Ammonium aluminum sulfate hydroxide［NH4Al(SO4)2·12H2O］

the precursor of Al2O3

was prepared with the method of sintering

leaching and adjusting the pH value by using fly ash and ammonium sulfate as raw materials.High-purity alumina was prepared by calcining NH4Al(SO4)2·12H2O.The effects of the temperature and time of sintering

molar ratio of(NH4)2SO4 vs the Al2O3 in fly ash and the grain size of fly ash on the extraction efficiency of Al2O3 from fly ash were studied.The efficiency of Al2O3 extraction could reach 95.6 percent under the optimum conditions.The purity of the Al2O3 from calcining NH4Al(SO4)2·12H2O that was refined by recrystallization was higher than 99.9 percent.