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Study of Ion Exclusion Using Artificial Reference Samples for Rocks

Published online by Cambridge University Press:  10 February 2011

Matti Valkiainen ,
Hannu Aalto ,
Jarmo Lehikoinen  and
Markus Olin
Matti Valkiainen
Affiliation:
VTT Chemical Technology P.O. Box 1404, FIN-02044 VTT, Finland, matti.valkiainen@vtt.fi
Hannu Aalto
Affiliation:
VTT Chemical Technology P.O. Box 1404, FIN-02044 VTT, Finland, matti.valkiainen@vtt.fi
Jarmo Lehikoinen
Affiliation:
VTT Chemical Technology P.O. Box 1404, FIN-02044 VTT, Finland, matti.valkiainen@vtt.fi
Markus Olin
Affiliation:
VTT Chemical Technology P.O. Box 1404, FIN-02044 VTT, Finland, matti.valkiainen@vtt.fi
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Abstract

Matrix diffusion in rocks has been extensively studied experimentally with various methods including tracer experiments. Comparing the rock-capacity factors (α) for Cl-36 to corresponding values for H-3, an anion-exclusion tendency has been observed in many cases. This study uses a well-characterized reference material: porous silica (Geltech Inc.), with pore diameters of 2.5, 5, 7.5 and 20 nanometers. The equilibration-leaching method and tracers H-3 (H-3) and Cl-36 (Cl−) were used to determine the capacity factors of the samples in three molarities of NaCl solution: 0.0026, 0.01 and 0. 1 mol/liter. The ratio αcl/αH-3 gives the anion exclusion for each solution/pore diameter combination. A clear anion-exclusion tendency was seen both as a function of the decreasing pore diameter and liquid molarity.

The modeling was based on the assumption that the silica surface acts as a proton donor according to SiOH = SiO− + H+. The pore dimensions are also included in the calculations. In the case of the silica samples, good agreement was found when comparing the experimental and calculated values of chloride exclusion. This suggests that the surface complexation model for matrix diffusion can explain the observed exclusion phenomena in rocks although the parameters needed for the application of the model are difficult to obtain in the case of rocks.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 556: Symposium QQ – Scientific Basis for Nuclear Waste Management XXII , 1999 , 641
Copyright
Copyright © Materials Research Society 1999

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References

REFERENCES

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