Description
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Iodine is a halogen that is a dark violet-grey color in its natural solid state. Iodine is the least reactive halogen that will undergo sublimation into a pink gas at standard temperatures. Iodine has an atomic weight of 126.90447, a melting point of 236.66 °F, and a boiling point of 363.7 °F. The main use of iodine is in a tincture form for medicinal and sterilization purposes; silver iodide is commonly used in photography development, and tungsten iodide is used as a component in light bulbs.
Isolation
Iodine occurs in nature in the mineral caliche, and in the form of iodide in seawater. Different chemical processes are used to isolate iodine from these sources.
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The extraction of iodine from seawater is not normally used for large scale commercial needs as the process is not energetically efficient. Electrolysis must be used to isolate iodine from seawater. Bromide processing from seawater can be turned to a brine that is flushed with air and chlorine gas. Through the electrolysis process, the iodide is oxidized to pure iodine by the chlorine.
The caliche mineral reserves in Chile are the largest source for commercial extraction and isolation of iodine. This caliche ore is composed of nitrate salt deposits including sodium iodide. During the isolation process, a solution of iodine is formed and reacted with sulfuric acid. This produces gaseous iodine which is reacted with is oxidized further to produce a pure iodine gas. The evaporated iodine is collected in a tower where acid and sulfur dioxide are used to further reduce the iodine. The last step of this process uses chlorine to further concentrate the iodine.