Sulfidation of heavy-metal-containing neutralization sludge using zinc leaching residue as the sulfur source for metal recovery and stabilization

• Zinc leaching residue was used as a sulfur source to sulfidize neutralization sludge.
• 82.6% of Zn and 95.6% of Pb in waste can be converted to ZnS and PbS.
• Zn and Pb in sulfidation product can be enriched and recovered by flotation.
• By a conventional flotation process, a concentration was obtained with 21.3% Zn and 3.4% Pb.
• Heavy metal leaching concentrations of sulfidation product reduced significantly.

Heavy-metal-containing neutralization sludge (NS) and sulfur-containing zinc leaching residue (ZLR), both of which are difficult to dispose of, are two of the main solid wastes produced in the Pb/Zn smelting process. This study focused on the application of ZLR as a sulfur source to sulfidize NS, which could then be separated by flotation for metal recovery. A mixture of NS, ZLR and additional sulfur was first mixed by ball milling, and then successively treated by hydrothermal sulfidation and flotation. Based on the chemical properties of NS and ZLR, the effects of the mass ratio of NS-to-ZLR, the amount of sulfur and ball milling time on sulfidation and the floatability and stability of the sulfidation product were investigated. The sulfidation percentages of Zn and Pb were as high as 82.6% and 95.6%, respectively. Flotation tests revealed that Zn and Pb can be enriched with a concentrate grade of 21.3% Zn and 3.4% Pb. Toxicity characteristic leaching procedure (TCLP) results indicated that stabilization of NS and ZLR occurred after sulfidation.