China Clay or Kaolin

Kaolin (Al2O3.2SiO2.2H2O), is probably more widely known as the clay mineral, china clay [11]. It is found in hydrothermal, residual and sedimentary deposits (probably about 1000 are still commercially worked) around the world with the most important resources being in Cornwall in SW England and in South Carolina and Georgia in the USA. Large 

Hydrothermal and residual deposits are classified as primary occurrences, although some authorities call them secondary as they are found in the rocks from which they have been formed. Sedimentary deposits are always secondary. The kaolins are formed by the hydrothermal alteration and weathering of feldspathic igneous and metamorphic rocks (especially granite) under relatively low temperatures and pressures. The most common parent minerals are feldspars and muscovite micas. The primary deposits will usually be mixed with unaltered granite, mica, feldspar and quartz. Secondary deposits are usually found in layered qualities with very variable purity. 

Micromineral separation is being used increasingly in both types of production routes with flotation, selective flocculation and magnetic separation being used to remove impurities from the clay. 

Secondary clays are usually very much finer than primary clays and products that are approximately 100% finer than 5 pm can be obtained by a fairly simple air-float or degritting procedure. 

Although kaolin, china clay (and even clay) are often used interchangeably as names, the main mineral present is usually (but not invariably) kaolinite. In fact some china clays are sold that contain only 25% kaolinite, but normally kaolins will contain 50-99% kaolinite with the main impurities being mica, quartz and feldspar. Other silicates, metal oxides and organic matter are usually found in trace amounts. 

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Certain properties of clays were known and exploited in ancient times in particular, clays were used for the fabrication of pottery, bricks and tiles. The chief constituent of china clay (or kaolin) is kaolinite, which is still used on a very large scale in the manufacture of paper and refractories. Ball clay, a line-grained form of kaolinite, contains some mica and quartz and is now favoured for crockery, porcelain and floor tiles. 

China clay or kaolin, which is predominantly kaolinite. is particularly valuable because it is essentially free from iron impurities (and therefore colourless). World production in 1991 was 24.7M( (USA 39%, UK 13%. Colombia, Korea and USSR "7% each). In the USA over half of this vast tonnage is used for paper filling or paper coating and only 130000 tonnes was used for china, crockery, and earthenware, which is now usually made from ball clay, a particularly fine-grained, highly plastic material which is predominantly kaolinite together with clay-mica and quartz. Some 800000 tonnes of bail clay is used annually in the USA for white ware, table ware, wall and floor tiles, sanitary ware, and electrical porcelain. 

Other thixotroping agents include Bentones and Tixogels, of which a number of grades are available, and China clay or kaolin, usually added as a filler, but which imparts thixotropy to the formulated product. Organofunctional silanes are extremely effective... 

The Fats and Oils—Olive-oil—Tallow—Lard—Falm-oil—Cocoa-nut Oil— Oastor-oil —Bone-grease—Horse-grease—Kitchen-stuff— Oleine, or Tallow-oil—Fish-oils— Eesin, or Colophony—Be-oovered Grease or Yorkshire Fat—The Alkalies—Oaustio Soda -Potash—Silicate of Soda, or Soluble Glass-China Clay, or Kaolin—Sulphate of Soda, or Glauber s Salt. ... 

Sedimentary rocks are derived from weathered rock masses and deposited by the action of water or other means, or by the sedimentation of bioliths (mineral skeletons, shells, etc., of plants and animals) into layers, or, rarely, by chemical precipitation. Massive deposits of china clay or kaolin are found as a result of weathering, followed by movement and deposition. Limestone, the general term for natural calcium carbonate rocks, is the most abundant of the sedimentary rocks and is formed by the deposition of countless skeletons and shells. Gypsum and diatomaceous earths occur widely in sedimentary rocks. Sedimentary rocks are almost universally found in layered beds, which may have folded or otherwise been altered by subsequent geological events. Layers will differ from each other in texture, mineralogy and particle size. 

China clay or Kaolin (from the Chinese "kao-ling," hill) is a hydrated aluminium silicate crystalline mineral (kaolinite) formed over many millions of years by the hydrothermal decomposition of granite rocks. Hydrous kaolin is characterized by its fine particle size, plate like or lamellar particle shape and chemical inertness. There are many production sites in China and in... 

