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Kinetics and microstructural evolution of iron oxide pellets reduced by H2/CO mixtures: Implications for hydrogen-based direct reduction.

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Title: Kinetics and microstructural evolution of iron oxide pellets reduced by H2/CO mixtures: Implications for hydrogen-based direct reduction.
Authors: Cheng, Qiang1 (AUTHOR), Guo, Hongwei1 (AUTHOR), Yan, Bingji1 (AUTHOR) bjyan@suda.edu.cn
Source: International Journal of Hydrogen Energy. Jan2026, Vol. 205, pN.PAG-N.PAG. 1p.
Subjects: Chemical reduction kinetics, Iron oxides, Mass transfer coefficients, Morphology, Iron, Gas mixtures, Industrial applications, Diffusion control
Abstract: This study systematically examines the reduction kinetics and associated microstructural evolution of high-purity iron oxide (Fe 2 O 3) pellets during gas-based reduction in H 2 /CO mixtures at temperatures ranging from 850 to 1000 °C. The reduction mechanism is determined to conform to the unreacted core model, exhibiting a distinct kinetic transition: the initial stage is governed by the Spherical Shrinking Model, while the later stage shifts to diffusion control, following the Ginstling-Brounshtein Diffusion Model. Microstructural characterization via Scanning Electron Microscopy and Industrial Computed Tomography reveals that the reducing agent profoundly influences the morphology of the metallic iron product. H 2 reduction generates a highly porous, sponge-like iron structure with extensive pore connectivity, facilitating gas permeability. In contrast, CO reduction results in denser, layered iron formations with irregular pores, phenomena exacerbated by carbon deposition and swelling. Quantitative analysis corroborates that H 2 -reduced pellets possess superior pore sphericity (14.6 % > 0.8 sphericity) and connected porosity (24.26 %), thereby optimizing reduction efficiency. Conversely, CO-reduced pellets exhibit inferior sphericity (3.2 % > 0.8 sphericity) and a higher proportion of isolated pores (16.32 % connectivity), which impedes deep reduction. These findings provide critical insights for optimizing Direct Reduction Iron (DRI) processes, underscoring the significant advantages of employing H 2 in industrial applications. • H 2 creates superior porous microstructure with high connectivity. • The properties of pores provide insights into kinetic mechanisms. • Findings strongly support the H 2 -rich DRI production. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:This study systematically examines the reduction kinetics and associated microstructural evolution of high-purity iron oxide (Fe 2 O 3) pellets during gas-based reduction in H 2 /CO mixtures at temperatures ranging from 850 to 1000 °C. The reduction mechanism is determined to conform to the unreacted core model, exhibiting a distinct kinetic transition: the initial stage is governed by the Spherical Shrinking Model, while the later stage shifts to diffusion control, following the Ginstling-Brounshtein Diffusion Model. Microstructural characterization via Scanning Electron Microscopy and Industrial Computed Tomography reveals that the reducing agent profoundly influences the morphology of the metallic iron product. H 2 reduction generates a highly porous, sponge-like iron structure with extensive pore connectivity, facilitating gas permeability. In contrast, CO reduction results in denser, layered iron formations with irregular pores, phenomena exacerbated by carbon deposition and swelling. Quantitative analysis corroborates that H 2 -reduced pellets possess superior pore sphericity (14.6 % > 0.8 sphericity) and connected porosity (24.26 %), thereby optimizing reduction efficiency. Conversely, CO-reduced pellets exhibit inferior sphericity (3.2 % > 0.8 sphericity) and a higher proportion of isolated pores (16.32 % connectivity), which impedes deep reduction. These findings provide critical insights for optimizing Direct Reduction Iron (DRI) processes, underscoring the significant advantages of employing H 2 in industrial applications. • H 2 creates superior porous microstructure with high connectivity. • The properties of pores provide insights into kinetic mechanisms. • Findings strongly support the H 2 -rich DRI production. [ABSTRACT FROM AUTHOR]
ISSN:03603199
DOI:10.1016/j.ijhydene.2025.153100