Recent advances in leaching copper smelting slag 9786010432802

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AL-FARABI KAZAKH NATIONAL UNIVERSITY

R. K. Nadirov

RECENT ADVANCES IN LEACHING COPPER SMELTING SLAG Monograph

Almaty «Kazakh university» 2018

UDC 669.0 (075.8) LBC 34.2 я 73 N 13 Recommended for publication by the Academic Council (Protocol No.5, 29.12.2017) and the Editorial Committee of al-Farabi KazNU (Protocol No.4, 29.12.2017) Reviewers: Doctor of Technical Sciences, professor M. S. Satayev Doctor of Chemical Sciences V. N. Statsyuk Doctor of Chemical Sciences G. A. Seilkhanova

Nadirov R.K. Recent advances in leaching copper smelting slag: monograph / R. K. Nadirov. – Almaty: Kazakh university, 2018. ‒ 118 p. ISBN 978-601-04-3280-2

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Copper smelting slag is recognized as an important raw material for valuable metals production. A contribution to documenting current and future best practice in copper smelting slag processing by leaching seems timely. The focus of the monograph is on advances in the current situation in the mentioned field. Sufficient coverage is given to the chemistry and engineering aspects of copper smelting slag leaching. The book may be of interest to specialists working in hydrometallurgy, teachers and students of chemical and metallurgical faculties.

UDC 669.0 (075.8) LBC 34.2 я 73 © Nadirov R.K., 2018 © Al-Farabi KazNU, 2018

ISBN 978-601-04-3280-2

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CONTENT INTRODUCTION .............................................................................. 5 1. GENERAL INFORMATION ABOUT COPPER SMELTER SLAG ............................................................................... 8 1.1. Smelting of copper concentrate. Copper smelter slag formation ... 8 1.2. Composition of copper smelter slag .............................................. 9 1.3. Physical and mechanical properties ............................................... 13 1.4. Ways of copper smelter slag processing ........................................ 14 1.4.1. Pyrometallurgical copper smelter slag processing .............. 14 1.4.2. Flotation enrichment of copper slags .................................. 15 1.4.3. Use of slag for the production of building materials ........... 17 2. GENERAL PRINCIPLES OF LEACHING COPPER SMELTER SLAG. MODELS AND MECHANISM OF LEACHING PROCESSES ............................... 19 2.1. Methods of leaching smelter slag .................................................. 19 2.2. Leaching models ............................................................................ 20 2.2.1. Shrinking core model (SCM) .............................................. 20 2.2.2. Variable activation energy model. ...................................... 21 2.2.3.Thermodynamic approach ................................................... 22 2.2.4. Empirical models. ............................................................... 24 2.3. Mechanism of leaching reactions .................................................. 24 2.3.1. General issues ..................................................................... 24 2.3.2. Electrochemical mechanism of dissolution ........................ 25 2.3.3. Mechanism of silicates dissolution ..................................... 26 3. AGITATIONAL LEACHING OF SLAGS WITHOUT PRELIMINARY THERMAL PROCESSING ................................. 28 3.1. Leaching with sulfuric acid ........................................................... 28 3.1.1. Use of sulfuric acid without additives. ................................ 28 3.1.2. Use of sulfuric acid together with hydrogen peroxide ........ 36 3.1.3. Use of sulfuric acid in conjunction with sodium chlorate ... 41 3.1.4. Use of sulfuric acid in conjunction with potassium dichromate ................................................................... 44 3.1.5. Use of sulfuric acid together with iron (III) sulfate ............. 46 3.2. Ammonia-ammonium leaching ..................................................... 48 3.3. Leaching by using organic acids .................................................... 56 3.3.1. Use of organic acids for leaching of slags of non-ferrous metallurgy ................................................................. 56

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3.3.2. Use of organic acids for leaching copper slag of Balkhash copper plant ....................................................... 57 4. ELECTROCHEMICAL LEACHING OF THE SLAG .............. 60 4.1. General issues ................................................................................ 60 4.2. Slag leaching by electrochemical activation of sulfuric acid solution ........................................................................ 61 4.2.1. Electrochemical activation of sulfuric acid solution ........... 61 4.2.2. Electrochemical leaching of slag in sulfuric acid solution ..................................................................... 63 4.3. Electrochemical chlorination of slag ............................................. 64 4.4. Application of the internal electrolysis for slag leaching............... 69 5. LEACHING WITH PRELIMINARY ROASTING .................... 72 5.1. Roasting with ammonium chloride ................................................ 72 5.2. Roasting with sulfuric acid ............................................................ 81 6. BACTERIAL LEACHING ............................................................ 87 6.1. Use of microorganisms for leaching copper slag ........................... 88 6.2. Application of bioleaching for processing copper smelter slag of Balkhash copper plant .................................................. 89 7. PRESSURE OXIDATIVE LEACHING ...................................... 96 7.1. General information on the pressure oxidative leaching ................ 96 7.2. Pressure oxidative leaching of the slag .......................................... 96 7.3. Pressure oxidative leaching of the slag from Balkhash copper plant ................................................................. 98 CONCLUSIONS ................................................................................. 102 REFERENCES ................................................................................... 106

