EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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16 resultados
Resultados da Pesquisa
Item Defining the hematite topotaxial crystal growth in magnetite–hematite phase transformation.(2020) Oliveira, Flavia Braga de; Silva, Gilberto Henrique Tavares Álvares da; Graça, Leonardo MartinsMagnetite and hematite iron oxides are minerals of great economic and scientific importance. The oxidation of magnetite to hematite is characterized as a topotaxial reaction in which the crystallographic orientations of the hematite crystals are determined by the orientation of the magnetite crystals. Thus, the transformation between these minerals is described by specific orientation relationships, called topotaxial relationships. This study presents electronbackscatter diffraction analyses conducted on natural octahedral crystals of magnetite partially transformed into hematite. Inverse pole figure maps and pole figures were used to establish the topotaxial relationships between these phases. Transformation matrices were also applied to Euler angles to assess the diffraction patterns obtained and confirm the identified relationships. A new orientation condition resulting from the magnetite–hematite transformation was characterized, defined by the parallelism between the octahedral planes {111} of magnetite and rhombohedral planes f1011 g of hematite. Moreover, there was a coincidence between one of the octahedral planes of magnetite and the basal {0001} plane of hematite, and between dodecahedral planes {110} of magnetite and prismatic planes f1120 g of hematite. All these three orientation conditions are necessary and define a growth model for hematite crystals from a magnetite crystal. A new topotaxial relationship is also proposed: (111)Mag || (0001)Hem and ð111 ÞMag || ð1011 ÞHem.Item Ore-waste and ore type classification using portable XRF : a case study of an iron mine from the Quadrilátero Ferrífero, Brazil.(2020) Urbano, Emílio Evo Magro Corrêa; Costa, João Felipe Coimbra Leite; Graça, Leonardo Martins; Cipriano, Ricardo Augusto ScholzGrade control is a fundamental activity for Short-Term Mine Planning as it validates the ore-waste and ore type classification of mine faces. Geological mapping and quasi-mining sampling provide indispensable information for the Short-Term Mine Planning team to update block models and for grade control of the run-of-mine (ROM). However, laboratory turnaround can take too long and not be timely for operational needs, affecting mining efficiency. To propose a solution for this issue we tested the accuracy of portable X-Ray Fluorescence (XRF) for ore-waste and ore type classification according to iron and phosphorus grade. Thus, iron ore run-of-mine samples from the Quadrilátero Ferrífero were analyzed with the portable XRF as pressed pellets. As a result, the overall accuracy of ore-waste classification was above 92% for different cut-off grades. On the other hand, while ore type classification had a better accuracy without calibration factors for iron, the use of calibration factors significantly improved the accuracy of ore type classification for phosphorus. Therefore, despite the portable XRF presenting good accuracy for ore-waste and ore type classification, further developments are still necessary on automatic information processing systems and sample support validation so that this analytical tool can be used on a large scale by grade control teams. Finally, the combined use of portable XRF and other techniques, such as Hyperspectral Sensing or XRD, can be of great value for mine operations.Item Polycrystals of “imperial” topaz from Minas Gerais state, Brazil.(2019) Araújo, Teodoro Gauzzi Rodrigues de; Silva, Gilberto Henrique Tavares Álvares da; Diniz, Rafael Silva; Graça, Leonardo Martins“Imperial” topaz is a gemstone variety that occurs in the Ouro Preto region (Minas Gerais state, Brazil). Polygonal sectors within the core and rims of topaz crystals, were optically observed but without consensual explanations about them. With the aid of optical microscopy, scanning electron microscopy-cathodoluminescence (SEM-CL), backscattered electrons (BSE) imaging, electron probe micro-analyser (EPMA) chemical analyses and electron backscatter diffraction (EBSD) maps, the present study intended to demonstrate the distinct crystallographic orientations within “imperial” topaz and relate the polygonal sectors with the compositional data. Cross-polarised transmitted-light photomicrographs show a well delimited and optically heterogeneous central rhombic area at (21 l) in the cores, and quadrant-like and alternated extinction areas at (200, (010) and (110) in the rims. Scanning electron microscopy-cathodoluminescence images show a central rhombic area heterogeneously luminescent in the core, and dark and homogeneous rims. Grey and completely homogeneous BSE images and EPMA results corroborate constant and homogeneous major composition of “imperial” topaz. Electron backscatter diffraction maps collected in the rim region show different areas and microstructural features instead of a uniform microstructure. The respective pole figures of orthorhombic system yielded multiple (001) poles disoriented in higher than 15° from each other. These results display numerous c-axes, suggesting distinct crystallographic orientations, and no reduction in the orthorhombic symmetry. Therefore, the presumed monocrystal of “imperial” topaz actually is a polycrystal.Item A cathodoluminescence-assisted LA‑ICP‑MS study of topaz from different geological settings.