2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 3
Presentation Time: 8:30 AM


THURSTON, Roland S., Chemistry, Colorado School of Mines, 1500 Illinois St, Golden, CO 80401, MANDERNACK, Kevin W., Department of Chemistry and Geochemistry, Colorado School of Mines, 1500 Illinios Street, Golden, CO 80401 and SHANKS III, Wayne C., rthurso@mines.edu

The oxidation of copper sulfide minerals in acid mine drainage (AMD) systems can result in the release of transition metals such as copper into the environment, which can in turn have drastic effects on organisms present in the system. To prevent or remediate such affected sites requires an understanding of the various chemical (aerobic vs. anaerobic) and biological (biotic vs. abiotic) pathways by which these minerals are oxidized. Some bacteria have been shown to increase the rate of oxidation in these systems therefore we have conducted laboratory experiments with and without bacteria at acidic pH under both aerobic and anaerobic conditions. We have explored the oxidation of three different copper sulfide minerals: chalcopyrite (CuFeS2), chalcocite (Cu2S), and covellite (CuS) using Acidithiobacillus ferrooxidans, a bacterium known to oxidize sulfide minerals. Preliminary results show that A. ferrooxidans has no effect on the oxidation of covellite under aerobic conditions relative to abiotic controls. However, A. ferrooxidans does have a significant effect on the oxidation of chalcopyrite relative to abiotic controls. In the chalcopyrite aerobic experiment, the biotic samples show a decrease in pH relative to the abiotic controls which increase in pH. Also, the biotic samples show a huge increase in sulfate relative to the abiotic controls, producing ~800 ppm sulfate biotically compared to essentially no sulfate formed abiotically after ~1 month. The abiotic chalcopyrite samples also showed ~20 mg/L of copper released to solution after the same time period compared to ~ 200 mg/L of copper released in the biotic samples. This corresponds to ~20% of the copper released from the mineral which compares very well with other experimental data (Konishi et al., 2001). Further understanding of the reaction pathways results from the study of oxygen and sulfur isotopes that comprise the sulfate formed during the oxidation process. We have specifically addressed this by using two isotopically distinct waters and observing fractionation effects under different conditions.