decomposition of uranium. Chemical element uranium: properties, characteristics, formula. Extraction and use of uranium. Applications and types of uranium isotopes

26.10.2019

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

Finding in nature.

The content of uranium in the earth's crust is 0.003%, it is found in the surface layer of the earth in the form of four types of deposits. Firstly, these are veins of uraninite, or uranium pitch (uranium dioxide UO 2), very rich in uranium, but rare. They are accompanied by deposits of radium, since radium is a direct product of the isotopic decay of uranium. Such veins are found in Zaire, Canada (Great Bear Lake), the Czech Republic and France. The second source of uranium is conglomerates of thorium and uranium ore, together with ores of other important minerals. Conglomerates usually contain sufficient quantities of gold and silver to extract, and uranium and thorium become accompanying elements. Large deposits of these ores are found 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 the fourth source of deposits. 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.

Uranium 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 obtained by Klaproth was not elemental uranium, but an oxidized form of it, and elemental uranium was first obtained by the French chemist E. .Peligot in 1841. From the moment of discovery until the 20th century. uranium was not as important as it is now, although many physical properties, and atomic mass and density were determined. In 1896, A. Becquerel found that uranium salts have radiation that illuminates a photographic plate in the dark. This discovery stimulated chemists to research in the field of radioactivity, and in 1898 the French physicists, the spouses P. Curie and M. Sklodowska-Curie, isolated salts of the radioactive elements polonium and radium, and E. Rutherford, F. Soddy, C. Faience and other scientists developed the theory of radioactive decay, which laid the foundations of modern nuclear chemistry and nuclear energy.

First applications of uranium.

Although the radioactivity of uranium salts was known, its ores in the first third of this century were used only to obtain the accompanying radium, and uranium was considered an undesirable by-product. Its use was concentrated mainly in the technology of ceramics and in metallurgy; uranium oxides were widely used to color glass in colors 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 light. During the First World War and soon after, uranium in the form of carbide was used in the manufacture of tool steels, similarly to Mo and W; 4–8% uranium replaced tungsten, which was limited in production at the time. To obtain tool steels in 1914–1926, several tons of ferrouranium were produced annually, containing up to 30% (mass.) U. However, this use of uranium did not last long.

Modern use 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 era of the atom, when uranium turned from a minor element into 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 created a demand for uranium that increased astronomically. An interesting chronology of the growth in uranium demand is based on the history of deposits in the Great Bear Lake (Canada). In 1930, resin blende, a mixture of uranium oxides, was discovered in this lake, and in 1932 a technology for purifying radium was established in this area. From each ton of ore (tar blende), 1 g of radium was obtained and about half a ton of a by-product - uranium concentrate. However, radium was scarce and its extraction was stopped. From 1940 to 1942, development was resumed and uranium ore was shipped to the United States. In 1949 a similar purification of uranium, with some modifications, was applied to produce pure UO 2 . This production has grown and is now one of the largest uranium productions.

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 (a complex crystal lattice of a tetragonal type), stable in the range of 668–774 ° С; 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 of its compounds exhibit radioactivity.

Isotopes of uranium

238 U, 235 U, 234 U are found in nature in a ratio of 99.3:0.7:0.0058, and 236U in trace amounts. All other isotopes of uranium from 226 U to 242 U are obtained artificially. The isotope 235 U is of particular importance. Under the action of slow (thermal) neutrons, it is divided with the release of enormous energy. Complete fission of 235 U results in the release of a "thermal energy equivalent" of 2h 10 7 kWh/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 isotopic uranium can be used in nuclear reactors to produce neutrons produced by 235U fission, while excess neutrons not required by the chain reaction can be captured by another natural isotope, resulting in plutonium production:

When bombarded with 238 U by 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 action of slow neutrons.

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

Some other artificial uranium isotopes are often used as radioactive tracers (tracers) in chemical and physical research; it 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 divided uranium is especially reactive, and at temperatures above 500°C it often enters into reactions characteristic of uranium hydride. Lumpy uranium or shavings burn brightly at 700–1000°C, while uranium vapors burn already at 150–250°C; uranium reacts with HF at 200–400°C, forming UF 4 and H 2 . Uranium slowly dissolves 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 reactions of uranium with dilute and concentrated HNO 3 proceed most actively and rapidly with the formation of uranyl nitrate ( see below). In the presence of HCl, uranium rapidly dissolves in organic acids, forming organic salts U 4+ . Depending on the degree of oxidation, uranium forms several types of salts (the most important among them with U 4+, one of them UCl 4 is an easily oxidized green salt); uranyl salts (UO 2 2+ radical) of the UO 2 (NO 3) 2 type are yellow and fluoresce in green. Uranyl salts are formed by dissolving amphoteric oxide UO 3 (yellow color) in an acidic medium. In an alkaline environment, UO 3 forms uranates of the Na 2 UO 4 or Na 2 U 2 O 7 type. 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 the 1940s–1950s, as they were the basis for the development of methods for separating uranium isotopes for an atomic bomb or a nuclear reactor. Uranium trifluoride UF 3 was obtained by reducing UF 4 with hydrogen, and uranium tetrafluoride UF 4 is obtained different ways by reactions of HF with oxides of the UO 3 or U 3 O 8 type or by the 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 mmHg); the compound is volatile (sublimes at 56.54 ° C under normal pressure conditions). Uranium oxohalides, for example, oxofluorides, have the composition UO 2 F 2 (uranyl fluoride), UOF 2 (uranium oxide difluoride).

And Saturn), is remarkable, first of all, for its unusual movement around the Sun, namely, unlike all other planets, Uranus rotates "retrograde". What does it mean? And the fact that if other planets, including our Earth, are like moving spinning tops (due to torsion, day and night change), then Uranus is like a rolling ball, and as a result, the change of day / night, as well as the seasons on this planets are very different.

