Microporosity of BIF hosted massive hematite ore, iron quadrangle, Brazil

Abstract

Massive hematite ore (MHO) is a special high-grade iron ore, used as lump ore in the process of obtaining direct reduction iron (DRI). The influence of porosity on the reducibility of MHO from the Capitão do Mato Mine (Iron Quadrangle, Brazil) was investigated using optical and scanning electron microscopes on drill core and open pit samples. Hematite is the main component of the samples and occurs as granular crystals (10 μm), microplates (1 μm) and euhedral martite (10 to 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 11%, whereas unweathered samples have a porosity less than 2.5%. Reducibility is strongly enhanced by porosity, but inhibited by structure (bedding).