Magnesium oxide reduction

Thermal Reduction. Magnesium metal can also be formed by the thermal reduction of magnesium oxide with a reactive metal, such as siUcon [7440-21-3] which forms a stable oxide. 

Three basic processes exist for the thermal reduction of magnesium oxide the Pidgeon process, the Magnetherm process, and the BoKano process. 

The reaction is carried out under an inert atmosphere in an open crucible at approximately 830°C. Figure 1 shows typical equipment used for direct oxide reduction. Vitrified magnesium oxide ceramic is commonly used as a container material, but tungsten and tantalum can also be used(3). If the latter are used, CaF2 is added to lower the temperature needed to liquify... 

Metallic magnesium is produced by either chemical or electrolytic reduction of its compounds. In chemical reduction, first magnesium oxide is obtained from the decomposition of dolomite. Then ferrosilicon, an alloy of iron and silicon, is used to reduce the MgO at about 1200°C. At this temperature, the magnesium produced is immediately vaporized and carried away. The electrolytic method uses seawater as its principal raw material magnesium hydroxide is precipitated by adding slaked lime (Ca(OH)2, see Section 14.10), the precipitate is filtered off and treated with hydrochloric acid to produce magnesium chloride, and the dried molten salt is electrolyzed. 

The reaction of magnesium metal with aqueous strong acid, which appears in Figure 4-12. illustrates the fundamental principles of oxidation-reduction. When a piece of magnesium is dropped into a solution of hydrochloric acid, a reaction starts almost Immediately. The metal dissolves, and gas bubbles from the solution. The gas is H2, and analysis of the solution reveals the presence of ions. A list of chemical species before and after the reaction... 

The above reaction shows that the oxychloride decomposes at the sublimation temperature into the volatile tetrachloride and the nonvolatile oxide. Reduction starts as soon as the chloride vapour contacts the molten magnesium, and this exothermic reaction raises the temperature of the reaction mixture. The temperature of the reduction crucible is maintained in the range of 800 to 875 °C. The process is carefully controlled by matching the sublimation rate of zirconium tetrachloride with the reduction rate. The conclusion of the reduction is indicated by a fall in temperature and pressure. 

Hess, C. and Lunsford, J.H. (2003) N02 Storage and Reduction in Barium Oxide Supported on Magnesium Oxide Studied by in Situ Raman Spectroscopy,./. Phys. Chem. B, 107, 1982. 

Preparation. Magnesium is obtained by electrolysis of magnesium chloride melts or by metallothermic reduction of magnesium oxide. 

A new production technique fully cost competitive with current processes could be the reduction of magnesium oxide by carbon to produce magnesium metal as a vapour and carbon monoxide gas this technique, according to Brooks et al. (2006), will involve rapid quenching of the Mg vapour through a nozzle at supersonic velocity to avoid Mg reversion to magnesium oxide. 

Although many commercial processes have heen developed since the first electrolytic isolation of Mg metal hy Davy and Faraday, and Bussy, hy chemical reduction, the principles of the manufacturing processes have not changed. At present, the metal is most commonly manufactured by electrolytic reduction of molten magnesium chloride, in which chlorine is produced as a by-product. In chemical reduction processes, the metal is obtained by reduction of magnesium oxide, hydroxide, or chloride at elevated temperatures. 

Many metals are also vulnerable to acids, undergoing an oxidation /reduction reaction that produces the metal ion and hydrogen gas. The balanced equation for the reaction between HCl and magnesium is... 

In 1792 Anton Rupprecht prepared impure magnesium (contaminated with iron) by reduction of magnesium oxide with carbon and called the metal austrium in honor of Austria (68). 

The reaction of magnesium and oxygen is an example of an oxidation reaction. The combination of an element with oxygen was the traditional way to define an oxidation reaction. This definition of oxidation has been broadened by chemists to include reactions that do not involve oxygen. Our modern definition for oxidation is that oxidation takes place when a substance loses electrons. Anytime oxidation takes place and a substance loses one or more electrons, another substance must gain the electron(s). When a substance gains one or more electrons, the process is known as reduction. Reactions that involve the transfer of one or more electrons always involve both oxidation and reduction. These reactions are known as oxidation-reduction or redox reactions. 

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