Ion Activities in Sodium‐Clay Suspensions

Abstract

AbstractA study has been made of dissociation and hydrolysis of Na‐clay as a function of the degree of Na+ saturation of the clay and the concentration of NaCl in the clay suspension. The activities of Na+, H+, HCO3‐, and Cl‐ in the clay suspension were measured by the Donnan equilibrium method. From the Donnan distribution of ions between the two phases, it has been possible to apportion the observed Na+ activity in the clay suspension to Na+ dissociated from the clay and to diffusible sodium salts present in the clay suspension. The activity of Na+ dissociated from the clay and the activity of Na+ due to the presence of diffusible sodium salts in the clay suspension were both found to increase with the increasing degree of Na+ saturation of the clay and increasing concentration of NaCl or Na‐clay in the clay suspension. The anomalous increase in the activity of Na+ dissociated from the clay with the increasing concentration of NaCl or Na‐clay in the suspension may be attributed to the decrease in the thickness of the ionic atmosphere around the clay particle, resulting in greater concentration of osmotically active Na+ ions in the outer part of the diffuse double layer.