Everything about Magnesium Chloride totally explained
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Magnesium chloride is the name for the
chemical compounds with the
formulas MgCl
2 and its various
hydrates MgCl
2(H
2O)
x. These salts are typical ionic halides, being highly soluble in water. The hydrated magnesium chloride can be extracted from
brine or
sea water.
Anhydrous magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale.
Structure, preparation, basic properties
MgCl
2 crystallizes in the
cadmium chloride motif, which features octahedral Mg. A variety of hydrates are known with the formula MgCl
2(H
2O)
x, and each loses water with increasing temperature: x = 12 (-16.4 °C), 8 (-3.4 °C), 6 (116.7 °C), 4 (181 °C), 2 (ca. 300 °C). In the hexahydrate, the Mg
2+ remains
octahedral, but is coordinated to six water
ligands.
As suggested by the existence of several hydrates, anhydrous MgCl
2 is a
Lewis acid, although a relatively weak one.
In the
Dow process, magnesium chloride is regenerated from magnesium hydroxide using
hydrochloric acid:
» Mg(OH)2(
s) + 2 HCl → MgCl
2(aq) + 2
H2O(
l)
It can also be prepared from
magnesium carbonate by a similar reaction.
In most of its derivatives, MgCl
2 forms octahedral complexes. Derivatives with tetrahedral Mg
2+ are less common. Examples include salts of (
tetraethylammonium)
2MgCl
4 and
adducts such as MgCl
2(
TMEDA.
Applications
Magnesium chloride serves as precursor to other magnesium compounds, for example by precipitation:
» MgCl
2(
aq) +
Ca(OH)2(aq) →
Mg(OH)2(
s) +
CaCl2(aq)
It can be
electrolysed to give
magnesium metal:
» MgCl
2(
l) → Mg(
l) + Cl
2(
g)
This process is practiced on a substantial scale: In 1990, US production was around one million
tonnes, with a bulk price around $180 per tonne.
The thermal dehydration of the hydrates MgCl
2(H
2O)
x (x = 6, 12) doesn't occur straightforwardly.
Magnesium chloride is used for a variety of other applications besides the production of
magnesium: the manufacture of
textiles,
paper,
fireproofing agents,
cements and
refrigeration brine,
and dust and erosion control. Mixed with hydrated magnesium oxide, magnesium chloride forms a hard material called
Sorel cement. Magnesium chloride is also used as an important component in the
polymerase chain reaction, a procedure used to amplify DNA fragments.
Culinary use
Magnesium chloride is an important coagulant used in the preparation of
tofu from
soy milk. In Japan it's sold as
nigari (the term is derived from the Japanese word for "bitter"), a white powder produced from seawater after the
sodium chloride has been removed, and the water evaporated. In China it's called "lushui"(卤水 in Chinese). Nigari or Lushui consists mostly of magnesium chloride, with some
magnesium sulfate and other trace elements. It is also an ingredient in baby formula milk.
Use as an anti-icer
A number of state highway departments throughout the United States have decreased the use of
rock salt and sand on roadways and have increased the use of liquid magnesium chloride as a de-icer or anti-icer. Magnesium chloride is much less toxic to plant life surrounding highways and airports, and is less corrosive to concrete and steel (and other iron alloys) than sodium chloride. The liquid magnesium chloride is sprayed on dry pavement (tarmac) prior to precipitation or wet pavement prior to freezing temperatures in the winter months to prevent snow and ice from adhering and bonding to the roadway. The application of anti-icers is utilized in an effort to improve highway safety. Magnesium chloride is also sold in crystal form for household and business use to de-ice sidewalks and driveways. In these applications, the compound is applied after precipitation has fallen or ice has formed, instead of previously.
The use of this compound seems to show an improvement in driving conditions during and after freezing precipitation yet it seems to be negatively affecting electric utilities. Two main issues have been raised regarding the anti-icer magnesium chloride as it relates to electric utilities: contamination of insulators causing tracking and arcing across them, and corrosion of steel and
aluminium poles and pole hardware.
Use in dust and erosion control
Road departments and private industry may apply liquid or powdered magnesium chloride to control dust and erosion on unimproved (dirt or gravel) roads and dusty job sites such as quarries. Its
hygroscopy makes it absorb moisture from the air, controlling the number of small particles which become airborne. Similarly, owners of indoor arenas (for example for horse riding) may apply magnesium chloride to sand or other floor materials to control dust.
Use in hydrogen storage
Magnesium chloride has shown promise as a storage material for
hydrogen.
Ammonia, which is rich in hydrogen atoms, is used as an intermediate storage material. Ammonia can be effectively absorbed onto solid magnesium chloride, forming Mg(NH
3)
6Cl
2. Ammonia is released by mild heat, and is then passed through a catalyst to give hydrogen gas.
Further Information
Get more info on 'Magnesium Chloride'.
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