Who discovered Uranus

But let's start our story about this unusual planet with the history of its discovery. The planet Uranus was discovered by the English astronomer William Herschel in 1781. Interestingly, observing her unusual movement, the astronomer first mistook her for, and only after a couple of years of observations did she receive planetary status. Herschel wanted to call it "Georg's Star", but the scientific community preferred the name proposed by Johann Bode - Uranus, in honor of the ancient god Uranus, who is the personification of the sky.

The god Uranus in ancient mythology is the oldest of the gods, the creator of everything and everyone (including other gods), and also the grandfather of the supreme god Zeus (Jupiter).

Features of the planet Uranus

Uranium is 14.5 times heavier than our Earth. Nevertheless, this is the lightest planet among the giant planets, so the planet next to it, although it is smaller, its mass is greater than that of Uranus. The relative lightness of this planet is due to its composition, a significant part of which is ice, and the ice on Uranus is the most diverse: there is ammonia, water, and methane ice. The density of Uranus is 1.27 g/cm3.

Temperature of Uranus

What is the temperature on Uranus? In view of the distance from the Sun, of course, it is very cold, and the point here is not only in its remoteness, but also in the fact that the internal heat of Uranus is many times less than that of other planets. The heat flow of the planet is extremely small, it is less than that of the Earth. As a result, one of the lowest temperatures ever recorded on Uranus solar system-224 C, which is even lower than that of Neptune, which is even further from the Sun.

Is there life on Uranus

At the temperature described in the paragraph above, it is obvious that the origin of life on Uranus is not possible.

Atmosphere of Uranus

What is the atmosphere like on Uranus? The atmosphere of this planet is divided into layers, which are determined by temperature and surface. The outer layer of the atmosphere begins at a distance of 300 km from the conditional surface of the planet and is called the atmospheric corona, this is the coldest part of the atmosphere. Further closer to the surface is the stratosphere and troposphere. The latter is the lowest and densest part of the planet's atmosphere. The troposphere of Uranus has a complex structure: it consists of water clouds, clouds of ammonia, methane clouds mixed with each other in a chaotic manner.

The composition of the atmosphere of Uranus differs from the atmospheres of other planets due to the high content of helium and molecular. Also, a large proportion of the atmosphere of Uranus belongs to methane, a chemical compound that makes up 2.3% of all molecules in the atmosphere there.

Photos of the planet Uranus

Surface of Uranus

The surface of Uranus consists of three layers: a rocky core, an icy mantle, and an outer shell of hydrogen and helium, which are in a gaseous state. It is also worth noting another important element that is part of the surface of Uranus - this is methane ice, which creates what is called the signature blue color of the planet.

Also, scientists using spectroscopy detected carbon monoxide and carbon dioxide in the upper atmosphere.

Yes, and Uranus also has rings (however, like other giant planets), albeit not as big and beautiful as his colleague. On the contrary, the rings of Uranus are dim and almost invisible, as they consist of many very dark and small particles, ranging in diameter from a micrometer to fractions of a meter. Interestingly, the rings of Uranus were discovered before the rings of other planets, with the exception of Saturn, even the discoverer of the planet W. Herschel claimed that he had seen the rings of Uranus, but then they did not believe him, since the telescopes of that time did not have enough power so that other astronomers could confirm what Herschel saw. Only two centuries later, in 1977, American astronomers Jameson Eliot, Douglas Mincom and Edward Dunham, using the Kuiper onboard observatory, managed to observe the rings of Uranus with their own eyes. Moreover, this happened by chance, since scientists were simply going to observe the atmosphere of the planet and, without expecting it, discovered the presence of rings in it.

At the moment, 13 rings of Uranus are known, the brightest of which is the epsilon ring. The rings of this planet are relatively young; they were formed after her birth. There is a hypothesis that the rings of Uranus are formed from the remains of some destroyed satellite of the planet.

Moons of Uranus

Speaking of moons, how many moons do you think Uranus has? And he has as many as 27 of them (at least known at the moment). The largest are: Miranda, Ariel, Umbriel, Oberon and Titania. All the moons of Uranus are a mixture rocks with ice, except for Miranda, which is made entirely of ice.

This is what the moons of Uranus look like compared to the planet itself.

Many satellites have no atmosphere, and some of them move inside the rings of the planet, through which they are also called inner satellites, and all of them have a strong connection with the ring system of Uranus. Scientists believe that many satellites were captured by Uranus.

Rotation of Uranus

The rotation of Uranus around the Sun is perhaps the most interesting feature this planet. As we wrote above, Uranus rotates differently than all other planets, namely “retrograde”, just like a ball rolls on the earth. As a result of this, the change of day and night (in our usual sense) on Uranus occurs only near the planet's equator, moreover, it is located there very low above the horizon, approximately like in the polar latitudes on Earth. As for the poles of the planet, there the “polar day” and “polar night” replace each other every 42 Earth years.

As for the year on Uranus, one year there is equal to our 84 Earth years, it is during this time that the planet makes a circle in its orbit around the Sun.

How long is the flight to Uranus

How long does it take to fly to Uranus from Earth? If at modern technologies a flight to our closest neighbors, Venus, Mars takes several years, then a flight to such distant planets as Uranus can take decades. At the moment there is only one spacecraft made a similar trip: Voyager 2, launched by NASA in 1977, flew to Uranus in 1986, as you can see, the one-way trip took almost a decade.

It was also supposed to send the Cassini apparatus to Uranus, which was engaged in the study of Saturn, but then it was decided to leave Cassini near Saturn, where he died quite recently - in September last 2017.

Three years after its discovery, the planet Uranus became the setting for a satirical pamphlet. Science fiction writers often mention this planet in their science fiction works.
Uranus can be seen in the night sky and with the naked eye, you just need to know where to look, and the sky must be perfectly dark (which, unfortunately, is not possible in modern cities).
The planet Uranus has water. That's just the water on Uranus is frozen, like ice.
The planet Uranus can be confidently assigned the laurels of "the most cold planet» Solar system.

