ALUMINA PRODUCTION PROCESS Russian patent published in 2004 - IPC

FIELD: nonferrous metallurgy. SUBSTANCE: alumina production according to Beyer process comprises grinding bauxite, leaching it in presence of calcium-containing additives, separating aluminate solution from insoluble precipitate, decomposing aluminate solution to give aluminum hydroxide and mother liquor, which mother liquor is evaporated in two steps: first to concentration of caustic alkali (Na₂O_k) 180-220 g/l and then to concentration of Na₂O_k 250-300 g/l. Liquor after the first evaporation step is leached and that after the second evaporation step is mixed with mother liquor. According to invention, mother liquor, prior to be evaporated, is completed by calcium-containing additives in amounts 1 to 20 g/l in the form of calcium oxide, hydroxide, or carbonate. EFFECT: enhanced process efficiency. 4 cl