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Removal of alkali in the red mud by SO2 and simulated flue gas under mild conditions



In the present work, SO2 and SO2-based dealkalization agents (SO2+N2 and SO2+CO2+N2), which were the simulated flue gases, were used to remove the alkali in red mud (RM) for wide applications of RM. Effects of reaction time, temperature, solid to liquid ratio, and SO2 concentration on dealkalization of RM were studied. Under the optimized conditions, the residue Na2O in RM after dealkalization could decrease to below 1 wt % no matter which simulated flue gas is used. But, as SO2+CO2 +N2 is used to remove Na2O in RM, longer time is needed due to the decreased SO2 concentration in the simulated flue gas. X-ray diffraction (XRD), scanning electron microscope (SEM), and zeta potential were used to ascertain the change of RM before and after dealkalization. The results indicated that the structure of hydroxysodalite (Na8Al6Si6O24(OH)2) in the initial RM were destroyed and soluble sodium salts formed in the suspension which can be easily neutralized by acidic gas and then contributed to the decrease of Na2O in RM. The residue components in RM after dealkalization by SO2, and SO2-based dealkalization agents are mostly SiO2, Fe2O3, and AlOOH. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 81–87, 2015