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Extraction and Processing
Talc is produced by conventional selective opencast mining or by underground mining followed by crushing, grinding, beneficiation, and classification. After the crude rock is crushed, it is often subjected to a manual selection process, although automated techniques are now being introduced. It is then ground in a variety of ball mills, hammer mills, and fluid mills with air classification systems included in a closed-loop system to produce products with a range of particle-size distributions but with the majority having top cuts of 100, 200, and 300 mesh, 20 and 10 pm.
Some talcs may also be subjected to beneficiation by froth flotation. In this case, the talc is ground and dispersed in water, before being subjected to froth flotation using the appropriate surfactant to achieve a separation. The talc may then be subjected to grinding, classification, or both to achieve the desired particle-size distribution.
Properties of Talc
Pure talc is the softest known mineral with a hardness of 1 on the Mohs’ hardness scale; its specific gravity is 2.8, and it has three indices of refraction, 1.539, 1.589, and 1.589, according to crystal direction.
Pure talc has a trioctahedral crystal structure in which an octahedral brucite [Mg (OH)2] sheet is sandwiched between two tetrahedral siloxane S2O5 sheets. This structure is electrically neutral and will bond to an adjacent layer only through van der Waals forces. Thus, talc undergoes cleavage very readily, is very soft, and has a soapy feel. Faces of the layers consist of oxygen atoms, and reactive hydroxyl groups are only found at broken edges, and so talc is fairly hydrophobic.
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