Control effects of p(epsilon) and pH on the generation and stability of chlorine dioxide.J Environ Sci (China). 2003 Sep; 15(5):680-4.JE
A new method, without assistance of activity ratio diagram, was applied to construct the p(epsilon)-pH diagrams for chlorine system. The optimal pH range for generation of C1O2 by contacting Cl2 (g) directly with ClO2- solution is within pH 1.35-1.94, particularly within pH 1.35-4.00 only if minimizing the formation of Cl2. It is unachievable to synthesize pure ClO2 from the reaction of Cl2 and ClO2- . Conversely, ClO2 may be present a variation of stability in different waters owing to the changed p(epsilon) and pH. ClO2 could be relatively stable if not disproportionate into ClO3-, coexisting with ClO2- (p(epsilon) 17.63 and pH > 9.68), Cl2(pH < or = 0.92) or Cl- (pH 0.92-9.68). When chlorine system has already reached the ultimate equilibria, ClO2 is a stable species in strongly acid media. As the acidity decreases, ClO2 disproportionates into ClO3- and Cl2. Aqueous ClO2 is unstable within the normal pH range. This work initially, theoretically elucidates the generation and stability of ClO2 by way of the p(epsilon)-pH diagrams.