Phase equilibria at various temperatures in the ternary liquid system containing solvates of thorium(IV) and uranyl(VI) nitrates with tri-n-butyl phosphate and tetradecane

Abstract

The phase diagram of the ternary liquid system [Th(NO3)4(TBP)2]-[UO2(NO3)2(TBP)2]-tetradecane (where TBP stands for tri-n-butyl phosphate) has been investigated at temperatures from 298.15 to 333.15 K. The ternary liquid system is characterized by a region of homogeneous solutions and a region of two-phase liquid systems (stratified systems). One phase is enriched with solvates [Th(NO3)4(TBP)3] and [UO2(NO3)2(TBP)2] (phase I), and the other is enriched with tetradecane (phase II). The temperature (T = 298.15–333.15 K) does not substantially affect the two-phase region. In the two-phase systems, the preferential distribution of [UO2(NO3)2(TBP)2] into phase I is observed in spite of the fact that the binary system [UO2(NO3)2(TBP)2]-tetradecane is a single phase at all temperatures investigated. The distribution of [UO2(NO3)2(TBP)2] into phase I leads to the redistribution of [Th(NO3)4(TBP)2] into phase II. At all temperatures investigated, the critical solution points of the ternary liquid system have compositions with close contents of the solvates [Th(NO3)4(TBP)2] and [UO2(NO3)2(TBP)2].