Caracterização microestrutural e mineralógica de minérios de ferro itabiríticos com graus diferentes de complexidade

• Ano de defesa: 2014
• Autor(a) principal: Ana Claudia Carioca
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Engenharia metalúrgica e de minas; Tecnologia mineral; Engenharia de minas; Minérios de ferro; Hematita; Quartzo
• Link de acesso: http://hdl.handle.net/1843/BUOS-B3DFZA

Mineral characterization is a broad and important topic in the academic context, because there are still gaps in the composition and/or microstructure of the ores found. Due to the complexity of existing itabirite ores in the Ferriferous Quadrangle region, microstructure characterization studies have been required for better utilization of the ores. One of the main tools for microstructure study of ores has been the scanning electron microscope (SEM) with a coupled X-ray energy-dispersive spectrometer (EDS). Recently, software and automation systems have been developed using SEM and EDS analysis for identification and quantification, as well as for research and microstructure analysis of the degree of liberation of minerals in an ore of interest. One such system is the MLA (Mineral Liberation Analyzer). Combinations of analytical and mineralogical techniques such as chemical analysis, optical microscopy, automated microscopy (SEM/EDS/MLA), spectroscopy methods (FTIR, Mössbauer) and X-ray diffraction are used to identify and quantify the minerals present in the ore of interest and its size fractions and their microstructures. This work evaluates iron ores with agrowing degree of microstructure complexity, using these techniques, with emphasis on computerized microscopy. Samples showed the complex mineralogical composition from simple to complex, such as itabirites containing quartz and hematite as major minerals andthe coexistence of goethite, gibbsite and magnetite in some samples, at low concentrations; these results were consistent for the techniques used. The MLA system consists of several programs, where one acquires the data (MLA Measurements),a second analyzes the generated images (MLA DataView) and a third processes the data generated (MLA Processing). Of all the results provided by the system, the greatest interest is in the study of mineral liberation, because it aims at the efficiency of the ore beneficiation process. This aspect is analyzed by means of mineral associations, locking, liberation by composition and by free surface. Comparing all analyzes, in most of the samples and their particle sizes studied, quartz was already practically liberated. Some notable advantages of the MLA are: to analyze up to fourteen samples (polished sections) in a batch, which allows studying thousands of particles, a very high statistical significance. There are various means of data acquisition (XBSE, GXMAP, XMOD), excellent image quality, the use of significant magnifications, and a great number of mineral data in its portfolio. However, there are some disadvantages such as time-consuming analysis for data acquisition, lasting up to several hours, as well as for data processing, and the difficulty of analyzing minerals with similar chemical composition, even when grayscale image levels are close but distinct, e.g. hematite (Fe2O3) and magnetite (Fe3O4). For quantification of magnetite in this study, a specific technique for Fe, Mössbauer spectroscopy was used, which identified, with in its detection limit, magnetite only in one sample (APV3). The results obtained by the MLA technique for the samples analysed have emphasized the validity of the method for studies of mineralogical characterization, by means of minerals associations, liberation by composition and free surface and modal analysis. It also allows the study of each particle and each grain that make up the sample. Therefore, it is possible to focus on interesting mineralogical aspects of particles and on the study of fabrics, textures and structural aspects of them