Magnetic separation

Last updated January 24, 2024

Magnetic separation is the process of separating components of mixtures by using a magnet to attract magnetic substances.^[1] The process that is used for magnetic separation separates non-magnetic substances from those which are magnetic. This technique is useful for the select few minerals which are ferromagnetic (iron-, nickel-, and cobalt-containing minerals) and paramagnetic.^[2] Most metals, including gold, silver and aluminum, are nonmagnetic.

A large diversity of mechanical means are used to separate magnetic materials.^[2] During magnetic separation, magnets are situated inside two separator drums which bear liquids. Due to the magnets, magnetic particles are being drifted by the movement of the drums. This can create a magnetic concentrate (e.g. an ore concentrate).^[2]

History

Michael Faraday discovered that when a substance is put in a magnetic environment, the intensity of the environment is modified by it.^[3] With this information, he discovered that different materials can be separated with their magnetic properties. The table below shows the common ferromagnetic and paramagnetic minerals as well as the field intensity that is required in order to separate 𝚝𝚑𝚎 minerals.^[3]

Common Ferromagnetic and Paramagnetic Minerals
	Mineral	Formula	Field Strength (kG)
Ferromagnetic	Magnetite	${\ce {Fe3O4}}$	1
Ferromagnetic	Pyrrhotite	${\ce {Fe7S8}}$	0.5 - 4
Paramagnetic	Ilmenite	${\ce {FeTiO3}}$	8 - 16
	Siderite	${\ce {FeCO3}}$	9 - 18
	Chromite	${\ce {FeCr2O4}}$	10 - 16
	Hematite	${\ce {Fe2O3}}$	12 - 18
	Wolframite	${\ce {(Fe,Mn)WO4}}$	12 - 18
	Tourmaline		16 - 20

In the 1860s, magnetic separation started to become commercialized. It was used to separate iron from brass.^[3] After the 1880s, ferromagnetic materials started to be magnetically separated. In the 1900s, high intensity magnetic separation was inaugurated which allowed the separation of pragmatic materials.^[3] After the Second World War, systems that were the most common were electromagnets. The technique was used in scrap yards. Magnetic separation was developed again in the late 1970s with new technologies being inaugurated.^[2] The new forms of magnetic separation included magnetic pulleys, overhead magnets and magnetic drums.

In mines where wolframite was mixed with cassiterite, such as South Crofty and East Pool mine in Cornwall or with bismuth such as at the Shepherd and Murphy mine in Moina, Tasmania, magnetic separation is used to separate the ores. At these mines, a device called a Wetherill's Magnetic Separator (invented by John Price Wetherill, 1844–1906)^[4] was used. In this machine, the raw ore, after calcination was fed onto a conveyor belt which passed underneath two pairs of electromagnets under which further belts ran at right angles to the feed belt. The first pair of balls was weakly magnetized and served to draw off any iron ore present. The second pair were strongly magnetized and attracted the wolframite, which is weakly magnetic.^[4] These machines were capable of treating 10 tons of ore a day.

Common applications

Magnetic separation can also be used in electromagnetic cranes that separate magnetic material from scraps and unwanted substances.^[1] This explains its use for shipment equipments and waste management. Unwanted metals can be removed from goods with this technique. It keeps all materials pure.^[1] Recycling centres use magnetic separation often to separate components from recycling, isolate metals, and purify ores.^[1] Overhead magnets, magnetic pulleys, and the magnetic drums were the methods used in the recycling industry.^[1]

Magnetic separation is also useful in mining iron as it is attracted to a magnet.^[3]

Another application, not widely known but very important, is to use magnets in process industries to remove metal contaminants from product streams.^[1] This takes a lot of importance in food or pharmaceutical industries.

Magnetic separation is also used in situations where pollution needs to be controlled, in chemical processing, as well as during the benefaction of nonferrous low-grade ores.^[1]

Magnetic separation is also used in the following industries: dairy, grain and milling, plastics, food, chemical, oils, textile, and more.

