The goal of the extraction process is to obtain dry, powdered, sodium alginate. The calcium and magnesium salts do not dissolve in water; the sodium salt does. The rationale behind the extraction of alginate from the seaweed is to convert all the alginate salts to the sodium salt, dissolve this in water, and remove the seaweed residue by filtration. The alginate must then be recovered from the aqueous solution. The solution is very dilute and evaporation of the water is not economic. To the Sodium alginate from the initial extraction solution, a calcium salt is added. This causes calcium alginate to form with a fibrous texture; it does not dissolve in water and can be separated from it with relative ease using a metal screen.