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Chalcopyrite is the main ore mineral used in industrial copper extraction. However, when passivation processes occur during hydrometallurgical treatment, a large percentage of the mineral being treated is not solubilized, so the copper recovery is limited. Galvanic interactions between semiconductor minerals are the basis of many strategies to achieve a more efficient process for increasing copper dissolution. These interactions concern generally two metallic sulfides. The present study describes a new galvanic interaction between chalcopyrite-magnetite (CuFeS2-Fe3O4) in an acid microbial culture medium, used routinely in biomining processes. The electrochemical characterization of CuFeS2, Fe3O4 and a mineral containing CuFeS2-Fe3O4 is performed. Galvanic interactions are demonstrated by comparing Evans diagrams constructed from current transients obtained by imposing the potential pulses to each species studied. It is determined that CuFeS2 and Fe3O4 fulfil the role of anode and cathode, respectively, in the behavior of the corresponding mineral. Stripping voltammetry is used to quantify electro-dissolved ions; the electrooxidation of CuFeS2-Fe3O4 mineral in acid culture medium releases twice as many copper ions as pure chalcopyrite. This corroborates that the galvanic interactions prevent the formation of typical passivating components observed in chalcopyrite. Fil: Saavedra Olaya, Albert Ulises. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: García Meza, J. Viridiana. Universidad Autonoma de San Luis Potosi; México Fil: Corton, Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: González, Ignacio. Universidad Autónoma Metropolitana - Iztapalapa; México

To develop a bioelectrochemical system (BES) to couple the biooxidation of chalcopyrite (CuFeS2), bioelectrogenesis, and the cathodic Cu2+ reduction, bioanodes of acidophilic (pH

A bioelectrochemical study of charge transfer in the biofilm/chalcopyrite interface was performed to investigate the effect of surficial sulfur reduced species (SRS), as non-stochiometric compounds or polysulfides (Sn2-), and elemental sulfur (S0) on a biofilm structure during the earliest stages (1, 12 and 24 h) of chalcopyrite biooxidation by A. thiooxidans alone and adding Leptospirillum sp. The surface of massive chalcopyrite electrodes was exposed to the bacteria, which were analyzed electrochemically, spectroscopically, and microscopically. At the studied earlier times, charge transfer and significant differences in the biofilm structure were detected, depending on the presence of Leptospirillum sp. acting on A. thiooxidans biofilms. Such differences were a consequence of a continuous chalcopyrite pitting and promoting changes in biofilm hydropathy. A. thiooxidans modifies the reactive properties of SRS and favors an acidic dissolution, which shifts into ferric when Leptospirillum sp. is present. A. thiooxidans allows H+ and Fe3+ diffusion, and Leptospirillum sp. allows surpassing the charge transfer (reactivity) barrier between the mineral interface and the ions. The observed changes of hydropathy on the interface are associated to ions and electrons activity and transfer. Finally, a model of S0 biooxidation by A. thiooxidans alone or with Leptospirillum sp., is proposed.

Total and bioaccessible concentrations of arsenic (As) and lead (Pb), as well as their bearing phases in the adjacent soil area (residential area) of the historic and active Fe-oxide-rich mining district of Cerro de Mercado, Durango (Mexico), were evaluated. Results indicated the presence of arsenopyrite, galena, and As-bearing phases in ultrafine (

Massive pyrite (FeS2) electrodes were potentiostatically modified by means of variable oxidation pulse to induce formation of diverse surface sulfur species (S n 2−, S0). The evolution of reactivity of the resulting surfaces considers transition from passive (e.g., Fe1−x S2) to active sulfur species (e.g., Fe1−x S2−y , S0). Selected modified pyrite surfaces were incubated with cells of sulfur-oxidizing Acidithiobacillus thiooxidans for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the attached cells density and their exopolysaccharides were analyzed by confocal laser scanning microscopy (CLMS) and atomic force microscopy (AFM) on bio-oxidized surfaces; additionally, S n 2−/S0 speciation was carried out on bio-oxidized and abiotic pyrite surfaces using Raman spectroscopy. Our results indicate an important correlation between the evolution of S n 2−/S0 surface species ratio and biofilm formation. Hence, pyrite surfaces with mainly passive-sulfur species were less colonized by A. thiooxidans as compared to surfaces with active sulfur species. These results provide knowledge that may contribute to establishing interfacial conditions that enhance or delay metal sulfide (MS) dissolution, as a function of the biofilm formed by sulfur-oxidizing bacteria.

Surfaces of massive chalcopyrite (CuFeS2) electrodes were modified by applying variable oxidation potential pulses under growth media in order to induce the formation of different secondary phases (e.g., copper-rich polysulfides, S n 2−; elemental sulfur, S0; and covellite, CuS). The evolution of reactivity (oxidation capacity) of the resulting chalcopyrite surfaces considers a transition from passive or inactive (containing CuS and S n 2−) to active (containing increasing amounts of S0) phases. Modified surfaces were incubated with cells of sulfur-oxidizing bacteria (Acidithiobacillus thiooxidans) for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the density of cells attached to chalcopyrite surfaces, the structure of the formed biofilm, and their exopolysaccharides and nucleic acids were analyzed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy coupled to dispersive X-ray analysis (SEM-EDS). Additionally, CuS and S n 2−/S0 speciation, as well as secondary phase evolution, was carried out on biooxidized and abiotic chalcopyrite surfaces using Raman spectroscopy and SEM-EDS. Our results indicate that oxidized chalcopyrite surfaces initially containing inactive S n 2− and S n 2−/CuS phases were less colonized by A. thiooxidans as compared with surfaces containing active phases (mainly S0). Furthermore, it was observed that cells were partially covered by CuS and S0 phases during biooxidation, especially at highly oxidized chalcopyrite surfaces, suggesting the innocuous effect of CuS phases during A. thiooxidans performance. These results may contribute to understanding the effect of the concomitant formation of refractory secondary phases (as CuS and inactive S n 2−) during the biooxidation of chalcopyrite by sulfur-oxidizing microorganisms in bioleaching systems.