Bioleaching of As from mine tailings using an autochthonous Bacillus cereus strain

Contamination of heavy metals has been a serious environmental problem due to increasing anthropogenic activities such as mining, smelting, livestock, landfills, waste dumps, and agriculture. Bioleaching experiments were conducted using native Bacillus cereus MAMPE19 BCG, isolated and characterized from previous research, to test removal of arsenic (As) from actual mining waste. Mineralogical characterization by XRD was performed to identify mineral associations with As. The experimental design included a bioleaching system with agitated flasks (triplicate) and the effects of pH (5, 7, and 9) and pulp density (10, 15, and 20%) were evaluated. Finally, based on the results of the ANOVA, the system that achieved the highest percentage of As dissolution was selected and scaled to a stirred tank bioreactor. The composition of the mineral was mainly calcite (CaCO3), gismondine (CaAl2Si2O8 center dot 4(H2O)), akermanite (Ca2MgSi2O7), and silicon oxide (SiO2). Native Bacillus cereus dissolved 40.6 +/- 4.9 and 37.4 +/- 2.7 % of As in 10 d, in agitated flasks at a pH of 5 and a pulp density of 10 and 15%, respectively; and a 27.5 +/- 2.9% dissolution of As was achieved in the stirred tank bioreactor at pH 5 and pulp density of 15%, supported by significant statistical differences.