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Magnetic Separation.pptx
- 3. Magnetic separation is a process in which magnetically susceptible material is extracted from a mixture using a magnetic force. All materials have a response when placed in a magnetic field, although with most, the effect is too slight to be detected. Depending on the response, materials are classified as: 1. Diamagnetic 2. Paramagnetic 3. Ferromagnetic
- 5. How to deal with ferro & para-magnetic: • Ferromagnetics require relatively weak magnetic fields to be attracted and devices to separate these materials usually have magnets that are permanently magnetised (“Permanent” magnets do not require electricity to maintain their magnetic fields). • Paramagnetics require stronger magnetic fields and these can only be achieved and maintained by “electro" magnets (large wire coils around an iron frame - current is continuously passed through the coils creating the magnetic field within the iron. The field is concentrated across an air gap in the circuit).
- 7. Application in Mineral Processing: Magnetic separation has two major applications in mineral processing plants: 1. The removal of tramp iron (which would deleteriously affect subsequent processes) from an ore stream. This is usually achieved by a low intensity magnet suspended above, or at the head of, a conveyor.
- 8. 2. Separation of magnetic minerals from less magnetic minerals.
- 9. Types of magnetic separator: 1. Low intensity: • For ferromagnetic materials • Examples are: 1. Drum separator Dry (for feed size>0.5mm) Wet (for feed size<0.5mm) i. Concurrent type ii. Counter-rotation type 2. Cross belt separator 3. Disc separator 2. High intensity • For paramagnetic materials • Examples 1. Induced roll magnetic separators (IRMs) 2. Wet high-intensity magnetic separator (WHIMs) 3. High Gradient magnetic separator 4. Superconducting separator
- 10. Types
- 14. Induced roll separator For continuous extraction of small magnetic particles from certain minerals to produce mineral purification for a wide range of mineral and ceramic processing industries.
- 15. Application: 1. Recovery of ilmenite, garnet, chromite and monazite into the magnetic fraction and rutile, leucoxene and zircon into the non-magnetic fractions from mineral sands suites 2. Magnetic gangue removal from tin and tungsten ores, glass sands and a variety of industrial mineral products
- 16. Application: To concentrate plutonium and uranium in waste streams and contaminated soils from magnetic particles.
- 17. Superconducting magnet: Eriez Magnetics produces MF of 15T Application: Kaolinite
Editor's Notes
- Concurrent: rotation of drum and feed flow are in the same direction. Produces clean magnetic concentrate, especially in HMS c,rcuit. Relatively for coarse material. Counter current type : Tailings flow in the opposite direction to the rotation, Counter current separator is used in roughing operations and magnetic material losses are held to a minimum. Relatively for fine material < 250 μm.
- Used to concentrate moderately magnetic ores. It consists of two or more horseshoe electromagnets, arranged one above the other. The cross – belts prevent the magnetic particles from adhering to the pole. The poles of the upper magnets are wedge shaped while the lower poles are flat.
- It permits a much smaller air gap than the belt separator and a greater degree of selectivity. It consists of a series of discs, incorporating concentrating grooves, revolving above a conveyor belt, magnetised by induction from a powerful stationary electromagnets situated below the belt. Each disc permits to extract and separate 2-products of different permeability. Progressive intensification of the magnetic field is obtained by vertical adjustment of the discs (gap) The flux is 0,8 – 1,5 T (which is strong enough to pick up many paramagnetic minerals). Explanation: Typically, a Disc Separator will feature up to three high-intensity electromagnetic discs, each set at a different height from a feed conveyor. The first disc will be set the furthest from the feed material, in order to extract only the most magnetically susceptible particles. The second and third discs are set at lower gaps, increasing the magnetic force at each disc and therefore separating different grades of magnetic material. Magnetic intensity can also be further adjusted by varying the current of each coil to suit each clients specific mineral separation requirements. Operation Feed material is discharged from a hopper onto a Vibratory Feeder tray. A thin layer of material is continuously fed between the rotating high-intensity magnetic discs, where magnetic particles are attracted to the high-gradient zones on the discs. These captured particles are then carried by the rotating discs to the discharge chutes where they are released. Scrapers that are mounted on each of the chutes ensure the total discharge of the extracted magnetic particles. Any feed material that is non-magnetic will pass under each of the three discs and discharge at the end of the conveyor.
