Effects of vacuum conditions on activation of high-alumina fly ash roasted using conventional and microwave heating

In this study, Na₂CO₃ was used as activator to roast and activate high-alumina fly ash (HAFA), and the vacuum roasting technology was used to enhance the activation process of HAFA. The effects of the vacuum conditions on the activation of HAFA roasted using conventional and microwave heating were investigated. It was determined that the reaction time was shortened and the activation effect of HAFA was improved under vacuum conditions; however, the effect of the vacuum conditions on the roasting temperature was negligible. The activation process of HAFA-Na₂CO₃ mixtures (HAFA/Na₂CO₃ mass ratio of 1:1) was promoted by conducting conventional and microwave heating experiments under vacuum (-0.04 MPa). The leaching rate of aluminium of 93.00% was reached at the roasting temperature of 900 °C after only 20 min when the HAFA-Na₂CO₃ mixture was subjected to conventional heating under vacuum, and after 60 min when conventional heating occurred under normal atmospheric pressure. Moreover, the leaching rate of aluminium of 96.00% was reached at the roasting temperature of 700 °C after only 20 min when the HAFA-Na₂CO₃ mixture underwent microwave heating under vacuum, and after 30 min when microwave heating occurred under normal atmospheric pressure.