为探究不同淋洗方式下螯合型表面活性剂LED3A(N-十二酰基乙二胺三乙酸钠盐)对重金属污染土壤的淋洗效果,采用室内土柱淋洗法研究了LED3A在不同流速条件下对Pb、Zn单一污染砂土的淋洗效果,并通过优化的BCR法分析了淋洗前、后土柱中不同深度处Pb、Zn的形态变化特征.结果表明:LED3A对Pb、Zn单一污染砂土的淋洗规律基本类似,淋出液中ρ(Pb)、ρ(Zn)随淋洗液累积孔隙体积数目的增加呈现急剧增大、达到峰值后逐渐降低的趋势;Pb、Zn的淋洗曲线中均存在不同程度的拖尾现象,且对称性较差;淋出液中ρ(Pb)、ρ(Zn)峰值和Pb、Zn最大累积去除率均随流速的增大而减小.随着淋洗深度和流速的增加,各形态Pb、Zn的去除率均呈现减小的趋势,LED3A对酸可提取态Pb、Zn的去除效果最为显著,去除率均大于50％;对氧化物结合态、有机结合态和残渣态Pb、Zn的去除率大小顺序与淋洗深度和流速有关;对比淋洗前、后土柱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的占比明显减少,不易或不能被生物利用的氧化物结合态、有机结合态和残渣态的占比明显增加.研究显示,LED3A低流速淋洗不仅能够去除一定量的土壤重金属,同时可有效降低残留重金属对环境的潜在风险.%Column leaching of Pb and Zn in Pb and Zn-contaminated sandy soils by using sodium N-lauroyl ethylenediamine triacetate (LED3 A) under different leaching velocities was studied. The objective of this study was to provide reference for remediation of heavy metal contaminated soils by LED3 A leaching. The chemical forms of Pb and Zn at different depths in the soil columns were compared before and after the leaching treatment. The experimental results showed that the leaching behavior of Pb and Zn in the contaminated sandy soils was similar. The concentrations of Pb and Zn in the leachates increased, and reached the maximum, and then decreased with increasing cumulative pore volumes of the leaching solutions. There were different degrees of tailing phenomenon in the leaching curves of Pb and Zn by LED3 A. The symmetry of leaching curves was poor. Both the peak concentrations and the maximum cumulative removal rates of Pb and Zn in leachate decreased with increasing leaching velocity. The removal rates of Pb and Zn showed a decreasing trend with the increase in leaching depth and velocity. The removal efficiency of acid extractable form of Pb and Zn by LED3 A was highest as compare to the other forms, which was greater than 50％. The order of removal efficiencies of the other forms, such as oxide bound, organic bound and residual forms of Pb and Zn, were correlated with the leaching depth and velocity. Low-flow leaching can effectively reduce the environmental risks of Pb and Zn. The percentage distribution of Pb and Zn in the contaminated soil before and after the LED3 A washing illustrated that the mobile fractions (acid-extractable fraction) decreased and immobile fractions (oxide bound organic bound and residual fraction) increased. The research shows that the low velocity leaching of LED3 A can not only remove a certain amount of heavy metals in soils, but also effectively reduce the potential risks of the residual heavy metals to the environment.
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