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% N-2-30% (H-2/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 mu m) 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 H-2 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% N-2-30% (H2/CO = 5) and 1223 K and 70% N-2-30% (H-2/CO = 2), respectively.