Abiotic Reaction and Diffusion of Chlorinated Solvents in Fe2+ Bearing Intact Limestones and Mudstones

地下水污染物在水饱和低渗透岩石基质中的扩散是一个非常缓慢的过程，也是许多地下修复活动取得有限成功的原因。尽管经过数十年的清理努力，氯化溶剂仍然是最相关的地下水污染物之一，特别是在城市空间形成大规模的羽状物。缓慢扩散导致在岩石基质中停留时间很长，因此涉及含铁矿物（如硫化铁、磁铁矿、层状硅酸盐）的缓慢非生物反应可能对氯化化合物的转化有效，应在评估自然衰减电位时予以考虑。本提案的目标是测量三氯乙烯和过氯乙烯在裂隙含水层和含水层岩石样品中缓慢扩散过程中的非生物转化。由于母体化合物的反应速率可能太慢，无法通过实验测量，因此重点是鉴定和分析转化中间体和产物（例如部分氯化的乙炔、乙烯和乙烷）。反应扩散实验必须用完整的岩石样品进行，因为矿物（如石英、黄铁矿）的破碎可能会引入反应表面，从而可能导致母体化合物的脱卤。与早期的研究相反，反应将与矿物类型及其在岩石基质中的原始尺寸有关。结果不仅与氯化溶剂羽流的长期行为有关，而且对放射性废物处理或还原岩石的化学风化（氧化）也具有重要意义。

Diffusion of groundwater contaminants into and out of water-saturated low permeability rock matrices is a very slow process and responsible for the limited success of many subsurface remediation activities. Chlorinated solvents are still among the most relevant groundwater contaminants forming large scale plumes especially in urban space despite decades of clean-up efforts. Slow diffusion results in very long residence times in the rock matrix and thus slow abiotic reactions involving Fe2+ bearing minerals (e.g. iron sulfides, magnetite, phyllosilicates) may become effective in transformation of chlorinated compounds and should be considered in assessment of natural attenuation potentials. Goals of this proposal is to measure abiotic transformation of tri- and perchloroethene during slow diffusion in rock samples from fractured aquifers and from aquitards. Since reaction rates of the parent compounds are likely too slow to be measurable experimentally, focus is on identification and analysis of transformation intermediates and products (e.g. partly chlorinated acetylenes, ethenes and ethane). Reactive diffusion experiments have to be performed with intact rock samples since crushing of minerals (e.g. quartz, pyrite) may introduce reactive surfaces resulting potentially in dehalogenation of the parent compounds. In contrast to earlier studies reactions will be related to types of minerals and their original size in the rock matrix. Results are not only relevant for long-term behavior of chlorinated solvent plumes, but in general important for radioactive waste disposal or chemical weathering (oxidation) of reduced rocks.