Hall-Heroult Centennial: First Century of Aluminum Process Technology, 1886 - 1986 0873395409, 9780873395403

Table of contents :
Cover......Page 1
Title Page......Page 2
Copyright Info......Page 3
Abbreviations......Page 6
Preface......Page 4
Acknowledgements......Page 5
Pictorial Review......Page 9
Reduction Technology......Page 10
Carbon Technology......Page 38
Alumina/Bauxite......Page 52
Cast Shop Technology......Page 66
Environmental Control......Page 92
Invited Papers......Page 101
"Charles Martin Hall - The Young Man, His Mentor, and His Metal" by Norman C. Craig......Page 102
"Paul Heroult - The Man Behind the Invention" by Christian Bickert......Page 108
"History of Electrical Energy Consumption by Hall-Heroult Cells" by Warren Haupin......Page 112
"Evolution of Electrolytes for Hall-Heroult Cells" by N.E. Richards......Page 120
"Gaining That Extra 2 Percent Current Efficiency" by B.J. Welch......Page 126
"Carbon Electrodes in the Hall-Heroult Cell: A Century of Progress" by David Belitskus......Page 136
"Outlook of the Bayer Process" by Nils Oeberg and Rudolf O. Friedrich......Page 150
"Cast Shop Technology and Reclamation: 100 Years fo Progress" by Warren S. Peterson......Page 160
"Fluoride Control in the Aluminum Industry - 100 Years of Technology" by Patrick R. Atking......Page 168
"Environmental Control in our Industry - An Historical Overview" by J.P. McGreer......Page 174

Citation preview

H A L L -

8

1

C

E

8

N

H E R O U L T

1

6

T

E

N

8

9

N

I

6

A

L

Hall-Hbroult Centennial First Century of Aluminum Process Technology 1886 - 1986 The anniversary volume sponsored by the Light Metals Committee of The Metallurgical Society and presented at the 115th TMS Annual Meeting held in New Orleans, Louisiana, March 2-6, 1986. >

Edited by Warren S. Peterson, Consultant Metallurgical Chemical Processes 2113 East 37 Avenue Spokane, Washington 99203 and Ronald E. Miller Alcoa Technical Center Alcoa Center, Pennsylvania 15069

A Publication of TMS (The Minerals, Metals & Materials Society) 184 Thorn Hill Road Warrendale, Pennsylvania 15086-7528 (724) 776-9000 Visit the TMS web site at http://www.tms.org TMS (The Minerals, Metals & Materials Society) is not responsible for statements or opinions and is absolved of liability due to misuse of information contained in this publication.

Printed in the United States of America Library of Congress Catalog Number 2002109113 ISBN Number 0-87339-540-9 Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by TMS (The Minerals, Metals & Materials Society) for users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that the base fee of $7.00 per copy is paid directly to Copyright Clearance Center, 27 Congress Street, Salem, Massachusetts 01970. For those organizations that have been granted a photocopy license by Copyright Clearance Center, a separate system of payment has been arranged.

© 2002

If you are interested in purchasing a copy of this book, or if you would like to receive the latest TMS publications catalog, please telephone 1-800-759-4867 (U.S. only) or 724-776-9000, EXT. 270.

Preface One hundred years ago, two young men, oceans apart, independently devised a new method of making aluminum. This discovery in 1886 by Charles M. Hall in the United States and Paul T. HCroult in France gave the world the shiny light metal at costs that made it competitive in the market place. The Light Metals Committee of The Metallurgical Society is proud to celebrate the anniversary of this important event by publishing Volume I of Light Metals 1986 as a Centennial Edition. This special edition has two parts: a pictorial section and a series of invited papers. The objective is to highlight with pictures and text the important developments in the past one hundred years in the process metallurgy of aluminum. This includes the electrolytic method of making aluminum, emission and waste control measures in plant operations, manufacture of carbon electrodes, methods of processing bauxite and alumina, technology for melting and casting process ingots and processes for reclamation and recycling.

Pictorial Review This collection shows “how it was’ and “how it is now”, during the years in which the infant aluminum industry grew into a giant. Many companies from all over the world opened their archives to provide a large collection of photos from which to

make selections. The Russians were invited, but, regrettably, did not respond. Wherever possible, photographs were chosen which show people at work. This is fitting because this Centennial Edition is a tribute, not only to Hall and HCroult, but to all the men and women who have made contributions to the Aluminum Industry. In addition to material from industry, we have drawn heavily upon the literature for drawings and photographs to provide a visual record of the changing nature and scale of the numerous processes involved in making aluminum and aluminum process ingots.

Invited Papers An important part of this Hall-HCroult Centennial volume is a series of papers by experts in their fields. A pair of human interest reports tell us about the personal lives of Charles Hall and Paul HCroult at the time of their discovery. These reports are followed by papers describing developments in technology, equipment, and practice in the various areas of aluminum process metallurgy during the past one hundred years. Ronald E. Miller, Chairman Light Metals Committee iii

Acknowledgements Pictorial Review

iv

This Pictorial Review is the result of efforts Foster, R. Zabreznik (KACC); F.R. of many individuals and companies. Mollard (KBI); A. Nussbaum (Loma Without their willingness to open their files Machine); N. Bjune (Mosal); E. Keul (Norsk Viftefabrikk); Prof. N. Craig and send photos, this Review could not have been assembled. (Oberlin College); Christian Bickert We are indebted to the following com(Pechiney); A. Roy (Pyrotek); C.M. panies: Air Industrie, Alcan, Alcoa, Almeq, McMinn, S. Levy, J. Creel (Reynolds Alusuisse, Aluminum Association, Arc0 Metals); T. Matshushima (Showa); K. Metals, ASV, British Alcan, Consolidated Yamada (Sumitomo); G. Winkhaus (VAW); Aluminum Company (Conalco), ComW. Wagstaff (Wagstaff Engineering). monwealth Aluminum Company (Comalco), Also, special appreciation and thanks to Elkem, Granges Aluminum, Hazelett, Elizabeth Luzar, Gayle Geddes and the Hunter Engineering, Intalco, Japan TMS staff, and particularly to my wife. Aluminum Federation, Kaiser Aluminum Thanks to Interscience Publishers (Diviand Chemical Corporation (KACC), KBI sion of John Wiley & Sons), Aluminium (Cabot Corporation), Loma Machine, Verlag, Journal of Chemical and Mitsui Aluminum, National Southwire Metallurgical Engineering, and The Aluminum, Norsk Viftefabrikk (Flakt), Metallurgical Society for permission to use Pechiney, Properzi International, Pyrotek, materials from their publications. Reynolds Metals Company, Showa Invited Papers Aluminum K.K., Sumitomo Aluminum, Union Carbide (Linde Division), VAW, A special thanks is extended to Dr. Wagstaff Engineering. Subodh K. Das of Arc0 Metals for solicitI will not list, but hereby, thank all con- ing the invited papers, and to each invited tributors. A special acknowledgement is due author who contributed to this volume: to: Kjell Nielson (consultant); W.O. Stauf- P. Atkins, D. Belitskus, C. Bickert, N. Craig, fer (consultant); J. Peter McGeer, R. Friederich, W. Haupin, J. P. McGeer, G.G.Robertson (Alcan); Vergi Sapp, Ronald N. Oberg, W. Peterson, N. Richards, E. Miller, Gordon Bell (Alcoa); Ulrich B. Welch. Mannweiler (Alusuisse); Andreas Anderson W.S. Peterson (ASV); David Williams, H. McDonald R.E. Miller (Conalco); Gunnar Sem (Elkem); T. Pritchard, H.E. Miller, W. Kramer, B.J.

Table of Contents Abbreviations Abbreviations used in the captions to the photos and figures include: CWPB DC EM HDC HSS kA MW PBA SWPB

vss

center work prebake pot direct chill electromagnetic horizontal direct chill horizontal stud Soderberg kilo amperes mega watts prebake anode side work prebake pot vertical stud Soderberg

Page iii ........................ Preface ..... ............................ Acknow iv ... V Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pictorial Review Reduction Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbon Technology ... ...................................... 32 Alumina Bauxite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cast Shop Technology ........................................ . . . . . . . . . . . . . 86 Environmental Control . . . . . . . . . . . . . . . . . . . . . . . . . Invited Papers Charles Martin Hall - The Young Man, His Mentor and His Metal, N. C. Craig, Oberlin College. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Paul Hkroult - The Man Behind the Invention, C. Bickert, Pechiney . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . History of Electrochemical Energy Consumption by Hall-HC W. Haupin, retired from Alcoa . . . . . . . . . . . . . . . . . . . . . . . Evolution of Electrolytes for Hall-Htroult Cells, N. E. Richards, Reynolds Metals . . . . . . . . . . . . . . . . . . . . . . Gaining That Extra 2 Percent Current Efficiency, . . . . . . . . . . . . . 120 B. J. Welch, University of Auckland . . . . . . . . . . . . Carbon Electrodes in the Hall-HCroult Cell: A centu . . . . . . . . . . . . . . 130 D. Belitskus, Alcoa.. . . . . . . . . . . . . . . . . . . . . . . . . Outlook of the Bayer Process, N. Oeberg, R. Friederich, Swiss Aluminium Limited Cast Shop Technology and Reclamation: 100 Years of Progress, . . . . . . . . . . . . . . . . . . . . . . 154 W. S. Peterson, consultant. . . echnology, Fluoride Control in the Aluminu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 P. R. Atkins, Alcoa.. . . . . . . . Environmental Control in Our Industry - An Historical Overview, J. P. McGeer, Alcan International Limited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

V

1. Charles Martin Hall. Born December 6, 1863 in Thompson, Ohio and later moved with his family to Oberlin, Ohio. Graduated from Oberlin in 1885. Worked in family woodshed on aluminum experiment. Died December 27, 1914 at the age of 51.

2 . Original Hall patent. Alcoa.

3. Hall's home in Oberlin, Ohio with wood shed in rear 1886. Alcoa.

x

1

4. Paul Louis Toussaint Hiroult. Born April 10, 1863 in Saint Benin, Normandy. Worked in family tannery on aluminum experiment. Died May 9, 1914 at the age of 51.

5. Hkroult cell for pure aluminum circa 1892 Alcoa.

6. The Hkroult Tannery, Geulette, France, where Paul Hkroult discovered the electrolytic process for producing aluminum. Alcoa.

2

Pictorial Review

Reduction Technology

7

7 . Aluminum reduction pots at the Pittsburgh Reduction Company’s plant in 1889. Alcoa.

8. The Pittsburgh Reduction Company’s original office building in New Kensington, Pennsylvania. The struggling young company moved here due to expansion plans. Alcoa.

5

9. The 1890 site of the first European aluminum smelter near the “Rhinefall”, Switzerland. Alusuisse.

10. Report of analysis of raw materials, Neuhausen Plant, November, 1892. Alusuisse.

11. Hkrouit’s pots in Froges circa 1889. Pechiney.

6

12. Interior view of the Pittsburgh Reduction Company's steam powered dynamos in 1888. Alcoa.

13. Interior of the Pittsburgh Reduction Company's Smallman Street Plant showing aluminum reduction pot circa 1888. Alcoa.

14. Niagra Falls Pittsburgh Reduction Company Plant in the late 1890’s. Alcoa.

15. Pot with six cylindrical anodes corresponding to the first type of pot installed by Hkroult at the La Praz Plant in 1893. Pechiney.

16. Hkroult pot with four electrodes; his first attempt to lower the current density in 1892-93..Pechiney.

8

17. Alcan’s first smelter and cable plant at Shawinigan located on hilltop above powerhouses. Electricity was conducted uphill on bundles of aluminum rods erected 1901. Alcan.

18. The Pittsburgh Reduction Company’s smelter rises brick by brick, leading to the first aluminum production in Canada, October, 1901. Alcan.

9

19. The original Hall pot as installed in 1901 with its small pre-baked anodes up to 64 in number at Shawinigan. Alcan.

20. Hall pots at Shawinigan Plant during the early 1900s. Alcan.

21. Hall type aluminum smelting pots circa 1914. Alcoa.

22. Alcoa Tennessee

Smelting Works pictured here February 4, 1952, originally installed in 1914. Last line of so-called Hall type pots closed down after 38 years. Except for size, same type of cell had been used since production began in 1888. Alcoa.

10

23

23,24. Prebake pots at Hoyanger, Norway circa 1917. ASV.

25. 16kA PBA pot circa 1920 in Neuhausen, Switzerland. Alusuisse.

26. St. Jean-de-Maurienne Plant circa 1920. Pechiney.

11

21. Development of the aluminum furnace in Europe circa 1888-1933. Alusuisse.

28. 12 kA reduction cell with prebaked anodes, VAW Innwerk, Southern Germany in 1921. VAW.

29. The “Arvida type pot” which succeeded the old Hall pot used at Shawinigan. It had only fourteen larger rectangular-shaped prebaked electrodes. Alcan.

13

30. 30 kA HSS pot Sundsvall, Sweden in 1940. Granges Aluminum.

31. 3 kA pot with side tap prior to 1934. Showa Aluminum Industries K.K.

32. Tapping metal in early Japanese plant. Japanese Aluminum Federation.

33. Prebake pot line Ohomachi Works in 1934. Showa Aluminum Industries K.K.

14

34. 3 kA test pot circa 1934. Showa Aluminum Industries K.K.

35. 12 kA cell design in Japan circa 1934. Japanese Aluminum Federation.

36. The Electromechanical Society Aluminum Anniversary Dinner at the Waldorf Astoria on February 17, 1936. Arthur Vining Davis was seated at the main table (eleventh from right). Alcoa.

15

37. Tapping of round Soderberg pot in 1937. ASV.

38. Tapping of prebake pot in 1937. ASV.

16

39. In 1941 the pots were punched - Listerhill 35 kA HSS. Reynolds.

40. Sweeping alumina Listerhill 35 kA HSS - 1941. Reynolds.

41. Adjusting the voltage or anode position. Reynolds Metals - Listerhill, Alabama, plant - 1941.

17

42. Fifteen buckets of

alumina per pot. Reynolds Metals - Listerhill, Alabama plant - 1941.

43. Aluminum siphoned

from the cell into a crucible placed in a pit in the floor. Reynolds Metals - Listerhill, Alabama plant - 1941.

44. Sometimes manpower

was used to move the tapping crucible. Reynolds Metals - Listerhill, Alabama plant - 1941.

45. Siphon tap removing aluminum from a Soderberg pot - circa 1945. Alcoa.

18

46. Aluminum oxide being fed to a Soderberg pot - circa 1945. Alcoa.

47. Stirring a Soderberg pot to break the crust - circa 1945. Alcoa.

48. HSS pot line - WW 11. Left mechanical crust breaker; right siphon to remove aluminum from pot Alcan.

19

49. 32 kA HSS pot line 1948. ASV.

50. Development of VSS

pots - 1949. Elkem.

51. Tapping operation in Auzat out of a horizontal studs 30 kA pot - circa 1946. Pechiney.

52. Mechanical crust breaker on VSS Pot - 1949.Elkem.

20

53. 60 kA HSS pot line at Chalmette - 1953. KACC.

54. 60 kA HSS plant at Chalmette - 1953. KACC.

55. Crust breaking on a 100 kA Soderberg pot in St. Jean-de-Maurienne - 1952. Pechiney.

56. 75 kA VSS pot

1955-1960. VAW.

21

-

57. 150 kA VAW-type PBA pots - 1958. ASV.

58. 150 kA VSS potline 1958. ASV.

59. Original no. 1 VSS potline, 40 kA, 1955-1964.4oooO A Soderberg pots. Initial capacity of plant 12,000 tons/annum.

60. “Hot-change” conversion of no.1 line pots. Replacement of anode superstructure without cooling of bath.

22

61. No. 1 line operating as pre-baked - 1964-1981.

62. 85 kA installed between 1962 and 1981 in lines 2, 3 and 4. KACC design. Comalco Aluminum Smelter at Bell Bay on Tasmania North Coast. Comalco.

63. Siphoning metal at Kittimat VSS plant - 1965. Alcan.

64.135-150 kA PBA potline

- startup 1968. ASV.

23

65. 150 kA PBA plant. Hawesville, Kentucky, USA - 1970. National Southwire.

66. Ore feeding. Intalco -1960s. Painting by J. Johnson.

67. Crustbreaking. lntalco -1960s. Painting by J. Johnson.

24

68. Ardal line 1 , 150 kA PBA - 1970-1971. ASV.

69. 130 kA pot - 1972. Mitsui Aluminum.

70. Molten aluminum being siphoned from a PBA cell circa 1977. Alcoa.

71. Lynnmouth, United Kingdom, potroom - 1972. Alcan.

25

72. P-155 155 kA potline at Badin - 1964. Light Metals 1980 (TMS-AIME), page 404.

73,74. Alusuisse 170 kA potline and multipurpose bridge-crane - 1970s - Light Metals 1977 (TMS-AIME), vol. 1, pages 62-63.

75. Temperature studies on Alcan 150 kA prebake cell late 1970s. Light Metals 1980, (TMS-AIME), page 305.

26

76. Workman removing butt from pot - late 1970s. Alcoa.

77. The 180 kA pot of Alusuisse - 1980s. Light Metals 1983 (TMS-AIME), page 603.

78. Pechiney 180 kA prototype pots, LRF Centre Saint Jean du Maurienne late 1970s. Light Metals 1982 (TMS-AIME), page 449.

79. 180 kA cell with multipurpose crane, VAW Innwerk, 1984. VAW.

27

80. 200-210 kA trial pots 1978-80. ASV.

81. 200 kA pot - 1984. Mitsui Aluminum.

82. KACC 195 kA PBA Cell

- 1980s. Light Metals 1984 (TMS-AIME), page 455.

83. Boyne Island potline near Gladstone, Queensland

- 1983. Comalco.

28

84,85. Valesul (Reynolds

P-19) 155 kA pot at Santa Cruz, B r a d - early 1980s.Light Metals 1984 (TMS-AIME), page 435.

29

86. Wheel crust breaker 1980s. ASV.

87. End crust breaking machine - 1980s. ASV.

88. Anode changing machine

- 1980s. ASV.

30

Carbon Technology

39

Coal Tar Pitch 89. Batch tar still,

1900-1940. Light Metals 1985, (TMS-AIME) page 191.

33

Coke Calcination 90,91. Coke calcination circa 1917. ASV.

92. Coke kiln at Norco Plant installed in 1965. KACC.

34

Green Anode and Cathode Preparation 93. Anode blocks circa 1918.

ASV.

94. Anode press circa 1917.

ASV.

95. Ramming cathode blocks circa 1918. ASV.

35

96.Anode press circa 1937. ASV.

97. Anode presses circa 1935. ASV.

36

99. In 1977, baking of cathode carkBoris up to four meters long. ASV.

98. Manufac:ture of anodes using vibrati on system in 1960. ASV.

100. During, t h e 1980s, the Showa Savclie Plant in Nagahama, Japan, was responsible for the production of cath odes. Pechinev.

37

Anode Baking

101. Electrode baking furnace circa 1917. ASV.

102. Electrode baking furnace circa 1935. ASV.

103. Electrode baking furnace circa 1919. ASV.

38

104. Anode baking furnace circa 1937. ASV.

105. Hydraulic potlining machine circa 1984. ALMEQ, Norway.

106. Crane for handling full row of anodes in and out of baking furnace in 1977. ASV.

39

Anode Developments

107 - 118. Changes in anode design from the late 1880s through mid 1960s. Jean Grolee, Pechiney.

I ~

114

42

119. 2:3 kA horizontal stud Soderl.)erg electrode circa 1930s. Elkem.

120. 35 kA continuous prebake anode system circa 1960. VAW.

121. 1937 cell with round Soderberg anode. ASV.

122. 100 kA continuous prebake anode system. VAW.

43

123. Anode removal by crane during the 1980s. Light Metals 198s (TMSAIME), page 943.

125. Typical 1970 anode rodding room at National Southwire Aluminum, Hawesville, Kentucky.

124. Baked anodes made with 86% butts during the 1980s. Light Metals 198s (TMS-AIME), page 942.

44

Alumina/Bauxite

126a Alumina 126. Angle of repose of typical aluminas: (a) sandy; (b) floury; (c) starchy. Extractive Metallurgy of Aluminum, vol. I , Alumina (Interscience), 1963, page 222.

b 127. Bayer process equipment used prior to 1930. The Aluminum Industry, vol. I , Aluminum And Its Production, McCraw-Hill, 1930. (a) Concentrating and washing aluminum hydrate, page 131. (b) Digester room in alumina works, page 128. (c) Filter presses for red mud, page 129. (d) Calcining kilns for alumina; view from feed end, page 132.

41

C

128. Horizontal digesters circa 1940 - Arvida Works. Alcan.

129. Pedersen Process for producing alumina Hoyanger, Norway; Plant commissioned 1928. ASV.

130. Cleaning Kelly presses circa 1940 - Arvida Works. Alcan.

48

131. Mud settlers and precipitators. Alcan Jamaica.

132. Top view of batch precipitator. Alcan.

133. Settler, batch precipitator. Alcan Jamaica.

49

134. Ball mill for grinding bauxite was installed in 1940. KACC.

135. These vertical digesters were installed in 1968. KACC.

136. In 1940, this multideck washer was installed. KACC.

137. Evaporator units installed in 1940 pictured with alumina cars in foreground. KACC.

50

138. In 1951, the typical approach to storing alumina was in bags. ASV.

139. Bulk handling of alumina was introduced in 1954. ASV.

140. Pneumatic system for handling alumina circa 1954 ASV.

51

141. Vacuum drum filter for red mud separation . VAW Lippewerk.

142. Alumina hydra te filtration circa 1955. VA W Lippewerk.

143. Transportation of filtered red mud for disposal circa 1960. VAW LiIPpewerk.

52

144. Modern Bayer plant at Elbe riverside was installed in 1973. Aluminum Oxide Stade GmbH, Stade. Plant to the right is the VAW Smelter.

145. Fluid bed calciner circz 1980. Sumitorno Al.

146. Bauxite slurry heater circa 1970. Sumitorno Al.

147. Evarton Alumina plal installed 1967 in Jamaica. Alcan

53

Bauxite 148. Mining of bauxite at Bauxite, Arkansas - 1920 1930s. Alcoa. (a) hand mining operations separating rocks from fines, November 28, 1922. (b) road building at Bauxite, Arkansas in Novemoer 1922. (c) operating empire drill in December 1922. (d) shovel leading ore at the Julia Mine on September 12, 1924. (e) loading and hauling operations in February 1930. (f) auger drilling in Neilson underground mine June 10, 1938. Underground mining was discontinued in Arkansas during the mid 1950s.

54

55

149. Exploration and discovery of bauxite r eserves in the tropical forest 1NaS difficult work. Earlier hand drills were replaced b! i diamond drills (pictured) driven by mechanical power units. British Guiana. 1936. Alcan.

150. Bauxite mining in Georgia, 1920 - 1930. Alcoa.

56

151. 1936 bauxite mining in British Guiana. Alcan.

152. Bauxite exploration camp, Paranam, Surinam, circa late 1940s. Alcoa.

57

153. Bauxite mining in Brignolis, France in 1950. Alcan.

154. Recent bauxite mining in Jamaica. Alcan.

155. Bauxite loading, Paranarn, Surinam, circa late 1940s. Alcoa.

58

Cast Shop Technology

Melting 156. Rousseu’s furnace - early 1900s- retort is graphite and furnace fired with coke. “Ingots up to 1.1 x 1.1 x 0.12 meters weighing 300 to 400 kg. may be cast for rolling sheets” - Chemical and Metallurgical Engineering, 19 (12) 1918.

157. Aluminum ingots being hauled between the old Niagara no. 1 and no. 2 works of the Pittsburgh Reduction Company (Alcoa) before the turn of the century. (Small building in right foreground was no. 2 works office). Metal made at no. 2 was taken to no. I for remelting before shipment to customers. Hauling was done by William Young Transportation, Inc., before the company aquired a team of horses. Circa late 1890s. Alcoa.

61

158. Oil-fired melting furnace for aluminum - 1917. ASV.

159. Charging a remelt furnace, Alcoa’s Tennessee plant, circa 1920. Alcoa.

160. Casting tilt nnold ingots for rolling - 1923. ASV.

62

161. Removal of skim from casting furnace - 1926. ASV.

162. Casting pig ingots 1933. ASV.

163. Early electric melting furnace for casting rolling slabs - 1937. ASV.

63

164. “Heading up” a tilt mold sheet ingot at Australuco (Sidney) - 1945. Alcan.

165. Pouring foundry ingots 1945. Alcoa.

-

166. Early electrically heated tilting furnaces for melting aluminum at Nordisk Aluminum Industries - 1948. Alcan.

64

169

167. Loading 50 Ib. tri-lock ingot into melting furnace at Unidare, Ireland plant 1965. Alcan.

168. Round melting furnace, top charging, 100,ooO Ib. capacity - installed 1963. KACC.

169. Bucket for placing charge into round furnace by crane - 10,OOO Ib. capacity. KACC.

65

170. Transfer of molten aluminum to casting furnace 1982. ASV.

171. Induction melting furnace for aluminum-lithium alloys, at Kitts Green plant 1980s. British Alcan.

66

I173

Metal Treatment 172. First commercial in-line system for fluxing aluminum (flux bay outside furnace) 1952. KACC.

173. In-line fluxing system 1970s. Alcoa 622.

174. In-line fluxing, (a) SNIF “T” system - Union Carbide, Linde Division, (b) Alpur fluxing system Pechiney, (c) Alcoa 94 process, (d) Alcoa 181 process, (e) Alcoa 528 process, (f) Dufi filter process Alusuisse.

67

174d

174c

/FLUXING GAS n

TABULAR ALUMINA FLAKE TO CASTING UNIT

TO CASTING UNIT

IFURNACE HOLDING 1-1

TABULAR ALUMINA BALLS

TABULAR I ALUMINA BALLS

174f

174e

528

Petrol coke 1

\ Corundum

68

175. Placing Sellee disposable ceramic filter in transfer trough. Conalco.

176. Ceramic control devices and cloth filters - 1980. Pyrotek

69

1 /b

117. System for continuous addition of grain refiner alloy rod to aluminum being cast -1980s. KBI.

178. Sections of cast extrusion billet illustrating the importance of proper grain refining materials and practices. KBI.

70

Direct Chill Casting 179. Early direct chill (DC) casting systems for aluminum, (a) and (b) Berthold Zunckel (1935), (c) Vereinigte Leichtmetall Werke (1936), and (d) Alcoa (1938 patent based on 1935 work at Massena, N.Y.) -Handbuch des Stranggiessens, p. 125.

180. DC casting of extrusion billet at Australuco plant -1942. Alcan.

179

71

A

n

181. DC billet caster fed by induction furnace - 1950s. Loma.

182. First successful DC casting of 32 inch diameter 7075 alloy ingots - ca 1952. KACC, Trentwood.

72

183. DC casting sheet ingot 20” x 45” in cross section ingot - installed 1963. KACC, Trentwood.

184. Tilt back mold system for DC casting sheet ingots -installed 1963. KACC.

185. Horizontal DC cast remelt ingot, after casting cut to customer specifications - 1961. ASV.

73

186. Horizontal DC casting -KACC Newark - 1960s. KACC.

187. Horizoiital D(2 sheet ingot Icasting - 1963. Alcoa.

14

188. DC casting of s1heet ingots - Howrnet (now Alurna) - 1980. Lorna.

189. DC cast extrusiiIn ingot, vacuum furnace in background - 1970s. ASV.

lma, b. DC casting of extrusion billet using hlot top system with Air-Slip molds at Dubai Aluminum - 1985. Wagstaff.

76

Electromagnetic Casting 191. Basic EMC patent, Z.N. Getselev et al., September 1969 - U.S. Patent 3, 467, 166.

192. Electromagnetic casting of sheet ingot at Trentwood Works - 1982. KACC.

77

193. Comparison of surfaces of rolling ingots and edges of sheet at hot line between electromagnetic and DC casting processes - 1982. KACC.

194. 3004 alloy sheet ingot EMC cast - Conalco, Hannibal Plant, Ligh/ Metals 1985 (TMS-AIME), p. 1307.

195. Alusuisse EM caster at a licensee plant - 1980s Alusuisse

78

Continuous Casting 1%. Continuous SPA, Milan, Italy - Early 1950s Properzi aluminum casting machine. Properzi.

197. Pechiney jumbo 3C continuous caster for aluminum strip - 1970s -Light Metals 1978, vol. 2 (TMS-AIME), p. 299.

198. First experimental Hazelett casting machine for aluminum strip - 1948. Hazelett.

79

199. Twin belt castiing machine (Model 24) for casting 66 in. wide iilurninum strip at Leichtmetall Gesellschaft, Essen, West Germany. 1972.

80

Recycling Loop Reclamation and Recycling

203. 30” x 62” 3004 alloy sheet ingot for can stock 1980s. Arco Metals.

204. The beginning of the recycling process - 1980s. Reynolds.

205. Reverse vendingaluminum can recycling machine - 1980s. Reynolds.

206. “.

,

. Modest at

first”.

207. “. . . and growing”-aluminum can recycling center - 1980s. Alcoa.

208. “. . . and growing”-compressed and baled scrap aluminum cans before remelting - 1980s. Alcoa.

210

40

209. Charging a furnace at the Bellwood, Virginia reclamation plant - 1980s. Reynolds.

___-....26

210. Technology specific to can recycling was developed December 1978 - U.S. Patent 4,128, 415. Alcoa.

81

40

4)

TO

72

ICollection

I

Processing

82

211a. b. Skim/Dross Reclamation. Rotary barrel furnaces for reclaiming aluminum from scrap, skim and dross - installed 1964. KACC Trentwood.

212. System for melting scrap aluminum chips; chips fed into stream of molten aluminum; pump provides closed loop circulation of metal, 1970s, Light Metals 1978, vol. 2 (TMS-AIME) p. 265.

83

Safety 213. Cast shop worker -

attire includes safety glassed and face shield, jacket and pants made of fire-resistant cloth, and approved foot gear - 1980s. KACC.

214. Preheating of sow

before charging into molten aluminum - Guidelines for Handling Molten Aluminum Aluminum Association 1980 (All materials which are added to molten aluminum or placed in contact with molten aluminum must be preheated (dried) first to ensure they are free of water and films of moisture.

84

Environmental Control

215. Pot gas removed at A W t - HSS Pots -1930s. Elkem.

216. Gas cleaning at Rheinfelden during 1936.

Elkem.

217. Roof scrubber in reduction plant during the 1960s.

Japan Aluminum Federation.

87

218. Roof scrubbers in PBA plant during the late 1950’s.

Primary emission control added later. Design Of Metal Producing Processes (AIME 1969), page 171. 219. Primary emission control for VSS in the 1950s. Extractive Metallurgy Of

Aluminum. (Interscience Publishing), vol. 2, page 100. 220. Roof scrubber in HSS plant in the 1950s. Extractive Metallurgy of

Aluminum. (Interscience Publishing). vol. 2, page 101. 221. Natural ventilation in VSS plant installed in 1955.

Design Of Metal Producing Processes (AIME 1969), page 168.

222. Primary emission con-

trol and roof scrubber in VSS plant installed in 1960. Design Of Metal Producing Processes (AIME 1969), page 170.

88

224

Emission control systems at various locations from 1962 to 1982. Air Industrie.

223. 1962 HSS, twelve AIRMIX units in parallel at VAW Toging, Germany.

224. 1973 SWPB pots, dry scrubbers at Intalco Ferndale, USA.

225. 1963 VSS pots, electrostatic precipitator and two scrubbers at Pechiney Lannemezan, France.

89

221. 1981 CWPB pots, dry scrubbers, Alussuisse-STEG.

228a, b. Reclamation activities associated with bauxite mining in 1972. Alcoa. Bauxite. Arkansas.

229. Alcoa’s reforestation project after bauxite mining in.

91

230. In 1976, scrubbers removing 88% o f particulates in smoke from carbon baking furnaces at Massena. New York. Alcoa.

231. Boxlike electrostatic precipitators at Bauxite, Arkansas in 1973. Alcoa.

92

232. In 1984, operating Lurgi system dry scrubbing unit. VAW.

233. Air to water heat exchanger mounted on clean gas exit at top of dry scrubber filter chamber. 5MW recovered as hot water (6070°C) from 46,000 metric tons per year potline or about 1 KWH/kg metal. In. stalled in 1982. ASV.

234. In 1970-71, dry scrubber installed after original wet scrubbers. ASV.

235. Gas cleaning anode baking furnace, cooling tower, electrostatic precipitator, sea water washing tower and stack, and electrostatic filter erected during 1970 and 1971. ASV.

93

235. During the late 1970s, the Hartmann Pneumatic Unloader vacuum pickup nozzles reduced worker’s exposure to particulates. Light Metals 1981 (TMS-AIME), page 993.

236. Emission control system

on carbon baking furnaces circa 1976. Alcoa.

