Interaction of NpO2+ with Cl- in NaCaCl-type solutions at ionic strength of 6M: Effect of presence of Ca ion on interaction

The interaction of NpO2+ with Cl- was studied using visible-near-infrared spectroscopy in NaClCaCl2NaClO4, NaClNaClO4, and CaCl2NaClO4 solutions with ionic strength (I) of 6M. The spectra of NpO2+ around 980 nm varied with Cl- concentration in the NaClCaCl2NaClO4 and NaClNaClO4 solutions at [Cl-] ≥ 3.5M, but not in the CaCl2NaClO4 solution. Assuming the 1:1 interaction between NpO2+ and Cl-, the apparent equilibrium constants at I = 6M were evaluated. The presence of Ca2+ was found to destabilize overall interaction between NpO2+ and Cl-. The observations were consistent with the density functional theory calculation.