Alkali desilicated coal fly ash as substitute of bauxite in lime-soda sintering process for aluminum production

By desilication treatment, the Al2O3/SiO2 molar ratio of coal fly ash could be improved to the range of 1.63–2.0. The desilicated coal fly ash (DSCFA) was enriched in alumina extraction. A processing technology was developed for alumina extraction from the DSCFA with the lime sintering process. Ca/(SiO2+TiO2) molar ratio, and NaO/Al2O3 molar ratio, sintering time, and temperature were the most significant parameters impacting on the aluminum extraction efficiency. The optima aluminum extraction efficiency was obtained under conditions of Ca/(SiO2+TiO2) molar ratio of 2.0, NaO/Al2O3 molar ratio of 0.98, and sintering at 1 200 °C for 60 min. A standard industrial dissolution method was used under conditions of caustic ratio (αk=n(NaO)/n(Al2O3) of 2.0, Al2O3 concentration of 50 g/L, sodium hydroxide concentration(Nk) of 60.78 g/L, Na2CO3 concentration of 10 g/L, temperature of 85 °C, and dissolution duration of 10 min. The final aluminum extraction efficiency was 90%.