Reaction of Np(VI) with N-(2-Hydroxyethyl)ethylenediaminetriacetic acid in perchloric acid solutions

Abstract

The stoichiometry of the reaction Np(VI) + H₃hedta [hedta is N-(2-hydroxyethyl)ethylenediaminetriacetate, HEDTA, anion] in a 0.05 M HClO₄ solution was studied by spectrophotometry. With Np(VI) in excess, 1 mol of HEDTA reduces 4 mol of Np(VI) to Np(V). In 0.125–1.0 M HClO₄ solutions (the ionic strength of 1.0 was maintained constant by adding LiClO₄), containing 3–29.2 mM HEDTA, at 20–45°С Np(VI) at a concentration of 0.4–3.5 mM is consumed in accordance with a first-order rate law until approximately 40% of Np(VI) remains. Then, the reaction decelerates. The reaction rate has first order with respect to [HEDTA] and the order of–1.6 with respect to [Н⁺]. The activated complex arises with the loss of one and two Н⁺ ions. The activation energy is 88.4 ± 5.3 kJ mol^–1.