Enhanced reductive dechlorination of tetrachloroethene by nano-sized zero valent iron with vitamin B12

We demonstrated that the addition of vitamin B12 can significantly enhance the reductive dechlorination of tetrachloroethene (PCE) by nano-sized zero valent iron (nZVI). A remarkable reductive dechlorination of PCE (0.25 ± 0.01 h−1) was observed in nZVI suspension (0.05 g/24 mL) with 0.5 mM vitamin B12 in 6 h, while no significant reductive dechlorination of PCE was observed in the nZVI suspension without vitamin B12. Vitamin B12r of which central metal is Co2+ was identified as predominant specie during the dechlorination of PCE. The dechlorination kinetic rate constant of PCE in nZVI/vitamin B12 system was significantly dependent on the suspension pH and concentrations of vitamin B12, nZVI, and PCE. An enhancement in PCE dechlorination kinetic (0.180 ± 0.006–0.709 ± 0.004 h−1) due to the formation of hydroxovitamin B12r was observed by increasing the suspension pH (5–9). The dechlorination kinetic rate constant of PCE increased proportionally (0.0010 ± 0.0009–1.3660 ± 0.2940 h−1) as the concentration of vitamin B12 increased (5 nM to 5 mM). As the concentration of nZVI increased by 50 times (0.01–0.50 g), the dechlorination kinetic increased approximately 137 times (0.007 ± 0.001–0.961 ± 0.182 h−1). However, the dechlorination kinetic decelerated (0.184 ± 0.010–0.039 ± 0.006 h−1) as PCE concentration increased (0.005–1.0 mM). This study provides basic understanding on the role of vitamin B12/vitamin B12r as an electron mediator in the enhanced reductive dechlorination of PCE by nZVI occasionally observed in remediation sites.