Experimental study and mechanism analysis of chelating agent enhanced on electrokinetic removal of copper and lead from loess
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摘要: 中国西部地区高速发展导致黄土受到重金属污染的问题日益严重。电动修复因其出色的可操作性而受到关注，然而由于极化现象和重金属在阴极附近沉淀等因素导致电动修复效率降低。因此，以铜铅污染黄土为研究对象，将螯合剂耦合电动修复的技术同时结合阴极电解液投加，研究酒石酸、柠檬酸、EDTA 3种螯合剂及作为阴极电极液对黄土中铜铅金属的去除效率影响并探讨其强化去除机理。结果表明：酒石酸、柠檬酸、EDTA均可通过络合作用提高铜、铅金属的迁移能力，使铜、铅金属的去除效率有不同程度的提升，其中以阴极附近区域的铜、铅金属去除效果提升较为明显；在3种螯合剂中，EDTA由于螯合能力较强，能在不同的pH范围内与铜、铅金属反应，从而生成较为稳定的络合物，强化了电动修复效率；与对照组相比，EDTA通过与重金属进行六原子配位而形成稳定的络合物，将其他形态的重金属向迁移能力较强、较易去除的可交换态进行转化，把铜、铅金属的整体去除效率分别提高到55.4%，27.2%。Abstract: The rapid development in the western areas of China has resulted in a growing problem of heavy metal pollution in the loess land. The electrokinetic remediation has gained attention due to its great maneuverability. However, certain factors such as polarization phenomena and precipitation of heavy metals near the cathode have lead to a decrease in the efficiency of the electrokinetic remediation. Therefore, focusing on studying the copper and lead-contaminated loess as the research subject, by combining the technology of chelating agent coupling electric remediation with the addition of catholyte, the effects of tartaric acid, citric acid and EDTA as the cathode electrode liquid on the removal efficiency of copper and lead metals in loess as well as the removal mechanism are investigated. The results indicate that the tartaric acid, citric acid and EDTA can enhance the migration capability of copper and lead through complexation, thereby improving the removal efficiency of these metals to varying estents. The improvement in the removal efficiency of copper and lead metals is particularly noticeable in the vicinity of the cathode. Among the three chelating agents, the EDTA exhibits strong chelating capability and can react with copper and lead metals across different pH ranges, resulting in the formation of a more stable complex and enhancing the removal efficiency. Compared with the control group, the EDTA forms a stable complex by coordinating with heavy metals through six atoms, converting them into exchangeable states with enhanced migration capabilities, and making them easier to remove. As a result, the overall removal efficiencies of copper and lead increase to 55.4% and 27.2%, respectively.
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图 4 电动修复后试样各截面电导率的分布
Figure 4. Distributions of electrical conductivity in different sections of sample after electrokinetic remediation
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图 6 电动修复过程中电渗流的变化
Figure 6. Variations of electroosmotic flow during electrokinetic remediation
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图 7 试样各截面重金属Cu、Pb的去除效率
Figure 7. Removal efficiencies of heavy metals Cu and Pb in different sections of sample
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图 8 试样各截面不同形态重金属Cu、Pb的残余浓度
Figure 8. Residual concentrations of different forms of heavy metals Cu and Pb in different sections of sample
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图 9 EDTA强化电动修复作用示意图
Figure 9. Schematic diagram of EDTA-enhanced electrokinetic remediation
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表 1 黄土初始物理化学特性
Table 1 Initial physicochemical properties of loess
理化参数 数值 理化参数 数值 砂粒/% 3.3 液限/% 31.6 粉粒/% 87.4 塑限/% 19.5 黏粒/% 9.3 渗透系数/(cm·s-1) 2.55×10-6 孔隙比 0.898 有机质含量/(mg·g-1) 4.1 重度/(kN·m-3) 16.2 pH值 8.30 相对质量密度 2.69 电导率/(μs·cm-1) 244 含水率/% 16.5 比表面积/(m2·g-1) 24.1 
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表 2 强化试验方法设计
Table 2 Design of enhanced EK experiments
编号 阳极电极液 阴极电解液 电场强度/
(V·cm-1)修复时
间/hEK1 去离子水 去离子水 1.5 72 EK2 去离子水 0.1 mol/L酒石酸 1.5 72 EK3 去离子水 0.1 mol/L柠檬酸 1.5 72 EK4 去离子水 0.1MEDTA-2Na 1.5 72
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