Chemical elements
  Uranium
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    PDB 1anv-3pu4

Element Uranium, U, Actinide or Actinoid





History

Uranium had been discovered in 1789 by the German chemist Martin Klaproth who called this element uranium after the last planet to have been discovered 8 years before that. In fact the substance obtained by Klaproth was the oxide of a yet-undiscovered element which actually was separated by Eugene-Melchior Peligot in 1841. From that time and to the 20th century uranium did not have that significance which it has today, although many of its physical properties as well as the atomic mass and density had been found out.

In 1896 the French scientist Henri Becquerel discovered the radioactive property of uranium by exposing a photographic plate to it. This discovery encouraged physicists to initiate the radioactivity investigations, and in 1898 Pierre Curie and Maria Sklodowska-Curie separated salts of such radioactive element as polonium and radium; meanwhile E. Rutherford, F. Soddy, K. Fajans and many other scientists developed the theory or radioactive fission putting the foundation of modern nuclear chemistry and nuclear power industry.


Occurrence

Uranium is a member of actinide (or actinoid) group of chemical elements is a specific element of granite layer and sedimentary shell of the Earth crust. The crustal abundance is 2.5x10-4% by mass; concentration in acidic igneous rocks is 3.5x10-4%, 3.2x10-4% in clays and slates, and 5x10-5% in basic rocks and 3x10-7% in ultrabasic rocks. Uranium actively migrates in cold and hot, alkaline and neutral water, in the form of simple and complex, especially carbonate ions. Redox reactions are very important in uranium geochemistry, because its compounds are highly soluble in oxidizing water environment and very poorly soluble in reducing environment (for instance, in hydrosulfuric). Minute amounts (10-5%) of uranium are found in plant, animal and human tissues and 1.5x10-5% in plant cinder if the concentration in soil is 1x10-4%. Uranium is accumulated mostly by mushrooms and seaweed; the latter actively participates in biogenic chain uranium migration by scheme "water -> seaweed -> fish -> human".

Occurrence of Uranium in nature is low. It occurs as an essential constituent in only a few minerals, and these are not very abundant. The most important ore is pitchblende or uraninite, which may contain 40 to 90 per cent, of uranium oxide, usually expressed as U3O8, together with small quantities of iron, lead, bismuth, thorium, and the rare earths. It occurs massive with indistinct crystallisation, and also in grains; crystals are rare, but well-defined octahedra and cubes are sometimes found. The mineral occurs as a constituent of granitic rocks, and also in metalliferous veins with sulphides of silver, lead, iron, cobalt, nickel, and copper. It is brittle, of hardness 5.5 and, when crystalline, of density 9.0 to 9.7; of massive altered forms, the density varies from 6.4 upwards. In appearance uraninite resembles pitch and is usually black and slightly lustrous, but some specimens are grey to greenish or brownish. It is found at Joachimsthal in Bohemia, at various localities in Saxony, Hungary, Norway, and Turkey; in Connecticut, North Carolina, Colorado, and Utah; in Bengal and East Africa; associated with monazite in the Villeneuve mica veins, Quebec; and associated with torbernite (see below) near Redruth in Cornwall. In composition the mineral appears to be essentially a uranate of uranyl, but the ratio UO2:UO3 varies widely, even in specimens from the same locality, and it has been suggested that the mineral was originally the dioxide, UO2, isomorphous with thorianite, ThO2, and that the trioxide has been produced by oxidation. The formula (UO2)3(UO3)2, or UIV3(UVIO6)2, has been proposed for the purified mineral, but it is not of general application.

Cleveite and broggerite are varieties of uraninite, rich in thoria and rare earths, occurring in Norway. Cleveite is generally found in cubic crystals of density 7.49, whilst broggerite yields octahedra of density 9.03. Nivenite is similar to cleveite, and like the latter mineral contains about 10 per cent, of the yttrium earths. It occurs in Texas, and is generally found massive with indistinct crystallisation. Hardness 5.5; density 8.01. It dissolves more readily than other varieties of uraninite in dilute acid, being completely decomposed by digesting with very dilute sulphuric acid at 100° C. A very pure form of uraninite occurs in the Morogoro district of Tanganyika Territory, in the form of crystals containing 87 to 88 per cent. U3O8. These are largely altered to a yellow uranyl carbonate known as rutherfordine.

Uranothallite occurs as an incrustation, consisting of minute indistinct crystals, on uraninite at Joachimsthal. It contains the carbonates of calcium and uranium, its composition corresponding to the formula 2CaCO3.U(CO3)2.10H2O. It is greenish, translucent, and vitreous in appearance; hardness 2.5 to 3.0. Liebigite is a similar mineral, found near Adrianople, Turkey, and at Joachimsthal, the composition of which is probably CaCO3.(UO2)CO3.20H2O. It is transparent, of a beautiful apple-green colour, and has hardness 2.5. Voglite, also found at Joachimsthal in aggregations of green crystalline scales, contains carbonates of calcium, uranium, and copper.

Gummite is an alteration-product of uraninite of doubtful composition. It appears to be a hydrated silicate of uranium, containing lead, calcium, and sometimes iron. It occurs in rounded or flattened pieces, reddish yellow to reddish brown in colour, resembling gum. Hardness 2.5 to 3.0; density 3.9 to 4.2. It is found in North Carolina and in Saxony. Varieties of gummite found near Joachimsthal are known as eliasite and pittinite; soddite and chinkolobwite from Katanga, Belgian Congo, contain uranium and silica, and probably have the composition 12UO3.5SiO2.14H2O; yttrogummite occurs with cleveite; thorogummite is found in Texas. A uraninite partly altered to gummite, and known as coracite, occurs north of Lake Superior.

