Definição da tipologia e caracterização mineralógica e microestrutural dos itabiritos anfibolíticos das Minas de Alegria da Samarco Mineração S.A. - Minas Gerais

Abstract

The world iron ore production boomed by an expanding steel market forced the producers to seek for larger reserves achieved only through the better understanding of their mineral resources. This is possible through a detailed characterization of the natural resource and of the ores to be exploited. In this study it was performed a detailed mineralogical characterization of the Alegrias mines amphibolitic itabiriteswhich represents 36% of the total resources and more than 20% of Samarcos reserves and are mined either as ore and waste. The first purpose of this study was to identify different types of amphibolitic itabirites based on their chemical and mineralogical characteristics as well as on their performance through laboratory tests that simulate Samarcos production processes. The second purpose was to have amore detailed chemical and mineralogical characterization of the several aliquots coming from the products of the laboratory simulating processes tests. It was identified in Alegrias Mines five visual different amphibolitic itabirites and from each one it was taken 400kg to compose the samples. The samples were submitted to size and chemical analysis, x-Ray diffratometry, infrared spectrometry, thermogravimetry, opticaland scanning electron microscopy, microprobe, grinding, desliming and flotation laboratory tests. The products of these laboratory processes tests were also analyzed. More five tons of each sample was taken in order to produce concentrates to generate pellets to be tested in Pot Grate furnace. The five amphibolitic itabirites are not compact and potentially ore. Their iron content are typical of the poor itabirites (<50%), the LOIs are considered high tenures (>3%), the Al2O3, as well as MnO2 and FeO contents are within the typical values presented by the Alegrias ores. The main iron ore minerals are goethite (botryoidal, massive,pseudomorphs of amphibole, product of the alteration of the magnetite and earthy) and the porous martitic hematite. The iron ore minerals alteration and porosity grades are elevated and the size of their particles variable (from few micrometers to millimeters). The goethites loss their hydroxyl content in an abrupt way and around 315°C. The slimes percentages of these itabirites are high and by their weight and metallic global recoveries numbers they can be classified as potential ores. Simple modifications on the ignition Pot Grate furnace parameters leaded to improvements and to pellets within the required specifications. The five amphibolitic itabirites are suitable to be divided into four different types. The mineralogical association of amphiboles, iron oxides, quartz and carbonates present on the fresh amphibolitic itabirites recently found in Alegrias mines reinforce their origin to be the iron ore formations of the silicate or oxide-silicate facies associated with carbonates impurities or layers.