Reduction Kinetics of Non-spherical Hematite Particle in CO Atmosphere with Multi-step Limited Reaction Zone Modification

In-situ experimental and modeling study was carried out for the reduction of single hematite particle under the CO atmosphere with multi-step limited reaction zone modification. Conventional model fitting methods were employed to analyze the gas–solid reaction, while no single model adequately described the complete kinetic process. Model-free analysis revealed significant changes in the reaction mechanism during reduction. The one-interface and three-interface unreacted shrinkage core models revealed that the chemical reaction resistance was the rate-controlling step. As temperature increased, chemical reaction resistance decreased, while diffusion effects became more significant. To address the multiple steps involved, a modified Johnson–Mehl–Avrami–Kolmogorov (JMAK) model with delay time and limited reaction zone was developed to decouple the three reaction steps (Fe₂O₃→Fe₃O₄, Fe₃O₄→FeO, and FeO→Fe). The reduction process occurred in three stages: simultaneous reduction of Fe₂O₃ and Fe₃O₄, parallel reduction of Fe₃O₄ and FeO, and reduction of FeO. Apparent activation energies of 50.0, 40.3, and 47.1 kJ/mol were obtained for the decoupled reactions. Among the fitting methods and models used, the modified JMAK model has the superior accuracy.