Interaction of actindes with carboxylate in solution: Complexation of U(VI), Th(IV), and Nd(III) with acetate at variable temperatures

The complexation of uranium (VI), thorium (IV), and neodymium (III) with acetate was studied from 10 to 70 \ub0C. The formation constants and the enthalpies of complexation were determined by titration potentiometry and calorimetry. The complexes become stronger at higher temperatures, despite that the enthalpy of complexation becomes more positive and unfavorable to the complexation as the temperature is increased. Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and optical absorption spectroscopy provide additional information to support the thermodynamic results. The effect of temperature on the thermodynamic parameters is discussed in terms of the electrostatic model