Introduction

Magnesium oxide, commonly known as magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium. It has a chemical formula of MgO and has significant commercial uses due to its unique physical and chemical properties.

Chemical Properties

Magnesia is an ionic compound consisting of magnesium cations (Mg2+) and

oxide anions (O2-). It has a cubic crystal structure and each magnesium ion is surrounded by six oxide ions and vice versa. This results in a very stable crystalline structure that imparts useful properties to magnesia.

It is thermally stable up to about 2,800°C as it requires considerable energy for the magnesium and oxygen to separate into their elemental forms. Due to ionic bonding, it is an electrical insulator with high melting point of 2,852°C. Magnesium oxide is also highly refractory due to its ionic lattice structure and thermal stability.

Physical Properties

Magnesium oxide is a white crystalline solid that exists in nature as periclase. Its theoretical density is 3.58 g/cm3 and it has a Mohs hardness of 5.5-6 on the hardness scale. It has a relatively high bulk density of around 2.4-3.0 g/cm3 which depends upon factors like grain size, impurities and production method.

Due to its ionic character, it is highly stable and is hydroscopic in nature. Exposure to water results in hydration to magnesium hydroxide. Its significant solubility in acids allows it to be used as an antacid. Magnesia also has a high refractive index in the range of 1.728 - 1.738 and is optically isotropic.

Commercial Production

Naturally occurring magnesia is obtained by mining as periclase crystals mainly from serpentine ore deposits. Globally important areas include Cyprus, Kazakhstan and Serbia. However, magnesite (MgCO3) deposits are a more important commercial source for magnesium compounds.

The two main industrial processes for its production are calcination of naturally occurring magnesium hydroxide/carbonate minerals and thermal decomposition of magnesium hydroxide precipitates. Sea water is another feedstock that is concentrated for magnesium extraction.

The ore is calcined at high temperatures ranging from 1,000-2,000°C depending on composition and purity requirements. Calcination decomposes the mineral into magnesium oxide and releases carbon dioxide or water. The calcined product is then crushed and screened to obtain commercially useful magnesia powder.

Major Applications

Refractories: Due to high melting point and thermal conductivity, MgO is used as a refractory lining material in high temperature furnaces, kilns and incinerators operating above 1,000°C. Dead burned magnesite and caustic calcined types are suitable in basic and neutral environments respectively.

Agriculture: Finely ground magnesium oxide, also called magnesia alba, is spread as a soil conditioner to neutralize soil acidity and supply magnesium to plants. It is particularly beneficial for crops like fruits, vegetables, sugarcane etc.

Pharmaceuticals: Magnesium Oxide finds use as a dietary supplement, antacid and laxative due to its ability to neutralize gastric acid. It has low toxicity and does not cause systemic effects in moderate doses.

Construction: Cement, plaster and paint industries use magnesia as a flame retardant filler and additive. Its high refractoriness allows production of fire resistant products. Ground calcium carbonate is a suitable mineral filler.

Other Applications: As an electrical insulator, magnesia is used in the manufacture of telecommunication cables, capacitors and motor components. In metallurgy, it is employed as a deoxidizing agent, inoculant for iron and desulphurizing agent. It also finds niche applications in rubber, plastics and textile industries.

Conclusion

Magnesium Oxide is a commercially important mineral that exhibits desirable properties arising from its stable crystalline ionic structure. Its applications are widespread in refractories, agriculture, pharmaceuticals and construction industries due to high melting point, acid neutralizing ability and flame retardancy. Further research is being conducted to develop advanced ceramics utilizing the unique characteristics of Magnesia.