- To treat beach sands, tin ores, wolframite, glass sands and phoshate rock. Nonmagnetic particles are thrown off the roll into the tailings compartment, whereas magnetics are gripped, carried out of the influence of the field and deposited into the magnetics compartment. The gap between the feed pole and rotor is adjustable and is usually decreased from pole to pole to take off successively more weakly magnetic products. Field strengths of up to 2,2 T are attainable in the gap between the feed pole and roll. The gap between the feed pole rotor is adjustable and is usually decreased from pole to pole to take off successively more weakly magnetic products. Explanation: The roll is placed between specially shaped poles of an electromagnet and the electromagnet induces a magnetic field in the magnetic laminations of a roll forming local regions of high magnetic field gradient. Ferro magnetic material should be removed with a separate magnetic scalper before feeding to IRMS. The gap between the feed pole and rotor is adjustable; and is usually decreased from pole to pole to extract weaker magnetic products.
- Perhaps the most well-known WHIMS machine is the Jones separator, the design principle of which is utilised in many other types of wet separator used today. The machine consists of a strong main frame made of structural steel. The magnet yokes are welded to this frame, with the electromagnetic coils enclosed in air-cooled cases. The actual separation takes place in the plate boxes which are on the periphery of the one or two rotors attached to the central roller shaft. The feed, which is thoroughly mixed slurry, flows through the separator via fitted pipes and launders into the plate boxes , which are grooved to concentrate the magnetic field at the tip of the ridges. Feeding is continuous due to the rotation of the plate boxes on the rotors and the feed points are at the leading edges of the magnetic fields. Each rotor has two symmetrically disposed feed points. The feebly magnetic particles are held by the plates, whereas the remaining non-magnetic slurry passes straight through the plate boxes and is collected in a launder. Before leaving the field any entrained non-magnetics are washed out by low-pressure water and are collected as a middlings product. When the plate boxes reach a point midway between the two magnetic poles, where the magnetic field is essentially zero, the magnetic particles are washed out with high pressure scour water sprays operating at up to 5 bar (Figure 13.14). Field intensities of over 2 T can be produced in these machines. The production of a 1.5 T field requires an electric power consumption in the coils of 16 kW per pole. Of the 4t of water used with every tonne of solids, approximately 90% is recycled.
- Continuing interest in processes that will effect separations in the fine particle size range has prompted intense interest in the use of high gradient magnetic separation (HGMS) for beneficiation of uranium ores. Some of the uranium minerals are paramagnetic and hence are amenable to concentration by HGMS. HGMS is a powerful method in the upgrading of diamagnetic and paramagnetic minerals due to its ability to apply high gradients and high magnetic fields on the particles in the range of one micron to several hundred microns. The process has been studied for the beneficiation of a number of minerals, and other processes as diverse as the separation and purification of blood cells. The extracted particulates are then flushed from the matrix when the magnetic field is turned off. Major components of a HGMS device as shown in Figure 1 are an electromagnetic coil to generate the field, a canister to contain magnetic matrix, an entry for feed slurry, wash water and discharge chutes for the nonmagnetic and magnetic fractions below the canister. The feed slurry can enter the separator either from the top or bottom, whereupon magnetic particles are held in the matrix, allowing non-magnetics to pass through to a discharge chute. When the trapped magnetic particles move out of the field zone, they are released and flushed out using water.
- Special alloys which do not present any resistance to electric current are used at extremely low temperature. e.g., Niobium – tantalum at 4.2 K (the temperature of liquid He) Once a current commences to flow through a coil, which was made of superconducting material, it will continue to flow without being connected to a power source, the coil will become a permanent magnet. Superconducting magnets can produce magnetic fields up to 15 T. Example : Eriez Magnetics (superconducting HGMS) process kaolinite clay in U.S. This machine use only 0,007 kW in producing 5 T; the ancient equipment require 20 kW. Conventional 2 T HGMS needs about 250 kW.