Depleted uranium. Chemical element uranium: properties, characteristics, formula. Mining and use of uranium How is uranium designated in chemistry

Uranium is a chemical element of the actinide family with atomic number 92. It is the most important nuclear fuel. Its concentration in the earth's crust is about 2 parts per million. Important uranium minerals include uranium oxide (U 3 O 8), uraninite (UO 2), carnotite (potassium uranyl vanadate), otenite (potassium uranyl phosphate), and torbernite (hydrous copper uranyl phosphate). These and other uranium ores are sources of nuclear fuel and contain many times more energy than all known recoverable fossil fuel deposits. 1 kg of uranium 92 U provides the same energy as 3 million kg of coal.

History of discovery

The chemical element uranium is a dense, hard metal with a silvery-white color. It is ductile, malleable and polishable. In the air, metal oxidizes and, when crushed, ignites. Conducts electricity relatively poorly. The electronic formula of uranium is 7s2 6d1 5f3.

Although the element was discovered in 1789 by the German chemist Martin Heinrich Klaproth, who named it after the recently discovered planet Uranus, the metal itself was isolated in 1841 by the French chemist Eugene-Melchior Peligot by reduction from uranium tetrachloride (UCl 4) with potassium.

Radioactivity

Creation periodic table Russian chemist Dmitri Mendeleev in 1869 focused on uranium as the heaviest known element, which it remained until the discovery of neptunium in 1940. In 1896, French physicist Henri Becquerel discovered the phenomenon of radioactivity in it. This property was later found in many other substances. It is now known that uranium, radioactive in all its isotopes, consists of a mixture of 238 U (99.27%, half-life - 4,510,000,000 years), 235 U (0.72%, half-life - 713,000,000 years) and 234 U (0.006%, half-life - 247,000 years). This allows, for example, to determine the age of rocks and minerals to study geological processes and the age of the Earth. To do this, they measure the amount of lead, which is the end product of the radioactive decay of uranium. In this case, 238 U is the initial element, and 234 U is one of the products. 235 U gives rise to the decay series of actinium.

Discovery of a chain reaction

The chemical element uranium became the subject of widespread interest and intensive study after German chemists Otto Hahn and Fritz Strassmann discovered nuclear fission in it at the end of 1938 when it was bombarded with slow neutrons. In early 1939, Italian-American physicist Enrico Fermi suggested that among the products of atomic fission there could be elementary particles capable of generating a chain reaction. In 1939, American physicists Leo Szilard and Herbert Anderson, as well as French chemist Frederic Joliot-Curie and their colleagues confirmed this prediction. Subsequent studies showed that, on average, 2.5 neutrons are released when an atom fissions. These discoveries led to the first self-sustaining nuclear chain reaction (12/02/1942), the first atomic bomb (07/16/1945), its first use in warfare (08/06/1945), the first nuclear submarine (1955) and the first full-scale nuclear power plant ( 1957).

Oxidation states

The chemical element uranium, being a strong electropositive metal, reacts with water. It dissolves in acids, but not in alkalis. Important oxidation states are +4 (as in UO 2 oxide, tetrahalides such as UCl 4 , and the green water ion U 4+ ) and +6 (as in UO 3 oxide, UF 6 hexafluoride, and the uranyl ion UO 2 2+ ). In an aqueous solution, uranium is most stable in the composition of the uranyl ion, which has a linear structure [O = U = O] 2+. The element also has states +3 and +5, but they are unstable. Red U 3+ oxidizes slowly in water, which does not contain oxygen. The color of the UO 2+ ion is unknown because it undergoes disproportionation (UO 2+ is both reduced to U 4+ and oxidized to UO 2 2+) even in very dilute solutions.

Nuclear fuel

When exposed to slow neutrons, fission of the uranium atom occurs in the relatively rare isotope 235 U. This is the only naturally occurring fissile material, and it must be separated from the isotope 238 U. However, after absorption and negative beta decay, uranium-238 turns into the synthetic element plutonium, which is split under the influence of slow neutrons. Therefore, natural uranium can be used in converter and breeder reactors, in which fission is supported by rare 235 U and plutonium is produced simultaneously with transmutation of 238 U. The fissile 233 U can be synthesized from the widely occurring naturally occurring isotope thorium-232 for use as nuclear fuel. Uranium is also important as the primary material from which synthetic transuranium elements are obtained.

Other uses of uranium

Compounds of the chemical element were previously used as dyes for ceramics. Hexafluoride (UF 6) is a solid with an unusually high vapor pressure (0.15 atm = 15,300 Pa) at 25 °C. UF 6 is chemically very reactive, but despite its corrosive nature in the vapor state, UF 6 is widely used in gaseous diffusion and gas centrifuge methods for producing enriched uranium.

Organometallic compounds are an interesting and important group of compounds in which metal-carbon bonds connect the metal to organic groups. Uranocene is an organouranic compound U(C 8 H 8) 2 in which the uranium atom is sandwiched between two layers of organic rings associated with cyclooctatetraene C 8 H 8. Its discovery in 1968 opened up a new field of organometallic chemistry.

Depleted natural uranium is used as radiation protection, ballast, in armor-piercing shells and tank armor.

