天然有机酸和DTPA组合工艺对Cr(Ⅵ)污染土壤的淋洗修复

Washing remediation of Cr(Ⅵ)contaminated soil by the combination process of natural organic acids and DTPA

针对重庆市某工业废弃地Cr(Ⅵ)污染土壤,分别采用不同浓度草酸、柠檬酸、乙酸组合二乙基三胺五乙酸(DTPA)对其进行淋洗处理,结合XRD和SEM-EDS电镜扫描分析,探究组合淋洗剂对土壤Cr(Ⅵ)残留量和淋洗机理的影响。结果表明:有机酸单一淋洗优劣顺序为草酸>柠檬酸>乙酸(P<0.05),DTPA在5 g·L-1时达到最大淋洗量;组合淋洗顺序对Cr(Ⅵ)去除率具有显著影响(P<0.05),5 g·L-1 DTPA与0.2 mol·L-1草酸顺序淋洗在液固比10∶1、淋洗60 min时效果最佳,粒级>2 mm和粒级<2 mm土壤Cr(Ⅵ)残留含量分别为35.42和45.57 mg·kg-1,去除率达到89.20%和86.99%。ExpDec1、Elovich和双常数模型均适用于Cr(Ⅵ)淋洗动力学过程(R2>0.98)。经组合淋洗后,土壤表面Cr元素含量减少,且未检出Cr(Ⅵ)化合物,矿物学形态变化明显。草酸和DTPA组合顺序淋洗可作为较好的复配淋洗剂,该研究结果可为异位淋洗修复Cr(Ⅵ)污染土壤的实际应用提供参考。

Different concentrations of oxalic acid,citric acid and acetic acid combined with diethylene triamine pentacetate acid(DTPA)were used as eluents to wash the hexavalent chromium(Cr(Ⅵ))contaminated soil in the derelict industrial land of Chongqing,respectively.Being combined with the analysis of diffraction of Xrays(XRD)and scanning electron microscope-energy dispersive spectrometer(SEM-EDS),the effects of different eluents on the residual amounts of Cr(Ⅵ)and washing mechanisms were studied.The results showed that the order of organic acid alone washing was oxalic acid>citric acid>acetic acid(P<0.05),and the highest washing amount of Cr(Ⅵ)occurred at 5 g·L-1 DTPA.The sequence of combined eluents had a significant effect on removal rate for Cr(Ⅵ)(P<0.05),the best effect occurred for a 60 min-sequential washing by 5 g·L-1 DTPA and 0.2 mol·L-1 oxalic acid combination at a liquid to solid ratio of 10∶1.The residual amounts of Cr(Ⅵ)in soils with particle size larger than 2 mm and with particle size lower than 2 mm were 35.42 mg·kg-1 and45.57 mg·kg-1,and the corresponding removal rates were 89.20%and 86.99%,respectively.The kinetic of washing can be fitted by ExpDec1,Elovich and Double constant models(R2>0.98).After combined washing,the content of Cr element in the soil surface decreased,Cr(Ⅵ)compound was not detected,while significant change occurred in the mineralogical morphology of surface soil.Accordingly,the sequential washing of oxalic acid and DTPA combination is an optimal combined eluent,this result can provide reference for practical application of ex-situ washing and remediation of Cr(Ⅵ)-contaminated soil.