Abstract:
Four representative types of classF coal fly ash (CFA) including low calcium contained ash (FCFA), high calcium contained ash (CCFA), high alumina contained ash (ACFA) and high loss on ignition ash (LCFA) were selected to investigate chemical compositions, phase components and chemical reactivity, causes of alumina extraction varieties and a novel method for elevating alumina extraction from CFA using the measurements such as XRF, XRD and hydrochloride acid extraction. The results showed that mullite and quartz were major minerals in FCFA, quartz and lime in CCFA, mullite in ACFA and amorphous phases in LCFA. The alumina content in CCFA and LCFA mainly presented in the amorphous phase and 47.62% and 79.13% of Al2O3 could be directly extracted using hydrochloride acid. The Al2O3 extraction from CCFA and LCFA sintered at 900 ℃ for 1 h increased largely due to the formation of anorthite. Anorthite was formed in FCFA and ACFA sintered at 900 ℃ for 1 h after the addition of calcium additive and the Al2O3 extraction increased to 85.31% and 70.22% correspondingly.