Magnesium hydroxide

Last updated
Magnesium hydroxide
Hydroxid horecnaty.PNG
IUPAC name
Magnesium hydroxide
Other names
Magnesium dihydroxide
Milk of magnesia
3D model (JSmol)
ECHA InfoCard 100.013.792 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 215-170-3
E number E528 (acidity regulators, ...)
PubChem CID
RTECS number
  • OM3570000
  • InChI=1S/Mg.2H2O/h;2*1H2/q+2;;/p-2 Yes check.svgY
  • InChI=1/Mg.2H2O/h;2*1H2/q+2;;/p-2
  • [Mg+2].[OH-].[OH-]
Molar mass 58.3197 g/mol
AppearanceWhite solid
Odor Odorless
Density 2.3446 g/cm3
Melting point 350 °C (662 °F; 623 K) decomposes
  • 0.00064 g/100 mL (25 °C)
  • 0.004 g/100 mL (100 °C)
22.1·10−6 cm3/mol
1.559 [1]
Hexagonal, hP3 [2]
P3m1 No. 164
a = 0.312 nm, c = 0.473 nm
77.03 J/mol·K
64 J·mol−1·K−1 [3]
−924.7 kJ·mol−1 [3]
−833.7 kJ/mol
A02AA04 ( WHO ) G04BX01 ( WHO )
GHS labelling:
GHS-pictogram-exclam.svg [4]
Warning [4]
H315, H319, H335 [4]
P261, P280, P304+P340, P305+P351+P338, P405, P501 [4]
NFPA 704 (fire diamond)
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
8500 mg/kg (rat, oral)
Safety data sheet (SDS) External MSDS
Related compounds
Other anions
Magnesium oxide
Other cations
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Magnesium hydroxide is the inorganic compound with the chemical formula Mg(OH)2. It occurs in nature as the mineral brucite. It is a white solid with low solubility in water ( Ksp = 5.61×10−12). [5] Magnesium hydroxide is a common component of antacids, such as milk of magnesia.



Treating the solution of different soluble magnesium salts with alkaline water induces the precipitation of the solid hydroxide Mg(OH)2:

Mg2+ + 2OH → Mg(OH)2

As Mg2+
is the second most abundant cation present in seawater after Na+
, it can be economically extracted directly from seawater by alkalinisation as described here above. On an industrial scale, Mg(OH)2 is produced by treating seawater with lime (Ca(OH)2). A volume of 600 m3 (or 160,000 US gallons) of seawater gives about one ton of Mg(OH)2. Ca(OH)2(Ksp = 5.02×10−6) [6] is far more soluble than Mg(OH)2(Ksp = 5.61×10−12) and drastically increases the pH value of seawater from 8.2 to 12.5. The less soluble Mg(OH)
precipitates because of the common ion effect due to the OH
added by the dissolution of Ca(OH)
: [7]

Mg2+ + Ca(OH)2 → Mg(OH)2 + Ca2+


Precursor to MgO

Most Mg(OH)2 that is produced industrially, as well as the small amount that is mined, is converted to fused magnesia (MgO). Magnesia is valuable because it is both a poor electrical conductor and an excellent thermal conductor. [7]


Only a small amount of the magnesium from magnesium hydroxide is usually absorbed by the intestine (unless one is deficient in magnesium). However, magnesium is mainly excreted by the kidneys; so long-term, daily consumption of milk of magnesia by someone suffering from kidney failure could lead in theory to hypermagnesemia. Unabsorbed magnesium is excreted in feces; absorbed magnesium is rapidly excreted in urine. [8]

Bottle used for Phillips' Leche de Magnesia (Milk of Magnesia) in the Amber Museum, Santo Domingo, Dominican Republic Santo Domingo - Museo de Ambar 0669.JPG
Bottle used for Phillips' Leche de Magnesia (Milk of Magnesia) in the Amber Museum, Santo Domingo, Dominican Republic



As an antacid, magnesium hydroxide is dosed at approximately 0.5–1.5 g in adults and works by simple neutralization, in which the hydroxide ions from the Mg(OH)2 combine with acidic H+ ions (or hydronium ions) produced in the form of hydrochloric acid by parietal cells in the stomach, to produce water.


