Interaction of NpO₂⁺ With Cl^- in Na-Ca-Cl Type Solutions With High Ionic Strength

Abstract

The interaction of NpO₂⁺ with Cl^- was studied using UV-Vis spectroscopy in the NaCl-CaCl₂-NaClO₄, NaCl-NaClO₄ and CaCl₂-NaClO₄ solutions with ionic strength (I) of 6 M. The spectra of NpO₂⁺ around 980 nm varied with Cl^- concentration in the NaCl-CaCl₂-NaClO₄ and NaCl-NaClO₄ solutions at [Cl^-] ≥ 3.5 M, but not in the CaCl₂-NaClO₄ solution. Assuming the 1:1 interaction between NpO₂⁺ and Cl^-, the apparent equilibrium constants at I = 6 M were evaluated. The apparent equilibrium constant in the NaCl-CaCl₂-NaClO₄ solution was found to be smaller than that in the NaCl-NaClO₄ solution. The observations were consistent with the density functional theory calculation.