Formal oxidation potentials of ion pairs of americium and neptunium in potassium phosphotungstate solutions

Formal oxidation potentials of neptunium (6)-neptunium (5) (Esub(f)) in potassium phosphotungstate (PT) solutions at different pH are measured. Analogy in the character of Esub(f) dependence on acidity for neptunium and americium Me6-Me5 pairs is determined. Basing on kinetic data and potential shift values for neptunium and americium ions the values of the stability concentration constants for the complexes formed by phosphotungstate-ions and pentavalent neptunium and americium are presented. Esub(f) for Np5-Np4 and Am5-Am4 pairs are estimated. Schemes of formal oxidation potentials for neptunium and americium ion pairs in PT solutions at pH=3-5 are presented