Bulk density as method of evaluating reducibility of hard hematite ore in direct reduction process

Massive hematite ore (MHO) is a special high grade iron ore used as lump ore in the process of obtaining direct reduced iron (DRI). The influence of porosity on the reducibility has been investigated using optical and scanning electron microscopes. Hematite is the main component of the samples and occurs as granular crystals (10 μm), microplates (1 μm) and euhedral martite (10-30 μm). Quartz, maghemite, kenomagnetite and goethite are minor components. Primary micropores (Å to 1 μm) are associated with microplaty crystals that fill cavities between granular hematite. Secondary micropores (Å to 5 μm) related to euhedral martite crystals are the most important. The total porosity of weathered samples, measured using nitrogen adsorption and mercury injection, attains values up to 18%, whereas unweathered samples have a porosity less than 2·5%. Varajão et al. showed that reducibility is strongly enhanced by porosity and this work shows that reducibility can be indirectly evaluated by bulk density.