零价铁/四聚磷酸盐活化分子氧去除土壤中五氯酚的机理研究

Although the organic ligand ethylenediaminetetraacetate (EDTA) could enhance the activation of molecular oxygen with zero-valent iron (ZVI), EDTA competes for the reactive oxygen species (ROS) consumption which would result in decrease of the organic pollutants degradation efficiency. Recently, our group found that an inorganic ligand tetrapolyphosphate (TPP) could achieve much higher degradation rate of organic pollutants with ZVI and molecular oxygen than EDTA. In the present project, we aim to explore the removal efficiency and mechanism of a representative persistent organic pollutants (POPs) pentachlorophenol from contaminated soil by activation of molecular oxygen with TPP and ZVI. The influence of the interaction between TPP and soil organic matter (SOM) on the interfacial behavior of pentachlorophenol, and the roles of oxidation/reduction species on the degradation of pentachlorophenol are studied to disclose the migration and transformation mechanism of pentachlorophenol during the process. The characteristics of iron species and the generation of reactive oxygen species affected by the interaction of TPP and iron minerals are investigated in detail to reveal the influence of iron minerals on the removal of pentachlorophenol. The project is supposed to provide theoretical basis and technical support for the remediation of pentachlorophenol contaminated soils by activation of molecular oxygen with TPP and ZVI.

虽然有机配体EDTA能促进零价铁活化分子氧去除有机污染物，但EDTA自身会竞争消耗活性氧物种，降低有机污染物去除效率。申请人所在课题组近期研究发现，无机配体四聚磷酸盐在促进零价铁活化分子氧去除水中有机污染物方面表现出比EDTA更好的效果。本项目以典型持久性有机污染物五氯酚污染土壤为研究对象，探究零价铁/四聚磷酸盐活化分子氧去除土壤中五氯酚的效率和机理。项目将通过考察土壤四聚磷酸盐与土壤有机质的相互作用对五氯酚界面行为的影响，研究体系中氧化/还原物种降解五氯酚的途径，阐明土壤中五氯酚在反应体系中的界面迁移/转化机理；深入分析土壤铁矿物与四聚磷酸盐之间相互作用对铁物种形态和活性氧物种产生效率的影响，揭示土壤铁矿物影响五氯酚去除的机理。项目的研究成果将为零价铁/四聚磷酸盐活化分子氧修复五氯酚污染土壤提供理论依据和技术支持。

五氯酚污染土壤对生态环境和人体健康构成严重威胁，亟待修复。本项目研究了零价铁/四聚磷酸盐活化分子氧去除土壤中五氯酚的效率和机理，主要研究内容包括：（1）四聚磷酸盐对污染土壤中五氯酚界面行为的影响机制，（2）零价铁/四聚磷酸盐活化分子氧去除土壤中五氯酚的效率及机制，（3）土壤有机质对零价铁/四聚磷酸盐活化分子氧去除土壤中五氯酚的影响，（4）土壤典型铁矿物对土壤中五氯酚去除的影响机制。主要研究结果包括：（1）四聚磷酸盐能显著促进土壤中五氯酚的解吸。在中性条件下，2 mmol/L四聚磷酸盐对污染土壤中五氯酚的解吸率达到52.8%。其作用机理首先来源于四聚磷酸盐对土壤颗粒的分散作用，有利于五氯酚的暴露，随后四聚磷酸盐对五氯酚的増溶作用将吸附态五氯酚转化为溶解态五氯酚。（2）零价铁/四聚磷酸盐活化分子氧在中性条件下能够高效地去除土壤中的五氯酚，当添加5 g/L零价铁和10 mmol/L四聚磷酸盐时，反应8 h，土壤中五氯酚的去除率为81.2%。零价铁/四聚磷酸盐活化分子氧体系降解五氯酚的关键活性物种是羟基自由基。（3）土壤有机质的含量能显著影响土壤中五氯酚的界面分配和五氯酚的氧化降解。土壤有机质含量的升高会增加土壤对疏水性有机污染物的吸附位点，从而强化土壤对五氯酚的吸附作用，进而抑制四聚磷酸盐对土壤中五氯酚的解吸。吸附态五氯酚迁移能力弱，与活性氧物种之间传质阻力大，难以被降解，同时土壤有机质与五氯酚竞争消耗产生的活性氧物种，导致土壤有机质含量的增加抑制零价铁/四聚磷酸盐活化分子氧去除五氯酚。（4）土壤中典型铁矿物硫化亚铁在四聚磷酸盐作用下也能活化分子氧产生羟基自由基，进而高效地氧化降解五氯酚。超声能强化硫化亚铁/四聚磷酸盐活化分子氧产生羟基自由基，从而促进五氯酚的降解。本项目研究将为五氯酚污染土壤的原位化学氧化修复提供理论和技术依据。