Abstract:The digestion kinetics of sintered clinker to extract alumina from fly ash with ammonium hydrogen sulfate roasting process was investigated. The effects of temperature, stirring intensity and mass ratio of liquid to solid (L/S) on aluminum dissolution rate were studied. The results show that digestion process is controlled by external diffusion. The digestion process includes the first stage for 0~20 min, and the second stage for following 20~60 min. The activation energies of the two stages are 8.013 kJ/mol and 4.973 kJ/mol respectively. The aluminum dissolution rate reaches 93% under the optimal conditions including temperature of 90 ℃, stirring intensity of 300 r/min, L/S of 9∶1 and duration of 60 min.