Gaseous Reduction of MgO-doped Fe₂O₃ Compacts with Carbonmonoxide at 1173-1473 K

Abstract

Fired pure Fe₂O₃ and 0.5-5.0% MgO-doped Fe₂O₃ compacts, were isothermally reduced with CO at 1173-1473 K. The course of reduction was followed up by thermogravimetric technique. The structure of compacts were microscopically examined while the different phases were identified by X-ray diffraction analysis. Mercury pressure porosimeter was used to characterize the pore structures. The isothermal reduction curves obtained showed that MgO revealed different effects on the reduction behaviour of Fe₂O₃. At the initial stages up 25% extents, the doping of MgO showed no measurable influence on the reduction process. At the intermediate stages (25-85% extents), the doping of 0.5% MgO retarded the reduction while the presence of 1.0% MgO promoted the reduction of Fe₂O₃. The retardation and promotion effects were increased with the extent of reduction and decreased with rise in temperatures. At final stages of reduction, a slowing down in the rate due to the doping of MgO was observed which was attributed to the formation of hardly reducible magnesiowustite phase. The rate controlling step in the reduction process was determined from the values of apparent activation energy, gas-solid mathematical formulations and the microstructure of partially reduced compacts. It was found that the reduction was controlled by a combined effects of gaseous diffusion and interfacial chemical reaction at the initial stages. While at the latter stages, a solid-state diffusion is contributed to interfacial chemical reaction as the rate controlling mechanism depending on MgO content in compacts.