Carbothermic Smelting Reduction of Copper Slag for Fe and Cu Recovery Using Calcium Aluminate Refining Slag as the Modifier

CaO-Al₂O₃-based refining slag, as a low-cost and low-carbon alternative to lime, has been used as a modifier in the smelting reduction of copper slag. The influence of refining slag/copper slag mass ratio (RS/CS) on the reduction behavior, metal recovery, and slag–refractory interaction was studied through experimental and thermodynamic methods. The refining slag was well dissolved in copper slag during the reduction process at 1550°C, ensuring the slag's basicity and helping to depolymerize the silicate slag after FeO reduction. Only a few iron oxides were detected in the slag residue regardless of the RS/CS ratio, and, meanwhile, both the iron and copper recovery was over 97.5%. However, this achievement was made on the significant dissolution of MgO from the crucible when the RS/CS ratio was below 0.45. The MgO dissolution was dramatically suppressed at higher RS/CS ratios (> 0.45), contributing to the refractory protection. Moreover, the toxic elements in the slag have been substantially removed as vapors after smelting reduction, which ensures the cleanliness and safety of the slag.