Effects and Mechanism Research of the Desilication Pretreatment for High-Aluminum Fly Ash

The chemical composition and morphology properties of high-aluminum fly ash were studied by means of XRF, XRD, SEM, and EDS. It was found that silicon in high-aluminum fly ash mainly existed as mullite and amorphous SiO2 with hardly any quartz, and both the surface of fly ash particles and the smaller fly ash particles attached on the larger ones were enriched in silica. The desilication process was used to remove the amorphous SiO2 from high-aluminum fly ash. The desilication process was carried out using a low concentration of sodium hydroxide at a relatively low temperature. In order to improve the desilication efficiency, pretreatment was added before the desilication reaction. After comparing results of pretreatment reactions under different temperatures, the sample treated at 65 °C was analyzed in detail because its desilication effect was the best. After additional pretreatment using the desilication process, the ratio of Al/Si in desilication fly ash was increased from 1.92 to 2.51. The silica con...