Bioleaching of a zinc sulfide ore by thermophilic consortia isolated from Copahue volcano

Bioleaching of a sulfide ore was investigated using a consortium of thermophilic bacteria and archaea. The consortium was obtained through successive enrichment procedures (using M88 with tetrathionate) after isolating from two different places into the geothermal area (Ba (n) over tildeo 9 and Las Maquinitas) of the Copahue volcano (in the north of Neuquen province in Argentina). Bioleaching experiments were carried out in 250-ml shake flasks with 100 ml of media and 1 g of the sulfide ore. Flasks were incubated at 150 rpm and 70 degrees C. The major constituents of the ore (La Resbalosa, Argentina) were sphalerite, pyrite, chalcopyrite and galena. The sample used throughout bioleaching experiments contained 22.5 % Zn. Two different media (0K and M88) were evaluated with and without the addition of elemental sulfur. Genetic diversity analysis of the microbial community was performed by PCR amplification of bacterial 16S rDNA fragments and analyzed by DGGE (denaturing gradient gel electrophoresis). The 16S rDNA was amplified by using eubacteria and archaea primers. Metal concentration, Eh and pH were periodically analyzed. Solid residues were filtered, washed, dried and finally analyzed by XRD and XRF. After 45 days, more than 50 % of zinc and about 100 % of the copper were solubilized. Galena and jarosite were detected in the solid residues. The data indicated that the dominant acidophiles were bacteria or archaea according to the media. M88 media allowed an important decrease of pH and higher zinc extractions while the presence of sulfur did not show significant influence on the zinc recovery.