Dry dechlorination of polychlorinated biphenyls in contaminated soil by using nano-sized composite of metallic Ca/CaO and its mechanism

Soil contamination by PCBs is still known as a serious problem across the world, and the development of new technologies or the improvement of existing ones (e.g. higher efficiency, shorter processing time, lower input energy) are more and more important. Moreover, understanding the chemistry of the entire process, from a mechanistic point of view, can accelerate the process of improvement. In these circumstances, we attempted a clarification of the highly efficient degradation of PCBs by nano-sized particle of metallic Ca in CaO ("nCa") at 250 °C in dry solid state conditions. The reaction involved the hydrodechlorination, simple reduction, reductive coupling and hydroxylation processes. The detoxification efficiency reached over 99%. A tentative pathway and mechanism is proposed for explaining the final reactions products. Finally, the process was applied to real PCBs-contaminated soil, containing various amounts of PCBs, with a total success in completely eliminating the toxic polychlorinated compounds.