Magnetic cell separation

Magnetic cell separation is on the rise. It is currently being used in clinical therapies, more specifically in cancers and hereditary diseases researches.^[5] Magnetic cell separation took a turn when, Zborowski, an Immunomagnetic Cell Separation (IMCS) pioneer, analyzed commercial magnetic cell separation. Zborowski uncovered crucial revelations that were then used, and are still used today, in the human understanding of cell biology.^[5] Today, the manufacture of therapeutic products concerning cancers and genetic diseases, are being innovated due to these discoveries.^[5]

In microbiology

Magnetic separation techniques are also used in microbiology. In this case, binding molecules and antibodies are used in order to isolate specific viable organisms, nucleic acids, or antigens.^[6] This technology helps isolating bacterial species to identify and give diagnostics of genes targeting certain organisms.^[6] When magnetic separation techniques are combined with PCR (polymerase chain reaction), the results increase in sensitivity and specificity.^[6]

Low-field magnetic separation

Low-field magnetic separation is often in environmental contexts such as water purification and the separation of complex mixtures.^[7] Low magnetic field gradients are field gradients that are smaller than one hundred tesla per meter.^[7] Monodisperse magnetite ( ${\ce {Fe3O4}}$ ) and nanocrystals ( ${\ce {NCs}}$ ) are used for this technique.^[7]

Magnetic filters are fitted on the boiler's pipework to collect magnetite from the circulating water before it has a chance to build up and lower the efficiency of the heating system. The water circulating around the heating system picks up bits of sludge (or magnetite) which can build up. The magnetic filter attracts all these bits of debris with a strong magnet as the water flows around it, preventing a build-up of sludge in the pipework or in the boiler.^[8]

Weak magnetic separation

Weak magnetic separation is used to create cleaner iron-rich products that can be reused.^[9] These products have low levels of impurities and a high iron load. This technique is used as a recycling technology.^[9] It is coupled with steelmaking slag fines as well as a selection of particle size screening.^[9]

Magnetic Separation Force Calculations

It can be shown ^[10] that magnetic force per unit volume on a permeable particle with relative permeability mu sub (pr) is proportional to the spatial gradient of the square of the magnetic flux density. The formula can be used in magnetic finite element analysis software to compute force densities on a wide variety of practical examples, obtaining results agreeing with Oberteuffer's paper [2].

Related Research Articles

<span class="mw-page-title-main">Ferromagnetism</span> Mechanism by which materials form into and are attracted to magnets

Ferromagnetism is a property of certain materials that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagnetic materials are familiar metals that are noticeably attracted to a magnet, a consequence of their substantial magnetic permeability. Magnetic permeability describes the induced magnetization of a material due to the presence of an external magnetic field. This temporarily induced magnetization, for example, inside a steel plate, accounts for its attraction to the permanent magnet. Whether or not that steel plate acquires a permanent magnetization itself depends not only on the strength of the applied field but on the so-called coercivity of the ferromagnetic material, which can vary greatly.

Hematite, also spelled as haematite, is a common iron oxide compound with the formula, Fe₂O₃ and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of Fe^₂O^₃. It has the same crystal structure as corundum (Al^₂O^₃) and ilmenite (FeTiO^₃). With this it forms a complete solid solution at temperatures above 950 °C (1,740 °F).

Magnetism is the class of physical attributes that occur through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, magnetism is one of two aspects of electromagnetism.

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. and attracts or repels other magnets.

An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.

<span class="mw-page-title-main">Iron ore</span> Ore rich in iron or the element Fe

Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe^₃O^₄, 72.4% Fe), hematite (Fe^₂O^₃, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H₂O), 55% Fe) or siderite (FeCO₃, 48.2% Fe).

In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation from a specific source rock during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early years of many gold rushes, including the California Gold Rush. Types of placer deposits include alluvium, eluvium, beach placers, aeolian placers and paleo-placers.

<span class="mw-page-title-main">Iron(III) oxide</span> Chemical compound

Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe₂O₃. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe₃O₄), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe₂O₃ is the main source of iron for the steel industry. Fe₂O₃ is readily attacked by acids. Iron(III) oxide is often called rust, since rust shares several properties and has a similar composition; however, in chemistry, rust is considered an ill-defined material, described as hydrous ferric oxide.

A ferrimagnetic material is a material that has populations of atoms with opposing magnetic moments, as in antiferromagnetism, but these moments are unequal in magnitude so a spontaneous magnetization remains. This can for example occur when the populations consist of different atoms or ions (such as Fe²⁺ and Fe³⁺).

<span class="mw-page-title-main">Magnetite</span> Iron ore mineral

Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe²⁺Fe3+2O₄. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the exception of extremely rare native iron deposits, it is the most magnetic of all the naturally occurring minerals on Earth. Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of magnetism.

In electromagnetism, an eddy current is a loop of electric current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a magnetic field. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced within nearby stationary conductors by a time-varying magnetic field created by an AC electromagnet or transformer, for example, or by relative motion between a magnet and a nearby conductor. The magnitude of the current in a given loop is proportional to the strength of the magnetic field, the area of the loop, and the rate of change of flux, and inversely proportional to the resistivity of the material. When graphed, these circular currents within a piece of metal look vaguely like eddies or whirlpools in a liquid.

