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 degrees 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.