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Belo Horizonte, Brazil

Majuste D.,Federal University of Minas Gerais | Ciminelli V.S.T.,Federal University of Minas Gerais | Osseo-Asare K.,INCT ACQUA | Osseo-Asare K.,Pennsylvania State University | Dantas M.S.S.,INCT ACQUA
Hydrometallurgy | Year: 2012

The present paper quantifies the separate and combined effects of pyrite (FeS 2) inclusions, dissolved oxygen (0.001 mol/L) and ferric ion (0.01-0.05 mol/L) on the electrochemical behavior of chalcopyrite (CuFeS 2) electrodes by means of potentiometry and linear sweep voltammetry. The experiments were carried out in 0.1 mol/L H 2SO 4 solutions at room temperature (26 ± 1 °C). Naturally associated pyrite-chalcopyrite electrodes were selected with the aims to better represent the sulfide association in the ore, thus minimizing the voltage losses across the mineral-mineral contact. The presence of ferric ion and oxygen was shown to increase in approximately 53% the mixed potential of CuFeS 2 electrodes; the dissolution current density increased up to 55 times. In the presence of these oxidants and pyrite (42% FeS 2 of the electrode surface), the mixed potential was further increased in 14%. For these mixed electrodes, the dissolution current density increased by a factor of approximately 2.6 and 2.2, respectively, in solutions containing 0.001 mol O 2/L and 0.05 mol Fe 3 +/L, and by 1.6 times in presence of both oxidants (0.001 mol O 2/L with 0.05 mol Fe 3 +/L). Therefore, more pronounced effect of pyrite inclusions on chalcopyrite oxidation rate was observed under the lower oxidizing conditions. The effects of the oxidants were described by electrochemical models. The galvanic effect of pyrite on the dissolution of this important sulfide was discussed by the kinetics of the half-cell reactions occurring in the pyrite-chalcopyrite coupling. © 2012 Elsevier B.V. Source


Majuste D.,Federal University of Minas Gerais | Ciminelli V.S.T.,Federal University of Minas Gerais | Osseo-Asare K.,INCT ACQUA | Osseo-Asare K.,Pennsylvania State University | And 2 more authors.
Hydrometallurgy | Year: 2012

The formation of bornite (Cu 5FeS 4), an iron-deficient sulfide, and its correlation with the slow oxidation rate of chalcopyrite (CuFeS 2) in acidic media under atmospheric conditions is demonstrated. Chalcopyrite electrodes oxidized in 0.1 mol/L H 2SO 4 solutions at room temperature (25 ± 1 °C) were analyzed by micro Raman spectroscopy and synchrotron small angle X-ray diffraction (S-SAXRD), techniques indicated for thin films analysis. Anodic polarization curves of chalcopyrite electrodes showed two well-defined behaviors: quasi-potential-independent regime and potential-dependent regime. When the critical potential (Ec) is attained, which ranged from 0.75 to 0.90 V vs. Standard Hydrogen Electrode (SHE), the mineral oxidation rate becomes strongly dependent on potential. Potentiostatic current-time profiles at 0.60 and 0.70 V vs. SHE indicated a current decay, which suggests the formation of a progressively thickening protective layer. The profiles at 0.80 V vs. SHE showed a similar current decay, but also an active oxidation process for some samples. After chronoamperometry at 0.70 and 0.80 V vs. SHE, respectively, for 6 and 2 h, analyses by using S-SAXRD revealed peaks of bornite on oxidized chalcopyrite electrodes. Elemental sulfur (S 8) was also detected by S-SAXRD at 0.80 and 1.00 V vs. SHE, respectively, for 2 and 0.5 h. An unidentified metal-deficient phase and covellite (CuS) were detected on chalcopyrite by micro Raman spectroscopy after chronoamperometry at 0.60 and 0.80 V vs. SHE, respectively. The formation or absence of these product phases under a constant applied potential correlated well with a hindered dissolution or active oxidation processes. The results of this work support the hypothesis that the formation of intermediate iron-deficient sulfides contributes to the slow oxidation rate of chalcopyrite under atmospheric conditions. © 2011 Elsevier B.V. All rights reserved. Source


