Industrial clays: kaolin (china clay), ball clay and bentonite

Abstract

Kaolin (or china clay), ball clay and bentonite are the dominant ‘industrial clays’, and are mined for a wide variety of uses (Table 3.1), which exploit the special properties of each of the three clay types: Kaolin (china clay) — is chemically inert and can be prepared as a white powder specified (in part) according to its whiteness and brightness. It is ideal for a wide range of ceramic, filling and coating applications, where the appearance of the finished product is important (Jepson, 1984). It is particularly valuable as a surface coating pigment on high quality glossy paper, which might contain up to 30% of the mineral. It is present as a filler in the paper on which this book is printed. Ball clay — is a plastic clay used in the ceramic industry to provide strength and malleability to a ceramic body prior to firing. Also, during firing, ball clay is one of the components which fuses to act as a ‘cement’ binding together the refractory, non-shrinking components of the ceramic body. Much of the ceramic ware produced using ball clay is moulded (such as sanitaryware) and the use of ball clay is essential to ensure that mouldings do not sag or lose shape prior to firing. Bentonite — is both physically and chemically reactive. It shrinks or swells in response to its ability to readily accept or release interlayer water (and organic molecules), and it exhibits important cation exchange and chemical sorption properties. It is ideal for applications where absorbance is important (particularly in the handling of waste materials), and in suspensions or slurries where its interaction with the liquid gives a fluid with particular mechanical properties (viscosity or plasticity; Odom, 1984). Table 3.1 Summary of important uses for kaolin (china clay), ball clay and bentonite Kaolin (china clay) for paper coating and filling as fillers in plastics, paints and pharmaceuticals forms part of the ceramic body with applications similar to those of ball clay. Ball clay ceramic raw material used in the production of fine tableware, stoneware (pottery), wall and floor tiles, sanitaryware and bricks lower grade clays increasingly are finding applications as sealing materials for landfill waste disposal sites (see Chapter 11). Bentonite in the formulation of oilfield drilling fluids as cat litter and other animal husbandry products in civil engineering to produce hydraulic barriers (as in waste disposal applications; Chapter 11).