mercury cell
Quick Summary
The mercury cell is a method used in the chlor-alkali industry to produce chlorine and caustic soda simultaneously through the electrolytic decomposition of salt (sodium chloride). In this process, mercury acts as the cathode (negative terminal). This is significant because mercury has a high overpotential, meaning it requires a much higher voltage to reduce water molecules compared to iron. This allows sodium ions in the brine to be reduced to sodium metal at the mercury cathode without reducing water.1
The metallic sodium dissolves in the mercury, forming an amalgam. This amalgam then flows out of the cell and reacts with water in a separate vessel to produce sodium hydroxide (caustic soda) and hydrogen gas. The advantage of the mercury cell is that it produces high-purity sodium hydroxide, free from salt, which is desirable for certain applications like rayon manufacturing. Mercury's unique properties, such as its low melting point and high specific gravity, also make it useful in various other applications, including thermometers, barometers, and electrical switches. However, mercury is highly toxic, and care must be taken to prevent mercury poisoning through proper handling and ventilation.12
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