uranium

Uranium (Uranium). Atomic number For 92 elements, the Element symbols U is one of the most important elements of nature can be found in the. There are three kinds of isotopes in nature, with radioactivity Have a very long. half life (~ year hundreds of millions of billions of years). There are 12 kinds of artificial isotope (uranium uranium -226~ -240). Uranium in 1789 by Martin Heinrich Klaproth (Martin Heinrich Klaproth) found. Early for uranium compounds Porcelain In the coloring. Nuclear fission The phenomenon was discovered as nuclear fuel .
uranium

uranium Discovery history

Uranium (Y U) English Uranium, named for the Uranus The name "Uranus". By 1789. Germany The chemist Klaproth (M.H.Klaproth) isolated from pitchblende, with a newly discovered planet -- 1781 Uranus Named it uranium, element symbol for U. In 1841, Paley Gott (E.M.Peligot) pointed out that klaproth isolated "uranium", is actually Uranium dioxide . He used the reduction of potassium Four uranium chloride , successfully Uranium metal . In 1896, someone discovered uranium Radioactive decay . 1939, Hahn (O.Hahn) and Strassman (F.Strassmann) found the phenomenon of nuclear fission of uranium. Since then, uranium becomes invaluable.

uranium Distribution range

 Chalcolite Chalcolite
Uranium is usually considered a Rare metal Although, in uranium The crust The content is very high, than mercury , bismuth , silver Much more, but because of the difficulty of extracting uranium, so it is doomed to be mercury than these elements found much later. Despite the widespread distribution of uranium in the crust, but only Pitchblende And carnotite two common deposit .
The average content of uranium in the crust is about 2.5 ppm, namely average per ton of crustal material contains about 2.5 grams of uranium, which is more than tungsten , mercury , gold , silver Other elements of the content is high. The content in a variety of rocks in uranium is not uniform. For example, in Granite The content is higher, the average per ton containing 3.5 grams of uranium. In the first layer of the crust (from the surface of 20 km * 10^14) containing nearly 1.3 tons of uranium. It is estimated that a cubic kilometers of granite will contain approximately ten thousand tons of uranium. The concentration of uranium in sea water is relatively low, the average per ton of seawater contains only 3.3 milligrams of uranium, but because the amount of water greatly (seawater total uranium content can reach 4.5 * 10^9 tons), and extracted from water have its convenience, so many countries, especially in countries that lack of uranium resources, is in the exploration Extraction of uranium from seawater The method.
Because of the chemical properties of uranium is very active, so nature Non-existent Free state The uranium metal, it is always the state exists. Known Uranium minerals There are more than and 170 types of uranium deposits, but with mining industry value is only two, thirty, of which the most important are the pitchblende (the main component of Eight oxidation three uranium )), quality (the main component of uranium Uranium dioxide ), Uranium ore and Uranium black Etc.. A lot of uranium minerals are yellow, green or yellow green. Some of the uranium minerals in Ultraviolet rays Can send a strong fluorescence . It is the uranium minerals (uranium Chemical compound ) characteristics of the fluorescent, can cause The phenomenon of radioactivity The discovery of.
 Vandenbrandeite Vandenbrandeite
although Uranium The distribution is very wide, but Uranium deposit The distribution is very limited. Uranium resources Mainly in U.S.A , Canada , South Africa Southwest, non, Australia Other countries and regions. It is estimated that the proven Industrial reserves In 1972 to more than one million tons. China Uranium resources are also very rich.
A series of uranium and its decay progeny is the best sign of uranium are radioactive. The human eye can not see the radioactive, but with the help of special instrument can easily put it detected. Therefore, prospecting and exploration of uranium resources in almost all use of the uranium has the characteristics of radiation: if you find an area of rock, soil And water, and even plant radioactive particularly strong, that area may be a uranium exists.

