) When milling high grade ores in particular, take care not to lose the less dense gangue minerals as dust. (vi) In sample preparation, avoid the use of mild steel mills or bucking boards which may wear and contaminate the sample. Introduction of one gram or more of steel into a 250g sampie in this way has been en-

IOOOkgr-------------r-------------r---------~-,

0.01

0.1

10

1.0

d (cm) Fig. 2 Fundamental sampling enors for concentrates with 63% Sn (80% Sn0 2 ) and Iiberation size 1 mm

154

[Ref.p.170

Analysis of Tin Ores & Concentrates

countered in some exceptional instances by the author. (vii) Critical comparisons of mills, mixers and sample dividers are available in the Iiterature [4, 9, 10]. Large mills should be easily cleaned and enable complete recovery of the sample; for sample preparation ring mills of the 'Tema' type are satisfactory, although for samples smaller than 50g agate mortars are preferred. Spinning riffles are the most accurate means of sample division [4, 9 ], but almost all other means are acceptable for tin concentrates. Sampie mixers should be thoroughly tested before use, as some may actually induce Segregation. Rolling the sample on a plastic sheet, followed by quartering is a reliable means of dividing 5 kg of concentrate or Jess. Care should be taken to avoid loss of f"mes by vigorous mixing.

2.5 Determination of Moisture This should be carried out on 10 - 20kg of material obtained from the primary sample. If this is not available immediatelyaseparate moisture sample of about

IOgL------L--~~-L---L--~--~~----------~

0.01

0.1

1.0

d (cm) Fig. 3 Fundamental sampling errors for concentrates with 30% Sn (38% Sn02) and Iiberation size 0.1 mm

Ref.p.170]

2.5 Determination of Maisture

155

1% of the Iot weight should be taken and reduced to 10- 20kg. Moisture is deterrnined as a weight loss on heating in an oven at 105°C ± 0.5°C. Some low grade concentrates may releaseeiemental sulphur which sublimes inside the oven. This can be detected by smell and by yellow deposits of sulphur in the oven flues. In such cases the only solution is to make sure that the sample is heated to constant weight and that the dried material for the assay sample is heated to constant weight at the same temperature. It is good practice to check the moisture deterrnination by recording the weight loss on drying fines for the assay sample. Agreements to within 0.3% moisture are obtained fairly easily; the moisture content of the assay sample will always be lower as a result of milling, dividing etc.

~9~~~~--~~~~~----~----------~ 0.01

0.1

1.0

10

d (cm) Fig. 4 Fundamental sampling errors for concentrates with 10% Sn (12.6% Sn0 2 ) and Iiberation size 0.01 mm

156

Analysis of Tin Ores & Concentrates

[Ref.p.l70

3. Pretreatment of Sampie Removal of impurities by preliminary treatment of tin concentrates before dissolution is traditional practice which is not usually followed at present. The following treatments are of value in special circumstances, usually for the determination ofless than 5%Sn. 3 .I Roasting Arsenic may be removed by roasting at 500 - 700°C for 30 min [ 11] although this should not be necessary for volumetric assays involving a peroxide fusion. Sulphur may give rise to undesirably vigorous fusion with sodium peroxide when present in stannite concentrates or flue dusts and may be removed by roasting although this is not absolutely necessary (see below). In the author's opinion, roasting of concentrates should be avoided as tin is easily lost at red heat as the volatile sulphide. 3.2 Nitric Acid Treatment Concentrates may be moistened with nitric acid and evaporated to dryness to oxidise sulphur prior to sodium peroxide fusion or reduction with hydrogen or ammonia. This overcomes the objections of vigorous oxidations with peroxide fusions and prevents Iosses of volatile sulphides with reductive decompositions. Nitric acid oxidation is invariably preferable to roasting for overcoming the effects of sulphur, even so, it is very rarely necessary even with concentrates containing 30% sulphur. Preliminary treatment of concentrates with nitric and hydrochloric acids followed by flltration and fusion of the residue has been traditionally used to remove Bi, Cu, Ge, Mo, S and V. In practice, 0.3 - 5 g of sample are evaporated to dryness with 1Oml HN0 3 ; the residue issimmered for 10 min with 100m! of 5% HN0 3 and filtered on a Whatman 42 paper. The residue and filter are removed, dried, ashed and subjected to the decomposition proper. This approach suffers from the objections that eiemental sulphur should be picked out of the 5% HN0 3 solution and that tin Iosses to the filtrate are probable. 3.3 Hydrofluoric Acid Treatment Removal of silica by fuming 0.2 - 5 g of concentrate with 1Oml of HF and a few drops of conc. H2 S0 4 may be necessary with siliceous ores where serious precipitation of silica in acid solution creates a problern [36, 37]. Slight precipitation may be overcome by addition of a few drops of HF to the acid solution obtained after fusion.

4. Decomposition Procedures 4.1 Fusion Methods Cassiterite is incompletely attacked by alkali carbonates, hydroxides or borates and if present as !arge particles may be almost unaffected. (i) Sodium peroxide fusion is widely used for the decomposition of allgrades of tin concentrate and is particularly useful for medium and low-grade ores (below 50% Sn), for which reductive attacks are less suitable. Fusions are carried out in iron, nicke! or

4.1 Fusion Methods

Ref.p. 170]

157

zirconium crucibles of approximately 40ml capacity over a Meker burner; a single Bunsen burner is not usually adequate. In 1951 Petretic [12] reported the superior resistance of zirconium metal to attack by malten sodium peroxide. Systematic studies on crucible materials have been carried out by Blake andHolbrook [13] and Beleher [ 14] with the conclusion that zirconium is an outstanding first choice. This author finds the service life of zirconium crucibles to be of the order of several thousand fusions compared with about five fusions for iron or nickel. Where zirconium is not available, iron crucibles are preferable to nickel.

WEIGHT

LOSS (mg)

ISOOr---------------~--------------~------------~

600

700

800 TEMPERATURE (°C I

Fig. 5 Weight loss (rng/5g of sodiurn peroxide) against ternperature for crucibles of various rnaterials [ 13]

Fusion with sodium peroxide alone is very effective with cassiterite ores but is exceptionally corrosive towards iron or nicke! crucibles. It is recommended that 0.3 - 2g of ore be weighed on to 1.5g of sodium carbonate, lOg of sodium peroxide added and the solids mixed throughly with a knife or wire. After brushing any adhering solids from the knife into the crucible, lg of sodium peroxide is added as a cover and the mixture heated over a low flame. Just before the melting point the peroxide darkens in colour; at this point the crucible should be moved about to avoid 'hot spots'. As melting takes place the crucible should be moved and finally swirled when the mass is completely malten. The burner should be turned up until the melt is a dull cherry-red; continue heating and swirling for a full 5 rnin. Before cooling, the melt should be exarnined for complete fusion. Incomplete fusion should always be looked for after the melt has been leached first with water then dissolved in hydrochloric acid. Clean, high-grade ores are often resistant to fusion and may require prolonged fusion with up to 25 g of sodium peroxide. Cassiterite concentrates of particle size greater then B.S. 150 mesh (104p.rn sieve aperture) require careful, prolonged fusion.

158

Analysis ofTin Ores & Concentrates

[Ref.p. 170

Sulphide ores of up to 25% sulphur may be decomposed by the above fusion method if care is taken avoid 'hot spots' at the melting point and to swirl the crucible thoroughly. lf this is still ineffective, the sample should be weighed out on to 1.5 g sodium carbonate as before, lOg of sodium hydroxide pellets added and the mixture fused. Sodium peroxide (5 g) should be added cautiously to the melt insmall portians and the fusion completed as usual. Alternatively fusions with Na 2 C0 3 /Na 2 0 2 mixtures (2: 1) are much less vigoraus than peroxide alone.

Marvin and Schumb [ 15] mixed a 1 g sample with 15 g of sodium peroxide and 1 g of sugar charcoal in a 40ml nicke! crucible. The crucible was surrounded in cold, flowing water whilst the contents were ignited. (ii) Freibergian Jusion - using mixtures of alkali carbonates and sulphur has been described by Kaliman [ 16] as leaving a residue of insoluble carbonates and hydroxides. Tin is converted to soluble thiostannate SnS~-: The sample is mixed with six to eight times its weight of powdered sulphur and Na 2 C0 3 or K 2 C0 3 (3 :5). The mixture is covered with 2g of the flux and heated in a covered porcelain crucible over a low flame for 15 - 20 min during which time an alkali polysulphide is formed in the flux. The temperature is then raised for a further 10 - 15 min to form meta! sulphides. The crucible is cooled slowly to avoid cracking. When the contents are leached with hot water and flltered, As, Ge, Mo, Sb, Sn, V and Ware present in solution. The residue should be washed with 1% Na 2 S solution then with hot water. To remove sulphur, the solution may be treated with sodium sulphite, potassium cyanide or hydrogen peroxide [38, 39]. Acidification precipitates the metals as insoluble sulphides although tin may be retained in solution in the presence of fluoride or tartrate [40]. Freibergian fusion has been used [40] for ores containing canfieldite, cassiterite and stannite. Difficulties are associated with high iron contents [ 16] where colloidal iron sulphide may form. If the solution is greenish rather than golden-yellow, it should be treated with 1 g KCl or NH 4 Cl and warmed until it clears completely [40]. (iii) Fluoride Jusion - complete attack of cassiterite is possible using a three to fivefold excess of potassium hydrogen fluoride [ 17, 18, 19] or a threefold excess of sodium fluoride with a twelvefold excess of potassium hydrogen sulphate [20]. Platinum crucibles are used and excess fluoride may be removed by heating with H 2 S0 4 [ 18] or hot H 3 B0 3 [ 19]. In a11 cases, fumes of HF are evolved in copious amounts and extreme care should be taken even if an efficient fume cupboard is used. In the early stages of fusion it is advisable to heat at a low temperature after melting- KHF 2 will decompose to KF and HF; the melt will gradually solidify. Then raise the temperature to 700- 800°C and heat strongly until the melt is clear. (iv) Reductive Jusions - alkali hydroxides used alone give incomplete attack on cassiterite [40]. Complete decomposition has been claimed for small particles ofless than 30,um diameter [25] or if an iron crucible is used [ 17]. Fusion of 0.5 - lg of tin concentrate with I 0- ISg NaOH and 0.05g carbon at red heat gives complete attack in a nicke! or silver crucible [21, 22]. Similarly, additions of other reducing agents to alkali fusions have been advocated and include: 50- IOOmg ofNaCN (23], 0.2- O.Sg zinc [40] and sodium meta!. This author's experience has been that low or high-grade tin concentrates (20 - 78% Sn) of less than 76,um partide diameter are incompletely attacked by alkali fusion. Additions of 0.2 1 g of zinc allow complete attack, however, the melt spits continuously as hydrogen

4.2 Reduction Methods

Ref.p. 170]

159

is evolved; great care must be taken to avoid losses and as a clear melt is never obtained it is impossible to ascertain if fusion is complete. Sodium peroxide fusion is by far superior. Fusion with sodium or lithium tetraborates or metaborates in carbon crucibles has been used for tin concentrates in conjunction with X-ray fluorescence spectroscopy [24 ]. Potassium cyanide fusions are descended from the dry assay procedures of antiquity when 20g or so of concentrate was fused in a fireclay pot with 40 - lOOg of sodium or potassium cyanide [17]. For volumetric assay it is sufficient to fuse 0.5 g of concentrate with 3 g of potassium cyanide in a porcelain crucible [26, 27]. Flux is removed by boiling with water and metallic tin is filtered off. It is usual to carry out an acid cleaning procedure beforehand with HCl and HN0 3 ; sulphide ores are oxidised first by evaporation to dryness with HN0 3 • Corrections must be established and applied for tin losses in the acid cleaning Solution, the cyanide flux, the crucible and Iid. A volumetric assay is carried out on the metallic tin obtained and although this may be a simplified procedure, omitting separations and possibly reduction steps, there appears to be little advantage over the conventional peroxide fusion approach. As an alternative, the tin button may be weighed and impurities determined spectrographically. 4.2 Reduction Methods Some methods which use reductive fusions have been described already in Section 4.1; this section describes the so-called "dry" reductions. (i) Reduction with Hydrogen or Ammonia- 0.3- O.Sg sample is weighed into the crucible shown in Fig. 6, containing approximately 3g of lime (CaO). The charge is mixed thoroughly using a knife or wire and is covered with a further 2g of lime. Alternatively, the mixed charge may be placed on a bed of lime in the crucible then covered as before. The crucible is supported ~H 2 orNH 3

LI ME

MIXED CHARGE

Fig. 6 Crucible for hydrogen/ammonia reduction of tin concentrates on a triangle and is heated over a Meker burner to about 600°C (temperature of the charge) for 5 min, then hydrogen or ammonia is led in at 1 - 2 cu.ft/hr/assay. The temperature is raised to 800 - 900°C for a further 30 min and allowed to cool with gas flowing. When cool, the residue is knocked out into a 250m! beaker, moistened with water and 40ml concentrated HCI added. The beaker is warmed on a hotplate for 1 hr or preferably left overnight. The crucible is washed out with concentrated HCI into the beaker and a little saturated potassium chlorate solution added to oxidise and dissolve metals present. The solution should be at 40 - 55°C at this stage. Add 1 g of iron powder and c_ontinue with the assay as detailed under the Ni or Al reduction methods in section 5.1 of this chapter.

