생물학적 산화작용을 이용한 석회석내 존재하는 금정광의 Au․Ag 품위 향상

Abstract

In order to up grade the Au-Ag content in gold ore through biooxidation, indigenous bacteria were collected from five mine water sites. The five indigenous bacteria were grown in a subculture-medium, and Uljin bacteria was selected from these indigenous bacteria, as it had the best oxidation potential during subculturing over 28 days. And in this bacteria we investigated the polymerase chin reaction and 16S rRNA sequence. In order to increase the bacteria's tolerance to heavy metals, the Uljin indigenous acidophilic bacteria was repeatedly subcultured in an adaptation-medium containing Cu 382.98 mg/l for a 2nd period of 21 days. The adapted bacteria were inoculated into Manjang gold ore, and then the bioleaching experiment was carried out for 30 days at 32 ℃. In comparison with sequences of the strain Acithiobacillus ferrooxidans (ATCC 23270), the similarity of Uljin bacteria obtained was 100%. Thus it is confirmed that the indigenous Uljin bacteria is the same species as Acithiobacillus ferrooxidans(ATCC 23270). As the adaptation experiment proceeded with the Uljin bacteria, the more the pH value was decreased, the more adapted the bacteria became. In decreasing the pH value in the adaptation-medium, it was identified that the indigenous acidophilic bacteria became adapted to the Cu ions, and that these bacteria have a tolerance potential with heavy metals. In SEM analysis, numerous acidic indigenous bacteria were observed in the adaptation-medium. The result of the bioleaching experiment with Uljin bacteria, the Cu and Pb content was much greater in the non-adapted bacterial sample than in the control sample, as well these contents were greater in the adapted bacterial sample than in the non-adapted bacterial sample. In SEM observation, the rod-shaped indigenous bacteria having sizes ranging from 0.5×0.6 ㎛ to 0.5×1.7 ㎛, were attached to the surface of the ore in the leaching-medium, and were observed in the leaching-solution. It is confirmed that these bacteria attaching to the surface of the ore can be a evidence of a direct contact oxidation mechanism, whereas with these bacteria in solution there can be an indirect contact oxidation mechanism. The result of leaching the solid-residue with an aqua regia and fire-assay analysis, the Au and Ag content was much greater in the non-adapted bacterial sample than in the control sample, and these content was greater in the adapted bacterial sample than in the non-adapted bacterial sample. The reason a higher value of Au and Ag content were obtained using the adapted bacterial sample is that gold and silver were liberated from the ore due to direct and indirect contact biooixidation. Accordingly, it is expected that more Au and Ag can be leached from the gold ore, if the bacteria is adapted with an optimization of pH and heavy metal conditions in future bioleaching processes.