uranium Physical property

uranium Elemental properties

 Uranium metal Uranium metal
Uranium is Periodic table of ele ments In the seventh cycle of MB elements, Actinides One is important Natural radioactive elements U, symbol, Atomic number 92, Atomic weight 238.0289. In the whole element sequence In about iron The position after each Atomic nucleus There are division The trend Just because a gate, stop before it split. The last element of uranium found in nature, is the weakest Sluice gate By 1936. Hahn Strassman and his colleagues first break in the experiment, this element is.
Character Silver white metal,
melting point : 1132.5`C,
boiling point C: 3745,
density : 18.95g/cm^3,
resistivity 30.8X10-8n M: ",
tensile strength : 450MPa,
Yield strength : 207MPa,
Modulus of elasticity : 172GPa.
Thermal neutron absorption cross section of 7.60b uranium, uranium 15 isotope The atomic weight, from 227-240. All Uranium isotope Is not stable, with a weak radioactivity .
Natural uranium isotopic composition For:
238U: natural abundance of 99.275%, Atomic weight 238.0508, half life 4.51X109a
235U: natural abundance of 0.720%, Atomic weight 235.0439, half life 7.00X108a
234U: natural abundance of 0.005%, Atomic weight 234.0409, half life 2.47X105a
Where 235U is the only natural fissile nuclide, by thermal neutron A fission neutron absorption bombardment, total release energy 195MeV, and 2~3 neutrons, triggering a chain of nuclear fission; 238U is the production of nuclear fuel plutonium The raw material.
In fact, there are a lot of people uranium That is nature The most heavy metal, Osmium The density is 22.48g/cm^3, the most heavy metal and plutonium are naturally occurring the biggest heavy nuclear elements.

uranium The properties of the elements

 uranium uranium
Chinese: uranium
English Name: Uranium
Symbol: U
Elemental: actinides
The element type: metal elements
The periodic table positioning: Seventh f column
The content in the sun: 0.001ppm
The content of the water in 0.00313ppm
Found: Martin Heinrich Klaproth (Martin Heinrich Klaproth) (1789)

uranium Atomic properties

Relative atomic mass: 238.0289
The atomic radius (calculated): 175pm
Fan Dehua radius: 186pm
Ion radius: 0.81 (+6).
The oxidation state of U+6 (U+2, U+3, U+4, U+5)
Negative: 1.38 (Bao Linbiaodu)
Extranuclear electrons:
(2, 8, 18, 32, 21, 9, 2)
The first ionization energy: 597.6KJ/mol
Second ionization energy: 1420KJ/mol
The crystal structure of orthogonal lattice
Crystallization: orthorhombic, tetragonal variants, BCC
The cell parameters: a=285.37pm
B=586.95pm
C=495.48pm
Alpha =90 degrees
Beta =90 degrees
Gamma =90 degrees

uranium isotope

The earth is the largest uranium isotope stock -238, and can be used as fuel for nuclear power uranium -235, at least is the abundance of uranium -234. There are 12 kinds of artificial isotope (uranium uranium -226~ -240).
isotope abundance half life decay mode Decay energy (MeV) Decay product
U-232
artificial
68.9 years
Spontaneous fission
-
-
Alpha decay
Five point four one four
Th-228
U-233
artificial
159200 years
Spontaneous fission
One hundred and ninety-seven point nine three
-
Alpha decay
Four point nine zero nine
Th-229
U-234
0.006%
245500 years
Spontaneous fission
One hundred and ninety-seven point seven eight
-
Alpha decay
Four point eight five nine
Th-230
U-235
0.72%
7.038 x 10^8
Spontaneous fission
Two hundred and two point four eight
-
Alpha decay
Four point six seven nine
Th-231
U-235
artificial
About 25 minutes
Isomeric transition
<1
Kr-92, Ba-141, 2 neutrons
U-236
artificial
2.342 x 10^7
Spontaneous fission
Two hundred and one point eight two
-
Alpha decay
Four point five seven two
Th-232
U-236
artificial
121 x 10^-9 seconds
Spontaneous fission
<1
-
U-237
artificial
The 6.75 day
Beta decay
Zero point five one nine
Np-237
U-238
99.275%
4.468 x 10^9
Spontaneous fission
Two hundred and five point eight seven
-
Alpha decay
Four point two seven zero
Th-234

U-232
artificial
68.9 years
Spontaneous fission
-
-
Alpha decay
Five point four one four
Th-228
U-233
artificial
159200 years
Spontaneous fission
One hundred and ninety-seven point nine three
-
Alpha decay
Four point nine zero nine
Th-229
U-234
0.006%
245500 years
Spontaneous fission
One hundred and ninety-seven point seven eight
-
Alpha decay
Four point eight five nine
Th-230
U-235
0.72%
7.038 x 10^8
Spontaneous fission
Two hundred and two point four eight
-
Alpha decay
Four point six seven nine
Th-231
U-235
artificial
About 25 minutes
Isomeric transition
<1
Kr-92, Ba-141, 2 neutrons
U-236
artificial
2.342 x 10^7
Spontaneous fission
Two hundred and one point eight two
-
Alpha decay
Four point five seven two
Th-232
U-236
artificial
121 x 10^-9 seconds
Spontaneous fission
<1
-
U-237
artificial
The 6.75 day
Beta decay
Zero point five one nine
Np-237
U-238
99.275%
4.468 x 10^9
Spontaneous fission
Two hundred and five point eight seven
-
Alpha decay
Four point two seven zero
Th-234