237. System for removal of tar, fluorides and SO, from anode baking plant circa 1977. Flakt.

94

Invited Papers

Charles Martin Hall The Young Man, His Mentor, and His Metal Norman C. Craig, Professor of Chemistry Oberlin College, Oberlin, Ohio 44074

Charles Martin Hall

The history of Hall’s discovery and development of the electrolytic process for refining aluminum is described. It begins in the fall of 1880 when two young men met on the campus of Oberlin College. Charles M. Hall was a local youth who was selfeducated in science and eager to make his mark as an inventor. Professor Frank F. Jewett was an exceptionally well-educated chemist and mineralogist who had studied in Germany and taught in Japan. This account includes a reconstruction of the chemistry Hall explored until he achieved the successful experiment on February 23, 1886. It outlines the steps in the commercialization of the process, of which the production of the first ingot of aluminum metal in Pittsburgh on Thanksgiving Day 1888 was the highlight. Hall’s personal qualities, which were so different from those of his French counterpart, Paul Hkroult, are brought out.

Introduction One hundred years ago aluminum was a semiprecious metal. It was produced commercially on a small scale by Henri St. Clair Deville’s chemical reduction method, which was the reaction of metallic sodium with anhydrous aluminum chloride. Aluminum sold for $12.00 per pound; silver was only $15.00 per pound. When the Washington Monument was completed in 1884, a small, six-pound pyramid of ornamental aluminum metal was placed at the very top. Intended as the tip of a lightning rod system, this aluminum cap was a practical application of the high electrical conductivity as well as the corrosion resistance of this remarkable new metal. Meanwhile, many investigators, mostly in Europe, sought economical methods to wrest aluminum from its abundant ore, which, as Deville had remarked, “could be found in every clay bank.”

In 1880 two men who were interested in aluminum metal had met on the campus of Oberlin College, near Cleveland, Ohio. The older was a world traveler who was as well educated in chemical science as any young American academic of his day. The younger was a local youth who was self-educated in science and intent on becoming a successful inventor. The outcome of their association over the next five-and-one-half years was the discovery of a practical electrolytic process for reducing aluminum oxide to aluminum metal. Within three more years the younger man had developed this new process from the laboratory scale to a practical industrial scale. As a consequence, aluminum metal was swiftly transformed from a curiosity into a widely useful material, and the younger man was launched on a successful career in technology and industry.

96

Professor and Student Frank Fanning Jewett had received his undergraduate education and some graduate in chemistry and mineralogy at Yale University. For two more years, 1873 to 1875, he had studied chemistry at the University of Gdttingen in Germany. There he had become well acquainted with current European science, and, in particular, he had learned about the promise of aluminum. What is more he had met Friedrich Wdhler, who had isolated aluminum in 1827, and he had obtained a sample of aluminum metal. Jewett returned to America to become Wolcott Gibbs’ private assistant at Harvard University. Soon he was nominated by the president of Yale to teach at the Imperial University in Tokyo, Japan, where, from 1876 to 1880, he was one of the small group of Westerners who initiated the teaching of science at that university. In 1880 at the age of 36 he became the professor of chemistry and mineralogy at Oberlin College.

97

Curricular and Extracurricular Studies

For example, he prepared pure aluminum oxide from alum and washing soda, which were common household substances of the time. In preparing some chemicals such as alumina and in other ways, Hall was helped by his older sister Julia Hall, who had studied chemistry and who followed his experiments closely. Through most of his life Hall maintained a lively correspondence with his sister. She saved these letters and some of his notebooks. Together these materials helped provide an exceptional record of the day-to-day life of an inventor. At the beginning of his investigations Hall explored chemical reduction methods for obtaining aluminum. He tried, as had others, to adapt to aluminum oxide the graphite-based reduction methods that were used for obtaining iron and other metals of intermediate chemical activity. In a second initiative, he attempted to find an inexpensive way to prepare anhydrous aluminum chloride for use in the Deville process. He also treated cryolite (A1F3.3NaF) with sodium metal but obtained disappointing results.

Hall did not take a formal course in chemistry until two years later-the junior year was the customary time for such study in those years-but, under Professor Jewett’s guidance and encouragement, he worked on aluminum chemistry in Jewett’s laboratory and in his own laboratory at home. He also began investigations in two other notable areas of invention: one was tungsten metal for filaments in electric light bulbs, and the other was fuel cells, in which he hoped to use hydrogen gas or illuminating gas to produce electrical energy directly. (Some of Hall’s ideas were not so good. In the late 189O’s, perhaps encouraged by the then current discoveries of natural radioactivity, he thought he had found evidence of the transmutation of iron into platinum metals.) When Hall finally took the chemistry course in 1882-83, he reportedly heard Jewett lecture on the chemistry of aluminum, display his sample of the metal, and predict the fortune that Charles Martin Hail had learned some awaited the person who devised an chemistry as a serious-minded youth in the economical method for winning aluminum town of Oberlin by reading in 1840’s textfrom its oxide ore. To a fellow student Hall book found on the shelves of his minister declared his intention to be that person. father’s study and by doing experiments at It is likely that Hall spent the following Electrolysis Experiments home. This was the beginning of a lifelong year, when he was not enrolled in college, Finally, Jewett and Hall recognized that enthusiasm for doing experimental work in largely engaged in experiments. He returned electrolysis could provide the potent reducthe laboratory. An avid reader in many tion conditions that were needed. Perhaps to college in the fall of 1884 and was fields, he also followed closely the popular graduated in June 1885. Eight months later, pertinent to this decision was the accessionliterature of invention in Scientific in the woodshed laboratory attached to his ing in 1883 by the college library of the American. Young Hall already knew about family’s home, he obtained his first globules book, The Theory and Practice of Electrothe romance of aluminum when, as a of aluminum metal. He was barely 22 years deposition by George Gore (Houlston and 16-year-old freshman in college in the fall of old. Wright, London, 1859). Whatever the par1880, he went to the chemistry laboratory to To accomplish this, Hall had not only to ticular sources, we may presume that Hall obtain some items for his experiments at devise the method to isolate aluminum had access to much scientific literature from home. There he met Professor Jewett. Jewett’s personal library and from the colmetal but also to fabricate most of his apparatus and prepare many of his chemicals. lege’s library.

To obtain electricity for electrolysis experiments in a small college town in the 1880’s one had to construct batteries. Hall and Jewett used the classical Bunsen battery, which consists of a zinc electrode in a 1:10 dilute sulfuric acid solution surrounding a porous ceramic cup which contains a carbon-rod electrode in concentrated nitric acid. (This description of the Bunsen cell can be found in Jewett’s Laboratory Exercises in inorganic Chemistry.) This cell has an output of about 1.9 V and a good current capacity. Nonetheless, assembling enough of these cells to provide adequate electrical energy for aluminum production was a large undertaking. About one pound of zinc metal would have been consumed in securing one ounce of aluminum. In his first experiment of this type Hall attempted electrolysis of aluminum fluoride dissolved in water. Unfortunately, this electrolysis system gave only unwanted hydrogen gas and aluminum hydroxide at the cathode. However, the selection of a fluoride was probably a turning point in his work. Most likely he chose aluminum fluoride because, unlike aluminum chloride, it had not been tried before. Using aluminum fluoride was certainly not a matter of convenience because he had to prepare it from hazardous hydrogen fluoride in special lead vessels in Jewett’s laboratory. Nonetheless, aluminum fluoride was easier to make from aluminum oxide than was aluminum chloride. Hall did the first electrolysis experiments in Jewett’s Iaboratory during spare time in his senior year of 1884-85, but after his graduation in June 1885 he continued work fulltime in his woodshed laboratory. Experimentation with fused salts as solvents was Hall’s next, important step. As

his sister reports, it is possible that he came to this crucial idea while playing classical sonatas on the family’s “ancient” piano (Throughout his adult life HalI, who was an accomplished pianist, played the piano in order to renew his spirits.) To work with fused salts of fluorides he had to build a furnace capable of producing and sustaining higher temperatures than the coal-fired, bellows-driven furnace of his earlier experiments. For this purpose he adapted a second-hand, gasoline-fired stove to heat the interior of a clay-lined iron tube. Despite the higher temperature of this furnace, he was unable to melt some of the fluoride salts he tried. Such was the case with calcium fluoride (melting point 1360°C), aluminum fluoride (m.p.129l0C), and magnesium fluoride (m.p. 1266°C). Otherspotassium and sodium fluorides-melted in the furnace but did not dissolve useful amounts of aluminum oxide. Hall and Jewett understood that the salts had to be of metals that were more electropositive than aluminum. No doubt they were aware of the earlier work on the electrolysis of aluminum chloride/sodium chloride melts by Deville and Bunsen and on the electrolysis of cryolite by Deville. Certainly they recognized that the flouride salts had the advantage of not being hygroscopic.

ide. He did this signal experiment on 10 February 1886. Six days later on 16 February, Hall first attempted to prepare aluminum metal by fused-salt electrolysis. He used graphite-rod electrodes, dipping them into a fiery solution of aluminum oxide in molten cryolite in a clay crucible. Hall let the current pass a while. In his sister Julia’s presence he poured the melt out in a frying pan and broke apart the cooled mass. They found only a greyish deposit on the negative electrode-a deposit that did not have the shiny metallic apperance of aluminum. After several repetitions, Hall reaIized that this deposit was probably eIemental silicon originating in the silicates of the clay crucible. Had he not been acquainted with the appearance of metalic aluminum from seeing Jewett’s sample, Hall may have been slower to interpret this false result.

Success

Ha11 then fashioned a small crucible of graphite to serve as a Iiner for the clay crucible. The first electrolysis experiment with this new system was performed 23 February 1886. The electric current ran for several hours. Once again in his sister’s presence, he cooled the melt and broke it open. This time they found several small silvery globules. Immediately he took these Hall moved on to experiments with synto Professor Jewett, who confirmed that thetic cryolite, the double fluoride of they were aluminum. sodium and aluminum. Probably he was Because of his familiarity with the aware that mixtures of salts could have literature of invention, Hall was aware of lower melting points than the constituent the need to record definitively the date and salts. Also Hall had worked with cryolite in the essentials of important discoveries. He some of the chemical reduction experiments. did not regard his regular notebook entries Hall synthesized his cryolite, found that he as sufficient. Consequently, he mailed two could melt it (m.p.l000”C), and showed letters to his brother George Hall, who was that it was a good solvent for aluminum ox- a minister in Dover, N.H. The second of

98

these letters, mailed on 24 February, described the technical aspects of the discovery in considerable detail. As requested, George Hall kept these letters.

Commercialization

99

Hall was as adept in overcoming the obstacles to commercialization of his new electrolytic process as he was in discovering it. He survived the defection of his original Boston backers and an awkward, year-long association with the Cowles Electric Smelting and Aluminum Company of Cleveland. He also withstood a challenge to his application for US patent rights by the Frenchman Paul Hkroult, who held a French patent dated 23 April 1886 that included a similar electrolytic process using cryolite and aluminum oxide. (Remarkably, HCroult was the same age as Hall.) Julia Hall and Professor Jewett contributed to the testimony before the patent examiner that established the priority of Hall’s discovery in the US on 23 February 1886. The postmarked letters to George Hall were also important evidence. Subsequently, there were two more legal struggles, which were with the Cowles Company, over the Hall patent rights. In the first trial, presided over by Judge William Howard Taft, later President Taft, Hall’s interests were upheld. The outcome of the second trial, in which an additional patent on electric-arc furnaces that had been secured by the Cowles Company played a role, was finally a “draw” in 1903. (The records of these trails are another detailed source of information about Hall’s work.) A group of investors, organized by Captain Alfred Hunt in the summer of 1888, provided the crucial financial backing and patient support for Hall while he worked at

the fledgling Pittsburgh Reduction Company, the predecessor of Alcoa, to bring his process from the laboratory to the commercial scale. Hunt, an MIT graduate and former Army engineer, was experienced in the metals business. By Thanksgiving Day 1888 with the able technical assistance of Arthur Vining Davis, Hall was producing aluminum on a pilot plant scale on Smallman Street in Pittsburgh. Soon after achieving this result, Hall confirmed his earlier belief (letter to his sister in 1886) that the process could be simplified by using only the resistive heating in the reduction pots to achieve and maintain the molten state. (This feature of the commercial process was claimed as the prior discovery by the Cowles Company in the second lawsuit.) He also found that larger pots worked better than the smaller ones that had caused difficulty in the initial scale-up experiments. The electricity for the process was obtained from new steam-engine-driven Westinghouse dynamos. Indeed, major developments in the manufacture of such dynamos in the preceding decade were a critical technological contribution to the rapid commercialization of the whole field of electrometallurgy in the last decade of the nineteenth century. Within two more years Hall and his partners were producing aluminum metal in quantity, producing it faster than markets for its use could be developed. Meanwhile, Hkroult in France was preoccupied with the commercial development of that part of his patent which was concerned with an electric-arc aluminum-alloy process, one similar to that employed by the Cowles Company. He was not involved in making any pure aluminum on a commercial scale until the end of 1889. According to J. W. Richards the author of Aluminium, Third

Edition, 1895, “it appears that Hkroult was not aware of the possibilities of his process until Hall’s process showed the way.”

Recognition Among scientists, engineers, and industrialists Hall soon gained wide recognition. He was elected to membership in AIME in 1890. He was a charter member and vice president of the American Electrochemical Society upon its founding in 1902. He was also a member of the American PhiIosophical Society and of the Franklin Institute. In 1911 Hal1 became the fifth recipient of the Perkin Medal, which was awarded for “valuable work in applied chemistry,” by the combined action of the Electrochemical Society, the American Chemical Society, and the Society of Chemical Industry (Great Britian). Paul HCroult attended the award ceremony in New York and made a graceful contribution to the speeches. Hall responded with equal warmth. How could it be the Paul Hkroult in France and Charles Hall in the US made nearly simultaneous, yet independent discoveries of the same process for refining aluminum? Such simultaneity in scientific discovery is not infrequent when “the time is right.” In this case, many factors seem to have contributed to the time being right. Finding an economical process for refining aluminum was widely recognized as a prime target for invention. Electrochemistry had begun to mature as a science. Large electricity generating dynamos had recently come into commerical production. Interest had been aroused in the chemistry of fluorine-containing substances. Perhaps more surprising to a distant scientific observer is that one of the successful inven-

tors was working in Paris while the other was located in a small U.S. college town. Yet, this account has shown that Hall had access to the latest in scientific thought through Jewett. Hall, like HCroult, was a resourceful experimentalist with a burning desire to be a successful inventor and businessman.

The Person A number of Charles Martin Hall’s personal qualities have emerged in the description of the discovery and commercialization of the electrolytic process for refining aluminum. However, we shall conclude this account with a few more remarks about Hall the person. Throughout his life colleagues found him to be serious-minded and exceptionally hard-working. According to his brother, “The sports and games in which youth of his day delighted had no place in his thoughts.’’ So God-fearing was Hall that in writing letters he referred to the devil as the d 1. Until he was 39 years old he lived frugally in boarding houses, although his skill as a player of classical music led him to furnish these rooms with rented pianos. As he prospered in the aluminum industry and had increasing opportunities to travel, he satisfied his interest in concert music and opera by attending performances in the great halls of the United States and of Europe. And, he developed a collector’s eye for fine oriental rugs and porcelains. Hall had intended to marry his college sweetheart, Josephine Cody. Though engaged for a while, she grew tired of waiting for Hall to make his fortune and broke the engagement. Disappointed, Hall found solace in his strong ties to his family and in his continuing interest in Oberlin College, for which he served as a

trustee from 1905 until his death. In characterizing this latter interest, his brother commented, “the College was to him wife and children and all, - his life.” Upon his death in 1914 at the age of 51, Hall left most of his material possessions and a substantial part of his Alcoa stock to Oberlin College. Another significant part of his bequest went to Berea College in Kentucky. Much of the rest went to other educational enterprises at home and abroad.

100

References 1.

Junius Edwards, The Immortal Woodshed, (New York, New York; Dodd, Mead, and Company,

2.

George E. Hall, Biographical sketch of Charles M. Hall, read by Henry Churchill King at the January 22, 1915 Memorial Service (Oberlin News, January 27, 1915; Oberlin, OH). Julia B. Hall, 1915 letter to Homer C. Johnson (News Tribune, Oberlin, OH; February 18,

1955).

3.

1936).

4.

5.

Harry N. Holmes, “Fifty Years of Industrial Aluminum,” Bultetin of Oberlin College, N0.346 (August 1937) 1-30. F. F. Jewett and F. G. Jewett, “The Chemical Department of Oberlin College from 1833 to 1912,’’ Chemistry Supplement, Oberlin Alumni Magazine, 18 (July 1912) 1-15.

6.

Frances Gulick Jewett, Frank Fanning Jewett: The Beloved Teacher, private publication (HonoIuhu,HA, 1930).

7.

Frank F. Jewett, Laboratory Exercises in Inorganic Chemistry, Fourth Edition (Oberlin, OH; News Printing Company, 1904).

8.

Henry Churchill King, Remarks made by the President of Oberlin College at the January 22, 1915 Memorial Service (Oberlin News, January 27, 1915; OberEin, OH). Seabury C. Mastick, “Chemical Patebts,” Parts 11-IV, Journal of Industrial and Engineering Chemistry, 7 (1915) 879-883, 984-991, 1071-1081.

9.

10. “The Perkin MedaI Award,” Journal of Zndustrial and Engineering Chemistry,” 3 (191 1) 143-151. 11. Joseph W. Richards, Alwninium: Its History,

Occurence, Properties, Metallurgy and Appfications, Including its Alloys, Second Edition (Philadelphia, PA, Henry Carey Baird and Company, 1890); Third Edition (1895).

Norman C. Craig Professor Norman C. Craig earned his PhD in Physical Chemistry from Harvard in 1957. He then accepted a faculty position at his undergraduate Alma Mater, Oberlin College. He remains an active researcher with 40 technical papers to his credit, mostly in the field of vibrational spectroscopy and thermal dynamics. He has been a visiting professor at the University of Minnesota, U.C. Berkeley, Princeton, and with the National Institute of Health. During the summer of 1982 he served as a lecturer in China

Paul Hhoult The Man Behind the Invention Christian Bickert, Pechiney Corporation 475 Steamboat Road, Greenwich, CT 06836-1960

Paul Louis Toussaint Heroult

Friends: I intend to give you the portrait of a man, without whom perhaps aluminum would not exist. You know his name, Paul HCroult, the French inventor of the electrolytic process for producing aluminum. I will not go into the details of the invention, which are no secret to you. Nor will I attempt to retrace all the steps in his eventful life: it would be too ambitious and timeconsuming. The purpose of these few words is rather to bring out the extraordinary personality of this man of genius. Paul HCroult had none of the attributes of the traditional scholar. He was highstrung, unruly, occasionally hard and insolent; he did not fit the image of wise, disciplined men of science. He loved games, the company of women, travels by land and sea; he was a free spirit in an impetuous body. No comparison with the austere scientist, struggling with stubborn mysteries. His discoveries were not the result of long sleepless nights spent in a laboratory, or of complicated scientific demonstrations.

HCroult loved life, and could not have borne such restrictions. Instead, his inventions appeared suddenly, out of the blue, a stroke of common sense, or of genius, sometimes during a lively game of billiards, his favorite pastime. An unusual working pattern, to say the least. Perhaps the very key to his success. HCroult imagined more than he invented, and often seemed more of an amateur than a professional, but in the end he proved more prolific than his white-coated peers. Behind his perfect inventions was his artistic approach, passionate yet seemingly disinterested. Along with his lucid and practical intelligence, and his determined perseverance, went a tremendous love of life in which research and work were basic pleasures. HCroult was not only a remarkable inventor but, in spite of himself, the very opposite of the learned scientist stereotype, alone in his ivory tower, sacrificing his entire life to science. As such he deserves our warmest praise and gratitude for his invention, now

in its centennial year, which has contributed so much to our daily life. Here, in a few words, is his story: Paul Louis Toussaint HCroult, was born almost 123 years ago, the evening of April 10, 1863, into a world of country folk and cottage industries, hardly a portent of his future career. His father, Patrice, managed a small tannery on the banks of the Orne River, at Saint-Bknin, not far from a lush farming area dubbed “Swiss Normandy,’’ a peaceful spot where the Hkroult family had lived for generations. Paul might have been expected to continue the business his grandfather had started, but rather than an honorable tanner, he became an inventor. A mischevious child, boisterous and undisciplined, he spends most of his time teasing the fishermen catching eels in the neighboring inlets. The river is his world. But already there are signs of his budding ingenuity. For instance, to shorten the distance he travels to school, young Paul

102

103

decides to build a canal. He gathers together his best playmates, hands around the family shovels, and directs his first jobsite. Since he is still not 7, the “age of reason,’’ he is forgiven his first eccentricity. But soon his parents are concerned; their son can’t settle down. He is sent for a brief period to England, to stay with an elderly aunt, and then his mother turns to a religious boarding school in Caen in hopes of bringing him into line. The rules are strict, the program austere, a Spartan life that turns him forever against classical teaching. Fortunately, his father decides to leave Saint-Bknin to start up a new larger tannery near Paris, at Gentilly. Paul is sent as boarder to the Sainte-Barbe Academy, a rather liberal school, more appealing to his independent spirit. The major influence, however, was the fortuitous meeting with an old friend of his father’s, Mr. Belliot, a lawyer by profession, highly cultured, with a magnificent personal library. After school, Paul spends hours there, discovering the joys of reading. Jules Verne’s heroes become his own, especially Cyrus Smith, the engineer, who, you will remember, managed to create the entire industry of the mysterious island from a small steel blade taken from his dog’s collar. Science, and particulary, research and discovery, begin to fascinate the young student. His interest reaches its highest point the day he comes upon the famous work of Sainte-Claire Deville, with the unglamorous title, “Aluminum, its properties, its production and applications.” The book is like a bomb exploding: he feels certain that the problem set forth by the author is solvable and tells anyone who will listen that he will succeed in producing aluminum by electrical means at a reasonable price.

He now applies himself to his studies with total dedication. Aluminum becomes more than a hobby, a passion, an obsession. He enters the prestigious Ecole des Mines after a brilliant entrance examination in 1882, at age 19. A friendship develops between him and his chemistry professor, who is also fascinated by aluminum. Hkroult does sketch after sketch, tries one assumption after another, at the expense of the other subjects he should have been studying. As a result, he fails his first year and is dismissed. Later he tells the story that his rejection was actually the result of a practical joke making him both the instigator and the victim; a sodden sponge thrown at a classmate hit the dean instead. . . True or not, it is not lacking in humor. Paul Hkroult is thus back on his own; his father dies unexpectedly during 1883, leaving him the tannery buildings, which he decides to use for his experiments. He induces a few fellow students from 1‘Ecole des Mines to join him, such as Louis Merle and Lucien Van Kerguistel, and they begin to work on electrolysis. His mother gives him her last FF 50,000 to acquire the Brkguet dynamo (400 amperes, 30 volts) which he needs for the purpose. But the attempts are indecisive. Aluminum does appear, but remains elusive - until the moment when a flash of insight suggests lowering the temperature of the bath and adding a trace of metallic oxide. The oxide is reduced, falls to the bottom of the crucible and triggers the joining of the new metal into a mass. Eletrolytic aluminum was born. Without missing a beat, Hkroult applies for a patent. This is the 23rd of April 1886; Paul is 23 years old. Just like Charles M. Hall who,. as you know, had a strangely - . parallel and similar destiny (same age, same

invention within a few months, same year of death), he has just achieved his dream, with makeshift materials of course, but propelled by his formidable perseverance. And yet, the hardest part lay ahead. Hkroult had to convince businessmen of the validity of his process, by constantly improving it and by making the old guard appreciate the qualities of the new metal. A difficult task in the last few years of the 19th century, when steel was at the height of its popularity. He suffered many setbacks, one of them at the hands of a Mr. Pechiney, also known as Alfred Rangod, who had taken over at Henri Merle’s death the management of the company “Produits Chimiques d’Alais et de la Camargue.” Hkroult asked for an appointment with Mr. Pechiney, who agreed to see him at his Salindres manor house. They discussed the matter of aluminum very cordially, ending the evening with a game of billiards, which unfortunately resulted in the host’s resounding defeat. Irritated, Pechiney revised his earlier judgment, and stated, “Aluminum is a metal with few applications, it serves to make eyeglass cases, and whether you sell it for FF 10 or FF 100 per kilo, you won’t sell a kilo more. If you were making aluminum bronze, that would be another matter, since it has many uses, and if you could produce it cheaply, the prospects would surely be worth looking into.” After which, he warmly congratulated his visitor on his youthful enthusiasm, and sent him on his way. Frustrated but not discouraged, Hkroult looked for support elsewhere. Legend has it that one evening he was seated at the terrace of a Paris cafk, expostulating to all who would listen that businessmen and bankers understood nothing, least of all his own invention. A man is said to have come forth,

saying, “My name is Jules Dreyfus, I may be able to help you.” And thanks to him, Hkroult was put in touch with a Swiss company, the sons of J. G. Neher, who operated a metallurgical plant at Neuhausen, on the banks of the Rhine. They immediately grasped the possibilities, and agreed to create a Swiss metallurgical company with HCroult as technical director. Another step toward the distant goal was achieved. But work had to continue and the process had to be perfected in order to reduce the cost of the kilo of aluminum produced. HCroult thought of nothing else, as shown in his letters to his young wife, Berthe Belliot, whom he married in August 1888. And again, he succeeded. Jules Dreyfus then decided to focus on the French market. He joined with the Paris bank of Goldschmidt and together they founded on October 17, 1888, the SociCtC Electromttallurgique Francaise,” for the purpose of producing aluminum, of course, but also silicon and various alloys. HCroult, again, retained only the technical responsibility for the business, and did not acquire any of the capital. The new plant of the company, located at Froges, in the Isere, had extremely difficult beginnings. The cost of the kilo of aluminum, while three times less than the cost of chemically-obtained aluminum at the Salindres Pechiney plant, was still too high; the staff broke down, personnel was laid off for incompetence or for financial reasons, right and left, panic set in, and enthusiasm soon flagged. But HCroult, as usual, was not discouraged and continued to work as one possessed. He built more pots, with four anodes, and then six. This was 1892 and costs began to drop. Our inventor, however, was not

satisfied with these results which would have pleased those about him. He wanted to improve both the quality of the product and the profitability of the operation. He succeeded, by lining the pot with a layer of carbon and pitch, reducing the electric voltage to 6 then to 5 volts. The Swiss were aghast in Neuhausen, so were the French in Froges. But with growing charisma, HCroult was able to persuade the SociCtC Electromttallurgique Francaise to build a new, larger capacity plant, at La Praz in the Maurienne Valley. He did not at first participate in its installation, because at the very same time a brand new company, the SociCtC Francaise de 1‘Aluminium Pur” was experimenting with the new Bayer process. Naturally, HCroult was asked to study and evaluate it. His findings led the management of SEMF to absorb the new company in 1895. This was the beginning of a period of collaboration between Hkroult and Bayer, both tirelessly searching for a lower cost in the production of aluminum. Together they went to the United States to study at close range the Hall process, as used in the South Wilmington alumina plant. The process did not appear to give better results than their own. A visit to the British Aluminium Company in England was not the answer either. It was 1895, and HCroult felt he was standing still. He was running out of steam, and to make things worse, his wife died suddenly, leaving two small children, Paul 4 and Henriette 2. A cruel year for him. He then turned to the sole task of starting up the La Praz plant. Orders began pouring in, and he suggested increasing the production capacity by damming another waterfall, 240 ft. high, on the other side of the torrent. The project fascinated him. It was another challenge, the very thing he liked

best. His imagination and his daring were fired up. He proposed, not a bridge, but a self-sustained conduit in the shape of an arch, supported only by concrete abutments on either side of the torrent. Everyone called the proposal wild and bound to fail. HCroult then suggeted placing his mother and his children, the day the floodgates were to be opened, in the center of the conduit, a forfeit that at last convinced his peers. On D-day, the floodwaters rushed through the conduit, and as HCroult had predicted, did not even shake up his loved ones. Once again HCroult’s methods had triumphed. In regaining his confidence in his inventive powers, he also gradually recovered his ability to enjoy life which had deserted him for a few years. He remarried and had three more children, Patrice, Elisabeth and AnneMarie. The happy father and ardent husband then decided to grant himself a long honeymoon: a trip around the world, an eight-month long cruise, back in his preferred element, the sea. On his return to France, Paul Hkroult temporarily stepped back from what had been a constant passion, aluminum. But only long enough to renew himself and to think through other inventions. Among them, one was to remain famous and bear his name, the electric steel furnace, which from 1902 on was universally adopted, particularly in the U.S. Others did not work out, as the general technology of the period seemed unable to keep up with his overflowing imagination. One example was his “phaneroptere,” a flying machine, precursor of the yet-to-come helicopter, or his hydroslip, a sort of boat on runners, lifted by four propulsive vanes, designed with the American inventor Cooper Hewitt.

104

105

One might think of HCroult at that stage, closer to Leonard0 da Vinci’s dreams than to the development of the aluminum industry. But that would be wrong. In 1912 he forged ahead again within a new organization, “1‘Aluminium Francais,” one of whose objectives was to build an aluminum plant in the United States. The everlasting pioneer embarked on this new adventure, and found himself lost in a wild, mosquito- and snake-ridden jungle, at the foot of the Yadkin River falls in North Carolina, along with his wife and his son, Paul, who helped on horseback with the surveying. But our inventor’s health was affected and he had to continue his work bedridden, in the tropical heat, within the old colonial house that had been lent him. Those about him urged him to return to France, and get some much deserved rest, but he would not listen. On the contrary, he seemed to offset his physical handicap by increased determination, until two unfortunate events occurred, the illness of his son, stricken with malaria, which forced him to go home, and the threat of war, which postponed the building of the plant. Deeply discouraged, he returned to his homeland in 1913, and attempted a last, desperate throw of the dice. He tried to persuade financial interests to transform a cargo ship into a floating plant, to produce iodine by treating algae right on the ocean. But this time, no one would listen. He finally gave up, bought a huge, 100-ft. yacht, the SAMVA, and made it his home, sailing around the Mediterranean, a little likeL Mathias Sandorf, the Jules Verne hero who had so inspired him when he was 10 years old. On May 9, 1914, when he was 51 years of age, Paul HCroult died, a victim of typhoid

fever, snuffing out suddenly this exceptional man, the larger-than-life scientist who never looked like one. Beyond the fundamental technique he left us, I hope to have given you, in these few words, a vision of the inspiring qualities of this remarkable man, untiring perseverance, passion, dedication to research in various domains, aluminum in particular, and, finally, total confidence in the future.

History of Electrical Energy Consumption by Hall-HCroult Cells Warren Haupin 2820 7th Street Road, Lower Burrell, PA 15068

The first commercial aluminum cells at Neuhausen, Switzerland (HCroult) and Pittsburgh, Pa. (Hall) required more than 40 kWh / kg (18 kWh / lb) of aluminum produced and had current efficiencies ranging from 75 to 78 % . Today the best cells require less than 13 kWh/kg (5.9 kWh/lb) of aluminum produced and have current efficiencies ranging between 94 and 96 % . Early improvements were achieved, first by using larger, more closely spaced anodes, then by increasing the cell’s size. As the cell’s size was increased, electromagnetic problems arose. The current in the molten aluminum cathode interacted with the magnetic field of the current supply like an electric motor. It became necessary to understand and calculate these forces. Further development was based upon physical and mathematical models - work that continues even today. At the same time, studies were made of the chemistry of the electrolyte, electrode reac-

tions, and how these and other factors inCommercialization of fluenced the current efficiency. The latest Process by Hall improvements came from computer control Hall, armed with his patent and only of the process coupled with automated feed- laboratory tests, found it difficult to find ing of alumina to the cells. adequate financing. The Cowles brothers, who were producing aluminum bronze carEarly History bothermally in an electric arc furnace, In 1886, Hall in the United States and financed an externally heated 250 A HCroult in France independently patented, demonstration cell as an insurance policy, in each without knowledge of the other’s case the Hall process worked. Hall made work, nearly identical processes for the elec- the error of using his latest thinking and trolysis of alumina dissolved in a molten built the cell with an “inert” copper oxide fluoride electrolyte to produce aluminum anode and a potassium cryolite electrolyte. metal. Both used consumable carbon When the cell lasted only a few days and anodes. This process continues to be used operated at less than 20% current efficientoday. Let’s follow how the two inventors cy, the Cowles Company terminated their commercialized the process and how relationship with Hall and thereby lost their through improvements in cell design, elecinsurance policy. But Romaine Cole, an aptrolyte chemistry and control, the electrical plications engineer for the Cowles Company power required has dropped from as high as was impressed by Hall and his new process, 74 kWh/ kg of aluminum initially to under and convinced Captain Alfred Hunt and a 13 kWh/ kg in today’s best cells. group of Pittsburgh industrialists to support

106

Fig. I - Potline of early Hall cells on Smallman Street, Pittsburgh in 1890.

Fig. 2 - The original Niagara cells. Small anodes were individually adjusted. Tapping ports have been sealed shut.

