Extractlng alumina from coal fly ash using acid sintering-leaching process

Abstract

Local shortages of bauxite in recent years present a challenge to the development of sustainable aluminum industry in China. Coal fly-ash from coal-fired power plants is rich in Al2O3 content with potential use as a resource for alumina refinery. This paper will describe recent investigation in extracting Al2O3 from coal fly-ash using an acid sintering-leaching process. Thermal weight loss testing against temperature is first carried out to find out an appropriate sintering temperature so as to avoid heavy volatilization of the coal fly ash - H2SO4 (98 %) mixture. Then, the mixture is subjected to sintering at 220 °C, dissolving in water at 85 °C, adjusting alkali level in solution by CaCO3, removing iron by KMnO4 and MnSO4, precipitating Al2(SO4)3 · 17H2O particles, and heating-treated at 850 °C to produce Al2O3 powders. The rate of recycling Al2O3 can reach 70 - 90 % with relative lower processing temperature and less solid residues.