Free radical reactions of monochloramine and hydroxylamine in aqueous solution

Abstract

The use of Advanced Oxidation Technologies to destroy organic contaminants in drinking water may be impacted by the presence of disinfection chemicals such as monochloramine (NH 2Cl). To allow a quantitative evaluation of the effect of NH 2Cl on the destruction of organics in water rate constants for its reaction with the hydrated electron, the hydroxyl radical and the hydrogen atom were determined in this study. The corresponding values of (2.2±0.2)×10 10, (2.8±0.2)×10 9, and (1.2±0.1)×10 9 M −1 s −1, respectively, were incorporated into a kinetic computer model whose predictions were in good agreement with experimental chloramine removal under large scale, steady-state electron-beam irradiation conditions. Rate constants were also determined for the reaction of the hydroxyl radical and hydrogen atom with the chloramine hydration product hydroxylamine to supplement established literature data. Hydroxyl radical rate constants for the basic (NH 2OH) and acidic (NH 3OH +) forms were determined as (8.5±0.4)×10 9 and ⩽5×10 7 M −1 s −1, respectively, while for hydrogen atom reaction, corresponding rate constants of (4.5±0.1)×10 7 and (3.6±1.5)×10 5 M −1 s −1 were found.