107

Hall. They incorporated as the Pittsburgh Reduction Company (renamed in 1907 The Aluminum Company of America) capitalized at $20,000 (about $230,000 in today’s dollars) with Hunt as president and Hall as vice-president. The new company erected an approximately 6 by 35 metre (20 by 115 ft) building on Smallman Street in Pittsburgh and purchased a coal fired 125 horsepower steam engine and two 1,OOO ampere 25 volt DC dynamos. Hall designed the cells with an externally heated cast iron shell 610 mm long by 405 mm wide, 510 mm deep (24” by 16” by 20”), lined with 75 mm (3”) of baked carbon. Eight carbon anodes 75 mm (3”) diameter by 40 mm (15”) long dipped into the electrolyte from the top. The anodes were suspended in two rows on threaded 9.5 mm (3 / 8”) diameter copper rods. Based on his bench scale work, Hall chose an electrolyte of cryolite, aluminum fluoride and calcium fluoride giving a bath ratio (weight ratio NaF / AlF3) of about 0.5. A large excess of aluminum fluoride was used to lower the melting point. The cell was operated at 4 volts, 1800 amperes, but lasted only six days before it started to leak. During that time, it produced 30 lbs. of aluminum giving an average current efficiency of 16% and a power requirement of 74 kWh / kg or 34kWh / lb. Hall concluded that external heating had caused the leakage and found that by increasing the cell potential to 8 volts, enough heat was generated internally to maintain cell temperature without external heating. But when he operated the next cell without external heating, he had trouble dissolving the alumina and the resulting muck caused very unstable cell operation. In subsequent runs he raised the bath ratio to improve alumina solubility. This overcame the problem. By

mid January 1889, they were producing 25 Within 6 months the Niagara Plant was lbs. of aluminum per day at 1800 amperes operating smoothly and producing nearly and 8 volts (78% current efficiency and 30 80% current efficiency at 31 kWh/ kg (14 kWh/ kg. or 13.8 kWh/lb.) A second cell kWh / lb.). It was no longer necessary to was added in series doubling the produccontinue the higher cost steam power reduction. The demand for aluminum increased tion operations, therefore reduction operaand in 1890, additional generating capacity tions at New Kensington were terminated in was purchased to give 5,000 amperes at 50 Feb. 1896, and the fabrication operations volts. Additional cells of the design shown there expanded. in Fig. 1, which were twice the length of the Commercialization of the original cells, were added. This increased Process by Hbroult productivity to 470 lbs. a day. In late 1891, property for an expanded plant was purHkroult gained financial backing quicker chased along the Allegheny River about 20 than Hall, perhaps because he had done his miles north of Pittsburgh near the borough experimental work on a larger scale (400 A). of Parnassus and the Smallman Street He contacted Alfred Rangod Ptchiney, the operation was moved to this new location. manager of the Salindres Works of the Soon thereafter additional generating equip- Compagnie de Produits Chimiques d’Alais ment was installed and the number of pots et de la Camargue, where aluminum was beincreased from 7 to 17. The communities of ing produced by the Deville process of New Kensington and Arnold developed adsodio-thermic reduction of aluminum joining the plant site. chloride. Pkchiney was interested but conSoon it was realized that if the company sidered the market for pure aluminum too was to increase the sale of aluminum it limited and suggested that aluminum bronze needed a large quantity of cheaper electric would be a better product. Hkroult had, in power. Accordingly on June 28, 1893 the some of his early tests, electrolyzed Pittsburgh Reduction Company made a aluminum into a copper cathode to improve contract for 1500 electrical horsepower (1.12 metal coalescence. From this, he knew that MW) with the Niagara Falls Power Commaking aluminum bronze was easier than pany. The Niagara plant started operations making pure aluminum. Financial arAug. 26, 1895 with 26 third generation rangements were made through Jules reduction pots in the line, Fig. 2. These cells Dreyfus. The site of Neuhausen, were designed with a tapping ports to avoid Switzerland was chosen because hydroelechaving to ladle aluminum from the cell. The tric power was available, and the Sociktk port was opened by arcing with a carbon rod. Aluminum flowed into a crucible resting in a recess in the floor. When bath flow was observed, flow was stopped with a clay dough ball. This operation was dangerous and was soon replaced by tapping from above through a cast iron siphon, a practice still used in modern plants.

Metallurgique Suisse was formed in August 1887. The cells were designed jointly by Hkroult and Dreyfus. A water cooled carbon lined Plumbago crucible was used as the cell container. Plumbago is a natural graphite. A single 250 mm by 250 mm carbon anode dipped into the electrolyte from above. The cell was rotated while the anode remained stationary, an innovation of Dreyfus to promote rapid dissolution of the alumina. The cell ouerated at 8 to 10 volts with the current of 4,000 amperes giving a very high anodic current density (6.2 A/cm2 or 40 A/in2). Hkroult soon replaced the water cooled crucibles with carbon lined, air cooled cast iron.“pot bellies.” The workers applied the name “pots” to these cells, a terminology that continues even today, although the cells no longer look like pots. In 1890, when the equipment to rotate the pots failed but the cells continued to operate as well as before, rotation was discontinued. These cells produced aluminum bronze with a current efficiency of 75% and an energy consumption of 37.5 kWh/kg aluminum or 17 kWh/lb. Energy efficiency was improved by replacing the single anode first with 4 and then with 8 anodes in each cell. This lowered the anode current density from 6.2 to 1.6 and then to 0.78 A / cm2 (40, 10, 5 A / in*) and lowered the cell voltage from the initial 9.5 volts to 5 volts at 4,000 amperes. Eventually the cells were converted

108

Fig. 3 - A Hbroult cell at Forges, France, being tapped. Pi(: m e taken in 1889, provided by PCchiney Alumin iurn.

Further Impro vements

from producing aluminum bronze to producing pure aluminum. This required an improved pot lining, that consisted of charcoal and pitch, to reduce impurity pickup. These improvements resulted in an energy consumption in 1892 of 19.8 kWh/kg (9 kWh / lb) and a current efficiency of 75 % . Hall at this time was achieving about 80% current efficiency but required 3 1 kWh / kg (14 kWh/lb) of aluminum. Over the years as further improvements were made, the Hkroult followers continued to achieve superior energy efficiencies while the Hall followers, until the last few years, had higher current efficiencies. To a large degree this was deliberate and reflected the dif-

109

ferent economies in United States and Europe. The lower electric power cost in the United States made it profitable to maximize productivity at the expense of electric energy. Lower current densities were used in Europe. This gave lower specific energy consumption but required larger more costly cells to achieve the same productivity. The success at Neuhausen resulted in a new company, Aluminium Industrie Aktiengesellschaft (AIAG) being formed in Nov. 1888. In France the SociCtk Electromktallurgique Francaise (SEMF) was formed and built a plant at Froges in April 1889 after purchasing the patents of Hkroult and Dreyfus. Fig. 3 shows one of these cells being tapped.

As we have seen, in the early years productivity and power efficiencies were increased by increasing the current and physical size of the cell. Larger size cells improved the surface to volume ratio thereby reducing the heat loss per unit of cavity volume. Cells of 50 kA capacity had been designed by 1935 and 100 kA by 1950. Most of this development was by scaling up the physical size of previous cells by trial and error. Round anodes were replaced by rectangular ones. Retrofitting of older cells with larger anodes became a common practice. The Niagara cell, installed also at Badin, North Carolina and Alcoa, Tennessee, is a typical example. The cell initially had forty 5” diameter anodes. These were replaced with thirty two 7” by 7” rectangular anodes which were replaced later by ten 13” by 15” anodes and finally by ten 13” by 17” anodes. The pot shells were not straightened when they were relined but were allowed to bow. When bowing reduced the cavity depth, steel sideboards were added. This allowed the cavity size to increase and accommodate the larger anodes as illustrated in Fig. 4. As the anode size was increased, the cell current also was increased from an initial 9,000 amperes to 13,000 to 19,000 to 23,000. At the same time energy consumption fell from 31 to 24 to 22 to 21 kWh/kg (14, 11, 10, 9.7 kWhl1b) of aluminum.

127mm (5") Dia. Anodes (40) cover Thermal Insulation Hector Linina

Niagara Cell - As Installed in 1895 9000 A, 8.4 V, 59 kg (130 Ib)/Day, 31 kWWkg (14 kWhllb.) Al

Ore Cove

Ten Anodes 330 by 432 mm (13" x 17")

Electrolyte Composition

Heat Balance

In the forties, serious fundamental studies of bath chemistry were instituted. The low bath ratio, advocated by Hall to gain lower operating temperatures, was found to provide a benefit in addition to current efficiency improvement resulting from the slower kinetics of back reaction at the lower temperature. Lower bath ratio was found also to lower the amount of metal dissolved in the electrolyte and therefore reduce the metal available for reoxidation. The principal disadvantages of low ratio bath are lower alumina solubility and higher volatility. However, a low bath ratio permits a lower operating temperature, which lowers volatility, making the overall effect small. The loss in alumina solubility is significant. Automated ore feeders, however, reduce this problem by adding alumina in very small batches at one or more locations. Other additives, such as CaF,, MgF,, and LiF were examined. They lower the electrolyte's liquidus temperature and provide some reduction of metal solubility, hence have potential for improving power efficiency.

Above 50 kA, the more complex geometry of the cell required a more sophisticated method for the calculation of cell voltage and heat balance. Most frequently the choice was a finite difference mathematical model. As this was before computers were available, solution of the matrix was obtained by an iterative method called relaxation, which often took several weeks. With the advent of the computer solution times were reduced to minutes and fewer simplifying assumptions were needed. Finite element models then became preferred over finite difference models, because finite elements tolerated boundaries between materials of very different conductivities without having to resort to fine grids. Center aisle feeding and larger anodes, placed close to the cell wall to maximize productivity in a given shell size, made it necessary to calculate the heat transfer coefficient at the melt interface and design the wall to have the proper thermal resistance to assure that the wall remained covered with a protective layer of frozen electrolyte that would not extend too far and interfere with anode changing.

Same Cell Retrofitted With Larger Anodes 23000 A, 5.8 V, 150 kg (330 Ibs.)/Day, 21 kWWkg (9.7 kWh/lb.) Al

Fig. 4 - Upgrading of Niagara cell.

110

Electromagnetic Problems As cell sizes approached 100 kA, electromagnetic instabilities became a severe problem. Old rules of thumb derived from experience were no longer adequate. Most designs at that time used the guidelines that longitudinal fields produced little trouble. Strong transverse fields produced curvature of the aluminum pad and asymmetry of transverse fields produced instability. Vertical fields were the most harmful because they interact with horizontal currents and create swirl and instability. Magnetic fields in existing cells were measured by flip coils. The output from the coil was measured on Fig. 5 - Air cooled probe. Diameter to length ratio expanded.

Electrical Lead,:

Compressed Air In

\

111

Thermal Insulation

a ballistic galvanometer as the coil was rotated through 180 degrees. Inside the cell the coil was protected from heat by placing it inside an air cooled probe, Fig. 5 . Each of the three vectors of field had to be measured in sequence. In 1959, Hall crystals, solid state devices, became available for measuring the three vectors of magnetic flux simultaneously. They required air cooling, similar to the flip coils. Scale models of new cell designs or modifications of existing cells were constructed including appropriate magnetic and nonmagnetic components. With these models, the effects of many changes in bus configuration and placement of shielding could be evaluated quickly. While it was much less expensive to change a scale model than a full size cell, physical models still were expensive. In recent years, several computer programs have been developed to calculate the magnetic fields including the effect of iron parts. Magnetic flux models are generally linked with models that calculate current flow. With current flow and magnetic fields known, the electromagnetic force fields in the cell can be calculated. In addition to electromagnetic forces there are bubble generated forces, thermal density difference forces, and the relatively small surface tension difference forces. With this information, metal pad and electrolyte flow, and dynamic and standing waves can be calculated. These calculations are on the cutting edge of today’s science. New relationships are being developed to improve the accuracy of predictions. But even though some of the relationships used probably are defective or incomplete, reasonable results that can be used in design are being obtained. The goal, of course, is to produce a flat, wave-free aluminum pad

in order to reduce inter-electrode spacing and thereby save voltage and power. It is difficult to assess the independent effect of improved magnetics on power consumptionbecause the adoption of computer control occurred simultaneously. In the future, another route may be available to lower inter-electrode spacing. It would employ a motionless, wetted, insoluble solid cathode from which the molten aluminum would drain into a remote sump.

Control

As the ratio of cell current to bath volume increased, alumina concentration control became more and more difficult and the need for automatic feeders became recognized. Installation of feeders started early in the 1960’s. Early feeders were set manually to feed slightly less than the cell’s calculated need. Feed rates were altered depending upon anode effect frequency and indications of muck. Soon computer control relieved the pot operator from having to make most of these adjustments. Automatic feeders certainly played a part in the continuing improvement in power consumption, but it is difficult to separate out its effect from other changes made during the same period. The major inputs for computer control remain, even today, cell volts and amperes. These inputs are used to determine a pseudo resistance, so called because the value calculated contains some non-ohmic components. The average value of the zero current intercept of volts vs. amperes is determined over the operating range of current, a very small band. Subtracting this value from cell volts, then dividing by current gives a pseudo resistance that does not change with small fluctuations of current. In control ter-

I

minology the signal is less noisy. This pseudo resistance is a function of alumina concentration and anode - cathode distance, Fig. 6 . At high alumina concentrations, the resistance is high. As the alumina decreases, resistance decreases because the electrical conductivity of the electrolyte improves until at about 3% alumina, increasing overvoltage starts to exceed the falling ohmic resistance and the curve rises until anode effect occurs. The anode effect and the minimum resistance each occurs for a particular cell at fairly reproducible alumina concentrations. Several control schemes have been devised to control both anode - cathode distance A(Preudo)

Mu

Distance 4.8 cm

4.4 4.0

Mil

0

1

2

3

4 A1203 ( X )

Fig. 6 - Pseudo resistance is a function o f alumina concentration and interelectrode spacing. Rpseudo = (Eceli-K)/Icell, K 1.65 V.

5

6

7

8

and alumina concentration from this signal. One scheme is to feed alumina at the calculated proper rate and use the resistance signal to control anode - cathode distance. Any deviation in the alumina feed rate from the proper value will cause a deviation in anode - cathode distance which will accumulate and must be corrected periodically. This is accomplished by stopping both the anode movement and alumina feed and tracking the pseudo resistance curve as the cell approaches anode effect. This recalibrates the alumina concentration and anode - cathode distance; then the cycle is repeated. Another scheme is to move the anode at the calculated proper rate to maintain constant anode - cathode separation and use the resistance signal to control alumina concentration. Error, which accumulates, is removed periodically by tracking the resistance curve for recalibration as in the former scheme. A third scheme, called demand feeding, is to feed a sizable quantity of alumina and then follow the change in pseudo resistance with time. As the resistance goes through a minimum, it provides a calibration point to correct the anode - cathode spacing. Then alumina is fed again and the process repeated. Feeding large batches of alumina, however, eliminates the benefit of continuous feeding.

One of the most recent control schemes (US Pat. 4431491 assigned to Pbchiney) uses two feed rates, one slightly higher and one slightly lower than required by the cell. Switch-over from the low feed to the high feed rate occurs when the rate of change of pseudo resistance exceeds some set value. The high feed rate continues for a fixed time than switches back to the low feed rate. Anode - cathode distance is controlled by the pseudo resistance. A big advantage of computer control is the ability to change control philosophies simply by changing the computer instructions. The development of better control strategies is a continuing activity.

112

Summary Fig. 7 shows the reduction in power consumption over the years. Very early improvements were obtained largely through increasing the cell size and lowering of current density. Continuing improvement resulted in part from further increases in cell size and larger anodes, but improved understanding of electrolyte chemistry and improved control played significant parts. Large cells lead to electromagnetically induced instabilities. Improvements in recent years resulted largely from improvements in electromagnetic stability, and improvements in cell control. While incremental imk W g Al

Fig. 7 - Energy consumption trend of Hall-Hiroult cells.

k W l b . Al

61

26

51

provements will continue to be made, it is my opinion that drained refractory hard metal cathodes offer the greatest hope for significant further reduction in power consumption. Replacing the wave prone molten metal pad with a stable cathode surface would allow reduction of anode - cathode distance to save between 0.8 and 1.25 volts. A refractory hard metal cathode connected directly to metallic collector bars should reduce the ohmic voltage drop in the cathode by at least 0.3 volts. Together this would reduce power consumption between 3.5 and 4.9 kWh/ kg of aluminum produced. The principal deterrents to the present use of titanium diboride are its short life, and high cost. Inert anodes also hold promise but are further from commercialization; and probably will require a drained inert cathode to be successful.

22

41

18

30

14

10 20

6 10

THEOREnCAL UUwlUY \

2 0

0

YEAR 1 W

113

1920

1940

1960

1900

Warren E. Haupin Last year Warren Haupin retired from Alcoa, concluding a career spanning 43 years. He joined Alcoa shortly after graduating from Penn State University in Electrochemical Engineering, and proceeded to become a world-class authority on the physical chemistry of molten salts. Warren has held adjunct professorships at Carnegie-Mellon University, Chatham College, and Penn State University; in addition to a visiting professorship at the Norwegian Institute of Technology in Trondheim, Norway. In 1984 Warren was honored for a lifetime of distinguished technical achievement by being chosen as the first recipient of Alcoa’s pretigious Francis C. Frary Award. Today he lives with his wife in New Kensington, PA.

Evolution of Electrolytes for Hall-HCroult Cells N . E. Richards, Reduction Laboratory Reynolds Metals Company P. 0. Box 1200, Sheffield, A L 35660

While we think there has been considerable advancement in the optimization of the electrolyte for electrolytic alumina reduction tailored for conditions peculiar to a particular industrial operation, the basic framework and even many of the interrelationships of properties were perceived before 1900. So it can be quite humbling to think that we disciples have been “merely filling in the detail” for three quarters of a century. Of course, this is an oversimplification and the factors of inspiration, innovation, discovery and evaluation have all been evident in the growth and maturity of knowledge characterizing electrolytes for the Hall-Hkroult Process. However, after the revolutionary discoveries of Hall and Hkroult, this subsequent knowledge can only be considered evolutionary. My objective in this paper is to review the Course of evolution of baths over the years. A few of the points I wish to make relate to the changing concern for control of the

ing, nodules of aluminum (or alloy?) were separated from the crushed contents. In France, Minet (2) missed the key point for the future of alumina electrolysis in his experimentation with cryolite-sodium chloride baths, electrolyzed, he specifed, between a carbon anode and carbon cathode. In working with 37.5 wt.% Na3A1F,-62.5 wt. % NaCl, he discovered that CF, was evolved while the bath became depleted in Baths of the Beginning A1F3. Additions of cryolite only led to the Some groundwork for Hall and Hkroult enrichment of NaF and eventually, liberamay have been laid through the pioneering tion of sodium. Continued evolution of of Dr. Edward Kleiner-Fiertz (1) who pracfluoride vapors and CF, accompanied ticed pilot scale electrothermal decomposimaintenance of the AlF, content. He said, tion of Greenland cryolite in iron crucibles “If the bath is renewed by placing alumina lined with bauxite. The cryolite was packed in the state of a fine powder in the bath, around carbon electrodes through which a dropping it especially around the anode (he current of about 150 amp at an initially took special care to catch the cathodically high voltage, 80-100V, was passed to melt liberated aluminum in a carbon collector), the cryolite. At lower voltage, 50V, the vapors and fluorine reacted with the bauxite the fluorine set free may reform aluminum fluoride by attacking the alumina, setting lining to take alumina into the bath. After two to three hours for reaction, upon cool- free oxygen which combines with the carbon composition of the bath, the quality of basic information being published about the properties of the fluoride-oxide systems and the trends and continuing emphasis on selecting and modifying the constituents in accordance with admixtures of the following constraints: Economics, environmental concerns and improved technologies.

114

115

anode to form carbonic acid. If the fluorine were not completely absorbed by the alumina, the amount escaping would have to be made up by adding aluminum fluoride to the bath. The bath should therefore be fed by both alumina and aluminum fluoride’’ (3). A close encounter. It was unfortunate that Minet concluded that the alumina sank through the bath and reacted with fluorine rather than fluoride, probably a consequence of the noticeable solubility with a high proportion of NaQ. Whether or not Minet adopted the view of his followers that the alumina in the homogeneous-appearing liquid was not dissolved is now academic. If obdurateness was a factor, it was a pity because he was amongst the earliest bath formulators who made measurements of temperature, decomposition voltage and conductivity. Furthermore, Minet recognized what amounted to an electromotive series of metals in his bath, then referred to as “weaker compounds than aluminum or sodium salts.” The genius of Charles Martin Hall was his discovery that fluorides and particularly cryolite could be used as the solvent for forming a stable electrolyte by reaction with what he perceived to be the cheapest pure compound of aluminum, alumina. To repeat what will have been quoted many times in this celebration, “ . . . and in general terms the invention consists in the electrolysis of a solution of alumina in a fused fluoride salt of aluminum. . .” (4); this was the kernel of the revolutionary breakthrough for the practical and profitable production of aluminum. Hall’s insight and strength at integrating chemistry, homologous and colligative properties of compounds (what we now call material

science), and a keen sense for how things would work in practice are evident in his carefully worded patents (5,6). The collected claims still embrace the essential features of most baths used in the electrolytic decomposition of alumina, as he taught, and are essentially unchanged during the electrochemical reactions. Paul L. V. Hkroult (7) had equal insight. According to L. Ferrand (8) he wrote, “The principle that I want to patent for the production of aluminum consists of decomposing alumina in solution in molten cryolite bath by means of electric current leading into the bath on one hand by means of electric contact with the carbon crucible which contains cryolite and on the other hand another agglomerated carbon electrode which is submerged in the bath. This combination produces the decomposition of alumina when applying current of weak potential. Oxygen moves to the anode and burns it. Aluminum is deposited on the sides of the crucible which makes the cathode and precipitates as droplets in the bottom.” “The bath remains indefinitely constant and is fed with alumina.” “The positive electrode, meaning the anode, is to be replaced after oxidation but this oxidation prevents polarization and assures at the same time the constant energy and action of the electric current.” Published information on the actual composition and means of controlling chemical composition used in the early cells at either Pittsburgh, New Kensington, Niagara or in Europe is difficult to find. This is understandable in view of the litigation through which Hall and his business partners had to prevail to protect their process. The bath probably approximated cryolite 53-60wt. %,

AlF, 40%, CaF, (by natural contamination) 3% and Si02-A1,03balance. Whereas the freezing point of this mixture may have been low (approximately 690”C), the vapor pressure was high at cryolite weight ratio near 0.5. From Richards (9), we can infer that 0.15 lb of fluoride / lb A1 might have been used. In Europe, where the earliest cells had weight ratios of 0.41 (lo), consumption was 0.34 lb fluoride/lb Al.Inspite of the clear claims by Hall and Hkroult, there was ongoing controversy about whether the A1,0, was suspended or dissolved, and whether or not the fluorine was reacting with A1,03 to make 4.This was put to rest by emphasizing the formation of oxide on copper when used as the anode. Control of the chemical composition of the electrolyte in the early days, 1889-1905, by inference from the paucity of information about it was probably quite secondary to the titanic efforts in managing the actual smelting, the generators, the pots and removing the aluminum. The key elements for varying the fusibility, density and conductivity of the bath were understood. Those early solutes, 2 5 4 % excess AlF, and 1520% CaF,, had melting points from 685 to about 780°C assuming that as much as 3 wt.% A1,03 was actually in true solution. The properties of electrical conductivity and density would have been of the order of 0.9 to 1.3, and 2.2 to 2.3 at what we now view as normal elevation above freezing point, so the baths were probably used well above those temperatures in order to promote solubilization of alumina. In the early days at New Kensington, bath materials were 5.2% of the production cost, power 18.2% and alumina 61.5%. This distribution, and the anecdote told by

Arthur Vining Davis on the occasion of the fiftieth anniversary of the Hall-Hkroult process, seem to reflect that bath was not a high economic or technical priority in the early days. He told a story about a dedicated technician as part of an address to the Electrochemical Society (1 l), “My most vivid recollection of Mike is in connection with making aluminum fluoride for which we used alumina and hydrofluoric acid in lead carboys. We had a formula for the mixing operation but our aluminum fluoride never seemed to come out right. I watched Mike one day and discovered he was not weighing the hydrofluoric acid. Asked why, he said that it was not necessary, for he had discovered that there was a pound for every gurgle and a gurgle for every pound! During this epoch, we did not know whether we were making aluminum or not - some days we did, some days we did not, but after a year we began to eliminate the variables and so we were pretty sure to make our estimated output of 30 lb a day.” This began a new epoch. Although Charles Martin Hall was a founding member of the American Electrochemical Society (address 130 Buffalo Avenue, Niagara Falls), his strong discipline for teaching and writing powerfully worded patents seemed not to spread to publications in those proceedings. F. R. Pyne (12) presented a study of the melting point of some cryolite-alumina mixtures starting with pure cryolite (mp. 1000°C) and going to 10 wt.% A1203 (980°C). There is no indication that Richardson’s (13) (of Pennsylvania State College) selection of a bath for what may have been the first little cell run in a university in the United States, reflected industrial practice

of the time, but he chose Na3AlF,-Al,O, in the weight combinations, 80-20% and 85-15% to expose students to the Hall Process. The cell, containing about 10 lb of bath, was run at 500 amp with an anodic current density of about 3 amp cm2 in a closed container. In an otherwise wellplanned experiment lasting four hours over five runs he measured current efficiencies of 46 to 93% with temperatures judged (not measured) to be 900-1OOO”C because of unavailability of a thermocouple. Today we would question their practice of placing crushed coke around the anode to “keep the crust soft.” The anode effect and means to suppress it were described. In discussion of this paper, it is noteworthy that J. W. Richards argued for a decomposition potential of A1,0, (not on carbon) of 2.25V, and that 100% current efficiency should be theoretical with 90% or greater being a reasonable practical target if the temperature could be lowered to slow the dissolution of aluminum. Cowles thought redissolution had to occur by a voltaic process involving reaction with a double fluoride salt, particularly in contact with the carbon walls; Dr. Richardson emphasized that whenever a fused salt was electrolyzed, there was a tendency for the metal liberated to redissolve into the fused bath and that this redissolution was proportional to temperature. If it were possible to work with bath near the freezing point of aluminum, nearly 100% efficiency could be obtained. Practical reasons, including specific gravities, precluded that (14).

Characterization of Bath Reviewing properties of bath is not within the scope of this presentation: That great service has been provided for us by our esteemed peers of the past (15, 16, 17) and present (18) (19). From operational aspects, information most needed to manage an existing or plan the strategy for slection of a new electrolyte is probably freezing point and phase relations, which would include solubility of alumina, density and conductivity. This does not imply that the role and control of impurities should be discounted. The electrochemical series of ions in cryolite melts has to be understood also in maintaining quality. During the first 50 years of the aluminum industry, more data on basic information concerning the physicochemical properties of electrolytes was published from Europe than the United States. However, the appreciation of how the salient properties varied with composition and temperature may have been comparable. For example, from reading discussions in the TRANSACTIONS OF THE ELECTROCHEMICAL SOCIETY (papers by Lorenz and M. deKay Thompson, and Ferrand’s annotations on the contributions of early researchers) one can discern that fusibility, rate of solubility of powder (1 to 9 seconds), density varia(and some additives), tion with N203 temperature, electrical conductivity, concepts for ionic species, the general value and trends of limiting current density, hydrolysis of bath, carbon wettability, some knowledge of “fog” and solubility of metals, emf series in fluorides, etc., were quite well understood in principle. 116

Through the expansion of coherent studies of electrolytes in both laboratories and plants (1945 and beyond) beginning with Europe and following with the United Kingdom, Russia and then North America, which have been definitive in the broadest sense, we have been “filling in the squares” of the matrix set up by our founders.

More Recent Industrial Baths

117

One has to surmise that early industrial experience with the variables; alumina solubility, vaporization (fluoride consumption), conductivity and density, that industrial baths trended to lower proportions of CaF, and AlF, than Hall and Hkroult’s first specifications. For example, Frary (20) in reviewing the aluminum reduction industry in Germany reports, “Natural cryolite was usually the preferred bath material although synthetic cryolite was used to a large extent. Bath depths ranged from 7 to 11.8 inches with the lesser depths in prebaked electrode pots. There appeared to be no conscious effort to lower the melting point of the bath by the addition of calcium fluoride, but this material built up through the raw materials. It was variously said that the bath contained 3 to 13% CaF,. Most plants maintained the bath a little on the acid side of neutral. Control was by visual inspection of the fracture. This was sometimes compared with standard samples prepared by the plant laboratory.” With these baths in the 1935-1945 period, unit power consumption was 8 to 9.5 DC kWh / lb A1 and bath consumption about 0.05 lb total fluoride compound/lb Al. Except for the wide range of CaF,, this is not so different from that with which Reynolds started Listerhill: About 7% CaF,

and 2-4% excess AlF,, allowing pots to operate 970 to 990°C. In the 1930-1950’s, I believe changes in bath were apprised in terms of whether they would suppress fog formation; in effect, raise the current efficiency. Hence, producers might modify what I choose to call “classical bath,” 3 wt.% AlF,, 7 wt.% CaF, with more AlF, to suppress “fog” or with CaF, to suppress freezing point. Of course, the “fog theory” is still a controversy. But we do know that no matter what the theory of dissolution of A l , Na may be, in fact, the trend to lower “solubility.” Consequently, some European and North American companies were using about 7 wt.% AlF, (weight ratio 1.25) in this era. Control of ratio in this epoch in Germany, the United Kingdom and our company depended strongly upon the observations of an “experienced” technician. Samples of bath taken with tongs were broken and observed for both color and porosity. Very white or pink, brittle bath was considered acid; coarse or greyish bath or bath having too much “dirt” was ruled “basic.” Depending on their (g$nerally!) firm convictions of the person, an indicator may be used, e.g., phenolphthalein, phenol red, etc. In the mid-1960’s in a plant where this practice no longer determined the daily maintenance, the performance of “one of the old” operators was evaluated by comparison with a chemically standardized pH method. The reliability was 50%. After the disclosures of Fiquet, Armand (21), Lobos and Black (22) and others, the target acid base condition of a bath is controlled by automated pH, X-ray diffraction or X-ray fluorescent detection of the chemistry or structure in quenched samples,

coupled with analyses for additional components by atomic absorption or inductively coupled plasma. Compositions of bath today can be regulated within small ranges in great contrast to the forties. Leveraged by cost containment and current efficiencies plateauing at 86 3 % for cells typically rated at 60+25 kA, then aluminum industry after fifty years of improvements tested knowledge of the day through evaluations of NaCl and LiF. Sodium chloride, although cheap and giving encouraging initial results, caused too much corrosion through evolution/condensation of chlorides. In those days, much reliance was placed on “reading the flame” and sman concentrations of NaCl changed those characteristics completely with respect to the experienced scale of productivity. Russian literature in the 1950’s (23,24,25) gave a very adequate base from which to project and evaluate the properties and performance of industrial baths modified with MgF, and / or LiF (26). Kaiser reported positively on experiences with LiF modified electrolytes in 1958 and 1967 (27,28), in between which times plants had profited from the data available. As a consequence, it became understood that the operating temperature and voltage of cells had to be decreased to allow the improvement attributable to the properties of modified baths. By this time a typical cell was rated at 150 to 180 kA requiring as much as 8-9 tons of bath. Standards for emissions of fluorides from reduction plants were imposed which were more stringent than those to which many companies had engineered for economic and social reasons. And then came the energy crisis of 1973.

*

Table I BATH COMPOSITIONS ENCOUNTERED IN INDUSTRY Value at 2OoC above Freezing Point Composition, wt.% Company

Early USA “Classical” Low Ratio, 1940 Pechiney (F Cell) Nippon Light Metals (Kambara) Alusuisse

A1F3

CaF,

28 3

15.6 7 5 5 5

7 13 2

.I -L11-2

Revere Intalco

1 1 6

Even then the keen perception and brilliant mind of Charles Martin Hall became reinforced. Alkaline earth fluorides, lithium fluoride, separately or in combination, offered opportunities for designing baths that were both more “energy efficient” (29) and also showed reduced emissions (reduced vapor Pressures of NaAlF,) (30,31). Hall had already anticipated such, and made such generic claims that there was no room for innovation - just practice! Some properties of industrial baths for which evaluations have been published are summarized in Table I and compared with baths of older technologies.