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INTRODUCTION

About three-quarters of copper are produced by pyrometallurgical methods. Application of these methods leads to the generation of socalled copper smelter slag as a byproduct of pyrometallurgical copper production. The production of each ton of copper is accompanied by the formation of about 2.2 -3.0 tons of slag [1-3]. Annually about 50 million tons of copper are produced by pyrometallurgical methods in the world; thus, the annual increase in the amount of accumulated copper smelter slag is more than 120 million tons or more than 40 million cubic meters. This amount of slag contains millions of tons of toxic or potentially toxic elements, such as arsenic, lead, copper, zinc. Copper smelter slag can be considered in two aspects. First, it is a potential source of environmental pollution, due to the inevitable dissolution of toxic components of slag, primarily arsenic and lead. Slag, being in open space, is exposed to various bio-hydro-climatic conditions and over time undergo weathering processes leading to release metallic elements. Also, the formation of fine particles of slag takes place. This circumstance leads to pollution of ecosystems, such as soil, as well as surface and groundwater [4-6]. Unfortunately, this aspect is not given due attention, and the slag mountains near the nonferrous metallurgy enterprises represent a serious problem at present [7-10]. In this connection, the requirements for the disposal of metallurgical wastes are tightened all over the world. On the other hand, copper smelter slag can be considered as a valuable raw material resource for the production of non-ferrous metals. Depending on the melting conditions of copper concentrates, the following content of valuable metals in the copper smelter slag is observed, wt. %: Cu ~ 0.5-2, Zn ~ 2-5, Pb 0.2 ~ 1. It can be noted that the content of these metals in slags is comparable to their content in ores, and often exceeds this content. Gold and silver are also present in the copper slag. Also, about 40% of the total mass of the slag is iron. Finally, silicon dioxide, which is about one-fifth of the slag, is an important mineral raw material. Thus, the processing of copper slag can solve two important problems. First, the negative impact of slag on the environment will decrease, and the land previously used for slag 5

disposal will be freed. And secondly, the raw material base of the number of non-ferrous and precious metals, as well as iron and silicon dioxide (to a lesser extent) will expand. However, there is a big problem that greatly hinders the extraction of these metals from the copper slag. This problem is related to the mineralogical composition of the slag. The slag matrix consists of fayalite and silicon dioxide, into which the compounds (mainly sulphide) of valuable metals are embedded. Until now, there are no cost-effective technologies for the extraction of non-ferrous and precious metals from copper slag. There are three approaches to processing slags with the extraction of valuable components: (i) flotation enrichment, (ii) pyrometallurgical processing, and (iii) hydrometallurgical processing. Pyrometallurgical slag processing is mainly carried out in electric furnaces at temperatures of 1350 ‒ 1450 °С. At the same time, an acceptable separation of copper and zinc from the slag is achieved. However, such shortcomings as high power consumption, high capital costs, and low environmental friendliness, do not allow pyrometallurgical methods to be used for the processing of poor copper slags on an industrial scale. The most common method of slag processing is flotation enrichment. The method consists in grinding the slag to the required size, with further flotation in several stages. Flotation enrichment of copper smelter slag is a well-studied process and is described in some scientific papers. This method is implemented on an industrial scale in some countries around the world, including China, Russia, Kazakhstan, and others. In particular, flotation enrichment of copper smelter slag is used at the Balkhash concentrator (Central Kazakhstan). Over more than 70 years of operation of the Balkhash copper smelter, more than 31 million tons of copper slag have been accumulated. In recent years, more than 500 thousand tons of slag are produced annually. This slag is subjected to grinding and flotation enrichment to produce a copper concentrate with a copper content of about 12-15 %, copper recovery to the concentrate is about 50 – 60 %. Zinc from slag is practically not extracted. Tailings of flotation enrichment are not used. Meanwhile, shredded enrichment tails represent a much greater danger to the environment than the original slag, due to the reduction in particle size. 6

