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Interactions of pH-Dependent and Permanent Charges of Clays: II. Calcium and Rb Bonding to Bentonite and Illite Suspensions—Clay-Phase Retention¹

ABSTRACT

Panther Creek bentonite and Fithian illite suspensions were reciprocally saturated with Ca and Rb. ⁴⁵Ca and ⁸⁶Rb were added as tracers for Ca and Rb, respectively. Increments of H-clay were added as a source of (i) permanent charges for adsorbing Ca and Rb, and (ii) H ions for inactivation of pH-dependent charges. Fifty-milliliter volumes of clay suspensions were membrane-equilibrated with similar volumes of water. Three-component systems of bentonite, illite, and dialyzate were also equilibrated. After equilibration, assay of Ca and Rb was made in each phase.

Except where Rb fixation occurred, decreasing the Ca and increasing the Rb saturations (decreasing Ca/Rb ratio) shifted Ca from pH-dependent to permanent charges, causing increased bonding and thus increased retention of Ca by the clays. Similarly, decreased Ca/Rb ratio increased the number of Rb ions adsorbed to permanent charges causing increased percentage retention. Rubidium fixation by illite markedly increased percentage Rb retained and decreased Ca retained. When pH-dependent charges were inactivated by addition of H, retention of both cations increased and became uniform at all Ca/Rb ratios. The distribution of ions in the three-component systems was predictable from the results of the two-phase systems.

¹ Published with the permission of the Director of the Ohio Agricultural Research & Development Center as Journal Article no. 30-68. Presented before Div. S-2, Soil Science Society of America, Washington, D.C., Nov. 7, 1968. The results are contained in a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree, The Ohio State University, 1967. Supported in part by grant no. GB1101 from the National Science Foundation.

² Former Research Assistant, now Assistant Professor, Everglades Exp. Sta., Belle Glade, Fla.; and Professor and Associate Professor of Agronomy, The Ohio State University and the Ohio Agr. Res. & Devel. Center.

Received for publication December 2, 1968. Accepted for publication January 16, 1969.