Hydrothermal Sulfidation and Flotation of Oxidized Zinc-Lead Ore
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BECAUSE of the limitation of sources and supplies of zinc and lead sulfide ores, the need to treat zinc and lead ores of increasingly lower grades, as well as those that are fine, complex mineralogically, and refractory, has gained much attention. Therefore, how to improve the metal recoveries from low-grade oxidized zinc-lead ore has become more important in recent years. Flotation is the most common process, and it is the primary method of recovering zinc and lead from sulfide or oxide minerals. It is well known that there is a difference between sulfurized and oxidized minerals regarding their separation by flotation. Flotation of zinc and lead oxidized minerals is extremely complex because of the similarities in the physicochemical and surface chemistry of the constituent minerals. There are no known directacting collectors capable of producing single metal concentrates.[1,2] Therefore, it is common practice to sulfurize oxide lead-zinc minerals prior to flotation to prepare their surfaces to receive the collectors generally adopted for concentrating sulfide. There have been extensive investigations into the sulfidation of oxidized zinc-lead ore and zinc-lead ores containing oxidized constituents. The ore is treated by (1) a sulfidizing operation, such as a treatment with hydrogen sulfide gas or its equivalents,[3] (2) sodium sulfide,[4–9] or (3) sulfidation roasting with the element sulfur.[10] Based on these and other studies, sodium sulfide is one of the most widely used sulfides in the sulfidization-flotation process. Nevertheless, the use of sodium sulfide as a sulfidizing agent is accompanied by the emission of secondary wastes and the release of toxic CUN-XIONG LI, CHANG WEI, ZHI-GAN DENG, XING-BIN LI, MIN-TING LI, and HONG-SHENG XU, PhDs, are with the Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, P.R. China. Contact e-mails: [email protected]; [email protected] Manuscript submitted July 19, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
gases, and its effectiveness is not entirely satisfactory, possibly because the sulfidized layer detaches readily. An insufficient amount of sulfide gives poor recoveries because of inadequate sulfidization, whereas excess sulfide causes poor flotation due to the depressant action of sulfide ions. Hence, sulfur has been suggested as a substitute for sulfide, and the use of sulfur for sulfidizing of nonferrous natural or secondary resource to enhance recovery has received much attention.[11–15] The objective of this study was to investigate the hydrothermal sulfidation of an oxidized zinc-lead ore with sulfur, which was applied prior to flotation and could contribute to improving the flotation recovery of zinc and lead. In such a sufidizing operation, the oxidized ore constituents may be merely filmed with the stable metal sulfide compounds, or they may be converted to a greater or lesser extent into stable metal sulfide compounds. In the first part of the current study, we studied the hydrothermal sulfidation of oxidized zinc
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