电场促进碳微球负载纳米零价铁在多溴联苯醚污染土壤中的传质修复作用与机理研究

China is facing severe problems with soil contamination by brominated flame retardants. Application of nano zerovalent iron is a very important technology for remediating soil contaminated by brominated flame retardants, but the transport of material particles in the soil becomes the bottleneck restricting the promotion and application of this technology. It is of great scientific significance and great prospects to study the transport of nano zerovalent iron in soil and its impact on the degradation of polybrominated diphenyl ethers. The goal of this project is to enhance the transport of nano zerovalent iron in soil. We embed nano zerovalent iron on uniform carbon microspheres to improve the mobility and stability of material in soil. We try to remove organic pollutants in situ by infiltration injection of environmental friendly material into polybrominated diphenyl ethers contaminated soil. In the mean time with the help of electric field the injection diffusion radius of material in soil and the reactivity can be improved. We are going to reveal the behavior of the material under the electric field and illustrate the removal mechanism of polybrominated diphenyl ethers in situ. The critical technology and theoretical basis will be provided to solve the key problem with on-site remediation of polybrominated diphenyl ethers.

我国面临着严峻的溴代阻燃剂土壤污染问题。纳米零价铁法是修复溴代阻燃剂污染土壤的重要技术，但是该材料在土壤中的传质问题是制约该技术推广应用的瓶颈。研究纳米零价铁在土壤介质中的传质及其对溴代阻燃剂的降解是土壤有机污染修复的关键技术，具有重要的科学意义及应用前景。本项目以促进纳米零价铁传质为思路，将纳米零价铁负载于碳微球上提高材料在土壤中的稳定性和迁移性，通过渗透注射方式将具有环境友好特性的材料原位注入多溴联苯醚污染土壤中，实现材料对污染物的原位降解，同时辅以外加交换电场增强材料在土壤中的扩散性能及反应活性,揭示材料在电场作用下的行为过程，阐明多溴联苯醚的原位降解机理，为解决多溴联苯醚修复技术的现场应用问题提供关键技术与理论依据。

针对纳米零价铁原位修复溴代阻燃剂污染土壤传质难的问题，本研究提出了采用电场促进以及材料负载相结合修复多溴联苯醚污染土壤的新思路，研究了具有分散性好、反应活性高、稳定性强的碳微球负载纳米零价铁材料的制备及其在电场促进作用下土壤系统中迁移传质的优化模式及影响因素，阐明了电场促进下碳微球负载纳米零价铁材料对土壤中多溴联苯醚的降解模式及机理。经研究得出如下结论：.(1)制备的碳微球负载纳米零价铁材料提高了材料的比表面积、减小了零价铁粒子的团聚，提高了零价铁的反应性能。O2、低pH值（<4）、共存离子HCO3-和H2PO4-会影响碳微球负载纳米零价铁材料的稳定性，且对BDE 209的降解活性的影响较明显。.(2)阴极附近铁含量的显著提高证明了碳微球负载纳米零价铁在电场促进下往阴极区域迁移传质。研究确定了原位注射条件为：速率600mL/min，注射量为150mL，注射浓度为1.5g/L（Fe），分3次注射，CMC含量为0.2%。在实验条件范围内，碳微球负载纳米零价铁的传质随电压梯度、初始pH、含水率的升高而提高。电场促进碳微球负载纳米零价铁传质的优化条件为：电压梯度1.0V/cm，初始pH7，初始含水率为30%，电解液由Ca(HCO3)2（0.006 M）、CaCl2(0.002 M)、MgCl2（0.001 M）构成。.(3)电场促进了碳微球负载纳米零价铁对土壤中BDE-209的降解。研究表明，在变换电场的作用下，碳微球负载纳米零价铁材料和BDE 209及其降解产物在电场作用下迁移，结合反应。BDE 209吸附在碳微球负载纳米零价铁表面随着时间分步渐进还原脱溴，在反应30d后，回收率为77%，实验系统未检测到BDE 209，主要产物为BDE 7、BDE 8、BDE15、BDE 3以及DE，脱溴产物主要集中在靠近阴极的区域S4、S5，而固定电场下仍能检测到大量的多溴产物。在未施加电场的情况下，碳微球负载纳米零价铁仅发生原位扩散，对BDE 209的降解基本只发生在S3区域。施加电场的情况下，BDE 209在装置中往阴极区域迁移，且变换电场中，BDE 209的迁移更明显。.