Magnesium carbonate

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Safety data
Other names Magnesite
dihydrate: Barringtonite
trihydrate: Nesequehonite
pentahydrate: Lansfordite
White gold:
Identifiers
CAS number [546-93-0]
RTECS number OM2470000
Properties
Molecular formula MgCO3
Molar mass 84.32 g/mol
Appearance white solid
Density 2.958 g/cm3, solid
Melting point

350 °C decomp.
Solubility in water 10.6 mg/100 ml
Structure
Crystal structure Trigonal
Thermochemistry
Std enthalpy of
formation ΔfHo298		 -1111.69 kJ/mol
Standard molar
entropy So298		 65.84 J.K−1.mol−1
Related compounds
Other cations Calcium carbonate
Strontium carbonate
Barium carbonate
Related compounds Artinite
Hydromagnesite
Dypingite
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Magnesium carbonate, MgCO3, is a white solid that occurs in nature as a mineral. Several hydrated and basic forms of magnesium carbonate also exist as minerals. In addition, MgCO3 has a variety of applications.

Contents

[edit] Forms

The most common magnesium carbonate forms are the anhydrous salt called magnesite (MgCO3) and the di, tri, and pentahydrates known as barringtonite (MgCO3·2H2O), nesquehonite (MgCO3·3H2O), and lansfordite (MgCO3·5H2O), respectively. Some basic forms such as artinite (MgCO3·Mg(OH)2·3H2O), hydromagnestite (4MgCO3·Mg(OH)2·4H2O), and dypingite (4MgCO3· Mg(OH)2·5H2O) also occur as minerals. Magnesite consists of white trigonal crystals. The anhydrous salt is practically insoluble in water, acetone, and ammonia. All forms of magnesium carbonate react in acids. Magnesium carbonate crystallizes in the calcite structure wherein Mg2+ is surrounded by six oxygen atoms. The dihydrate has a triclinic structure, while the trihydrate has a monoclinic structure.

References to 'light' and 'heavy' magnesium carbonates actually refer to the magnesium hydroxy carbonates hydromagnesite and dypingite (respectively)[1].


[edit] Reactions

Although magnesium carbonate is ordinarily obtained by mining the mineral magnesite, the trihydrate salt, MgCO3·3H2O, can be prepared by mixing solutions of magnesium and carbonate ions under an atmosphere of carbon dioxide. Magnesium carbonate can also be synthesized by exposing a magnesium hydroxide slurry to carbon dioxide under pressure (3.5 to 5 atm) below 50 °C, which gives soluble magnesium bicarbonate:

Mg(OH)2 + 2 CO2 → Mg(HCO3)2

Following the filtration of the solution, the filtrate is dried under vacuum to produce magnesium carbonate as a hydrated salt:

Mg2+ + 2 HCO3- → MgCO3 + CO2 + H2O

When dissolved with acid, magnesium carbonate decomposes with release of carbon dioxide:

MgCO3 + 2 HCl → MgCl2 + CO2 + H2O
MgCO3 + H2SO4 → MgSO4 + CO2 + H2O

At high temperatures (800C-1000C), MgCO3 decomposes to magnesium oxide and carbon dioxide with reaction enthalpy 118 kJ / mole, this process is called calcining:

MgCO3 → MgO + CO2

[edit] Uses

Magnesite and dolomite minerals are used to produce magnesium metal and basic refractory bricks. MgCO3 is also used in flooring, fireproofing, fire extinguishing compositions, cosmetics, dusting powder, and toothpaste. Other applications are as filler material, smoke suppressant in plastics, a reinforcing agent in neoprene rubber, a drying agent, a laxative to loosen the bowels, and color retention in foods. In addition, high purity magnesium carbonate is used as antacid and as an additive in table salt to keep it free flowing.

Because of its water-insoluble, hygroscopic properties MgCO3 was first added to salt in 1911 to make the salt flow more freely. The Morton Salt company adopted the slogan "When it rains it pours" in reference to the fact that its MgCO3-containing salt would not stick together in wet weather.[2]

Magnesium carbonate, most often referred to as 'chalk', is used as a drying agent for hands in rock climbing, gymnastics, and weight lifting.

[edit] Food additive

As a food additive it's known as E504. And the only known side effect is that it may work as a laxative in high concentrations. [3]

[edit] References

  1. ^ A. BOTHA and C. A. STRYDOM; “Preparation of a magnesium hydroxy carbonate from magnesium hydroxide;” Hydrometallurgy; Elsevier Science; December 2001; 62 (3): pp. 175–183.
  2. ^ Morton Salt FAQ.
  3. ^ Food-Info.net : E-numbers : E504: Magnesium carbonates. 080419 food-info.net
  • Magnesium Carbonate Light (pdf). Safety Data Sheet. Vet Way Limited. Retrieved on 2008-01-06.
  • Patnaik, Pradyot (2003). Handbook of Inorganic Chemicals. New York: McGraw Hill. 
  • Trotman-Dickenson, A.F "(ed.)" (1973). Comprehensive Inorganic Chemistry. Oxford: Pergamon Press. 

[edit] External links