Uranus is one of the heavy metal elements of the periodic table. Uranium is widely used in the energy and military industries. In the periodic table it can be found at number 92 and is designated by the Latin letter U with a mass number of 238.
How Uranus was discovered
In general, such a chemical element as uranium has been known for a very long time. It is known that even before our era, natural uranium oxide was used to make yellow glaze for ceramics. The discovery of this element can be traced back to 1789, when a German chemist named Martin Heinrich Klaproth recovered a black metal-like material from an ore. Martin decided to call this material Uranus to support the name of the new discovered planet of the same name (the planet Uranus was discovered in the same year). In 1840, it was revealed that this material, discovered by Klaproth, turned out to be uranium oxide, despite the characteristic metallic luster. Eugene Melchior Peligot synthesized atomic Uranium from oxide and determined its atomic weight to be 120 AU, and in 1874 Mendeleev doubled this value, placing it in the farthest cell of his table. Only 12 years later, Mendeleev’s decision to double the mass was confirmed by the experiments of the German chemist Zimmermann.
Where and how is uranium mined?
Uranium is a fairly common element, but it is common in the form of uranium ore. So that you understand, its content in the earth’s crust is 0.00027% of the total mass of the Earth. Uranium ore is typically found in acidic mineral rocks with a high silicon content. The main types of uranium ores are pitchblende, carnotite, casolite and samarskite. The largest reserves of uranium ores, taking into account reserve deposits, are in countries such as Australia, Russia and Kazakhstan, and of all these, Kazakhstan occupies a leading position. Mining uranium is a very difficult and expensive procedure. Not all countries can afford to mine and synthesize pure uranium. The production technology is as follows: ore or minerals are mined in mines, comparable to gold or precious stones. The mined rocks are crushed and mixed with water to separate the uranium dust from the rest. Uranium dust is very heavy and therefore it precipitates faster than others. The next step is to purify the uranium dust from other rocks by acid or alkaline leaching. The procedure looks something like this: the uranium mixture is heated to 150 °C and pure oxygen is supplied under pressure. As a result, sulfuric acid is formed, which purifies uranium from other impurities. Well, at the final stage, pure uranium particles are selected. In addition to uranium dust, there are also other useful minerals.
The danger of radioactive radiation from uranium
Everyone is well aware of the concept of radioactive radiation and the fact that it causes irreparable harm to health, which leads to death. Uranium is one such element that, under certain conditions, can release radioactive radiation. In free form, depending on its variety, it can emit alpha and beta rays. Alpha rays do not pose a great danger to humans if the irradiation is external since this radiation has a low penetrating ability, but when they enter the body they cause irreparable harm. Even a sheet of writing paper is enough to contain external alpha rays. With beta radiation, things are more serious, but not much. The penetrating power of beta radiation is higher than that of alpha radiation, but 3-5 mm of tissue will be required to contain beta radiation. Can you tell me how this is? Uranium is a radioactive element that is used in nuclear weapons! That's right, it is used in nuclear weapons, which cause colossal damage to all living things. It’s just that when a nuclear warhead detonates, the main damage to living organisms is caused by gamma radiation and a flux of neutrons. These types of radiation are formed as a result of a thermonuclear reaction during the explosion of a warhead, which removes uranium particles from a stable state and destroys all life on earth.
Varieties of uranium
As mentioned above, uranium has several varieties. Varieties imply the presence of isotopes, so you understand, isotopes imply the same elements, but with different mass numbers.
So there are two types:
- Natural;
- Artificial;
As you may have guessed, the natural one is the one that is mined from the earth, and the artificial one is created by people on their own. Natural isotopes include uranium isotopes with mass numbers 238, 235 and 234. Moreover, U-234 is a daughter of U-238, that is, the first is obtained from the decay of the second under natural conditions. The second group of isotopes, which are created artificially, have mass numbers from 217 to 242. Each of the isotopes has different properties and is characterized by different behavior under certain conditions. Depending on the needs, nuclear scientists try to find all kinds of solutions to problems, because each isotope has a different energy value.
Half-lives
As mentioned above, each of the isotopes of uranium has a different energy value and different properties, one of which is half-life. In order to understand what it is, you need to start with a definition. The half-life is the time during which the number of radioactive atoms is reduced by half. The half-life affects many factors, for example its energy value or complete purification. If we take the latter as an example, we can calculate how long it will take to completely clear the radioactive contamination of the earth. Half-lives of uranium isotopes:
As can be seen from the table, the half-life of isotopes varies from minutes to hundreds of millions of years. Each of them finds application in different areas of people’s lives.
Application
The use of uranium is very widespread in many fields of activity, but it is of greatest value in the energy and military sectors. The isotope U-235 is of greatest interest. Its advantage is that it is capable of independently maintaining a nuclear chain reaction, which is widely used in military affairs for the manufacture of nuclear weapons and as fuel in nuclear reactors. In addition, uranium is widely used in geology to determine the age of minerals and rocks, as well as to determine the course of geological processes. In the automotive and aircraft industries, depleted uranium is used as a counterweight and centering element. Application was also found in painting, and more specifically as a paint for porcelain and for the manufacture of ceramic glazes and enamels. Another interesting point can be considered the use of depleted uranium for protection against radioactive radiation, as strange as it may sound.
Uranus(lat. uranium), u, radioactive chemical element of group III of the Mendeleev periodic system, belongs to the family actinides, atomic number 92, atomic mass 238.029; metal. Natural U. 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% (t 1 / 2 = 7.13 10 8 years) and 234 u – 0.0057% (t 1 / 2 = 2.48 10 5 years). Of the 11 artificial radioactive isotopes with mass numbers from 227 to 240, the long-lived one is 233 u (t 1 / 2 = 1.62 10 5 years); it is obtained by neutron irradiation of thorium. 238 u and 235 u are the ancestors of two radioactive series.