As a laxative, magnesium hydroxide is dosed at 2–5 g, and works in a number of ways. First, Mg2+ is poorly absorbed from the intestinal tract, so it draws water from the surrounding tissue by osmosis. Not only does this increase in water content soften the feces, it also increases the volume of feces in the intestine (intraluminal volume) which naturally stimulates intestinal motility. Furthermore, Mg2+ ions cause the release of cholecystokinin (CCK), which results in intraluminal accumulation of water and electrolytes, and increased intestinal motility. Some sources claim that the hydroxide ions themselves do not play a significant role in the laxative effects of milk of magnesia, as basic solutions (i.e., solutions of hydroxide ions) are not strongly laxative, and non-basic Mg2+ solutions, like MgSO4, are equally strong laxatives, mole for mole. [9]

History of milk of magnesia

On May 4, 1818, American inventor John Callen received a patent (No. X2952) for magnesium hydroxide. [10] In 1829, Sir James Murray used a "condensed solution of fluid magnesia" preparation of his own design [11] to treat the Lord Lieutenant of Ireland, the Marquess of Anglesey, for stomach pain. This was so successful (advertised in Australia and approved by the Royal College of Surgeons in 1838) [12] that he was appointed resident physician to Anglesey and two subsequent Lords Lieutenant, and knighted. His fluid magnesia product was patented two years after his death, in 1873. [13]

The term milk of magnesia was first used by Charles Henry Phillips in 1872 for a suspension of magnesium hydroxide formulated at about 8% w/v. [14] It was sold under the brand name Phillips' Milk of Magnesia for medicinal usage.

Although the name may at some point have been owned by GlaxoSmithKline, USPTO registrations show "Milk of Magnesia" [15] and "Phillips' Milk of Magnesia" [16] have both been assigned to Bayer since 1995. In the UK, the non-brand (generic) name of "Milk of Magnesia" and "Phillips' Milk of Magnesia" is "Cream of Magnesia" (Magnesium Hydroxide Mixture, BP).

As food additive

It is added directly to human food, and is affirmed as generally recognized as safe by the FDA. [17] It is known as E number E528.

Magnesium hydroxide is marketed for medical use as chewable tablets, as capsules, powder, and as liquid suspensions, sometimes flavored. These products are sold as antacids to neutralize stomach acid and relieve indigestion and heartburn. It also is a laxative to alleviate constipation. As a laxative, the osmotic force of the magnesia acts to draw fluids from the body. High doses can lead to diarrhea, and can deplete the body's supply of potassium, sometimes leading to muscle cramps. [18]

Some magnesium hydroxide products sold for antacid use (such as Maalox) are formulated to minimize unwanted laxative effects through the inclusion of aluminum hydroxide, which inhibits the contractions of smooth muscle cells in the gastrointestinal tract, [19] thereby counterbalancing the contractions induced by the osmotic effects of the magnesium hydroxide.

Other niche uses

Magnesium hydroxide is also a component of antiperspirant. [20] Magnesium hydroxide is useful against canker sores (aphthous ulcer) when used topically. [21]

Waste water treatment

Magnesium hydroxide powder is used industrially to neutralize acidic wastewaters. [22] It is also a component of the Biorock method of building artificial reefs. The main advantage of Mg(OH)
over Ca(OH)
, is to impose a lower pH better compatible with that of seawater and sea life: pH 10.5 for Mg(OH)
in place of pH 12.5 with Ca(OH)

Fire retardant

Natural magnesium hydroxide (brucite) is used commercially as a fire retardant. Most industrially used magnesium hydroxide is produced synthetically. [23] Like aluminium hydroxide, solid magnesium hydroxide has smoke suppressing and flame retardant properties. This property is attributable to the endothermic decomposition it undergoes at 332 °C (630 °F):

Mg(OH)2 → MgO + H2O

The heat absorbed by the reaction retards the fire by delaying ignition of the associated substance. The water released dilutes combustible gases. Common uses of magnesium hydroxide as a flame retardant include additives to cable insulation, insulation plastics, roofing, and various flame retardant coatings. [24] [25] [26] [27] [28]


Brucite crystals (mineral form of Mg(OH)2) from the Sverdlovsk Region, Urals, Russia (size: 10.5 x 7.8 x 7.4 cm). Brucite-169935.jpg
Brucite crystals (mineral form of Mg(OH)2) from the Sverdlovsk Region, Urals, Russia (size: 10.5 × 7.8 × 7.4 cm).