The use of tailings in the construction and road industries is difficult due to the presence of toxic components, primarily lead and arsenic. Hydrometallurgical methods are the most promising for processing copper smelter slags. There is a significant number of scientific papers on the hydrometallurgical processing of copper slag in well-known peer-reviewed journals. Leading groups now include scholars from China, the United States, Australia, and some other countries. As a leaching agent, aqueous solutions of acids (sulfuric, hydrochloric, nitric, acetic, etc.) and ammonium salts are used. To intensify the leaching process, oxidants (ferric sulfate, sodium chlorate, hydrogen peroxide, oxygen, iron (III) chloride, potassium dichromate, etc.) are exploited. In this monograph, the author summarized the latest achievements in the leaching copper slag, including the results of his research on the leaching of the slag of the Balkhash copper smelter. For the convenience of perception, the book is divided into seven chapters. The first chapter provides general information on the copper smelter slag, the ways of its formation, properties, as well as the methods of slag processing. The second chapter is devoted to the principles underlying the leaching of slag. Chapters 3-7 are directly devoted to the leaching of copper slag. Chapter 3 deals with slag leach processes without preliminary roasting of the starting material. Chapter 4 is devoted to the application of electrochemical methods for leaching slag. The fifth chapter deals with the leaching of copper slag, previously subjected to roasting with chemical agents. Biological leaching, as well as pressure oxidative leaching of copper smelter slag, are discussed in Chapters 6 and 7, respectively. It is assumed that this monograph will help accelerate the development of new efficient technologies for hydrometallurgical processing of copper slag. The book may be of interest to specialists working in hydrometallurgy, teachers and students of chemical and metallurgical faculties.

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1. GENERAL INFORMATION ABOUT COPPER SMELTER SLAG

1.1. Smelting of copper concentrate. Copper smelter slag formation The pyrometallurgical process for copper production includes several processing steps: (i) obtaining copper concentrate (copper ore enrichment), (ii) melting the concentrate to produce copper matte, (iii) converting copper matte to blister copper, and (iv) blasting refining of blister copper with obtaining anodic copper, (v) electrolytic refining of blister copper to produce cathode copper (99.5-99.9% Cu). Target components of commercial copper concentrate include, in the majority, sulphide copper minerals such as chalcopyrite (CuFeS2), bornite (Cu5FeS4), and chalcocite (Cu2S). In addition, concentrates contain components such as iron sulphides (FeS, FeS2, etc.), silicon dioxide (SiO2), zinc sulphide (ZnS), calcium and magnesium carbonates (CaCO3, MgCO3), aluminium oxide (Al2O3), and some other components. Smelting of copper concentrates carried out in special metallurgical units (furnaces), in the presence of oxygen (air). Under these conditions, the oxidation of sulphur and iron present in the concentrate takes place with the formation of Cu-rich molten matte: 2CuFeS2 + 3.25O2

Cu2S×0.5FeS +1.5FeO + 2.5SO2

(1.1)

The addition of siliceous flux (SiO2) to the charge allows to bind a part of iron in the form of fayalite (2FeO×SiO2, or Fe2SiO4): 2FeO×SiO2

2FeO + SiO2

(1.2)

To reduce the viscosity of the melt, the oxide fluxes (e.g. CaO, CaCO3) are added to the charge. As a result of melting, two liquid products are formed in a furnace: Cu-rich molten matte and copper smelter slag. The matte is a melt of copper and iron sulphides. Slags 8

of copper smelting are rich in both iron and silicon and are a melt of ferrosilicates with a small admixture of other oxides. The basis of these slags is the FeO-SiO2 binary system. Due to the segregation process (difference in densities), these products are divided: matte as heavier, is located from below, and slag, as more light, is located, respectively, from above. The process of melting copper concentrate to produce copper matte, copper slag, as well as sulphur dioxide, is presented in Fig. 1.1.