Historical reference. U. opened in 1789. chemist M. G. Klaproth and named him in honor of the planet Uranus, discovered by V. Herschel in 1781. In the metallic state, U. was obtained in 1841 by the French. chemist E. Peligo during the reduction of ucl 4 with potassium metal. Initially, U. was assigned an atomic mass of 120, and only in 1871 D.I. Mendeleev I came to the conclusion that this value should be doubled.
For a long time, uranium was of interest only to a narrow circle of chemists and found limited use in the production of paints and glass. With the discovery of the phenomenon radioactivity U. in 1896 and radium in 1898, industrial processing of uranium ores began in order to extract and use radium in scientific research and medicine. Since 1942, after the discovery in 1939 of the phenomenon of nuclear fission , U. became the main nuclear fuel.
Distribution in nature. U. is a characteristic element for the granite layer and sedimentary shell of the earth's crust. The average content of uranium in the earth's crust (clarke) is 2.5 10 -4% by weight, in acidic igneous rocks 3.5 10 -4%, in clays and shales 3.2 10 -4%, in basic rocks 5 · 10 -5%, in ultrabasic rocks of the mantle 3 · 10 -7%. U. migrates vigorously in cold and hot, neutral and alkaline waters in the form of simple and complex ions, especially in the form of carbonate complexes. Redox reactions play an important role in the geochemistry of uranium, since uranium compounds, as a rule, are highly soluble in waters with an oxidizing environment and poorly soluble in waters with a reducing environment (for example, hydrogen sulfide).
About 100 uranium minerals are known; 12 of them are of industrial importance . Over the course of geological history, the carbon content in the earth's crust decreased due to radioactive decay; This process is associated with the accumulation of Pb and He atoms in the earth's crust. Radioactive decay of carbon plays an important role in the energetics of the earth's crust, being a significant source of deep heat.
Physical properties. U. is similar in color to steel and is easy to process. It has three allotropic modifications - a, b and g with phase transformation temperatures: a ® b 668.8 ± 0.4 ° C, b® g 772.2 ± 0.4 ° C; a-shape has a rhombic lattice a= 2.8538 å, b= 5.8662 å, With= 4.9557 å), b-form – tetragonal lattice (at 720 °C A = 10,759 , b= 5.656 å), g-shape – body-centered cubic lattice (at 850°c a = 3.538 å). Density of U. in a-form (25°c) 19.05 ± 0.2 g/cm 3 ,t pl 1132 ± 1°С; t kip 3818 °C; thermal conductivity (100–200°c), 28.05 Tue/(m· TO) , (200–400 °c) 29.72 Tue/(m· TO) ; specific heat capacity (25°c) 27.67 kJ/(kg· TO) ; electrical resistivity at room temperature is about 3 10 -7 ohm· cm, at 600°c 5.5 10 -7 ohm· cm; has superconductivity at 0.68 ± 0.02K; weak paramagnetic, specific magnetic susceptibility at room temperature 1.72 · 10 -6.
The mechanical properties of carbon depend on its purity and on the modes of mechanical and heat treatment. The average value of the elastic modulus for cast U. 20.5 10 -2 Mn/m 2 tensile strength at room temperature 372–470 Mn/m 2 , strength increases after hardening from b - and g -phases; average Brinell hardness 19.6–21.6 10 2 Mn/m 2 .
Irradiation by a neutron flux (which occurs in nuclear reactor) changes the physical and mechanical properties of uranium: creep develops and fragility increases, deformation of products is observed, which forces the use of uranium in nuclear reactors in the form of various uranium alloys.
U. – radioactive element. Nuclei 235 u and 233 u fission spontaneously, as well as upon capture of both slow (thermal) and fast neutrons with an effective fission cross section of 508 10 -24 cm 2 (508 barn) and 533 10 -24 cm 2 (533 barn) respectively. 238u nuclei fission upon capturing only fast neutrons with an energy of at least 1 Mev; upon capture of slow neutrons, 238 u turns into 239 pu , whose nuclear properties are close to 235 u. Critical the mass of U. (93.5% 235 u) in aqueous solutions is less than 1 kg, for an open ball - about 50 kg, for a ball with a reflector - 15 - 23 kg; critical mass 233 u – approximately 1/3 of the critical mass 235 u.
Chemical properties. Configuration of the outer electron shell of the atom U. 7 s 2 6 d 1 5 f 3 . U. is a reactive metal; in compounds it exhibits oxidation states + 3, + 4, + 5, + 6, sometimes + 2; the most stable compounds are u (iv) and u (vi). In air it slowly oxidizes with the formation of a film of dioxide on the surface, which does not protect the metal from further oxidation. In a powdered state, U. is pyrophoric and burns with a bright flame. With oxygen it forms dioxide uo 2, trioxide uo 3 and a large number of intermediate oxides, the most important of which is u 3 o 8. These intermediate oxides have properties close to uo 2 and uo 3. At high temperatures uo 2 has a wide range of homogeneity from uo 1.60 to uo 2.27. With fluorine at 500–600°c it forms tetrafluoride (green needle-shaped crystals, slightly soluble in water and acids) and hexafluoride uf 6 (a white crystalline substance that sublimes without melting at 56.4°c); with sulfur - a number of compounds, of which us (nuclear fuel) is the most important. When uranium reacts with hydrogen at 220°C, the hydride uh 3 is obtained; with nitrogen at temperatures from 450 to 700 °C and atmospheric pressure - nitride u 4 n 7, at a higher nitrogen pressure and the same temperature you can get un, u 2 n 3 and un 2; with carbon at 750–800°c – uc monocarbide, uc 2 dicarbide, and also u 2 c 3; forms alloys of various types with metals . U. slowly reacts with boiling water to form uo 2 and h 2, with water vapor - in the temperature range 150–250 ° C; soluble in hydrochloric and nitric acids, slightly soluble in concentrated hydrofluoric acid. U (vi) is characterized by the formation of the uranyl ion uo 2 2 + ; uranyl salts are yellow in color and are highly soluble in water and mineral acids; salts u (iv) are green and less soluble; uranyl ion is extremely capable of complex formation in aqueous solutions with both inorganic and organic substances; The most important for technology are carbonate, sulfate, fluoride, phosphate and other complexes. A large number of uranates (salts of uranic acid not isolated in pure form) are known, the composition of which varies depending on the conditions of production; All uranates have low solubility in water.
