Fundamentals of Clays Surface and Colloid Science, and Rheology

Abstract

Introduction Relating bulk properties of clays and clay suspensions to their particle morphology or surface chemistry is a complex process due to the multiple possible types of interaction and the large number of bodies over which these forces act. The work that has been done on simple, idealized suspensions can be extended to complex multi-component suspensions, such as clay in water, with caution. This allows the observation of trends in behaviour to be given some meaning and predictions to be made. This chapter combines the surface and colloid science with macroscopic rheological behaviour due to the strong causal relationships involved. For example, what affects clay swelling behaviour also affects the rheology, and the swelling itself leads to complex rheological behaviour. Mineral Structure Silicate Minerals Silicate minerals are by far the most commonly occurring minerals in the world. All silicate minerals are based on tetrahedral building blocks. These tetrahedral units are composed of a central Si atom bonded to four surrounding O atoms, more commonly known as the silica tetrahedron. Different families of silicate minerals are based upon the numerous ways in which these tetrahedra may be combined (Klein and Hurlbut, 1993), either as isolated tetrahedra (e.g. olivine), single or double chains of tetrahedra (e.g. orthopyroxene, hornblende), as an interlocking tetrahedral framework (e.g. feldspar, quartz), or as tetrahedral sheets (e.g. talc, kaolinite). The different combinations of tetrahedral blocks are illustrated in Fig. 2.1. This review focuses on the phyllosilicate mineral family, as all clay minerals fall within this family (Deer et al., 1992). Phyllosilicate Minerals Phyllosilicate minerals are so named because the sheets of silica tetrahedral tend to give the minerals a platy/leafy habit, as illustrated in an SEM image in Fig. 2.2. There are a large number of different types of phyllosilicates in existence with a variety of different properties. The detailed structure of phyllosilicates is composed of a combination of tetrahedral and octahedral sheets. Individual octahedra are made up of two layers of four oxygen/hydroxyl atoms, with embedded magnesium or aluminium atoms arranged in an octahedral coordination, as illustrated in Fig. 1.4 and already discussed in Chapter 1.