Catalytic Dechlorination Of Chlorinated Endocrine Disrupting Chemicals In Water By Pd/Fe

Reductive dechlorination of chlorinated Endocrine Disrupting Chemicals(EDCs) in Water by metallic catalytic reduction was studied for further understanding the application of palladiumized iron-scrap(Pd/Fe) bimetallic catalytic reduction technology in treating high molecular weight and structure complicated refractory chlorinated organic pollutans, especially, the reductive dechlorination reaction of the three chlorinated EDCs: 2,4-dichlorophenoxyacetic acid(2,4-D), Hexachlorocyclohexane(HCH), and chlordane.In this research, the iron-scrap wastes obtained from the mechanical processing factory were the source of the zero-valent iron. Using electroless plating method to prepare the Pd/Fe bimetallic catalyst with superior property. X-ray diffraction(XRD), scanning electron microscope(SEM) were used to characterize the surface conditions of the bimetallic systems. Subsequently, comparing the reductive dechlorination performance between the different bemetallic systems, such as Cu/Fe, Ag/Fe, Pd/Fe, and so on, for halogenated methane, 2,4-D, HCH and chlordane. Results showed that the three chlorinated EDCs could be effectively dechlorinated by Pd/Fe. 2,4-D could be totally dechlorinated in 30min, and HCH could reach the most chlorine loss in 10min; Chlordane could also loss the most chlorine in more than ten hours. The fact that they could hardly be dechlorinated by the bimetallic systems, such as Cu/Fe and Fe, illuminated that Pd/Fe has its own superior property in the dechlorination reaction of the chlorinated organics.Studying the effects of solid-liquid ratio, initial concentration of pollutants, initial pH value and the mass fraction of Pd in the bimetal(w(Pd/Fe)) on the reaction rate and dechlorination effects of 2,4-D. Results showed that the dechlorination rate was decreased with the increasing initial concentration of 2,4-D. And the optimum pH was 4-6 for the dechlorination reaction of 2,4-D, and pH between 2 and 8 were all suited for the reaction in Pd/Fe systems.Intermediate and final products of 2,4-D, HCH and chlordane with Pd/Fe were determined by GC/MS, and the possible dechlorination pathways were concluded: 2,4-D can be converted to phenoxyacetic acid through gradual hydrogenolysis, and HCH can be transformed to cyclohexatriene through dichloroelimination or dehydrochlorination.Combination of the literatures correlated with the Pd/Fe catalytic reductive mechanism and the experimental research in this paper, it can be deduced that the catalytic hydrogenation of Pd plays an important role in the reductive dechlorination reaction of the chlorinated EDCs. Meanwhile, the processes of reductive elimination and the direct reduction by Fe~0 are also involved in the reaction.