4 4 4 2 6 4.8

LiF

-

-

4.3

4 2.5-3 2.5

2

MgF,

Calculated Freezing Point (” C) at 3% A l z 0 3

Conductivity, mhocm“

Density Difference, g/cm3

A1203 Solubility, wt.%

183.5 970.9 967 936.9 940.1

1.21 2.41 2.29 2.03 2.57

0.05 0.16 0.19 0.19 0.16

7.2 1.2 6.2 6.9

910.0 945.8 939.7 953.7 963.8 952.8

2.31 2.61 2.41 2.39 2.21 2.36

0.20 0.17 0.16 0.21 0.18 0.18

1.6 7.4 6.8 7.7 6.8 6.9

Notice that despite significant differences in composition, the saturation solubility of alumina for all is adequate for either continuous or periodic additions of alumina (for the latter, the maximum dissolved alumina will rarely exceed 0.75[A1,03]sat). Targeting operation at 20°C above freezing point and assuming a margin of 0.15 g / cm3 difference in density of bath and aluminum to be a desirable threshold, three systems, “classical,” Nippon’s high LiF and low AlF,, and one option evaluated by Alusuisse have a calculated difference of 0.16. The conductivities of baths permitting lower temperature operation, because of a proportion of LiF are not always higher than

-

“classical,” 2.41 mho-cm-’, because the mobility of all ions is decreased with that reduction in temperature. Baths with excess AlF, greater than lo%, in spite of decreased electrical conductivity, can correlate with good current efficiency through coupling of continuous stability of the bath-metal pad interface and electrolyte composition which permits short interelectrode distances. This is state-of-the-art technology for the more recently built cells in the world supplied current by buswork designed to balance magnetic field strength and equipped with automated alumina and voltage control and dry scrubbing systems. 118

There will be at least two trends for References 23. U. P. Mashovets and V. I. Petrov, Zhu Priklad Khim, 32 (1959), 1528. modifying electrolytes for the future. These, 1. E. C. Kleiner-Fiertz, British Patent 8531 (1886); 24. G. A. Abramov, M. M. Vetyuka, I. P. Gupalo, British Patent 15322 (1896). and indeed any of the innumerable degrees A. A. Kostyukov and L. N. Lozhkin, 2. A. Minet, British Patent 10057 (1887). of freedom available, will have the same ob- 3. “Theoretical Principles of the Electrometallurgy J. W. Richards, Aluminium, Its Properties, of Aluminum,” Metallurgizdat, Moscow (1953). jectives - lower unit costs and reduced Metallurgy and Alloys, Henry Carey Baird, 25. A. I. Belyaev, “The Electrolysis of Aluminum Philadelphia, 3rd Edition, Rev. (1896), 358. emissions. Cells,” Metallurgizdat, Mocow (1961). 4. C. M. Hall, U. S. Patent 400766, Line 15 For older cells, some of which are 26. N. E. Richards, “The Properties of LiF and Its (1889). Effects on Performance of the Hall Hkroult 5. fighting obsolescence and ever increasing C. M. Hall, U. S. Patent 400664, e.g., Lines Cell,” Reynolds Reduction Laboratory, Report 55-60 (1889). power costs for which the magnetic fields No. 67 (1960). 6. C. M. Hall, U. S. Patent 400665, e.g., Lines cannot be changed, the suitability and 27. J. B. Todd, “Increased Metal Production with 5-15 (1889). Lithium Modified Bath,” Kaiser Chalmette 7. P. L. V. Hkroult, French patent 175.711 (1886). economics of modifying current electrolyte Plant (1958). 8. L. Ferrand, History of the Science and by different proportions of 28. R. A. Lewis, Journal of Metals, 19 (1%7), 30. Technology of Aluminum and Its Industrial LiF-(CaF, + MgF,) and AIF, should be 29. H. Kvande, Erzmetall, 35 (1982), 597. Development, Humbert and Sons, Largentiere, 30. G. Wendt, Metallurgical Transactions, 2 (1971), Vol. I (1959), 165. evaluated since it has been demonstrated 155. 9. J. W. Richards, op. cit., 381. that such baths, through reduced tempera31. V. Kuxmann and V. Tillessen, Erzmetall, 20 10. Ferrand, op. cit., 249. ture of operation, give better indices for (1967), 147. 11. Arthur Vining Davis, Trans. American Elec32. A. T. Tabereaux, Light Metals 1985, AIME trochemical Society, 69 (1936), 55. production, carbon consumption, cell life, (1985), 751. electrolyte maintenance and therefore emis- 12 F. R. Pyne, Trans. American Electrochemical 33. H. Minghon, Q. Zhuxian and L. Qingfon, Society, 10 (1906), 63. sions. “Low Melting Baths in Aluminum Electrolysis,” 13. H. K. Richardson, ibid, 19 (1911), 159. Light Metals 1985 (1985), 529. For modern cells, highly automated, a 14. “Production of Aluminum in the Laboratory,” H. Kvande, K. Grjotheim, B. J. Welch, TMSMetallurgical and Chemical Engineering, Vol. 10 34. data base is becoming available (32,33) for AIME Conference, New Orleans, Proceedings (191 l), 269. tailoring baths that will operate at tempera- 15. G. A. Abramov, M. M. Vetyukov, I. P. (1986). tures lower than the 945965°C of today. In Gupalo, A. A. Kostyukov and L. N. Lozhkin, “Theoretical Principles of the Electrometallurgy this very session of this Centennial ConNolan E. Richards of Aluminum,” Metallurgizdat, Moscow (1953). ference our knowledge is to be supT. G. Pearson, “The Chemical Background of Nolan E. Richards received his PhD from the Univer16. plemented (34). sity of Auckland, did Post-Doctorate work at the the Aluminum Industry,” Memograph No.3, 17. 18.

19. 20.

21. 22.

119

Royal Institute of Chemistry, London (1955), 43-63. L. Ferrand, op. cit., Vols. I and 11. K. Grjotheim, C. Kohn, M. Malinovsky, K. Mahasovsky and J. Thonstad, Aluminum Electrolysis, Fundamentals of the Hall Hbroult Process, 2nd Edition, Aluminium Verlag, Dbeldorf (1982). K. Grjotheim, B. J. Welch, Aluminium Smelter Technology, A Pure and Applied Approach, Aluminium Verlag, Difsseldorf (1982). A. J. Rice and F. C. Frary, “The Aluminium Reduction Industry in Germany,” Office of Military Government for Germany (U.S.), First Final Report No. 993, Nov. 14 (1946). M. Fiquet and M. Armand, Aluminio, 22 (1953), 621. J. S. Lobos and R. H. Black, Extractive Metallurgy of Aluminium, Vol. 12, G . Gerard, Editor, Interscience, New York (1963), 277.

University of Pennsylvania and accepted a fellowship at Imperial College prior to beginning his career with Reynolds Metals Co. in 1957. During his distinguished career he has been a research scientist, a Department Manager and today holds the position of Reduction Laboratory Manager in Sheffield, Alabama.

Gaining That Extra 2 Percent Current Efficiency B. J. Welch Department of Chemical and Materials Engineering University of Auckland, New Zealand

Introduction Current efficiencies gained in aluminium smelters have much in common with fishing exploits. They are both talked about extensively in appropriate circles, they are frequently exaggerated, people always look towards greater achievements in the future and too much emphasis is placed on it. In support of the latter statement, in fishing it is the quality that really counts while in aluminium smelting it is the power requirements. However, in aluminium smelting the goals looked to are not as great as in fishing, most potroom operators would be happy with a current efficiency gain of 2%. In both instances it is important to define the methods necessary to our goals. The options in aluminium smelting that have been cosidered are much broader than better bait and better equipment in fishing. The preoc-

cupation with current efficiency goes back even more than a century. Hall’s own account of his first experiment (1) illustrates the difficulties: “I melted some cryolite in a clay crucible and dissolved alumina in it and passed an electric current through the molten mass for about two hours. When I poured out the molten mass I found no aluminium.” Hall attributed this failure to impurities from clay. “I next made a carbon crucible and repeated the experiment with better success. After passing the current for about two hours, I poured out the material and found a number of small globules of aluminium.”

For commercial success he needed to improve current efficiency and this dominated

his work over the next two years enabling him to lay the foundation for our understanding of factors affecting current efficiency. “I have now gained a thorough knowledge of the requirements of my process. It is now certain that very pure materials will not be required.” and “In order to make it pure and to make it more economically, all that is required is less crude apparatus.” Table I shows that over the first 70 years, significant improvement in current efficiency were achieved, but this has been accompanied by major increases in cell size - from 4 kiloamps to 150 kiloamps. The basic current efficiencies being achieved some 30 years ago were between 85 and 90%.

120

Table I ADVANCES IN CURRENT EFFICIENCY (C.E.) & ENERGY UTILIZATION OVER THE FIRST 70 YEARS (2) Year

1889 1893 1914 1937 1950 1952 1956

Cell Type Prebaked

Soderberg

CellSize C.E. kA

4 5 20 50 30 loo 150

(%)

Energy Use kW / kg

70

40

I1

26 26 21 19 16 14.5

74 80 87

90 88

In the last 30 years, and particularly since 1962, numerous publications have been presented highlighting options available for improving current efficiency. These options include: - modifying the bath by adding lithium fluoride - modifying the bath by making it extremely acid . - modifying the bath by adding magnesium fluoride - using a center break and feed system - using a point feeder system - using refractory hard metal cathode contacts and refractory side walls - installing computer control system - using a demand feed control strategy -using magnetic field compensation to control the metal pad - optimizing the anode effect frequency In almost all cases, efficency gains of at least 2% have been claimed for the changes implemented. 121

Besides these options the view has always been expressed that operations play an extremely important role in ensuring good performance. Although combining all above features should give more than 100% current efficiency the best figure cited today is 95 k 0.5 % (3), but for long term operation 94% (4). Let me now ask the questions; what knowledge, advances in theory, design features, operating or control strategies, have enabled us to make these gains? What changes can we achieve in the future? I will attempt to answer these points by reviewing progress under the following broad headings: a) A better understanding of reasons for loss of current efficiency. b) Process Control and Operating Strategy. c) Cell design. d) Communication. While these are useful headings for discussion, it is difficult to incorporate the most important aspects. These have been innovation, guile and enthusiasm of the potroom operators and supervisors themselves. It is at that level that new approaches have had to be justified and treated, and it is they who suffer the consequences in event of failure. More important they had to convince management of the worth of doing the work, but the task was invariably easier if the trial was aimed at improving current efficiency by, say, 2%.

Better Understanding One could spend a whole lecture on theoretical aspects of current efficiency, the falacies and significances of the many

publications. I only want to highlight two important theoretical relationships. The first important milestone is the Pearson and Waddington equation (5), which is quite frequently cited in the literature. This equation, relating current efficiency to anode gas composition by the relationship CE% = 100 - !h(%CO) (1) is but one of the many important contributions we associate with the late Dr. T.G. Pearson. (His monograph “The Chemical Background of the Aluminium Industry’’ (6) was for many years the best summary and exposition of principles related to the process.) This equation assumes that the only source of carbon monoxide is by reduction of carbon dioxide with metal. It also assumes that the only way efficiency is lowered is by dissolved metal being oxidized with carbon dioxide and implies (incorrectly) that the minimum efficiency possible is 50%. With our modern knowledge of the process we could readily invalidate the equation, but such an effort is only of use for considering the future gains that may be possible. The importance of this equation is that it gave the industry a tool to work with especially when combined with a gas chromatograph. (The development of gas chromatographs followed shortly after the Pearson & Waddington equation was published). Despite its assumptions it gives accurate reflection of changes and therefore as a tool it has enabled valuable short term studies to be made on operating smelters. Even today the principle is used in laboratories to determine how changes in variables are likely to effect the current efficiency. The second important equation I want to highlight was published’in Light Metals

1985 (7) and presented by Warren Haupin

Bath ChemistrylA4etal Solubility

Over the years a combination of (another person who has made an outstandlaboratory studies and plant trials have coning contribution to the advancement of aluminium production). To me this equation firmed that the best approaches for lowering metal solubility either directly or indirectly which is, is through varying bath chemisty. The imCE% = 100 219 [ - 1 ~ D o . 6 7 ~ - - ” U o . 8 3 d - o .‘.5C*(1.f) 17 .(2) P portant changes that can be made to achieve says it all, because it highlights all the imthis are to lower the electrolyte liquidus portant variables - even though the equation temperature, and to reduce the equivalent is only applicable to cells with an advanced concentration of sodium fluoride since most degree of magnetic field-force compensaof the dissolved metal arises from that. tion. In equation (2) the cell current, I, is in Modification to the bath that could be kiloamps, Am is the surface area of made and enable these goals to be achieved aluminium, f the fraction of metal saturahave already been highlighted and include tion solubility (C* in wt%) at the boundary addition of magnesium fluoride, addition of layer / melt interface, is the electrolyte lithium fluoride, and additional aluminium viscosity, is density, D the molecular diffu- fluoride. The relative effects of these sion coefficient of dissolved metal, U the changes have been estimated by correlating average velocity of electrolyte referenced to data published for the solubility of metal. metal and d is interelectrode distance. One such correlation is Like the Pearson & Waddington equation we could argue about its absolute accuracy C*(wt%)= -0.288 + 0.0003 t + 0.027 (BR) -0.0019[CaF2] 0.0036 [LiF] (3) but, we would be debating extremely minor points. Unlike the Pearson & Waddington where temperature (t) is in “C, the bath equation (which focuses attention on the ratio (BR) is on a weight basis and the adreoxidation) equation (2) focuses attention ditive concentrations are in weight percent. on the removal of the metal from the pad - (the actual correlation that is derived is since any metal removed from the pad will dependent on the data used and reliability ultimately be lost. We see reducing the inattached to it.) terfacial velocity between bath and metal is Practically the extent of changes made are very important, and this is achieved by im- limited by either operating procedures, or proving the stability of the operations and secondary implications that negate advanby appropriate compensation of the magnet- tages of current efficiency gain. Virtually all ic fields. Other points the equation tells us electrolytes used differ substantially from are that it is extremely important to reduce those used in 1960, even though they are the metal solubility, and the physical prop- still all within the electrolyte range encomerties such as density and viscosity of the passed in the original patents of Hall and electrolyte also play an important role. Hkroult. The penalty paid when going to an extremely acid electrolyte is the reduced alumina solubility and therefore low ratios

can only be effectively used when operations tend toward point feeding and are associated with good control strategy (4).Use of low ratio baths also results in a reduced bath electrical conductivity which has a countering effect on energy consumption. Use of lithium fluoride modified electrolytes is easier, but if significant amounts (eg above 3%) are used, then subsequent metal treatment is sometimes required to lower the limited amount of lithium that is present through codeposition with the metal (8). (However, metal treatment is becoming more important generally with the extensive use of dry scrubbers and the greater emphasis placed on the quality control of the metal for some of the modern applications.) Successful use of lithium modified baths has necessitated a relearning of cell operating characteristics and procedures at the potroom. Any conversion must be carefully planned and targets set. But then if basic procedures are followed (8) a current efficiency gain of at least 2% will be achieved as a consequence of the reduced metal solubility. Details of modern plant experience using magnesium fluoride is less well documented, its use being more widespread in the Asian and Eastern European zones. As it is a substitute for calcium fluoride, its use is automatically restricted when the alumina is derived from bauxites that are processed via the conventional (Bayer) process because of the natural calcium levels that usually result. Laboratory studies have indicated that magnesium fluoride addition will increase the efficiency. However its greater tendency to co-deposit (than lithium) also limits the extent it can be used without either metal treatment or restricting the metal use. 122

Mass Transfer Control Besides reducing the solubility of the metal, major advances have been made in reducing the rate whereby the dissolved metal can be transported away from the metal-bath interface. Approaches used include: - flattening the contours of the metal Pad - reducing the metal pad circulating velocity, -optimizing the inter-electrode separation, - minimizing operating disturbances that can cause local metal pad turbulence or waves.

123

Note: LM80-401 is article in Light Metals 1980 starting uape 401.

Table I1 illustrates the importance of metal pad control. In this table current efficiences are compared for different technologies of a similar size, but with varying degrees of magnetic compensation. While direct comparison between technologies is seldom justified the correlation is still obvious. Innovation and laboratory studies have also played an important role development of techniques for measuring bath and metal velocities and metal pad contours. This has provided background information for the magnetic Progress on the first two of these are modelling. closely aligned to advances in magnetic field Optimizing the inter-electrode distance is modelling. While these advances have been more closely related to energy consumption, primarily applied to cell design (for increas- but it is also related to current efficiency ed size and reduced energy consumption) because of the importance of temperature they have had an obvious implication on that results at the optimum inter-electrode mass transfer. spacing. The many studies of ledging, insulating qualities of refractories and heat Table I1 RELATING CURRENT EFFICIENCY TO balance modelling have been aimed at ensuring that the cells operate at their METAL / BATH INTERFACIAL minimum superheat without unnecessarily VELOCITIES sacrificing inter-electrode distance. (Technologies Developed in 1960’s) The efforts directed towards minimizing Cell C.E. Reference Feature operating disturbances are much more (%) Size subtly documented. However, in the new or 150kA 85-87 Table I11 High velocity retrofilled cells (discussed below) invariably distorted metal pad anode effect frequencies are reduced, and 155kA 90-92 LM80-401 First generation control strategies minimize sludging through magnetic field comover-feeding. Stability has also been pensation improved by lowering thermal disturbances 130kA 89 LM82-559 No magnetic comthrough operating procedures as this ensures pensation the amount of frozen ledge is constant. 150kA 92 LM82-559 Same cell retrofitted Current efficiency gains (of the order of with mag field com2%) by stabilizing the operation were pensation and imdemonstrated in 1962 by C.E. Ransley (10). proved control

His presentation on the use of titanium diboride rods for contacting the metal pad aroused considerable interest. While it was aimed at voltage reduction, the better contact with the metal pad reduced the effect sludge pad on metal pad disturbances hence the higher cell efficiencies. The role of stability is further reinforced by efficiency comparisons between Soderberg and prebake cells. Prior to the modern era of point feeders and advanced control strategies, the efficiences of Soderberg cells were generally better. Soderberg technology has few operating disturbances in the important zone between anode and cathode as anodes are not changed. Like the magnetic modelling these advances have also been aided by fundamental developments - in this instance via efforts that developed techniques for measuring turbulence and short term fluctuations in metal pad height, for example.

Process Control & Operating Strategy Process control necessitates sensors to indicate cell condition as well as automation for adjusting cell voltage, inter-electrode distance and adding known amounts of alumina - then one must decide how one will control the cell. The first significant step enabling useful control was the development of mechanical crust-breakers coupled to a volumetric alumina feeder /metering. Schmitt’s description of a centre break and feed system (10) in 1962 aroused considerable interest and this saw the dawning of a new era for process control. (Incidentally Schmitt obtained more than 2% current efficiency gain but his work incorporated many other changes.) About the time I left the industry in 1963

anode effects at regular intervals. Some even allowed for the operators assessment of an individual cell condition to be input into the control strategy (e.g. warming trends, noisy pots, yellow flame, etc). The main function of the process control was to adjust the cell voltage after assessing whether the variations were of a short or long term duration. The adjustment was to a constant value on the assumption that this maintained optimum inter-electrode distance. Such an assumption was wrong as it had previously been shown (12) that at constant inter-electrode distance cell voltage would vary with alumina concentration. However, these resistance control systems did minimize variations in cell heat input and problems associated with noisy cells and thus led to more stable operations. Thus a general efficiency improvement of 1-2 % was achieved. Economic justification was supported by reduced labor costs, quicker anode effect termination and better data access. In retrospect one of their greatest weaknesses was the excessive emphasis placed on the need for operators to overProcess Control Systems ride the system, and general lack of trust (as reflected in the need to have anode effects). From the early 1960’s these have The real benefit of these early analogue developed in three stages despite the divergence in approaches. The stages have control systems was the reduced disturbeen cell resistance control with prebances and better stability rather than mainprogrammed regular feeding, resistance con- taining conditions at their optimum. trol with feeding reference to a notable About the time the virtues of various event (such as the occurrence or approach resistance control strategies were being exof an anode effect), and systems based on haulted (in Light Metals 1971-1976) there the rate of change in resistance. was also a series of papers demonstrating The first generation of systems used that the cell conditions were dynamic. Beanalogue instrumentation for the regular tween feeds changes in a number of process feeding of alumina. The amount added was conditions, such as temperature, voltage and based on an assumed consumption rate and ledge condition occurred. Therefore single bulk density of the alumina. Many of the point assessment was not a good way to systems deliberately underfed resulting in make control decisions. Furthermore these

my employers (then) were embarking on their first computer control project. I never did get a satisfactory answer to my question ‘what were they really going to control?’ but they did assure me they would be gaining 2% efficiency through the change. In 1970 I visited a smelter in Europe where a young engineer was extolling the virtues of the new computer-control system they had installed. In that case it was based on a demand-feed strategy just prior to anode effect. In discussion the engineer confidentially confessed that it was not economic - he had convinced management it would give a 2% efficiency gain, but they were only achieving 1% improvement. These comments illustrate the dilemma the industry was faced with - control hardware existed, but there were no sensors that could monitor performance and very few variations that could be made. Inter-related operating strategy influenced the development and hence a divergent range of systems resulted.

papers also recognized the harm anode effects had on current efficiency. (Schmitt (1 1) had given correlations earlier while others have erroneously claimed efficiency drops to zero during an anode effect.) Thus a second generation of control strategies emerged that made some allowance for the expected variation in resistance with time, and were generally based on demand-feed over-ride. They still had limitations for example, they could not discern when a cell was genuinely running cold. However, with the advent of microprocessors and inexpensive minicomputers more frequent data acquisition and processing was possible and therefore statistical techniques could be applied to trends, while rates of change could also be evaluated (13). Thus anode effect frequencies of less than 0.5 per pot day could be achieved and the more stable operation led to efficiency gains of about 2%.

The most advanced control strategies (developed over the last 7 years) are reliant on a combination of efficient point feeders, extensive use of microprocessors for tracking cell trends and a good theoretical basis for the changes to be observed. They are being applied to the new generation of cell designs and therefore their contribution to further efficiency gains cannot be directly assessed. One such system (14) controls against an expected resistance-alumina concentration curve in the region where the alumina concentration is close to the optimum for both efficiency and energy consumption. It operates by cycling the average alumina concentration around a mean value for defined underfeeding and overfeeding periods. This enables inter-electrode distance to be controlled also. However, it should be noted that even this system does not main-

124

tain conditions constant and the cell temperature still cycles by about 10°C even though the anode effect frequency is reduced to about 0.2 per pot day.

Operating Strategy

125

The development of control systems has been hindered by lack of in-situ process sensors. While effective alumina concentration meters have been developed in the laboratory, they lack robustness and sensitivity for continuous potroom operation. Likewise corrosion prevents the continuous use of thermocouples. Thus it has been necessary to maintain the human element -the judgement and skills of the potroom operator. This directly leads to operating strategy. The importance of operating experience was recognized in the era before automation. From a visual inspection people could assess whether a pot was running hot or cold, whether it was noisy or not, or whether it was making metal - or could they? (The operations were more dynamic then and conditions would swing widely over a few hours.) However, in the 60’s efficiency results obtained from trial cells were usually about 2% higher that those obtained in a full potline and that was attributed to the extra attention cell recieved. Or was it due to inexperience with that technology? As seen in Table I11 experience does play an important part in obtaining good performance. This table compares different plants that all installed the same centre break prebake technology (including control system) that had been developed in 1969. This cell had good design features for emission capture, for plant layout and for operating procedures,

but did not incorporate any magnetic field compensation. The supervisory staff had experience with different technologies yet it is seen that quite similar performances were obtained in the first year (especially after allowing for line current differences).

Table 111 PERFORMANCE ACHIEVEMENTS OF 1969 TECHNOLOGY INSTALLED AT SEVERAL LOCATIONS Plant & Year

Performace Performance Footnote in 1st Year in 1984 kA CE(%) kA CE(%) A-1972 138.7 85.0 149.7 89.8 88.3 85.3 146.2 B-1972 139.3 89.5 (1) 87.0 150.1 CI-1972 146.2 89.9 (1) 88.8 149.9 CII-1976 144.9 Footnote: 1. Bath chernistrv has been chanced.

However, when a plant started up a new potline using the same technology and workers with experience on the same cells, higher performances are achieved - about 2%. Over the years these plants have trialed numerous process changes including optimizing line current, changing both chemistry, changing feeding strategy (both size and frequency of alumina dumps) and varying the volume of metal reservoir. While the conditions now differ in each of the plants, they are all now operating with efficiencies about 2% above those achievable after their initial familiarization with the technology. Thus in the absence of full automation, experience with a technology does play an important role while operating strategy developed locally also plays a vital role. In the more automated point fed generation of cells, the need for operator skills

and technology experience is probably diminshed but the need for attention to detail is even more important.

Cell Design As seen in Table I, we have had a steady increase in cell size, from a modest 4kA immediately following the establishment of the industry, to the 250kA cells that are being tested today. Motivation for increasing cell size; i.e. reduced labor costs, improved energy efficiency can readily be understood (in the latter case heat losses are automatically reduced.) However, increasing cell size has presented challenges, especially when the object of improving current efficiency is included. Hall’s statement (1): “It appears that in enlarging the operation no complicated problems will arise, but that by following a few simple principles success can easily be obtained. ” could not have been more wrong - if only he had known about the magnetic forces in the metal! As is highlighted by Warren Haupin in his Energy Efficiency Review, mathematical modelling has enabled the magnetic forces to be balanced, and this has led to metal pad velocity control. The state of today’s technology is such that extremely flat and quiet metal pads can be developed - sometimes they are too quiet. Current efficiency gains have resulted because this has reduced the interfacial velocity which, as illustrated by equation 2, needs to be minimized. Increasing size and controlling the metal pad are not the only important design changes that have been made that have helped current efficiency. Advances in

alumina feeder design and materials of construction of cell have been concurrent necessary features.

Alumina Feeding Undoubtedly the first big step forward was the development of the automated breaker beam and interfaced volumetric hopper discharge system. This led to improved cell stability, allowed other operating conditions to be more finely tuned and led to more than a 2% efficiency gain(l1). The cost of the installation and variability in properties of alumina meant that it could only be effectively used on large cells that could tolerate large volumes of alumina at a given time. While being “a giant step forward for aluminium smelting,” the automated break and feed system has its limitations. The large alumina dump invariable leads to sludge formation and therefore it is important to have a reasonable metal pad velocity to disperse the sludge before instability arises. Similar problems persist if the length of the section to be broken is reduced. Reducing the dump size and increasing the break frequency leads to excessive heat losses and air burning, Thus it has been necessary to develop a better feeding system. Use of point feeders has grown substantially in the last decade. By using better quality alumina, breaking only a small (less than 100 mm diam.) feeding hole and only adding 1-3kg, most of the problems associated with the previous generation of feeder have been overcome. Most important, they have minimized the short term variations in temperature and alumina concentration while simultaneously reducing the tendency to form sludge. Thus the operation can be

carried out with lower melting electrolytes (usually high excess aluminium fluoride) and with smaller levels of superheat. Hence efficiency gains of the order of 2% have been achieved (15) by retrofitting cells with point feeders.

Materials of Construction Good design is aimed at maintaining a stable side-freeze/ ledge profile during operation and therefore heat-balance control is also important. The thermal requirements of the material used at the corners and ends of cells differs from those in other zones. This is more noticeable when changing corner anodes when poor thermal design can lead to excessive freezing while the anode is not drawing current (16). Such an occurrence results in instability and a lowering in efficiency. Sidewall materials have been developed that have varying thermal conductivities and improved corrosion resistance. These enable cells to be constructed that give more stable operation. Although the publications relating to advances in cathode materials are usually directed towards lowering energy consumption, the advances have also aided gains in current efficiencies. For example the use of graphitic blocks and glueing techniques (17) has led to more uniform current distributions and hence more stable operation and higher current efficiencies.

time they tend to be “designed” rather than “evolving from the previous generation.” Although modelling has been used extensively the designs emerging still have unique differences. Table IV summarizes the efficiencies of some of these cells - but it must be borne in mind that efficiency alone is not the important measure of the quality of design.

Table IV THE PERFORMANCE OF SOME MODERN CELLS Cell Size

Current Efficiency

kA

(so)

195 180

94.7 95k0.5

185 270 150

93.2 90 92

Energy

(kW/ kg)

Reference

13.1 13.0 12.97 13.76 13.9 12.6

LM84-455 LM83-595 LM82-449 LM80-401 LM83-587 LM82-559

The impressive thing emerging is that, despite each of the cells having some unique characteristic, they are all extremely good performers. They approach the best that can be achieved by integrating the knowledge and experience accumulated over a century. However, integrating knowledge relies on the knowledge that is communicated.

Advanced Through Communication Although smelting companies are con-

Efficiencies of Modern Cell Designs cerned about secrecy - and hence potential Today’s public knowledge is based on design concepts constructed about 1980. The designs incorporate better materials of construction, point feeders, the cells are magnetically balanced and have advanced microprocessor control logic. For the first

technological advantage - the advances achieved would not have eventuated were it not for the more open communication that has existed in recent years. Fortunately a more open approach js possible because technologies differ and applications are not

126

always transferable between designs. Furthermore with the high cost of R & D companies are more likely to buy technology and therefore a need has evolved for the more open approach. That is why we are all here today - to obtain a better understanding of the process through communication. It is the cornerstone for sounding out ideas, formulating new ones, but also important for dispelling falacies that are invariably presented in the smelting industry through erroneous interpretation of data.

AIME International Symposia

127

In February 1962 AIME organized the first truly international symposia on aluminium smelting and this saw the dawning of a new era. Because many of the technical contributions relate to current efficiency I would like to highlight its role briefly. The papers ranged from modelling through design, materials, techniques for monitoring performance to cell operations. The recorded discussion illustrated the diversity of views held then. Some technologies presented to the meeting such as centre break and feed (1 1) were subsequently implemented more generally. Others - such as continuous prebake anodes (18) - quickly faded because of obstacles to their implementation. The relevance of the Pearson & Waddington equation to accurate current efficiency determination was questioned by some authors (19,20). Questions included presentations related to the nature of the dissolved metal (21), techniques to measure the metal content and efficiency (22, 23) and the analysis of the bath ratio (24). The meeting also saw the emergence of a more analytical approach to cell design with several papers relating to modelling. Probably the most important thing was the matur-

ing of a new generation of people who clashed in debate as can be seen from the recorded discussion. (Ethan Hollingshead easily won the “most asked” questions contest from Nolan Richards with Warren Haupin being a distant fourth. However Reynolds Metals Co. representatives were the most inquisitive in contrast to the Alcoa personnel who quietly listened.)

Light Metals The Light Metals series of publications represents the greatest collection of papers on aluminium smelting and the organizing committee can take considerable credit for this. It is a direct consequence of their endeavours to improve communication for aluminium smelting. Over the years Light Metals has summarized many ideas that have been tested for improving current efficiency and if we were to integrate them all in the ideal cell it would run at an efficiency well in excess of 100%. Probably the greatest advantage of published proceedings has been to seed new ideas in the minds of people as to how they may to improve the current efficiency of their own operation by 1 or 2% more.

Retrofitting Cells This will never give rise to performances comparable to new cell designs because of limitations imposed by cell size and existing plant layout. As seen in Table V retrofit technology has been quite successful. The changes made incorporate some or all of the following: bath chemistry; process control; point feeding heat balance; and magnetic compensation. Incorporating some of these changes - such as control bath chemistry and heat balance is easy, while others - such as magnetic field compensation - difficult or virtually impossible for some plants. They are all expensive because they are being applied to smaller production units. However retrofitting cells does offer several options for improving current efficiency by at least 2%.

Table V ADVANCES IN EFFICIENCY THROUGH RETROFITTING CELLS Original

Ref

Type kA CE%

kA

VSS 70 87

PB94 90.7 LM80

PB 155 92

PB180 93.5 LM80 -401 PB150 92 LM82 -559

PB 130 89

Future Utilization of Knowledge Through design of new cells we can now achieve 95% current efficiency and consistently operate to 94% - but what next? We cannot abandon the extensive installed capacity based on yesterday’s technology so can we utilize the knowledge and improve the cells by retrofitting them? What knowledge or achievements are needed to improve the efficiency further in the next generation of cells?

Retrofit Cell

cell

Major Change

CE%

VSS 100 90

VSSl00 92 LM82 -435

PB 70 89

PB70

91 LM82 -461

Mag .Camp., 1-1 p Control, Heat Balance Batter Mag. Comp. PF’s Mag. Comp. Heat Blance, Control Strategy Bath Chem. Control Strategy, Anode quality. P.F’s Improved Control

Abbreviations: Mag.Comp. is Magnetic Compensation: P.F‘s - point feeders, and ~1p microvrocessor.

FUture A dvances Gaining another 2% in current efficiency (based on the best installed technology) is feasible but dependent on

- better training documentation and understanding at the potroom level.

- further design advances that eliminate sludge formation and minimize operating disturbances. - further refinements to control systems and strategies. Training and understanding are needed to de-emphasize important concepts of yesteryear that are no longer applicable to today’s technology. It is necessary to minimize anode-effect frequency, or even eliminate them. Process disturbances when coming out of abnormal conditions should be minimized and it needs to be realized there are other ways to remove sludge besides simply using prolonged heating. Some myths need to be dispelled and more confidence given to automation and less reliance placed on visual assessment. The biggest single obstacle to maintaining stable conditions is the anode changing operation. This introduces a process disturbance (25), negating benefits derived from magnetic field balancing. For almost half the cell’s life one anode is drawing little or no current and this gets worse as the bath and metal pad velocities are reduced. Perhaps we need to re-examine our advances in carbonaceous materials and see if, through innovation, we can redesign the continuous prebake anode. Point feeders are not the ideal design either and innovation is required to find better ways to introduce the alumina so that it doesn’t introduce a process disturbance and the alumina disperses sufficiently to

avoid aggregation and sludge formation. A continuous feed of preheated alumina is necessary. But how is it going to be dispersed uniformly through a cell that has such a low velocity electrolyte? Process control strategy still has scope for improvement - especially if better use is made of techniques for analyzing “noise” in cells (26). Microprocessors can be used to discern wave patterns and therefore control strategies can be modified to minimize disturbances as action is taken to quell the disturbance. Materials may also continue to play a part and the design options opened by using diboride cathodes (27) still presents a tantalizing incentive. At the best, solving all of these problems will only result in a current efficiency gain of another 2% - the greater implications will be on energy consumption and labor costs. What then is the limit? I highly doubt if we can ever go beyond 98% C.E. - losses through mechanisms ignored by Pearson & Waddington (such as carbide formation on cathode lining and sodium deposition into the lining) are becoming more significant proportionately. Furthermore, diffusional transport of dissolved carbon dioxide or dissolved metal will still occur. Realistically, as the remaining problems are solved, it is going to be better to squeeze inter-electrode distance. Thus the glamour topic of yesteryear - Current efficiency - will move aside for energy consumption.

