Combined time-resolved laser fluorescence spectroscopy and extended x-ray absorption fine structure spectroscopy study on the complexation of trivalent actinides with chloride at T = 25-200 °c

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Output type: Journal article

Author list: Skerencak-Frech A., Fröhlich D., Rothe J., Dardenne K., Panak P.

Publisher: American Chemical Society

Publication year: 2014

Journal: Inorganic Chemistry (0020-1669)

Volume number: 53

Issue number: 2

Start page: 1062

End page: 1069

Number of pages: 8

ISSN: 0020-1669

eISSN: 1520-510X

URL: http://api.elsevier.com/content/abstract/scopus_id:84892703612

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Abstract

The complexation of trivalent actinides (An(III)) with chloride is studied in the temperature range from 25 to 200 C by spectroscopic methods. Time-resolved laser fluorescence spectroscopy (TRLFS) is applied to determine the thermodynamic data of Cm(III)-Cl complexes, while extended X-ray absorption fine structure spectroscopy (EXAFS) is used to determine the structural data of the respective Am(III) complexes. The experiments are performed in a custom-built high-temperature cell which is modified for the respective spectroscopic technique. The TRLFS results show that at 25 C the speciation is dominated mainly by the Cm aquo ion. Only a minor fraction of the CmCl complex is present in solution. As the temperature increases, the fraction of this species decreases further. Simultaneously, the fraction of the CmCl complex increases strongly with the temperature. Also, the CmCl complex is formed to a minor extent at T > 160 C. The conditional stability constant log β′ is determined as a function of the temperature and extrapolated to zero ionic strength with the specific ion interaction theory approach. The log β (T) values increase by more than 3 orders of magnitude in the studied temperature range. The temperature dependency of log β is fitted by the extended van't Hoff equation to determine ΔH , ΔS , and ΔC . The EXAFS results support these findings. The results confirm the absence of americium(III) chloride complexes at T = 25 and 90 C ([Am(III)] = 10 m, [Cl] = 3.0 m), and the spectra are described by 9-10 oxygen atoms at a distance of 2.44-2.48 Å. At T = 200 C two chloride ligands are present in the inner coordination sphere of Am(III) at a distance of 2.78 Å. © 2014 American Chemical Society.

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