Abstract: The dealkalization process of the Bayer leaching slag of high alumina fly ash was studied. The influences of ［n(C)/n(S)］(the molar ratio of CaO to SiO₂)， reaction temperature， reaction time， liquid-solid ratio and alkaline concentration on dealkalization rate， and the effect of dealkalization process on the alumina leaching efficiency were investigated. The results indicated that the lime-adding method can realize the removal of sodium oxide from the Bayer leaching slag of high alumina fly ash and recover part of alumina. The recovery of sodium oxide and alumina is significantly affected by reaction temperature， but［n(C)/n(S)］ only affects the dissolution of sodium oxide. The alkali removal ratio and alumina recovery ratio are 91.2% and 28.0% respectively under the conditions of 260℃， NaO concentration less than 80g/L， liquid-solid ratio 4， ［n(C)/n(S)］ 1.8 and reaction time 2h. The phase of Bayer leaching slag transforms from sodium aluminosilicate hydrate to hydrogarnet in the dealkalization process.

Key words: high alumina fly ash, Bayer leaching slag, alkali recovery, alumina recovery, solid phase transformation