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Magnesium hydroxide

Description main application Chemical properties antacids Side Effects Uses Production method Sources
Magnesium hydroxide
Magnesium hydroxide structure
Chemical Name:
Magnesium hydroxide
Molecular Formula:
Formula Weight:
MOL File:

Magnesium hydroxide Properties

Melting point:
350 °C(lit.)
2,36 g/cm3
5 M HCl: 0.1 M, clear, yellow
Specific Gravity
Water Solubility 
0.9 mg/100 mL (18 ºC)
Air Sensitive
λ: 260 nm Amax: 0.030
λ: 280 nm Amax: 0.025
Solubility Product Constant (Ksp)
pKsp: 11.25
CAS DataBase Reference
1309-42-8(CAS DataBase Reference)
NIST Chemistry Reference
Magnesium hydroxide(1309-42-8)
  • Risk and Safety Statements
  • Hazard and Precautionary Statements (GHS)
Hazard Codes  Xi
Risk Statements  36/37/38
Safety Statements  26-36-37/39-24/25
WGK Germany  -
RTECS  OM3570000
HS Code  28161000
Hazardous Substances Data 1309-42-8(Hazardous Substances Data)
Signal word:
Hazard statements:
Code Hazard statements Hazard class Category Signal word Pictogram P-Codes
H315 Causes skin irritation Skin corrosion/irritation Category 2 Warning P264, P280, P302+P352, P321,P332+P313, P362
H319 Causes serious eye irritation Serious eye damage/eye irritation Category 2A Warning P264, P280, P305+P351+P338,P337+P313P
H335 May cause respiratory irritation Specific target organ toxicity, single exposure;Respiratory tract irritation Category 3 Warning
Precautionary statements:
P261 Avoid breathing dust/fume/gas/mist/vapours/spray.
P304+P340 IF INHALED: Remove victim to fresh air and Keep at rest in a position comfortable for breathing.
P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continuerinsing.
P405 Store locked up.

Magnesium hydroxide price More Price(14)

Manufacturer Product number Product description CAS number Packaging Price Updated Buy
Sigma-Aldrich 310093 Magnesium hydroxide reagent grade, 95% 1309-42-8 2kg $175 2018-11-13 Buy
Sigma-Aldrich 1374260 Magnesium hydroxide United States Pharmacopeia (USP) Reference Standard 1309-42-8 1g $348 2018-11-13 Buy
Alfa Aesar 012367 Magnesium hydroxide, 95-100.5% 1309-42-8 2.5kg $140 2018-11-16 Buy
Alfa Aesar 012367 Magnesium hydroxide, 95-100.5% 1309-42-8 100g $18.8 2018-11-16 Buy
Strem Chemicals 93-1229 Magnesium hydroxide, 95% 1309-42-8 500g $29 2018-11-13 Buy

Magnesium hydroxide Chemical Properties,Uses,Production


Magnesium hydroxide is best known as the active ingredient in Milk of Magnesia, an antacid and laxative which has been used for 150 years. It forms a suspension in water, and its reaction with acid only dissolves it gradually, giving it long-lasting effects. At higher doses, rather than acid neutralization, its primary action is to hold water, as it is not absorbed by the large intestine, relieving constipation.
It is also used as a fire retardant and smoke repressor in various applications due to an endothermic decomposition reaction which takes place at 332°C, releasing magnesia and water. Further applications include wastewater treatment, as a fuel additive, and production of magnesium salts.