160

Analysis of Tin Ores & Concentrates

[Ref.p. 170

With very pure concentrates it may be acceptable to eliminate the use of iron powder completely and proceed directly with the reduction after adding 20ml HCI. Standardsaremade from 0.3g tin dissolved in 30ml HCI and KC10 3 with reduced lime blanks added. Hydrogen or ammonia are interchangeable for this procedure, although a fume cupboard must be used with the latter. Gas flows of 0.8 - 2.0 cu.ft/hr/ assay give complete recoveries. It is important to cool with a flow of reducing gas as reoxidation occurs easily. Instead of lime, it is possible to use either calcium hydroxide or calcium carbonate - ignition before use is unnecessary but these must be free from sulphur impurities which tend to give slightly lower results; presumably by loss of volatile stannous sulphide. A small quantity of HF may be added to assay solutions before treatment with iron to dissolve silica if this appears in suspension. (ii) Reduction with Metals- the Beringer assay is based on reduction of a tin concentrate with zinc powder at 950°C. This has been modified by Beringerand Stephens [28). Afteracid cleaning with HCl and HN0 3 (if necessary), the residue or 0.5g of concentrate is mixed with 0.25g Na 2 C0 3 and 6g zinc dust. This is placed in a fireclay crucible lined with zinc oxide and is covered with zinc oxide. A mica sheet covers the charge and is weighed down with an iron washer or a small cupel. Alternatively, an inverted crucible Iid may be used instead of a mica sheet. The crucible is heated in a muffle furnace to red heat (600- 750°C) and then for a further 10 min. When the crucible has been removed and cooled, the Iid may be removed and the contents added to a 250 ml flask containing 20 ml of water. The crucible and Iid are washed out with 70ml of concentrated HCI which is added to the flask. A bung and delivery tube are fitted and the flask heated to boiling. When all the meta! has dissolved, the flask is cooled under co2 and titrated as usual.

The use of sodium carbonate is claimed [28] to aceeierate the reduction process such that it may be carried out at red heat rather than 950°C. In the above procedure there are no provisions for removal of impurities, other than by acid washing. Gangue elements remain in the assay solution as an insoluble residue, and complete attack cannot be inspected easily. More recently Mischenko and Kiparisova [30] decomposed tin concentrates by sirrtering 0.3 g with 3 - 4 g of zinc dust and ammonium chloride (1 :2 v/v) in a sealed tube at 600°C. Sulphide samples were ignited before sintering. Hempel [29] used reduction by either metallic sodium or magnesium to reduce starrnie oxide but no applications have been developed. 4.3 Sublimation with Ammonium Iodide Sublimation with ammonium iodide is a very convenient method of separating small quantities of tin from large quantities of gangue. Forthis reason it is particularly suited to the analysis of ores before concentrating and tailings [31 - 35]. In most reported procedures 0.2- 0.5g of sample is mixed with 0.5 - 2g of NH 4 I and heated at 450- 550"C for ab out 20 min. Stannic iodide condenses on the cooler parts of the glass tube. The sublimate and residue is leached with 50 ml of warm 2M HCI, flltered and tin determined on the filtrate.

This separation has been used in conjunction with several finishes including: spectrophotometric [31], volumetric [32) and atomic absorption [34, 50). Details of automatic apparatus [50] for the fusion are given in the Atomic Absorption Spectroscopy chapter tagether with the method of Bowman [34 J. With the volumetric finish [32), it is recommended that the residue and sublimate are washed with 20ml of water, 8 ml of 10 ,ug/ml ferric solution and aqueous ammonia until strongly alkaline to remove copper and other impurities. The residue is then leached with 50ml concentrated

Ref.p. 170]

5.1 Determination ofTin

161

HCI; the solution is diluted with 150ml of water, reduced with nicke! and titrated against 12 or KI/KI0 3 . Cassiterite is completely decomposed by heating with NH 4 1, however, tin present in a silicate lattice is unaffected. For this reason a prior decomposition by heating to dryness with HF/HN0 3 (2: 1) has been recommended (31]. 4.4 Decomposition by Acids The most successful means of decomposing tin concentrates with mineral acids is by treatment with HF in a PTFE (polytetrafluoroethylene) bomb: A 0.5- lg sample is weighed into a PTFE vessel and 20m! of concentrated HF added, leaving a headspace of at least 20 ml. The PTFE Iid is put into place and the vessel is heated in a stainless steel pressure vessel at 200°C for 12 hours. The vessel should be cooled for several hours before opening.

The use of a PTFE bomb is necessitated by the high temperature required for decomposition and the volatility of tin fluorides. Acid attack has an advantage over fusion methods in that !arge amounts of dissolved solids are absent from the assay solution. The extent of decomposition will vary according to the type of rock exarnined. The technique has been used in the author's laboratory for the determination of alkali metals in low and medium grade concentrates by atomic absorption spectroscopy [5]. A wider range of minerals may be decomposed by using mixtures of equal volumes of HF with either H2 S04 or HCI04. Wood tin (hydrated tin oxide) and stannite (Cu 2 FeSnS 4 ) have been [41] selectively dissolved from ores and concentrates by heating 0.5 - 1g of sample with 1OOml of concentrated sulphuric acid for 1 hour at just under the boiling point of the acid. Stannite may be dissolved [41] by refluxing 0.5 - l.Og of sample with 2ml ethanol saturated with bromine and 5 ml of carbon tetrachloride. The residue is washed with lOml of ethanol and the ftltrate evaporated at low temperature to remove most of the bromine. Tinhydroxideis precipitated by addition of ammonia. Zverev and Petrova [42] reacted 0.5- 2g of sample for 2 1/ 2 hours with 25m! of carbon tetrachloride, 1Oml of bromine and 1g of sulphur to dissolve stannite. Tin was extracted from the organic layer by shaking with an equal volume of 1M H 2 S0 4 • Stannite has also been selectively dissolved by the action of potassium chlorate in concentrated HCI (43] or by evaporation nearly to dryness with 1 g ofNaN0 3 and 70ml of glacial acetic [44]. In the latter procedure the beaker is washed down with 5 ml of concentrated hydrochloric acid and 50ml of water. If a volumetric assay is to be undertaken tin must be first separated from nitrate by precipitation with ammonia.

5. Analytical Methods

5.1 Determination of Tin

Lister and Ga/lacher [45] conducted a comparative survey of the analysis of four tin ores by twenty laboratories using a variety of techniques. The ores consisted of a 75.7% Sn comniercial concentrate, and mixtures of this concentrate with quartz to give 6.4% Sn, 0.63% Sn and 0.08% Sn. Their results are summarised in Table 4. The laboratories involved included government geological surveys, mining companies, me-

[Ref.p. 170

Analysis of Tin Ores & Concentrates

162

tallurgical companies and commercial assay laboratories. Techniques included volumetric, gravimetric and X-ray fluorescence for all samples with colorimetric, polarographic and ernission spectrochernical methods for the 0.63% Sn and 0.08% Sn samples. Volumetrieanalysis was the most popular method and was fairly reliable. Polarography and colorimetry gave fairly good agreements at low levels with volumetric methods. Gravimetrie and X-ray methods gave widely scattered results. A survey by Faye, Bowman and Sutarno [46] included 237 results on a complex CuPbSnZn ore MP - 1 issued by the Canadian Mineral Seiences Division (Mines Branch) Ottawa. This work suggested that the metal used as reductant in the volumetric determination influenced the assay; Steger [48] obtained results of 2.44% Sn, 2.42% Sn, 2.40% Sn and 2.39% Sn using aluminium foil, iron granules, nickel powder and Iead shot respectively on MP - 1. The differences were said to be significant although the reasons for this were not clear. The survey conducted by the Warren Spring Labaratory [4 7] involved volumetric methods used by European tin smelters (Table 4). The rather better standard deviations obtained in this survey probably resulted from the restricted range of technique and the fact that the laboratories concemed used the methods routinely under close supervision. Good agreement was obtained with clean, high-grade concentrates and "dirty", low-grade concentrates. Rather wider scatter was obtained with concentrates containing more than 1 % tungsten or with 1% niobium. The latter was particularly difficult to fuse with sodium peroxide. The following procedures have been used routinely for the assay of a wider variety of tin ores, particularly where the impurities present are known only approximately. It is probable that for weil characterised ores, more abbreviated methods could be employed.

(i) Peroxide Fusion and Nickel Reduction Method. Suitable for Sn 5 · 40% (1 g sample) and Sn 40 · 78% (0.5 g sample) in concentrates containing Cu 2% and W0 3 5%.

Table 4. Interlaboratory Surveys of Analysis of Tin in Ores and Concentrates No.of Labs

No. of Assays

19 18 19 18 5 5 5 5 5 5 5 5 5 5

45 46 49 47 19 22 18 19 20 23 24 20 19 19

Mean

Median

%Sn

%Sn

0.081 0.629 6.40 75.70 49.05 43.83 57.61 75.55 45.47 21.37 30.59 16.42 24.29 73.97

0.077 0.63 6.43 76.0

Std.Dev. a

%Sn

0.022 0.040 0.262 0.85 0.332 0.245 0.118 0.047 0.098 0.082 0.029 0.035 0.105 0.237

Coeff.Var.

Ref.

%

26.8 6.4 4.1 1.1 0.67 0.56 0.20 0.06 0.22 0.38 0.10 0.21 0.43 0.32

45 45 45 45 47 47 47 47 47 47 47 47 47 47

~tandard deviations of Ref 4 7 are calculated from the mean values obtained by each of the five laboratories

Ref.p. 170]

5.1 Determination ofTin

163

Mix 0.5g or l.Og of sample with 1.5g of Na2 C03 and lOg of Na2 0 2 in a zirconium (preferable) or iron crucible. Cover with 1 g of Na 2 0 2 and fuse as described in section 4.1 of this chapter until decomposition is complete. Cool and place the crucible in a covered 400ml beaker containing 100m! of water. Leach the melt carefully then wash the crucible out with 100m! of concentrated HCI. Finally wash the crucible with water and inspect for complete dissolution. Add a few crystals of KI and 3g of iron powder, heat at approxirnately 70°C to dissolve the iron powder but do not boil. When the iron has almost dissolved, filter into a 500 ml round flask through a small cotton wool plug. Wash with two 20m! portians of hat 2% HCI and reserve the filtrate. Transfer the plug back to the original beaker and dissolve the residue with 30m! of concentrated HCI and 0.5g KC10 3 . Heat to remove excess chlorine, add 3g of iron powder and heat at 70°C until the iron has nearly dissolved. Filter through a cotton wool plug into the 500ml flask containing the first filtrate. Wash with six lOml portians ofhot 2% HCI and dilute to 300m! with water. Insert a bung carrying an activated nicke! coil, boil gently for 60 min and cool under a supply of carbon dioxidein a water bath. When cold, remove the coil, wash with the minimum of water, add two or three marble chips and starch indicator. Titrate rapidly with N/6 potassium iodate to a permanent blue colour. Standardise by dissolving 0.3 or 0.4g of pure tin foil in 30m! of warm concentrated HCI and 2ml of 0.1% SbCl 3 solution. Add a blank fusion leached with 100m! of water and 70ml of concentrated HCI and proceed as above. N/6 Potassium iodate. Dissalve 6.0g of KI0 3 and lOOg of KI in water. Add 2g of NaOH and dilu te to 1 litre.

Notes 1. The nicke! coil should be activated by boiling in 1:1 HCI containing 5% N aCl. 2. Dissolution of the first cementate and reprecipitation by a second treatment with iron powder is unnecessary with low grade ores containing less than about 2% total base metal irnpurities. 3. The method may be applied in the range 0.1-5% Sn by using a 5g sample fused with 20g of Na 2 0 2 and titrated with N/50 iodate. 4. The assay may be left after dissolution of the fusion product, or just before insertion of the nicke! coil.

(ü) Peroxide Fusion and Aluminium Reduction Method Suitable for Sn 5-40% (1 g sample) and Sn 40- 78% (0.5 g sample) in concentrates containing Cu < 2 % and W0 3 < 2 %. Foilow the method for nicke! reduction up to the point where the nicke! coil is inserted into the flask. Add 20m! of concentrated HCI and 3g of aluminium instead. Warm until the reaction starts and shake continuously. When the reaction ceases, add 40ml of concentrated HCI, 0.5 g_ of aluminium and fit a Göckel trap containing saturated NaHC0 3 solution. Allow to react, boil to dissolve tin sponge, cool, rinse down the inside of the flask with the minirnum of water, add two or three marble chips and starch indicator. Titrate rapidly with N/6 potassium iodate to a permanent blue coiour. Not es 2, 3 and 4 of the previous method also apply.

