Interfacial processes cation-exchanged montmorillonites

The negative layer charge is mostly neutralized by the hydrated cations in the interlayer space. These cations are bonded to the internal surfaces by electrostatic forces, and they are exchangeable with other cations. The interaction strength between the hydrated cation and the layers (the internal surface) increases when the charge of the cation increases, and the hydrated ionic radius decreases. Cations with hydrate shell can be considered as outer-sphere complexes. Cation exchange is the determining interfacial process of the internal surfaces of montmorillonite. 

The other interfacial process involving hydrogen ion is the cation-exchange process in the interlayer space. When montmorillonite is suspended in water or in an electrolyte solution, a part of exchangeable cations can be dissolved. In Table 2.7, the relative quantity of calcium ions dissolved in water or in acidic solutions is shown. 

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