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ore dressing[′ȯr ‚dres·iŋ]
Treatment of ores to concentrate their valuable constituents (minerals) into products (concentrate) of smaller bulk, and simultaneously to collect the worthless material (gangue) into discardable waste (tailing). The fundamental operations of ore-dressing processes are the breaking apart of the associated constituents of the ore by mechanical means (severance) and the separation of the severed components (beneficia-tion) into concentrate and tailing, using mechanical or physical methods which do not effect substantial chemical changes.
Comminution is a single- or multistage process whereby ore is reduced from run-of-mine size to that size needed by the beneficiation process. The process is intended to produce individual particles which are either wholly mineral or wholly gangue, that is, to produce liberation. Since the mechanical forces producing fracture are not susceptible to detailed control, a class of particles containing both mineral and gangue (middling particles) are also produced. Comminution is divided into crushing (down to 6- to 14-mesh) and grinding (down to micrometer sizes).
Screening is a method of sizing whereby graded products are produced, the individual particles in each grade being of nearly the same size. In beneficiation, screening is practiced for two reasons: as an integral part of the separation process, for example, in jigging; and to produce a feed of such size and size range as is compatible with the applicability of the separation process. See Screening
Beneficiation consists of two fundamental operations: the determination that an individual particle is either a mineral or a gangue particle (selection); and the movement of selected particles via different paths (separation) into the concentrate and tailing products. When middling particles occur, they will either be selected according to their mineral content and then caused to report as concentrate or tailing, or be separated as a third product (middling), which is reground to achieve further liberation. See Flotation, Leaching, Mechanical separation techniques
Separation is achieved by subjecting each particle of the mixture to a set of forces which is usually the same irrespective of the nature of the particles excepting for the force based upon the discriminating property. This force may be present for both mineral and gangue particles but differing in magnitude, or it may be present for one type of particle and absent for the other. As a result of this difference, separation is possible, and the particles are collected in the form of concentrate or tailing.
Magnetic separation utilizes the force exerted by a magnetic field upon magnetic materials to counteract partially or wholly the effect of gravity. Thus under the action of these two forces, different paths are produced for the magnetic and nonmagnetic particles. See Magnetic separation methods