(iii) Hydrogen or ammonia decomposition Described in section 4.2 of this chapter, reductive decomposition is valuable for the analysis of clean, high-grade ores where complete fusion using sodium peroxide may sometimes be difficult. This is particularly true ifNb or Ta are present at the level of a few percent. Reductive decomposition is likely to give low results with lew-grade, complex ores of Sn 35% or less. (iv) Copper/Silver Concentrates If Cu> 3% or Ag> 0.5 %, these elements should be removed or low results are likely: Dissalve 1 g of sample by fusion with 1.5 g sodium carbonate and 11 g sodium peroxide. Be particularly careful as copper/tin ores contain !arge amounts of sulphur and either slow heating or fusion with 3g Na 2 C03 and 3g Na 2 0 2 with a 1g cover of Na 2 0 2 may be necessary. Dissalve the cooled melt in 100m! water and 100m! of concentrated HCI, add 10m! of 10% ferric ammonium sulphate and 1g of potassium chlorate. Boi! for 10 min, cool and add ammonium hydroxide until the solution is deep blue. Heat to boiling, filter hat through a Whatman 40 paper and wash twice with 20m! of hat 2% ammonium hydroxide. Dissalve the precipitate in 90ml of concen-

164

Analysis of Tin Ores & Concentrates

[Ref.p. 170

trated HCl. If the solution is more than slightly blue repeat the addition of potassium chlorate and ammonia. lf not, continue with the nicke! or aluminium reduction methods by adding potassium iodide and iron powder.

Not es 1. Hydrofluoric acid should not be added to dissolve silica when the fusion products are dissolved in HCJ. This may render tin soluble and hence give low results. Fluorides in the sample are masked by the use of iron as the coprecipitant.

(v) Concentrates containing Nb, Ta or W. The errors caused by relatively large amounts of Nb or Ta present in the sample are unlikely to compensate for the Iosses which are almost unavoidable in the following procedure given by De Carvalho [49]. This may also be used for the removal of tungsten which will obscure the end-point if present in large amounts. Fuse 0.5 -LOg of sample with 5- 8g potassium pyrosulphate (K 2 S2 0 7 ) in a silica crucible. Cool, then warm with 25 ml of 25% tartaric acid and wash with 80 ml of hat water containing 5ml of concentrated H 2 S0 4 . Add saturated H 2 S solution until precipitation is complete or bubble the gas for 20 min. Allow to settle for 1 - 2 hours and filter on a Whatman No. 3 paperwashing with 2% H 2 S04. lgnite the residue in an iron or zirconium crucible then fuse with sodium peroxide and continue with either the nicke! or aluminium reduction method.

< I% Volumetrie methods -the direct classical tin assays already given may be applied down to about 0.1% Sn by fusing 5g samples with 20g ofNa 2 0 2 and titrating with N/60 iodate. Precipitation of silica can offer problems and a preliminary separation may be required. Fuming with HF/H 2 S0 4 [36, 37], sublimation with NH 4 I [32], distillation from HBr/H 2 S0 4 /H 3 P0 4 [53], co-precipitation with Mn0 2 [51, 52] or Be(OHh [32] may be used. At low Ievels, the interference ofiron becomes significant and, therefore, iron crucibles should be avoided. Where possible, the amount of iron used for cementation should be reduced to 1 gor eliminated entirely. A 'double iron' cementation is usually unnecessary. Determinations of 0.002% Sn in iron ores [51, 52] using precipitation with an Mn0 2 collector probably represent a limit to the volumetric technique at present. Sublimation with NH 4 I (section 4.3 this chapter) followed by cementation, nickel reduction and titration is probably the most convenient and reliable approach. ( vi) Ores containing Sn

Photometrie methods - Procedures for the determination of tin in geological materials have been outlined in Chapter 5 -Photometrie Methods. Phenylfluorone (2, 3, 7-trihydroxy-9-phenyl-6-fluorone) has been used [32] following treatment with HF to remove silica and Na 2 0 2 fusion. The melt was leached toseparate ferric hydroxide before acidifying. Tin was then precipitated by addition of ammonia solution in the presence of EDTA and a beryllium coprecipitant. After dissolution in H 2 S0 4 , Sn(IV) was determined using phenylfluorone. With a 1 - 2g sample a precision of ± 0.006% Sn was claimed for up to 0.5% Sn. Agterdenbos and Vlogtman [31] decomposed silicate rocks with a mixture of HF /HN0 3 (2: 1) then heated with NH 4 I. After dissolution, tinwas extracted into benzene from a iodide solution, stripped into 0.25M H 2 S0 4 and determined with phenylfluorone. Pollock and Zopatti [54] and Smith[55] used phenylfluorone methods for tin in complex silicates, whi1st Nazarenko and Lebedeva [56] used p-nitrophenylfluorone for amounts greater than 0.0001% Sn in low grade ores. GaUein ( 4'5' dihydroxyfluorescein) has been investigated by a number of groups [57- 61] for the determination of tin in minerals and mining products- details of some of these methods are given in Chapter 5 -Photometrie Analysis. Varand [37] treated 0.2 - 2 g sample (0.001 - 0.5% Sn) with 25 ml HF and IOml H2 S0 4 (I: 1) in a platinum dish and heated to fumes twice to remove silica. The residue was dissolved in water and ammonia solution added to precipitate tin. The residue after flltration

Ref.p. 170]

5.1 Determination of Tin

165

was ignited at 500- 600°C, fused with 0.5 g Na 20 2 and 5 g NaOH, extracted with hot water, acidified with H 2 S0 4 (1: 1) and filtered. The filtrate was treated with 2m! of 10% MnS0 4 and 1 rnl of 4% KMn0 4 solutions and boiled for 10- 15 min. The precipitate ofMn0 2 was flltered off, dissolved in 1Oml of HCI (1: 1) and diluted to 25m!. An aliquot of 1- Sm! was neutralised with ammonia solution; lml of 2.5M H2 so4 and 2m! of saturated thiourea Solution added to reduce Fe(III) and after 15 - 20 min, 1Ornl of ethanol and 2m! of ethanolic quercetin (I mg/ml) added. The solutionwas diluted to 25m! and measured photometrically at 420- 450nm after 15 min. Toluene-3, 4-dithiol forms a magentared precipitate with stannous salts on warming and has been used for the determination of tin in geological materials [62]; a detailed procedure is given by Sandeli [63]. Salicylidene aminobenzene [64] and butylrhodamine S [65] have also been used but may be difficult to obtain commercially. Scherbov et al. [66] decomposed 0.1 - 0.5 g of sample with HF /H 2S04, fused the residue with Na 2B4 0 7 /Na 2C0 3 , leached the melt with H2S04 (1: 10) and diluted to Süml with the same acid. An aliquot containing 0.05 - 5Jlg Sn was extracted into benzene after addition of 4mfof 10% KI solution and water. Antimony may be stripped from the extract by washing with 10m! of 0.2M HCI and tin by washing with 10m! of O.OSM HCI. To each extract was added 1ml of 0.05%morin and the two metals determined fluorimetrically. Polarography- In 6M HCI at 25°C the half wave potential of tin(IV) at the dropping mercury electrode occurs at- 0.52V vs S.C.E. For simple silicate matrices the direct method of Love and Sun [67] may be applied : a 1g sample is fused with Sg of Na 20 2 , leached with 150m! of boiling water and diluted to 200m! with water. After allowing any residue to settle, 25 ml is pipetted into a SOml volumetric flask and diluted to volume with concentrated HCI. Sampies containing more than 2% tin require the addition of 0.1 ml of 2% gelatin solution before dilution. Iron hydroxide remairring in the leach residue after fusion is said to retain Iead, but not tin which is present as soluble stannate. Bond et al. [68, 69] polarograph tin in SM HCI after fusion with NaF and H 3 B0 3 • Limits of detection were 0.0005% Sn (and 0.00005% Sn by anodic stripping voltammetry). Interfering elements [70] include Tl, W, Pb and to a lesser extent Ti and As: V and Ge distort the wave. Tin may be separated after evaporation with HN0 3 and fusion with Na 20 2 , then by precipitating with ammonia from a solution containing excess EDTA. Blyum and Zyryanova [71] fused with Na 20 2 , dissolved in HCI, precipitated tin with ammonia and dissolved this in H 2S0 4 /HCI/H 3 P0 4 before distilling tin as the bromide. The distillate was treated with FeCI 3 and ammonia. The precipitate was dissolved in 1:1 HCI, reduced with 0.2g of iron powder, deaerated with hydrogen and polarographed after addition of gelatin. This time-consuming method was recommended [71] for 0.005- 0.1% Sn in ores of any kind. A rather similar method [72] for 0.025 - 1.5% Sn uses separation by distillation as the bromide, coprecipitation with aluminium hydroxide and polarography in 2M HCI/15% NH4 Cl solution. Weiss [39] fused 0.5 - 2.5 g of sample with a sevenfold excess of KNaC0 3 /S (2: I) in a covered porcelain crucible for 20 min at low heat then strongly for 15 min. The melt was then boiled with 150m! of water and lüg NaOH added. The solutionwas oxidised with 30% H 20 2 and 5 ml added in excess. After boiling to remove H 20 2 , 30m! HCI were added and 5% KMn0 4 until pink. The solutionwas treated with 100m! ofhot 6M HCI and 0.5 g of iron powder. When the iron had dissolved O.Srnl of saturated HgCI 2 and 15m! of 50% NaH 2 P0 2 were added and the solution boiled. A small amount ofNaHC0 3 was added to generate a C0 2 atmosphere, 3m! of 5% gelatin added and the solution diluted with 6 M HCI to 250m!. A portion of the solution was

166

Analysis of Tin Ores & Concentrates

[Ref.p. 170

polarographed after bubbling nitrogen and the method was said to be suitable for the determination of 0.01 - 10% Sn in ores containing Iead. Atomic Absorption Spectroscopy - the rather poor sensitivity of atomic absorption for tin invariably demands the use of a separation precedure to remove the bulk of the sample matrix. Sublimation with NH 4 I [34, 35, 50, 73] is convenient and allows determinations in the range 0.02% Sn upwards. Separation by electrolysis [74] of an HCl/hydroxylamine solution containing copper and Iead following a Na 2 0 2 fusion gives a Iimit of detection of 0.0002% Sn. (See Chapter 8, Table 6). D.C. Are Spectrography- Table 5 of the Chapter on Emission Spectrography summarises eleven methods for tin in ores and silicate samples. Under suitable conditions as little as 111g/ g Sn may be detected directly. Precision is usually poor ( coefficient of variation typically 20%) andin the correlation programme of Listerand Ga/lacher [45] low results were generally obtained by arc spectrographic methods. X-Ray Fluorescence - This is used widely throughout the world by mines and geological institutions and the reader is referred to the Chapter on X-Ray Fluorescence Spectroscopy. Other methods -Neutron activation of 1OOmg samples has been used for the determination of traces of tin in granites and ores [75- 78]. Irradiation times varied from 10 min with a flux of 10 16 neutrons/m 2 /sec [75] to 14 days at 10 18 neutrons/ m 2 /sec [76]. All methods required a decay period of a further 24- 28 hours. Amounts of tin down to 0.1 11g were reported. Mössbauer spectroscopy has been used to determine tin in the range 0.1 - 1% with a coefficient of variation of 10% for 30 sec counting times [79, 80]. Mass spectroscopy has been used for traces of tin in granites and basalts after fusion with Na 2 B4 0 7 at 1000°C in the presence of graphite. No account of the assay of tin in ores and concentrates would be complete without mentioning the Vanning Assay. The account below is tak:en from Beringer's 'Textbook of Assaying' of 1912 and is one ofthe few printed descriptions ofthe technique. About one ounce (28g) of crushed calcined ore is weighed on to a vanning shovel having a concave blade. The vanner stands in front of a tub of water and allows 30 - 40ml of water to flow on to the ore. He raises the shovel and with an elliptical swirling motion causes the gangue mud to become suspended in the liquid, which is run off into the tub. This is repeated until the water is almost clear. About half as much wateras before is added but ajerk is introduced into the swirling motion to create a wave which draws with it the lighter gangue and carries it to the front of the shovel. The best of the "black tin" is then thrown weil up on one side of the shovel to form a cresent (the "head ") leaving room to work with the "tailings". The tailings are crushed with a 2 lb hammer to separate iron oxide and worked up with rather less water and a more vigorous, rapid motion. The whole of the black tin is finally brought to the centre of the shovel and washed two or three tirnes to remove traces of waste. The residue is dried, iron removed with a magnet and weighed to give the yield of concentrate. The amount of tin is determined by running down the concentrate in a fire und er potassium cyanide.

