Solubilization of a K-silicate rock by Acidithiobacillus thiooxidans

Abstract Sulfur-oxidizing bacteria are used in bioleaching processes to recover metals such as gold and copper. The mechanisms for solubilizing metals used by the bacterium Acidithiobacillus thiooxidans involve sulfur oxidation reactions, with the consequent formation of acid. In this study, solubilization of a K-silicate rock (verdete rock, VR) was investigated in a biological trial using A. thiooxidans and elemental sulfur (S 0 ). Erlenmeyer flasks containing modified 9 K medium, bacterial cultures and VR were incubated at 30 °C for periods ranging from 0 to 49 days. pH, redox potential were determined, and chemical and mineralogical analyses were performed after each incubation period. In the presence of A. thiooxidans , the estimated initial pH of 4.2 was reduced to 0.57 after 49 days of incubation. Under acidic conditions, partial solubilization of VR was detected by increases in the concentrations of structural elements of rock minerals, such as K, Al, Fe and Si in the medium containing bacteria, which corresponded to 6.6, 5.8, 14.1 and 1.7% of the total content of these elements in VR, respectively. Mineralogical analysis showed similar changes in X-ray Diffraction spectra (XRD) for VR samples in the absence and presence of A. thiooxidans at 49 days. Our study shows that solubilization of VR occurs when A. thiooxidans and S 0 are included in the culture medium, suggesting potential use of a biological route to leach value metals from silicate minerals using low energy input, compared to conventional processes in which pure acids/bases or high temperatures are used.