1 Preparation 2 Uses
2.1 Precursor to MgO 2.2 Health
2.2.1 Metabolism 2.2.2 History of milk of magnesia
2.3 Other niche uses
2.3.1 Waste water treatment 2.3.2 Fire retardant
3 Mineralogy 4 References
Preparation Combining a solution of many magnesium salts with alkaline water induces precipitation of solid Mg(OH)2:
Mg2+ + 2 OH− → Mg(OH)2
On a commercial scale, Mg(OH)2 is produced by treating seawater with lime (Ca(OH)2). 600 m3 of seawater gives about one ton of Mg(OH)2. Ca(OH)2 is far more soluble than Mg(OH)2, the latter precipitates as a solid:
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.
When the patient drinks magnesium hydroxide, the suspension enters the
stomach. Depending on how much was taken, one of two possible outcomes
As an antacid, magnesium hydroxide is dosed at approximately
0.5–1.5 g in adults and works by simple neutralization, where
the hydroxide ions from the Mg(OH)2 combine with acidic H+ 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, electrolytes, and
increased intestinal motility. Although it has been stated in some
sources, 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
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 renal failure could lead in theory to hypermagnesemia. Unabsorbed
drug is excreted in feces; absorbed drug is excreted rapidly in urine.
History of milk of magnesia
On May 4, 1818, American inventor John Callen received a patent (No.
X2952) for magnesium hydroxide. In 1829, Sir James Murray used a
"condensed solution of fluid magnesia" preparation of his own
design to treat the Lord Lieutenant of Ireland, the Marquis of
Anglesey, of stomach pain. This was so successful (advertised in
Australia and approved by the Royal College of Surgeons in 1838)
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.
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. 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" and
"Phillips' Milk of Magnesia" 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"
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 (i.e. cables for high quality cars, submarines, the Airbus A380, the Playstation 4, etc.), insulation plastics, roofing (e.g. London Olympic Stadium), and various flame retardant coatings. Other mineral mixtures that are used in similar fire retardant applications are natural mixtures of huntite and hydromagnesite. Mineralogy
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.
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. References
^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002,
^ Toshiaki Enoki and Ikuji Tsujikawa (1975). "Magnetic Behaviours of a
Random Magnet, NipMg(1-p)(OH2)". J. Phys. Soc. Jpn. 39 (2): 317–323.
^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton
Mifflin Company. p. A22. ISBN 0-618-94690-X.
^ Handbook of Chemistry and Physics (76th ed.). CRC Press.
^ a b Margarete Seeger; Walter Otto; Wilhelm Flick; Friedrich
Bickelhaupt; Otto S. Akkerman (2005), "
v t e
MgB2 MgBr2 MgCO3 MgC2O4 MgC6H6O7 MgC14H10O4 MgCl2 Mg(ClO4)2 MgF2 MgH2 Mg(HCO3)2 MgI2 Mg(NO3)2 MgO MgO2 Mg(OH)2 MgPo MgS MgSO3 MgSO4 MgU2O7 Mg2Al3 Mg2Si Mg2SiO4 Mg2Si3O8 Mg3N2 Mg3(PO4)2 Mg2(CrO4)2
v t e
B C NH3.H2O O F Ne
Al(OH)3 Si P S Cl Ar
KOH Ca(OH)2 Sc(OH)3 Ti V Cr(OH)2 Cr(OH)3 Mn(OH)2 Fe(OH)2 Fe(OH)3 Co(OH)2 Ni(OH)2 CuOH Cu(OH)2 Zn(OH)2 Ga(OH)3 Ge(OH)2 As Se Br Kr
RbOH Sr(OH)2 Y(OH)3 Zr(OH)4 Nb Mo Tc Ru Rh Pd AgOH Cd(OH)2 In(OH)3 Sn(OH)2 Sn(OH)4 Sb(OH)3 Te I Xe
CsOH Ba(OH)2 * Hf Ta W Re Os Ir Pt Au(OH)3 Hg(OH)2 TlOH Tl(OH)3 Pb(OH)2 Pb(OH)4 Bi(OH)3 Po At Rn
Fr Ra ** Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
* La(OH)3 Ce(OH)3 Pr(OH)3 Nd(OH)3 Pm(OH)3 Sm(OH)3 Eu(OH)3 Gd(OH)3 Tb(OH)3 Dy(OH)3 Ho(OH)3 Er(OH)3 Tm(OH)3 Yb(OH)3 Lu(OH)3
** Ac Th(OH)4 Pa UO2(OH)2 Np Pu Am Cm(OH)3 Bk Cf Es Fm Md No Lr
v t e
Urologicals, including antispasmodics (G04B)
Urinary antispasmodics (primarily antimuscarinics)
Darifenacin Desfesoterodine Emepronium Fesoterodine Flavoxate Imidafenacin Meladrazine Mirabegron Oxybutynin Propiverine Solifenacin Terodiline Tolterodine Trospium chloride
v t e
Drugs for acid related disorders: Antacids (A02A)
Combinations and complexes of aluminium, calcium and magnesium
Almagate Almasilate Hydrotalcite Magaldrate
v t e
Drugs for constipation (laxatives and cathartics) (A06)
Dietary fiber Ethulose Ispaghula Methylcellulose Polycarbophil calcium Sterculia Triticum
Linaclotide Lubiprostone Oxyphenisatine Prucalopride Te