Recycling

The chemical element, although very dense (19.1 g/cm3), is a relatively weak, non-flammable substance. Indeed, the metallic properties of uranium seem to place it somewhere between silver and the other true metals and non-metals, so it is not used as a structural material. The main value of uranium lies in the radioactive properties of its isotopes and their ability to fission. In nature, almost all (99.27%) of the metal consists of 238 U. The rest is 235 U (0.72%) and 234 U (0.006%). Of these natural isotopes, only 235 U is directly fissioned by neutron irradiation. However, when it is absorbed, 238 U forms 239 U, which ultimately decays into 239 Pu, a fissile material of great importance for nuclear power and nuclear weapons. Another fissile isotope, 233 U, can be formed by neutron irradiation of 232 Th.

Crystal forms

The characteristics of uranium cause it to react with oxygen and nitrogen even under normal conditions. At higher temperatures it reacts with a wide range of alloying metals to form intermetallic compounds. The formation of solid solutions with other metals is rare due to the special crystal structures formed by the atoms of the element. Between room temperature and the melting point of 1132 °C, uranium metal exists in 3 crystalline forms known as alpha (α), beta (β) and gamma (γ). Transformation from α- to β-state occurs at 668 °C and from β to γ ​​at 775 °C. γ-uranium has a body-centered cubic crystal structure, while β has a tetragonal crystal structure. The α phase consists of layers of atoms in a highly symmetrical orthorhombic structure. This anisotropic distorted structure prevents alloying metal atoms from replacing uranium atoms or occupying the space between them in the crystal lattice. It was found that only molybdenum and niobium form solid solutions.

Ore

The Earth's crust contains about 2 parts per million of uranium, which indicates its widespread occurrence in nature. The oceans are estimated to contain 4.5 × 10 9 tons of this chemical element. Uranium is an important constituent of more than 150 different minerals and a minor component of another 50. Primary minerals found in magmatic hydrothermal veins and pegmatites include uraninite and its variant pitchblende. In these ores the element occurs in the form of dioxide, which due to oxidation can range from UO 2 to UO 2.67. Other economically significant products from uranium mines are autunite (hydrated calcium uranyl phosphate), tobernite (hydrated copper uranyl phosphate), coffinit (black hydrated uranium silicate) and carnotite (hydrated potassium uranyl vanadate).

It is estimated that more than 90% of known low-cost uranium reserves are located in Australia, Kazakhstan, Canada, Russia, South Africa, Niger, Namibia, Brazil, China, Mongolia and Uzbekistan. Large deposits are found in the conglomerate rock formations of Elliot Lake, located north of Lake Huron in Ontario, Canada, and in the South African Witwatersrand gold mine. Sand formations in the Colorado Plateau and Wyoming Basin of the western United States also contain significant uranium reserves.

Production

Uranium ores are found in both near-surface and deep (300-1200 m) deposits. Underground, the thickness of the seam reaches 30 m. As in the case of ores of other metals, uranium is mined at the surface using large earth-moving equipment, and the development of deep deposits is carried out using traditional methods of vertical and inclined mines. World production of uranium concentrate in 2013 amounted to 70 thousand tons. The most productive uranium mines located in Kazakhstan (32% of all production), Canada, Australia, Niger, Namibia, Uzbekistan and Russia.

Uranium ores typically contain only small amounts of uranium-containing minerals and are not smeltable by direct pyrometallurgical methods. Instead, hydrometallurgical procedures must be used to extract and purify the uranium. Increasing the concentration significantly reduces the load on the processing loops, but none of the usual ways beneficiation commonly used for mineral processing, such as gravity, flotation, electrostatic and even manual sorting, are not applicable. With few exceptions, these methods result in significant uranium loss.

Burning

Hydrometallurgical processing of uranium ores is often preceded by a high-temperature calcination stage. Firing dehydrates the clay, removes carbonaceous materials, oxidizes sulfur compounds to harmless sulfates, and oxidizes any other reducing agents that may interfere with subsequent processing.

Leaching

Uranium is extracted from roasted ores by both acidic and alkaline aqueous solutions. For all leaching systems to function successfully, the chemical element must either initially be present in the more stable hexavalent form or be oxidized to this state during processing.

Acid leaching is usually carried out by stirring a mixture of ore and lixiviant for 4-48 hours at ambient temperature. Except in special circumstances, sulfuric acid is used. It is supplied in quantities sufficient to obtain the final liquor at a pH of 1.5. Sulfuric acid leaching schemes typically use either manganese dioxide or chlorate to oxidize tetravalent U4+ to hexavalent uranyl (UO22+). Typically, approximately 5 kg of manganese dioxide or 1.5 kg of sodium chlorate per ton is sufficient for U 4+ oxidation. In either case, oxidized uranium reacts with sulfuric acid to form the uranyl sulfate complex anion 4-.

Ore containing significant amounts of essential minerals such as calcite or dolomite is leached with a 0.5-1 molar solution of sodium carbonate. Although various reagents have been studied and tested, the main oxidizing agent for uranium is oxygen. Typically, ore is leached in air at atmospheric pressure and at a temperature of 75-80 °C for a period of time that depends on the specific chemical composition. Alkali reacts with uranium to form the readily soluble complex ion 4-.

Solutions resulting from acid or carbonate leaching must be clarified before further processing. Large-scale separation of clays and other ore slurries is achieved through the use of effective flocculating agents, including polyacrylamides, guar gum and animal glue.

