Degradation of organic compounds during the corrosion of ZVI by hydrogen peroxide at neutral pH: Kinetics, mechanisms and effect of corrosion promoting and inhibiting ions

Abstract

The corrosion of zero valent iron (ZVI) by hydrogen peroxide (H₂O₂) generates hydroxyl (⋅OH) and other radical oxygen species (ROS) that degrade organic materials. To better understand the factors that govern the ROS formation during the H₂O₂-induced corrosion, we investigated the degradation of an organic probe compound (acesulfame (ACE)) in slurries of ZVI powder in unbuffered laboratory water at pH 6.5 ± 0.5. Chloride ions accelerated the corrosion of ZVI by H₂O₂ and the formation ROS and, therefore, the degradation of organic materials. Conversely, slowing corrosion by phosphate buffer inhibited ROS formation and the degradation of organic compounds. The rate of H₂O₂ decomposition was correlated with the liberation of Fe²⁺(aq) and the ACE degradation rate. The kinetics of H₂O₂ decomposition was pseudo-first-order and zero-order at low (<0.04 mM/mg) and high [H₂O₂]/[ZVI] initial ratios, respectively, and was consistent with Langmuir kinetics. The H₂O₂ decomposition rate was proportional to the ZVI reactive surface area (SA) and nearly independent of the extent of ZVI oxidation, the presence of a Fe²⁺(aq) chelating agent, and ⋅OH quenchers (methanol and tert-butanol). Kinetic data suggest a mechanism involving rapid cathodic reduction of H₂O₂ at the metallic ZVI surface which causes the liberation of Fe²⁺(aq) that generate ⋅OH via the homogeneous Fenton reaction. The stoichiometric efficiency (SE) of organics degradation ranged from 0.0008% to 0.014% and increased with decreasing H₂O₂ decomposition rate.

Keywords: Corrosion; Fenton reaction; Hydrogen peroxide; Hydroxyl radical; Zero valent iron.