Reduction of Np(VI) with Hexamethylenetetraacetic Acid in HClO₄ Solution

Abstract

Spectroscopic method was used to examine the stoichiometry of the reaction of No(VI) with hexamethylenediaminetetraacetic acid (HMDTA, H₄hmdta) in a 0.05 M HClO₄ solution. At an excess of Np(VI), 1 mole of complexon reduces about 4 moles of Np(VI) to Np(V). In 0.1–1.0 M HClO₄ solutions (the ionic strength of 1.0 was maintained with LiClO₄) containing 2–20 mM HMDTA, neptunium(VI) with concentration of 0.3–3.0 M decreases at 35–55°C by the first-order rate law until the instant when less than 20% Np(VI) remains. The initial reaction rate has the first order in [HMDTA] and –2 order in [H⁺]. An activated complex is formed with loss of two H⁺ ions. The activation energy is 102 ± 7 kJ/mol.