(2018) Araújo, Teodoro Gauzzi Rodrigues de; Graça, Leonardo MartinsIn this study, the crystallization dynamics and the fingerprints of two topaz crystals from the Ouro Preto region (Brazil), two from the Eastern Brazilian Pegmatite Province (EBPP), one from the Western part of the United States (US) and one from Pakistan were characterized. The combination of scanning electron microscope-cathodoluminescence (SEM-CL) and laser ablation inductively coupled plasma mass spectrometry (LA‑ICP‑MS) data allowed for the characterization of these samples. Samples from the Ouro Preto region showed primary crystallization and recrystallization processes, which were demonstrated by a CL-heterogeneous core and CL-homogeneous rims in the SEM-CL images. Their fingerprint was composed of Ca, Ti, V, Cr, Mn, Fe, Cu and Zn. Samples from the EBPP showed both dark and CL-homogeneous SEM-CL images, implying slow and late-stage crystallization, typical of pegmatites. Their fingerprints were composed of Li, Nb, LREE, Ta and W, and of Ti, Nb and HREE. A sample from a Western part of the US displayed CL-heterogeneity with growth and resorption events and well-preserved growth zones, which were noticeable through the SEM-CL images. Its fingerprint was composed of Li, Ti, V, Mn, Nb, LREE, Ta and W. A sample from Pakistan showed an evident metamorphic recrystallization process, which was visible by the incipient and CL-homogeneous luminescence given by the SEM-CL images. Its fingerprint was composed of Ca, Cr, V, Zn, LREE, HREE and W.Item Toward the influence of iron oxide morphology on the grinding and filtration processes and on the cold crushing strength (CCS) of heat-treated iron ore pellets.(2020) Graça, Leonardo Martins; Silva, Gilberto Henrique Tavares Álvares da; Machado, Marcos Meyer; Silva, Josué Bortolini Sette da; Ávila, Carlos Fernando; Cipriano, Ricardo Augusto Scholz; Lagoeiro, Leonardo EvangelistaThe present study demonstrates the effect of the different morphological types on the cold crushing strength (CCS) of heat-treated iron ore pellets. Blends with different iron ore oxides morphologies were subjected to grinding, filtering and pot grate tests on industrial scale trials. Results of grinding tests showed the hematite-goethite aggregates the most influent one on energy consumption. The martitichematite content was straightly related to the final moisture and filtration productivity. The hematitegoethite aggregates, therefore the goethite content, influences CCS, being the lower the goethite content, the higher the values of CCS.Item The fingerprint of imperial topaz from Ouro Preto region (Minas Gerais state, Brazil) based on cathodoluminescence properties and composition(2017) Araújo, Teodoro Gauzzi Rodrigues de; Graça, Leonardo Martins; Lagoeiro, Leonardo Evangelista; Mendes, Isolda Maria de Castro; Queiroga, Gláucia NascimentoA study of the cathodoluminescence (CL) properties of imperial topaz from Ouro Preto region (Minas Gerais state, Brazil) and its relation with trace-element composition was conducted, using scanning electron microscope cathodoluminescence (SEM-CL), optical microscope cathodoluminescence (OM-CL), cathodoluminescence-spectrometry (CL-spectrometry), electron microprobe analysis (EMPA), laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) and Raman spectrometry. Each analytical technique allowed characterization of the imperial topaz fingerprint. SEM-CL panchromatic images show different crystal growth and resorption events in imperial topaz crystals. Colour CL images indicate only blue to violet emissions. The CL-spectra indicate a broad emission band with low intensity peak at ∼417 nm and a broad emission band with high intensity and major peaks at 685, 698, 711 and 733 nm. The EMPA indicates high OH content, in which the OH/(OH + F) ratio ranges between 0.35–0.43 (0.72 ≤ OH ≤ 0.86 apfu). High Cu and Zn concentrations (LA-ICP-MS) were measured in the high luminescence areas of SEM-CL images, suggesting both elements as CL-activators in imperial topaz. Raman and CL-spectra indicate high Cr concentrations, corroborated by EMPA and LA-ICP-MS results. The high Cr caused strong luminescence intensities that enabled their superimposition over the OH stretching mode (∼3650 cm–1) of topaz in all Raman spectra. Among trace elements, the concentrations of Ti, V, Cr, Mn, Fe, Cu, Zn, Ga and Ge provide the fingerprint of imperial topaz.Item Magnetite-hematite transformation : correlation between natural and synthetic features.