Red mud valorization: From waste management to metal resource recovery in the circular economy

Red mud (bauxite residue) is generated globally at more than 200 million tons per year, with accumulated stockpiles exceeding 4 billion tons. It typically contains 30-50% Fe₂O₃ and 15-25% Al₂O₃, together with Ti, Ga, V and rare-earth elements (REEs), making it both a hazardous alkaline waste and a potential secondary resource. Literature evidence shows that semi-industrial suspension magnetization roasting can achieve Fe recoveries above 95%, whereas representative bioleaching studies have reported REE recoveries of approximately 79-87% but required about 32 days of leaching. These contrasting results illustrate the persistent trade-off among recovery efficiency, selectivity and sustainable process intensity. Direct comparison of reported performance remains difficult because studies use different residues, pretreatments, operating conditions, recovery definitions and system boundaries. This review critically examines recovery pathways for Fe, Al, Ti, Ga, V and REEs, and synthesizes emerging integrated process flowsheets. Based on this analysis, a "Sequential Decoupling-Synergistic Recovery-Circular Metabolism" framework is proposed, which restructures the red-mud matrix stepwise, coordinates multi-metal recovery, closes alkali and CO₂ loops, and valorizes final residues as construction materials. In conclusion, the industrial valorization of red mud requires a system-level design approach supported by digital modelling, circular product design, standardized LCA and TEA, and policies that promote industrial symbiosis.