Acknowledgements I would like to thank my many friends in the industry - from many companies - for providing me with technical information. Often the information has been confidential. I want to especially thank Comalco Ltd. who, over the years have supported my research and thus enabled me to maintain an interest in such a challenging process.

128

References 1. 2. 3. 4. 5. 6. 7. 8.

9. 10.

11.

12.

13. 14.

129

J.D. Edwards, F.C. Frary & Z. Jefferies “The Aluminum Industry” McGraw Hill, N Y (1930) ~~16-25. P.Barrand & R.Gadeau “L’Aluminium” Vol. 1. Eyrolles, Paris (1964) pp 194-247. E.Bosshard, O.Knaishc, W.Schmidt-Hatting & J.Blanc “EPT 18: The new 180 kA Pot of Alusuisse” Light Metals (1983) pp595-605. M.Keinborg & J.P.Cuny “Aluminium Pechiney 180kA Prebake Pot from Prototype to Potline” Light Metals (1982) pp449-460. T.G.Pearson & J.Waddington Disc. Faraday SOC. No.1 (1947), 307. T.G.Pearson “The Chemical Background of the Aluminium Industry” Royal Znst. of Chem. Mono & Reports No.3 (1955) 103 pages. K.Crjotheim, W.E.Haupin & B.J.Welch “Current Efficiency - Relating Fundamentals to Practice” Light Metals (1985) pp679-694. G.Kusche1, B.J.Welch & G.French “Lithium Losses During Addition & Dissolution of Various Forms of Lithium Carbonate to Electrolytes” Light Metals (1986) to be published. R.G.Cheney “Potline Operation With Lithium Modified Bath” Light Metals (1983) pp519-536. C.E.Ransley “The Application of Refractory Carbide and Borides to Aluminium Reduction Cells” in AIME Ext. Met. of Aluminium VoI.2 ed. G.Gerard - Wiley (1963) pp487-505. H.Schmitt “New Methods in Construction and Operation of Electrolytic Cells for Aluminium Reduction” in AIME Ext.Met. of Aluminium V01.2 ed. G. Gerard -Wiley (1963) pp169-182. B. J.Welch “Technology of Electrolytic Reduction of Alumina by the Hall-Hkroult Process: I A Voltage Analysis Under Conditions of Varying Alumina Concentration”. Proc. A m . I M&M NO.214, (1965) ppl-19. C.A. Wilson & A.T.Tabereaux “Alumina Control in Centre-break Cells” Light Metals (1983) pp479-493. U.S.Patent 4,431,491 “Process and apparatus for accurately controlling the rate of introduction and the content of Alumina in an igneous electrolysis tank in the production of Aluminium” P.Bonny el a1 Pechiney (1981).

15. 16.

17. 18.

19.

20.

21.

22.

23.

S.Casdas “Revamping Side-worked Prebake Pots” Light Metals (1982) pp461-469. G.T.Holmes, D.C.Fisher, J.F.Clark & W.D.Ludwig “Development of Large prebaked anode cells by Alcoa” Light Metals (1980) ~~401-411. K.Etqe1, F.Brandmair, P.Aeschbach &H.Friedli “Gluing of Cathode and Anodes - a proven technology” in Light Metals (1983) pp885-896. G.Lange & G.Wilde “Large Aluminium Electrolytic cells with continuous Prebaked Anodes” in AIME Ext. Met. of Aluminium V01.2 ed. G.Gerard - Wiley N . Y. (1963) pp197-208. E.A.Hollingshead & V.A.Braunworth “Laboratory Investigations of Anode consumption in the Electrolytic Production of Aluminium” in AIME Ext. Met. of Aluminium V01.2 ed. G.Gerard, Wiley, N Y (1963) pp 31-48. J.D.Hamlin & N.E.Richards “Studies of the Anode Gas from Hall-Hkroult Cells” in AIME Ext. Met. of Aluminium V01.2 ed. G.Gerard, Wiley, N Y (1963) pp51-61. J.J.Stokes & W.B.Frank “Spectroscopic Investigation of the Occurence of Sodium in Fumes above Molten Cryolite” in AIME Ext. Met of Aluminium V01.2 ed G. Gerard Wiley, N Y (1963) pp3-13. R.Smart “The Determination of Aluminium Cell Current efficiencies by very small copper additions” in AIME Ext. Met. of Aluminium VoL2. ed G.Gerard Wiley, N Y (1963) pp249-258. T.Hiraoka & T.Hirayama, M.Nitto and K.Hamada “Determination of Metal Content in

24.

25.

26. 27.

Aluminium Cells by means of a reactor Irradiation method” in AIME Ext. Met. of Aluminium Vol. 2. ed. G.Gerard Wiley, N Y (1963) ~~261-273. J.S.Lobos & R.H.Black “Control of Cryolite Bath Ratio” in AIME Ext.Met. of Aluminium V01.2 ed. G.Gerard Wiley, N Y (1963) ~~277-292. M.P.Taylor & B.J.Welch “Bath/Freeze Heat transfer coefficients: Experimental Determination and industrial Implications” Light Metals (1985) ~~781-792. N.Urata “Magnetics & Metal Pad Instability” Light Metals (1985) pp581-592. A.V.Cooke & W.M.Buchta “Use of TiB, Cathode Materials: Demonstrated Energy conservation in VSS Cells” Light Metals (1985) ~~545-566.

Barry J. Welch Professor Barry J. Welch holds a PhD from the University of New Zealand, and a DSC from the University of Auckland. Barry was employed by Reynolds Metals Co. prior to joining the faculty of the University of NSW (Australia) in 1964. His keen interest in extractive metallurgy (primarily aluminum smelting) has resulted in nearly 100 technical papers, and the co-authorship of two books. The several visiting professorship positions he has held attest to his international technical reputation. In 1980 Barry joined the University of Auckland where he currently holds the title of Professor and Head of the Department of Chemical and Materials Engineering.

Carbon Electrodes in the Hall-HCroult Cell: A Century of Progress David Belitskus, Alcoa Laboratories Aluminum Company of America Alcoa Center, PA 15069

Abstract Charles Martin Hall and Paul L. T. HCroult were fortunate that the development of suitable carbon anode and cathode materials in commercial quantities preceded their independent discoveries, in 1886, of a commercially successful electrolytic method for producing aluminum. However, even though suitable carbon materials were available for the early commercial cells, the tremendous increase in cell size, efficiency, and productivity over the past century has required substantial carbon electrode developments. This paper reviews the state of the art of carbon electrode technology a century ago and traces developments in raw material Processing and electrode manufacture.

Introduction Although many of the manufacturing principles of carbon electrodes for use in

Hall-Hkroult aluminum production cells have not changed radically in the 100 years since conception of the process, steady improvements in raw material and manufacturing technology have permitted electrode performance to keep pace with the added demands from ever-increasing cell sizes and amperages during that period. This paper describes the state of development of carbon technology prior to 1886 and traces some significant developments during the past century. Since attempts to locate published descriptions of many developments were limited by time and resource constraints, this paper is not claimed to be an allinclusive historical review. Rather, selected developments, in more-or-less chronological order, will be described in varying amounts of detail. It is hoped that these vignettes will prove to be of interest to the reader, despite the lack of completeness.

Carbon Technology Developments Prior To The Year 1886 Although the independent discoveries by Charles Martin Hall and Paul L. T. Hkroult of a commercially viable process for producing aluminum provided the foundation for a huge industry, it must be noted that had this invention not been preceded by commercially available sources of relatively pure and inexpensive manufactured carbon, it might have remained a laboratory curiosity for many years. In turn, manufactured carbon developments depended to a great extent on developments in the petroleum and coal industries. Petroleum was used for centuries in ancient Mesopotamia, Egypt, Persia, China, and elsewhere for heating, lighting, road making, and building (1). Marco Polo is said to have noticed “oil springs” near the Caspean Sea in the thirteenth century. In

130

131

the Americas, Raleigh described the Trinidad Pitch Lake in 1595. However, before the middle of the nineteenth century almost all oil for lighting was from animal or vegetable sources, and machines were lubricated with castor oil or whale oil. The first commercial well drilled specifically for oil was sunk by Drake in Titusville, Pennsylvania, in 1859, a mere 27 years before the Hall-HCroult invention. Oil was struck at a depth of less than 70 feet, in contrast to modern wells, which may exceed depths of 15,000 feet. Coking was soon developed in petroleum refineries as a method of maximizing thermal cracking products (distillates). However, originally there were no important uses for the resultant coke. At the Standard Oil Company near Cleveland, Ohio, coke was disposed of by burning under oil stills (2). In 1877, Charles F. Brush and Washington H. Lawrence began experiments to develop coke as a filler in manufactured carbon. Initial attempts were with as-produced coke, but shrinkage and cracking during baking were excessive. Eventually, Brush discovered that calcining the coke prior to forming pitch-bonded shapes resulted in good carbons. Like petroleum, coal was discovered in ancient times (3). The Chinese reportedly used coal as early as 1000 BC. The Greeks and Romans knew of it by about 400 BC, but had little use for it. The Romans did mine and utilize coal in England in the early part of the Christian era. It is reported that trade in coal began in England in 1215 AD. Although early use of coal was for heating, use of coal coke for iron smelting laid the foundation for by-product tar recovery. The Reverend John Clayton had distilled coal in a retort in the mid-1600s to form a

liquor, tar, and coal gas. The beehive oven was used for the distillation of wood in the seventeenth century, but was first used for coal coking in England around 1750. In some beehive ovens by-products could be recovered, but the first practical by-product ovens were yet to be developed. The first commercial distillation of coal tar was carried out in 1818. The horizontal flued coke oven is considered to be the first satisfactory byproduct recovery oven, and one hundred of these were installed in 1851 (3). Thus, as with petroleum coke, tars for binder production became abundant only a few decades prior to the Hall-HCroult invention. Another significant development in coal technology, heavy media washing, occurred in 1858 (3). This technique eliminated the need for extensive hand-picking of noncarbonous material from as-mined coal, and thus helped facilitate use of coal (especially anthracite) in Hall-Hkroult cell linings. Patents on mixing coke with tar, molding, and baking appeared at least as early as 1858 (by DeGrasses B. Fowler of New York). From a commercial standpoint, Carre in France was probably the first to have notable success in manufactured carbon, chiefly for electrodes for arc lighting (2). Brush and Lawrence were largely responsible for the development of the American carbon industry. In addition to the work described earlier, they experimented with different filler particle size distributions and binder types. Hall used some electrodes supplied by Brush in his early work on aluminum production.

Carbon Electrodes In The Early Years Of Commercialization Of The Hall-HCroult Process In this section, available information on carbon in early commercial aluminum smelting cells will be described. Before discussing carbon use in the successful operation of Hall’s process by the Pittsburgh Reduction Company (later renamed the Aluminum Company of America), an interesting failure will be noted. Hall’s first financial backing for development of his process came from the Cowles Smelting and Aluminum Company in Lockport, New York, which was commercially producing aluminum-bronze by a carbothermic process (4). Despite Hall’s use of carbon anodes in his pioneering experiments, he favored a copper “inert anode,” on which he proposed that a copper oxide layer would form and protect the remainder of the anode from additional oxidation. Unfortunately, in his work at Cowles this concept was not successful. To complicate matters, Hall used potassium cryolite rather than sodium cryolite in the smelting cell electrolytes at Cowles. It is now known that potassium has a greater disruptive effect than sodium on carbon cathodes, but Hall may have been unaware of the reason for severe disintegration of his cathodes at Cowles. These two factors (and, perhaps, others) led to termination of his contract with the Cowles Company on April 27, 1888. Anodes in the first commercial cells at the Pittsburgh Reduction Company on Smallman Street in Pittsburgh, Pennsylvania, were 3 inches in diameter by about 15 inches long and were suspended from threaded 3 / 8-inch diameter copper rods

from an overhead copper bus (4). The cells were about 2 feet long, 1 ‘/2 feet wide, and 20 inches deep, with a 3-inch thick baked carbon lining. They carried 1700-1800 amps at 16 volts. A layer of powdered carbon butts was placed on top of the molten bath to reduce heat loss. There were reportedly 10 anodes per cell, arranged in 2 rows (5). However, one photograph of a cell in the Smallman Street plant (Figure 1) shows 8 anodes. If only the bottom surface of the anode is considered, anode current density was at least 25 amps/in2, very high by today’s standards. Carbon anodes and cathode mix came from the Faraday Carbon Company, across the street from the works. This company’s major products were carbon brushes for dynamos and carbons for arc lights (6). The anodes and cathode mix were transported across the street by wheelbarrow. Although no mention is made of the nature of the carbon lining material in the references cited, it presumably was similar or identical to the anode material (petroleum coke filler); therefore, life must have been quite low because of the considerable swelling due to sodium typical of non-graphitized petroleum coke base material. Six pots containing 20 anodes each were added to the 2 original pots in 1889 (7). In 1891, production was moved to New Kensington, Pennsylvania, where 8 pots, each containing 30 anodes, were operated by the end of the year. Figure 2 is another photograph of an early cell. Limited information is also available on HCroult’s cells operating at Froges (France) in 1889 (4). At first, water-cooled crucibles, rotated to promote rapid solution of alumina and containing a single anode, were used. Hkroult replaced the water-cooled

Fig. 1 - An early Pittsburgh Reduction Company aluminum smelting cell.

Fig. 2 - A larger Pittsburgh Reduction Company aluminum smelting cell.

crucibles with air-cooled cast iron “pots” and, eventually, the rotation was found to be unnecessary. The pots carried 4000 amps at 8-10 volts. After some time, the single anode was replaced by four anodes, reportedly reducing the anode current density from 40 to 10 amps/in*, which reduced anode voltage drop and bath temperature. Additional improvements included increasing the number of anodes to eight. Potlining was a mixture of charcoal and pitch; no mention of anode composition was included in the reference cited.

132

oil distillers were changing over to processes that produced no coke. It was mentioned also that sulfur, one of the undesirable constituents of petroleum coke, was greater in Although several references contain useful cokes from Mexican crudes than from other fields. information on carbon technology during The coker at that time was far different the late 1800s and early 1900s, a series of from today’s delayed coker. The still was six articles in the journal, “Chemical and horizontal, with the coke depositing on the Metallurgical Engineering,” published in 1922 by Charles L. Mantel1 of the Pratt In- lower wall (Figure3). No attempt was made stitute, Brooklyn, New York, provide by far to control the volatile matter in the coke. After completion of a run and 4-6 hours of the most comprehensive coverage (8). cooling, workmen wrapped their hands, head, and feet in wet cloths and entered the still through a manhole. They broke off coke from the sides and bottom of the still box and unloaded it. Since the heat in the still was excessive, the men remained in the still for only a short while. As shown in Figure 3, there were two types of coke: a low volatile shell coke up to 2-3 inches in thickness and a higher volatile top layer. It was not until 1929 that the delayed coking process still used today was invented by Standard Oil in Whiting, Indiana (9). In contrast to today’s essentially exclusive use of coke oven by-product tars for coal tar binder pitch production, additional sources of coal tar were available at the turn As today, petroleum coke was then the major filler material for aluminum smelting of the century (8b). These included retort gas tar (obtained in the hydraulic mains, cell anodes, although purified anthracite scrubbers, and condensers in the manufacwas reported to have been used in Europe. ture of coal gas for ilIumination), water gas Ash in Welsh anthracite was reduced to as tar (obtained from the manufacture of carlow as 0.6% by treatment with sodium hydroxide (8b). buretted water gas for illumination), and It was stated that the market price of Pintsch or oil gas tar (obtained from the petroleum coke had trebled in recent years manufacture of oil gas used for railroad and that petroleum refineries began to lighting). Coal tar, often a mixture of the regard it as a valuable commercial material. types described above, was distilled to produce pitch or used directly in molded carHowever, it was noted that the quantity available was growing smaller because many bons.

State Of The Art And Developments In Manufactured Carbon Technology In The Late Nineteenth And Early Twentieth Centuries

Fig. 3 - Schematic view of an intermittent-type oil still, showing coke formation. (Redrawn from Reference

8b.)

133

Both electric and gas-fired calciners or “shrinkers” were used in the early days of aluminum production (8c). An example of an intermittent electric calciner is shown in Figure 4. The top electrodes were first lowered nearly to the bottom of the calciner. Green material to be calcined was added and an arc was produced when current passed. The top electrodes were then gradually raised, and heating was then by resistance. Typically, the calciner was filled in 8-12 hours, and heating was continued for another 12 hours. After about 24 hours of cooling, coke was unloaded by rakes through a discharge door.

Fig. 4 - Schematic diagram of an intermittent type of electric calciner. (Redrawn from Reference 8c.)

Fig. 5 - Schematic view o f a Woodall-Duckan calciner. (Redrawn from Reference 8c.)

Typical of a gas-fired kiln was the Woodall-Duckam retort first introduced in England in 1903. Figure 5 is a schematic diagram of this type of kiln. Coal or coke was fed through a hopper at the top of a vertical retort, which was heated on the sides. The speed of descent was regulated by the rate of discharge of material from the bottom of the retort, the coke being gradually calcined as it descended. These retorts were rectangular and tapered from the top to the bottom. The retort walls were formed from tongue-and-groove bricks, paneled out at the back so that heat from the vertical flues was readily conducted to the charge. Producer gas or calciner gas from the operation and secondary air were admitted at the top of the vertical flues and burned downward. Temperatures between 1050°C and 1250°C were reached. The coke was cooled by a water jacket before discharge. A significant milestone in coke calcination was adoption of the rotary kiln calciner. An early calciner for petroleum coke was built by Great Lakes Carbon Corporation in 1935 in Port Arthur, Texas, adjacent to a Texaco refinery (10). This type of calciner was installed at five other locations over the next ten years, and this has remained the dominant method of coke calcination. It is obvious from Mantell’s article on grinding, mixing, molding, and extrusion (8d) that most of the principles required for good quality manufactured carbon were known by 1922. As today, a number of crushing and grinding machines and a variety of pitch handling practices were employed. The potential explosiveness of pitch dust was recognized at that time. Weighing by means of automatic weighing machines, with scales based on the balanced

Fig. 6 - Schematic diagram

Charging Aperture

of a paddle mixer. (Redrawn from Reference 1 1 ) .

Magnesia Covering

I

Door *

beam principle, is described. The most common mixer was a steam-jacketed drum mounted on its side (Figure 6) (1 1). Mixing was accomplished by rotating a central shaft equipped with arms with a forward tilt so that the mix was carried toward a discharge door. The problem of inability to accurately predict optimum binder level was recognized, and attempts to predict optimum level based on raw material properties were made by the National Carbon Company, with limited success (8d). In practice, the mixer-man would take a handful of mix and “feel” whether it contained the right amount of binder. Both molded and extruded anodes were used in early aluminum smelting cells. Molded anodes began to be used exclusively when anode sizes began to increase significantly and when it was recognized that chamfering of anode tops would reduce the amount of butt that had to be recycled

134

Fig. 7 - Sketches of early chamfered molded anodes. (Redrawn from Reference 12).

Fig. 8 - Schematic diagram of a vertical hydraulic electrode press. (Redrawn from Reference 13).

135

(Figure 7) (12). A typical hydraulic press is shown schematically in Figure 8 (13). This press was about 15 feet high, and pressures of 500 atmospheres were attainable. Electrodes were said to vary in cross sectional dimensions from about 8 to 16 inches. A cubical electrode was said to be common in large European cells. Baking in “ring” furnaces was already practiced in these early days of carbon electrode manufacture (8e). Although details of construction and operation have obviously improved considerably over the years, the general principles of good construction and operation seem to have been quite well understood by 1922. Mantell’s description of ring furnaces is quite detailed, but will not be covered in depth in this paper. Figures 9 and 10 are schematic diagrams of these early ring furnaces. As today, both open top and closed top furnaces were used. A major difference from today’s practice was that relatively small size anodes were manually pulled from the pits by means of long-handled tongs. After the carbons were removed and the pits cooled, workmen entered the pits and removed packing material and deposits on the walls. The fuel for firing the furnaces was generally producer gas. No reference to fuel efficiency was given. It was noted that waste gas from the baking furnaces was usually a “heavy greenishyellow color, having a marked deleterious effect on vegetation.” As population began to increase near carbon baking facilities, scrubbing of waste gas began to be carried out. Use of a “tunnel kiln” in which the carbons are placed on trucks that are pushed through the furnace by hydraulic pistons is described also (13).

A History Of Prebaked Anode Cell Development At One Smelter A brief summary of prebaked anode cell evolution at Alcoa’s Tennessee Operations provides some interesting information on anode size increases and, to some extent, on cathode developments. The first aluminum smelting cells installed at Tennessee Operations in 1914 or 1915 had internal dimensions of 4% feet by 7% feet by 2 feet deep (14). The collector bars were bolted directly to the steel shell, with the bus to the next pot connected to a tab on the back of the shell. These cells had 40 cylindrical anodes, 5 inches in diameter. Each cell operated at about 10 volts and produced about 130 pounds of aluminum per day. The original pots were not removed and straightened during relining, but were allowed to bow. A 5 / 8-inch diameter copper rod was hammered into a hole drilled into the top of each anode. In 1926, the 40 cylindrical anodes were replaced by 32 anodes having 7-inch square cross sections, which doubled the anode area. Line load was increased from 10,000 to 13,000 amps. In 1934, these anodes were replaced by 10 rectangular cross section, 13-inch by 15-inch anodes and the line load raised to 19,000 amps. In about 1950, anode cross section was increased to 13 inches by 17 inches.

r C a r b o n Pits ,--Flue

Insulating Brickwork

Floor Level 7

Wast Ga Flu

Gas Mains

Floor Level

\L Ports to Flues

To Waste Gas Flue

I

Port to FlueA

Fig. 9 - Schematic of a gasfired longitudinal pit type baking furnace. Top: through pit walls; bottom: through equalizing chambers. (Redrawn from Reference 8e).

7

Ports From Flues

Pit Lengthy

Gas

Air

Fig. 10 - Schematic view through the middle of a flue showing horizontal (top) and vertical (bottom) types of baffles. (Redrawn from Reference 8e).

I

\

Port From Flue

Equalizing Chamber

136

Fig. 11 - An early 1900s Alurniniim Company of Arne:rica aluminum smellting cell.

The anodes were adjusted individually with a hand-operated lifting and lowering device. Cells were tapped from a hole in the lining, which was resealed with a clay “dough ball.” Average lining life was 490 days. Another type of cell, nominally 40,000 amps, was installed in 1926 and 1927. This cell had 20 anodes, 13 inches by 17 inches in cross section. This was later increased to 22 anodes, 15 inches by 21 inches. Cells of the general type described in this section are shown in Figures 11 and 12.

Fig. 12 - A 1930s vintage Alurninum Company of Amf :rica aluminum smelting cell.

137

Beginning in the 1950s, a number of prototype cells were installed prior to introduction at other Alcoa smelters. Although these cells included a number of innovations, only electrode information will be given here. Friction welded copper to aluminum anode bars were first used on a 1954 prototype cell for the Massena, New York, smelter. The first prebaked cathode block bottom cells used by Alcoa were installed in 1954 and 1955. The idea of a “heat window’’ in a cell lining was first tried on a 93,000 amp prototype cell for the Rockdale, Texas, smelter.

Fig. 13 - Schematic diagram

Along with these and many other successful electrode innovations, description of a few failures provides interesting contrast. A continuous prebaked anode pot was tried (Figure 13), but the problem of properly cementing the blocks together and the high labor cost contributed to its abandonment. Another novel design was a sloping, bare graphite cathode bottom cell, which was intended to reduce bus cost, decrease lining voltage drop, and eliminate magnetic problems with the metal pad. This cell was unsuccessful, allegedly due to carbiding problems with the bare bottom. Potroom data records indicate that during its 3-month life, this cell produced aluminum at a current efficiency of only about 50%.

of a continuous prebaked

P r e b a k e d Anodes

anode aluminum smelting cell.

Development Of The Soderberg Anode The continuous, self-baking anode was developed by C.W. Soderberg in Norway prior to 1919. However, for adaption in aluminum smelting cells, a long series of developments were necessary (15). The first Soderberg electrodes used iron ribs to carry current to the baked part of the electrode and to make a good mechanical connection between the suspension device and the electrode. These ribs introduced considerable amounts of iron into the metal when tried in aluminum smelting cells. The first Soderberg anode cell at Vigeland, Norway, in 1923 had an aluminum casing with iron ribs that were reduced in size, and only a small fraction of an inch thick. Although iron introduced into the metal was only about 0.1 %, which was considered satisfactory, extensive testing at several locations throughout the world indicated that anode voltage drop was too

high. When rib size was increased, iron contamination was too great. One by one, trial Soderberg cells were being shut down. It was obviously necesary to find a better way to conduct electrical current to the anode. In 1925, individual “horizontal” (actually, diagonal) contact studs were developed by Elektrokemisk. In the course of the downward movement of the anode, the studs were gradually baked into the anodes, then removed before they came in contact with the bath. This resulted in

good electrical contact without metal contamination. In 1927, commercial plants were installed in France, Spain, and at Alcoa’s Tennessee Operations. The cells at the Alcoa plant were rated at 30,000 amps. Up to 1930, Soderberg anode cells were of circular cross section (Figure 14). The largest cells required electrodes about 7 feet in diameter. With anodes of this size, cells did not operate well with an anode current density greater than about 4.5 amp/in2; a similar size cell with prebaked anodes could have an anode current density of

138

Fig. 14 - Schematic drawing of a circular Soderberg anode aluminum smelting cell. (Redrawn from Reference 15).

significantly reducing the number of contact studs needed by adopting the practice of removing the studs from the lower portions of the anodes and immediately reinserting them, along with electrode paste, at a higher level in the hole. Therefore, no studs were left for any length of time in an unbaked portion of the anode, where -they are not productive. Since the vertical studs could be more uniformly distributed with respect to the cross section of the anode than horizontal studs, current distribution was improved. Suspension of the electrode was also simplified. By the late 1940s, cells as large as 100,000 amps were being tried.

Soderberg Electrode

Electrode Clamp Molten Electrolyte Thermal Insulation

Vibration Formed Anodes

L Carbon Lining Collector Plate

139

over 6.0 amp/in2. It was speculated that this had to do with the longer path of escape of gas developed under Soderberg anodes. Since operating results of large, round Soderberg anode cells were not as good as cells with prebaked anodes, rectangular Soderberg cells were tried in the United States and France, with considerable success. First suspension devices were steel frame sections removed before they touched the bath, but the slotted permanent casing was eventually developed. Closed cells with gas collection systems were developed also.

As far back as 1919, work on vertical, screwed studs had been carried out by Elektrokemisk (15). However, good contact was not obtained. Montecatini in Italy developed conical contact screws, with the larger diameter at the lower end. This improved contact, but cracked the electrode and did not stand up satisfactorily. Hence, this system was abandoned after a few years of trial, and vertical contact studs were not successfully applied until the principle of coking the stud surface into the anode was developed. The French engineer, Robert Jouannet, is given credit for

While Soderberg anode cells proliferated in the 1940s and 1950s, prebaked anode cell developments continued also. In the late 1950s ASV in Norway decided to install 66 cells in half a potline with a special VAW (Germany) anode, about 7% feet by 3 feet by 2% feet and weighing 2 tons (16). However, no existing press was able to produce such big blocks. Instead, they were first hand-made by a crew using pneumatic ramming tools. In November 1958 a vibration unit from screening apparatus was adapted for anode forming, and vibration formed anodes were successfully produced and baked by May 1959. Anodes were uniform, with baked apparent densities of 1.56 to 1.58 g/cm3. A permanent installation was completed in 1960. Vibration forming of cathode blocks was also started in 1960. Development of the vibration forming process has been a major factor in the succesful operation of large, high amperage prebaked anode cells.

Cathode Developments Although comments on cathode technology have been included throughout this paper, this section offers additional information. As mentioned earlier, Hall’s original cells apparently had non-graphitized petroleum coke base linings, and Hkroult’s cathodes had a charcoal base. Over the years, a number of other carbon sources including bituminous coal coke, anthracite calcined in gas-fired kilns, electrically calcined anthracite, and graphite particles have been used as filler materials. Baking temperature of the pitch and tar bonded material has varied from less than 1000°C to over 2000°C. A great many published reports on relative merits of various materials, baking temperature effects, and formulation factors are available; no attempt will be made to summarize and critically judge these reports. It does appear that many of the important factors were identified at least 50 years ago. For example, internal reports of Alcoa from 1933-1936 cover very extensive work on raw material types, particle size distribution, and baking rates (17). All early cells were lined with monolithically formed carbon paste baked in the cell. As cells became larger lining life became unacceptably short, and block linings were developed. The first reported use in North America was in 1929, and the first full plant use in North America was in Canada in 1952 (18). It has been reported that reduction cells above 80,000 amps could readily justify the more expensive block linings and that block-lined cells of this amperage typically have longer lives than much smaller monolithically lined cells, 50,000 amps or less (19). A plot of

E p“

45 40 35 30 25 20 15 10 5 0 1926 1931 1936 1941 1946 1951 1956 1961 1966

Fig. 15 - Percentage of United States total primary aluminum production using prebaked carbon cathodes. (Taken from Reference 19).

Year

percentage of cells in the United States having block linings, up to the year 1961, is given in Figure 15. Since it was known quite early that the more graphitic the carbon lining material the more resistant it is to swelling and deterioration from sodium attack during cell operation, fully graphitized linings had been tried prior to 1940 (19). However, the high cost of graphite as well as its softness have deterred its use. Nonetheless, use of graphite particles as part or all of the filler and use of “semi-graphitized” blocks have become common. In addition, replacement of gas-fired, rotary kiln calcined anthracite by higher temperature (electrically) calcined anthracite was initiated at least as early as 1960, with increased lining life (20). A major recent development in block lining installation is use of seam mix tampable at ambient temperature, greatly reducing exposure of workmen to pitch fumes during seam installation.

Carbon Characterization Tests There are a considerable number of tests developed for carbon electrode raw material characterization. Many that are commonly used today had their origins during the relatively early days of aluminum production. For example, the Conradson carbon test for yield on carbonization of an organic material such as pitch was first reported in 1912 (21). Although alternate test methods have been developed, the Conradson coking value is still reported most often. In contrast, another test that is very simple in concept and believed to be an important quality criterion, bulk density of calcined petroleum coke, has seen the independent development of many variations. Results from the various test versions are not very comparable. However, a recent version has been standardized by the American Society for Testing and Materials (22). As with carbon raw material characterization, there have been many fabricated car140

bon tests carried out over the years that State Of The Art Of Hall-Hdroult have contributed to improvement of HallCell Electrode Technology Htroult cell electrodes. Two of these, each Although a summary of today’s developed about 30 years ago, merit menknowledge concerning the important printion. Proof of their significance is the freciples of aluminum smelting cell electrode quent citation of the original papers. technology would certainly be appropriate In 1957, Rapoport and Samoilenko first in this paper, the author believes that this used the combination of a reverse polarity would excessively add to the length of the test cell (with the cathode suspended in the paper and, moreover, that this information bath and the container serving as the anode) can be conveniently gleaned from other and use of measuring rods contained in sources. Information of this type is readily holes drilled to different depths in the available from many of the Carbon cathode to determine swelling during elecTechnology papers in the AIME “Light trolysis (23). In contrast to earlier tests that Metals” volumes over the past 15 years. A necessitated measurement of sample dimen- few other state-of-the-art type papers are sions after electrolysis, this test provided a available also (25-27). dynamic, accurate record of swelling. “The Proof Is In The Pudding” Although other tests have at times been Many Hall-HCroult cell electrode claimed to be superior in characterizing developments have been outlined in this swelling behavior of cathode materials, paper. The proof of their value can be results using various versions of this test demonstrated by the vastly improved perforcontinue to be reported frequently. mance over the early days of aluminum In 1962, Hollingshead and Braunwarth smelting. Figure 16 shows average net anode reported on a test for anode characterization (4). This test is even simpler in concept consumption for Alcoa smelters over much of the past century (28). Since theoretical than the cathode test mentioned above, carbon consumption is affected by current merely a bench-scale Hall-HCroult cell. However, solution of difficult experimental efficiency, this is included in the figure. Two points should be kept in mind in viewproblems by these workers and demonstraing this figure. One is that while the net cartion of reasonable and reproducible results from a small-scale cell have led to extensive bon curve is not quite as impressive as it use of different versions of such a cell for determining “dusting” tendencies of anodes.

141

might be without the decrease in theoretical consumption due to improving current efficiency, some of the improvement in current efficiency may well have been due to improved anode quality. A second point is that these are averages for all the smelters and thus are increased by the inclusion of performance from some rather old potlines. Best values are appreciably lower. Figure 17 shows average cell lining life in Alcoa smelters over a good part of the last century. It can be seen that average life has improved about six-fold over the time period. As mentioned above for anodes, recent values would be even more impressive if results of only the best lines were considered.

Acknowledgments The author wishes to thank the Aluminum Company of America for permission to write this historical review and to cite unpublished company information. The valuable contribution of Virgie Jo Sapp of Alcoa Laboratories Information Department in obtaining relevant reference sources is also appreciated, as is the permission to use the net carbon consumption and lining life data compiled by Dr. J. J. Trebendis of Alcoa’s Corporate Planning Division.

z-5

0.80

-

U 0.70

-

.-

Fig. 16 - Average net anode consumption for Aluminum Company of America aluminum smelting cells.

