Dealkalization of Red Mud Generated in Alumina Production by Sub-molten Salt Process under Atmospheric Pressure

The dealkalization of red mud from sub-molten salt process under atmospheric pressure and low temperature was investigated. The effects of temperature, CaO addition, Na2O concentration of solution and time on the process were examined. The experimental results indicated that the content of Na2O in the final red mud decreased with the increase of CaO addition, reaction temperature and reaction time, but not so as to the initial concentration of Na2O in the NaOH solution, and it could be as low as 1.41% while mass ratio of Na2O to SiO2 was decreased to 0.07 when dealkalizing in 60 g/L Na2O solution with mass ratio of CaO to red mud 0.22 at 95℃ for 10 h. After leaching under the above conditions, the new phase of calcium silicate formed, and the morphology of the red mud changed from rod-like crystals to fluffy agglomerate with flakes.