A Comparative Study of Ultra-Fine Iron Ore Tailings from Brazil

This paper presents a characterization study of ultra-fine solid particles contained in slimes of some iron mines from the Iron Quadrangle, Minas Gerais State, and from the Carajás region, Pará State, Brazil. This characterization is expected to provide a basis for the development and choice of mineral-processing techniques suitable for the tailings characteristics of each mine. Particle size separation was done by wet sieving and in a cyclosizer, whereas particle size distribution was determined by laser diffraction (Cilas). The powders were further characterized by chemical analysis, X-ray diffraction, scanning electron microscopy, and Mössbauer spectroscopy. The tailings had a significant content of iron (from 44% to 64%), mainly in the form of hematite (α-Fe2O3) and goethite (α-FeOOH). Mössbauer results showed that the amount of goethite increased as the particle size decreased. Furthermore, the hematite content was always greater in the coarser fractions (>10 μm). The phosphorus contents were high and associated with the presence of goethite in most samples. Scanning electron microscopy showed that the vast majority of the particles were not spherical and that the cyclosizer does not separate the material in the intended fractions efficiently. The particles obtained by wet sieving had much more uniform shape and size.