Morphological varieties of goethite in iron ores from Minas Gerais, Brazil

It is important to know the mineralogical and microstructural characteristics of iron ores and to determine the relationships between their observed characteristics and their behaviour during ore processing and in final concentrates properties. Therefore, mineralogical and microstructural characterisation was accomplished on typologies of iron ore from the Alegria Mine, Minas Gerais State, Brazil. The characterisation studies carried out on samples showed extensive occurrence of goethite with morphologic, textural and compositional variations: botryoidal, microporous, earthy varieties and goethite forming fine intergrowths with martitic hematite were observed. The earthy varieties (earthy-like goethite) occur as crusts, surrounding particles and grains, filling cavities and larger cracks inside or between hematite grains (intergranular goethite) and filling micropores and interstices in martitic hematite (intragranular goethite). Botryoidal goethite also occurs involving grains or particles. Earthy-like goethite is made up of a very fine material, having high iron content and variable Al2O3 and SiO2 contents. In the samples studied goethite is an aluminium-bearing phase and occurs in a great extension. It also contributes to increasing the amount of fine material in the final concentrate. Both aspects can cause problems in the production of pellets.