Magnesium Extraction and Properties

• Magnesium (Mg) extraction from oxides is discussed.
• Magnesium is a lightweight, silvery-white metal.
• Mg has an atomic number of 12 and a symbol "Mg"
• Has an atomic mass of about 24.3 amu.
• Mg has a Hexagonal Close-Packed (HCP) structure.
• The density of Mg is 1.74 g/cm³.
• Magnesium's melting point is 650 °C, and its boiling point is 1090 °C.
• Magnesium is commonly found as magnesium oxide (MgO) and magnesium silicate (MgSiO3) in nature.
• It is the eighth most abundant element in the Earth's crust.
• Minerals containing magnesium include dolomite, magnesite, and carnallite.
• Magnesium burns with an extremely bright white flame due to the high-temperature reaction with oxygen (Mg + O2 → MgO).
• Burning Mg has application in fireworks and flares
• Formerly, it was used in flash photography in the early 1900s.

Minerals of Magnesium

• Dolomite (CaMg(CO3)2) contains approximately 13.2% Mg.
• Magnesite (MgCO3) contains about 28.8% Mg.
• Carnallite (KMgCl3·6H2O) contains roughly 8.75% Mg.
• Brucite (Mg(OH)2) contains about 41.7% Mg.
• Talc (Mg3Si4O10(OH)2) contains approximately 19.2% Mg.
• Olivine ((Mg,Fe)2SiO4) contains about 34.5% Mg.
• Magnesium oxide (MgO) is one of the most common Mg-containing minerals.

Methods for Magnesium Extraction

• Thermal reduction and electrolytic methods can be used for Mg extraction.
• Pidgeon process is a thermal reduction method of Magnesium extraction that is used commercially.
• Magnetherm, carbothermic, and silicothermic reduction are also thermal reduction methods
• Dow process is an electrolytic method of Magnesium extraction that is used commercially.
• Fused Salt Electrolysis and IG Farben Process are also electrolytic methods

Thermal Reduction Inefficiency

• Thermal reduction methods for Mg extraction are inefficient because magnesium oxide (MgO) is structurally stable, which makes reduction difficult using conventional means.
• Reduction process requires high temperatures (about 2000°C), which is not energy-efficient.
• Magnesium has a low boiling point (1090°C), causing significant losses through vaporization during high-temperature processing.
• High energy demand and CO2 emissions make thermal reduction uneconomical and environmentally unfriendly.

Electrolytic Methods Inefficiency

• Electrolytic methods are inefficient because molten salt used (like MgCl2) is corrosive, which leads to equipment damage and maintenance costs.
• Special materials and designs are needed to handle the extreme conditions, increasing setup costs.
• Chlorine gas (Cl2) released as a byproduct poses environmental and handling challenges.
• Impurities in the electrolyte can affect efficiency and require additional refining steps.

Pidgeon Process

• It is a thermal reduction method used to extract magnesium metal from dolomite using ferrosilicon as a reducing agent.
• Operating temperature is lower (around 1100-1200°C) compared to other methods using 1400-2000°C temperatures.
• It uses ferrosilicon as a cheap reducing agent and is carried out in simple retort furnaces.
• A RETORT-TYPE furnace is used (~1100-1200°C) in the process.
• Raw material is MgO
• Dolomite is heated to remove carbon dioxide (CO2), forming magnesium oxide (MgO) and calcium oxide (CaO): CaMg(CO3)2 → CaO + MgO + 2CO2.
• MgO is mixed with ferrosilicon (FeSi) and heated in a vacuum retort furnace (~1100-1200°C).
• Ferrosilicon reduces MgO to form magnesium vapor: 2MgO + 2CaO + FeSi → 2Mg(g) + Ca2SiO4 + Fe2.
• Mg vaporizes because of low boiling point.
• Magnesium vapor travels to a cooler part of the chamber and solidifies into a "magnesium crown".
• Solid magnesium is melted and poured into molds to form Mg ingots.

Dow Process

• It is an electrolytic method used to extract magnesium metal from seawater or brines, using electrolysis of magnesium chloride (MgCl2).
• The process yields high-purity magnesium.
• No high-temperature reduction is needed, which reduces CO2 emissions and is more environmentally friendly.
• A suspension of Ca(OH)2 is added to seawater to form insoluble magnesium hydroxide (Mg(OH)2): Mg2+ + 2OH- → Mg(OH)2↓.
• Mg(OH)2 is filtered out and washed.
• Mg(OH)2 is converted to magnesium chloride: Mg(OH)2 + 2HCl → MgCl2 + 2H2O; water is then removed from this solution.
• Dry MgCl2 is melted (~700°C) and electrolyzed in an electrolytic cell: MgCl2 → Mg↓ + Cl2↑.
• Molten magnesium is collected at the cathode.
• Solidified Mg is cast into ingots for industrial use.
• Chlorine gas (Cl2) is recycled.

Refining of Magnesium

• Primary magnesium produced by Pidgeon or Dow process contains impurities, such as iron (Fe), silicon (Si), manganese (Mn), and aluminum (Al).
• Vacuum distillation, electrorefining, and flux refining are common magnesium refining methods.
• Vacuum distillation is used because Magnesium has a low boiling point (~1090 °C) allowing Mg to vaporize under vacuum leaving impurities behind.
• Vapors are condensed in a separate chamber.
• Vacuum distillation is very effective for high-purity magnesium.
• Electrorefining is used rarely for Mg due to cost and complexity
• In electrorefining, Magnesium is dissolved in a molten salt bath and refined via electrolysis.
• High-purity Mg is deposited at the cathode.
• Flux Refining involves melting crude magnesium with fluxes (like NaCl, KCI, CaF2) and flux removes non-metallic inpurities.
• Vacuum distillation is most commonly used in industry for 99.9%+ pure magnesium.

Uses of Magnesium Metal

• Used in aircraft and spacecraft due to its lightweight and high-strength properties.
• Magnesium alloys are used in car bodies and engine blocks.
• Used in laptop casings, camera bodies, and mobile phones.
• Magnesium alloys are used in structural components due to their corrosion resistance and strength.
• Used in military vehicles, missiles, and weapons for lightweight yet strong structural components.

Conclusion

• Magnesium is an important metal used in aerospace, automotive, medicine, and fireworks due to its lightweight and high-strength properties.
• Pidgeon Process (thermal reduction using ferrosilicon) and Dow Process (electrolysis of MgCl2 from seawater) are two major extraction methods.
• High energy consumption and environmental impact (chlorine gas in Dow process, slag in Pidgeon process) are challenges in magnesium extraction.
• Scientists are looking for better, eco-friendly methods that use less energy and cause less pollution.
• There's also focus on recycling old magnesium products instead of extracting from raw materials, which saves energy and resources.