Química, micromorfologia e refinamento por Rietveld das fases minerais da Argila de Belterra em Rondon do Pará

Bauxite deposits in the Amazon region are commonly covered by yellowish or reddish clays that can reach up to 25m thick, known as Belterra Clay (BC), term attributed after Sombroek in 1966 describe similar clays, but not related to bauxites in the region of Belterra, Lower Amazon. In Rondon do Pará, the BC has between 10 and 13 m thick, covering world-class bauxite reserves. Representative samples of BC from three pilot bauxite mines (Branco, Décio and Ciríaco) in Rondon do Pará were studied. The BC covers laterite-bauxite regoliths with well-defined horizons. From the basis to the top, they are composed of: bauxite clay, followed by massive bauxite, massive iron-aluminous crust, dismantled iron-aluminous crust, ferruginous spherolites, and a horizon with bauxite nodules in a clayey matrix. In discordant contact with the lateritic profile, the BC has reddish brown colors at the base, with yellowish tones towards the top. It has a homogeneous appearance with no visible sedimentary structures, silt-clayey aspect and with fragments of porcelain bauxite (popcorn like) at its base. The mineral composition of the material is dominated by kaolinite, with Al-goethite, gibbsite, hematite, anatase and residual quartz. The SiO2/Al2O3 ratio of about 1.050 is lower than the theoretical kaolinite (1.178), confirming the existence of gibbsite and even Algoethite as aluminum carrier. As observed by X-ray diffraction analysis, kaolinite is of low structural order, evidenced by the low distinction of the diffraction bands at the 19-22° 2ϴ (Cu anode) region and because this mineral has no satisfactory correlation with any structural model of kaolinite, which was considered the principal difficulty in the application of the Rietveld method. Al-goethite has about 32 mol% of Al and is responsible for the ocher / yellowish color of the BC. This mineral associated with hematite and amorphous iron hydroxide (up to 0.5% Fe) is responsible for up to 13% of Fe2O3 contents. Quartz rarely exceeds 1% as fragments in the clayey matrix. Anatase has concentrations between 2.4 and 2.8%. As observed by SEM, with the exception of quartz, the minerals represent pseudohexagonal crystals measuring from 150 to 700 nm. The thermal behavior of the material confirms its mineralogical composition. Its mineral quantification by thermogravimetric analyzes is in accordance with the Rietveld method and stoichiometric (FRX) results, despite a precise correlation between these methods was unfeasible.CNPq - Conselho Nacional de Desenvolvimento Científico e TecnológicoDepósitos de bauxitas na região amazônica são comumente cobertos por argilas de coloração amarelada ou avermelhada que podem chegar a 25 m de espessura, denominadas de Argila de Belterra (ABT), termo atribuído a esse material após Sombroek em 1966 descrever argilas similares, porém sem relação com as bauxitas, na região de Belterra, Baixo Amazonas. Em Rondon do Pará, as ABTs possuem entre 10 e 13 m de espessura e cobrem reservas de bauxita de classe mundial. Amostras representativas da ABT de três lavras piloto de bauxita (Branco, Décio e Ciríaco), foram estudadas. A ABT sotopõe perfis laterítico-bauxíticos que consistem em horizontes bem definidos, da base para o topo compostos por: argila bauxítica, seguida por bauxita maciça, crosta ferroaluminosa maciça, crosta ferroaluminosa desmantelada, esferólitos ferruginosos e um horizonte com nódulos bauxíticos tipo popcorn envoltos por matriz argilosa. Em contato discordante e ondulado com o perfil laterítico sotoposto, a ABT é marrom avermelhada na base indo a tons amarelados em direção ao topo, apresenta aspecto homogêneo sem estruturas sedimentares visíveis, silte-argilosa e com fragmentos de bauxita porcelanada (tipo popcorn) em sua base. A composição mineral do material é dominada por caulinita, com Al-goethita, gibbsita, hematita, anatásio e quartzo residual. A razão SiO2/Al2O3 em torno de 1,05 é menor que a teórica de caulinita (1,178), confirmando a existência de gibbsita e ainda Al-goethita. Conforme observado por DRX a caulinita é de baixa ordem estrutural, evidenciado pela baixa distinção do triple localizado na região 19-22° 2ϴ (ânodo de Cu) e por esse mineral não ter correlação satisfatória com nenhum modelo estrutural ICSD de caulinita, o que foi considerado a principal dificuldade de aplicação do método de Rietveld. A Al-goethita possui cerca de 32% mol de Al e é responsável pela tonalidade ocre/amarelada da ABT. Esse mineral associado à hematita e a hidróxido de Fe amorfo (até 0,5% de Fe) é responsável por teores de Fe2O3 de até 13%. Quartzo raramente excede 1% e consiste em fragmentos em meio a matriz argilosa. Anatásio se apresenta em teores entre 2,4 e 2,8%. Conforme observado sob MEV, excetuando-se o quartzo, os minerais constituem cristais pseudo-hexagonais medindo entre 150 e 700 nm. O comportamento térmico do material confirma sua composição mineralógica e, a quantificação mineral a partir de análises termogravimétricas, está de acordo com as obtidas pelo método de Rietveld e por estequiometria (FRX), embora uma correlação precisa entre os métodos seja ainda inviável

Production of CO2-reduced Eco-cements using bauxite-mining overburden Belterra Clay and bauxite washing residue from Brazilian Amazon

