Red Mud Neutralisation by CO2 Promotes Alkali Recovery and Higher Scandium Extraction

Abstract

To ensure the complete utilization of red mud and parallel reduction in carbon footprints from alumina production, it is very important to tackle the alkalinity in red mud which poses problems in the processing of bauxite residue. Despite various methods, this article stresses the use of CO2 neutralization which has been employed to address alkalinity (2176 ppm) and simultaneously recovers the alkali under atmospheric pressure, which assisted in improved scandium extraction. Under conditions of particle size < 50 mu m, 20% pulp density, 3-4 atm pressure, room temperature, in 30 min brought down the pH from 9.99 to 6.26, with 36-37% alkali recovery and capturing 28.8 g CO2/kg red mud. The neutralized red mud serves as an excellent feed for acid leaching to extract Ti and REEs. With 2 M sulfuric acid at 10% pulp density and 90 degrees C, 96% La, 95% Ce, and similar to 90% Sc were recovered in 2 h. The residue after the second stage operation was rich in Fe, Al and Si and thus can be processed by a hybrid pyro-hydro-metallurgical process, for achieving complete valorization of red mud while recovering critical metals.