Selective Sulfidation of Lead Smelter Slag with Sulfur
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LEAD is primarily produced from lead sulfide concentrates using conventional oxidizing roasting-reduction smelting processes in the world. A problem of this process is a generation of considerable amount of reduction smelter slags, with 5 to 30 pct Zn, 0.5 to 5 pct Pb, 17 to 31 pct Fe and minor and trace heavy metals, such as Cu, Cd, As, Cr, Hg, and Ni, which are considered as potential hazardous wastes.[1] Statistically, about one to two tons of the slag will be discharged with one ton crude lead produced from the concentrates, and the volume of slag is three to six times of crude lead depending on the difference in density.[2,3] The stockpiling of these slags not only occupies precious land but also leads to potential environment threat and the loss of valuable metal resources.[4,5] Consequently, the recycle of heavy metals from waste slags has become the most promising treatment approach based on social, economical, and environmental pressures. A number of pyrometallurgical and hydrometallurgical methods have been developed for the recovery of zinc, lead, and other metals from lead smelter slag.[6,7] The most common process commercially now is fuming furnace method,[8] in which the slag is subjected to a reduction roasting using large quantity of powdered coal or other reducing agents and air or oxygen-rich air at above 1473 K (1200 C). Valuable metals, such as Zn, Pb, and Cd, are reduced and volatilized from the slag, are then reoxidized to metal oxides in the outlet gas stream and collected as dust, and thereafter are JUNWEI HAN, WEI LIU, and FEN JIAO, Doctors, DAWEI WANG, Master, and WENQING QIN, Professor, are with the School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, P.R. China. Contact e-mails: [email protected]; [email protected] Manuscript submitted September 25, 2015. Article published online November 30, 2015. 344—VOLUME 47B, FEBRUARY 2016
recovered by acid leaching or other processes. This technology, however, has some deficiencies including high energy consumption, strict requirement on dust collection system, low recovery of metals, and high risk to workers’ health resulted from volatilization of heavy metals, such as Pb, Cd, and As. Therefore, green alternative technologies for the treatment of lead smelter slag urgently need to be developed. Sulfidation–flotation technology recently has received much attention as a potential means for the recovery of heavy metals from low-grade oxide ore or wastes. The metal oxides are converted into sulfides with good floatability, which can easily be concentrated by conventional flotation process.[9,10] Literatures suggest that the conventional sulfidation with Na2S or NaHS has been widely applied to process low-grade copper, zinc, and lead ores,[5,11] and recently has also been employed to recycle Ag, Pb, and Au from zinc leach residues.[12,13] But this process is only suitable for treating those easily vulcanized materials and also poses some problems, such as the secondary emission of wastes and the release of toxic ga
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