Correlation of 2-Chlorobiphenyl Dechlorination by Fe/Pd with Iron Corrosion at Different pH

• Published in: Environmental science & technology 2008-09, Vol.42 (18), p.6942-6948
• Main Authors: Fang, Yuanxiang, Al-Abed, Souhail R
• Format: Article
• Language: English
• Subjects: Applied sciences; Biphenyl Compounds - chemistry; Chemical reactions; Chlorine; Corrosion; Corrosion potential; Electricity; Electrodes; Exact sciences and technology; Halogenation; Hydrogen-Ion Concentration; Iron; Iron - chemistry; Kinetics; Oxidation; Palladium - chemistry; Pollution; Reaction kinetics; Remediation and Control Technologies; Solutions
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es800805y

The rate of 2-chlorobiphenyl dechlorination by palladized iron (Fe/Pd) decreased with increasing pH until pH > 12.5. Iron corrosion potential (E c) and current (j c), obtained from polarization curves of a rotating disk electrode of iron, followed the Tafel equation at pH ≤ 5.5 and pH ≥ 9.5. The pH dependence of the dechlorination rate constant (k 1) suggests four pH regimes. In the low pH regime (3−5.5), |E c| and j c decreased with increasing pH and k 1 was linearly correlated to |E c| and j c 0.5. The correlation between k 1 and j c 0.5 indicates direct involvement of active hydrogen species (on the Pd surface) in PCB dechlorination. In the mid pH regime (5.5−9.5), no significant effect of pH was evident on the values of k 1, j c, and E c, a combined result of limiting anodic oxidation of iron to an intermediate product (iron hydroxide) and a proton-independent overall reaction. Both |E c| and j c increased significantly as pH increased from 9.5 to 14. A clear trough of the k 1 values in solutions of pH between 12 and 13 and the mismatch between the kinetic and corrosion data suggest two pH regimes (9.5−12.5 and 12.5−14) of different corrosion mechanisms.