DE1917350A1 - Process for the recovery of uranium from an aqueous solution - Google Patents

Description

DIPIi. ING. NT
R. ATTORNEY
WOODB 89 A Basement SBURG H ₁ 1137 »

w.

Augsburg, April 1, 1969

Westinghouse Electric Corporation, 3 Gateway Center, Pittsburgh, Pennsylvania, United States of America

Process for the recovery of uranium from an aqueous solution

The invention relates to a method for the recovery of uranium from aqueous solutions which uranyl ions and Contain fluoride ions, and in particular the precipitation of ammoniuradiuranate from such solutions by means of ammonium hydroxide.

A process for the preparation of uranium dioxide (UO ₂ ) from

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Uranium hexafluoride (UPg) requires a primary reaction of the UPg with water to form an aqueous solution of uranyl fluoride (UO ₂ P ₂ ) and hydrogen fluoride (HP). An advantage of this process is that the aqueous uranyl fluoride is lighter and easier to handle than the gaseous uranium hexafluoride. A large excess of concentrated ammonium hydroxide is then added as usual

^ above the stoichiometric equilibrium amount of ammonium hydroxide, so that after a reaction with the uranyl fluoride solution, the uranium is precipitated in the form of ammonium diuranate (NHjL) ₂ U ₂ O ₇ . This latter compound is then boiled at a certain temperature, whereupon further ammonium hydroxide is added, so that a complex formation between uranyl ions and fluoride ions is essentially prevented. Of course, these process steps require a large excess of ammonium hydroxide. A . such a method and a modified form thereof are described in US Pat. Nos. 2 K66 II8 and 3,399,997.

The precipitation of ammonium diuranate (NHp) ₂ U ₂ O ₇ . ammonium hydroxide does not take place completely due to the complex formation of the uranyl fluoride solution at the stoichiometric ratio. A large excess of ammonium hydroxide is required for the reaction to proceed to completion. A

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Example of the course of the reaction is- in the following formula (1) specified:

2UO ₂ P ₂ + 4HF ■ + 1ONH ₄ - ^ (NH ^) ₂ U ₂ O ₇ + 8NH ₂₁ F + 7H _g 0 (1)

The disadvantage of this course of the reaction is the large excess of ammonium hydroxide required. Another major disadvantage is that the ammonium diuranate precipitate that is formed does not lead to complete precipitation and complete recovery of all of the uranium from the fluoride. These reaction products normally contain 1.5 % to 2.0 % uranium fluoride in the form of a mixed ^{fluoride, in particular:} UOpFp * 3NHhF, which is comparatively easily soluble and thus leads to a loss of uranium in the runoff flow. Such fluoride complexes are extremely difficult to break down for the purpose of separating uranium.

Extensive investigations have shown that the formula (1) reproduces a course of the reaction which does not proceed quantitatively even under ideal conditions. In fact, the reaction of the formula (1) leads to a number of side reactions which proceed so quickly that the HF. does not react completely with the NH ₄ OH. Rather, further reactions between HF,

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UO ₀ P ₀ and NHi ₁ OH, which lead to complex formation, namely to UOpPp · JNHhP. Once these uranium complexes are formed, they go into solution; the relevant original components "-" are lost because they cannot be easily separated, but rather are carried along by the runoff due to their solubility in water.

In addition, the process according to US Pat. No. 2,466,118 requires a concentrated ammonium solution (8 to 15 molar) because the uranium solubility in this fluoride preparation is lowest when the ammonium-uranium ratio is as large as possible. The initial addition of concentrated ammonium hydroxide is sufficient to precipitate a major part of the uranium and also forms an excess of ammonium hydroxide compared to the stoehiometric equilibrium, so that the acidity is neutralized and so that all uranium is precipitated in the absence of fluoride ions. The end product UO ₀ is finely divided and therefore difficult to drain and dry.

The process according to US Pat. No. 3,394,997 requires a large amount of dilute, aqueous ammonium solution, essentially less than 2 molar, to precipitate the ammonium diuranate (NHh) pUpO ~, which in comparatively

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19173SD

is in crystalline and granular form. Even if the end product is vergiehs'weise easy to dehydrate and quickly too dry} it is difficult to sinter. In the course of this procedure there is at least a loss of oil of i % to S fo,

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NH ₁₁ OH below. Low weight conditions for a hydrate ITCu (0Ή) «

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side reactions are likely to occur (e.g. dimerization, hydration, ammonization), which prevents the otherwise desired reaction. Bisiärig korinte in any case in a single step from ¹ ÄmmoniUmdiUrärtät an aqueous Lösung'in stoichiometric VerhMithiä erhälteh werdehi without polymerization

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INSPECTED

19173SÖ

The object of the invention is to create a method; for eirii largely complete recovery of uranium from aqueous' solutions.

