Grantee Research Project Results
Copper Isotope Compositions of Copper-bearing Reservoirs in Acid Mine Drainage EnvironmentsEPA Grant Number: F5E10991
Title: Copper Isotope Compositions of Copper-bearing Reservoirs in Acid Mine Drainage Environments
Investigators: Kimball, Bryn E.
Institution: Pennsylvania State University
EPA Project Officer: Hahn, Intaek
Project Period: August 30, 2005 through August 29, 2008
Project Amount: $111,148
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
Understanding the sources of metals and the processes that influence their transport in watersheds affected by acid mine drainage (AMD) is central to improving stream water quality. Acidophilic iron (Fe)- and sulfur (S)-oxidizing microorganisms play an important role in the mobility of metals by catalyzing the dissolution of metal sulfide minerals to support their metabolic pathways. To understand metal mobility in AMD-impacted environments resulting from both biotic and abiotic processes, including sorption, dissolution, and precipitation, I propose to measure the copper (Cu) isotope ratio ( 65Cu/ 63Cu) in Cu-bearing reservoirs from AMD-impacted watersheds in the Rocky Mountains, USA. The natural variation of Cu isotope ratios in terrestrial materials is greater than that for other transition metals; therefore, measurement of Cu isotopes may become an important tool in understanding the biogeochemical cycling of metals. The goal of field surveys will be to identify characteristic environmental Cu isotope fractionation factors among Cu-bearing reservoirs that result from biotic and abiotic isotope effects. Laboratory experiments will tease apart the various fractionating steps that may contribute to cumulative environmental fractionation. If Cu isotope ratios are significantly different among Cu-bearing reservoirs, we can then attempt to track mobile Cu through an AMD system using mass balance, and thereby gain insights into the mechanisms that control the mobility of Cu and other transition metals in these environments.
The 65Cu/ 63Cu ratio in Cu sulfide ore minerals, AMD, streamwater, suspended stream material, and precipitated streambed minerals will be measured. Samples of the microorganisms that populate mine waste piles, AMD, streamwater, and streambeds will also be collected and cultured in order to conduct microbial community analyses and batch mineral dissolution experiments with Fe- and S-oxidizing microorganisms. Sulfide ore minerals and precipitated streambed minerals will be characterized by X-ray diffractometry, and Cu-bearing samples will be acid digested and purified to extract Cu using wet ion exchange chromatography. Copper isotope ratios will be measured using multi-collector inductively coupled plasma mass spectrometry.
Based upon previous work, I expect aqueous dissolved Cu in AMD to be enriched in 65Cu, and precipitated Cu (e.g., suspended stream material) to be depleted in 65Cu relative to primary sulfide ore minerals such as chalcopyrite. I also expect to identify and experiment with Fe- and S-oxidizing bacteria and archaea: including species related to the Ferroplasma, Acidithiobacillus, Leptospirillum, Thiomonas, and Solfolobus genera, to name a few. Experimental work with Fe- and S-oxidizing microorganisms will allow exploration of mechanisms for isotopic fractionation under controlled conditions.