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Mineralogical Reconstruction of Lead Smelter Slag for Zinc Recovery

The lead smelter slag may be regarded as an important secondary resource, since tons of the slag containing 10 to 25% Zn, 3% Pb and other minor valuable elements are discharged every year by industries. It is difficult to economically justify the recovery of valuable metals (mainly zinc) using traditional technologies. In this study, mineralogical reconstruction obtained by sulfidation roasting with pyrite and carbon in the presence of sodium carbonate was conducted to recover Zn from the lead smelter slag. The effects of temperature, dosage of sodium carbonate, carbon and pyrite, and the time on the formation of ZnS were studied by XRD and optimum condition was established. The average crystal size of ZnS obtained was 2.63 µm under the optimal condition and its existence as both sphalerite and wurtzite was confirmed. The flotation tests performed indicated that zinc sulfides produced could be separated from the treated slag. The zinc grade increased from 13.63 to 32.76% and a total zinc recovery of 88.17% was obtained in the open circuit flotation test.