Electrolysis of molten magnesium chloride

Calculate the mass of magnesium that can he plated onto the cathode hy the electrolysis of molten magnesium chloride, using a current of 3.65 A for 55.0 min. 

Magnesium metal is produced by the electrolysis of molten magnesium chloride using inert electrodes. 

Extracting magnesium from sea water is an efficient and economical process. Sea water is mixed with lime, CaO, from oyster shells to form insoluble magnesium hydroxide, Mg(0H)2, which can be easily filtered out. Hydrochloric acid is added to the solid to form magnesium chloride. The electrolysis of molten magnesium chloride will produce pure magnesium metal. 

The final step in the production of magnesium from seawater is the electrolysis of molten magnesium chloride, in which the overall reaction is... 

If the cost of electricity to produce magnesium by the electrolysis of molten magnesium chloride is 155 per ton of metal, what is the cost (in dollars) of the electricity necessary to produce (a) 10.0 tons of aluminum, (b) 30.0 tons of sodium, (c) 50.0 tons of calcium ... 

The Aluminum Company of America (known as Alcoa since 1999) was foimded in 1909 and became a msgor producer of aluminum by the HaU-Heroult process. Canada-based company Rio Tinto Alcan and Norvray-based Norsk Hydro are also msgor producers of aluminum. Msgnesium was first made commercially in Germany by I. G. Farben in the 1890 s, and later in the United States by Dow Chemical. In both instances, electrolysis of molten magnesium chloride was used to produce the magnesium. 

Electrowinning of Other Metals. Magnesium, like aluminum, is a low-density metal and is also manufactured by electrolysis. The electrolysis of molten magnesium chloride (in the presence of other metal chlorides to lower the melting point) yields mj ne-sium at the cathode. The scale of ms nesium production is not as large as that of aluminum, amounting to several hundred thousand metric tons per year. Ms -nesium is used in aircraft alloys, flares, and chemical syntheses. 

How long wiU it take to produce 1.00 X ICP kg of magnesium metal by the electrolysis of molten magnesium chloride using a current of 5.00 X 10 A ... 

Calculate the number of grams of magnesium that can be produced by supplying 1.00 F to the electrode. Consider the electrolysis of molten barium chloride, BaCl2. (a) Write the half-reactions, (b) How many grams of barium metal can be produced by supplying 0.50 A for 30 min ... 

Electrolysis of molten NaCl is also carried out on a large scale, yielding sodium metal at the cathode rather than hydrogen. Still other processes involve the electrolysis of fused magnesium chloride (MgCU) or the oxidation of hydrogen chloride by oxygen or air in the presence of a copper catalyst. 

FIGURE 12.18 A schematic diagram of the electrolytic cell used in the Dow process for magnesium. The electrolyte is molten magnesium chloride. As the current generated by the external source passes through the cell, reduction occurs at the cathode and oxidation at the anode. The products of the electrolysis are magnesium metal and chlorine gas. 

Davy discovered several elements in this way, beginning in 1807. After releasing purified potassium metal from potassium hydroxide, it took him only a year to produce magnesium, strontium, barium, and calcium. Fewer than 30 elements had been isolated by 1800, but by 1850, more than 50 were known. Most of these new elements were isolated using electrolysis. Figure 17.2 shows the modern commercial electrolysis of molten rock salt. Rock salt is sodium chloride, NaCl. In this process, pure sodium metal and chlorine gas are produced. 

Metallurgy. — The metals of most of the cerium group elements have been prepared, three general methods having been used t (1) fusion of the anhydrous halides with sodium, potassium, calcium, or aluminium (2) electrolysis of the fused chlorides or of a solution of the oxide in the molten fluoride (3) heating the oxides with magnesium, calcium, or silicon. Reduction with aluminium has also been tried, but it is not satisfactory except possibly for cerium itself. Electrolysis has been the most successful, the other methods usually giving at best an alloy. 

These metals are all produced by electrolysis of a mixture of molten metal chlorides the electrolyte composition is selected to minimize the process temperature and to ensure that it is the desired metal that is discharged at the cathode. The estimated annual world production of sodium and magnesium is a few hundred thousand tons while that for lithium is only a few thousand tons. The... 

Worldwide, 94% of the chlorine is made by the electrolysis of brine. Sodium hydroxide and hydrogen are prodnced as by-products. A few plants produce potassium hydroxide as well as, or instead of, sodinm hydroxide by the electrolysis of potassium chloride solutions. Abont 3% of the chlorine is made by other processes. These include electrolysis of hydrochloric acid electrolysis of molten sodinm or magnesium chloride, which, respectively, produce sodium or magnesium metal as well as chlorine " nitric acid oxidation of potassinm chloride to make nitrosyl chloride, which is further oxidized by oxygen to make potassium nitrate, and the oxidation of hydrochloric acid directly with oxygen or air using a catalyst, or indirectly throngh the formation and snbsequent oxidation of metal chlorides. ... 

Oyster shells or other seashells are calcined in a kiln to produce calcium oxide, which when added to seawater precipitates magnesium ion as magnesium hydroxide.This is neutralized with hydrochloric acid to give magnesium chloride. Electrolysis of molten MgClj yields magnesium metal and chlorine. Hydrochloric acid can be recovered by burning the chlorine with natural gas. 

Some metals are extracted in electrolytic cells. In section 11.3, you saw the extraction of sodium from molten sodium chloride in a Downs cell. Other reactive metals, including lithium, beryllium, magnesium, calcium, and radium, are also extracted industrially by the electrolysis of their molten chlorides. 

Like the alkali metals, the pure alkaline earth elements are produced commercially by reduction of their salts, either chemically or through electrolysis. Beryllium is prepared by reduction of BeF2 with magnesium, and magnesium is prepared by electrolysis of its molten chloride. 

There are no chemical reducing agents strong enough to reduce compounds of the most active metals, so these metals are produced by electrolytic reduction (Section 18.12). Lithium, sodium, and magnesium, for example, are obtained by the electrolysis of their molten chlorides. Aluminum is manufactured by the electrolysis of purified AI2O3 in molten cryolite (NaaAlFg). 

Recently, Sharma [299], at General Motors, proposed a low cost method for the production of Al-Mg alloys, which can be used in the automobile industry and for desulfurization of steel. The unit cell is shown in Figure 29. The cathode of liquid aluminum is at the bottom of the cell where magnesium is deposited. The electrolyte is a mixture of molten chlorides in which partly dehydrated MgCl2 is dissolved and the electrolysis temperature is 750°C. The same author also described another method to produce magnesium metal using an electrochemical cell with bipolar electrodes, shown in Figure 30. 

---