Castner process

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 metal would start to dissolve in the melt.

History

The Castner process for production of sodium metal was introduced in 1888 by Hamilton Castner. At that time (prior to the introduction in the same year of the Hall-Héroult process for electrowinning aluminum) the primary use for sodium metal was as a reducing agent to produce aluminum from its purified ores. The Castner process reduced the cost of producing sodium in comparison to the old method of reducing sodium carbonate at high temperature using carbon. This in turn reduced the cost of producing aluminum, although the reduction-by-sodium method still could not compete with Hall-Héroult. The Castner process continued nevertheless due to Castner's finding new markets for sodium. In 1926, however, the Downs cell replaced the Castner process.