淋洗剂乙二胺四乙酸对重金属污染土工程特性的影响

以重金属铅（Pb2+）污染土和淋洗剂乙二胺四乙酸（EDTA）为研究对象，通过批次试验研究了不同浓度EDTA的淋洗对Pb2+污染土的渗透特性、持水特性、压缩特性、抗剪强度等工程特性的影响，为淋洗修复后土壤的二次利用提供参数支持。基于矿物成分、孔隙结构等微观试验，揭示了土壤工程特性变化的内在机制。研究结果表明，当淋洗剂EDTA浓度从0增加到0.15 mol/L，经淋洗修复后的污染土壤pH值从7.94下降到5.12，渗透系数降低超过一个数量级，黏聚力降低50%以上，而内摩擦角增大，持水性能提高，孔隙比从0.81下降到了0.76。微观试验的结果表明，随着淋洗剂浓度的增大，土壤中的蒙脱石、钠长石和伊利石矿物含量减少，石英矿物含量增加，其中蒙脱石含量从7.87%下降到了0.07%，而石英矿物含量增加了11.09%；淋洗后土壤单位质量进汞量由0.22 ml/g降低到0.15 ml/g，土壤总孔隙体积减少。重金属污染土淋洗修复工程在考虑重金属去除率及经济性指标的同时，还应考虑淋洗剂对土壤工程特性的弱化。

Impaction of EDTA on the engineering properties of heavy metal contaminated soil

To provide the reference for secondary utilization of the heavy metals contaminated soil washed by EDTA (Ethylene Diamine Tetraacetic Acid), batch tests are conducted to determine the permeability, water holding characteristics, deformation characteristics, and shear strength of lead contaminated soil after washing remediation by EDTA with different concentrations. And X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests are conducted to reveal the mechanism of changes on the engineering characteristics. Results show that pH of the washes soil decreases from 7.94 to 5.12, hydraulic conductivity decreases by more than one order of magnitude, cohesion reduces by more than 50% and void ratio decreases from 0.813 to 0.764 as the concentration of EDTA increased from 0 to 0.15 mol/L, but the internal friction angle and water holding capacity increase. XRD test results show that the mineral content of montmorillonite (from 7.87% to 0.07%), illite, albite decrease and quartz increases by 11.09%. MIP test results show that the total void volume reduces as the concentration increasing, and the amount of intrudes mercury per unit mass decreases from 0.22 ml/g to 0.15 ml/g. Research results indicate that it is imperative not only considering about the removal rate of heavy metals in soil and economic index of the remediation engineering, but also the weaken soil engineering properties brought by the process of washing remediation.