Study on the behavior and mechanism of iron extraction by sodium carbonate-coal-based synergistic enhancement of red mud reduction roasting

Abstracts: In response to the challenges posed by the complex mineralogy of red mud and the low efficiency of conventional beneficiation processes, this study proposes a synergistic reduction roasting approach using sodium carbonate and coal for iron extraction. Through systematic investigation of key factors—including roasting temperature, additive dosage, grinding time, and magnetic intensity—the optimal conditions were identified as roasting at 1150 °C for 1.5 h with 7.5% sodium carbonate and 15% pulverized coal, yielding an iron concentrate grade of 90.37% and a recovery rate of 82.23%. Response surface methodology revealed a significant interactive effect between temperature and coal dosage, and a corresponding predictive model was established. XRD and SEM-EDS analyses indicated that sodium carbonate facilitates melt-phase reconstruction, enhances porosity to improve permeability for the reducing agent, and catalyzes the conversion of olivine (Fe₂SiO4) and hercynite (FeAl2O4) to metallic iron. Combined kinetic and thermodynamic analyses confirmed the reduction pathway: Fe2O3→Fe3O4→FeO→Fe. The addition of sodium carbonate significantly reduces the Gibbs free energy (ΔG) of the reaction through the formation of low-melting-point compounds, thereby promoting the spontaneous reduction of iron oxides. This study provides both theoretical insights and practical strategies for the sustainable valorization of red mud.