Relations of Geological Origin and Interfacial Properties

As seen previously, bentonite samples from the same bentonite deposit (Sajobabony) show no significant differences in the montmorillonite content, but the circumstances of their geological formation are different. The sedimentary bentonites (B-I.b. and B-II.a.) show similar interfacial properties, while the bentonitic tuff (B-II.b.) behaves differently. This is probably caused by the large amount of the x-ray amorphous phase. 

Some characteristic properties of bentonites (CEC, sorption properties) are mainly governed by the montmorillonite content and the layer charge of montmorillonite. Other properties, however, depend on the circumstances under which the rock is formed. These are particle size distribution, external specific surface area, and surface acid-base properties. The quantity of the edge sites mainly depends on the specific surface area. The protonation and deprotonation reactions take place on the edge sites of other silicates and aluminosilicates present beside montmorillonite, so their effects manifest via surface reactions. Consequently, the origin of bentonite determines all properties that are related to external surfaces. 

The differences among these properties indicate the various stages of the formation processes for sedimentary bentonites and the bentonitic tuff. 

The swelling of bentonites in water and, as will be discussed in Section 3.2.2, the migration of a nonadsorbing ion show no direct relationship to the montmoril-lonite content or other geological characteristics in this narrow range (35%-48% montmorillonite content, Table 3.1). However, they are influenced by several other factors, for example, the quality of the exchangeable cation (Chapter 2, Section 2.1), particle size distribution, aggregation, density, free pore size, other minerals, etc. 

As a consequence of this, the properties and possible application of bentonites are determined by both the montmorillonite content and geological origin. The origin appears in the particle size and external surface properties. 

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