Determination des constantes cinetiques de reaction des radicaux hydroxyles sur quelques s‐triazines

Abstract

Rate constants for the reaction of hydroxyl radicals with atrazine (k_A), simazine (kg) and propazine (kp) have been measured in water, using competitive kinetic methods. Hydroxyl radicals were generated in the decomposition of ozone by hydroxide ions or by hydrogen peroxide (O₃/H₂O₂). Assuming that hydroxyl radical reactions are predominant in the degradation of s‐triazines by O₃ and by O₃/H₂O₂, the data showed that the relative rate constants for the reaction of hydroxyl radicals with s‐triazines obtained from O 3 and from O₃/H₂O₂ experiments carried out in phosphate buffered water (pH = 7.5; [HCO₃ ^‐] range: 0 to 20 mmol l‐¹) or in drinking water and in batch and semi‐batch reactors were identical: k_S/kA = 1.28 and kp/k_A = 0.75 (20 ± 2°C). By mixing a reference substrate (chlorobenzene k_CB = 4.3 10⁹ 1 mol^‐1 s^‐1) to the solution of s‐triazines, the following values for the reaction of hydroxyl radicals with atrazine, simazine and propazine could be determined from competitive experiments: k_A = 1.7 10⁹; kg = 2.1 10⁹ and kp = 1.2 10⁹ 1 mol‐¹ s‐¹.

Keywords:

• s‐triazines
• advanced oxidation processes
• hydroxyl radicals
• competitive kinetics
• water treatment