The vanning testnot only gave an estimate of the yield of tin after dressing and smelting, but was a necessary part of the cyanide reduction assay which gives very poor results with material containing 1ess than 50% Sn. 5.2 Determination of Impurity Elements Kaliman [16] describes methods for the determination of Al, As, Bi, Ca, Cu, Fe, Mg, Pb, S, Sb, Si, Ti, Wand Zn in Bolivian concentrates. It is this author's opinion that the most satisfactory general technique for impurity and gangue elements is ato-

Ref.p. 170]

5.2 Determination of Impurity Elements

167

mic absorption spectroscopy. This combines ease of operation with speed and freedom from interference. Determination of Al, Bi, Cd, Cu, Fe, In, Mg, Pb, Sb, Si and Zn [5] Weigh 1g of powdered concentrate on to 1.5g ofNa 2C0 3 in a zirconium crucible. Add lOg of Na 2 0 2 , stir well and cover with 1 g of Na 2 0 2 . Fuse gently at dull red heat. Cool and place crucible on its side in a 400ml beaker containing 100m! of water. When the reaction stops, remove the crucible and wash clean with water then with 100m! of HCI, finally rinse with water. Add a few drops of HF to dissolve silica (using up to Sm! if necessary), add 2- 3g of potassium hydrogentartrate and dilute to 200m! in a volumetric flask. Dilute a further five times for atomic absorption. Standards should contain 0.5 g of potassium hydrogen tartrate and a blank fusion solution carried out as above. Conditions for the determination are given in Table 5.

Not es 1. The ranges in Table 5 may be exceeded at both ends, although precision is inadequate for the higher Ievels of Cu, Fe and Pb. 2. Iron crucibles arenot recommended for the fusion as Bi, Cu and Sb are removed from solution by cementation. 3. Background correction for scatter is recommended for the detennination of Bi, Cd, Cu, Pb and Sb. 4. Rotation of the burner may be required to reduce sensitivity.

Table 5. Conditions for Determination of lmpurities in Tin Concentrates by Atomic Absorption Spectroscopy [5] Element Al Bi Cd Cu In Fe Mg Pb Sb Si Zn

Range(%)

Wavelength (nm)

(0.2 - 2%) (0.05 - 0.5%) (0.005- 0.1%) (1 - 10%) (0.1 - 1%) (0.01 - 0.1%) (0.05 0.5%) (1 -10%) (0.1 1%) (0.1 - 1%) (1 - 10%) (0.1 - 1%) (0.01 1%) (0.05 - 0.5%) (1 - 15%) (0.1 - 1%)

309.3 223.1 228.8 327.4 324.8 324.8 303.9 372.0 248.3 285.2 261.4 283.3 283.3 217.6 251.6 213.9

Standards (pg/ml) 2 20 0.5 - 5 0.05- 1 10 -100 1.0 - 10 0.1 - 1.0 0.5 - 5 10 - 100 1 - 10 1 - 10 - 100 10 1.0 - 10 0.1 - 1.0 0.5 - 5 10 - 150 1.0 - 10

Flame N20/C2H2 air/C2H2 air/C2H2 air/C2H2 air/C2H2 air/C2H 2 air/C2H2 air/C 2H2 air/C2H 2 N20/C2H2 air/C2H2 air/C2H2 air/C2H2 air/C2H2 N20/C2H2 air/C2H2

Determination of Arsenic (above 0.5%) [16] Weigh lg of concentrate into a 250m! beaker, add 20m! of HN0 3, 15m! of H 2S0 4 and evaparate to strong fumes of S03. Cool, add 15 ml of saturated S0 2 water, evaparate to fumes, add 10m! of water and evaparate to fumes once more. Transfer to a distillation flask with a small amount of water. Add 45 ml of hydrazine sulphate solution (10 g/1 hydrazine sulphate, 20 g/1 KBr) and 70ml of HCI. Immerse the outlet of the condenser beneath the surface of 250 ml of cold water in a 500 ml conical flask cooled in water. Distil until the volume has been reduced to 75ml, add 40ml of HCI and distil again to 75ml. Rinse the condenser into the conical flask, make alkaline with ammonia to methyl orange then acid with HCI. Cool to below l5°C, add 8g of NaHC0 3 and titrate with 0.02N iodine solution using a starch indicator.

168

Analysis of Tin Ores & Concentrates

[Ref.p. 170

Standardise against 0.05g As 2 0 3 dissolved in 10m! of 10% NaOH, then diluted to 250 ml, 100m! of HC! added, neutralised with ammonia and acidified with HCI. Cool then and proceed as above. 1ml0.02N I2 = 0.00075g As

Determination of Arsenic (below 0.5%) Weigh 0.2g of sample into a 250m! beaker, add 10m! of HN0 3 , 20m! of 1 : 1 H 2S04 and evaparate to fumes of S0 3 • Cool, add 20m! of water and 1g of ammonium oxalate and evaporate again to fumes. Add 20m! water, break up solids thoroughly, transfer to a 200m! volumetric flask and di!ute. Pipette an aliquot of this solution into a 250m! Quickfit conical flask (Fig. 7) (use 10m! for 0.01-0.1% As, Sm! for 0.1-0.5% As). Add 50ml ofwater, 20m! of 1 : 1 H2S04, 2m! of 15% KI solution and 1 ml of 40% SnCI 2 solution. Stand for 10- 15 min then add 5g of granulated zinc and assemble the apparatus immediately. The side arm should contain 8.0ml of 0.5% silver diethyldithiocarbamate in pyridine and should be shielded from direct sunlight. Leave for at least 1 1/ 2 hours and measure the absorbance of the solution at 540 nm. Calibrate using so!utions from 5- 50J.J.g As. Carry out a blank with each set of determinations. This is not applicable to copper/tin concentrates.

Determination o[Calcium Fuse 0.5g of sample with 1.5g of Na 2C0 3 and llg Na 20 2 in a zirconium crucible. Leach with 100 ml of water in a 400ml beaker and acidify with HC!. Remove crucible, rinse and add 1 g po-

/ /

0 5°/o SILVER DIETHYLDITHIOCAP.BAMATE IN PYRIDINE

COTTON WOOL SOAKED IN SAT'D LEAD ACETATE AND DRIED

Fig. 7 Apparatus for the determination of arsenic

tassium chlorate, boil for 10 rnin. Make alkaline with arnmonia, heat to boiling and filter hot through a Whatman 541 paper reserving the flltrate. Wash thoroughly with hot water. Open the paper and wash the precipitate into the original beaker with hot water. Dissolve the precipitate in HCI and reprecipitate with ammonia. Filterhot into the original filtrate and wash with water. Add 3.5g of ammonium oxalate to the filtrate, warm and boil for 1 min. Filter through a pulp pad, wash eight times with hot water then wash pad and residue into a beaker with 150m! of water. Add 10m! of 1 : 1 H2S0 4 , warm to 80°C for 5 min and titrate hot against 0.1N KMn04 SOlution to a permanent pink.

5.2 Determination of lmpurity Elements

Ref.p. 170]

169

1 ml of 0.1 N KMn04 = 0.002804g CaO = 0.002004g Ca. Calcium may also be deterrnined in an N 2 0/C 2 H2 flame by atomic absorption spectroscopy following Na 2 0 2 fusion and addition of 10g/llanthanum. In silicate samples the use of an air/C 2 H 2 flame is not recommended even in the presence of lanthanum.

Determination of Fluorine Fuse 0.2g of sample with a weighed 2.0g of Na 2 C0 3 and a weighed 4.0g Na 2 0 2 in a zirconium crucible. (The use of zirconium does not affect the result). Knack the cooled melt into a plastic beaker and wash the crucible out with 50ml of water and lml of HCI. Warmgentlyon a water bath to dissolve soluble components and dilute to 200 ml in a volumetric flask. Filter a little of this solution and pipette 10m! of filtrate into a 100m! Volumetrie flask. Acidify with HC! to bromothymol blue, add 50ml of Complexing Buffer Solution and dilute to volume. (CBS contains: 18g/11,2 diaminocyclohexane tetracetic acid CDTA; 20g/l NaOH; 300g/l sodium citrate; 30g/l NaÖ;adjusted to pH 6.0 with HCI). Determine fluorine using a fluoride ion-selective electrode and standards in the range 10-s 10- 3 M F. Standardsaremade from blankfusionstaken through the determination and with additions of stock fluoride so!ution before the last dilution. Plastic volumetric ware and beakers should be used throughout although glass Volumetrie flasks are permissible provided solutions are immediately transferred to plastic bottles after dilution.

Determination of Iran Take the precipitate produced by addition of ammonia in the calcium determination and dissolve in 25 ml of HCJ. Wash the paper with 2% HCJ and heat to boiling. Add 150g/l stannous chloride solution until the solution is colourless; add 3 - 4 drops in excess. Fit the flask with a bunsen valve, cool in a water bath to 1s•c and add 15 ml saturated mercuric chloride solution. Stand for 5 minutes. A silky white precipitate should be obtained. Dilute to 250m!, add 10m! 1: 1 H 2 S0 4 , Sm! of H 3 P0 4 and 8 drops of0.2% diphenylamine sulphonic acid. Titrate with 0.1 N K 2 Cr 2 0 7 from green to purple. lml O.lN K2 Cr 2 0

7

= 0.005585g Fe

Alternatively Fe may be deten;üned by atomic absorption (see Table 5 ].

Determination of Silica Fuse 0.5 - 1 g of sample in a nicke! crucible with 1.5 g of Na 2 C0 3 and 6g Na 2 0 2 . Cool and leach with 50ml water. Acidify, and wash out the crucible with 25m! of HCI. Evaparate to dryness and bake on a hotplate for 15 min. Cool, add 50 ml of HC!, 100 ml of water and boil. Filter through a small pulp pad, wash with hot 2% HCI. Transfer the precipitate and pad to a porcelain crucible and ignite at 900°C to constant weight. lf the precipitate is contaminated, transfer to a platinum crucible and weigh. Add 3 drops of H 2 S0 4 and 5 ml of HF, evaparate to dryness, cool and weigh. The loss is entirely due to silica.

Determination of Silver Mix 5 - lOg of sample with 50 g of PbO, 20g of Na 2 C0 3 , 26g of borax glass and 6g of potassium hydrogen tartrate. Transfer to a fireclay pot and cover the surface with borax glass. Heat in a crucible fire until the action has completely ceased (approximately 900°C). Remave the pot, pour off the slag into a mould and the meta! into a button mould. Return the slag to the pot tagether with any slag adhering to the meta! add 30 g of PbO, 10 g of Na 2 C0 3 and 3 g of potassium hydrogen tartrate and repeat the fusion. Prepare standards containing the same weight of silver asthat expected in the assay. Wrap in Iead foil equal in weight to the two assay buttons. Heat a number of 1 inch or 1 1/ 2 inch (25 or 36 mm) bone ash cupels to 950°C in a muffle and on each place the standards or the two assay buttons. Close the muffle door. When the black ernst of Iead oxide melts and Iead oxide flows from the meta! bead into the cupel, open the muffle door slightly and continue cupellation at 850°C (cupel temperature). Towards the end of cupellation, close the muffle door. Remave cupels, cover !arge prills with an asbestos mat and cool. Detach the prill from the cupel and weigh. Add to this weight the weight lass an the standard and subtract the weight of silver in the litharge. Notes 1. Gold and other precious metals are not usually present in significant quantities. Partingof the prill in nitric acid and cupellation ofthe residue is unnecessary. 2. Formation of a white crust on the cupel indicates tin interference. This may be removed by evaporation to dryness twice of the sample with 20m! of HCI, 20m! of HBr and 10m! of Br 2 before

170

Analysis of Tin Ores & Concentrates

carrying out the pot fusion. Clean up the evaporated residue with 3g of moist Na 2 C0 3 and fiiter paper. Use only 5g ofpotassium hydrogentartratein the frrst fusion to allow [or the reducing action of the filter paper.

Determination of Sulphur Weigh 0.5 g of sample and grind in an agate mortar with 3 g of sintering mixture (100 g ZnO, 50 g Na 2 C0 3 , 50g KN0 3). Transfer to a small procelain crucible, cover with lg of sintering mixture and heat for 1 - 1 1h hours at 700°C in a muffle. Cool, damp slightly with water and priseout the cake with a knife. Wash the crucible with hot water, and 10m! of H 2 0 2 (20 vols.). Add to the cake in a beaker, wash the crucible with hot water and boil the cake with the washings for 3 min. Decant the Iiquor through a pulp pad, add 75ml of water and 10m! of H 2 0 2 , boil for 3 min and filter through the pad. Wash the pad with hot water six tinles. To the filtrate and washings add methylorange and neutralise with concentrated HCI. Add 4ml of HCI in excess, dilute to 400ml and bring to the boil. Add slowly 25m! of 100 g/1 BaCI 2 solution and leave overnight. Filter through a pulp pad, washing eight tinles with hot water. Ignite the pad at 700°C in a silica crucible, cool in a desiccator and weigh as BaS04. Notes

1. The use of a fusion with Na 2 0t gives a satisfactory attack, but coprecipitation of sodium, iron and tin sulphates gives low results [16].

