Uranium compounds. Radioactive uranium

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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 sediments. Firstly, 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 isotope 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 quantities 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 significance it has today, although many of its physical properties, as well as its 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 grew from an insignificant element to one of the most important elements in life 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 lattice), 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, a large number of artificial isotopes of uranium have been obtained. 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).

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 uranium-235 isotope, 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.

DEFINITION

Uranus- ninety-second element of the Periodic Table. Designation - U from the Latin “uranium”. Located in the seventh period, IIIB group. Refers to metals. The nuclear charge is 92.

Uranium is a silver-colored metal with a glossy surface (Fig. 1). Heavy. Malleable, flexible and soft. Inherent properties of paramagnets. Uranium is characterized by the presence of three modifications: α-uranium (orthorhombic system), β-uranium (tetragonal system) and γ-uranium (cubic system), each of which exists in a certain temperature range.

Rice. 1. Uranium. Appearance.

Atomic and molecular mass of uranium

Relative molecular weight of the substance(M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and relative atomic mass of an element(A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 the mass of a carbon atom.

Since in the free state uranium exists in the form of monatomic U molecules, the values ​​of its atomic and molecular masses coincide. They are equal to 238.0289.

Isotopes of uranium

It is known that uranium does not have stable isotopes, but natural uranium consists of a mixture of those isotopes 238 U (99.27%), 235 U and 234 U, which are radioactive.

There are unstable isotopes of uranium with mass numbers from 217 to 242.

Uranium ions

At the outer energy level of the uranium atom there are three electrons, which are valence:

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 5f 3 6s 2 6p 6 6d 1 7s 2 .

As a result of chemical interaction, uranium gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:

U 0 -3e → U 3+ .

Molecule and atom of uranium

In the free state, uranium exists in the form of monatomic U molecules. Here are some properties characterizing the uranium atom and molecule:

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

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 the production of atomic bombs (critical mass of about 16 kg).

The core of a 30 mm caliber projectile (GAU-8 cannon 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.