uranium Chemical property

The outer layer: [Rn]5f electronic configuration 6D 7S
Common: +3, +4, valence of +5, +6, +4 and +6 price Chemical compound Stable。
Character: lively, and all Non metal The role of (inert gas except), can be formed with a variety of metal alloy. The air oxidation, generating a layer of dark film.
Spontaneous combustion easily crushed highly uranium in air, massive uranium in air oxidation and loss of metallic luster, burning and heating in the air,
At the temperature of 250 DEG C and sulfur The reaction at the temperature of 400 DEG C, and nitrogen The reaction at the temperature of 1250 DEG C and nitride. carbon The reaction temperature and 250-300 carbide. hydrogen The reaction of UH3 and UH3 in vacuum under 350-400 DEG C decomposition, release hydrogen .
Uranium and halogen The reaction of uranium halides, and mercury , tin , copper , lead , aluminum , bismuth , iron , nickel , manganese , cobalt , zinc , beryllium Effect of formation of intermetallic compounds.
Uranium is slowly dissolved in sulphuric acid and phosphoric acid And the existence of oxidizing agent will accelerate the dissolution of uranium. freely soluble to nitric acid The solution was alkaline, uranium inertia But, Oxidant There, can make the dissolved uranium.
The toxicity of uranium and its compounds are more soluble uranium compounds in the air, allowing the concentration of 0.05mg/m3, insoluble uranium compounds allowed concentration is 0.25mg/m3, the natural radioactive body allows dose of soluble uranium compounds for 7400Bq, insoluble uranium compounds 333Bq.

uranium Preparation method

from Etc.. Purification of uranium compounds (also called refined) products, must meet the requirements of nuclear pure. Refined products to further drying and calcining process of uranium dioxide oxidation of three or eight for the production of uranium, or reactor components Uranium hexafluoride (for U-235 Isotope separation Use). The whole process is subject to the following Unit operation Uranium ore, uranium ore crushing and grinding Leaching The pulp, solid-liquid separation, ion exchange and Solvent extraction method The extraction of uranium concentrate, solvent extraction and purification of uranium concentrate. According to the different ore types, product requirements, select the appropriate process consists of the unit operation.

uranium Crushing and grinding

The ore is broken Jaw crusher Round or dimension crusher Hammer crusher Coarse and medium crushing and fine crushing in order to achieve the required size. Then the fine grinding, in order to achieve Leaching The size of the required process.

uranium Leaching

use solvent The selective dissolution in uranium ore. Uranium ore Leaching After the separation of uranium and most of gangue, leaching uranium and impurities in liquid ratio than the original ore increased about 10~30 times, therefore, the process is the leaching process of uranium and preliminary separation of the impurities.
uranium ore Leaching Methods generally have two kinds of acid and alkali method. The majority of uranium Shuiye Factory by acid Leaching A factory method, alkali leaching method, only the individual plant that uses two kinds of acid and alkali leaching process. Acid leaching method for general use sulphuric acid As the leaching agent and sulfuric acid reaction in uranium ore, produce soluble Uranyl Ion UO2 and URANYL SULPHATE Ion [UO2 (SO4) x; leaching often adding oxidant (commonly used manganese dioxide , Sodium chlorate ), to maintain appropriate Redox potential (approximately 450 MV), the tetravalent uranium oxidized into six price, in order to improve the leaching rate of uranium. contain carbonate Alkali method mainly used in uranium ore Leaching Commonly used as leaching agent. sodium carbonate and Sodium bicarbonate The water solution in the air condition, uranium and sodium carbonate to generate sodium uranyl carbonate ores in the Na4[UO2 (CO3) 3], dissolved in leaching solution.

uranium The solid-liquid separation of the pulp

Get the ore leaching or acid alkalinity pulp (including uranium solution, impurity and solid slag) in solution and is subject to the separation of slag. According to the need can also be carried out to remove the rough grading, +200~40 fine sand, mud slurry. The solid-liquid separation equipment are used to filter, settling tank ( Thickener Grading equipment); Spiral classifier , Hydrocyclone . The China Fluidization tower Grading and washing.
The available solution separated Ion exchange method Separation of uranium, also available solvent extraction separation and purification of uranium or uranium will precipitate out of solution containing uranium.

