Enhanced performance of copper ore oxygen carrier by red mud modification for chemical looping combustion

Copper ore has been considered as a promising low-cost oxygen carrier candidate for chemical looping combustion (CLC) due to its high reactivity, but pure Cu ore suffers from serious deactivation during long term redox cycling. The present work proposes to combine Cu ore with red mud, an abundant polluting waste of aluminum industry, to improve the reactivity and stability of Cu ore for CLC of methane. Characterizations, redox experiment and kinetic analysis are performed on the mixed oxygen carriers to study the relationship between the physiochemical properties and the redox activity. The results show that the addition of a suitable proportion of red mud (30 wt%) significantly improves the reactivity of Cu ore. Specifically, the average CH4 conversion increases from 67% to 86%, and the actual oxygen carrying capacity rises from 8.2% to 13.8%. In addition, the activation energy for the reduction of Cu ore oxygen carrier by methane decreases from 76.6 kJ/mol to 58.5 kJ/mol after modification. The synergy among CuO in copper ore, Fe2O3 and other components (e.g., Na+ Ca2+, SiO2 and Al2O3) in red mud play an important role in this enhancement. The interaction between CuO and Fe2O3 promotes the reducibility of oxygen carrier via forming a more active oxide (CuFe2O4), and the presence of foreign ions (Na+ and Ca2+) and inert oxides (Al2O3 and SiO2) contributes to the enhanced redox stability of oxygen carrier via acting as supports or additives.