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: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.