Porous iron oxide pellets prepared from the pulverized Brazilian ore, high quality hematite, were reduced with H₂-H₂O mixtures in the temperature range from 800°C to 1100°C and the rate of reduction was measured by a thermobalance. Cross sections of partially reduced pellets were examined under the microscope and poresize distributions were measured. The microscopic observation of the cross sections showed that the reduction from hematite to wustite had finished in the early stage of overall reduction period and the reduction from wustite to iron proceeded in the topochemical fashion.
On the assumption that the region in more than 30% reduction in the reduction curve of pellet was correspond to the latter step in the reduction reaction, the process was analysed on the basis of the mixed control mechanism, in which the interface chemical reaction, gaseous diffusion in the particle and surface film, and the dilution effects of produced gas were taken into account. The chemical reaction constant k_c and the intraparticle diffusivity D_e for the reduction in the temperature range from 900°C to 1100°C were obtained. The apperent activation energies of k_c and D_e were 28.0 and 17.2kcal/mol, respectively.
These large values are attributed to the high porosity of the pellets and to the large temperature dependence of physical properLies of reduced pellets, such as pore size and iron grain.