PLEASE DO NOT REMOVE FROM LIBRARY iRII9055 Bureau of Mines Report of Investigations/1986 Hydrometallurgical Process for Producing Lead and Elemental Sulfur From Galena Concentrates By Agnes Y. Lee, Ann M. Wethington, and Ernest R. Cole. Jr. UNITED STATES DEPARTMENT OF THE INTERIOR Report of Investigations 9055 Hydrometallurgical Process for Producing Lead and Elemental Sulfur From Galena Concentrates By Agnes Y. lee, Ann M. Wethington, and Ernest R. Cole, Jr. UNrrED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES Robert C. Horton, Director Library of Congress Cataloging in Publication Data: Lee, A. Y. IIydrometallurgical process for producing lead and elemental sulfur from galena concentrates. (Bureau of Mines report of investigations; (lOnG) Bibliography: p. 13. Supt. of Docs. no.: I 28.23:9055. 1. HydrometalJurgy. 2. Lead - Metallurgy. 8. Sulphur. 4. Galena. ro. Leaching. I. Wethington, Ann M. II. Cole, E. R. (Ernest R.) Ill. Title. IV. Serie:-;: RepIH't of inve,tiga­ tions (United States. Em'cau of Mines) j 9055. TN23.U43 [TN688] 622 s [669'.4] 86-600269 .....,..---------- --------- CONTENTS Abstract •••••• 1 Introduction •• 2 Materials, equipment, and procedures. 3 Oxidative leaching....... • ••••• 3 Lead electrowinning •••••• 4 Recycling of electrolyte. 4 Sulfur extraction ••••• 4 Results and discussion. ..... 4 Leaching reactions... • ••••••••• 4 Leaching parameters--bench-scale tests. .'," ... 6 Oxidan t s •••••• 6 Temperature ••• 6 Time ..••••••.• 6 Fluosilicic acid •••••••••••••••••• 7 Large-scale leaching tests ••••••••••• . ......... 7 Electrowinning •••••••••••••••• 9 Bench scale (I-L cell). 9 Large scale (20-L cell) 10 Impurities •• 10 Sulfur •••••• . .. .. .. .... 11 Residue ••••• • •••••••• II , ••••••••••• 12 Conclusions ••• 13 References •.••••..•....• 13 ILLUSTRATIONS 1. Flow diagram for producing Pb from galena concentrates by leaching and electrowinning ...................•.•.•......•......•......... Go ••••••••••• 2 2. Sulfur extraction apparatus ••••••••••••••••••••••••••••••••••••••••••••••• 5 3. Dissolution of Pb in H2 SiF6 solution during oxidative leaching at 95° C ••• 7 4. Dissolution of impurities with leaching time •••••••••••••••••••••••••• 7 5. Effect of ferric ions on current efficiency ••••• ·................. 11 6. Impurity buildup with number of times recycled •• ·.. ~ ........ " . 11 TABLES 1. Analyses of galena concentrates •••••••••••••••• ........................ 3 2. Screen analysis of galena concentrates ••••••••• 3 3. Effect of various amounts of oxidation agents on lead extraction. 6 4. Effect of time and temperature on lead extraction.... • ••••• 6 5. Effect of leach time on lead extraction at 95° C ••••• 6 6. Effect of H2 SiF6 concentration on lead extraction at C for 90 min. 8 7. Large-scale leaching tests ••••••••••••••••••••••••••••••••••••••••••••• 8 8. Analysis of electrolyte and the resulting lead deposits •••••••••••••••• 9 9. Results of 10 consecutive recyclings of electrolyte in bench-scale leach- electrowinning experiments •••••••••••••••••••••••••••••••• 9 10. Effect of current density on lead electrowinning •••••••••• 10 11. Twenty-liter-cell electrowinning tests •••••••••••••••••••••••••••••••••••• 10 12. Effect of various mixtures of kerosene and tetrachloroethylene on sulfur recovery ................................................................ 12 13. Comparison of galena concentrates and residues •••••••••••••••••••••••••••• 12 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT A ampere kW'h/kg kilowatt hour per kilogram A/m2 ampere 1>ei7 square meter L liter if. cent m meter °c degree Celsius square meter cm2 square centimeter min minllte g gram mV millivolt giL gram per liter pct percent h hour I tr oz/mt tr.oy oUllce per metric ton kg kilogram v volt kw kilowatt W watt kilowatt hour wt pct weight percent II I' 'I 'I· I HYDROMETALLURGICAL PROCESS FOR PRODUCING LEAD AND ELEMENTAL SULFUR FROM GALENA CONCENTRATES By Agnes Y. Lee,1 Ann M. Wethington,2 and Ernest R. Cole, Jr.3 ABSTRACT The Bureau of Mines has developed an effective hydrometallurgical method to recover high-purity Pb metal and elemental S from con­ centrates. This low-temperature process eliminates S gases and Pb emis­ sions, in contrast to the current high-temperature smelting technology. The method consists of (1) oxidative leaching with H202 , Pb02 , and waste fluosilicic acid at 95° C to produce a solution of PbSiF6 and a residue containing elemental S, (2) electrowinning the PbSiF6 solution at 35° C to produce 99.99 pct Pb metal and H2 SiF6 , and (3) solvent ex­ traction to recover S, leaving a residue containing Cu, Ag, and other metal values. Spent electrolyte was recycled repeatedly, with impurity buildup con­ trolled by controlling the leach parameters. , Chemica I engineer. 