Iodine was discovered in 1811 by Bernard Courtois who was the manufacturer of saltpeter (potassium carbonate) and soap. Since old ages alkaline metals carbonates (soude de varech or salin de varech in French), crucially necessary for gunpowder manufacture were extracted in France and other countries from seaweed (varech in French) gathered at the coasts of Normandy and Brittany. For this purpose seaweed was burned and the ash then washed with water. After the process, the remaining wastes were destroyed by adding sulphuric acid. In 1811 Courtois accidentally added excess sulphuric acid resulting in a violet vapor cloud that condensed on colder objects forming dark, lustrous crystals, which as Courtois suspected, belonged to a new element.
Louis-Joseph Gay-Lussac and Andre M. Ampere also investigated the new element, after which Gay-Lussac offered to name it iode. Ampere had given his sample to Sir Humpry Davy, who visited Paris travelling to Italy. He sent off a paper to the Royal Society of London in 1813 describing his experiments and recognizing the similarities between the new substance and chlorine. He named it iodine, after the Greek ιοειδης [ioeides] = violet coloured (from ιον [ion] = violin), which was analogous to chlorine and fluorine, the name, which is now fully accepted in English-speaking environment. |
Iodine is the least abundant of the halogen elements, approximately 4x10-5% on average of the Earth's crust. It is rarer than thulium the most inaccessible among all lanthanides.
A feature which resembles rare earth elements are it's a literally trace element; being a rare element, it is almost omnipresent. Even in superfine rock quartz crystals iodine micro impurities may be found. In calcite crystals Iodine concentration may reach 5x10-6%. Iodine occurs in soils, in fresh (rivers) and seawaters, in plant cells and in animal tissues. However minerals rich of iodine, are very rare. Lautarite Ca(IO3)2 is the most well-known among them, however it does not form commercially significant deposits.
Iodine may be recovered only from such concentrated natural sources as slat lakes water, associated oil waters, or seaweed. One ton of laminaria contains up to 5 kg of iodine; meanwhile its concentration in seawater is 20 - 30g in 1 ton.
As most vitally important elements iodine is in process cycling turnover in nature. Many of iodine compound a soluble in water; that brings to leaching iodine from magmatic rocks into sea and oceans. Seawater, vaporizing, passes elemental iodine into air. "Elemental" is a key word; compounds of the iodine oxidize until I2 in the presence of carbon dioxide.
Winds transfer iodine with mass of air from oceans to continents where iodine precipitates getting into soil, ground waters and into living organisms, which accumulate iodine and return it into soil after dying.
This is just the general description of iodine turnover, which is researched very well because of iodine's importance for life. |