0.90

Theoretical Net Carbon Consumption Based on Current Efficiency Data

d

2 0

0.60

e

$ d -I c)

Q

0.50 0.40

z 0.30 1885

1905

1925

1945

1965

1985

Year

Fig. 17 - Average lining life of Aluminum Company of America aluminum smelting cells.

1905

1925

1945

1965

1985

Year

142

References The Petroleum Handbook, compiled by the staff of the Royal Dutch/Shell Group of Companies (Amsterdam, The Netherlands: Elsevier Science Publishers B.V., 1983), 3. 2. C. L. Mantell, Carbon and Graphite Handbook, (Huntington, NY: Robert Krieger Publishing Co., 1979), 247. 3. A. E. Martin and G. R. Yohe, “The Coal Industry and Coal Research and Development in Perspective,” Chapter I in Chemistry of Coal Utilization (New York, NY: Wiley-Interscience, 1981), 1 . 4. P. T. Stroup, “Hall, Hkroult, Aluminum and Fused Salt Electrochemistry,” Transactions of the ASM, 62, (1%9), 1045-1078. 5 . ‘J. G. Tayor, “History of Pittsburgh Works, Pittsburgh Reduction Company, September 1888 -September 1891” (unpublished report of the Aluminum Company of America, November 1938). 6. J. G . Taylor, “Reminiscences of Smallman Street Plant, an Interview with A. V. Davis” (unpublished report of the Aluminum Company of America, November 1938). 7. C. Bradley, “History of Charles and Edward Bradley with the Aluminum Company of America” (unpublished report of the Aluminum Company of America, January 1938). 8. a.C. L. Mantell, “The Technology of the CarbonElectrode Industry - I The History of its Development,” Chemical and Metallurgical Engineering, 27, (3), (1922), 109-112. b.“II Raw Materials for Electrode Manufacture,” 27, (4), (1922), 161-165 c. “I11 A Critical Review of the Calcination Process,’’ 27, (9,(1922), 205-210. d. “IV Grinding, Mixing, Molding and Extrusion,” 27, (6), (1922), 258-264. e. “V Baking and Baking Furnaces,” 27, (7), 1.

143

9.

10. 11.

12. 13.

14.

15.

16. 17.

18. 19.

20.

(1922), 312-318. f. “VI Cleaning, Testing, Machining and Shipping,” 27, (8), (1922), 353-359. J. W. Conners, “Changes in Petroleum Coke Quality and Future Prospects” (paper presented at the 110th AIME Annual Meeting, Chicago, 11linois, 1981 February 22-26). The Great Lakes Story (pamphlet from Great Lakes Carbon Corporation, 1965). G. A. Roush, “The Manufacture of Carbon Electrodes,” The Journal of Industrial and Engineering Chemistry, (May 1909), 286-295. H. Ginsberg, “Carbon Anodes in the Production of Aluminum,” Metal1 und Erz, 36, (3) (1939), 72-76. 0. Nissen, “Aluminium-Manufacturing Process Used in Europe,” Chemical and Metallurgical Engineering, 19, (12), (1918), 804-815. W. R. Allen, “History of Hall Pot Development in Tennessee” (unpublished report of the Aluminum Company of America, January 1972). M. Sem, J. Sejersted, and 0. Bockmann, “Twenty-Five Years’ Development of the Soderberg System in Aluminum Furnaces,” Journal of the Electrochemical Society, 94, (4), (1948), 220-231 . Kjell Nielsen, “Vibrating Carbon Blocks” (private communication from Andreas Anderson, ASV, Oslo, Norway, 1985 August 13). C. B. Willmore and R. Shawcross, “Improvement of Pot Linings - Progress Reports” (unpublished reports of the Aluminum Company of America, 1933-1936). ibid. Ref. 2, 301. L. E. Bacon, “Trends in Cathode Lining Materials,” Extrative Metallurgy of Aluminum, 2 (New York, NY: Interscience Publishers, 1962), 461. M. M. Williams, “Electrically Calcined Anthracite for Potlining,” Light Metals 1971, (War-

21.

22.

23.

24.

25.

26.

27.

28.

rendale, PA: The Metallurgical Society of AIME, 1971), 163. P. H. Conradson, “C Test and Ash Residue in Petroleum Lubricating Oils,” The Journal of Zndustrial Engineering Chemistry, 4, (1 l), (1912), 903. D. Belitskus, “Standardization of a Calcined Coke Bulk Density Test,” Light Metals 1982, (Warrendale, PA: The Metallurgical Society of AIME, 1982), 673; also, ASTM Standard Test Method D-4292 (1984). M. B. Rapoport and V. N. Samoilenko, “The Deformation of Cathode Blocks in Aluminum Baths During Electrolysis,” Non-Ferrous Metals (Russ.), 30, (2), (1957), 44-51. E. A. Hollingshead and V. A. Braunwarth, “Laboratory Investigation of Carbon Anode Consumption in the Electrolytic Production of Aluminum,” Extractive Metallurgy of Aluminum, 2, (New York, NY: Interscience Publishers, 1962), 31. S. S. Jones, “Anode Carbon Usage in the Aluminum Industry,” reprints from the Symposium on Petroleum Derived Carbons, American Chemical Society, St. Louis Meeting, (April 1984), 457-465. a.G. J. Houston and H. A. Oye, “Consumption of Anode Carbon During Aluminium Electrolysis (1),” Aluminium, 61, (3), (1985), 25 1-254. b.(II), 61, (4), (1985), 346-349. c.(III), 61, (9,(1985), 426-428. D. Belitskus, “Optimization of Raw Materials and Formulations for Hall-Hhoult Cell Electrodes,’’ reprints from the Third Yugoslav Symposium on Aluminum, Ljubjana (1978). J. J. Trebendis (unpublished data compilation of the Aluminum Company of America, February 1983).

David Belitskus David Belitskus joined Alcoa in 1964 shortly after receiving his PhD in Physical Chemistry from the University of Pittsburgh. His research on carbon electrodes for smelting has led to numerous technical publications and presentations. Today David holds the title of Fellow in the Ceramics Division of the Alcoa Laboratories.

Outlook of the Bayer Process Nils Oeberg and Rudolf 0. Friederich Alumina Division Swiss Alum inium L imited, Zurich, Switzerland

This paper concentrates on giving an historical review of alumina plants in the Western World, which utilize the Bayer process for manufacturing alumina from bauxite. Some trends of further developments will be discussed.

Plant Unit Sizes The first industrial alumina plant using the Bayer patent was started up at Gardanne (France) in February 1894. The plant was originally designed for a capacity of 4 t/day, its output, however, bearly exceeded 1 t/day.(Nearly 75 years later, this was the rated capacity of the pilot plant Alusuisse used for the design of its Gove plant). Only one year later, in 1895, a second plant using the Bayer process was started up at Larne (Northern Ireland). Precise figures about its original capacity are not available, but within a few years its production was in the range of 15,000 tpy of calcined alumina.

Both of these plants produced fluory alumina. A few years later, in 1902/03, the first sandy alumina plant was started up at East St. Louis (USA/Illinois). No accurate information is available on the original size, but it is assumed to have been in the range of 10 - 20,000 tpy. To evaluate and compare plant capacities, only unit sizes must be considered. For the determination of unit-sizes the capacity of digestion is the governing factor. The evolution of sandy and floury alumina plants shows a different pattern; it is illustrated in Figures 1 and 2. According to Figure 1, the unit capacity of floury alumina plants developed steadily but slowly in Europe until World War I. Only years after the post war crisis did the European industry start to grow faster. New alumina plants were built in the thirties with capacities in the range of 50,000 tpy and

shortly before World War 11, even 100,000 tPY. Then, a war and its consequences imposed a halt on the floury alumina industry, which lasted into the fifties. A dramatic recovery started worldwide in the sixties with the construction of a number of new plants with increasing unit sizes as well as some major expansions, which were achieved by adding new units with modern equipment to existing plants (capacities of about 200,000 tpy/unit were typical). Finally the unit size for floury alumina plants reached 500 - 600,000 tpy between 1970 and 1980. After that, all major floury alumina plants were gradually converted to the production of sandy alumina with varying degrees of success. No new production units for floury smelter grade alumina will be built.

144

ALUMINA PLANT: UNIT SIZE (FLOURY)

SO

1980

Figure 2 shows the explosive evolution of the sandy alumina industry starting essentially with World War I1 after a rather depressed period between 1900 and 1940, when almost all the American alumina demand was covered by the production of the East St. Louis plant or through imports. The unit sizes built around World War I1 averaged 200,000 tpy (with one exception of 450,000 tpy).

YEAR

Fig. 1 - Alumina Plant: Unit size (Floury)

Thereafter plant sizes continued to grow without, however, abandoning the standard capacities of roughly 200-250,000 tpy for new units and/or expansions. Typical nominal unit sizes finally reached a range of 500 to 800,000 tpy in the seventies and early eighties. Obviously, there is no general rule for an optimum unit size. Each plant is a special case depending on its location, sources of supply and corresponding markets.

ALUMINA PLANT: UNIT SIZE (SANDY) A

Small units are better suited for gradual expansions or shutdowns, meeting the market’s demand more accurately. Big units, obviously, have lower operating and capital costs under similar conditions, but are less flexible. Whether the present level of maximum unit sizes and equipment will further increase is doubtful. Equipment sizes would become very cumbersome for operation, and maintenance and flexibility would suffer even more. YEAR Fig. 2 - Alumina Plant: unit size (Sandy)

145

Nevertheless, the capacities, irrespective of their present nominal size, will be further increased by debottlenecking, retrofitting and/or optimization of equipment and process. A number of reasons may accelerate such a development, as described below.

Plant Capacities The present cost-price relation is deteriorating, creating a critical situation for most of the alumina plants. The range of relative operating costs of these plants is shown in Figure 3 as a function of cumulative alumina, capacities. The low cost end is populated by a few large plants, which commenced operation 5 - 15 years ago. The upper end contains many small, old or otherwise disadvantaged plants, while some large new plants hover around the center. It is further known, that the nominal alumina capacity exceeds the corresponding primary aluminum capacity by about 25 % . Several simultaneous moves are likely to occur in order to bring alumina and primary metal capacity into balance during the present period, of extreme cost pressure: - the large low cost alumina plants will be expanded concentrating essentially on energy-saving modifications. - the large new plants in the average cost range will reduce their financial charges as they are depreciated. They are also amenable to process modifications, which increase capacity and lower costs. Thus they will eventually join the above group of low cost producers. - the many small, old and/or disadvantageously located plants will either have to be upgraded to compete with other large plants or stop production of smelter grade alumina. The potential capacity increase of 20 - 30% (requiring much less capital expenditure than new plants) available to large modern plants, together with the current overcapacity, will make the construction of new grassroot plants quite unlikely during the next 10 - 15 years.

REL

:OST

TPY CUMULATIVE A1203 - CAPACITY Fig. 3 - Cumulative A1203. capacity.

Thus smaller units will disappear and the bigger units will increase in capacity. Maximum unit sizes in the range of 750,000tpy may become quite customary, and 1.0 Mio tpy may be reached under exceptional conditions.

Productivity Strongly related to unit size and plant capacity is obviously the liquor productivity. Little information was received from other plants on this subject; we therefore will concentrate on Alusuisse records as shown in Figure 4. The first Alusuisse Bayer plant started its operation in 1908 with a capacity of 26 t of floury alumina per day, making it the largest plant in Europe at that time and up to World War I. Even though the analytical methods have changed during the years, it is interesting to

summarize the evolution and trend of its liquor productivity. After initial good results, productivity dropped to an extremely low value of 36 g AI,O,/l pregnant liquor. The high liquor concentration, as recommended by Bayer, was not suitable for the equipment available at that time, and increasing impurity levels deteriorated the situation. Low caustic concentration and saturation levels had to be imposed in order to operate mud and hydrate filters, with a consequent reduction in liquor productivity. Once a modus vivendi was found, productivity remained quite steady at about 45 g/l with a liquor concentration of 110 g Na,O/ 1, rather high temperatures, moderate amounts of seed and a holding time of several days. With the gradual introduction of heat exchangers, thickeners and new filtration equipment, operating conditions were improved, and productivity jumped to 60 - 70 g / l in plants for floury alumina. Most Alusuisse plants, producing floury alumina, operated during 1960 - 1980 in the range of 160 - 180 g Na,O/l at precipitation temperatures of about 50 - 60 " C , a seed addition of 300 g / l , a holding time of 2 - 4 days and a productivity level of about 70 g/l. Sandy alumina plants in turn maintained a steady productivity of about 45 g / l throughout the years. Only recently (around 1980) were process modifications introduced and liquor productivities for the standard sandy alumina plants raised. At present productivities of about 55 g / l are being reported. One reason for producing two types of alumina with substantially different produc-

g ~ ~ n ~ s PRODUCTIVITY / ~

OF LIQUORS

Fig. 4 - Productivity of Liquors.

146

147

tivities may be found in the different raw material sources. Europe started processing the locally mined monohydrate bauxites, which require rather high temperatures and caustic concentrations in digestion. High energy costs further demanded a minimization of dilution and maximization of liquor productivities. Thus a rather fine hydrate was produced, which had to be calcined at high temperatures to limit dusting. On the other hand American plants started to operate with trihydrate bauxites. Therefore, low caustic concentrations were adopted, which at low productivities gave a rather coarse material. With low energy costs, high productivity was not necessarily required and, therefore, despite the introduction of cooling equipment, rather high pregnant liquor temperatures were maintained to produce sandy alumina, which was easily classified and filtered and which required no excessive calcination. Nevertheless, the drastic increase in energy costs during the seventies definitely required the implementation of higher productivity levels in sandy alumina plants. At the same time ecologic restrictions for smelters and hence modified smelter practice, called for aluminas with high adsorptive capacities, which only sandy aluminas have. Floury alumina plants, therefore, in order to meet these new requirements, had to reduce the degree of calcination,which however, is only feasible with a coarse product, in order to contain dustiness. These plants accordingly had to adapt their operations to meet the new specifications, hopefully without losing productivity. Alusuisse introduced a new process for sandy alumina

in its floury alumina plant at Gove, which even exceeded the original productivity by about 10%. Alumina plants producing floury alumina will thus disappear, and sandy alumina production will have to strive for higher productivity levels to reduce specific energy costs. It is estimated that liquor productivities in the range of 80 to 90 g/l may soon become common, provided raw materials (e.g. caustic soda) consumption can be controlled.

Plant Location In connection with the above consideration of production economy, site selection should also be evaluated. During the first century of the Bayer process, dramatic changes occurred in the aspects governing the choice of location of an alumina plant. The first industrial plants in Europe were preferentially located near sources of cheap fuel. Martins-werk is an example. It is located in Bergheim near Cologne (FRG) in the immediate vicinity of large brown coal mines. In 1915, economics dictated that it was less costly (per ton of alumina) to carry 3 tons of bauxite to the source of coal than to carry 7 tons of coal to the source of bauxite. The same consideration was valid for many of the original alumina plants like Gardanne or St. Louis les Aygalades. The highly fuel efficient Bayer process of today has reversed the argument: a ton of alumina requires about 2 tons of bauxite and only 0.3 tons of fuel; thus plants would preferentially be sited near the bauxite source. The alumina plants of Gove and Western Australia are examples, from where the alumina is then exported. It is worthwhile to remember, that the first bulk ship-

ment of alumina in an ocean-going vessel was made only in 1954, from Jamaica to Norway. Before that, alumina was shipped in bags. As the overall efficiency of the alumina manufacturing process increased, transportation costs for raw materials and products became more and more significant. Thus a plant location with easy access for oceangoing vessels (e.g. St. Croix, Aughinish) but with long transport for raw material and product are no longer sufficient incentives for plant siting, even if rendered attractive by tax reductions or other incentives. The future alumina plant would, if the planner had a choice, be located where an accumulation of economically favorable “physical” factors occur, such as:

- within conveyor distance of bauxite mine

- within conveyor distance of smelter - ready access to fuel (order of preference: gas, oil, coal)

- ready access to caustic soda and lime - availability of water - economic labor force (low rates and/or well trained)

- existing infrastructure - access to deep water harbor (for export capacity). Few places in the world offer entirely ideal conditions. Alumina manufacturers have grown weary of “man-made” advantages to attract alumina plants, e.g. - tax incentives - governmental assurances of various kinds - subsidies of banks, communities, publicly owned enterprises. There are many examples of alumina plants, which are no longer (or never were)

economic producers, because too much importance was attached to the “man-made” factors at the expense of “physical” factors. Too often tax incentives, government assurances or subsidies faded away, once the plant was built. Sound and sober economic analysis and far-sighted planning are necessary prerequisites for the choice of the next alumina plant site.

Quality Definition of a proper smelter grade alumina quality has always been a problem with frequent changes of specification throughout the Bayer plant history. The historic evolution of some major quality parameters for floury aluminas has been evaluated below, using the information available from Alusuisse plant records. Figure 5 shows the concentration of the total caustic content in calcined aluminas expressed in % Na,O. Well known facts are confirmed: Curve No. 1 shows a typical development. With falling temperatures, reduced holding time and rising concentration, contamination escalated until it reached values around 0.7%. At that time supersaturation played a subordinate role. The other two curves initially running in parallel show the impact of World War 11. After an initial increase in production with a consequent increase in caustic content, production had to be confined during the forties. Thus, with less stringent precipitation conditions (e.g. 140 g Na20/l), the caustic contamination again decreased. Later on, with the recovery of the worldwide economy, the demand for alumina increased. Alumina plants again pushed the operating conditions more or less to the limit. Curve No. 2 shows the effect of a

“moderate” increase in caustic concentration up to 160 g/l, whilst curve No. 3 similar to No. 1 operated almost at 180 g/l. The corresponding caustic content increased to 0.5 and 0.8% respectively. Sandy alumina plants with a consistent high starting temperature in precipitation and rather low concentration usually produce a low caustic alumina in a typical range of 0.3 - 0.5% Na20. With the change-over of floury plants to sandy alumina or higher liquor productivities, most plants will be confronted with a new caustic problem in alumina. Some I I I I means to control caustic content are already available. Quite a number of quality parameters are controlled by type and degree of calcinaFig. 5 - Calcined alumina tion, such as BET, LO1 alpha-alumina con- quality caustic content. tent, density, etc. Little information, however, is available on the behavior of these values during the past. Today, with sandy alumina being the preferred smelter grade quality, a moderate source only and producing floury alumina degree of calcination is required to produce: at high caustic concentration. For the first 30 years, not shown, its silica content - a high BET surface area in the range of 600 ppm. After that with an imaveraged 40 - 60 compared with a floury alumina of proved dedication, a steady improvement a few M2/g to an average value of 180 ppm was ob- a high LO1 of up to 1% vs 0.1 - 0.3% for tained. floury alumina - a low alpha-content - lower density of 3.5 - 3.6 compared with the high values of 3.9 for floury alumina. Important quality parameters are impurity levels. They are primarily influenced by bauxite composition but may be controlled more or less effectively by variations of the Bayer process. Figure 6 shows the trend of SiO, in alumina (Curve No. 1) for an Alusuisse plant operating with bauxite from one

I

I

148

ALUMINA

Fig. 6 - Calcined alumina quality Si0,-content.

149

trations and productivities reasonably well. Iron, another of the many impurities influenced by bauxite quality and controlled by proper operation shall be briefly mentioned. With increasing know-how of process and equipment, iron contamination in alumina was gradually reduced. Optimization of clarification and security filtration was essential. Average figures for Alusuisse plants are in the range of 150 - 300 ppm, with one plant being regularly below 100 ppm Fe203. The future trend in alumina quality is bound to remain subject to changes due to the increasing emphasis on efficiency and purity in primary metal production, which is governed by rising economic pressure, customer deyand as well as the need to accommodate recycled metal and alumina from Curve No. 2, in turn is typical for a dry adsorption systems. The direction of floury plant operating with a number of dif- change may be judged by the following exferent bauxites with S O 2 variations in the amples: product between 100 and 230 uum (1950Reduction into the region 1985). Curve No. 3 (Bauxite quality) com- -Na&ontent: of 0.3-0.4% because of pared with Curve No. 2 (alumina quality), lower flux losses (longer shows a familiar trend: as the silica percenpot life, vapor recovery in tage in bauxite increases, the better the dry adsorption). desilication and the lower the silica con- Heavy metals: Reduction in alumina in tamination of the alumina and vice versa. order to gain flexibility Not enough information is available for with use of recycled comparison with sandy alumina. Neverthealloys. less, the sandy plants with low caustic concentration have more favorable conditions - BET-surface: A balance must be found between dry adsorption for a good desilication with little contaminaefficiency and moisture tion of calcined alumina. adsorption. Again the general trend towards higher li- Alpha-alumina: There are indications that quor productivities will unfavorably ina low alpha-alumina confluence silica contamination in the near future. However, in this case too, a number tent (5-10%) increases the of methods are available to control any difefficiency of the modern ficulty which may arise with higher concensmelter.

CALCINED ALUMINA QUALITY SiO2-CONTENT

It is interesting to note that quality changes have a very long lead time. Dry adsorption, recycling of metal and point-fed pots have been in use for many years, yet the process of defining the “ideal” alumina is still in progress.

Energy A major component of the operating costs for alumina plants is energy. A historical analysis of energy consumption in the liquor circuit (expressed as tons of steam per ton of alumina produced) for a typical European floury alumina plant treating monohydrate bauxite is presented in Figure 7. Initially a consumption of 15 - 16 t / t was reported. By 1927, this figure was practically halved to 8 - 9 t/t due to improved process and equipment. No major breakthrough was recorded in the following years. On the contrary, with a sudden increase in alumina demand (prior to the war) and subsequent deterioration of the industry (during and after the war), steam consumption returned to 11 - 12 t/t. It was only in 1948 that the typical pre-crisis consumption of 8 - 9 t/t was regained. Optimization of process conditions with the introduction of new equipment allowed a further reduction of the steam consumption to about 4 t/t. In the sixties an additional breakthrough was achieved with the introduction of continuous digestion, which resulted in a further saving of 1.6 t/t obtaining a typical consumption of 2.4 t/t. With the subsequent industrial boom again, priority was assigned to production with a consequent deterioration of steam consumption. As of 1973, with the first down-ward trend in the last few years in the aluminum industry and

STEAM CONSUMPTION FOR AN EUROPEAN ALUMINA PLANT

Fig. 7 - Steam consumption for an European alumina plant.

ENERGY CONSUMPTION

Fig. 8 - Energy consumption.

escalation of fuel prices, alumina plant operators again became energy-minded. Optimization resulted in a gradual reduction to a steam consumption of less than 2 t/t alumina. Conventional production of sandy alumina requires more energy in the liquor circuit than floury alumina. Calcination, on the other hand, needs somewhat less energy for a sandy product. Therefore, overall energy consumption for a sandy alumina plant will ih general exceed the requirements of a floury operation. In this context the example of Gove, a plant converted from floury to sandy alumina, may be of interest. Figure 8 reflects the historic development of the overall energy consumption since 1974, the first year of full production of this Alusuisse plant. Some of the improvements in the period of 1974 - 1978 were due to experience of personnel and improved systems. The balance was achieved by increasing liquor productivity. During 1978/79, the plant was converted to sandy alumina. This changeover resulted in a slight increase in energy consumption due to tie-ins and commissioning, but the original level was soon restored after introducing the Alusuisse precipitation process. An intermediate peak, due to unrelatedproblems, interrupted the downward trend. Reduced fuel consumption in calcination and continuous optimization of process and controls then allowed a stable plant operation at high productivity and production levels with a further reduction of overall energy consumption. Thus the adaptation to sandy alumina does not necessarily mean an increase in energy consumption. Further energy saving will, no doubt, be the future trend. Major efforts will concen-

150

SETTLERS AND WASHERS

I

+CONVENTIONAL

I

I

RAKES SUSPENDED RAKES---+

Fig. 9 - Settlers and washers.

AREA m2

Fig. 10 - Mud security filters.

151

MUD SECURITY FILTERS

Simultaneously, modifications of standard units were introduced. Depending on priorities set by the owner (operation/maintenance, etc.) cones with/without scalloped bottoms with a low, medium or high slope Emphasis will also be on process control were adopted. Others used flat or negative and retrofitting of equipment in an attempt slope with outward raking. Finally the fixed to achieve the above goal. No generalized rakes, prone to high scaling rates, were statement can be made as to future energy replaced by the suspended type. The reducconsumption levels. It is expected, however, ed weight and scale load of these rakes in the above case of Gove, to further reduce were, however, not utilized by the owners to the energy requirements by another reduce the torque requirements. Feed wells, 20 - 30 %. launders, etc., were subject to continuous modifications to solve particular problems. As mentioned earlier, a further increase in Equipment the size of thickeners and washers seems In the course of this historic review, procunlikely. The trend goes in the direction of ess equipment has been mentioned retrofitting of equipment. Improved flocrepeatedly as an important issue in the culation, modifications of feedwell, changes technical and economic evolution of the of tank - geometry, implementation of new Bayer process. A few examples have been control systems as well as optimization of chosen to illustrate this statement. raking devices will result in substantial Figure 9 summarizes the development of reductions of operating and maintenance thickeners and washers. It was only in the costs in the future. twenties that thickeners were slowly acFigure 10 deals with mud and security cepted by the industry, in particular in the filtration. Originally the labor intensive USA. filter presses, operated within a narrow Originally multi-deck or tray-units were range of conditions, were the only equipused with a diameter of 10 -15 m and low ment available for mud separation. torque of 50,000 Nm peak load. With time The situation was somewhat alleviated and experience, the advantage of single with the introduction of thickeners and compartment units was recognized (imwashers. Liquor concentration was diluted proved clarity with similar or even increased prior to mud filtration permitting on the capacity). other hand the concentration in digestion to be increased. Thus in the fifties most of the alumina The same filter presses used for mud filplants introduced single deck units or modified old ones accordingly. Diameters of tration were also used in security filtration 20 - 25 m with peak torques of 100 -200,000 for many years. Apparently these filters only disappeared Nm became common. The trend towards after World War 11. Counter current decanlarger units continued. Diameters of 30 to tation was introduced and wherever mud fil40 m with torques of 800,000 to 1,200,000 tration was still in use, pressure filters were Nm became nothing unusual.

trate on increasing liquor productivity with a related reduction in energy requirement. Liquor concentration and purity are some of the parameters under investigation.

DIGESTERS

YEAR OF INSTALLATION Fig. 11

- Digesters.

PRECIPITATORS

INSTALLATION Fig. 12 - Precipitators.

installed. Also security filtration switched to the same type of pressure filters. Most of the batch operated pressure filters were later replaced by the continuous vacuum drum filters in mud filtration. Filter areas used in pressure and vacuum filters for mud amounted up to 270 and 100 m2 respectively. Pressure filters for security filtration in turn have reached effective filtration areas of over 400 m2. Other filters used for this purpose are batch and/or continuously operated sand filters. The conventional mud and security filter areas will hardly be increased in the near future. In particular, maximum size of security filters will not change; a certain number of filters is needed for adequate operational flexibility. Even if plant unit capacities increase, flows will remain at today’s level. Also in this area retrofitting and/or optimization will be promoted. Automatic washing/discharging will reduce water requirements and save manpower. New filter media and/or filter aids may assist in reducing operating and maintenance costs. In digestion, major improvements were achieved in continuous operation, heating of liquor/slurry and agitation. Figure 1 1 shows the evolution of the digester size in the Alusuisse designed plants. Some of the new high pressure plants for sandy alumina have gone to even larger sizes. Growth of equipment size in precipitation shows a similar trend (Figure 12) for the precipitators. For some new plants, precipitators of 4500 m3 appear to be the biggest

152

153

in operation to date. Other changes in thus created will in part compensate the precipitation involved agitation, mode of above losses. operation (bath vs continuous), cooling, etc. The potential spare capacity of several A review of details of process modificamillion tpy still available will gradually be tion, however, is beyond the scope of this activated as the market and the cost/price paper. Nevertheless, apart from purely structure improve. The above capacity may mechanical improvements, major changes in be fully utilized in the early nineties. operation and process control will favorably Additional capacities will thereupon be influence the future trend in the process and created by expansion of alumina plants. utilities areas. Major retrofitting, substantial increases in liquor productivities and implementation of Conclusions advanced process control will be the Obviously many more topics would be of methods of first choice. For this kind of exinterest for such a review. Unfortunately, an pansion new investments will be required, inquiry on Bayer plant history addressed to which however, will remain far below the all major alumina producers, was only parcapital requirements for greenfield plants. tially answered. Thus, only those items were The next step will involve the construction considered, where sufficient reliable data, of additional units with the improved often only in-house information, was availtechnology within existing plants. Such exable. The highlights evaluated above, howpansions will take advantage of available inever, are considered quite typical and frastructure and services. The corresponding representative for a historic review and investment for this added capacity will acoutlook of the Bayer process. cordingly still remain below the cost of In 1985, about 25 million tpy of alumina green field plants. will be produced with nearly 22.5 million The construction of new plants has to be tpy of smelter grade quality. The industry’s considered a luxury as long as the present utilization factor will amount to 83% conexpansion potential, which is in the range of sidering the western world’s alumina capaciseveral million tpy, has not been fully utity of 30 million tpy. lized. The start up of new plants may not Some of this capacity, as already menbe justified before the beginning of the next tioned, has been or will be lost in the very near future due to shutdowns of obsolete or century. During the remarkable progress in disadvantaged plants not amenable to a reaalumina plant operation expected for the sonable cost-restructuring. next decade, particular attention will be Many other plants will enforce measures paid to the quality of smelter grade to limit operating and capital costs by alumina. Specifications will become more reducing manpower, raw materials and stringent as smelter design and operation energy consumption via improved process control, removal of minor bottlenecks, step- develops. But Bayer process specialists, wise increase of liquor productivity or other equipment suppliers, plant designers and means. These improvements will be realized operators are confident they can meet this with only minor investments. New capacities challenge.

The smelter operator must keep in mind that increasing demands on purity and other properties of the alumina will invariably increase the cost of his major raw material. In conclusion, due to the existence of large deposits of good trihydrate bauxite and the availability of a technology with a continuously improving efficiency, the Bayer process will survive for quite some time to come.

Acknowledgement The authors wish to acknowledge the contributions received, thanking in particular Alcan, Comalco, Dorr Oliver, Eimco, Nippon Light Metals and Reynolds. Nils Oeberg In 1984 Nils Oeberg earned a degree in chemical engineering from the Swiss Federal Institute of Technology in Zurich. He then began a career of truly international scope. At various times he has worked in Chile, Italy, Australia, the United States and Venezuela, and as a consequence is fluent in 6 languages. Since 1973 Nils has been with Alusuisse in the Bauxite and Alumina Division working on the planning, construction, supervision, training, and ultimately assisting with start-up of new plant projects. He currently holds the title of Assistant Vice President in Alusuisse.

R. 0. Friederich Rudolf 0. Friederich joined Alusuisse in 1970 soon after receiving a PhD in Chemical Engineering from Clemson University. He subsequently held positions in Germany, Sweden, Australia, Switzerland, and in 1979 became plant manager of the Interalumina plant in Venezuela. In 1985 he was named Assistant Vice President for the Bauxite and Alumina Subdivision, located at corporate headquarters in Zurich, Switzerland.

Cast Shop Technology and Reclamation: 100 Years of Progress Warren S. Peterson, Consultant Metallurgical Chemical Processes 2113 East 37 Avenue, Spokane, WA 99203

This paper, along with the others in this series, celebrates the Centennial of the HallHCroult process for making aluminum. It presents an overview of developments in the melting and casting of process ingots and the reclamation of metal for that purpose. First a definition: Process ingot - the form in which aluminum is cast for subsequent mechanical working into semifabricated products, such as sheet, extrusions, and forgings. We will not discuss the products of the foundery, i.e. sand, die, and permanent mold castings. The process ingot form is quite different in size, metallurgical structure and chemical composition. Next, some observations and explanations: As an overview of 100 years of the development of practices and equipment in the Cast Shop, this presentation can only hit the high spots. There may be areas and specific developments which some feel are important, but not addressed here. I’ve tried to correct this in the selection of photos and drawings in the Cast Shop section of the Pictorial Review. This piesentation tends to report

American accomplishments. In part this may reflect my personal experience and judgement; but also, the paper relies heavily on material in the Pictorial Review to reveal changes in practices and equipment. As you can see, response from companies outside the United States varied considerably. In writing this paper, I have used a journal or personal approach for several reasons: 1) This is the form used by early workers before the rigid, third person, past tense engineering report was forced upon us after World War I. The early reports give me much more of a feeling for the people who conceived the ideas and did the work than present day papers; and this Centennial celebration is a tribute, not only to Hall and HCroult, but to all the men and women who have made contributions to our industry. 2) It allows me to relate some of the cast shop and reclamation developments from my own experience which began in 1942 when I joined Alcoa as a research engineer.

