- Brazil
Magela da Costa
Universidade Federal de Ouro Preto, Departamente de Química, Faculty Member
ABSTRACTParisite-(La) (IMA2016-031), ideally CaLa2(CO3)3F2, occurs in a hydrothermal vein crosscutting a metarhyolite of the Rio dos Remédios Group, at the Mula mine, Tapera village, Novo Horizonte county, Bahia, Brazil, associated with... more
ABSTRACTParisite-(La) (IMA2016-031), ideally CaLa2(CO3)3F2, occurs in a hydrothermal vein crosscutting a metarhyolite of the Rio dos Remédios Group, at the Mula mine, Tapera village, Novo Horizonte county, Bahia, Brazil, associated with hematite, rutile, almeidaite, fluocerite-(Ce), brockite, monazite-(La), rhabdophane-(La) and bastnäsite-(La). Parisite-(La) occurs as residual nuclei (up to 5 mm) in steep doubly-terminated pseudo-hexagonal pyramidal crystals (up to 8.2 cm). Parisite-(La) is transparent, yellow-green to white, with a white streak and displays a vitreous (when yellow-green) to dull (when white) lustre. Cleavage is distinct on pseudo-{001}; fracture is laminated, conchoidal, or uneven. The Mohs hardness is 4 to 5, and it is brittle. Calculated density is 4.273 g cm−3. Parisite-(La) is pseudo-uniaxial (+), ω = 1.670(2) and ε = 1.782(5) (589 nm). The empirical formula normalized on the basis of 11 (O + F) atoms per formula unit (apfu) is Ca0.98(La0.83Nd0.51Ce0.37Pr0.16Sm...
Research Interests:
Research Interests: Geology and Soil sciences
Research Interests:
Research Interests:
This paper presents a characterization study of ultra-fine solid particles contained in slimes of some iron mines from the Iron Quadrangle, Minas Gerais State, and from the Carajás region, Pará State, Brazil. This characterization is... more
This paper presents a characterization study of ultra-fine solid particles contained in slimes of some iron mines from the Iron Quadrangle, Minas Gerais State, and from the Carajás region, Pará State, Brazil. This characterization is expected to provide a basis for the development and choice of mineral-processing techniques suitable for the tailings characteristics of each mine. Particle size separation was
Research Interests:
Quick Search: All GSW Journals, GSW + GeoRef. advanced search. ...
Research Interests: Geology and Geochemistry
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Microesferas poliméricas à base de metacrilato de metila (MMA), divinilbenzeno (DVB) e material magnético foram preparadas via polimerização por suspensão. Foi estudada a influência da polimerização em suspensão ou semisuspensão,... more
Microesferas poliméricas à base de metacrilato de metila (MMA), divinilbenzeno (DVB) e material magnético foram preparadas via polimerização por suspensão. Foi estudada a influência da polimerização em suspensão ou semisuspensão, concentração de material magnético e concentração de divinilbenzeno sobre as características das microesferas obtidas. As partículas poliméricas foram caracterizadas por espectroscopia vibracional na região do infravermelho por transformada de Fourier (FT-IR), microscopia eletrônica de varredura, analisador de área específica e porosimetria, espalhamento de luz e magnetometria de amostra vibrante. O material magnético também foi caracterizado por FT-IR, além de difratometria de raios X e espectroscopia Mössbauer. Foram obtidas, com sucesso, microesferas poliméricas magnéticas à base de MMA e DVB (P(MMA-co-DVB)-M), contendo partículas magnéticas tanto na superfície quanto no interior da microesfera. As partículas obtidas através de polimerização em semisuspe...
