United States Patent im [in 3,758,664 Gerrald [45] Sept. 11, 1973 [54] PROCESS FOR PRODUCING AMMONIUM Primary Examiner—Carl D. Quarforth DIURANATE Assistant Examiner—F. M. Gittes Attorney—F. Shapoe [75] Inventor: Lonnie D. Gerrald, Columbia, S.C. [73] Assignee: Westinghouse Electric Corporation, [57] ABSTRACT Pittsburgh, Pa. A process for the recovery of uranium as ammonium [22] Filed: Dec. 29, 1970 diuranate from aqueous solutions having uranyl and fluoride ions such as produced by hydrolyzing UF6, and [21] Appl. No.: 102,451 for reducing soluble uranium losses in the liquid waste stream, by forming a first neutralized solution of uranyl [52] U.S. CI 423/15, 423/253, 423/261 fluoride (U02F2), with concentrated ammonium hy- [51] Int. CI COlg 43/00 droxide, at a pH of about 4.5 to 6.0, and then by precip- [58] Field of Search 23/335, 346, 355 itating essentially all of the uranium, as ammonium di- uranate, [(NH4)2U207], (ADU), from the solution by [56] References Cited adding concentrated ammonium hydroxide under con- UNITED STATES PATENTS trolled conditions preventing formation of any soluble fluoride complexes that would otherwise be ordinarily 3,579,311 5/1971 McCoy.. 23/335 formed during the precipitation of the ammonium di- 3,394,997 7/1968 Hollander 23/335 uranate, to produce an ADU slurry which is calcinable 3,272,602 9/1966 Suehiro et al 23/335 2,466,118 4/1949 Miller et al 23/335 to U02 having good ceramic pelletizing properties. 2 Claims, 1 Drawing Figure 22^ CONCENTRATED NHjOH SUPPLY t.g 24-29% NH3 -58.6 LBS. -20 FIRST NEUTRALIZED SOLUTION a STORAGE 100 LBS. PH45-6D x(50 °F 26-, U02F2 + HF+H20 U02F2+NH4F+HF+HgO Patented Sept. 11, 1973 3,758,664 . UJ Q li. i_ CaO o io« <n —1CZ ** .U O cr <t;o5cc 2 in WITNESSES: INVENTOR Lonnie D. Gerrold ATTORNEY 3,758,664 1 2 PROCESS FOR PRODUCING AMMONIUM mation of the soluble uranium complexes, i.e., DIURANATE UOIFI-3NH4F. Once these uranium complexes are . formed they remain in solution and the uranium values BACKGROUND OF THE INVENTION are ^ Jcause they cannot be readjly recovered 1. Field of the Invention 5 therefrom and are carried away in the waste stream or This invention relates to a process for the recovery of require costly ion exchange or other treatments for uranium values from aqueous solutions containing ura- their recovery. nyl and fluoride ions, and, more particularly, it pertains In addition, the process of U.S. Pat. No. 2,466,118 to the conversion of uranium hexafluoride to ammo- employs a concentrated solution of ammonia (8 to IS nium diuranate by a two stage treatment with concen- 10 molar), because in that fluoride system the solubility of trated ammonium hydroxide. uranium is lowest when the ratio of ammonia to ura- 2. Description of the Prior Art nium is highest. Thus, the initial addition of concen- One method of preparing uranium dioxide (UOt) trated ammonium hydroxide is sufficient to precipitate from uranium hexafluoride (UFS), involves an initial a major portion of uranium, and suitably constitutes an reaction of the UF( with water to form an aqueous hy- IS excess over the stoichiometric quantity of ammonium drolysis solution of uranyl fluoride (UOjF,) and hydro- hydroxide required to neutralize any acidity and to pre- fluoric acid (HG). Thereafter, it has been one conven- cipitate all of the uranium in the absence of fluoride tional practice, as set forth in U.S. Pat. No. 2,466,118, ions. The resulting product, UOt, is finely divided and to add a concentrated solution of ammonium hydrox- is difficult to dewater and dry. ide greatly in excess of the necessary stoichiometric 20 The process of U.S. Pat. No. 3,394,997 employs a amount of ammonium hydroxide, preferably 2 to 3 large volume of dilute aqueous ammonium solution times greater than stoichiometric, to react with the ura- substantially less than 2 molar, and preferably 0.7 to 1 nyl fluoride solution in order to precipitate the uranium molar, to precipitate ammonium diuranate [ in the form of ammonium diuranate [ (NH4),Ui07 ]. (NH4)1Ul07 ], which is relatively crystalline and granu- The latter compound was then digested at a specific 25 lar in nature. While the resulting product UOj readily temperature after which additional ammonium hydrox- dewaters and dries rapidly it does not possess optimum ide was added, at least 5 times and preferably 7 to 13 ceramic sinterability properties. The process is still sub- times stoichiometric, to prevent substantial complexing ject to a complex recovery procedure to minimize ura- of the uranyl ions by any fluoride ions. It will be under- nium loss. stood that these processes required large excesses of 30 jn a copending application Ser. No. 865,232, as- ammonium hydroxide. Another variation thereof is dis- signed to the assignee of the present invention, there is closed in U.S. Pat. No. 3,394,997, wherein large vol- disclosed a process for converting a hydrolysis solution umes of dilute, less than 1.2 molar, ammonium hydrox- of uranium hexafluoride by adding thereto only dilute ide to provide from 7 to 12 moles of NH3 for each mole ammonium hydroxide (about 1 molar). The dilute am- of uranium. 