Microwave-enhanced Fe/Al recovery from red mud: Mechanistic role of carbothermal reduction and alkali activation in mineral transformation

Red mud, a globally prevalent industrial byproduct, poses critical environmental risks due to its alkaline nature and heavy metal content, while conventional treatment methods remain energy-intensive and inefficient. This study develops a microwave-assisted strategy combining carbothermal reduction and alkaline activation to enable synchronous Fe/Al recovery. Microwave facilitates rapid mineral phase transformation through internal heating and selective heating, while sodium carbonate additives preferentially convert aluminum-bearing phases into acid-soluble aluminates (NaAlO₂/NaAlSiO₄) without compromising carbothermal reduction of Fe₂O₃ to FeO/NaFeO₂. Experimental results demonstrate 92.1 % Fe and 92.9 % Al recovery under optimized conditions (900°C, 10 min), representing a 20.4 % Al recovery improvement compared to conventional methods. Mechanistic investigations through characterization and thermodynamic analyses elucidate the distinct phase evolution pathways of Fe and Al, emphasizing sodium-mediated restructuring of aluminosilicates and high-temperature iron oxide reduction facilitated by microwave. The iron-aluminum-rich leachate exhibits potential for secondary resource utilization. This work elucidates a dual Fe/Al activation mechanism for red mud recovery, achieving high recovery efficiencies (Fe: 92.1 %, Al: 92.9 %) and providing theoretical insights into sustainable resource utilization.