High-efficiency Separation of Iron–Manganese Ore Based on Mineral Phase Transformation Theory: A Microwave- Roasting and Pulverized-Coal Synergistic Iron and Manganese Recovery Technoloy,Y

As strategic mineral resources that underpin the development of China’s manufacturing industry, iron and manganese are facing a series of technical bottlenecks in the utilization of iron–manganese ores, including the increasingly poor resource endowment, low reduction efficiency of traditional separation processes, high energy consumption and pollutant emissions, and insufficient selectivity in iron–manganese separation. On the basis of mineral phase–oriented transformation theory, the development of high-efficiency recovery technologies is of great strategic significance for improving resource utilization efficiency and ensuring a stable supply of industrial raw materials. In this study, a new route for the high-efficiency separation of iron–manganese ore by pulverized-coal–synergistic microwave roasting is proposed. By constructing a synergistic reaction system of ”microwave-enhanced heat conduction–pulverized-coal-directed reduction”, low-cost pulverized coal is used as the reductant, with key process parameters such as the pulverized coal to ore ratio, microwave roasting temperature, holding time, reaction atmosphere composition, and feed particle size being optimized. The roasted and modified minerals are subsequently subjected to a combined process of ”two-stage grinding–gradient magnetic separation” to achieve efficient separation of iron and manganese. The results show that under the optimal process conditions (roasting temperature of 720 °C, holding time of 30 min, pulverized coal dosage of 28%, feed size with 88% passing -200 mesh, and gas flow rate of 0.35 atN/min, with a CO₂ volume fraction of 28%), an iron concentrate with a grade of 62.1%, yield of 63.2%, and recovery of 91.62% is obtained, while a manganese concentrate with a grade of 26.37%, yield of 35.19%, and recovery of 82.72% is produced. XRD phase analysis, XPS surface valence characterization, and TEM microstructural observation confirm that iron oxides undergo a selective mineral phase transformation of Fe₂O₃ → Fe₃O₄ in the synergistic system, whereas manganese oxides follow a stepwise reduction pathway of MnO₂ → Mn₂O₃ → MnO, with the generated products exhibiting high purity. The interplanar spacing of the Fe₃O₄ characteristic crystal plane (311) is 0.253 ± 0.003 nm, and that of the MnO characteristic crystal plane (200) is 0.202 ± 0.002 nm, both of which are consistent with the theoretical values in the standard PDF cards. Micro-mechanism analysis indicates that the instantaneous heating effect of the microwave field and the reductive gases (CO, CH₄) produced by pulverized coal pyrolysis act synergistically, inducing lattice distortion and stress release within the minerals and consequently generating a loose and porous microstructure with penetrating fractures. This not only reduces the aggregation effect among mineral particles, but also accelerates the interfacial reaction mass transfer process between the reductant and the mineral lattice, significantly enhancing the directionality and completeness of iron and manganese oxide mineral phase transformation and thereby creating favorable conditions for subsequent magnetic separation.