Uranus (lat. Uranium), U ( read " uranium "), a radioactive chemical element with atomic number 92 , atomic weight 238. 0289. Actinides. half-life 2. 45 · 105 years to 4. 51 · 109 years. The configuration of the three external electron layers 5 s 2 p 6 d 10 f 3 6 s 2 p 6 d 17 s 2 , uranium refers to the f- elements. Located in the IIIB group 7 of the periodic table of elements. In the compounds exhibit oxidation state +2 , +3 , +4 , +5 and +6 valence II, IV, V and VI. Electronegativity according to Pauling 1. 22.
Uranus was discovered in 1789 by German chemist M. Klaproth in the study of mineral "Pitchblende". He named in honor of the planet Uranus, open W. Herschel in 1781. B metallic state of uranium was obtained in 1841 French chemist E. Peligot. The radioactivity of the uranium found in the 1896 French Becquerel. Initially attributed to uranium atomic mass 116, but in 1871, Mendeleev came to the conclusion that it should be doubled. After the discovery of elements with atomic numbers 90 to 103 American chemist G. Seaborg came to the conclusion that these elements (actinides) is correctly positioned in the periodic system in the same cell with the element actinium № 89. This arrangement is due to the fact that the completion of actinides occurs 5 f-elektoronnogo sublevel. 2
Uranus - the characteristic element of the granite layer and sedimentary shell of the Earth's crust. Content in the crust of 2. 5 × 10 -4% by weight. In seawater uranium concentration than 10 -9 g / L, only seawater contains from 109 to 1010 tons of uranium. In the free form of uranium in the earth's crust is not found. There about 100 uranium minerals, the most important of them pitchblende U 3 O 8, uraninite (U, Th) O 2, uranium ore resin (containing uranium oxides of variable composition) and Tyuyamunite Ca [(UO 2) 2 (VO 4) 2] · 8 H 2 O. 3
Uranium is obtained from uranium ore containing 0, 05 -0, 5% U. uranium extraction starts with a concentrate. Ore is leached with solutions of sulfuric acid, nitric acid or alkali. The solution obtained is recovered as uranium oxide or tetrafluoride UF 4, by metallothermy: UF 4 + 2 Mg = 2 Mg. F 2 + U Resulting uranium contains minor amounts of boron impurities, cadmium and some other elements, so-called reactor poisons. Absorbing generated during operation of the nuclear reactor neutrons, they make uranium unsuitable for use as nuclear fuel. To get rid of impurities, metallic uranium is dissolved in nitric acid to yield uranyl nitrate UO 2 (NO 3) 2. Uranyl nitrate is extracted from the aqueous solution by tributyl phosphate. The product was purified from the extract again converted to uranium oxide or tetrafluoride from which the newly obtained metal. Part of the uranium produced by regeneration of spent nuclear fuel in the reactor. All operations are carried out on the regeneration of uranium remotely.
Uranium - silvery-white lustrous metal. Metallic uranium exists in three allotropic modifications. Up to 669 ° C stable a-modification with the orthorhombic lattice. From 669 ° C to 776 ° C stable b-modification with a tetragonal lattice. The melting temperature of 1135 ° C is stable g-modification with the bodycentered cubic lattice. The boiling point of 4200 ° C.
The chemical activity of uranium metal is high. In the air it is covered with an oxide film. Powdered uranium pyrophoric when burned uranium and thermal decomposition of its many compounds in air is formed of uranium oxide U 3 O 8. If this oxide is heated in a hydrogen atmosphere at a temperature above 500 ° C, produced uranium dioxide UO 2: U 3 O 8 + H 2 = 3 UO 2 + 2 H 2 O Interacting with halogens, halides gives uranium. Among them hexafluoride UF 6 is a yellow crystalline solid, sublimes easily even at low heat (40 -60 ° C) and as is readily hydrolyzed by water. Practical importance is uranium hexafluoride UF 6.
When reacting with hydrogen formed uranium hydride uranium UH 3, having a high chemical activity. Hydride decomposes when heated, forming hydrogen and uranium powder. Since carbon forms three uranium carbide UC, U 2 C 3 and UC 2. Reacting with the silicon obtained uranium silicide U 3 Si, U 3 Si 2, USi, U 3 Si 5, USi 2 and U 3 Si 2. Obtained uranium nitride (UN, UN 2, U 2 N 3) and uranium phosphide (UP, U 3 P 4, UP 2). With gray uranium forms a series of sulfides: U 3 S 5, US 2, US 3 and U 2 S 3. Metallic uranium is dissolved in HCl and HNO 3, slowly reacts with H 2 SO 4 and H 3 PO 4. There are salts comprising a cation uranyl UO 22 +. 7
In aqueous solutions, there are uranium compounds in the oxidation of +3 to +6. U 3 + ion in solution is unstable, U 4 + ion is stable in the absence of air. U 3 + ions have a characteristic red coloring ions U 4 + - green, ions UO 22 + - yellow. In solution, the most stable uranium compounds in oxidation +6. All the compounds of uranium in solutions prone to hydrolysis and complexation, most strongly - cations U 4 + and UO 22 +. 8
In trace (10 -5 -10 -8%) found in the tissues of plants, animals and humans. Uranium compounds are absorbed in the gastrointestinal tract (about 1%) in the lung - 50%. The main depot in the body: the spleen, kidneys, bones, liver, lungs and bronchopulmonary lymph nodes. The content in organs and tissues of humans and animals does not exceed 10 -7 years. Uranium and its compounds are highly toxic. Especially dangerous aerosols of uranium and its compounds. For aerosols, water-soluble compounds of uranium in the air MPC 0. 015 mg / m 3 for insoluble forms of uranium MCL of 0. 075 mg / m 3. When ingested uranium acts on all the organs, being obschekletochnym poison. The molecular mechanism of action of the uranium is associated with its ability to inhibit the activity of enzymes. Primarily affects the kidneys (protein and sugar appearing in the urine, oliguria). In chronic intoxication possible violations of blood and nervous system. 9
Metallic uranium and its compounds used primarily as nuclear fuel in nuclear reactors. Maloobogaschennaya mixture of uranium isotopes is used in the stationary reactor nuclear power plants. Product high degree of enrichment - in nuclear reactors operating on fast neutrons. 235 U is source of nuclear energy in nuclear weapons. 238 U is a source of secondary nuclear fuel - plutonium. 10
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