2Research chemist. 3Supervisory metallurgist. Rolla Research Center, Bureau of Mines, Rolla, MO. 2 INTRODUCTION A major cost factor in the sintering and PbS04 salts have a very limited solu­ and smelting process for producing Pb is bility in aqueous solution, making aque­ the control needed to meet existing envi­ ous electrolysis difficult (11). Lead ronmental standards for Pb emissions. metal was recoverable from -PbC1 2 by Another issue is the current concern over molten-salt electrolysis (7) operated at acid rain, which will in all probability 450 0 C. It is known that -electrowinning result in even more stringent controls on of Pb in HN03 and H2 SiF6 solutions yields emission of S gases. Pb metal at the cathodes and at the same Researchers at the Bureau of Mines have time Pb02 at the anodes (~-1). developed an effective low-temperature Recent investigations on Pb recovery leaching-electrowinning method (!)4 to from battery sludge (l-~,~) have shown produce Pb metal and elemental S from that small amounts of a phosphate or an galena concentrates. The method reduces arsenic compound in the H2 SiF6 electro­ .,' Pb emissions and totally eliminates the lyte will prevent the formation of PbOz I' formation of S gases. The elemental S on anodes, making Pb electrowinning a J i: produced is more economical to store and viable process. ship than the sulfuric acid (H2 S04 ) gen­ Figure 1 is the flow diagram of the erated by the high-temperature smelting oxidative leaching-electrowinning pro­ process. cess. The parameters for each unit pro­ This hydrometallurgical method consists cess were investigated in bench-scale of leaching galena concentrates in waste experiments and tested on a larger scale. fluosilicic acid (H2 SiF6 ) with hydrogen The unit process included oxidative peroxide (H2 02 ) and lead dioxide (Pb02 ) leaching, lead electrowinning, activated as oxidants: carbon treatment of spent electrolyte, and S removal by solvent extraction. 2PbS + 3H2 SiF6 + H2 02 + Pb02 (A) After solid-liquid separation to obtain the Pb fluosilicate solution and the res­ idue containing elemental S, electro­ 1 winning of the aqueous PbSiF6 solution at i 35° C produces Pb metal and H2 SiF6 (l- 2): PbSiF'6 + 2H+ + 2e- + Pb + H2 SiF6 • (B) The H2 SiF6 is then recycled to leach more PbS. Sulfur is recovered from the leach residue by solvent extraction. Several galena leaching processes have been investigated, including processes using ferric chloride (7), ferric sulfate (8), nitric acid (9), and ammonium ace­ tate solutions (10). The leached PbC1 2 Filtration 4Underlined numbers in parentheses re­ •s fer to items in the list of references at FIGURE 1.-Flow diagram for producing Pb from galena the end of this report. concentrates by leaching and electrowinning. .,... 3 MATERIALS. EQUIPMENT, AND PROCEDURES OXIDATIVE LEACHING Later, waste Hz SiF6 and recycled spent electrolyte (HzSiF6 + PbSiF6 ) were em­ Galena concentrates, obtained several ployed. The waste H2 SiF6 was a byproduct times from a Missouri Pb smelter, were of phosphate fertilizer manufacturing analyzed and found to contain 74.4 to (2). The oxidants used were hydrogen 78.3 pct Pb depending on the acquisition peroxide (35 pet H2 02 ) solution and PbOz date. The results of chemical and screen powder (86.1 pct Pb), both technical analysis of typical samples are given in grade. tables 1 and 2, respectively. Sample 1 A redox meter with a Pt electrode and was used in bench-scale tests and sample an Ag-AgCl reference electrode were used 2 in large-scale tests. to measure the redox potential of the An ore mineralization study showed that oxidative leaching reaction. the galena was present largely as free The amounts of galena concentrates and particles, and only small amounts were H2 SiF6 acid used in each leach experiment found in association with chalcopyrite, were calculated so that the resulting quartz, pyrite, dolomite, and sphalerite. leachate would contain about 90 gIL Pb Initially, technical-grade H2 SiF6 was and 90 gIL free H2 S1.F6 • used to leach the PbS concentrates. The leach procedure, for bench-scale tests, was to mix 100 mL H2 SiF6 (200 giL) TABLE 1. - Analyses of galena concen­ solution with 2 mL H2 0z and 0.5 g PbOz in trates, weight percent a 250-mL tall form beaker, followed by the addition of 20 g pbS concentrate. As Element Sample Sample the mixture was heated to the desired 1 2 temperature, H2 Oz was slowly added to pb •••••..••••.•••••••••• 78.30 74.40 initiate the leach reaction. Subsequent­ S ••••••••••••••••••••••• 14.10 13.70 ly, Pb02 powder was added to maintain the Zn •••••••••••••••••••••• 2.38 1.10 redox potential. When the redox poten­ Fe •••••••••••••••••••••• .92 1.25 tial of the leach mixture dropped below Mg ••••••••••••••••••••••