Research Interests:
Research Interests:
Research Interests:
Mulita é o único composto termodinamicamente estável no sistema binário Al2O3 - SiO2, na faixa 70,5 a 74,0% em peso de Al2O3. Mulita metaestável na faixa de 74 a 83,6% de Al2O3, entretanto, pode ser obtida. Devido às suas excelentes... more
Mulita é o único composto termodinamicamente estável no sistema binário Al2O3 - SiO2, na faixa 70,5 a 74,0% em peso de Al2O3. Mulita metaestável na faixa de 74 a 83,6% de Al2O3, entretanto, pode ser obtida. Devido às suas excelentes propriedades físicas e mecânicas a altas temperaturas, como alto ponto de fusão, baixa expansão térmica, boa resistência à fratura e ao choque térmico, alta resistência à fluência, estabilidade térmica, baixa densidade e baixa constante dielétrica, tem tido um uso cada vez maior em corpos cerâmicos. O mineral mulita, porém, é raro e quase inexistente na natureza. Para atender a um mercado crescente, mulitas sintéticas são produzidas, por meio de misturas de pós de Al2O3 e SiO2 em escala molecular, usando técnica sol-gel, ou por meio da calcinação de minerais que contenham sílica e alumina em suas estruturas, os chamados alumino-silicatos. Normalmente estes minerais contêm impurezas e, muitas vezes, produzem uma mulita acompanhada de uma fase vítrea. Nest...
Research Interests:
Research Interests:
ABSTRACT Although bauxites usually have a quite simple mineralogy – gibbsite (+boehmite), quartz, kaolinite, hematite, goethite, anatase (+rutile) and minor or less common phases, fine particle size, low crystallinity and variable... more
ABSTRACT Although bauxites usually have a quite simple mineralogy – gibbsite (+boehmite), quartz, kaolinite, hematite, goethite, anatase (+rutile) and minor or less common phases, fine particle size, low crystallinity and variable compositions of the iron minerals might render phase quantification difficult, as well as impairing bauxite processing. A reliable and complete characterisation is therefore necessary in order to predict processing performance and ensure compliance to plant specifications. X-ray diffraction is the most important single tool for bauxite characterisation, and the constrained refinement of the Al-for-Fe substitution in goethite during one-step phase quantification by fundamental parameters Rietveld method has been successfully used. The same method was developed to analyse the coupled Al-for-Fe and OH−-for-O2− substitutions in hematite. The method was tested against Mössbauer spectroscopy iron distribution on bauxite samples with a large compositional range, and on bauxite Certified Reference Materials from the main Brazilian mines, with improved results and widened range of conclusions that can be drawn related to bauxite processing.
Research Interests:
A quantificação de boehmita em bauxita é de fundamental importância para a determinação da temperatura de digestão no processo Bayer, mas não existe, na literatura, nenhum método rápido e confiável, para se realizar essa determinação.... more
A quantificação de boehmita em bauxita é de fundamental importância para a determinação da temperatura de digestão no processo Bayer, mas não existe, na literatura, nenhum método rápido e confiável, para se realizar essa determinação. Portanto, nesse trabalho, utilizou-se a difração de raios X, para se realizar a quantificação de boehmita, gibbsita, hematita e goethita em bauxita. Uma amostra de bauxita, oriunda de Gana e contendo 45% de gibbsita e 43% de boehmita, foi submetida a uma lixiviação cáustica a 160ºC, para a remoção da gibbsita. O resíduo da lixiviação, completamente isento de gibbsita, foi tratado com o sistema ditionito-citrato-bicarbonato, para a remoção dos oxi-hidróxidos de ferro, resultando em uma amostra contendo cerca de 85%-89% de boehmita e 9% de TiO2. Curvas de calibração correlacionando as intensidades dos picos de difração com os teores das fases mineralógicas foram obtidas, para padrões preparados pela mistura de quantidades conhecidas de gibbsita, hematita...
Research Interests:
Algumas formas de aproveitamento econômico do topázio incolor e, às vezes, do topázio imperial requerem o uso de tratamento térmico à alta temperatura. Nesse trabalho, revemos o comportamento térmico do topázio à alta temperatura. São... more
Algumas formas de aproveitamento econômico do topázio incolor e, às vezes, do topázio imperial requerem o uso de tratamento térmico à alta temperatura. Nesse trabalho, revemos o comportamento térmico do topázio à alta temperatura. São mostrados os efeitos da temperatura sobre a composição química, estrutura e propriedades ópticas, assim como as condições nas quais o topázio transforma-se em outro material denominado de mulita.