Melting And Casting Process Ingot - Then And Now

The First Fifty Years The earliest reports on aluminum do not provide much detail on melting casting operations. This is understandable because existing methods for melting and casting other metals were readily used for aluminum. The early workers found it easy to melt and cast the shiny, light weight metal, and the primary emphasis was on new ways to make aluminum at low cost. St. Clair Deville, who devoted his life to aluminum - sometimes called “silver from clay’’ - stated in 1859 (1) that all that is needed to melt aluminum is an earthen crucible, and, compared to other metals, no flux such as borax or glass to prevent oxidation. Mierzinski, however, in 1885 (1) pointed out the problem of using common clay crucibles “because it reduces silicon from them, by which the metal becomes grey and brittle.” Biederman (1) about the same time countered with the instruction that “Aluminum can be melted with perfect safety in com-

154

mon clay or sand crucibles, if they are lined with carbon.” He reported further, “I have been told that in a large European works, where 500 to lo00 lbs. of aluminum are melted at once on the bed of a reverberatory furnace, the hearth was formerly protected by pure bauxite, closely rammed in and strongly fired before using.” I give these early observations because it is interesting to find that, before the HallHkroult discovery, not only were relatively large furnaces used for melting aluminum, but workers had identified the cause and adverse effect of “silicon pickup” by molten aluminum, an occurrence which, in my experience, was not understood in some cast shops as late as the 1950’s.

155

On the subject of process ingot, Deville (1) advises that casting into iron ingot molds gives “the best metal for rolling or hammering.” We also learn in J.W. Richard’s 1890 book (1) about Dr. C.C. Carroll of New York and his use of under-pouring to obtain “sharp castings free of cavities.” It took us a long time to put this latter finding into cast shop practice. As you see in the Pictorial Review, my efforts to obtain photographs which show details of furnaces for melting aluminum before 1900 were not succesful, and this tended to be true for the remainder of the 100 year period. It’s difficult to take photos in the Cast Shop. For the situation just prior to 1930, however, we are fortunate to find detailed descriptions of melting and casting operations in a book by Edwards, Frary and Jeffries. (2) Chapter VI tells us that the four most common types of furnaces at that time, in order of increasing importance, were (a) crucible, (b) barrel, (c) iron pot and (d) open-hearth or reverberatory. E.H. Dix, Jr., the author of Chapter VI, mentions reverberatory furnaces with capacities as high as 30,000 pounds and melt rates on the order of 2000 lbs. per hour. In general, oil and gas were preferred for all furnaces, but coal and coke were used to heat large openhearth furnaces where oil and gas were not economical.

Interesting pictures of the several furnace types for remelting aluminum before 1930 are shown in the Pictorial Review. Note the use of the word “remelting” as opposed to just “melting.” Why Remelt? I’ve had this question in my mind for a long time because I always worked in Remelt, and many of our American plants still use the term instead of Cast Shop or Ingot Plant. We find the answer when Dix tells us that the alumminum coming from the reduction works at that time contained oxides, electrolytic inclusions, and also varied in impurity content. To produce process ingot suitable for sheet and other forms, it was essential to put the pigs from the reduction plant through a remelting operation to improve quality and to control composition. Initially, process ingot, or “slabs” as they were called were quite small. The chapter “Working of Aluminum” in Reference 2 mentions a 4% inch x 12 inch x 20 inch long slab (about 110 pounds). The size of process ingots increased as new, larger rolling mills were installed to meet the increased demand for sheet and plate. As an indication of this demand, production of primary aluminum in the US.grew from 36 million pounds in 1910 to 230 million pounds in 1930, (3) a six-fold increase in just 20 years. This phenomenal growth, in less than fifty years since the Hall-Hkroult discovery, reflects not only the cost reductions made possible by that discovery, but also the industry’s drive to promote new applications. The importance of meeting consumer needs is noted in papers marking the 50th anniversary, and remains as a hallmark of our industry today. Your attention is called to two excellent articles that describe the extensive process and product development work in

Europe up to the mid 1930’s. These are: the special edition of Revue de l’aluminium in 1936 (4)’ and the article, “The Developments of the Aluminum Industry in Switzerland” which appeared in Metallurgia in 1938. (5) Both emphasize the effort and foresight of the aluminum industry to meet the needs and desires of the consumer. So, at the halfway point of this review of 100 years of cast shop operations, we find that melting furnaces were relatively small (usually less than 40,000 pound capacity with melt rates of less than 35 pounds per hour per square foot of hearth). And coal continued to be used where it was not economical to burn oil or gas. Melts were treated in the furnace with solid fluxes and chlorine, and the short list of available alloys was dominated by the old standbys, 2S, 3S, 24s and 61s and their European equivalents. Process ingot was still made in cast iron molds with the pouring operation controlled by hand or machine, with the largest ingots still only weighing on the order of 2000 pounds. (2,6)

Present Day (1980’s) Operations Jumping ahead, we find that our present day cast shops conduct melting, melt treatment and casting operations at almost breathtaking rates. In this case, “Bigger is Better” not only in respect to production rate, but in terms of manpower and energy requirements.

Melting In recent installations, melting furnace have increased in size with capacities of 200,000 to 250,000 pounds, and furnaces of 400,000 pound capacity are being considered. The 20 foot diameter round furnaces installed in the late 50’s - early 60’s

had a capacity of about 100,000 pounds, and a cold metal melt rate of about 20,000 pounds per hour. A U.S. Vendor now offers a 27 foot diameter round furnace with 150,000 pound capacity with 35,000 pound per hour melt rate. The use of high momentum burners and recouperators in aluminum melting furnaces in some installations have brought energy consumption down to less than 1400 Btu per pound of cold metal melted. Because of much higher fuel costs, European producers took measures to improve energy efficiency in melting aluminum long before their U.S. counterparts. The operations of charging, strirring, skimming and fluxing, which used to be done by hand, are now carried out by machines. A major portion of the charge to the furnaces in many cast shops is molten aluminum from the reduction cells, which may be next door or many miles away. In these shops, the term “Remelt Department” really no longer applies.

make 48 inch wide sheet, would dwarf the largest tilt mold in our visitor’s memory. In some shops, the Old Timer would be shown automated equipment now used in making process ingots. The guide would recite the technical data that are fed into and monitored by the computer, which, in turn, controls cooling conditions and casting speed, both at the start and duration of the drop. Our visitor shakes his head almost in disbelief over the list which includes alloy composition, ingot cross section, melt temperature, cooling water temperature and flow rate, and height of molten metal in the mold. Moving on to an area where casting is in progress, our Old Timer (who has been given the proper safety equipment to wear) sees that as the molten aluminum goes from the furnace to the casting pit, it passes through one of several types of boxes for what is called “in-line treatment.” The guide explains that the equipment in the box, which he might refer to as a bed filter, or perhaps as SNIF, or ALpur, or Alcoa Direct Chill (DC) Casting 622 unit - operates to remove tiny nonIt’s in the production of process ingots metallic inclusions and, dissolved gas, i.e. where the person who last saw the operation hydrogen from the melt. (More on this in the mid 1930’s would be both amazed later.) and delighted. The Old Timer visiting a cast Our visitor might also see disposable glass shop for making sheet ingot in the 1980’s cloth and ceramic filters used to remove might see several ingots weighing as much non-metallic particles from the molten as 40,000 pounds each, being withdrawn metal, and later, observe process ingots befrom what appeared to be a hole in the ing tested by ultrasonic devices for the floor, and would be told that the hole was presence of inclusions, cracks, gas porosity, Direct Chill or DC casting station. The and shrinkage voids. guide would then explain how the DC process works and how the cross section dimensions of DC sheet ingots are adjusted to the product to be made. Even the common 16 inch thick x 54 inches wide ingots, used to 156

Electromagnetic Casting After checking that the Old Timer has top clearance, the guide moves on to what is proudly announced as an electromagnetic (EM) casting station. Our visitor can’t see much difference between this and the earlier DC station, but he snaps his head in surprise when the guide points out that there is no confining mold; instead the liquid metal at the head of the ingot is held suspended by an electromagnetic force. The guide says this system originated with the Russians (7,s) and was introduced into several U.S. plants in the 1970’s and 1980’s. The Old Timer notes the smooth surface on the EM ingots and is told that scalping is not needed and that hot line edge trim is reduced considerably. He is shown some literature on EM casting operations. (9,10,11)

Aluminum Alloys When questioned, the guide says that there are now some 70 wrought aluminum alloys listed by the Aluminum Association; (12) and our Old Timer leaves, still amazed, but satisfied that the Aluminum Industry has continued its drive to cut costs, create new products, and meet consumer needs.

Extrusion Ingot (Frequently Called Billet)

Casting Between Moving Molds, i.e. Continuous Casting

As expected, there has been a tremendous change in the number of billets cast per drop since the 1950’s. The push for productivity has resulted in DC casting stations capable of producing as many as 120 strands at a time in the smaller diameters (6 inch or less). Marked improvement has also been made in internal and surface quality of extrusion ingots, and, as in the case of sheet, this translates into improved product at lower cost to the customer. Some of this has come about through the use of Hot Top or Level Pour modification of the DC casting process. There are a number of Hot Top systems, but all involve the provision of an insulated reservoir of molten metal immediately above and integral with the mold. (8, 13). The Showa Hot Top (14) and Wagstaff Air-Slip (15) mold systems are claimed to produce ingots with particularly smooth surfaces by reducing the air gap formed between the mold and the solidifying, and shrinking, ingot. A description of the significance of the air gap on surface quality was given in the 1956 paper by Lewis and Savage. (16) Another variation of the DC process is the Horizontal Casting Process (HDC). This is essentially a Hot Top system turned 90” so that the solidifying ingot is withdrawn horizontally.

Just as we honor Hall and Hbroult for their efforts in the electrolytic reduction of aluminum, it is appropriate to honor Dr. Ing. E.H. Siegfried Junghans, the pioneer in the continuous casting of metals. It was his early efforts and ingenuity that gave rise to the systems we have today. Details of the numerous casting machines now available for aluminum are described in E. Herrmann’s book, Handbook on Casting Aluminum, (8) and in papers in Light Metals books since 1973. These systems produce strip or rod which is usually fed directly to a continuous mill for further size reduction. Because of lower capital and operating costs, the trend toward continuous casting is accelerating. I have included a number of photographs of continuous casting systems in the Pictorial Review.

Some Important Developments On The Way To The 1980’s In addition to the powerful forces from within the aluminum industry to expand, many external influences have acted to cause the aluminum industry to grow in size and importance. These include the several wars, new industries such as aircraft and automotive, and the more recent use of aluminum in construction and packaging, including the beverage can.

Direct Chill (DC) Casting

157

The commercialization of the Direct Chill (DC) casting process for aluminum process ingot stands out in the list of technical achievements in aluminum cast shop technology. The application of this technology

background - huge extrusion and forging presses used in Germany in World War I1 for the production of large components of military aircraft were liberated to the U.S. as part of war reparations. In the late 1940’s, a program was initiated by the U.S. Air Force to use these and new presses for the manufacture of extrusions and forgings in high strength aluminum alloys. However, the largest process ingots made commercially in the high strength alloys of interest, at that time, were completely inadequate as starting stock for the large extrusions and forgings to be made in the mammoth presses. The problem was that ingots of thicknesses greater than 12 inches in 7075 alloy cracked during or just after casting due to internal residual stresses. 7075 alloy has a particularly wide solidification range and a tendency to hot shortness. After only two years of development effort, Kaiser Aluminum announced in 1952 that sound 32 inch diameter process ingot could be made Heavy Press Program in the United in 7075 alloy using a modification of the States DC process. This modification employed an It is fascinating how frequently a new activi- interruptible quench of the ingot during ty sets off a whole series of additional efcasting such that the rate and intensity of forts and improvements. An example is the the build-up of stresses in the ingot were Heavy Press Program in the U S . following reduced. (19) Details of patents by P.P. World War 11. The often overlooked efforts Ziegler and S.A. Kilpatrick covering the required to make the huge ingots for this modification are given in Reference 8. program subsequently had a far reaching inNot presented understandably in the 1952 fluence on the size and metallurgical quality KACC announcement was the associated of process ingots for other commercial pro- work which was done to develop molds, ducts. I was part of this effort, and in the controls, and practices for making sound, following, I describe some of the developlarge ingots in this crack sensitive alloy. ments in one company which had their These included control of silicon content, origin in the Heavy Press Program. Similar flow of molten metal into and distributed valuable work was done in other organizawithin the mold, casting rates, flow rates tions, and the results were most beneficial and uniformity of flow of water coolant, to the entire aluminum industry. As and a means of removing coolant to achieve

substantially increased the production rate of fine grained ingot with minimal segregation, for use in high quality sheet, extrusions and forgings. As in the case of the electrolytic reduction of aluminum, there is some question as to who was first to introduce the idea into practice. But this is not important now, and it is likely that a number of workers had the same concept in the early 1930’s. An equipment drawing is shown in the Pictorial Review which according to E. Herrmann (17) represent the first DC casting systems for aluminum. In the US., Alcoa further commercialized the pioneering work of William T. Ennor. (18) The numerous embodiements of DC casting are well known and will not be reviewed here. A description of systems currently used by some of the major aluminum companies in the Free World is given in E. Herrmann’s Handbook on Continuous Casting (18) published in 1980.

the interrupted quench. Here we drew not only on the ingenuity of our team, but also, on the teachings of the early contributors like Walter Roth and Paul Brenner, and reports of the British Intelligence Objectives Subcommittee (BIOS). The control of silicon content of 7075 alloy was critical to the production of sound ingots and was made difficult by the “pickup” from the refractory linings of the furnaces. Studies of refractory materials continued; (20) and a by-product of the Heavy Press Program was a new refractory, developed in-house, to minimize reaction with molten aluminum and “pickup” of silicon. As usual, the ultimate customer - in this case, the air frame manufacturers - were not satisfied just with larger starting stock for their extrusions and forgings. They wanted higher quality products of all sizes, and they particularly wanted metal that was free of non-metallic inclusions. Work continued on improved transfer troughs and underpour devices to eliminate turbulence and metal free fall as it flowed from the furnace to the mold. This was necessary to minimize oxidation and reduce the formation of insoluble oxides and spinels. The biggest pay-off came, however, when we found we had to do a better job of removing gas, i.e. hydrogen, from the molten metal before we could properly evaluate the quality of the process ingots with respect to non-metallic inclusions. Ultrasonic testing had become available and gas porosity in the ingots tended to mask the presence of inclusions which could ruin costly extruded forged parts during machining. We observed that fluxing of the molten metal in open hearth furnaces, although helpful in removing both gas and inclusions, was a losing proposition if process ingot

158

159

Aluminum FILD system. Details on these with hydrogen content lower than the solusystems and their performances may be bility limit in solid metal was required. In found in papers in Light Metals volumes. fuel-fired, open hearth furnaces, the products of combustion include quantities of water which react with molten aluminum, to Reclamation and Recycling The re-use of scrap has been an essential form aluminum oxide & hydrogen. The hyaspect of the aluminum industry ever since drogen then acted to regas the melt. its beginning, and the terms reclamation and This observation led to the development recycling have been used interchangeably. It of a process and equipment for gaseous is only recently that we have begun to idenfluxing of molten aluminum and its alloys in such a way that the molten metal was not tify these operations as two separate activities. In this review, I use the definitions exposed to the products of combustion. of J.M. Creel 11: (22) Further, the method provided for much Recycling - The system that collects more efficient use of fluxing gas as only the aluminum scrap from a variety of metal flowing to the casting station was sources, prepares it to specification, and treated. delivers it to a reclamation process, all at The first embodiment of the concept was economically viable costs. called, “Tap Hole Fluxing,” and it took Reclamation - The process of turning place in a small enclosure inside the furnace scrap into useful products, either for a adjacent to the tap hole. The next applicacompany’s further internal use or putting tion was the Flux Bay located immediately into product for sale to the open market. adjacent to the furnace but outside of the On the other hand, until about the tap hole so that molten aluminum exiting 1970’s, in dealing with reclaimed scrap, we the furnace was treated by gaseous fluxes used to carefully distinguish between out of contact with combustion products. primary and secondary sources of alumiUse of the Flux Bay provided molten num, particularly when making process inmetal virtually free of inclusions and low got. The secondary producers obtained gas content, i.e., below the solid solubility metal from a wide variety of scrap material of hydrogen. Coupled with proper metal transfer and filtration devices, the goal of a and secondary aluminum was metal whose original identity was lost. Because of high Zero Defect product, set by the manageimpurity content virtually all of this metal ment in the mid 1950’s, was achieved. was used to produce foundry or casting The Flux Bay was the first of a long line of processes and equipment for in-line treat- alloys. Process ingot in general was made from metal from the reduction plant, inment of molten aluminum. In the Pictorial plant scrap, and a relatively small amount Review I have included photographs of of carefully identified purchase scrap. As Alcoa, Dufi and Selee filters and spinning late as 1939, there was only one primary nozzle devices identified as SNIF, Alpur, and not many secondary producers in the and Alcoa 622, also a Mint reactor. Not shown is an early Intalco unit and a British U.S. Shortages of materials during World War I1 in all participating countries brought the

public into direct recycling of aluminum. In some cases this must have been ineffective. For example, I can recall seeing many large balls of aluminum foil taken from used chewing gum wrapper and other thin packing material. The yield of reclaimed metal must have been very low. The energy crunch precipitated by OPEC in the 1970’s really brought recycling by industry and the public to the forefront. We all learned that aluminum scrap can be reclaimed with an energy expenditure of only 5 % of that required to make new metal in a reduction cell. The use of aluminum in packaging and in beverage cans had been expanding rapidly and recycling activities ‘‘exploded.’’ Now in the 1980’s, nearly all primary producers are involved in large scale scrap reclamation, and some have been leaders in the challenging complex of issues and activities involved in recycling of aluminum. In addition, the number of independent companies in the Secondary Industry has grown. As of 1975, there were 60 in the U.S., (23) and additional companies are being formed, particularly in other parts of the world. The distinction between primary and secondary source has become blurred and a number of secondary companies now produce metal to primary specifications. For example, during the shortages of pure primary aluminum pig in 1973, when a large portion of the U.S. domestic primary production was exported for a higher price, secondary smelters produced significant quantities of “primary” alloy. (23) Both primary and secondary producers have devised effective ways of reclaming aluminum from skim and dross from melting operations, finely divided materials such as scalpings and turnings and now, used

beverage cans (UBC). A description of some of these methods is given in a paper by C.L. Brooks. (24) Photos in the Pictorial Review also show an example of a system for melting chips and light gauge scrap in which the hips are fed into a stream of superheated molten aluminum in a furnace where a pump is used to provide closed-loop circulation of the molten metal. A paper by J.M. Marr (25) describing this system reports 90% recovery of metal from aluminum alloy chips, compared to 50% to 70% for the same material melted in an external charging we11 of a reverberatory furnance using a mechanical puddling device. Marr reports recovery as high as 97% in induction furnaces, but observed that in his company’s circumstance “capital outlay necessary for the construction of an induction melting facility would have resulted in an unfavorable return on investment. ”

Recycling and Reclamation of Used Aluminum Beverage Cans Reynolds Metals Company has been a pioneer in this effort in the U.S. and has developed innovative programs to educate the public and municipalities in the values and importance of recycling. One of the recent developments is the Reverse Vending system, an automatic system or robot placed strategically to buy used aluminum beverage cans from the public, twenty-four hours a day. The robot returns cash, or other forms of payment directly to the individual presenting the cans. Table I (26) indicates the explosive growth of reclamation of cans and the importance of this source of metal to the aluminum industry.

Safety When Handling Molten Aluminum I consider safety an important part of reduction, melting and casting operations. Since the days of Hall and HCroult, we have seen remarkable steps forward in technology, production rate, and quality of product. But, sad to say, in spite of our automation, we still have explosions which result in terrible burns and death to our people and major economic loss to our companies. Note that: At least 100 explosions involving molten aluminum occured in the U.S. in the past five years. In 1984 alone, eight people died in the U.S. as a result of molten aluminumwater explosions. In one of the 1984 explosions, the supervisors and the workers were not aware of the dangers of charging sows to molten aluminum without proper preheating, nor were they aware of the dangers of wearing polyester clothing while working with molten aluminum. In this case, a 1500 pound sow, which had been stored outside, was added to molten aluminum without proper treatment to remove moisture. An explosion followed, and the sow was blown some 40 feet through a wall to the outside of the building. Molten metal from the explosion splashed onto a worker and his polyester clothes caught fire. Two weeks later, he died of third degree burns.

The aluminum industry everywhere, and agencies of a number of governments are, of course, concerned with this problem. In the U.S., the Aluminum Association has sponsored a number of research projects with the objective of determining the causes of these explosions and devising methods of prevention. Findings up to 1979 are given in Guidelines to Handling Molten Aluminum (27) and in a series of papers in Light Metals 1980.(28) Major changes have taken place since the early days in safety practices and requirements for personal safety equipment in the work place. Even up to the 1950’s, most of the men working in melting and casting operations shown in photos in the Pictorial Review did not wear safety glasses. Of particular importance is the recent availability of fire-resistance clothing for workers handling molten aluminum. The Pictorial Review shows a cast shop worker whose attire includes safety glasses, face shield, jacket and pants made of fire-resistant cloth and approved foot gear.

Table I RECLAMATION OF ALUMINUM BEVERAGE CANS

Year 1973 1979 1980 1981 1982 1983 1984

Pounds collected (millions) 68 360 609 1,017 1,124 1,144

_____

Yo of Production of cans

15.2 25.7 37.3 53.2 55.5 52.9 55-57’/0 estimate

160

References 1.

2. 3.

4.

5. 6. 7 8.

9.

10.

11.

12.

13. 14.

15.

16. 17.

161

J.W. Richards, Aluminium, Second Edition (Philadelphia, PA), Henry Carey Baird & Co., 1890. J.D. Edwards, F.C. Frary, Z. Jeffries, The Aluminum Industry, (New York, NY: McGraw Hill Co., 1930). Historical Statistics of the US.,Part I , U.S. Bureau of the Census, 1975. Revue de l’Aluminium, No. 84, Numero Special, 1936. A. von Zeerleder, “The Developments of the Aluminium Industry in Switzerland”, Metallurgia, Feb., 1938. “Grooved Ingot Eliminates Scalping”, Light Metal Age, December, 1972, p. 10. Z.N. Getselef, “Casting is an Electromagnetic Field”, Journal of Metals, 23, (lo), pp. 38, 39. E. Herrmann in colaboration with D. Hoffmann, Handbook on Continuous Casting (Dusseldorf, Germany: Aluminium-Verlag, 1980). H.A. Meir, G.B. Loconte and A.M. Odok, “Alusuisse Experience with Electromagnetic Molds”, Light Metals, Vol. 2, AIME, 1977, pp. 223-233. D.F. Goodrich, J.L. Dassel and R.M. Shogren, “Kaiser Aluminum Plant Implementation of Electromagnetic Casting”, Light Metals, AIME, 1982, pp. 781-791. R. Sautebin and W. Haller, “Industrial Application of Electromagnetic Casting (EMC) of Aluminum”, Light Metals, AIME, 1985, pp. 1301-1308. Aluminum Standards and Data, The Aluminum Association, Inc., 818 Connecticut Ave., NW Washington DC, June 1982, p. 15. R.V. Anderson and J.F. Harris, “Level Feed Billet Casting at Kaiser-Chalmette”, Light Metals, AIME, 1981, pp. 827-843. R. Mitamura et al., “New Hot Top Continuous Casting Method Featuring Application of Air Pressure to Mold”, Light Metals, Vol. 2, AIME, 1978, pp. 281-291. J.P. Faunce and A. Valdo, “The Air-Slip Process Casting Mold - An Established Technology”, Light Metals, AIME, 1985, pp. 1317-1330. D.M. Lewis and J. Savage, “The Principles of Continuous Casting of Metals”, Metallurgical Reviews, 1956, Vol. 1 , part 1, pp. 55-89. E. Herrmann, Handbuch des Stranggiesseus (Dusseldorf, Germany: Aluminium-Verlag, 1958).

18. 19 20.

21. 22.

23. 24. 25.

26. 27. 28.

W. Ennor, US. Patent 230 1027. A.T. Taylor D.H. Thompson and J.J. Wagner, “Direct Chill Casting of Large Aluminum Ingots”, Metal Progress, 1957 (1 I), pp. 70-74. H.A. McDonald, J.E. Dore and W.S. Peterson, “How Molten Aluminum Affects Plastic Refractories”, J. of Metals, 1958, (lo), pp. 35-37. W.S. Peterson and W.A. Klemm, U.S. Patent 2,821,472. J.M. Creel, 11, “Aluminum Recycling Economic Potential and Limitations”, paper presented at the 114th AIME Anuual Meeting, New York, NY, Feb. 27, 1985. R.E. Bruner, “Contemporary Aluminum Recycling”, Light Metals, Vol. 2, TMS-Aime, 1972, pp.337-34. C.L. Brooks, “New Technology in Recovery and Reuse of Aluminum Scrap”, Light Metals, Val. 2, TMS- AIME, 1976, pp. 249-261. J.M. Marr, “High Recovery Reclamation of Light Gauge Aluminum Scrap Utilizing Low Volume Recirculation of Superheated Molten Metal”,Light Metals. Vol. 2, TMS-AIME, 1978, pp. 263-278. “Aluminum Statistical Review for 1983”, The Aluminum Association Book No. 94, Dec. 1984, pp. 26-28. Guidelines f o r Handling Molten Aluminum, The Aluminum Association Inc., 8 I8 Connecticut Ave., NW, Washington DC, 20006, Sept. 1980. “Safety in the Aluminum Industry”, Two sessions consisting of seven papers, Light Metals, 1980, pp. 817-910.

Warren S. Peterson Warren S. “PETE” Peterson’s career spanned four decades of R&D and plant experience. After earning PhD from the Polytechnic Institute of New York he has worked at various times for Alcoa, Kaiser, O h and Martin Marietta, accumulating more than 20 patents and publications. He has been a very active member of the Light Metals Committee since 1958, serving as Chairman in both 1960 and 1978. Today Pete lives in Spokane, Washington, where he enjoys sailing and hunting, when not working as a private consultant.

Fluoride Control in the Aluminum Industry 100 Years of Technology Patrick R . Atking, Aluminum Company of America Pittsburgh, PA 15219

Change is the byword of the ’ ~ O Sand , two areas where change is most apparent are technology and social responsibility. It is most appropriate to talk about these subjects in the context of the aluminum industry since the two are so closely linked. The aluminum industry was founded on a technological breakthrough that occurred 100 years ago, and since that time, the culture of the industry has encouraged continued technology advancement in production, fabrication, use and reuse. This technology thrust has also included environmental management to an extent unparalleled in other basic industries. Environmental control has now become such an integral part of the aluminum production process that all new reduction facilities constructed throughout the free world utilize “state-of-the-art” fluoride control systems that are directly linked with the production process. Fluoride control has come of age in the aluminum industry and has played an important role not only in environmental

control but also in the technology development programs that have produced the highly efficient reduction facilities used throughout the world. Environmental management has matured! Some industries now recognize that environmental management is an integral part of business operations and treat it as such. Others are learning fast, and those that don’t learn quickly enough or well enough may find that time has passed them by. I believe that the aluminum industry falls into the first category, and I am pleased to discuss one of the industry’s environmental management successes-a case study that should be useful as a guide within and outside our industry. Fluoride control has turned a major liability into an asset and has made environmental control a fullyintegrated part of our primary production operation. I would like to begin this discussion by quoting from a paper published in January 1980 by Daniel Yankelovich and Bernard

Lefkovitz. These prognosticators were discussing the issue “National Growth - The Question of the ’80s.” “As the 1980s approach, a fateful decision hangs over America. Should we try during the coming decade to satisfy heightened demands for social services, for a cleaner and safer environment, and for larger constraints upon business and government? Or should we seek instead to replenish our aging industrial stock and invest heavily in economic development? Or should we-can we-try to do both?” The authors go on to say that Amitai Etzioni, who was then a part-time advisor to the White House, observed “it will not be possible to do both.” Ultimately, they state, Herman Kahn believes that the adherents of restrained growth will prevail. Yankelovich and Lefkovitz, and remember they are writing in the late 1970s, informed the reader that they don’t believe there is going to be a rigid policy decision that would make a 90 degree turn in the dir-

162

163

ection of this country or any other. Rather, my opinion, the culture of the industry that they speculated, through a series of discusled us to a strong recycling program early in sions ranging from the halls of Congress to the life of the beverage can, has paid off the executive board room to the company handsomely, not only in an environmental cafeteria to the grocery store, thousands of and energy conservation sense, but also in proposals and ideas would collectively be terms of business acumen. brought together to set the direction of Sometimes it is difficult for those of us America. This direction would, by definiwho are involved deeply in industrial action, be consonant with the public’s emerg- tivities aimed at efficient utilization of ing values and priorities. resources to understand the concerns raised It is not hard for us to see what these by those outside our sphere of activity. I values and priorities are. The public in the think it was put in extremely sharp focus by United States and, indeed, the public world- Mr. M. E. Gantz, Jr., in a presentation he wide is very vocal in expressing concerns made to a group of Alcoa Environmental about social issues, quality of life, enManagers on March 27, 1980. Mr. Gantz, vironmental quality, resource protection and who was at that time an Executive Vice the legacy left for future generations. Even President for Mill Products, Aluminum polls taken during the depths of the recesCompany of America, was asked to address sion in the early 1980s continued to show this group and express to them the corstrong support for environmental protecporate expectations for Environmental tion, even when jobs were at issue, and that Managers throughout the Alcoa system. In is still the case today. his speech he outlined three axioms that In this environment, the aluminum inwere helpful in trying to understand the dustry has competed very well. In terms of reasons why we in industry have a somegrowth rates, we have nothing to be asham- what different perspective on pollution and ed of. Aluminum has outgrown all other resource utilization than others. I’ll quote nonferrous materials during its brief history Marv’s three axioms: as an industrial metal, and continued “My first axiom is that enterprises in a growth is assured. I admit that the future is free market system do not use commonly a bit fuzzy, but I continue to feel that it is owned resources efficiently. It is not too bright. For example, let’s look at the hard to reach the conclusion that if the aluminum can in the context of the ownership of a resource is shared by all the Yankelovich prognostication. people, as a businessman I may see little We all know the sort of growth rate and reason to conserve a commonly owned market penetration that the aluminum can resource or to use it efficiently. As a matter has had. Well, I opine, and I think at least of fact, the more rapidly I use the resource, some in the marketing business agree, that the more advantage I should have over my the fact that aluminum cans are recycled efcompetitors. So that’s the first axiom. ficiently-better than any other packaging material-has made our product more apThe second axiom is that enterprises in a pealing to the public. This concepts fits well free market society do not save commonly with the predictions of Yankelovich, and, in owned resources for future generations, and

I guess we can find evidence of this. Man has been on this earth for a couple of mllion years and hopefully will be around for several million more, but we’re doing the best we can to use up the fossil fuel resources of the earth in maybe a thousand years or so. The fact that these fossil fuels are the principle and maybe the only source for certain medicines and chemicals essential to life doesn’t bother us at all. We can solve anything with technology, and future generations won’t really need fossil fuels. My third axiom is that anything that has a price QT value will be economized on, or to put it another way, anything which a free market economy fails to put a value on will be exploited.” Thus, for a long time, business has attempted to externalize costs and use all available resources efficiently. Cost accounting as applied to commonly held resources is very complex and difficult. Therefore, sometimes when costs are externalized, it takes a long time for all of the accounting procedures to be put in place and the true cost of an action assessed. We talk and sometimes smile about not being able to see across the street in Pittsburgh, catching a river on fire in Cleveland or not being able to hold a sporting event in Los Angeles during the smog season. Yet, as obvious as those problems are, it is difficult to place a cost or a benefit on the actions that cause or prevent those situations from occurring throughout the world. Society must conduct that cost benefit analysis and a collegial decision must be made concerning how to develop and implement strategies to meet the goals that are developed from those decisions. I was struck by the words expressed at graduation exercises for the 4,199 students who received

degrees from Northeastern University last June. Phillip Johnson, Executive Director of the relief agency CARE, spoke at the 75th anniversary of the Cooperative Education Program at Northeastern, a school that is heavily involved with industry and provides a strong technical education. Dr. Johnson said: “Society needs you where you will be most productive. . . Balance your efforts between those that advance society technologically and those that advance it qualitatively. Enrich your life, make an active socid commitment and reap the joys of enriching the lives of others.” Edward Francis Hennessey, Chief Justice of the State Supreme Judicial Court was also a speaker and stated: “AS educated Americans our response to justice and charity lies in service. Our service can be as wide as our conscience and as tall as our talents.” I find that advice to be most encouraging and the forum at which it was delivered to be most reassuring. It is another indication of the direction that society is taking and the importance that is ‘being placed on issues such as the quality of life. O The technical thrust of the industry has been a bonus for our environmental control efforts and has allowed many in the industry to use their creativity and ingenuity to solve problems and at the same time positively impact our environmental intrusions. A good example is electric power. Over the last four decades, the power requirements to produce the average ton of aluminum in the U.S. have been reduced by almost half. The newest plants operating today produce metal at approximately’onethird the energy requirements of the 1930 vintage cells. This energy reduction has

benefited the industry in a variety of ways, including our environmental thrust. In 1973, the Franklin Institute estimated that the average ton of aluminum produced in the U.S. for beverage can production resulted in approximately 240 pounds of sulfur dioxide released to the atmosphere. Today, that number would be more like 136 pounds of sulfur dioxide per ton of aluminum for beverage can production-at the same recycling rate that existed in 1973-due largely to the technological thrust of the industry. Increased recycling has reduced that impact even further. A wise man once said “Success is not a destination but a journey.” I believe that is most applicable to the environmental management situation that faces industry throughout the world. Success can’t be a destination that we reach and say “Aha, we have made it,” but rather success in environmental management is a continuing journey-a journey that will constantly be filled with challenge. It is my personal belief that the aluminum industry has risen to that challenge and is embarked upon that journey of success. We have a rich history, strong support, proven creativity, drive, motivation and efficiency on our side. I would like to describe a little of the journey of success in enviromental management for the aluminum industry and use fluoride control as the vehicle. The aluminum industry’s concern with environmental management has its roots in the beginnings of the industry. I recently looked through some of the personal papers of Charles Martin Hall who is one of the individuals who discovered the Hall-Hkroult process to make aluminum. In those letters, written before or near the turn of the 19th

century, there were a number of references to concerns about worker safety and health and about equipment to be used in the aluminum production process. It was Hall’s belief that equipment such as dust chambers on calciners for alumina had to be different from the equipment used by others because without these modifications the impacts would be intolerable. The concerns were rudimentary by today’s standards. They dealt with dust, heat and exposure of people to moving belts and rotating equipment. However, the concerns were there and they were expressed and acted upon by those individuals who were involved in the birth of a major industry. The litany of the aluminum industry’s efforts to manage fluoride emissions is, in my opinion, an excellent example of how environmental control issues can and should be approached by industry in general. Fluoride is a complex and insidious pollutant that is difficult to quantify and even more difficult to control. Yet, with proper application of technology, ingenuity and dedication, it has been understood and it is being controlkd. In many ways, the fluoride emission control technology utilized by aluminum producers can be viewed as a leading indicator of the technological revolutions that have impacted aluminum production since the patenting of the HallHkroult process. According to Peter Martyn, Secretary General of the International Primary Aluminium Institute, three basic technological cycles have had major impacts on the aluminum industry during the last 100 years. I would like to build on Peter’s idea. The initial technological cycle allowed commercial production of aluminum to

164

165

begin. During this timeframe, the plants that produced primary metal were small and relatively inefficient. Yet, they made it possible for aluminum to be produced at a cost and social impact that allowed the industry to become viable. Production plants grew throughout the world in both size and number, but basic technology remained the same for the first several decades. During this period, pollution control was also in an embryonic state. Potroom ventilation was the major method used to protect workers and minimize the impacts of cell operation on the environs of the facilities. Since the plants were of small capacity and the technology used was such that fluoride evolution rates were relatively low, this type of environmental protection was adequate for the times. The second technological cycle began in the early 1930s when larger plants were built and emphasis on efficiency and productivity increased. The acceleration of technology was stimulated by the rapid rise in the need for aluminum as a result of World War 11. During this time period, the technology used to produce aluminum changed rapidly and dramatically. Simultaneous with this production technological change, changes began to occur in the environmental protection methodologies used by the various aluminum producers. Large-scale experiments were undertaken to determine if roof scrubbers could be utilized for fluoride emission control. Hooded cells were developed initially on a retrofit basis and subsequently as an integral part of new cell designs. Primary off-gas systems were tested and a variety of methods were utilized to treat collected offgases from both prebake and Soderberg cells.

