The formation of Pu(IV)-colloid by the alpha-reduction of Pu(V) or Pu(VI) in aqueous solutions

The effects of alpha-particle self-irradiation have been investigated in solutions of 239Pu in the pH range from 1.3 to > 2.2. The ionic strengths of the solutions ranged from 0.01M to 1.0M, made up with NaCl or LiClO4. The initial solutions contained Pu(VI), Pu(V), colloidal Pu(IV) or various mixtures of these. Composition versus time was determined for periods up to 618 days. Colloidal Pu(IV) formed slowly in mixtures with initial average oxidation states greater than about 4.5. Colloidal Pu(IV) reacts slowly to give mixtures of Pu(V) and Pu(VI). The two most important reactions in the system appear to be: (a) the disproportionation of Pu(V) to give Pu(VI) and colloidal Pu(IV), and (b) the alpha-particle induced reduction of Pu(VI) to give Pu(V). Steady-states were reached very slowly and required at least 400 days for most of the mixtures. No evidence was found for equilibrium in the disproportionation reaction. A simplified model has been developed to help understand the complicated set of reactions involved. (orig.)