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Abstract
The interaction between soil particles and the soil solution depends on the types and amounts of soil clays. Montmorillonite is the most reactive clay. Ca-clay forms tactoids (quasi crystals) and has limited swelling and dispersion. Na-clay forms single platelets and disperses freely. In a mixed Na/Ca system, “demixing” of the cations occurs as the Na ions concentrate on the external and the Ca ions on the internal surfaces of the tactoids. The demixing explains why a small percentage of exchangeable Na sharply increases the zeta potential and dispersion of montmorillonite clay.