Microbial oxidation of refractory gold sulfide concentrate by a native consortium
(1. Centro de Investigación y Desarrollo en Fermentaciones Industriales (CINDEFI, CCT LA PLATA-CONICET, UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Calle 50 N° 227, 1900 La Plata, Argentina;
2. Departamento de Minería, Facultad de Ciencias Físico-Matemáticas y Naturales, Universidad Nacional de San Luis, Chacabuco 917, 5700 San Luis, Argentina;
3. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas (PROBIEN, CONICET-UNCo), Departamento de Química, Facultad de Ingeniería, Universidad Nacional del Comahue, Buenos Aires 1400, 8300 Neuquén, Argentina)
2. Departamento de Minería, Facultad de Ciencias Físico-Matemáticas y Naturales, Universidad Nacional de San Luis, Chacabuco 917, 5700 San Luis, Argentina;
3. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas (PROBIEN, CONICET-UNCo), Departamento de Química, Facultad de Ingeniería, Universidad Nacional del Comahue, Buenos Aires 1400, 8300 Neuquén, Argentina)
Abstract: A defined mesophilic consortium including an iron oxidizing bacterium and a sulfur oxidizing bacterium was constructed to evaluate its ability for bioleaching a flotation concentrate from Andacollo mine in Neuquén, Argentina. Experiments were performed in shake flasks with a pulp density of 10% (w/v), using a basal salt medium containing ferrous iron at pH 1.8. The leaching solutions were analyzed for pH, redox potential (using specifics electrodes), ferrous iron (by UV-Vis spectrophotometry) and metal concentrations (by atomic absorption spectroscopy). The results showed that the consortium was able to reduce the refractory behavior of the concentrate, allowing 91.6% of gold recovery; at the same time, high dissolution of copper and zinc was reached. These dissolutions followed a shrinking core kinetic model. According to this model, the copper solubilization was controlled by diffusion through a product layer (mainly jarosite), while zinc dissolution did not show a defined control step. This designed consortium, composed of bacterial strains with specific physiological abilities, could be useful not only to optimize gold recovery but also to decrease the leachates metallic charge, which would be an environmental advantage.
Key words: biooxidation; refractory gold concentrate; native consortium; kinetic analysis