Magnetic separation, magnetic dressing (de. Magnetscheidung; fr. triage magnetique, separation magnetique, triage d’aimant; it. separacion magnetic) – mineral dressing based on differences in magnetic properties (magnetic susceptibility, remanent induction, coercive force, etc.), components of the separated mechanical mixture (minerals, their joints, etc.) below 150 mm in heterogeneous constant or alternating magnetic field.
Information about the use of magnetic separation for iron-ore dressing appeared in the XVIII century. Sweden was the first country to use magnetic separation in 1892. In 1911 the first magnetic separator appeared in Russia, in the Urals, for magnetite ore dressing. Magnetic separation for coarsely disseminated feebly magnetic ore came into use in the ‘40s, for finely disseminated ore – in the ‘70s of the XX century. The process of magnetic separation of both strongly and feebly magnetic ore consists in the following: mineral grains with greater magnetic susceptibility are attracted to the poles of magnets. Then, with the help of transporting systems, they are fed to receivers of magnetic products, whereas non-magnetic or finely magnetic grains are transported to receivers of non-magnetic products.
In dressing sphere magnetic separation is done primarily in heterogeneous magnetic fields and presents the main method of iron ore dressing (app.70% in the world and 90% in the USSR) and manganese ore dressing (more than 90% in the USSR). In ferrous metal dressing magnetic separation enables to achieve high-grade concentrated product, with Fe up to 68% and Mn to 43%. Separation of magnetic minerals into concentrated products constitutes more than 90%. Magnetic separation is also used for nonferrous metal ores and rare earth ores, mining, chemical, and nonmetallic feed as a finishing operation after gravity dressing and for separation of metal and iron-containing impurities from such materials as kaolin clay, moulding sand, etc.
According to magnetic susceptibility, magnetic separation is classified into feebly and strongly magnetic. According to the conditions separation takes place in, it is divided into wet and dry magnetic separation.
Thermal processing (magnetizing roasting) is used in oxidizing atmosphere (siderite, carbonate, and other ore) or reducing atmosphere (oxide ore) to intensify the contrast of magnetic properties of the separated mixture.
Magnetic separation takes place in magnetic separators.
According to physical and chemical properties of the processed material and its size, different types of magnetic separators are used (drum, roll, belt, disc, rotor, etc.). Strongly magnetic materials are primarily separated with drum separators, feebly magnetic materials – with roll and rotor types. The main components of magnetic separators are: a magnetic system, a feeder, a tank (for wet separation), transporting equipment (drums, rolls, and rotors), troughs and chutes for the separated products, a motor, and chassis.
Dry separation on drum separators. Ore (at least 3 mm in size) is fed onto the upper part of the drums. Magnetic fines are attracted to the surface of the drums, whereas non-magnetic and feebly magnetic parts fall from the drum in chutes and go to recleaning separation.
Wet separation. Milled ore as pulp goes under the drum. Further movements of pulp depend on the type of the tank (straight-through, counter-current, or half counter-current). The type of the tank is selected according to the size of the separated material (straight-through – for material 3–6 mm, counter-current – for material not less than 3 mm, half counter-current – for material smaller than 0.15 mm in size).
In rotor separators retained parts leave strong magnetic field as the rotor runs and go into receivers of magnetic products. The magnetic system in drum and rotor separators is fixed.
Magnetic separators are made in different sizes. The capacity of separators depends on the size of the separated material.
The application spheres of magnetic separation and the volume of separation of ore minerals are intensively growing since this way of dressing is highly effective, simple, cheap, and eco-friendly. Rotor separators have led to larger application in base feebly magnetic ore dressing.
Literature
Derkach V.G. Special methods of mineral ore dressing (Специальные методы обогащения полезных ископаемых) , M., 1966;
Karmazin V.V., Karmazin V.I., Binkevich V.A. Magnetic regeneration and separation in ore and coal dressing (Магнитная регенерация и сепарация при обогащении руд и углей), M.,1968;
Karmazin V.V., Karmazin V.I., Magnetic methods of separation (Магнитные методы обогащения), M., 1984.
Ostapenko P.E., Iron ore dressing, M., 1977;
Горная энциклопедия. — М.: Советская энциклопедия. Под редакцией Е. А. Козловского. 1984–1991.