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Influence of Electrolyte Concentration on Quaternary Cation Exchange by Silver Hill Illite

Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521

Garrison Sposito^*

Dep. of Plant and Soil Biology, Univ. of California, Berkeley, CA 94720

* Corresponding author.

ABSTRACT

A study of Na-K-Ca-Mg exchange on specimen illite in a perchlorate background of varying ionic strength is reported. Sodium-saturated Silver Hill illite was reacted at pH 7 with perchlorate solutions of differing Na/Ca or Na/Mg ratio and total electrolyte concentration (9.2, 5, 3.6, 2 and 1 mol_c m^–3). All soluble and exchangeable cations were measured directly. No effect of the total electrolyte concentration on the total adsorbed charge was observed. The exchange isotherms and Vanselow selectivity coefficients based on the composition data showed that Silver Hill illite exhibited more or less equal affinity for Ca and Mg. Both bivalent cations were slightly preferred to Na in the three more concentrated electrolyte backgrounds, but at concentrations of 2 and 1 mol_c m^–3, a slight preference for Na over Ca and Mg was observed. Exchangeable K, which represented 6 to 18% of the total adsorbed charge, decreased with the content of exchangeable Ca or Mg and, at a given bivalent charge fraction, was dependent on the total perchlorate concentration. The clay exhibited a very high preference for K over the three other cations which increased as the content of exchangeable K decreased.

Contribution from Dep. of Soil and Environmental Sciences, Univ. of California, Riverside.

Received for publication June 20, 1988.