Planet Uranus, video

And finally, an interesting video about the planet Uranus.

This article is available at English language — .

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Finding in nature.

Opening.

Uranium 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 obtained by Klaproth was not elemental uranium, but an oxidized form of it, and elemental uranium was first obtained by the French chemist E. .Peligot in 1841. From the moment of discovery until the 20th century. uranium was not as important as it is today, although many of its physical properties, as well as atomic mass and density, have been determined. In 1896, A. Becquerel found that uranium salts have radiation that illuminates a photographic plate in the dark. This discovery stimulated chemists to research in the field of radioactivity, and in 1898 the French physicists, the spouses P. Curie and M. Sklodowska-Curie, isolated salts of the radioactive elements polonium and radium, and E. Rutherford, F. Soddy, C. Faience and other scientists developed the theory of radioactive decay, which laid the foundations of modern nuclear chemistry and nuclear energy.

First applications of uranium.

Modern use of uranium.

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.

Isotopes of uranium

When bombarded with 238 U by 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 action of slow neutrons.

At present, a large number of artificial isotopes of uranium have been obtained. Among them, 233 U is especially notable in that it also fissions when interacting with slow neutrons.

Some other artificial isotopes of uranium are often used as radioactive labels (tracers) in chemical and physical research; it 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 divided uranium is especially reactive, and at temperatures above 500°C it often enters into reactions characteristic of uranium hydride. Lumpy uranium or shavings burn brightly at 700–1000°C, while uranium vapors burn already at 150–250°C; uranium reacts with HF at 200–400°C, forming UF 4 and H 2 . Uranium slowly dissolves 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 reactions of uranium with dilute and concentrated HNO 3 proceed most actively and rapidly with the formation of uranyl nitrate ( see below). In the presence of HCl, uranium rapidly dissolves in organic acids, forming organic salts U 4+ . Depending on the degree of oxidation, uranium forms several types of salts (the most important among them with U 4+, one of them UCl 4 is an easily oxidized green salt); uranyl salts (UO 2 2+ radical) of the UO 2 (NO 3) 2 type are yellow and fluoresce green. Uranyl salts are formed by dissolving amphoteric oxide UO 3 (yellow color) in an acidic medium. In an alkaline environment, UO 3 forms uranates of the Na 2 UO 4 or Na 2 U 2 O 7 type. 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 the 1940s–1950s, as they were the basis for the development of methods for separating uranium isotopes for an atomic bomb or a nuclear reactor. Uranium trifluoride UF 3 was obtained by 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 mmHg); the compound is volatile (sublimes at 56.54 ° C under normal pressure conditions). Uranium oxohalides, for example, oxofluorides, have the composition UO 2 F 2 (uranyl fluoride), UOF 2 (uranium oxide difluoride).

Where did uranium come from? Most likely, it appears during supernova explosions. The fact is that for the nucleosynthesis of elements heavier than iron, there must be a powerful neutron flux, which occurs just during a supernova explosion. It would seem that later, during condensation from the cloud of new star systems, uranium, having gathered in a protoplanetary cloud and being very heavy, must sink in the depths of the planets. But it's not. Uranium is a radioactive element and it releases heat when it decays. The calculation shows that if uranium were evenly distributed throughout the entire thickness of the planet, at least with the same concentration as on the surface, then it would release too much heat. Moreover, its flow should decrease as uranium is consumed. Since nothing of the kind is observed, geologists believe that at least a third of uranium, and perhaps all of it, is concentrated in the earth's crust, where its content is 2.5∙10 -4%. Why this happened is not discussed.

Where is uranium mined? Uranium on Earth is not so small - in terms of prevalence, it is in 38th place. And most of all this element is in sedimentary rocks - carbonaceous shales and phosphorites: up to 8∙10 -3 and 2.5∙10 -2%, respectively. In total, the earth's crust contains 10 14 tons of uranium, but the main problem is that it is very dispersed and does not form powerful deposits. About 15 uranium minerals are of industrial importance. This is uranium pitch - its base is tetravalent uranium oxide, uranium mica - various silicates, phosphates and more complex compounds with vanadium or titanium based on hexavalent uranium.

What are Becquerel rays? After the discovery of X-rays by Wolfgang Roentgen, the French physicist Antoine-Henri Becquerel became interested in the glow of uranium salts, which occurs under the action of sunlight. He wanted to understand if there were X-rays here too. Indeed, they were present - the salt illuminated the photographic plate through the black paper. In one of the experiments, however, the salt was not illuminated, and the photographic plate still darkened. When a metal object was placed between the salt and the photographic plate, the darkening under it was less. Consequently, the new rays did not arise at all due to the excitation of uranium by light and did not partially pass through the metal. They were called at first "Becquerel rays". Subsequently, it was found that these are mainly alpha rays with a small addition of beta rays: the fact is that the main isotopes of uranium emit an alpha particle during decay, and the daughter products also experience beta decay.

How high is the radioactivity of uranium? Uranium has no stable isotopes, they are all radioactive. The longest-lived is uranium-238 with a half-life of 4.4 billion years. The next is uranium-235 - 0.7 billion years. Both of them undergo alpha decay and become the corresponding isotopes of thorium. Uranium-238 makes up over 99% of all natural uranium. Because of its long half-life, the radioactivity of this element is small, and besides, alpha particles are not able to overcome the stratum corneum on the surface of the human body. They say that IV Kurchatov, after working with uranium, simply wiped his hands with a handkerchief and did not suffer from any diseases associated with radioactivity.

Researchers have repeatedly turned to the statistics of diseases of workers in uranium mines and processing plants. For example, here is a recent article by Canadian and American experts who analyzed the health data of more than 17,000 workers at the Eldorado mine in the Canadian province of Saskatchewan for the years 1950-1999 ( environmental research, 2014, 130, 43–50, DOI:10.1016/j.envres.2014.01.002). They proceeded from the fact that radiation has the strongest effect on rapidly multiplying blood cells, leading to the corresponding types of cancer. The statistics showed that the workers of the mine have a disease various types less blood cancer than the average Canadian. At the same time, the main source of radiation is considered not uranium itself, but the gaseous radon generated by it and its decay products, which can enter the body through the lungs.

