Parameters Influencing Third-Phase Formation in the Extraction of Th(NO3)4 by some Trialkyl Phosphates

Third-phase formation in the extraction of Th(IV) by trialkyl phosphates (TalP) such as tri-n-butyl phosphate (TBP), tri-iso-butyl phosphate (TiBP), tri-sec-butyl phosphate (TsBP), tri-n-amyl phosphate (TAP), tri-2-methylbutyl phosphate (T2MBP), tri-iso-amyl phosphate (TiAP), tri-sec-amyl phosphate (TsAP), and tri-cyclo-amyl phosphate (TcyAP) has been investigated under various conditions. Formation of a third phase in the extraction of Th(IV) by TBP/n-dodecane as a function of TBP concentration at 303K was studied. Measurements were also carried out on the extraction of Th(IV) from its solution with near-zero free acidity by various phosphate/diluent binary solutions (1.1M) as a function of temperature. Third-phase formation in the extraction of Th(IV) by 1.1M TalP in various diluents from nitric acid media has also been studied as a function of equilibrium aqueous-phase acidity at 303K. Empirical equations to predict limiting organic concentration with respect to various parameters for third-phase formation in the extraction of Th(IV) by TBP and TAP from nitric acid media have been derived. Some of the above phosphates have been investigated for the distribution of Th(NO3)4 between the diluent-rich phase (DP) and third-phase (TP) in the extraction of Th(IV) by 1.1M TalP in various diluents from its saturated solution with near-zero free acidity at 303K. Results of the above studies are presented in this paper. Based on these studies, the effects of extractant concentration, the temperature, the nature of the diluent, the equilibrium aqueous-phase acidity, and the structure of the extractant on third-phase formation behavior of trialkyl phosphates are described in this paper.