还原剂作用下Cr(Ⅵ)污染土渗透淋滤特性及成分分析

Percolation leaching characteristics and composition analysis of hexavalent chromium contaminated soil under the remediation of reductant

以湖南某铬污染场地中典型污染土壤为对象,采用硫酸亚铁(FeSO^(4))和多硫化钙(CaS^(x))2种还原剂,开展土壤修复实验和渗透淋滤实验,探讨不同还原剂对铬污染土渗透淋滤特性的影响规律,利用BCR形态提取和X射线衍射分析方法,评估不同还原剂对铬污染土中Cr(VI)的还原效果。结果表明,FeSO^(4)修复试样的渗透系数随FeSO^(4)/Cr(Ⅵ)摩尔比的增加呈先增加后降低的趋势,CaS^(x)修复试样的渗透系数变化呈现相反规律。相同条件下,FeSO^(4)修复试样的渗透系数较CaS^(x)修复试样的渗透系数更大,表明CaS^(x)修复试样的抗渗效果更好。随着还原剂掺量增加,修复试样渗出液中Cr(Ⅵ)浓度随之降低,当FeSO^(4)/Cr(Ⅵ)摩尔比大于3时,渗出液中Cr(Ⅵ)浓度低于Ⅲ类地下水标准Cr(Ⅵ)浓度基准值0.05mg·L^(-1)。类似地,当CaS^(x)/Cr(Ⅵ)摩尔比大于3时,淋滤实验后期渗出液Cr(Ⅵ)浓度也降至0.05 mg·L^(-1)以下。修复土中铬的赋存形态随还原剂掺量的增大而发生变化,铬由弱酸提取态向可还原态和可氧化态转化,且还原剂摩尔比也会对修复土壤组成成分产生影响。本研究结果可为Cr(Ⅵ)污染场地土壤修复工程提供参考。

Taking the typical contaminated soil in a chromium contaminated site in Hunan Province as an object,the effects of different reductants on the percolation and leaching characteristics of chromium contaminated soil were studied through soil remediation tests and percolation leaching tests using ferrous sulfate(FeSO^(4))and calcium polysulfide(CaS^(x))as reductants.The effects of different reductants on the reduction and remediation of Cr(Ⅵ)in chromium contaminated soil were analyzed by BCR morphology extraction technology and X-ray diffraction analysis method.The results showed that the permeability coefficient of FeSO^(4)repair sample first increased and decreased with the increase of FeSO^(4)/Cr(Ⅵ)molar ratio,which was contrary to the change rule of permeability coefficient of CaS^(x)repair sample.Under the same conditions,the permeability coefficient of FeSO^(4)repair sample was higher than that of CaS^(x)repair sample,indicating that CaS^(x)had better impermeability.With the increase of the amount of reducing agent,the concentration of Cr(Ⅵ)in the exudate of the reducing agent repair sample decreased.When the FeSO^(4)/Cr(Ⅵ)molar ratio was greater than 3,the concentration of Cr(Ⅵ)in the exudate was lower than the concentration limit of Cr(Ⅵ)in the ClassⅢgroundwater standard.Similarly,when the molar ratio of CaS^(x)/Cr(Ⅵ)was greater than 3,the concentration of Cr(Ⅵ)in leachate at the later stage of leaching test also droped below 0.05 mg·L^(-1).The occurrence form of chromium in stabilized soil changed with the increase of the amount of reducing agent.Chromium was transformed from the weak acid extraction state to the reducible and oxidable state,and different molar ratios of reducing agent would also affect the composition of the repaired soil.The research results can provide a theoretical reference for the application of soil remediation in Cr(Ⅵ)contaminated sites.