Reinhardt Klenze

Aqueous Solutions of Uranium(VI) as Studied by Time-Resolved Emission Spectroscopy: A Round-Robin Test

Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO22+aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.

A study of intramolecular energy transfer in Cm(III) complexes with aromatic ligands by time-resolved laser fluorescence spectroscopy

Abstract Sensitized fluorescence emission of f-element ions was studied for the humate and fulvate complexes of Cm(III) by time-resolved laser fluorescence spectroscopy. Complexation with chelating aromatic carboxylic acids, which may be regarded as complexing functional groups of humic substances, e.g. phthalic and salicylic acids, was investigated in parallel for comparison. Excitation and emission spectra, together with lifetimes of excited states, were investigated for the Cm(III) complex species as well as for the individual pure ligans. The fluorescence enhancement was found to be weak in the Cm(III)-phthalate and strong in the Cm(III)-salicylate. The latter is comparable with the Cm(III)-fulvate. The efficiency of energy transfer was calculated from the excitation at 308 nm. The results are discussed in terms of energy overlapping between triplet states of ligands and excited levels of Cm(III).

A study of the carbonate complexation of CmIII and EuIII by time-resolved laser fluorescence spectroscopy

Abstract Carbonate complexation of Cm III and Eu III is studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). The carbonato species M(CO 3 ) + , M(CO 3 ) 2 − and M(CO 3 ) 3 3− (Mue5fbCm III and Eu III ) are characterized by measuring excitation and emission spectra, and lifetime. Stability constants for the first carbonato complex in 0.1 M NaClO 4 are found to be log β 11 = 6.65 ± 0.07 for Cm(CO 3 ) + and log β 11 = 6.57 ± 0.08 for Eu(CO 3 ) + . The constant for Cm III compares well with the values for Am III derived spectroscopically and by solubility measurement. No difference is found for the stability constant of Eu(CO 3 ) + in the excited state as determined by TRLFS and in the ground state as determined by solubility measurement.

Formation of Cm(III) chloride complexes in CaCl2 solutions

Abstract The chloride complexation of curium(III) in trace amounts at very high chloride ion concentrations was studied by time-resolved laser fluorescence spectroscopy at 25 °C. The chloride ion concentration was varied from 0 to about 20 mol kg −1 H 2 O with CaCl 2 at acidic pH. The Cm species Cm 3+ , CmCl 2+ and CmCl 2 + were quantified spectroscopically from the fluorescence emission spectra by peak deconvolution and the chloride complexation constants β 1 and β 2 were evaluated at each given CaCl 2 molality. The experiment verifies that at low Cl − concentrations (below 3 mol kg −1 H 2 O) the chloride complexation is less important (less than 5% of chloride complexes are formed) and hence it can be neglected in moderately concentrated brines.

A complexation study of Cm(III) and Tb(III) with chelating aromatic ligands by time-resolved laser fluorescence spectroscopy

Abstract Complexation of Tb(III) and Cm(III) with 5-sulfo-salicylic acid (SSA) is studied by time-resolved laser fluorescence spectroscopy (TRLFS). The chelating aromatic ligand is supposed to represent a dominating complexing entity of humic substances for the interaction with metal ions. The free ligand concentration is varied by changing the total ligand concentration or pH. By peak deconvolution of emission spectra the pure spectral components of complex species are analyzed and their mole fraction in the mixture are ascertained. The stability constants derived are: log β 101 (Cm)=6.44±0.03, log β 102 (Cm)=11.99±0.04, log β 101 (Tb)=7.32±0.04, log β 102 (Tb)=12.85±0.05.

Theoretical investigation of the water/corundum (0001) interface

For the reliable long-term modeling of the actinide migration in geological formations, the adsorption/desorption properties and the reactivity of mineral surfaces must be understood at the molecular level. The adsorption of radioisotopes at mineral surfaces of the aquifer is an important process that leads to the retention of contaminants such as radionuclides. Their transport by the ground water is either retarded or even completely inhibited by the presence of such a surface. Accordingly, this subject is of main importance for the safety assessment of nuclear waste repositories. As part of a joint theoretical/experimental effort, the interaction of water with the corundum (0001) surface is studied using several theoretical methods (Moller-Plesset perturbation theory, coupled cluster singles doubles with triplet corrections, as well as density functional theory). We focus in this study on the determination of the bond lengths and tilt angles of the surface OH species and their respective vibrational frequencies. The theoretical results are confirmed by subsequent simulation of the interface selective nonlinear sum frequency spectra. The excellent agreement of the simulated with the experimental spectra allows an assignment of the observed peaks in the sum frequency spectra of the water/corundum (0001) interface on the basis of our theoretical data. In this theoretical study we are able to give a unique interpretation of the observed sum frequency spectra of the water/corundum (0001) interface.