Iodine natural deposits

In Nature there is an iodine cycle and indeed thousands of tonnes of iodine escape from the oceans every year as iodide in sea spray or as molecules containing iodine, which are produced by marine organisms. Marine algae emit volatile iodine as iodomethane (CH3I) and diiodomethane (CH2I2) and these may even moderate the world s climate by helping cloud formation. Some of this iodine is deposited on land where it may become part of the bio-cycle. Recently it has been shown that rice plants also emit iodomethane and that this accounts for about 4% of that which is present in the atmosphere. 

Although natural deposits of mineral salts may contain useful quantities of essential trace elements, they are not necessarily present in balanced proportions. The iodine content of Chile salt-petre has been cited in its favour and it has also been reported as having a useful boron content (Lehr,... 

Manufacture and Processing. The industry related to iodine production began a few years after the discovery of the element by Courtois in 1811. The production processes are based on the raw materials containing iodine seaweeds, mineral deposits, and oh-weh or natural gas brines. 

Occurrence. Iodine [7553-56-2] is widely distributed in the Hthosphere at low concentrations (about 0.3 ppm) (32). It is present in seawater at a concentration of 0.05 ppm (33). Certain marine plants concentrate iodine to higher levels than occur in the sea brine these plants have been used for their iodine content. A significant source of iodine is caUche deposits of the Atacama Desert, Chile. About 40% of the free world s iodine was produced in Japan from natural gas wells (34), but production from Atacama Desert caUche deposits is relatively inexpensive and on the increase. By 1992, Chile was the primary world producer. In the United States, underground brine is the sole commercial source of iodine (35). Such brine can be found in the northern Oklahoma oil fields originating in the Mississippian geological system (see Iodine and iodine compounds). 

Although it does not physically explain the nature of the removal process, deposition velocity has been used to account for removal due to impaction with vegetation near the surface or for chemical reactions with the surface. McMahon and Denison (12) gave many deposition velocities in their review paper. Examples (in cm s ) are sulfur dioxide, 0.5-1.2 ozone, 0.1-2.0 iodine, 0.7-2.8 and carbon dioxide, negligible. 

The first iodine-containing mineral (Agl) was discovered in Mexico in 1825 but the discovery of iodate as an impurity in Chilean saltpetre in 1840 proved to be more significant industrially. The Chilean nitrate deposits provided the largest proportion of the world s iodine until overtaken in the late 1960s by Japanese production from natural brines (pp. 796, 799). 

Iodine is widely distributed in nature, found in rocks, soils and underground brines. An important mineral is lautarite, which is anhydrous calcium iodate found in nitrate deposits in Chde. The element also occurs in brown seaweeds, in seawater, and in many natural gas wells. Its concentration in the earth s crust is an estimated 0.5 mg/kg and in seawater 0.06 mg/L. 

Diffusion of Iodine in Nature. The presence of iodine in the Chile saltpeter deposits was first noted by A. A. Hayes, who found it to be present as iodate (142,143). 

Knapp, H.A. (1964) Iodine-131 in fresh milk and human thyroids following a single deposition of nuclear test fallout. Nature, 202, 534-7. 

Solid iodine is purple, as is its vapor (I2), but iodine is often brown in solution, for example, in oxygen-containing solvents such as ethanol tincture of iodine antiseptic) or in water, in which its solubility is increased by formation of a complex ion Is" with iodide ion. Iodine is obtained by oxidizing the ash of dried seaweeds (kelp) alternatively, sodium iodate, which is present in the NaNOs deposits of the Atacama desert in Chile, may be reduced to iodide with aqueous HSO3" ion, followed by the iodide/iodate analog of reaction 12.23 if elemental iodine is wanted. Most of the U.S. production, however, comes from chlorination of natural I"-bearing brines in Michigan (cf. reaction 12.21). Since iodine is a fairly volatile solid, it can be conveniently purified by sublimation. 

Tests of Faraday s Law Tinder Varying Conditions. We have already seen that, if disturbing effects are taken into account, Faraday s law applies to all electrochemical reactions which have been carefully studied. The tests so far mentioned, however, have all been made at ordinary temperature, under atmospheric pressure, and in aqueous solutions. A number of researches have been carried out to find out whether variations in the nature of the solvent, or variations in the physical conditions, such as temperature and pressure, have any influence on the constant in Faraday s law. No real variation in the constant has yet been observed. There are, to be sure, many apparent deviations from the law, such as that observed with the copper coulometcr, which gives a deposit at the cathode which is lighter than the computed value. In this case, as has been seen, the cause of the discrepancy has been found to be the occurrence of a disturbing reaction, In every similar case a simple explanation of the apparent deviation has been readily found. The comparison of the iodine, and of the copper coulometer, with the silver coulometer, as has been described in previous sections, affords precise evidence, for these reactions at least, that Faraday s law is indc-... 

Between 1982 and 1986, the world iodine production remained fairly stable and amounted to approximately 12 500 tons per year. Japan accounted for 57% of the world s production, followed by Chile (23%) and the former Soviet Union (15%). In Japan, iodine is produced entirely as a byproduct of natural gas production. Chile has large reserves of iodine associated with sodium nitrate deposits (Lyday 2002). 

Most of the world s production of iodine comes from the saltpeter deposits in Chile and natural brines in Japan. In Chile, calcium iodate is found in caliche deposits extracted from open pit mines in the Atacama Desert. Applying an alkaline solution to the caliche yields sodium iodate and iodine is obtained from the sodium iodate by reduction with sulfur dioxide. In Japan, iodine is a by-product of the production of natural gas, which is extracted from brine deposits a mile or two below ground. Iodine is recovered from the brines by one of the following two methods. In the blowout process elemental iodine is liberated as a result of the reaction of chlorine with sodium iodide in the brines. Elemental iodine is blown out of the brine with air and then purified in subsequent reaction steps. The second method, ion exchange, involves recovery of dissolved iodine from oxidized brines using anion-exchange resins packed in columns. In 2010, Chile produced 18 000 metric tons of iodine, compared to Japan s output of 9800 metric tons. Chile has reserves of 9 million metric tons, some 60% of the world s total reserves of iodine [10],... 

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