Investigation of the Reduction Mechanism and Comparative Reaction Kinetics of Milled Scale Goethite–Hematite Pellets in the Carbothermic Atmosphere from Non-Coking Coal for Application in Sponge Iron Synthesis
Publication Type
Journal Article
Publication Date (Issue Year)
2025
Journal Name
Journal of Sustainable Metallurgy
Abstract
Iron ore’s non-contact direct reduction (NDR) process is an innovative method for producing sponge iron, offering a sustainable alternative to traditional iron and steelmaking techniques. With the depletion of high-quality iron ore and metallurgical coke, there is a growing need to utilize alternative iron-bearing materials. This study examines the gangue-laden goethite–hematite ore’s reduction mechanism and reaction kinetics, containing 58.6% theoretical total iron and 1.31% SiO2. The ore was isothermally reduced at room temperature to 1273 K, with a heating rate of 278 K/min in a nitrogen atmosphere. The CO gas used was generated via non-coking coal gasification. The iron ore and coal were ground to 150 µm using a ball mill and formed into 6, 9, and 12 mm pellets. These pellets underwent a non-contact direct reduction (NDR) process inside a carbon-activated furnace at a nitrogen flow rate of 1.2 L/min and an atmospheric pressure of 0.5 bar, with reduction times of 20, 40, and 60 min. The Unreacted Core and Ginstling–Brounshtein models were employed to analyze the reaction kinetics. Results revealed that increased temperature and reduction time enhanced the reduction ratio, swelling extent, and metallization degree, achieving a maximum reduction ratio of 0.94–0.98 and a metallization degree of 92–98.8% at 1273 K with an iron-to-coal ratio of 1:3 by mass. The Unreacted Core model has an activation energy of 61.68 kJ/mol and a rate constant of 5.56 × 10–5 s1. The Ginstling–Brounshtein model, also known as the 3D phase boundary diffusion, is identified as the rate-controlling mechanism with an activation energy of 68.69 kJ/mol and a rate constant of 15.72 × 10⁻5 s⁻1 for larger size pellets (9–12 mm) at 60 min. The apparent activation energy averaged 80 kJ/mol for 20-min reductions, influenced by gangue elements and ash-layer buildup. XRF, EDS, and SEM analyses confirmed phase transformations and morphological changes, with prolonged reduction (40–60 min) promoting metallic iron formation. Despite achieving lower swelling extent and particle disintegration at higher temperatures (1173–1273 K), this study highlights the NDR process as a viable pathway for high-quality sponge iron synthesis, supporting sustainable steelmaking practices.
Keywords
Comparative Reaction Kinetics, Milled Scale Goethite–Hematite Pellets, Carbothermic Atmosphere, Non-Coking Coal, Sponge Iron Synthesis
Rsif Scholar Name
Joseph Ekhebume Ogbezode
Thematic Area
Minerals, Mining and Materials Engineering
Africa Host University (AHU)
African University of Science and Technology (AUST), Nigeria
Recommended Citation
Ogbezode, J.E., Anye, V.C., Ajide, O.O. et al. Investigation of the Reduction Mechanism and Comparative Reaction Kinetics of Milled Scale Goethite–Hematite Pellets in the Carbothermic Atmosphere from Non-Coking Coal for Application in Sponge Iron Synthesis. J. Sustain. Metall. 11, 4167–4194 (2025). https://doi.org/10.1007/s40831-025-01237-6