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25 results on '"Angélica, R.S."'

20. Estudo do comportamento térmico e propriedades físico-mecânicas da lama vermelha

Author

Mercury, J.M. Rivas, Galdino, L.G., Vasconcelos, N.S.L.S., Paiva, A.E.M, Cabral, A.A., and Angélica, R.S.

Subjects
materiais cerâmicos, ceramic materials, lama vermelha, Resíduo de bauxita, red mud, characterization, caracterização, Bauxite tailing
Abstract

Neste trabalho, estudou-se o comportamento térmico, a evolução das fases cristalinas com a temperatura e as propriedades físico-mecânicas da Lama Vermelha (LV) procedente da indústria de alumínio do Estado do Maranhão. O estudo foi realizado por Análise Termogravimétrica (TG) e Calorimetria Exploratória Diferencial (DSC), Dilatometria Ótica até 1350 ºC; enquanto a evolução das fases cristalinas com a temperatura foi realizada no intervalo entre 750 a 1150 ºC por Difração de Raios-X (DRX). As propriedades físico-mecânicas como Superfície Específica, Granulometria, Limite Plástico (LP), Limite de Liquidez (LL), Índice de Plasticidade (IP), Tensão de Ruptura a Flexão (TRF), Absorção de Água (AA), Retração Linear Após Queima (R L) e Porosidade Aparente (PA) foram determinadas nas mesmas temperaturas. As seguintes fases cristalinas foram detectadas: hematita, sodalita e anatásio entre 750-850 ºC; e hematita, nefelina e sodalita entre 950-1150 ºC. Os ensaios tecnológicos demonstraram que a LV pode ser aplicada para o processamento de materiais cerâmicos estruturais, pois apresenta pouca reatividade entre 870-950 ºC, com elevada AA, e baixas R L e TRF. Entre 950 e 1350 ºC, a LV sofreu uma retração que variou entre 5-50 %, com fusão total a 1350 ºC, devido à presença de fases minerais do tipo feldespatoides em sua composição. The present work studied the thermal behavior, the evolution of the crystalline phases with temperature and the ceramic properties of the red mud (bauxite tailing) from an aluminium industry of the Maranhao state. The research was carried out by Simultaneous Thermal Analysis (TG-DTA), Optical Dilatometry up to 1350 ºC, while the evolution of the crystalline phases was performed by X-ray diffraction analysis upon heating between 750 to 1150 ºC. Physical-mechanical properties, like Specific Surface Area, Particle Size Distribution, Plastic Limit (PL), Liquid Limit (LL), Plasticity Index (PI), Flexural Strength, Water Absorption (WA), Linear Shrinkage After Firing (LS) and the Apparent Porosity (AP) were also determined at the same range of temperature. The following major crystalline phases were detected: hematite, sodalite, and anatase at 750 < T < 850 ºC; and hematite, nepheline and sodalite at 950 < T < 1150 ºC. The technological experiments indicated that red mud can be used for the processing of structural ceramic materials, since it is an inert material between 870-950 ºC and presents highest water absorption and lowest shrinkage and flexural strength. At 950 < T < 1350 ºC, red mud presented a high shrinking of almost 5 to 50 % with total fusion at 1350 ºC, due to the presence of feldspathoids phases in its mineral composition.

Published
2010

21. Mafic dykes intrusive into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt (Parnaíba Province), north-northeastern Brazil: Geochemistry, Sr-Nd-Pb-O isotopes, 40Ar/39Ar geochronology, and relationships to CAMP magmatism

Author

Klein, E.L., Angélica, R.S., Jourdan, Fred, Babinski, M., Harris, C., Klein, E.L., Angélica, R.S., Jourdan, Fred, Babinski, M., and Harris, C.

