Calcification-Carbonation Method for Cleaner Alumina Production and CO2 Utilization

In this study, a calcification-carbonation method is proposed to change the equilibrium structure of red mud produced from the Bayer process. The thermodynamics of both calcification and carbonation processes has been elucidated. In addition, the non-isothermal kinetics involved in the calcification process and the effects of different parameters on the hydrogarnet synthesis and carbonation decomposition are experimentally investigated using pure reagents. The results indicate that through a two-step carbonation treatment of calcified slag by the new method, the mass ratio of alumina to silica (A/S) of the modified red mud has decreased to 0.44 and the Na2O content drops to 0.12 wt.% at the carbonation temperature of 120A degrees C under the CO2 pressure of 1.2 MPa. The newly modified red mud could be directly used in the cement industry.