Reduction kinetics and characterization study of synthetic magnetite micro fines

Abstract

The present work deals with the characterization of pure magnetite microfines (<5 μm) and its hydrogen reduction. The structural and morphological properties of magnetite powder were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption analysis by five points isotherm BET method, and scanning electron microscopy along with energy dispersive X-ray spectroscopy (SEM-EDS). The hydrogen reduction of the magnetite powder was carried out in a thermogravimetric analyzer (TGA) under a steady flow of hydrogen or hydrogen-argon mixture (to produce different partial pressures of hydrogen). The variables studied were reduction temperature (973–1273 K), hydrogen partial pressure (0.25–1 atm) and sample bed height (0.184–0.68 cm). The apparent activation energy was obtained as 22 kJ mol−1. The rate equations developed for the reaction system under study were applied to determine the rate controlling step. The reduction was found to be rate controlled by diffusion through the stagnant gas film enclosed above the sample inside the crucible. The true activation energy was calculated to be 9 kJ mol−1.