Manufacture of Magnesium Metal

Dow seawater A process for extracting magnesium from seawater. Calcined dolomite (CaO-MgO, dololime), or calcined oyster shell, is added to seawater, precipitating magnesium hydroxide. This is flocculated, sedimented, and filtered off. For use as a refractory it is calcined for the manufacture of magnesium chloride for the manufacture of magnesium metal, it is dissolved in hydrochloric acid. Developed by the Dow Chemical Company and later operated by the Steetly Company in West Hartlepool, UK, and Sardinia. 

Fig. 137. Manufacture of magnesium metal from a sea water source.

The proposed process offers a scheme that provides three products as compared to one product only by the Solvay process. Magnesium chloride is an important product for the manufacture of magnesium metal. As a matter of fact, one can claim that the proposed process could compete with the well-known Dow process for the extraction of magnesium chloride from seawater. 

About 75 percent of the caustic produced is concentrated. The remainder is used directly as alkaline cell liquor—as, for example, in the conversion of propylene to propylene oxide by the chlorhydrin process. Similarly, there is some chlorine produced by methods that do not produce caustic, as shown in Table 12.18. Fused chloride salt electrolysis produces chlorine in the manufacture of magnesium metal by the Dow process, and of sodium metal in the Downs cell. The only other process of note is the Kel-Chlor process. This process converts by-product HCl to chlorine by oxidation with NO2 through the intermediates NOCl and HNSO5. 

The manufacture of refractory metals such as titanium, zirconium, and hafnium by sodium reduction of their haHdes is a growing appHcation, except for titanium, which is produced principally via magnesium reduction (109—114). Typical overall haHde reactions are... 

The ease of oxidation of magnesium is important in the commercial manufacture of titanium metal. Titanium, when quite pure, shows great promise as a structural metal, but the economics of production have thus far inhibited its use. One of the processes currently used, the Kroll process, involves the reduction of liquid titanium tetrachloride with molten metallic magnesium ... 

The harnessing of electricity led to the manufacturing of magnesium and aluminum metals by electrolysis in the latter part of the 19th century, and bright white sparks and white light could... 

Economic Importance Since the manufacture of magnesium chloride is closely linked with the manufacture of metallic magnesium, it follows developments in this sector. In the mid-1970 s ca. 600 10 t/a of magnesium chloride was produced in the Western World, whereas it was ca. 520 10 t/a in 1996. 

Calcium is utilized in the manufacture of special metals such as zirconium, thorium, uranium and the rare earths, as a refining agent in metallurgy (steel, copper, magnesium, tantalum, lead) and in the manufacture of calcium hydride (hydrogen source). 

Use Refractory for furnaces manufacture of magnesium compounds and magnesium metals as building material in fertilizers stock feeds papermaking ceramics mineral wool removal of sulfur dioxide from stack gases. 

The most important single use of calcium oxide is in metallurgy, particularly in the production of steel. When calcium oxide is added to the furnace in which steel is made, it reacts with sulfur, phosphorus, silica, and other impurities present in the mixture from which steel is produced. The complex mixture that results can be poured off the top of the molten steel in the form of a slag, a nonmetallic waste formed during the production of metals. Calcium oxide plays a comparable role in the manufacture of other metals, such as aluminum and magnesium. About 40 percent of all the calcium oxide produced in the United States goes to metallurgical applications. 

Electrolysis is employed widely in the manufacture of both metals and chemicals. For instance, the method is used to extract the metals sodium, magnesium and aluminium from their fused salts. In the chemicals industry, one of the largest processes is the electrolysis of an aqueous solution of sodium chloride (brine) for the manufacture of chlorine and caustic soda, i.e.. 

Manufacture of important metals such as aluminium and magnesium by electrolysis of melted metal oxides. 

Magnesium fluoride is a by-product of the manufacture of metallic beryllium and uranium. The beryllium or uranium fluorides are intimately mixed with magnesium metal in magnesium fluoride-lined cmcibles. On heating, a Thermite-type reaction takes place to yield the desired metal and Mgp2 (13). Part of the magnesium fluoride produced in this reaction is then used as a lining for the cmcibles used in the process. 

Magnesium metal can be manufactured by electrolytic and metaHothermic reduction. The method of choice depends on several variables including raw material availabiUty, location, and integration into other chemical faciUties. Producers and corresponding capacities are shown in Table 2 (see also... 

Additioaal components such as alumiaa [1344-28-1] are also added to obtaia more favorable thermodyaamics, and to obtain a slag having favorable properties. Many different feed and slag compositions exist, as do alternative reductants for ferrosiUcon. It is also theoretically possible to manufacture magnesium metal by the reduction of MgO with carbon. 

Isopropyl alcohol can be oxidized by reaction of an a,P-unsaturated aldehyde or ketone at high temperature over metal oxide catalysts (28). In one Shell process for the manufacture of aHyl alcohol, a vapor mixture of isopropyl alcohol and acrolein, which contains two to three moles of alcohol per mole of aldehyde, is passed over a bed of uncalcined magnesium oxide [1309-48-4] and zinc oxide [1314-13-2] at 400°C. The process yields about 77% aHyl alcohol based on acrolein. 

Hexachloroethane has been suggested as a degasifter in the manufacture of aluminum and magnesium metals. Hexachloroethane has been used as a chain-transfer agent in the radiochemical emulsion preparation of propylene tetrafluoroethylene copolymer (152). It has also been used as a chlorinating agent in the production of methyl chloride from methane (153). 

The magnesium metal is thus recovered for repeated use in reaction (7). Chlorine produced in reaction (5) is also put to use in the manufacture of TiCh, the other reactant in reaction (7). 

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