Synthesis of Ferroalloys via Mill Scale-Dross-Graphite Interaction: Implication for Industrial Wastes Upcycling

Abstract

Mill scale and aluminum dross are the industrial wastes from steel and aluminum industries, which have high concentrations of Fe2O3 and Al2O3, respectively. This paper reports the conversion of reducible metal oxides in scale and dross into an alloy via carbothermic reduction at 1550 °C. Scale and dross were mixed with graphite into three different C/O molar ratios of 1, 1.5, and 2 to produce a pellet. The pellets were heated at 1550 °C for up to 6 h under an argon atmosphere. By this method, carbothermic reductions were found to proceed and formed Fe–Si–Al–C alloy that consists of Fe3Al and Fe3Si phases. The presence of Si in the alloy came from the reduction of SiO2 in aluminum dross. Levels of Al and Si in the alloy increase with increasing C/O molar ratios. However, the Si level in the alloy was found to stabilize since 3 h, while the Al level increases with increasing time up to 6 h. Unreacted oxides in the wastes had an insignificant effect on the ferroalloy formation. These results provide evidence for carbothermic reduction of the Fe2O3-Al2O3-SiO2 system at 1550 °C and show the novel method to upcycling aluminum dross and mill scale toward a circular economy.