Plutonium disproportionation: maxima in the fractions of two oxidation states.

The equilibrium fractions of soluble tri- and hexavalent Pu depend on the pH and the Pu oxidation number. Both fractions can exhibit maxima as the pH changes at constant N. A fraction at maximum can be used to estimate the equilibrium constant of the first hydrolysis reaction of tetravalent Pu. A new formula that renders least-squares estimates of this constant is illustrated. [ABSTRACT FROM AUTHOR]