POPs-重金属复合污染土壤的等离子体/粘土矿物联合修复行为与机理研究

Mixtures of POPs and heavy metals are frequently found in the soil environment, and their presence can have significantly detrimental effects on the flora and fauna and on human health. As a result of the different compositions and reactivities of these pollutants, their remediation is often difficult using conventional techniques. Therefore, new techniques are required to overcome this environmental problem and it is of importance to promote research on remediation of the co-contaminated soil. One new approach to achieve a simultaneous remediation of the co-contaminatants is to set up a concurrent process of POPs degradation and heavy metals reduction. Many varieties of active species, including oxidizing and reducing species, can be produced during a generation process of pulsed corona discharge. So the pulsed discharge plasma technology can be used to remediate the soil polluted with POPs and heavy metals. In order to achieve an effective remediation, clay minerals are inroduced to the pulsed discharge plsma system to promote plasma mass transfer efficiency. Accordingly, a combined and efficient remediation system of plasm/clay minerals is used in this research to treat POPs and heavy metals pollutants in soil, and corresponding mechanisms are reviewed. Main contents of the research include: Controlling the remediation process by studying the correlation between plsma generating conditions and active species production; Achieving a synergistic treatment of the co-contaminants by combining plasm and clay minerals; Analyzing the relation between remediation efficiency and adsorption effect of clay minerals; Quantizing the increase of plasma mass transfer efficiency; Clarifying the synergistic mechanism and stating the remediation mechanism through reviewing formation of active species, detecting intermediate products of POPs degradation, analyzing distributional pattern of heavy metals, discussing translation and conversion behavior of co-contaminants, and characterization of clay structure. The research would provide a new idea for expanding soil remediation methods and also provide fundamental experimental data for deepening application fields of low temperature plasma.

开展典型POPs-重金属复合污染土壤的修复研究对土壤环境生态安全具有重要意义，建立POPs降解与重金属还原并行的修复过程是实现复合污染土壤有效修复的新思路。脉冲放电等离子体内富含多种活性粒子（包括氧化性和还原性物种），可以用于完成土壤复合污染物的同时修复；在该体系中引入粘土矿物，是提高等离子体传质效率、实现土壤高效修复的有效途径之一。据此，本研究拟建立POPs-重金属复合污染土壤的等离子体/粘土矿物联合、高效修复体系。通过考察等离子体发生条件与各类活性粒子生成量的相关性，调控修复过程；联合粘土矿物的吸附作用使复合污染物得到耦合处理；分析修复效果与粘土矿物的关系；考察活性粒子生成规律，鉴定POPs降解产物，分析重金属形态分布，探讨复合污染物迁移转化途径，表征粘土矿物结构变化，量化等离子体传质效率的提高，揭示粘土矿物增效机制及土壤修复机理。该研究可以拓展土壤修复方法、深化低温等离子体应用领域。

本项目针对我国日益严重的土壤污染问题，建立了基于低温等离子体技术的针-网电极和网-网电极形式的脉冲放电等离子体污染土壤修复体系，分别以芘和硝基酚为目标物，以有机物的降解比率和降解动力学常数为指标，优化了脉冲放电等离子体的发生条件和该土壤修复体系的操作参数；考察了重金属离子（Cr6+和Cu2+）和粘土矿物（高岭土）添加对污染土壤修复效果（降解比率和降解动力学常数）的影响规律；并从有机物降解产物分析和修复体系活性物质检测的角度，分析了脉冲放电等离子体修复污染土壤的作用机理和粘土矿物添加的协同作用。研究获得的主要结论如下：（1）针-网电极和网-网电极形式的脉冲放电等离子体体系均可有效地修复目标有机污染土壤，其共有的较优操作条件为：10 mm电极间距、1 L/min载气速率、1 mm土壤粒径和5%的土壤初始含水率，而针对不同的有机污染物，较有利的土壤初始pH值条件不同；（2）有机污染土壤中重金属的存在可以消耗脉冲放电等离子体体系中的还原性物质，进而促进了修复体系中氧化性物质产量的提高，达到提高修复体系中目标有机污染物降解效果的作用；（3）脉冲放电等离子体与粘土矿物相联合的有机污染土壤修复体系相比于单独的脉冲放电等离子体体系对土壤中的有机物有更高的去除效果，较优的粘土矿物添加条件为：15%的粘土添加比例，吸附3天后放置于脉冲放电等离子体体系中进行修复，含水率和pH值条件均控制为所制备的目标土壤的初始含水率和pH值。（4）脉冲放电等离子体作用过程可以有效矿化土壤中的有机物，提高其可生化性能：HPLC和GC/MS分析手段鉴定修复体系中芘氧化降解的主要产物为邻苯二甲酸酯类，高浓度对硝基酚降解的主要产物为邻苯二酚、苯酚及小分子酸类；光谱分析和化学分析的结果分别证明了•OH、•O和O3在脉冲放电等离子体用于土壤中目标有机物降解的关键作用。