Fig. 1.1 ‒ Flowsheet of smelting copper concentrate

The following furnaces are used as metallurgical units for melting copper concentrates: (i) reflecting furnace, (ii) autogenous melting furnace (Vanyukov furnace), (iii) electric furnace, etc. The choice of the furnace is determined by the characteristics of the particular concentrate being processed. 1.2. Composition of copper smelter slag Copper slags are characterised by a complex chemical and mineralogical composition, depending on the composition of concentrates, fluxes, and also the technological cycle of their producing [11-18]. The paper [19] contains information on the chemical composition of the copper slag obtained from the slag of some plants in Russia (RUS), Kazakhstan (KZ) and Uzbekistan (UZ) (Table 1.1). 9

Table 1.1

Chemical composition of copper smelter slag of some copper smelting plants [19] Name of copper plant Sredneuralsk (RUS) Krasnouralsk (RUS) Dzhezgazgan (KZ) Karabash (RUS) Almalyk (UZ) Karsakpai (KZ) Kirovograd (RUS) Balkhash (KZ) Mednogorsk (RUS) Irtysh (KZ)

Cu

Zn

Pb

Fe

S

SiO2

Al2O3

CaO+ MgO

0.64

4.63

-

32.5

1.57

33.9

6.6

5.0

0.43

3.0

-

34.0

-

34.0

10.0

7.0

0.55

-

0.3

18.8

-

53.2

8.5

19.6

0.3

2.5

-

34.0

1.5

33.0

8.0

7.1

0.6 0.47

0.46 1.2

0.2 0.59

33.0 20.0

1.3 -

34.0 48.1

7.4 14.5

5.0 13.0

0.33

3.1

-

30.0

1.0

-

-

-

0.4

0.53

0.06

22.0

0.28

40.0

10.0

-

0.25

0.35

0.04

32.0

1.0

37.0

-

7.0

0.5

6.6

0.8

32.0

-

31.5

4.5

4.5

Differences in the chemical composition of the copper smelter slag are due to the following factors: (i) the composition of copper concentrates, (ii) the composition of the charge, (iii) the characteristics of the melting unit (furnace), and (iv) the technological mode of the smelting process [20-27]. The content of alkali metals (not listed in Table 1.1) may also differ in the slag, depending on their content in the starting material [28]. At a low efficiency of the firing step preceding the melting of the material, the slag contains a relatively high amount of sulphur [29]. In addition, the long-term presence of slag in contact with the environment also affects the composition of copper slags, due to chemical and physical processes involving slag components [30]. There are two types of phases in slag: the primary phase formed as a result of the melting of copper concentrate in the furnace; and a secondary phase formed as a result of the environment impact (weathering). Fayalite and silicate glass are the main primary phases of slag. Pure crystals of fayalite (Fe2SiO4) correspond to the content of iron (II) oxide 10

of 70.51% and silicon dioxide of 29.49%. Olivine-group phases, mainly the kirschsteinite (CaFeSiO4) and the forsterite (Mg2SiO4) are also present in the copper smelter slag [31-34]. Spinels (MgAl2O4), hematite (Fe2O3), wüstite (FeO) and magnetite (Fe2+Fe3+2O4) are also quite common present [31-35]. Metallic elements are mostly associated with copper sulphides such as bornite, chalcopyrite and chalcocite, as well as phases such as pyrrhotite (Fe(1-X)S), sphalerite ((Zn,Fe)S), galena (PbS) and wurtzite ((Zn,Fe)S) [32-36]. The phase composition of copper slag strongly depends on the period of its production (Table 1.2) [37]. M. Shabalina studied the copper slags of the Sredneuralsk copper smelter [42]. The size of the copper minerals grains in the silicate slag mass represented by the fayalite, and glassy structure which does not exceed 0.08 mm with a predominant grain size of 0.005-0.04 mm. Copper minerals in the slag are 90% in the form of minute impregnations in silicate slag (fayalite, glass) and magnetite. Copper minerals are bornite, chalcopyrite, chalcocite, covellite (CuS), and cuprite (Cu2O). Chalcopyrite grains are characterized by a fineness of 0.005-0.01 mm, which accounts for 6% of the mass of copper minerals; bornite and chalcocite are in close relationship with chalcopyrite and rock grains, the total mass of which is about 23%. Covellin is represented by grains of 0.005-0.01 mm in size in the amount of 22%. Cuprite and metallic copper of 0.005-0.01 mm in size are about 3-5%. The content of magnetite in slags is 5-10%, precious metals are present as impurities in copper minerals. Iron is mainly represented by 90% fayalite, magnetite of 5-10%, insignificant amount of goethite, and pyrrhotite. K. Sanakulov and A. Khasanov studied the mineralogical composition of the copper smelter slag of several copper smelters [19]. The main minerals of the slag were fayalite and magnetite. Magnetite is present in the form of dendrites and octahedra, the sizes of which reach 250-280 microns. Most often magnetite is in the form of precipitates in crystals associated with fayalite and copper sulphides in sizes from 10-100 microns. Fayalit is a prismatic crystal, sometimes a grain, 25-50 × 100-160 μm in size (up to 30-50%) of the silicate phase, saturated with magnetite (≈30%). Crystals of magnetite of 25-65 microns in size have, basically, the shape of octahedra. 11

