Effect of Chloride Ions on the Dechlorination of Hexachlorobenzene in the Presence of Zero-Valent Iron

Hexachlorobenzene (HCB) is highly refractory and cannot be treated by typical biological treatment processes. Hence, it can be extracted out from effluent and sediment in local flora and fauna. This toxic chemical is transferred to humans as the final end of the food chain, causing severe health problems to the community. HCB can be an acceptor to receive the electron from iron oxidation, simultaneously releasing the chloride iron. Therefore, the effect of chloride ions on the dechlorination of HCB by zero-valent iron was investigated because of the high concentration of chloride ions in the area of the estuary, which may affect the iron corrosion as well as the dechlorination reaction. Additionally, iron content and reductant of sodium sulfide affecting the HCB transformation were also investigated in this study. In the absence of chloride ions, 2.72× 10−5 M of HCB was completely degraded in 3 h . The dechlorination extent of HCB was reduced when chloride ions were present in the reaction solution. When the concentration of chloride ions was 0.84 M , which is almost equal to that in seawater, only 40% of 2.72× 10−5 M HCB was degraded in the same reaction time. When 0.42 M of chloride ions was introduced, 65% of HCB was transformed. In addition, Na2 S also inhibited the HCB dechlorination. Only 18% of HCB disappeared after 24 h of reaction. This indicates that the chloride ions and sodium sulfide existing in the reaction solution can retard the dechlorination of HCB by zero-valent iron.