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 , 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 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 or sea water. In North America and South America, it is obtained primarily from Great Salt Lake 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 () 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, magnesium chloride is regenerated from magnesium hydroxide using hydrochloric acid: : It can also be prepared from magnesium carbonate by a similar reaction.

Structure

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

in molten salt.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). : 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, and wind erosion 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 reactions.

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 ...

s, sidewalks, and parking lots. 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 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 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) 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. In Japan it is sold as '' nigari'' ( 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. 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 plants can make them more susceptible to disease caused by infection of the bacterium '' Xanthomonas campestris'', 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

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 ...

s, coralline algae, clams, 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 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. A few cases of oral 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