Determination o[Tungsten

>

Weigh sample (lg for 0- 2% W0 3 : 0.5g for 2- 10% W0 3 ; 0.25g for 10% W03) into a zirconium crucible and fuse with 5 g of Na 2 0 2 . Extract the cooled melt in a 400ml beaker with 100 ml of water, add 1 ml of 20 vol. H 2 0 2 and bring just to boiling. Cool, transfer to a 200 ml Volumetrie flask, wash the beaker with a few drops of HCI and dilute to volume. Allow the residue to settle. Decant 50ml of solution through a dry Whatman 541 filter and pipette an aliquot into a 100m! graduated flask (10m! for 0-5% W0 3 ; 5ml for 5% W0 3 ). Add, whilst mixing, 10m! of H2 S0 4 , 20m! of HCI, !Oml of 2M stannous chloride Solution, 1 ml of 1% titanaus chloride. Heat on a boiling water bath for 5 min then cool in a water bath. Cool in running water for 15 min then add 10m! of IM sodium thiocyanate, mixweiland dilute to volume. Replace in cold waterandstand for lSmin. Measure absorbance using 2cm cells at 400nm. Standardise using aliquots of a solution containing 0.1 mg/ml W0 3 (0.14227g/l sodium tungstate). Vanadium and, to a much lesser extent, molybdenum interfere. There is no interference from niobium, tantalum or titanium.

>

Other impurities The other elements of interest in the analysis of tin ores and concentrates include: Ge, Mo, Nb, Ti and Ta. Classical procedures for these elements are fairly complex [81] and wherever possible X-ray fluorescence methods are recommended. Sodium and potassium may be determined by dissolution of 0.1 - 0.5 g of sample in 15 rnl of HF in a closed PTFE pressure vessel at 200° C. On cooling add 20m! of saturated boric acid solution and dilute for atomic absorption spectroscopy in an air/C 2 H2 flame for both elements.

References 1. Ramdohr, P.: The Ore Mineralsand their Intergrowths, Oxford: Pergarnon (1969) 2. Ingamells, C.O.: Talanta 21, 141 (1974) and Talanta 23, 263 (1976) 3. Japanese Industrial Standard JIS M8100 General Rules for Methods of Sampling of Bulk Materials, 1972 4. Sampling in the Mineral and Metallurgical Processing Industries. Spec. Pub!. Inst. Min. Metall. 1974 5. Unpublished Work and Standard Methods- Capper Pass, Ltd. 6. Davies, O.L.: Statistical Methods in Research and Production, 3rd Edn., London: Oliverand Boyd 1957 7. Bailey, E.G.: J. Ind. Eng. Chem. 1, 161 (1909) 8. Gy, P.: Trans. Inst. Min. Metall. 74, 165 (1965) 9. Allen, T., Khan, A.A.: Chem. Eng. 238, 108 (1970) 10. Urban,M.R., Levin, E.: S. Afr. Chem. Process. 1, 89 (1966)

References

171

11. Bayula, A.G., Lozinskaya, V.S.: Soobsch. Dal'nevost. Fil. Sibirsk. Otd., Akad. Nauk SSSR. 49 (1960). Anal. Abstr. 9, 610 (1962). 12. Petretic, G.J.: Anal. Chern. 23, 1183 (1951) 13. Blake, H.E., Ho/brack, W.F.: ehernist Analyst 46, 42 (1957) 14. Be/eher, C.B.: Talanta, 10,75 (1963) 15 .. Marvin, G.G., Schumb, W.C.: J.Arner.Chem.Soc. 52, 574 (1930) 16. Kallman, S.: Ind.Eng.Chern. (Anal.Ed.) 15, 166 (1943) 17. Parry, L.: The Assay ofTin and Antirnony, London: Mining Journal Office, 1906 18. Gibbs, W.: J. Arner. Chern. Soc. 37, 358 (1864) 19. Lurje, J.J., Troitzkaja, M.l.: Zavod. Lab. 6, 153 (1937) 20. C/arke, F. W.: Arner.J.Sci. 45, 173 (1868) 21. Burghardt, C.Z.: Chern. Newsbl. 61, 260 (1890) 22. Gilbert, A.: Z. OffentaL Chem. 16,441 (1910) 23. Brunck, 0., Höltje, R.: Angew. Chern. 45, 331 (1932) 24. Payne, K. W., Philips: X-Ray Conference, Durharn, England (1970) 25. Tamaru, S., Ando, N.: Z. Anal. Chern. 84, 89 (1931) 26. Liebig, J.: Ann. 41, 285 (1845) 27. Rose, H.: Pogg. Ann. 91,112 (1854); 75, 1 (1848); 9, 45 (1827) 28. Beringer, H.R., Stephens, A.F.H.: Mining Mag. 360 (1928) 29. Hempel, W.: Pharrn. Zentralhalle Deutschland 38, 84 7 (1897) 30. Mischenko, L. V., Kiparisova, L.S.: Zavod. Lab. 36, 1048 (1970) 31. Agterdenbos, J., Vlogtman, J.: Talanta 19, 1295 (1972) 32. Schweinsberg, D.P., Hefferman, B.J.: Talanta 17, 332 (1970) 33. Ward, F.N., Lakin, H.W., Canney, F.C.: U.S.Geol. Surv. Bull. 1155,74 (1963) 34. Bowman, J.A.: Anal. Chirn. Acta 42, 285 (1968) .35. Sierra, J., Leon, J.M.: Trans.Inst.Min.Metall. 76B, 210 (1967) 36. Baumgärtel, E., Gärtner, P.: Z. Anal. Chern. 208, 416 (1965) 37. Varand, V.L.: Nauch. Trudy lrkutsk. Nauch-Jssled. Jnst. Redk. Met. 11,56 (1963). Anal. Abstr. 12, 1673 (1965) 38. Dolezal, J., Beran, P.: Coll. Czech. Chern. Cornrn. 22, 727 (1957) 39. Weiss, D.: Chern. Listy 52, 1817 (1958). Anal. Abstr. 6, 2083 (1959) 40. Dolezal, J., Povondra, P., Sulcek, Z.: Decornposition Techniques in lnorganic Analysis, London: Jliffe, 1968 41. Karapetyan, E.T., Sharko, E.D.: Obogasch. Rud. 102 (1970). Anal. Abstr. 20,2980 (1971) 42. Zverev, L. V., Petrova, N. V.: Zavod. Lab. 23, 1403 (1957) 43. Vlasova, GM.: Uck. Zap. Tsentr. Nauchn.-lssled.Jnst.Olovyan. Prorn. 14 (1965) 44. Steger, H.F.: Talanta 22, 543 (1975) 45. Lister, B., Ga/lacher, M.J.: Trans. Jnst. Min. Metall. 79, 213 (1970) 46. Faye, G.H., Bowman, W.S., Sutarno, R.: Anal. Chirn. Acta 67, 202 (1973) 4 7. Gregory, G.R.E.C.: Warren Spring Labaratory, Report CR 488 (PC), Departrnent of Trade and lndustry, February (1971) 48. Steger, H.F.: Anal. Chirn. Acta 77, 337 (1975) 49. De Carvalho, R.A.G.: Rev. Port. Quirn. 5, 55 (1963) 50. Guimont, J., Bouchard, A., Pichette, M.: Talanta 23, 62 (1976) 51. Tan, H.B., Thng, S.T.: Overseas Geol. Miner. Resource 10, 231 (1969) 52. Jkegami, T., Suematsu, K., Kammori, 0.: Japan Analyst 5, 379 (1956) 53. Scherrer, J.A.: J. Res. Nat. Bur. Stds. 16,253 (1936) and 21,95 (1938) 54. Po/lock, E.N., Zopatti, L.P.: Anal. Chern. 37, 290 (1965) 55. Smith, D.J.: Anal. Chirn. Acta 57, 371 (1971) 56. Nazarenko, V.A., Lebedeva, N. V.: Zavod. Lab. 28, 268 (1962) 57. Wood, G.A.: Geochern. Res. Centre, imperial College, London, Tech. Cornrn. No. 11.(1957) 58. Stanton, R.E., McDonald, A.J.: Trans. Inst. Min. Metall. 71, 27 (1961) 59. O'Keefe, J.O.: Carnbourne School of Mines Mag. 61, 18 (1961) 60. Heegn, H.: Freiherger Forsch. A 455,47 (1969) 61. Hutchin, F., Fiander, S.J.: Trans. lnst. Min. Metall. 76,69 (1967) 62. Famsworth, M., Pekola, J.: Anal. Chern. 26,735 (1954) 63. Sande//, E.B.: Colornetric Determination of Traces of Metals, p. 856, New York: Wiley Interscience 1959 64. Gregory, G.R.E.C., Jeffery, P.G.: Analyst 92, 293 (1967) 65. Shumova, T.J., Blyum, I.A.: Zavod. Lab. 34,659 (1968) 66. Scherbov, D.P., Astaf'eva, I.N.: Plotnokova, R.N., Zavod.Lab. 39, 546 (1973) 67. Love, D.L., Sun, S.C.: Anal. Chern. 27, 1557 (1955) 68. Bond, A.M., O'Donnell, T.A., Waugh, A.B., McLauchlin, R.J. W.: Anal. Chem. 42, 1168 (1970) 69. Bond, AM.: Anal. Chern. 42,1165 (1970) 70. Bouber/ova-Kosinova, L.: Vest. Ustred. Ustavu Geol. 29, 13 (1954) 71. Blyum, I.A., Zyranova, N.G.: Zavod. Lab. 22,46 (1956)

172 72. 73. 74. 75. 76. 77. 78. 79. 80.

Analysis of Tin Ores & Concentrates

Richardson, J., Alvin, J.F.: Proc. Austr. Inst. Min. Metall. 203, 95 (1962) Mensik, J.D., Seidemann, J.: Perkin Eimer A.A. Newsletter 13, 8 (1974) Mo/dan, B., Rubeska, /., Mikovsky, M., Huka, M.: Anal. Chim. Acta 52, 91 (1970) Bowen, H.J.M.: Radiochem. Radioanalyt. Lett. 7, 75 (1971) Johansen, 0., Steinnes, E.: Analyst 94,976 (1969) Schmidt, D., Starke, K.: Radiochim. Acta 11, 197 (1969) Das, H.A., Van Raaphorst, J.G., Umans, H.J.L.M.: J. Radioanalyt. Chem. 4, 21 (1979) Stuart, R.A., Donahoe, A.J., Boy/e, A.J.F.: Proc. Austr. Inst. Min. Metall, 230, 69 (1969) Shumilovski, N.N., Salakhutdinov, N., Jalmakov, A.A.: Izv. Akad. Nauk. Uzbek SSR, Ser. Tekh. Nauk. 5, 29 (1964). Anal. Abstr. 13, 1223 (1966) 81. Schoeller, W.R., Powell, A.R.: The Analysis of Mineralsand Ores of the Rarer Elements, London: Griffin 1940 82. Progress Rept., West Malaysia: Malaysia Geol. Surv. Ann. Rept. 156 (1969)

CHAPTER 13

ANALYSIS OF SECONDARY MATERIALSAND INTERMEDIATES By R. Smith

It is impossible to Iist the wide range of valued intermediates and secondary materials which contain tin. In all cases, the actual sampling of these items is more demanding than their analysis. Because of the many ways in which they are transported it is impossible to give recommended sampling methods for primary sampling. Almost always, quantities of up to a few tonnes will have tobe manipulated and large-scale machinery such as mechanical diggers, jawcrushers and hydraulic breakers must be either hired or purchased.

The guidelines given here are empirical and where they have been tested, the sampling error has been found to be less than ± 0.5% Sn. Whenever possible, dissimilar materials should be separated. Where this is not practicable, thorough mixing should be carried out.

1 . Drosses and Ashes Drosses cover a wide range of materials from completely nonmetallic to metallic. They are all products from the top of baths of malten metals and usually consist of oxidation products, liquation residues or products of chemical treatment to remove impurities. Great care should be taken in sampling as drosses are usually very valuable but also heterogeneous. Drosses containing acidic flux residues of zinc chloride (so-called "chloriney drosses") should be treated with sodium carbonate otherwise a stable sample will not be obtained. If the dross is very hygroscopic and is not treated it will become physically wet during milling. Similarly, caustic drosses should be stabilised by milling with sodium bicarbonate. Aluminium or calcium is used in some meta! refineries to remove antimony. The greatest care should be taken with these drosses as exposure to moist air or water is likely to generate arsine or stibine. This type of material should be isolated and neutralised at the works where it is made and not transported in its active form. As the first stage of primary sampling, the consignment should be sorted into different types according to appearance and apparent metallics content before emptying. Each type should be weighed and sampled separately. Sampling can only be carried out during unloading- a 10% by weight sample should be taken from each drum from fines and small metallics. Large non-metallic lumps should be broken and samplied- if this is not possible, all the !arge lumps should be pulled out for separate treatment. Alllarge pieces of meta! should be pulled out and treated separately. The primary bulk samples should be mixed separately and reduced to 100 or 200 kg for treatment in a pot or by milling. The first stage of treatment should aim to separate meta!

