Formation and transformation of green rust and its influence on the mobility of trace elements in the environment

绿色锈是在还原条件下在天然土壤中形成的羟基氧化铁矿物相。此外，这种矿物是可渗透零价铁屏障中铁金属腐蚀的重要产物，这是一种用于净化地下水中放射性核素、有毒金属和有机污染物的新型修复技术。绿色锈通常由微小颗粒-纳米颗粒-组成，其具有非常高的表面积，这使得它们能够从溶液中吸收高浓度的物质。绿色锈的形成可以通过非生物和生物途径发生，形成含有还原和氧化形式的铁即Fe（II）和Fe（III）的矿物结构。高表面积和在其结构内存在还原铁使得绿色锈在还原和亚氧环境中成为无机（例如铀）和有机（例如四氯乙烯）物质的重要还原剂。这对于在这种还原过程中可能被固定的污染物种类（例如铬）特别重要。然而，尽管假设绿色锈病在自然和污染系统中的重要性，但绿色锈病对铁的地球化学循环的贡献迄今尚未量化。这主要是由于绿色锈的高反应性，这意味着当与空气接触时，矿物在几分钟内分解。因此，使用常规分析技术对该相进行表征是有问题的。该项目的目的是获得定量数据的动力学和GR形成和氧化转化的机制，使用国家的最先进的原位同步加速器为基础的技术。与此同时，我们将研究如何形态，即氧化态和性质的绑定到矿物，微量元素（如U和Cr）的变化，作为矿物颗粒的生长，然后在氧化过程中转化。通过应用新的同步加速器为基础的技术，我们将能够第一次监测这些反应在原位。这将提供关于反应的高质量的新数据，并且还最小化制备用于离线分析的材料的需要，离线分析可能导致氧化伪影发生。在这个项目中，我们将回答以下问题：1。绿色锈是如何成核和生长的？2.在氧化过程中，是什么控制着绿色锈向Fe 3 +-羟基氧化物的转化？3.在氧化过程中，与绿色锈形成和转化有关的微量元素的形态是由什么决定的？4.生物过程如何影响绿色锈病的形成和微量元素的形态？5.绿色锈是在什么样的环境条件下形成的，它如何影响环境中的微量元素和污染物的流动性？前4个目标将包括广泛的实验研究，检查绿色锈病在各种条件下类似于那些在自然环境中发现的。为了回答问题5，实验方案的数据将被纳入地球化学计算机模拟包，这将使我们能够预测绿色锈病在自然系统和受污染土地中的行为。例如，它将使我们能够在模拟核废料储存库内形成绿色锈的条件下进行建模，因此我们可以量化这一阶段对铀的流动性和生物利用度的影响。

Green rust is an iron oxyhydroxide mineral phase which forms in natural soils under reducing conditions. In addition, this mineral is an important product of iron metal corrosion in permeable zero-valent iron barriers, which are a novel remediation technology being used to decontaminate groundwaters of radionuclide, toxic metal and organic contaminants. Green rust generally consists of minute particles - nanoparticles - that have a very high surface area which gives them the ability to absorb a high concentration of species from solution. The formation of green rust can occur via both abiotic and biotic pathways forming a mineral structure containing both the reduced and oxidised forms of iron i.e. Fe(II) and Fe(III). The high surface area and presence of reduced iron within its structure make green rust an important reducing agent of both inorganic (e.g. uranium) and organic (e.g. tetrachloroethene) species within reducing and sub-oxic environments. This is particularly important for contaminant species which can be immobilised during such a reduction process (e.g. chromium). However, despite the hypothesised importance of green rust in natural and contaminated systems the contribution of green rusts to the biogeochemical cycle of iron has so far not been quantified. This is primarily due to the highly reactive nature of green rust, which means that the mineral breaks down within minutes when in contact with air. The characterisation of this phase has therefore been problematic using conventional analytical techniques. The aim of this project is to obtain quantitative data on the kinetics and mechanisms of GR formation and oxidative transformation using state-of-the-art in situ synchrotron-based techniques. In conjunction with this we will examine how the speciation i.e. oxidation state and nature of binding to the mineral, of trace elements (e.g. U and Cr) changes as the mineral particles growth and then transform during oxidation. By application of novel synchrotron based techniques we will be able for the first time to monitor these reactions in situ. This will provide high quality novel data on the reactions and also minimise the need to prepare the material for off-line analysis, which may cause oxidation artefacts to occur. During the project we will answer the following questions: 1. How does green rust nucleate and grow? 2. What controls the transformation of green rust to Fe3+-oxyhydroxides during oxidation? 3. What determines the speciation of trace elements associated with green rust as it forms and transforms during oxidation? 4. How do biogenic processes affect green rust formation and trace element speciation? 5. Under what environmental conditions does green rust form and how does this effect trace element and contaminant mobility in the environment? The first 4 objectives will consist of extensive experimental studies examining green rust under a variety of conditions analogous to those found in the natural environment. To answer question 5, the data from the experimental programme will be incorporated into geochemical computer modelling packages which will allow us to predict how green rust behaves in both natural system and contaminated land scenarios. For example, it will allow us to perform modelling under the conditions that green rust will form within a simulated nuclear waste repository so we can quantify the affect this phase will have on the mobility and bioavailability of uranium.