Selective Sulfidation of Lead Smelter Slag with Pyrite and Flotation Behavior of Synthetic ZnS
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ST of nonferrous metals such as Cu, Pb, and Zn are mainly produced from sulfide ores via beneficiation and metallurgy processes, in which tons of heavy metal containing wastes are generated every year.[1–3] These wastes generally contain various heavy metals that are rarely in sulfide form but rather are oxides and oxidized compounds.[4,5] The stockpiling of these wastes not only causes an environment threat due to the possibility of releasing toxic elements such as Pb, Cd, and As, but also results in a waste of considerable amounts of secondary resources containing plenty of valuable metals, such as Zn, Pb, and Ag.[6] With the ceaseless exploitation of high-grade sulfide ores, the continuous strictness of environmental requirements and the declining of metal prices in recent years, reclaiming and recycling these metals from such secondary resources are highly desirable and urgent. Lead smelter slag is a typical kind of heavy metal containing wastes; considerable amounts of which are generated annually by the lead pyrometallurgical process. In general, the slag contains 10 to 25 pct Zn, 0.5 to 5 pct Pb, and other minor valuable metals, and is thus considered to be a potential hazardous waste or a secondary zinc resource. Mineralogical studies showed that the zinc and lead were mainly in the form of amorphous zinc silicates and metallic lead, respectively.[7,8] If an effective and reliable technology to sulfidize these metals were developed, the existing JUNWEI HAN, WEI LIU, and FEN JIAO, Doctors, DAWEI WANG and TIANFU ZHANG, Masters, and WENQING QIN, Professor, are with the School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, P.R. China. Contact e-mail: [email protected] Manuscript submitted March 6, 2016. Article published online May 27, 2016. 2400—VOLUME 47B, AUGUST 2016
beneficiation and metallurgical processes could be used to recycle these synthetic metal sulfides economically. After tireless efforts made by researchers in the past decades, various sulfidation technologies have been developed to improve the floatability of valuable metals in low-grade oxide ores or metallurgical wastes. The most common approach commercially is to sulfidize the surface of those metal oxide particles using Na2S as modifier in flotation process.[9–11] However, this method is only suitable for treating those easily sulfidized materials and also poses some problems, including the generation of secondary wastes and the emission of H2S gas, etc. Recently, mechanochemical and hydrothermal sulfidation have received much attention as potential green processes for waste treatment. Yuan et al. suggested that mechanochemical sulfidation and flotation process might be used to recover lead from various kinds of leaded glass wastes, but the related experimental reports have not been found.[12] Liang et al. studied the hydrothermal sulfidation of heavy metal-containing neutralization sludge with sulfur in high pressure reactor at 473 K (200 °C) for metal recovery by flotation process.[13,14] The results indicated that 33.3 pc
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