土壤污染已成为威胁全球人类生存的重大战略性问题。据统计, 中国至少有1/5的耕地受到重金属污染, 总面积达2 000万ha。由土壤污染引发的食品安全问题、人类健康问题、生态环境问题愈演愈烈, 污染程度有逐年加重的趋势。及时有效地治理污染土壤已成为学者们关注的重点。化学淋洗法是较为有效的污染土壤修复方法, 但土壤淋洗过程组分流失现象不可忽视, 因为这可能在去除土壤污染物的同时, 导致土壤肥力下降、理化属性改变或土壤生态功能的彻底丧失。土壤淋洗过程淋溶组分的光谱特性研究, 可以为污染场地修复工程提供决策参考, 对于恢复土壤生态功能具有重要的指导意义, 但目前来看这方面的研究还略显欠缺。本研究以乙二胺四乙酸(EDTA)为淋洗液, 通过异位柱淋洗实验研究铅/镉复合污染黄土淋洗过程中的组分淋失特性, 主要包括黄土盐基离子、黄土养分、粘土矿物和有机质。借助X射线衍射(XRD) 和扫描电镜 (SEM) 分析淋洗过程对黄土粘土矿物的影响, 同时跟踪识别淋洗液中可溶性有机质 (DOM) 的三维荧光光谱 (3D-EEM) 特性。研究表明: EDTA对污染黄土的淋洗过程能够造成组分淋失。淋洗过程结束的240 min时, EDTA对铅和镉最终淋洗率分别为49.86%和62.25%。盐基离子中的Na离子和黄土养分中的硝态氮最易淋失, 淋洗过程对黄土粘土矿物的影响基本可以忽略。反应前期(10 min) 淋洗液中最先出现的是类富里酸类物质(Eex/em=240～250/320～340, Eex/em=260～290/450~470);到淋洗中期 (60 min) 类胡敏酸类物质荧光峰(Eex/em=290~320/430~490) 开始出现, 同时类富里酸荧光峰(Eex/em=240/320)有减弱趋势;反应后期(120和240 min) 荧光峰强度均明显降低, 这反映了淋洗液中荧光组分组成特性差异。光谱联用技术可以有效表征污染黄土淋洗过程淋失组分特性差异。

Soil contamination is regarded as one of the most serious issues to humanity all over the world. It is statistically believed that over one-fifth of the farmland, that is 20 million ha, is found to be contaminated by heavy metals in China. And the related issues, caused by soil contamination, of food safety, human health and eco-environmental quality attract much attention by public with more serious contamination than before. The technological approach for soil remediation is widely investigated. The technology of soil washing is effective for contaminants removal, while the treatment procedure might lead to component leaching from soil system, harmful for soil fertility, physicochemical properties and ecological functions. The study of spectral characteristics on leaching component is significant for decision-making of contaminated sites remediation and ecological function recovery, while the related investigation seems weaker nowadays. The paper mainly revealed the leaching characteristics of component from Pb/Cd contaminated loess in the washing process with Ethylene Diamine Tetraacetic Acid (EDTA) in reaction column, and the research objectives included base cations, loess nutrients, clay minerals and organic matter. The variation of clay minerals was analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM), and 3D-EEM fluorescence spectrum was used for the identification of dissolved organic matter (DOM). The experimental results showed: the leaching component from loess is detected in the washing reaction. The final removal efficiency (240 min) of Pb and Cd from loess are 49.86% and 62.25%, respectively. The sodium ions and nitrate nitrogen are the most easily leaching component, and little difference of clay minerals is identified before and after washing reaction. The fulvic acid-like (FA-like) material was firstly (10 min) detected around Eex/em=240~250/320~340 and Eex/em=260~290/450~470 in 3D-EEM fluorescence spectrum, and the humin acid-like (HA-like, Eex/em=290~320/430~490) appeared at 60 min with weaker fluorescence intensity of FA-like (Eex/em=240/320). The decreased fluorescence intensity of FA-like and HA-like, shown after 120 min and 240 min, indicated the component variation of DOM in the leaching solution. The spectroscopy approach is appropriate for characteristics identification of leaching component from co-contaminated loess.