Kaolin products

EPK Kaolin Product Information Sheet, Zemex Industrial Minerals, Atlanta, GA, 2002. 

Calcination is used to produce value-added kaolin products. Commonly, there are two families of calcined kaolin. One is metakaolin, which is produced by heating... 

Kaolin or china clay, like many minerals, is used much more widely outside the plastics industry than within it, especially in the paper industry but also to a lesser extent in paint, rubber and pharmaceuticals. It is currently used to improve the electrical properties of PVC wire and cable insulation. Other applications are in automotive parts and as an antiblocking agent in plastic films. It can benefit thixotropy, and calcined kaolin can improve dimensional stability. (Calcined kaolin is also competing with silica in the antiblocking agent market.) Polarite 102A from Imerys is an example of a premium kaolin product, targeted at polyamide automotive applications. 

Case study IQAotgoo et al., 2008) The Upper Tagus Natural Park is one of the largest and most valuable protected areas in Spain (Guadalajara Province). In this area, a spatial coincidence of extraordinary natural resources takes place. On the one hand, exceptional kaolin deposits occur within sediments of the Upper Cretaceous strata (Utrillas Formation). 30% of the kaolin production of Spain comes frxrm this area, mining being the second economic activity here (13.5% of the local employment). On the other hand, this portion of land supports unique bio and geodiversity in Spain, with distinctive aquatic... 

The main commercial source of mica is pegmatite rock, where large books of mica can be hand separated from feldspar and quartz. Finer flake size mica is mechanically separated from deposits of schist where quartz is the main co-mineral. Large tonnages of mica are generated as a by-product of kaolin production and some of this fine particle size mica is separated by froth flotation. Another commercially important source is as a by-product from apatite (calcium phosphate) mining. 

Bird Machine applied for a patent early in 1946 on kaolin production [6]. in which decanters were included merely as items in a flowsheet, as processing tools not otherwise described, while a patent granted in 1947. but which had been filed in 1940 [7], showed a similar use in the cement industry, for classification by size. A December 1949 application by Milliken and Topping (also for Bird Machine) shows a three-section bowl, ready for solid washing on... 

According to Heaton (1928) Devonshire clay was a then-current alternate term for china clay (kaolin, q.v.). Most kaolin production in the UK comes from Cornwall, where there are extensive deposits in the western half of the St Anstell granite. However, commercially exploitable deposits also occur in nearby granites such as diose on Dartmoor in Devon as well as other granite masses of south-west England. 

Descriptive classifications of kaolin products are many and in eertain cases specific to particular markets. The most common designations are as follows. 

One more obvious example illustrates strong influence of particle s sedimentation upon the sensitivity threshold. Assume that we have to ensure the detection of the cracks with the depth 10 > 2 mm in the case when the same product family indicated above is applied and h = 20 pm. The calculation using formula (1) shows that in the absence of sedimentation only the cracks with the width H > 2 pm could be detected. But when the effect of sedimentation results in the reduction of the value of developer layer thickness from h = 20 pm to h = 8 pm, then the cracks of substantially smaller width H > 0,17 pm can be revealed at the same length lo = 2 mm. Therefore we can state that due to the sedimentation of developer s particles the sensitivity threshold has changed being 12 times smaller. Similar results were obtained using formula (2) for larger particles of the developers such as kaolin powder. 

Fig. 16. Two-hquid flotation flow sheet (39). The original ROM is kaolin (white clay) that contains 11% impurity in the form of mica, anatase, and siUca. Treatment produces high purity kaolin and a Ti02-rich fraction. A, Kaolin stockpile D, dispersant (sodium siUcate plus alkah) W, water K, kerosene C, collector (sodium oleate) RK, recycled kerosene S, screen M, inline mixer SPR, separator CFG, centrifuge P, product and T, to waste.

C or higher for the kaolin-based products to 1425°C and above for the zirconium-containing materials. At temperatures above 1000°C these ceramic fibers tend to devitrify and partially crystallize. Specially prepared ceramic fibers are used to protect space vehicles on re-entry and can withstand temperatures above 1250°C (see Ablative materials Refractory fibers). 

A process has been developed by J. M. Huber Co. to treat kaolin clay pigments using a hydrothermal process (see Clays) (25). The products, called synthetic alkah metal aluminosihcates (SAMS), have superior pigmentary quahties for paper (qv) coating. 

The main by-products of mica processiag plants are kaolin, quart2, and feldspar. Some plants produce all of these products for sale. 

