Iodine elements

Iodine, elemental Iodine, resublimed Iron sulfate Isotopes, radioactive Laboratory chemicals, inorganic... 

Iodine is still commonly used in liquid and sofid forms for use in emergency preparation of drinking water sources. The solid forms are sold commercially by various vendors, and are widely distributed by the U.S. Army for use in austere environments. The U.S. Army iodine water purification tablets release 8 mg/1 iodine per tablet (Department of the Army, 2002). Current guidefines specify two tablets per 1-quart canteen of water with a minimum contact time of 35 min to disinfect and prevent giardiasis (Department of the Army, 2002). Among the species of iodine, elemental iodine (fy) and hypoiodous acid (HIO) are the forms with the greatest biocidal efficacy (White, 1999). At pH 8.0 and 25°C, the concentrations of fy and HIO are approximately equal (Snoeyink and Jenkins, 1980). 

Electra 7458. See Com (Zea mays) starch Electrofine S-70. See Paraffin, chlorinated Electrolyte acid. See Sulfuric acid Elefac 1-205. See Octyidodecyl neopentanoate Elemental iodine. See Iodine Elemental selenium. See Selenium Elemi Elemi absolute Elemi anhydrol. See Elemi gum,... 

Table 18.1 Some names of redox titration methods involving the iodine element...

Table 18.1 summarizes the titrimetric methods involving the iodine element studied in this book. In addition to direct and indirect iodometries, other interesting... 

Figure 18.1 shows the diagram F/pH of some species containing the iodine element. It only describes the species that are in true equilibrium. This is the reason why iodine at oxidation numbers -K and -t-VII is not mentioned in this diagram (see iodometry in alkaline medium and periodimetry). 

Concerning this point, the only species derivating from the iodine element to be stable (from a thermodynamic standpoint) in acidic medium are iodine, tri-iodide and iodide ions, iodic acid, and iodate ions. In basic medium, only iodate and iodide ions are stable. 

Among the non-metals, nitrogen and chlorine, for example, are gases, but phosphorus, which resembles nitrogen chemically, is a solid, as is iodine which chemically resembles chlorine. Clearly we have to consider the physical and chemical properties of the elements and their compounds if we are to establish a meaningful classification. 

A complete set of trihalides for arsenic, antimony and bismuth can be prepared by the direct combination of the elements although other methods of preparation can sometimes be used. The vigour of the direct combination reaction for a given metal decreases from fluorine to iodine (except in the case of bismuth which does not react readily with fluorine) and for a given halogen, from arsenic to bismuth. 

Sulphur is less reactive than oxygen but still quite a reactive element and when heated it combines directly with the non-metallic elements, oxygen, hydrogen, the halogens (except iodine), carbon and phosphorus, and also with many metals to give sulphides. Selenium and tellurium are less reactive than sulphur but when heated combine directly with many metals and non-metals. 

The large value for fluorine, and the marked decrease from fluorine to iodine, are points to be noted. The high value for fluorine means that the bond between an element M and fluorine is likely to be more ionic (more polar) than a bond formed by M with any other elements. The low value for iodine indicates the possibility that iodine may be electropositive in some of its compounds. 

Ultrapure iodine can be obtained from the reaction of potassium iodide with copper sulfate. Several other methods of isolating the element are known. 

Iodine is a bluish-black, lustrous solid, volatizing at ordinary temperatures into a blue-violet gas with an irritating odor it forms compounds with many elements, but is less active than the other halogens, which displace it from iodides. Iodine exhibits some metallic-like properties. It dissolves readily in chloroform, carbon tetrachloride, or carbon disulfide to form beautiful purple solutions. It is only slightly soluble in water. 

Iodine compounds are important in organic chemistry and very useful in medicine. Iodides, and thyroxine which contains iodine, are used internally in medicine, and as a solution of KI and iodine in alcohol is used for external wounds. Potassium iodide finds use in photography. The deep blue color with starch solution is characteristic of the free element. 

Chemical ingenuity in using the properties of the elements and their compounds has allowed analyses to be carried out by processes analogous to the generation of hydrides. Osmium tetroxide is very volatile and can be formed easily by oxidation of osmium compounds. Some metals form volatile acetylacetonates (acac), such as iron, zinc, cobalt, chromium, and manganese (Figure 15.4). Iodides can be oxidized easily to iodine (another volatile element in itself), and carbonates or bicarbonates can be examined as COj after reaction with acid. 

