Citation:

FANG, J. AND S. R. AL-ABED. Correlation Of 2-Chlorobiphenyl Dechlorination By Fe/Pd With Iron Corrosion At Different pH. J. Schnoor (ed.), ENVIRONMENTAL SCIENCE AND TECHNOLOGY. ACS, Washington, DC, 42(18):6942-6948, (2008).

Impact/Purpose:

To evaluate the pH effect on PCB dechlorination by Fe/Pd using 2-chlorobiphenyl (2-CIBP) as a model compound, and to investigate the relationships between the rates of dechlorination and the iron corrosion parameters.

Description:

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 (k₁) suggests four pH regimes. In the low pH regime (3--5.5), |E_c| and j_c decreased with increasing pH and k₁ was linearly correlated to |E_c| and j_c^0.5. The correlation between k₁ 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 k₁, 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 k₁ 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.

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