Dissolving impure uranium tetra:fluoride in nitric acid

摘要

To obtain a uranyl nitrate soln. which can easily be filtered to remove solids, the impure UF4 is dissolved in a hot soln. in two stages (a,b). Stage (a) consists of using insufficient amts. of HNO3 and an Al cpd. to dissolved all the UF4, and to stir the hot mixt. for min. 0.5 hr. Stage (b) consists of adding more HNO3 and an Al cpd. at least in amts. sufficient for complete dissoln. of the UF4, and with stirring of the mixt. The Al cpd. is pref. AlCl3, Al(NO3)3, Al2(SO4)3, Al2O3 or Al(OH)3 and its tot 1 amt. is pref. 1.15-1.5 times the stoichiometric amt. needed to form the trivalent ions AlF6(3-). - Similar convention methods of dissolving UF4 in HNO3 result in a mixt. which is extremely difficult to filter, e.g. needing a filtering time of 12 hrs. The invention provides a soln. which can be filtered in 12 mins. (0/0) EPAB- EP-101395 B A method of dissolving impure uranium tetrafluoride hot in a nitric acid solution in the presence of an aluminium compound, characterised in that, for the purpose of obtaining a uranyl nitrate solution which can easily be separated from the solid phase formed during treatment, dissolving is carried out in two stages at a temperature from 60 to 110 degrees C, the first stage comprising introducing a quantity of nitric acid at most equal to 0.9 times the total quantity of nitric acid required to solubilise the uranium and a quantity of the aluminium compound at most equal to 0.95 times the stoichiometric quantity corresponding to the formation of (AlF6)3- and keeping the resultant suspension agitated for a period of at least 0.5 hour, and the second stage comprising introducing such quantities of nitric acid and of the aluminium compound that at both stages the total amount of aluminium compound is at least equal to the stoichiometric quantity corresponding to the formation of (AlF6)3- and the total quantity of nitric acid is corresponding to a free acidity at least 0.5 mole of HNO3 per litre of solution while keeping the suspension agitated. - (6pp) USAB- US4576802 A Process for dissolving hot, crude UF4 in HNO3 in the presence of an Al cpd., (which complexes with F(-) ions) comprises addn., of some of the HNO3 (e.g., 55% commercial acid; up to 90 mol% of the total required) and part of the total Al cpd., (up to 95 mol% of that needed to form AlF6(3-), and agitation of the suspension for at least 30 min.; and addn., of the rest of the HNO3 (such that the final concn., is at least 0.5 mol/dm3) and Al cpd., (to provide at least enough for the complete conversion of F(-) to AlF6(3-), with agitation, all at 60-110 deg. Pref., Al cpds., are the chloride, sulphate, nitrate and hydroxide.