Rate Constants of the Initial Reduction of a Single Iron Ore Pellet by CO-H2 Gas Mixture

As the global community moves toward carbon neutrality by 2050, the iron and steel industries are facing significant pressure to reduce CO2 emissions. Direct reduction processes using hydrogen-rich gases are emerging as a critical alternative to traditional blast furnace methods. This study investigates the reduction behavior of single hematite pellets using varying H2-CO gas mixtures. Thermogravimetric analysis (TGA) was employed to measure reduction rates, while exhaust gas analysis helped elucidate the reaction mechanism. The results indicate that while higher temperatures and H2 concentrations accelerate reduction, carbon deposition presents a significant challenge for real-time TGA measurements at lower temperatures. By focusing on the initial stage of reduction, this study effectively excluded the influence of carbon formation on the weight change. Under these controlled conditions, a topochemical receding interface model was found to be the most appropriate for determining rate constants and activation energies under different gas mixing ratios. The derived kinetic parameters and the understanding of H2-CO reduction behavior provide essential fundamental data for optimizing the operating conditions of gas-based direct reduction processes.