PRODUCTION OF SODIUM, LEAD AND BISMUTH

Sodium is among the most abundant elements. Its content in the earth s crust is about 2.5 wt.%. The most important sodium compound, produced in the amount of millions of tons, is NaCl, the content of NaCl in seawater being about 3%. 

Sodium can be produced by high-temperature reaction from almost any its compound (NaCl, NaOH, Na2C03 and Na2S). The method of sodium production that has enjoyed the widest application is electrolysis of the molten salts, for example  

Since water interacts with the one-half amount of sodium produced in this reaction, sodium yield cannot exceed 50% of theoretical value. In other electrolysis reactions, the yield of sodium could be even lower. Metallic sodium production by electrolysis of molten NaCl having melting point about 800°C is the most wide spread method. In order to reduce melting temperature such salts as CaCb, Na2COs, etc. are used. For instance, mixture consisting of 40% NaCl and 60% CaCU has melting temperature of 580 C, while mixture of 35.6% NaCl and 64.4% Na2C03 melts at 600°C. 

In electrolytic vat, the anode is usually made of graphite, the cathode being made of metal (Fe). Chlorine being by-product of this process is either discharged into atmosphere or accumulated for further using. Electric energy needed for sodium production is about 15 kW-h/kg Na. 

Sodium produced by electrolysis contains 99.7 to 99.8% of basic metal and impurities ( 0.1%K, 0.001% Fe, 0.15% Ca and others, such as Ba, Zr and Sn). It should be noted that the use of graphite electrodes causes sodium to be polluted with carbon. The worldwide sodium production data is given in Table 4.1 [4.1, 4.2]. 

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