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Sodium-Calcium and Sodium-Magnesium Exchange on Wyoming Bentonite in Perchlorate and Chloride Background Ionic Media¹

ABSTRACT

The exchange of calcium and magnesium for sodium at 298 K on Wyoming bentonite was investigated in perchlorate and chloride background media maintained at pH 7.0 and at a total cation normality of 0.05N. In the perchlorate medium, the apparent total adsorbed metal charge was independent of the exchanger composition and equal to 0.97 ± 0.06 mol_c kg^–1 (average for Na-Ca and Na-Mg exchanges). In the chloride medium, the apparent total adsorbed metal charge increased with the amount of calcium or magnesium adsorbed, tending to a value near 1.3 mol_c kg^–1 as the clay became saturated with the bivalent metal cation. These results were interpreted as evidence for the adsorption of CaCl⁺ or MgCl⁺ complexes in the exchange experiments conducted in the chloride medium. A detailed analysis of the exchange data led to the conclusion that a Ca-montmorillonite or Mg-montmorillonite suspension in a chloride background consists of quasicrystals with bivalent cations adsorbed on the internal surfaces and monovalent metal-chloride complexes adsorbed on the external surfaces.

¹ Contribution from the Dep. of Soil and Environmental Sciences, University of California, Riverside, CA 92521.

² Professor of Soil Science, Research Associate IV, Graduate Research Assistant, Visiting Postdoctoral Fellow, and Professor of Soil Science, respectively.

Received for publication July 14, 1982. Accepted for publication September 27, 1982.

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