- 學位論文
以奈米零價鐵和雙金屬鐵觸媒對含五氯酚土壤之整治效率探討
Remediation of Pentachlorophenol-contaminated Soil with Nano-zero Valent Iron and Bimetallic Iron
摘要
零價鐵和雙金屬鐵觸媒已被應用於降解水相中含氯化合物。本研究探討應用實驗室合成之奈米零價鐵（nZVI）及工業用的雙金屬鐵觸媒（BioCAT）以降解含五氯苯酚（PCP）之沙質土壤之還原動力和機制之研究。nZVI和BioCAT降解五氯苯酚（PCP）符合一階動力，nZVI對土壤泥漿中之五氯酚的去除率達98％，但主要歸因於nZVI的表面吸附，脫氯效率僅有4％。相較之下，經21天BioCAT處理後之脫氯效率約70％、PCP去除率則為90％。推測原因乃鐵和雙金屬鐵之間反應速率的差異，可能涉及氯酚與活性氫在奈米鐵上之競爭吸附以及鐵觸媒表面鏽蝕的吸附影響。中間產物的形成以及氯的釋放證實PCP之脫氯。此外，在反應過程中pH值上升和ORP值急劇下降也證明PCP的還原脫氯機制。最終產物包含三種TeCP同分異構物、四種TrCP同分異構物、四種DCP同分異構物。本研究也提出nZVI和BioCAT之PCP脫氯途徑。還原脫氯反應後，這些中間產物之毒性低於PCP。這些低氯數氯酚比PCP更容易在環境中生物降解或光降解。研究結果顯示BioCAT可應用於含PCP土壤之處理。 關鍵字：脫氯、奈米零價鐵、雙金屬鐵觸媒、含五氯酚土壤
並列摘要
Zerovalent iron and bimetallic iron have been studied mostly for the degradation of chlorinated compounds in aqueous phase. In this study, laboratory synthesized particles of nano zerovalent iron and commercial bimetallic iron were applied to investigate the reduction kinetics and degradation mechanisms of pentachlorophenol (PCP) spiked sandy soil. Degradation of PCP by nZVI and BioCAT follows the first-order kinetics. The 98% PCP removal efficiency from soil slurries in contact with nano zerovalent iron (nZVI) was mostly attributable to adsorption to nZVI surfaces and only 4% was due to dechlorination. By comparison, approximately 70% dechlorination rate were achieved along with 90% PCP removal efficiency with BioCAT dosage of 600 mg after 21 days of treatment. Possible explainations for the differences in the reaction rates between iron and bimetallic iron may involve competitive sorption of chlorinated phenols and reactive hydrogen on iron and catalytic surfaces as well as the effects of sorption on corrosion. PCP dechlorination was confirmed by the appearance of the intermediate products as well as chloride release. Additionally, the increase of pH values and rapid decrease of ORP values during the reaction also proved reductive dechlorination of PCP. The lower chlorinated phenols and the endproduct including three TeCP isomers; four TrCP isomers; four DCP isomers; two MCP isomers and phenol by BioCAT were found. The intermediates by nZVI contained one TeCP isomer, one TCP isomer. The stepwise dechlorination pathways of PCP by nZVI and BioCAT were proposed in this study. After reductive dechlorination reactions, these intermediates are less toxic than PCP. Furthermore, these lower chlorinated phenols can be biodegraded or photodegraded more easily than PCP in the environment. These findings indicate that using BioCAT with mild temperature and no pH adjustment could have implications for field treatment of PCP-contaminated soil.
參考文獻
延伸閱讀
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