School of Environmental Studies, China University of Geosciences, 430074 Wuhan, China.
School of Environmental Science & Engineering, Southern University of Science and Technology, 518055 Shenzhen, Guangdong, China.
Environ Sci Technol. 2020 Dec 1;54(23):14974-14983. doi: 10.1021/acs.est.0c03587. Epub 2020 Nov 10.
Heterogeneity in physical and chemical properties is a common characteristic in a subsurface environment. This study investigated the effect of physico-chemical heterogeneity on arsenic (As) sorption and reactive transport under water extraction in a layered system with preferential flow paths. A flume experiment was performed to derive the spatio-temporal data of As reactive transport. The results indicated that the heterogeneous system significantly accelerated downward (vertical direction) As migration as a coupled effect of physical and chemical heterogeneity that led to fast As transport with low As sorption along the preferential flow paths. The results also indicated that such a heterogeneity effect was driven by water extraction that enhanced the downward groundwater flow along the preferential flow paths. Numerical simulations were performed by matching the experimental results to provide insights into the dominant processes controlling the As migration in the heterogeneous systems. The simulation results highlighted the importance of the kinetic oxidation of mineral-bonded Fe(II) to Fe(III) in the clay matrix that dynamically increased As sorption affinity and retarded As reactive transport. A coupled model of reactive transport along the preferential flow paths, sorption-retarded diffusion from the preferential flow paths into the clay matrixes, and reactions that change sorption affinity in the matrix was required to describe the As reactive transport systems with physico-chemical heterogeneities. The results have strong implications for understanding and modeling As downward migration from shallow to deep aquifers under groundwater pumping conditions in field systems with inherent heterogeneity.
物理化学性质的非均质性是地下环境的一个普遍特征。本研究探讨了物理化学非均质性对具有优先流路径的层状系统中水分提取下砷（As）吸附和反应输运的影响。通过水槽实验获得了 As 反应输运的时空数据。结果表明，非均相体系显著加速了向下（垂直方向）的 As 迁移，这是物理和化学非均质性的耦合效应，导致优先流路径中 As 快速传输和低 As 吸附。结果还表明，这种非均质性效应是由增强优先流路径中地下水向下流动的水分提取驱动的。通过匹配实验结果进行数值模拟，深入了解控制非均相体系中 As 迁移的主要过程。模拟结果强调了矿物结合的 Fe(II)在粘土基质中向 Fe(III)的动力学氧化的重要性，该过程动态增加了 As 的吸附亲和力并减缓了 As 的反应输运。需要建立一个优先流路径上的反应输运、优先流路径向粘土基质中扩散的吸附阻滞以及改变基质中吸附亲和力的反应的耦合模型，以描述具有物理化学非均质性的 As 反应输运系统。研究结果对理解和模拟在具有固有非均质性的野外系统中，地下水抽取条件下从浅层到深层含水层的 As 向下迁移具有重要意义。
