Reduction of Iron Ore Pellets: A Microstructural Perspective?

Twenty different iron ore pellets, consisting primarily of Hematite (Fe2O3) phase, were subjected to ‘simulated’ reduction studies. A wide range of reduction time periods, Rt of 122 to 211 minutes, were obtained. Detailed microstructural characterizations were then conducted at different locations of ten selected specimens. The Rt did not relate with initial phase mix or chemistry but determined the final iron (Fe) to Wüstite (FeO1−x) ratio. In particular, numerical Rt values defined the relative presence of a bright Fe-rich rim. Further, relative density or porosity before the reduction scaled, as expected, with Rt. However, this was tenuous. The correlation appeared excellent in the post-reduction-densified specimens. This indicated the role of ‘acquired porosity’ and transformation strain. Several other microstructural parameters also scaled with Rt. These included grain size and crystallographic texture and estimated dislocation density. Lower Rt specimens had, in general, finer Fe2O3 and coarser Fe grains, but weaker crystallographic textures of Fe2O3 and FeO1−x. However, the most striking correlation appeared between Rt and post-reduction dislocation density. The acquired defect density, representing the transformation strain, appeared to be the controlling feature for the reduction of iron ore pellets.