Reductive Dechlorination of Chlorinated Biphenyls by Palladized Zero-Valent Metals

Laboratory-scale reductive dechlorination studies using bimetals were conducted to detoxify chlorinated biphenyls, which are known as one of the most recalcitrant organic compounds. Palladized iron and palladized zinc readily dechlorinated mono- and di-chlorinated biphenyls while plain metals were not active. Biphenyl and less chlorinated biphenyls were detected as the major products and calculated mass balance was around 100%, indicating that predominant degradation reaction was dechlorination. For Pd/Fe, degradation rates of mono-chlorobiphenyls were higher than those of di-chlorobiphenyls. Pd/Zn showed higher reactivity than Pd/Fe for the degradation of chlorobiphenyls. Degradation rates of three mono-chlorobiphenyls were in order of 4-CBP > 3-CBP > 2-CBP and this order was matched with the selectivity and dechlorination rate of dichlorobiphenyls. Based on the detected daughter products, it was considered that degradation reaction of dichlorobiphenyls was mainly governed by stepwise dechlorination. However, sequential reaction model fittings indicated that concerted dechlorination was also partly involved in the dichlorobiphenyl degradation. This study demonstrated that catalytically modified ZVM could be successfully applied for the detoxification of chlorinated aromatic compounds including PCBs.