In situ anion diffusion experiments using radiotracers

Diffusion experiments in compacted bentonite have been carried out in situ using the borehole laboratory CHEMLAB. The “ordinary” anion iodide and the redox-sensitive pertechnetate ion have been investigated. In spite of strongly reducing groundwater conditions, technetium was found to diffuse mostly...

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Bibliographic Details
Published in:	Journal of contaminant hydrology Vol. 68; no. 3; pp. 183 - 192
Main Authors:	Jansson, Mats, Eriksen, Trygve E
Format:	Journal Article
Language:	English
Published:	Amsterdam Elsevier B.V 01-02-2004 Elsevier Science
Subjects:	Anion Bentonite bentonite clay CHEMLAB compacted bentonite Diffusion Earth sciences Earth, ocean, space Engineering and environment geology. Geothermics Exact sciences and technology fuel Hydrogeology Hydrology. Hydrogeology In situ Iodide iron Oxidation-Reduction Pertechnetate Pollution, environment geology products Radioisotopes - analysis reduction Soil technetium Water Movements Scandinavia Sweden Iodide Pertechnetate In situ Bentonite Diffusion Anion CHEMLAB experimental studies impact statements diffusion technetium ground water bentonite pollution radioactive waste iodides safety ions anions clastic rocks laboratory studies models Europe concentration high-level waste halides in situ sedimentary rocks diffusivity radioactive tracers
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Summary:	Diffusion experiments in compacted bentonite have been carried out in situ using the borehole laboratory CHEMLAB. The “ordinary” anion iodide and the redox-sensitive pertechnetate ion have been investigated. In spite of strongly reducing groundwater conditions, technetium was found to diffuse mostly unreduced as TcO 4 −, although in some spots in the compacted clay, the activity was significantly higher, which may be explained by reduction of some TcO 4 − by iron-containing minerals in the bentonite. The measured concentration profiles in the clay cannot be accommodated by assuming one single diffusion process. The experimental data are modeled assuming two diffusion paths, intralamellar diffusion and diffusion in external water. The apparent diffusivity for the intralamellar diffusion was found to be 8.6×10 −11 m 2 s −1 for iodide with a capacity factor of 0.1, while the apparent diffusivity for the diffusion in external water was found to be 5×10 −14 m 2 s −1 with α=2.26. The corresponding values for Tc were found to be D a=6×10 −11 m 2 s −1, α=0.1 and D a=1×10 −13 m 2 s −1, α=0.46, respectively. The diffusion constants and capacity factors obtained in this study are in accordance with data from laboratory experiments.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0169-7722 1873-6009 1873-6009
DOI:	10.1016/S0169-7722(03)00149-9