Brucite, the mineral form of Mg(OH)2 commonly found in nature also occurs in the 1:2:1 clay minerals amongst others, in chlorite, in which it occupies the interlayer position normally filled by monovalent and divalent cations such as Na+, K+, Mg2+ and Ca2+. As a consequence, chlorite interlayers are cemented by brucite and cannot swell nor shrink.

Brucite, in which some of the Mg2+ cations have been substituted by Al3+ cations, becomes positively charged and constitutes the main basis of layered double hydroxide (LDH). LDH minerals as hydrotalcite are powerful anion sorbents but are relatively rare in nature.

Brucite may also crystallise in cement and concrete in contact with seawater. Indeed, the Mg2+ cation is the second most abundant cation in seawater, just behind Na+ and before Ca2+. Because brucite is a swelling mineral, it causes a local volumetric expansion responsible for tensile stress in concrete. This leads to the formation of cracks and fissures in concrete, accelerating its degradation in seawater.

For the same reason, dolomite cannot be used as construction aggregate for making concrete. The reaction of magnesium carbonate with the free alkali hydroxides present in the cement porewater also leads to the formation of expansive brucite.

MgCO3 + 2 NaOH → Mg(OH)2 + Na2CO3

This reaction, one of the two main alkali–aggregate reaction (AAR) is also known as alkali–carbonate reaction.

See also

Related Research Articles

<span class="mw-page-title-main">Hydroxide</span> Chemical compound

Hydroxide is a diatomic anion with chemical formula OH. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. The corresponding electrically neutral compound HO is the hydroxyl radical. The corresponding covalently bound group –OH of atoms is the hydroxy group. Both the hydroxide ion and hydroxy group are nucleophiles and can act as catalysts in organic chemistry.

<span class="mw-page-title-main">Magnesium</span> Chemical element, symbol Mg and atomic number 12

Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray solid which shares many physical and chemical properties with the other five alkaline earth metals.

<span class="mw-page-title-main">Alkaline earth metal</span> Group of chemical elements

The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.

<span class="mw-page-title-main">Calcium carbonate</span> Chemical compound

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite and is the main component of eggshells, gastropod shells, shellfish skeletons and pearls. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues.

<span class="mw-page-title-main">Brine</span> Concentrated solution of salt in water

Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, brine may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for brining foods) up to about 26% (a typical saturated solution, depending on temperature). Brine forms naturally due to evaporation of ground saline water but it is also generated in the mining of sodium chloride. Brine is used for food processing and cooking (pickling and brining), for de-icing of roads and other structures, and in a number of technological processes. It is also a by-product of many industrial processes, such as desalination, so it requires wastewater treatment for proper disposal or further utilization (fresh water recovery).

<span class="mw-page-title-main">Magnesium oxide</span> Chemical compound naturally occurring as periclase

Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions held together by ionic bonding. Magnesium hydroxide forms in the presence of water (MgO + H2O → Mg(OH)2), but it can be reversed by heating it to remove moisture.

<span class="mw-page-title-main">Aluminium hydroxide</span> Chemical compound

Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric, i.e., it has both basic and acidic properties. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide or alumina (Al2O3), the latter of which is also amphoteric. These compounds together are the major components of the aluminium ore bauxite. Aluminium hydroxide also forms a gelatinous precipitate in water.

<span class="mw-page-title-main">Brucite</span> Magnesium hydroxide mineral

Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites. Brucite is often found in association with serpentine, calcite, aragonite, dolomite, magnesite, hydromagnesite, artinite, talc and chrysotile.

<span class="mw-page-title-main">Magnesium carbonate</span> Chemical compound

Magnesium carbonate, MgCO3, is an inorganic salt that is a colourless or white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals.

