Halides: Yodargyrite

Diagnostic card.

Ag I (silver iodide)
Shingoniya hexagonal
Hardness 1,5
Specific weight 5.69
Cleavage is perfect
Color from dull yellow to white
Wax gloss

The crystals are mostly tabular (plates with hexagonal contours) or prismatic with unequal development of the faces at both ends of the crystal. Cleavage is perfect along the base, but it is not always possible to observe it on mineral samples, because its crystals are rare, it mostly represents a waxy mass. Yodargyrite has a very characteristic dull yellow color, to an almost white, but less intense shade than that of silver bromides (bromargyrite, embolite).

Diagnostic signs.
Yodargyrite is quite plastic - pressed against the paper, it bends at the corners, like a scrap of skin, and leaves a dull yellow line.

Place of Birth.
In Europe, iodargyrite is found in several places in France (Montmen, department of Allier) and Spain (nondelenzina, near the city of Guadalajara). In addition, its tiny crystals are found in Dernbach (Nassau, Germany). In America, the classical location is Tonopa, Nevada, where interesting crystals are found. Other important locations are Messina (Zacatecas, Mexico) and Chagnarsillo (Chile). The world-famous deposit is Broken Hill, Australia.

Iodine (Iodum), I, the chemical element of the VII group of the periodic system of Mendeleev, refers to halogens (in the literature there is also the name Iodine and the symbol J); Atomic number 53, atomic mass 126,9045; Crystals of black-gray color with metallic luster. Natural Iodine consists of one stable isotope with a mass number of 127. Iodine was discovered in 1811 by the French chemist B. Courtois. Heating the mother brine of seaweed ash with concentrated sulfuric acid, he observed the liberation of violet vapor (hence the name Yod - from the Greek iodes, ioeides - like the color of violet, violet), which condensed in the form of dark shiny lamellar crystals. In 1813-1814, the French chemist J.L. Gay-Lussac and chemist G. Davy proved the elementary nature of Yoda (a chemical element).

Propagation of iodine in nature. The average content of iodine in the earth's crust is 4 * 10-5% by mass. The compounds of Yoda are scattered in the mantle and magmas and in the rocks (granites, basalts and others formed from them); The deep minerals of Yoda are unknown. The history of Yoda in the earth's crust is closely related to living matter and biogenic migration. In the biosphere, processes of its concentration are observed, especially marine organisms (algae, sponges and others). There are eight hypergenic Yoda minerals formed in the biosphere, but they are rare.

The main reservoir of Yoda for the biosphere is the World Ocean (in 1 liter, an average of 5 * 10-5 g of Yoda). From the ocean, Yoda compounds, dissolved in drops of sea water, enter the atmosphere and are transported by winds to the continents. (Locations remote from the ocean or fenced off from sea winds by mountains are depleted by Yod). Iodine is easily adsorbed by organic substances of soils and sea ooze. When these sludge is compacted and sedimentary rocks form, desorption takes place, part of the Yoda compounds passes into underground waters. Thus, iodine-bromine waters used for the extraction of Yoda are formed, which are especially characteristic for oil fields (in places, 1 liter of this water contains more than 100 mg of Yoda).

Physical properties of iodine. Iodine density 4.94 g / cm3, mp 113.5 ^° C, tbp 184.35 ^° C. The liquid and gaseous Yod molecule consists of two atoms (I2). Noticeable dissociation of I2 = 2I is observed above 700 ^° C, and also under the action of light. Even at normal temperatures, Iodine evaporates, forming a sharply smelling violet vapor. With mild heating, iodine sublimes, settling in the form of shiny thin plates; This process serves to purify Yoda in laboratories and in industry. Iodine is poorly soluble in water (0.33 g / l at 25 ^° C), well in carbon disulphide and organic solvents (benzene, alcohol and others), as well as in aqueous solutions of iodides.

