AsFePO - A model concept for in situ investigation of arsenic and phosphate adsorption to predefined iron minerals and to characterize transformation processes of iron minerals

亚洲大型三角洲系统（如越南的红河三角洲）的浅层地下水往往富含无机砷（As），威胁着数百万居民的健康。这些地区大规模抽取地下水，造成无砷地下水资源与富砷地下水资源不可逆转地混合。竞争性阴离子浓度的增加，特别是磷酸盐（PO 43-），降低了沉积物的固定能力。在运输过程中，在当地的含水层中溶解的砷的流动性受到强烈的影响，吸附沉积和无处不在的铁（oxyhydr）氧化物。此外，富含砷的地下水通常也富含还原铁（Fe 2+），这能够与铁（羟基）氧化物反应，从而诱导矿物转化。这种转变永久影响砷的吸附和固定能力的沉积物。在本研究项目的范围内，有关的运输和由此产生的威胁砷无地下水资源的基本机制的特点是与瑞士联邦研究所水产科学和技术（Eawag）的合作。研究概念的目的是在红河附近的一个研究地点，在野外条件下评估砷-铁-磷酸盐系统内复杂的相互作用。首先，过滤实验，使用当地的地下水富含As和PO 43-将被用来确定不同的和以前的地球化学特征的铁（oxyhydr）氧化物的吸附能力。在第二步中，将含有As负载铁（羟基）氧化物的样品载体引入研究场地的含水层部分附近的表面（通过现有的地下水监测威尔斯井）。这些样品将暴露于当地地下水，其特征是增加的As，Fe 2+和PO 43-浓度在接下来的9个月。使用预定义的铁（oxyhydr）氧化物的原位曝光，这将是可能的区分潜在的矿物转化及其对各自的铁（oxyhydr）oxides.By结合现场实验的结果和成果的固定能力的影响，新的和重要的结论，关于移动的As可以得出。这些数据可以用来建立一个水化学传输模型，描述调查区域内的活性As传输。此外，在原位曝光实验的结果将允许得出结论，在各自的长期作为固定能力不同的铁（oxyhydr）氧化物，这是一个重要的信息，在原位去污技术。

Shallow groundwater of the huge deltaic systems of Asia like the Red River Delta in Vietnam is often enriched in inorganic arsenic (As), threatening the health of millions of residents. The massive abstraction of groundwater in these areas locally causes an irreversible mixing of arsenic-free groundwater resources with arsenic-rich groundwater. Increased concentrations of competitive anions, especially phosphate (PO43-), decrease the immobilization capacity of the sediments. During transport, the mobility of dissolved As in local aquifers is strongly influenced by adsorption to sedimentary and ubiquitously occurring iron(oxyhydr)oxides. Additionally, arsenic-rich groundwater is often enriched in reduced iron (Fe2+) as well, which is capable to react with iron(oxyhydr)oxides, thereby inducing mineral transformations. Such transformations permanently affect the arsenic adsorption and immobilization capacity of the sediments.Within the scope of this research project, the underlying mechanisms related to As transport and the resulting threat to arsenic-free groundwater resources will be characterized in cooperation with the Swiss Federal Institute of Aquatic Science and Technology (Eawag). The research concept aims at assessing the complex interactions within the arsenic-iron-phosphate-system under field conditions at a study site next to the Red River. First, filtration experiments using local groundwater enriched in As and PO43- will be used to determine the As adsorption capacity of different and previously geochemically characterized iron(oxyhydr)oxides. In a second step, sample carrier containing As loaded iron(oxyhydr)oxides will be introduced into surface near aquifer parts of the study site (via existing groundwater monitoring wells). These samples will be exposed to local groundwater characterized by increased As, Fe2+ and PO43- concentrations for the following nine months. Using the in situ exposition of predefined iron(oxyhydr)oxides, it will be possible to distinguish potential mineral transformations and their influences on the As immobilization capacity of the respective iron(oxyhydr)oxides.By combining the results and outcomes of the field experiments, new and important conclusions regarding the mobility of As can be drawn. The data can be used to create a hydrochemical transport model describing reactive As transport within the investigation area. In addition, the results of the in situ exposition experiments will allow to draw conclusions in respective to the long term As immobilization capacity of different iron(oxyhydr)oxides, which is an essential information regarding in situ decontamination techniques.