Sodium diuranate, Na
2U
2O
7·6H
2O, is a
uranium
Uranium is a chemical element with the 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. Uranium is weak ...
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
also known as the yellow oxide of uranium. Sodium diuranate is commonly referred to by the initials SDU. Along with
ammonium diuranate it was a component in early
yellowcake
Yellowcake (also called urania) is a type of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before f ...
s.
The ratio of the two compounds is determined by process conditions; however, yellowcake is now largely a mix of
uranium oxide
Uranium oxide is an oxide of the element uranium.
The metal uranium forms several oxides:
* Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende)
* Diuranium pentoxide or uranium(V) oxide (U2O5)
* Uranium trioxide or u ...
s.
Preparation
In the classical procedure for extracting uranium,
pitchblende
Uraninite, formerly pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium causes t ...
is broken up and mixed with
sulfuric and
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
s. The uranium dissolves to form
uranyl sulfate
Uranyl sulfate describes a family of inorganic compounds with the formula UO2SO4(H2O)n. These salts consist of sulfate, the uranyl ion, and water. They are lemon-yellow solids. Uranyl sulfates are intermediates in some extraction methods used for ...
and sodium carbonate is added to precipitate impurities. If the uranium in the ore is in the tetravalent
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
, an oxidiser is added to oxidise it to the hexavalent oxidation state, and
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
is then added to make the uranium
precipitate
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
as sodium diuranate.
The
alkaline
In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...
process of milling uranium ores involves precipitating sodium uranate from the pregnant
leaching
Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). and may refer to:
* Leaching (agriculture), the loss of water-soluble plant nutrients from the soil; or applying a small amou ...
solution to produce the semi-refined product referred to as
yellowcake
Yellowcake (also called urania) is a type of uranium concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before f ...
.
These older methods of extracting uranium from its
uraninite ores has been replaced in current practice by such procedures as
solvent extraction
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
,
ion exchange
Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...
, and
volatility methods.
Sodium uranate may be obtained in the amorphous form by heating together urano-uranic oxide and
sodium chlorate
Sodium chlorate is an inorganic compound with the chemical formula Na ClO3. It is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 300 °C to release oxygen and leaves sodium chloride. Sever ...
; or by heating sodium uranyl acetate or
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
. The crystalline form is produced by adding the green oxide in small quantities to fused sodium chloride, or by dissolving the amorphous form in fused sodium chloride, and allowing crystallization to take place. It yields reddish-yellow to greenish-yellow prisms or leaflets.
Uses
![AW U glass bowl on fiestaware plate](https://upload.wikimedia.org/wikipedia/commons/a/ac/AW_U_glass_bowl_on_fiestaware_plate.jpg)
In the past it was widely used to produce
uranium glass
Uranium glass is glass which has had uranium, usually in oxide diuranate form, added to a glass mix before melting for colouration. The proportion usually varies from trace levels to about 2% uranium by weight, although some 20th-century piec ...
or vaseline glass, the
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
salt dissolving easily into the
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
matrix during the firing of the initial melt.
It was also used in
porcelain
Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises mainl ...
dentures
Dentures (also known as false teeth) are prosthetic devices constructed to replace missing teeth, and are supported by the surrounding soft and hard tissues of the oral cavity. Conventional dentures are removable (removable partial denture or ...
to give them a
fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
similar to that of natural
teeth
A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
and once used in
pottery
Pottery is the process and the products of forming vessels and other objects with clay and other ceramic materials, which are fired at high temperatures to give them a hard and durable form. Major types include earthenware, stoneware and por ...
to produce ivory to yellow shades in
glazes. It was added to these products as a mix with
cerium oxide Cerium oxide may refer to:
*Cerium(III) oxide, Ce2O3, also known as dicerium trioxide
* Cerium(III, IV) oxide, Ce3O4 (dark blue)
*Cerium(IV) oxide
Cerium(IV) oxide, also known as ceric oxide, ceric dioxide, ceria, cerium oxide or cerium dioxide, ...
.
The final uranium composition was from 0.008 to 0.1% by weight uranium with an average of about 0.02%. The practice appears to have stopped in the late 1980s.
References
External links
NRC GlossaryMSDS*
{{DEFAULTSORT:Sodium Diuranate
Sodium compounds
Uranates
Nuclear materials