Magnetic Separation
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Magnetic separation is the process of separating components of mixtures by using a magnet to attract magnetic substances. 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 Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...
(iron-, nickel-, and cobalt-containing minerals) and
paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, d ...
. Most metals, including gold, silver and aluminum, are nonmagnetic. A large diversity of mechanical means are used to separate magnetic materials. 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 Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 Apr ...
concentrate).


History

Michael Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...
discovered that when a substance is put in a magnetic environment, the intensity of the environment is modified by it. With this information, he discovered that different materials can be separated with their
magnetic properties Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particles ...
. The table below shows the common ferromagnetic and paramagnetic minerals as well as the
field intensity In physics, field strength means the ''magnitude'' of a vector-valued field (e.g., in volts per meter, V/m, for an electric field ''E''). For example, an electromagnetic field results in both electric field strength and magnetic field strength. A ...
that is required in order to separate 𝚝𝚑𝚎 minerals. In the 1860s, magnetic separation started to become commercialized. It was used to separate iron from brass. 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. After the
Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, systems that were the most common were
electromagnet 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 ...
s. The technique was used in scrap yards. Magnetic separation was developed again in the late 1970s with new technologies being inaugurated. The new forms of magnetic separation included magnetic pulleys, overhead magnets and magnetic drums. In mines where
wolframite Wolframite is an iron, manganese, and tungstate mineral with a chemical formula of that is the intermediate between ferberite ( rich) and hübnerite ( rich). Along with scheelite, the wolframite series are the most important tungsten ore minerals ...
was mixed with
cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains t ...
, such as
South Crofty South Crofty is a metalliferous tin and copper mine located in the village of Pool, Cornwall, United Kingdom. An ancient mine, it has seen production for over 400 years, and extends almost two and a half miles across and down and has mine ...
and
East Pool mine East Pool mine (later known as East Pool and Agar mine), was a metalliferous mine in the Camborne and Redruth mining area, just east of the village of Pool in Cornwall, England. Worked from the early 18th century until 1945, first for copper and ...
in
Cornwall Cornwall (; kw, Kernow ) is a historic county and ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Atlantic ...
or with bismuth such as at the Shepherd and Murphy mine in
Moina, Tasmania Moina is a town 45 km inland from Devonport on the north-west coast of Tasmania, Australia. Moina was the site of a brief gold rush in the late nineteenth century and then one of the largest wolfram and bismuth mines in Tasmania. It has ...
, magnetic separation is used to separate the ores. At these mines, a device called a Wetherill's Magnetic Separator (invented by
John Price Wetherill John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Second E ...
, 1844–1906) was used. In this machine, the raw ore, after
calcination Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), genera ...
was fed onto a conveyor belt which passed underneath two pairs of
electromagnet 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 ...
s 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. 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. This explains its use for shipment equipments and
waste management Waste management or waste disposal includes the processes and actions required to manage waste from its inception to its final disposal. This includes the collection, transport, treatment and disposal of waste, together with monitoring ...
. Unwanted metals can be removed from goods with this technique. It keeps all materials pure. Recycling centres use magnetic separation often to separate components from recycling, isolate metals, and purify ores. Overhead magnets, magnetic pulleys, and the magnetic drums were the methods used in the recycling industry. Magnetic separation is also useful in mining
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
as it is attracted to a
magnet 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, ...
. Another application, not widely known but very important, is to use magnets in process industries to remove metal contaminants from product streams. 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 In metallurgy, non-ferrous metals are metals or alloys that do not contain iron (allotropes of iron, ferrite, and so on) in appreciable amounts. Generally more costly than ferrous metals, non-ferrous metals are used because of desirable proper ...
low-grade ores. 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
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
s and
hereditary diseases A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...
researches. 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 Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living and ...
. Today, the manufacture of therapeutic products concerning cancers and genetic diseases, are being innovated due to these discoveries.


In microbiology

Magnetic separation techniques are also used in
microbiology Microbiology () is the scientific study of microorganisms, those being unicellular (single cell), multicellular (cell colony), or acellular (lacking cells). Microbiology encompasses numerous sub-disciplines including virology, bacteriology, prot ...
. In this case, binding molecules and antibodies are used in order to isolate specific viable organisms, nucleic acids, or antigens. This technology helps isolating bacterial species to identify and give diagnostics of genes targeting certain organisms. When magnetic separation techniques are combined with PCR (
polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) t ...
), the results increase in sensitivity and specificity.


Low-field magnetic separation

Low-field magnetic separation is often in environmental contexts such as
water purification Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...
and the separation of complex mixtures. Low magnetic field gradients are field gradients that are smaller than one hundred tesla per meter. Monodisperse magnetite (Fe3O4) and nanocrystals (NCs) are used for this technique. 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.What is a magnaclean filter?
(page visited on 14 March 2020)


Weak magnetic separation

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


Equipments

With today's technology advances, a variety of equipments is available to perform magnetic separation. Grates, plate magnets, magnet housing, basic cartridges,
pulley A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that ...
s, drums, and self-cleaning separators are designed to separate metals with either
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
,
pneumatic Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air. Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A central ...
, or
magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particle ...
conveying systems.


Magnetic Separation Force Calculations

It can be shown Brauer, J. R. (2014). Magnetic Actuators and Sensors (2nd ed.). Hoboken NJ: Wiley IEEE Press. . 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


References

{{Reflist Solid-solid separation Magnetic devices Magnetism