Ion Transfer from Surface to Crystal: Mechanisms of Pollutant Trapping (POLLTRAP)
ANDRA (French National Nuclear Waste Management Agency), Châtenay- Malabry, France
In the context of the safety assessment of an underground repository for nuclear waste, sorption reactions are one of the main processes to take into account to predict the migration of the radionuclides which might be transferred from the waste canisters to underground waters over geological time scales. Sorption of aqueous species on minerals can include adsorption processes, surface (co)-precipitation, and even incorporation in the bulk of the material, which can lead to the irreversibility of some sorption reactions.
This work focused on two elements: Eu(III) as an analogue of trivalent actinides and Ni(II) as activation product. Calcite was chosen as adsorbent due to its presence in Callovian-Oxfordian clay rocks. Our study combined batch experiments with spectroscopic techniques (TRLFS, RBS and SEM-EDXS) to elucidate the mechanisms occurring at Eu(III)/Ni(II) calcite interface. To obtain a better understanding on the systems, before starting sorption experiments, aqueous chemistry of Eu(III) and Ni(II) was carefully investigated.
Macroscopic results showed a strong retention of Eu(III) on calcite, no matter the initial concentration, contact time and CO2 partial pressure. Ni(II) was also readily sorbed by calcite, but the retention was influenced by contact time and concentration. Time-dependent sorption experiments showed a marked and slow increase of retention upon a long time range (up to 4 months). Desorption results indicated a partly reversible sorption for Ni(II).
TRLFS highlighted the influence of initial concentration and contact time on the interaction of Eu(III) with calcite. With the help of RBS and SEM-EDXS, it enabled to discriminate between different mechanisms like surface precipitation, inner-sphere complexation and incorporation. RBS showed incorporation of Eu(III) into calcite up to 250 nm, contrary to Ni(II) which was located at the surface.
Fig. 1.: Depth concentration profiles of Eu(III) (initial sorption with 10−4 mol·L−1 solution during 1 week and 1 month) reacted with calcite single crystals (lines are only plotted to guide the eyes) obtained by RBS
- A. Sabau, Y. Pipon, N. Toulhoat, C. Lomenech, N. Jordan, N. Moncoffre, A. Barkleit, N. Marmier, V. Brendler, S. Surblé, E. Giffaut: "Interaction of Europium and Nickel with calcite studied by Rutherford Backscattering Spectrometry and Time-Resolved Laser Fluorescence Spectroscopy." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, (2014), 332, 111-116.
Conference contributions (Oral presentations and posters):
- A. Sabau, N. Jordan, C. Lomenech, N. Marmier, V. Brendler, A. Barkleit, N. Toulhoat, Y. Pipon, S. Surble, E. Giffaut, N. Moncoffre, Interaction of Eu(III) with calcium carbonate: spectroscopic characterization. Goldschmidt 2013 (25.-30.08.2013, Florence, Italy).
- A. Sabau, C. Lomenech, N. Marmier, N. Jordan, A. Barkleit, V. Brendler, N. Toulhoat, Y. Pipon, N. Moncoffre, E. Giffaut, Rétention de l’europium par la calcite : de l’adsorption à l’incorporation dans le matériau. XIIIe Journées Nationales de Radiochimie et Chimie Nucléaire (04.-05.10.2012, Nantes, France).
- A. Sabau, N. Jordan, C. Lomenech, N. Marmier, V. Brendler, A. Barkleit, S. Surblé, N. Toulhoat, Y. Pipon, N. Moncoffre, E. Giffaut, Study of Europium and Nickel interaction with calcite - batch experiments and spectroscopic characterization. 14th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (08.-13.09.2013, Brighton, United Kingdom).
- N. Toulhoat, Y. Pipon, N. Moncoffre, A. Sabau, C. Lomenech, N. Jordan, A. Barkleit, N. Marmier, V. Brendler, S. Surblé, E. Giffaut, Incorporation of Europium and Nickel in calcite studied by Rutherford Backscattering Spectrometry. 21st International Conference on Ion Beam Analysis (23.-28.06.2013, Seattle, USA).
- A. Sabau, N. Marmier, N. Jordan, C. Lomenech, A. Barkleit, N. Toulhoat, Y. Pipon, N. Moncoffre, V. Brendler, E. Giffaut, Interaction between europium and calcite: macroscopic and spectroscopic studies. 5th International Meeting on Clays and Engineered Barriers for Radioactive Waste Confinement (22.-25.10.2012, Montpellier, France).