Magnetic separation

Last updated October 28, 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 those 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. Among others, Thomas Edison tried to commercialize the magnetic enrichment of poor iron ores but failed. 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. N52 magnets are used in magnetic separation for food processing, recycling, and manufacturing.^[5] They improve food safety, enhance recycling quality, and protect equipment in manufacturing, ensuring efficiency and high standards across these industries.^[6]^[7]

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.^[8] 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.^[8] Today, the manufacture of therapeutic products concerning cancers and genetic diseases, are being innovated due to these discoveries.^[8]

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.^[9] This technology helps isolating bacterial species to identify and give diagnostics of genes targeting certain organisms.^[9] When magnetic separation techniques are combined with PCR (polymerase chain reaction), the results increase in sensitivity and specificity.^[9]

Low-field magnetic separation

Low-field magnetic separation is often in environmental contexts such as water purification and the separation of complex mixtures.^[10] Low magnetic field gradients are field gradients that are smaller than one hundred tesla per meter.^[10] Monodisperse magnetite ( ${\ce {Fe3O4}}$ ) and nanocrystals ( ${\ce {NCs}}$ ) are used for this technique.^[10]

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.^[11]

Weak magnetic separation

Weak magnetic separation is used to create cleaner iron-rich products that can be reused.^[12] These products have low levels of impurities and a high iron load. This technique is used as a recycling technology.^[12] It is coupled with steelmaking slag fines as well as a selection of particle size screening.^[12]

Magnetic Separation Force Calculations

It can be shown ^[13] 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.

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 noticeably attracted to a magnet, which is a consequence of their substantial magnetic permeability.

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.

<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 materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism. The phenomenon of antiferromagnetism was first introduced by Lev Landau in 1933.

<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.

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.

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

Iron(II,III) oxide, or black iron oxide, is the chemical compound with formula Fe₃O₄. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe₂O₃) which also occurs naturally as the mineral hematite. It contains both Fe²⁺ and Fe³⁺ ions and is sometimes formulated as FeO ∙ Fe₂O₃. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is ferrimagnetic, but is sometimes incorrectly described as ferromagnetic. Its most extensive use is as a black pigment (see: Mars Black). For this purpose, it is synthesized rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production.

Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. Historically this was first used in the mining industry, where it was one of the great enabling technologies of the 20th century. It has been described as "the single most important operation used for the recovery and upgrading of sulfide ores". The development of froth flotation has improved the recovery of valuable minerals, such as copper- and lead-bearing minerals. Along with mechanized mining, it has allowed the economic recovery of valuable metals from much lower-grade ore than previously possible.

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.

A ferrite is one of a family of iron oxide-containing magnetic ceramic materials. They are ferrimagnetic, meaning they are attracted by magnetic fields and can be magnetized to become permanent magnets. Unlike many ferromagnetic materials, most ferrites are not electrically conductive, making them useful in applications like magnetic cores for transformers to suppress eddy currents.

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

Magnetic nanoparticles (MNPs) 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.

Hemerdon Mine, also known as Hemerdon Ball Mine, Hemerdon Bal Mine and (briefly) previously as Drakelands 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.

A primary mineral is any mineral formed during the original crystallization of the host igneous primary rock and includes the essential mineral(s) used to classify the rock along with any accessory minerals. In ore deposit geology, hypogene processes occur deep below the Earth's surface, and tend to form deposits of primary minerals, as opposed to supergene processes that occur at or near the surface, and tend to form secondary minerals.

The scientific production association ERGA is Russia's largest manufacturer of magnetic systems and industrial equipment based on them. Production and the central office are located in Kaluga. The key activity is the development and production of equipment for mineral processing, air-gravity separation, integrated solutions for the processing of various wastes and the separation of materials according to electrical properties.

<span class="mw-page-title-main">Magnetization roasting technology</span> Method for processing iron ores

Magnetic roasting technology refers to the process of heating materials or ores under specific atmospheric conditions to induce chemical reactions. This process selectively converts weakly magnetic iron minerals such as hematite (Fe₂O₃), siderite (FeCO₃), and limonite (Fe₂O₃·nH₂O) into strongly magnetic magnetite (Fe₃O₄) or maghemite (γ-Fe₂O₃), while the magnetic properties of gangue minerals remain almost unchanged.

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.
↑ Marchio, Cathy (Apr 24, 2024). "N52 Grade Magnet". Stanford Magnets. Retrieved Oct 28, 2024.
↑ Kang, Yi; Shi, Shuo (2022). "Magnetic Nanoseparation Technology for Efficient Control of Microorganisms and Toxins in Foods: A Review". Journal of Agricultural and Food industry. 70: 16050–16068. doi:10.1021/acs.jafc.2c07132.
↑ Xiao, Fangbin; Li, Weiqiang (2022). "Advances in magnetic nanoparticles for the separation of foodborne pathogens: Recognition, separation strategy, and application". Comprehensive Reviews in Food Science and Food Safety. 21 (5): 4478–4504. doi:10.1111/1541-4337.13023.
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.

[5] Marchio, Cathy (Apr 24, 2024). "N52 Grade Magnet". Stanford Magnets. Retrieved Oct 28, 2024.

[6] Kang, Yi; Shi, Shuo (2022). "Magnetic Nanoseparation Technology for Efficient Control of Microorganisms and Toxins in Foods: A Review". Journal of Agricultural and Food industry. 70: 16050–16068. doi:10.1021/acs.jafc.2c07132.

[7] Xiao, Fangbin; Li, Weiqiang (2022). "Advances in magnetic nanoparticles for the separation of foodborne pathogens: Recognition, separation strategy, and application". Comprehensive Reviews in Food Science and Food Safety. 21 (5): 4478–4504. doi:10.1111/1541-4337.13023.

[:3-8] 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.

[:4-9] 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.

[:5-10] 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.

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

[:8-12] 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.

[:11-13] 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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