Separation of Antimony from a Stibnite Concentrate Through a Low-Temperature Smelting Process to Eliminate SO 2 Emission
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is the largest producer of antimony in the world. Current estimates place the antimony output of China at more than 80 pct of the total global output. Antimony deposits are found in Guizhou, Guangxi, and in many other provinces throughout China; of these, Hunan has the richest deposits. In particular, Xikuangshan, near Lengshuijiang City, has been celebrated for a long time for the quality and quantity of its antimony.[1,2] The commercial route for the extraction of antimony from its sulfide mineral stibnite at Xikuangshan is a pyrochemical process (1423 K to 1623 K [1150 C to 1350 C]), which involves roasting the concentrate in a blast furnace, volatilizing the resultant antimony trioxide, and reducing the trioxide with carbon to a metallic antimony in reverberatory furnaces.[1–3] However, smelting antimony under these high temperatures causes the following serious problems in the form of serious environmental pollution and large energy consumption: (a) Serious environmental pollution. During roasting, considerable quantities of antimony sulfide and some associated low-boil-point metals, such as lead, arsenic, and cadmium, together with low concentrations of SO2, JIAN-GUANG YANG, CHAO-BO TANG, YONG-MING CHEN, and MO-TANG TANG, Associated Professors, are with the Department of Metallurgical Science and Engineering, Central South University, 41008 P.R. China. Contact e-mail: jianguang_yang@ hotmail.com Manuscript submitted August 28, 2010. Article published online November 23, 2010. 30—VOLUME 42B, FEBRUARY 2011
are emitted because of volatilization. At present, the smelting of nearly all nonferrous metals has overcome the problem of low concentrations of SO2 emission by adopting enhanced oxygen-rich smelting technologies such as the Ausmelt process, Noranda process, Mitsubishi process, etc. However, because of a comparatively small industry and because the antimony sulfide boil point is comparatively low (1353 K to 1363 K [1080 C to 1090 C]), it is difficult to apply the enhanced oxygen-rich smelting technology to antimony smelting. Therefore, large numbers of low-concentration SO2, together with some escaped heavy metals, result in serious environmental pollution in the areas surrounding the smelting plants brought about by the use of obsolete technology. In addition, antimony and its compounds are highly toxic. Although some improved methods have been developed,[4,5] traditional and improved methods for producing antimony are still carried out at high temperatures ranging from 1423 K to 1623 K (1150 C to 1350 C). At these temperatures, antimony sulfide, antimony, and its compounds possess a high volatility and, as a result, pass in considerable quantities into the gas phase, thereby polluting the environment with toxic antimony and lowconcentration sulfurous gas. To date, not a single known method for antimony recovery can ensure adequate environmental control at the positions of the operator and in areas adjoining such antimony-recovering enterprises.[6–11] As a result, the antimony concentrations in the atmospher
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