استخراج منیزیم ، Production Magnesium

China is the dominant supplier of magnesium, with approximately 80% of the world market share. China is almost completely reliant on the silicothermic Pidgeon process (the reduction of the oxide at high temperatures with silicon, often provided by a ferrosilicon alloy in which the iron is but a spectator in the reactions) to obtain the metal.

The process can also be carried out with carbon at approx 2300 °C: 2MgO (s) + Si (s) + 2CaO (s) → 2Mg (g) + Ca 2SiO 4(s) MgO (s) + C (s) → Mg (g) + CO (g) In the United States, magnesium is obtained principally with the Dow process, by electrolysis of fused magnesium chloride from brine and sea water. A saline solution containing Mg2+ ions is first treated with lime (calcium oxide) and the precipitated magnesium hydroxide is collected: Mg2+ (aq) + CaO (s) + H 2O → Ca2+ (aq) + Mg(OH) 2(s) The hydroxide is then converted to a partial hydrate of magnesium chloride by treating the hydroxide with hydrochloric acid and heating of the product: Mg(OH) 2(s) + 2 HCl → MgCl 2(aq) + 2H 2O (l) The salt is then electrolyzed in the molten state.

At the cathode, the Mg2+ ion is reduced by two electrons to magnesium metal: Mg2+ + 2 e− → Mg At the anode, each pair of Cl− ions is oxidized to chlorine gas, releasing two electrons to complete the circuit: 2 Cl− → Cl 2 (g) + 2 e− A new process, solid oxide membrane technology, involves the electrolytic reduction of MgO. At the cathode, Mg2+ ion is reduced by two electrons to magnesium metal. The electrolyte is Yttria-stabilized zirconia (YSZ).

The anode is a liquid metal. At the YSZ/liquid metal anode O2− is oxidized. A layer of graphite borders the liquid metal anode, and at this interface carbon and oxygen react to form carbon monoxide. When silver is used as the liquid metal anode, there is no reductant carbon or hydrogen needed, and only oxygen gas is evolved at the anode. It has been reported that this method provides a 40% reduction in cost per pound over the electrolytic reduction method.

This method is more environmentally sound than others because there is much less carbon dioxide emitted. The United States has traditionally been the major world supplier of this metal, supplying 45% of world production even as recently as 1995. Today, the US market share is at 7%, with a single domestic producer left, US Magnesium, a Renco Group company in Utah born from now-defunct Magcorp.

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