Influence of pH and metal ion loading on the Cm(III) humate complexation: a time resolved laser fluorescence spectroscopy study

Applications of time-resolved laser fluorescence spectroscopy to the environmental biogeochemistry of actinides

Time-resolved laser fluorescence spectroscopy (TRLFS) is a useful means of identifying certain actinide species resulting from various biogeochemical processes. In general, TRLFS differentiates chemical species of a fluorescent metal ion through analysis of different excitation and emission spectra and decay lifetimes. Although this spectroscopic technique has largely been applied to the analysis of actinide and lanthanide ions having fluorescence decay lifetimes on the order of microseconds, such as UO , Cm, and Eu, continuing development of ultra-fast and cryogenic TRLFS systems offers the possibility to obtain speciation information on metal ions having room-temperature fluorescence decay lifetimes on the order of nanoseconds to picoseconds. The main advantage of TRLFS over other advanced spectroscopic techniques is the ability to determine in situ metal speciation at environmentally relevant micromolar to picomolar concentrations. In the context of environmental biogeochemistry, TRLFS has principally been applied to studies of (i) metal speciation in aqueous and solid phases and (ii) the coordination environment of metal ions sorbed to mineral and bacterial surfaces. In this review, the principles of TRLFS are described, and the literature reporting the application of this methodology to the speciation of actinides in systems of biogeochemical interest is assessed. Significant developments in TRLFS methodology and advanced data analysis are highlighted, and we outline how these developments have the potential to further our mechanistic understanding of actinide biogeochemistry.

Chemical status of U(VI) in cemented waste forms under saline conditions

Retention of U(VI) in cemented waste forms reacting with NaCl and MgCl2brines is investigated in long-term leaching experiments on full scale monoliths. Solution compositions were monitored over a period of 17 to 18 years. After termination of the leaching experiments, chemical and mineralogical compositions of solid reaction products were studied intensively. XRD, TRLFS and XANES/EXAFS analyses indicate uranophane (Ca(UO2)2(SiO3OH)2·5H2O) to be the dominant uranium bearing phase in the corroded cement. Other possible uranium phases such as soddyite, meta-schoepite, and di-uranate phases could not be identified by combining the results of the various experimental techniques.

Bi-exponential decay of Eu(III) complexed by Suwannee River humic substances: spectroscopic evidence of two different excited species

The bi-exponential luminescence decay of europium (III) complexed by Suwannee River fulvic acid (SRFA) and humic acid (SRHA), is studied in time-resolved luminescence spectroscopy using two different gratings at varying delay after the laser pulse, increasing accumulation time in order to obtain comparable signals. The two hypotheses found in the literature to interpret this bi-exponential decay are (i) a back transfer from the metal to the triplet state of the organic ligand and (ii) the radiative decay of two different excited species. It is shown that evolutions of the (5)D(0)-->(7)F(0) and (5)D(0)-->(7)F(2) luminescent transitions are occurring between 10 and 300 micros delay. First, the (5)D(0)-->(7)F(0) transition is decreasing relative to the (5)D(0)-->(7)F(1) showing a slightly greater symmetry of the 'slow' component, and is also slightly red shifted. Second, a slight modification of the (5)D(0)-->(7)F(2) transition is also evidencing a slightly different ligand field splitting. No significant modification of the (5)D(0)-->(7)F(1) magnetic dipole, which is less susceptible to symmetry changes, is noted in line with expectations. The (5)D(0)-->(7)F(0) transitions are adjusted with either one or two components. The use of a simple component fit seems to be well adapted for representing an average comportment of these heterogeneous compounds, and a two-component fit constrained by the bi-exponential decay parameters and accumulation times yields in the proposition of the spectra for the fast and slow components.