Fe-Si alloys production and alumina extraction from coal fly ash via the vacuum thermal reduction and alkaline leaching

Abstract

The comprehensive utilization of coal fly ash (CFA) has attracted extensive attentions owing to increasing awareness of environmental protection and secondary resource recycling. In this paper, a vacuum thermal reduction followed by magnetic separation and alkaline leaching was employed to produce FeSi alloys and extract alumina from CFA. The effects of Fe/Si ratios on the reduction of silica-containing phases in CFA and the magnetic separation of FeSi alloys were investigated. The results show that the reduction of metakaolinite and quartz in CFA was strengthened by increasing the Fe/Si ratios from 1.0 to 2.0, which makes the mean particle size of FeSi alloys increased from 14.11 μm to 20.54 μm. The magnetic separation efficiency of FeSi alloys was mainly depended on the Fe/Si ratios. As the Fe/Si ratios increased from 1.0 to 1.4, the magnetic separation efficiency increased from 79.68% to 89.03%; however, it decreased to 82.90% as the Fe/Si ratios further increased to 2.0. Meanwhile, the alumina extraction from non-magnetic fraction using the alkaline leaching was also studied. It is proved that the leaching rate of alumina can reach 96.95% under the optimal conditions. Compared with the traditional routes, the proposed process shows a good prospect for environmentally friendly utilization of CFA.