174

Analysis of Secondary Materialsand Intermediates

from non-metallic and to stabilise the sample. The example below serves to illustrate the sampling of an acidic solder dross with metallics. With samples of dry tin or solder ashes it is usually preferable to separate metallics by milling and/or screening before treating in a pot. Consignments of high grade material ( 40% Sn or greater) should be divided into lots of 20 tonnes or less for sampling and assay. Example The consignment consists of 15,030 kg of acidic solder dross in 200 litre (45 gallon) drums. The drums are emptied and treated as one sub-sample. Large metallic pieces are removed, cleaned off and weighed. The weight of the remainder is obtained by difference. The finesandsmall metallics are sampled, mixed and reduced.

Fines etc. Large Metallics

Weight kg

Sample kg

14045 985

1400 985

Reduced Sample kg 179 985

% 93.45 6.55 100.00

The large metallics are melted in a pot, a dip sample of metal is taken and the dross is reduced to 20kg. To Pot Metallics From Pot Metal A Dross A Loss A

kg 985

6.55

893 79 13

5.94 0.52 0.09

985

6.55

%

The fines etc. are treated in apotat very low heat. Na 2C0 3 is added to prevent lasses of tin by fuming and to neutralise the "chloriney" flux residues. To Pot Fines Na2C03

From Pot Meta] B Dross B Loss B

kg 179 14

9 3.45 7.31

193

100.76

105 42 46

54.82 21.93 24.01

193

100.76

%

The meta] is dip sampled, the dross because of its ]arge volume contains some occluded metal. It is mixed after cooling and reduced to 21.93 kg then milled with 0.52 kg of dross from the !arge metallics. The millings are graded on sieves, the coarse fractions are metallic. Fractions frorn the rnill are weighed, the fines determined by difference. To Mill Dross A Dross B

From Mill Fines- 2mm +2mm -4mm +4mm- 8mm +8mm

kg 0.52 21.93

0.52 21.93

22.45

22.45

16.38 2.45 1.89 1.73

16.38 2.45 1.89 1.73

22.45

22.45

%

2. Slags

175

The metals are cornbined by rnelting tagether portians of the dip sarnples and the + 4 rnrn and + 8rnrn rnill fractions. Note that at this stage, proportionate weights give a 2000g sarnple. Metal Sampies Metal A Meta! B + 4rnrn- 8rnrn + 8rnrn Cornbined Metals

g 118.8 1096.4 37.8 34.6

% 5.94 54.82 1.89 1.73

1287.6

64.38

The dry fines (- 2rnrn; 327.6g) and oversize (+ 2rnrn;49.0g) are rnilled through a BS 60 rnesh (250 J.lm) sieve and any rnetallics granulated with fines through the sieve. (See Chapter on Tin Alloys- section 1.3). The fines are graded on a B.S. 85 rnesh sieve (178J.1rn) to give fmes and roughs fractions. Final proportians are: Fines - 85 rnesh Roughs+ 85 rnesh Metallics Loss

%

12.23 6.60 64.38 24.10 107.31 (Na 2 C0 3 added 7.31 %)

If the above portians are assayed separately, multiplication by the appropriate fraction will give a correct retum of metal values in the original sample. Because Na 2 C0 3 has been added, some of the loss is due to the neutralisation reaction. It is impossible in this case to give an accurate loss and a sample which is stable. Because of the uncertainty in the loss, assays or weights expressed on a 'dry state' basis will be meaningless. Assays and weights expressedas 'natural or original state' will be correct.

The metal fractions are assayed using sawings and the methods given in the Chapter on Tin Alloys and Solders. Fines may be assayed according to the methods in the Chapter on Ores and Concentrates. Roughs may be assayed by a combination of these methods - usually the methods for fmes are adequate.

2. Slags Furnace slags should be sampled by selection of a 10% bulk sample. Unless the slag is of very low grade ( 10% Sn or less) the bulk sample should be: (i) Crushed to- 25mm, then reduced to 300kg. (ii) Crushed to- 6mm, then reduced to lOOkg. (iii) Milled to- 2mm, then reduced to 2kg. (iv) Milled to- 124J.lffi (B.S. 120 mesh) for the assay sample. If during crushing, metallic pieces should separate, these should all be reserved and treated as aseparate portion. Even if they can be reduced to a powder during sample preparation it is wiser to keep them separate as they are usually of very different composition from the slag itself.

The sampling ofslags by the above procedure is not entirely satisfactory in that it applies to materials of less than 150mm particle size and of low grade (Sn 30% or less). Outside this range it may be necessary to crush or break up the whole consignment before sampling or to crush the bulk sample to- 5mm. Slags may be assayed by methods appropriate to low grade tin concentrates using separations for interfering elements if these are present.

176

Analysis of Secondary Materialsand Intermediates

Themaisture determination should be carried out on 20kg of- Smm material. Assay as a tin concentrate. Slags in fumaces may be sarnpled by inserting a cold steel rod into the melt or by sampling with a hand !adle at intervals during slag tapping.

3. Fume, Flue Dusts These are often high grade materials (Sn greater than 50%) but this depends on their origin. The main difficulty is the hygiene problern associated with sampling dry dusts. If the consignment arrives in paper bags it is satisfactory to sample by spearing the bags, using a 10mm wide open spear which samples the length of one whole bag, provided the contents are homogeneous. Material packed in other ways should be treated as a concentrate and a 10% sample taken. Once sampled the dusts may be treated as concentrates. (i) Mix and reduce bulk sample to 100kg. (ii) Mill to- 2mm, reduce to 2kg. (iii) Mill to- 250J,Ull (B.S. 60 mesh) for the assay sample. It will be almost impossible to screen many flue dusts through a finer sieve because of their tendency to aggregate during screening. Formostdusts it is unlikely that milling will be necessary at any stage. The maisture determination should be carried out on reject from the bulk sample. Assay as a tin concentrate but beware of carbonaceous or sulphur-containing flue dusts which require fusion with NaOH before small additions ofNa 2 0 2 are made.

4. Turnings, Borings Small turnings and chippings are relatively easy to sample; a primary sample of 10% should be taken, reduced to about 100 kg and treated as below. Large tumings and borings are difficult to separate but the same approach should be followed. Consignment sizes should be limited to 5 tonnes because of the !arge bulk of turnings and their relative inhomogeneity. The reduced sample should be heated in a pot to determine maisture plus oil and to separate white metal if this is possible. It often suffices to set fire to the sample in an open metal tray using kerosene. Cool and mill the residue, grade on a series of sieves; separate magnetic materials. Depending on the material and the facilities available it is possible to treat the sieve fractions in two ways.lf a melting crucible is available, at least 2kg of screenings may be melted or converted to a sulphide (or aluminium) matte as described in the sampling of copper-based alloys. If this is not available, the Screenings may be combined in proportion to give a 2 kg total sample and rnilled in a ring-mill of the Tema type, through a 178J,Ull (B.S. 85 mesh) sieve, then graded on a 124~m (B.S. 120 mesh) sieve for the assay sample. Aluminium-based borings will contain an apparently higher maisture content because of their low density. Losses of 30% or so are often found with wet borings. Aluminium may be reduced to a crushable alloy by heating at 900°C with an equal weight of iron powder. Titanium alloy turnings are almost impossible to grind in a ring mill but may be reduced to a crushable alloy by heating at 900°C with an equal weight of aluminium.

4. Turnings, Borings

Large Iosses of tin may be encountered during matting with sulphur and for this reason it should be restricted to the treatment of materials where tin is present in insignificant amounts. Aluminium treatments may result in the production of an alloy which may produce arsine or stibine on exposure to water or moist air. lf this happens the sample will be unacceptable. Assay as a solder or copper-base alloy, depending on material. Example A consignment consists of 3,583 kg of oily whitemetal turnings contaminated with !arge amounts of steel and coppery turnings. A bulk sample of 350kg is taken, this is reduced to 100 kg approximately and treated in a pot. To Pot Oily Turnings

kg 98.32

100.00

From Pot Turnings Whitemetal Loss

68.53 12.08 17.71

69.70 12.29 18.01

98.32

100.00

%

Whitemetal is dip sampled during stirring, remelted into thin strips and sawings taken. The turnings are milled and graded. Magnetics are separated, fractions weighed - the fines fraction being obtained by difference. kg To Mill 68.53 Turnings From Mill 42.01 Fines - 2mm + 2mm,- 4mm 7.02 + 2 mm,- 4 mm (iron) 4.32 5.18 + 4mm,- 8mm + 4mm,- 8mm (iron) 2.84 2.95 + 8mm, -12mm + 8mm,-12mm (iron) 1.96 + 12mm 0.87 + 12 mm (iron) 1.38

42.72 7.14 4.39 5.28 2.89 3.00 1.99 0.89 1.40

68.53

69.70

%

69.70

Mill 854.4g of fines (- 2mm) with 142.8g of + 2mm/-4mm and 87.8g of + 2mm/-4mm iron, through a 178J.l.m sieve (B.S. 85 mesh). Call this: Fines A. To a plumbago crucible add proportians of + 4mm fractions and greater. Add an equal weight of pure lump aluminium and heat at 900- 1200°C in a frre, stir frequently with caution until the sample has decomposed. Lift out the pot, cool in an isolated position, invert and knock out the product which willberather like a piece of metallic clinker. Clean out the pot and weigh the product. Mill through a 178J.l.m sieve (B.S. 85 mesh) to give:Fines B. To Pot + 4mm,- 8mm + 4mm,- 8mm iron + 8mm, -12mm + 8mm,- 12mm iron + 12mm + 12mm iron

Aluminium From Pot Matte

g 264.0 144.5 150.0 99.5 44.5 70.0

5.28 2.89 3.00 1.99 0.89 1.40

772.5

15.45

%

800.0 g

1634.3

%

32.71

177

178

Analysis of Secondary Materialsand Intennediates

Note the apparent weight gain due to oxidation. Finalproportions for assay are: Fines A Fines B , Whitemetal Loss on burning

% 54.25 32.71 12.29 18.01 117.26

If the assay results are multiplied by the appropriate fraction and added together, a correct 'original state' assay will be obtained.

5. Muds, Slimes, Detinning Residues During unloading any supernatant liquor should be decanted off and sampled. The consignrnent should then be reweighed. -As with other secondaries, a 10% prirnary sample should be taken. This is then reduced to about 50- 150kg. Muds arriving loose in 20 tonne containers or trucks should be sampled and reduced separately then combined in proportion to the container weights to give a total sample of about 150kg. If the sample isahomogeneaus paste it may be mixed in a pan or mulling mill, and a sample of 10- 20kg taken for maisture determination and subsequent sample preparation. Heterogeneaus samples i.e. containing lumps of hard material, should be heated gently in a pot (150kg) with constant stirring to give analmostdry product. This should be cooled, weighed and milled. Any oversize should be graded and magnetic constituents separated. A maisture determination should be carried out on 10- 20kg ofmixed fme material and this added to the loss found at the pot. A final sample of I or 2kg should be prepared from the milled, dried, fmes and any oversize material by milling through a B.S. 60 mesh (250,um) sieve. Caustic residues should fust be milled with sodium bicarbonate to give a stable sample. The amount required is usually but not always 5 - 25% by weight. Supernatant Iiquors should be evaporated to dryness and any residue mixed in proportion with sample fines för final milling. The evaporation loss should be added to any moisture· determined on the sample. Assay as a low-grade tin concentrate.

6. Hardhead and Irony Intermediates Hardhead is a tin-iron alloy produced by exhaustive smelting of tin slags, usually to remove the last traces of tin before the slag is discarded. These are normally encountered in very large pieces often up to 1 m in length. If the consignrnent consists of very large pieces these should all be broken up with a hydraulic breaker or pneumatic drill. If the consignrnent is very large and there are many such pieces it is permissible to select a primary sample by breaking up 20% of the large pieces. Usually it is sufficient to take a 10% primary sample. If the Ioad is very valuable a 20% sample should be selected. The whole of the bulk sample should be crushed to less than 25mm then treated as a slag as in Section B of this Chapter.

6. Hardhead and Iron Intermedials

Irony intermediates containing tungsten crush with difficulty and resist milling to the point where they may darnage the mill. They may sometimes be attacked by heating at 900°C in a crucible with no additives. The cooled, oxidised product may then be milled. Smaller quantities may be attacked by heating with aluminium at 900- 1200°C but the almost certain presence ofphosphorus, arsenic or antimony in these materials gives a product which will generate toxic hydrides on exposure to moist air. Treatment with aluminium is unlikely tobe practicable for this reason.

179

CHAPTER 14 ANALYSIS OF TIN ALLOYS AND SOLDERS By R. Smith

Tin alloys cover a wide range of composition and uses, the most irnportant being: a) Solders. b) Printing alloys. c) Bearing alloys. d) Pewter and casting alloys. Tables 1 - 3 give the compositions of several important solders and whitemetals.

Table 1. Chemical Composition of British Standard Solders [ 1]

B.S. Solder A K

F R

c

H

J V

w B M

c

L D N

95A 5Sa !Sa 62Sb 9asc T

min.