uranium The extraction method of ion exchange

After solid-liquid separation Leaching Liquid Eight oxidation three uranium The content is approximately 500~1000 mg / L. For the low concentration uranium leaching solution by ion exchange method suitable for uranium extraction. Ion exchange The general method of using strong alkalinity Anion exchange resin The adsorption of uranium. According to the number of adsorption liquid containing solid content, adsorption can be divided into liquid adsorption, turbid liquid adsorption and pulp adsorption. When the resin adsorption saturation, after washing, and then Leaching agent (sulfuric acid sodium chloride And sulfuric acid ammonium chloride And nitric acid Sodium nitrate And nitric acid ammonium nitrate , Dilute sulfuric acid or Dilute nitric acid From uranium) resin Elution down.

uranium Extraction and purification

The solution is dilute solution of large volume, low concentration, high impurity content of uranium, uranium and separation of impurities and shall make preliminary enrichment, and in the refining process, the uranium containing solution of high concentration, the quality of the products reached the requirements of nuclear pure. In the extraction process of uranium used in organic phosphine and alkyl amine extractants Three butyl phosphate (TBP), two (2 - ethylhexyl) phosphoric acid, Three octylamine Etc..
In uranium mill, extraction of sulfuric acid system by phosphorus and amine extraction process (two alkalinity The commonly used extraction system quaternary ammonium salt The extraction process, such as alkyl phosphine) extraction and amine extraction process, which is widely used in the world. Application of Chinese is eluex. The unsaturated resin adsorption uranium leaching with sulfuric acid, 1mol/L, and then the eluent was extracted. Such as the extraction agent for Eluex is 0.2mol/L two (2- ethylhexyl) three alkyl phosphine oxide phosphate system - 0.1mol/L. organic phase The saturation in control of more than 85%, after washing, use Ammonium carbonate The crystallization of reverse extraction, available nuclear pure uranyl tricarbonate. In the process of leaching and extraction, reduced the liquid volume extraction process, high metal recovery rate, saving reagent, the product purity is high.
Uranium plant products for general industrial uranium concentrate, still contain sulfate , silicon , calcium , magnesium Impurities should be further refined, in order to get nuclear pure products. The refining process is the most commonly used TBP extraction process, TBP of uranium saturation capacity, can handle the high amount of solution containing uranium in organic phase, near saturation conditions, the purification ability of high impurity elements.

uranium Precipitation from solution

stay Leaching The resulting solution and can also be state uranium to insoluble compounds separated; and through repeated dissolution of precipitates and precipitation and purification. The main method and alkali neutralization hydrogen peroxide Precipitation method :

uranium Alkali neutralization method

Alkaline Precipitation agent as ammonia , magnesium oxide So, gaseous ammonia added to acidic solution containing uranium, and control the final The value of pH 6.5~8.0, the uranium diuranate form completely precipitated. Yes alkalinity Leaching The main liquid sodium hydroxide Precipitation agent Well, Sodium uranate or Sodium diuranate Precipitation. If the precipitation of uranium from the acidic solution is purified, the precipitate of ammonium diuranate high purity.

uranium Hydrogen peroxide precipitation method

The solution containing uranium pH to 2.5~4.0, slowly adding ratio Chemical calculation The amount of hydrogen peroxide in excess of 30%, then add to ammonia. Neutralization reaction Production process of acid, so that the final pH value of 2.8, generating uranium peroxide (UO4 - xH2O) precipitation. Hydrogen peroxide precipitation of uranium with high selectivity and can obtain crystalline and easy processing products, also has industrial significance.

