Sustainable Iron Recovery from Red Mud via Biomass Reductive Roasting: Insights from Targeted Transformation of Iron Minerals

Red mud (RM) possesses a high iron content; however, the recovery of valuable iron resources is hindered by its fine particle size and complex mineralogy, resulting in serious resource waste and environmental burdens. In this study, density functional theory calculations were employed to predict and quantify the interfacial energies between iron minerals (hematite, magnetite, and metallic iron) and silicon-bearing minerals (quartz and cancrinite) within RM, revealing that metallic iron exhibits the greatest dissociation potential from silicon-bearing minerals. Guided by these theoretical insights, a strategy integrating biomass-assisted reductive roasting with magnetic separation was proposed. Optimization via response surface methodology yielded an iron recovery rate of 88.09% with a concentrate grade of 72.70%. During the roasting, iron minerals catalyze the pyrolysis of biomass-derived CH4, continuously generating CO and H2 to maintain a reducing atmosphere, thereby providing a sustained driving force for the reduction of iron minerals. Meanwhile, the inherent sodium within RM acts as a flux, lowering the reduction temperature and promoting the growth of iron particles, which further facilitates magnetic separation. This work not only provides a highly efficient and sustainable pathway for RM valorization but also offers a novel framework for using fundamental interfacial theory to treat complex iron-rich solid wastes.