Why is uranium harmful?? It, like other heavy metals, is highly toxic and can cause kidney and liver failure. On the other hand, uranium, being a dispersed element, is inevitably present in water, soil and, concentrating in the food chain, enters the human body. It is reasonable to assume that in the process of evolution, living beings have learned to neutralize uranium in natural concentrations. The most dangerous uranium is in water, so the WHO set a limit: at first it was 15 µg/l, but in 2011 the standard was increased to 30 µg/g. As a rule, there is much less uranium in water: in the USA, on average, 6.7 μg / l, in China and France - 2.2 μg / l. But there are also strong deviations. So in some areas of California it is a hundred times more than the standard - 2.5 mg / l, and in southern Finland it reaches 7.8 mg / l. Researchers are trying to understand whether the WHO standard is too strict by studying the effect of uranium on animals. Here is a typical job BioMed Research International, 2014, ID 181989; DOI:10.1155/2014/181989). French scientists fed rats for nine months with water supplemented with depleted uranium, and in a relatively high concentration - from 0.2 to 120 mg / l. The lower value is water near the mine, while the upper one is not found anywhere - the maximum concentration of uranium, measured in the same Finland, is 20 mg / l. To the surprise of the authors - the article is titled: "The unexpected absence of a noticeable effect of uranium on physiological systems ..." - uranium had practically no effect on the health of rats. The animals ate well, put on weight properly, did not complain of illness and did not die of cancer. Uranium, as it should be, was deposited primarily in the kidneys and bones, and in a hundredfold smaller amount - in the liver, and its accumulation, as expected, depended on the content in the water. However, this did not lead to kidney failure, or even to the noticeable appearance of any molecular markers of inflammation. The authors suggested starting a review of the strict WHO guidelines. However, there is one caveat: the effect on the brain. There was less uranium in the brains of rats than in the liver, but its content did not depend on the amount in water. But uranium affected the work of the antioxidant system of the brain: the activity of catalase increased by 20%, glutathione peroxidase increased by 68–90%, while the activity of superoxide dismutase fell by 50% regardless of the dose. This means that uranium clearly caused oxidative stress in the brain and the body reacted to it. Such an effect - a strong effect of uranium on the brain in the absence of its accumulation in it, by the way, as well as in the genital organs - was noticed earlier. Moreover, water with uranium at a concentration of 75–150 mg/l, which researchers from the University of Nebraska fed to rats for six months ( Neurotoxicology and Teratology, 2005, 27, 1, 135–144; DOI:10.1016/j.ntt.2004.09.001) affected the behavior of animals, mainly males, released into the field: they crossed the lines, stood up on their hind legs, and brushed their fur, unlike the control ones. There is evidence that uranium also leads to memory impairment in animals. The change in behavior correlated with the level of lipid oxidation in the brain. It turns out that rats from uranium water became healthy, but stupid. These data will still be useful to us in the analysis of the so-called Persian Gulf syndrome (Gulf War Syndrome).

Does uranium pollute shale gas mining sites? It depends on how much uranium is in the gas-containing rocks and how it is associated with them. For example, Associate Professor Tracy Bank of the University at Buffalo has explored the Marcelus Shale, which stretches from western New York State through Pennsylvania and Ohio to West Virginia. It turned out that uranium is chemically bound precisely with the source of hydrocarbons (recall that related carbonaceous shales have the highest uranium content). Experiments have shown that the solution used for fracturing the seam perfectly dissolves uranium. “When the uranium in these waters is on the surface, it can cause pollution of the surrounding area. It does not carry a radiation risk, but uranium is a poisonous element, ”Tracey Bank notes in a university press release dated October 25, 2010. Detailed articles on the risk of environmental pollution with uranium or thorium during the extraction of shale gas have not yet been prepared.

Why is uranium needed? Previously, it was used as a pigment for the manufacture of ceramics and colored glass. Now uranium is the basis of nuclear energy and nuclear weapons. In this case, its unique property is used - the ability of the nucleus to divide.

