A Review of Hydrogen (H₂) Utilization for Iron Oxide Reduction in the MIDREX Process

In recent years, the intensification of global warming has been largely attributed to the increasing emission of greenhouse gases, particularly carbon dioxide (CO₂). Owing to its strong dependence on carbon-based reduction routes and its high energy demand, the steel industry represents one of the largest industrial sources of CO₂ emissions. After iron ore preparation, reduction is conventionally performed using reducing gases composed of carbon monoxide, hydrogen, or their mixtures. In this study, a hydrogen-based reduction scenario is proposed as a carbon-neutral alternative for ironmaking, with the potential to substantially reduce CO₂ emissions. In parallel, the reduction kinetics of iron ore from hematite to metallic iron are systematically investigated, with particular focus on intrinsic and induced porosity, pore connectivity, and microstructural defects. The reduction behavior reveals a rapid reaction rate at the initial stage, followed by a progressive deceleration as reduction proceeds. Quantitative microstructural analysis shows that exposure to a hydrogen atmosphere for 10 minutes increases the free structural volume by up to 5%, while reducing the average pore diameter to 1.29 μm. Prolonging the reduction time to 2 hours further increases the free volume to 13% and enlarges the average pore diameter to 4.5 μm. These results provide insight into the structure–kinetics relationship during hydrogen-based iron ore reduction and support the feasibility of hydrogen as a key enabler for low- and near-zero-carbon ironmaking.