Bioleaching of chalcopyrite using indigenous acidophilic bacteria under moderate thermopile conditions

Abstract

This study focused on the successful growth of the indigenous acidophilic bacteria living in Japanese acid hot springs in a growth medium containing elemental sulfur under moderate thermopile conditions. As the bacteria grew in the growth medium, its pH decreased and Eh increased. While the rod-shaped bacteria of about 1 μm grew into many populations at the medium length of 5 μm, a strain of above 9.8 μm grew only in a small minority. When the bacteria were stained with Gram, some bacteria 1 μm in length were proved Gram negative, and larger bacteria which were 5-6 times longer than those of 1 μm were proved Gram positive. The colonies of rod-shaped bacteria 1 μm in morphology and 1 μm in length were attached to the chalcopyrite surface and those with filament morphology ranging from 6 μm to 8.5 μm in length were attached singularly. When the indigenous acidophilic bacteria were inoculated on a chalcopyrite surface, the ion concentrations in Cu, Fe and Zn leached were two, four and six times higher than those of the controlled sample, respectively. In particular, as the indigenous acidophilic bacteria were inoculated with the chalcopyrite-leaching medium and the pH was not adjusted using sulfuric acid, the capacity of bioleaching could be compared with the capacity of inorganic leaching. The ion concentrations in Cu and Fe were very high in the sample with bacteria due to their excellent leaching capacity. However, the behavior of the leaching curve of the Zn and As in concentrations showed similarity to both the sample with and that without bacteria.