The alumina enrichment and Fe-Si alloy recovery from coal fly ash with the assistance of Na2CO3

A clean process for the enrichment of alumina and preparation of Fe-Si alloy from coal fly ash (CFA) with the assistance of Na2CO3 was proposed in the present work. This process mainly consists of two stages, e.g., vacuum carbothermal reduction and magnetic separation. The effects of Na2CO3 addition, reduction temperature and reduction duration on the decomposition of mullite (Al6Si2O13) in CFA and the growth of Fe-Si alloy particles were investigated thoroughly. Moreover, the effect of Na2CO3 on the magnetic separation of Fe-Si alloys was also discussed. The results show that the addition of Na2CO3 under vacuum condition could effectively accelerate the decomposition of mullite and enhance the formation of Fe-Si alloys. The mean particle size of the Fe-Si alloy increased from 23.94 μm to 42.74 μm by adding 10 wt% Na2CO3, and the separation efficiency reached 88.95% with the assistance of the Na2CO3. After magnetic separation, the alumina content, silica content, and the mass ratio of alumina/silica in the non-magnetic part of the separation product was 80.36 wt%, 6.49 wt%, and 12.38, respectively, indicating that a highly efficient recovery of alumina was achieved. This process will not pollute the environment and there almost no waste residue or waste acid is generated. Therefore, this provides a good potential for the industry application and delivers favourable conditions for commercial viability.