Uranyl
The uranyl ion with the chemical formula has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen, with uranium in the oxidation state +6. Four or more ligands may be bound to the u ...
peroxide or uranium peroxide hydrate (UO
4·nH
2O) is a pale-yellow, soluble
peroxide
In chemistry, peroxides are a group of Chemical compound, compounds with the structure , where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical) and O's are single oxygen atoms. Oxygen atoms are joined ...
of
uranium
Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...
. It is found to be present at one stage of the
enriched uranium
Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (23 ...
fuel cycle and in
yellowcake prepared via the ''in situ'' leaching and resin
ion exchange
Ion exchange is a reversible interchange of one species of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid. Ion exchange is used in softening or demineralizing of water, purification of ch ...
system. This compound, also expressed as UO
3·(H
2O
2)·(H
2O), is very similar to
uranium trioxide hydrate UO
3·''n''H
2O. The dissolution behaviour of both compounds are very sensitive to the hydration state (n can vary between 0 and 4). One main characteristic of uranium peroxide is that it consists of small needles with an average AMAD of about 1.1 μm.
The uranyl minerals
studtite
Studtite, chemical formula UO2)O2(H2O)2�2(H2O) or UO4·4(H2O), is a secondary uranium mineral containing peroxide formed by the alpha- radiolysis of water during formation. It occurs as pale yellow to white needle-like crystals often in acicula ...
, UO
4·4H
2O, and metastudtite, UO
4·2H
2O, are the only minerals discovered to date found to contain peroxide. The product is a light yellow powder.
Synthesis
In general, uranyl peroxide can be obtained from a solution of uranium(VI) by adding a peroxide, usually hydrogen peroxide solution. The dihydrate is obtained from a boiling solution of uranyl nitrate with the addition of hydrogen peroxide and drying of the precipitate, while the trihydrate is precipitated from a solution of ammonium uranyl oxalate.
Crystal structure
The
unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector
In mathematics, a unit vector i ...
consists of
uranyl
The uranyl ion with the chemical formula has a linear structure with short U–O bonds, indicative of the presence of multiple bonds between uranium and oxygen, with uranium in the oxidation state +6. Four or more ligands may be bound to the u ...
cations coordinated to two
water molecules and two
peroxide
In chemistry, peroxides are a group of Chemical compound, compounds with the structure , where the R's represent a radical (a portion of a complete molecule; not necessarily a free radical) and O's are single oxygen atoms. Oxygen atoms are joined ...
anions. The latter are μ
2-coordinated to the cation—that is, end-on. Additional water molecules are bound in the crystal by
hydrogen bonding
In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...
. Only the tetrahydrate has been characterized by
X-ray crystallography
X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...
, but
density functional theory
Density functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body ...
offers a good approximation to the dihydrate.
Polyperoxouranylate allotrope
When
uranyl nitrate
Uranyl nitrate is a water-soluble yellow uranium salt with the formula . The hexa-, tri-, and dihydrates are known. The compound is mainly of interest because it is an intermediate in the preparation of nuclear fuels. In the nuclear industry, it ...
is dissolved in an aqueous solution of
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...
and an
alkali metal hydroxide, it forms cage clusters akin to
polyoxometalate
In chemistry, a polyoxometalate (abbreviated POM) is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks. The metal atoms are ...
s or
fullerene
A fullerene is an allotropes of carbon, allotrope of carbon whose molecules consist of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to six atoms. The molecules may ...
s.
Syntheses also typically add organic materials, such as
amine
In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...
s, to serve as templates, akin to
zeolite
Zeolites are a group of several microporous, crystalline aluminosilicate minerals commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a meta ...
s.
Applications
Radiolysis
Radiolysis is the dissociation of molecules by ionizing radiation. It is the cleavage of one or several chemical bonds resulting from exposure to high-energy flux. The radiation in this context is associated with ionizing radiation; radiolysis is ...
of uranium salts dissolved in water produces peroxides; uranyl peroxide has been studied as a possible end component of spent
radioactive waste
Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear ...
.
References
Some Chemistry of Uranium*
*
{{DEFAULTSORT:Uranyl Peroxide
Uranyl compounds
Peroxides
Nuclear materials
Oxidizing agents