单一及复合淋洗去除土壤中的铅及其机理研究

Removal of lead from soil by single and compound washing and their mechanism

为了探讨环境友好型有机酸对铅(Pb)污染土壤的淋洗修复效果和淋洗机制,采用震荡淋洗的方法,考察了淋洗剂在不同参数(浓度、液固比、时间、pH值)条件下对土壤中Pb淋洗效果的影响,并在最优条件下将柠檬酸和苹果酸复配淋洗。结果表明:柠檬酸、苹果酸和酒石酸单一淋洗时对Pb的去除率分别为76.87%、69.73%和61.39%。柠檬酸与苹果酸复配比为3∶2对Pb的淋洗率高达87.31%,且复配淋洗后土壤中Pb的浸出毒性降低至3.71 mg/L,低于危险废物鉴别标准值。机理分析结果表明:复配淋洗能有效降低土壤中Pb的弱酸可提取态、可还原态和可氧化态的含量,使残渣态含量增加,降低了后续的环境风险;复配淋洗去除Pb的可能机理包括酸溶解、离子交换和表面络合。柠檬酸与苹果酸复配是一种高效且环境友好型的淋洗剂,本研究成果可为Pb污染土壤的修复治理提供了参考。

To explore the effect of environmentally friendly organic acids on the washing repair effect and washing mechanism of lead-contaminated soil,this paper investigates the effect of eluent on the lead elution effect in soil under different parameters(concentration,liquid-to-solid ratio,time,pH value)by oscillating washing method,and conducts compound washing of citric acids and malic acids under optimal conditions.The results show that the removal rates of lead by single washing of citric,malic and tartaric acids are 76.87%,69.73%and 61.39%respectively.When the compound ratio of citric and malic acids is 3∶2,the washing rate of lead is as high as 87.31%,and the washing toxicity concentration of lead in soil reduces to 3.71 mg/L after compound washing,which is lower than the identification standard value of hazardous waste.The results of the mechanism analysis show that compound washing can effectively reduce the content of extractable state,reducible state and oxidizing state in the weak acids of the lead-contaminated soil,increase the content of the residuary fraction,and reduce the subsequent environmental risks.Possible mechanisms of Pb removal by compound washing include acid dissolution,ion exchange,and surface complexation.The compound of citric and malic acids is an efficient and environmentally friendly washing agent,which provides a reference for the remediation of lead-contaminated soil in the future.