Bauxite waste with low Fe2O3 and high Na concentration as a promising oxygen carrier in chemical looping combustion

Development of a cost-effective oxygen carrier (OC) for chemical looping combustion (CLC) technology remains an important task to be accomplished. Bauxite waste red mud from the United States has shown promise as an OC, but bauxite waste from China has not been evaluated extensively although huge quantities of it exists. In comparison, the Chinese bauxite waste usually contains low Fe₂O₃ and high Na concentration. Hence, the purpose of this study was to evaluate a typical red mud (from Zibo, China) with low Fe₂O₃/Na mass ratio for its potential as a cost-effective OC during CLC processing. Parametric reactor testing was accomplished with a focus on OC reactivity during CLC, and evaluations were accomplished of morphologies, elemental concentrations, and mechanical strengths before and after reaction testing; special attention was paid to the stability of Na. These results showed that Zibo red mud (a) used as an OC during CLC had satisfactory reactivity particularly after pre-calcination at 1250°C, (b) had high contents of Na that were stable and uniformly distributed during reaction testing and formed NaAlSiO₄ during sample calcination and reaction testing, and (c) showed high mechanical strengths that were similar to those of other oxygen carriers. Considering that huge amounts of this inexpensive Zibo red mud are located within areas near aluminum processing plants, it may become a promising material as an OC for CLC processing.