Ferrofluid is a liquid that is attracted to the poles of a magnet. It is a colloidal liquid made of nanoscale ferromagnetic or ferrimagnetic particles suspended in a carrier fluid. Each magnetic particle is thoroughly coated with a surfactant to inhibit clumping. Large ferromagnetic particles can be ripped out of the homogeneous colloidal mixture, forming a separate clump of magnetic dust when exposed to strong magnetic fields. The magnetic attraction of tiny nanoparticles is weak enough that the surfactant's Van der Waals force is sufficient to prevent magnetic clumping or agglomeration. Ferrofluids usually do not retain magnetization in the absence of an externally applied field and thus are often classified as "superparamagnets" rather than ferromagnets.

Rock magnetism is the study of the magnetic properties of rocks, sediments and soils. The field arose out of the need in paleomagnetism to understand how rocks record the Earth's magnetic field. This remanence is carried by minerals, particularly certain strongly magnetic minerals like magnetite. An understanding of remanence helps paleomagnetists to develop methods for measuring the ancient magnetic field and correct for effects like sediment compaction and metamorphism. Rock magnetic methods are used to get a more detailed picture of the source of the distinctive striped pattern in marine magnetic anomalies that provides important information on plate tectonics. They are also used to interpret terrestrial magnetic anomalies in magnetic surveys as well as the strong crustal magnetism on Mars.

Mineral processing is the process of separating commercially valuable minerals from their ores in the field of extractive metallurgy. Depending on the processes used in each instance, it is often referred to as ore dressing or ore milling.

Magnetosomes are membranous structures present in magnetotactic bacteria (MTB). They contain iron-rich magnetic particles that are enclosed within a lipid bilayer membrane. Each magnetosome can often contain 15 to 20 magnetite crystals that form a chain which acts like a compass needle to orient magnetotactic bacteria in geomagnetic fields, thereby simplifying their search for their preferred microaerophilic environments. Recent research has shown that magnetosomes are invaginations of the inner membrane and not freestanding vesicles. Magnetite-bearing magnetosomes have also been found in eukaryotic magnetotactic algae, with each cell containing several thousand crystals.

An electrostatic separator is a device for separating particles by mass in a low energy charged beam.

Magnetic nanoparticles are a class of nanoparticle that can be manipulated using magnetic fields. Such particles commonly consist of two components, a magnetic material, often iron, nickel and cobalt, and a chemical component that has functionality. While nanoparticles are smaller than 1 micrometer in diameter, the larger microbeads are 0.5–500 micrometer in diameter. Magnetic nanoparticle clusters that are composed of a number of individual magnetic nanoparticles are known as magnetic nanobeads with a diameter of 50–200 nanometers. Magnetic nanoparticle clusters are a basis for their further magnetic assembly into magnetic nanochains. The magnetic nanoparticles have been the focus of much research recently because they possess attractive properties which could see potential use in catalysis including nanomaterial-based catalysts, biomedicine and tissue specific targeting, magnetically tunable colloidal photonic crystals, microfluidics, magnetic resonance imaging, magnetic particle imaging, data storage, environmental remediation, nanofluids, optical filters, defect sensor, magnetic cooling and cation sensors.

Drakelands Mine, also known as Hemerdon Mine or Hemerdon Ball Mine, is a tungsten and tin mine. It is located 11 km northeast of Plymouth, near Plympton, in Devon, England. It lies to the north of the villages of Sparkwell and Hemerdon, and adjacent to the large china clay pits near Lee Moor. The mine had been out of operation since 1944, except for the brief operation of a trial mine in the 1980s. Work started to re-open it in 2014, but it ceased activities in 2018. It hosts the fourth largest tin-tungsten deposit in the world.

<span class="mw-page-title-main">Iron oxide nanoparticle</span>

Iron oxide nanoparticles are iron oxide particles with diameters between about 1 and 100 nanometers. The two main forms are composed of magnetite and its oxidized form maghemite. They have attracted extensive interest due to their superparamagnetic properties and their potential applications in many fields including molecular imaging.

An eddy current separator (ECS) is a machine that uses a powerful magnetic field to separate non-ferrous metals from an input waste or ore stream. The device makes use of eddy currents to effect the separation. Non-ferrous metals typically separated by an ECS include aluminum, copper and die-cast metals.