Biege Äüfgäfee WiM gettiljS the 'invention thereby solvedj däJ3 in dii hosting a little less than the stSehidniettfisehe Part of the diluted ammonium hydroxide introduced becomes, that only iii with the hydrogen fluoride under. Formation voti Ammonium fluoride reacts, whereas a small proportion of hydrogen fluoride reacts Oiöht is deeply retried and thus an easy one ferment i ^ siirig ffiit aiii iH- ¥ ert of 6.1 - 0.2 conditional} and that on it diluted Äriimohiümnydroxyd with a normal value of less than 3 in a »as much amount as we'dji admitted that · geriügiiid Äm'iöMümioheh Bür reaction iiiit the üraliyifiüörid and the fitiörWäögergtolf at your disposal däthiit Ättiniöiliümii geöiiiet Ütid äliä äeM Eö§tin§ äiisgefMiM Mrdi,

ffli Uli äiis'iä fir'fährlriilbiäTifi riäeli dir ^: Irflnäürife Will dai. Ätiiifeigii vöi! FlÜörid ^ lliMliie ^ eäfetiöäSn hiiC i i liy Mi gieilÜieilii die liiäMfig viE

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ORIQlNAL INSPECTED

so that about 90 % of the HF forms ammonium fluoride. After the equilibrium has been established, more dilute ammonium hydroxide (approximately 1 normal) is added in a second process step so that ammonium diuranate is precipitated essentially quantitatively. The reaction is preferably carried out at about 70 CJ, although it can be carried out at room temperature or lower. The ammonium diuranate reaction is essentially complete and there is hardly any uranium-fluoride complex formation. A large amount per mole of uranium is required in both stages of the process. The ammonium diuranate can easily be separated off and can then easily be reduced to Ürandioxyd in any desired manner.

The invention will now be based on a preferred embodiment with reference to the attached Drawings explained. They represent:

Fig. 1 * a titration diagram for three

different molar concentrations of NHhOH and for three different ones Ratios ΝΗ, / U and

Fig. 2 is a flow chart for the invention

vascular procedures.

ORIGINAL INSPECTED

According to the invention, the process for the recovery of uranium from an aqueous solution with uranyl-fluoride ions requires formed by introducing UPg into water can be two stages. The first stage of the process is based on the formula:

UO ₀ F ₀ + 4NH ,. OH + 4HF- ^ UO ₀ F ₀ + 4NH..F + 4H "Q + HF in a slight ^{22 4 2 2 4} * excess (2;

with an equilibrium pH of about 6.1. According to formula (2), the amount of ammonium hydroxide added to the solution containing uranyl fluoride and hydrogen fluoride is limited to slightly less than the stoichiometric amount of ammonium hydroxide required for reaction with the hydrogen fluoride present. Because it is important that a small amount of HF does not remain neutralized so that the pH of the solution in the equilibrium state is about 6.1 i. Is 0.2.

According to formula (2) only NH ^ OH and HF react _{with one another to form NHj, F and H 0} O, whereas in this process stage the UO ₀ Fp remains essentially unchanged.

Limiting the amount of ammonium hydroxide added and controlling the pH is preferred

Ammonium fluoride formed. The reactivity of the uranium compound within the solution formed is reduced, so that the formation of undesirable complexes such as UOpFp · J-NHji, F is limited. Thus, as in formula (2) shown, essentially all fluoride ions of HF preferentially with the ammonium ions with the formation of ammonium fluoride combined while the uranyl compound to react with the subsequently added, dilute ammonium hydroxide remains free. After the equilibrium has been established the solution obtained is treated with a further addition of dilute ammonium hydroxide, e.g. by adding at least six or more moles per mole of UOpFp, which is far sufficient to neutralize the HF present. the The reaction takes place according to the following formula:

+ 7NHj ₊ OH + HF- * 2UO ₂ (OH) ₂ + 5NH ₂₊ F + 2NHj ₊ OH + 2 ^U 2 ° 7 ⁺

In this formula it is assumed that there is one mole of HF for two moles of UOgF ₂ . The intermediate product then reacts immediately in the form of uranyl hydroxide with the additional ammonium hydroxide to form ammonium diuranate, which precipitates out of the solution. It essentially takes place

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complete precipitation of uranium in the form of ammonium

diuranate, and practically no uranium compound remains in the liquid.