Three different magnetic samples with particle sizes ranging from 10 to 30 nm were prepared by wet chemical methods. The powders were heated at 100, 150, 200, and 250 °C during 30 min under air. Ferrous and total iron contents were... more
Three different magnetic samples with particle sizes ranging from 10 to 30 nm were prepared by wet chemical methods. The powders were heated at 100, 150, 200, and 250 °C during 30 min under air. Ferrous and total iron contents were determined immediately after the synthesis and after the thermal treatments. All samples were characterized by X-ray diffraction, transmission and integral low-energy electron Mössbauer spectroscopy (ILEEMS) at 298 K. These samples are composed of a mixture of individual particles of maghemite and magnetite, which implies that once oxidation starts in this kind of material, it occurs throughout the entire particle volume. The existence of a maghemite/magnetite core-shell model was ruled out. A linear correlation between the average isomer shift and the magnetite content was found, allowing the estimation of the amounts of magnetite and maghemite in an unknown sample without the need of performing chemical analysis.
Research Interests:
Research Interests:
The quantification of goethite, magnetite, martite and specularite in iron ores was successfully achieved by a combination of wet chemical analysis and x-ray diffraction. It was found that the intensity of the goethite (111) peak is... more
The quantification of goethite, magnetite, martite and specularite in iron ores was successfully achieved by a combination of wet chemical analysis and x-ray diffraction. It was found that the intensity of the goethite (111) peak is constant for a certain sample provided that the same sample holder is used. Calibration curves with a linear behavior have been derived using the areas of the above mentioned peak and the amounts of goethite obtained by Mössbauer spectroscopy and optical microscopy. In addition, the integral width of the hematite (012) line broadens linearly as the amount of martite increases, thus allowing an estimation of the amounts of martite and specularite.
Research Interests: Iron and Phase Analysis
Research Interests:
... Identification and Characterization of Maghemite in Ceramic Artifacts and Archaeological Black Earth of ... These artifacts may be important tools to understand the ancient people from ... ceramicartifacts, emphasizing the... more
... Identification and Characterization of Maghemite in Ceramic Artifacts and Archaeological Black Earth of ... These artifacts may be important tools to understand the ancient people from ... ceramicartifacts, emphasizing the relationship between the minerals, mainly iron oxides, found ...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Chemical Engineering, Principal Component Analysis, Minerals, Minerals Engineering, Quality Control, and 10 moreMinas Gerais, Magnetic Susceptibility, Iron, Chemical Analysis, Diffuse reflectance, X ray diffraction, Reflectance, Diffuse Reflectance Spectroscopy, Principal Component Regression, and Selective Sampling
This paper presents a characterization study of ultra-fine solid particles contained in slimes of some iron mines from the Iron Quadrangle, Minas Gerais State, and from the Carajás region, Pará State, Brazil. This characterization is... more
This paper presents a characterization study of ultra-fine solid particles contained in slimes of some iron mines from the Iron Quadrangle, Minas Gerais State, and from the Carajás region, Pará State, Brazil. This characterization is expected to provide a basis for the development and choice of mineral-processing techniques suitable for the tailings characteristics of each mine. Particle size separation was
Research Interests:
A lateritic nickel ore (-3.36 mm fraction) and a fraction obtained from the cyclosizer overflow (-8 µm fraction) were investigated with the aim to identify the nickel-bearing phases. Both samples were subjected to selective leaching with... more
A lateritic nickel ore (-3.36 mm fraction) and a fraction obtained from the cyclosizer overflow (-8 µm fraction) were investigated with the aim to identify the nickel-bearing phases. Both samples were subjected to selective leaching with hydrogen peroxide, ammonium oxalate and finally with the dithionite-citrate-bicarbonate system. Dissolution in warm concentrated HCl was also performed. Mössbauer spectroscopy, X-ray diffraction and chemical analysis were