Passivation effect of Fe0 in the removal of Cr (Ⅵ) from groundwater and the optimization of electrochemical depassivation parameters
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摘要:
零价铁（Fe0）广泛用于Cr（Ⅵ）污染地下水的修复，但存在Fe0钝化降低修复效率的问题。首先使用Fe0去除地下水中的Cr（Ⅵ）并制备不同钝化程度的钝化铁屑，然后采用电化学方法对钝化铁屑进行解钝，并通过单因素试验和正交试验研究电极设置、电解电压、电解时间及电极距对解钝效果的影响，同时对解钝溶液和解钝前后的铁屑及解钝过程中产生的沉淀进行分析。结果表明：以钝化铁屑作阳极时解钝效果最佳；解钝效果随电解电压增大先上升后降低，随电极距增大而降低，随电解时间增加而上升，3个因素对解钝效果的影响依次为电解时间>电解电压>电极距；X射线衍射仪、扫描电子显微镜和能谱分析表明，钝化铁屑在电化学作用下因表面沉淀脱落使得其活性得到有效恢复；钝化铁屑解钝的最佳条件（以钝化铁屑作阳极，电解电压为10 V，电解时间为60 min，电极距为2 cm）下，解钝后铁屑对Cr（Ⅵ）的去除率可恢复至原来的90%以上；解钝过程中不会促使Cr（Ⅲ）沉淀溶解，但会增加溶液中Fe的浓度。上述研究成果对提高Fe0修复Cr（Ⅵ）污染地下水的修复效果及材料使用率具有参考作用。
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关键词:
- 地下水修复 /
- 零价铁(Fe0) /
- 六价铬〔Cr(Ⅵ)〕 /
- 钝化 /
- 电化学解钝
Abstract:Zero-valent iron (Fe0) is widely used in the remediation of groundwater polluted by Cr(Ⅵ). However, there is a problem that passivation reduces the remediation efficiency. First of all, Fe0 was used to remove Cr (Ⅵ) in groundwater, and passivated iron filings with different passivation degrees were prepared. Subsequently, the electrochemical method was used to deactivate the passivated iron filings, and the effects of electrode setting, electrolysis voltage, electrolysis time and electrode distance on the depassivation effect were studied by single factor test and orthogonal test. Meanwhile, the depassivation solution and the iron filings before and after depassivation as well as the precipitate produced during the depassivation process were analyzed. The results showed that the depassivation effect was the best when passivated iron filings were used as anode. The depassivation effect first increased and then decreased with the increase of electrolysis voltage, decreased with the increase of electrode distance, and increased with the increase of electrolysis time. The influence of three factors on the depassivation effect from high to low was as follows: electrolysis time > electrolysis voltage > electrode distance. The results of the X-ray diffractometer, scanning electron microscope and energy dispersive spectroscopy analysis showed that the activity of passivated iron filings could be recovered effectively due to surface precipitation shedding under electrochemical action. The optimum conditions for depassivation of passivated iron filings were as follows: passivated iron filings for anode, electrolysis voltage = 10 V, electrolysis time = 60 min, electrode distance = 2 cm. Under these conditions, the removal rate of Cr (Ⅵ) by iron filings after depassivation could be restored to more than 90% of the original; Cr (Ⅲ) precipitate could not be dissolved, but the concentration of Fe in the solution could be increased during depassivation process. These research results could provide a useful reference for improving the remediation effect and material utilization rate of Cr (Ⅵ) polluted groundwater by Fe0.
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图 2 Fe0去除Cr（Ⅵ）的过程中去除率随反应时间的变化
Figure 2. Variation of removal rate of Fe0 to remove Cr(Ⅵ) with reaction time
图 3 P-Fe作为不同电极对解钝效果的影响
Figure 3. Influence of P-Fe as different electrodes on the depassivation effect
图 6 不同钝化程度的P-Fe在不同电解电压下解钝后对Cr（Ⅵ）的去除率
Figure 6. Cr(Ⅵ) removal rate of P-Fe with different degrees of passivation after depassivation at different electrolytic voltages
图 7 不同钝化程度的P-Fe在不同电极距下解钝后对Cr（Ⅵ）的去除率
Figure 7. Cr(Ⅵ) removal rate of P-Fe with different degrees of passivation after depassivation at different electrode distances
图 8 不同钝化程度的P-Fe在不同电解时间下解钝后对Cr（Ⅵ）的去除率
Figure 8. Cr(Ⅵ) removal rate of P-Fe with different degrees of passivation after depassivation at different electrolysis times
图 9 P-Fe解钝过程中电解液的CTCr、CCr（Ⅵ）及CTFe变化
Figure 9. Variations of CTCr, CCr（Ⅵ） and CTFe in the electrolyte during the process of P-Fe depassivation
图 10 P-Fe电化学解钝所产生沉淀的XPS分析
Figure 10. Analysis of precipitated XPS resulting from electrochemical depassivation of P-Fe
表 1 电极影响试验分组
Table 1. Experimental grouping of electrode influence
组别 其他参数 P-Fe作为阳极，石墨
作为阴极电解电压为10 V，电极距为2 cm，电解时间为10 min，
在0.8 g/L的Na2SO4电解质
溶液中进行电化学解钝P-Fe作为阴极，石墨
作为阳极P-Fe作为阴阳极
（交叉电极）
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表 2 正交试验因素水平
Table 2. Factor level table of orthogonal test
水平 电解电压/V 电极距/cm 电解时间/min 1 5 2 10 2 10 4 30 3 20 6 60
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表 3 正交试验设计及结果
Table 3. Orthogonal test design and result table
编号 A B C Cr（Ⅵ）去除率/% 1 1 1 1 55.5 2 1 2 2 63.2 3 1 3 3 70.4 4 2 1 2 85.2 5 2 2 3 88.1 6 2 3 1 62.3 7 3 1 3 76.4 8 3 2 1 58.2 9 3 3 2 73.4 水平1均值 63.0 72.4 58.6 水平2均值 78.5 69.8 73.9 水平3均值 69.3 68.7 78.3 极差 15.5 3.7 19.7
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表 4 方差分析结果
Table 4. Results of variance analysis
方差来源 偏差平方和 自由度 F F临界值 P 电解电压 364.6 2 11.50 6.9 <0.05 电极距 21.1 2 0.69 6.9 电解时间 637.6 2 20.10 6.9 <0.05 误差 63.3 4
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