Interfacial processes montmorillonites

USE OF MONTMORILLONITE AS A MODEL SUBSTANCE THE IMPORTANT INTERFACIAL PROCESSES ON MONTMORILLONITE... 

The montmorillonite (Chapter 1, Table 1.2) clay mineral can be used as a model substance in the study of the interfacial processes of rocks and soils. It is a layer silicate, a member of the smectite group. Its structure is appropriate for modeling the most important interfacial processes in geological formations. Besides, it is a fairly widespread mineral in rocks and soils, and plays an important role in the nutrient cycle of soils. In addition, it has many agricultural, industrial, and environmental applications. 

Montmorillonite has some important characteristics that justify its use as a model substance for the study of the interfacial processes of rocks and soils. It is a dioctahedral three-layer clay (2 1 clays, TOT) an A10(0H) octahedral sheet is between two tetrahedral Si04 layers (Chapter 1, Table 1.2). The distance between the layers is not fixed (—O—O-bonds) the layers can be expanded. Because of the layered structure, it has two surface types external and internal surfaces. The external surface is the surface of the particles (edge surface), and its size depends on particle size distribution. Its area can be measured by the BET method, usually by the adsorption of nitrogen gas at the temperature of liquid nitrogen (Chapter 1, Section 1.1.3). The internal surface is the surface between the layers (interlayer surface), and its size can be determined by introducing substances into the interlayer space (e.g., water) (Chapter 1, Section 1.1.3). The internal surface area is independent of particle size distribution. 

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. 

As seen earlier, zinc ions can be a part of different interfacial processes on cal-cium-montmorillonite. The ion exchange in the interlayer space and the other sorption on the external surfaces can be separated by measuring ions entering and leaving the montmorillonite phase. The quantitative separation of sorption isotherms will be discussed in Section 2.6. 

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. 

Examines interfacial processes in a montmorillonite model system... 

In Chapter 2 the interfacial processes are discussed in a model system. A clay mineral, montmorillonite, has been chosen to illustrate important interfacial processes of geological formations. Some transformations initiated by interfacial processes are demonstrated. 

ROLE OF HYDROGEN IONS IN THE INTERFACIAL AND DISSOLUTION PROCESSES OF MONTMORILLONITE... 

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