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Diffusion and Adsorption in Porous Silica Considered as a Reference Material for Crystalline Rock

Published online by Cambridge University Press:  21 March 2011

Hannu Aalto ,
Jarmo Lehikoinen ,
Arto Muurinen  and
Matti Valkiainen
Hannu Aalto
Affiliation:
VTT Chemical Technology, P.O. Box 1404, FIN-02044 VTT, Finland Email: [email protected]
Jarmo Lehikoinen
Affiliation:
VTT Chemical Technology, P.O. Box 1404, FIN-02044 VTT, Finland
Arto Muurinen
Affiliation:
VTT Chemical Technology, P.O. Box 1404, FIN-02044 VTT, Finland
Matti Valkiainen
Affiliation:
VTT Chemical Technology, P.O. Box 1404, FIN-02044 VTT, Finland
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Abstract

In the present study, well-characterized mesoporous silica was used as a reference material for crystalline rock. Saturation-leaching and through-diffusion tracer experiments were systematically carried out to determine the adsorption capacity factors and apparent and effective diffusivities for the radioactive tracers 3H, 22Na and 36Cl. The ionic strength of the supporting NaCl electrolyte, in equilibrium with atmospheric air, was either 0.002 M or 0.1 M. The apparent diffusivities derived from saturation-leaching experiments reveal that equilibrium adsorption on a negatively charged silica surface does not act to retard the mass transfer of sodium ions. The steady-state diffusion results are found to demonstrate the increasing break-through for sodium with decreasing ionic strength of the background electrolyte in comparison to 3H. These observations are consistent with the picture of chloride ion exclusion and of the diffuse double layer surface-excess for sodium ions being transported in the direction of the macroscopic concentration gradient. Furthermore, they are shown to be at odds with the widely adopted macroscopic pore diffusion model, which neglects the mobility of the counter-ion surface- excess.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 663: Symposium – Scientific Basis for Nuclear Waste management XXIV , 2000 , 1215
Copyright
Copyright © Materials Research Society 2001

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References

REFERENCES

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