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Experimental Study and Monte Carlo Modeling of Calcium Borosilicate Glasses Leaching

Published online by Cambridge University Press:  19 October 2011

Mehdi Arab ,
Celine Cailleteau ,
Frederic Angeli  and
Francois Devreux
Mehdi Arab
Affiliation:
[email protected]/SECM/Laboratoire d'études du Comportement à Long TermeCEA Centre ValrhôBP 17171Bagnols-sur-cèze30207France, Metropolitan+33 4 66 79 76 93+33 4 66 79 66 20
Celine Cailleteau
Affiliation:
[email protected]/SECM/Laboratoire d'études du Comportement à Long TermeCEA Centre ValrhôBP 17171Bagnols-sur-cèze30207France, Metropolitan+33 4 66 79 76 93+33 4 66 79 66 20
Frederic Angeli
Affiliation:
[email protected]/SECM/Laboratoire d'études du Comportement à Long TermeCEA Centre ValrhôBP 17171Bagnols-sur-cèze30207France, Metropolitan+33 4 66 79 76 93+33 4 66 79 66 20
Francois Devreux
Affiliation:
[email protected]/SECM/Laboratoire d'études du Comportement à Long TermeCEA Centre ValrhôBP 17171Bagnols-sur-cèze30207France, Metropolitan+33 4 66 79 76 93+33 4 66 79 66 20
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Abstract

During aqueous alteration of glass an alteration layer appears on the glass surface. The properties of this alteration layer are of great importance for understanding and predicting the long-term behavior of high-level radioactive waste glasses. Numerical modeling can be very useful for understanding the impact of the glass composition on its aqueous reactivity and long-term properties but it is quite difficult to model these complex glasses. In order to identify the effect of the calcium content on glass alteration, seven oxide glass compositions (57SiO2 17B2O3 (22−x)Na2O xCaO 4ZrO2; 0 < x < 11) were investigated and a Monte Carlo model was developed to describe their leaching behavior. The specimens were altered at constant temperature (T = 90°C) at a glass-surface-area-to-solution-volume (SA/V) ratio of 15 cm 1 in a buffered solution (pH 9.2). Under these conditions all the variations observed in the leaching behavior are attributable to composition effects. Increasing the calcium content in the glass appears to be responsible for a sharp drop in the final leached boron fraction. In parallel with this experimental work, a Monte Carlo model was used to investigate the effect of calcium content on the leaching behavior. The glass structure was built with a random distribution of silicon and boron on the lattice points of a diamond lattice with sodium atoms located in interstitial position. The model was upgraded to take into account the effect of zirconium and calcium. Zirconium atoms are placed in interstitial position (with cations acting as charge compensators) and interact with six lattice atoms (Si or B) by decreasing their dissolution probability. Acting like sodium but with less effect, calcium atoms increase the dissolution probability of atoms placed in their neighborhood. Monte Carlo simulations performed with this model are in good agreement with the experimental results. The dependence of the dissolution rate on the calcium content can be described by a quadratic function: fitting the simulated points gives a minimum alteration rate at about 7.4 mol% calcium. This value is consistent with the figure of 8.0 mol% obtained from the experimental work. The model was also used to investigate the role of calcium in the glass structure and it pointed out that calcium act preferentially as a network modifier rather than a charge compensator in this kind of glasses.

Keywords

waste managementsimulationCa
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 985: Symposium NN – Scientific Basis for Nuclear Waste Management XXX , 2006 , 0985-NN06-02
Copyright
Copyright © Materials Research Society 2007

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References

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