Magnesium chloride is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

. It forms

hydrates In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

, where ''n'' can range from 1 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in nature, have a variety of practical uses.

Anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale. Hydrated magnesium chloride is the form most readily available.

Production

Magnesium chloride can be extracted from

brine Brine (or briny water) is a high-concentration solution of salt (typically sodium chloride or calcium chloride) in water. In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawat ...

sea water Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximate ...

. In North America and South America, it is obtained primarily from

Great Salt Lake The Great Salt Lake is the largest saltwater lake in the Western Hemisphere and the eighth-largest terminal lake in the world. It lies in the northern part of the U.S. state of Utah and has a substantial impact upon the local climate, partic ...

brine. In the Jordan Valley, it is obtained from the

Dead Sea The Dead Sea (; or ; ), also known by #Names, other names, is a landlocked salt lake bordered by Jordan to the east, the Israeli-occupied West Bank to the west and Israel to the southwest. It lies in the endorheic basin of the Jordan Rift Valle ...

. The mineral

bischofite Bischofite is a hydrous magnesium chloride mineral with formula MgCl2·6H2O. It belongs to halides and is a sea salt concentrate. It contains many macro- and micro-elements vital for human health, in much higher concentrations than can be found ...

() is extracted (by solution mining) out of ancient seabeds, for example, the

Zechstein The Zechstein ( German either from ''mine stone'' or ''tough stone'') is a unit of sedimentary rock layers of Late Permian ( Lopingian) age located in the European Permian Basin which stretches from the east coast of England to northern Poland. T ...

seabed in northwest Europe. Some deposits result from high content of magnesium chloride in the primordial ocean. Some magnesium chloride is made from evaporation of seawater. In the

Dow process The Dow process may refer to: * Dow process (bromine), a method of bromine extraction from brine * Dow process (magnesium), a method of magnesium extraction from brine * Dow process (phenol), a method of phenol production through the hydroly ...

, magnesium chloride is regenerated from magnesium hydroxide using

hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...

: : It can also be prepared from

magnesium carbonate Magnesium carbonate, (archaic name magnesia alba), is an inorganic salt that is a colourless or white solid. Several hydrated and Base (chemistry), basic forms of magnesium carbonate also exist as minerals. Forms The most common magnesium car ...

by a similar reaction.

Structure

crystallizes in the

cadmium chloride Cadmium chloride is a white crystalline compound of cadmium and chloride, with the formula CdCl2. This salt is a hygroscopic solid that is highly soluble in water and slightly soluble in alcohol. The crystal structure of cadmium chloride (describe ...

motif, therefore it loses water upon heating: ''n'' = 12 (−16.4 °C), 8 (−3.4 °C), 6 (116.7 °C), 4 (181 °C), 2 (about 300 °C). In the hexahydrate, the is also

octahedral In geometry, an octahedron (: octahedra or octahedrons) is any polyhedron with eight faces. One special case is the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex. Many types of i ...

, being coordinated to six water

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s. The octahydrate and the dodecahydrate can be crystallized from water below 298K. As verified by

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

, these "higher" hydrates also feature g(H₂O)₆sup>2+ ions. A decahydrate has also been crystallized.

Preparation, general properties

Anhydrous is produced industrially by heating the complex salt named hexamminemagnesium dichloride . The thermal dehydration of the hydrates (''n'' = 6, 12) does not occur straightforwardly. As suggested by the existence of hydrates, anhydrous is a

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any ...

, although a weak one. One derivative is

tetraethylammonium Tetraethylammonium (TEA) is a quaternary ammonium cation with the chemical formula , consisting of four ethyl groups (, denoted Et) attached to a central nitrogen atom. It is a counterion used in the research laboratory to prepare lipophilic salt ...

tetrachloromagnesate . The

adduct In chemistry, an adduct (; alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is ...

is another. In the

coordination polymer Coordination may refer to: * Coordination (linguistics), a compound grammatical construction * Coordination complex, consisting of a central atom or ion and a surrounding array of bound molecules or ions ** A chemical reaction to form a coordinat ...

with the formula , Mg adopts an octahedral geometry. The Lewis acidity of magnesium chloride is reflected in its

deliquescence Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance' ...

, meaning that it attracts moisture from the air to the extent that the solid turns into a liquid.

Applications

Precursor to metallic magnesium

Anhydrous is the main precursor to metallic magnesium. The reduction of into metallic Mg is performed by

electrolysis In chemistry and manufacturing, electrolysis is a technique that uses Direct current, direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of c ...

molten salt Molten salt is salt which is solid at standard temperature and pressure but liquified due to elevated temperature. A salt that is liquid even at standard temperature and pressure is usually called a room-temperature ionic liquid, and molten salts ...

