期刊
APPLIED GEOCHEMISTRY
卷 98, 期 -, 页码 426-434出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.apgeochem.2018.08.021
关键词
Sorption; Radioactive waste; Actinides; Cement; C-S-H; X-ray photoelectron spectroscopy (XPS); High-energy resolution X-ray absorption near- edge structure (HR-XANES); Th; U; Np; Pu; Am
资金
- Federal Ministry for Economic Affairs and Energy (BMWi) [02E11415A]
The sorption of actinides (Th, U - Am) was studied in dependence of the solid-to-liquid (S/L) ratio (0.5-20.0 g/L) and the calcium-to-silicon (C:S) ratio. The C:S ratio was varied between 1.80 and 0.70 to simulate the changing composition of the C-S-H phases during cement degradation from high to low C:S ratios. The decrease of the calcium content in the C-S-H phases by time is accompanied by a decrease in pH in the corresponding suspensions from 12.6 to 10.2. X-ray photoelectron spectroscopy (XPS) of the C-S-H phases showed an increasing depletion of Ca on the surface with increasing C:S ratio in comparison to the composition of the solid phase as a whole. The sorption experiments were performed with the redox stable species Am(III), Th(IV) and U(VI), as well as the redox sensitive Np(V) and Pu(III). The average distribution coefficients R-d for all investigated actinides are around 10(5)L/kg. The oxidation state of Pu retained by the C-S-H phases was investigated with high-energy resolution X-ray absorption near-edge structure (HR-XANES) spectroscopy. Samples with C:S ratios of 0.75 and 1.65 showed that the initially added Pu(III) was oxidized to Pu(IV) in the course of the experiment.
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