Electrolytic Production

Anhydrous magnesium chloride in the molten state has been produced extensively from MgO obtained either from calcined magnesium hydroxide from seawater or from calcined magnesite, as shown in reaction (14.7)  

The reduction process is carried out in refractory-lined electrolytic cells, the chlorine gas being collected and reused in the process, while molten magnesium metal is collected from the cathodes. 

and Wardle, R. W. (1981). Magnesium Compounds. In Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 14, 3rd ed. Wiley New York. Dawson, C. R., Ratner, H., and Roberts, L. R. (1959). Presentation before the Division of Petroleum Chemistry of the American Chemical Society, Atlantic City Meeting, September 13-19. 

Spearot, J. (1974). National Meeting of the American Chemical Society, Los Angeles, March 31-April 5, 19(3), 598. 

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Other Chlorine Production Processes. Although electrolytic production of CI2 and NaOH from NaCl accounts for most of the chlorine produced, other commercial processes for chlorine are also in operation. 

Chlorine from Potassium Hydroxide Manufacture. One of the coproducts during the electrolytic production of potassium hydroxide employing mercury and membrane ceHs is chlorine. The combined name plate capacity for caustic potash during 1988 totaled 325,000 t/yr and growth of U.S. demand was expected to be steady at 2% through 1990 (68). 

The lime—soda process is practiced mainly in isolated areas in some process operations, in the Kraft recovery process, and in the production of alurnina. It is not as efficient a route as electrolytic production. 

Sodium Hydroxide. Before World War 1, nearly all sodium hydroxide [1310-93-2], NaOH, was produced by the reaction of soda ash and lime. The subsequent rapid development of electrolytic production processes, resulting from growing demand for chlorine, effectively shut down the old lime—soda plants except in Eastern Europe, the USSR, India, and China. Recent changes in chlorine consumption have reduced demand, putting pressure on the price and availabiHty of caustic soda (NaOH). Because this trend is expected to continue, there is renewed interest in the lime—soda production process. EMC operates a 50,000 t/yr caustic soda plant that uses this technology at Green River it came onstream in mid-1990. Other U.S. soda ash producers have aimounced plans to constmct similar plants (1,5). 

A low grade fluoroboric acid (16) is used in the manufacture of cryoflte (28) for the electrolytic production of aluminum ... 

Kh. L. Strelets, Electrolytic Production of Magnesium, TT76-50003, U.S. Dept, of Commerce, Technical Information Service, Springfield, Va., translated byJ. Schmorak, Keter PubHshing House Jemsalem Ltd., 1977. 

Regulations. In order to decrease the amount of anthropogenic release of mercury in the United States, the EPA has limited both use and disposal of mercury. In 1992, the EPA banned land disposal of high mercury content wastes generated from the electrolytic production of chlorine—caustic soda (14), accompanied by a one-year variance owing to a lack of available waste treatment faciUties in the United States. A thermal treatment process meeting EPA standards for these wastes was developed by 1993. The use of mercury and mercury compounds as biocides in agricultural products and paints has also been banned by the EPA. 

Examples of similar processes are the decomposition of precipitated aluminum trHiydroxide to alumina, which is the feed for the electrolytic production of aluminum metal, and the drying of wet sulfide concentrates in preparation for flash roasting (see Aluminumand aluminum alloys). 

Electrolysis of Fused Sodium Hydroxide. The first successful electrolytic production of sodium was achieved with the Castner cell (2) ... 

Air pollution problems and labor costs have led to the closing of older pyrometaHurgical plants, and to increased electrolytic production. On a worldwide basis, 77% of total 2inc production in 1985 was by the electrolytic process (4). In electrolytic 2inc plants, the calcined material is dissolved in aqueous sulfuric acid, usually spent electrolyte from the electrolytic cells. Residual soHds are generally separated from the leach solution by decantation and the clarified solution is then treated with 2inc dust to remove cadmium and other impurities. 

Fig. 2. Electrolytic production of cadmium from 2inc electrolyte purification residue (5,6).

Chemical Production. Electrolytic production of chemicals is conducted either by solution (water) electrolysis or fused-salt electrolysis. Fluorine, chlorine, chlorate, and manganese dioxide are Hberated from water solutions magnesium and sodium are generated from molten salt solutions. 

