Base-catalyzed destruction of hexachlorobenzene with zero-valent iron

The dechlorination pathways and detoxification mechanism of base-catalyzed decomposition (BCD) of hexachlorobenzene (HCB) with zero-valent iron were investigated. Results showed that HCB was effectively destructed using the BCD technology. The thorough dechlorination efficiencies of HCB (HDEs) improved with increasing reaction time and the addition of zero-valent iron. HCB remaining in the reaction system was almost 100% removed, and HDE reached 93% after 4 h at 360 °C with a zero-valent iron catalyst. The chlorinated intermediates contained pentachlorobenzene (PeCB), three tetrachlorobenzene (TeCB) isomers, three trichlorobenzene (TCB) isomers, three dichlorobenzene (DCB) isomers, and monochlorobenzene (MCB). The base-catalyzed dechlorination of HCB was observed as a stepwise dechlorination process. The main dechlorination pathway for HCB was proposed as HCB → PeCB → 1,2,3,5-TeCB → 1,2,4-TCB → 1,2-DCB → MCB. The residual HCB and chlorobenzenes were mainly distributed in the condensate and active carbon. Chlorobenzenes made up only 0.02% and 0.04% of the paraffin oil and residues, respectively. The innocuous treatment should be further considered for these trace amounts of chlorinated intermediate products.

► Decomposition of HCB with zero-valent iron was investigated with a BCD reactor.
► The dechlorination efficiency of HCB improved with the addition of zero-valent iron.
► The removal of HCB achieved almost 100% at the best condition.
► The HCB dechlorination pathway were examined and discussed.
► The present study is significant for the disposal of POPs waste.