Chemical properties of Yoda. The configuration of the external electrons of the Yoda atom is 5s25p5. Accordingly, iodine exhibits variable valence in the compounds (degree of oxidation): -1 (in HI, KI), +1 (in HIO, KIO), +3 (in ICl3), +5 (in HIO3, KIO3) and + 7 (in HIO4, KIO4). Chemically, Iodine is quite active, although to a lesser extent than chlorine and bromine. With metals, iodine reacts vigorously when lightly heated, forming iodides (Hg + I2 = HgI2). With hydrogen, iodine reacts only when heated and not completely, forming hydrogen iodide. With carbon, nitrogen, oxygen, iodine does not directly combine. Elementary Iodine is an oxidizer, less strong than chlorine and bromine. Hydrogen sulfide H2S, sodium thiosulfate Na2S2O3 and other reducing agents reduce it to I- (I2 + H2S = S + 2HI). Chlorine and other strong oxidants in aqueous solutions convert it to IO3- (5Cl2 + I2 + 6H2O = 2HIO3H + 10HCl). When dissolved in water, Iodine partially reacts with it (I2 + H2O = HI + HIO); Iodide and Iodate (3I2 + 6NaOH = 5NaI + NaIO3 + 3H2O) are formed in hot aqueous solutions of alkalis. Adsorbed on starch, Iodine stains it in a dark blue color; It is used in Iodometry and qualitative analysis for the detection of Yoda.

Yoda vapor is poisonous and irritates the mucous membranes. On the skin Iodine has a cauterizing and disinfecting effect. Stains from Yoda are washed off with solutions of sodium or sodium thiosulfate.

Getting Yoda. The raw materials for the industrial production of Yoda are oil drilling fluids; Seaweed, mother liquors of Chilean (sodium) nitrate, containing up to 0.4% of iodine in the form of sodium iodate. To extract iodine from petroleum waters (containing usually 20-40 mg / l Iodine in the form of iodides) they are first acted upon by chlorine (2 NaI + Cl2 = 2NaCl + I2) or nitrous acid (2NaI + 2NaNO2 + 2H2SO4 = 2Na2SO4 + 2NO + I2 + 2H2O). The released iodine is either adsorbed with activated charcoal or air blown. Iodine adsorbed by charcoal is treated with caustic alkali or sodium sulphite (I2 + Na2SO3 + H2O = Na2SO4 + 2HI). Of the reaction products, free Iodine is isolated by the action of chlorine or sulfuric acid and an oxidizing agent, for example potassium dichromate (K2Cr2O7 + 7H2SO4 + 6NaI = K2SO4 + 3Na2SO4 + Cr2 (SO4) S + 3I2). When air is blown, Iodine is absorbed by a mixture of sulfur dioxide (IV) with water vapor (2H2O + SO2 + I2 = H2SO4 + 2HI) and then displaced with Iodine by chlorine (2HI + Cl2 = 2HCl + I2). Crude crystalline Iodine is purified by sublimation.

Application of iodine. Iodine and its compounds are used mainly in medicine and in analytical chemistry, as well as in organic synthesis and photography.

Iodine in the body. Iodine is a microelement necessary for animals and humans. In soils and plants of taiga-forest non-chernozem, dry-steppe, desert and mountain biogeochemical zones, Iodine is not present in sufficient quantities or is not balanced with some other trace elements (Co, Mn, Cu); This is associated with the spread in these zones of endemic goiter. The average content of iodine in soils is about 3 * 10-4%, in plants about 2 * 10-5%. In surface drinking waters, Yoda is small (from 10-7 to 10-9%). In the coastal areas, the amount of iodine in 1 m3 of air can reach 50 mcg, in continental and mountain - it is 1 or even 0.2 mcg.

The uptake of iodine by plants depends on the content in the soils of its compounds and on the species of plants. Some organisms (so-called Yoda concentrators), for example, seaweed - fucus, kelp, phyllophora, accumulate up to 1% of Yoda, some sponges - up to 8.5% (in the skeletal substance of the spongin). Algae concentrating Iodine are used for its industrial production. In the animal organism, Iodine is supplied with food, water, air. The main source of Yoda - plant foods and feed. Iodine absorption occurs in the anterior parts of the small intestine. In the human body, from 20 to 50 mg of Iodine is accumulated, including about 10-25 mg in the muscles, in the norm of 6-15 mg in the thyroid gland. With the help of radioactive iodine (131I and 125I) it is shown that in the thyroid gland Iodine accumulates in the mitochondria of epithelial cells and is part of the diiodic and monoiodotyrosins that form in them, which condense into the hormone tetraiodothyronine (thyroxine). Yod is excreted from the body mainly through the kidneys (up to 70-80%), dairy, salivary and sweat glands, in part with bile.

In various biogeochemical provinces, the content of iodine in the diets varies (for a person from 20 to 240 μg, for a sheep from 20 to 400 μg). The need for an animal in Yoda depends on its physiological state, season, temperature, adaptation of the organism to the content of iodine in the environment. The daily requirement for human and animal Yoda is about 3 μg per 1 kg of mass (increases with pregnancy, increased growth, cooling). Introduction to the body Yoda increases basal metabolism, increases oxidative processes, tones muscles, stimulates sexual function.