Gasparon M.,University of Queensland | Ciminelli V.S.T.,INCT ACQUA | Ciminelli V.S.T.,Federal University of Minas Gerais | Cordeiro Silva G.,INCT ACQUA | And 6 more authors.
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

Conventional methods for the analysis of arsenic in atmospheric particulate matter provide only bulk concentrations in different particle size fractions. We have developed a method that combines traditional gravimetric and bulk elemental ICP-MS analysis with automated SEM characterization of individual particles. By using this method, it is possible to establish which mineral phases (and non-crystalline matter) and which particle size fractions contribute to the total arsenic content in the atmospheric particulate matter. A less labor-intensive alternative method is currently being trialed using Mineral Liberation Analysis (MLA). Results of the first pilot study carried out in the Paracatu area (Minas Gerais, Brazil), where gold mineralization is associated with arsenopyrite, show that at this specific mine site atmospheric arsenic is primarily associated with organic combustion residues of forest fires, and not with the dispersion of arsenopyrite from the local mine site as previously postulated. This method can be applied in principle to trace the source of any element in atmospheric particulate matter, and can therefore be used to identify and manage activities and sources responsible for the release of potentially toxic elements into the atmosphere. © 2014 Taylor & Francis Group. Source


Majuste D.,Federal University of Minas Gerais | Ciminelli V.S.T.,Federal University of Minas Gerais | Eng P.J.,University of Chicago | Osseo-Asare K.,INCT ACQUA | Osseo-Asare K.,Pennsylvania State University
Hydrometallurgy | Year: 2013

In situ synchrotron X-ray diffraction (S-XRD) techniques are potentially versatile research tools for advancing the current understanding on dissolution reactions of commercially important minerals. The paper presents a review on the applications of S-XRD to investigate solid phase transformations in aqueous media, with emphasis on reactions relevant to hydrometallurgy, including the dissolution of nickel laterite ores and metal sulfides, such as pyrite (FeS 2), bornite (Cu5FeS4) and chalcocite (Cu 2S). The results of an in situ synchrotron time-resolved X-ray diffraction (S-TRXRD) study of the dissolution of chalcopyrite (CuFeS 2) are also reported. The S-TRXRD measurements were carried out in capillary-based cells containing fine particles by using two different experimental approaches - flow method (FM) and non-flow method (NFM). At 25 °C (FM), no transformation of the crystal structure was observed, in agreement with the well-known slow dissolution rate of the mineral. In the temperature range 100-200 °C (NFM), the formation of covellite (CuS), elemental sulfur (S8), and metal sulfates (ferrous or cupric sulfates) was detected on CuFeS2 particles. Our results demonstrate that the mineral conversion to such product phases commenced about 10 min after the start of measurements, and suggested that the formation of elemental sulfur is possibly related to an initial oxidation of CuFeS2 by Fe 3+ ions, followed by CuS oxidation by the same oxidants. The new results in combination with the previous reports demonstrate that the S-XRD techniques can be used to improve our knowledge on key hydrometallurgical processes. This work highlights the features of different experimental set-ups and the possibilities to be explored by applying in situ methods, alone or in combination with other analytical tools. © 2012 Elsevier B.V. All rights reserved. Source


Silva G.C.,Federal University of Minas Gerais | Ciminelli V.S.T.,Federal University of Minas Gerais | Duarte G.,Federal University of Minas Gerais | Oliveira A.M.,Federal University of Minas Gerais | And 5 more authors.
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

A food survey was conducted focusing on most commonly consumed staple dietary items obtained from local markets of three different towns in the State of Minas Gerais, Brazil. The samples were analyzed for total arsenic. The daily intake was estimated based on a Brazilian food consumption statistics and compared with the recommendation of international organizations. The data represent national samplings; the analyses were carried out by laboratories approved in inter-laboratory evaluations. Rice and beans alone contribute to approximately 90% of the total As intake from food. The calculated daily intake (0.399 μg/kg of body weight per day) is below the BMDL0.5 of 3.0 μg kg-1 of body weight per day. © 2014 Taylor & Francis Group. Source

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