Extraction

The 4- and 4- complex ions can be sorbed from their respective ion exchange resin leach solutions. These specialty resins, characterized by their adsorption and elution kinetics, particle size, stability and hydraulic properties, can be used in a variety of processing technologies, such as fixed bed, moving bed, basket resin and continuous resin. Typically, solutions of sodium chloride and ammonia or nitrates are used to elute sorbed uranium.

Uranium can be isolated from acidic ore liquors by solvent extraction. Alkylphosphoric acids, as well as secondary and tertiary alkylamines, are used in industry. Generally, solvent extraction is preferred over ion exchange methods for acid filtrates containing more than 1 g/L uranium. However, this method is not applicable to carbonate leaching.

The uranium is then purified by dissolving in nitric acid to form uranyl nitrate, extracted, crystallized and calcined to form UO 3 trioxide. Reduced dioxide UO2 reacts with hydrogen fluoride to form thetafluoride UF4, from which uranium metal is reduced by magnesium or calcium at a temperature of 1300 °C.

Tetrafluoride can be fluorinated at 350 °C to form UF 6 hexafluoride, which is used to separate enriched uranium-235 by gaseous diffusion, gas centrifugation or liquid thermal diffusion.

Uranium is not a very typical actinide; its five valence states are known - from 2+ to 6+. Some uranium compounds have a characteristic color. Thus, solutions of trivalent uranium are red, tetravalent uranium is green, and hexavalent uranium - it exists in the form of uranyl ion (UO 2) 2+ - colors the solutions yellow... The fact that hexavalent uranium forms compounds with many organic complexing agents, turned out to be very important for the extraction technology of element No. 92.

It is characteristic that the outer electron shell of uranium ions is always completely filled; The valence electrons are in the previous electron layer, in the 5f subshell. If we compare uranium with other elements, it is obvious that plutonium is most similar to it. The main difference between them is the large ionic radius of uranium. In addition, plutonium is most stable in the tetravalent state, and uranium is most stable in the hexavalent state. This helps to separate them, which is very important: the nuclear fuel plutonium-239 is obtained exclusively from uranium, ballast from the energy point of view of uranium-238. Plutonium is formed in a mass of uranium, and they must be separated!

However, first you need to get this very mass of uranium, going through a long technological chain, starting with ore. Typically a multi-component, uranium-poor ore.

Light isotope of a heavy element

When we talked about obtaining element No. 92, we deliberately omitted one important stage. As you know, not all uranium is capable of supporting a nuclear chain reaction. Uranium-238, which accounts for 99.28% of the natural mixture of isotopes, is not capable of this. Because of this, uranium-238 is converted into plutonium, and the natural mixture of uranium isotopes is sought to either be separated or enriched with the isotope uranium-235, which is capable of fissioning thermal neutrons.

Many methods have been developed for separating uranium-235 and uranium-238. The gas diffusion method is most often used. Its essence is that if a mixture of two gases is passed through a porous partition, then the light will pass faster. Back in 1913, F. Aston partially separated neon isotopes in this way.

Most uranium compounds under normal conditions are solids and can be converted into a gaseous state only at very high temperatures, when there can be no talk of any subtle processes of isotope separation. However, the colorless compound of uranium with fluorine, UF 6 hexafluoride, sublimes already at 56.5 ° C (at atmospheric pressure). UF 6 is the most volatile uranium compound and is best suited for separating its isotopes by gaseous diffusion.

Uranium hexafluoride is characterized by high chemical activity. Corrosion of pipes, pumps, containers, interaction with the lubrication of mechanisms - a small but impressive list of troubles that the creators of diffusion plants had to overcome. We encountered even more serious difficulties.

Uranium hexafluoride, obtained by fluoridation of a natural mixture of uranium isotopes, from a “diffusion” point of view, can be considered as a mixture of two gases with very similar molecular masses - 349 (235+19*6) and 352 (238+19*6). The maximum theoretical separation coefficient in one diffusion stage for gases that differ so slightly in molecular weight is only 1.0043. In real conditions this value is even less. It turns out that it is possible to increase the concentration of uranium-235 from 0.72 to 99% only with the help of several thousand diffusion steps. Therefore, uranium isotope separation plants occupy an area of ​​several tens of hectares. The area of ​​porous partitions in the separation cascades of factories is approximately the same order of magnitude.

Briefly about other isotopes of uranium

Natural uranium, in addition to uranium-235 and uranium-238, includes uranium-234. The abundance of this rare isotope is expressed as a number with four zeros after the decimal point. A much more accessible artificial isotope is uranium-233. It is obtained by irradiating thorium in the neutron flux of a nuclear reactor:

232 90 Th + 10n → 233 90 Th -β-→ 233 91 Pa -β-→ 233 92 U
According to all the rules of nuclear physics, uranium-233, as an odd isotope, is divided by thermal neutrons. And most importantly, in reactors with uranium-233, expanded reproduction of nuclear fuel can (and does) occur. In a conventional thermal neutron reactor! Calculations show that when a kilogram of uranium-233 burns up in a thorium reactor, 1.1 kg of new uranium-233 should accumulate in it. A miracle, and that’s all! We burned a kilogram of fuel, but the amount of fuel did not decrease.

However, such miracles are only possible with nuclear fuel.

The uranium-thorium cycle in thermal neutron reactors is the main competitor of the uranium-plutonium cycle for the reproduction of nuclear fuel in fast neutron reactors... Actually, only because of this, element No. 90 - thorium - was classified as a strategic material.

