À empresa Mineração Rio do Norte (MRN), por possibilitar a realização deste estudo por meio do fornecimento das amostras e da execução de parte das análises químicas aqui apresentadas. À Profa. Dra. Lilia Mascarenhas Sant'Agostino, pela excelente orientação, dedicação e fundamental participação no desenvolvimento do projeto.
ResumoNesse trabalho, é apresentada a classificação de 110 amostras de minério de cobre da Mina do Sossego, com base nas técnicas de difração de raios X e análise estatística por agrupamento (cluster analysis). A comparação, baseada na posição e intensidade dos picos difratados, permitiu a distinção de sete tipos de minérios, cujas diferenças referem-se às proporções dos principais minerais constituintes: quartzo, feldspato, actinolita, óxidos de ferro, mica e clorita. Observou-se forte correlação entre os grupos com a localização das amostras nos corpos Sequeirinho e Sossego. Essa relação deve-se aos diferentes tipos e intensidades das alterações hidrotermais atuantes em cada corpo, que refletem na composição mineralógica e, consequentemente, nos difratogramas de raios X das amostras.
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This work focused on the acquisition of chemical and mineralogical detailed information in samples from Brazilian alkaline and alkaline-carbonatitic deposits containing rare earths, in order to provide subsidies for process development. These deposits present high volumes of resources, low contents of rare earth elements (essentially light rare earths) and high mineralogical complexity. The studied samples are lateritic materials, with a total content of rare earth oxides between 1.27 and 6.45%, being monazite the main rare earth bearing mineral, except in one of the samples, where bastnaesite is predominant; cerianite, xenotime and a scandium-phosphate occur as trace. Rare earth minerals tend to enrich toward the finest sieve fractions with an medium grain size of 15 μm in the fractions greater than 0.008 mm and decreasing below 0.1 μm in finer fractions. These minerals occur preferentially in intimate associations with the gangue; liberation greater than 60% (in area) are observed under 0.020 mm fractions. The concentration potential of these minerals was evaluated through physical separation and hydrometallurgical extraction. Physical separations (heavy liquid and magnetic) did not succeed in obtaining products enriched in rare earths. The most promising result were the possibility of removing magnetic phases above 0.020 mm (responsible for 30%, on average, of the total Fe2O3 contained in the samples) without significant losses of rare earths. The rare earths acid leaching protocols and conditions were established by statistical experimental design. For samples comminuted below 0.30 mm, the best rare earths solubilization (77%) and with minimum gangue leaching was obtained in concentrate sulfuric acid, low solids concentration, environmental temperature and four hours of reaction. Higher levels of rare earths solubilization can be achieved, however accompanied by higher gangue solubilization.
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