A potentiometric and microcalorimetric study of the complexation of trivalent europium with lactate: The ionic strength dependency of log \u3b2\u2019n, \u394rHm,n and \u394rSm,n

The complexation of Eu(III) by lactate and the ligand protonation were studied at 25\u2009\ub0C as a function of the ionic strength (Im\u2009=\u20090.10 - 5.61\u2009mol kg 121 H2O, NaCl). The experimental formation constants of the three [Eu(Lac)n]3-n (n\u2009=\u20091, 2, 3) mononuclear complexes (log \u3b2\u2019n) and the protonation constant of lactate (log \u3b2\u2019HLac) were determined by potentiometric titrations. The experimental values were extrapolated to zero ionic strength by means of the SIT approach, yielding the thermodynamic constants (log \u3b20n) and the specific ion interaction coefficients of the ionic species (\u3b5(i,k)). The reaction enthalpies (\u394rH\u2019m,n), determined independently by isothermal calorimetry, and entropies (\u394rS\u2019m,n) are also reported. The ionic strength dependence of \u394rH\u2019m,n was fitted by means of the enthalpy SIT approach, giving the standard reaction enthalpies (\u394rH0m,n), entropies (\u394rS0m,n) and the partial molar enthalpy specific ion interaction coefficients (\u394\u3b5L(i,k)). The results show negative conditional reaction enthalpies for all complexes, which become more exothermic with increasing ionic strength. Simultaneously, the \u394rS\u2019m,n decrease steadily with Im, resulting in a gradual change of the driving force of the reactions: at low ionic strength the reaction is driven almost exclusively by entropy. As Im increases the contribution of the enthalpy term becomes relevant and the reactions are driven almost equally by \u394rH\u2019m,n and \u394rS\u2019m,n at the highest value of Im studied

Modified Diglycolamides for actinide separation: Solvent Extraction and Time-Resolved Laser Fluorescence Spectroscopy Complexation Studies

In this work, the back-bone of the diglycolamide-structure of the TODGA extractant was modified by add-ing one or two methyl groups to the central methylene carbon-atoms. The influence of these structural modifica-tions on the extraction behavior of trivalent actinides and lanthanides and other fission products was studied in solvent extraction experiments. The addition of methyl groups to the central meth-ylene carbon atoms leads to reduced distribution ratios, also for Sr(II). This reduced extraction efficiency for Sr(II) is beneficial for process applications, as the co-extraction of Sr(II) can be avoided, resulting in an easier process design. The use of these modified diglycolamides in solvent extraction processes is discussed. Furthermore, the complexation of Cm(III) and Eu(III) to the ligands was studied using Time-Resolved-Laser-Fluorescence-Spectroscopy (TRLFS). The com-plexes were characterized by slope analysis and condi-tional stability constants were determined