Other artificial isotopes of uranium do not play a significant role. It is only worth mentioning uranium-239 - the first isotope in the chain of transformations of uranium-238 plutonium-239. Its half-life is only 23 minutes.

Isotopes of uranium with a mass number greater than 240 do not have time to form in modern reactors. The lifetime of uranium-240 is too short, and it decays before it has time to capture a neutron.

In the super-powerful neutron fluxes of a thermonuclear explosion, a uranium nucleus manages to capture up to 19 neutrons in a millionth of a second. In this case, uranium isotopes with mass numbers from 239 to 257 are born. Their existence was learned from the appearance of distant transuranium elements - descendants of heavy uranium isotopes - in the products of a thermonuclear explosion. The “founders of the genus” themselves are too unstable to beta decay and pass into higher elements long before the products of nuclear reactions are extracted from the rock mixed by the explosion.

Modern thermal reactors burn uranium-235. In already existing fast neutron reactors, the energy of the nuclei of a common isotope, uranium-238, is released, and if energy is true wealth, then uranium nuclei will benefit humanity in the near future: the energy of element N° 92 will become the basis of our existence.

It is vitally important to ensure that uranium and its derivatives burn only in nuclear reactors of peaceful power plants, burn slowly, without smoke and flame.

ANOTHER SOURCE OF URANIUM. Nowadays, it has become sea water. Pilot-industrial installations are already in operation for extracting uranium from water using special sorbents: titanium oxide or acrylic fiber treated with certain reagents.

WHO HOW MUCH. In the early 80s, uranium production in capitalist countries was about 50,000 g per year (in terms of U3Os). About a third of this amount was provided by US industry. Canada is in second place, followed by South Africa. Nigor, Gabon, Namibia. Of the European countries, France produces the most uranium and its compounds, but its share was almost seven times less than the United States.

NON-TRADITIONAL CONNECTIONS. Although it is not without foundation that the chemistry of uranium and plutonium is better studied than the chemistry of traditional elements such as iron, chemists are still discovering new uranium compounds. So, in 1977, the journal “Radiochemistry”, vol. XIX, no. 6 reported two new uranyl compounds. Their composition is MU02(S04)2-SH20, where M is a divalent manganese or cobalt ion. X-ray diffraction patterns indicated that the new compounds were double salts, and not a mixture of two similar salts.

The content of the article

URANUS, U (uranium), a metal chemical element of the actinide family, which includes Ac, Th, Pa, U and transuranium elements (Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr). Uranium has gained prominence due to its use in nuclear weapons and nuclear power. Uranium oxides are also used to color glass and ceramics.

Being in nature.

The uranium content in the earth's crust is 0.003%, and it is found in the surface layer of the earth in the form of four types of deposits. First, these are veins of uraninite, or uranium pitch (uranium dioxide UO 2), very rich in uranium, but rare. They are accompanied by radium deposits, since radium is a direct product of the isotopic decay of uranium. Such veins are found in Zaire, Canada (Great Bear Lake), Czech Republic and France. The second source of uranium is conglomerates of thorium and uranium ores together with ores of other important minerals. Conglomerates usually contain sufficient amounts of gold and silver to be recovered, with uranium and thorium being associated elements. Large deposits of these ores are located in Canada, South Africa, Russia and Australia. The third source of uranium is sedimentary rocks and sandstones rich in the mineral carnotite (potassium uranyl vanadate), which contains, in addition to uranium, a significant amount of vanadium and other elements. Such ores are found in the western states of the United States. Iron-uranium shales and phosphate ores constitute a fourth source of sediment. Rich deposits are found in the shales of Sweden. Some phosphate ores in Morocco and the United States contain significant amounts of uranium, and phosphate deposits in Angola and the Central African Republic are even richer in uranium. Most lignites and some coals usually contain uranium impurities. Uranium-rich lignite deposits have been found in North and South Dakota (USA) and bituminous coals in Spain and the Czech Republic.

Opening.

Uranus was discovered in 1789 by the German chemist M. Klaproth, who named the element in honor of the discovery of the planet Uranus 8 years earlier. (Klaproth was the leading chemist of his time; he also discovered other elements, including Ce, Ti and Zr.) In fact, the substance Klaproth obtained was not elemental uranium, but an oxidized form of it, and elemental uranium was first obtained by the French chemist E. .Peligo in 1841. From the moment of discovery until the 20th century. uranium did not have the meaning that it has now, although many of it physical properties, and atomic mass and density were determined. In 1896, A. Becquerel established that uranium salts have radiation that illuminates a photographic plate in the dark. This discovery activated chemists to research in the field of radioactivity and in 1898, the French physicists spouses P. Curie and M. Sklodowska-Curie isolated salts of the radioactive elements polonium and radium, and E. Rutherford, F. Soddy, K. Fayans and other scientists developed the theory of radioactive decay, which laid the foundations of modern nuclear chemistry and nuclear energy.

First uses of uranium.

Although the radioactivity of uranium salts was known, its ores in the first third of this century were used only to obtain accompanying radium, and uranium was considered an undesirable by-product. Its use was concentrated mainly in ceramic technology and metallurgy; Uranium oxides were widely used to color glass in colors ranging from pale yellow to dark green, which contributed to the development of inexpensive glass production. Today, products from these industries are identified as fluorescent under ultraviolet rays. During World War I and shortly thereafter, uranium in the form of carbide was used in the production of tool steels, similar to Mo and W; 4–8% uranium replaced tungsten, the production of which was limited at the time. To obtain tool steels in 1914–1926, several tons of ferrouranium containing up to 30% (mass) U were produced annually. However, this use of uranium did not last long.