.Hill, Petrucci, McCreary, Perry, ''General Chemistry'', 4th ed., Pearson/Prentice Hall, Upper Saddle River, New Jersey, USA. As it is also the case for

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

, an electrolysis in aqueous solution is not possible as the produced metallic magnesium would immediately react with water, or in other words that the water would be reduced into gaseous before Mg reduction could occur. So, the direct electrolysis of molten in the absence of water is required because the reduction potential to obtain Mg is lower than the stability domain of water on an E_h–pH diagram (

Pourbaix diagram In electrochemistry, and more generally in solution chemistry, a Pourbaix diagram, also known as a potential/pH diagram, EH–pH diagram or a pE/pH diagram, is a plot of possible thermodynamically stable phases (''i.e.'', at chemical equilibrium) ...

). : The production of metallic magnesium at the

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device such as a lead-acid battery. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. Conventional curren ...

(reduction reaction) is accompanied by the oxidation of the chloride anions at the

anode An anode usually is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, which is usually an electrode of the device through which conventional current leaves the devic ...

with release of gaseous

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

. This process is developed at a large industrial scale.

Dust and erosion control

Magnesium chloride is one of many substances used for dust control,

soil stabilization Soil stabilization is a general term for any physical, chemical, mechanical, biological, or combined method of changing a natural soil to meet an engineering purpose. Improvements include increasing the weight-bearing capabilities, tensile streng ...

, and

wind erosion Aeolian processes, also spelled eolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth (or other planets). Winds may erode, transport, and deposit material ...

mitigation. When magnesium chloride is applied to roads and bare soil areas, both positive and negative performance issues occur which are related to many application factors.

Catalysis

Ziegler-Natta catalysts, used commercially to produce

polyolefin A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More speciali ...

s, often contain as a

catalyst support In chemistry, a catalyst support or carrier is a material, usually a solid with a high surface area, to which a catalyst is affixed. The activity of heterogeneous catalysts is mainly promoted by atoms present at the accessible surface of the ma ...

. The introduction of supports increases the activity of traditional catalysts and allowed the development of highly stereospecific catalysts for the production of

polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer Propene, propylene. Polypropylene belongs to the group of polyolefin ...

. Magnesium chloride is also a

catalyst in

aldol reaction The aldol reaction (aldol addition) is a Chemical reaction, reaction in organic chemistry that combines two Carbonyl group, carbonyl compounds (e.g. aldehydes or ketones) to form a new β-hydroxy carbonyl compound. Its simplest form might invol ...

Ice control

Magnesium chloride is used for low-temperature de-icing of

highway A highway is any public or private road or other public way on land. It includes not just major roads, but also other public roads and rights of way. In the United States, it is also used as an equivalent term to controlled-access highway, or ...

sidewalk A sidewalk (North American English), pavement (British English, South African English), or footpath (Hiberno-English, Irish English, Indian English, Australian English, New Zealand English) is a path along the side of a road. Usually constr ...

s, and

parking lot A parking lot or car park (British English), also known as a car lot, is a cleared area intended for parking vehicles. The term usually refers to an area dedicated only for parking, with a durable or semi-durable surface. In most jurisdi ...

s. When highways have dangerous ice buildup, road maintainers apply magnesium chloride to deter ice from bonding to the pavement, allowing

snow Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water througho ...

plows to clear treated roads more efficiently. For the purpose of preventing ice from forming on pavement, magnesium chloride is applied in three ways: anti-icing, which involves spreading it on roads to prevent snow from sticking and forming; prewetting, which means a liquid formulation of magnesium chloride is sprayed directly onto salt as it is being spread onto roadway pavement, wetting the salt so that it sticks to the road; and pretreating, when magnesium chloride and salt are mixed together before they are loaded onto trucks and spread onto paved roads.

Calcium chloride Calcium chloride is an inorganic compound, a Salt (chemistry), salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with cal ...

damages concrete twice as fast as magnesium chloride. The amount of magnesium chloride is supposed to be controlled when it is used for de-icing as it may cause pollution to the environment.

Nutrition and medicine

Magnesium chloride is used in

nutraceutical Nutraceutical is a terminology evolved scientifically & also through marketing which is used to imply a pharmaceutical effect from plant extracts, compounds, food products which have efficacy and therapeutic influence on clinical outcomes and patien ...

and pharmaceutical preparations. The hexahydrate is sometimes advertised as " magnesium oil". Magnesium Chloride is also an

electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...

Cuisine

Magnesium chloride (

E511 Magnesium chloride is an inorganic compound with the formula . It forms hydrates , where ''n'' can range from 1 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which o ...

) is an important coagulant used in the preparation of

tofu or bean curd is a food prepared by Coagulation (milk), coagulating soy milk and then pressing the resulting curds into solid white blocks of varying softness: ''silken'', ''soft'', ''firm'', and ''extra (or super) firm''. It originated in Chin ...

from

soy milk Soy milk (or soymilk), also known as soya milk, is a plant-based milk produced by soaking and grinding soybeans, boiling the mixture, and filtering out remaining particulates. It is a stable emulsion of oil, water, and protein. Its original ...

. In Japan it is sold as ''

nigari Bittern (pl. bitterns), or nigari, is the salt solution formed when halite (table salt) precipitates from seawater or brines. Bitterns contain magnesium, calcium, and potassium ions as well as chloride, sulfate, iodide, and other ions. Bi ...

