Choi Hyeok, Al-Abed Souhail R, Agarwal Shirish
National Risk Management Research Laboratory, U.S. Environmental Protection Agency, 26 West Martin Luther King Drive, Cincinnati, Ohio 45268, USA.
Environ Sci Technol. 2009 Jun 1;43(11):4137-42. doi: 10.1021/es803535b.
Reactive activated carbon (RAC) impregnated with palladized iron has been developed to effectively treat polychlorinated biphenyls (PCBs) in the environment by coupling adsorption and dechlorination of PCBs. In this study, we addressed the dechlorination reactivity and capacity of RAC toward aqueous 2-chlorobiphenyl (2-ClBP), and its aging and longevity under various oxidizing environments. RAC containing 14.4% Fe and 0.68% Pd used in this study could adsorb 122.6 mg 2-ClBP/g RAC, and dechlorinate 56.5 mg 2-ClBP/g RAC which corresponds to 12% (yield) of its estimated dechlorination capacity. Due to Fe0 oxidation to form oxide passivating layers, Fe2O3/Fe3O4 (oxide-water interface) and FeOOH/FeO (oxide-metal interface), RAC reactivity decreased progressively over aging under N2 < H2O + N2 < H2O + 02 conditions. Considering nanoscale Fe/Pd corrosion chemistry, the decline was quite slow at only 5.6%, 19.5%, and 32.5% over one year, respectively. Dissolved oxygen played a crucial role in enhancing 2-ClBP adsorption but inhibiting its dechlorination. The reactivity change could be explained with the properties of the aged RAC including surface area, Fe0 content and Fe species. During the aging and oxidation, the RAC showed limited dissolution of Fe and Pd. Finally, implementation issues regarding application of RAC system to contaminated sites are discussed.
负载钯铁的反应性活性炭（RAC）已被开发出来，通过耦合多氯联苯（PCBs）的吸附和脱氯作用来有效处理环境中的多氯联苯。在本研究中，我们研究了RAC对水中2-氯联苯（2-ClBP）的脱氯反应活性和能力，以及其在各种氧化环境下的老化和寿命。本研究中使用的含14.4%铁和0.68%钯的RAC能够吸附122.6 mg 2-ClBP/g RAC，并使56.5 mg 2-ClBP/g RAC脱氯，这相当于其估计脱氯能力的12%（产率）。由于Fe0氧化形成氧化钝化层，即Fe2O3/Fe3O4（氧化物-水界面）和FeOOH/FeO（氧化物-金属界面），在N2 < H2O + N2 < H2O + 02条件下，RAC的反应活性随着老化而逐渐降低。考虑到纳米级铁/钯的腐蚀化学，在一年时间里，其下降相当缓慢，分别仅为5.6%、19.5%和32.5%。溶解氧在增强2-ClBP吸附但抑制其脱氯方面起着关键作用。反应活性的变化可以用老化RAC的性质来解释，包括表面积、Fe0含量和铁物种。在老化和氧化过程中，RAC显示出铁和钯的有限溶解。最后，讨论了将RAC系统应用于污染场地的实施问题。
