Recovery of Iron from Copper Slag Using Coal-Based Direct Reduction: Reduction Characteristics and Kinetics

The Fe3O4 and Fe2SiO4 in copper slag were successfully reduced to metallic iron by coal-based direct reduction. Under the best reduction conditions of 1300 °C reduction temperature, 30 min reduction time, 35 wt.% coal dosage, and 20 wt.% CaO dosage (0.75 binary basicity), the Fe grade of obtained iron concentration achieved 91.55%, and the Fe recovery was 98.13%. The kinetic studies on reduction indicated that the reduction of copper slag was controlled by the interfacial reaction and carbon gasification at 1050 °C. When at a higher reduction temperature, the copper slag reduction was controlled by the diffusion of the gas. The integral kinetics model research illustrated that the reaction activation energy increased as the reduction of copper slag proceeded. The early reduction of Fe3O4 needed a low reaction activation energy. The subsequent reduction of Fe2SiO4 needed higher reaction activation energy compared with that of Fe3O4 reduction.