新型螯合性表面活性剂淋洗修复重金属-有机物复合污染土壤的作用机制

The combined pollution of heavy metals and organic compounds is very common in the contaminated soils. However, the current techniques to remediate soils always focus on the removal of one type contaminants. It is urgent to study and develop some techniques for the combined contaminated soils. In view of existing situation where organic contaminants in soils are removed with surfactants and heavy metals are removed with chelating agents, a kind of novel ehancing agent with the abilities to solubilize organic compounds and chelate heavy metals, the chelating surfactants, are slected and the objectives of our project are 1) to test the solubilization of organic compounds (phenanthrene, pyrene and benzo[a]pyrene) and the chelation of heavy metals (copper, cadmium, lead and zinc) using the chelating surfactants in the solution systems and illustrate the factors in and mechanisms on solubilization and chelation; 2) to investigate the adsorption of the chelating surfactants onto soil (loess soil) and find out the washing efficiencies of heavy metals and organic compounds, the factors in the washing process and the mechanisms on washing of heavy metals and organic compounds while the chelating surfactants are used in water-soil systems; 3) to explore the column flushing efficiencies of heavy metals and organic compounds, the factors in the flushing process and the regular patterns on flushing of heavy metals and organic compounds, and set up a prediction model for the migration of surfactants and contaminants under non-equilibrium conditions, while the chelating surfactants are used in the column experiments. In a word, the project aims to simultaneously and efficiently remove heavy metals and organic compounds from soils using a single enhancing agent and the results could be the theoretical sources for the economical, efficient and safe remediation of the combined contaminated soils by in-situ flushing and ex-situ washing methods.

在土壤环境所发生的污染中,重金属-有机物复合污染是一种比较普遍的现象。但现有修复技术多针对单一类型污染，迫切需要研发复合污染土壤的修复技术。针对表面活性剂、螯合剂洗脱土壤有机污染物和重金属存在的问题，本项目拟选用同时具有增溶和螯合能力的增效试剂-螯合性表面活性剂，系统研究溶液体系下其对菲、芘、苯并[a]芘等有机物的增溶作用及对Cu、Cd、Pb、Zn等重金属的螯合作用、影响因素及机理；研究其在土壤（黄土）表面的吸附行为及其对复合污染土壤中有机污染物和重金属的洗脱作用、影响因素及机制，探寻洗脱作用的构效关系；探明在动态非平衡条件下螯合性表面活性剂对有机污染物和重金属的洗脱效率、影响因素及规律，建立相应的预测模型，有效调控洗脱过程。旨在以单一增效试剂同时有效洗脱去除土壤中的重金属和有机污染物，为拟定经济、高效、安全的重金属-有机物复合污染土壤原位淋洗和异位清洗技术提供理论依据。

选择典型多环芳烃和重金属污染物，以黄土为受试土壤，选用螯合性表面活性剂N-十二酰基乙二胺三乙酸钠盐（N-LED3A），系统研究了其对有机污染物的增溶作用及对重金属的螯合作用、影响因素和机理；研究了其在黄土表面的吸附行为及其对污染黄土中有机污染物和重金属的洗脱作用、影响因素和机制；初步研究了在动态非平衡条件下其对土壤中重金属的洗脱效率和规律，以期为重金属-有机物复合污染土壤修复提供新的技术途径。研究取得了如下主要成果：. （1）N-LED3A临界胶束浓度较低，增溶效率高，对有机物的增溶能力与常用阴离子表面活性剂SDBS相近，较SDS略低；螯合能力较强，可与重金属离子形成稳定可溶的配合物。N-LED3A可实现同时增溶有机物和螯合重金属离子，且溶液体系中二者共存时，N-LED3A对污染物的增溶和螯合效果均优于单独存在时的效果。. （2）土壤有机质和粘土矿物对N-LED3A在土壤上的吸附起到重要作用。溶液pH增大N-LED3A在土壤上的吸附量明显减小，吸附量随温度的升高有所降低，随离子强度和水土比增大而增加。N-LED3A的存在对有机物在黄土上的吸附具有一定的促进作用，对重金属在黄土上的吸附影响较为复杂。N-LED3A可有效洗脱单一重金属、单一有机物、复合重金属及重金属-有机物复合污染土壤，洗脱机制符合二级动力学方程，一次洗脱率均大于60%。. （3）动态非平衡条件下（柱淋洗），随着淋洗液LED3A的累计孔隙体积数逐渐增大，淋洗中重金属离子的浓度呈现先急剧增大，之后减小的趋势，同时存在不同程度的拖尾现象。低流速有利于LED3A淋洗去除污染土壤中的重金属。流速对土柱上、中、下层重金属的形态影响因重金属种类不同而不同。柱淋洗可有效去除土柱中单一或复合重金属。经低流速LED3A淋洗后的污染土壤，其中重金属的环境风险明显降低。. N-LED3A可以实现一种试剂对重金属和有机污染物的同时有效去除，且易于生物降解，生态风险较小，将其用于重金属-有机物复合污染土壤化学修复前景广阔。