BY JOSE PALU-AY DACUDAO
2 Al2O3 (aluminum oxide) + 3 C (elemental carbon) → 4 Al (elemental aluminum) + 3 CO2 (carbon dioxide)
Magnesium is the third most commonly used structural metal, following iron and aluminum. (Elemental chromium, the fourth most commonly used metal, as explained above mostly goes into the production of stainless steel, alloyed with iron.) Magnesium is particularly valued for its lightness, and when alloyed to other metals, its strength.
The main applications of magnesium are: aluminum alloys (including in so-called aluminum cans, aircraft, road vehicles, personal gadgets like cellphones and computers), zinc alloys in die-casting, removal of sulfur in the production of iron and steel, and the production of elemental titanium (another structural metal, and an outstanding one, though less commonly used because it’s so expensive to produce) in the Kroll process (a reduction process wherein magnesium is the reducing agent).
Almost 90% of the world’s elemental magnesium is made in China in the silicothermic Pidgeon process, the reduction of magnesium oxide with silicon.
2 MgO (magnesium oxide, solid) + Si (elemental silicon, solid) + 2 CaO (calcium oxide, solid) → 2 Mg (elemental magnesium), gas when produced during smelting temperature and thus easily separated) + Ca2SiO4 (calcium silicate, solid).
If we remove the calcium oxide and calcium silicate from the above formula, we essentially simplify the net process to: 2 MgO (magnesium oxide) + Si (elemental silicon) → 2 Mg (elemental magnesium) + SiO2 (silicon dioxide).
In this case it is silicon and not carbon (for chemical and physical reasons) that is used as the reducing agent. This is called silicothermic reduction (literally chemical reduction by silicon and heat).
Note however that silicon is separated from its main mineral, silicon dioxide (the compound that makes up common beach sand and many other rocky minerals), by carbothermic reduction.
SiO2 (silicon dioxide) + 2 C (elemental carbon) → Si (elemental silicon) + 2 CO (carbon monoxide)
***
Additional Note
The silicon we need in semiconductors and integrated circuits is produced this way.)
If we combine the carbothermic reduction of silicon dioxide, and the silicothermic reduction of magnesium oxide, over-all we essentially get:
MgO (magnesium oxide) + C (elemental carbon) → Mg (elemental magnesium) + CO (carbon monoxide)
The carbon monoxide (CO) waste product eventually oxidizes into carbon dioxide (CO2) in the atmosphere.
Note that in all cases above, it is elemental carbon is that is eventually consumed, and carbon dioxide (CO2) that is produced.
This suggests a simple solution if we assume that net anthropomorphic carbon dioxide emission into the atmosphere is taken to be a problem.
(Again, a caveat: there are some scientists that hold a contrary opinion, that an increase in atmospheric carbon dioxide is over-all good for humanity because of the increased and faster plant growth carbon dioxide fosters, consequently increasing the productivity of natural ecosystems, and forests and croplands.) (To be continued)/PN
