Neutralization of Red Mud Using CO2 Sequestration and their Utilizations

Abstract

Red mud is a highly caustic waste product of alumina industry. More than 70 million tons of red mud has been generated worldwide per annum. It pollutes the industry area due to its alkaline nature. Its storage and maintenance is costly and causes great problem to the industries. Moreover, CO2 is a global warming gas generated from fossil fuel power plant. Each 500 MW coal power plant emits about 3 million tons of CO2 per year which may cause serious disruption to the global climate change. A laboratory study was conducted to investigate the ability of neutralization of red mud (RM) using carbon dioxide gas sequestration cycle at ambient conditions.The neutralized red mud (NRM) was characterized by XRD, SEM, EDX, FT-IR, CHNS, TG-DSC and auto titration method. X-ray diffraction pattern of NRM was revealed that the intensity of gibbsite was increased prominently and formed ilmenite due to dissolution of minerals. EDX analysis was showed that the %(w/w) of Na, C, O, Si were higher in the carbonated filtrate as compared to the RM and NRM.The permanently sequestered CO2 %(w/w) per 10 g of red mud were ~26.33, ~58.01, ~55.37, and ~54.42 in NRM and first, second, third cycles of carbonated filtrate, respectively. Amount of CO2 removed for cycle 1, 2, 3 of carbonated filtrate and NRM were 3.54, 2.28, 0.63, 0.57 g CO2/100 g of red mud, respectively, as determined by CHNS analyzer at 1150°C. So, total calculated CO2 removal was 7.02 g/100 g of red mud. The pH of red mud was decreased from ~11.8 to ~8.45 and alkalinity was decreased from ~10,789 to ~178 mg/L. The acid neutralizing capacity of NRM was ~0.23 mol H+/kg of red mud. The specific advantages of these cyclic processes are that, large amount of CO2 can be captured as compared to single step. Subsequently, this study has shown the effective neutralization of red mud.