Compositional Characterization of Organic Phases after the Phase Splitting in the Extraction of Th(NO₃)₄by 1.1 M Tri-<i>n</i>-butyl phosphate/<i>n</i>-Alkane

Abstract

Third phase formation in the extraction of Th(IV) by 1.1 M solutions of tri-n-butyl phosphate (TBP) in n-decane and n-hexadecane from Th(NO3)4 solution in 1 M HNO3 has been investigated as a function of equilibrium aqueous phase Th(IV) concentration ([Th(IV)]aq,eq) to estimate the concentrations of Th(NO3)4, HNO3, and TBP in the third phase (TP) and the diluent-rich phase (DP). In this connection, new methods for the estimation of TBP in the organic phases after the phase splitting have been developed by exploiting the linear relationships of the density and refractive index of the solvent, the limiting organic concentration (LOC) for the third phase formation in the extraction of Th(IV) from solution with near-zero free acidity with TBP concentration in the solvent. TBP concentrations estimated by the above-mentioned methods have been validated by nitric acid (8 M) equilibration method. Experimental values for the concentration of TBP in the TP and DP for 1.1 M TBP/n-alkane–Th(NO3)4/1 M HNO3 systems have been compared with the values computed based on a model proposed earlier. In addition, the density of organic phases and the ratio of the volume of the DP to that of the TP have been measured for the above-mentioned systems as a function of [Th(IV)]aq,eq at 303 K.