Section 26.—CONCENTRATING AND SEPARATING.
Sifting, riddling, and screening are treated of under [Section 72]. For concentrating ores many methods are in use, of which the water processes are the most important.
[475]. Circular revolving concentrating table. The lightest particles are discharged over the edge, and the heaviest remain in the centre.
The ordinary magneting machine, for separating particles of iron or steel from mixed borings, &c., consists of a series of magnets drawn through the material, and then through fixed brushes, which brush off the iron particles adhering to the magnets.
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[476]. Separating dust from grain, &c., by a current of air driven through the stream of material as it falls from hopper to hopper. See also [Nos. 1268], [1270].
[477]. Ore concentrator; consists of an endless rubber belt with flanges (see [No. 1082]), having a slow longitudinal motion, and a rapid shaking motion, either sideways, as in the “Frue Vanner,” or endwise, as in the “Embrey” concentrator; a stream of water runs over the ore, the heavy particles settle on the belt, and the mud is washed off.
[478]. Jig for separating ores by motion of a piston in water, the heavy parts settle to the bottom and the light parts are removed at the top.
Filtration through various substances—as sand, charcoal, calcined ores, &c., is employed to separate suspended matter from liquids.
Separation by subsidence in a tank, similar to [No. 1571], is employed for lime, &c.
Chemical deposition and evaporation are necessary in many cases.