Disproportionation of Plutonium(V) in EDTA Solutions

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Abstract

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 PuO2HY2–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).

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About the authors

A. M. Fedoseev

Frumkin Institute of Physical Chemistry and Electrochemistry

Author for correspondence.
Email: A.Fedosseev@gmail.com
Russian Federation, Leninskii pr. 31, korp. 4, Moscow, 119071

V. P. Shilov

Frumkin Institute of Physical Chemistry and Electrochemistry

Email: shilov.ipce@gmail.com
Russian Federation, Leninskii pr. 31, korp. 4, Moscow, 119071

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2. 1. Kinetic curve of accumulation of Pu(IV) as a result of disproportionation of Pu(V) in a solution of 28 mmol/l of EDTA (pH 2.91) at 45°C. [Pu(V)]0 = 2.87 mmol/L.

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3. Fig. 2. Anamorphosis of the kinetic curve of Pu(IV) accumulation according to Fig. 1.

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4. 3. Effect of pH on the rate constant of disproportionation of Pu(V) at 45°C. 1 – 0.95 mol/L NaClO4 + 10 mmol/L EDTA; 2 – 0.90 mol/L NaClO4 + 28 mmol/L EDTA; 3 -28 mmol/L EDTA; 4 -196 mmol/L EDTA.

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