What is nuclear fission? The disintegration of the nucleus into two unequal large pieces. It is precisely because of this property that during nucleosynthesis due to neutron irradiation, nuclei heavier than uranium are formed with great difficulty. The essence of the phenomenon is as follows. If the ratio of the number of neutrons and protons in the nucleus is not optimal, it becomes unstable. Usually such a nucleus ejects either an alpha particle - two protons and two neutrons, or a beta particle - a positron, which is accompanied by the transformation of one of the neutrons into a proton. In the first case, an element of the periodic table is obtained, spaced two cells back, in the second - one cell forward. However, the uranium nucleus, in addition to emitting alpha and beta particles, is capable of fission - decaying into the nuclei of two elements in the middle of the periodic table, for example, barium and krypton, which it does, having received a new neutron. This phenomenon was discovered shortly after the discovery of radioactivity, when physicists exposed everything they had to the newly discovered radiation. Here is how Otto Frisch, a participant in the events, writes about this (“Successes physical sciences ", 1968, 96, 4). After the discovery of beryllium rays - neutrons - Enrico Fermi irradiated them, in particular, uranium to cause beta decay - he hoped to get the next, 93rd element, now called neptunium, at his expense. It was he who discovered a new type of radioactivity in irradiated uranium, which he associated with the appearance of transuranium elements. In this case, slowing down neutrons, for which the beryllium source was covered with a layer of paraffin, increased this induced radioactivity. The American radiochemist Aristide von Grosse suggested that one of these elements was protactinium, but he was wrong. But Otto Hahn, who was then working at the University of Vienna and considered protactinium discovered in 1917 to be his brainchild, decided that he was obliged to find out what elements were obtained in this case. Together with Lise Meitner, in early 1938, Hahn suggested, based on the results of experiments, that whole chains of radioactive elements are formed, arising from multiple beta decays of the nuclei of uranium-238 that absorbed the neutron and its daughter elements. Soon Lise Meitner was forced to flee to Sweden, fearing possible reprisals from the Nazis after the Anschluss of Austria. Gan, continuing his experiments with Fritz Strassmann, discovered that among the products there was also barium, element number 56, which could not have been obtained from uranium in any way: all chains of uranium alpha decays end in much heavier lead. The researchers were so surprised by the result that they did not publish it, they only wrote letters to friends, in particular Lise Meitner in Gothenburg. There, at Christmas 1938, her nephew, Otto Frisch, visited her, and, walking in the vicinity of the winter city - he is on skis, his aunt is on foot - they discussed the possibility of the appearance of barium during the irradiation of uranium due to nuclear fission (for more on Lise Meitner, see "Chemistry and Life ", 2013, No. 4). Returning to Copenhagen, Frisch, literally on the gangway of a steamer departing for the USA, caught Niels Bohr and informed him about the idea of division. Bor, slapping his forehead, said: “Oh, what fools we were! We should have noticed this sooner." In January 1939, Frisch and Meitner published an article on the fission of uranium nuclei under the action of neutrons. By that time, Otto Frisch had already set up a control experiment, as well as many American groups that received a message from Bohr. They say that physicists began to disperse to their laboratories right during his report on January 26, 1939 in Washington at the annual conference on theoretical physics, when they grasped the essence of the idea. After the discovery of fission, Hahn and Strassmann revised their experiments and found, just like their colleagues, that the radioactivity of irradiated uranium is not associated with transuraniums, but with the decay of radioactive elements formed during fission from the middle of the periodic table.

How does a chain reaction work in uranium? Shortly after the possibility of fission of uranium and thorium nuclei was experimentally proved (and there are no other fissile elements on Earth in any significant amount), Niels Bohr and John Wheeler, who worked at Princeton, as well as independently the Soviet theoretical physicist Ya. I. Frenkel and the Germans Siegfried Flügge and Gottfried von Droste created the theory of nuclear fission. Two mechanisms followed from it. One is related to the threshold absorption of fast neutrons. According to him, to initiate fission, the neutron must have a rather high energy, more than 1 MeV for the nuclei of the main isotopes - uranium-238 and thorium-232. At lower energies, the absorption of a neutron by uranium-238 has a resonant character. So, a neutron with an energy of 25 eV has a thousand times large area capture cross section than with other energies. In this case, there will be no fission: uranium-238 will become uranium-239, which with a half-life of 23.54 minutes will turn into neptunium-239, the one with a half-life of 2.33 days will turn into long-lived plutonium-239. Thorium-232 will become uranium-233.

The second mechanism is the non-threshold absorption of a neutron, followed by the third more or less common fissile isotope - uranium-235 (as well as plutonium-239 and uranium-233, which are absent in nature): by absorbing any neutron, even a slow one, the so-called thermal, with an energy of for molecules participating in thermal motion - 0.025 eV, such a nucleus will be divided. And this is very good: for thermal neutrons, the capture cross-sectional area is four times higher than for fast, megaelectronvolt ones. This is the significance of uranium-235 for the entire subsequent history of nuclear energy: it is it that ensures the multiplication of neutrons in natural uranium. After hitting a neutron, the uranium-235 nucleus becomes unstable and quickly splits into two unequal parts. Along the way, several (on average 2.75) new neutrons fly out. If they fall into the nuclei of the same uranium, they will cause the neutrons to multiply exponentially - a chain reaction will start, which will lead to an explosion due to the rapid release of a huge amount of heat. Neither uranium-238 nor thorium-232 can work like this: after all, during fission, neutrons with an average energy of 1-3 MeV are emitted, that is, if there is an energy threshold of 1 MeV, a significant part of the neutrons will certainly not be able to cause a reaction, and there will be no reproduction. This means that these isotopes should be forgotten and neutrons will have to be slowed down to thermal energy so that they interact with uranium-235 nuclei as efficiently as possible. At the same time, their resonant absorption by uranium-238 cannot be allowed: after all, in natural uranium this isotope is slightly less than 99.3%, and neutrons more often collide with it, and not with the target uranium-235. And acting as a moderator, it is possible to maintain neutron multiplication at a constant level and prevent an explosion - to control a chain reaction.

The calculation carried out by Ya. B. Zeldovich and Yu. B. Khariton in the same fateful 1939 showed that for this it is necessary to use a neutron moderator in the form of heavy water or graphite and enrich natural uranium with uranium-235 by at least 1.83 times. Then this idea seemed to them pure fantasy: “It should be noted that approximately double the enrichment of those fairly significant amounts of uranium that are necessary to carry out a chain explosion,<...>is an extremely cumbersome task, close to practical impossibility." Now this problem has been solved, and the nuclear industry is mass-producing uranium enriched with uranium-235 up to 3.5% for power plants.

What is spontaneous nuclear fission? In 1940, G. N. Flerov and K. A. Petrzhak discovered that uranium fission can occur spontaneously, without any external influence, although the half-life is much longer than with ordinary alpha decay. Since such fission also produces neutrons, if they are not allowed to fly away from the reaction zone, they will serve as the initiators of the chain reaction. It is this phenomenon that is used in the creation of nuclear reactors.

