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

Abstract

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 (H2O2) plays a key role in minimizing the formation of I-DBPs by reduction of HOI during H2O2-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 H2O2 were determined in the pH range of 4.0–12.0. H2O2 showed considerable reactivity with HOI near neutral pH (kapp = 9.8 × 103 and 6.3 × 104 M−1s−1 at pH 7.1 and 8.0, respectively). The species-specific second order rate constants for the reactions of H2O2 with HOI, HO2− with HOI, and HO2− with OI− were determined as kH2O2+HOI = 29 ± 5.2 M−1s−1, kHO2-+HOI = (3.1 ± 0.3) × 108 M−1s−1, and kHO2-+OI− = (6.4 ± 1.4) × 107 M−1s−1, respectively. The activation energy for the reaction between HOI and H2O2 was determined to be Ea = 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 H2O2–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 H2O2 to HOI- and phenol-containing solutions. During water treatment with the O3/H2O2 process or peracetic acid in the presence of I−, O3 and peracetic acid will be consumed by a catalytic oxidation of I− due to the fast reduction of HOI by H2O2. The O3 deposition on the ocean surface may also be influenced by the presence of H2O2, which leads to a catalytic consumption of O3 by I−.