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

铁(II)/铁（III）氧化还原对土壤和含水层的生物地球化学循环和污染物转化动力学起着重要作用。尽管地下环境中有丰富的粘土矿物，但粘土矿物中结构铁的氧化还原过程及其对无机污染物迁移和毒性的影响尚不清楚。为了解决这一知识差距，拟议的研究旨在确定水中铁（II）（天然厌氧环境中丰富的还原剂）与粘土矿物中的结构铁（III）之间是否发生电子转移，以及该反应如何影响无机污染物Hg（II）和Cr（VI）的转化。利用同位素选择57Fe-Mössbauer光谱和红外光谱对粘土矿物中铁的氧化态和结构环境进行监测，并用显微和光谱方法对Fe（III）产物进行表征。为了更好地理解粘土矿物结合铁（II）、汞（II）和铬（VI）对无机污染物的还原作用，我们选择了铁（II）、汞（II）和铬（VI）作为示例污染物，它们在接触粘土矿物的不同表面方面表现出互补的特性。稳定同位素分馏测量非传统元素Hg和Cr的应用将对粘土矿物-污染物界面的过程产生新的见解，并将有助于这些新型同位素系统作为源和过程示踪剂的进一步发展。这一发现将有助于理解黏土矿物结合铁作为环境中氧化还原等价物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.