main application

Magnesium hydroxide is an excellent flame retardant for plastics and rubber products. In environmental protection, it is taken as flue gas desulfurization agent and can replace the caustic soda and lime as the neutralizer of acid-containing waste water and the absorbent of the heavy metal. In addition, it can also be used for the electronics industry, medicine, sugar refining, as insulation materials and for the manufacturing of other magnesium salt products.
Magnesium hydroxide is used as a flue gas desulfurization absorbent. In the 20th century, before the 1970s, most flue gas desulfurization applied sodium hydroxide method, limestone gypsum method. However, due to the secondary pollution of the byproducts to the environment, it has been switched to hydrogen magnesium oxide method since the 20th century; as acidic wastewater neutralizer; as the flame retardants of the synthetic resin; it was previously often used of bromine, phosphorus, chlorine and inorganic salt system. In these products, it had been mostly used of the aluminum hydroxide in these products. However, it has now been converted to magnesium hydroxide , mainly due to that in the thermoplastic resin, it can be increased of decomposition temperature to 350 ℃ or more with magnesium hydroxide; it is medically used for the control of gastric acid and laxatives; food additives, as a mineral additive, color protection agent, desiccant, alkali agent and aid of sugar production; used as a chemical reagent for measuring ammonium salt: Mg (OH) 2 + 2NH4Cl → MgCl2 + 2NH4OH.
This product has a variety of advantage including being smoke-free, non-toxic, non-corrosive, cheap and easy to get advantages. Moreover, the temperature of its decomposition for release of water is higher than aluminum hydroxide, being more suitable for the requirement of high-temperature processing. Magnesium hydroxide can be used as the flame retardants of polyethylene, polypropylene, PVC, EPDM, unsaturated polyester and other plastics and rubber. It can also be used as the flame retardant of paint.

Chemical properties

It appears as white crystals or powder, being soluble in dilute acid and ammonium salt solution, but almost insoluble in water and alcohol. The solubility in water (18 ° C) was 0.0009 g/100 g.


Antacids are drugs that reduce the acidity of the gastric juice. Antacids can be used for the treatment of hyperacidity, gastric and duodenal ulcers. The ideal antacid should have strong anti-acid and long-term effect. Moreover, it is preferably that it doesn’t generate carbon dioxide during the neutralization of gastric acid and is not absorbed by the digestive tract. Even if absorbed, it should be harmless. The antacid, based on whether it can be absorbed by the digestive tract, is divided into absorbent antacids and non-absorbable antacids.
Magnesium hydroxide is a kind of non-absorption of antacid. This kind of drugs is not absorbed at all or only absorbed of a small amount by the digestive tract, thus having no systemic effects. Magnesium hydroxide has an effect similar to that of magnesium oxide. Its reaction with hydrochloric acid is slow and lasting effect. The fraction that is not reacted with hydrochloric acid can stay in the stomach for further reaction with the new secreted hydrochloric acid. It has similar laxative effect as the magnesium oxide. The above information is compiled and edited by Tongtong from Chemicalbook.

Side Effects

Treatment of gastric acid with magnesium hydroxide, the following Side effects that you should report to your doctor or health care professional as soon as possible:
allergic reactions like skin rash, itching or hives, swelling of the face, lips, or tongue
feeling faint or lightheaded, falls
loss of appetite
nausea, vomiting
rectal bleeding
unusually weak or tired
Side effects that usually do not require medical attention (report to your doctor or health care professional if they continue or are bothersome):
chalky taste
stomach cramps


1,In medicine, it can be used as antacids and laxatives, can also be used for manufacturing of sugar and magnesium oxide and so on
2,Magnesium hydroxide is an excellent flame retardant for plastics and rubber products. In environmental protection, it can be used as flue gas desulfurization agent, being able to replace the caustic soda and lime as acid-containing waste water neutralizer. It can also used as oil additive with anti-corrosion and desulfurization effect. In addition, it can also be used for the electronics industry, medicine, sugar refining, for insulation materials and the manufacture of other magnesium salt products.
3,For sugar refining, pharmaceutical industry;
4,Used as analytical reagents, but also for the pharmaceutical industry
Mainly used as flame retardant.

