Magnesium Sulphate (MgSO4)
Magnesium sulphate is a chemical compound containing magnesium, sulphur, and oxygen which occurs naturally in seawater, mineral springs as well in minerals such kieserite and epsomite. It is commercially available in various types with Magnesium Sulphate Heptahydrate, also known as Epsom salt, being the most commonly available form. Magnesium sulphate heptahydrate is a white, crystalline powder or brilliant colourless needle-like crystals. It is freely soluble in water but practically insoluble in alcohol.
The main applications of magnesium sulphate are -
Agriculture
Magnesium sulphate is used as a fertilizer in agriculture because magnesium is one of the main components of chlorophyll. Magnesium sulphate fertilizer is designed for fast correction or prevention of magnesium deficiencies in all types of crop and soil conditions.
Industrial
It is often used in combination with calcium salts for wine brewing water. Used for tanning, explosives, paper, porcelain, and mineral water additives.
Medical
Magnesium sulphate is used both externally (as Epsom salt) and internally. The main external use is the formulation as bath salts. Potential health effects of magnesium sulphate are reflected in medical studies on the impact of magnesium on resistant depression and as an analgesic for migraine and chronic pain. Internal uses include replacement therapy for magnesium deficiency, treatment of acute and severe arrhythmias, as a bronchodilator in the treatment of asthma, preventing eclampsia, a tocolytic agent, and as an anticonvulsant.
Other
Magnesium sulphate 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.
Magnesium Hydroxide (Mg(OH)2)
Magnesium hydroxide is the inorganic compound which can be derived primarily from brucite, magnesite or brine. There is a strong differentiation in grade in the market which strongly impacts applications and pricing. Medical Grade, with a purity of >99,5% is an important application of Mg(OH)2 in the pharmaceutical industry. Industrial Grade, with a purity level of <95% is used extensively as a flame retardant, acidity regulator, as precursor for other magnesium materials (most notably MgO) and in wastewater treatment for heavy metal precipitation and acid neutralisation.
The main applications of magnesium hydroxide are –
Pharmaceutical
One important application of Mg(OH)2 is the use of the material in the pharmaceutical industry, for example as antacid to neutralise stomach acids. Although the use of Mg(OH)2 for this purpose was already described in 1829, it was first sold under the brand name “Phillips’ Milk of Magnesia” by Charles Henry Phillips in 1872. Today, medicinal type Mg(OH)2 is sold in liquid form, chewable tablets or tablets. Magnesium hydroxide can effectively control the gastric acid and duodenal ulcers.
Food
Mg(OH)2 is used in food additives, where the material is used as acidity regulator.
Water Treatment
Magnesium hydroxide slurry has been widely utilised for heavy metal precipitation and acid neutralisation of industrial wastewater. Many industrial and municipal wastewater facilities are now converting to magnesium hydroxide for utilisation in aerobic and anaerobic biological treatment systems.
Flame Retardants
The largest industrial application of Mg(OH)2 is flame retardants for articles such as roofing, isolation materials, plastic articles and coatings. The mechanism of flame retardancy is based on the endothermic decomposition of the material into MgO and H2O. This reaction adsorbs heat, which delays ignition of the associated substance. The water that is released dilutes combustible gases and inhibits oxygen from aiding the combustion. Historically, cable compounds made from PVC often contained ATO (antimony trioxide) as flame retardant synergist to the chlorine in the PVC chain. However, due to the working mechanism of ATO and chlorine, large amounts of smoke is formed when an ATO-containing PVC compound starts to burn. To reduce the smoke formation, magnesium hydroxide can be used in addition to or instead of ATO.
Other
Magnesium hydroxide is used as a fuel additive to treat heavy fuel oils and crude oils due to its fine particle size in power gas turbines. It prevents gas turbines from corrosion by treating the vanadium and sulphur gas emissions. It effectively replaces caustic soda in chemical pulp bleaching processes which reduces the cost of the process by providing higher yield whilst maintaining brightness and physical properties. In the cosmetic industry, Mg(OH)2 is used as a pH controller, absorbent, buffering agent and neutralising agent in bath, hair and skin care products. It is also used in various sunscreens.