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Complementary Ion Effects on Potassium, Sodium, and Calcium Displacement from Bi-Ionic Bentonite and Illite Systems as Affected by pH-Dependent Charges¹

ABSTRACT

Bi-ionic systems of bentonite and illite clay suspensions containing K-Ca, K-Na, and Na-Ca were prepared in reciprocal saturation ratios at 100, 90, and 80% base saturations of bentonite and at 100, 80, and 60% saturations of illite. Each system was equilibrated with equal volumes of water, and then aliquots of each suspension were extracted with water, BaCl₂, or HCl at 0.1 or 0.3 symmetry concentrations.

Displacement of a given cation varied greatly depending on the accompanying cation adsorbed to the exchange sites of the clays. This complementary ion effect, although occurring on both types of charge, was much greater when the exchange was from pH-dependent charges. Thus, maximum complementary ion effects on K and Na displacement were at low saturations of the clays with these cations, while these effects on Ca displacement were greatest at high Ca saturations. Since BaCl₂ generally displaced more basic cations from pH-dependent charges than did HCl, the combined effects of higher valency of Ba and higher pH of displacement in BaCl₂ than in HCl evidently were greater than the single effect of preferential H-bonding to pH-dependent charges.

¹ Published with permission of the Director of the Ohio Agr. Res. and Dev. Center as Journal Article no. 99-72. Appreciation is expressed for financial support from USAID and Fundaco de Ampara a Pesquisa do Est. de Sao Paulo.

² Professor, and former USAID participant the Ohio State Univ., now Associate Professor Escola Superior de Agricultura Luiz de Queiroz, Piracicaba, Sao Paulo, Brazil, respectively.

Received for publication October 12, 1972. Accepted for publication February 12, 1973.