Humic acid and metal ions accelerating the dechlorination of 4-chlorobiphenylby nanoscale zero-valent iron

Transformation of polychlorinated biphenyls (PCBs) by zero-valent iron represents one of the latest innovative technologies forenvironmental remediation. The dechlorination of 4-chlorobiphenyl (4-ClBP) by nanoscale zero-valent iron (NZVI) in the presence ofhumic acid or metal ions was investigated. The results showed that the dechlorination of 4-ClBP by NZVI increased with decreasedsolution pH. When the initial pH value was 4.0, 5.5, 6.8, and 9.0, the dechlorination efficiencies of 4-ClBP after 48 hr were 53.8%,47.8%, 35.7%, and 35.6%, respectively. The presence of humic acid inhibited the reduction of 4-ClBP in the first 4 hr, and thensignificantly accelerated the dechlorination by reaching 86.3% in 48 hr. Divalent metal ions, Co2+, Cu2+, and Ni2+, were reduced andformed bimetals with NZVI, thereby enhanced the dechlorination of 4-ClBP. The dechlorination percentages of 4-ClBP in the presenceof 0.1 mmol/L Co2+, Cu2+ and Ni2+ were 66.1%, 66.0% and 64.6% in 48 hr, and then increased to 67.9%, 71.3% and 73.5%, after 96hr respectively. The dechlorination kinetics of 4-ClBP by the NZVI in all cases followed pseudo-first order model. The results providea basis for better understanding of the dechlorination mechanisms of PCBs in real environment.