BIOMINERALIZATION OF GOLD AND HEAVY METALS FROM MINE WASTE BY THREE MICROBIAL SPECIES

Clean up and remediation of mine waste and acid mine drainage are important issues that have been studied for decades to improve environmental safety and provide clean water for humanity and ecosystems. In this pilot study, we test the biomineralization capacity of two bacterial species and one fungi to precipitate gold and other heavy metals from gold chloride and copper sulfate solutions, as well as water from the Berkeley pit acid mine drainage lake of Butte, MT. We hypothesized that if the microbe successfully precipitates gold and other heavy metals into its cells or absorbs the particles to its membrane the concentration of the dissolved metals will decrease in the solutions. Two bacteria strains (B. cereus and C. crescentus) and a yeast strain (S. cerevisiae) were inoculated into three separate solutions of gold chloride, copper sulfate, and water from the Berkeley pit lake of Butte, MT and kept in the dark at 30°C for 11 days in 250 mL Erlenmeyer flasks. Samples were then filtered through 0.2 micron syringe filters and the filtrates analyzed with ICP-OES and FA-AA.

The B. cereus bacterium was able to precipitate gold by a yet unknown mechanism. This was also supported by the chemical analyses because concentration of the gold chloride solution decreased significantly while the other microorganisms did not change the solution chemistry significantly. The Berkley pit water did not contain detectable amounts of gold, but iron, zinc, copper and sulfur concentrations were high. Based on our experimental results C. crescentus lowered the iron, zinc and sulfur concentrations of the water, but did not change the copper significantly. The other species did not affect the Berkley pit water chemistry significantly. The copper sulfate experiment produced inconclusive results, mainly due to the extremely high concentrations of copper sulfate used in this experiment. In conclusion, biomineralization of gold and heavy metals from toxic acid mine drainage are dependent on the microbial species present and the initial concentrations of the solutions. Further experiments are planned to elucidate the capabilities of various bacteria and fungi to biomineralize gold and heavy metals as a method of bioremediation for polluted sites and to determine if biomineralization is a cost-effective method of remediation or ore mineralization.