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Salt (sodium chloride) has been a valuable commodity since prehistoric times, and its extraction from seawater also goes back to prehistory. Salt is extracted from seawater in many countries around the world, but the majority of salt put on the market today is mined from solid evaporite deposits.
The ancient Chinese gradually mastered and advanced the techniques of producing salt. Salt mining was an arduous task for them, as they faced geographical and technological constraints. Salt was extracted mainly from the sea, and salt works in the coastal areas in late imperial China equated to more than 80 percent of national production. [5]
Diagram of Castner process apparatus. The Castner process is a process for manufacturing sodium metal by electrolysis of molten sodium hydroxide at approximately 330 °C. Below that temperature, the melt would solidify; above that temperature, the molten sodium would start to dissolve in the melt.
The first type, shown on the right and left of the diagram, uses an electrolyte of sodium chloride solution, a graphite anode (A), and a mercury cathode (M). The other type of cell, shown in the center of the diagram, uses an electrolyte of sodium hydroxide solution, a mercury anode (M), and an iron cathode (D). The mercury electrode is common ...
The sodium–mercury amalgam flows to the center cell, where it reacts with water to produce sodium hydroxide and regenerate the mercury. Mercury cell electrolysis, also known as the Castner–Kellner process , was the first method used at the end of the nineteenth century to produce chlorine on an industrial scale.
Open-pan salt making is a method of salt production wherein salt is extracted from brine using open pans. Virtually all European domestic salt is obtained by solution-mining of underground salt formations, although some is still obtained by the solar evaporation of seawater.
Sodium chloride (NaCl) melts at 801 °C (1074 Kelvin), but a salt mixture can be kept liquid at a temperature as low as 600 °C at the mixture containing, by weight: 33.2% NaCl and 66.8% CaCl 2. If pure sodium chloride is used, a metallic sodium emulsion is formed in the molten NaCl which is impossible to separate.
The Solvay process or ammonia–soda process is the major industrial process for the production of sodium carbonate (soda ash, Na 2 CO 3).The ammonia–soda process was developed into its modern form by the Belgian chemist Ernest Solvay during the 1860s. [1]