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Ciminelli V.S.T.,Federal University of Minas Gerais | Ciminelli V.S.T.,National Institute of Science and Technology on Mineral Resources
One Century of the Discovery of Arsenicosis in Latin America (1914-2014): As 2014 - Proceedings of the 5th International Congress on Arsenic in the Environment | Year: 2014

Mining and metallurgical activities involve the disposal of arsenic residues, in amounts that are expected to increase due to population and industrial growth combined with mining of low-grade ores. Key questions arise: What are the conditions that will ensure the structural and chemical stability of the wastes and tailings materials now and in the foreseeable future? How can one rigorously assess the potential, long-lasting risks associated to disposal of arsenic residues related to the mineral sector? In addition to the traditional tests for classification of residues, other tools are needed and increasingly used. These tools include assessment of bioaccessibility and bioavailability to better evaluate the risks to human health, and advanced analytical techniques to understand at a molecular level the mechanisms of arsenic fixation in the environment. This information is expected to provide the technical and scientific basis for the design of better strategies for As fixation in mining tailings. © 2014 Taylor & Francis Group. Source


Souza C.,Federal University of Minas Gerais | Majuste D.,Federal University of Minas Gerais | Ciminelli V.S.T.,Federal University of Minas Gerais | Ciminelli V.S.T.,National Institute of Science and Technology on Mineral Resources
Hydrometallurgy | Year: 2014

Copper cyanocomplexes have been recognized as important competitors for the adsorption sites of activated carbons during gold adsorption. In the present paper, an adsorption mechanism of negatively charged Cu cyanocomplexes on available sites of different activated carbons is proposed. The mechanism considers the (i) solution chemistry (e.g., effects of pH, CN/Cu molar ratio, and ionic strength by adding Na+, K+, and Ca2 + cations); (ii) surface properties of the activated carbon samples (e.g., density of surface functional groups and point of zero charge - PZC); and (iii) copper speciation. The adsorption experiments demonstrated that the enhanced interaction of copper species at pH < PZC and low ionic strength can be ascribed to the net positive charge on the surface of the solid phase. When the basic surface groups are completely deprotonated (i.e., pH > PZC > pK a basic groups), electrostatic repulsion inhibits the adsorption of negatively charged Cu species. It is also proposed that the interaction of Ca2 + ions with acid groups generate an excess of locally positive charges on the surface of the activated carbon, and such positive charges enhance the adsorption of negatively charged copper cyanocomplexes, even when the net surface charge is negative. The results from thermodynamic and Raman analyses indicated that under typical, practical conditions of gold adsorption from cyanide solutions (pH > 9 and CN/Cu molar ratio > 4), the main competitor for the adsorption sites of the activated carbon is the Cu(CN) 3 2 - species and not the Cu(CN)2 - species. © 2013 Elsevier B.V. Source


Lobato N.C.C.,Federal University of Minas Gerais | Ferreira A.D.M.,Federal University of Minas Gerais | Ferreira A.D.M.,National Institute of Science and Technology on Mineral Resources | Mansur M.B.,Federal University of Minas Gerais | And 2 more authors.
Separation and Purification Technology | Year: 2016

In this study, a magnetic organic liquid called ferrofluid was used to improve the speed and efficiency of the phase disengagement of solvent extraction processes applied to hydrometallurgical systems. The ferrofluid consisted of magnetic nanoparticles (mean diameter of 10.2 nm), comprised of magnetite (Fe3O4) and maghemite (γ-Fe2O3), which were coated by oleic acid and dispersed in an organic diluent. The nanoparticles were characterized by applying various methods: transmission electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric and magnetic analysis. The effect of the nanoparticles on the solvent extraction of cobalt sulfate with Cyanex 272 was investigated using ferrofluids at different concentrations (0, 10, 20, and 30 g/l of magnetic nanoparticles in commercial aliphatic kerosene Exxsol D80). It was observed that, under the conditions studied, the presence of nanoparticles does not interfere in the efficiency of metal extraction and stripping, and that the time necessary for phase disengagement can be up to five times faster. However, the ferrofluid containing nanoparticles coated solely by oleic acid is not stable when in contact with aqueous solutions at pH ≤ 2.0. Limited stability restricts the application of the magnetic fluid used in the present study in solvent extraction processes that operate at a pH level beyond 2. © 2016 Elsevier B.V. Source