U. and its compounds are radiation and chemically toxic. Maximum permissible dose (MAD) for occupational exposure 5 rem in year.
Receipt. U. is obtained from uranium ores containing 0.05–0.5% u. The ores are practically not enriched, with the exception of a limited method of radiometric sorting based on the radiation of radium, which always accompanies uranium. Basically, ores are leached with solutions of sulfuric, sometimes nitric acids or soda solutions with the transfer of uranium into an acidic solution in the form of uo 2 so 4 or complex anions 4-, and into a soda solution - in the form of 4-. To extract and concentrate uranium from solutions and pulps, as well as to purify it from impurities, sorption on ion-exchange resins and extraction with organic solvents (tributyl phosphate, alkylphosphoric acids, amines) are used. Next, ammonium or sodium uranates or u (oh) 4 hydroxide are precipitated from the solutions by adding alkali. To obtain compounds of high purity, technical products are dissolved in nitric acid and subjected to refining purification operations, the final products of which are uo 3 or u 3 o 8; these oxides are reduced at 650–800°c by hydrogen or dissociated ammonia to uo 2, followed by its conversion to uf 4 by treatment with gaseous hydrogen fluoride at 500–600°c. uf 4 can also be obtained by precipitation of crystalline hydrate uf 4 · nh 2 o with hydrofluoric acid from solutions, followed by dehydration of the product at 450°C in a stream of hydrogen. In industry, the main method of obtaining uranium from uf 4 is its calcium-thermal or magnesium-thermal reduction with the yield of uranium in the form of ingots weighing up to 1.5 tons. The ingots are refined in vacuum furnaces.
A very important process in uranium technology is the enrichment of its 235 u isotope above the natural content in ores or the isolation of this isotope in its pure form , since it is 235 u that is the main nuclear fuel; This is done by gas thermal diffusion, centrifugal and other methods based on the difference in masses 235 u and 238 u; in separation processes, uranium is used in the form of volatile hexafluoride uf 6. When obtaining highly enriched carbon or isotopes, their critical masses are taken into account; the most convenient method in this case is the reduction of uranium oxides with calcium; The resulting slag, cao, is easily separated from the carbon by dissolution in acids.
Powder metallurgy methods are used to produce powdered carbon dioxide, carbides, nitrides, and other refractory compounds.
Application. Metal U. or its compounds are used mainly as nuclear fuel in nuclear reactors. A natural or low-enriched mixture of carbon isotopes is used in stationary reactors of nuclear power plants; a highly enriched product is used in nuclear power plants or in fast neutron reactors. 235 u is a source of nuclear energy in nuclear weapons. 238 u serves as a source of secondary nuclear fuel - plutonium.
V. M. Kulifeev.
Uranium in the body. In trace quantities (10 -5 –10 -5%) it is found in the tissues of plants, animals and humans. In plant ash (with a U content in the soil of about · 10 -4), its concentration is 1.5 · 10 -5%. To the greatest extent, uranium is accumulated by some fungi and algae (the latter actively participate in the biogenic migration of uranium along the chain water - aquatic plants - fish - humans). U. enters the body of animals and humans with food and water into the gastrointestinal tract, with air into the respiratory tract, and also through the skin and mucous membranes. U. compounds are absorbed in the gastrointestinal tract - about 1% of the incoming amount of soluble compounds and no more than 0.1% of sparingly soluble ones; 50% and 20% are absorbed in the lungs, respectively. U. is distributed unevenly in the body. The main depots (places of deposition and accumulation) are the spleen, kidneys, skeleton, liver and, when inhaling poorly soluble compounds, the lungs and bronchopulmonary lymph nodes. U. (in the form of carbonates and complexes with proteins) does not circulate in the blood for a long time. The U content in organs and tissues of animals and humans does not exceed 10 -7 y/y. Thus, the blood of cattle contains 1 10 -8 g/ml, liver 8 10 -8 y/y, muscles 4 10 -8 y/y, spleen 9 10 -8 y/y. The U content in human organs is: in the liver 6 10 -9 y/y, in the lungs 6 10 -9 –9 10 -9 g/g, in the spleen 4.7 10 -9 y/y, in blood 4 10 -9 g/ml, in the kidneys 5.3 10 -9 (cortical layer) and 1.3 10 -9 y/y(medullary layer), in bones 1 10 -9 y/y, in bone marrow 1 10 -9 y/y, in hair 1.3 10 -7 y/y. U. contained in bone tissue causes its constant irradiation (the half-life of U. from the skeleton is about 300 days) . The lowest concentrations of U are in the brain and heart (10 -10 y/y). Daily intake of U. from food and liquids – 1.9 10 -6 g, s air – 7 10 -9 G. The daily excretion of U from the human body is: with urine 0.5 · 10 -7 –5 · 10 -7, with feces – 1.4 · 10 -6 –1.8 · 10 -6 g, s hair – 2 10 -8 g.
According to the International Commission on Radiation Protection, the average U content in the human body is 9·10 -8 g. This value may vary for different regions. It is believed that U is necessary for the normal life of animals and plants, but its physiological functions have not been clarified.
G. P. Galibin.
Toxic effect Uranium is due to its chemical properties and depends on solubility: uranyl and other soluble uranium compounds are more toxic. Poisoning with uranium and its compounds is possible at enterprises for the extraction and processing of uranium raw materials and other industrial facilities where it is used in the technological process. When it enters the body, it affects all organs and tissues, being a general cellular poison. Signs of poisoning are due primarily to kidney damage (the appearance of protein and sugar in the urine, subsequent oliguria) , the liver and gastrointestinal tract are also affected. There are acute and chronic poisonings; the latter are characterized by gradual development and less severe symptoms. With chronic intoxication, disorders of hematopoiesis, the nervous system, etc. are possible. It is believed that the molecular mechanism of action of U. is associated with its ability to suppress the activity of enzymes.
