Brines electrolytic reduction

In 1808, Sir Humphry Davy reported the production of Mg in the form of an amalgam by electrolytic reduction of its oxide using a Hg cathode. In 1828, the Fr scientist A. Bussy fused Mg chloride with metallic K and became the first to produce free metallic Mg. Michael Faraday, in 1833, was the first to produce free metallic Mg by electrolysis, using Mg chloride. For many years, however, the metal remained a laboratory curiosity. In 1886, manuf of Mg was undertaken on a production scale in Ger, using electrolysis of fused Mg chloride. Until 1915, Ger remained the sole producer of Mg. However, when a scarcity of Mg arose in the USA as a result of the Brit blockade of Ger in 1915, and the price of Mg soared from 1.65 to 5.00 per lb, three producers initiated operations and thus started a Mg industry in the USA. Subsequently, additional companies attempted production of Mg, but by 1920 only two producers remained — The Dow Chemical Co (one of the original three producers) and. the American Magnesium Corn. In 1927. the latter ceased production, and Dow continued to be the sole domestic producer until 1941. The source of Mg chloride was brine pumped from deep wells. In 1941, Dow put a plant into operation at Freeport, Texas, obtaining Mg chloride from sea-... 

Sludges result from the pretreatment of resaturated brine for removal of impurities, and from brine to be discharged, which was occasionally necessary because of water buildup in the brine circuit. These sludges contain 8-15 mg/g (dry basis) mercury as a complex mixture of compounds. To recover the mercury, most of the water is removed, and then the sludge is resuspended in aqueous sodium hypochlorite. The hypochlorite oxidizes the sulfide and any elemental mercury present (Eqs. 8.46 and 8.51) in order to produce a concentrated aqueous stream of dissolved mercury salts. Insoluble components are then removed by filtration, and the solution is then returned to the brine circuit. When this reaches the electrolyzer, electrolytic reduction recovers the dissolved mercury present (Eq. 8.52). 

The brine containing some 15 per cent of sodium chloride is admitted to the electrolyzer at Oj and flows through the compartments which are arranged in cascades, and is let out at o2. The warmed electrolyte is cooled in a suitable cooler, and recirculated until the required concentration of active chlorine is attained. An electrolyzer with 36 compartments takes 60 A at a total voltage of 220 V. The temperature of the brine is maintained at 21 °C. Calcium chloride and Turkey red oil are added to the brine to lower cathodic reduction. 

Electrolysis of brine The decomposition of brine, an aqueous solution of sodium chloride, is another process that is accomplished by electrolysis. Figure 21-19 illustrates the electrolytic cell and products of the electrolysis of brine. Two reactions are possible at the cathode, the reduction of sodium ions and the reduction of hydrogen in water molecules. 

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