Sulfidation of copper oxide with CaSO4 for copper flotation: Experimental study and first-principles calculation

Efficient recovery of valuable metals from copper smelting slag and the resource utilization of phosphogypsum are both urgently needed. To explore the feasibility of their synergistic recycling, this study used CuO and CaSO 4 as model materials to systematically investigate the sulfidation roasting process followed by flotation separation and to clarify the underlying reaction mechanism. Thermodynamic calculations coupled with TG-FTIR-MS analysis revealed a preferential reaction pathway leading to the formation of Cu 2 S and CaCO 3 while effectively suppressing the generation of pollutant gases such as SO 2 . The introduction of NaCl/KCl composite salt additives successfully promoted the growth of Cu 2 S grains, achieving an average particle size exceeding 25 μm under optimized conditions. Flotation tests confirmed the selective separation behavior of copper and calcium in the roasted products. Density functional theory (DFT) calculations indicated that amyl xanthate (PAX) preferentially chemisorbs on the Cu 2 S(100) surface through directional Cu–S coordination, whereas sodium silicate shows stronger interaction with CaCO 3 (104) and remains stable under hydrated conditions. These results provide theoretical support for the selective flotation separation of copper and calcium. This work establishes a theoretical and technical foundation for the co-treatment and green disposal of copper smelting slag and phosphogypsum.