Process for desilication of aluminate liquors in the production of alumina

摘要

The process consists of two desilication stages. In the first stage the aluminate liquor resulting from digestion of the sinter is subjected to an autoclave treatment to remove the major portion of impurities of SiO2 and Fe2O3. In the second stage the aluminate liquor is treated with a desilication agent comprising a lime pulp containing oxides CaO, Al2O3, SiO2, Fe2O3, Na2O in a mass ratio of CaO:(SiO2+Fe2O3)=1,000 to 5,000:1 and Na2Al2O3=0.25-0.60:1, wherein CaO is active, Na2O-in the carbonate form. This lime pulp is employed in such an amount as to ensure the content of active CaO in the aluminate liquor within the range of from 5 to 10 g/l . The impurities of SiO2 and Fe2O3 present in the liquor pass into the solid phase with the formation of calcium hydrogarnets of the formula 3 CaO(Al,Fe)2O3 mSiO2(6-2m)H2O, wherein m=0.01-0.5 which are separated as a mud.