Diuranate

The uranium is later precipitated and recovered in the diuranate form by introducing gaseous ammonia which causes the pH to rise to about 7. The amine is transformed from the sulfate form to free base by regeneration with sodium carbonate before returning to the extraction step. 

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. 

ADU [Ammonium diuranate] A process for converting uranium hexafluoride into uranium dioxide, for use as a nuclear reactor fuel. The hexafluoride is hydrolyzed in water ... 

The amine (B) is a proprietary mixture of C8 and C10 primary alkylamines dissolved in kerosene. The uranium is stripped from the organic solution with an alkaline stripping solution and precipitated as ammonium diuranate. See also Dapex. 

Uranium is best known as a fuel for nuclear power plants. To prepare this fuel, uranium ores are processed to extract and enrich the uranium. The process begins by mining uranium-rich ores and then crushing the rock. The ore is mixed with water and thickened to form a slurry. The slurry is treated with sulfuric acid and the product reacted with amines in a series of reactions to give ammonium diuranate, (NH4)2U20 . Ammonium diuranate is heated to yield an enriched uranium oxide solid known as yellow cake. Yellow cake contains from 70—90% U3Og in the form of a mixture of U02 and U03. The yellow cake is then shipped to a conversion plant where it can be enriched. 

Enriched UF6 is processed into U02 powder at fuel fabrication facilities using one of several methods. In one process uranium hexafluoride is vaporized and then absorbed by water to produce uranyl fluoride, U02F2, solution. Ammonium hydroxide is added to this solution and ammonium diuranate is precipitated. Ammonium diuranate is dried, reduced, and milled to make uranium dioxide powder. The powder is pressed into fuel pellets for nuclear reactors. 

The crystalline potassium mixed valent diuranate salt 65 was prepared as shown... 

Ammonium Diuranate. Pour 5 ml of a uranyl nitrate solution into a 50-ml beaker. Heat the solution to 80 °C and add several drops of a methyl orange solution to it. What causes the colour of the indicator to change Carefully pour in a 10% ammonia solution containing no carbon dioxide dropwise until the colour of the indicator changes. What substance precipitates Write the equation of the reaction. 

How can the formed complex compound be decomposed What substances prevent the precipitation of ammonium diuranate ... 

Figure 16.4 Ammonium diuranate (yellowcake) after solvent extraction. (Photo courtesy of UIC.) (Figure also appears in color figure section.)...

Ammonium hydroxide is added to the uranyl fluoride solution to quantitatively precipitate ammonium diuranate... 

In the 1950s, uranyl sulfate was stripped from the strong-base resins with a concentrated solution of chloride or nitrate, these being the two most efficient anions in the above sequence. Uranium was recovered from the strip solution by precipitation of the diuranate species with ammonia ... 

In the alkaline process, uranyl carbonate is eluted from the resin by concentrated (approximately 1 M) solutions of chloride, carbonate or bicarbonate, and is recovered from the eluate by treatment with an acid to destroy the carbonate complex, followed by precipitation of the diuranate, e.g. 

Weak-base resins have been tested from time to time but have not found wide acceptance in the uranium industry, The main reason for this is that the major advantage of weak- over strong-base resins, viz. elution by neutralization, cannot be utilized in uranium processing since it is not possible for the weak-base resin to be converted to the free-base form without diuranate precipitating within the pores of the resin (unless a complexing agent such as carbonate is added to the eluate). In the presence of carbonate, uranium remains in solution as the uranyl carbonate anion, even in very alkaline solution, so is readily eluted from a weak-base resin in the free-base form. This eluate would then be treated as depicted in equations (105) and (106) for the recovery of uranium. Alternatively, weak-base resins can be eluted by ion-exchange mass action. 

The recovery of uranium from the leach liquor is effected either by acidification to about pH 6 to liberate C02 or, more usually, by addition of hydroxide to precipitate diuranate, as shown in equation (27). In this latter case the pH is maintained at about 11. The species present in 0.055 M UVI solutions, acidified to pH 4.56 under 1 bar C02 pressure, have been summarized73 in a study of the reactive ion exchange adsorption of uranyl nitrate on to a bicarbonate loaded anion... 

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