Prevention of poisoning: continuity of technological processes, use of sealed equipment, prevention of air pollution, treatment of wastewater before discharging it into water bodies, honey. monitoring the health status of workers and compliance with hygienic standards for the permissible content of U and its compounds in the environment.
V. F. Kirillov.
Lit.: The doctrine of radioactivity. History and modernity, ed. B. M. Kedrova, M., 1973; Petrosyants A.M., From scientific research to the nuclear industry, M., 1970; Emelyanov V.S., Evstyukhin A.I., Metallurgy of nuclear fuel, M., 1964; Sokursky Yu. N., Sterlin Ya. M., Fedorchenko V. A., Uranium and its alloys, M., 1971; Evseeva L. S., Perelman A. I., Ivanov K. E., Geochemistry of uranium in the hypergenetic zone, 2nd ed., M., 1974; Pharmacology and toxicology of uranium compounds, [trans. from English], vol. 2, M., 1951; Guskova V.N., Uranus. Radiation-hygienic characteristics, M., 1972; Andreeva O. S., Occupational hygiene when working with uranium and its compounds, M., 1960; Novikov Yu. V., Hygienic issues of studying the uranium content in the external environment and its effect on the body, M., 1974.
When the radioactive elements of the periodic table were discovered, man eventually came up with a use for them. This happened with uranium. It was used for both military and peaceful purposes. Uranium ore was processed, the resulting element was used in the paint and varnish and glass industries. After its radioactivity was discovered, it began to be used in How clean and environmentally friendly is this fuel? This is still being debated.
Natural uranium
Uranium does not exist in nature in its pure form - it is a component of ores and minerals. The main uranium ores are carnotite and pitchblende. Also, significant deposits of this strategic mineral were found in rare earth and peat minerals - orthite, titanite, zircon, monazite, xenotime. Uranium deposits can be found in rocks with an acidic environment and high concentrations of silicon. Its companions are calcite, galena, molybdenite, etc.
World deposits and reserves
To date, many deposits have been explored in a 20-kilometer layer of the earth's surface. All of them contain a huge number of tons of uranium. This amount can provide humanity with energy for many hundreds of years to come. The leading countries in which uranium ore is found in the largest volumes are Australia, Kazakhstan, Russia, Canada, South Africa, Ukraine, Uzbekistan, USA, Brazil, Namibia.
Types of uranium
Radioactivity determines the properties of a chemical element. Natural uranium is composed of three isotopes. Two of them are the founders of the radioactive series. Natural isotopes of uranium are used to create fuel for nuclear reactions and weapons. Uranium-238 also serves as a raw material for the production of plutonium-239.
Uranium isotopes U234 are daughter nuclides of U238. They are recognized as the most active and provide strong radiation. The U235 isotope is 21 times weaker, although it is successfully used for the above purposes - it has the ability to support without additional catalysts.
In addition to natural ones, there are also artificial isotopes of uranium. Today there are 23 known of them, the most important of them is U233. It is distinguished by its ability to be activated under the influence of slow neutrons, while the rest require fast particles.
Ore classification
Although uranium can be found almost everywhere - even in living organisms - the strata in which it is found can vary in type. The extraction methods also depend on this. Uranium ore is classified according to the following parameters:
- Conditions of formation - endogenous, exogenous and metamorphogenic ores.
- The nature of uranium mineralization is primary, oxidized and mixed uranium ores.
- Aggregate and grain size of minerals - coarse-grained, medium-grained, fine-grained, fine-grained and dispersed fractions of ore.
- Usefulness of impurities - molybdenum, vanadium, etc.
- The composition of impurities is carbonate, silicate, sulfide, iron oxide, caustobiolite.
Depending on how the uranium ore is classified, there is a method for extracting the chemical element from it. Silicate is treated with various acids, carbonate - soda solutions, caustobiolite is enriched by combustion, and iron oxide is smelted in a blast furnace.
How is uranium ore mined?
As in any mining business, there is a certain technology and methods for extracting uranium from rock. Everything also depends on which isotope is located in the lithosphere layer. Uranium ore is mined in three ways. It is economically feasible to isolate an element from rock when its content is 0.05-0.5%. There are mine, quarry and leaching methods of extraction. The use of each of them depends on the composition of the isotopes and the depth of the rock. Quarry mining of uranium ore is possible in shallow deposits. The risk of radiation exposure is minimal. There are no problems with equipment - bulldozers, loaders, and dump trucks are widely used.
Mine mining is more complex. This method is used when the element occurs at a depth of up to 2 kilometers and is economically profitable. The rock must contain a high concentration of uranium in order for it to be worth mining. The adit provides maximum safety, this is due to the way uranium ore is mined underground. Workers are provided with special clothing and work hours are strictly limited. The mines are equipped with elevators and enhanced ventilation.
Leaching - the third method - is the cleanest from an environmental point of view and the safety of mining company employees. A special chemical solution is pumped through a system of drilled wells. It dissolves in the formation and is saturated with uranium compounds. The solution is then pumped out and sent to processing plants. This method is more progressive; it allows reducing economic costs, although there are a number of restrictions on its use.
Deposits in Ukraine
The country turned out to be the lucky owner of deposits of the element from which it is produced. According to forecasts, uranium ores of Ukraine contain up to 235 tons of raw materials. Currently, only deposits containing about 65 tons have been confirmed. A certain amount has already been developed. Some of the uranium was used domestically, and some was exported.
The main deposit is considered to be the Kirovograd uranium ore district. The uranium content is low - from 0.05 to 0.1% per ton of rock, so the cost of the material is high. As a result, the resulting raw materials are exchanged in Russia for finished fuel rods for power plants.
The second large deposit is Novokonstantinovskoye. The uranium content in the rock made it possible to reduce the cost by almost 2 times compared to Kirovograd. However, since the 90s, no development has been carried out; all the mines have been flooded. Due to the worsening political relations with Russia, Ukraine may be left without fuel for
Russian uranium ore
In terms of uranium production, the Russian Federation is in fifth place among other countries in the world. The most famous and powerful are Khiagdinskoye, Kolichkanskoye, Istochnoye, Koretkondinskoye, Namarusskoye, Dobrynskoye (Republic of Buryatia), Argunskoye, Zherlovoye. In the Chita region, 93% of all mined Russian uranium is mined (mainly by quarry and mine methods).
