Separation by Electrical Methods
Separation by Electrical Methods
the separation of loose fine-grained or pulverized minerals or materials—for example, abrasives or tailings—in the electric field of a separator. In separation by electrical methods, particles acquire different electric charges and are sorted into bins. The charge acquired by a particle depends on, for example, the particle’s electrical properties, chemical composition, size, and density.
The following types of electrical methods of separation are distinguished: electrostatic, corona-discharge, triboadhesive, fluidized-bed electrostatic, and combined.
Electrostatic methods make use of either the pyroelectric effect or differences in electrical conductivity, electrification by friction, or dielectric constants. In separation according to electrical conductivity, particles that are good conductors make contact with an electrode, acquire the same kind of charge, and are repelled from the electrode, while other particles remain virtually neutral. In frictional electrostatic methods, particles become charged when they are sprayed into a separator and collide with the surface of the apparatus, so that friction develops; dissimilar particles acquire equal but opposite charges. In pyroelectric separation, a heated mixture is cooled when it makes contact with an electrode in the form of a cold drum. Some components of the mixture become polarized, while the other components remain neutral. The dielectric separation of mineral mixtures is based on differences in the trajectories of particles with different dielectric constants in an inhomogeneous electric field.
In corona-discharge separation, a corona discharge is produced in the air between an electrode in the form of a point and a ground electrode in the form of a drum. In this case, conducting particles discharge to the ground electrode.
Triboadhesive separation is based on the use of two phenomena: polarization by friction and adhesion. The initial materials are separated in drum separators mainly according to the size and chemical composition of the particles.
In fluidized-bed electrostatic separation, particles in a fluidized bed become charged when friction develops either between the particles themselves or between the particles and the walls of the separator. The particles are separated when they pass through electrostatic fields generated by wire electrodes.
An example of a combined method is the corona-discharge electrostatic technique.
Electrostatic, corona-discharge, and triboadhesive separation methods are used both in the USSR and in other countries, for example, the USA, Canada, and Sweden. In electrostatic separators, materials with particle sizes of 1.2 (1.5)-0.05 mm may be concentrated. In corona-discharge separators, materials with particle sizes of up to 8 mm may be concentrated; fractions with particle sizes of 50 micrometers (μm) or less may be separated. In triboadhesive separators, materials with particle sizes of up to 5 mm may be sorted in any range; fractions with particle sizes of 20 (μm or less may be separated. In fluidized-bed electrostatic separators, powders with particle sizes of 100 μm or less may be sorted in any range.
In separation by electrical methods, about 92–98 percent of the useful component is extracted. The content of the useful component in the concentrate is 95–97 percent. The electric power consumption in the separation process is approximately 0.1 kilowatt-hour per ton.
The first attempts to use an electric field for separation were made in the late 19th century. The electrostatic separator was invented in 1901 in the USA. The following types of separators were invented in the USSR: the corona-discharge separator (1936), the triboadhesive separator (1952), the continuous dielectric separator (1961), and the fluidized-bed electrostatic separator (1967). The lot production of electrostatic separators in the USSR was begun in 1971.
REFERENCESOlofinskii, N. F., and V. A. Novikova. Triboadgezionnaia separatsiia. Moscow, 1974.
Volkova, Z. V., G. V. Zhus’, and D. V. Kuz’min. Dielektricheskaia separatsiia razlichnykh polikontsentratov i materialov. Moscow, 1975.
Olofinskii, N. F. Elektricheskie metody obogashcheniia, 4th ed. Moscow, 1977.
Revnivtsev, V. I., and N. F. Olofinskii. Sostoianie iperspektivy razvitiia elektroseparatsii poleznykh iskopaemykh i materialov. Moscow, 1977. (Vsemirnyi elektrotekhnicheskii kongress. Moscow, 1977. Section 4B, paper 58.)
N. F. OLOFINSKII