Synergistic N/S/Cl Elimination from Waste Aluminum Can Coatings via Red Mud Oxygen Carriers during Chemical Looping Combustion: A Waste-Treat-Waste Concept

Waste aluminum can recycling is essential for achieving circular economy and carbon neutrality goals, yet organic coatings on aluminum cans release nitrogen-, sulfur-, and chlorine-containing pollutants during conventional thermal decoating processes. Meanwhile, red mud, a massive industrial waste generated from the alumina industry, suffers from extremely low utilization rates. Herein, we propose a red mud-mediated chemical looping combustion (CLC) strategy that integrates aluminum can decoating, pollutant abatement, and red mud valorization into a single process. Three red mud samples were directly employed as low-cost oxygen carriers (OCs) to investigate their performance in coating degradation and N/S/Cl pollutant removal. Among them, Na/Ca-rich W900-RM (Wenshan red mud) exhibited the best performance, achieving approximately 98% sulfur fixation, 98.7% chlorine fixation, and 92.1% nitrogen removal at 900 °C with an oxygen carrier-to-feed mass ratio of 4. The system maintained over 90% carbon conversion and 86% CO2 selectivity during 20 redox cycles, demonstrating excellent cyclic stability and application potential. Mechanistic analysis revealed that Fe species promote oxidation reactions during chemical looping combustion, while Na and Ca species play critical roles in immobilizing sulfur- and chlorine-containing pollutants through the formation of stable sulfates and chlorides. The gradual decrease in alkalinity during cycling confirms the continuous participation of alkali/alkaline earth metals in pollutant fixation. This work establishes a waste-treat-waste chemical looping pathway for eco-friendly aluminum can recycling and red mud valorization, providing a promising strategy for sustainable waste-to-energy conversion and industrial solid waste utilization.