How is magnesium hydroxide made from seawater?

To produce magnesium hydroxide from seawater, industrial methods such as the Dow process utilize a chemical precipitation technique. Seawater is mixed with lightly burned, reactive dolomite in a flocculator.1

During this process, the magnesium in the seawater reacts with the dolomite to form insoluble magnesium hydroxide. This substance precipitates and settles to the bottom of a settling tank. Once it has settled, the magnesium hydroxide is pumped out as a slurry and subsequently filtered for further use, such as conversion into magnesium chloride.1