Production facilities became large enough that the aggregate emissions from the operating pots produced concentrations of fluorides large enough to cause visible impacts on vegetation, and to produce fluoride concentrations in forage near the plants significant enough to cause measureable impacts on grazing ruminants. Fluoride emission control became a necessity for continued operation of large-scale aluminum production facilities. However, cost was always a significant factor in decisions concerning the type of fluoride emission control and, in some cases, even determined whether or not a plant should continue to operate. During this second technological cycle, the Hall process itself was maturing. The industry was beginning to develop a deeper understanding of the parameters which control process efficiency and reliability. Simultaneously, a better understanding of emission control requirements and the various impacts of fluoride emissions was also occuring. The third technological cycle that affected the aluminum industry began late in the decade of the 50s. Strong emphasis was placed on cell efficiency, cell productivity and cell size. During the first ten years of this period, the size of operating cells used throughout the industry essentially doubled and large plants became the norm. As the Hall process was fine tuned and efficiency increases were gained, the capability of the cell to generate fluoride emissions was also enhanced. Many of the steps taken by some producers to improve the Hall process productivity also increased evolution rates of fluorides and other potential pollutants. Simultaneously with this

rapid technological improvement in the “third cycle,” dry scrubbing technology was also initiated. The problems associated with water treatment, sludge management, corrosion and maintenance drove the aluminum industry to consider alternatives for fluoride emission control. As evolution rates of fluoride increased, it became apparent that any viable process must effectively reuse the fluoride off-gases to minimize costs asociated with fluoride losses. In 1958, the first plant in the world utilizing dry scrubbing for emission control went on stream. Those dry scrubbing systems resulted from a number of years of trial and error research where a variety of adsorbing media were studied to determine how best to control fluoride emissions at reasonable costs. The initial system used a special grade of alumina that could be recycled into the process. However, through subsequent testing and development efforts, it was determined that with proper contact, metal grade alumina could be used as the adsorbing media. In 1967, the first dry scrubbing system using metal grade alumina was installed on an operating facility. The process made it possible for the “loop to be closed.” Fluoride off-gases were treated with the raw material that was to be fed back to the operating cell; thus making it possible to control cell emissions without producing a waste product that required further treatment. Dry scrubbing has, in my opinion, impacted the aluminum industry far beyond the pollution control aspects. Highly efficient dry scrubbing equipment that produces no by-products or waste products to be processed or managed makes it possible for cell operation to be modified without being

significantly constrained by fluoride evolution rates. It becomes imperative that the cell itself and the associated hooding and control equipment be upgraded to handle increased evolution, but there is not a significant economic penalty for increased fluoride evolution. This capability has provided alternative cell operating procedures and made it possible for aluminum producers to use flexible production approaches to meet their objectives and respond to electric power, labor, capital and operating cost pressures in a wider variety of ways. Thus, fluoride emission control has become an integrated part of the aluminum production process. It is no longer considered and add-on but rather a part of the process that must be considered in the overall system design. Since 1974, there has not been a single new primary aluminum facility constructed in the free world that is not equipped with dry scrubbing technology; and, approximately one-half of the facilities that were controlled by wet scrubbers have been converted to dry scrubbing systems. The scrubbing technologies developed by several companies are easily available to all aluminum producers. Companies can shop for and purchase “the best” control systems, since the entire industry culture suggests that such technology be shared, even with competitors. The U. S. Aluminum Association, through its Environmental Committee and the Environmental Research Subcommittee, has sponsored numerous projects to assist the U. S. industry in fluoride management strategies. I’m sure that other associations throughout the world have fostered similar cooperation.

The impact of dry scrubbing technology application has been dramatic. When aluminum plants were small and essentially uncontrolled, fluoride losses from the cells ranged from 12 to 20 kilograms per ton of metal produced. The first control systems that utilized low pressure scrubbing techniques reduced the emission rates to approximately 10 kilograms per ton. More sophisticated scrubbers and electrostatic precipitators were used after World War I1 to reduce the levels further, resulting in emission rates on the order of 3 to 5 kilograms per ton. Studies by the U. S. EPA in the early 1970s’ produced data that demonstrated a continued reduction in fluoride levels as plants were retrofitted and improved with control systems. The International Primary Aluminium Institute (IPAI) report entitled, “Fluoride Emission Control: Costs for New Aluminum Reduction Plants,’’ published in 1975, concluded that based on a “model plant” concept modern facilities in operation at that time had an average fluoride emission rate estimated to be 1.65 kilograms per ton of aluminum produced. An update of that report was published in February 1985. Based on a survey of 10 modern plants operated throughout the world, it found the average emission rate for these facilities to be 1.0 kilograms per ton of aluminum produced (range 0.5 to 2.20 kilograms per ton). Progress in fluoride emission reduction continues and the final conclusion of the IPAI report states: “. . .the primary aluminum industry continues to make a major commitment to the application, development and improvement of pollution control technology. The industry has developed pollution control

technology which is able to achieve a high overall degree of emission control. This pollution control technology has become an integral part of the production process. At the present time, the pollution control technology is no longer an “add-on” process, but now constitutes an essential element of new plants. This updated report serves as an excellent indication of the substance of the industry’s environmental commitment.” Another indication of the technological impact of the industry’s pollution control program is the Arthur Vining Davis Technology Award presented in July 1985 by Alcoa to 36 employees who were instrumental in developing the dry scrubber system employed by Alcoa. This award is the highest technical award that that company gives and is designed to recognize outstanding achievements that significantly impact the enterprise. It is meaningful that a fluoride control technology team was recognized for their contributions-meaningful indeed. It is my opinion that the technological culture of the aluminum industry is demonstrated by the three technology cycles suggested by Peter Martyn and the technological innovation that resulted in integrated control technology places the aluminum industry in an excellent position to maintain its reputation as an environmentally aware and environmentally conscious industry. The culture that has developed as the aluminum industry has matured is to our advantage. Aluminum continues to be in serious competition with a wide variety of materials in an environment where energy, raw materials and labor costs are escalating rapidly. Since our industry is energyintensive and capital-intensive, the only

166

167

means of economic survival is rapid and effective technological development and implementation. This commitment to the development and innovative implementation of new and emerging technologies has provided the mindset required for creative and effective management of environmental problems. Good examples are our highly successful drive to reduce energy costs without the need for oversight regulation and implementation by government agencies and the rapid increase in recycling of aluminum cans that has occurred in the United States and other countries-not because of regulatory pressures but because it makes good business sense. The dry scrubber technologies that I described earlier were first developed in the 1950s and 1960s long before regulations required that such innovative technologies be used to control emissions from aluminum reduction facilities. Therefore, I conclude that it is safe to say that the aluminum industry is innovative in a variety of areas including environmental protection. including environmental protection. Events have occurred over the last several years that have underlined the importance of public acceptance and public trust in an industry if that industry is to be viable and successful. Spills and leaks, major discharges, acute and chronic impacts on the environment and misuse of resources will not be tolerated by the public. There are too many ways for the public to affect an enterprise, both in the short term and the long term. It is becoming clear in the United States, at least, that public trust of an industry is a primary criterion for the success of any enterprise. Without public trust, the regulatory maze that will develop will become so burdensome that an industry will

find it difficult if not impossible to operate. Therefore, it is incumbent upon such industries as the aluminum industry to continue to demonstrate that environmental awareness and environmental protection capabilities are an integral part of its philosophy, and that the industry is capable of maintaining programs to assure environmental protection. The track record of the aluminum industry is a good one. It would be erroneous to say that there are no environmental problems that have not yet been addressed. However, I believe we can look to the history of the aluminum industry with regard to fluoride emission control and point with pride to the progress that has been made. Integration of pollution control technology of the basic production process is essentially complete and the program will be self-sustaining. We have 100 years of technology in our background and, I believe, that we will continue as an industry to build on that technological base to solve the problems and meet the challenges which face us, not only in the environmental area but in all areas of our business activities.

References 1.

2.

3. 4.

5. 6.

7.

Daniel Yankelovich and Bernard Lefkowitz, “National Growth: The Question of the ~ O S , ”Public Opinion, December/January 1980, 44-57. Remarks by M. E. Gantz, Jr., Executive Vice President, Aluminum Company of America, before the Alcoa Environmental Managers, March 27, 1980. “Make Social Commitment, Grads Told,” The Northeastern Edition, Vol. 7 , No.18, June 27, 1985. Samuel H. Armacost, “Free Trade Under Fire: A Call to the Counterattach,” (Paper presented at the 13th Annual General Meeting of the International Primary Aluminium Institute, San Francisco, CA, 1-2 May 1985. Peter Martyn, “Primary Aluminium and Alumina Production and the Environment,” (In Press). International Primary Aluminium Institute Environmental Committee Report, “Fluoride Emissions Control: Costs for New Aluminium Reduction Plants,” April 1975. International Primary Aluminium Institute Environmental Committee Report, “Fluoride Emissions Control: Updated Costs for New Aluminium Reduction Plants,” February 1985.

Patrick R. Atkins Patrick R. Atkins earned a PhD in 1968 from Stanford University where he specialized in environmental engineering. For the next four years he was a Professor and Researh Analyst in the Environmental Health Engineering Department at the University of Texas. Pat joined Alcoa in 1972 and was named to his present position of General Manager - Environmental Control in 1981. He has authored numerous technical articles, and currently serves as an Adjunct Professor at the University of Pittsburgh, where he teaches industrial waste treatment technology in both the Graduate School of Public Health and the School of Engineering.

Environmental Control in our Industry An Historical Overview J. P. McGeer, Alcan International Limited Kingston Research and Development Centre P. 0. Box 8400, Kingston, Ontario, Canada K71424

The aluminum industry has faced and solved many problems in the area of the environment. The one that has had the greatest impact, fluoride evolution from the Hall-Hkroult process, is the subject of another paper at this Conference. This presentation will cover the evolution of practices and equipment in other areas including disposal of refinery and chemical plant effluent streams, hydrocarbon evolution, heat and physical stress, disposal of used potlining, disposal of casting plant dross, chlorine fluxing of metal prior to casting, explosion hazards, effluents from remelting scrap, and dusts and noise in many parts of the aluminum production process.

Introduction It is difficult to trace the historical activities of the aluminum industry in the field of environmental control. Literature prior to the last decade and one-half is scanty. This paper attempts to deal with the first eighty years or so of the industry, that is from 1890 to 1970. About 1970 the major focus on preserving the environment rose to the surface in the western world primarily as a result of Rachel Carson’s “Silent Spring”. Also, about that time, the Metallurgical Society started its annual publication of Light Metals. When we think of environmental control in the aluminum industry, many of us tend to think almost exclusively of the emissions from the cell rooms. I found this out when I turned to industry associates for information about environmental control. Invariably the response related almost exclusively to how gases from the HallHkroult process were handled.

Certainly, the Hall-Hkroult fluoride evolution has been one of the major problems. As early as 1909 vegetation damage by fluorides had been noticed. Dr. Paul Hollande wrote a report at that time about what was happening in the upper Valley of La Maurienne. He said, “It is in fact public knowledge that the aluminum plants are devastating vegetation. . . . The equipment being experimented with on the roof of the Calypso plant is unable to stop the evil.” The equipment described was a water curtain or water mist sprayed in the roof vents, but “it had to be stopped during tapping operations because of the risk of accidents resulting from droplets of water falling onto the molten aluminum”. This is certainly the earliest record that I could find of any attempt at environmental control in our industry (1). Such early recognition, however, was far from universal. In 1971 R.W. Andrews, Jr., of Aloca, stated that “just prior to and during World War 11, bits of evidence began to

168

accumulate to show that effluent fluorides from the cells could, if uncontrolled, effect damage to some sensitive species of vegetation and could under some circumstances produce harmful effects upon grazing animals” (2). Although another paper in this symposium is to focus on cell room environmental control, the considerable information which I accumulated has been summarized in an Appendix to this paper. This paper is not as complete or extensive as I wished it to be. I did consult the major aluminum companies, and I did, with the assistance of my colleagues in the libraries of Alcan, search the literature. With those caveats this paper presents the accumulated information, running from the Bayer process through to casthouse. I have not, to any degree, covered mining and restoration of mine sites on the one hand, nor discussed the environmental control measures required in rolling, extrusion and other fabricating processes. This limitation was chosen to coincide with the fields of interest of the Light Metals Committee of the Metallurgical Society.

169

Bayer Process Waste (Red Mud) The general way to treat red mud has been to dewater it to the extent possible, which generally meant 35-50% solids, depending upon the bauxite concerned, and pump it to a pond near the plant. In the pond the mud tended to settle and consolidate, the supernatant liquid could be returned to the plant, or possibly, given the correct climate conditions, would be lost by evaporation. In a number of cases, after the pond was full, top soil was added and vegetation was grown. This practice has been followed by Alcan in Jamaica for over 25 years. In other areas this system could not be followed because of the lack of appropriate land. Disposal at sea was therefore investigated. The British Aluminium Company Limited had a smelter on the Bristol Channel at Newport in Wales. In this case a ship was loaded at high tide from holding tanks or ponds at the plant. The ship then moved downstream with the ebb tide, to a dredged cut, and discharged the slurry (3). Pechiney experimented with discharging red mud into the Mediterranean. In this case they used two pipes ending three and one-half miles offshore at depths of 320 and 300 metres. The discharge was into a submarine canyon named Cassidaigne (near Marseilles). It was found that the red mud spread into the deeper part of the canyon. No intoxication of the marine biota was found. In general, suspension feeders, species feeding on the sediment and various kinds of fish prospered and appeared to be unaffected by the presence of the red mud (4).Pechiney used this system to discharge

the muds from their plants at Gardanne and La Barasse. It was pointed out that they were discharging approximately one million tons of sediment per year against the 25 million tons per year which were being brought into the Mediterranean by the adjacent Rhone River. Another development has been reported, and I include it here although it doesn’t quite meet my deadline. In Louisiana Kaiser developed a system of sand bed filtration to minimize the waste storage volume. This has been described (5). Finally, one other case. In Germany, from its Martinswerke plant, Alusuisse is pumping the red mud slurry into a minedout brown coal mine for land reclamation (6). I have not attempted to cover in this review the many attempts at finding some use for “red mud.” There have been other very extensive literature reviews, but we know that all work has been unsuccessful.

Calciners For The Production of Alumina The first electrostatic precipitators for moving dust from exhaust gases from calcining kilns for alumina were installed as early as 1921. These were a vertical type with preliminary separation by multiclones to reduce the dust loading at the electrostatic precipitator. Subsequently, the vertical electrostatic precipitators, which had a high construction cost, were abandoned and horizontal electrostatic precipitators dominated the field (7). There has been a continuing evolution of electrostatic precipitators and they still dominate the field, whether for rotary kilns or stationary circulating fluid bed kilns.

Carbonaceous Fumes Little appears to have been developed in this area. Kaiser reports that for their green carbon facility they use delayed coke and a fabric filter as a dry scrubbing system for the green carbon facility (8). Pechiney is reported to use a similar system which has been developed by Air Industrie. For Reidhammer anode baking furnaces, electrostatic precipitators have been known for some time. For the open type of ring furnace dry scrubbing systems are common. Reynolds reports using a packed coke bed followed by alumina-coated bags (9), and various other systems have been described (10). Soderberg anodes in cell rooms are, of course, another major source of carbonaceous fume. In an appropriately operated VS cell, much of this fume appears under the gas skirt, and if burners are operated between the gas skirt and the duct, much of the fume will be destroyed. By the early 1970’s Sumitomo Aluminum developed a “dry paste” technology which minimized the escape of fume by evaporation from the top of the VS anode. With HS anodes, no satisfactory solutions have been found.

Potlining The most common method for dealing with potlining has been to use a cryolite recovery plant based on a caustic leach of the potlining. This does leave the problem of disposal of the black mud, but this can generally be ponded. It is claimed that the process serves to destroy the cyanides, and it recycles the fluorides to the Hall-Hkroult process (1 1). A more recent description of this process has been given (12).

The only other system which has been used was designed by Electrokemiske (13). This pyrohydrolysis process has been developed and is operated, but it is not economically attractive enough to be further exploited. Various other processes have been proposed and development work is still going on. Treatment of scrap potlinings is the subject of a special program at this conference.

Aluminum Remelting And Chlorine Fluxing

basis. To prevent the discharge of acid effluents, a caustic scrubber liquor can be used, but this system requires periodic solids cleanout and disposal. Other systems are floating bed and Venturi caustic scrubbers (17). As an alternate to these systems, it has been claimed that fluxing with a tri-gas mixture (nitrogen, chlorine and carbon monoxide) has eliminated the need for any environmental protection devices (18).

Explosions

As has been pointed out, molten metal explosions are not limited to aluminum (19). Other molten metals, and, indeed, slag from steel furnaces will produce explosions if contact with water is allowed. Once D.C. casting came into vogue, the hazard increased since, by its very nature, this process led to large quantities of molten metal being in close proximity to water. Starting in the 1950s, the aluminum industry has made an intensive effort to understand these explosions and means of preventing them. The Aluminum Company of America took the lead in this work, but many other organizations and most aluminum companies have contributed. The (16). In the ‘50s the need for demagging and Aluminum Association has sponsored basic for cleaning metal received increasing em- studies at the Battelle Memorial Institute, phasis, and use of chlorine fluxing of the the Illinois Institute of Technology Research metal to achieve these became a common Institute, and Alcoa Laboratories. The practice. A variety of systems were devel- Aluminum Association has thoroughly documented these studies and has issued a set oped and tested. It was discovered that a of guidelines for safe practices during 90% nitrogen and 10% chlorine mixture was as effective as pure chlorine. Nelson has casting of aluminum (20). described a number of systems. Included in these was a water scrubber but this has a highly acid liquid discharge which requires a good supply of water for a once-through

In remelting aluminum, fine particulates result from the partial burning of any carbonaceous material on the surface. There is emission of fumes from the fluxes, generally chlorides, and from the refining by chlorine injection. In addition to the problem of fine particulate collection, there is the difficulty of the corrosive nature of the chloridecontaining materials. One solution has been to use a Venturi-type scrubber which has special linings (14). An alternate system using a bag filter with a pre-cooler is also claimed to be very effective (15). Wet scrubbers and electrostatic precipitators have also been used

170

Heat And Physical Stress

171

It has been pointed out that North American aluminum technology was characterized by cheap energy available in large quantities (1). This led to cells which maximized capital productivity and, as a consequence, tended to work with higher heat losses. In Europe, on the other hand, the focus was on minimizing energy consumption, and lower heat losses resulted. It is not surprising, therefore, that concentration on protecting the worker from physical stress due to heat tended to focus in North America. In 1943 one of Alcan’s plants was faced with a strike over summer work loads in the potrooms. A Government Commission was appointed to investigate the physical demands of potroom workers’ jobs. Dr. Lucien Brouha, of The Harvard Fatigue Laboratory, served on the Commission, and as a result of this, he developed procedures to measure and interpret the physiological cost of work under various conditions. Numerous experiments were conducted in Alcan’s smelters (21, 22). As a result of these experiments, which compared the physiological cost of various working methods, many improvements were carried out. These involved changes in working conditions, work schedules, and of course improved mechanization. Another study was carried out in Louisiana, and in this case the work place measurements were taken before and after reflective shielding had been installed between the work station and hot molds (23). This shielding was shown to be effective in lowering radiant temperatures, body temperatures, pulse rates and sweat output. It was suggested that the workmen could be used

as a biological metering system for environmental stresses on the job. Of course, what we didn’t realize at the time was that physical work is one form of aerobics; nonetheless, it is clear that we need to protect the worker from undue physical stress, and a listing has been given of the potential application for physiological studies (24). At the same time over the years there has been a continual development of machines to reduce the physical effort required to produce aluminum. A leading proponent and developer of such machines was the SociCtC ECL under its director, Monsieur Duclaux. Many excellent pieces of equipment were developed for tending vertical stud and prebake pots. Over the same period, all the horizontal stud operators developed various machines for the same purpose.

Noise

Consciousness of noise as an environmental hazard has received much attention recently. The problem of noise depends very much on the area of work and the kind of machines used, and of course the intensity of sound which is generated. An analysis of some of the effects has been given (25).

Disease And Damage To Vegetation The exposure of aluminum workers to industrial fluorosis has been documented (26). The same paper covers the effects on animal husbandry of fluorine contamination of herbage. Recognition of this problem led to extensive studies, supported by the Aluminum Association, at the Boyce Thomson Institute.

Industrial fluorosis was also studied in other countries. In Norway in a study reported in 1938, no cases of acute cryolite poisoning were found, although one possible case of fluorosis was noted (27). Another study reported no symptoms of fluorine poisoning or fluorosis of the bones (28). A review paper in 1944 on working conditions and their effect on health reported no definite effects, but suggested that fluorides might be capable of irritating the skin or causing osteosclerosis in the long run (29). A study in 1946 reported concentrations of fluoride in the air in a building containing a single row of pots; exposure was calculated but no symptoms of disease were noted (30). On the other hand, cases of skeletal fluorosis have been reported (31). Four cases were reported, two in the very first stage of the disease, and two in the second. It was reported that the teeth contained unusually high fluoride levels. Early detection of possible fluorosis was also examined (32). It was reported that there did not appear to be any way to detect a preoccurence of the disease. A number of studies have examined the occurrence of asthma in cell room workers (27). The author suggested that the incidence of asthma might represent an allergic reaction to one or more of the substances used or generated during the work process. Another study contained the suggestion that the respiratory symptoms might be attributed to alumina dust (28). A later paper examined the incidence of bronchial asthma in a variety of working situations in the industry (33). Typical ways to improve the environment were suggested, including better ventilation and the use of gas

masks. Strangely enough, in this case, the author suggested that the aluminum industry should employ an electrolyte which “does not contain fluorine”. Other occupational diseases for aluminum were discussed in 1950 (34). This document concluded that, except for fluorosis, there was little danger from aluminum. It is also one of the first references to demonstrate that use of aluminum cooking utensils constitutes no hazard. The intake of aluminum from other sources far out-weighs any amount which could arise from the use of aluminum utensils in cooking. Finally, there was an examination of whether or not employment in the aluminum industry could lead to warts (35). The author carried out a histological and statistical enquiry into the prevalence of warts in potroom workers. He concluded that there was no evidence that any industrial agent was causing skin warts. In some areas an attempt was made to reduce the concentration of fluoride in vegetation through improved dispersion. In the 1940s and 1950s, Kaiser used tall stacks as a means to do this (8). Alcan attempted the same thing at a later date. Such an approach tends to be less than effective, since atmospheric inversions can severely limit the dispersion.

Ackowledgements A number of people provided the information I have used in this somewhat limited review. For their help my thanks go to P. Bridenbaugh and P. Atkins of Alcoa, to S. Nielsen a former employee of Ardal og Sunndal Verk a s . of Norway, to T.R. Pritchett and R.J. Schlager of Kaiser Aluminum, to M. Reverdy and Y. Lallement of PCchiney Aluminium, to Nolan Richards of Reynolds Aluminum, and certainly not least, but last, to H.O. Bohner and R.E. Frankenfeldt of the Swiss Aluminium Company. If I have misinterpreted any of the information which they gave me, I apologize.

172

APPENDIX A TREATING CELL ROOM GASEOUS EFFLUENT Year

173

Corporation

Aim

1935

A.I.A.G.

Up to 1950 1940’s 1940’s

Pechiney Kaiser A.I.A.G.

1948 1950 (?)

ASV A.I.A.G.

1950’s 1950’s

Kaiser Pechiney

1954 1957 1958 1958

ASV Reynolds Alusuisse ASV

Treatment HSS Collection and Treatment VSS Treatment HSS Collection, Unhooded PB Treatment VSS Treatment HSS Treatment Treatment VSS

1959

Pechiney

Treatment VSS

1969

ASV

Treatment VSS

1970 Now

Reynolds All

Treatment HSS Treatment all types

Collection and Treatment HSS Treatment at Roof Dispersion Treatment at Roof

Effluents Controlled

Technology Hoods (first installation) Spray Tower, Electrostatic Pptr. Water spray in monitor Tall stacks Water spray in monitor to compensate for low collection efficiency of hood Spray nozzles, milk of lime Gas skirt, cyclone, water spray (later added electrostatic pptr.) Net scrubber Small hood over blow hole Cyclones & milk of lime scrubber Wet scrubber Efficient roof scrubber Electrostatic pptr. & milk of lime scrubber Gas skirt burner + electrostatic pptor + alkaline scrubber Burner + Electrostatic + sea water scrubbing Cyclone + Wet Electrostatic Dry Scrubbing

References 1. 2. 3.

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

12.

13. 14.

15. 16.

Y. Lallement, Pkchiney Aluminium, private communication. R.W. Andrews, Jr., Aluminum Company of America, Special Centennial Symposium, University of Missouri, Rolla, February 9, 1971. V.E. Davies, Experience in Disposal of Red Mud in the Sea, Environmental Protection in the Aluminium and Non-Ferrous Smelting Industry, Symposium on the Protection of the Environment, 1972, Stuttgart. English translation by E.J. Groom, Technicopy Limited, Stonehouse, Gloustershire, England, 1973. Michel Bourcier and Helmut Zibrowius, Les Boues Rouges Diversees dans le Canyon de la Cassidaigne, TETHYS 4 (4) 1972 (1973). M.F. Vogt and D.L. Stein, Sand Bed Filtration of Bauxite Residue, Light Metals, 1976, Volume 2, Ed. S.R. Leavitt. R.E. Frankenfeldt, Swiss Aluminium Limited, private communication. K. Arras, New developments in the electrostatic cleaning of exhaust gases from calciners. See reference (3) for full details. R. J. Schlager, Kaiser Aluminum, private communication. N.E. Richards, Reynolds Aluminum, private communication. Philippe Dumortier, “Treatment of Anode Baking Furnace Fume”, Review de l’aluminium, June 1981. W. Fulda and H. Ginsberg, Tonerde Und Aluminium, Part V, W. de Gruyter and Co., Berlin, 1953. G. Findeis, Working up the Cathode Linings from Electrolytic Cells for Aluminium. See reference (3) for full details. Austrian Patent Application No. 12 678/68, Electrokemiske a / s Olso, Norway. R. Johansson and G. Walker, Treatment of Salt Fume by the Venturi Scrubber, Proceedings of an International Conference on Air Pollution and Water Conservation, Basle, Switzerland, October 1969, Garden City Press Limited, London, England. A. Margraf, Filters for Treating Waste Gases from Aluminium Remelt and Holding Furnaces. See reference (14) for full details. Egmont Bruch, Exhaust Gas Cleaning in Aluminium Remelting Plants. See reference (3) for full details.

17. Alvin H.Nelson, The American Approach to the Treatment of Chlorine Fume. See reference (14) for full details. 18. P. Presche, The Treatment of Aluminium Melts with Gas Mixtures. See reference (3) for full details. 19. George Long, Explosions of Molten Aluminum in Water - Cause and Prevention, Metal Progress, Vol. 71, No. 5, 1957. 20. Aluminum Association, Inc., Guidelines for Handling Molten Aluminum, Ed. W.S. Peterson, October 1982. 21. F. de N. Brent, Pulse Rate Studies for Evaluation of Physical Demand of Manual Work, Work Physiology Symposium, University of Toronto, School of Hygiene, September, 1968. 22. G. Kaine, Physiological Studies in Industry, 30 Years Experience, Graham Ross Memorial Lecture, Industrial Medical Association of the Province of Quebec, 1973. 23. W.F. Lienard, R.S. McClintock, and J.P. Hughes, Appraisal of Heat Exposures in an Aluminum Plant, Proceedings of the Thirteenth International Congress on Occupational Health, U.S. Executive Committee on the Thirteenth International Congress on Occupational Health, 1961. 24. P.E. Holsgrove and G. Kaine, Modern Technology in the Measurement of Physiological Reactions of Workers in Industry and its Practical Applications in the Aluminum Industry, Light Metals 1973, Volume 1, Ed. A.V. Clack. 25. H.D. Thomassen, The Noise Problem in the Aluminium Industry. See Reference (3) for full details. 26. J.N. Agate, Industrial Fluorosis, Medical Research Council Memorandum No. 22, A Study of the Hazard to Man and Animals near Fort William, Scotland; London, His Majesty’s Stationery Office, 1949. 27. K. Evang, Examination of Norwegian Aluminium Workers for Occurrence of Asthma Bronchiale, Acute Cryolite Poisoning and “Fluorosis”, Nordisk Hygienisk Tidskrift, Vol. 19, 21 references, 1938. 28. E. Hjort, Investigation of Possible Fluorine Poisoning Among Workers in an Aluminum Plant, Nordisk Medicin Tidsskrift, Vol. 15, 7 references, 1938. 29. F.J. Tourangeau, The Health of Workers in the Aluminum Extraction Industry, Lava1 Medical, Vol. 9, 1944.

30. C.D. Yaffe, Atmospheric Concentrations of Fluorides in Aluminum Reduction Plants, Journal of Industrial Hygiene and Toxicology, Vol. 28, No. 2, 3 references, March 1946. 31. J. Lezovic and L. Arnost, Occupational Skeletal Fluorosis, Fluoride Quarterly Reports, VoI. 2, No. 2, 2, references, April 1969. 32. A. Lanyi, Diagnosis of Occupationally-Induced Fluorosis, Bratislavske lekarske listy, Vol. 51, No. 1 , 13 references, August 16, 1969. 33. 0. Midttun, Bronchial Asthma in the Aluminum Industry, Acta Allergologica, Vol. XV, 20 references, 1960. 34. K.H. Sroka, Occupational Diseases in the Light Metal Industry, Metall, No. 4, 171 18. 1950. 35. R. Lockhart, An Investigation of Warts Prevalent Among Workers in the Reduction Works of the Aluminum Industry, British Journal of Industrial Medicine, Vo. 1 1 , No. 4, 2 references, October 1954.

J. Peter McGeer Peter McGeer began his career with Alcan International Limited in 1949, soon after earning a PhD in Physical Chemistry from Princeton University. His research in aluminum extractive metallurgy and the science of carbon has been documented in numerous technical papers. Pete has been a very active member of the Light Metals Committee for the last 15 years, serving as Chairman in 1983-84. He participates in many technical advisory and executive committees, both in the United States and Canada. Currently he holds the title of Director, Kingston Research and Development Centre of Alcan International Limited.

174