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

废弃地下矿山的酸性矿井排水（AMD）一直是美国矿区最严重的水质和流域退化问题。由于地下煤炭和金属开采作业，黄铁矿（FeS2）暴露于水中，导致其溶解并将铁和硫酸释放到溶液中，以及酸诱导其他矿物溶解的金属和其他成分。此外，全球河流硫酸盐通量的很大一部分来自黄铁矿的溶解，而且由于采矿活动，这一贡献正在增加。虽然黄铁矿溶解在硫循环和AMD形成中非常重要，但我们对这一过程的理解和建模能力非常有限。该项目将利用铁同位素测量技术的最新进展，以一种新的方式在实验室和现场研究黄铁矿的溶解。一个重要的目标将是测试和证明使用铁同位素量化和来源跟踪废弃煤矿流出物中黄铁矿溶解的能力。假设不同条件下形成的沉积黄铁矿的56Fe/54Fe同位素比值不同，黄铁矿溶蚀过程本身可能导致可测量的同位素分异。为了验证这一点，我们将测定Appalachian盆地不同沉积环境中沉积黄铁矿的56Fe/54Fe同位素比值。其中一些样品的溶解速率，以及由此产生的水相同位素分馏，将在实验室中使用专门为定量黄铁矿溶解而开发的间歇式反应器，在严格控制的氧化还原和水相条件下进行研究。实验室和现场数据将使我们能够评估我们使用56Fe/54Fe作为AMD流出物中铁的主要来源的示踪剂的能力。获得的结果将为进一步研究更复杂的系统提供基础，特别是有细菌存在的系统，可以介导黄铁矿溶解过程。

0228903DzombakAcid 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.