不同奈米零價鐵與油相液體中三氯乙烯之反應性

Abstract

土壤及地下水受重質非水相液體汙染為現今整治工作最棘手之問題。奈米零價鐵因其高表面反應性及在地下水層中之傳輸性，應用於土壤及地下水整治之研究逐漸增多。過去研究，奈米鐵降解含氯碳氫化合物之反應多在水相中進行，較少研究評估奈米鐵於油相中之反應。本研究針對油相中之反應，探討以不同奈米零價鐵及不同水分含量降解三氯乙烯之反應速率與途徑，俾建立以奈米零價鐵處理重質非水相汙染物之理論基礎及設計經驗參數。 研究結果顯示，油相中之三氯乙烯可以被奈米零價鐵或雙金屬零價鐵降解。以市售鐵 (F)、市售並自行改質之雙金屬鐵 (DF) 及自行合成聚丙烯酸之雙金屬鐵 (ADF)，於油相中降解三氯乙烯之降解反應並不完全符合擬一階反應動力式。如果以零階反應估計其單位表面奈米鐵之反應速率kSA，在最佳之情況下分別為1.891×10-5，6.272×10-5，5.066×10-5 (mmol∙L∙h-1∙m-2)。本研究之非水相液體反應中，三氯乙烯之劑量較奈米鐵高，且氫離子活性較低，使得三氯乙烯濃度對於降解反應之影響不顯著，三氯乙烯之降解速率亦較水相中慢，約千分之一至萬分之一倍。相同奈米鐵於不同含水率下，含水率較高者，DF組之kSA較高，但ADF及F組則沒有顯著差異。

Due to the special characteristics of dense non-aqueous phase liquids (DNAPLs), singnificant solubility and low mobility, the contamination of soil and groundwater by DNAPLs is still an intractable problem for environmental engineers. Even more, if DNAPLs were transported to impermeable boundary, they would form DNAPL pools and become continuous contamination sources. The application of nano zero-valent iron (nZVI) in soil and groundwater treatment is given increasing attention because of its high surface reactivity and transportation ability in the underground. However, the researches about the reaction of chlorinated aliphatic hydrocarbons with nZVI were mostly conducted in aqueous phase instead of in non-aqueous phase. The purpose of this research is to investigate the reaction rates and pathways of trichloroethene reduction by different nZVI with different water content and to shed light on the theory and values of the empirical parameters of the reaction. The results show that nZVI and bimetallic nZVI could reduce trichloroethene in non-aqueous phase. The trichloroethene reduction by physical vapor deposition (PVD) iron (F), PVD bimetallic iron (DF) and surface modified bimetallic iron (ADF) in non-aqueous phase were better to explained by zero-order reaction kinetics. The zero-order reaction rate, kSA, are 1.891×10-5，6.272×10-5，5.066×10-5 (mmol∙L∙h-1∙m-2). In this research, the molar equivalent of trichloroethene was higher than that of nZVI, so that the hydrogen ion produced was consumed immediately and its activity was low in the microcosm systems. The reduction rates of trichloroethene in non-aqueous phase are much slower than the rates in aqueous phase. Under the same nZVI dosage with different water content, the kSA with higher water content is higher in DF group, but with no significant difference in F and ADF groups.