Kinetics of the reaction between hydrogen peroxide and aqueous iodine: Implications for technical and natural aquatic systems

Oxidative treatment of iodide-containing waters can lead to a formation of potentially toxic iodinated disinfection byproducts (I-DBPs). Iodide (I − ) is easily oxidized to HOI by various oxidation processes and its reaction with dissolved organic matter (DOM) can produce I-DBPs. Hydrogen peroxide (H 2 O 2 ) plays a key role in minimizing the formation of I-DBPs by reduction of HOI during H 2 O 2 -based advanced oxidation processes or water treatment based on peracetic acid or ferrate(VI). To assess the importance of these reactions, second order rate constants for the reaction of HOI with H 2 O 2 were determined in the pH range of 4.0–12.0. H 2 O 2 showed considerable reactivity with HOI near neutral pH ( k app  = 9.8 × 10 3 and 6.3 × 10 4  M −1 s −1  at pH 7.1 and 8.0, respectively). The species-specific second order rate constants for the reactions of H 2 O 2 with HOI, HO 2 − with HOI, and HO 2 − with OI − were determined as k H2O2+HOI  = 29 ± 5.2 M −1 s −1, k HO2 - +HOI  = (3.1 ± 0.3) × 10 8  M −1 s −1, and k HO2 - +OI −  = (6.4 ± 1.4) × 10 7  M −1 s −1, respectively. The activation energy for the reaction between HOI and H 2 O 2 was determined to be E a  = 34 kJ mol −1. The effect of buffer types (phosphate, acetate, and borate) and their concentrations was also investigated. Phosphate and acetate buffers significantly increased the rate of the H 2 O 2 –HOI reaction at pH 7.3 and 4.7, respectively, whereas the effect of borate was moderate. It could be demonstrated, that the formation of iodophenols from phenol as a model for I-DBPs formation was significantly reduced by the addition of H 2 O 2 to HOI- and phenol-containing solutions. During water treatment with the O 3 /H 2 O 2 process or peracetic acid in the presence of I −, O 3 and peracetic acid will be consumed by a catalytic oxidation of I − due to the fast reduction of HOI by H 2 O 2. The O 3 deposition on the ocean surface may also be influenced by the presence of H 2 O 2, which leads to a catalytic consumption of O 3 by I −.