Navegando por Autor "Ciminelli, Virgínia Sampaio Teixeira"

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Arsenic determination in complex mining residues by ICP OES after ultrasonic extraction.
(2012) Paula, Jéssica F. R.; Froes, Roberta Eliane Santos; Ciminelli, Virgínia Sampaio Teixeira
The impact caused by mining residue deposits with high amounts of arsenic is a potential environmental problem and motive for investigations. Arsenic is always associated with gold ores and is present in mining areas, probably due to sulfide oxidation and the high pH range where arsenic is soluble. It has been shown that some samples of residues coming from the studied deposits presented arsenic concentrations above 2500 mg kg−1. The aim of this work is to develop methods for arsenic extraction in mining residues employing ultrasound assistance extraction and analyte determination by hydride generation ICP OES. The analytical method provided analysis precision and a better evaluation of environmental impact of mining residue deposits. Optimal conditions for ultrasound assisted extraction were obtained by evaluation of parameters such as the position of the sample flask inside the ultrasound bath and temperature as a function of the immersion time. These tests identified the ideal position of the sample flask and indicated that the maximum time that the sample could be analyzed without arsenic lost due to increase of the temperature was 180 minutes. With these conditions, an experimental design was developed to obtain the optimal conditions of arsenic extraction, evaluating the type of extraction solution and the sonication time. A 22 Central Composite Design (CCD) was employed to evaluate the acid concentration (HCl, HNO3 and H3PO4) and the sonication time (maximum 180 minutes). The quadratic equation of response surface generated by CCD, employing HNO3, indicated that the best condition for arsenic extraction is using an acid concentration of 2.7 mol L−1 and sonication for 136 minutes to give an average concentration of 1847±17 mg kg−1. Recovery studies were carried out and the obtained values were close to 100%. Optimal conditions of arsenic extraction were obtained by evaluating the operational parameters of ultrasound bath and the analysis conditions with the experimental design. The method developed contributes significantly to a more precise evaluation of the real environmental impact caused by the mining residues deposit.
Lixiviação de bornita, calcopirita e dos produtos da sulfidização desta última em meio híbrido sulfato-cloreto.
(2016) Veloso, Tácia Costa; Leão, Versiane Albis; Leão, Versiane Albis; Ciminelli, Virgínia Sampaio Teixeira; Dutra, Achilles Junqueira Bourdot; Gameiro, Danton Heleno; Silva, Carlos Antônio da
Apesar das intensivas pesquisas realizadas nos últimos cinquentas anos, a lixiviação da calcopirita ainda é um desafio tanto do ponto de vista acadêmico quanto industrial. Na presente tese investigou-se a lixiviação da calcopirita de duas formas diferentes: (i) dissolução da calcopirita em meio contento sulfato e cloreto (este meio foi escolhido devido ao efeito catalítico dos íons cloretos na lixiviação e considerando o aumento da utilização de água salina em processos hidrometalúrgicos); (ii) sulfidização da calcopirita com enxofre elementar, convertendo-a em bornita e covelita, que são sulfetos de cobre que apresentam cinética de lixiviação mais favorável. A investigação foi concluída com uma análise cinética da lixiviação da bornita e um mecanismo para a dissolução desta fase com íons cúpricos foi proposto. Primeiramente, uma extensão do SCM (shrinking core model) que leva em consideração a PSD (particle size distribution) da amostra foi empregada para determinar os parâmetros cinéticos da lixiviação da calcopirita. Especificamente, os efeitos da temperatura (70 °C a 90 °C) e concentração dos reagentes Cl-, Fe3+ e Cu2+ na cinética de lixiviação foram avaliados. Os resultados mostraram que a calcopirita foi mais rapidamente lixiviada com íons Cu2+ (maior constante de velocidade) do que com íons férricos, porém os valores de energia de ativação aparente em ambos os sistemas de lixiviação foram semelhantes, ou seja, 66,6 kJ/mol com 0,5 mol/L de Cu2+ e 66,8 kJ/mol com 1,0 mol/L Fe3+. Subsequentemente, a sulfidização da calcopirita objetivando produzir bornita e covelita foi estudada. O concentrado de cobre foi reagido com enxofre elementar em um forno tubular e no intervalo de 300 °C a 450 °C, seguido de lixiviação atmosférica dos produtos de reação por Fe3+. As fases minerais foram quantificadas utilizando o método de Rietveld, e foi observado que a calcopirita foi convertida em covelita (41%) e pirita (34%), nos ensaios conduzidos em temperaturas abaixo de 400 oC. Quando a temperatura estava acima de 400 oC, os produtos de reação foram bornita (45%) e pirita (31%). Independentemente do sulfeto gerado, a extração de cobre foi consideravelmente maior quando comparada à extração de cobre a partir do concentrado calcopirítico inicial. Quando a bornita oriunda da transformação foi lixiviada (6h a 80°C), aumentos na extração de cobre da ordem de 70% foram observados. Além disso, esta apresentou um comportamento similar à de uma amostra de bornita natural. Esta tese foi conclúida com a investigação da lixiviação da bornita utilizando íons cúpricos como oxidante em um meio sulfato-cloreto. Os efeitos do tamanho de partícula (37 μm-75 μm), concentração íons cúpricos (0 mol/L-0,5 mol/L) e temperatura (30 °C-90 °C) na velocidade de lixiviação da bornita foram avaliados. O parâmetro que influenciou a dissolução da bornita de maneira mais significativa foi a temperatura, resultando em um aumento de 11,3% a 30°C para 100% a 90°C. Devido ao aparecimento das trincas e à presença dos subcristalitos durante a lixiviação, o modelo cinético utilizado para descrever a dissolução da bornita com íons cúpricos foi o modelo do grão. Os dados experimentais apresentaram um bom ajuste ao controle químico e energia de ativação aparente obtida foi de 65.27 kJ/mol. Os interiores dos grãos apresentaram a composição química do intermediário Cu3FeS4, determinada por microssonda eletrônica e em função deste intermediário um mecanismo para dissolução foi proposto.