The 2eohtes are prepared as essentially bindedess preformed particles. The kaolin is shaped in the desired form of the finished product and is converted in situ in the pellet by treatment with suitable alkaU hydroxide solutions. Preformed pellets of 2eohte A are prepared by this method. These pellets may be converted by ion exchange to other forms such as molecular sieve Type 5A (1). ZeoHtes of higher Si02/Al202 ratios, eg, 2eohte Y, can be obtained by the same method, when sodium metasiUcate is incorporated in the preshaped pellets, or when acid-leached metakaolin is used. 

Both the Toth and Alcoa processes provide aluminum chloride for subsequent reduction to aluminum. Pilot-plant tests of these processes have shown difficulties exist in producing aluminum chloride of the purity needed. In the Toth process for the production of aluminum chloride, kaolin [1332-58-7] clay is used as the source of alumina (5). The clay is mixed with sulfur and carbon, and the mixture is ground together, pelletized, and calcined at 700°C. The calcined mixture is chlorinated at 800°C and gaseous aluminum chloride is evolved. The clay used contains considerable amounts of silica, titania, and iron oxides, which chlorinate and must be separated. Silicon tetrachloride and titanium tetrachloride are separated by distillation. Resublimation of aluminum chloride is requited to reduce contamination from iron chloride. 

In the United States, aluminum sulfate is usually produced by the reaction of bauxite or clay (qv) with sulfuric acid (see Sulfuric acid and sulfur trioxide). Bauxite is imported and more expensive than local clay, generally kaolin, which is more often used. Clay is first roasted to remove organics and break down the crystalline stmcture in order to make it more reactive. This is an energy intensive process. The purity of the starting clay or bauxite ore, especially the iron and potassium contents, are reflected in the assay of the final product. Thus the selection of the raw material is governed by the overall economics of producing a satisfying product. 

Fireclay Refractories. These products are made from clay minerals containing ca 17—45% AI2O2. Pure kaolin has the highest alumina content. 

In electrical porcelains (often called steatite bodies), high purity talc products with low levels of alkali metals ate preferred. A typical steatite is made from 85% talc, 10% plastic kaolin, and 5% BaCO. Steatites ate used as insulators on high voltage equipment such as automotive starters, microwave oven generators, and laser generators. 

Adhesives. Clays, especially kaolin and attapulgite, are widely used in various adhesive formulations. Adhesives (qv) containing clays can be derived from natural products such as starch or protein, or be whoUy synthetic, eg, latex, hot melt, emulsion, etc. 

Chemical Raw Material. In addition to use as a catalyst raw material, clays are used or have been extensively studied as chemical raw material. For example, kaolin has been investigated as a raw material for aluminum metal production. Kaolin has a 38 to 40% alumina content and is available in the United States in large quantities whereas the higher alumina bauxite reserves are very limited. The Bureau of Mines has actively carried out research in the aluminum from ka olin area for many years. Activity increases whenever imports of bauxite are threatened by war or other trade intermptions (1,22,23). 

In the United States, kaolin is the principal clay product and about 9 million metric tons were reported mined and processed during 1991 (25). Bentonite production was reported as being 2 million tons for the same year. World production data for clays, often as a function of geographical location, use, or specific producer, are available (26). 

Additions of new flocculants after conventional thickening produce further dewatering of mineral slimes. A clay flocculated with polyacrylamides and rotated in a dmm can produce a growth of compact kaolin pellets (84), which can easily be wet-screened and dewatered. A device called a Dehydmm, which flocculates and pelletizes thickened sludges into round, 3-mm pellets, was developed for this purpose. Several units reported in commercial operation in Japan thicken fine refuse from coal-preparation plants. The product contains 50% moisture, compared with 3% soflds fed into the Dehydmm from the thickener underflow (85). In Poland, commercial use of the process to treat coal fines has been reported (86), and is said to compare favorably both economically and technically to thickening and vacuum filtration. 

Making paper without pollution requires that each part of the process be nonpolluting. The chemicals most commonly used in the production of pulp are NaOH and Na2 S. In modem paper mills, sulfur-containing by-products are scmbbed from the plant exhaust, and the aqueous sodium hydroxide is reclaimed and recycled. The fillers used to make paper opaque—titanium dioxide, calcium carbonate, and kaolin (a clay)—are natural, nonpolluting minerals. The polymer binders and sizers are relatively easy to recapture from the aqueous waste stream. 

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