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Seaweed is a macroscopic, multicellular, benthic marine algae. Seaweed is a source of iodine, primarily used in nutrition and other industrial and medicinal purposes. Ribbon seaweeds (sp. laminaria) contain iodine compounds which they obtain by extracting iodide ions from seawater. This iodine can be extracted from the seaweed by heating it in air to an ash, in which the iodine is present as iodide. The iodide is dissolved out of the residue by boiling water, the solution filtered and the iodide oxidised to iodine using hydrogen peroxide. The iodine colours the solution brown at this stage. Isolating the iodine from this solution can be done by solvent extraction, followed by evaporation of the solvent.