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Radiochimica Acta

International Journal for chemical aspects of nuclear science and technology

Editor-in-Chief: Qaim, Syed M.


IMPACT FACTOR 2018: 1.339

CiteScore 2018: 1.20

SCImago Journal Rank (SJR) 2018: 0.333
Source Normalized Impact per Paper (SNIP) 2018: 0.720

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2193-3405
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Volume 96, Issue 9-11

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A TRLFS study of Cm(III) hydroxide complexes in alkaline CaCl2 solutions

Thomas Rabung / Marcus Altmaier / Volker Neck / Thomas Fanghänel
Published Online: 2009-09-25 | DOI: https://doi.org/10.1524/ract.2008.1536

Abstract

Time-resolved laser fluorescence spectroscopy (TRLFS) is used to study Cm(III) solutions ([Cm]tot=2×10−7 M) in 0.1−3.5 M CaCl2 at pHc≈11.7 and in three sets of experiments at constant ionic strength (1.0, 2.5 and 3.5 M CaCl2) with pHc varying from 10.8 to 11.9. The fluorescence spectra show Cm(III) emission bands in the range 605−620 nm. Increasing the CaCl2 concentration strongly enhances the intensity of the observed bands. The concentration of aqueous Cm(III) species determined after 10 kD ultrafiltration increases as well, indicating that the Cm(III) hydroxide complexes are stabilized by a strong interaction with Ca2+ ions. In 5 M NaCl-NaOH solutions studied for comparison, the curium is almost completely precipitated as Cm(OH)3 colloids which show no fluorescence emission bands.

Peak deconvolution and the evaluation of the pH dependence of the spectroscopic data show that three emission bands with λmax=607.5, 609.9 and 614.7 nm come from Cm(III) complexes with three, four and six OH ligands, respectively. The tri- and tetrahydroxide complexes are dominant in 0.1−1.0 M CaCl2, the hexahydroxide complex dominates at higher CaCl2 concentrations and pHc>11.5. As a consequence of the strong dependence on the Ca2+ concentration and the absence of these complexes in NaOH-NaCl solutions, thermodynamic modelling of the apparent equilibrium constants for stepwise complex formation and the solubility of colloidal Cm(OH)3(am) requires that the observed species are treated as ternary Ca−Cm(III)−OH complexes: Cax[Cm(OH)3]2 x, Cay[Cm(OH)4]2 y −1 and Caz[Cm(OH)6]2 z −3 where x may be 0 or 1, y=2 and z=3.

Keywords: Curium; TRLFS; CaCl2 solution; Hydrolysis; Solubility

About the article

* Correspondence address: Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung, Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, Deutschland,


Published Online: 2009-09-25

Published in Print: 2008-11-01


Citation Information: Radiochimica Acta International journal for chemical aspects of nuclear science and technology, Volume 96, Issue 9-11, Pages 551–560, ISSN (Print) 0033-8230, DOI: https://doi.org/10.1524/ract.2008.1536.

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