Petra J. Panak

Effect of humic acid on the sorption of Cm(III) onto γ-Al2O3 studied by the time-resolved laser fluorescence spectroscopy

Summary Sorption of Cm(III) onto γ-alumina coated with humic acid (HA) is studied by the Time Resolved Laser Fluorescence Spectroscopy (TRLFS). The experiments are performed at 0.1 M NaClO4, 0.44 g/L γ-Al2O3, 10 mg/L HA and at a metal ion concentration of 2×10-7 mol/L. At the investigated pH range (4 to 10) HA is completely sorbed to γ-Al2O3. The excitation spectrum of Cm(III) bound to HA/γ-Al2O3 in the wavelength range 370-400 nm exhibits broad flat bands very different from those obtained for the Cm(III) aquo ion and the Cm(III)-γ-Al2O3 surface complex, respectively. The spectrum, lacking distinctive structure due to intramolecular energy transfer processes, points to the predominant binding of the Cm(III) to surface-bound HA. TRLFS experiments performed at two different excitation wavelengths (λex=355 and 396.6 nm) allow for a differentiation of humic-bound and non-humic-bound Cm(III). Differences in fluorescence spectra obtained at the different excitation wavelengths are found at pH<6.9. They are due to the presence of the non-complexed Cm(III) aquo ion which is not detected in the indirect excitation mode (λex=355 nm). At pH≥7, the fluorescence spectra obtained by indirect and direct excitation become congruent and again point to the existence of only humic-bound Cm(III) species. Comparison of peak maxima and fluorescence lifetimes for Cm(III)-HA and Cm(III)-HA/γ-Al2O3, however, reveal differences. The results clearly indicate a contribution of the γ-Al2O3 surface to the Cm(III) binding and, thus, suggest the formation of ternary complexes such as >Al-O-Cm(III)(HA).

EXAFS investigation of uranium(VI) complexes formed at Bacillus cereus and Bacillus sphaericus surfaces

Uranium(VI) complex formation at vegetative cells and spores of Bacillus cereus and Bacillus sphaericus was studied using uranium LII-edge and LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. A comparison of the measured equatorial U-O distances and other EXAFS structural parameters of uranyl species formed at the Bacillus strains with those of the uranyl structure family indicates that the uranium is predominantly bound as uranyl complexes with phosphoryl residues.

An Improved Hydrolytically-Stable Bis-Triazinyl-Pyridine (BTP) for Selective Actinide Extraction

Abstract Bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl)pyridine (CA-BTP) is presented as a novel optimized extracting agent for the separation of americium(III) and curium(III) from lanthanides(III). CA-BTP is synthesized and studied concerning its extraction properties under conditions relevant to the SANEX process. It is demonstrated that CA-BTP is the first relevant molecule to show both high stability towards highly-acidic process solutions and satisfactory extraction kinetics. Its high solubility in 1-octanol adds to CA-BTPs favorable properties. Furthermore, CA-BTP is synthesized from a commercially available and moderately priced precursor molecule, reducing extracting-agent production costs.

Interaction of aerobic soil bacteria with plutonium(VI)

We studied the interaction of Pu(VI) with Pseudomonas stutzeri ATCC 17588 and Bacillus sphaericus ATCC 14577, representatives of the main aerobic groups of soil bacteria present in the upper soil layers. The biosorption studies have shown that these soil bacteria accumulate high amounts of Pu(VI). The relative sorption efficiency toward Pu(VI) related to the amount of biomass used decreased with increasing biomass concentration due to increased agglomeration of the bacteria resulting in a decrease of the number of available complexing groups. Spores of Bacillus sphaericus showed a higher biosorption than the vegetative cells at low biomass concentration which decreased significantly with increasing biomass concentration. At higher biomass concentrations (>0.7 g/L), the vegetative cells of both strains and the spores of B. sphaericus showed comparable sorption efficiencies. Investigations on the pH dependency of the biosorption and extraction studies with 0.01 M EDTA solution have shown that the biosorption of plutonium is a reversible process and the plutonium is bound by surface complexation. Optical absorption spectroscopy showed that one third of the initially present Pu(VI) was reduced to Pu(V) after 24 hours. Kinetic studies and solvent extraction to separate different oxidation states of Pu after contact with the biomass provided further information on the yield and the kinetics of the bacteria-mediated reduction. Long-term studies showed that also 16% of Pu(IV) was formed after one month. The slow kinetics of this process indicate that under our experimental conditions the Pu(IV) was not a produced by microbial reduction but seemed to be rather the result of the disproportionation of the formed Pu(V) or autoreduction of Pu(VI).

A Study of Ternary Complexes of Cm(III) with Humic Acid and Hydroxide or Carbonate in Neutral pH Range by Time-Resolved Laser Fluorescence Spectroscopy

The gloss of energy-curable coating and ink compositions is reduced by exposing such compositions to actinic radiation in an oxygen-rich atmosphere at differential intensity levels. The intensities are selected to effect at a first intensity range substantially complete cure of the composition except for the surface, with final cure of the surface being effected subsequently at a different and higher intensity range. Gradient Intensity Cure can be employed with substantially any composition which is curable by free radical-induced addition polymerization using a photosensitizer-photoinitiator photocatalyst system.

