Collaborative Research: Field and Experimental Iron Isotope Investigation of Sedimentary Pyrite Dissolution in Appalachian Coal Mine Drainage

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0229019 CapoAcid mine drainage (AMD) from abandoned underground mines is and has long been the most serious water quality and watershed degradation problem in the mining regions of the U.S. As a result of underground coal and metal mining operations, pyrite (FeS2) becomes exposed to water, resulting in its dissolution and release of iron and sulfuric acid to solution, as well as metals and other constituents from acid-induced dissolution of additional minerals. Moreover, a significant fraction of the global fluvial sulfate flux arises from pyrite dissolution, and the contribution is increasing due to mining activities. While pyrite dissolution is of great importance in sulfur cycling and in AMD formation, our understanding of this process and our ability to model it are very limited. This project will exploit recent advances in iron isotope measurement techniques to study pyrite dissolution in a novel manner in the laboratory and in the field. An important objective will be to test and demonstrate the power of using iron isotopes to quantify and source-track the dissolution of pyrite in abandoned coal mine outflows. It is hypothesized that the 56Fe/54Fe isotopic ratio will be distinct for sedimentary pyrites formed under different conditions, and that the process of pyrite dissolution itself could lead to measurable isotopic fractionation. To test this, the 56Fe/54Fe isotopic ratio in sedimentary pyrite from different depositional environments of the Appalachian basin will be determined. The rates of dissolution of some of these samples, and resulting aqueous phase isotopic fractionation, will be investigated in the laboratory using a batch reactor developed specifically for quantifying pyrite dissolution under tightly controlled redox and aqueous phase conditions. The laboratory and field data will allow us to evaluate our ability to use 56Fe/54Fe as a tracer for the primary source of Fe in AMD outflows. Results obtained will provide the basis for moving forward with additional studies of more complex systems, especially systems with bacteria present that can mediate the pyrite dissolution process.