不同化学淋洗剂对复合重金属污染土壤的修复机理

Remediation mechanism of multi-heavy metal contaminated soil by using different chemical washing agents

化学淋洗技术是一种常用的重金属污染土壤修复技术,化学淋洗剂的选择尤为重要。以乙二胺四乙酸二钠(EDTA),柠檬酸(CA)和三氯化铁(FeCl_3)为化学淋洗剂,采用振荡淋洗法研究淋洗时间与淋洗剂浓度对Cu、Zn、Pb和Cd去除效果的影响,分析重金属污染土壤淋洗前后重金属形态与基本理化性质的变化。结果表明:3种化学淋洗剂对重金属的快速反应阶段基本在60 min内,在240 min达到淋洗平衡,对Pb和Cd的淋洗主要是非均相扩散过程;EDTA、柠檬酸和FeCl_3对重金属的去除能力依次为Pb>Cd>Cu>Zn,Cd>Zn>Cu>Pb与Pb≈Cd>Cu>Zn,EDTA的淋洗效率最高,Cd的解吸能力最强;EDTA和FeCl_3可有效去除弱酸可溶态与可还原态重金属,柠檬酸能有效去除弱酸可溶态重金属,修复后的土壤仍有环境风险;3种淋洗剂修复后的土壤中总有机碳与粒径分布无明显变化,FeCl_3会酸化土壤。综合考虑,EDTA、柠檬酸和FeCl_3均为淋洗效果好的环境友好型化学淋洗剂,该研究成果可用于现场淋洗去除土壤中重金属的小试。

Chemical washing technology is a commonly used technology in the remediation of heavy metal contaminated soil, where the selection of washing agents is particularly important. Batch experiments were conducted to study the duration and concentration effects of three chemical agents, including EDTA, citric acid, and FeCl3 on removal of Cu, Zn, Pb and Cd from contaminated soil. The changes in the form of heavy metals and soil physicochemical properties were also analyzed before and after washing treatment. The results indicated that the rapid reaction was completed within 60 minutes, and all reactions reached equilibrium in 240 minutes. The desorption of Pb and Cd was observed as a heterogeneous diffusion process. The extraction efficiencies of EDTA, citric acid, and FeCl3 on removal of target heavy metals were Pb〉Cd〉Cu〉Zn, Cd〉Zn〉Cu〉Pb and Pb≈Cd〉Cu〉Zn, respectively. Among them, EDTA had the highest washing efficiency and Cd was the easiest to be desorbed in an integrated point of view. The EDTA and FeCl3 can effectively remove the acid extractable and reducible fractions of heavy metals, whereas citric acid was more effective in removing the acid extractable fraction. The use of three washing agents did not change the TOC contents and distortional pattern of particle size in target soil, while FeCl3 acidified the soil. In sum, EDTA, citric acid and FeCl3 are environmentally friendly agents and this study can be applied to a bench-scale experiment concerning site ex-situ remediation of multi-heavy metal contaminated soil.