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Hydrogen has received much attention in the development of direct reduction of iron ores because hydrogen metallurgy is one of the effective methods to reduce CO2 emission in the iron and steel industry. In this study, the kinetic mechanism of reduction of hematite particles was studied in a hydrogen atmosphere. The phases and morphological transformation of hematite during the reduction were characterized using X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy. It was found that porous magnetite was formed, and the particles were degraded during the reduction. Finally, sintering of the reduced iron and wüstite retarded the reductive progress. The average activation energy was extracted to be 86.1 kJ/mol and 79.1 kJ/mol according to Flynn-Wall-Ozawa (FWO) and Starink methods, respectively. The reaction fraction dependent values of activation energy were suggested to be the result of multi-stage reactions during the reduction process. Furthermore, the variation of activation energy value was smoothed after heat treatment of hematite particles.

In this paper, a new kinetic model has been developed for reduction of metal oxides with hydrogen under both isothermal and non‐isothermal conditions. This model describes the kinetics of single reductive reaction and double reductive reactions by considering the diffusion and chemical reaction controlling mechanisms. In particular, the model is in the analytic form of expressing the reduction extent as an explicit function of time, temperature, radius of the particle, and hydrogen partial pressure, which is convenient for using and theoretical analysis. The reduction kinetics of nickel oxide, natural ilmenite, and Fe2MoO4 agree well with the theoretical results by the present model.

Reduction of titano-magnetite powder containing 56.9 mass% of iron and 9.01 mass% of TiO2 with H2-Ar gas mixtures was investigated in isothermal experiments using thermo-gravimetric analyzer (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The reduction of titano-magnetite was proved to proceed via a dual reactions mechanism. The first reaction is reduction of titano-magnetite to wüstite and ilmenite and the second one is reduction of wüstite and ilmenite to iron and titanium-containing phase. It was found that the dual reactions occurred simultaneously during the reduction. The reduction kinetics of titano-magnetite was analyzed according to a dual reactions kinetic model and the results indicated that the gaseous species diffusion in product layer was the rate controlling step for the first reaction, and interfacial chemical reaction was that for the second reaction. The apparent activation energies were extracted to be 98 kJ/mol and 115 kJ/mol for the first and second reaction, respectively.