How does the Dow process make magnesium chloride from seawater?

The Dow process does not extract magnesium chloride directly from seawater; rather, it uses seawater as a source to produce magnesium hydroxide, which is subsequently converted into magnesium chloride.1

The process involves the following steps:

• Precipitation: Seawater is mixed with lightly burned reactive dolomite in a flocculator. This causes insoluble magnesium hydroxide to precipitate out of the solution.1
• Collection: The precipitate settles to the bottom of a settling tank, where it is pumped out as a slurry and filtered.1
• Conversion: The filtered magnesium hydroxide is reacted with hydrochloric acid to produce magnesium chloride.1
• Dehydration: The resulting solution is dried through a series of evaporation steps until it reaches approximately 25 percent water content. Final dehydration occurs later during the smelting process.1