Zemente auf Kalziumsulfoaluminatbasis (CSA) wurden als Alternative zur Verringerung der CO2-Emissionen im Zementsektor genannt. In dieser Arbeit wurden Bauxitabbaurückstände für die Herstellung von CSA getestet. Diese Rückstände sind Belterra-Tone, welche die Bauxite im Amazonasgebiet bedecken, und Tone aus der Aufbereitung der Bauxitwäsche. Die Rohmehle, die aus Kalzit, Gips und Tonen bestehen, wurden mit Hilfe von Versuchsplanung und Stöchiometrie modelliert. Bis zu 38% der Tone konnten durch brennen bei 1250 °C verwertet werden. Die Klinker enthielten bis zu 45% Ye'elimit und große Mengen Belit, außerdem Brownmillerit und Fe-Perowskit. Im Vergleich zu Portlandzementen (PZ) wurde beim Klinkerprozess mindestens 30% weniger CO2 ausgestoßen. Die Haupthydrate waren Ettringit und Monosulfoaluminat. Die hergestellten Mörtel entwickelten eine ähnliche oder sogar höhere Druckfestigkeit als PZ. Beide Tonabfälle sind für die Herstellung von Ökozementen auf CSA-Basis geeignet.Calcium sulfoaluminate based cements (CSA) have been quoted as an alternative to reduce CO2 emissions from the cement sector. In this work, residues of bauxite mining were tested as alumina source to produce CSA. These residues are the Belterra Clays that cover the bauxites in the Amazon and the clay from the bauxite washing beneficiation. Raw meals composed of calcite, gypsum and the clays were modelled using design of experiments and stoichiometry. Up to 38% of the clays could be used by clinkering at 1250°C. The clinkers had up to 45% of ye'elimite and high amounts of belite, besides brownmillerite and Fe-perovskite forming a discontinuous solid solution. At least 30% less CO2 was generated in the clinkering process compared to ordinary Portland cements (OPC). The main hydrates were ettringite and monosulfoaluminate. The produced mortars developed similar and higher compressive strength than an OPC. Both clay residues are suitable to produce CSA-based eco-cements

Mineralogical Appraisal of Bauxite Overburdens from Brazil

Mineralogical appraisal is an important tool for both mining and industrial processes. X-ray powder diffraction analysis (XRPD) can deliver fast and reliable mineralogical quantification results to aid industrial processes and improve ore recoveries. Furthermore, X-ray fluorescence (XRF) chemical data, thermal analysis (TA), and Fourier-transformed infrared spectroscopy (FTIR) can be used to validate and refine XRPD results. Mineralogical assessment of non-traditional ores, such as mining wastes, is also an important step to consider them for near-future industries. In the Brazilian Amazon, alumina-rich clays cover the largest and most important bauxitic deposits of the region and have been considered as a possible raw material for the local cement and ceramic industry. In this work, a mineralogical evaluation of these clays (Belterra Clays) is performed using XRPD, XRF, TA, and FTIR. XRPD-Rietveld quantification confirmed that kaolinite is the main phase of the clay overburden, followed by variable contents of gibbsite and goethite and minor quantities of hematite, anatase, and quartz. The chemistry derived from Rietveld, based on stoichiometric phase compositions, presents a good correlation with the XRF data and is also supported by the TA and FTIR data. The initially assumed homogeneous composition of Belterra Clay is revealed to be variable by the present mineralogical study

The Belterra Clay On The Bauxite Deposits Of Rondon Do Pará, Eastern Amazon

Bauxite deposits in the Amazon region are commonly covered by yellowish clays which can reach up to 25m thick, known as Belterra Clay (BTC). In Rondon do Pará, Eastern Amazon, BTC is 13m thick and covers world-class bauxite reserves. Three pilot bauxite mines were investigated in Rondon do Pará for an initial characterization of the local BTC. In discordant contact with the lateritic profile, the BTC has reddish brown colors at its base to ocher tones towards the top. It has a massive structure with silt-clayey texture and nodular bauxitic fragments at its base. Rietveld mineral quantification of the material attests that it is dominated by kaolinite, with goethite, gibbsite, hematite, anatase and residual quartz. The thermal behavior of the material also confirms its mineralogical composition. Kaolinite is of low structural order, which was considered the main difficulty in the application of the Rietveld method. Goethite has up to 33 mol% of Al. As observed by scanning electron microscopy (SEM), the minerals represent pseudo-hexagonal crystals measuring from 150 to 700 nm. The BTC in the studied area is correlated to BTC on others bauxitic deposits of the Amazon region, suggesting this material experienced the same genesis and geological evolution, probably during the Pliocene.PETROBRASNEGRÃO, L. B. A; COSTA, M. L. Universidade Federal do Par

Holocene coastal environmental changes inferred by multi-proxy analysis from Lago Formoso sediments in Maranhão State, northeastern Brazil

The history of the coastal environment in the northern part of northeastern Brazil and the role of sea-level and climate change as well as the human impact during the past has been still little know. In order to shed more light on coastal ecosystem dynamics and its influencing factors, a 300 cm long sediment core has been taken using a Russian corer from Lago Formoso (3°15'14S / 45°23'10W; elevation of 10 meters above sea-level) located around 150 km distance from the present-day coast in Maranhão State. The fieldwork has been carried out during the dry season, with the sampling on the 10th of December 2018. The lake has an area of approximately 500 ha and is inserted into the coastal plains of Maranhão. During the rainy season (in May is the maximum) the lake is seasonally inundated with the highest water stand of up to 8 m, while during the dry season the shallow lake has a 1.3 m water depth. The core has been radiocarbon dated and analyzed by pollen, spores, charcoal, X-Ray Fluorescence (XRF), X-ray Powder Diffraction (XRPD), LOI, and sedimentary characteristics. The main aim of this work is to answer the specific research questions: 1) How were the dynamics of vegetation in the study area? 2) How sea-level and climate influenced the coastal environment since the mid-Holocene? 3) When occurred the Atlantic Ocean regression? 4) Since when and how strong did humans have influenced the environment in the region