螯合型表面活性剂对Pb-Zn复合污染土壤的洗脱效果

为了探究螯合型表面活性剂对重金属污染土壤的洗脱效果,通过室内模拟试验,采用振荡洗脱法研究了新型螯合型表面活性剂LED3A(N-十二酰基乙二胺三乙酸钠盐)对Pb-Zn复合污染土壤的洗脱作用,并重点分析了洗脱时间、ρ(LED3A)、洗脱温度等因素对洗脱效果的影响. 结果表明:室温下LED3A洗脱Pb-Zn复合污染土壤的最佳质量浓度为7.0 g/L、洗脱时间为7.0 h. 洗脱平衡时间随ρ(LED3A)的增加而缩短,洗脱过程符合准二级动力学模型；孔隙扩散为LED3A对Pb和Zn洗脱速率的控制过程,但内扩散并非唯一的洗脱速率控制机制. 等温平衡洗脱试验结果显示,洗脱温度升高有利于LED3A配位污染土壤中的Pb和Zn,LED3A对重金属的洗脱过程为吸热过程. Pb、Zn的BCR形态分级结果显示,LED3A对酸可提取态Pb、Zn的去除率最大,分别达到79.87%、72.51%；氧化物结合态、有机结合态、残余态Pb的去除率分别为31.82%、18.83%、2.30%,相应形态Zn的去除率分别为21.81%、17.60%、26.22%；对比洗脱前、后土壤中重金属的形态分布可知,最易释放和被生物利用的酸可提取态Pb和Zn的质量分数所占比例明显降低,不易或不能被生物利用的氧化物结合态、有机结合态和残余态Pb和Zn的质量分数所占比例明显增加. 研究显示,LED3A洗脱不仅能够去除污染土壤中一定量的重金属,同时可降低污染土壤中重金属对环境的潜在危害,而且不会产生二次污染. 

Washing Lead and Zinc from Co-Contaminated Soils by Chelating Surfactant

Abstract:Batch experimentation was conducted to investigate the washing effect of a chelating surfactant, sodium N-lauroyl ethylenediamine triacetate (LED3A), on Pb and Zn co-contaminated soils. The influences of washing time, LED3A concentrations and washing temperature on washing efficiency and changes of metal speciation in the soil before and after LED3A elution were investigated. The results showed that LED3A could effectively remove Pb and Zn at 7.0 g/L of LED3A within 7.0 h. The time to reach equilibrium was shortened with the increase of initial LED3A concentrations. The washing processes could be well fitted by the pseudo-second-order kinetic equation. The results of the intra-particle diffusion model implied that the overall rates of Pb and Zn desorption were controlled by pore diffusion, and intra-particle diffusion was not the only rate-limiting step. The isothermal equilibrium washing experiments indicated that high temperature was conducive to the coordination of LED3A with heavy metal, and desorption of Pb and Zn was an endothermic process. By analyzing the data of metal speciation before and after washing, the washed percentages of acid-extractable, reducible, oxidizable and residual fractions of metals were as follow:Pb-79.87%, 31.82%, 18.83%, 2.30%, and Zn-72.51%, 21.81%, 17.60%, 26.22%, respectively. The percentage distributions of Pb and Zn in contaminated soil before and after LED3A washing illustrated that the mobile fractions (acid-extractable fraction) decreased and immobile fractions (reducible fraction, oxidizable fraction and residual fraction) increased. LED3A was an effective chelator for treatment of heavy metal contaminated soil, and a kind of environmentally friendly chelating reagent.