Thermodynamic Properties of Solutions of Di-(2-ethylhexyl)phosphoric Acid-Lanthanum (Lutetium) Di-(2-ethylhexyl)phosphate-o-Xylene

In the present work, complexes formed by the rare earth elements (La, Lu) and di-(2-ethylhexyl)phosphoric acid were synthesized and identified. The densities of D2EHPA-lanthanum (lutetium) di-(2-ethylhexyl)phosphate-o-xylene solutions forming an organic phase in the lanthanide extraction processes were measured; the volumetric properties of D2EHPA-di-(2-ethylhexyl)phosphate REE-o-xylene systems were described using the Redlich-Kister polynomial model. The data on the saturated vapor pressure over D2EHPA-lanthanum (lutetium) di-(2-ethylhexyl)phosphate-o-xylene solutions are obtained at temperatures of 298.15, 303.15, and 308.15 K. The temperature-concentration dependencies of the activity coefficients of o-xylene in the investigated ternary systems were described with the UNIQUAC thermodynamic model taking into account the formation of D2EHPA dimers in solution.