Recovering accessory minerals from lead and zinc process wastes

Abstract

This research is part of a continuing effort to reduce environmental conflicts and occupational hazards associated with mineral processing and to recover valuable constituents in wastes. A laboratory process for lead smelter flue dust (sulfation roasting followed by water leaching) extracts over 950 of the Cd and Zn. Ninety-nine percent of the Cd is recovered from solution by sponging with zinc dust, and Zn is electrowon from the resulting solution after purification. The Cd and Zn leach residue consists largely of PbSO 4, which is converted to PbCO 3 and leached with H 2SiF 6 to produce PbSiF 6 electrolyte for lead electrolysis. Accessory minerals (such as Co and Ni) are separated into purification residues for subsequent recovery. A copper-cake residue treatment process consists of leaching with sulfuric acid to extract Cd and Zn, which are recovered as in the flue dust processing. The insoluble residue, containing Cu, As, Co, and Ni, is leached with manganese dioxide and sulfuric acid to solubilize those metals while leaving a residue of PbSO 4. The solubilized metals are recovered from the leach solution by caustic purification (As and Fe removal) and sequential sulfide precipitations. The products are copper sulfide and cobalt-nickel sulfide. The manganese is reclaimed from the leach liquor as manganese dioxide for recycle.