Diuranate precipitation

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. 

Before diuranate precipitation the excess sulfate and iron have to be removed. 

The UO2F2 solution is treated with ammonia, whereupon ammonium diuranate precipitates out, although not in a strictly stoichiometric composition ... 

The diuranate precipitate is separated from the mixed NaG and Na SO4 salt solution by a system of thickeners and filters. Filter cake from the first filter is washed with water, reslurtied with water, filtered a second time, and washed again to reduce its content of NaG and Na2S04. When it is necessary to reduce the amount of sodium diuranate, a third stage of filtration is used, and the filter cake is reslurried with ammonium sulfate instead of water to replace most of the sodium with ammonium ion. Washed filter cake is dried by heating to 160 to 180°C. 

R VUILLERNEY, Contribution to the Chemical and Technological Study of Ammonium Diuranate Precipitation, CEA 2204, Centre D Etudes NuclSiires De Saclay, France (1962). 

Fig. 31.16. UFe conversion to UO2 by ammonium diuranate precipitation. (Courtesy USDOE.)...

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. 

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. 

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. 

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 ... 

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. 

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... 

Ammonia solution yellow precipitate of ammonium diuranate, insoluble in excess of the reagent, but soluble in ammonium carbonate or sodium carbonate, forming the tricarbonatouranylate(VI) ion ... 

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). 

For production of uranium compounds suitable for use in nuclear reactors or for isotope separation, further chemical procedures are applied, as indicated in Fig. 11.9. Nuclear purity means that the compounds are free of nuclides with high neutron absorption cross section, i.e. free of boron, cadmium and rare-earth elements. Selective extraction procedures are most suitable for this purpose. Uranyl nitrate hexa-hydrate (U02(N03)2 6H2O UNH) is obtained by concentration of solutions of U02(N03)2, and ammonium diuranate ((NH4)2U207 ADU) by precipitation with ammonia. 

Carnotite may be fused Avith potassium hydrogen sulphate and the residue extracted with Avater. From the solution the double sulphates of potassium AAuth uranium and vanadium may be obtained by crystallisation. These are reduced by means of zinc and sulphuric acid, and the vanadium precipitated from the solution by means of ammonia and ammonium carbonate. Ammonium diuranate separates from the filtrate on boiling. ... 

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