Effect of Ionic Charge on Effective Diffusion Coefficient in Compacted Sodium Bentonite

Abstract

Effective diffusion coefficients(De) in bentonite were measured as a function of ionic charge to evaluate the degree of surface diffusion and anion exclusion. The De measurements for Ni2+, Sm3+ and Se3 2− were carried out for 1.8Mg•m−3 by through-diffusion method. Sodium bentonite, Kunigel-V1® was used. The order of obtained De values was Sm3+>Ni2+>SeO3 2−. These De values were compared with those reported to date. Consequently, the order of De values was Cs+>Sm3+>HTO>Ni2+>anions(I, Cl, CO3 2−, SeO3 2−, TcO4 , NpO2CO3 , UO2(CO3)3 4−), showing a tendency of cations>HTO>anions. The reason that the De of Ni2+ was lower than that of HTO may be because the free water diffusion coefficient(Do) of Ni2+ is about 1/3 of that of HTO. The formation factors(FF) were in the order, Sm3+>Cs+>Ni2+>HTO>anions, indicating a possibility of surface diffusion in cations and of anion exclusion in anions. In this case, the FF of Sm3+ was approximately 5 times greater than that of HTO. However, since the Do of Sm3+ is about 1/3 of that of HTO, the De of Sm3+ may have been a little higher than that of HTO. Based on this, it is presumed that surface diffusive effect on De in bentonite is insignificant.

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Sato, H. Effect of Ionic Charge on Effective Diffusion Coefficient in Compacted Sodium Bentonite. MRS Online Proceedings Library 608, 267 (1999). https://doi.org/10.1557/PROC-608-267

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