Zhang Yuting, Chen Meng, Wang Jinguo, Deng Yirong, Li Zhaofeng
Guangdong Key Laboratory of Contaminated Environmental Management and Remediation, Guangdong Provincial Academy of Environmental Science, Guangzhou 510045, China; School of Earth Science and Engineering, Hohai University, No.8 Focheng West Road, Nanjing 211100, China; Department of Civil & Mineral Engineering, University of Toronto, 35 St. George Street, Toronto, ON M5S 1A4, Canada.
Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment, Nanjing 210042, China.
J Hazard Mater. 2023 Oct 5;459:132049. doi: 10.1016/j.jhazmat.2023.132049. Epub 2023 Jul 13.
Electrokinetic (EK) technology is promising for removing heavy metals from contaminated unsaturated soils. It is crucial to accurately determine the unsaturated electro-osmotic permeability for predicting the efficiency of EK treatment, optimizing treatment strategies, and accurately predicting the distribution of contaminant concentrations. However, the current approach of estimating unsaturated electro-osmotic permeability, which involves measuring effective voltage, drainage volume, and performing exponential fitting, fails to address the issue of uneven voltage gradient distribution during EK treatment. Herein, a novel method was presented for estimating the electro-osmotic permeability of unsaturated porous media. This method quantifies the electro-osmotic flow in an unsaturated porous medium by considering the difference in mass-transfer efficiency (MTE) between real (with electro-osmotic flow) and hypothetical cases (without electro-osmotic flow). This difference serves as a metric for estimating the electro-osmotic permeability. Results revealed a linear relationship between the electro-osmotic permeability and the product of volumetric moisture content and tortuosity, with the slope related to the ionic mobility of target ions, hypothetical and actual MTE. To validate this method, hexavalent Cr (Cr(VI)) was selected as the target contaminant and six EK experiments were conducted with varying initial volumetric moisture content. The feasibility of the method was evaluated by fitting the results of these experiments to obtain the specific slope of the porous medium used. Compared to the existing effective voltage-drainage volume-exponential fitting method, the proposed method offers several advantages. First, it effectively addressed the issue of nonuniform voltage distribution during EK treatment in the unsaturated porous medium. Second, it overcame the problem of a nonzero electro-osmotic permeability at zero volumetric moisture content in the exponential empirical formula. Third, the proposed method was based on theoretical derivations instead of relying solely on empirical fitting. Finally, the proposed method does not require a prior estimate of the saturated electro-osmotic permeability of the porous medium.
电动（EK）技术在去除污染非饱和土壤中的重金属方面具有广阔前景。准确测定非饱和电渗渗透率对于预测EK处理效率、优化处理策略以及精确预测污染物浓度分布至关重要。然而，当前估算非饱和电渗渗透率的方法，即测量有效电压、排水量并进行指数拟合，未能解决EK处理过程中电压梯度分布不均的问题。在此，提出了一种估算非饱和多孔介质电渗渗透率的新方法。该方法通过考虑实际情况（存在电渗流）与假设情况（不存在电渗流）之间传质效率（MTE）的差异，对非饱和多孔介质中的电渗流进行量化。这种差异作为估算电渗渗透率的指标。结果表明，电渗渗透率与体积含水量和曲折度的乘积之间存在线性关系，斜率与目标离子的离子迁移率、假设和实际的MTE有关。为验证该方法，选择六价铬（Cr(VI)）作为目标污染物，并进行了六个初始体积含水量不同的EK实验。通过拟合这些实验结果以获得所用多孔介质的特定斜率，对该方法的可行性进行了评估。与现有的有效电压 - 排水量 - 指数拟合方法相比，该方法具有多个优点。首先，它有效解决了非饱和多孔介质中EK处理过程中电压分布不均匀的问题。其次，它克服了指数经验公式中体积含水量为零时电渗渗透率非零的问题。第三，该方法基于理论推导，而非仅依赖经验拟合。最后，该方法不需要预先估计多孔介质的饱和电渗渗透率。
