A Thermodynamic Model of Nitric Acid Extraction by Tri-n-Butyl Phosphate

A thermodynamic model is presented for nitric acid extraction by tri-n-butyl phosphate (TBP). This model is based on the formation of the organic phase species: TBP·HNO₃ and (TBP)₂.·HNO₃. The model works successfully at TBP concentrations of 5 to 100 vol% and was found to be effective at predicting the extraction of HNO₃ from HNO₃/NaNO₃ and HNO₃/ LiNO₃ solutions. Within the TBP concentration range of 5 to 30%, a single set of extraction constants was sufficient to fit extraction data. Stoichiometric activity coefficients of nitric acid in HNO₃/NaNO₃ and HNO₃/LiNO₃ mixtures were calculated using a model developed by Bromley.