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Matrix Diffusion of Some Alkali- and Alkaline Earth-Metals in Granitic Rock

Published online by Cambridge University Press:  03 September 2012

H. Johansson ,
J. Byegård ,
G. Skarnemark  and
M. Skålberg
H. Johansson
Affiliation:
Department of Nuclear Chemistry, Chalmers University of Technology, S-412 96 Göteborg, Sweden
J. Byegård
Affiliation:
Department of Nuclear Chemistry, Chalmers University of Technology, S-412 96 Göteborg, Sweden
G. Skarnemark
Affiliation:
Department of Nuclear Chemistry, Chalmers University of Technology, S-412 96 Göteborg, Sweden
M. Skålberg
Affiliation:
Department of Nuclear Chemistry, Chalmers University of Technology, S-412 96 Göteborg, Sweden
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Abstract

Static through-diffusion experiments were performed to study the diffusion of alkali- and alkaline earth-metals in fine-grained granite and medium-grained Äspö-diorite. Tritiated water was used as an inert reference tracer. Radionuclides of the alkali- and alkaline earth-metals (mono- and divalent elements which are not influenced by hydrolysis in the pH-range studied) were used as tracers, i.e. 22Na+, 45Ca2+ and Sr The effective diffusivity and the rock capacity factor were calculated by fitting the breakthrough curve to the one-dimensional solution of the diffusion equation. Sorption coefficients, Kd, that were derived from the rock capacity factor (diffusion experiments) were compared with Kd determined in batch experiments using crushed material of different size fractions.

The results show that the tracers were retarded in the same order as was expected from the measured batch Kd. Furthermore, the largest size fraction was the most representative when comparing batch Kd with Kd evaluated from the diffusion experiments. The observed effective diffusivities tended to decrease with increasing cell lengths, indicating that the “transport” porosity decreases with increasing sample lengths used in the diffusion experiments.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 465: Symposium II – Scienfific Basis for Nuclear Waste Management XX , 1996 , 871
Copyright
Copyright © Materials Research Society 1997

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References

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