Table 1.2

Phase composition of copper slag collected from several industrial areas [обзор] Location (period of Phase composition slag generation) The Penn Mine Silicates: Zn-fayalite, willemite, feldspar, California, USA quartz, pyroxene. (XIXth-XXth century) Spinel: gahnite, franklinite. Sulfides: pyrite, chalcopyrite, sphalerite, galena, bornite, covellite, cubanite, wurtzite. Secondary phases: barite, cerussite, chalcanthite, hydrozincite, malachite, hydrous ferric oxides. Campigilia Marittima Silicates: olivine: (fayalite, kirschsteinite), pyroxene: (hedenbergite), quartz. district: Capattoli Sulfides: galena, sphalerite. Valley, Italy (XIth-XIIIth century) Huelva Province, Silicates: olivine (Fe-tephorite – Mn Cabezo Jure, Spain fayalite), pyroxene (diopside-hedenbergite), (3000 B.C.) ferrobustamite, pyroxmangite, titanite. Others: quartz, Ca-rich plagioclase. Oxides: magnetite, maghemite, cuprite, delafossite, fluorapatite, cassiterite, ulvöspinel. Sulfides: chalcocite and copper phase. Secondary phases: Fe-Mn oxides, chrysocolla, conichalcite, copper chloride. Vermont/Tennessee, Silicates: fayalite-forsterite, quartz, Fe-AlUSA Ca rich glass. (XIXth-XXth century) Oxides: spinels, hematite. Sulfides: pyrrhotite, Cu-Fe sulfides and pure metals. Secondary phases: amorphous Fe, Al oxyhydroxides, crystalline chalcanthite, siderotil, jarosite, brochantite, gypsum.

References [38]

[39]

[40]

[41]

In addition, small drops of delayed matte and secondary sulphide inclusions are present in considerable quantities in the slag. These inclusions are formed as a result of the release of dissolved sulphides from the slag during its crystallization. The slag of the reflective melting consisted of fayalite in the form of crystals of 30 × 150-200 μm in size and saturated with a silicate mass of magnetite of 20-30 μm 12

in size. Sulfide particles of 1-30 μm in size are distributed in the vitreous mass and are associated with magnetite crystals. Ye. Kharchenko has investigated the slags of the Balkhash copper plant (Central Kazakhstan) [43]. Copper and iron sulphides are present in slag in the form of chalcocite of non-stoichiometric composition Cu1-xS, chalcopyrite, bornite and pyrrhotite, amounting to 2-5%. Copper in the slag is 80% contained in the form of sulphides. A typical chemical composition of the copper smelter slag of the Balkhash copper plant is presented in Table 1.3. Table 1.3

Typical chemical composition of copper smelter slag produced at Balkhash copper plant [43] Component composition, % Slag source

Cu

Reflective 0.6 melting Autogenous 1.3 melting

SiO2

Fe

38.8

28.4

8.0

31.6

35.6

6.8

S

Pb

Zn

As

Sb

Au, g/t

Ag, g/t

6.6

0.9

0.2

0.8

0.07

0.04

0.10

4.3

2.0

1.6

0.3

2.0

0.3

0.03

0.88

9.58

Al2O3 CaO

It can be noted that the content of copper and zinc in the copper smelter slag is comparable to the content of these components in the ores. This fact makes it possible to treat copper smelter slag as an important resource for the recovery of valuable metals. 1.3. Physical and mechanical properties The physical and mechanical properties of the slag are highly dependent on the cooling method. Some physical and mechanical properties of copper slag are presented in Table 1.4. Air-cooled slag has a black colour and glassy appearance. The specific gravity varies with iron content, from 2.8 to 3.8. The unit weight of copper slag is higher than that of conventional aggregate. The absorption capacity of the material is very low (0.13%). The granulated copper slag is made up of regularly shaped, angular particles, mostly between 4.75 and 0.075 mm in size [44, 45]. 13

Table 1.4

Typical physical and mechanical properties of copper smelter slag [44, 45] Properties Appearance Unit weight Absorbtion, % Bulk density Conductivity Sp. gravity Hardness Moisture Water-soluble chloride Abrasion loss, % Sodium sulphate soundness loss Angle of internal friction

Characteristics Black, glassy, more vesicular granulated 2800-3800 kg/m3 0.13 144-162 lbs per cubic feet 500 μc/cm 2.8-3.8 6-7 Moh