Investigation of Reduction Rate Difference of Hematite Powder and Magnetite Powder

Abstract

The demand for using the magnetite powder ore will be increased in the near future because of depleted deposit of high-grade hematite ore. However, it is known that magnetite ore has low reducibility compared to hematite ore. On the other hand, the chemical reduction difference of magnetite powder with hematite powder has not been clearly investigated. Therefore, this study is focused on finding reduction rate difference between magnetite powder and hematite powder with the reduction gas CO.To find out the effect of particle size and temperature on the surface morphology causing the reduction behavior of hematite and magnetite powder, comparing reduction behaviors of both hematite and magnetite powder, for the five size ranges as ~63μm, 63~125μm, 125~250μm, 250~425μm, and 425~1000μm were investigated using thermo-gravimetric analysis (TGA) and scanning electron microscope (SEM). As the temperature increases, surface area decreases to affect the reduction rate of hematite and magnetite. In addition, the porous structure of magnetite, instead of average particle size of powder, could affect the reduction behavior. However, it is suggested that controlling the average particle size of magnetite powder and hematite powder is not sufficient to control the surface area.Therefore, reduction behaviors of magnetite powder which was oxidized to hematite were investigated, with comparing to the original magnetite powder. In this investigation, surface morphologies of both original magnetite powder and hematite powder are shown similar, without any crack formation during oxidation of magnetite or initial reduction of this hematite to magnetite. Therefore, initial reduction rate of hematite powder is the only difference from magnetite, and is 33% faster than that of magnetite powder. Furthermore, using Edström`s data (1953) at 1273K [2] and current research at 1073K, the activation energy and rate constant of magnetite reduction can be obtained, if reduction rate is considered as r=k(T)×S×Pco.Ea=300.0kJ/mol,k=253099 exp(- 299790/RT) mol/(cm^2∙sec∙atm)