An innovative route for valorising iron and aluminium oxide rich industrial wastes: Recovery of multiple metals

Several industrial wastes including biomass, fly ashes, red mud, mill scales, water treatment residues, have significant concentrations of metal oxides: Fe₂O₃, Al₂O₃, TiO₂, SiO₂ etc. Several efforts have been made towards recovering metals within these wastes. Rather than recovering one metal at a time, we report a novel approach for simultaneously extracting multiple metals from mixed oxides in a single process step. Using three distinct furnaces/heating regimes, the carbothermic reduction of Fe₂O₃/Al₂O₃/SiO₂ system was investigated at 1450–1700 °C for up to 2 h over a wide composition range. Complete reduction was achieved for both Fe₂O₃ and SiO₂ in all cases leading to the formation of Fe and Fe–Si alloys. The reduction of alumina at moderate temperatures was the key challenge. No alumina reduction was observed during reductions at 1450 °C. A partial reduction of alumina and the formation of Fe–Al alloys was detected in the Al₂O₃/Fe₂O₃/C system at 1550 °C. The formation of Fe–Si–Al alloys was also observed in the Fe₂O₃/SiO₂/Al₂O₃/C system at 1550 °C. Complete reduction of alumina was observed at 1600–1700 °C, even for up to 50 wt% alumina in the system. Optimal operating conditions and reference standards were established for the simultaneous recovery of multiple metals from waste oxides. While conserving natural resources, this novel route will lower the burden on waste storage facilities with significant contributions to the economic and environmental sustainability of industrial waste management.