(2014) Barbosa, Paola Ferreira; Lagoeiro, Leonardo Evangelista; Cipriano, Ricardo Augusto Scholz; Graça, Leonardo Martins; Mohallem, Nelcy Della SantinaThe iron-oxide system can be used as a marker of oxidized and reduced conditions in closed systems. However, natural rocks with iron oxide minerals also exhibit such reactions, although the natural system is typically open. To understand the behaviour of this natural system, some similarities were investigated, in terms of crystallographic textures, between the microstructures of two systems: natural open system and synthetic closed system of iron oxide phase transformation. Particular cases of phase transformation in iron oxide minerals, described as natural reactions of magnetite to hematite and synthetic reactions of hematite to magnetite, were chosen. It is observed, in both scenarios, that the transformation obeys the topotaxial and epitaxial relationship, which are well described for the iron oxide system. However, in natural open systems, the precipitation of a new phase during the in situ transformation modifies the microstructures and must be taken into account as an important factor to describe them.Item Electron Backscattering Diffraction (EBSD) as a tool to evaluate the topotactic and epitactic growth of minerals : the example of the magnetite and hematite.(2011) Barbosa, Paola Ferreira; Lagoeiro, Leonardo Evangelista; Cipriano, Ricardo Augusto Scholz; Graça, Leonardo Martins; Silva, Gilberto Henrique Tavares Álvares daItem Bench-scale calcination and sintering of a goethite iron ore sample.(2016) Silva, Mônica Suede Santos; Lima, Margarida Márcia Fernandes; Graça, Leonardo Martins; Lima, Rosa Malena FernandesThis work presents the results of bench calcination and sintering studies conducted on an iron ore sample from Iron Quadrangle, Brazil with high goethite content. The natural samples and the products of calcination and sinteringwere characterised by inductively coupled plasma optical emission spectroscopy (OES/ICP), X-ray spectrometry and gravimetric methods. Optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) were used to identify the phases in the studied samples. Density, specific surface area, specific pore volume and pore diameter were determined through gas pycnometry. All of the natural sinter feed samples had a Fe grade N64% and a very high phosphorus grade (~0.17%). After calcination, a 3.1–3.4% increase was observed in the Fe grade compared to that of the natural sinter feed samples. The average Fe grade of the sintered samples was 59.1%. The identified phases with XRD in the raw materials were hematite and goethite. In the calcined samples, only hematite was identified because of the thermal decomposition of goethite. The density, specific surface area, specific pore volume and pore diameter of the calcined samples increased compared to those of the natural sinter feed samples. Hematite, brownmillerite, anorthite, and gehlenite were identified in the sintered samples. The sites for phosphorus occurrence were calcium silicates and apatite. The sintered samples exhibited specific surface areas lower than those of the calcined samples. This result was ascribed to the destruction of the pore structure by the sintering process.No relationship between the proportions of nucleate, intermediate and agglomerate particles used inmixture of sinter testswith the results of microtumbler was identified.Item Effects of hematite surface characteristics on filtration process.(2016) Graça, Leonardo Martins; Lagoeiro, Leonardo Evangelista; Galery, Roberto; Peres, Antônio Eduardo ClarkIn iron ore pelletizing plants a range of process parameters such as particle size distribution, specific surface area, and moisture, must be controlled to achieve opti¬mized operation conditions. Particle size distribution and specific surface area are con¬trolled during the grinding operations. Moisture, however, is controlled during filtra¬tion of the ground products. This work investigates the relationship between particle morphology, filter cake moisture and filter capacity. The samples were taken during the filtration tests and referred to three different blends presenting distinct mineralogical features and similar chemical compositions in order to investigate the effects of only the hematite surface characteristics. Six types of morphology are distinguished: granu¬lar hematite, tabular hematite, martitic hematite, polycrystalline hematite, hematite-goethite aggregates and goethite. For each filtration test, the filter cloth product was characterised. The characterisation analysis revealed that blends containing martitic hematite concentration above 11.45 percent increased substantially the filter capacity. However, it had also caused an increasing in final moisture content that reached values around 10.0 % compared with industrial moisture specification that can vary on the range of 8.5 to 9.5 %.