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Evaluating Chemical Reactivity And Mechanical Stability Of Nano Palladized Iron Embedded In Activated Carbon On Dechlorination Of Polychlorinated Biphenyls
Citation:
AL-ABED, S. R. AND H. Choi. Evaluating Chemical Reactivity And Mechanical Stability Of Nano Palladized Iron Embedded In Activated Carbon On Dechlorination Of Polychlorinated Biphenyls. Presented at PacificChem Conference, Honolulu, HI, December 15 - 20, 2010.
Impact/Purpose:
To evaluate chemical reactivity and mechanical stability of nano palladized iron embedded in activated carbon on dechlorination of PCBs.
Description:
Remediation of contaminated sites with hydrophobic organic compounds such as polychlorinated biphenyls (PCBs) remains a scientific and technical challenge. The high stability, low aqueous solubility, and high organic affinity of PCBs make them difficult to treat. Many physical, chemical and biological remediation strategies have been proposed, but limited success has been achieved. Adsorptive materials such as activated carbon (AC) have been shown to effectively sequester PCBs desorbed from sediment and thus reduce their bioavailability in the aquatic environment. Meanwhile, reactive metal particles such as Fe, and Fe/Pd have been proven to electrochemically dechlorinate PCBs to lower congeners and eventually to bio-available biphenyl (BP). We synthesized and tested reactive activated carbon (RAC) impregnated with nano palladized iron using its coupling of adsorption and dechlorination of polychlorinated biphenyls (PCBs). RAC containing 14.4% Fe and 0.65% Pd could adsorb 122.6 mg 2-CIBP/g RAC, and dechlorinate 56.5 mg 2-CIBP/g RAC which corresponds to 11.6% of its estimated dechlorination capacity. Short term testing of RAC to treat PCBs was prompt and sustainable; however the reactivity of RAC was decreased gradually over a period of one year due to Fe0 oxidation. RAC's reactivity to dechlorinate PCBs was decreased progressively over ageing under N2 < H2O + N2 < H2O + O2 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 PCB adsorption but inhibiting its dechlorination. The change in reactivity could be explained with the properties of the aged RAC including surface area, Fe0 content and Fe species. Data on detachment of Fe/Pd particles during mechanical mixing at 60 rpm and their dissolution upon the reaction at pH 6.5-8.9 will be also presented.