Kinetics of the Np(VI) + EDTA reaction in perchloric acid solutions

Abstract

The stoichiometry of the Np(VI) + H2C2O4 and Np(VI) + H4Y reactions (Y is EDTA anion) in 0.2 M HClO4 solution was studied by spectrophotometry. With excess Np(VI), 1 mol of H2C2O4 or EDTA reduces, respectively, 2 or 4 mol of Np(VI) to Np(V). In 0.1–1.0 M HClO4 solution (the ionic strength of 1.0 was supported by adding LiClO4) containing 3–20 mM EDTA at 20–45°C, Np(VI) at a concentration of 1 mM and higher is consumed in accordance with the first-order rate law until less than 0.4 mM Np(VI) remains in the solution, after which the reaction decelerates. The reaction rate has the order of 1 with respect to EDTA and −1.5 with respect to H+ ions. The activated complex is formed with the loss of 1 and 2 H+ ions. The activation energy is 86.0 ± 3.5 kJ mol−1.