The situation is a little different with the deposits in Buryatia and Kurgan. Uranium ore in Russia in these regions is deposited in such a way that it allows the extraction of raw materials by leaching.
In total, deposits of 830 tons of uranium are predicted in Russia; there are about 615 tons of confirmed reserves. These are also deposits in Yakutia, Karelia and other regions. Since uranium is a strategic global raw material, the numbers may be inaccurate, since much of the data is classified and only a certain category of people has access to it.
URANUS (named after the planet Uranus discovered shortly before; lat. uranium * a. uranium; n. Uran; f. uranium; i. uranio), U, is a radioactive chemical element of group III of the Mendeleev periodic system, atomic number 92, atomic mass 238.0289, belongs to actinides. Natural uranium consists of a mixture of three isotopes: 238 U (99.282%, T 1/2 4,468.10 9 years), 235 U (0.712%, T 1/2 0.704.10 9 years), 234 U (0.006%, T 1/2 0.244.10 6 years). There are also 11 known artificial radioactive isotopes of uranium with mass numbers from 227 to 240. 238 U and 235 U are the founders of two natural decay series, as a result of which they turn into stable isotopes 206 Pb and 207 Pb, respectively.
Uranium was discovered in 1789 in the form of UO 2 by the German chemist M. G. Klaproth. Uranium metal was obtained in 1841 by the French chemist E. Peligot. For a long time, uranium had very limited use, and only with the discovery of radioactivity in 1896 did its study and use begin.
Properties of uranium
In its free state, uranium is a light gray metal; below 667.7°C it is characterized by an orthorhombic (a=0.28538 nm, b=0.58662 nm, c=0.49557 nm) crystal lattice (a-modification), in the temperature range 667.7-774°C - tetragonal (a = 1.0759 nm, c = 0.5656 nm; G-modification), at a higher temperature - body-centered cubic lattice (a = 0.3538 nm, g-modification). Density 18700 kg/m 3, melting point 1135°C, boiling point about 3818°C, molar heat capacity 27.66 J/(mol.K), electrical resistivity 29.0.10 -4 (Ohm.m), thermal conductivity 22, 5 W/(m.K), temperature coefficient of linear expansion 10.7.10 -6 K -1. The temperature of transition of uranium to the superconducting state is 0.68 K; weak paramagnetic, specific magnetic susceptibility 1.72.10 -6. The nuclei 235 U and 233 U fission spontaneously, as well as upon the capture of slow and fast neutrons, 238 U fission only upon the capture of fast (more than 1 MeV) neutrons. When slow neutrons are captured, 238 U turns into 239 Pu. The critical mass of uranium (93.5% 235U) in aqueous solutions is less than 1 kg, for an open ball it is about 50 kg; for 233 U critical mass is approximately 1/3 of the critical mass of 235 U.
Education and keeping in nature
The main consumer of uranium is nuclear energy (nuclear reactors, nuclear power plants). In addition, uranium is used to produce nuclear weapons. All other areas of uranium use are of strictly subordinate importance.
(according to Pauling)
U←U 3+ -1.66V
U←U 2+ -0.1V
| U | 92 |
| 238,0289 | |
| 5f 3 6d 1 7s 2 | |
| Uranus | |
Uranus(old name Uranium) is a chemical element with atomic number 92 in the periodic table, atomic mass 238.029; denoted by the symbol U ( Uranium), belongs to the actinide family.
Story
Even in ancient times (1st century BC), natural uranium oxide was used to make yellow glaze for ceramics. Research on uranium developed like a chain reaction generated by it. At first, information about its properties, like the first impulses of a chain reaction, arrived with long interruptions, from case to case. The first important date in the history of uranium is 1789, when the German natural philosopher and chemist Martin Heinrich Klaproth restored the golden-yellow “earth” extracted from Saxon resin ore to a black metal-like substance. In honor of the most distant planet known at that time (discovered by Herschel eight years earlier), Klaproth, considering the new substance an element, named it uranium.
For fifty years, Klaproth's uranium was considered a metal. Only in 1841 did Eugene Melchior Peligot, a French chemist (1811-1890), prove that, despite the characteristic metallic luster, Klaproth's uranium is not an element, but an oxide UO 2. In 1840, Peligo managed to obtain real uranium, a heavy metal of a steel-gray color, and determine its atomic weight. The next important step in the study of uranium was made in 1874 by D. I. Mendeleev. Based on the periodic system he developed, he placed uranium in the farthest cell of his table. Previously, the atomic weight of uranium was considered to be 120. The great chemist doubled this value. 12 years later, Mendeleev’s prediction was confirmed by the experiments of the German chemist Zimmermann.
The study of uranium began in 1896: the French chemist Antoine Henri Becquerel accidentally discovered Becquerel's rays, which Marie Curie later renamed radioactivity. At the same time, the French chemist Henri Moissan managed to develop a method for producing pure uranium metal. In 1899, Rutherford discovered that the radiation of uranium preparations is inhomogeneous, that there are two types of radiation - alpha and beta rays. They carry different electrical charges; Their range in matter and ionizing ability are far from the same. A little later, in May 1900, Paul Villar discovered a third type of radiation - gamma rays.
Ernest Rutherford conducted the first experiments in 1907 to determine the age of minerals when studying radioactive uranium and thorium based on the theory of radioactivity he created together with Frederick Soddy (Soddy, Frederick, 1877-1956; Nobel Prize in Chemistry, 1921). In 1913, F. Soddy introduced the concept of isotopes(from the Greek ισος - “equal”, “same”, and τόπος - “place”), and in 1920 he predicted that isotopes could be used to determine the geological age of rocks. In 1928, Niggot implemented, and in 1939, A.O.K. Nier (Nier, Alfred Otto Carl, 1911 - 1994) created the first equations for calculating age and used a mass spectrometer to separate isotopes.
