LAUSR

Abstract A hydrometallurgical calcification‑carbonation method is proposed to change the structure of the red mud of Bayer alumina production for clean utilization of low-grade bauxite resources. The utilization process consists of the flowing steps: i) silicon containing phases in bauxite are transformed into hydrogarnet; ii) hydrogarnet subsequently changed into Al(OH)3, CaO·SiO2 and CaCO3 through the carbonation process by CO2; and iii) Al(OH)3 is digested by alkali when the digestion temperature is below 100 °C. The thermodynamics of the calcification and carbonation processes were elucidated, and the effects of the saturation coefficient of SiO2 in hydrogarnet on the new process were investigated. The results show that the silicon saturation coefficient rapidly increases with temperature. The digestion ratio of alumina from hydrogarnet exceeds 50% when the saturation coefficient is either higher than 0.79 or