Clay mine
Clay is defined as a natural, earthy, fine-grained material, largely of a group of crystalline hydrous silicate minerals known as clay minerals. Clay minerals are composed mainly of silica, alumina, and water, but they may also contain appreciable quantities of iron, alkalies, and alkaline earths. Clay is formed by the mechanical and chemical breakdown of rocks.
Open-pit methods
Most domestic clay is mined by open-pit methods using various types of equipment, including draglines, power shovels, front-end loaders, backhoes, scraper-loaders, and shale planers. In addition, some kaolin is extracted by hydraulic mining and dredging. Most underground clay mines are located in Pennsylvania, Ohio, and West Virginia, where the clays are associated with coal deposits. A higher percentage of fire clay is mined underground than other clays, because the higher quality fire clay deposits are found at depths that make open-pit mining less profitable.
Clays usually are transported by truck from the mine to the processing plants, many of which are located at or near the mine. For most applications, clays are processed by mechanical methods, such as crushing, grinding, and screening, that do not appreciably alter the chemical or mineralogical properties of the material. However, because clays are used in such a wide range of applications, it is often necessary to use other mechanical and chemical processes, such as drying, calcining, bleaching, blunging, and extruding to prepare the material for use.
Clays crushing Process
Primary crushing reduces material size from as much as one meter to a few centimeters in diameter and typically is accomplished using jaw or gyratory crushers. Rotating pan crushers, cone crushers, smooth roll crushers, toothed roll crushers, and hammer mills are used for secondary crushing, which further reduces particle size to 3 mm (0.1 in.) or less. For some applications, tertiary size reduction is necessary and is accomplished by means of ball, rod, or pebble mills, which are often combined with air separators. Screening typically is carried out by means of two or more multi-deck sloping screens that are mechanically or electromagnetically vibrated. Pug mills are used for blunging, and rotary, fluid bed, and vibrating grate dryers are used for drying clay materials. At most plants that calcine clay, rotary or flash calciners are used. However, multiple hearth furnaces often are used to calcine kaolin.
Material losses through basic mechanical processing generally are insignificant. However, material losses for processes such as washing and sizing can reach 30 to 40 percent. The most significant processing losses occur in the processing of kaolin and fuller’s earth.
Relative Solutions
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