Mechanisms of arsenic removal from simulated surface water based on As (III) retention on thiol chelating resins.
(2021) Duarte, Graziele; Teixeira, Mônica Cristina; Olusegun, Sunday J.; Ciminelli, Virgínia Sampaio Teixeira
A novel system for arsenic speciation in the aqueous environment has been developed based on the high affinity of As(III) for the sulfhydryl groups present in thiol resins (R-S). The performance of tailor-made cartridges filled with the thiol resin was then compared with a commercial silica-based anion exchange cartridge with a qua- ternary ammonium group (R-N) typically used for As(V) speciation. Both were able to separate arsenic species efficiently, As(V) and As(III), within a broad pH range using flow rates of up to 5 ml min− 1 . The R-S resin was shown to be suitable for the inorganic arsenic speciation in aqueous systems containing calcium, magnesium, ferrous and ferric ions. The R-S selectivity for As(III) was affected only at sulfate or phosphate/As mass ratio > 500, in a behavior similar to R-N for As(V). The thiol resin’s selectivity for As(III) and its immobilization mechanism were investigated through X-ray Absorption Spectroscopy. At pH 5, each arsenic atom bounds to three sulfur atoms, with an As-S inter-atomic distance of 2.26 ± 0.01 Å, and a coordination number (CN) of 2.8 ± 0.3. The separation of the neutral As(III) species by a thiol resin presents itself as an alternative to the available anion exchange methods. The sorption of As(III) on the thiol resin followed a pseudo-second-order kinetic model and can be described by the Langmuir isotherm.
Microwave-hydrothermal synthesis of nanostructured Na-birnessites and phase transformation by arsenic(III) oxidation.
(2008) Dias, Anderson; Sá, Rodrigo Gomes; Spitale, Matheus Calonge; Athayde, Maycon; Ciminelli, Virgínia Sampaio Teixeira
Microwave-hydrothermal synthesis was employed to produce Na-birnessites. Crystalline, single-phase materials were obtained at temperatures as low as 120 8C and times as short as 1 min. X-ray diffraction and Raman spectroscopy were used to characterize the structural features of the nanostructured powders. Birnessites possessed a monoclinic structure in space group C2/m with nine Raman-active bands, all of which were observed for the first time due to optimized acquisition of the spectroscopic data. The highly reactive materials produced were submitted to sorption experiments with As(III). An oxidative precipitation occurred with the production of Mn(II) arsenate at higher arsenic concentrations. In addition, the formation of hausmannite (Mn3O4) was confirmed by X-ray diffraction and Raman analyses of the reacted solid phase. The observed 14 Raman-active modes were adjusted according to the tetragonal I41/amd space group for hausmannite. An additional band related to the breathing mode of the arsenate was observed, leading to the conclusion that adsorption onto hausmannite takes place in addition to the oxidative precipitation of manganese arsenate.
Simultaneous production of impurity-free water and magnetite from steel pickling liquors by microwave hydrothermal processing.
(2006) Ciminelli, Virgínia Sampaio Teixeira; Dias, Anderson; Braga, Henrique Costa
Pickling plants produce large amounts of toxic and hazardous wastes containing heavy metals, thus creating an important environmental problem associated with steel production. This communication reports the use of the microwave-hydrothermal technology to remove metals from pickling liquors and also to produce electroceramics, which results in the simultaneous generation of impurity-free water and value-added materials. The results showed that the microwave-hydrothermal processing was efficient to produce magnetically soft ferrites, as well as to eliminate the heavy metal contamination from the spent liquor.
The dependence of sorbed copper and nickel cyanide speciation on ion exchange resin type.
(2001) Leão, Versiane Albis; Lukey, Grant C.; Deventer, Jannie S. J. van; Ciminelli, Virgínia Sampaio Teixeira
The present study investigates the influence of functional group structure and resin matrix on the speciation of copper and nickel cyanides sorbed onto two commercially available ion exchange resins. Batch experiments were performed using synthetic copper and nickel solutions containing 50 and 200 mgrL free cyanide, respectively. Despite the presence of CuŽCN.32y and CuŽCN.43y in solution, it has been found using Raman spectroscopy that the Imac HP555s resin, which has a polystyrene–divinylbenzene matrix, loads predominantly the CuŽCN.32y complex. In contrast, the polyacrylic resin, Amberlite IRA958, sorbed significant amounts of both CuŽCN.32y and CuŽCN.43y. It has been found that the speciation of nickel cyanide sorbed onto each resin was the same. A recently developed mathematical model based on statistical thermodynamic principles has been used as a tool to understand further the equilibrium sorption of copper and nickel cyanide complexes onto each resin studied. A higher sorption energy for nickel compared to copper has been observed for the sorption onto Imac HP555s. In contrast, the sorption energy for copper was found to be higher than for nickel for the polyacrylic resin, Amberlite IRA958. The values of the model parameters obtained were correlated with the chemical features of each complex in solution as well as sorbed onto the resins.