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Proton Effects on Quaternary Cation Exchange and Flocculation of Silver Hill Illite

Dep. of Soil Science, Univ. of California, Berkeley, CA 94720

Catherine Thellier and Kenneth M. Holtzclaw

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

* Corresponding author.

ABSTRACT

The investigation of quaternary cation exchange and flocculation in dilute suspensions of illite with mixed Na-K-Ca-Mg perchlorate solutions was extended to consider the effect of aqueous protons. The exchange reactions and flocculation of Silver Hill illite at inial pH (pH_i) = 6 or 8, three total perchlorate concentrations (9, 5, or 2 mol_c m^–3), and varying initial Na/Ca or Na/Mg ratios in the aqueous solution phase were studied. It was found that pH_i had little or no effect on exchangeable cation selectivity or total adsorbed metal charge. The degree of flocculation, as described by the percentage light transmission through the illite suspensions, was found to be highly pH_i dependent. The effect of pH_i was greatest in the 5 mol_c m^–3 perchlorate background, where, at an exchangeable bivalent charge fraction near 0.3, the suspension was almost completely flocculated at pH_i = 6 but dispersed at pH_i = 8. Overall, at a given exchangeable bivalent charge fraction, the illite suspensions became less flocculated, and showed greater sensitivity to exchangeable Ca vs. Mg, as pH_i increased from 6 to 8. Changes in pH_i thus produced colloidal effects just the inverse of changes in the total perchlorate concentration. Analysis of the pH dependence of the light-transmission data suggested that the mechanism of illite flocculation was affected greatly by the adsorption-desorption reactions of a small number of protons on the edge surfaces of suspended particles.

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

Received for publication March 7, 1991.