Highly-effective mechanochemical destruction of hexachloroethane and hexachlorobenzene with Fe/Fe3O4 mixture as a novel additive

Abstract

In this study, Fe/Fe3O4 mixture was first applied as an additive to achieve the highly-effective mechanochemical destruction (MCD) of two halogenated organic pollutants (HOPs), hexachloroethane (HCE) and hexachlorobenzene (HCB). The MCD of HCE was more effective than that of HCB in virtue of the lower dissociation energy of CCl bond. The MCD of HOPs occurred mainly via the reduction by Fe, Fe3O4 and Fe/Fe3O4. The oxidation of Fe3O4 and reduction of FeO (formed on account of the oxidation of Fe by oxygen-containing species) may also contribute to the HOP destruction. Fe/Fe3O4 mixture exhibited a higher dechlorination rate (DR) than other three effective additives (i.e., Fe/SiO2, Al/Al2O3 and Mg/Al2O3 mixture), owing to the electrical property of Fe3O4 and its electron transfer with Fe. The HOP destruction was significantly impacted by the mass fraction of Fe3O4 (MFmag) and achieved the maximum level with an MFmag of 70%. The DR of HOPs in the atmosphere of air was higher than those of pure oxygen and nitrogen because of the oxygen vacancy in Fe3O4 and oxidation of Fe. The presence of water dramatically inhibited the HOP destruction due to the decrease of collision energy and its competition for the active sites in both Fe and Fe3O4. As expected, the DR of HOPs increased with rotation speed, and the mass ratio of ball to reactant and additive to pollutant. The analysis of intermediates indicates that HCB destruction was mainly via dechlorination and polymerization, while HCl cleavage also played an important role in HCE destruction. The results demonstrate that Fe/Fe3O4 mixture is a suitable additive for MCD process.