Tin%

64 59 49 44 39 34 29 19 14 49 44 39 31 29 18 94.5 4.75 1.0 61.5 96.3 49

max.

Antimony% max. min.

65 60 50 45 40 35 30 29 15 50 45 40 32 30 18.5 95.5 5.25 1.5 62.5 96.5 50

0.6 0.5 0.5 0.4 0.4 0.3 0.3 0.2 0.2 3.0 2.7 2.4 1.9 1.8 1.1 5.25 0.10 0.10 0.2 0.1 0.1

2.5 2.2 2.0 1.6 1.5 0.9 4.75

Melting Range °C 183-185 183-188 183-212 183-224 183-234 183- 244 183-255 183-276 227- 288 185-204 185-215 185- 227 185-243 185 - 248 185-275 236- 243 296- 301 309- 310 178 221 145

In addition: As 0.1 Total other impurities :I> 0.05 ::1>0.20 ::1>0.90 Total other impurities ::1>0.10

0.002 0.002 0.002 0.002 0.002

0.001 0.001 0.001 0.001 0.001

0.002 0.002 0.002 0.002 0.002

Total other impurities :I> 0.03 Total other impurities )> 0.05

1. Sampling Ingots [1] shall be selected from a consignment according to Table 2. The ingots shou1d be placed side by side in rows of five and a line drawn diagonally across the row from the top of the first to the bottarn of the fifth, ignoring any Iug on the in-

0.002 0.002 0.005 0.005 0.005

Ref.p 198]

2.1 Determination of Tin

193

gots. A saw cut shall be made, with a coarse, widely set saw at the side of each ingot at a point opposite the intersection of the diagonal and the centre line. Saw halfway through each ingot and collect the sawings. The sawings should be mixed and any iron removed with a magnet and rejected; if any oil is present the sawings should be cleaned in petroleum ether and dried. Sufficient sawings should be taken to provide a final sample of 1 kg.

Table 2. Selection of Sampie from a Consignment of Tin Ingots [1] Number of Ingots in Consignrnent 1- 4 5-44 45-54 55-64 N

Number of Ingots in Sampie All 4 5 6 4+ (N-4)/10

The above British Standard method of sampling is generally acceptable in that a 10% sample is taken and impurities are unlikely tobe introduced or lost in sampling. If sawings aretobe melted for emission spectroscopy, this should be donein an acidcleaned silica crucible over a Bunsen burner. The melt should be stirred with a thin rod of spectroscopic graphite. The mould and sample file should be specially reserved for this purpose.

2. Analysis 2.1 Determination of Tin lt is almost universal practice to express the puri ty of metals as 100% minus the total sum of impurities. Few metals are usually assayed as such for the principal component, exceptions being electrolytic copper, silver and gold.

B.S. 3338 gives a method for the determination of tin in ingot tin having a range from 99.0 - 99.8% Sn and a reproducibility of ± 0.05% Sn. The method requires considerable skill and practice but is capable of the performance claimed. Weigh accurately to 0.0001g, six portians of dried KI0 3 (-60 mesh) and transfertosmall beakers. To each add 1 g of NaHC0 3 and 50 ml of boiled, cooled water; cover, warm to dissolve and reserve. Weigh accurately to 0.0001 g (at the same time as the iodate) triplicate portians of 2.5 g of sample or pure tin and transfer each to a 250m! tall beaker. To each add 50ml of HCI and 1 drop of 0.1% antimony chloride solution. Cover and heat at 45°C on a hotplate until only a small black residue of impurities remains. Add 4.0ml of 200g/l sodium chlorate slowly with stirring and cool to 30°C in running water. At 5 min intervals (timed with a clock) remove three beakers at a time and to each add 1 g ± 0.25 g of iron powder. Allow to stand for 5 min then replace in running water. During the 5 min standing period of the second and subsequent sets, filter the contents of the previous set of beakers through a pad of asbestos pulp on a fritted funnel into 500ml flat bottomed flasks containing 180m! of 1 : 1 HCI and 0.25g of iron powder. Wash with warm (30- 35°C) 1: 10 HCI and combine the washings with the filtrate. The volume in each flask should be 300 to 350 ml.

194

Analysis of Ingot Tin

[Ref.p. 198

Add Sg of aluminium strip, connect to a supply of C0 2 and warm if necessary to start the reaction then immerse in a cold water bath. When the aluminium has almest dissolved, loosen the Stopper hoiding the CÜ2 inlet and rinse down the neck of the flask and bung with warm 1; 10 HCL Replace the bung and heat the flask to boiling on a hotplate slowly to dissolve the deposited tin. Boi! gently to dissolve tin, close the exit tube with a rubber cap and cooi in running water under C0 2 . Remave each flask from the water-bath, wash the stopper with water. Cap the neck with the palm of the hand and add one of the previously prepared iodate solutions, rinsing this into the flask with boiled, cooled water. Add 1-2m! of starch indicator and titrate with 3g/l KI0 3, 3g/l KI and O.S g/1 NaHC03, which has been purged with C0 2 ; swirl gently during titration. The titrant should be kept in a 10 ml burette graduated in 0.02ml. Tin% = (A + B) F x 100

w

where:

Note

weight of KI0 3 added (g). weight of KI0 3 added in titrant (g). weight of sample (g). w Ws where subscript, s, refers to standard. F A +B s s For pure tin weigh 1.493g of solid KI0 3 (Sn 99.9%). For refined tin weigh 1.490g of solid KI03 (Sn 99.8%). For common tin weigh 1.478g of solid KI0 3 (Sn 99.0%). A B

2.2 Photometrie Methods for Impurities Standard methods are given below; other published work is summarised. Antirnony [3] Dissalve 0.2Sg of sample in 10m! of H 2S0 4 , cool, add 30m! of water then SOml of HCI, transfer to a 100m! volumetric flask and dilute to volume. To a separating funnel add 10m! of this solution (for O.OS- 0.1% Sb use Sm! and for 0.01- 0.2S% Sb use 2m!- dilute to 10m! with 1 : 1 HCI) and O.Sml of lOg/! sodium metabisulphite solution. Cool to below 2S°C, add 3m! of ceric sulphate (3.3g in 100m! H 2 S04 ) and O.Sml of lOg/1 hydroxylammonium chloride solution. Stand until the ceric sulphate is reduced then dilute to 60ml. Add lO.Oml of isopropyl ether and shakefor 30 sec. Runoff the aqueous layer, wash twice with 2ml of 1:10 HCI and finally add 2m! of 0.2g/l Rhodamine Bin 1 : 10 HCI and shake for 10 sec. Discard the aqueous layer tagether with a few drops of the organic layer, dry the stem of the funnel with a roll of paper and run off into a stoppered bettle. Measure the absorbance in a 2 cm (0.004- 0.024% Sb) or 1 cm (0.024- O.OS% Sb), cell at SSOnm. Calibrate with 1- Sm! aliquots of 2.4mg/l Sb in HCI solution diluted to Sm! with HCL Add 5 ml of water and carry through the procedure from the addition of sodium metabisulphite.

Arsenic B.S. 3338 [4] recommends a procedure involving separation of arsenic by distillation as AsCI 3 followed by reaction with arnmonium rnolybdate and reduction with hydrazine sulphate to molybdenum blue. A more rapid alternative is to dissolve 0.1 g of tin in 20m! of 1:1 H 2 S0 4 in an arsine generation apparatus filled with 0.05% silver diethyldithiocarbamate in pyridine ( see Chapter 12). When the tin has dissolved, except for a few black specks, add 2ml of 15% Kl, 50ml of water and 5 g of granulated zinc. Reassemble the apparatus quickly and shield frorn direct sunlight. Leave for at least 1 1I 2 hours and measure the absorbance at 540nrn. Calibrate using solutions from 5 - 50J.,Lg As.

Ref.p. 198]

2.2 Photometrie Methods for Impurities

195

Bismuth [5] Dissalve 2g of sample in 18 ml of HBr, 2m! of Br2 and Sml of HCl04 and evaparate to fuming (in a perchloric acid compatible fume cupboard). lf the solution is cloudy add more HBr. Cool, dilute and transfer to a 50ml volumetric flask. Pipette 25m! of 8% w/v thiourea solution and dilute to volume. Measure the absorbance with a 1 cm cell at 465 nm for Bi 0.07% or with a 4cm cell for Bi 0.001 -0.015%. Calibrate with standards in the range 0.05- 1.4mg Bi taken through the full procedure. Carry out all measurements at 20° ± 1°C.

The ASTM method for bismuthin solders [6] is very sirnilar. The colour formed is extremely sensitive to temperature. Copper B.S. 3338 [7] gives a method for 0.001 - 0.04% Cu using a photometric deterrnination in gum arabic solution with rubeanic acid, after removal of tin with HBr/Br 2 • The photometric method [8, 9] using HBr/H 3 P0 4 afterremoval of tin with HBr/Br 2 is suitable for 0.01- 2% Cu on a 1 g sarnple with 4crn cells. (See Chapter 14, Section 2.4). Considerable increases in sensitivity may be obtained by the use of a lOg sarnple. Iron This may be deterrnined by the photometric 1,10 phenanthroline method given in Section 2.5 ofChapter 14 [8, 10]. Lead The B.S. method for lead in ingot tin [11] involves tinremoval with HBr/Br 2 followed by extraction with dithizone into chloroforrn from a solution containing sodium tartrate, hydroxylarnmonium chloride and potassium cyanide. Other References of Interest: Ag Al

General scherne for

13 irnpurities after precipitation on La(OHh

[12]

Atornic absorption, graphite tube

[44]

Eriochrorne cyanine R, colorirnetric

[13]

Chrome Azurol S (C.I. Mordant Blue 29), colorirnetric

[14]

As

Neutron activation

[15]

B

Extraction of BF 4/rnethylene blue cornplex into CH 2CI 2 colorirnetric

[16]

Benzoin, fluorirnetric

[17]

Bi

See Ag

[12, 44]

Anodic stripping voltamrnetry

[18]

Thionalide extraction colorirnetric

[19]

Cd

See Ag

[12, 44]

Co

See Ag

[12, 44]

Cr

Diphenylcarbazide colorirnetric

[20]

Cu

See Ag

[12,44]

Neutron activation

[21]

Anodic stripping voltamrnetry

[18]

Polarography

[22]

Diethyldithiocarbamate extraction colorirnetric

[23]

Ion exchange separation

[24]

Arnrnonia colorirnetric

[25]

Dithio-oxamide extraction colorirnetric

[25]

196 Cu Fe

Analysis of lngot Tin

[Ref.p.198

Square wave polarography

[261

See Ag

[121 [27,291

Bipyridyl extraction colorimetric Thiocyanate colorimetric

[281

Coulometric

[301

Hg

See Ag

[121

In

See Ag

[121

5, 7 Dichloro-8-hydroxyquinoline extraction colorimetric

[31 1

Neutron activation

[321

See Ag

[12 1

Neutron activation

H

Mn Ni

See Ag

[321 [12,441

0

'Y·Activation

[331

Fusion gravimetric

[34 1

p

Reduced phosphomolybdate extraction colorimetric

[35, 361

Pb

See Ag

[12,441

Anodic stripping voltammetry

[181

Ion exchange separation

[241

s

Combustion conductimetric

[37, 381

Sb

Anodic stripping voltammetry Neutron activation

[39, 401

Se

Neutron activation

[15 1

Si

Reduced silicomolybdate colorimetric

[41 1

Tl

See Ag

[121

Zn

See Ag

[121

Potassium ferricyanide titration, crude tin

[421

[15 1

2.3 Emission Spectroscopic Methods for Impurities A wide range of impurities may be deterrnined in tin by direct photographic emission spectroscopy on metal samples down to 1p.g/g with comparative ease [431. Whenever possible, tin should be sampled from a well-stirred melt and chill-cast into spectrographic rods or discs. Remelting, if necessary, shou1d be carried out in a clean porcelain or glass vessel; the melt should be stirred with a rod of spectrographic carbon. Standardsaremade from master alloys, diluted by melting with 99.999% or 99.9999% tin. Formost purposes the forrner is adequate as the 10p.g/g of impurity is usually much less than the specification lirnit and is distributed between several elements. Master alloys may be made in a number of different ways: (i) Melting under glycerol or palm oil - absolute standards may be made by separately melting Al, As, Bi, Cd, In, Pb, Sb and Zn to give a 1% alloy of each. With some metals it may be neccessary to melt at a rather higher temperature (500°C) in the absence of an oil. Losses by Vaporisation or oxidation should be less than 10%. (ii) Melting under borax or potassium cyanide - the standards produced are usually absolute but it is wise to check by chemical assay. Elements such as Ag, Au, Cu and

2.3 Emission Spectroscopic Methods for Impurities

Ref.p. 198]

197

Fe require heating at 900°C to obtain a 1% solution in a reasonably short time. Copperand silver may be dissolved by prolonged heating at temperatures as low as 400°C. Iranstandardsare best obtained from works intermediates if these are available. Spectrographic conditions are: (i) High Purity Tin (99.999%). (0.5mH, 120pF, 4mm gap, 60° carbon electrode, 3 min burn) Standards (J.Lg/g): Ag Bi Cu Fe In Pb Sb 5 5 5 10 5 10 10 2 2 2 52 55 111 21 2 2 Wavelengths (nm) 328.1, 306.8, 327.4, 259.84, 325.9, 262.4, 259.8 (ü) Electrolytic Tin (99.95 %)

(0.5mH, 120J.lF, 4mm gap, 60° carbon electrode, 30 sec burn) Standards (J.Lg/g):

Wavelength (nm) (nm) Sn Ref.

