Kaolin

Kaolinite is a mineral belonging to the group of aluminosilicates. It is commonly referred to as “China Clay” because it was first discovered at Kao-Lin, in China. The term kaolin is used to describe a group of relatively common clay minerals dominated by kaolinite and derived primarily from the alteration of alkali feldspar and micas. Kaolin is an industrial mineral used primarily as an inert filler and customers combine it with other raw materials in a wide variety of applications. Kaolin is a white, soft, plastic clay mainly composed of fine-grained plate-like particles. Kaolin is formed when the anhydrous aluminium silicates which are found in feldsparrich rocks, like granite, are altered by weathering or hydrothermal processes. The process which converted the hard granite into the soft matrix found in kaolin pits is known as “kaolinisation”. The quartz and mica of the granite remain relatively unchanged whilst the feldspar is transformed into kaolinite. Smectite may also form in small quantities in some deposits. The refining and processing of the fine fraction of the kaolinised granite yields predominantly kaolinite with minor amounts of mica, feldspar, traces of quartz and, depending on the origin, organic substances and/or heavy minerals. Individual kaolins vary in many physical aspects, which in turn influence their end use. Of particular commercial interest is the degree of crystallinity which influences the brightness, whiteness, opacity, gloss, film strength, and viscosity. Kaolin is part of our natural world. Its uses are multiple and diversified. Kaolin’s whiteness and plasticity make it extremely suitable for its extensive use as a filler, extender, ceramic raw material and pigment. It is also an important raw material to refractories, and to catalyst, cement and fibre glass industries. Kaolin is used in many applications. It is a unique industrial mineral, which remains chemically inert over a relatively wide pH range and it offers excellent covering when used as a pigment or extender in coated films and filling applications. In addition, it is soft and non-abrasive and has a low conductivity of heat and electricity. The two largest applications of kaolin are the coating of paper to hide the pulp strands and the production of highgrade ceramic products. It is also used in many other industrial processes.