Effect of particle size on reduction kinetics of hematite ore in suspension roaster

Suspension magnetization roasting followed by magnetic separation is an innovative and effective way to recover iron from refractory iron ores, and the particle size of the ore greatly affects the roasting index. To identify the effect of particle size on the reduction kinetics for the transformation of hematite to magnetite, a high-purity hematite ore with different size fractions were isothermally reduced using a suspension roaster. The pure hematite ore was divided into -1000+500 µm, -500+150 µm, -150+74 µm, -74+37 µm and -37 µm size fractions, while the gas mixture of CO and CO2 with a volume ratio of 1:4 was used as reductant. The results showed that the most suitable mechanism function for the reduction of -37 µm size fraction hematite ore is the Avrami-Erofeev model. In the case of -500+37 µm size fraction, the reduction process can be described by first-order chemical reaction model. For -1000+500 µm size fraction, the reduction of hematite ore is restricted by the second-order chemical reaction. In addition, scanning electron microscopy (SEM) analysis results demonstrated that the transformation of hematite particles to magnetite is in accordance with the characteristics of shrinking core model. The phase transformation primarily occurs at the edge of hematite particles and then develop towards the inner side of particles. The findings of this paper provide a theoretical basis for the development and utilization of refractory hematite ore via suspension magnetization roasting technology.