Boosting chemical looping combustion performances of red mud with transition metal oxides

Abstract

Red mud (RM) is industrial solid waste that severely threatens environmental safety, and its resource utilization is significant both economically and ecologically. The presence of ferric oxides (Fe2O3) makes RM potential oxygen carriers (OC) for chemical looping combustion (CLC), which is a promising, novel and low-carbon combustion technology. This work examined the CLC performance of two kinds of RM using gaseous and solid fuels. Both Fe2O3 and alkali and alkaline-earth metals (AAEM) species within RM enhance carbon conversion during CLC. Nevertheless, the reactivity of original RM is unsatisfactory due to its low oxygen transporting capacity (R0, lower than 0.1), carbon conversion (XC, less than 0.8), CO2 selectivity (YCO2, less than 0.9) and instable performance. Transition metal oxides including CuO and NiO were used to modify the RM through wet impregnation. Both oxides notably improve RM performances, i.e., XC and YCO2 are notably increased. Still, deteriorations during redox cycles are observed because of particle agglomeration and sintering, especially for the RM modified with NiO. Considering the cost, potential environmental risk and efficacy, CuO is superior to NiO thanks to the enhanced performances of the modified RM-based OC including higher XC (about 0.9), YCO2(approximately 1) and stronger sintering resistance.