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

As a refractory iron ore, achieving 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 micro-morphology, microstructure, and mineral phase transformation of the roasted products were meticulously analyzed using scanning electron microscope (SEM), automatic surface area and porosity analyzer, X-ray diffractometer (XRD), and vibrating sample magnetometer (VSM). Additionally, kinetic analysis was conducted to identify the factors limiting the roasting reaction rate. Microwave fluidization roasting has significantly increased the specific surface area of limonite, increased the opportunity of CO and limonite, and accelerated the transformation from FeO(OH) and then to α-Fe2O3 and subsequently to Fe3O4. In addition, the water in the limonite ore and the newly formed magnetite have 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 a Fe grade of 59.26 wt% and a recovery of 90.07 wt%. Kinetic analysis revealed that the reaction mechanism function model was consistent with the diffusion model D1, with the mechanism function described as k=0.08208exp(−20.3441/RgT). Microwave fluidization roasting demonstrates significant potential in the beneficiation of limonite, offering a promising approach for the exploitation of refractory iron ores.