Magnesium metallurgy

This article deals with the extractive metallurgy of magnesium and the production of its oxide, magnesia. It is an update of P.H. Gavin's article published in 1994.

Geological magnesium resources are immense, from carbonate deposits (magnesite and dolomite) to magnesium salts in seawater. Pre-metallurgical processing of these natural resources poses no major technical obstacles.

Magnesium metal is extracted by electrolysis of seawater or by thermal reduction of oxides. Raw magnesium, obtained in the form of electrolytic cathodes or metallo-thermal condensates, then requires refining based on smelting. The main uses for magnesium metal are in the manufacture of light, resistant alloys and high-purity industrial salts.

Magnesia, MgO, is obtained from the roasting of magnesite by thermal decomposition. Its three industrial forms are caustic magnesite, dead-burned magnesite and fused magnesite, whose main outlets are in the agricultural, pharmaceutical, chemical and environmental treatment sectors, as well as in the steel, cement and glass industries, which use special refractories.

The production of magnesium metal involves environmental risks (release of hydrogen and ignition). The risks involved in magnesium production, on the other hand, are very limited.

The production of metal or its oxides consumes a great deal of energy, especially electrical energy. These costs can be reduced by replacing raw materials-based processes with processes that recycle end-of-life products or manufacturing offcuts that already have a high energy content (magnesium and special alloy scraps, magnesium refractory linings).

The ubiquity of natural resources, the potential for recycling and the growing need for magnesium and magnesia point to major industrial development in the third millennium.