Characterization of redox reactions and phase transformation processes at iron mineral surfaces

地下水中高度生物可利用的铁相是在表面结合的铁被非生物过程重新氧化的条件下形成的。这种铁相虽然大多只以表面涂层的形式存在，但被认为有助于通过调节异质氧化和还原过程来支持电子循环。铁(氢)氧化物表面对溶解的亚铁有很高的亲和力，可以同时作为化学和微生物过程中的电子供体和电子受体。直到最近，人们才充分认识到还原环境中铁矿物表面性质和表面拓扑的高度动态化。在这里，我们集中于对铁矿物中发生的异相氧化还原反应和随后的相变的更好的理解。然而，用现有的光谱方法对矿物表面活性氧化还原物种的类型和动力学进行原位表征是非常困难的，如果可行的话。因此，我们建议开发、验证和应用一种间接方法(反应示踪法)，该方法基于模型氧化剂与表面结合的Fe(II)物种特异反应的稳定同位素组成的变化。使用这种新的方法，我们打算通过在间歇和柱状系统中良好控制的条件下进行的实验，来表征活性铁涂层的性质、形成动力学以及最终在地球化学相关环境中的重要性。

Highly bioavailable iron phases in groundwater form at conditions where surface bound Fe(II) is re-oxidized by abiotic processes. Such iron phases, though mostly present only as surface coatings, are thought to be instrumental in supporting an electron cycle by mediating heterogeneous oxidation and reduction processes. Through their high affinity for dissolved ferrous iron, surfaces of iron (hydr)oxides may act as electron donors and electron acceptors at the same time both for chemical and microbial processes. Only recently the high dynamics of surface properties and surface topologies of iron minerals in reducing environments has been fully recognized. Here, we focus on an improved understanding of heterogeneous redox reactions and subsequent phase transformations taking place at iron minerals. In situ characterization of the type and the dynamics of active redox species at mineral surfaces with existing spectroscopic methods, however, is very difficult if feasible at all. We therefore propose here to develop, validate and apply an indirect method (reactive tracer approach) based on changes of the stable isotopic composition of model oxidants reacting specifically with surface bound Fe(II) species. Using this novel approach we intend to characterize the properties, the dynamics of formation and eventually the significance of reactive iron coatings at geochemically relevant settings with experiments conducted under well controlled conditions in batch and column systems.