Reductive dechlorination of chlorinated hydrocarbons as non-aqueous phase liquid (NAPL): Preliminary investigation on effects of cement doses

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• 作者：Si-Hyun Do^a ; ^{sihyun2@hanyang.ac.kr} ; Bill Batchelor^b
• 关键词：Reductive dechlorination ; Non-aqueous phase liquid ; Ferric iron ; Portland cement ; Lime ; Second-order kinetics
• 刊名：Science of the Total Environment
• 出版年：2012
• 期刊代码：63_00489697
• 类别：env
• 出版时间：15 July, 2012
• 卷：430
• 期：Complete
• 页码：82-87
• 文件大小：555 K

摘要

The reactivities of various types of iron mixtures to degrade chlorinated hydrocarbons (PCE, TCE and 1,1,1-TCA) in the form of non-aqueous phase liquids were investigated. The iron mixtures included a mixture of Fe(II) and Portland cement (Fe(II)-C), a mixture of Fe(II), Fe(III) and Ca(OH)₂ (Fe(II/III)-L), and a mixture of Fe(II), Fe(III), Ca(OH)₂, and Portland cement (Fe(II/III)-C). When the same amount of Fe(II) was used, Fe(II)-C was more reactive with chlorinated ethylenes (i.e. PCE and TCE) than Fe(II/III)-L. The reductive pathway for high concentrations of total PCE (i.e. above solubility) with Fe(II)-C was determined to be a combination of two-electron transfer, 尾-elimination and hydrogenolysis. Increasing the cement dose from 5%to 10%in Fe(II)-C did not affect PCE dechlorination rates, but it did favor the 尾-elimination pathway. In addition, when Fe(II/III)-C with 5%C was used, PCE dechlorination was similar to that by Fe(II)-C, but this mixture did not effectively degrade TCE. A modified second-order kinetic model was developed and shown to appropriately describe degradation of TCE at high concentrations. Fe(II/III)-L effectively degraded high concentrations of 1,1,1-TCA at rates that were similar to those obtained with Fe(II)-C using 10%C. Moreover, both increasing cement doses and the presence of Fe(III) increased dechlorination rates of 1,1,1-TCA, which was mainly through the hydrogenolysis pathway. The reactivity of Fe(II/III)-L was strongly dependent on the target compound (i.e. less reactivity with TCE, more with 1,1,1-TCA). Therefore, Fe(II/III)-L could be a potential mixture for degrading 1,1,1-TCA, but it should be modified to degrade TCE more effectively.