Sodium diuranate

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Sodium diuranate
Na2U2O7.png
Identifiers
13721-34-1 N
PubChem 160982
Properties
Na2O7U2
Molar mass 634.03 g·mol−1
Density 6.44 g/cm3
Melting point 1,646 °C
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Sodium diuranate or Yellow uranium oxide, Na2U2O7·6H2O, is a uranium salt also known as the yellow oxide of uranium. Along with ammonium diuranate it was a component in early yellowcakes, the ratio of the two species determined by process conditions; yellowcake is now largely a mix of uranium oxides. It is commonly referred to by the initials SDU. It was also used in porcelain dentures to give them a fluorescence similar to that of natural teeth and once used in pottery to produce ivory to yellow shades in glazes. It was added as a mix with cerium oxide. The uranium composed 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.

In the classical procedure for extracting uranium, pitchblende is broken up and mixed with sulfuric and nitric acids. The uranium dissolves to form uranyl sulfate, and sodium hydroxide is added to make the uranium precipitate as sodium diuranate. This older method of extracting uranium from its uraninite ores has been replaced in current practice by such procedures as solvent extraction, ion exchange, and volatility methods.

In the past it was widely used to produce uranium glass or vaseline glass, the sodium salt dissolving easily into the silica matrix during the firing of the initial melt.

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

Sodium Uranate may be obtained in the amorphous form by heating together urano-uranic oxide and sodium chlorate; or by heating sodium uranyl acetate or carbonate. 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.

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