Modern uses of uranium.

The uranium industry began to take shape in 1939, when the fission of the uranium isotope 235 U was carried out, which led to the technical implementation of controlled chain reactions of uranium fission in December 1942. This was the birth of the age of the atom, when uranium went from an insignificant element to one of the most important elements in the life of society. The military importance of uranium for the production of the atomic bomb and its use as fuel in nuclear reactors caused the demand for uranium to increase astronomically. The chronology of the growth in uranium demand based on the history of sediments in Great Bear Lake (Canada) is interesting. In 1930, resin blende, a mixture of uranium oxides, was discovered in this lake, and in 1932, radium purification technology was established in this area. From each ton of ore (resin blende) 1 g of radium and about half a ton of by-product, uranium concentrate, were obtained. However, there was little radium and its mining was stopped. From 1940 to 1942, development was resumed and uranium ore began to be shipped to the United States. In 1949, similar uranium purification, with some improvements, was used to produce pure UO 2 . This production has grown and is now one of the largest uranium production facilities.

Properties.

Uranium is one of the heaviest elements found in nature. Pure metal is very dense, ductile, electropositive with low electrical conductivity, and highly reactive.

Uranium has three allotropic modifications: a-uranium (orthorhombic crystal cell), exists in the range from room temperature to 668 ° C; b-uranium (complex crystal lattice of tetragonal type), stable in the range of 668–774° C; g-uranium (body-centered cubic crystal lattice), stable from 774°C up to the melting point (1132°C). Since all isotopes of uranium are unstable, all its compounds exhibit radioactivity.

Isotopes of uranium

238 U, 235 U, 234 U occur in nature in a ratio of 99.3:0.7:0.0058, and 236 U occurs in trace amounts. All other isotopes of uranium from 226 U to 242 U are obtained artificially. The isotope 235 U is particularly important. Under the influence of slow (thermal) neutrons, it divides, releasing enormous energy. Complete fission of 235 U results in the release of a “thermal energy equivalent” of 2H 10 7 kWh h/kg. The fission of 235 U can be used not only to produce large amounts of energy, but also to synthesize other important actinide elements. Natural isotope uranium can be used in nuclear reactors to produce neutrons produced by the fission of 235 U, while excess neutrons not required by the chain reaction can be captured by another natural isotope, resulting in the production of plutonium:

When 238 U is bombarded with fast neutrons, the following reactions occur:

According to this scheme, the most common isotope 238 U can be converted into plutonium-239, which, like 235 U, is also capable of fission under the influence of slow neutrons.

Currently received big number artificial isotopes of uranium. Among them, 233 U is particularly notable because it also fissions when interacting with slow neutrons.

Some other artificial isotopes of uranium are often used as radioactive tracers in chemical and physical research; this is first of all b- emitter 237 U and a- emitter 232 U.

Connections.

Uranium, a highly reactive metal, has oxidation states from +3 to +6, is close to beryllium in the activity series, interacts with all non-metals and forms intermetallic compounds with Al, Be, Bi, Co, Cu, Fe, Hg, Mg, Ni, Pb, Sn and Zn. Finely crushed uranium is especially reactive and at temperatures above 500 ° C it often enters into reactions characteristic of uranium hydride. Lump uranium or shavings burn brightly at 700–1000° C, and uranium vapor burns already at 150–250° C; uranium reacts with HF at 200–400° C, forming UF 4 and H 2 . Uranium dissolves slowly in concentrated HF or H 2 SO 4 and 85% H 3 PO 4 even at 90 ° C, but easily reacts with conc. HCl and less active with HBr or HI. The most active and rapid reactions of uranium with dilute and concentrated HNO 3 occur with the formation of uranyl nitrate ( see below). In the presence of HCl, uranium quickly dissolves in organic acids, forming organic U4+ salts. Depending on the degree of oxidation, uranium forms several types of salts (the most important among them are with U 4+, one of them UCl 4 is an easily oxidized green salt); uranyl salts (radical UO 2 2+) of the type UO 2 (NO 3) 2 are yellow in color and fluoresce green. Uranyl salts are formed by dissolving the amphoteric oxide UO 3 (yellow color) in an acidic medium. In an alkaline environment, UO 3 forms uranates such as Na 2 UO 4 or Na 2 U 2 O 7. The latter compound (“yellow uranyl”) is used for the manufacture of porcelain glazes and in the production of fluorescent glasses.

Uranium halides were widely studied in 1940–1950, as they were used to develop methods for separating uranium isotopes for the atomic bomb or nuclear reactor. Uranium trifluoride UF 3 was obtained by the reduction of UF 4 with hydrogen, and uranium tetrafluoride UF 4 is obtained in various ways by reactions of HF with oxides such as UO 3 or U 3 O 8 or by electrolytic reduction of uranyl compounds. Uranium hexafluoride UF 6 is obtained by fluorination of U or UF 4 with elemental fluorine or by the action of oxygen on UF 4 . Hexafluoride forms transparent crystals with a high refractive index at 64 ° C (1137 mm Hg); the compound is volatile (under normal pressure it sublimes at 56.54 ° C). Uranium oxohalides, for example, oxofluorides, have the composition UO 2 F 2 (uranyl fluoride), UOF 2 (uranium oxide difluoride).

