Disproportionation of Plutonium(V) in EDTA Solutions

The kinetics of disproportionation of Pu(V) in EDTA solutions with pH 2.5–4.8 at a temperature of 45°C was studied using the spectrophotometric method. Pu(V) was obtained by reduction of Pu(VI) with EDTA ions. The rate of disproportionation in the pH range 2.9–4.8 is described by the equation –d[Pu(V)]/dt = 2k[Pu(V)]2. As pH increases, the value of 2k decreases. In a solution of 28 mmol/L EDTA at pH 2.91, 45 °C, and an ionic strength of 0.09 and 1.0 mol/L, 2k is 0.064 and 0.040 L mol^–1 s^–1, respectively. A dimer is formed from PuО₂⁺ ·5H₂O and the PuO2HY^2–nH₂O complex, which becomes an activated complex. Its decomposition leads to the appearance of Pu(IV) and Pu(VI). The latter, being bound to Y, is reduced intramolecularly to Pu(V). The activation energy is estimated at 86 kJ/mol (25–45°C).