Preparation of Al-Si composite from high-alumina coal fly ash by mechanical-chemical synergistic activation

High-alumina coal fly ash (HAFA) is a special solid waste because it contains more than 45% alumina and 35% silica. This material can be applied to prepare Al-Si series ceramics if the impurities can be removed and the Al/Si mass ratio can be elevated to a high level. In this work, a new mechanical-chemical synergistic activation-desilication process is proposed and optimized. During the synergistic activation, the morphology, ironic leaching ratios, efficient desilicated ratio (EDR), and mineral phases of different treatments are investigated. The reactivity of amorphous silica can be elevated to a high level (EDR>11%). After the desilication process, the contents of different impurities can be lowered up to less than 1%, and the Al/Si mass ratio can be elevated from 1.26 to 2.71. Mullite refractories are prepared from desilicated HAFA by forming and sintering process, and the bulk density and apparent porosity can reach to 2.85 g/cm3 and 2.07%, respectively.