Effects of aging and oxidation of palladized iron embedded in activated carbon on the dechlorination of 2-chlorobiphenyl.

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.