'' ( にがり, derived from the Japanese word for "bitter"), a white powder produced from

seawater Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximat ...

after the

sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...

has been removed, and the water evaporated. In China, it is called ''lushui'' ( 卤水). Nigari or Iushui is, in fact, natural magnesium chloride, meaning that it is not completely refined (it contains up to 5%

magnesium sulfate Magnesium sulfate or magnesium sulphate is a chemical compound, a salt with the formula , consisting of magnesium cations (20.19% by mass) and sulfate anions . It is a white crystalline solid, soluble in water but not in ethanol. Magnesi ...

and various minerals). The crystals originate from lakes in the Chinese province of

Qinghai Qinghai is an inland Provinces of China, province in Northwestern China. It is the largest provinces of China, province of China (excluding autonomous regions) by area and has the third smallest population. Its capital and largest city is Xin ...

, to be then reworked in Japan.

Gardening and horticulture

Because magnesium is a mobile nutrient, magnesium chloride can be effectively used as a substitute for

(Epsom salt) to help correct magnesium deficiency in plants via

foliar feeding Foliar feeding is a technique of feeding plants by applying liquid fertilizer directly to the leaves. Plants are able to absorb essential elements through their leaves. The absorption takes place through their stomata and also through their epiderm ...

. The recommended dose of magnesium chloride is smaller than the recommended dose of magnesium sulfate (20 g/L). This is due primarily to the chlorine present in magnesium chloride, which can easily reach toxic levels if over-applied or applied too often. It has been found that higher concentrations of magnesium in

tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...

and some

pepper Pepper(s) may refer to: Food and spice * Piperaceae or the pepper family, a large family of flowering plants ** Black pepper ** Long pepper ** Kampot pepper * ''Capsicum'' or pepper, a genus of flowering plants in the nightshade family Solanacea ...

plants can make them more susceptible to disease caused by infection of the bacterium ''

Xanthomonas campestris ''Xanthomonas campestris'' is a gram-negative, obligate aerobic bacterium that is a member of the Xanthomonadaceae, a family of bacteria that are commonly known for their association with plant disease. This species includes ''Xanthomonas campe ...

'', since magnesium is essential for bacterial growth.

Wastewater treatment

It is used to supply the magnesium necessary to precipitate phosphorus in the form of struvite from agricultural waste as well as human urine.

Occurrence

Magnesium concentrations in natural

seawater Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximat ...

are between 1250 and 1350 mg/L, around 3.7% of the total seawater mineral content.

minerals contain a significantly higher magnesium chloride ratio, 50.8%. Carbonates and calcium are essential for all growth of

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

coralline algae Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of re ...

clam Clam is a common name for several kinds of bivalve mollusc. The word is often applied only to those that are deemed edible and live as infauna, spending most of their lives halfway buried in the sand of the sea floor or riverbeds. Clams h ...

s, and

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s. Magnesium can be depleted by

mangrove A mangrove is a shrub or tree that grows mainly in coastal saline water, saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen a ...

plants and the use of excessive

limewater Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime ( calcium oxide) is mixed with water. Annually, approxi ...

or by going beyond natural calcium,

alkalinity Alkalinity (from ) is the capacity of water to resist Freshwater acidification, acidification. It should not be confused with base (chemistry), basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength of a buffer s ...

, and pH values. The most common mineral form of magnesium chloride is its hexahydrate, bischofite. Anhydrous compound occurs very rarely, as chloromagnesite. Magnesium chloride-hydroxides, korshunovskite and nepskoeite, are also very rare.

Toxicology

Magnesium ions are bitter-tasting, and magnesium chloride solutions are bitter in varying degrees, depending on the concentration. Magnesium toxicity from magnesium salts is rare in healthy individuals with a normal diet, because excess magnesium is readily excreted in

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

by the

kidneys In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and right in the retro ...

. A few cases of

oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or ora ...

magnesium toxicity have been described in persons with normal renal function ingesting large amounts of magnesium salts, but it is rare. If a large amount of magnesium chloride is eaten, it will have effects similar to

, causing diarrhea, although the sulfate also contributes to the laxative effect in magnesium sulfate, so the effect from the chloride is not as severe.

Plant toxicity

Chloride () and magnesium () are both essential nutrients important for normal plant growth. Too much of either nutrient may harm a plant, although foliar chloride concentrations are more strongly related with foliar damage than magnesium. High concentrations of ions in the soil may be toxic or change water relationships such that the plant cannot easily accumulate water and nutrients. Once inside the plant, chloride moves through the water-conducting system and accumulates at the margins of leaves or needles, where dieback occurs first. Leaves are weakened or killed, which can lead to the death of the tree.

Notes and references

;Notes ;References * ''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990.

External links

Magnesium Chloride as a De-Icing Agent

MSDS file for Magnesium Chloride Hexahydrate
{{Mineral supplements Chlorides Magnesium compounds Alkaline earth metal halides Deliquescent materials Food additives E-number additives