Mineralogical characterization of itabiritic iron ores mainly by Mineral Liberation Analyser (MLA)

Due to the complexity of itabirite ores, their characterization is required, with emphasis on microstructure. Widely used is the scanning electron microscope (SEM) with the chemical energy-dispersive microanalyzer (EDS). An efficient computerized analytical system is MLA (Mineral Liberation Analyzer) which uses backscattered electrons images (BSE) and X-ray spectra (EDS) to identify the minerals in polished sections of ore particles. Thus, microstructural composition maps are generated, with very important information such as liberation, mineral associations and modal analysis. There is excellent statistical significance because several thousand particles are analyzed. Four samples of iron ores from the Iron Quadrangle, Minas Gerais, with different degrees of microstructural complexity have been studied. The particle sizes (-0.500 +0.300 mm and -0.300 +0.212 mm) were analyzed by X-ray diffraction, Mössbauer spectroscopy and MLA. By the instrumental methods, abundant minerals were quartz and hematite, obviously; also identified were goethite, and minor gibbsite and magnetite. In general, these data were consistent with MLA's. Some minor inconsistences between the global chemical analyses and the quantitative microstructure data are due to the different localized analytical sampling and the degree of homogenization. Quartz liberation was above 90% in three samples; the exception was the APV4 sample with only 60% quartz liberation, where quartz is associated with hematite (mainly) and goethite. (author)