Mossbauer study of the gas-based direct reduction of iron ore fines and application of the Johnson-Mehl-Avrami kinetic model to the reduction process

We report a Mossbauer study on the direct reduction of an Australian iron ore with the aim of understanding various phase changes and associated kinetics. The iron oxides in the ore comprised 95 wt.% Hematite (α-Fe ₂O ₃) and 5 wt.% Wustite (Fe _xO, x<1). The samples were heated to temperatures ranging from 600°C to 800°C and then reduced in pure hydrogen for different times. The concentration of reduced iron and various iron oxides in partially reduced samples was monitored as a function of reduction time using Mossbauer spectroscopy. 3 kinetic stages leading to the evolution of α-Fe were observed. These results were corroborated with weight-loss measurements. The Johnson - Mehl-Avrami (JMA) kinetic model was also used to analyze the evolution of the product iron. Formation of Fe in the direct ore reduction had an Avrami exponent of 1, corresponding to a case of instantaneous nucleation of iron on the surface of the ore followed by 1-dimensional inward growth towards the center. Our study demonstrates that the JMA analysis can be of considerable value in the field of direct iron ore reduction.