Silva G.C.,Federal University of Minas Gerais | Silva G.C.,National Institute of Science and Technology on Mineral Resources | Ciminelli V.S.T.,Federal University of Minas Gerais | Ciminelli V.S.T.,National Institute of Science and Technology on Mineral Resources | And 6 more authors.
Materials Research Bulletin | Year: 2014

Degradation of methylene blue (MB) is investigated using Mn 3O4 as an oxidant. Discrete Mn3O4 particles and Mn3O4/Fe3O4 nanocomposites are synthesized via coprecipitation by using air as an oxidant in the absence and presence of previously synthesized magnetite nanoparticles, respectively. Characterization results show that superparamagnetic magnetite nanoparticles of ∼10 nm were synthesized. The Mn3O4 synthesis in the presence of these magnetite nanoparticles favors the formation of a pure, highly ordered Mn3O4/Fe3O 4 superparamagnetic nanocomposite, which can be separated by an external magnetic field. This nanocomposite is applied to the oxidative decolorization of methylene blue (MB) and is capable of catalyzing the complete N-demethylation of MB, forming thionine as the final product and removing 93% of the dye in approximately 1 h.© 2013 Elsevier Ltd. All rights reserved. Source


Souza C.,Federal University of Minas Gerais | Souza C.,National Institute of Science and Technology on Mineral Resources | Majuste D.,Federal University of Minas Gerais | Majuste D.,National Institute of Science and Technology on Mineral Resources | And 3 more authors.
Hydrometallurgy | Year: 2014

Copper cyanocomplexes have been recognized as competitors for the adsorption sites of activated carbon during gold adsorption. In this paper, the effects of practical parameters (excess free cyanide, calcium ions and aeration conditions) on the selective adsorption of Au over Cu cyanocomplexes on activated carbon samples from different sources are discussed. In addition to the adsorption experiments, the aqueous and solid phases were characterized by Raman spectroscopy in an attempt to elucidate the observed trends. Four solid samples with different structures as regards the relative amount of graphitic planes and density of surface functional groups were selected. The results indicated the highest adsorption of Au and the lowest adsorption of Cu on the sample with the lowest density of surface groups and relative higher crystalline character. In contrast, the highest adsorption of Cu and the lowest adsorption of Au were obtained using the sample with the highest density of surface groups and relative lower crystalline character. These findings support the industrial application of activated carbons with low density of surface functional groups for gold recovery, such as the product obtained from coconut shell, and are consistent with the hypothesis of different preferential sites for the adsorption of Au and Cu. The results also indicate that if there is an excess of free cyanide in the solution, a higher Au/Cu selectivity is observed, but the Au loading on the activated carbon samples declines. In the presence of Ca 2 + ions in the cyanide solution, positive effects on Au adsorption and negative effects on Cu adsorption were demonstrated for a CN/Cu molar ratio above 4 (i.e., Cu(CN)4 3 - as the predominant species), and these behaviors resulted in a higher Au/Cu selectivity. A previous adsorption of Ca2 + ions on the activated carbon surface creates new sites for Au(CN)2 - adsorption, in addition to the graphene layers. From aerated solutions, the adsorption experiments revealed a positive effect on Cu adsorption, and negative impact on Au adsorption, thus affecting the Au/Cu selectivity. The aeration of the solution results in a decrease of the cyanide concentration, which reduces the CN/Cu molar ratio. Therefore, the addition of Ca2 + ions in the process solution and an optimal concentration of free cyanide, which should take into account the loss of cyanide by oxidation and volatilization, may help to improve Au/Cu selectivity. © 2014 Elsevier B.V. Source

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