Effect of Na₂CO₃ Roasting Activation on Acid Leaching Property of Fly Ash

By using high-alumina fly ash as raw material, a process was proposed for activating the fly ash with Na₂CO₃ calcination and extracting aluminum from activated clinker with sulfuric acid leaching. The feasibility of roasting process of activated fly ash by Na₂CO₃ was discussed based on thermodynamic analysis. The experimental results showed that Na₂CO₃ gradually reactes with mullite over 700 K to produce NaAlSiO₄. The optimal process conditions for the activation stage are: a material ratio of 1:1 between sodium carbonate and fly ash, a calcination temperature of 900 °C, and a calcination time of 2.5 hours. Under these conditions, the leaching rate of aluminum is 90.3%. By comparing the SEM and XRD analysis of raw and clinker materials, it could be concluded that the mullite phase of fly ash is almost completely destroyed and transformed into sodium aluminosilicate with good acid solubility.