Calorimetric measurement of the enthalpy of extraction of uranyl nitrate by Tri-n-Amyl Phosphate

Abstract

Enthalpy of extraction of uranyl nitrate by tri n-amyl phosphate (TAP) and its solutions in n-dodecane has been directly measured by solution calorimetry for the first time. Measurements have been made at 303+1 K, in both forward as well as the reverse extraction modes. The enthalpies of the accompanying reactions such as the dilution of the uranyl nitrate in the aqueous phase, the hydration of TAP, the mixing of TAP and n-dodecane, the mixing of the metal-solvate (U02(NO3)2.2TAP) and n-dodecane and mixing of the metal-solvate and TAP have also been independently measured and used to derive both the equilibrium state enthalpies and the standard state enthalpies for the extraction reaction. Two distinct standard states have been used for the organic phase, viz.,1) all solutes infinitely diluted in diluent (AH*) and 2) all solutes infinitely diluted in the water saturated extractant (ΔH°). The results have been compared with the enthalpies of extraction measured by employing the temperature dependence of the distribution ratio as well as calorimetry reported in the literature for extraction of uranyl nitrate by TAP and TBP. © 2002 Atomic Energy Society of Japan.