In-situ synergistic sulfidation and enrichment of Cu-Pb-Zn from molten copper slag using hazardous gypsum residue

Copper slag cleaning has always been critical for ensuring an efficient copper recovery in copper smelting system. However, current cleaning methods focus on copper enrichment, regardless of zinc and lead recovery. In order to address the severe resource wastage of lead‑zinc values in copper smelting slag, this study proposed an innovative copper slag cleaning technique for efficient and in-situ synergistic sulfidation recovery of Cu, Pb and Zn, and investigated the sulfidation mechanisms. A systematic characterization of copper slag was conducted and revealed that Zn 2 SiO 4 and PbSiO 3 are two of the main occurrence phases lost in slag, respectively, and they are the most difficult phases to recovery. Furthermore, thermodynamic, thermogravimetric analysis and experimental results regarding Zn 2 SiO 4 and PbSiO 3 in-situ synergistic sulfidation by CaSO 4 gypsum residue revealed that PbSiO 3 sulfidation mechanism progressed via CaSO 4  → CaS conversion, followed by diffusion of molten PbSiO 3 to CaS particle surfaces where Pb S bonding produced PbS shells. At the same time, Zn 2 SiO 4 involves calcium-promoted decomposition into ZnO and SiO 2 , and subsequent ZnO-CaS interfacial reaction producing ZnS and CaO. In addition, pilot experiments were conducted to detect the feasibility and stability of the proposed technique. Optimal conditions (12.02% sulfurizing agent dosage, 1 °C/min slow cooling) were determined and achieved comprehensive sulfidation rates of 88.55% Cu, 66.26% Pb, and 59.24% Zn, with effective enrichment as matte. Lead‑zinc sulfides attained flotation-required particle sizes (>40 μm) while residual phases showed minimal metal contents. This study addresses the challenge of lead‑zinc resource wastage in copper slag, introducing a novel approach and methodology for its resource utilization.