Uranophane or uranotil, a further alteration-product of uraninite, is a hydrated silicate of uranium and calcium, of composition CaO. 2UO3.3SiO2.7H2O. It is found with the uranium minerals in Silesia, Bavaria, Saxony, and North Carolina, occurring in aggregations of minute yellow acicular prisms, often as an incrustation upon, and penetrating into, gummite.

Uranosphcerite, a bismuth uranate of composition Bi2O3.2UO3. 3H2O, occurs in Saxony in orange-yellow half-globular aggregated forms, of hardness 2.3 and density 6.36.

Autunite, calco-uranite, or lime-uranite, a hydrated phosphate of uranium and calcium, Ca(UO2)2(PO4)2.8H2O, is generally found with uraninite. One of its chief sources is near Autun in France, but it also occurs in various localities in Germany and the United States, in Madagascar, Portugal, near Limoges, and in Cornwall. It usually occurs as thin, yellow, transparent or translucent, tabular crystals of the orthorhombic system, or in foliated aggregates with micaceous structure, with hardness 2 to 2.5 and density 3.05 to 3.19. Its uranium content is equivalent to 55 to 62 per cent. UO3. The Cornish autunite appears to be distinct from the original mineral from Autun, alid to belong to two different species which have been named bassetite and uranospathite. Both form yellow crystals with a micaceous cleavage; bassetite is monoclinic,

a:b:c = 0.3473:1:0.3456; β = 89° 17',

and of density 3.1; uranospathite is orthorhombic and pseudotetragonal, and of density 2.5.

Torbernite, torberite, chalcolite, cupro-uranite, or uranium mica is a related mineral to autunite, but is greenish in colour and yields tetragonal crystals of density 3.4 to 3.6 and of hardness 2.0 to 2.5. It is a hydrated phosphate of uranium and copper, Cu(UO2)2(PO4)2.8H2O, but the phosphorus may in part be replaced by arsenic. The mineral exhibits a perfect basal cleavage which often imparts to it a micaceous structure. It occurs chiefly in Cornwall and in the pitchblende districts of Saxony, Bohemia, and Belgium. It generally contains 56 to 60 per cent. UO3. Both torbernite and autunite are included under the common name of uranite. Minerals closely related to these are: zeunerite, a greenish arsenate of copper and uranium, Cu(UO2)2(AsO4)2.8H2O; uranospinite, an arsenate corresponding to autunite, of composition Ca(UO2)2(AsO4)2.8H2O; uranocircite, a phosphate of barium and uranium, Ba(UO2)2(PO4)2.8H2O; walpurgite, probably a basic arsenate of bismuth and uranium; dewindtite and stasite, apparently dimorphous forms of a lead uranium phosphate, of composition 4PbO.8UO3.3P2O5.12H2O, which occur with torbernite in the Katanga district, Belgian Congo.

Phosphuranylite, a hydrated phosphate, (UO2)3(PO4)2.6H2O, occurs as a lemon-yellow pulverulent incrustation on quartz, felspar, and mica in North Carolina.

Trogerite is a hydrated arsenate, of composition (UO2)3(AsO4)2.12H2O, found in Saxony and Portugal.

Carnotite is a double vanadate of potassium and uranium, of probable composition K2(UO2)2(VO4)2.8H2O, but generally very impure with silica. It occurs as a yellow crystalline powder, or in loosely cohering masses, chiefly in Colorado and Utah, but also in South Australia and Portugal. The mineral has attained considerable importance in America as a source of uranium and radium.

Other minerals containing uranium are: thorianite, generally regarded as an isomorphous mixture of the dioxides of uranium and thorium, containing 10 to 30 per cent. UO2, found chiefly in Ceylon; uranothorite, a name given to varieties of thorite containing uranium, as much as 10 per cent. UO3 sometimes being present; gilpinite, occurring in Colorado in aggregates of minute yellow crystals intermixed with gypsum on pitchblende and copper ore, and having the composition RO.UO3.SO3.4H2O (R = Cu, Fe, Na2); uranopilite, from Cornwall, is a similar mineral to gilpinite and probably identical with it; euxenite and polyerase, columbates and titanates of yttrium, erbium, cerium, and uranium, containing 4 to 16 per cent, uranium; priorite and blomstrandine-priorite, similar to euxenite and polycrase, but containing less uranium; blomstraudited containing tantalum in addition to columbium and titanium; tyrite, complex columbates of yttrium, cerium, uranium, calcium, and iron; pyrochlore, columbate of calcium rich in uranium; samarskite, a uranotantalate of iron and yttrium, found in Siberia and North Carolina; fergusonite, complex columbates of yttrium, cerium, uranium, calcium, and iron; brannerite from Idaho and delorenzite from Piedmont are probably complex titanates. Many other rare earth minerals, such as cesclienite, cerite, xenotime, monazite, and yttrocrastite, contain small quantities of uranium. Traces also occur in holm, a variety of bituminous coal found in Sweden, the ash of which contains 1 to 3 per cent. U3O8.

The presence of uranium in the sun has been shown spectroseopically.

Uranium gets into human organism with food and water, through gastrointestinal tract (1% highly soluble and poorly soluble of the whole amount), respiratory system (50% and 20% correspondingly)., skin and mucosae. The most uranium depots (accumulation locations) are the spleen, kidneys, liver, and, if hardly soluble compounds are breathed, in the lungs and bronchus-lung lymphatic nodes. The circulation of uranium compounds in the form of carbonates and protein complexes) in blood does not take long time. The concentration in tissues does not exceed 10-7%.

Neighbours



Chemical Elements

57La
138.9
Lanthanum
72Hf
178.5
Hafnium
73Ta
180.9
Tantalum
91Pa
231.0
Protactinium
92U
238.0
Uranium
93Np
237.0
Neptunium

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