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The Swelling of Clay: I. Basic Concepts and Empirical Equations¹

ABSTRACT

The primary objective of the present study was to elucidate the relative contributions of exchangeable cations and surface forces to the swelling pressure, , of montmorillonite. To achieve this objective, measurements were made of the amount of water imbibed by Na-saturated montmorillonites having different cation exchange capacities, b dimensions, and specific surface areas under applied pressures of 0, 1, 3, and 5 atm. The resulting data were used to develop the empirical equation ( + 1) = exp [/(m_w/m_m)] in which m_w/m_m is the mass ratio of water to montmorillonite and is a linear function of the specific surface area and cation exchange capacity. Analysis of double-layer theory in the light of this equation led to the conclusion that is affected less by exchangeable cations than by surface forces. It was suggested that exchangeable cations have a secondary effect because few of them dissociate from the layer surfaces.

¹ Journal Paper no. 7101; contribution from the Dept. of Agronomy, Purdue Univ. Agric. Exp. Stn., West Lafayette, IN 47907.

² Professor of Soil Chemistry and former Graduate Research Assistant, respectively.

Received for publication March 29, 1978. Accepted for publication December 11, 1978.