Magnesium Sulfate Heptahydrate (MgSO4·7H2O)

2015-1-13 5:56:47 Sulfates

Magnesium Sulfate Heptahydrate

Magnesium Sulfate Heptahydrate


Chemical Formula: MgSO4·7H2O

Identification CAS: 10034-99-8


Magnesium sulfate (or magnesium sulphate) is an inorganic salt (chemical compound) containing magnesium, sulfur and oxygen, with the formula MgSO4. It is often encountered as the heptahydrate sulfate mineral epsomite (MgSO4·7H2O ), 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 mineralkieserite. The overall global annual usage in the mid-1970s of the monohydrate was 2.3 million tons, of which the majority was used in agriculture.

Physical and Chemical Characteristics (Typical)





White or transparent crystal granule


99.5% min


48.0% min


12.0% min


16.0% min


9.0% min




0.014% max


15ppm max


6ppm max


2ppm max


2ppm max


0.5ppm max

Particle Size

0.1~0.5mm, 1~2mm, 2~3mm, 4~6mm



-          In pp bags with liner, 25kgs net each.

-          In jumbo bags, 1 ton or 1.25 tons net each.

-          Or as customer's requested.



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 micronutrient. 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.



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'sspecific 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.[citation needed] 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:

Cu + MgSO4+ 2 H2O → H2 + CuSO4 + Mg(OH)2


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.

Pregnancy usage

Magnesium sulfate was once used as a tocolytic, but meta-analyses have failed to support it as an anti-contraction medication. And its use for prolonged periods (more than five to seven days) may result in health problems for the baby.

In those at risk of an early delivery, magnesium sulfate appears to decrease the risk of cerebral palsy.It is unclear if it helps those who are born at term.


A study carried out in February 2015 found that Epsom salt minutely raises magnesium levels in those who bathe in it regularly. Therefore, although Epsom salts may help relieve some muscle tightness, Epsom salts are less beneficial than once thought.

Physical properties

Magnesium sulfate is highly soluble in water. The anhydrous form is strongly hygroscopic, and can be used as a desiccant. It 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.


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, SO4·11H2O, 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 was 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.


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.


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.