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Sodium/Calcium Exchange in Montmorillonite and Illite Suspensions
Author(s) -
Shainberg I.,
Oster J. D.,
Wood J. D.
Publication year - 1980
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1980.03615995004400050017x
Subject(s) - montmorillonite , illite , dilution , chemistry , ion exchange , adsorption , sodium , clay minerals , electrolyte , cation exchange capacity , mineralogy , calcium , selectivity , inorganic chemistry , soil water , geology , ion , thermodynamics , organic chemistry , soil science , physics , electrode , catalysis
The effect of salt concentration and exchanger composition on Na/Ca exchange in montmorillonite and illite suspensions (0.02 to 0.08 g clay/g water) was studied, where the equivalent fraction of exchangeable Ca, E Ca , ranged from 0.6 to 1. A theoretical evaluation based on double‐layer theory for montmorillonite indicates that the formation of tactoids and internal surfaces at the Ca 3+ end of the exchange isotherm can cause the Vanselow selectivity coefficient, K V , to depend on exchangeable cation composition and total electrolyte concentration. Whereas for montmorillonite, K V increased with E Ca (0.6 < E Ca < 1), as predicted for internal surfaces, the reverse was true for illite, where external surfaces predominate. Likewise, for a given Na adsorption ratio, dilution of the equilibrium solution for illite (0.6 < E Ca < 1) and for montmorillonite ( E Ca ≃ 0.6) decreased K V as predicted for external surfaces. The average Gapon selectivity coefficient for the montmorillonite (0.011) and illite clays (0.023) with E Ca ≤ 0.8, suggests that the value for soils, (0.0148) reflects their mixed mineralogy.