In 1939, Frederic Joliot-Curie and German physicists Otto Frisch and Lise Meitner discovered an unknown phenomenon that occurs with a uranium nucleus when it is irradiated with neutrons. There was an explosive destruction of this core with the formation of new elements much lighter than uranium. This destruction was explosive in nature, fragments of food scattered in different directions at enormous speeds. Thus, a phenomenon called nuclear reaction was discovered.
In 1939-1940 Yu. B. Khariton and Ya. B. Zeldovich were the first to theoretically show 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, to give the process a chain character.
Being in nature
Uraninite Ore
Uranium is widely distributed in nature. The Clarke of uranium is 1·10 -3% (wt.). The amount of uranium in a 20 km thick layer of the lithosphere is estimated at 1.3 10 14 tons.
The bulk of uranium is found in acidic rocks with a high content silicon. A significant mass of uranium is concentrated in sedimentary rocks, especially those enriched in organic matter. Uranium is present in large quantities as an impurity in thorium and rare earth minerals (orthite, sphene CaTiO 3, monazite (La,Ce)PO 4, zircon ZrSiO 4, xenotime YPO4, etc.). The most important uranium ores are pitchblende (uranium pitch), uraninite and carnotite. The main minerals that are satellites of uranium are molybdenite MoS 2, galena PbS, quartz SiO 2, calcite CaCO 3, hydromuscovite, etc.
| Mineral | Basic composition of the mineral | Uranium content, % |
|---|---|---|
| Uraninite | UO 2, UO 3 + ThO 2, CeO 2 | 65-74 |
| Carnotite | K 2 (UO 2) 2 (VO 4) 2 2H 2 O | ~50 |
| Kasolite | PbO 2 UO 3 SiO 2 H 2 O | ~40 |
| Samarskit | (Y, Er, Ce, U, Ca, Fe, Pb, Th) (Nb, Ta, Ti, Sn) 2 O 6 | 3.15-14 |
| Brannerite | (U, Ca, Fe, Y, Th) 3 Ti 5 O 15 | 40 |
| Tyuyamunit | CaO 2UO 3 V 2 O 5 nH 2 O | 50-60 |
| Tseynerit | Cu(UO 2) 2 (AsO 4)2 nH 2 O | 50-53 |
| Otenitis | Ca(UO 2) 2 (PO 4) 2 nH 2 O | ~50 |
| Schreckingerite | Ca 3 NaUO 2 (CO 3) 3 SO 4 (OH) 9H 2 O | 25 |
| Ouranophanes | CaO UO 2 2SiO 2 6H 2 O | ~57 |
| Fergusonite | (Y, Ce)(Fe, U)(Nb, Ta)O 4 | 0.2-8 |
| Torburnite | Cu(UO 2) 2 (PO 4) 2 nH 2 O | ~50 |
| Coffinit | U(SiO 4) 1-x (OH) 4x | ~50 |
The main forms of uranium found in nature are uraninite, pitchblende (uranium pitch) and uranium blacks. They differ only in their forms of location; there is an age dependence: uraninite is present mainly in ancient (Precambrian rocks), pitchblende - volcanogenic and hydrothermal - mainly in Paleozoic and younger high- and medium-temperature formations; uranium blacks - mainly in young - Cenozoic and younger formations - mainly in low-temperature sedimentary rocks.
The uranium content 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. First, there are veins of uraninite, or uranium pitch (uranium dioxide UO2), 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 quantities to be extracted gold And silver, and the accompanying elements are uranium and thorium. 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, in addition to uranium, contains a significant amount vanadium and other elements. Such ores are found in the western states USA. Iron-uranium shales and phosphate ores constitute a fourth source of sediment. Rich deposits found in shale 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 were discovered in North and South Dakota (USA) and bituminous coals Spain And Czech Republic
Isotopes of uranium
Natural uranium consists of a mixture of three isotopes: 238 U - 99.2739% (half-life T 1/2 = 4.468×10 9 years), 235 U - 0.7024% ( T 1/2 = 7.038×10 8 years) and 234 U - 0.0057% ( T 1/2 = 2.455×10 5 years). The latter isotope is not primary, but radiogenic; it is part of the radioactive 238 U series.
The radioactivity of natural uranium is mainly due to the isotopes 238 U and 234 U; in equilibrium, their specific activities are equal. The specific activity of the 235 U isotope in natural uranium is 21 times less than the activity of 238 U.
There are 11 known artificial radioactive isotopes of uranium with mass numbers from 227 to 240. The longest-lived of them is 233 U ( T 1/2 = 1.62×10 5 years) is obtained by irradiating thorium with neutrons and is capable of spontaneous fission by thermal neutrons.
The uranium isotopes 238 U and 235 U are the ancestors of two radioactive series. The final elements of these series are isotopes lead 206 Pb and 207 Pb.
Under natural conditions, the most common isotopes are 234 U: 235 U : 238 U= 0.0054: 0.711: 99.283. Half of the radioactivity of natural uranium is due to the isotope 234 U. Isotope 234 U is formed due to decay 238 U. The last two, unlike other pairs of isotopes and regardless of the high migration ability of uranium, are characterized by geographic constancy of the ratio. The magnitude of this ratio depends on the age of the uranium. Numerous field measurements showed its slight fluctuations. So in rolls the value of this ratio relative to the standard varies within the range of 0.9959 - 1.0042, in salts - 0.996 - 1.005. In uranium-containing minerals (pitched pitch, uranium black, cyrtolite, rare earth ores), the value of this ratio ranges from 137.30 to 138.51; Moreover, the difference between forms U IV and U VI has not been established; in sphene - 138.4. Isotope deficiency was detected in some meteorites 235 U. Its lowest concentration in terrestrial conditions was found in 1972 by the French researcher Bujigues in the town of Oklo in Africa (deposit in Gabon). Thus, normal uranium contains 0.7025% uranium 235 U, while in Oklo it is reduced to 0.557%. This supported the hypothesis of a natural nuclear reactor leading to isotope burnup, predicted by George W. Wetherill of the University of California at Los Angeles and Mark G. Inghram of the University of Chicago and Paul K. Kuroda, a chemist at the University of Arkansas, described the process back in 1956. In addition, natural nuclear reactors were found in these same districts: Okelobondo, Bangombe, etc. Currently, about 17 natural nuclear reactors are known.
