Photochemical oxidation of chloride ion by ozone in acid aqueous solution
2015
Levanov, Alexander V. | Isaykina, Oksana Ya | Amirova, Nazrin K. | Antipenko, Ewald E. | Lunin, Valerii V.
The experimental investigation of chloride ion oxidation under the action of ozone and ultraviolet radiation with wavelength 254 nm in the bulk of acid aqueous solution at pH 0–2 has been performed. Processes of chloride oxidation in these conditions are the same as the chemical reactions in the system O₃ – OH – Cl⁻(aq). Despite its importance in the environment and for ozone-based water treatment, this reaction system has not been previously investigated in the bulk solution. The end products are chlorate ion ClO₃ ⁻ and molecular chlorine Cl₂. The ions of trivalent iron have been shown to be catalysts of Cl⁻ oxidation. The dependencies of the products formation rates on the concentrations of O₃ and H⁺ have been studied. The chemical mechanism of Cl⁻ oxidation and Cl₂ emission and ClO₃ ⁻ formation has been proposed. According to the mechanism, the dominant primary process of chloride oxidation represents the complex interaction with hydroxyl radical OH with the formation of Cl₂ ⁻ anion-radical intermediate. OH radical is generated on ozone photolysis in aqueous solution. The key subsequent processes are the reactions Cl₂ ⁻ + O₃ → ClO + O₂ + Cl⁻ and ClO + H₂O₂ → HOCl + HO₂. Until the present time, they have not been taken into consideration on mechanistic description and modelling of Cl⁻ oxidation. The final products are formed via the reactions 2ClO → Cl₂O₂, Cl₂O₂ + H₂O → 2H⁺ + Cl⁻ + ClO₃ ⁻ and HOCl + H⁺ + Cl⁻ ⇄ H₂O + Cl₂. Some portion of chloride is oxidized directly by O₃ molecule with the formation of molecular chlorine in the end.
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