This work focuses on the geochemistry and iron isotope systematics of pyrite from hydrothermal and coal-forming environments. Dissolution of pyrite, even under abiotic conditions, is difficult to study experimentally and previous studies have demonstrated that the rate of pyrite oxidation is dependent upon environmental conditions. Knowledge of dissolution mechanisms enables more accurate reaction rate measurements, and will improve the ability to predict the temporal changes in chemistry of ground and surface waters that come into contact with pyrite. The first aspect of the research presented here focuses on the need for standardization of sample preparation techniques to allow for experimental and interlaboratory comparison of pyrite dissolution experiments. A reproducible sample preparation technique for pyrite that yields clean, uniform grains within a narrow size range of interest was developed. It was shown that use of this method in pyrite dissolution experiments significantly reduces artifacts related to unconstrained surface area exposure to fluids. In the second portion of this work, iron isotopes were analyzed to quantify and source-track the dissolution of pyrite during abiotic pyrite dissolution experiments performed on hydrothermal and sedimentary pyrites. The hydrothermal pyrite δ⁵⁶Fe values fall within the range of previously measured values, but the coal/sedimentary values are higher than those previously measured for any Phanerozoic sedimentary pyrite. Leachates from oxidative dissolution of the pyrite at pH=3 tend, with minor exceptions, to yield δ⁵⁶Fe values equal to or below those of the coexisting bulk pyrite, by up to ~1‰. This is generally consistent with theoretical fractionation calculations. Iron isotopes could be a useful tool in distinguishing between waters that interact with coal-derived pyrite and pyrite formed under marine conditions. The third section focuses on extracting sedimentary pyrite and other minerals under typical near-surface temperatures and environments, which is complicated by the small grain size and complex nature of the phases found in the sedimentary environment. An extraction method was developed to better characterize the nature of iron behavior between phases present in coal forming environments. A proposed iron extraction method and testing procedure is outlined for future studies of Fe speciation in coal.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-12102010-015700 |
| Date | 30 January 2011 |
| Creators | Wolfe, Amy Lynn |
| Contributors | Dr. Brian Stewart, Dr. Daniel Bain, Dr. David A. Dzombak, Dr. Rosemary Capo, Dr. Michael Rosenmeier, Dr. Thomas H. Anderson |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-12102010-015700/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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