Triuranium octaoxide
Encyclopedia
Triuranium octoxide is a compound of uranium
. It is present as an olive green to black, odorless solid. In spite of its color, it is one of the more popular forms of yellowcake
and is shipped between mills and refineries in this form.
Triuranium octoxide occurs naturally as the olive-green-colored mineral pitchblende. U3O8 is readily produced from UF6 and has potential long-term stability in a geologic environment
. In the presence of oxygen
(O2), uranium dioxide
(UO2) is oxidized to U3O8, whereas uranium trioxide
(UO3) loses oxygen at temperatures above 500°C and is reduced
to U3O8. The compound can be produced by any one of three primary chemical conversion processes, involving either uranium tetrafluoride
(UF4) or uranyl fluoride
(UO2F2) as intermediates. It is generally considered to be the more attractive form for disposal purposes because, under normal environmental conditions, U3O8 is one of the most kinetically and thermodynamically stable forms of uranium and also because it is the form of uranium found in nature. Its particle density is 8.3 g cm−3.
atoms, each layer contains uranium atoms which are in different coordination environments in the above diagram these are shown in plum and green.
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
. It is present as an olive green to black, odorless solid. In spite of its color, it is one of the more popular forms of yellowcake
Yellowcake
Yellowcake is a kind of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. Yellowcake concentrates are prepared by various extraction and refining methods, depending on the types of ores...
and is shipped between mills and refineries in this form.
Triuranium octoxide occurs naturally as the olive-green-colored mineral pitchblende. U3O8 is readily produced from UF6 and has potential long-term stability in a geologic environment
Deep geological repository
A deep geological repository is a nuclear waste repository excavated deep within a stable geologic environment...
. In the presence of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
(O2), uranium dioxide
Uranium dioxide
Uranium dioxide or uranium oxide , also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reactors. A mixture of uranium and plutonium dioxides is used...
(UO2) is oxidized to U3O8, whereas uranium trioxide
Uranium trioxide
Uranium trioxide , also called uranyl oxide, uranium oxide, and uranic oxide, is the hexavalent oxide of uranium. The solid may be obtained by heating uranyl nitrate to 400 °C. Its most commonly encountered polymorph, γ-UO3, is a yellow-orange powder.-Production and use:There are three methods...
(UO3) loses oxygen at temperatures above 500°C and is reduced
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
to U3O8. The compound can be produced by any one of three primary chemical conversion processes, involving either uranium tetrafluoride
Uranium tetrafluoride
Uranium tetrafluoride is a green crystalline solid compound of uranium with an insignificant vapor pressure and very slight solubility in water. Uranium in its tetravalent state is very important in different technological processes...
(UF4) or uranyl fluoride
Uranyl fluoride
Uranyl fluoride , a compound of uranium, is an intermediate in the conversion of uranium hexafluoride UF6 to an uranium oxide or metal form and is a direct product of the reaction of UF6 with moisture in the air. It is very soluble in water. Uranyl fluoride also is hygroscopic and changes in color...
(UO2F2) as intermediates. It is generally considered to be the more attractive form for disposal purposes because, under normal environmental conditions, U3O8 is one of the most kinetically and thermodynamically stable forms of uranium and also because it is the form of uranium found in nature. Its particle density is 8.3 g cm−3.
Solid state structure
The solid is a layered structure where the layers are bridged by oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
atoms, each layer contains uranium atoms which are in different coordination environments in the above diagram these are shown in plum and green.