Why is nuclear power needed? Zel'dovich and Khariton were among the first to calculate the economic effect of nuclear energy (Uspekhi fizicheskikh nauk, 1940, 23, 4). “... At the moment, it is still impossible to make final conclusions about the possibility or impossibility of implementing a nuclear fission reaction in uranium with infinitely branching chains. If such a reaction is feasible, then the reaction rate is automatically adjusted to ensure that it proceeds smoothly, despite the huge amount of energy at the disposal of the experimenter. This circumstance is exceptionally favorable for the energy utilization of the reaction. Therefore, although this is a division of the skin of an unkilled bear, we present some numbers that characterize the possibilities for the energy use of uranium. If the fission process proceeds on fast neutrons, therefore, the reaction captures the main isotope of uranium (U238), then<исходя из соотношения теплотворных способностей и цен на уголь и уран>the cost of a calorie from the main isotope of uranium turns out to be about 4000 times cheaper than from coal (unless, of course, the processes of "burning" and heat removal turn out to be much more expensive in the case of uranium than in the case of coal). In the case of slow neutrons, the cost of a "uranium" calorie (based on the above figures) will, taking into account that the abundance of the isotope U235 is 0.007, is already only 30 times cheaper than a "coal" calorie, all other things being equal.

The first controlled chain reaction was carried out in 1942 by Enrico Fermi at the University of Chicago, and the reactor was manually controlled by pushing and pulling out graphite rods as the neutron flux changed. The first power plant was built in Obninsk in 1954. In addition to generating energy, the first reactors also worked to produce weapons-grade plutonium.

How does a nuclear power plant work? Most reactors now operate on slow neutrons. Enriched uranium in the form of a metal, an alloy, for example with aluminum, or in the form of an oxide is put into long cylinders - fuel elements. They are installed in a certain way in the reactor, and rods from the moderator are introduced between them, which control the chain reaction. Over time, reactor poisons accumulate in the fuel element - uranium fission products, also capable of absorbing neutrons. When the uranium-235 concentration falls below the critical level, the element is decommissioned. However, it contains many fission fragments with strong radioactivity, which decreases over the years, which is why the elements emit a significant amount of heat for a long time. They are kept in cooling pools, and then they are either buried or they try to process them - to extract unburned uranium-235, accumulated plutonium (it was used to make atomic bombs) and other isotopes that can be used. The unused part is sent to the burial grounds.

In so-called fast neutron reactors, or breeder reactors, reflectors of uranium-238 or thorium-232 are installed around the elements. They slow down and send too fast neutrons back to the reaction zone. Slowed down to resonant speeds, neutrons absorb these isotopes, turning into plutonium-239 or uranium-233, respectively, which can serve as fuel for a nuclear power plant. Since fast neutrons do not react well with uranium-235, it is necessary to significantly increase its concentration, but this pays off with a stronger neutron flux. Despite the fact that breeder reactors are considered the future of nuclear energy, since they provide more nuclear fuel than they consume, experiments have shown that they are difficult to control. Now there is only one such reactor left in the world - at the fourth power unit of the Beloyarsk NPP.

How is nuclear energy criticized? If we don't talk about accidents, the main point in the arguments of the opponents of nuclear energy today was the proposal to add to the calculation of its efficiency the costs of protecting the environment after decommissioning the plant and when working with fuel. In both cases, the task of reliable disposal of radioactive waste arises, and these are the costs that the state bears. There is an opinion that if they are shifted to the cost of energy, then its economic attractiveness will disappear.

There is also opposition among supporters of nuclear energy. Its representatives point to the uniqueness of uranium-235, which has no replacement, because alternative isotopes fissile by thermal neutrons - plutonium-239 and uranium-233 - are absent in nature due to a half-life of thousands of years. And they are obtained just as a result of the fission of uranium-235. If it ends, the beautiful will disappear natural source neutrons for a nuclear chain reaction. As a result of such extravagance, mankind will lose the opportunity in the future to involve thorium-232 in the energy cycle, the reserves of which are several times greater than those of uranium.

Theoretically, particle accelerators can be used to obtain a flux of fast neutrons with megaelectronvolt energies. However, if we are talking, for example, about interplanetary flights on an atomic engine, then it will be very difficult to implement a scheme with a bulky accelerator. The exhaustion of uranium-235 puts an end to such projects.

What is weapon-grade uranium? This is highly enriched uranium-235. Its critical mass - it corresponds to the size of a piece of matter in which a chain reaction spontaneously occurs - is small enough to make a munition. Such uranium can be used to make an atomic bomb, as well as a fuse for a thermonuclear bomb.

What disasters are associated with the use of uranium? The energy stored in the nuclei of fissile elements is enormous. Having escaped from control due to an oversight or due to intent, this energy can do a lot of trouble. The two worst nuclear disasters occurred on August 6 and 8, 1945, when the US Air Force dropped atomic bombs Hiroshima and Nagasaki, resulting in the death and injury of hundreds of thousands of civilians. Smaller scale disasters are associated with accidents on nuclear power plants and enterprises of the nuclear cycle. The first major accident happened in 1949 in the USSR at the Mayak plant near Chelyabinsk, where plutonium was produced; liquid radioactive waste got into the river Techa. In September 1957, an explosion occurred on it with an ejection a large number radioactive substance. Eleven days later, the British plutonium reactor at Windscale burned down, a cloud of explosion products dissipated over Western Europe. In 1979, the reactor at the Trimail Island nuclear power plant in Pennsylvania burned down. Accidents at the Chernobyl nuclear power plant(1986) and the nuclear power plant in Fukushima (2011), when millions of people were exposed to radiation. The first littered vast lands, throwing out 8 tons of uranium fuel with decay products as a result of the explosion, which spread throughout Europe. The second polluted and, three years after the accident, continues to pollute the Pacific Ocean in the areas of fisheries. The elimination of the consequences of these accidents was very expensive, and if these costs were decomposed into the cost of electricity, it would increase significantly.

A separate issue is the consequences for human health. According to official statistics, many people who survived the bombing or live in contaminated areas benefited from exposure - the former have a higher life expectancy, the latter have fewer cancers, and experts attribute a certain increase in mortality to social stress. The number of people who died precisely from the consequences of accidents or as a result of their liquidation is estimated at hundreds of people. Opponents of nuclear power plants point out that accidents have led to several million premature deaths on the European continent, they are simply invisible against the statistical background.

