柠檬酸对蒙脱石黏性土中铅的淋洗试验研究

Soil Washing on Lead Removal by Citric Acid in Contaminated Smectite Clayey Soils

以人工Pb(NO3)2污染的蒙脱石黏性土为研究对象,采用振荡淋洗试验研究柠檬酸对蒙脱石黏性土中铅(Pb)的淋洗行为,探讨淋洗因素,如淋洗剂柠檬酸浓度、淋洗反应时间、pH值、离子强度、液固比对蒙脱石黏性土中Pb淋洗效果的影响以及Pb的淋洗动力学方程,并利用Tessier连续提取法分析柠檬酸淋洗前后受污染的蒙脱石黏性土中Pb的形态变化。试验结果表明:淋洗反应在6h达到平衡,最佳淋洗条件为柠檬酸的浓度为0.08mol/L、pH值为4、液固比为20∶1,离子强度对淋洗反应几乎无影响;双常数方程较准一级动力学方程和准二级动力学方程能更好地描述柠檬酸对蒙脱石黏性土中Pb的淋洗过程;受污染的蒙脱石黏性土中,Pb主要以可交换态、碳酸盐结合态、铁锰氧化态的形式存在,采用柠檬酸淋洗后可以有效地去除可交换态、碳酸盐结合态、铁锰氧化态的Pb,Pb的去除率分别达到65.40%、89.78%、76.02%。

This paper applies soil washing experiment to researching the washing behavior of(N0 3)2 contaminated smectite clayey soils by citric acid.The paper discusses the influence of washing factors on the washing effect,such as eluent concentration,washing reaction time,pH,ionic strength,liquid-solid ratio,and also the kinetic models.Then the paper uses Tessier sequential extraction to analyze the chemical Pb before and after soil washing by citric acid.The results show the optimal condition in which reaction time is 6 h,citric acid concentration is 0.08 mol/L,pH is 4,and liquid-solid ratio is 20:1.Ionic strength has few effect on experiment.The kinetic data show that the elution process of Pb can fit better pseudo-firtt-order equation and pseudo-second-order equation.Pb mainly exists in exchangeable state and Fe-Mn oxidation state in contaminated smectite clayey soils and can be effectively removed by citric acidwith the removal rate up to 65.4 0%,89.7 8%and 76.0 2%respectively.