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Extractive metallurgy of magnesium

Dr. Dmitri Kopeliovich

Magnesium is the sixth most abundant element in the earth’s crust.

The main sources of magnesium compounds are:

  • seawater (magnesium chloride, MgCl2)

and minerals:

  • dolomite (CaCO3·MgCO3),
  • magnesite (MgCO3),
  • carnallite (KCl·MgCl2·6H2O).

There are two principal magnesium extraction processes:

Silicotermic process (Pidgeon, Magnetherm, Bolzano)

The process involves reducing molten magnesium oxide slag by ferrosilicon under low gas pressure at a temperature of about 2500F (1400ºC).

The metallic magnesium, formed in the process, evaporates and then condensates away from the hot region.

The condensed magnesium, having purity of 99,95% is then remelt and cast.

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Electrolytic process

The first stage of the process is a preparation of magnesium chloride feed which is followed by the electrolytic dissociation of magnesium chloride.

Industrial cell feeds consist of a mixture of dehydrated magnesium chloride, partly dehydrated magnesium chloride or dehydrated carnallite.

Dehydrated magnesium chloride is prepared by one of two methods: chlorination of magnesium oxide (IG Farben process) or dehydration of magnesium chloride brines.

magnesium extraction.png

The electrolytic cell consists of a brick-lined vessel, divided into anode and cathode compartments by a semi-wall. Air- or water-cooled Graphite plate anode and steel cathode are submerged in electrolyte composed of alkaline chlorides with addition of magnesium chloride.

The operating temperature is 1260°F to 1380°F (680°C to 750°C).

Magnesium chloride decomposes in the electrolytic cell according to the reaction:

MgCl2 Mg + Cl2(g)

Metallic magnesium is formed at the cathode. It floats up (it is lighter than electrolyte) collecting in the cathode compartment.

Chlorine, which is by-product of the process, is collected in the anode compartment.

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extractive_metallurgy_of_magnesium.txt · Last modified: 2023/12/13 by dmitri_kopeliovich
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