In a message from the Iraqi Ambassador to the UN Mohammed Ali al-Hakim dated July 9, it is said that ISIS extremists (Islamic State of Iraq and the Levant) are at their disposal. The IAEA (International Atomic Energy Agency) hastened to declare that the nuclear substances previously used by Iraq have low toxic properties, and therefore the materials seized by the Islamists.

A US government source familiar with the situation told Reuters that the uranium stolen by the militants was most likely not enriched and therefore unlikely to be used to make nuclear weapons. The Iraqi authorities officially notified the United Nations about this incident and called on them to “prevent the threat of its use,” RIA Novosti reports.

Uranium compounds are extremely dangerous. AiF.ru talks about what exactly, as well as who and how can produce nuclear fuel.

What is uranium?

Uranium is a chemical element with atomic number 92, a silvery-white shiny metal, designated in the periodic table by the symbol U. In its pure form, it is slightly softer than steel, malleable, flexible, found in the earth's crust (lithosphere) and in sea water, and in its pure form is practically does not occur. Nuclear fuel is made from uranium isotopes.

Uranium is a heavy, silvery-white, shiny metal. Photo: Commons.wikimedia.org / Original uploader was Zxctypo at en.wikipedia.

Radioactivity of uranium

In 1938 the German physicists Otto Hahn and Fritz Strassmann irradiated the uranium nucleus with neutrons and made a discovery: capturing a free neutron, the uranium isotope nucleus divides and releases enormous energy due to the kinetic energy of fragments and radiation. In 1939-1940 Yuliy Khariton And Yakov Zeldovich for the first time theoretically explained that with a small enrichment of natural uranium with uranium-235, it is possible to create conditions for the continuous fission of atomic nuclei, that is, give the process a chain character.

What is enriched uranium?

Enriched uranium is uranium that is produced using technological process of increasing the share of the 235U isotope in uranium. As a result, natural uranium is divided into enriched uranium and depleted uranium. After 235U and 234U are extracted from natural uranium, the remaining material (uranium-238) is called "depleted uranium" because it is depleted in the 235 isotope. According to some estimates, the United States stores about 560,000 tons of depleted uranium hexafluoride (UF6). Depleted uranium is half as radioactive as natural uranium, mainly due to the removal of 234U from it. Because the primary use of uranium is energy production, depleted uranium is a low-use product with low economic value.

In nuclear energy, only enriched uranium is used. The most widely used isotope of uranium is 235U, in which a self-sustaining nuclear chain reaction is possible. Therefore, this isotope is used as fuel in nuclear reactors and nuclear weapons. Isolation of the U235 isotope from natural uranium is a complex technology that not many countries can implement. Uranium enrichment allows the production of atomic nuclear weapons - single-phase or single-stage explosive devices in which the main energy output comes from the nuclear reaction of heavy nuclei fission to form lighter elements.

Uranium-233, artificially produced in reactors from thorium (thorium-232 captures a neutron and turns into thorium-233, which decays into protactinium-233 and then into uranium-233), may in the future become a common nuclear fuel for nuclear power plants (already now there are reactors that use this nuclide as fuel, for example KAMINI in India) and production atomic bombs(critical mass about 16 kg).

The core of a 30 mm caliber projectile (GAU-8 gun of an A-10 aircraft) with a diameter of about 20 mm is made of depleted uranium. Photo: Commons.wikimedia.org / Original uploader was Nrcprm2026 at en.wikipedia

Which countries produce enriched uranium?

• France
• Germany
• Holland
• England
• Japan
• Russia
• China
• Pakistan
• Brazil

10 countries producing 94% of world uranium production. Photo: Commons.wikimedia.org / KarteUrangewinnung

Why are uranium compounds dangerous?

Uranium and its compounds are toxic. Aerosols of uranium and its compounds are especially dangerous. For aerosols of water-soluble uranium compounds, the maximum permissible concentration (MPC) in the air is 0.015 mg/m³, for insoluble forms of uranium the MAC is 0.075 mg/m³. When uranium enters the body, it affects all organs, being a general cellular poison. Uranium, like many other heavy metals, almost irreversibly binds to proteins, primarily to sulfide groups of amino acids, disrupting their function. The molecular mechanism of action of uranium is associated with its ability to suppress enzyme activity. The kidneys are primarily affected (protein and sugar appear in the urine, oliguria). With chronic intoxication, disorders of hematopoiesis and the nervous system are possible.

Use of uranium for peaceful purposes

• A small addition of uranium gives the glass a beautiful yellow-green color.
• Sodium uranium is used as a yellow pigment in painting.
• Uranium compounds were used as paints for painting on porcelain and for ceramic glazes and enamels (painted in colors: yellow, brown, green and black, depending on the degree of oxidation).
• At the beginning of the 20th century, uranyl nitrate was widely used to enhance negatives and color (tint) positives (photographic prints) brown.
• Alloys of iron and depleted uranium (uranium-238) are used as powerful magnetostrictive materials.

An isotope is a variety of atoms of a chemical element that have the same atomic (ordinal) number, but different mass numbers.

