The present paper describes the surface complexation behaviour of trivalent metal ions, Am(III) and Eu(III), on well characterised γ-alumina. Experiments are conducted at different pH (4-8) and ionic strength (0.001 - 0.1 M NaClO

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Selected soft N-donor ligands are highly effective extractants for the separation of trivalent actinides (An(III)) from lanthanides (Ln(III)) in the partitioning and transmutation (P&T) strategy. Comparative structural investigations using X-ray absorption spectroscopy (EXAFS) on An(III) and Ln(III) complexed with tris[(2-pyrazinyl)methyl]amine (TPZA) and 2,6-di(5,6-dipropyl-1,2,4triazin-3-yl)pyridine (BTP) are performed in order to evaluate if ligand extraction performance is reflected in coordination structure differences, specifically in variations in the metal cationeN bond lengths. We observe U(III) to generally exhibit a decrease in the bond distance over that expected for pure ionic binding for the ligand complexes investigated and interpret this as higher covalent character of the U(III)eN binding. In contrast, no measurable differences for Am(III), Cm(III), and the Ln(III) elements in the middle of the 4f series are observed. Time-resolved laser fluorescence spectroscopy (TRLFS) investigations on solution BTP complexed with Cm(III) and Eu(III) reveal that the selective extraction behavior of this ligand can be explained by the large difference in conditional stability constants of their 1:3 complexes (K 13 ). The K 13 value for CmeBTP 3 is a number of orders of magnitude larger than that for EueBTP 3 .

Time-resolved laser fluorescence spectroscopy (TRLFS) is used to study the hydration of the Cm3+ ion in acidified (0.1 M perchloric acid) H2O and D2O from 20 to 200 degrees C. Strong temperature dependency is found for several of the spectroscopic quantities associated with the 6D'(7/2) --> 8S'(7/2) photoemission spectra, with similar relative changes in both solvents. The emission band shifts to lower energy with increasing temperature, which is attributed to an equilibrium between hydrated Cm3+ ions with different numbers of water molecules in the first coordination sphere, namely [Cm(H2O)9]3+ and [Cm(H2O)8]3+. Comparison with crystalline reference compounds and the analysis of hot bands corroborates the assignment of these species. The molar fraction of the octahydrated species increases from approximately 10% at room temperature to approximately 40% at 200 degrees C, indicating an entropy driven reaction. The corresponding thermodynamic parameters are obtained as Delta H degrees = + 13.1 +/- 0.4 kJ mol(-1), Delta S degrees = + 25.4 +/- 1.2 J mol(-1) K(-1), and Delta G298 = + 5.5 +/- 0.6 kJ mol(-1). Both the emission intensity and lifetime decrease with increasing temperature. The temperature dependency of the nonradiative decay rate of the emitting 6D'(7/2) level follows an Arrhenius equation with the activation energy 26.5 kJ mol(-1) (2250 cm(-1)) in both H2O and D2O, which is somewhat lower than the energy gap between 6D'(7/2) and 6P'(5/2) exited state levels.

Stable nine‐coordination: X‐ray diffraction reveals highly symmetrical [M(H2O)9]3+ entities for the actinides americium and curium in single crystals of their triflate salts (see picture, yellow M, red O). Comparison of absorption spectra in solution confirm that these transplutonium ions are large enough to remain ninefold coordinated also in aqueous solution.