维生素B12耦合球磨铝颗粒修复多溴联苯醚污染土壤的协同作用机制研究

Chemical reduction dehalogenation method, which has been used as the remediation technology of halogenated organic pollutants-contaminated soil, possesses the in-situ, low cost, and environment-friendly functions. This method will probably become an effective prescription for the remediation of electronic waste dismantling site and its surrounding soil in China. The aim of this project is to achieve the environmental remediation research through the debromination and detoxication of the ubiquitous and persistent polybrominated diphenyl ethers (PBDEs) in the above soil. The research will adopt the innovative coupling of Vitamin B12 (VB12) and ball-milling aluminum as a green reducing agent, which is based on the principle for the coordination catalysis dehalogenation of VB12. Moreover, this research focuses on two basic problems existing in the potential application of the above coupling agent: (1) the effectiveness of VB12 coupling ball-milling Al in the reductive degradation of PBDEs under various soil mass transfer conditions; (2) physicochemical and biochemical synergistic mechanism to remove PBDEs through VB12 and ball-milling Al in the complex soil system. Therefore, this research will employ the coupling reagent of VB12 and Al particles with various sizes prepared by ball-milling method; and then explore the effective mass transfer model of the coupling reducing agent released into soil. Simultaneously, it will be revealed about the adsorption process of VB12 on soil particles and the mechanism of the micro interface reaction between VB12 and PBDEs under the action of soil physical and chemical properties as well as various environmental factors. The migration and diffusion property of Al particles in soil micropores and its electron donating efficiency will also be studied and expounded during the remediation process. Finally, the research will evaluate the remediation performance through the above method and optimize the implementation scheme. As a result, this research will be able to provide the basic theory and technical support for in-situ remediation of PBDEs-contaminated soil.

以化学还原脱卤为基础的卤代有机物污染土壤修复技术具有原位、廉价和环境友好的特征，可能是修复我国电子垃圾拆解场地及周边土壤的良方。本项目以上述土壤中普遍存在的持久性多溴联苯醚脱溴去毒为修复目标，创新性耦合维生素B12(VB12)和球磨铝作为绿色还原剂，依据VB12配位催化脱卤原理，侧重研究该耦合剂应用前尚存的两大基础问题：(1)VB12耦合球磨铝在各种土壤传质条件下对多溴联苯醚还原降解的有效性；(2)VB12/球磨铝在土壤复杂体系下去除多溴联苯醚的物化与生化协同机制。本申请拟采用VB12与球磨法制备的各种粒径铝颗粒耦合，研究耦合还原剂施放土壤后有效的传质模式，揭示在土壤理化性质、各环境因子作用下VB12在土壤颗粒上的吸附及其与多溴联苯醚的微界面反应机制，明晰球磨铝颗粒在土壤孔隙的迁移扩散规律和供电子效能；评估修复效果并优化调控方法，为多溴联苯醚污染土壤原位修复提供理论依据与技术支撑。

首先采用球磨法制备金属超细颗粒，与维生素B12耦合，进行2,2',4,4'-四溴联苯醚（BDE47）还原脱溴降解，系统优化球磨工艺参数，通过材料表征和活性试剂识别等，发现纳米粒径的球磨铝粒可有效将VB12中心离子Co从三价还原到具有高还原活性的一价钴，从而协同发挥还原效应，实现BDE47的逐步还原降解，反应pH在4.0，球磨铝量在2.0g/L，VB12用量在0.3mM时，25mg/L的BDE47在反应2h能去除超过99%，反应以逐步脱溴机理进行。随后，开展了零价锌还原BDE47脱溴耦合Fenton试剂氧化降解研究，在表面活性剂助溶作用下，锌颗粒可有效传递电子给BDE47，进行高效脱卤并生成低（无）卤代产物，利用酸性原生反应条件，投入Fe2+和双氧水后，可将低溴代及无溴代产物完全矿化，从而建立彻底降解BDE47新的反应路径，经表面活性剂筛选，优化pH值、Zn投加量、温度等过程参数，针对5mg/L的BDE47溶液，采用0.05g/L的CTAB，在pH4.0，Zn投加量0.3g/L，25ºC下，反应1h可实现BDE47的较彻底去除和深度脱溴，低溴代产物经35mg/L的FeCl2、70mg/L的H2O2作用，反应2h，彻底矿化效率超过99.7%。另外，开展零价锌耦合VB12进行含BDE47土壤淋洗液的降解研究，模拟土壤淋洗液中BDE47浓度为5mg/L，研究对淋洗液水/醇比、锌投加量、VB12用量、初始pH值等进行优化，结果表明水含量在60%、锌量在100mg/L、VB12量为3mmol/L、pH值为6.0时，反应1.5h，BDE47的去除率超过90%，其反应呈现逐步脱溴机理，过程中零价锌、Co(I)形成复合还原剂，在H2O或H+作为氢供体作用下，协同增效完成BDE47的加氢脱溴过程。最后，零价锌耦合VB12进行实际土壤中BDE47直接降解研究，考察了土壤类型，以及土壤含水率、锌投加量、VB12用量的影响，结果沙质土、含水率50%、锌量8 mg/g土壤、VB12用量16 mg/g土壤时，土壤中10 mg/kg BDE47降解效率最高，10 h去除率超过90%，为逐步加氢脱溴机理。上述结果表明，经过处理的零价金属与VB12耦合，可实现土壤PBDE的有效脱溴降解，该项目成果为PBDE污染土壤的修复提供了较为全面有效的基础研究数据，有利于相关土壤修复技术的开发。