Monitoring and analysis of key indicators in the process of electrickinetic remediation of Cr(Ⅵ) contaminated groundwater
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摘要:
电动修复是去除地下水中重金属污染物的有效方法。采用电动修复方法对Cr(Ⅵ)初始浓度为1 000 mg/kg的污染浅层地下水进行为期4 d的处理，研究不同电压梯度（1、2、3 V/cm）对饱和带地下水中Cr(Ⅵ)去除率的影响。此外，对修复过程中的相关指标包括电流、阴阳极电解液pH、氧化还原电位（Eh）和不同位置地下水Cr(Ⅵ)浓度进行监测，并且对电动修复前后饱和带介质的pH、Eh和Cr(Ⅵ)去除率进行分析。结果表明：Cr(Ⅵ)的平均去除率随电压梯度升高而升高，当电压梯度为2 V/cm时去除效率和经济性较好，去除率提升与能耗提升比值为0.52，最高去除率91.41%出现在电压梯度为3 V/cm时，但此时相应能耗较高。修复过程中Cr(Ⅵ)会在阳极附近富集，特别是当电压梯度较低（1 V/cm）时，反应结束后近阳极地下水Cr(Ⅵ)富集浓度高达2 170.95 mg/L，介质中Cr(Ⅵ)浓度为1 497.45 mg/kg，此时去除率为负值；阳极电解液Cr(Ⅵ)浓度呈先增长后稳定的趋势，当Cr(Ⅵ)浓度接近4 000 mg/L时，已接近装置的最大迁移值，增加反应时间对Cr(Ⅵ)的回收率提升不大。修复过程中介质Eh降低、pH升高会促进Cr(Ⅵ)的还原和解吸，对Cr(Ⅵ)的去除具有促进作用。
Abstract:Electrokinetic remediation is an effective method to remove heavy metal contaminants from groundwater. The effect of different voltage gradients (1, 2, 3 V/cm) on the removal rate of saturated zone groundwater Cr(Ⅵ) was studied with an initial content of 1 000 mg/kg for 4 days by the electrokinetic remediation method. In addition, the relevant factors in the repair process, including current, pH and redox potential (Eh) of anode and cathode electrolytes, and the concentrations of Cr(Ⅵ) in different positions were monitored. PH, the removal rates of Cr(Ⅵ) and Eh of the saturated zone medium before and after treatments were analyzed The results showed that: 1) The average removal rates of Cr(Ⅵ) increased with the increase of voltage gradient. When the voltage gradient was set at 2 V/cm, the removal efficiency and economy were better. The removal rate increase/energy consumption increase ratio was 0.52. The highest removal rate of 91.41% was observed when the voltage gradient was set at 3 V/cm, and the higher corresponding energy consumption was observed. 2) During the repair process, Cr(Ⅵ) would be enriched near the anode, especially when the voltage gradient was low (1 V/cm). The Cr(Ⅵ) concentration in groundwater near the anode after the reaction was up to 2170.95 mg/L, and the concentration of Cr(Ⅵ) in the medium was 1497.45 mg/kg, with negative removal rate. The concentration of Cr(Ⅵ) in the anolyte showed a tendency to increase first and then stabilize. When the Cr(Ⅵ) concentration was close to 4000 mg/L, it was close to the maximum migration value of the device. Increasing the reaction time had little effect on the recovery rate of Cr(Ⅵ). 3) The decrease of Eh and the increase of pH during the repair process would promote the reduction and desorption of Cr(Ⅵ), which could promote the removal of Cr(Ⅵ).
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Key words:
- electrodynamic remediation /
- hexavalent chromium /
- groundwater pollution /
- heavy metal
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图 2 取样点示意
注：a1~a3为阳极室取样点；b1~b3为阴极室取样点；G1~G3为地下水取样点；S1~S5为反应结束后土壤介质取样点。
Figure 2. Schematic diagram of sampling points
图 4 电动处理后含水层中残留的Cr(Ⅵ)
Figure 4. Remaining Cr(Ⅵ) in the aquifer after electrokinetic process
图 5 土壤室地下水中Cr(Ⅵ)浓度变化
Figure 5. Variation of Cr(Ⅵ) concentrations in the groundwater in the soil chamber
图 9 电动修复过程中的累积能耗
Figure 9. Accumulated energy consumption during electrokinetic remediation
表 1 土壤样品的理化性质
Table 1. Physical and chemical properties of the soil sample
土壤粒径占比/% 土壤质地 pH Eh/mV 溶解性有机碳浓度/(mg/kg) 含水率/% 碳酸盐浓度/% 0.002 mm 0.002～0.0 5 mm 0.05～2 mm 13.5 44.1 42.4 中壤土 7.98 232 10.13 22 6.2 
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表 2 土壤中Cr(Ⅵ)浓度随机采样结果
Table 2. Random sampling results Cr(Ⅵ) concentration in soil
mg/kg 采样点 平均值 标准差 1 2 3 4 5 1 005.06 938.58 936.80 989.00 1 018.00 977.49 37.76
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表 3 电压提高与Cr(Ⅵ)去除率和能耗的关系
Table 3. Relationship between voltage increase and Cr(Ⅵ) removal rate and energy consumption
项目 电压梯度/(V/cm) 1→2 2→3 去除率提升/% 21.50 15.27 能耗提升/% 41.05 80.60 去除率提升/能耗提升 0.52 0.19
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