Unlocking the Power of Magnesium Sulfate: From Healing Baths to Thriving Crops, Discover Its Versatility and Impact!

Magnesium Sulfate CAS 7487-88-9

Magnesium sulfate or magnesium sulphate is a chemical compound, colourless rhombohedral crystal system. Soluble in water, ethanol, glycerol, insoluble in acetone. It is used in pharmacy and printing and dyeing industry, also can be used as desiccant, feed, fertiliser or compound fertiliser, also is the raw material for producing magnesium oxide. a salt with the formula MgSO4, consisting of magnesium cations Mg2+ (20.19% by mass) and sulfate anions SO2−4. It is a white crystalline solid, soluble in water but not in ethanol.

Magnesium sulfate is usually encountered in the form of a hydrate MgSO4·nH2O, for various values of n between 1 and 11. The most common is the heptahydrate MgSO4·7H2O, known as Epsom salt, which is a household chemical with many traditional uses, including bath salts.

The main use of magnesium sulfate is in agriculture, to correct soils deficient in magnesium (an essential plant nutrient because of the role of magnesium in chlorophyll and photosynthesis). The monohydrate is favored for this use; by the mid 1970s, its production was 2.3 million tons per year. The anhydrous form and several hydrates occur in nature as minerals, and the salt is a significant component of the water from some springs.

1. Anhydrous magnesium sulphate Properties

CAS No. 7487-88-9

Molecular formula MgSO4

Molecular weight 120.37

EINECS No. 231-298-2

Melting point：1124 °C

Density：1.07 g/mL at 20 °C

Vapour density：<0.01 (vs air)

Vapour pressure：<0.1 mm Hg ( 20 °C)

Storage：conditions no restrictions.

Solubility：H2O:1 Mat 20 °C, transparent, colourless.

Form：Powder (very fine)

Colour：Slightly grey

Specific gravity：2.66

Odour (Odor)：odourless

PH：7.9 (50g/l, H2O, 25 °C)

Odourless：Soluble in water. Slightly soluble in alcohol, glycerol. Insoluble in acetone.

Maximum wavelength(λmax)：λ: 260 nm Amax: 0.03；λ: 280 nm Amax: 0.02

Sensitivity：Hygroscopic

Merck：14,5691

Dielectric constant：8.2 (Ambient)

Stability：Stable. Hygroscopicity.

LogP：-1.031 (est)

2. Anhydrous Magnesium Sulfate Uses and Synthesis

A. Overview

Magnesium sulfate, also known as sulfur bitter, bitter salt, laxative salt, laxative salt, is a compound containing magnesium. Appearance is colourless or white weathering crystal or white powder. Odourless. Bitter and salty taste. With deliquescence. Magnesium sulfate heptahydrate loses six molecules of water of crystallisation at 150°C and all water of crystallisation at 200°C. The density of anhydrous material is 2.66%. Density of anhydrous material is 2.66, melting point is 1124℃, decompose at the same time. Soluble in water, soluble in alcohol, ether and glycerol, insoluble in acetone.

Magnesium sulphate is a commonly used chemical reagent and dry reagent, magnesium sulphate wet compress has anti-inflammatory and de-puffing effect, can reduce local tissue damage, magnesium sulphate wet compresses plus cling film wrapped around the outside of the treatment of chemotherapeutic phlebitis is one of the effective methods. Medicine used as a laxative, because it can increase the intestinal osmotic pressure, so that the intestines retain a lot of water, the volume increases, thus stimulating the intestinal mucosa, promote diarrhoea effect. Used for constipation, intestinal toxin elimination and anthelmintic drugs and used. And used for cholelithiasis. Also used in tanning, explosives, fertilisers, paper, porcelain, printing and dyeing industries. There are natural production. It can be produced by sulphuric acid acting on magnesium oxide, magnesium hydroxide or magnesium carbonate.

Magnesium sulphate is the ideal raw material for manufacturing compound fertiliser, it can be mixed with nitrogen, phosphorus and potassium into compound fertiliser or mixed fertiliser according to different needs, and it can also be mixed with one or more kinds of primitive elements into various kinds of fertilisers and photosynthesised micronutrient fertilisers respectively, and fertilisers containing magnesium are the most suitable for acidic soils, peat soils and sandy soils. After the rubber trees, fruit trees, tobacco, beans and vegetables, potatoes, cereals and other nine kinds of crops in the field of the actual fertiliser comparison test, magnesium-containing composite fertiliser than without magnesium composite fertiliser can make the crops grow 15-50%. In the pharmaceutical magnesium sulfate processing for laxatives, anticonvulsants, magnesium trisilicate, meprobamycin, acetylspiramycin and myxedrine and other drugs. Also used in industrial sewage treatment, the waste liquid sewage to play a role in coagulation and sedimentation, so that it meets the sewage standards.