Aluminium is not found free but its compounds are so widespread that it is the most abundant metal in the earth s crust. Aluminosilicates such as clay, kaolin (or china clay), mica and feldspar are well known and widely distributed. The oxide. AI2O3. occurs (anhydrous) as corundum and emery, and (hydrated) as bauxite. Cryolite. Na,AlF. (sodium hexafluoroaluminate). is found extensively in Greenland. 

Many inert pigments (often known as fillers) are incorporated into paper in addition to the cellulosic fibres. They may be added to improve certain optical properties—in particular opacity and brightness—or simply as a cheap replacement for costly fibre. The two most common pigments are kaolin (china clay) and chalk (limestone), but talc and speciality pigments such as titanium dioxide are also used. The particle size for general purpose fillers is normally expressed as an equivalent spherical diameter (esd) and this is determined from sedimentation data. Values for the common paper-... 

Silicates Many complex aluminosilicates or silicoaluminates are found in nature. Of these, clay in more or less pure fomi, pure day, kaolintte, kaolin, china clay TLSvA102G or Al203.2,Si02.2TT20 is of great importance. Clay is formed by the weathering of igneous rocks, and is used in the manufacture of bricks, pottery, procelain, and Portland cement. 

CHINA CLAY. A commercial term, more or less identical with kaolin, as applied lo the relatively pure clay concentrated by washing from a thoroughly kaolini/cd granite. England is the chief exporter of china clay. France has unique clays from which arc made Ihe famous Sevres and Limoges potteries. 

China-clay rack is a kaolinized granite made up chiefly of quartz and kaolin, with sometimes tire presence of muscovite and tourmaline. The rock crumbles easily in the lingers. China stone is 11) a partially kaolinized granite, which contains quartz, kaolin, and sometimes mica and fluorite, is harder than china-clay rock and is used as a glaze in the production ol china or (2i a fine-grained, compact mudstone or limestone found in England and Wales... 

Kaolin or China Clay - a white powder hydrated aluminium silicate with good absorbent properties suitable for greasy complexions prone to acne. 

Kaolin or china clay (RI 1.56) is hydrated aluminum silicates of very fine colloidal dimensions in the natural state. Clays are used in the paints because of their extremely good dispersibility in water-based systems, good suspension properties, and good brushability and opacity. However, they have poor weather resistance. 

The Chemical Dictionary defines porcelain as "ceramic wear made largely of baked clay (kaolin) coated or glazed with a fusible substance." Kaolin is defined as "(china clay white bole argilla porcelain clay white clay). A whiteburning clay, which, due to its great purity, has a high fusion point and is the most refractory of all clays." It gives the composition as "mainly kaolinite (40% alumina, 55% silica) plus impurities and water."... 

Major components of the pressed powder blusher include the powder phase and binder (or oil) phase. Components of the powder phase include mineral powder fillers such as talc (a magnesium silicate), mica (a magnesium ahuninum silicate), sericite (a form of hydrated mica), and kaolin (known as China clay). Talc is the most popular of all fillers used, as it tends to be virtually transparent depending on the particle size, and it is very soft to the touch. Although mica is also used extensively as a result of its transparency and smooth texture, it often exhibits a shiny appearance with skin application and has poor compression characteristics when used in a pressed powder. Modern non-oil control formulations rarely contain kaolin, as it tends to exhibit course texture, an extremely matte appearance, and excessive oil-absorption capabilities. Dry binders are also used to allow tlie compressed powder to retain form these include metallic soaps such as zinc stearate and magnesium stearate and... 

Kaolin A fine clay (China clay essentially a hydrated aluminum silicate). Common usages include porcelain, ceramics, heat-resistant mortar, clarifying liquids, drying and emollient agents, and as filler or coating for paper and textiles. 

Filtering Media.—Filter cloths soon become coated with a thin, slimy film of the suspended matters, which completely stops filtration, so that various substances have been tried with the object of obtaining a dry, firm cake in the filter press. Bagasse has been used, but has a tendency to give the juice a gummy consistency. Peat, lignite, kaolin, or China clay and diatomite, have aU found more or less application for this purpose. Sand filters of various forms are also used. In Hawaii wood fibre called Excelsior has proved satisfactory. 

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