An element of group III of the periodic table, belonging to the actinides; heavy, slightly radioactive metal. Thorium has a number of applications in which it sometimes plays an irreplaceable role. The position of this metal in the periodic table of elements and the structure of the nucleus predetermined its use in the field of peaceful uses of atomic energy.

*** Oliguria (from the Greek oligos - small and ouron - urine) - a decrease in the amount of urine excreted by the kidneys.

URANIUM (chemical element) URANIUM (chemical element)

URANIUM (lat. Uranium), U (read “uranium”), radioactive chemical element with atomic number 92, atomic mass 238.0289. Actinoid. Natural uranium consists of a mixture of three isotopes: 238 U, 99.2739%, with a half-life T 1/2 = 4.51 10 9 years, 235 U, 0.7024%, with half-life T 1/2 = 7.13 10 8 years, 234 U, 0.0057%, with half-life T 1/2 = 2.45 10 5 years. 238 U (uranium-I, UI) and 235 U (actinouranium, AcU) are the founders of the radioactive series. Of the 11 artificially produced radionuclides with mass numbers 227-240, the long-lived 233 U ( T 1/2 = 1.62 10 5 years), it is obtained by neutron irradiation of thorium (cm. THORIUM).
Configuration of three outer electronic layers 5 s 2 p 6 d 10 f 3 6s 2 p 6 d 1 7 s 2 , uranium belongs to f-elements. Located in group IIIB in the 7th period of the periodic table of elements. In compounds it exhibits oxidation states +2, +3, +4, +5 and +6, valences II, III, IV, V and VI.
The radius of a neutral uranium atom is 0.156 nm, the radius of ions: U 3 + - 0.1024 nm, U 4 + - 0.089 nm, U 5 + - 0.088 nm and U 6+ - 0.083 nm. The energies of successive ionization of the atom are 6.19, 11.6, 19.8, 36.7 eV. Electronegativity according to Pauling (cm. PAULING Linus) 1,22.
History of discovery
Uranium was discovered in 1789 by the German chemist M. G. Klaproth (cm. KLAPROT Martin Heinrich) when studying the mineral “resin blende”. He was named in honor of the planet Uranus, discovered by W. Herschel (cm. HERSCHEL) in 1781. In the metallic state, uranium was obtained in 1841 by the French chemist E. Peligot (cm. PELIGOT Eugene Melchior) when reducing UCl 4 with potassium metal. The radioactive properties of uranium were discovered in 1896 by the Frenchman A. Becquerel (cm. BECQUEREL Antoine Henri).
Initially, uranium was assigned an atomic mass of 116, but in 1871 D. I. Mendeleev (cm. MENDELEEV Dmitry Ivanovich) I came to the conclusion that it should be doubled. After the discovery of elements with atomic numbers from 90 to 103, the American chemist G. Seaborg (cm. SEABORG Glenn Theodore) concluded that these elements (actinides) (cm. ACTINOIDS) It is more correct to place it in the periodic table in the same cell with element No. 89 actinium. This arrangement is due to the fact that actinides undergo completion of 5 f-electronic sublevel.
Being in nature
Uranium is a characteristic element for the granite layer and sedimentary shell of the earth's crust. The content in the earth's crust is 2.5·10 -4% by weight. In sea water, the concentration of uranium is less than 10 -9 g/l; in total, sea water contains from 10 9 to 10 10 tons of uranium. Uranium is not found in free form in the earth's crust. About 100 uranium minerals are known, the most important of which are pitchblende U 3 O 8 and uraninite (cm. URANINITE)(U,Th)O 2, uranium resin ore (contains uranium oxides of variable composition) and tyuyamunite Ca[(UO 2) 2 (VO 4) 2 ] 8H 2 O.
Receipt
Uranium is obtained from uranium ores containing 0.05-0.5% U. Extraction of uranium begins with the production of concentrate. Ores are leached with solutions of sulfuric, nitric acids or alkali. The resulting solution always contains impurities of other metals. When separating uranium from them, differences in their redox properties are used. Redox processes are combined with ion exchange and extraction processes.
From the resulting solution, uranium is extracted in the form of oxide or tetrafluoride UF 4 using the metallothermic method:
UF 4 + 2Mg = 2MgF 2 + U
The resulting uranium contains small amounts of boron impurities (cm. BOR (chemical element)), cadmium (cm. CADMIUM) and some other elements, so-called reactor poisons. By absorbing neutrons produced during the operation of a nuclear reactor, they make uranium unsuitable for use as nuclear fuel.
To get rid of impurities, uranium metal is dissolved in nitric acid, obtaining uranyl nitrate UO 2 (NO 3) 2. Uranyl nitrate is extracted from an aqueous solution with tributyl phosphate. The purification product from the extract is again converted into uranium oxide or tetrafluoride, from which the metal is again obtained.
Part of the uranium is obtained by regenerating spent nuclear fuel in the reactor. All uranium regeneration operations are carried out remotely.
Physical and chemical properties
Uranium is a silvery-white shiny metal. Uranium metal exists in three allotropic forms (cm. ALLOTROPY) modifications. The a-modification with an orthorhombic lattice is stable up to 669°C, parameters A= 0.2854nm, V= 0.5869 nm and With= 0.4956 nm, density 19.12 kg/dm3. From 669°C to 776°C, the b-modification with a tetragonal lattice is stable (parameters A= 1.0758 nm, With= 0.5656 nm). The g-modification with a cubic body-centered lattice is stable up to a melting temperature of 1135°C ( A= 0.3525 nm). Boiling point 4200°C.
