The Membrane Electrowinning Separation of Antimony from a Stibnite Concentrate
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TRODUCTION
GENERALLY, the commercial pyrometallurgy route for the extraction of antimony from its sulphide mineral involves the evolution of toxic gases into the atmosphere.[1] During roasting, some valuable metals are lost because of volatilization, and the SO2 generated is a source of environmental pollution. Furthermore, such a pyrochemical process usually requires a highgrade concentrate and is not suitable for the treatment of low-grade antimonial mineral because it would result in the formation of a stable antimonate of impurity elements, which render subsequent processing difficult. The processing of low-grade stibnite concentrates for the extraction of antimony without entailing SO2 emission, therefore, has received considerable attention in recent years. So far, several hydrometallurgical methods have been proposed, and different leaching agents have been used for the treatment of stibnite concentrates, such as the mixture of hydrochloric and tartaric acids and the mixture of nitric and tartaric acid as well as hot concentrated sulfuric acid,[2] sodium sulfide and sodium hydroxide, and so on.[3–5] However, using chloride medium—mostly ferric chloride—to obtain metals from sulphidic ores, such as sphalerite, galena, chalcopyrite, cubanite, bornite, JIAN-GUANG YANG, Associate Professor, is with the Department of Metallurgical Science and Engineering and the Institute of Powder Metallurgy Research, Central South University, Changsha 410083 P.R. China. Contact e-mail: [email protected] SHENG-HAI YANG and CHAO-BO TANG, Associate Professors, are with the Department of Metallurgical Science and Engineering, Central South University, Changsha 410083, P.R. China. Manuscript submitted August 17, 2009. Article published online March 4, 2010. METALLURGICAL AND MATERIALS TRANSACTIONS B
pentlandite, pyrrhotite, mamatite, pyrite, molybdenite, and so on, is not a recent idea.[6–8] Because the reaction of these sulphidic ores with ferric chloride proceeds fairly rapidly, and because the reaction produces elemental sulphur in solid state, which is a great merit of this process when compared with the classical pyrometallurgical method giving gaseous SO2, the interest in technological application of this reaction has stimulated a great number of theoretical studies aimed at the elucidation of the mechanism of leaching recently. However, because of the ferric ions accumulating in solution as well as some inherent disadvantages of the hydrometallurgical process, this chlorination leaching process still has not been widely applied in the industry. In the present study, a process for the separation and recovery of antimony from a stibnite flotation concentrate by chlorination leaching, purification, and electrowinning was introduced. Antimony pentachloride, instead of ferric chloride, was used as leaching agent and as oxidant in this process, which avoided the ceaseless accumulation of ferric ions in solution. Furthermore, the subsequent electrowinning of antimony instead of antimony hydrolization or antimony replacement could
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