How was magnesium extracted from seawater during World War II?

During World War II, the Dow Chemical Company and Magnesium Elektron Limited pioneered the electrolytic reduction of magnesium from seawater to meet wartime demands.1

The extraction process, known as the Dow process, involved several key steps:

• Precipitation: Seawater was mixed with lightly burned reactive dolomite in a flocculator. This caused magnesium hydroxide to precipitate to the bottom of a settling tank.2
• Conversion: The resulting magnesium hydroxide slurry was filtered and reacted with hydrochloric acid to produce magnesium chloride.2
• Dehydration: The solution underwent a series of evaporation steps to reduce its water content to approximately 25 percent, with final dehydration occurring during the smelting process.2
• Electrolysis: The prepared magnesium chloride was fed into electrolytic cells. Within these cells, the compound was dissociated into magnesium metal, which floated to the top for collection, and chlorine gas, which could be reused.2

This industrial method allowed for the large-scale production of magnesium from sources like Galveston Bay and the North Sea.1