Ag 100 30 10 328.1 322.4

As 100 30 10 234.9 278.8

Bi 100 30 10 306.8 314.1

Cu

100 30 10 327.4 322.4

Fe Ge 100 20 30 10 10 0 259.8 265.1 278.8 278.8

In 20 10 0 235.9 322.4

Pb 100 30 10 288.3 276.2

Sb 300 100 50 259.8 278.8

(iii) Common Tin (99.0%) (0.5mH, 120J.lF, 4mmgap, 60° carbon electrode, 30 sec burn) Standards(%):

Wavelength (nm): Sn Ref:

As 0.30 0.10 0.05 0.03

234.9 278.8

Cu

0.10 0.05 0.02 0.005

296.1 327.4 314.1

Fe 0.5 0.2 0.08 0.01 0.003 259.8 278.8

Pb 1.0 0.4 0.2 0.1 0.05 282.3 283.3

Sb 0.5 0.25 0.1 0.05 0.025 0.01 259.8 278.8

For the analysis oftraces of impurities present at less than 1J.lg/g a number of Soviet researches are of interest. Yudelevich [45] used an 80mg powdered sample placed in a carbon anode in a 15 amp d.c. arc to obtain Iimits of detection of 0.2J.lg/g Cd, 4/lg/g Te and 0.4 J.lg/g Zn. At the end of the burn, 99% of the sample remained although the impurities had volatilised. Enhanced sensitivities were obtained for Co, Fe, Ni etc. by mixing the sample with an equal weight of sulphur to volatilise tin before the impurities. Traces of Al, Ca, Cu, Fe, Mg and Si were determined [46] down to lJ.lg/g or less by igniting the sample, then mixing 20mg of oxide with lOmg of carbon for excitation in a 1Oamp. d.c. arc with 2.5 mm electrode gap. Limits of detection ofthe order ofng/g were obtained [47] for many elements by treating 1- 5g of tin in a silica dish with 50mg of carbon, 2mg of NaC!, 2ml of CC14 and 2- 8ml of Br 2 (added in 0.5 ml portions). After decomposition was complete, the dish was heated to 180- 200°C to remove Sn as the bromide. The residue was packed in a carbon anode of 4mm diameter, 3mm depth for excitation in a d.c. arc. Synthetic standards were easily prepared for nineteen elements by adding aqueous solutions to carbon and NaC! and taking through the procedure.

198

Analysis of lngot Tin

References 1. Methods for the Sampling and Analysis of Tin and Tin A!loys British Standard, B.S. 3338, Part 1 (1961) 2. Reference 1, B.S. 3338, Part 2 (1961) 3. Reference !, B.S. 3338, Part 3 (1961) 4. Reference 1, B.S. 3338, Part 9 (1965) 5. Reference 1, B.S. 3338, Part 8 (1961) 6. 1975 ASTM Book of Standards Part 12, E46 (1972) 7. Reference 1, B.S. 3338, Part 6 (1961) 8. Price, J. W., Cappins, W.C.: The Analysis ofTin-Bearing Base Metals: Tin Research Institute Publication 161, London, 1954 9. Reference 1, B.S. 3338, Part 4 (1961) 10. Reference !, B.S. 3338, Part 10 (1961) 11. Reference 1, B.S. 3338, Part 5 (1961) 12. Marczenko, Z., Kasiura, K.: Chemia Analit. 10, 449 (1965) 13. Lel'chuk, Y.L., Sokalovich, V.B., Drelina, O.A.: Izv. Tomsk. Politekh. Inst.128, 101 (1964). Anal. Abstr. 13,5477 (1966) 14. Shvaiger, M.l., Rudenka, E.I.: Zavod. Lab. 26, 939 (1960). Anal. Abstr. 8, 1448 (1961) 15. Maenhaut, W.,Adams, F., Haste, J.: J. Radioanalyt. Chem. 6, 83 (1970) 16. Lel,chuk, Y.L., Jvashina, V.A.: lzv. Tomsk. Politekh. Inst. 148, 157 (1967) 17. Le/'chuk, Y.L., Jvashina, V.A.: lzv. Tomsk. Politekh. lnst. 148,152 (1967). Anal. Abstr. 17,115 (1969) 18. Brainina, K.Z., Neiman, E. Y., Trukhacheva, L.N.: Zavod. Lab. 38, 12 (1972). Anal. Abstr. 23, 130 (1972) 19. Lilie, H.: Z. Anal. Chem. 159,196 (1958) 20. Pilipenka, A.T., Voranina, A.l., Nabivanets, B.l.: Zavod. Lab. 36,273 (1970). Anal. Abstr. 20, 2389 (1971) 21. Wölfe, R., Herpers, U., Herr, W.: Z. Anal. Chem. 233, 241 (1968) 22. Stromberg, A.G., Zakharav, M.S., Garadavykh, V.E.: Zavod. Lab. 27, 517 (1961) 23. Jkeda, S., Nagai, H.: Japan Analyst 7, 76 (1958) 24. Kataev, G.A., Slezko, N.J.: Trudy. Tomsk. Gos. Univ. 170, 76 (1964). Anal. Abstr. 13, 1727 (1966) 25. Zhivopistev, V.P., Selezneva, E.A.: Uch. Zap. Permsk. Univ. 25, 84 (1963) 26. Jtsuki, K., Kaji, T.: Japan Analyst 8, 703 (1959) 27. Le/'chuk, Y.L., Kristalev, P. V., Skripava, L.L., Kristaleva, L.B.: Izv. Tomsk. Politekh. lnst. 128,96 (1964) 28. Bradshaw, G., Rands, J.: Analyst 85, 76 (1960) 29. Kristalev, P. V., Kristaleva, L.B.: Sb. Nauch. Trudy. Permsk. Politekh. Inst. 14, 65 (1963). Anal. Abstr. 12, 2737 (1965) 30. Yashimari, T.,lshiwari, S.: Talanta 17, 349 (1970) 31. Raby, R.A., Banks, C. V.: Anal. Chim. Acta 29,532 (1963) 32. Maenhut, W., Adams, F., Haste, J.: J. Radioanalyt. Chem. 9, 27 (1971) 33. Kapitza, S.P., Samasyuk, V.N., Tsipenyuk, Y.M., Kunin, L.L., Chapyzhnikov, B.A., Wasserman, A.M., Yakovlev, Y. V.: Radiochem. Radioanalyt. Lett. 5, 217 (1970) 34. Gumilevskaya, G.P., Chekanava, V.D., Guseva, K.S., Tashkava, Z.l., Murilina, A.J.: Trudy. Vses. Nauch. lssled. Proektno. Teknol. Inst. Elektrougol'n. Jzdelii. 1, 119 (1970). Anal. Abstr. 21, 129 (1971) 35. Sokolavich, V.B., Lel'chuk, Y.L., Drelina, D.A.: lzv. Tomsk. Politekh. Inst. 148, 162 (1967). Anal. Abstr. 17,117 (1969) 36. Lel'chuk, Y.L., Sakalovich, V.B., Detkava, G.A.: lzv. Tomsk. Politekh .. lnst. 148, 144 (1967). Anal. Abstr. 17, 116 (1969) 37. Pell, E., Malissa, H., Murphy, N.A., Chamberlain, B.R.: Anal. Chim. Acta 43,423 (1968) 38. Chamberlain, B.R., Murphy, N.A.: Anal. Chim. Acta 59, 151 (1972) 39. Zaichko, L.F., Zakharov, M.S., Mardvinava, V.D.: lzv. Tomsk. Politekh. lnst. 128,50 (1964) 40. Zaichka, L.F., Yankauskas, V.F., Zakharav, M.S.: Zavod. Lab. 31, 265 (1965). Anal. Abstr. 13, 3504 (1966) 41. Pilipenka, A.T., Nabivanets, B./., Shainskaya, L.G.: Zavod. Lab. 22,2214 (1972) 42. Papov, M.A., Repkina, A.E.: Uchen. Zap. Tsent. Nauch. Issled. Inst. Olovyan. Prom. 90 (1965). Anal. Absü. 14, 1364 (1967) 43. Unpublished Work and Standard Methods, Capper Pass, Ltd. 44. Medina, R.: Anal. Chem. 271, 346 (1974) 45. Yudelevich, J.G., Shelpakava, I.R., Sukankina, T.A., Prakharava, S.A.: Zavod. Lab. 34, 1074 (1968). Anal. Abstr. 8, 124 (1970) 46. Usenko, L.E., Kalinchuk, S. V.: Zavod. Lab. 34, 686 (1968). Anal. Abstr. 17, 2053 (1969) 47. Malakhav, V. V., Protapopava, N.P., Trukhacheva, V.A., Yudelevich, J.G.: Trudy. Korn. Analit. Khim. 16, 89 (1968)

z.

CHAPTER 16 TIN IN COPPER-BASE ALLOYS By R. Smith

Table 1 gives an illustrative selection of copper-based alloys where tin is an impor· tant element in the specification [ 1].

1. Sampling The sampling of copper-based materials (particularly scrap) is complex and because of the many situations which may arise, only guidelines can be given here. Meta! used for casting should be dip sampled and poured into a chill-cast mould. In any sampling scheme for assorted materials, it must be decided if the material can reasonably be sorted into different types or if a single primary sample is to be drawn.In the secondary copper industry, experienced samplers can grade articles such as castings, ingots, etc., into alloy types by examination of the meta! and its drilling characteristics. Wherever possible, consignments should be sorted into sub-samples and weighed. With small consignments, this exercise alone may be acceptable for valuation purposes. Where samples for assay are required the following guidelines illustrate current practice. Large castings, ingots - sampled by drilling completely through, bearing in mind that considerable segregation of Iead is probable in !arge castings. The weight of drillings taken should reflect the size of the casting. Whitemetal bearings, iron or steel items, etc., should be separated and treated separately. Whitemetal may be melted and sawings taken, iron or steel can usually be rejected after weighing. Drillings should be milled through a 5 mm screen and graded on a 2 mm screen to give oversize and undersize which are weighed. Assay samples may be prepared by milling 1 kg of the drillings, combined in proportion, through a B.S. 30 mesh screen. An example is given on p 201. The final assay results should be multiplied by the % to give the concentration in the original consignment. Small mixed castings - where drilling would be excessively time consuming and castings are small, a sarnple may be prepared by melting SOkg of castings in a crucible furnace usually without a flux. Copper-based alloy may then be poured off into an ingot mould leaving behind a residue of nicke! or irony material with small amounts of the alloy: whitemetals usually reside with the copper portion. The irony residue may be treated at red heat with rock sulphur and stirred to form a fluid matte of iron sulphide which may be cast and crushed on cooling. Iranpyrites (free from copper) or aluminium meta! may also be used for attacking irony residues. Losses of tin as the volatile sulphide during matte preparation may be considerable and this should only be considered when a good Separation from the bulk of the copper alloy has already been achieved. Direct treatment of copper alloys by heating with aluminium is possible to give a crushable aluminium/copper alloy (usually equal portians by

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Aluminium Bronze

Aluminium Bronze

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REM REM REM REM REM REM REM REM REM REM REM REM REM 70.0- 80.0 63.0- 70.0 60.0-63.0 58.0- 63.0 57.0- 60.0 >ss.o >55.0 REM REM REM REM

Phosphor Bronze Phosphor Bronze Phosphor Bronze Leaded Phosphor Bronze Copper Tin Leaded Bronze Leaded Bronze Leaded Bronze Gunmetal Nickel Gunmetal Leaded Gunmeta I Leaded Gunmetal Leaded Gunmetal Brass (Sand Casting) Brass (Sand Casting) Naval Brass Brass (Die Casting) Brass (Die Casting) Brass (High Tensile) Brass (High Tensile) Cu/Mn/Al Cu/Mn/Al

PB! PB2 PB4 LPB1 CTI LBl LB2 LBS GI G3 or G3-TF LG1 LG2 LG4 SCBl SCB3 SCB4 DCB3 PCBl HTBl HTB3 CMAl CMA2 AB1 AB2

Cu

British Standard Casting 10.0 11.0- 13.0 > 9.5 6.5-8.5 9.0 - 11.0 8.0- 10.0 9.0- 11.0 4.0-6.0 9.5- 10.5 6.5- 7.5 2.0- 3.5 4.0-6.0 6.0- 8.0 1.0- 3.0