Dechlorination of Pentachlorophenol by Zero Valent Iron and Modified Zero Valent Irons

Abstract

The disappearance of pentachlorophenol (PCP) from aqueous solutions in contact with zero valent metals (ZVMs) may be due to dechlorination reactions or sorption to ZVM-related surfaces. Previously reported results on PCP and zero valent iron measured only PCP loss from aqueous solutions and attributed this loss to reaction. In this study, the total amount of unreacted PCP, both that in aqueous solution and that sorbed to ZVM-related surfaces, was measured using a modified extraction method. PCP dechlorination was confirmed by following the appearance of tetrachlorophenol isomers. The results indicate that the rate of dechlorination is much slower than previously reported. In our experiments, electrolytic zero valent iron with a surface area of 0.12 m 2 /g resulted in an observed first-order rate constant (±95% confidence limits) of 3.9 (±0.7) × 10 - 3 h - 1 or a half-life of approximately 7.4 days. Normalized to surface area, the rate constant ( k SA ) is 3.2 (±0.6) × 10 - 4 L m - 2 h - 1 . Four amended irons prepared by coating iron with palladium (Pd/Fe), platinum (Pt/Fe), nickel (Ni/Fe), and copper (Cu/Fe) were also used and showed slower removal rates as compared to unamended iron (estimated half-lives of 36−43 days). Slower reaction rates obtained with amended irons as compared to iron have not been previously reported. Overall, this study conclusively demonstrates PCP dechlorination by iron and several bimetallic ZVMs and indicates that it is essential to separate reaction and sorption processes.