络合剂强化类Fenton氧化修复污染场地土壤中多氯联苯的机理研究

Polychlorinated biphenyl (PCBs), one of the listed twelve chemicals in the Stockholm Convention on the Persistent Organic Pollutants (POPs), has been largely produced and widely used all over the world. PCBs had been greatly used in capacitor oils in China and the leakage of capacitor oils containing high concentrations of PCBs from discarded capacitors result in lots of PCB-polluted sites that need to be urgently remediated because they have been the dominated sources of PCBs for other environment media. Ferric complex catalyzed Fenton-like reactions not only can directly remove POPs from soils effectively without adjusting the pH value, but also can enhance the remediation efficiency of POPs by bioremediation in soils. So it has been one of research hotspots in soil remediation field in recent years. However, there is little information about the remediation characteristic and mechanism of PCB-contaminated soils by ferric complex catalyzed Fenton-like reactions. Therefore, different types of PCB-polluted sites were chosen as study objects in this project and batch experimental method with modern instrument analysis techniques, such as GC-ECD/MS, HPLC-FLD/MS, and ATR-FTIR spectroscopy were used to investigate the effect of different chelating agents on improving remediation of PCB-contaminated soils by a ferric-catalyzed Fenton-like reaction. Firstly, the reaction conditions and the effect factors on the remediation efficiency and the degradation products of PCBs were determined. Secondly, the species and concentration of radicals and the contribution and reaction places of radicals on degradation of PCBs were also examined. Furthermore, investigating the effect of representative soil components on the remediation efficiency and mechanism of PCBs was one of the emphases of this project and determining the enhanced mechanism of chelating agents in a ferric complex catalyzed Fenton-like reaction was another emphasis of this project. The results of this project can supply scientific evidence and technology supports for applying this technology to remediate PCBs from contaminated soils.

多氯联苯（PCBs）是首批被列入全球控制的12种持久性有机污染物（POPs）之一。我国存在着大量迫切需要治理的因废弃电容器中PCBs泄露造成的污染场地。铁络合物类Fenton体系因无需调节pH便可直接用于实际土壤中POPs的高效降解与促进生物修复作用，使其成为近年来土壤修复领域的研究热点之一。但该体系用于PCBs污染土壤的修复研究还未见报道。因此，本项目采用批处理法和GC-ECD/MS、HPLC-FLD/MS、ATR-FTIR等技术手段，对不同反应条件下铁络合物类Fenton体系修复不同类型污染土壤中PCBs的降解动力学、降解产物和体系活性物种的种类、含量及其降解贡献率进行研究，并着重研究土壤代表性组分对PCBs降解的影响程度与机理和络合剂强化类Fenton体系催化活性的作用机理。本项目研究结果将为铁络合物类Fenton法用于实际PCBs污染场地修复提供理论指导和技术支持。

通过不同铁络合类Fenton体系对不同类型土壤中PCBs的降解动力学特征、降解产物组成以及降解机理，环境因素和土壤组分对铁络合物类Fenton体系降解PCBs的影响机理研究，发现Fe2+/CA/H2O2体系降解土壤中PCBs的能力显著优于Fe3+/CA/H2O2体系。无机络合剂SP强化效果优于有机络合剂EDDHA。Fe2+/EDDHA/ H2O2和Fe2+/SP/H2O2的最佳摩尔浓度比分别为1/0.5/20和1/1/20。络合剂对Fenton反应中PCBs降解的促进作用可归因于络合剂的加入有效减缓体系中H2O2的分解速率。Fe2+/SP/H2O2体系降解PCBs的主要活性物种为˙OH，而Fe2+/EDDHA/H2O2体系中则是˙OH和超氧负离子自由基共同作用结果。2,2′,5-三氯联苯的降解产物包括2种羟基化产物（4-OH-2,2′,5′-CB和2-OH-2′,5,5′-CB）和3种脱氯产物（联苯、2,2′-CB和2,5-CB），表明PCBs经历了氧化和还原脱氯两种反应途径。Fe2+/SP/ H2O2体系对红壤、水稻土、潮土和黑土中PCBs的降解效果依赖于SP的用量，当Fe2+/SP为2:1或1:2时，4种土壤中PCBs降解率存在显著性差异，而1:1时不存在差异，这归因于不同类型土壤中溶解铁含量和H2O2利用率的差异。Fe2+/SP/H2O2体系中，PCBs降解率随体系pH和温度的升高而增加；无机阴离子对降解PCBs的影响并不显著，Ca2+和Mg2+因水解降低体系pH而抑制PCBs降解，过渡金属能抑制PCBs降解，且抑制作用随金属离子浓度的升高而增强；胡敏酸的抑制作用随其浓度的升高而增强，而富里酸不影响PCBs的降解率，但降低其降解速率；腐殖质模式物五倍子酸能提高PCBs的降解率。经Fe2+/SP/H2O2修复后土壤pH趋于中性，且重金属溶出量很低，表明该体系更适用于实际的土壤修复。