MECHANISM AND KINETICS OF THE REACTION BETWEEN CHLORINE AND CHLORINE DIOXIDE IN DILUTE AQUEOUS-SOLUTION

The aim of this work was to study the mechanism and the rate of the reaction between chlorine and chlorine dioxide in dilute aqueous solution at pH values near neutrality. The results showed that chlorination of aqueous solutions of chlorine dioxide leads to the production of chlorate (as an end by-product) and to chlorite (as an intermediate). Secondary reactions between chlorite and chlorine yield chlorate. The overall stoichiometry for the reaction of chlorine with chlorine dioxide corresponds to the production of one mole of chlorate/mole of chlorine dioxide and to the consumption of 0.5 mole of chlorine/mole of chlorine dioxide. The data obtained from experiments carried out at different pH values (6.5 < pH < 10.8) and with different initial concentrations of reactants (chlorine and chlorine dioxide) showed that the rate of disappearance of chlorine dioxide can be described by a second-order kinetic equation (d[ClO2]/dt = k[Chlorine][ClO2]) and that the second-order rate constants increase when pH increases (k = 0.11 l mol-1 s-1 at pH 6.5 and k = 1.02 l mol-1s-1 at pH 10.8 ; 20-degrees-C). Moreover, a mechanism for the reactions between chlorine with chlorine dioxide or with chlorite in dilute aqueous solutions is proposed.