Magnesium sulfate Magnesium sulfate is an inorganic salt containing
magnesium, sulfur and oxygen, with the formula MgSO4. It is often encountered as the heptahydrate
sulfate mineral epsomite , commonly called Epsom salt, taking its name from a bitter
saline spring in Epsom in Surrey, England, where the salt was produced from the springs
that arise where the porous chalk of the North Downs meets non-porous London clay. The monohydrate,
MgSO4·H2O is found as the mineral kieserite. The overall global annual usage in the mid
1970s of the monohydrate was 2.3 million tons, of which the majority as used in agriculture.
Anhydrous magnesium sulfate is used as a drying agent. The anhydrous form is hygroscopic (readily
absorbs water from the air) and is therefore difficult to weigh accurately; the hydrate
is often preferred when preparing solutions (for example, in medical preparations). Epsom
salt has been traditionally used as a component of bath salts. Epsom salt can also be used
as a beauty product. Athletes use it to soothe sore muscles, while gardeners use it to improve
crops. It has a variety of other uses. Epsom Salts are also effective in the removal of
sub-cutaneous slivers. It is on the World Health Organization's List
of Essential Medicines, a list of the most important medication needed in a basic health
system. Uses
Medical Magnesium sulfate is a common pharmaceutical
preparation of magnesium, commonly known as Epsom salts, used both externally and internally.
Epsom salts are used as bath salts. The sulfate is supplied in a gel preparation for topical
application in treating aches and pains. Oral magnesium sulfate is commonly used as a saline
laxative or osmotic purgative. Magnesium sulfate is the main preparation of intravenous magnesium.
Bathing in a 1% solution of Epsom salts (about 500g of Epsom salts for a standard size bathtub
of 60 litres) is a "a safe and easy way to increase sulfate and magnesium levels in the
body". Indications for internal use are:
Replacement therapy for hypomagnesemia. Magnesium sulfate is the first-line antiarrhythmic
agent for torsades de pointes in cardiac arrest under the 2005 ECC guidelines and for managing
quinidine-induced arrhythmias. As a bronchodilator after beta-agonist and
anticholinergic agents have been tried, e.g. in severe exacerbations of asthma. Studies
conducted have revealed that magnesium sulfate can be nebulized to reduce the symptoms of
acute asthma. It is commonly administered via the intravenous route for the management
of severe asthma attacks. Magnesium sulfate can be used to treat eclampsia
in pregnant women. Intravenous magnesium sulfate has been shown
to prevent cerebral palsy in preterm babies. A recent systematic review suggests that antenatal
intravenous magnesium sulphate can reduce the risk of cerebral palsy and gross motor
dysfunction in preterm infants by on average 30%.
Magnesium sulfate has been used as an experimental treatment of Irukandji syndrome caused by
envenomation by certain species of Irukandji jellyfish, however the efficacy of this treatment
remains unproven. Solutions of sulfate salts such as Epsom salt
may be given as first aid for barium chloride poisoning.
An overdose of magnesium causes hypermagnesemia. The use of Epsom Salts is an effective method
of "drawing out" stubborn or buried slivers. Agriculture
In gardening and other agriculture, magnesium sulfate is used to correct a magnesium or
sulfur deficiency in soil; magnesium is an essential element in the chlorophyll molecule,
and sulfur is another important Macronutrient. It is most commonly applied to potted plants,
or to magnesium-hungry crops, such as potatoes, roses, tomatoes, lemon trees, carrots and
peppers The advantage of magnesium sulfate over other magnesium soil amendments (such
as dolomitic lime) is its high solubility, which also allows the option of foliar feeding.
Solutions of magnesium sulfate are also nearly neutral, as compared to alkaline salts of
magnesium, as found in limestone; therefore the use of magnesium sulfate as a magnesium
source for soil does not significantly change the soil pH.
Other Anhydrous magnesium sulfate is commonly used
as a desiccant in organic synthesis due to its affinity for water. During work-up, an
organic phase is saturated with magnesium sulfate until it no longer forms clumps. The
hydrated solid is then removed with filtration or decantation. Other inorganic sulfate salts
such as sodium sulfate and calcium sulfate may also be used in the same way.
Magnesium sulfate is used in bath salts, particularly in flotation therapy where high concentrations
raise the bath water's specific gravity, effectively making the body more buoyant. Traditionally,
it is also used to prepare foot baths, intended to soothe sore feet. The reason for the inclusion
of the salt is partially cosmetic: the increase in ionic strength prevents some of the temporary
skin wrinkling (partial maceration) which is caused by prolonged immersion of extremities
in pure water. However, magnesium sulfate can also be absorbed into the skin, reducing
inflammation. It is naturally present in some mineral waters.
It may also be used as a coagulant for making tofu.
Magnesium sulfate heptahydrate is also used to maintain the magnesium concentration in
marine aquaria which contain large amounts of stony corals as it is slowly depleted in
their calcification process. In a magnesium-deficient marine aquarium calcium and alkalinity concentrations
are very difficult to control because not enough magnesium is present to stabilize these
ions in the saltwater and prevent their spontaneous precipitation into calcium carbonate.
Magnesium sulfate is used as the electrolyte to prepare copper sulfate. A magnesium sulfate
solution is electrolyzed with a copper anode to form copper sulfate, magnesium hydroxide,
and hydrogen: Magnesium sulfate is used as a brewing salt
in beer production to adjust the ion content of the brewing water and enhance enzyme action
in the mash or promote a desired flavor profile in the beer.
Deprecated usage Magnesium sulfate was once used as a delay
labor, but meta-analyses have failed to support it as a tocolytic agent. And its use for prolonged
periods (more than 5 to 7 days) may result in health problems for the baby.
Physical properties Magnesium sulfate is highly soluble in water.
The anhydrous form is strongly hygroscopic, and can be used as a desiccant.
Magnesium sulfate is the primary substance that causes the absorption of sound in seawater
(acoustic energy is converted to thermal energy). Absorption is strongly dependent on frequency:
lower frequencies are less absorbed by the salt, so that the sound travels much farther
in the ocean. Boric acid also contributes to absorption, but the most abundant salt
in seawater, sodium chloride, has negligible sound absorption.
Hydrates Almost all known mineralogical forms of MgSO4
occur as hydrates. Epsomite is the natural analogue of "Epsom salt". Another heptahydrate,
the copper-containing mineral alpersite (Mg,Cu)SO4·7H2O, was recently recognized. Both are, however,
not the highest known hydrates of MgSO4, due to the recent terrestrial find of meridianiite,
MgSO4·11H2O, which is thought to also occur on Mars. Hexahydrite is the next lower (6)
hydrate. Three next lower hydrates — pentahydrite (5), starkeyite (4) and especially sanderite
(2) — are more rarely found. Kieserite is a monohydrate and is common among evaporitic
deposits. Anhydrous magnesium sulfate was reported from some burning coal dumps but
never treated as a mineral. The pH of hydrates is average 6.0 (5.5 to
6.5). Magnesium hydrates have, like copper(II) sulfate, coordinated water.
Manufacturing The heptahydrate can be prepared by neutralizing
sulfuric acid with magnesium carbonate or oxide, but it is usually obtained directly
from natural sources. Anhydrous magnesium sulfate is prepared only
by the dehydration of a hydrate. Occurrence
Magnesium sulfates are common minerals in geological environments. Their occurrence
is mostly connected with supergene processes. Some of them are also important constituents
of evaporitic potassium-magnesium (K-Mg) salts deposits.