Investigations are currently carried out in Saxony to study environmental impacts due to uranium-mining activities. Radioactive and other inorganic species were determined in both mining waters of different origin and leachates from mediumscale column experiments and batch-tests. Uranium concentrations were measured using -spectrometry, absorption spectrophotometry, square-wave polarography and inductively coupled mass spectrometry. For mining waters the concentration range was less than 1 to ca 4 mg·dm–3, in one case up to 7 mg·dm–3.
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)34− and UO2(CO3)22− were derived.
Authors:S. Lehmann, G. Geipel, G. Grambole, and G. Bernhard
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
. 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
Authors:M. Glorius, H. Moll, G. Geipel, and G. Bernhard
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 β111 = 17.34±0.06 and a 1: 2 complex with a stability constant of log β122 = 35.0±0.11 was identified. Also in the uranium(VI)-benzohydroxamate system the stability constants are determined to be
log β110 = 7.92±0.11 and log β120 = 16.88±0.49. In the uranium(VI)-benzoate system only a 1: 1 complex is existent with a stability constant of log β110 = 3.56±0.05.
Authors:S. Lehmann, G. Geipel, H. Foerstendorf, and G. Bernhard
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.
Authors:D. Vulpius, G. Geipel, L. Baraniak, A. Rossberg, and G. Bernhard
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