The chemical activity of uranium metal is high. In air it becomes covered with a film of oxide. Powdered uranium is pyrophoric; upon combustion of uranium and thermal decomposition of many of its compounds in air, uranium oxide U 3 O 8 is formed. If this oxide is heated in a hydrogen atmosphere (cm. HYDROGEN) at temperatures above 500°C, uranium dioxide UO 2 is formed:
U 3 O 8 + H 2 = 3UO 2 + 2H 2 O
If uranyl nitrate UO 2 (NO 3) 2 is heated at 500°C, then, when decomposing, it forms uranium trioxide UO 3. In addition to uranium oxides of the stoichiometric composition UO 2 , UO 3 and U 3 O 8 , uranium oxide of the composition U 4 O 9 and several metastable oxides and oxides of variable composition are known.
When uranium oxides are fused with oxides of other metals, uranates are formed: K 2 UO 4 (potassium uranate), CaUO 4 (calcium uranate), Na 2 U 2 O 7 (sodium diuranate).
Interacting with halogens (cm. HALOGEN), uranium produces uranium halides. Among them, UF 6 hexafluoride is a yellow crystalline substance that easily sublimes even with low heating (40-60°C) and is equally easily hydrolyzed by water. Uranium hexafluoride UF 6 is of the greatest practical importance. It is obtained by reacting uranium metal, uranium oxides or UF 4 with fluorine or fluorinating agents BrF 3, CCl 3 F (Freon-11) or CCl 2 F 2 (Freon-12):
U 3 O 8 + 6CCl 2 F 2 = UF 4 + 3COCl 2 + CCl 4 + Cl 2
UF 4 + F 2 = UF 6
or
U 3 O 8 + 9F 2 = 3UF 6 + 4O 2
Fluorides and chlorides are known that correspond to the oxidation states of uranium +3, +4, +5 and +6. Uranium bromides UBr 3, UBr 4 and UBr 5, as well as uranium iodides UI 3 and UI 4, were obtained. Uranium oxyhalides such as UO 2 Cl 2 UOCl 2 and others have been synthesized.
When uranium interacts with hydrogen, uranium hydride UH 3 is formed, which has high chemical activity. When heated, the hydride decomposes, producing hydrogen and powdered uranium. When uranium is sintered with boron, depending on the molar ratio of the reagents and the process conditions, borides UB 2, UB 4 and UB 12 appear.
With carbon (cm. CARBON) uranium forms three carbides UC, U 2 C 3 and UC 2.
Interaction of uranium with silicon (cm. SILICON) silicides U 3 Si, U 3 Si 2, USi, U 3 Si 5, USi 2 and U 3 Si 2 were obtained.
Uranium nitrides (UN, UN 2, U 2 N 3) and uranium phosphides (UP, U 3 P 4, UP 2) were obtained. With sulfur (cm. SULFUR) uranium forms a series of sulfides: U 3 S 5, US, US 2, US 3 and U 2 S 3.
Uranium metal dissolves in HCl and HNO 3 and reacts slowly with H 2 SO 4 and H 3 PO 4. Salts containing the uranyl cation UO 2 2+ arise.
In aqueous solutions, uranium compounds exist in oxidation states from +3 to +6. Standard oxidation potential of U(IV)/U(III) pair - 0.52 V, U(V)/U(IV) pair 0.38 V, U(VI)/U(V) pair 0.17 V, pair U(VI)/U(IV) 0.27. The U 3+ ion is unstable in solution, the U 4+ ion is stable in the absence of air. The UO 2+ cation is unstable and in solution disproportionates into U 4+ and UO 2 2+. U 3+ ions have a characteristic red color, U 4+ ions have a green color, and UO 2 2+ ions have a yellow color.
In solutions, uranium compounds are most stable in the oxidation state +6. All uranium compounds in solutions are prone to hydrolysis and complex formation, most strongly - U 4+ and UO 2 2+ cations.
Application
Uranium metal and its compounds are used primarily as nuclear fuel in nuclear reactors. A low-enriched mixture of uranium isotopes is used in stationary reactors of nuclear power plants. Product high degree enrichment - in nuclear reactors operating on fast neutrons. 235 U is the source of nuclear energy in nuclear weapons. 238 U serves as a source of secondary nuclear fuel - plutonium.
Physiological action
It is found in microquantities (10 -5 -10 -8%) in the tissues of plants, animals and humans. It accumulates to the greatest extent by some fungi and algae. Uranium compounds are absorbed in the gastrointestinal tract (about 1%), in the lungs - 50%. The main depots in the body: spleen, kidneys, skeleton, liver, lungs and bronchopulmonary lymph nodes. The content in organs and tissues of humans and animals does not exceed 10 -7 g.
Uranium and its compounds are highly toxic. Aerosols of uranium and its compounds are especially dangerous. For aerosols of water-soluble uranium compounds, the MPC in air is 0.015 mg/m 3 , for insoluble forms of uranium the MPC is 0.075 mg/m 3 . When uranium enters the body, it affects all organs, being a general cellular poison. The molecular mechanism of action of uranium is associated with its ability to suppress enzyme activity. The kidneys are primarily affected (protein and sugar appear in the urine, oliguria). With chronic intoxication, disorders of hematopoiesis and the nervous system are possible.

encyclopedic Dictionary. 2009 .

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