【作者】 李芬芳；

【导师】 戴友芝；

【作者基本信息】 湘潭大学 ， 环境工程， 2006， 硕士

【摘要】 本文应用超声波/零价铁(US/Fe~0)联合技术,以五氯酚为目标污染物,考察了超声波/零价铁的协同效应,研究了溶液初始pH值、初始浓度、零价铁投加量等因素对五氯酚(PCP)降解效果的影响,并在同一条件下考察了五种典型氯酚类有机物的降解效果;同时考察了协同体系中羟基自由基(·OH)的作用及其变化规律,重点研究了协同体系中超声波/零价铁的协同作用机理;初步探讨了五氯酚在协同体系中的降解途径,并对氯酚类有机物结构与降解性能的关系进行了定性研究。研究结果表明:超声波和零价铁有显著的协同效应;当五氯酚的初始浓度为5~200mg/L,溶液初始pH值2~11时,五氯酚去除率随其初始浓度和pH值的增加而减小;当铁粉投加量小于1.5g/L时,去除率随投加量的增加而增大,当投加量大于1.5g/L时,降解率随投加量的增加而减小;在同一条件下,五种典型氯酚在超声波/零价铁体系中的降解均符合一级反应动力学,降解速率常数呈一定的规律:2-氯酚<2,4-二氯酚<2,4,5-三氯酚<2,3,4,6-四氯酚<五氯酚,即苯环上的氯取代基数目越多,降解越容易。在超声波/零价铁体系,羟基自由基的氧化作用是五氯酚降解的主要原因,铁粉的颗粒效应和Fe2+(由铁的酸腐蚀而产生)的催化作用,促进了协同体系中羟基自由基的产生;同时,超声波对铁粉表面的清洗、侵蚀和粉碎作用,强化了液固传质,增加了铁表面积,相应的提高了反应速率。超声波/零价铁降解过程中,少量的五氯酚通过热解脱氯降解,大部分的五氯酚通过羟基自由基的加成、氧化脱氯、开环降解。结构与性能关系的研究结果表明,整个苯环可以看成一个大的碳正离子,当氯原子取代得越多,碳正离子的形成速度越快,反应活性越大;随着氯取代基越多,分子的(Elumo - Ehomo)2越小,表示该分子越不稳定。由此推测五种氯酚的降解难易为:五氯酚>2,3,4,6-四氯酚>2,4,5-三氯酚>2,4-二氯酚>2-氯酚,与超声波/零价铁协同降解上述物质所得实验速率结果一致。更多还原

【Abstract】 In this study, the degradation efficiency of pentachlorophenol (PCP) by ultrasound in the presence of iron was reported. The major affecting factors on PCP degradation such as iron loading, initial pH value of solution, initial concentration of PCP were studied. This study focus on the synergistic mechanism of the enhanced degradation of PCP by ultrasound in the presence of iron and the degradation pathway of PCP. At the same time, the structure-property relationship of chlorophenols was also studied.Ultrasound combined with elemental iron (US/Fe0) was effective in oxidizing organic contaminants in water. The sonolysis degradation of pentachlorophenol (PCP) was significantly enhanced with the addition of elemental iron. The effect of pH, iron loading and initial PCP concentration on the degradation of PCP by elemental iron combined with ultrasound radiation was investigated. It was shown that the degradation of PCP was enhanced by ultrasound and the degradation appeared to be a first order reaction. With the pH range of 2~11, iron loading range of 0.25~1.5gL?1 and initial dye concentration of 5~200 mgL?1, the PCP removal rate decreased with the increasing pH or initial PCP concentration, but increased with the increase of iron loading. With iron loading range of 1.5~3.0gL?1, the PCP removal rate decreased with the increase of iron loading. Under the same condition, the destruction of chlorophenols (CPs) follows an apparent first-order kinetic and the rate constant increased with the increased number of Cl on the benzene ring: 2-CP<2,4-DCP<2,4,5-TCP<2,3,4,6-TeCP<PCP. The degradation of PCP in US/Fe0 system mainly via reaction with hydroxyl radicals (?OH radicals), and the synergistic mechanism of the enhancement in the combined system was investigated. The results indicated that the rate enhancements in US/Fe0 system were attributed to (1) the iron solid effect and the catalysis of Fe(II) produced from corroded-iron with promoting the production of ?OH radicals; (2) the increased surface area of iron particles by acoustic cavitation with promoting the mass transfer process. In the combined system, most of PCP was degraded by ?OH radicals, and partial by pyrolysis. The structure-property relationship of chlorophenols was studied, and the result indicated that the activity of chlorophenols was related to the number of C-Cl bond, the chemical stabilization of chlorophenols (CPs) decreased with the increased number of Cl on the benzene ring更多还原