A novel process to extract alumina and prepare Fe-Si alloys from coal fly ash

Utilization of coal fly ash (CFA) has attracted extensive attentions in the last decades because of the increasing awareness of environmental protection and waste recovery. In the present paper, a new treatment process for utilization of CFA by extracting alumina and preparing Fe-Si alloys was proposed. The main procedures of the process contain carbothermic reduction and magnetic separation. Both of the thermodynamic analysis and experimental results show that an addition of Fe2O3 can significantly cut down the reduction temperature and strongly enhance the decomposition of stable mullite phase (Al6Si2O13) in CFA. Scanning electron microscopy (SEM) analysis with energy dispersive spectroscopy (EDS) demonstrated that spherical Fe-Si alloys were formed adjacent to the alumina (obtained from the decomposition of mullite) during the carbothermic reduction. The alumina and Fe-Si alloys in the reduced sample can be effectively separated by the subsequent magnetic separation, and the mass fraction of alumina in the non-magnetic part reached 91.33%. Compared with the conventional sinter process and acid leaching process, carbothermic reduction method with addition of Fe2O3 for extracting aluminum makes fewer residues, which may provide a new idea for large-scale utilization of CFA.