Kinetics of the reaction of Np(VI) with iminodiacetic acid

The stability of Np(VI) in 5–200 mM iminodiacetic acid (H₂IDA) solutions at 23.5–55°С was studied by spectrophotometry. In a solution with pH 2 and excess Np(VI), 1 mol of H₂IDA reduces 2 mol of Np(VI) to Np(V). In 1 and 0.5 M HClO₄ solutions containing 200 mM H₂IDA and 1 mM Np(VI), no more than 36 and 65% of Np(VI), respectively, is reduced at 44.5°С. Complete reduction of Np(VI) is observed in solutions containing 0.2 M HClO₄ and less. In the examined ranges of H2IDA concentrations and temperatures, Np(VI) is consumed in accordance with the first-order rate law. The reduction mechanism involves formation of a Np(VI) iminodiacetate complex, which is followed by intramolecular charge transfer. The generated radical reduces Np(VI). The activation energy is 107 ± 3 kJ mol^–1.