Kinetic studies on the self-decomposition of ozone in water, the decomposition of CN~and CNO~, and the decolorization of several dyes by ozone were performed over a wide range of pHusing a stopped-flow apparatus under homogeneousconditions at 298 K. The rate of selfdecomposition of ozone was measured in the pH range from 1 to 13.5, and it was found that in the pH range above 8 the rate was expressed bywhile in the acidic region the concentration dependence of the rate was complicated, and a simple rate expression could not be obtained. The purpose of this paper is to obtain the intrinsic reaction kinetics of the ozonation of several typical contaminants such as cyanide and cyanate ions and dyes in water using a stopped-flow technique under homogeneous conditions. The rate of self-decomposition of ozone in water, which is closely related to the degree of ozone utilization, was also investigated over a wide range of pH. ExperimentalKinetic measurements were performed by meansof a spectrophotometric method.Therates of reactions other than the self-decomposition of ozone at low pH were quite fast, and were measured by a stopped-flow apparatus (Union Giken RA-110). Water containing a known amount of ozone, prepared by bubbling ozone through deionized water, was mixed with the same volume of a buffer solution adjusted to the desired values of pHand of the concentration of a substrate in a cylindrical cell having 2 mmor 10 mmlight-path length, and the time-course of the absorbance of ozone or the reactant was followed. The self-decomposition of ozone at pH below 9 was followed by an ordinary spectrophotometer equipped with a glass-stoppered cell of 10 mmpath length. Calibration charts of the relation between absorbance and ozone concentration were prepared on the basis of the usual analytical method employing potassium iodide. The absorption 383
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