Activation of sodium percarbonate with ferrous ions for degradation of chlorobenzene in aqueous solution: mechanism, pathway and comparison with hydrogen peroxide

Abstract

Environmental contextIt is practicable to remediate chlorobenzene-contaminated groundwater by in situ chemical oxidation. This study shows highly efficient degradation of chlorobenzene by an Fe-based process in a wide range of pH values. The technology is feasible for the removal of chlorobenzene from aqueous solutions and is appropriate for remediation of groundwater. AbstractSodium percarbonate (SPC) could be applied as a strong oxidant to degrade organic compounds activated by transition metals. In this study, the degradation performance of chlorobenzene (CB) in the Fe2+-catalysed SPC system was investigated at different Fe2+ and SPC concentrations and pH conditions. Fe2+/Fe3+ conversion was also studied, and the SPC system was compared with the H2O2 and H2O2/Na2CO3 systems. Free radicals were identified through scavenging tests and electron paramagnetic resonance (EPR) experiments, and the reaction intermediates and by-products were determined as well. The results show that CB was completely removed when the molar concentration ratio of Fe2+/SPC/CB was 8 : 8 : 1 and that the decomposition of CB increased as the initial Fe2+/SPC dosage increased. The optimal molar concentration of Fe2+/SPC/CB was 2 : 1 : 1, and the degradation rate was inhibited when increasing or decreasing Fe2+ or SPC. CB degradation was not significantly affected by variation of initial pH, and the variation of pH during the degradation process corresponded well with the degree of Fe2+ to Fe3+ conversion and the formation of •OH. It was confirmed that •OH, O2•− and 1O2 participate in the degradation process. Moreover, not all the •OH takes part in the degradation process, as some transforms into O2•− and 1O2. The same degradation efficiency was obtained when replacing SPC by equal stoichiometric amounts of H2O2, compared with inhibition with the addition of Na2CO3. Further, a likely degradation pathway for CB is proposed based on the identified products. These results show that the Fe2+/SPC system can form the basis of a promising technology for the remediation of CB-contaminated groundwater.