Phase equilibria at various temperatures in ternary liquid systems consisting of thorium(IV) and lanthanide(III) nitrate solvates with tri-n-butyl phosphate and of isooctane

Abstract

The phase diagrams of ternary liquid systems (TLSs) [Th(NO3)4(TBP)2]-[Ln(NO3)3(TBP)3] (Ln = Nd, Gd, Ho; TBP = tri-n-butyl phosphate)-isooctane at 298.15–333.15 K were studied. The TLSs are characterized by the fields of homogeneous solutions and of two-phase liquid systems (systems with phase separation) in which one of the phases (I) is enriched in [Th(NO3)4(TBP)2] and [Ln(NO3)3(TBP)3], and the other phase (II), in isooctane. The temperature (298.15–333.15 K) does not noticeably affect the mutual solubility of [Th(NO3)4(TBP)2] and isooctane but decreases the field of phase separation in ternary systems. In two-phase systems, [Ln(NO3)3(TBP)3] is predominantly distributed into phase I, despite the fact that binary systems [Ln(NO3)3(TBP)3]-isooctane are single-phase at all the examined temperatures. The distribution of [Ln(NO3)3(TBP)3] into phase I results in the redistribution of [Th(NO3)4(TBP)2] into phase II and of isooctane into phase I. The critical composition points of the TLSs at various temperatures were determined; they depend on particular lanthanide(III).