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Current and Future Demands for Clays Minerals - An Industrial Perspective
Ansari, Deeba M., Imerys Minerals Ltd., Central Laboratories, Par Moor Road, St. Austell, Cornwall, PL24 2SQ, UK.
The industrial use of clay minerals goes back to the dawn of human civilization itself when plastic clays were used as a binder in walls, bricks and mortars. Their use in construction was revolutionised with the introduction of cementicious materials by the Phoenicians (1) and the addition of pozzolans became widely known throughout the Greek and Roman worlds. The introduction of fired pottery as a means of preparation, storage and serving of foods predates this considerably and an example dating from as early as 18,000 BP has recently been found in the Yunchanyan Caves (People’s Republic of China) (2). These applications, although refined over the centuries, have, in many instances, remained relatively unchanged. However, increases in demand for paper, advanced ceramics, paints and polymers during the late 19th and throughout the 20th centuries have lead to a new science of beneficiation and modification of clay materials to suit more contemporary purposes.
Current use of clay minerals is often split into the broad categories of “fillers and extenders” (primarily paper, paint, rubber and plastics) and “others” (most notably, ceramics, refractories, fibreglass and cements). A 2006 market report of kaolin use (3) gives a more detailed view of those applications and their volume split. Paper fillers and coatings accounted for some 10.5 million T of kaolin in 2005, with the remainder of extenders using 3.6 million T. Ceramics usage was given as 4.6 million T, with refractories demanding 2.15 m T and fibreglass an additional 1.05 million T. The total in 2005 of 23 million T is expected to rise to 24.3 million T in 2010. Whilst the use of many of these minerals is well known, there are many developments that broaden this envelope and create demands on the materials beyond their traditional application areas. This paper serves to illustrate advancements made in the refinement of kaolins by giving examples of recent developments in three specific areas: as a barrier material for reducing the permeability of water-based barrier coatings; as a calcined opacifier in advanced coatings; and as a surface modified calcined kaolin in polymers. In each of these illustrations it is evident that an understanding of the surface chemistry, particle shape and relative size distribution are crucial in developing such materials for an increasingly demanding and diverse world.
1. Mays G. (1992), Durability of Concrete Structures. 1: 3 E and F N Spon, London.
2. Boaretto E. et al (2009), Radiocarbon dating of charcoal and bone collagen associated with Yuchanyan Cave, Hunan Province, China. PNAS 106, No. 24: 9595-9600.
3. Roskill (2006), The Economics of Kaolin. 12: 219-220, Roskill Information Services Ltd.