Novel process of alumina extraction from coal fly ash by pre-desilicating-Na2CO3 activation-Acid leaching technique

Alumina extraction from coal fly ash (CFA) by Na2CO3 activation-acid leaching method could make Al2O3 and SiO2 in CFA achieve high value utilization simultaneously, which shows wide application prospects. The large consumption of Na2CO3, however, limits its industrial application. A novel process of alumina extraction from coal fly ash by “Pre-desilicating-Na2CO3 activation-acid leaching” has been proposed in this work. By this process, the consumption of Na2CO3 decreased significantly thanks to the adjustment of Al/Si molar ratio in the raw materials. The effects of pre-desilication conditions on the dissolution of SiO2 in coal fly ash, the effect of the novel process on the consumption of Na2CO3 and the phase transformations and the alumina dissolutions at various consumption of Na2CO3 were investigated. The results showed that the dissolution of SiO2 reached 37.3% at 20% (by weight) of NaOH concentration, 1 mL/g of liquid to solid ratio, 100 °C and 2.0 h, when the Al/Si molar ratio in coal fly ash could be raised to 1.21 from 0.81. The mixed coal fly ash with an Al/Si molar ratio of 1 could be obtained by mixing desilicated and the as-received coal fly ash. The dissolution of Al2O3 of the mixed coal fly ash reached ~ 87% at the Na/Al molar ratio of 1. The consumption of Na2CO3 decreased obviously and the reduction percentage reached 53.1% at Na/Al molar ratio of 1.0 after undergoing the pre-desilication process compared with the Na2CO3 direct activation process. This work could provide a novel thought for the utilization of coal fly ash with high value and high efficiency.