Kinetic and Thermodynamic Analysis of the Reduction of Oxides of Cu and Co in a SiO2-CaO-(Al,Fe)2O3 Slag

The investigation focuses on a low temperature recovery of Cu and Co from a 40 wt% SiO₂-(30 wt%Fe,6 wt%Al)₂O₃-10wt% CaO-7wt%CuO-7wt%CoO slag over a temperature range of 1173K to 1323K. The alloy phases containing Cu-Co and Fe-Co alloy formed via the carbothermic reduction of oxides: MO + C = M + CO(g), where M represents metallic copper, cobalt or iron. In the direct reduction of oxides, the recovery of metallic phase was well below 90% at 1323K, due to the kinetic barrier which was analysed and attributed to oxygen and metal-ion transport in the slag. This barrier was overcome by adding CaSO₄ and carbon, which yields a matte (MS) phase via MO + CaSO₄ + 4C = MS + CaO + 4CO reaction. Lime thus produced in situ participates in metal oxide/metal sulphide reduction reactions, which are analysed with the help of X-ray powder diffraction, scanning electron microscopy, and thermogravimetric analysis.