Reduction of hematite compacts by H2-CO gas mixtures

The reduction behaviour of hematite compacts by H-2-CO gas mixtures was investigated at 1073-1223 K. The total porosity, pore size distribution and surface area of the compact was measured using mercury pressure porosimeter, The reduction tests were carried out using Cahn balance. The reduction behaviour could not be described in terms of a single rate-determining step; the reduction process was initially controlled by the chemical reaction at the oxide/iron interface, controlled by the intraparticle diffusion through the reduced layer towards the end of reduction, and the mixed control, in between. Over the whole range, the reduction rate decreased with CO content in the gas mixture. The chemical reaction rate constants were two to three times higher for H-2 reduction than those of CO reduction, and the effective diffusivities of H-2 reduction were three to four times higher than those of CO reduction. Values of activation energy for chemical reaction were found to be 19.8-42.1 kJ/mol depending on the gas compositions; 100% CO showing the lowest.