Phase Equilibria in o -Xylene–Di-(2-ethylhexyl)phosphoric Acid–Lanthanum (Praseodymium, Terbium, Lutetium) Di-(2-ethylhexyl)phosphate Systems at 298.15 K

This study investigates the phase equilibria in the systems containing o-xylene, di-(2-ethylhexyl)­phosphoric acid (D2EHPA), and lanthanum, praseodymium, terbium, and lutetium di-(2-ethylhexyl)­phosphates at 298.15 K. The research provides insight into the solubility of these rare-earth element complexes in organic solvents. The study outlines an approximate homogeneity boundary for the solutions of lanthanum, praseodymium, terbium, and lutetium di-(2-ethylhexyl)­phosphates in D2EHPA and the o-xylene–D2EHPA mixture at 298.15 K. The study demonstrates a decreasing stability region for the solution of o-xylene–D2EHPA–rare earth elements (La, Pr, Tb, Lu) di-(2-ethylhexyl)­phosphates systems from La to Lu. The reported density of “liquid” praseodymium di-(2-ethylhexyl)­phosphate (PrA3) at 298.15 K, which is not available in the literature, is optimized based on experimental data, which are obtained using the Redlich–Kister polynomial equation. The interaction parameters of o-xylene–D2EHPA, along with the optimized density value of PrA3, enable a satisfactory description of the densities in o-xylene–D2EHPA–PrA3 solutions. These results have relevance for various industrial applications, particularly in the field of rare earth element extraction and separation processes.