References

1 2 3 4 5 6 7 "Magnet traps / metal separator for powder flow - A guide to magnetic separation". Powderprocess.net. Retrieved 2022-04-20.
1 2 3 4 Oberteuffer, J. (1974). "Magnetic separation: A review of principles, devices, and applications". IEEE Transactions on Magnetics. 10 (2): 223–238. Bibcode:1974ITM....10..223O. doi:10.1109/TMAG.1974.1058315.
1 2 3 4 5 Bronkala, William J. (2000-06-15), "Magnetic Separation", Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KGaA, doi:10.1002/14356007.b02_19, ISBN 3527306730
1 2 "Historical Markers - Samuel Wetherill". ExplorePAhistory.com. Retrieved 2012-08-20.
1 2 3 Brown, William H (1995). "Trends in patent renewals at the United States patent and trademark office". World Patent Information. 17 (4): 225–234. doi:10.1016/0172-2190(95)00043-7. ISSN 0172-2190.
1 2 3 Olsvik, O; Popovic, T; Skjerve, E; Cudjoe, K S; Hornes, E; Ugelstad, J; Uhlén, M (1994). "Magnetic separation techniques in diagnostic microbiology". Clinical Microbiology Reviews. 7 (1): 43–54. doi:10.1128/cmr.7.1.43. ISSN 0893-8512. PMC 358305 . PMID 8118790.
1 2 3 Yavuz, C. T.; Mayo, J. T.; Yu, W. W.; Prakash, A.; Falkner, J. C.; Yean, S.; Cong, L.; Shipley, H. J.; Kan, A. (2006-11-10). "Low-Field Magnetic Separation of Monodisperse Fe3O4 Nanocrystals". Science. 314 (5801): 964–967. doi:10.1126/science.1131475. ISSN 0036-8075. PMID 17095696. S2CID 23522459.
↑ What is a magnaclean filter? (page visited on 14 March 2020)
1 2 3 Ma, Naiyang; Houser, Joseph Blake (2014). "Recycling of steelmaking slag fines by weak magnetic separation coupled with selective particle size screening". Journal of Cleaner Production. 82: 221–231. doi:10.1016/j.jclepro.2014.06.092. ISSN 0959-6526.
↑ Brauer, J. R. (2014). Magnetic Actuators and Sensors (2nd ed.). Hoboken NJ: Wiley IEEE Press. ISBN 978-1-118-50525-0.

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[:1-1] 1 2 3 4 5 6 7 "Magnet traps / metal separator for powder flow - A guide to magnetic separation". Powderprocess.net. Retrieved 2022-04-20.

[:2-2] 1 2 3 4 Oberteuffer, J. (1974). "Magnetic separation: A review of principles, devices, and applications". IEEE Transactions on Magnetics. 10 (2): 223–238. Bibcode:1974ITM....10..223O. doi:10.1109/TMAG.1974.1058315.

[:6-3] 1 2 3 4 5 Bronkala, William J. (2000-06-15), "Magnetic Separation", Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KGaA, doi:10.1002/14356007.b02_19, ISBN 3527306730

[:0-4] 1 2 "Historical Markers - Samuel Wetherill". ExplorePAhistory.com. Retrieved 2012-08-20.

[:3-5] 1 2 3 Brown, William H (1995). "Trends in patent renewals at the United States patent and trademark office". World Patent Information. 17 (4): 225–234. doi:10.1016/0172-2190(95)00043-7. ISSN 0172-2190.

[:4-6] 1 2 3 Olsvik, O; Popovic, T; Skjerve, E; Cudjoe, K S; Hornes, E; Ugelstad, J; Uhlén, M (1994). "Magnetic separation techniques in diagnostic microbiology". Clinical Microbiology Reviews. 7 (1): 43–54. doi:10.1128/cmr.7.1.43. ISSN 0893-8512. PMC 358305 . PMID 8118790.

[:5-7] 1 2 3 Yavuz, C. T.; Mayo, J. T.; Yu, W. W.; Prakash, A.; Falkner, J. C.; Yean, S.; Cong, L.; Shipley, H. J.; Kan, A. (2006-11-10). "Low-Field Magnetic Separation of Monodisperse Fe3O4 Nanocrystals". Science. 314 (5801): 964–967. doi:10.1126/science.1131475. ISSN 0036-8075. PMID 17095696. S2CID 23522459.

[8] What is a magnaclean filter? (page visited on 14 March 2020)

[:8-9] 1 2 3 Ma, Naiyang; Houser, Joseph Blake (2014). "Recycling of steelmaking slag fines by weak magnetic separation coupled with selective particle size screening". Journal of Cleaner Production. 82: 221–231. doi:10.1016/j.jclepro.2014.06.092. ISSN 0959-6526.

[:11-10] Brauer, J. R. (2014). Magnetic Actuators and Sensors (2nd ed.). Hoboken NJ: Wiley IEEE Press. ISBN 978-1-118-50525-0.

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