Studies on Ozone Bleaching. I. The Effect of PH, Temperature, Buffer Systems and Heavy Metal-Ions on Stability of Ozone in Aqueous Solution

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Abstract
Ozone was found to be reasonably stable at moderately low pH (∼pH 3) and ambient temperature in acetic, sulfuric and nitric acid solutions. In these cases, the exact kinetic order of ozone decomposition could not be established. However, second order with respect to ozone was preferred on the basis of statistical analysis of the data. At pH 3, the ozone decomposition rate was found to be slightly higher at 15°C and moderately higher at 35°C than at 25°C for all three buffer systems. At lower concentration level (∼ 0.5 ppm), only Co(II) ion enhanced decomposition of ozone in sulfuric acid solution at pH 3 and 25°C. In contrast, at the higher concentration level (∼ 3.0 ppm), Ca(II), Cr(III), Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) ions were found to contribute the decomposition of ozone; the effect of Co(II) and Fe(II) ions was very pronounced as compared to the other ions. Using acetic acid instead of sulfuric acid as buffer reagent resulted in drastic and moderate reductions of the ozone decomposition catalyzed by Co(II) and Fe(II) ions, respectively. These indicate that acetic acid acts as radical scavenger for hydroxyl radical as postulated by Walling et al. Thus, the drastic increase in the ozone decomposition in the sulfuric acid solution with the presence of Co(II) or Fe(II) ion is caused by free radical chain reactions initiated by free radicals produced in the process.

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