Receipt
The very first stage of uranium production is concentration. The rock is crushed and mixed with water. Heavy suspension components settle faster. If the rock contains primary uranium minerals, they precipitate quickly: these are heavy minerals. Secondary uranium minerals are lighter, in which case the heavy waste rock settles out earlier. (However, it is not always truly empty; it may contain many useful elements, including uranium).
The next stage is leaching of concentrates, transferring uranium into solution. Acid and alkaline leaching are used. The first is cheaper because sulfuric acid is used to extract uranium. But if in the feedstock, such as uranium tar, uranium is in a tetravalent state, then this method is not applicable: tetravalent uranium is practically insoluble in sulfuric acid. In this case, you must either resort to alkaline leaching or pre-oxidize the uranium to a hexavalent state.
Acid leaching is also not used in cases where the uranium concentrate contains dolomite or magnesite, which react with sulfuric acid. In these cases, use caustic soda (hydroxide sodium).
The problem of uranium leaching from ores is solved by oxygen blowing. A stream of oxygen is supplied to a mixture of uranium ore and sulfide minerals heated to 150 °C. In this case, sulfuric acid is formed from sulfur minerals, which washes away the uranium.
At the next stage, uranium must be selectively isolated from the resulting solution. Modern methods - extraction and ion exchange - can solve this problem.
The solution contains not only uranium, but also other cations. Some of them, under certain conditions, behave in the same way as uranium: they are extracted with the same organic solvents, deposited on the same ion exchange resins, and precipitate under the same conditions. Therefore, to selectively isolate uranium, it is necessary to use many redox reactions in order to get rid of one or another unwanted companion at each stage. On modern ion exchange resins, uranium is released very selectively.
Methods ion exchange and extraction They are also good because they allow uranium to be extracted quite completely from poor solutions (uranium content is tenths of a gram per liter).
After these operations, uranium is converted into a solid state - into one of the oxides or into UF 4 tetrafluoride. But this uranium still needs to be purified from impurities with a large thermal neutron capture cross section - boron, cadmium, hafnia. Their content in the final product should not exceed hundred thousandths and millionths of a percent. To remove these impurities, a commercially pure uranium compound is dissolved in nitric acid. In this case, uranyl nitrate UO 2 (NO 3) 2 is formed, which, during extraction with tributyl phosphate and some other substances, is further purified to the required standards. Then this substance is crystallized (or peroxide UO 4 ·2H 2 O is precipitated) and carefully calcined. As a result of this operation, uranium trioxide UO 3 is formed, which is reduced with hydrogen to UO 2.
Uranium dioxide UO 2 is exposed to dry hydrogen fluoride at temperatures from 430 to 600 °C to produce UF 4 tetrafluoride. Uranium metal is recovered from this compound using calcium or magnesium.
Physical properties
Uranium is a very heavy, silvery-white, shiny metal. In its pure form, it is slightly softer than steel, malleable, flexible, and has slight paramagnetic properties. Uranium has three allotropic forms: alpha (prismatic, stable up to 667.7 °C), beta (tetragonal, stable from 667.7 °C to 774.8 °C), gamma (with a body-centered cubic structure, existing from 774. 8 °C to melting point).
Radioactive properties of some isotopes of uranium (natural isotopes are highlighted):
Chemical properties
Uranium can exhibit oxidation states from +III to +VI. Uranium(III) compounds form unstable red solutions and are strong reducing agents:
4UCl 3 + 2H 2 O → 3UCl 4 + UO 2 + H 2
Uranium(IV) compounds are the most stable and form green aqueous solutions.
Uranium(V) compounds are unstable and easily disproportionate in an aqueous solution:
2UO 2 Cl → UO 2 Cl 2 + UO 2
Chemically, uranium is a very active metal. Quickly oxidizing in air, it becomes covered with a rainbow film of oxide. Fine uranium powder spontaneously ignites in air; it ignites at a temperature of 150-175 ° C, forming U 3 O 8. At 1000 °C, uranium combines with nitrogen to form yellow uranium nitride. Water can corrode metal, slowly at low temperatures and quickly at high temperatures, as well as when uranium powder is finely ground. Uranium dissolves in hydrochloric, nitric and other acids, forming tetravalent salts, but does not interact with alkalis. Uranus displaces hydrogen from inorganic acids and salt solutions of metals such as mercury, silver, copper, tin, platinumAndgold. When shaken vigorously, the metal particles of uranium begin to glow. Uranium has four oxidation states - III-VI. Hexavalent compounds include uranium trioxide (uranyl oxide) UO 3 and uranium uranyl chloride UO 2 Cl 2 . Uranium tetrachloride UCl 4 and uranium dioxide UO 2 are examples of tetravalent uranium. Substances containing tetravalent uranium are usually unstable and become hexavalent when exposed to air for a long time. Uranyl salts, such as uranyl chloride, decompose in the presence of bright light or organic matter.
Application
Nuclear fuel
The greatest application is isotope uranium 235 U, in which a self-sustaining nuclear chain reaction is possible. Therefore, this isotope is used as fuel in nuclear reactors, as well as in nuclear weapons. Isolation of the U 235 isotope from natural uranium is a complex technological problem (see isotope separation).
The U 238 isotope is capable of fission under the influence of bombardment by high-energy neutrons; this feature is used to increase the power of thermonuclear weapons (neutrons generated by a thermonuclear reaction are used).
As a result of neutron capture followed by β-decay, 238 U can be converted into 239 Pu, which is then used as nuclear fuel.
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).
Uranium-233 is also the most promising fuel for gas-phase nuclear rocket engines.
Geology
The main use of uranium is determining the age of minerals and rocks in order to determine the sequence of geological processes. This is what Geochronology and Theoretical Geochronology do. Solving the problem of mixing and sources of matter is also essential.
