Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
Department of Civil, Environmental and Geomatic Engineering, ETH Zürich, 8092 Zürich, Switzerland.
Environ Sci Technol. 2022 Oct 4;56(19):13696-13708. doi: 10.1021/acs.est.2c02189. Epub 2022 Sep 12.
Arsenic (As) is a toxic element, and elevated levels of geogenic As in drinking water pose a threat to the health of several hundred million people worldwide. In this study, we used microfluidics in combination with optical microscopy and X-ray spectroscopy to investigate zerovalent iron (ZVI) corrosion, secondary iron (Fe) phase formation, and As retention processes at the pore scale in ZVI-based water treatment filters. Two 250 μm thick microchannels filled with single ZVI and quartz grain layers were operated intermittently (12 h flow/12 h no-flow) with synthetic groundwater (pH 7.5; 570 μg/L As(III)) over 13 and 49 days. Initially, lepidocrocite (Lp) and carbonate green rust (GRC) were the dominant secondary Fe-phases and underwent cyclic transformation. During no-flow, lepidocrocite partially transformed into GRC and small fractions of magnetite, kinetically limited by Fe(II) diffusion or by decreasing corrosion rates. When flow resumed, GRC rapidly and nearly completely transformed back into lepidocrocite. Longer filter operation combined with a prolonged no-flow period accelerated magnetite formation. Phosphate adsorption onto Fe-phases allowed for downstream calcium carbonate precipitation and, consequently, accelerated anoxic ZVI corrosion. Arsenic was retained on Fe-coated quartz grains and in zones of cyclic Lp-GRC transformation. Our results suggest that intermittent filter operation leads to denser secondary Fe-solids and thereby ensures prolonged filter performance.
砷（As）是一种有毒元素，饮用水中地球成因的高浓度砷对全球数亿人的健康构成威胁。在这项研究中，我们使用微流控技术结合光学显微镜和 X 射线光谱学，在基于零价铁（ZVI）的水处理过滤器的孔隙尺度上研究了零价铁腐蚀、次生铁（Fe）相形成和砷保留过程。两个 250μm 厚的微通道分别填充了单层 ZVI 和石英颗粒层，以间歇方式（12h 流动/12h 无流动）运行，使用合成地下水（pH7.5；570μg/L As(III))，持续 13 天和 49 天。最初，纤铁矿（Lp）和碳酸盐绿锈（GRC）是主要的次生 Fe 相，并经历了循环转化。在无流动期间，纤铁矿部分转化为 GRC 和少量的磁铁矿，动力学上受到 Fe(II)扩散或腐蚀速率降低的限制。当再次流动时，GRC 迅速且几乎完全转化回纤铁矿。更长的过滤器运行时间和更长的无流动时间加速了磁铁矿的形成。磷酸盐在 Fe 相上的吸附允许下游碳酸钙沉淀，从而加速了缺氧 ZVI 腐蚀。砷被保留在 Fe 涂覆的石英颗粒上和循环 Lp-GRC 转化的区域内。我们的结果表明，间歇式过滤器操作会导致更密集的次生 Fe 固体，从而确保更长的过滤器性能。
