A clean energy revolution is occurring across the world. As iron and steelmaking have a tremendous impact on the amount of CO₂ emissions, there is an increasing attraction towards improving the green footprint of iron and steel production. Among reducing agents, hydrogen has shown a great potential to be replaced with fossil fuels and to decarbonize the steelmaking processes. Although hydrogen is in great supply on earth, extracting pure H₂ from its compound is costly. Therefore, it is crucial to calculate the partial pressure of H₂ with the aid of reduction reaction kinetics to limit the costs. This review summarizes the studies of critical parameters to determine the kinetics of reduction. The variables considered were temperature, iron ore type (magnetite, hematite, goethite), H₂/CO ratio, porosity, flow rate, the concentration of diluent (He, Ar, N₂), gas utility, annealing before reduction, and pressure. In fact, increasing temperature, H₂/CO ratio, hydrogen flow rate and hematite percentage in feed leads to a higher reduction rate. In addition, the controlling kinetics models and the impact of the mentioned parameters on them investigated and compared, concluding chemical reaction at the interfaces and diffusion of hydrogen through the iron oxide particle are the most common kinetics controlling models.

The reduction behavior of two different iron ore pellets that are used in blast furnace (BF) and direct reduction (DRI) was investigated in this research. Single pellets reduction experiments were conducted isothermally using pure CO and H₂ as reducing agent in the temperature range 700 °C to 1100 °C. Reduction by H₂ was significantly faster than reduction by CO for both pellets and reduction rate increased with increasing the temperature. When CO was used as the reducing agent, the BF pellet achieved a reduction degree of 32% at 700 °C and 67% at 800 °C, while the DRI pellet reached 28% and 59% at the same temperatures. This difference is due to the lower magnetite content in BF pellets (1.93%) compared to DRI pellets (9.11%). However, at 1000 °C and 1100 °C, the DRI pellet achieved 93% and 100% reduction, and the BF pellet 88% and 94%, respectively, due to the higher porosity in the DRI pellet (38%) compared to BF (32%). Kinetics controlling model for hydrogen reduction of both pellets suggested as D2 (2D Diffusion through the solid ash), however, A1 (1D Nucleation and growth) and R3 (3D Chemical reaction) were found as the most compatible models for CO reduction of DRI and BF pellets, respectively. Graphical Abstract

This study investigates the influence of water vapour on the hydrogen reduction of iron ores, focusing on conditions closely aligned with industrial processes, including high temperatures and realistic gas compositions. Single-pellet reduction experiments were conducted isothermally in gas atmospheres with varying ratios of water vapour and hydrogen (30% H ₂ O + 70% H ₂ , 20% H ₂ O + 80% H ₂ , 10% H ₂ O + 90% H ₂ and 100% H ₂ ) over a temperature range of 800°C to 1000°C. The results demonstrate a consistent increase in the reduction rate with rising temperature across all gas compositions, highlighting the impact of water vapour on reduction kinetics under near-industrial conditions. At 30% H ₂ O, reduction was limited to wüstite, with no metallic iron formation observed. At 20% H ₂ O, reduction degrees increased from 36% at 800°C to 77% at 900°C, where a thick metallic iron layer formed, and to 95% at 1000°C, leaving only trace wüstite. Under 10% H ₂ O, reduction exceeded 97%, approaching completion. The study reveals that high water vapour content hinders hydrogen diffusion and blocks active sites on wüstite, impeding its reduction to metallic iron. These findings, supported by kinetic modelling, underscore a complex interplay of diffusion and chemical reaction as the controlling mechanisms. By examining the reduction process under conditions that closely replicate those in industrial hydrogen-based direct reduction, this study provides critical insights into optimising reduction efficiency for sustainable ironmaking.

Iron ore pellet reduction in shaft furnaces represents a critical process in the steelmaking industry, with energy consumption being a key factor influencing both economic viability and environmental sustainability. This study employs HSC Chemistry software to model and simulate the energy consumption of hydrogen reduction of iron ore pellets under varying water vapor content within the shaft furnace. Thermodynamic modeling was carried out as the first step to analyze the effect of water vapor on the thermodynamic equilibrium, determining the possible range of water vapor content. Subsequently, energy consumption of the process was modeled based on heat and mass balance. Through comprehensive analysis, we investigate the impact of water vapor on the overall energy efficiency of the process based on the two scenarios of supplying the required heat by preheating the feed materials or injection of oxygen to the furnace. Our findings reveal significant insights into optimizing energy consumption and operational parameters to enhance the sustainability and cost-effectiveness of iron ore pellet reduction. This research contributes to the ongoing efforts towards achieving greater efficiency and reduced environmental footprint in the steelmaking industry.