The withdrawal of land from human use in accident zones leads to interesting result: they become a kind of reserves where biodiversity grows. True, some animals suffer from diseases associated with radiation. The question of how quickly they will adapt to the increased background remains open. There is also an opinion that the consequence of chronic irradiation is “selection for a fool” (see Chemistry and Life, 2010, No. 5): more primitive organisms survive even at the embryonic stage. In particular, in relation to people, this should lead to a decrease in the mental abilities of the generation born in the contaminated territories shortly after the accident.

What is depleted uranium? This is uranium-238 left over from the extraction of uranium-235. The volumes of waste from the production of weapons-grade uranium and fuel elements are large - in the United States alone, 600 thousand tons of such uranium hexafluoride have accumulated (for problems with it, see "Chemistry and Life", 2008, No. 5). The content of uranium-235 in it is 0.2%. These wastes must either be stored until better times, when fast neutron reactors will be created and it will be possible to process uranium-238 into plutonium, or somehow used.

They found a use for it. Uranium, like other transition elements, is used as a catalyst. For example, the authors of an article in ACS Nano dated June 30, 2014, they write that a uranium or thorium catalyst with graphene for the reduction of oxygen and hydrogen peroxide "has great potential for energy applications." Because of its high density, uranium serves as ballast for ships and counterweights for aircraft. This metal is also suitable for radiation protection in medical devices with radiation sources.

What weapons can be made from depleted uranium? Bullets and cores for armor-piercing projectiles. Here is the calculation. The heavier the projectile, the higher its kinetic energy. But the larger the projectile, the less concentrated its impact. This means that heavy metals with a high density are needed. Bullets are made of lead (Ural hunters at one time also used native platinum, until they realized that it was a precious metal), while the cores of the shells were made of a tungsten alloy. Conservationists point out that lead pollutes the soil in places of war or hunting and it would be better to replace it with something less harmful, for example, with the same tungsten. But tungsten is not cheap, and uranium, similar in density to it, is a harmful waste. At the same time, the permissible contamination of soil and water with uranium is approximately twice as high as for lead. This happens because the weak radioactivity of depleted uranium (and it is also 40% less than that of natural uranium) is neglected and a really dangerous chemical factor is taken into account: uranium, as we remember, is poisonous. At the same time, its density is 1.7 times greater than that of lead, which means that the size of uranium bullets can be reduced by half; uranium is much more refractory and harder than lead - when fired, it evaporates less, and when it hits a target, it produces fewer microparticles. In general, a uranium bullet pollutes less environment than lead, however, it is not known for certain about such use of uranium.

But it is known that depleted uranium plates are used to strengthen the armor of American tanks (this is facilitated by its high density and melting point), and also instead of tungsten alloy in cores for armor-piercing projectiles. The uranium core is also good because uranium is pyrophoric: its hot small particles, formed when they hit the armor, flare up and set fire to everything around. Both applications are considered radiation safe. So, the calculation showed that, even after spending a year without getting out in a tank with uranium armor loaded with uranium ammunition, the crew would receive only a quarter of the allowable dose. And in order to obtain an annual allowable dose, such ammunition must be screwed to the surface of the skin for 250 hours.

Projectiles with uranium cores - for 30-mm aircraft guns or for artillery sub-calibers - were used by the Americans in recent wars, starting with the 1991 Iraq campaign of the year. That year, they poured 300 tons of depleted uranium on Iraqi armored units in Kuwait, and during their retreat, 250 tons, or 780,000 rounds, fell on aircraft guns. In Bosnia and Herzegovina, during the bombing of the army of the unrecognized Republika Srpska, 2.75 tons of uranium were used, and during the shelling of the Yugoslav army in the province of Kosovo and Metohija - 8.5 tons, or 31,000 rounds. Since the WHO had by that time taken care of the consequences of the use of uranium, monitoring was carried out. He showed that one volley consisted of approximately 300 rounds, of which 80% contained depleted uranium. 10% hit the targets, and 82% fell within 100 meters of them. The rest dispersed within 1.85 km. The shell that hit the tank burned down and turned into an aerosol, light targets like armored personnel carriers were pierced through by a uranium shell. Thus, one and a half tons of shells could turn into uranium dust in Iraq at the most. According to experts from the American strategic research center RAND Corporation, more than 10 to 35% of the used uranium has turned into an aerosol. Croatian uranium munitions fighter Asaf Durakovich, who has worked in a variety of organizations from the King Faisal Hospital in Riyadh to the Washington Uranium Medical Research Center, believes that in southern Iraq alone in 1991, 3-6 tons of submicron uranium particles were formed, which scattered over a wide area , that is, uranium pollution there is comparable to Chernobyl.

uranium (chemical element) uranium (chemical element)

