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Magnesium Chloride

Magnesium Chloride


Magnesium chloride (mag-NEE-zee-um KLOR-ide) is a white crystalline solid that is strongly deliquescent. It absorbs moisture from the air to become the hydrated form, magnesium chloride hexahydrate (MgCl2·6H2O). A deliquescent substance is one that takes on moisture from the air, often to the extent of dissolving in its own water of hydration. Magnesium chloride is an important industrial chemical, used in the production of magnesium, textile and paper manufacture, and cements; in refrigeration and fireproofing; and as a deicing agent.



Magnesium dichloride




Magnesium, chlorine


Inorganic salt; binary salt




95.21 g/mol


714°C (1,320°F)


1,412°C (2,574°F)


Soluble in water; moderately soluble in ethyl alcohol


Magnesium chloride is extracted from seawater or brine, of which it is a component, and from minerals, such as carnallite (KCl·MgCl2·H2O) and bischofite (MgCl2·6H2O). The usual procedure is to treat seawater, brine, or the mineral with lime (CaO), calcined dolomite (CaO·MgO), or caustic soda (sodium hydroxide; NaOH) to make magnesium hydroxide [Mg(OH)2], which is then treated with hydrochloric acid (HCl) to recover magnesium chloride, which is usually obtained as the crystalline hexahydrate. The pure compound is also produced by heating the double salt, magnesium ammonium chloride (MgCl2·NH4Cl·6H2O), which first loses its water of hydration to form the anhydous double salt (MgCl2·NH4Cl). With further heating, the ammonium chloride sublimes, leaving behind pure anhydrous magnesium chloride.


The largest single use of magnesium chloride is in the production of magnesium metal. The metal is obtained through the electrolysis of molten magnesium chloride in a process developed by the American chemist and inventor Herbert Henry Dow (1866–1930) in 1916. The Dow process is still the primary method used for the production of magnesium metal. Other commercial and industrial uses of magnesium chloride include:

  • In the manufacture of disinfectants;
  • In the fireproofing of steel beams, wooden panels, and other materials;
  • As a component of fire extinguishers;
  • In the manufacture of so-called Sorel cement, a mixture of magnesium chloride and magnesium oxide, also known as oxychloride cement;
  • As a binder to control dust on dirt roads;
  • As a deicing compound;
  • To remove suspended particles in water and sewage treatment plants;
  • For the treatment of cotton and wool fabrics;
  • In the processing of sugar beets;
  • To keep drilling tools cool; and
  • In the manufacture of paper and ceramic materials.

Interesting Facts

  • Tofu is traditionally prepared by treating soy milk with magnesium chloride or calcium sulfate.

Words to Know

A compound that lacks any water of hydration.
Describing a substance that takes on moisture from the air, often to the extent of dissolving in its own water of hydration.
A chemical compound formed when one or more molecules of water is added physically to the molecule of some other substance.
The process by which a solid changes directly into a gas without first melting.
Water that has combined with a compound by some physical means.

Magnesium chloride is a skin, nose, and eye irritant, although that hazard is usually a matter of concern only to those who work with the pure compound. It is also toxic by ingestion. Swallowing the compound can produce nausea, vomiting, and diarrhea. Inhalation of magnesium chloride fumes can irritate the lungs and respiratory tract, producing a condition known as metal fume fever that resembles the flu.


"Magnesium Chloride." (accessed on October 14, 2005).

"Magnesium Chloride." J. T. Baker. (accessed on October 14, 2005).

See AlsoMagnesium Hydroxide

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