Fe(II)-Fe(III) Electron Transfer at Fe-containing Clay Minerals and its Effect on Hg(II) and Cr(VI) Transformation

Fe（II）/Fe（III）氧化还原电对在土壤和含水层的地球化学循环和污染物转化动力学中起着重要作用。尽管在地下环境中的粘土矿物的丰度，氧化还原过程中的粘土矿物中的结构铁，以及它们对无机污染物的流动性和毒性的影响还没有得到很好的理解。为了解决这一知识差距，拟议的研究旨在确定是否电子转移之间的水溶液Fe（II），还原剂丰富的自然厌氧环境中，和结构的Fe（III）在粘土矿物发生，以及如何影响这种反应的转化的无机污染物汞（II）和铬（VI）。同位素选择性57 Fe-Mössbauer光谱和红外光谱将用于监测粘土矿物中Fe的氧化态和结构环境，并将用显微镜和光谱方法表征Fe（III）产物。为了更好地理解粘土矿物结合的Fe（II）、Hg（II）和Cr（VI）对无机污染物的减少，选择它们作为示例性污染物，它们在进入粘土矿物的不同表面方面表现出互补的性质。应用稳定同位素分馏测量的非传统元素汞和铬将产生新的见解过程中的粘土矿物-污染物界面，并将增加这些新的同位素系统作为源和过程示踪剂的进一步发展。 这些发现将有助于理解粘土矿物结合铁作为环境中氧化还原当量的可再生来源的作用，并将提高评估无机和有机污染物命运的能力。

The Fe(II)/Fe(III) redox couple plays an important role in biogeochemical cycles and for the dynamics of contaminant transformation in soils and aquifers. Despite the abundance of clay minerals in subsurface environments, redox processes of structural Fe in clay minerals as well as their impact on the mobility and toxicity of inorganic contaminants are not well understood. To address this knowledge gap, the proposed research aims to determine whether electron transfer between aqueous Fe(II), a reductant abundant in natural anaerobic environments, and structural Fe(III) in clay minerals occurs and how this reaction influences the transformation of the inorganic contaminants Hg(II) and Cr(VI). Isotope selective 57Fe-Mössbauer spectroscopy and infrared spectroscopy will be used to monitor the oxidation state and the structural environment of Fe in clay minerals and the Fe(III) product will be characterized with microscopic and spectroscopic methods. To gain a better understanding of inorganic contaminant reduction by clay mineral bound Fe(II), Hg(II) and Cr(VI) were chosen as exemplary contaminants, exhibiting complementary properties with regard to accessing the different surfaces of clay minerals. The application of stable isotope fractionation measurement to the non-traditional elements Hg and Cr will generate new insights into processes at the clay mineral-contaminant interface and will add to the further development of these novel isotope systems as source and process tracer. The findings will add to understanding the role of clay mineral bound Fe as a renewable source of redox equivalents in the environment and will improve the ability to assess the fate of contaminants, both inorganic and organic.