【作者】 吴兰艳；

【导师】 戴友芝；

【作者基本信息】 湘潭大学 ， 环境工程， 2007， 硕士

【摘要】 本论文在课题组前期研究基础上,以五氯酚为目标污染物,对超声波/零价铁(US/Fe0)体系降解五氯酚动力学与作用机理开展了进一步研究,采用气相色谱-质谱联用仪分析鉴定反应中间产物,据此探讨五氯酚降解途径,取得如下研究成果,为深入研究其它氯酚的降解动力学和降解机理奠定基础。(1)在US/Fe0体系中,五氯酚的降解符合拟一级反应动力学;US/Fe0体系对五氯酚的拟一级速率常数分别是单独US、单独Fe0体系的4倍和15倍,并大于两者之和。当五氯酚的初始浓度为0.5-20mg?L-1,溶液初始pH值2-8,铁粉投加量为0.5-6mg?L-1时,降解速率常数随着初始浓度和pH值的增加而减小、铁粉投加量的增加而增大;(2) US/Fe0体系对五氯酚的作用机理主要有羟基自由基的氧化作用和零价铁的还原作用,其中羟基自由基的氧化作用占主导;(3) US/Fe0体系中OH?的产生主要通过四种途径,其一:声空化导致水分子热解;其二:Fenton反应;其三:超声波与类Fenton反应的复合效应;其四:铁粉颗粒效应。并当pH值为2和3,铁粉投加量为2.0g?L-1时,OH?生成量相对较高;(4)在US/Fe0体系中,超声空化对零价铁具有冲刷、碎裂、清洗、气蚀和熔合等多种效应,活化和增强铁粉的表面性能;同时铁粉可以促进羟基自由基的生成,强化超声波作用;(5)在US/Fe0体系中降解五氯酚,检测到Fe2+和Fe3+,且前者浓度明显大于后者,Fe2+主要起催化分解超声空化过程中生成的H2O2以增加OH?生成量的作用;红外光谱分析证明了体系中存在铁聚合物:δ?FeOOH、γ?FeOOH、α?Fe2O3以及和以羟桥连接的聚合物(Fe-OH-Fe);(6)通过气相色谱-质谱联用分析检测到中间产物:2,3,4,6-四氯苯酚、四氯对苯二酚、八氯二苯并-p-二噁英;并结合相关研究,提出超声波/零价铁体系中五氯酚降解主要有羟基自由基的氧化脱氯,五氯酚氧自由基的自身耦合,以及零价铁的还原脱氯三种降解途径。更多还原

【Abstract】 In this paper, the mechanism and kinetics of the degradation of pentachlorophenol by the ultrasound/zero-valent iron system （US/Fe⁰） were further reported based on the success of the prophase’s researches. Its degradation intermediates were analyzed and identified by the Gas Chromatograph-Mass Spectrometer. On the basis of the above studies, the degradation pathway of pentachlorophenol was proposed. The following is main achievements. The achievements would provide a basis for the better understanding removal of other chlorophenols.（1） The degradation of pentachlorophenol in the US/Fe⁰ system was found to obey the pseudo-first-order reaction. The pseudo-first-order rate constant in the US/Fe⁰ system is 4 times as big as that of ultrasound alone and 15 times as big as that of zero-valent iron alone, and it is more than the sum of the latter two. With the initial PCP concentration of 0.5-20 mg?L-1, the initial pH range of 2-8 and the iron loading range of 0.5-6 mg?L-1, the rate constant in the combined system decreases with the increase of the initial concentration and the initial pH value, but it increases with the increase of the dosage of iron.（2） In the US/Fe0 system, the results indicate that the pentachlorophenol degradations are mainly attributed to the oxidation of hydroxyl radicals and the reduction of iron, and the oxidation of hydroxyl radicals plays a dominant role.（3） There are four main pathways in the hydroxyl radical production: molecular pyrolysis in the the cavitation process, Fenton reaction, the synergism of ultrasound and modified Fenton reaction, and the granular effect of Fe0. Its production was greater at pH value of 2 and 3 and the iron dosage of 2.0 g·L^-1.（4） Characterization of iron surface is highly improved by erosion, fragmentation, cleaning, cavitation erosion and melted of the acoustic cavitation; the effect of ultrasonic on the PCP degradation is strengthened by iron through advancing the generation of hydroxyl radical.（5） The ferrous ion and ferric ion were detected in the combined system, and the former concentration is larger than the latter. The ferrous ion can enhance the catalytic decomposition of hydrogen peroxide as to increasing the hydroxyl radical quantity. The infrared spectrophometry analysis of iron polymeric compound had indicated the presence ofδ-FeOOH,γ?FeOOH,α-Fe2O3 and Fe-OH-Fe.（6） 2,3,4,6-TeCP, TeCHQ and OCDD are identified as intermediates in the US/Fe0 system. Three pathways of the oxidative dechlorination of hydroxyl radicals, the coupling of pentachlorophenoxy radicals and the zero-valent iron dechlorination of pentachlorophenol are proposed on the basis of major intermediates and correlation studies.更多还原