The system: Tri-n-butyl phosphate (TBP)-nitric acid-water—I activities of TBP in equilibrium with aqueous nitric acid and partial molar volumes of the three components in the TBP phase

New experimental data are presented on the distribution of nitric acid and water between aqueous acid and 100% tri-n-butyl phosphate (TBP) solutions. A table of smoothed distribution data, obtained by a hand-smoothing procedure from these data combined with other literature data, is also presented. Several different mathematical representations of the data in terms of the Gibbs-Duhem relation are described, and the resulting activities of TBP, obtained by graphical integration, are compared. A table of rational activities of TBP (based on pure anhydrous TBP as the standard state) is presented for aqueous nitric acid concentrations ranging from 0 to 15 M. Partial molar volumes of the components in the TBP phase, determined by least-squares analysis of the density data, are 16·5, 43·3 and 273·9 ml/mole, respectively, for H2O, HNO3 and TBP.