Isothermal Reduction and Avrami–Erofeev Kinetic Model for Reducing Iron Ore Pellets in a 70% N₂–30% H₂/CO Atmosphere

Effective utilization of hydrogen-rich reduction gases becomes imperative with advancements in reduction processes. In this study, the reduction processes of hematite pellets with different iron grades reduced by a reducing atmosphere (70% N₂–30% (H₂/CO = 0/2/5)) at 1123, 1173, and 1273 K were systematically investigated using a thermal analyzer. Kinetic analysis of hematite pellets was performed using the Avrami–Erofeev kinetic model. The porosity and pore size distribution of pellets A and B were determined using mercury intrusion porosimetry (MIP). The results show that a suitable pore size distribution and the addition of hydrogen are favorable for the reduction of pellet. Combined with the results of the pellet XRD, SEM–EDS, and MIP, the analysis of the pore size distribution and iron grade (TFe%) showed that a suitable pore size distribution (0.7–7 µm) of the pellet had a greater effect on the degree of reduction than the iron grade of the pellet TFe%. Both pellets with different iron grades are mostly model as first-order (F1) at 1273 K and as geometrical contraction below 1223 K. When H₂ was added to the reducing gas for both pellets, the activation energy decreased to a large extent, from 92.72 to 78.73 kJ/mol and from 69.35 to 58.07 kJ/mol for pellets A and B, respectively. According to the reduction degree (R), reduction velocity index (RVI) and activation energy change rule of the ore after reduction, the suitable reduction process conditions for pellets A and B are 1273 K and 70% N₂–30% (H₂/CO = 5) and 1223 K and 70% N₂–30% (H₂/CO = 2), respectively.