Dechlorination of polychlorinated biphenyls, naphthalenes and dibenzo-p-dioxins by magnesium/palladium bimetallic particles

Abstract

The contamination of sediments with polychlorinated organics such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (Dioxins) and polychlorinated naphthalenes (PCNs) remains a significant problem in many rivers, harbors, and estuarine areas in the US and around the world. In this work, rapid dechlorination of PCBs, PCNs, and Dioxins by palladium—coated magnesium (0.01% by weight Pd) has been demonstrated in pure solvent systems (10% methanol in distilled water). This reaction was investigated with the goal of developing it as a future sediment treatment method. More than 90% of the initial single PCB congeners BZ 3 and 170 were removed in 1 to 10 minutes and about 58% of the total initial Arochlor 1260 was removed in 4 minutes. The removal of single Dioxin and PCN congeners also occurred rapidly resulting in a 69 to 95% reduction in 30 minutes. Rapid removal of biphenyl, the expected degradation end product for PCBs, was also observed (80% removal in 5 minutes). Experiments conducted with Arochlor 1260 and biphenyl did not identify significant volatile fractions. A significant amount of PCBs were extracted from the filtered Mg/Pd material suggesting that PCBs first adsorb to the surface of the bimetal and then dechlorination occurs; lesser chlorinated congeners and biphenyl were also found adsorbed to the Mg/Pd material. Experiments conducted with single PCB congeners BZ 194 and 204 demonstrated the formation of lower—chlorinated PCB congeners, indicating that dechlorination was occurring. A stepwise dechlorination process was suggested in which chlorines in the ortho position were removed last.

Keywords:

• Dechlorination
• contaminated sediments
• polychlorinated biphenyls
• polychlorinated dibenzo-p-dioxins
• polychlorinated naphthalenes
• palladized magnesium
• bimetals

Acknowledgements

The authors would like to acknowledge the Cooperative Institute for Coastal and Estuarine Environmental Technology (CICEET) for funding the project through the Environmental Research Group at the University of New Hampshire and the National Aeronautics and Space Administration (NASA), and in particular Dr. Jacqueline W. Quinn, for supplying the Mg/Pd material. The authors would also like to thank Jean M. Spear from the University of New Hampshire for her help in the GC/MS analysis and Cliff Chase from Resource Laboratories LLC in Portsmouth, NH for performing the HS-GC/MS analysis.