Advances in the characterization of industrial minerals
The use of minerals by man is as old as the human race. In fact the advancement of human civilization has been intimately associated with the exploitation of raw materials. It is not by chance that the distinction of the main historical eras is based on the type of raw materials used. Hence the passage from the Paleolithic and Neolithic Age to the Bronze Age is characterized by the introduction of basic metals, mainly copper, zinc and tin, to human activities and the Iron Age was marked by the introduction of iron. Since then the use of metals has increased and culminated in the industrial revolution in the mid-eighteenth century which marked the onset of the industrial age in the western world. However, during the past 50 years, although metals were equally important to western economies as they had been previously, the amount of metals extracted annually in western countries has decreased significantly and metal mining activity shifted mainly to third world countries (in Africa, South America, Asia) and Australia, due to economic and environmental constraints. At the same time the role of industrial minerals has become increasingly important for the western economies and today, in developed EU countries, the production of industrial minerals has surpassed by far the production of metals. In some EU countries, metal mining activities have stopped completely. The importance of industrial minerals is expected to increase further in the future.
Published:January 01, 2010
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.