Source & Extraction
To service growing demand, there is potentially no limit to magnesium output since magnesium comprises about 2.5% of the earth's surface. Seawater contains 0.14% magnesium and the element is abundant in minerals Carnallite, Dolomite, and Magnesite. Alloys used for structural applications can be recycled back into products displaying the same characteristics as primary material. Recycling requires only 5% of the energy required to produce the primary product.
Magnesium is produced for profit in such places as the United States and Canada, Western Europe, South America and Asia. In the Commonwealth of Independent States (CIS) it is produced for hard Western cash and, like aluminum, seems to be exported to the West.
Isolation Processes
Magnesium can be recovered commercially from massive seawater deposits as Magnesium Chloride (MgCl2) through initial reaction stages with Calcium Oxide (CaO):
Precipitation Chemical Summary
CaO + H2O → Ca2+ + 2OH-
Mg2+ + 2OH- → Mg(OH)2
Mg(OH)2 + 2HCl → MgCl2 + 2H2O
Electrolysis of hot molten MgCl2 affords magnesium as a liquid which is poured off, alongside chlorine gas:
Electrolysis Cells Reactions
Cathode: Mg2+(l) + 2e- → Mg
Anode: Cl-(l) → 1/2Cl2 (g) + e-
The alternative method involves "calcined" dolomite reacted with ferrosilicon alloy:
Thermal Reduction (Ferrosilicon) Reaction
2[MgO.CaO] + FeSi → 2Mg + Ca2SiO4 + Fe