紫外光/针铁矿耦合强化降解土壤洗脱液中氯丹的机制研究

Soil washing has been extensively investigated to remove Organochlorine Pesticides (OCPs) from contaminated soils because of its fast remediation, efficiency and low cost. A number of researches have been focus on the soil washing of OCPs-contaminated soils, whereas, few studies were related to the treatment of soil washing effluent. In fact, most of the current remediation technologies, such as activated carbon adsorption, solvent extraction, air stripping, membrane separation, can only extract OCPs from the soil washing effluent rather than thoroughly degradating the pollutants. As a result, the pollutants were still existent and might become a substantial hazardous threat to the environment. Therefore, it’s of great importance to degrade the OCPs and realize the harmless remediation. In this study, the performance of UV/goethite process on degradation of chlordane from soil washing effluent is investigated. Additionally, the effects of Triton X-100/HPCD and pH are also concerned, because the variation of the concentration of Triton X-100/HPCD and pH can directly influence the sorption of chlordane in the goethite. The work is to evaluate the feasibility of the UV/goethite system on the treatment of OCPs soil washing effluent, and to investigate the intermediates of chlordane and the mechanism during the reaction, and to evaluate the repeated use of Triton X-100/HPCD in soil washing. The main purposes in conducting these studies are to obtain the degradation mechanism of chlordane in soil washing effluent, and to provide theoretical basis for degradation of OCPs in soil remediation.

洗脱技术因其快速、高效、成本低等特点，成为有机氯农药（OCPs）污染土壤修复技术中应用较多的处理技术。虽然已有文献报道土壤洗脱的研究，但关于洗脱液后处理技术研究较晚，现有技术如有机溶剂萃取、活性炭吸附、空气吹脱、膜分离等，只是实现了污染物的转移，污染物仍然存在并可能危害生态环境。本项目从洗脱技术快速修复OCPs污染场地后处理过程中，污染物在洗脱液中的降解入手，在对针铁矿吸附氯丹的特性及曲拉通X-100（Triton X-100）和羟丙基-β-环糊精（HPCD）浓度、pH对吸附特性影响的基础上，探索紫外光（UV）/针铁矿体系对洗脱液中氯丹的降解效果、影响因素与氯丹的降解产物和降解机理；探索洗脱液在UV/针铁矿体系降解污染物后回收再利用的有效性；以期逐步阐明UV/针铁矿对土壤洗脱液中氯丹的降解机制，为开发与应用UV/针铁矿新技术在土壤修复中对OCPs的降解提供重要的理论依据。

本项目通过研究UV/针铁矿/H2O2体系对洗脱液中氯丹的降解效果、影响因素、针铁矿吸附氯丹的特性及氯丹的降解产物，阐明UV/针铁矿/H2O2体系降解氯丹的机理及其应用于土壤洗脱修复中的可行性。取得的主要成果如下：（1）研究了UV/针铁矿/H2O2降解模拟土壤洗脱液中氯丹的可行性及最佳工艺参数。在曲拉通X-100（Triton X-100）或羟丙基-β-环糊精（HPCD）洗脱液中，与单一UV、单一针铁矿、单一H2O2、UV/H2O2、针铁矿/H2O2、UV/针铁矿相比，UV/针铁矿/H2O2体系显著提高了氯丹的降解率。在Triton X-100或HPCD洗脱液中，氯丹降解率均随着针铁矿投加量的增加而呈现先增大后减小的趋势。随着H2O2浓度的增加，氯丹降解率先增加后平缓。UV/针铁矿/H2O2在pH3-9范围内可有效降解氯丹。（2）研究了针铁矿吸附氯丹的特性。针铁矿对氯丹具有良好的吸附能力，其吸附动力学与拟二阶动力学模型有很好的拟合度。针铁矿对氯丹等温吸附过程同时符合Langmuir模型与Freundlich模型。pH在3-11范围内，针铁矿对氯丹的吸附量随着pH升高而变小。随着Triton X-100和HPCD浓度的升高，针铁矿对氯丹的吸附量先增大后减小。（3）阐明了UV/针铁矿/H2O2降解洗脱液中氯丹的机制。UV/针铁矿/H2O2降解氯丹的过程中，羟基自由基发挥着强氧化作用。在Triton X-100体系中，氯丹降解的过程体现了表面催化反应机制；在HPCD体系中，表面催化反应机制和均相反应机制共同作用于氯丹的降解反应。UV/针铁矿/H2O2降解氯丹过程中氯丹首先发生氧化反应和脱氯反应，生成氯代化合物，之后逐渐开环，形成单环化合物。（4）研究了UV/针铁矿/H2O2技术应用于土壤洗脱修复中的可行性。氯丹污染土壤可以首先采用浓度为5 mmol/L的Triton X-100或5 g/L的HPCD进行洗脱，之后将洗脱液在UV/针铁矿/H2O2体系进行降解，可有效去除氯丹和洗脱剂，避免环境的二次污染。