The two-stage process requires a time relationship -If the overall reaction by the addition of Mkoh i ^m excess over the stöchiometrisehen portion that is required for neutralization of HF is carried out in a stage of the reaction is so sudden that the formed NHhF in training of Uranium complexes cannot be prevented before the essential UO ₂ (OH) _{2 is} formed.

Because of the two-step process, less uranium is lost in the runoff in the form of fluoride complexes, which are difficult to separate and prove.

For the success of the process of the invention it is necessary that something less than the stoichiometric Portion of dilute ammonium hydroxide to neutralize the NHhF added during the first reaction stage. The most appropriate molar ratio of NH- ^ to uranium is about 3.5: 1 at a pH of about 6.1 "-0.2. Therefore, for

each mole of uranyl ion in the aqueous solution is about four moles of ammonium hydroxide added. - 10 -

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BATH ORIQINAL

Ji

In Fig. 1, the relationship between the pH and the NHj, OB ^ addition of a milliliter is shown on the basis of studies that die.mit three different molar concentrations (11.8 molar, 7.4 molar, 2.7 molar ) of NH ₂ ^ OH. According to FIG. 1, the point of inflection at which the _{pH value changes the most for each NH 2} , OH addition, lies in each sample at a pH value of about 6.1-0.2, which is the case for every normal value of the NHnOH is reproducible. Therefore, a small amount of HF is left in solution in the first stage so that the pH value remains in the acidic range, namely 6.1-0.2. The three curves in FIG. 1 show the very different effects of adding different concentrations of ammonium hydroxide to uranyl fluoride solutions which each contain 166 g uranium per liter in the form of UO ₂ mp. The critical point of these titration curves occurs at a pH value of around 6. The curve on the left shows that the addition of one milliliter of 11.8 molar NHuOH changes the pH of the solution from about 6.3 to 8. According to the middle curve, 1 milliliter of 7.4 molar NH ^ OH results in a change in the pH value from about 6.3 to 7 * 2. In contrast, the right curve shows that an addition of 2 milliliters of 2.7 molar NH ₂ , OH den. pH changes from 6.1 to 6.3 and that another milliliter brings the pH to 6.6. _{UO 0} (OH) ₀ is formed within a range of the pH value of 6.1 i 0.2. Therefore, conditionally a

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00983571337

ORIGINAL INSPECTED

strong NHhOH causes an excessive rise in the pH value, as a result of which this desired reaction is reduced and an alkaline state occurs in which the undesired UO ₂ P ₂ 'J5NH ^ F complex can form.

An important feature of the invention is that there is no free ammonia in the solution at the end of the first process stage. As a result of the respective. The proportions and concentrations of UOpF ₂ , HF and NHjjF in connection with the critical pH fourth of 6.1-0.2 cannot cause side reactions with undesired uranium complex formation during the subsequent ammonia addition, if this is done carefully. When dilute NH ^ OH is subsequently added, the solution described reacts stoichiometrically in the manner described with the formation of a quantitative ammonium diuranate precipitate from UOpFp. A feature of the invention lies in the combination of the fluoride with the ammonia before the fluoride complex with uranium is formed.

In the second stage (Formula 3) are for each About seven moles of ammonium hydroxide are added to uranyl fluoride moles. The concentration of ammonium hydroxide should not be greater

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than 3N, preference is given to 1-normal ammonium hydroxide. The molar ratio of ammonium to uranium is at least 7: 1 * however, is not more than 10: 1, since there are no advantages with a large excess of ammonia.

It has been shown that the uranium losses in the Discharge flow in the context of the two-stage process according to the invention by a factor of more than 10 smaller than that The best loss values in a known one-step process are where a 7 to 1 ^ -fold excess of ammonium hydroxide versus uranyl fluoride. The method according to the invention thus solves the problem the disadvantage of the known method, namely the disadvantage of the formation of a comparatively stable, water-soluble fluoride complex with uranium, which reduces the uranium loss conditional in the pouring flow. Once these complexes are formed, they are extraordinary difficult to unlock. As a result, the invention enables essentially all of it to be recovered Uranium involved in the reaction. Less ammonium hydroxide is also required in the context of the invention. In addition, the process time is much shorter since no cooking or heating is required.