URANIUM (lat. Uranium), U (read "uranium"), a radioactive chemical element with atomic number 92, atomic mass 238.0289. Actinoid. Natural uranium consists of a mixture of three isotopes: 238U, 99.2739%, with a half-life of T 1/2 \u003d 4.51 10 9 years, 235 U, 0.7024%, with a half-life T 1/2 \u003d 7.13 10 8 years, 234 U, 0.0057%, with a 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, long-lived 233 U ( T 1/2 \u003d 1.62 10 5 years), it is obtained by neutron irradiation of thorium (cm. THORIUM).
Configuration of three outer electron layers 5 s 2 p 6 d 10 f 3 6s 2 p 6 d 1 7 s 2 , uranium refers to f-elements. Located in IIIB group in period 7 periodic system elements. In compounds, it exhibits oxidation states +2, +3, +4, +5 and +6, valencies II, III, IV, V and VI.
The radius of the neutral atom of uranium is 0.156 nm, the radius of the 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 an atom are 6.19, 11.6, 19.8, 36.7 eV. Electronegativity according to Pauling (cm. PAULING Linus) 1,22.
Discovery history
Uranium was discovered in 1789 by the German chemist M. G. Klaproth (cm. KLAPROT Martin Heinrich) in the study of the mineral "tar blende". Named after the planet Uranus, discovered by W. Herschel (cm. HERSHEL) in 1781. In the metallic state, uranium was obtained in 1841 by the French chemist E. Peligot (cm. PELIGO Eugene Melchior) when reducing UCl 4 with metallic potassium. 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) 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) came to the conclusion that these elements (actinides) (cm. actinoids) it is more correct to place in the periodic system 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 them are pitchblende U 3 O 8, 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. The extraction of uranium begins with the production of a 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 by 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, the so-called reactor poisons. By absorbing the neutrons produced during the operation of a nuclear reactor, they make uranium unsuitable for use as a nuclear fuel.
To get rid of impurities, metallic uranium is dissolved in nitric acid, obtaining uranyl nitrate UO 2 (NO 3) 2 . The uranyl nitrate is extracted from the 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 regeneration of spent nuclear fuel in the reactor. All uranium regeneration operations are carried out remotely.
Physical and chemical properties
Uranium is a silvery white lustrous metal. Uranium metal exists in three allotropic (cm. ALLOTROPY) modifications. Up to 669°C stable a-modification with an orthorhombic lattice, parameters A= 0.2854nm, V= 0.5869 nm and With\u003d 0.4956 nm, density 19.12 kg / dm 3. From 669°C to 776°C, the b-modification with a tetragonal lattice is stable (parameters A= 1.0758 nm, With= 0.5656 nm). Up to a melting point of 1135°C, the g-modification with a cubic body-centered lattice is stable ( A= 0.3525 nm). Boiling point 4200°C.
The chemical activity of metallic uranium is high. In air, it is covered with an oxide film. Powdered uranium is pyrophoric; during the combustion of uranium and the thermal decomposition of many of its compounds in air, uranium oxide U 3 O 8 is formed. If this oxide is heated in an atmosphere of hydrogen (cm. HYDROGEN) at temperatures above 500 ° C, uranium dioxide UO 2 is formed:
U 3 O 8 + H 2 \u003d 3UO 2 + 2H 2 O
If uranyl nitrate UO 2 (NO 3) 2 is heated at 500°C, then, 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. HALOGENS), uranium gives uranium halides. Among them, UF 6 hexafluoride is a yellow crystalline substance, easily sublimating even with low heating (40-60 ° C) and just as easily hydrolyzed by water. The most important practical value has uranium hexafluoride UF 6 . It is obtained by the interaction of metallic uranium, 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 \u003d 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 a high chemical activity. When heated, the hydride decomposes, forming hydrogen and powdered uranium. During the sintering of uranium with boron, depending on the molar ratio of the reactants and the process conditions, borides UB 2 , UB 4 and UB 12 arise.
With carbon (cm. CARBON) uranium forms three carbides UC, U 2 C 3 and UC 2 .
The 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) have been 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 .
Metallic uranium dissolves in HCl and HNO 3 and slowly reacts with H 2 SO 4 and H 3 PO 4 . There are salts containing the uranyl cation UO 2 2+ .
IN aqueous solutions there are uranium compounds 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 disproportionates into U 4+ and UO 2 2+ in solution. U 3+ ions have a characteristic red color, U 4+ ions are green, and UO 2 2+ ions are yellow.
In solutions, uranium compounds in the +6 oxidation state are the most stable. All uranium compounds in solutions are prone to hydrolysis and complex formation, the most strongly are U 4+ and UO 2 2+ cations.
Application
Uranium metal and its compounds are mainly used as nuclear fuel in nuclear reactors. A low-enriched mixture of uranium isotopes is used in stationary reactors of nuclear power plants. The product of a high degree of enrichment is 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
In microquantities (10 -5 -10 -8%) it is found in the tissues of plants, animals and humans. It accumulates to the greatest extent by some fungi and algae. Uranium compounds are absorbed into gastrointestinal tract(about 1%), in the lungs - 50%. The main depots in the body: the spleen, kidneys, skeleton, liver, lungs and broncho-pulmonary 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. Aerosols of uranium and its compounds are especially dangerous. For aerosols of water-soluble uranium compounds MPC in air is 0.015 mg/m 3 , for insoluble forms of uranium MPC is 0.075 mg/m 3 . When it enters the body, uranium acts on all organs, being a general cellular poison. The molecular mechanism of action of uranium is associated with its ability to inhibit the activity of enzymes. First of all, the kidneys are affected (protein and sugar appear in the urine, oliguria). With chronic intoxication, hematopoietic and nervous system disorders are possible.

encyclopedic Dictionary . 2009 .

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U (Uran, uranium; at O = 16 atomic weight U = 240) the element with the highest atomic weight; all elements, by atomic weight, are placed between hydrogen and uranium. This is the heaviest member of the metal subgroup of group VI of the periodic system (see Chromium, ... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

Uranium (U) Atomic number 92 Appearance a simple substance Properties of an atom Atomic mass ( molar mass) 238.0289 a. e.m. (g / mol) ... Wikipedia

Uranium (lat. Uranium), U, a radioactive chemical element of group III of the Mendeleev periodic system, belongs to the family of actinides, atomic number 92, atomic mass 238.029; metal. Natural U. consists of a mixture of three isotopes: 238U √ 99.2739% ... ... Great Soviet Encyclopedia

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- (Greek uranos sky). 1) the god of heaven, the father of Saturn, the oldest of the gods, in Greek. mythol. 2) a rare metal that has the appearance of silvery leaves in its pure state. 3) a large planet discovered by Herschel in 1781. Dictionary of foreign words included in ... ... Dictionary of foreign words of the Russian language

Uranus:* Uranus (mythology) ancient Greek god. Son of Gaia * Uranus (planet) planet of the solar system * Uranus ( musical instrument) ancient Turkic and Kazakh musical wind instrument * Uranus (element) chemical element * Operation ... ... Wikipedia

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