The influence of the silicon saturation coefficient on a calcification-carbonation method for clean and efficient use of bauxite

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 center dot 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 degrees 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 < 0.3. After a low-grade bauxite treatment, the alkali content in the new red mud decreases to 0.49 wt% and the A/S (ratio of alumina and silicon) decreases to below 0.5%. Furthermore, the recovery ratio of alumina increases by 15% compared to the traditional Bayer process. The new modified red mud can be used directly in the cement industry, and efficient and clean use of low-grade bauxite can be realized by this method.