B. Discovery history

Magnesium sulphate originated in Epsom, where it was discovered in 1695 by the Englishman Greyjoy during the evaporation of epsom mineral water, hence the name epsom salts, and has since been obtained from seawater. In more recent times, magnesium sulphate has been extracted from minerals such as epsomite.

C. Solubility

Water is vaporised at 150 degrees Celsius. The water solubility of magnesium sulphate is related to the specific temperature and pressure in a high-temperature, high-pressure reactor. The solubility of magnesium sulphate (g/100g of water) is 54g at room temperature and decreases above 70 degrees Celsius. Solubility of magnesium sulfate (g/100g water): 25.5g at 0 degrees; 30.4g at 10 degrees; 35.1g at 20 degrees; 37.4g at 25 degrees; 39.7g at 30 degrees; 44.7g at 40 degrees; 50.4g at 50 degrees; 54.8g at 60 degrees.

D. Pharmaceutical use

In medicine, magnesium sulfate is used to treat ingrown nails and as a laxative.

3. Chemical and Physical Properties

This product is a colourless rhombohedral crystal, relative density 2.66, melting point 1,124 °C. It is soluble in water, ethanol and glycerol. Soluble in water, ethanol and glycerol. Insoluble in acetone. Easily absorb moisture.

Magnesium sulphate relaxation is the main mechanism that causes seawater to absorb sound at frequencies above 10 kHz (sound energy is converted to heat). Salt absorbs less at lower frequencies, so low frequency sound travels further in the ocean. Boric acid and magnesium carbonate also contribute to sound absorption.

4. Uses

A. Medical treatment

Magnesium sulphate is used both externally (as a laxative salt) and internally.

The main external application is the preparation of magnesium sulphate into bath salts, especially for use in foot baths to soothe sore feet. The bath salts are also claimed to soothe and speed recovery from muscle pain, soreness or injury. Medical research on the effects of magnesium on antidepressants and as an analgesic for migraines and chronic pain reflects the potential health effects of magnesium sulfate. Magnesium sulfate has also been studied in the treatment of asthma, pre-eclampsia and eclampsia.

Magnesium sulphate is a common ingredient in concentrated salt solutions used in isolation tanks to increase their specific gravity to approximately 1.25-1.26. This high density allows patients to float effortlessly on the surface of closed tanks, eliminating as much irritation to the external senses as possible.

In the UK, a drug containing magnesium sulphate and phenol is known as ‘lassi cream’ and can be used to treat small boils or localised infections as well as to remove wood splinters.

Internally, magnesium sulphate can be administered by oral, respiratory or intravenous routes. Internal uses include replacement therapy for magnesium deficiency, treatment of acute and severe cardiac arrhythmias, as a bronchodilator in the treatment of asthma, prevention of eclampsia and cerebral palsy, haemolytic agent and anticonvulsant.

It is also used as a laxative.

B. Agriculture

In agriculture, magnesium sulphate is used to increase the magnesium or sulphur content of the soil. It is most commonly used for potted plants, or magnesium-demanding crops such as potatoes, tomatoes, carrots, peppers, lemons and roses. The advantage of magnesium sulphate over other magnesium-containing soil amendments, such as calcium dolomite, is its high solubility, making it an option for foliar application as well. The pH of magnesium sulphate solutions is close to neutral compared to the slightly alkaline magnesium salts found in limestone; therefore, the use of magnesium sulphate as a source of magnesium in the soil will not significantly alter the pH of the soil. Magnesium sulphate controls pests and slugs, helps seeds germinate, produces more flowers, improves nutrient uptake, and is environmentally friendly, but contrary to popular belief, magnesium sulphate does not have any effect other than correcting magnesium deficiencies in the soil.

Excessive use of magnesium sulfate can even contaminate water supplies.

Before the advent of chelation therapy, magnesium sulfate was historically used to treat lead poisoning because it was hoped that any lead ingested would be precipitated by the magnesium sulfate and then eliminated from the digestive system. In the early to mid-20th century, this application was particularly widespread in veterinary medicine; laxative salts were already available on many farms for agricultural use and were often prescribed in the treatment of farm animals that had inadvertently ingested lead.

C. Food preparation

Magnesium sulphate is used as

Brewing salt for brewing beer

Coagulant for tofu

A salt substitute

Ingredient in bottled water for mineral replenishment and taste enhancement

D. Chemical

Anhydrous magnesium sulphate is commonly used as a desiccant in organic synthesis because of its affinity for water and compatibility with most organic compounds. In the working process, the organic phase is treated with anhydrous magnesium sulphate. The hydrated solid is then removed by filtration, decantation or distillation (if the boiling point is low enough). Other inorganic sulfates (e.g., sodium sulfate and calcium sulfate) can be used in the same manner.

E. Construction

Magnesium sulphate is used to prepare specific cements by the reaction of magnesium oxide and magnesium sulphate solutions, which have good bonding capacity and are more abrasion resistant than Portland cement. These cements are primarily used in the production of lightweight insulation boards, but their poor water resistance limits their use.

