How is magnesium chloride recovered from seawater?

In the context of magnesium processing, magnesium chloride is not extracted directly from seawater in a single step. Instead, industrial methods like the Dow process utilize chemical precipitation to isolate the magnesium content first.1

In the Dow process, seawater is mixed with lightly burned reactive dolomite in a flocculator. This reaction causes magnesium hydroxide to precipitate out of the water. This precipitate is collected in a settling tank, filtered into a slurry, and then reacted with hydrochloric acid to convert it into magnesium chloride. The resulting solution is then dried through a series of evaporation steps to reach the desired water content before it is processed further for electrolysis.1

Alternatively, some methods involve precipitating magnesium hydroxide from seawater, filtering it, and calcining it to produce magnesium oxide. This oxide is then mixed with charcoal and magnesium chloride solution, formed into globules, and subjected to chlorination in a furnace to produce molten magnesium chloride.1