Sodium diuranate, Na₂U₂O₇·6H₂O, is a uranium salt also known as the yellow oxide of uranium. Sodium diuranate is commonly referred to by the initials SDU. Along with

ammonium diuranate Ammonium diuranate or (ADU) ((NH4)2U2O7), is one of the intermediate chemical forms of uranium produced during yellowcake production. The name "yellowcake" originally given to this bright yellow salt, now applies to mixtures of uranium oxides which ...

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 fu ...

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 ...

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 th ...

is broken up and mixed with

sulfuric Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

and nitric acids. 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 f ...

and sodium carbonate is added to precipitate impurities. If the uranium in the ore is in the tetravalent oxidation state, an oxidiser is added to oxidise it to the hexavalent oxidation state, and sodium hydroxide is then added to make the uranium precipitate as sodium diuranate. The

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of ...

process of milling uranium ores involves precipitating sodium uranate from the pregnant leaching solution to produce the semi-refined product referred to as

. These older methods of extracting uranium from its uraninite ores has been replaced in current practice by such procedures as solvent extraction,

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. Sev ...

; 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

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 salt dissolving easily into the silica matrix during the firing of the initial melt. It was also used in porcelain dentures to give them a fluorescence 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, tea ...

and once used in pottery 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, CeO2, also known as ceric oxide {{Chemistry index ...

. 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