Magnesium (or sodium) sulphate can also be used to test the integrity of aggregates when the material has no proven track record of being exposed to actual weathering conditions, according to the ASTM C88 standard. The test is performed by repeated immersion in a saturated solution followed by oven drying to dehydrate the salt precipitated from the permeable pores. The internal expansion force created by the rehydration of the salt on re-immersion mimics the expansion of water when it freezes.

Magnesium sulphate is also used to test the resistance of concrete to external sulphate attack (ESA).

F. Aquariums

Magnesium sulphate heptahydrate is also used to maintain magnesium concentrations in marine aquariums containing large numbers of stony corals, as magnesium is slowly depleted during the calcification process of stony corals. Calcium and alkalinity concentrations are difficult to control in magnesium-deficient marine aquariums because there is not enough magnesium to stabilise these ions in the seawater and prevent them from spontaneously precipitating into calcium carbonate.

5. Production process

At present, the production process of magnesium sulfate mainly adopts sulfuric acid method and sea lake bitter brine method, etc. In addition, there are some by-product method, using the by-products of the production of boric acid taiwanese powder to produce magnesium sulfate.

Sulphuric acid method: Magnesium oxide (magnesium hydroxide or magnesium carbonate) is used to react with sulphuric acid to produce magnesium sulphate. The reaction formula is as follows: Mg0+H2SO4+6H2O=MgSO4-7H2O

Salt lake brine method: using the production of manganese nitrate mother liquor natural evaporation crystallisation refining to get magnesium sulfate.

Bitter brine re-tanning method: use seawater to get crude magnesium sulphate heptahydrate containing NaCl, and produce magnesium sulphate heptahydrate by washing method or recrystallisation method.

6. Production method

Magnesium sulphate is usually obtained directly from dried lake beds and other natural sources. It can also be prepared by reacting magnesite (magnesium carbonate, MgCO3) or magnesium oxide (oxide, MgO) with sulphuric acid (H2SO4):

H2SO4 + MgCO3 → MgSO4 + H2O + CO2

Another possible method is to treat seawater or magnesium-containing industrial wastes to precipitate magnesium hydroxide and then react the precipitate with sulphuric acid.

In addition, magnesium sulphate heptahydrate (epsomite, MgSO4-7H2O) is made by dissolving magnesium sulphate monohydrate (kieserite, MgSO4-H2O) in water and then crystallising the magnesium sulphate heptahydrate.

Recrystallisation method adds industrial magnesium sulphate into the dissolving tank, dissolves it with water, purifies the solution to remove arsenic and heavy metals, filters it, and the filtrate is concentrated, cooled and crystallised, centrifuged and separated to obtain refined magnesium sulphate, which is dried and dehydrated at 200°C to produce finished anhydrous magnesium sulphate for feed.

Hot melt leaching method Inject the mother liquor of magnesium sulfate (30 g/100 ml) into the leaching apparatus, add the mixed salt solution (containing less than 30% of MgSO4 and less than 35% of NaCl), the volume ratio of the two is 2︰1. Dissolve and leach for 4 h at 45～50 ℃, and the obtained mixed liquor is filtered by the plate and frame press and the filtrate obtained is pumped into a pre-cooler to remove the NaCl, and then the clear liquid is cooled down to crystallise at about 5 ℃. Wash, filter, dry (dryer bottom temperature 350 ~ 400 ℃, the top temperature of 100 ~ 150 ℃), get magnesium sulfate monohydrate. Then use rotary drier to dry at 400～500 ℃ to get the finished product.

Magnesium sulfate can crystallize as several hydrates, including:

Anhydrous, MgSO4; unstable in nature, hydrates to form epsomite.

Monohydrate, MgSO4·H2O; kieserite, monoclinic.

Monohydrate, MgSO4·H2O; triclinic.

MgSO4·1.25H2O or 4MgSO4·5H2O.

Dihydrate, MgSO4·2H2O; orthorhombic.

MgSO4·2.5H2O or 2MgSO4·5H2O.

Trihydrate, MgSO4·3H2O.

Tetrahydrate, MgSO4·4H2O; starkeyite, monoclinic.

Pentahydrate, MgSO4·5H2O; pentahydrite, triclinic.

Hexahydrate, MgSO4·6H2O; hexahydrite, monoclinic.

Heptahydrate, MgSO4·7H2O (“Epsom salt”); epsomite, orthorhombic.

Enneahydrate, MgSO4·9H2O, monoclinic.

Decahydrate, MgSO4·10H2O.

Undecahydrate, MgSO4·11H2O; meridianiite, triclinic.

As of 2017, the existence of the decahydrate apparently has not been confirmed.

All the hydrates lose water upon heating. Above 320 °C, only the anhydrous form is stable. It decomposes without melting at 1124 °C into magnesium oxide (MgO) and sulfur trioxide (SO3).