X-ray absorption fine structure spectroscopy of plutonium complexes with bacillus sphaericus

Summary Knowledge of the plutonium complexes formed with bacterial cells is critical for predicting the influence of microbial interactions on the migration behavior of actinides in the environment. This investigation describes the interaction of plutonium(VI) with cells of the aerobic soil bacteria, Bacillus sphaericus. The studies include the quantification of carboxylate and phosphate functional groups on the cell walls by potentiometric titration and the determination of the plutonium speciation by X-ray absorption fine structure (XAFS). Extended-XAFS (EXAFS) was used to determine the identity of the Pu(VI) interfacial complex with the bacteria, and the Pu(VI) was found primarily bound to phosphate groups on the cell surface. No carboxylate complexation was detected.

Complexation of Europium(III) by Bis(dialkyltriazinyl)bipyridines in 1-Octanol

The present work focuses on highly selective ligands for An(III)/Ln(III) separation: bis(triazinyl)bipyridines (BTBPs). By combining time-resolved laser-induced fluorescence spectroscopy, nanoelectrospray ionization mass spectrometry, vibronic sideband spectroscopy, and X-ray diffraction, we obtain a detailed picture of the structure and stoichiometry of the first coordination sphere of Eu(III)-BTBP complexes in an octanolic solution. The main focus is on the 1:2 complexes because extraction studies revealed that those are the species extracted into the organic phase. The investigations on europium(III) complexes of BTBP with different triazin alkylation revealed differences in the formed complexes due to the bulkiness of the ligands. Because of the vibronic sidebands in the fluorescence spectra, we were able to detect whether or not nitrate ligands are coordinated in the first coordination sphere of the Eu-BTBP complexes. In solution, less sterically demanding BTBP offers enough space for additional coordination of anions and/or solvent molecules to form 9-coordinated Eu-BTBP 1:2 complexes, while bulkier ligands tend to form 8-fold-coordinated structures. We also report the first crystal structure of a Ln-BTBP 1:2 complex and that of its 1:1 complex, both of which are 10-coordinated.

2,6-Bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine as a Ligand for Efficient Actinide(III)/Lanthanide(III) Separation

The N-donor complexing ligand 2,6-bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine (C5-BPP) was synthesized and screened as an extracting agent selective for trivalent actinide cations over lanthanides. C5-BPP extracts Am(III) from up to 1 mol/L HNO(3) with a separation factor over Eu(III) of approximately 100. Due to its good performance as an extracting agent, the complexation of trivalent actinides and lanthanides with C5-BPP was studied. The solid-state compounds [Ln(C5-BPP)(NO(3))(3)(DMF)] (Ln = Sm(III), Eu(III)) were synthesized, fully characterized, and compared to the solution structure of the Am(III) 1:1 complex [Am(C5-BPP)(NO(3))(3)]. The high stability constant of log β(3) = 14.8 ± 0.4 determined for the Cm(III) 1:3 complex is in line with C5-BPPs high distribution ratios for Am(III) observed in extraction experiments.

TRLFS study on the complexation of Cm(III) with nitrate in the temperature range from 5 to 200 ◦ C

Abstract The formation of aqueous Cm(III) nitrate complexes is studied in the temperature range from 5 to 200 °C by time resolved laser fluorescence spectroscopy (TRLFS). The experiments are performed in a custom build high pressure and high temperature fluorescence cell. The complex formation is measured at nitrate concentrations ranging from 0.10 to 4.61 mol/kg H2O. The mono- and dinitrate complexes are quantified by peak deconvolution of the fluorescence spectra and the complexation constants are determined as a function of the temperature. The conditional equilibrium constants are extrapolated to zero ionic strength using the specific ion interaction theory (SIT) and the thermodynamic standard state data (ΔrH°m, ΔrS°m, ΔrG°m, ΔrC°p,m) are determined from the temperature dependence of the equilibrium constants at I=0. The equilibrium constants up to 75 °C are well described by the Van´t Hoff equation (ΔrH°m independent of T and ΔrC°p,m=0). Modelling of the data at higher temperatures requires an extended equation including a term for the heat capacity changes (ΔrC°p,m).

Spectroscopic studies on the interaction of U(VI) with Bacillus sphaericus

Summary We studied the interaction of U(VI) with vegetative cells, heat killed cells, spores, and decomposed cells of Bacillus sphaericus. The characterization of the formed complexes was performed by time-resolved laser fluorescence spectroscopy (TRLFS) and extended X-ray absorption fine structure spectroscopy (EXAFS). We observed no significant differences in the sorption behavior of vegetative and heat killed cells, whereas the spores showed a higher sorption of U(VI) (related to their dry weight). Regardless of the higher relative sorption of the spores of B. sphaericus, the fluorescence and EXAFS spectra of the vegetative cells, heat killed cells and spores were almost identical. Analysis of the data proved that U(VI) forms inner sphere complexes with organic bound phosphate groups on the cell surface. We observed no significant differences in the coordination numbers and the distances of the oxygen and phosphorus atoms in the inner coordination sphere. After eight weeks, the vegetative cells of B. sphaericus were completely decomposed. Lysing of the cell walls and activity of enzymes led to a release of various decomposition products. We found that large amounts of H2PO4− were released which caused a quantitative precipitation of bacterial U(VI) as UO2(H2PO4)2. The H2PO4− was detected by Raman spectroscopy. The decomposed bacterial suspension showed the same fluorescence spectrum as UO2(H2PO4)2 which differed significantly from those of the bacterial U(VI) surface complexes.