- Also called:
- china clay
kaolin
-
What is kaolin clay?
Kaolin clay is a soft, white clay primarily composed of the mineral kaolinite. Its name comes from Kao-ling, a hill in China where it was mined for centuries.
In its natural state, kaolin is a white, soft powder consisting mainly of the mineral kaolinite. It is widely used in the manufacture of china and porcelain and is widely used in the making of paper, rubber, paint, and many other products. It becomes plastic when mixed with 20 to 35 percent water.
Kaolinite forms in alumina-silica systems lacking alkalies or alkaline earths. Acid hydrothermal solutions also result in its formation.
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Where is kaolin clay commonly found?
Kaolin clay, essential for manufacturing china and porcelain, is named after Kao-ling hill in China, its original mining site. While kaolin is found worldwide, including in France, England, Saxony (Germany), and Bohemia (Czech Republic), the most well-known deposits in the United States are in the southeastern states.
Kaolin is also widespread in Africa. Notably, it can be found in Nigeria's Jos Plateau, as well as in Mali, Ghana, and Guinea. Similar deposits are present in central and East Africa, in addition to Southern Africa.
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What are the main uses of kaolin clay?
Kaolin, named after the hill in China (Kao-ling) from which it was mined, is a soft white clay that has many uses. Around 40% of produced kaolin is used in filling and coating paper to improve body, color, opacity, gloss, and printability.
Kaolin is also used in the ceramic industry for the manufacture of whiteware (china), porcelain, and refractories because of its high fusion temperature and white burning characteristics. It is also used as a filler in rubber to improve its mechanical strength and resistance to abrasion, as well as an extender and flattening agent in paints and adhesives. Furthermore, kaolin is an ingredient in ink, organic plastics, some cosmetics, and other products.
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How is kaolin clay different from other types of clay?
Kaolin clay, essential for producing china and porcelain, differs from other clays due to its purity and composition. In its natural state, kaolin is a soft, white powder primarily composed of the mineral kaolinite, known for its hexagonal, platy crystals.
Other clay minerals include montmorillonite and nontronite. The absence of iron, alkalies, or alkaline earths in kaolinite's molecular structure gives it desirable ceramic properties. This composition makes it suitable for whiteware, porcelain, and refractories, where it's mixed with silica, feldspar, and ball clay to achieve plasticity, shrinkage, and vitrification during firing.
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Why is kaolin clay important in making porcelain and paper?
Kaolin clay is essential to the production of porcelain and paper due to its unique properties.
In porcelain production, kaolin's high fusion temperature and white-burning characteristics make it suitable for creating whiteware. When mixed with silica, feldspar, and ball clay, kaolin provides the necessary plasticity, shrinkage, and vitrification properties for shaping and firing.
In paper manufacturing, kaolin is used as both a filler and a coating. As a filler, it enhances the paper's body, color, opacity, and printability. As a coating, it provides gloss, color, high opacity, and improved printability.
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How is kaolin clay mined and processed for commercial use?
Kaolin clay, named after the Kao-ling hill in China, is essential for manufacturing china and porcelain and is widely used in paper, rubber, paint, and other products.
In its natural state, kaolin is a soft, white powder, primarily consisting of the mineral kaolinite. Crude kaolin contains other minerals like muscovite, quartz, and feldspar and is often stained yellow by iron hydroxide pigments.
To prepare kaolin for commercial use, it is often necessary to bleach the clay chemically to remove the iron pigment and wash it with water to remove other minerals.
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kaolin, soft white clay that is an essential ingredient in the manufacture of china and porcelain and is widely used in the making of paper, rubber, paint, and many other products. Kaolin is named after the hill in China (Kao-ling) from which it was mined for centuries. Samples of kaolin were first sent to Europe by a French Jesuit missionary around 1700 as examples of the materials used by the Chinese in the manufacture of porcelain.
In its natural state kaolin is a white, soft powder consisting principally of the mineral kaolinite, which, under the electron microscope, is seen to consist of roughly hexagonal, platy crystals ranging in size from about 0.1 micrometre to 10 micrometres or even larger. These crystals may take vermicular and booklike forms, and occasionally macroscopic forms approaching millimetre size are found. Kaolin as found in nature usually contains varying amounts of other minerals such as muscovite, quartz, feldspar, and anatase. In addition, crude kaolin is frequently stained yellow by iron hydroxide pigments. It is often necessary to bleach the clay chemically to remove the iron pigment and to wash it with water to remove the other minerals in order to prepare kaolin for commercial use.
When kaolin is mixed with water in the range of 20 to 35 percent, it becomes plastic (i.e., it can be molded under pressure), and the shape is retained after the pressure is removed. With larger percentages of water, the kaolin forms a slurry, or watery suspension. The amount of water required to achieve plasticity and viscosity varies with the size of the kaolinite particles and also with certain chemicals that may be present in the kaolin. Kaolin has been mined in France, England, Saxony (Germany), Bohemia (Czech Republic), and in the United States, where the best-known deposits are in the southeastern states.
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Approximately 40 percent of the kaolin produced is used in the filling and coating of paper. In filling, the kaolin is mixed with the cellulose fibre and forms an integral part of the paper sheet to give it body, colour, opacity, and printability. In coating, the kaolin is plated along with an adhesive on the paper’s surface to give gloss, colour, high opacity, and greater printability. Kaolin used for coating is prepared so that most of the kaolinite particles are less than two micrometres in diameter.
Kaolin is used extensively in the ceramic industry, where its high fusion temperature and white burning characteristics makes it particularly suitable for the manufacture of whiteware (china), porcelain, and refractories. The absence of any iron, alkalies, or alkaline earths in the molecular structure of kaolinite confers upon it these desirable ceramic properties. In the manufacture of whiteware the kaolin is usually mixed with approximately equal amounts of silica and feldspar and a somewhat smaller amount of a plastic light-burning clay known as ball clay. These components are necessary to obtain the proper properties of plasticity, shrinkage, vitrification, etc., for forming and firing the ware. Kaolin is generally used alone in the manufacture of refractories.
Substantial tonnages of kaolin are used for filling rubber to improve its mechanical strength and resistance to abrasion. For this purpose, the clay used must be extremely pure kaolinite and exceedingly fine grained. Kaolin is also used as an extender and flattening agent in paints. It is frequently used in adhesives for paper to control the penetration into the paper. Kaolin is an important ingredient in ink, organic plastics, some cosmetics, and many other products where its very fine particle size, whiteness, chemical inertness, and absorption properties give it particular value.