Comparative kinetics study of different iron-containing pellets with hydrogen at isothermal conditions

Using hydrogen to produce iron is a promising way for the steel industry to achieve the goal of carbon neutrality. The reducibility of iron-bearing oxides by hydrogen significantly impacts the productivity and energy consumption during the reduction process. This study investigated the competitive kinetics of hydrogen reduction for different iron bearing pellets including iron ore pellets, bauxite residue pellets, and calcium-added bauxite residue sintered and self-hardened pellets at isothermal condition. Various characterization tools, such as X-ray diffraction, electron probe analysis, and X-ray fluorescence, were used to examine the properties of the pellets. These pellets exhibit different porosity, iron bearing oxides and overall composition. The time required to achieve 50 % reduction(R50) at 1000 °C approximately 2 min for bauxite residue and bauxite residue-CaO sintered and self-hardened pellets, while iron ore pellets required approximately 6 min. Moreover, at 700 °C, the R50 value is reduced for sintered bauxite residue CaO pellets as compared to other owing to the diminished reducibility of brownmillerite (Ca2(Alx,Fe(2-x))O5) in contrast to hematite found in the other pellets. It was highlighted that factors such as porosity of the unreduced pellets, types of iron bearing oxides and grainsize significantly influences the reducibility of different pellets. Furthermore, during the reduction process, all pellets were observed with a rapid initial stage, a subsequent transition stage, and a final slow reduction stage.