Sustainable pathway towards red mud valorization through biomass thermochemical conversion and metals recovery

Red mud is a hazardous waste of the alumina refining process, with 1-1.5 tons generated per ton of alumina produced. This study presents a first-of-its-kind understanding of a biomass-based pathway for recovering iron from red mud. Simultaneous red mud reduction and biomass gasification (SRG) is proposed as a viable pathway to produce zero-valent iron. This metallic iron can potentially be recovered by weak magnetic separation and integrated into the iron-making industry. The steps of the red mud-biomass phenomena were investigated through thermogravimetric analysis followed by XRD characterization. Complete reduction from Fe³⁺ to Fe⁰ was achieved at temperatures near 900 °C and verified by XRD, XPS, and FTIR. Bench-scale SGR experiments were also performed to survey the compositions of gaseous and tar products. Bench-scale SRG experiments confirmed increased syngas (CO and H₂) production and demonstrated the tar-cracking catalytic activity of red mud.