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In what order do dissolved salts precipitate as seawater evaporates?
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Salt crystal magnified.
When seawater evaporates, the dissolved salts precipitate in a specific order based on their solubility, moving from the least soluble to the most soluble components. As the solution becomes increasingly concentrated, the minerals form layers on the bottom of the evaporating basin.12
The general order of deposition is as follows:
- Calcium carbonate1
- Calcium sulfate (such as gypsum and anhydrite)132
- Sodium chloride (halite)124
- Magnesium sulfate1
- Potassium magnesium chloride1
- Magnesium chloride1
In industrial salt production, the process is often managed to isolate sodium chloride. Producers typically move the brine to a separate crystallization pond once it reaches saturation for sodium chloride but before the more soluble salts—such as those containing potassium and magnesium—begin to precipitate, ensuring the final product remains free from these contaminants.4