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The following exemplary embodiment explains the implementation of the invention. According to the flow chart of Fig. 2-. ■ ---.-. a batch of a solution containing 31.6 kg of concentrated NHnOH (24 % NH) was removed from the solution storage tank 10 and mixed with 343 * 0 kg of water from the storage tank 12, so that a 4.21-per - · centige NH ^ OH solution received. A batch of 403.0 kg of solution 16 containing 39.7 kg of UO ₂ F ₂ , 10.3 kg of HF and 353 kg of water was mixed with solution 14 in a mixing vessel 18. These proportions of the NHhOH solution 14 and the uranyl fluoride solution were selected so that, after the equilibrium was reached, a molar ratio between -NH-z and U (ΝΗ -, / U) with the value 3 * 5 and a pH value of 6 , Set 1 - 0.2. At the end of the first process stage, the output stream 20 of the mixing vessel 18 contained 39.7 kg of the original UO ₂ F ₂ , 1.3 kg of HF, 16.7 kg of NH ₂₁ F and 720.0 kg of HgO. ·.

An amount of a solution 22 with proportions of 27.0 kg of NHhOH and 27.0 kg of water and an amount 24 of 712 _a 1 kg of water were mixed, so that 766.2 kg of a 3.52 percent NHhOH solution 26 received. Equal amounts of solution 2β and solution 20 were atomized through nozzles to form a common flow within a precipitation vessel. This atomization provides a control of the

- 14 009835 / 1637.-

The course of the reaction is certain to take place at a pH of about 6.1. A circulating system for the solution with a pump 30 was used in connection with the precipitating vessel 28 so that a quick and complete reaction between the sprayed solutions 26 and 20 could take place. The exit stream 32 of the precipitation vessel 28 contained 40.2 kg. (NH ^) ₂ U ₂ O ₇ (in fine precipitation), 28.6 kg NH ^ F, 11.3 kg NH ₂ ^ OH and 1,464.0 kg HpO. The (NHIi) ₂ UpO ₇ . was completely recovered in a precipitated, crystalline form. The remainder of the stream with NHh ?, NHkOH and HpO was diverted, analysis revealed no soluble uranium in the effluent. In total! ■ 4-2.8 kg NHkOH were used, only 11.3 kg were lost. This is much less than was required by the known technique to recover a corresponding amount of uranium.

The method according to the invention can be carried out with enriched UF / -. For example, 3 * 5 % enriched UF / - can be dissolved in water to form UOpFp and HF, whereupon a reaction with ammonium hydroxide takes place in two stages, as has been explained in detail above.

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Claims (2)

Patent claims: 1. Process for the recovery of uranium in the form of Ammonium diuranate a.us an aqueous solution., The IJr an yl fluor id and contains hydrogen fluoride, characterized in that a little less than the stoichiometric proportion of dilute ammonium hydroxide is introduced into the solution only with the hydrogen fluoride with the formation of ammonium fluoride reacts, whereas a small proportion of hydrogen fluoride is not neutralized and thus a slightly acidic solution with a pH value of 6.1-0.2 conditional, and that diluted thereon Ammonium hydroxide with a normal value less than 3 is added in such an amount that sufficient Ammonium ions to react with the uranyl fluoride and the Hydrogen fluoride are available so that ammonium diuranate is formed and precipitated out of solution. 2. The method according to claim 1, characterized in that in the first preliminary stage for each mole of uranyl ions about 3.5 moles of ammonium hydroxide were added to the aqueous solution will. Method according to claim 1 or 2, characterized in that - 16 - 00 98 35/1637 that in the second stage of the process for every mole of uranyl ions 6 to 10 moles of ammonium hydroxide are added. k. Process according to one of claims \ to 3 *, characterized in that in the second process stage about 7 moles of ammonium hydroxide are added for each mole of uranyl fluoride, - so that the molar ratio of ammonium to uranium is not more than 10: 1 and thus the fluoride residue of the hydrogen fluoride and the Uranyl fluoride reacts with the ammonium ions to form ammonium fluoride and ammonium diuranate without the formation of fluoride-uranium complexes. - 17 - 009835/1637