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  • Author or Editor: G. Bernhard x
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Abstract  

The distribution of different radionuclides depends on their speciation in the real fission product solution and the electric charge of the alumina. The pH-value is the main parameter that influences the disyribution coefficient. By combination of an acidic adsorption and an alkaline desorption process, the interesting fission molybdenum can be separated. The distribution ratios of the relevant radionuclides are described.

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Abstract  

The complex formation of curium(III) with L2-aminobutyric acid was characterized by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at trace Cm(III) concentrations (3·10−7 M). The various curium(III) species, MpHqLr, identified are characterized by their individual luminescence spectra and luminescence lifetimes. The following formation constants were determined log β101 = 5.17±0.07, log β102 = 9.00±0.07, and log β103 = 11.30±0.09 at ionic strength I = 0.5M. Possible structures of the curium aminobutyrate species will be discussed on the basis of the luminescence lifetime measurements and the magnitude of the formation constants.

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The interaction of uranium(VI) with carbonate ions was studied with absorption spectroscopy and time-resolved laser-induced fluorescence spectroscopy due to the importance of these complexes in environmental relevant waters. In the pH range from 2 to 11 the influence of the temperature on the spectra was studied to check changes in the abundances of several binding forms. It was found that several binding forms are predominant at different temperatures and pH values. This observation can be explained by speciation changes due to the dependence of chemical equilibria on the temperature. Furthermore photoluminescence spectra of aqueous solutions of uranyl carbonate complexes were observed at ambient temperatures for the first time and single component absorption spectra of the uranyl carbonate complexes UO2(CO3)3 4− and UO2(CO3)2 2− were derived.

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Abstract  

The influence of highly functionalized saccharic and phenolic polymers that are formed in the process of hydrothermal wood degradation on the uranium(VI) adsorption onto metamorphic rocks and sediments from the Saxon uranium mining sites Schlema-Alberoda and Königstein was investigated in a laboratory study. Uranium(VI) adsorption from a simulated mine water takes place on the majority of rocks and sediments such as granite, gneiss, basalt, sandstone and clay marl. Exceptions are phyllite and clay stone that do not bind any uranium from the mine water. Polymeric wood degradation products such as fragments of celluloses and lignin increase the uranium(VI) adsorption whereas the presence of saccharic and phenolic monomers (vanillic acid and gluconic acid) leads to a lower adsorption.

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Abstract  

To characterize the future redox milieu caused by natural degradation of wood in flooded mines, the aquifer of a highland bog ground was studied as a natural analogue site. Going from the surface to a depth of one meter in the bog water, the redox potential measured with a platinum electrode changes from 593 mV to −95 mV. From the depth-water analyses and analyses of bog gas extracted from the ground, an Eh value of −119±5 mV could be calculated. Methane and hydrogen sulfide were found in the gas, characterizing the strongly reducing condition in the bog ground. From that, the conclusion for the future mine situation can be drawn that uranium(VI) and arsenic(V) will be reduced and precipitated as U(OH)4 and As2S3. In that way, decontamination of the mine water takes place as a consequence of a natural attenuation process.

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Abstract  

Heavy metals like the actinides possess a high risk potential to the environment not only because of their radiotoxicity but also due to their chemical toxicology. Uranium as one of the major actinide elements has to be considered in particular. Under reducing conditions, tetravalent uranium occurs primarily in the environment. To date, a lack of appropriate analytical techniques that featured sufficient sensitivity made it difficult to study the aqueous phosphate chemistry of uranium(IV) as such complexes show only low solubility. A novel time-resolved laser fluorescence spectroscopy system was set up recently and optimized to do research on uranium(IV). By application of this laser system we could successfully study uranium(IV) phosphate in concentration ranges where no precipitation or formation of colloids occurred. At pH = 1.0, U4+ and one uranium(IV) phosphate complex existed in parallel in aqueous solution. The complex could be identified as [U(H2PO4)]3+. Determination of its corresponding complex formation constant via two different evaluation methods resulted in the finding of (1)
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\log \beta_{121}^{ \circ } = 2 6. 3 7 \pm 0. 7 6$$ \end{document}
and (2)
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\log \beta_{121}^{ \circ } = 2 6. 4 3 \pm 0. 2 3$$ \end{document}
. Both values prove that [U(H2PO4)]3+ is a very stable complex in solution under experimental conditions. As they are in very good agreement with each other, the total complex formation constant was determined by means of the weighted average out of (1) and (2). It was calculated to be
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\log \beta_{121}^{ \circ } = 2 6. 4 2 \pm 0. 2 2$$ \end{document}
.
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Abstract  

The complex formation of uranium(VI) with salicylhydroxamic, benzohydroxamic, and benzoic acid was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS). We observed in all three systems a decrease in the fluorescence intensity with increasing ligand concentration. All identified complexed uranyl species are of the type MpLqHr. In the uranium(VI)-salicylhydroxamate system a 1: 1 complex with a stability constant of log β 111 = 17.34±0.06 and a 1: 2 complex with a stability constant of log β 122 = 35.0±0.11 was identified. Also in the uranium(VI)-benzohydroxamate system the stability constants are determined to be log β 110 = 7.92±0.11 and log β 120 = 16.88±0.49. In the uranium(VI)-benzoate system only a 1: 1 complex is existent with a stability constant of log β 110 = 3.56±0.05.

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Abstract  

In this study, the secondary uranium(VI) silicate minerals boltwoodite, sodium boltwoodite and uranophane were synthesized. Sodium boltwoodite was successfully obtained by the following new reaction procedure. Their analytical characterization was carried out by means of inductively coupled plasma mass spectrometry and atomic absorption spectroscopy, scanning electron microscopy, X-ray powder diffraction, differential thermal analysis combined with thermogravimetry and infrared spectroscopy. Furthermore, the fluorescence behaviour was measured using time-resolved laser fluorescence spectroscopy. Herewith, the fluorescence properties of the three silicious uranyl phases were determined at room temperature.

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Summary  

The complex formation of uranium(VI) with 4-hydroxy-3-methoxybenzoic acid as well as with benzoic acid and 4-hydroxybenzoic acid was studied. In aqueous solution weak carboxylic 1 : 1 complexes, are formed in which the carboxyl group is bidentately coordinated to the metal atom. The logarithmic stability constants of these complexes regarding the reaction of the uranyl ion with the single charged anion of the respective ligands are 2.78±0.02, 2.68±0.04, and 2.71±0.04 at an ionic strength of 0.1 mol/l (NaClO4) and at 25 °C. Bis(4-hydroxy-3-methoxybenzoato)dioxouranium(VI) was obtained as a crystalline compound if the concentrations of the starting components for the synthesis are increased. The monoclinic compound has a reflections-rich X-ray powder diffraction pattern. The lattice constants are a = 13.662(9) Å, b = 21.293(7) Å, c = 11.213(3) Å, b = 107.49(4), and V = 3111(2) Å.3

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Abstract  

With the background of uranium mine restoration the adsorption of radium on different kinds of sandstone, claystone and lime marl was studied as a function of such parameters as water composition, acidity, phase contact time and the concentration of radium, barium and sulfate by static butch experiments at the mine temperature of 14 °C.

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