Remediation of Aged Hexachlorobenzene Contaminated Soil by Nanoscale Zero-Valent Iron

Abstract

Abstract Currently, there are limited studies on the elimination of chlorinated organic compounds in aged soil. In this study, we utilized Nanoscale zero-valent iron (nZVI) to explore the removal of various chlorinated organic compounds presented in aged hexachlorobenzene (HCB)-contaminated soil. We also investigated the effects of initial pH values, as well as temperature, on the removal of HCB and other coexisting chlorobenzene congeners. Our results revealed that the highest removal efficiency for four chlorinated organic compounds was achieved under acidic conditions and elevated reaction temperatures. The maximum removal efficiency was higher than 80% for HCB and reached 90%, 60%, and 30% for pentachlorobenzene (PeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), and 1,2,4-trichlorobenzene (1,2,4-TCB), respectively. The removal of HCB by nZVI followed pseudo-first-order kinetics, which was different to other chemicals selected in this study. The reaction rate constant varied from 0.27 (initial pH value of 3) to 0.021 (initial pH value of 11). Furthermore, the reaction temperature was another affecting factor of the rate constant, which increased from 0.036 (15°C) to 0.192 (45°C). Notably, the presence of H+ did not significantly influence the rate-determining step of the chemical dehalogenation process for HCB and coexisting chlorobenzene congeners throughout the entire reaction. The removal of HCB and PeCB using nZVI in aged HCB-contaminated soil was characterized as an endothermic and diffusion-controlled process, with activation energies of 38.02 kJ/mol and 17.34 kJ/mol, respectively.