The solution to the problem is based on the equations of radioactive decay described by the equations.
Where 238 U o, 235 U o— modern concentrations of uranium isotopes; ; — decay constants atoms of uranium respectively 238 U And 235 U.
Their combination is very important:
.
Due to the fact that rocks contain different concentrations of uranium, they have different radioactivity. This property is used when identifying rocks using geophysical methods. This method is most widely used in petroleum geology during geophysical surveys of wells; this complex includes, in particular, γ - logging or neutron gamma logging, gamma-gamma logging, etc. With their help, reservoirs and seals are identified.
Other Applications
A small addition of uranium gives a beautiful yellow-green fluorescence to glass (Uranium glass).
Sodium uranate Na 2 U 2 O 7 was 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).
Some uranium compounds are photosensitive.
At the beginning of the 20th century uranyl nitrate widely used to enhance negatives and color (tint) positives (photographic prints) brown.
Uranium-235 carbide alloyed with niobium carbide and zirconium carbide is used as fuel for nuclear jet engines (working fluid - hydrogen + hexane).
Alloys of iron and depleted uranium (uranium-238) are used as powerful magnetostrictive materials.
Depleted uranium
Depleted uranium
After 235 U and 234 U 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 data, about 560,000 tons of depleted uranium hexafluoride (UF 6) are stored in the United States.
Depleted uranium is half as radioactive as natural uranium, mainly due to the removal of 234 U from it. Because the main use of uranium is energy production, depleted uranium is a low-use product with low economic value.
Its use is mainly associated with the high density of uranium and its relatively low cost. Depleted uranium is used for radiation shielding (ironically) and as ballast in aerospace applications such as aircraft control surfaces. Each Boeing 747 aircraft contains 1,500 kg of depleted uranium for these purposes. This material is also used in high-speed gyroscope rotors, large flywheels, as ballast in space landers and racing yachts, and when drilling oil wells.
Armor-piercing projectile cores
The tip (liner) of a 30 mm caliber projectile (GAU-8 guns of an A-10 aircraft) with a diameter of about 20 mm is made of depleted uranium.
The most famous use of depleted uranium is as cores for armor-piercing projectiles. When alloyed with 2% Mo or 0.75% Ti and heat treatment (quick quenching of metal heated to 850 °C in water or oil, further holding at 450 °C for 5 hours), uranium metal becomes harder and stronger than steel (the tensile strength is greater 1600 MPa, despite the fact that for pure uranium it is 450 MPa). Combined with its high density, this makes the hardened uranium ingot an extremely effective armor piercer, similar in effectiveness to the more expensive tungsten. The heavy uranium tip also changes the mass distribution of the projectile, improving its aerodynamic stability.
Similar alloys of the Stabilla type are used in swept-finned projectiles for tank and anti-tank artillery guns.
The process of armor destruction is accompanied by the grinding of a uranium pig into dust and its ignition in air on the other side of the armor (see Pyrophoricity). About 300 tons of depleted uranium remained on the battlefield during Operation Desert Storm (mostly the remains of 30 mm GAU-8 cannon shells from A-10 attack aircraft, each shell containing 272 g of uranium alloy).
Such shells were used by NATO troops in combat operations on the territory of Yugoslavia. After their application, the environmental problem of radiation contamination of the country's territory was discussed.
Uranium was first used as a core for projectiles in the Third Reich.
Depleted uranium is used in modern tank armor, such as the M-1 Abrams tank.
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 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/m³, for insoluble forms of uranium the MPC is 0.075 mg/m³. 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.
Production by country in tons by U content for 2005-2006.
Production by company in 2006:
Cameco - 8.1 thousand tons
Rio Tinto - 7 thousand tons
AREVA - 5 thousand tons
Kazatomprom - 3.8 thousand tons
JSC TVEL - 3.5 thousand tons
BHP Billiton - 3 thousand tons
Navoi MMC - 2.1 thousand tons ( Uzbekistan, Navoi)
Uranium One - 1 thousand tons
Heathgate - 0.8 thousand tons
Denison Mines - 0.5 thousand tons
Production in Russia
In the USSR, the main uranium ore regions were Ukraine (Zheltorechenskoye, Pervomaiskoye deposits, etc.), Kazakhstan (Northern - Balkashin ore field, etc.; Southern - Kyzylsay ore field, etc.; Vostochny; all of them belong predominantly to the volcanogenic-hydrothermal type); Transbaikalia (Antey, Streltsovskoe, etc.); Central Asia, mainly Uzbekistan with mineralization in black shales centered in the city of Uchkuduk. There are a lot of small ore occurrences and occurrences. In Russia, Transbaikalia remains the main uranium ore region. About 93% of Russian uranium is mined at the deposit in the Chita region (near the city of Krasnokamensk). Mining is carried out using the shaft method by the Priargunskoye Production Mining and Chemical Association (PPMCU), which is part of OJSC Atomredmetzoloto (Uranium Holding).
The remaining 7% is obtained by underground leaching by JSC Dalur (Kurgan region) and JSC Khiagda (Buryatia).
The resulting ores and uranium concentrate are processed at the Chepetsk Mechanical Plant.
Production in Kazakhstan
About a fifth of the world's uranium reserves are concentrated in Kazakhstan (21% and 2nd place in the world). Total uranium resources are about 1.5 million tons, of which about 1.1 million tons can be mined by in-situ leaching.
In 2009, Kazakhstan took first place in the world in uranium production.
Production in Ukraine
The main enterprise is the Eastern Mining and Processing Plant in the city of Zhovti Vody.
Price
Despite the prevailing legends about tens of thousands of dollars for kilogram or even gram quantities of uranium, its real price on the market is not very high - unenriched uranium oxide U 3 O 8 costs less than 100 US dollars per kilogram. This is due to the fact that to run a nuclear reactor using unenriched uranium, tens or even hundreds of tons of fuel are needed, and to manufacture nuclear weapons, a large amount of uranium must be enriched to obtain concentrations suitable for creating a bomb