The Bioleaching of copper sulfide ores in saline media : shake flask studies

The feasibility of bioleaching two Chilean copper ores under saline conditions was evaluated by batch tests. Total copper content of the ores were 3.87% and 1.64%, respectively. Lower ore mineralogy was comprised of atacamite, chrysocolla, bornite, chalcopyrite, chalcocite, and minor pyrite, while Zaldivar's included brochantite, chrysocolla, chalcocite, and pyrite. Mixed bacterial cultures dominated by Thiobacillus ferrooxidans were used in all test work. As the effect of chloride ion on copper extraction was of primary concern, shake flask tests at various chloride levels were conducted. Sterile (no bacteria) tests were run under conditions identical to corresponding bioleach tests to provide information on abiotic leaching. All bioleach tests demonstrated, by attaining high Eh levels, that adaptation occurred at all chloride levels tested. On initial exposure to concentrations above baseline culture tolerance, inhibition occurred, manifesting as lengthier lag times, the severity increasing with the difference in chloride concentration between culture tolerance level and the level in the test medium. With repeated exposure to media containing identical chloride levels, lag times decreased, demonstrating further evidence of bacterial adaptation to chloride ion. Successful adaptation by bacteria was reflected by high copper extractions at all chloride levels for the bioleach tests, averaging 91.9% (Lower (CI) test series) and 94.5% (Zaldivar (CI) test series). As expected, the corresponding sterile tests did not achieve the same level of extraction, averaging 43.6% (Lower (CI)) and 82.0% (Zaldivar (CI)). Clearly, the Zaldivar ore was much more reactive to abiotic leaching than the Lower ore. While chloride-enhanced cupric-ion leaching was a factor for both sets of sterile tests, other factors may also have enhanced abiotic Zaldivar ore leaching. These factors are believed to include (a) conspicuous differences in mineralogical content and distribution, (b) apparently more acid-soluble copper mineralization, and (c) chloride-enhanced galvanic leaching.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat