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The Effect of Exchangeable Aluminum on Conductance and Diffusion Activation Energies in Montmorillonite¹

ABSTRACT

Conductance and D₂O diffusion activation energies were determined for mixtures of Na⁺- and Al³⁺-montmorillonites prepared by batch washing techniques. Increases in activation energy with the percentage of aluminum on the exchange capacity were found when the exchangeable aluminum was greater than 50%. Below 50% exchangeable aluminum the activation energies were within experimental error of the bulk water value. These increases were explained on the basis of structural changes in the adsorbed water which may occur at high aluminum concentrations.

Alternating current conductance activation energies were measured for pre-H⁺-columnated Na⁺/Al³⁺-montmorillonites. These clays were unstable and it was found that drying at 70C could lead to erroneously high activation energies unless adequate equilibration time was allowed. Inadequate equilibration time could account for some of the high activation energies reported in the literature.

¹ Contribution from the Department of Agronomy, University of Illinois, Urbana, Ill. 61801. Based on a thesis submitted by the junior author to the University of Illinois for the M.S. degree.

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

Received for publication July 30, 1968. Accepted for publication January 13, 1969.