Formal Oxidation Potentials of the Np(VI)-Np(V) Couple and Schemes of Formal Oxidation Potentials of Np and Am Ions in HNO_(3) Solutions Containing Potassium Phosphotungstate K_(10)P_(2)W_(17)O_(61)

摘要

The formal oxidation potentials E_(f)~(0) of the Np(VI)-Np(V) couple in 1-3 M HNO_(3) solutions containing (1-3) X 10~(-3) M potassium phosphotungstate K_(10)P_(2)W_(17)O_(61) (KPW) were measured by the potentiometric method with spectrophotometric identification of the valence states. The potentials slightly decrease with an increase in the HNO_(3) and KPW concentrations, and the shift of the Np(VI)-Np(V) potential toward negative values relative to its value in 1 M HClO_(4) reaches 0.08 V. The formal oxidation potentials of the Np(V)-Np(IV) couple were calculated from the experimentally determined equilibrium constants (K_(eq)) of the redox reaction of the Np(V) disproportionation. Under the examined conditions, these potentials also vary insignificantly, and the shift of E_(f)~(0) toward positive values relative to its value in 1 M HClO_(4) is 0.53 V. The schemes of potentials of the Np and Am couples in 1 M HNO_(3) in the presence of KPW are suggested.