A Comprehensive Study on Determination of Kinetic Parameters of Ironmaking Ores Reduced by Hydrogen: Reduction Below 570 °C

To advance hydrogen metallurgy, it is critical to understand the micro-kinetics of diversified ironmaking ores reduced by hydrogen and to establish gene-pool like kinetic parameter library for specific ironmaking materials. However, it is usually difficult to determine the micro-kinetic mechanisms due to the compensation effect of model-fitting methods. In this paper, the modern thermogravimetry method is used to evaluate the non-isothermal kinetics of four types of iron-bearing mineral powders reduced by hydrogen throughout a temperature range of 50 °C to 570 °C. Both traditional model-fitting and cutting-edge model-free approaches were used. The reproduced level of original kinetic process was selected as a criterion to choose the optimal parameters in the analysis. The processes of different iron ore (the Australian ore powder, the Southern-African ore powder, the sinter powder and the pellet powder) reduction reactions are split as the first stage of Fe2O3 → Fe3O4 and the second stage of Fe3O4 → Fe, according to the classic two-stage analysis distinguished by a conversion ratio of roughly 0.11. The optimal first-stage activation energies of the various iron ore reductions are 141.20 kJ/mol (Vyazovkin’s model-free, order of 3/2), 60.67 kJ/mol (Friedman’s model-free, three-dimensional diffusion), 86.86 kJ/mol (Friedman model-free Anti-Ginstling-Brounshtein), and 74.53 kJ/mol (Vyazovkin’s model-free, Anti-Zhuravlev), respectively. The optimal second-stage activation energies of the various iron ore reductions are as follows: 58.44–75.37 kJ/mol (Vyazovkin’s model-free, order of 1/3), 52.63–74.96 kJ/mol (Friedman’s model-free, Avrami-Erofeev), 61.78–88.57 kJ/mol (Friedman model-free, order of 3/2), and 50.82–64.14 kJ/mol (Vyazovkin’s model-free, Interface contracting sphere). The master plot approaches were used to find the best reaction model and to derive the pre-exponential factor.