Production method

Brine-lime method:
Send the preliminarily purified and refined brine and digested lime-treated lime milk for precipitation in the sedimentation tank, and the flocculant is added to the obtained slurry, mixed thoroughly, and then enters the sedimentation tank for separation, filtering, washing, drying and pulverizing to obtain the finished product of magnesium hydroxide. Its
MgCl2 + Ca (OH) 2 → CaCl2 + Mg (OH) 2
. Brine-Ammonia water method:
Apply purification process to remove the sulfate, carbon dioxide, boron and other impurities of brine for using as raw material brine. Ammonia is taken as a precipitant in the reactor for precipitation reaction. Add a certain amount of crystal seed before the reaction and stir thoroughly. The ratio of brine to ammonia is 1: (0.9~0.93), and the temperature is controlled at 40 ℃. Add the flocculant after the end of the reaction, and apply filtering, washing, drying and crushing to the precipitate to obtain the finished product of magnesium hydroxide. The reaction equation is:
MgC12 + 2NH3 • H2O → Mg (OH) 2 + 2NH4Cl
The test method needs to be improved of the yield, shortened of the washing cycle and improved of the production process.
Magnesite-hydrochloric acid-ammonia water method: magnesite and anthracite or coke is subject to calcination in the vertical kiln to generate magnesium oxide and carbon dioxide. The magnesite powder is prepared into a magnesium chloride solution by reacting with a prescribed concentration of hydrochloric acid.
Magnesium chloride solution is reacted with a certain concentration of ammonia in the reactor. The resulting product is successively subject to washing, sedimentation, filtration separation, drying, grinding, to obtain the magnesium hydroxide products. If necessary, a surface treatment agent may be added for surface treatment.


Chemical Properties

Magnesium hydroxide, Mg(OHn, also known as magnesium hydrate and brucite, is a white powder that is very slightly soluble in water. It decomposes at 350°C (662 OF). It is used in the extraction of magnesium metal and as a reagent in the sulfite wood pulp process. Magnesium hydroxide is formed by the reaction of sodium hydroxide and a soluble magnesium salt solution. Brucite, a mineral composed of magnesium hydroxide with occasional traces of iron and manganese, is a white to grayish translucent secondary mineral found with serpentine and metamorphic dolomites.


Antacid; osmotic laxative.


Magnesium Hydroxide is an alkali that is a general purpose food additive. it exists as a white powder and has poor solubility in water and in alcohol. in frozen desserts it will increase the tendency for fat globules to clump, which results in an increase in dryness. it reacts with triglycerides in fatty acids to form soaps. it also functions as a drying agent in foods.


magnesium hydroxide: A white solid compound, Mg(OH)2; trigonal;r.d. 2.36; decomposes at 350°C. Magnesium hydroxide occurs naturally as the mineral brucite and can be prepared by reacting magnesium sulphate or chloride with sodium hydroxide solution. It is used in the refining of sugar and in the processing of uranium. Medicinally it isimportant as an antacid (milk of magnesia) and as a laxative.


ChEBI: A magnesium hydroxide in which the magnesium atom is bound to two hydroxide groups.

brand name

Oxaine M (Wyeth-Ayerst); Phillips Magnesia Tablets (Sterling Health U.S.A.); Phillips Milk of Magnesia Liquid (Sterling Health U.S.A.).

Pharmaceutical Applications

The synthesis of magnesium hydroxide [Mg(OH)2] is based on a metathesis reaction in which magnesium salts are reacted with sodium or potassium hydroxide.
Magnesium hydroxide (Mg(OH)2) has only limited solubility in water and the resulting suspension is called milk of magnesia, which is commonly used as an antacid and is known to be a mild base.
Magnesium hydroxide [Mg(OH)2] is present in antacids because of its laxative properties and is also the main ingredient of the ‘milk of magnesia’. The ‘milk of magnesia’ is a suspension of Mg(OH)2 in water, which has a milk-like appearance because of the low aqueous solubility of Mg(OH)2. It is considered as a strong electrolyte and a weak base and is given to the patient for indigestion and heartburn. The alkaline suspension neutralises any excess stomach acid and therefore works as an antacid. It also stimulates intestinal movement, as the magnesium ions increases the water content in the intestines through its osmotic effect and as a result softens any faeces present.

Safety Profile

Moderately toxic by intraperitoneal route. Human systemic effects: chlorine level changes, coma, somnolence. Incompatible with maleic anhydride, phosphorus. See also MAGNESIUM COMPOUNDS.

Magnesium hydroxide Preparation Products And Raw materials

Raw materials

Preparation Products

Magnesium hydroxide Suppliers

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Magnesium hydroxide Spectrum

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