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This study aims to examine the complexation behaviour of actinide ions with humic substances, and to thermodynamically describe the binding based upon a simple complexation model. The cations examined are: the trivalent lanthanides, UO(2)(2+), NpO(2)(+), Am(3+), and Cm(3+). The project is divided into three tasks: complexation reactions of actinide ions with well-characterized reference and site-specific humic and fulvic acids; complexation reactions with major cations in natural groundwaters; validation of the complexation data in nautral aquatic systems by comparison of calculation with spectroscopic experiment. The results are presented in the publication. The evaluated stability constants are similar for all participating laboratories when the same humic substance complexation model is applied. Humic acid is shown to reduce NpO(2)(+) to Np(4+), while no reduction of UO(2)(2+) is observed. Temperature effects are seen on the Np humate complex.. Competition is observed between UO(2)(2+) and Ca(2+), but not between the trivalent lanthanides and Ca(2+). No influence of humic acid purification on the evaluated stability constants is observed. Calculations for natural water systems indicate the complex to be an important species.

Additional information

Authors: CZERWINSKI K R ET AL, Technische Universität München (DE);MOULIN V ET AL, CEA, CEN Saclay, Gif-sur-Yvette (FR);MARQUARDT C ET AL, Universität Mainz (DE);DIERCKX A ET AL, Katolieke Universiteit Leuven (BE);BIDOGLIO G ET AL, JRC Ispra (IT)
Bibliographic Reference: EUR 16843 EN (1996) 162pp., FS, ECU 18.50
Availability: Available from the (2)
ISBN: ISBN 92-827-6471-0
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