The dissolution of sphalerite in ferric sulfate media
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I. INTRODUCTION
ALMOST all of the world’s primary zinc production is derived from the treatment of sulfide concentrates in which sphalerite, (Zn,Fe)S, is the dominant zinc mineral. Presently, over 80 pct of global zinc metal output originates from the roast-leach-electrolysis process in which zinc sulfide concentrates are roasted in air at about 925 °C to convert the sulfide minerals to oxides, prior to subsequent leaching in sulfuric acid media, solution purification, and zinc electrolysis. However, there is a growing interest in the direct leaching of zinc sulfide concentrates, with elemental sulfur production. This interest is based partly on the desire to separate zinc production from the manufacture and marketing of sulfuric acid, and in part on concerns about the rising capital costs of the conventional technology. Oxygen-H2SO4 pressure leaching of zinc sulfide concentrates was originally developed by Sherritt Inc. (now Dynatec) and Teck Cominco’s Trail operations to complement an existing roast-leach-electrolysis operation.[1] Similar technology is employed at the Kidd Metallurgical Division of Falconbridge Limited[2] and was previously used at Ruhr-Zink.[3] An all pressure leach process, without a complementary roasting circuit, is employed at Hudson Bay Mining and Smelting in Canada[4] and by Kazakhmys Corporation in Kazakhstan.[5] More recently, atmospheric pressure leaching of zinc sulfide concentrates has been implemented commercially,[6,7,8] and industrial interest in this option remains strong,[9–12] despite the slightly lower zinc extractions achieved relative to oxygen-H2SO4 pressure leaching.[13] There is also a continuing interest in bacterially assisted leaching processes. Although none of these processes have been implemented commercially for zinc sulfide ores or concentrates,[14] high zinc extractions J.E. DUTRIZAC, Research Scientist, is with the Mining and Minerals Sciences Laboratories, CANMET, Natural Resources Canada, Ottawa, ON, Canada K1A 0G1. Contact e-mail: [email protected] Manuscript submitted July 20, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS B
have been realized within 2 days using thermophilic bacterial cultures under closely controlled conditions.[15,16] The reactions involved in the leaching of zinc sulfide concentrates are complex and are not fully understood, although it is generally agreed that the ferric sulfate attack of the sphalerite plays an important role in the overall leaching process. Likely, several reactions occur in parallel, and this is especially true for bacterially assisted leaching processes where both direct bacterial attack and indirect ferric sulfate leaching have been proposed.[17,18] Mineralogical studies of reacted sphalerite particles suggest that the direct acid attack of the sphalerite plays some role in ferric sulfate-sulfuric acid leaching, with the dissolved H2S species being oxidized by the ferric ions.[19] ZnS H2SO4 S ZnSO4 H2Saqueous
[1]
H2Saqueous 2Fe1SO4 2 1.5 S S° 2FeSO4 H2SO4 [2] It has been demonstrated that the overa
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