<span class="mw-page-title-main">Calcium hydroxide</span> Inorganic compound of formula Ca(OH)2

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 or slaked with water. It has many names including hydrated lime, caustic lime, builders' lime, slaked lime, cal, and pickling lime. Calcium hydroxide is used in many applications, including food preparation, where it has been identified as E number E526. Limewater, also called milk of lime, is the common name for a saturated solution of calcium hydroxide.

<span class="mw-page-title-main">Magnesium chloride</span> Inorganic salt: MgCl2 and its hydrates

Magnesium chloride is the name for the chemical compound with the formula MgCl2. In addition to the anhydrous form, MgCl2 comes in its various hydrates MgCl2·nH2O. These salts are typical ionic halides, being highly soluble in water. The magnesium chloride can be extracted from brine or sea water. In North America, magnesium chloride is produced primarily from Great Salt Lake brine. It is extracted in a similar process from the Dead Sea in the Jordan Valley. Magnesium chloride, as the mineral bischofite, is also extracted out of ancient seabeds, for example, the Zechstein seabed in northwest Europe. This can be explained by high content of magnesium chloride in the primordial ocean. Some magnesium chloride is made from evaporation of seawater. 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.

<span class="mw-page-title-main">Water softening</span> Removing positive ions from hard water

Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also extends the lifetime of plumbing by reducing or eliminating scale build-up in pipes and fittings. Water softening is usually achieved using lime softening or ion-exchange resins but is increasingly being accomplished using nanofiltration or reverse osmosis membranes.

<span class="mw-page-title-main">Hydromagnesite</span>

Hydromagnesite is a hydrated magnesium carbonate mineral with the formula Mg5(CO3)4(OH)2·4H2O.

Sorel cement is a non-hydraulic cement first produced by the French chemist Stanislas Sorel in 1867.

<span class="mw-page-title-main">Fire retardant</span> Substance reducing flammability

A fire retardant is a substance that is used to slow down or stop the spread of fire or reduce its intensity. This is commonly accomplished by chemical reactions that reduce the flammability of fuels or delay their combustion. Fire retardants may also cool the fuel through physical action or endothermic chemical reactions. Fire retardants are available as powder, to be mixed with water, as fire-fighting foams and fire-retardant gels. Fire retardants are also available as coatings or sprays to be applied to an object.

<span class="mw-page-title-main">Layered double hydroxides</span> Class of ionic solids characterized by a layered structure

Layered double hydroxides (LDH) are a class of ionic solids characterized by a layered structure with the generic layer sequence [AcB Z AcB]n, where c represents layers of metal cations, A and B are layers of hydroxide anions, and Z are layers of other anions and neutral molecules. Lateral offsets between the layers may result in longer repeating periods.

<span class="mw-page-title-main">Huntite</span> Carbonate mineral

Huntite is a carbonate mineral with the chemical formula Mg3Ca(CO3)4. Huntite crystallizes in the trigonal system and typically occurs as platy crystals and powdery masses. For most of recorded history its main use was as a white pigment. Today the most common industrial use of huntite is as a natural mixture with hydromagnesite as a flame retardant or fire retardant additive for polymers.

Magnesium salts are available as a medication in a number of formulations. They are used to treat magnesium deficiency, low blood magnesium, eclampsia, and several other conditions. Magnesium is important to health.

<span class="mw-page-title-main">Shell growth in estuaries</span>

Shell growth in estuaries is an aspect of marine biology that has attracted a number of scientific research studies. Many groups of marine organisms produce calcified exoskeletons, commonly known as shells, hard calcium carbonate structures which the organisms rely on for various specialized structural and defensive purposes. The rate at which these shells form is greatly influenced by physical and chemical characteristics of the water in which these organisms live. Estuaries are dynamic habitats which expose their inhabitants to a wide array of rapidly changing physical conditions, exaggerating the differences in physical and chemical properties of the water.

Magnesium hydroxychloride is the traditional term for several chemical compounds of magnesium, chlorine, oxygen, and hydrogen whose general formula xMgO·yMgCl
, for various values of x, y, and z; or, equivalently, Mg
. The simple chemical formula that is often used is MgClOH, which appears in high school subject, for example.Other names for this class are magnesium chloride hydroxide, magnesium oxychloride, and basic magnesium chloride. Some of these compounds are major components of Sorel cement.