In connection with the greater or lesser deficiency of iodine in food and water, iodization of common salt, usually containing 10-25 g of potassium iodide per ton of salt, is used. The use of fertilizers containing Iodine can double and triple its content in crops.

Iodine in medicine. Preparations containing Iodine have antibacterial and antifungal properties, they also have anti-inflammatory and distracting effects; They are applied externally for the disinfection of wounds, the preparation of the operating field. When administered orally, Iodine preparations have an effect on metabolism, increase the function of the thyroid gland. Small doses of iodine (micro-yod) inhibit the function of the thyroid gland, acting on the formation of thyroid-stimulating hormone in the anterior pituitary gland. Since Iodine affects protein and fat (lipid) metabolism, it has found application in the treatment of atherosclerosis, as it reduces the cholesterol in the blood; Also increases the fibrinolytic activity of the blood. For diagnostic purposes, radiopaque substances containing Iodine are used.

With long-term use of Iodine preparations and with increased sensitivity to them, iodism may appear - runny nose, urticaria, Quincke's edema, saliva and lacrimation, acne (iododerma), etc. Yoda preparations can not be taken with pulmonary tuberculosis, pregnancy, kidney disease, chronic Podermia, hemorrhagic diathesis, hives.

Iodine is radioactive. Artificially radioactive isotopes of Yoda - 125I, 131I, 132I and others are widely used in biology and especially in medicine to determine the functional state of the thyroid gland and treat a number of its diseases. The use of radioactive iodine in diagnosis is associated with the ability of Yoda to selectively accumulate in the thyroid gland; Use for medicinal purposes is based on the ability of γ-radiation of radioisotopes of iodine to destroy the secretory cells of the gland. When the environment is contaminated with nuclear fission products, the radioactive isotopes of Yod are rapidly incorporated into the biological cycle, eventually reaching the milk and, consequently, into the human body. Especially dangerous is their penetration into the body of children, the thyroid gland is 10 times smaller than in adults, and has a greater radiosensitivity.

In order to reduce the deposition of radioactive isotopes of iodine in the thyroid gland, it is recommended to use preparations of stable Yoda (100-200 mg per reception). Radioactive iodine is quickly and completely absorbed in the gastrointestinal tract and selectively deposited in the thyroid gland. Its absorption depends on the functional state of the gland. Relatively high concentrations of radioisotopes of Yoda are found in salivary and mammary glands and in the mucosa of the gastrointestinal tract. Not absorbed by the thyroid gland radioactive iodine is almost completely and relatively quickly excreted in the urine. On the materials: http://chem100.ru

A significant amount of nuclear fission products (decay) of uranium U and plutonium Pt and other radioactive elements are formed in the course of natural (Earth, stars, space) and artificial (ChNPP, nuclear power plants, GOK, etc.) nuclear and thermonuclear reactions. Most modern "wet" boiling nuclear reactors of nuclear power plants use a uranium fuel (uranium-238 is enriched to increase the uranium-235 content in it, which is used as the main fissionable material) in the water reactor and cooling of the GOK type. As a result, in the case of release into the environment, inert gases (neon, xenon, krypton) are predominantly released - very dangerous, dissolved in the body, colored lamps, etc.

The most noticeable radiation trail is radioactive iodine (a short half-life) and cesium (a long half-life). In total, there are several radioactive isotopes of iodine, the main one is iodine-131, very low doses of which are used for X-ray examination of the thyroid gland and its treatment. This is an extremely radioactive chemical element, whose half-life is eight days (iodine-131). It was dumped by 99.3% in the Chernobyl NPP (Mine) in Ukraine, the CIS, during the accident at the end of the 20th century.

The high radioactivity of iodine-131 falls very rapidly: 1000 times every 80 days. It is used immediately even in medicine and goes away as quickly as possible (in a respirator, gas mask, in a parange, turban, protecting the neck as much as possible) with the area contaminated with radioactive iodine. This is a volatile substance (aerosol), so it spreads easily over long distances and can be found in air, water and soil, easily and quickly penetrates the body (air, food, contact with the body and contaminated objects). In the human body, it is excreted through urine and sweat. But it can also be delayed (most often it occurs in the thyroid gland).

In the case of a significant but short-lived exposure, there is an effective antidote: stable iodine taken immediately (including inhaling, drinking, smearing on the thyroid gland and even cutting, surgical treatment) does not allow excessive iodine 131 to linger in the body. On the materials: http://inosmi.ru/fareast/20110329/167865529.html

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