Complexation of neptunium(V) with fluoride in aqueous solutions at elevated temperatures

Abstract

Complexation of neptunium(V) with fluoride in aqueous solutions at elevated temperatures was studied by spectrophotometry and microcalorimetry. Two successive complexes, NpO2F(aq) and NpO2F 2 − , were identified by spectrophotometry in the temperature range of 10–70°C. Thermodynamic parameters, including the equilibrium constants and enthalpy of complexation between Np(V) and fluoride at 10–70°C were determined. Results show that the complexation of Np(V) with fluoride is endothermic and that the complexation is enhanced by the increase in temperature — a two-fold increase in the stability constants of NpO2F(aq) and more than five-fold increase in the stability constants of NpO2F 2 − as the temperature is increased from 10 to 70°C.