Mechanism and Kinetic Model of Chlorate and Perchlorate Formation during Ozonation of Aqueous Chloride Solutions

A mechanism (a set of significant reactions with rate constants) has been proposed for the complex chemical reaction of ozone with chloride ion in aqueous solution at pH 5.5-12, leading to the formation of chlorate ion ClO3- as the main product and perchlorate ion ClO4- as a byproduct. A mathematical model of chemical reaction kinetics in the O-3-Cl-(aq) system has been constructed. The most important chlorate formation channels are initiated by the oxidation of chloride ion with an ozone molecule or hydroxyl free radical. The reaction of Cl- with O-3 leads to the formation of hypochlorite ion in the primary stage. Subsequent oxidation reactions of ClO(- )give chlorine dioxide ClO2 center dot as an intermediate. When chloride is oxidized with OH center dot radicals, Cl-2(center dot-) anion radicals are formed, which then react with ozone to form chlorine monoxide ClO center dot. Subsequent oxidation and combination reactions of ClO center dot and ClO2 center dot and the hydrolysis of complex chlorine oxides Cl2Ox lead to the generation of chlorate and also perchlorate. The results obtained quantitatively characterize for the first time the complex reaction of O-3 with Cl-(aq), based on the mechanism, and make it possible to predict the kinetics of its product formation under various conditions.