Abstract

Dykes of diabase and microgabbro intruded into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt, which are tectonic and erosive windows of the Parnaíba Basin in north–northeastern Brazil. Ar–Ar ages were determined, and major, trace element, and Nd–Sr–Pb–O isotopic compositions of these dykes were measured to provide insights into their age, and into the nature of their mantle sources and petrogenetic processes. The data have also been used to compare the chemical and isotopic signatures of the dykes with those of the Central Atlantic Magmatic Province (CAMP). Four chemical groups of mafic dykes have been identified. These comprise two subtypes of high-Ti rocks (i) HTi-1 (TiO2 < 2.3 wt.%; SiO2 > 47 wt.%), (ii) HTi-2 (TiO2 > 2.7 wt.%; SiO2 > 47 wt.%), in addition to (iii) evolved high-Ti (TiO2 > 4 wt.%; SiO2 of ~ 46 wt.%) and (iv) low-Si (TiO2 > 2.2 wt.%; SiO2 < 45 wt.%) rocks. 40Ar/39Ar geochronology of plagioclase returned ages of 201 ± 4 Ma and 193 ± 10 Ma for the HTi-2 subtype, and of 201 ± 2 Ma and 207 ± 9 Ma for the evolved high-Ti group. The HTi-1 and low-Si groups presented highly disturbed age spectra, and did not allow the definition of their emplacement ages. The Argon data indicate an age > 200 Ma for the low-Si group and are dubious with respect to the age of theHTi-1 subtype, if coeval with (i.e., ~ 200 Ma), or older than, the HTi-2 and evolved high-Ti types.All groups present δ18O values of pyroxene that are compatible with uncontaminated mantle-derived magmas. The HTi-1 subtype (average 143Nd/144Nd200 = 0.512644; 87Sr/86Sr200 = 0.7035; 206Pb/204Pb of 17.86) shows the less enriched and less fractionated (more primitive) trace element distribution of all groups. The HTi-2 subtype shows enriched trace element pattern and depleted Nd–Sr signature (143Nd/144Nd200 = 0.512610; 87Sr/86Sr200 = 0.7037) and average 206Pb/204Pb ratios of 17.23. The evolved high-Ti chemical group shows average ratios of 143Nd/144Nd200 = 0.512558, 87Sr/86Sr200 =

Published
2013

24. Green synthesis of LaCrO3powder mediated by the extract of the Amazon rain forest native plant Himatanthus drasticus(Mart.) Plumel and their photocatalytic activity

Author

Silva, R.S., Matos, R.S., Andrade, R., Oliveira, R.M.P.B., Resende, C.X., Paz, S.P.A., Angélica, R.S., and Ferreira, N.S.

Abstract

Lanthanum chromite (LaCrO3) powder was successfully synthesized by plant-extract-assisted sol-gel method using milk of Janaguba (Himatanthus drasticus(Mart.) Plumel) as an eco-effective chelating agent. X-ray diffraction (XRD), Rietveld refinement, Fourier-transform infrared spectroscopy (FT-IR), and Scanning electron microscopy (SEM) analysis revealed an orthorhombic crystalline structure, with average crystallite and particle sizes of ∼40 and ∼640 nm, respectively, confirming the obtaining of LaCrO3powder. UV-vis absorption spectrum reveals a band with a well-defined maximum in the range of 230-350 nm, with an optical band-gap energy value of 3.33 eV. The photocatalytic degradation efficiency of MB in the presence of LaCrO3as photocatalyst after 120 min of illumination (in low light intensity of 2.87 Wcm-2) was 6.3%. Therefore, our study provides preliminary evidence that the LaCrO3powder is a potential photocatalyst for MB dye degradation, a pigment widely used by the textile industry that generates large amounts of effluents to be treated. Finally, the present synthesis proposal presents a cheap and eco-friendly alternative for the production of LaCrO3powder.

Published
2021
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25. Assessment of Hg-contamination in soils and stream sediments in the mineral district of Nambija, Ecuadorian Amazon (example of an impacted area affected by artisanal gold mining)

Author

Ramırez Requelme, M.E., Ramos, J.F.F., Angélica, R.S., and Brabo, E.S.

Subjects
*MERCURY, *SOIL pollution, *MERCURY in soils
Abstract

The Nambija Mineral District (NMD) is located in the southeastern part of Ecuador, east of Zamora (Zamora Chinchı´pe's country), Ecuadorian Amazon. In this district, Au occurrences have been know since colonial and pre-colonial times, but only after the early 1980s has intensive artisanal Au mining activity been developed. Currently, the different NMD Au occurrences continue to be exploited by artisanal operations and are difficult to control in the study area. The environmental impacts due to Au mining are a consequence of the illegal situation and deficiency in controlling the techniques of ore exploitation. The Au extraction is carried out by outdoor amalgamation, so the indiscriminate use of Hg by artisanal miners, associated with careless methods of tailings disposal, has caused occupational exposure and environmental degradation. The present study evaluated the geochemical dispersion and concentrations of local contamination of metallic Hg in soils, stream sediments and mine tailings in the NMD area. This article aims to contribute to the discussion of environmental changes caused by the artisanal Au mining in the Nambija district. A total of 82 samples (32 soil, 40 stream sediment and 10 mine tailings) were analyzed. The results were compared with the Hg levels in soil and stream sediments considered not to be contaminated in the Nambija mining area and in other areas where Hg is mined in the Amazon basin. In this work, mean total Hg (T-Hg) concentrations of 1.7 μg g−1 in soils and 2.7 μg g−1 in stream sediments have been found. Mercury values in the mine tailing samples revealed values ranging from 89 to 1555 μg g−1. The results found for Hg in the different analyzed materials pointed to contamination of the studied area by this metal, while soil erosion is responsible for an increase in stream sediment's T-Hg concentrations in the different aquatic ecosystems of the Nambija Creek and Nambija River. [Copyright &y& Elsevier]

Published
2003

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