NH4HSO4 roasting technology was used for preparing Al2O3 from fly ash. First, Al and Fe were extracted from fly ash by NH4HSO4 roasting and deionized water leaching. Then, the Al and Fe in the leached liquid were precipitated by adding NH4HCO3 solution. After the mixed precipitations of Al（OH）3 and Fe（OH）3 were leached by NaOH solution, the NaAl（OH）4 solution was decomposed by carbonation. Finally, the pure Al（OH）3 was calcined to α-Al2O3. The optimal conditions of the whole technology were determined by experiments. The quality ofa-Al2O3 product is up to the technical indicator of YS/T 274-1998 standard.
Kinetics of SiO2 leaching from Al2O3 extracted slag of fly ash with sodium hydroxide solution was studied.The effect of leaching temperature,mass ratio of NaOH to SiO2 and stirring speed on SiO2 leaching rate was investigated.The results show that increasing leaching temperature,mass ratio of NaOH to SiO2 and stirring speed increases SiO2 leaching rate.The SiO2 leaching rate is 95.66%under the optimized conditions.There are two stages for the SiO2 leaching process,and the leaching reaction is very rapid in the first stage but quite slow in the second stage.The whole leaching process follows the shrinking core model,and the outer diffusion of no product layer is the rate-controlling step.The activation energies of the first and second stages are calculated to be8.492 kJ/mol and 8.668 kJ/mol,respectively.The kinetic equations of the first and the second stages were obtained,respectively.
