Preparation of ultrafine α-Al2O3 powder from fly ash by ammonium sulfate roasting technology

(NH4)2SO4 roasting technology was used for extracting alumina from fly ash which located in Shandong Zibo power plant. The roasting temperature, the mole ratio of Al2O3 to (NH4)2SO4 and roasting time on the effect of the extraction rate of alumina was studied. The optimal roasting technology condition is 380°C for 120min with mole ratio of Al2O3 to (NH4)2SO4 of 1:6. Under the optimal roasting condition, the extraction rate of Al2O3 can reached 82% and a new phase NH4Al(SO4)2 was formed in clinker. NH4Al(SO4)2 in clinker was dissolved by distilled water and then separated from silicon-rich residue by filtration. Iron in NH4Al(SO4)2 solution was removed by goethite process, and then, NH4Al(OH)2CO3 was synthesized by adding (NH4)2CO3 in NH4Al(SO4)2 solution. Ultrafine α-Al2O3 powder was prepared by calcining NH4Al(OH)2CO3 in 1200°C for 120min, which was characterized by XRD and SEM.