Chapter 9: Industrial clays
Clays have been used by man since prehistoric times. Initially they were used almost exclusively in the fabrication of ceramics; nowadays they find numerous industrial and technological applications including the production of materials with large added value such as nanocomposites, cosmetics or pharmaceuticals. The term clay should not be considered as a synonym for clay mineral, because clays consist of more than one mineral. The versatile nature of clays is attributed to the presence of clay minerals, which impart significant physical properties to the raw materials, such as particle size and shape, ion exchange, hydration and swelling, plasticity, rheological properties, colour properties and reactions with organic and inorganic compounds. Four types of industrial clay raw materials are examined in this contribution, kaolins, bentonites, fibrous clays (palygorskite and sepiolite) and common clays and shales. The latter are used in the production of structural ceramics, bricks tiles and pipes. The industrial clay deposits are classified as primary (residual formed from in situ alteration of various precursors or hydrothermal) and secondary, formed from deposition of clastic clay materials which were transported from their sources. Assessment of industrial clay deposits comprises determination of physical properties and direct comparison with international or regional standards, which include industrial specifications for particular applications. These specifications are often dictated by the end industrial users. Exploitation of the clay deposits is usually by means of traditional open-cast methods and processing can involve anything from simple crushing, screening and tempering, to elaborate mineral beneficiation techniques such as alkali or acid activation, delamination, magnetic separation, selective flocculation, flotation and leaching. The method used and the extent of beneficiation are dictated by the final industrial application of the clay.
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