uranium Fan Dehua concentrated technology

purity 3% U-235 Nuclear power plant With low power enriched uranium U-235, more than 80% purity uranium highly enriched uranium Among them, the purity of more than 90% known as weapons grade highly enriched uranium, mainly used in the manufacture of Nuclear weapon . To obtain uranium is a series of process is very complex, through the prospecting and mining, beneficiation The leaching and smelting, mining, refining process, and the separation is one of the last process requires a high level of science and technology. 1 kilograms of weapons grade U-235 needs 200 tons of uranium ore. Due to problems involving nuclear weapons, uranium enrichment Technology is a sensitive technology diffusion of the international community is strictly prohibited. Except for a few nuclear powers, Japan Germany, India , Pakistan , Argentina Other countries have mastered uranium enrichment technology.
 For a piece of uranium nuclear fuel For a piece of uranium nuclear fuel
The main method of uranium enrichment Gas diffusion method And gas centrifuge.
Gas diffusion method The gas mixture to be separated into a diffusion film ( Separation membrane The device comes to) enrichment and dilution of two stream isotope separation method. The basic principle is: the collision between molecules is negligible under the condition of different quality of gas molecules in the gas mixture (e.g. 235UF6 and 238UF6) the average thermal motion rate Its quality is inversely proportional to the root of two. When the gas diffusion through the membrane, the rate of light molecules (235UF6) molecular weight by less than the rate of small (238UF6). So, through the film, will improve the content of light molecules, so as to achieve the purpose of isotope separation.
After the Second World War, the practice proved that the United states, Gas diffusion method Can be used for large-scale production of 235 uranium. It is the current large-scale uranium isotope separation method is the most mature, large-scale commercial application of the concentration method of various new challenges, is the basic point of the two ways. The United States and France large Gas diffusion The separation of power plants reached more than 10 thousand tons / year, energy consumption was 2400 kwh / kg. The gas diffusion method is Separation coefficient Small factories, large scale, high cost of consumption is huge.
Gas centrifuge method Gas centrifuge is one of the Key equipment . Uranium is placed in the reaction chamber to the centrifuge centrifuge center, 7-8 000 rpm speed rotation. The heavier U-238 atoms gradually close to the edge of the centrifuge, and the lighter U-235 is retained in the centrifuge parts center. The crystallization of U-235 was called the "uranium rich" (uranium), the rest of the depleted uranium "is discarded. A single centrifuge separation is not enough, must pass through more centrifuge processing, can separation and purification . The centrifuge "cascade configuration" connected. Therefore, the "cascade configuration" has become another important clue to use nuclear matter. In a purified uranium centrifuge, will be transferred to the next level to level with centrifuge purification. Due to the nuclear power station for uranium enrichment is relatively low, the less the centrifuge cascade level, thus appear to be relatively short. The concentration of uranium and used for nuclear weapons to reach more than 90%, the level of centrifuge cascade configuration is more natural, long and thin.
The United States and other countries usually have the device as to determine whether the nuclear weapons on a national standard. Nuclear power plant nuclear reactor Only 3%~5% U-235, and to the production of nuclear weapons, the concentration of U-235 to reach at least 90%. If it is found that the concentration of U-235 in one country to reach 90%, this is evidence of trying to build a nuclear weapon.

uranium application area

stay Curie couple find radium Later, due to radium treatment cancer The special effects, demand of radium is increasing, so many countries began to refine the radium from pitchblende, and refined uranium containing radium slag You pile on one side, the" waste ". However, Uranium After the discovery of uranium fission phenomenon, has become one of the most important elements. These "waste" will become a "baby". Since then, the uranium mining industry greatly developed, and quickly established independent complete atomic energy Industrial system.
Atomic bomb
The use of conventional explosives regularly placed in uranium around, and then use the Electronic detonator To make these explosives precise
 Atomic bomb mushroom cloud Atomic bomb mushroom cloud
At the same time explosion, huge pressure will generate pressure of uranium together and compressed, reach critical Conditions of explosion. The total mass of more than two pieces or Critical mass The uranium blocks together, will be a powerful explosion. Critical quality refers to the quality required to sustain the nuclear chain reaction of fissile material. Different fissile material, by the properties (such as nuclear fission cross section), Physical property The material, shape, purity Whether it is, neutron Is there, surrounded by reflection material Neutron absorption Influence of material factors and so on, and there will be a critical mass of different. May just combined to produce a chain reaction, called has reached critical point . This combination of more than the quality of the rate of nuclear reaction at Exponential growth Called. Super critical . If the combination can not delay in neutron chain reaction, this is called the critical threshold is. Super critical A. The critical combination will produce a nuclear explosion. If the combined ratio critical point Small fission will decrease over time, called the critical time. Nuclear weapons must be maintained in time critical to detonate before. With uranium Bomb For example, the uranium into several blocks, each quality is maintained at below critical. The combination of uranium blocks quickly detonated. Throw in Hiroshima The little boy" Atomic bomb Is a small piece of uranium through the barrel into another chunk of uranium, causing enough quality. This design is called "gun type". In this way, not a plutonium nuclear bomb detonated. (atomic bomb "fat" elements such as U-238, are uranium atomic bomb)
Another atomic bomb: implosion type plutonium bomb is a new design, the United States in July 16, 1945 The state of New Mexico A test called "gadgets" (Gadget) of the atomic bomb. The results of the test was very successful, the equivalent of twenty thousand tonnes, higher than previously expected two to four times.