Performance and Mechanisms of Iron Electrocoagulation for Removal of Chromium(VI) from Drinking Water

铬（VI）是一种有毒的污染物，已经在私人和公共供水以及处理过的饮用水中被观察到。目前的饮用水标准只适用于总铬，它可以以六价铬的形式存在，也可以以毒性小得多的三价铬的形式存在，三价铬在低浓度下甚至是一种营养物质。针对铬（VI）的新饮用水标准可能会实施，铁电凝是一种有可能实现所需低浓度的技术。在铁电凝中，两个铁电极之间施加直流电。其中一个电极被氧化释放出铁（II）到溶液中，这种可溶性铁（II）可以直接还原铬（VI）或被氧化成铁（III）生成氧化铁固体，在氧化铁固体上可以还原和吸附铬（VI）。铁电絮凝去除铬（VI）有多种去除途径，包括均相和非均相化学还原、吸附和共沉淀。本研究项目的主要目的是推进铁电絮凝去除六价铬的机理认识。该项目将在实验室规模的电混凝反应器中评估广泛的水化学条件下的电混凝性能。分析方法将跟踪总溶解铬和铬（VI）的变化，以达到正在考虑的法规的极低水平。该研究将使用先进的光谱和稳定同位素工具来确定电凝反应器中发生的主要反应机制。x射线吸收光谱将在国家用户设施中进行，将提供对与反应器中产生的固体相关的铬的氧化状态和分子尺度配位的见解。铬的稳定同位素分馏可以诊断特定的反应机理。电凝性能的数学模型将整合来自实验室规模实验的机理见解和数据，以便在广泛的条件下预测性能。该研究将使处理策略的优化设计和对六价铬处理性能的准确预测成为可能。该项目将提供科学信息，有助于改善饮用水中六价铬的去除，六价铬是一种事关国家利益的污染物。该研究将确定水化学对该过程中所涉及的反应的影响，这将使设计有效的策略来去除广泛的饮用水源中的铬（VI）。这些研究活动将决定环境工程、地球科学和材料科学中感兴趣的反应机制。该项目的光谱表征和稳定同位素工具的全面应用将推进环境工程研究的整体基础设施。该项目的教育和推广部分将加强研究生和本科生的教学，并促进早期学生对科学和工程的兴趣。

CBET-1335613Daniel GiammarWashington University in St. LouisChromium(VI) is a toxic contaminant that has been observed in private and public water supplies as well as in treated drinking water. Current drinking water standards are only applicable to total chromium, which can be present as chromium(VI) as well as the much less toxic form of chromium(III) that is even a nutrient at low concentrations. It is likely that new drinking water standards specific to chromium(VI) will be implemented, and iron electrocoagulation is a technology with the potential to achieve the low concentrations that may be required. In iron electrocoagulation a direct current is applied between two iron electrodes. One of the electrodes is oxidized to release iron(II) to solution, and this soluble iron(II) can directly reduce chromium(VI) or be oxidized to iron(III) to produce iron oxide solids on which chromium(VI) can be reduced and adsorbed. Iron electrocoagulation for chromium(VI) removal has multiple removal pathways that involve homogeneous and heterogeneous chemical reduction, adsorption, and co-precipitation. The primary objective of this research project is to advance the mechanistic understanding of chromium(VI) removal by iron electrocoagulation. The project will evaluate electrocoagulation performance over a broad range of water chemistry conditions in a laboratory-scale electrocoagulation reactor. Analytical methods will track changes in both total dissolved chromium and chromium(VI) to the very low levels that are being considered for regulations. The investigation will use advanced spectroscopic and stable isotope tools to identify the dominant reaction mechanisms occurring in the electrocoagulation reactor. X-ray absorption spectroscopy, which will be performed at national user facilities, will provide insights into the oxidation state and molecular-scale coordination of chromium associated with the solids generated in the reactor. Stable isotope fractionation of chromium can be diagnostic of specific reaction mechanisms. A mathematical model for electrocoagulation performance will integrate the mechanistic insights and data from the laboratory-scale experiments to enable predictions of performance over a broad range of conditions. The research will enable the optimal design of treatment strategies and accurate prediction of treatment performance for chromium(VI) removal.This project will provide scientific information that will help improve the removal of hexavalent chromium, a contaminant of critical national interest, from drinking water. The research will determine the influence of water chemistry on the reactions involved in the process, which will enable the design of effective strategies for chromium(VI) removal for a broad range of drinking water sources. The research activities will determine reaction mechanisms of interest in environmental engineering as well as earth science and materials science. The project's overall application of spectroscopic characterization and stable isotope tools will advance the overall infrastructure for environmental engineering research. The educational and outreach components of the project will enhance graduate and undergraduate teaching and promote early student interest in science and engineering.