Cationic Diffusion in Clay Minerals: I. Homogeneous and Heterogeneous Systems1
- T. M. Lai and
- M. M. Mortland2
Models of homogeneous and heterogeneous cationic diffusion systems were applied to clay minerals. The diffusion of Na and Cs ions in expanded Na-vermiculite, which has both internal and external surface available for cationic diffusion, decreased with increasing diffusion time, a characteristic of heterogeneous systems. Diffusion of those ions remained essentially constant in collapsed K-vermiculite which has only external surface available for diffusion and can thus be described as homogeneous. The property of homogeneity was further confirmed with cationic diffusion in the vermiculite whose exchange sites were clogged by p-phenylenediamine cation, and in Na- and K-kaolinite; while the heterogeneous property was observed for Na- and K-bentonite. The diffusion of Na ion in Na-vermiculite was related to a model originally derived for mathematical analysis of grain boundary problems. The evaluation of diffusion coefficients of external surface (De) and of interlayer surface (Di) was made, and De of Na ion in Na-vermiculite was found to be about 5 times larger than that of Di. The importance of considering the homo- and heterogeneity of the system in the study of cationic diffusion in clay minerals is suggested.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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