Kinetics of Pu(VI) Reaction with Ethylenediaminetetraacetic Acid

Abstract

The spectrophometric method was used to examine the stoichiometry of the reaction of Pu(VI) reduction by EDTA ions in 0.05–0.5 M HClO₄ solutions at a temperature of 23°C at an excess of Pu(VI), 1 mol of EDTA reduces 3.5 ± 0.5 mol of Pu(VI) in air, with the main reaction product being Pu(V). At a solution pH 4.5, 1 mol of EDTA reduces 5 ± 0.5 mol of Pu(VI). The reaction of Pu(VI) reduction by EDTA ions hardly occurs in 0.1 M HClO₄ in an inert atmosphere, whereas at pH 4.5, the reaction is complete in ∼1 min. In 0.05–0.5 N HClO₄ solutions (ionic strength of 1.0 was maintained by addition of LiClO₄) at temperatures of 23–45°C, Pu(VI) is consumed by the first-order rate law. The reaction rate is of the first order in EDTA and −2 order in H⁺ ions. An activated complex is formed with loss of two protons. The activation energy is 128 ± 10 kJ/mol. Assumptions are made about the possible involvement of oxygen in the reaction mechanism.