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Ion Diffusion: II. Comparison of Apparent Self and Counter Diffusion Coefficients¹

ABSTRACT

The experimental distributions of Rb⁸⁶ diffusing in soil materials are obtained using a quick-freeze method. The calculation of apparent diffusion coefficients of Rb from data obtained from these distributions is presented for the following geometries: (1) self diffusion and (2) counter diffusion of Rb diffusing from soil media initially saturated with Rb into the same soil media initially saturated with H⁺. The distribution of Rb⁸⁶ counter diffusing from kaolinite clay, montmorillonite clay, Sharkey clay soil and Dundee silt loam soil pastes into H⁺ saturated kaolinite, montmorillonite, Sharkey and Dundee pastes can be characterized using self diffusion theory.

The order of magnitude of apparent self diffusion coefficients is larger than those for counter diffusion in each of the four soil materials. The order of magnitude of the rate of Rb diffusion in the four soil materials is as follows: kaolinite clay > Dundee silt loam soil > Sharkey clay > montmorillonite clay. The values of the diffusion coefficients range from 3.9 x 10^–7 cm.² sec.^–1 to 24.3 x 10^–7 cm.² sec.^–1.

Qualitative apparent counter diffusion coefficients of Rb diffusing from soil media initially saturated with Rb into strong acid exchange-resin discs initially saturated with H⁺ are also presented for qualitative comparison purposes.

¹ Contribution from the Department of Agronomy, Arkansas Agr. Exp. Sta., Fayetteville. Presented before a Joint meeting of Div. S-1 and S-2, Soil Sci. Soc. Am., Nov. 20, 1963, at Denver, Colo.

² Associate Professor and Professor of Agronomy, respectively.

Received for publication March 11, 1964. Accepted for publication July 14, 1964.