Abstract: A process for recovery of silica and alumina from fly ash, in which, Si is leached out from the fly ash in the form of Na2SiO3 using a NaOH solution of NaOH >40% (w/w), followed by separation to obtain a Na2SiO3 solution and a residue having Al—Si ratio ?2; vaporizing the solution to obtain Na2SiO3 solutions of various concentrations, or producing silica by carbonation, and producing Al2O3 by prior art methods from residues obtained after alkali-leaching, ultimately producing filler or cement from the residue after the recovery of Al. The method permits recovery of Al2O3 directly from fly ash by removing Si before recovering the Al, which raises the Al—Si ratio of the residue after alkali-leaching and thus simplifies the recovery of Al2O3 and raises the rate of Al recovery from fly ash. The invention further includes calcining high Al coal gangue, kaolinite and middle-low-class bauxite at 900-1100° C.

Abstract: A process for recovery of silica and alumina from fly ash, in which, Si is leached out from the fly ash in the form of Na2SiO3 using a NaOH solution of NaOH >40% (w/w), followed by separation to obtain a Na2SiO3 solution and a residue having Al—Si ratio ?2; vaporizing the solution to obtain Na2SiO3 solutions of various concentrations, or producing silica by carbonation, and producing Al2O3 by prior art methods from residues obtained after alkali-leaching, ultimately producing filler or cement from the residue after the recovery of Al. The method permits recovery of Al2O3 directly from fly ash by removing Si before recovering the Al, which raises the Al—Si ratio of the residue after alkali-leaching and thus simplifies the recovery of Al2O3 and raises the rate of Al recovery from fly ash. The invention further includes calcining high Al coal gangue, kaolinite and middle-low-class bauxite at 900-1100° C.