  1. Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN   0-07-049439-8
  2. Toshiaki Enoki and Ikuji Tsujikawa (1975). "Magnetic Behaviours of a Random Magnet, NipMg(1-p)(OH)2". J. Phys. Soc. Jpn. 39 (2): 317–323. Bibcode:1975JPSJ...39..317E. doi:10.1143/JPSJ.39.317.
  3. 1 2 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. ISBN   978-0-618-94690-7.
  4. 1 2 3 4 "Magnesium Hydroxide". American Elements . Retrieved May 9, 2019.
  5. Handbook of Chemistry and Physics (76th ed.). CRC Press. 12 March 1996. ISBN   0849305969.
  6. Rumble, John (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–188. ISBN   978-1138561632.
  7. 1 2 Margarete Seeger; Walter Otto; Wilhelm Flick; Friedrich Bickelhaupt; Otto S. Akkerman. "Magnesium Compounds". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_595.pub2.
  8. "The Global Library of Women's Medicine | GLOWM".
  9. Tedesco FJ, DiPiro JT (1985). "Laxative use in constipation". Am. J. Gastroenterol. 80 (4): 303–9. PMID   2984923.
  10. Patent USX2952 - Magnesia, medicated, liquid - Google Patents
  11. Michael Hordern, A World Elsewhere (1993), p. 2.
  12. "Sir James Murray's condensed solution of fluid magnesia". The Sydney Morning Herald . Vol. 21, no. 2928. October 7, 1846. p. 1, column 4.
  13. Ulster History. Sir James Murray – Inventor of Milk of Magnesia. 1788 to 1871 Archived 2011-06-05 at the Wayback Machine , 24 February 2005
  14. When was Phillips' Milk of Magnesia introduced? FAQ,, accessed 4 July 2016
  15. results from the TARR web server: Milk of Magnesia
  16. results from the TARR web server: Phillips' Milk of Magnesia
  17. "Compound Summary for CID 14791 - Magnesium Hydroxide". PubChem.
  18. Magnesium Hydroxide – Revolution Health
  19. Washington, Neena (2 August 1991). Antacids and Anti Reflux Agents. Boca Raton, FL: CRC Press. p. 10. ISBN   0-8493-5444-7.
  20. Milk of Magnesia Makes Good Antiperspirant
  21. Canker sores, 2/1/2009
  22. Aileen Gibson and Michael Maniocha White Paper: The Use Of Magnesium Hydroxide Slurry For Biological Treatment Of Municipal and Industrial Wastewater, August 12, 2004
  23. Rothon, RN (2003). Particulate Filled Polymer Composites. Shrewsbury, UK: Rapra Technology. pp. 53–100.
  24. Hollingbery, LA; Hull TR (2010). "The Thermal Decomposition of Huntite and Hydromagnesite - A Review". Thermochimica Acta. 509 (1–2): 1–11. doi:10.1016/j.tca.2010.06.012.
  25. Hollingbery, LA; Hull TR (2010). "The Fire Retardant Behaviour of Huntite and Hydromagnesite - A Review". Polymer Degradation and Stability. 95 (12): 2213–2225. doi:10.1016/j.polymdegradstab.2010.08.019.
  26. Hollingbery, LA; Hull TR (2012). "The Fire Retardant Effects of Huntite in Natural Mixtures with Hydromagnesite". Polymer Degradation and Stability. 97 (4): 504–512. doi:10.1016/j.polymdegradstab.2012.01.024.
  27. Hollingbery, LA; Hull TR (2012). "The Thermal Decomposition of Natural Mixtures of Huntite and Hydromagnesite". Thermochimica Acta. 528: 45–52. doi:10.1016/j.tca.2011.11.002.
  28. Hull, TR; Witkowski A; Hollingbery LA (2011). "Fire Retardant Action of Mineral Fillers". Polymer Degradation and Stability. 96 (8): 1462–1469. doi:10.1016/j.polymdegradstab.2011.05.006.