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| Titel |
Neptunyl(V) coprecipitation with calcite, interfacial reactions studied with synchrotron x-ray radiation |
| VerfasserIn |
F. Heberling, M. A. Denecke, J. Lützenkirchen, D. Bosbach |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250025262
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| Zusammenfassung |
| In this experimental study a wide range of methods has been used to investigate processes
leading to incorporation of neptunyl(V) (NpO2+) cations into the calcite structure following
surface sorption and upon coprecipitation.
As part of the investigation calcite surface properties were characterized over a
wide range of pH and p(CO2) conditions using zetapotential and in situ crystal
truncation rod measurements. A detailed picture of surface charging phenomena and the
corresponding molecular surface arrangement under varying solution conditions could be
gained.
The NpO2+ adsorption species on the calcite surface were investigated by means of room
temperature and low temperature (15 K) EXAFS spectroscopy. NpO2+ seems to adsorb at the
calcite surface as an innersphere complex. Adsorption kinetic and desorption experiments
indicate that even under calcite equilibrium conditions NpO2+ might become incorporated
into the calcite structure.
Upon coprecipitation from calcite supersaturated solutions NpO2+ is readily incorporated
into the calcite structure. Incorporation species were investigated using room temperature,
low temperature (70 K), and polarization dependent EXAFS measurements, together with
conventional powder XRD, NIR and Raman spectroscopy. The linear NpO2+ molecule
seems to substitute one calcium ion and two adjacent carbonate ions in the calcite
structure. It is hence coordinated by four monodentate bound carbonate ions in the
equatorial plane. Np - Np interactions have not been observed. Polarization dependent
EXAFS measurements indicate, in agreement with NIR spectroscopic results, that the
coordination polyhedron is a distorted tetragonal bipyramid. Powder XRD data
indicates that NpO2+ incorporation causes local distortion in the calcite lattice. |
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