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In biohydrometallurgical processes, a mineral exhibits different oxidation phases due to the system's heterogeneity, especially in heap leach pads. Oxidation chemically modifies the mineral surface altering its interface, and thereby affecting the bacteria-mineral interaction, mineral reactivity and leaching velocity. Given that the mineral can be found in different oxidation states in heap bioleaching processes, three oxidation conditions of FeS2, in which iron and/or sulfur related compounds are formed on the mineral surface were assayed. This paper studies the interaction between the modified surface of a sulfide mineral, FeS2, and 0 K culture medium, typically used in biomining processes. Chemical and electrochemical changes on surfaces were characterized by subjecting them to weathering in an acidic culture medium (pH 1.8), without applying potential or current. The chemical species formed were identified by Raman spectroscopy. The modified pyrite surfaces showed significant interfacial transformations upon immersion in the culture medium, and the formation of passive chemical species, such as elemental sulfur, jarosite, phosphates and oxides, were identified. These interfacial modifications are correlated with changes in the open circuit potential (OCP) values during immersion of pyrite and surface modified pyrites in 0 K culture medium. Electrochemical characterization showed a decrease in mineral oxidation capacity, which directly affects the extent of leaching and possibly, of the interaction with other elements participating in the process, such as microorganisms. To study the interactions among bacteria and the pyrite mineral suffering different surface modifications, the attachment of the bioleaching bacterium Leptospirillum sp. was evaluated. 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

Bacterial cell attachment that results in biofilm formation is the first step of bacteria-mineral interaction, and it is known that they strongly depend on the chemical characteristics of the mineral surface. In some industrial processes, like those used in biohydrometallurgy, the minerals are present in different chemical oxidation states, especially when heterogeneous low-grade ore deposits and mining tailings are used as starting materials for microbial inoculation. This study describes a strategy for monitoring bacterial attachment to pyrite (FeS2) and surface modified pyrite weathered in the culture growth medium used (pH 1.8), by means of a non-invasive electrochemical technique such as electrochemical impedance spectroscopy (EIS). The EIS evaluation of Leptospirillum sp. interaction with pyrite and surface modified pyrite weathered electrodes revealed significant changes at low frequencies, depending of the compounds presented over the four samples used, including unmodified pyrite and three surface modified samples. Once the frequency at which the adhesion process can become uncover was selected (0.1 and 0.05 Hz), the phase angle variation at such frequency was determined using different microbial concentrations. Different microbial attachment values were obtained for the different electrodes and related to the initial inoculum (2 × 108 cells/mL), as follow: FeS2/Fe(OH)n,S0 (38 ± 3.2%); FeS2/Fe(OH)n (31 ± 5.5%); FeS2 (27 ± 4.7%) and FeS2/S0 (18 ± 3.8%). Microbial attachment to unmodified and modified surfaces, evaluated by EIS, was corroborated with the traditional method of bacterial attachment evaluation by cell count in a Neubauer chamber (r2 = ~0.9). This strategy could be used in developing sensors for the fast and efficient bacterial attachment evaluation in minerals.