Sulfidation of heavy-metal-containing metallurgical residue in wet-milling processing

• Wet-milling sulfidation was applied to realize the conversion of metal sulfide (MeS) in residue.
• Selective floatation behavior and particle properties of synthetic MeS were investigated.
• Wet-milling can efficiently improve the sulfidation extent and the recovery of heavy metals.

This paper describes the application of wet-milling sulfidation to achieve an efficient conversion of heavy metals (mainly Pb) in metallurgical residues to metal sulfide (MeS) for subsequent metal recovery through floatation. The effects of Na2S-to-Pb ratio (Na2S:Pb), ball-to-material mass ratio (B/M), and milling time on the extent of sulfidation were investigated under laboratory conditions. Under the optimal conditions, 73.2% of Pb in sludge can be converted to PbS within 1 h. The comparison of wet-milling sulfidation and contacting sulfidation was performed to test the efficiency of two sulfidation methods and the selective floatabilty of the synthetic sulfides. The results show that wet-milling efficiently improved the sulfidation extent as well as the floatation recovery. Compared with MeS(C) (sulfide formed by contacting sulfidation), MeS(M) (sulfide formed by milling sulfidation) had a smaller particle size, which was not beneficial for its floatability. However the improved sulfidation extent and dispersity can help to increase PbS(M) recovery.