If the spent fuel is processed in a nuclear fuel reprocessing plant, the radioactive iodine species (elemental iodine and methyl iodide) trapped in the spent fuel elements ate ultimately released into dissolver off gases. The radioactive iodine may then be captured by chemisorption on molecular sieve 2eohtes containing silver (89). 

Cobalt, copper, molybdenum, iodine, iron, manganese, nickel, selenium, and zinc are sometimes provided to mminants. Mineral deficiency or toxicity in sheep, especially copper and selenium, is a common example of dietary mineral imbalance (21). Other elements may be required for optimal mminant performance (22). ExceUent reviews of trace elements are available (5,22). 

Galhum triiodide [13450-914], Gal, is obtained by direct reaction of the elements or by reaction of iodine solution in carbon disulfide on galhum. 

Iodine [7553-56-2] I, atomic number 53, atomic weight 126.9044, is a nonmetaUic element belonging to the halogen family in Group 17 (VIIA) of the Periodic Table. The only stable isotope has a mass number of 127. There are 22 other iodine isotopes having masses between 117 and 139 14 of these isotopes yield significant radiation. 

Iodine was discovered by Curtois in 1811—1812, when he observed violet vapors rising upon heating saltpeter pots (1). Following its discovery and exarnination, the new element was named iode in French after the Greek word ioeides meaning violet-colored. The Fnglish term iodine comes from the same root (2). 

Occurrence in Nature. About 99.6% of the earth s mass results from 32 of the chemical elements. The remaining 0.4% is apportioned among 64 elements, all of which are present as traces. Iodine is one of these 64. Estimates about abundance of the constituent elements of the Hthosphere place iodine 46th on a restricted Hst of 59 elements (37 very rare elements are excluded) and 61st on a Hst in which 96 elements are included. Iodine is, indeed, one of the scarcest of the nonmetaUic elements in the total composition of the earth (3). 

Although not abundant in quantity, iodine is distributed in rocks, soils, waters, plants, animal tissues, and foodstuffs (3,4). Excepting the possible occurrence of elemental iodine vapor in the air near certain iodine-rich springs, iodine never occurs free in nature. It is always found combined with other elements. 

Iodine forms compounds with all the elements except sulfur, selenium, and the noble gases. It reacts only indirectly with carbon, nitrogen, oxygen, and some noble metals such as platinum. 

The equihbrium constant of this reaction is 5.4 x 10 at 25°C, ie, iodine hydrolyzes to a much smaller extent than do the other halogens (49). The species concentrations are highly pH dependent at pH = 5, about 99% is present as elemental at pH = 7, the and HIO species are present in almost equal concentrations and at pH = 8, only 12% is present as and 88% as HIO. The dissociation constant for HIO is ca 2.3 x 10 and the pH has tittle effect on the lO ion formation. At higher pH values, the HIO converts to iodate ion. This latter species has been shown to possess no disinfection activity. An aqueous solution containing iodate, iodide, and a free iodine or triodide ion has a pH of about 7. A thorough discussion of the kinetics of iodine hydrolysis is available (49). 

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. 

The first iodine recovery from caUche occurred in 1852 the first iodine was exported to Europe in 1868, becoming the most important by-product of the nitrate production in terms of value. There are two ways for producing iodine from caUche iodates first, from solutions containing more equivalent iodine than its solubiUty as elemental iodine in the same solution of about 0.4 g/L at 25°C and second, from more diluted equivalent iodine solutions. 

Up to 0.4 g/L of the iodine stays in solution and the rest precipitates as crystallized iodine, which is removed by flotation (qv). This operation does not require a flotation agent, owing to the hydrophobic character of the crystallized element. From the flotation cell a heavy pulp, which is water-washed and submitted to a second flotation step, is obtained. The washed pulp is introduced into a heat exchanger where it is heated under pressure up to 120°C to melt the iodine that flows into a first reactor for decantation. From there the melt flows into a second reactor for sulfuric acid drying. The refined iodine is either flaked or prilled, and packed in 50- and 25-kg plastic-lined fiber dmms. 

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