Chromic Acid Electrolysis. Alternatively, as shown in Figure 1, chromium metal may be produced electrolyticaUy or pyrometaUurgicaUy from chromic acid, CrO, obtained from sodium dichromate by any of several processes. Small amounts of an ionic catalyst, specifically sulfate, chloride, or fluoride, are essential to the electrolytic production of chromium. Fluoride and complex fluoride catalyzed baths have become especially important in recent years. The cell conditions for the chromic acid process are given in Table 7. 

Hydrogen fluoride Catalyst in some petroleum refining, etching glass, silicate extraction by-product in electrolytic production of aluminum Petroleum, primary metals, aluminum Strong irritant and corrosive action on all body tissue damage to citrus plants, effect on teeth and bones of cattle from eating plants... 

Unsaturated sulphone Reduction potential (Electrolyte) Product Coulometry (F mol-1) Ref. 

FIGURE 14.17 A diaphragm cell tor the electrolytic production of sodium hydroxide from brine (aqueous sodium chloride solution), represented by the blue color. The diaphragm (gold color) prevents the chlorine produced at the titanium anodes from mixing with the hydrogen and the sodium hydroxide formed at the steel cathodes. The liquid (cell liquor) is drawn off and the water is partly evaporated. The unconverted sodium chloride crystallizes, leaving the sodium hydroxide dissolved in the cell liquor. 

C19-0036. Explain why neither aqueous KF nor pure liquid HF can be used for the electrolytic production of fluorine, even though both liquids are easier to handle than molten potassium fluoride. 

Monofunctional and Polyfunctional Electrodes At monofunctional electrodes, one sole electrode reaction occurs under the conditions specified when current flows. At polyfunctional electrodes, two or more reactions occur simultaneously an example is the zinc electrode in acidic zinc sulfate solution. When the current is cathodic, metallic zinc is deposited at the electrode [reaction (1.21)] and at the same time, hydrogen is evolved [reaction (1.27)]. The relative strengths of the partial currents corresponding to these two reactions depend on the conditions (e.g., the temperature, pH, solution purity). Conditions may change so that a monofunctional electrode becomes polyfunctional, and vice versa. In the case of polyfunctional electrodes secondary (or side) reactions are distinguished from the principal (for the given purpose) reaction (e.g., zinc deposition). In the electrolytic production of substances and in other practical applications, one usually tries to suppress all side reactions so that the principal (desired) reaction will occur with the highest possible efficiency. 

Many electrochemical devices and plants (chemical power sources, electrolyzers, and others) contain electrolytes which are melts of various metal halides (particularly chlorides), also nitrates, carbonates, and certain other salts with melting points between 150 and 1500°C. The salt melts can be single- (neat) or multicomponent (i.e., consist of mixtures of several salts, for their lower melting points in the eutectic region). Melts are highly valuable as electrolytes, since processes can be realized in them at high temperatures that would be too slow at ordinary temperatures or which yield products that are unstable in aqueous solutions (e.g., electrolytic production of the alkali metals). 

Several factors are considered in the design of an electrolytic production cell. These include (i) the nature of the product desired, the starting materials, and the level of production to be achieved (ii) the current density, the current efficiency, the permissible recovery, and the electrolysis temperature (iii) the compatibility of the container material with the electrolyte and of the electrodes with the electrolyte and (iv) any specific requirements associated with the handling of the electrode products. 

A. K. Suri and C. K. Gupta, Electrolytic Production of Molybdenum from a Molten Chloride Bath Using Molybdenum Dioxide Carbon Anodes, J. Less Common Met., Vol. 37, p. 389,1973. 

A. J. Monhemius, The Electrolytic Production of Zinc, in Topics in Nonferrous Extractive Metallurgy, ed. A. R. Burkin, Blackwell Scientific, p. 104,1980. 

One of the major costs in the electrolytic production of chlorine is electrical power. Should the power be purchased, or is a power generating station to be built If a power generator is to be built, should it be built large enough so that it can provide power for future expansions and for other existing plants the company may own in the general area The answers to these questions will greatly affect the amount of capital the company must allocate for the project. 

Madaus, John H., and Herman B. Urbach. "Electrolytic Production of Dichloroformoxime." US Patent 2,918,418, December 22,1959. 

Bratt and Gorden (60) Purification of solutions for electrolytic production of zinc. 

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