Department of Environmental Engineering, Technical University of Denmark, Bygningstorvet, Building 115, 2800, Kgs. Lyngby, Denmark.
Department of Environmental Engineering, Technical University of Denmark, Bygningstorvet, Building 115, 2800, Kgs. Lyngby, Denmark.
J Contam Hydrol. 2022 Jan;244:103933. doi: 10.1016/j.jconhyd.2021.103933. Epub 2021 Nov 29.
The application of electrokinetic techniques in porous media has great potential to enhance mass transfer rates and, thus, to mobilize contaminants and effectively deliver reactants and amendments. However, the transport mechanisms induced by the application of an external electric field are complex and entail the coupling of physical, chemical and electrostatic processes. In this study we focus on electromigration and we provide experimental evidence of the impact of compound-specific properties, such as the aqueous diffusivity and the valence of charged species, on the macroscopic electrokinetic transport. We performed a series of multidimensional experiments considering the displacement of three different tracer plumes (i.e., permanganate, allura red and new coccine) in different background electrolyte solutions. The outcomes of the experiments clearly show that both the compound-specific diffusivity and the charge of the injected and resident ions impact the transport of the selected color tracer plumes, whose evolution was monitored with image analysis. The investigated experimental scenarios led to distinct plume behavior characterized by different mass distribution, average displacement velocities, longitudinal and lateral plume spreading, shape of the invading and receding fronts, as well as dilution of the injected solutes. A numerical simulator, based on the Nernst-Planck-Poisson equations and on aqueous speciation reactions in the pore water, allowed us to quantitatively interpret the experimental results, to capture the observed patterns of plume evolution, and to illuminate the coupling between the governing physico-chemical mechanisms and the controlling role of small scale compound-specific and electrostatic properties. Finally, the model was also extended to a typical configuration of in situ electrokinetic remediation of contaminated groundwater to show the impact of such mechanisms at larger scale.
电动技术在多孔介质中的应用具有很大的潜力，可以提高传质速率，从而使污染物迁移，并有效地输送反应物和改良剂。然而，外电场作用下的传输机制很复杂，涉及物理、化学和静电过程的耦合。在本研究中，我们专注于电动迁移，并提供了实验证据，证明了化合物特定性质（如水相扩散系数和带电物质的价态）对宏观电动传输的影响。我们进行了一系列多维实验，考虑了三种不同示踪剂羽流（即高锰酸盐、诱惑红和新胭脂红）在不同背景电解质溶液中的位移。实验结果清楚地表明，注入和驻留离子的化合物特定扩散系数和电荷都对所选颜色示踪剂羽流的传输有影响，我们用图像分析监测了其演化。所研究的实验场景导致了不同的羽流行为，其特征为不同的质量分布、平均位移速度、纵向和横向羽流扩展、侵入和后退前沿的形状以及注入溶质的稀释。基于纳斯特-普朗克-泊松方程和孔隙水中水相配体反应的数值模拟器，使我们能够定量解释实验结果，捕捉到羽流演化的观察模式，并阐明控制物理化学机制之间的耦合以及小尺度化合物特定和静电性质的控制作用。最后，该模型还扩展到典型的原位电动修复受污染地下水的配置中，以展示这种机制在更大规模上的影响。
