Microwave fluidization magnetization roasting of limonite ores: Phase transformation, microstructure and kinetics

As a refractory iron ore, the clean and efficient beneficiation of limonite is crucial for ensuring a sustainable long-term supply of iron metal. In this study, the microwave fluidization magnetization roasting of limonite was explored. The micromorphology, microstructure, and mineral phase transformation of the roasted products were analyzed using a scanning electron microscope, an automatic surface area and porosity analyzer, an X-ray diffractometer, and a vibrating sample magnetometer. Kinetic analysis was also conducted to identify the factors limiting the roasting reaction rate. Microwave fluidization roasting significantly increased the specific surface area of limonite, increased the opportunity of contact between CO and limonite, and accelerated the transformation from FeO(OH) to α-Fe₂O₃ and then to Fe₃O₄. In addition, the water in the limonite ore and the newly formed magnetite exhibited a strong microwave absorption capacity, which has a certain activation effect on the reduction roasting of limonite. At a temperature of 773 K, the saturation specific magnetization intensity and maximum specific magnetization coefficient increased to 23.08 A·m²·kg⁻¹ and 2.50 × 10⁻⁴ m³·kg⁻¹, respectively. The subsequent magnetic separation of the reconstructed limonite yielded an iron concentrate with an Fe grade of 59.26wt% and a recovery of 90.07wt%. Kinetic analysis revealed that the reaction mechanism function model was consistent with the diffusion model (G(α) = α²), with the mechanism function described as k = 0.08208exp(−20.3441/(R_gT)). Therefore, microwave fluidization roasting shows significant potential in the beneficiation of limonite, offering a promising approach for the exploitation of refractory iron ores.