0000000000324774
AUTHOR
Gert Bernhard
showing 7 related works from this author
Structural characterization of U(VI) surface complexes on kaolinite in the presence of humic acid using EXAFS spectroscopy.
2007
To determine the influence of humic acid (HA), pH, and presence of atmospheric CO2 on the sorption of U(VI) onto kaolinite, the structure of the surface complexes was studied by U L III-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The best fits to the experimental EXAFS data were obtained by including two uranium coordination shells with two axial (O ax) and five equatorial (O eq) oxygen atoms at 1.77+/-0.02 and 2.34+/-0.02 A, respectively, and two coordination shells with one Al/Si atom each at 3.1 and 3.3 A. As in the case of the binary system U(VI)-kaolinite, uranium forms inner-sphere surface complexes by edge sharing with aluminum octahedra and/or silicon tetrahe…
Sorption of uranium(VI) onto ferric oxides in sulfate-rich acid waters.
2003
The mechanisms of the uranium(VI) sorption on schwertmannite and goethite in acid sulfate-rich solutions were studied by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The samples were prepared under N2 atmosphere and initial uranium(VI) concentrations of 1 x 10(-5) (pH 6.5) to 5 x 10(-5) M (pH 4.2). The ionic strength was adjusted using 0.01 M Na2SO4 or 0.01 M NaClO4, respectively. The EXAFS structural parameters for uranium(VI) sorbed on goethite in sulfate-rich, acid and near-neutral solutions indicate that uranium(VI) forms an inner-sphere, mononuclear, bidentate surface complex. This complex is characterized by a uranium-ferric-iron distance of approximately 3.45 A. Ura…
Mixed complexes of alkaline earth uranyl cabonates: A laser-induced time-resolved fluorescence spectroscopic study
2008
The interaction of the alkaline earth ions Mg2+, Sr2+ and Ba2+ with the uranyl tricarbonate complex has been studied by time resolved laser-induced fluorescence spectroscopy. In contrast to the non-luminescent uranyl tricarbonate complex the formed products show slight luminescence properties. These have been used to determine the stoichiometry and complex stabilities of the formed compounds. As the alkaline earth elements are located in an outer shell of the complex the influence of the type of the alkaline earth element on the stability constant is not very drastic. Therefore all obtained data were averaged in order to derive an common stability constant for the described complexes. These…
Plutonium(III) complexation by humic substances studied by X-ray absorption fine structure spectroscopy
2006
Abstract We determined structural parameters for the near-neighbor surrounding of plutonium(III) in complexes with humic and fulvic acids at pH 1 and for the purpose of comparison also for the plutonium(III) aquo ion by means of X-ray absorption fine structure (XAFS) spectroscopy. It could be shown that in the complexes with humic substances as well as in the plutonium(III) aquo ion sample the trivalent oxidation state of plutonium was stable within the time of the experiment. In the humate and fulvate complexes, the plutonium(III) is surrounded by about eight oxygen atoms with an average Pu–O distance of 2.48 ± 0.02 A. The structural parameters determined for plutonium(III)–humate and –ful…
Spectroscopic characterization of alkaline earth uranyl carbonates
2005
A series of alkaline uranyl carbonates, M[UO{sub 2}(CO{sub 3}){sub 3}].nH{sub 2}O (M=Mg{sub 2}, Ca{sub 2}, Sr{sub 2}, Ba{sub 2}, Na{sub 2}Ca, and CaMg) was synthesized and characterized by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS) after nitric acid digestion, X-ray powder diffraction (XRD), and thermal analysis (TGA/DTA). The molecular structure of these compounds was characterized by extended X-ray absorption fine-structure (EXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). Crystalline Ba{sub 2}[UO{sub 2}(CO{sub 3}){sub 3}].6H{sub 2}O was obtained for the first time. The EXAFS analysis showed that this compound consists of …
Uranium speciation in plants
2002
The chemical characterization of the radionuclide species is essential for a reliable assessment of the migration of radionuclides and heavy metals into the geological and biological environment on the load pathway soil - plant - animal - human. Only a few is known about the speciation of uranium in plants. Therefore we investigate the change of speciation during the transfer of uranium from initial solution into plant. Various plants (lupins, dandelion e.g.) were grown in an agricultural test field and in the laboratory on contaminated soils (up to concentration of 1g U/kg soil) and as hydroponics in the uranium containing solutions (uranium concentration: 10-5 M - 10-2 M, pH: 3 - 8). For …
Study of the role of sulfur functionalities in humic acids for uranium(VI) complexation
2009
Humic substances influence the speciation and migration behavior of toxic and radiotoxic metal ions, such as actinides, in the environment. Depending on their origin, humic substances contain different amounts of sulfur ranging from 0.1 to 3.6% and 0.5 to 1.43% in soil and aquatic humic substances, respectively [1]. Reduced, intermediately oxidized and highly oxidized sulfur functionalities occur in humic substances [1]. Although sulfur functionalities occur in small concentrations, they can play an important role in the complexation of selected metal ions. Knowledge about the impact of sulfur functionalities on the metal ion complexation by humic substances and their significance compared …