THE EFFECT OF TEMPERATURE ON THE SYNERGISTIC EXTRACTION OF THORIUM(IV) AND URANIUM(VI) BY 2-ETHYLHEXYL PHENYLPHOSPHONIC ACID AND MICELLES OF DINONYL NAPHTHALENE SULFONIC-ACID

The influence of temperature in the range 15 to 75 degrees C on the ex traction of thorium(IV) and uranium(Vr) from nitric acid solutions int o ligroine solutions of 2-ethylhexyl phenylphosphonic acid (HEH phi P) , micellar dinonyl naphthalene sulphonic acid (HDNNS) extractants and mixture of the two extractants is reported. From the variation of the distribution ratio with temperature, the enthalpy changes associated w ith the extraction were determined, and an attempt was made to estimat e the free energy and entropy changes associated with the extraction p rocess. The results indicate that the extraction of thorium is favored by both entropy change and enthalpy change when the solvent is HEH ph i P and the mixture of HEH phi P and HDNNS, but entropy controlled whe n HDNNS is the extractant. On the other hand, the extraction of uraniu m by HEH phi P is enthalpy controlled but favored by entropy change wh en the solvent is HDNNS or a mixture of the two ligands. Temperature d id not affect the extraction stoichiometry.