Sodium diuranate

Dining outgassing of scrap uranium-aluminium cermet reactor cores, powerful exotherms led to melting of 9 cores. It was found that the incident was initiated by reactions at 350°C between aluminium powder and sodium diuranate, which released enough heat to initiate subsequent exothermic reduction of ammonium uranyl hexafluoride, sodium nitrate, uranium oxide and vanadium trioxide by aluminium, leading to core melting. 

Sodium hydroxide solution yellow amorphous precipitate of sodium diuranate, Na2U207, soluble in ammonium carbonate solution. 

Potassium hexacyanoferrate(II) solution brown precipitate of uranyl hexacyanoferrate(II), (U02)2[Fe(CN)6], in neutral or acetic acid solutions, soluble in dilute hydrochloric acid (difference from copper). The precipitate becomes yellow upon the addition of sodium hydroxide solution, due to its conversion into sodium diuranate (distinction from copper and from molybdenum). 

Other Systemic Effects. Several general effects have been attributed to uranium inhalation exposure. In animal studies, dogs exposed to 13 mg U/m as uranium hexafluoride for 30 days exhibited decreased water intake (Spiegl 1949). Reduced food intake was also observed in a 4-week study of rats and mice exposed to 16 mg U/m as uranium trioxide (Rothstein 1949c) and in a 5-week study of rats and mice exposed to 15 mg U/m as sodium diuranate for 6 hours per day, 5V2 days per week (Rothstein 1949d). 

No dermal effects were seen following application of a single dose of 618 mg U/kg as uranyl fluoride, 666 mg U/kg as uranium trioxide, 195 mg U/kg as sodium diuranate, 198 mg U/kg as ammonium diuranate, 410 mg U/kg as uranium peroxide, 458 mg U/kg as uranium dioxide, or 147 mg U/kg as triuranium octaoxide in 50% aqueous solution to the shaved skin of New Zealand white rabbits (Orcutt 1949). No dermal effects were observed on the shaved backs of New Zealand white rabbits to which a single dose of 98 mg U/kg as a 65% concentration of the uranium tetrafluoride in lanolin was applied (Orcutt 1949). Similarly, application of 3,929 mg U/kg as uranyl acetate dihydrate or 2,103 mg U/kg as ammonium uranyl tricarbonate in water-Vasehne emulsion to a 3 cm shaved area of the uncovered backs of 20 male Wistar rats in 1-10 daily applications had no effect on the skin of the rats (De Rey et al. 1983). 

Evidence also suggests that the toxicity of uranium varies according to the route of exposure and to its compounds. This finding may be partly attributable to the relatively low gastrointestinal absorption of uranium compounds. Only <0.1-6% of even the more soluble uranium compounds are absorbed in the gastrointestinal tract. On the basis of the toxicity of different uranium salts in animals, it was concluded that the relatively more water-soluble salts (uranyl nitrate hexahydrate, uranyl fluoride, uranium pentachloride) were primarily renal and systemic toxicants. The less water-soluble compounds (uranium trioxide, sodium diuranate, ammonium diuranate) were of moderate-to-low toxicity, while the insoluble compounds (uranium tetrafluoride, uranium dioxide, uranium peroxide, triuranium octaoxide) were... 

Uranium. Uranium is the rarest metal of the chromium group. Its principal ores are pitchblende, UgO, and carnotite, KoUoVoOi2 3H20. Its most important oxidation state is 4-6 (sodium diuranate, NaoU20(0H)j2 uranyl nitrate, U0o(N03)o 6H20 etc). 

Molybdenum and its uses. Molybdenite, molybdenum trioxide, ammonium molybdate. Wolfram (tungsten) and its uses. Scheelite, CaWO, and wolframite, (Fe,Mn)W04. Wolfram carbide. Uranium and its ores pitchblende, car-notite. Sodium diuranate, uranyl nitrate. Nuclear fission. 

Treatment of Uranium Minerals.—The chief source of uranium compounds is uraiiinite, but at the present time the working up of all uranium minerals has for its main object the extraction of radium, and the uranium salts are merely produced as by-products. The methods in use ary according to the nature of the desired product, which may be ammonium or sodium diuranate, or iiranyl nitrate. 

Ammonium Diuranate, (NH4)2U207, is obtained as a yellow voluminous precipitate when solutions of uranyl salts are treated with ammonia. It is prepared commercially (see p. 277) by boiling a solution of sodium uranyl carbonate with ammonium sulphate, or by boiling a solution of sodium diuranate with concentrated ammonium chloride solution. It is a deep yellow powder, which may be dried at 100° C. at higher temperatures it yields urano-uranic oxide. When fused with ammonium chloride, uranous oxide is formed. It is known commercially as uranium yellow (see also sodium diuranate) and is used in making fluorescent uranium glass. It is insoluble in ammonium hydroxide solution, and this fact is sometimes made use of (see p. 388) in the analytical separation of uranium. 

In the first process vanadium is coprecipitated and the sodium diuranate contains a nominal stoichiometric excess of sodium. The vanadium can be removed by roasting the yellow cake in the presence of sodium carbonate at 850°C followed by washing. The sodium carbonate solution from the washing is converted into sodium hydrogen carbonate and the sodium hydroxide solution into sodium carbonate by passing hot carbon dioxide into the solutions, which are returned to the leaching process. The consumption of solid sodium hydroxide is 10 to 20 kg/t ore. 

With sodium diuranate or uranoxy-hydrate a drying temperature of 120 to 175°C is sufficient. 

Redox Reactions. The initial chemical reaction is oxidation of uranium dioxide. In the equimolar sodium-potassium nitrate system the product is sodium diuranate. The following reactions are believed to be the only valid oxidation reactions that are possible. 

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