35 monjum hydroxide necessarily introduce very large The precipitation of ammonium diuranate [ volumes of water which not only require larger reaction (NH4)zU207 ] with ammonium hydroxide is not com- and holding or storage vessels, and larger piping and plete at the stoichiometric point because of the com- pumps but also require more equipment to separate the plex nature of the uranyl fluoride solutions. A large ex- ADU precipitate from the water with dissolved NH4F. 40 cess of the ammonium hydroxide is used to drive the The large volumes of NH4F solution impose a disposal reaction to completion. An example of the reaction is problem, because of its large NH4OH content, set forth in the following formula: Although the specific reaction for the precipitation 2UOjFj + 4HF + 10 NH4OH - (NH4),U,07 + of UOjF, under equilibrium conditions with NH4OH 8NH4F + 7HjO (Ti should lead, at least as an initial step, to hydrated UOt. 45 (OH),, it is believed that other additional reactions A disadvantage of the foregoing one step procedure occur (such as dimerization, hydration, and ammonia- is that it requires a great excess of ammonium hydrox- tion) to preclude the exclusive specific reaction in- ide. A more critical shortcoming is that the ammonium tended. Stoichiometric ammonium diuranate has never diuranate precipitate formed does not completely sepa- been reported as being directly produced from aqueous rate and recover all of the uranium from the uranyl flu- medium directly in a single step so that polymerization oride. These reaction products often include from 1.5 most probably must occur. to 2.0 percent of uranium fluoride present as a mixed Ammonium diuranate is believed to be a more corn- fluoride, particularly UOtF,-3NH4F, which is relatively plex compound than is indicated by the commonly ac- soluble and which therefore leads to a loss of uranium J5 cepted formula (NH,),Ut07. There are indications that in the waste stream. Such fluoride complexes are ex- some molecules may have many atoms of uranium, up tremely difficult to break in order to recover the ura- to 7 or more, and that more than two (NH4) groups nium. Also it is desirable to produce ADU precipitate may be present. However, the formula (NH4)2U207 with the smallest possible traces of fluorides. represents quite closely the average composition of this From extended investigation it has been found that 6Q complex uranium compound. formula (1) defines an ideal reaction which in fact does SUMMARY OF THP IMVPNTION not occur quantitatively even under the most ideal con- SUMMARY OF THE INVENTION ditions. In practice it has been found that the one step In accordance with this invention it has been found reaction of formula (1) results in a number of side reac- that the foregoing disadvantages may be overcome by tions which occur so rapidly that the HF does not pref- 6S first partially neutralizing with concentrated ammo- erentially react to completion with NH4OH to produce nium hydroxide the hydrolysis solution of uranium hex- NH4F. Rather, other reactions occur simultaneously afluoride which contains uranyl fluoride (UOtFt) to between HF, UO,F2> and NH4OH, which result in for- form the compound ammonium fluoride (NH4F) with 3,758,664 3 4 the solution being at a pH of from about 4.5 to about ent. However, it is critical that the resulting first neu- 6.0, a good average being a pH of 5.0, which prevents tralized solution be acidic with a slight amount of HF the uranyl ion from entering fluoride complexing reac- remaining unneutralized so that the pH of the solution tions at that time or during subsequent reactions. The at equilibrium is from about 4.5 to about 6.0, so that no process requires an initial addition of a solution of con- 5 ADU precipitate forms. Accordingly, in formula (2) centrated ammonium hydroxide at least about 3N, for only the NH4OH and HF interact to form NH4F and example, about 24 to 29% NH3, to the uranyl fluoride H20, the UO^ being essentially unreacted at this solution to form ammonium fluoride with about stage. 85-95% of the HF, with only 5 to 15 percent of the HF By limiting the amount of the ammonium hydroxide being unreacted. After equilibrium is reached, more 10 added, as well as by controlling the resulting solution concentrated ammonium hydroxide (from 3 to 6 mo- pH, only water soluble ammonium fluoride is preferen- lar) is thoroughly and rapidly admixed with the first tially formed.