Reduction of chlorinated hydrocarbons using nano zero-valent iron supported with an electric field. Characterization of electrochemical processes and thermodynamic stability

Electric field assisted remediation using nano iron has shown outstanding results as well as economic benefits during pilot applications (Černíková et al., 2020). This method is based on donating electrons to the zero-valent iron that possess an inherently strong reductive capacity. The reduction of chlorinated hydrocarbons may be characterized by a decrease in contaminants or better still by the evolution of ethene and ethane originating from the reduction of chlorinated ethenes. The evolution of ethene and ethane was observed predominantly in the vicinity of the anode despite reduction processes being expected near the cathode – the electron donor. The reduction near the anode occurred due to dissolved Fe2+ ions, whose presence was suggested by a Pourbaix diagram that combines Eh/pH values to characterize electrochemical stabilities between different species. No products of dechlorination were observed in the area of the cathode due to presence of oxidized Fe in the form of Fe3+ or Fe(OH)4-. The experimental work described in this research provides a deeper view of the processes of electrochemical reductive dechlorination using zero-valent iron and DC. It also showed an increase in the efficiency compared to the method using zero-valent iron only. [Display omitted] •Electric field amplifies the reductive effect of zero-valent iron.•The key parameters for the description of the reductive conditions are Eh-pH.•The Eh-pH diagrams depict reductive ability/capacity of the system with nZVI.•The reduction of chlorinated hydrocarbons occurs primarily in the area of the anode.•In the cathode area zero-valent iron is protected against oxidation.