This study presents a fluidization roasting technology for siderite-bearing iron ore without the use of carbon additives. Samples of Jingtieshan iron ore were subjected to fluidization magnetization roasting, and the effects of roasting temperature, time, and N₂ flow rate on the magnetic separation performance were explored. An iron concentrate with an iron grade of 57.40% and recovery of 91.17% was acquired at a roasting temperature of 700 °C, roasting time of 10.0 min, an N₂ flow rate of 600 mL/min, grinding particle size of −125 μm, and constant magnetic intensity of 99.47 kA/m. The samples were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy–energy dispersive spectroscopy, and vibrating sample magnetometry. The results revealed that hematite and goethite were reduced to magnetite by the CO generated during siderite decomposition; meanwhile, siderite was transformed into magnetite with the consumption of CO during the reduction process. The saturation magnetization of the roasted ore significantly increased owing to the formation of ferrimagnetic magnetite, which was easily recovered in the subsequent magnetic separation.

Mineral phase transformation (MPT) of hematite to magnetite by reduction roasting is a viable means of developing refractory iron ore resources. However, conventional coal-based reductants are prone to high carbon emissions and environmental pollution. Biomass, as a renewable green reductant, can make the MPT process more environmentally friendly while reducing the environmental impact associated with processing agricultural waste. This study systematically explored the feasibility of waste corn straw as a green reductant for hematite. Under the conditions of 8 min, 700 °C, a mass ratio of corn straw to hematite of 1:4, and a N₂ flow rate of 300 mL/min, the best beneficiation indexes were achieved, with an iron grade of 69.82% and an iron recovery of 93.95%. During the MPT process, hematite was reduced under the action of corn straw, and the new magnetite particles were loose and porous, showing an acicular crystal structure. Meanwhile, the corn straw was converted into porous biochar.