GB1596410A

GB1596410A - Liquid membranes and process for uranium recovery therewith

Info

Publication number: GB1596410A
Application number: GB50901/77A
Authority: GB
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1976-12-27
Filing date: 1977-12-07
Publication date: 1981-08-26
Also published as: BE862084A; JPS5382661A; ZA777333B; JPS613293B2; IT1090367B; DE2758546A1; FR2374931B1; CA1103227A; FR2374931A1

Description

(54) LIQUID MEMBRANES AND PROCESS FOR URANIUM RECOVERY THEREWITH (71) We, EXXON RESEARCH AND ENGINEERING COMPANY, a Corporation duly organised and existing under the laws of the State of Delaware, United States of America, of Linden, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to liquid membrane systems which are water-in-oil type emulsions dispersed in water. They are capable of efficiently extracting uraniumcontaining ions from wet process phosphoric acid at a temperature in the range of about 25 to about 80"C, which emulsion comprises an aqueous interior phase surrounded by a surfactant-containing exterior phase. The exterior phase is immiscible with the aqueous solutions of uranium-containing ions e.g. wet process phosphoric acid, and the interior phase. The exterior phase is permeable to the uranium-containing ions and comprises a transfer agent capable of transporting selectively the desired uranium-containing ions and a solvent for the transfer agent.

The interior phase comprises reactants capable of removing the uraniumcontaining ion from the transfer agent of the exterior phase and changing the values of the uranium and converting the uranium-containing ions into a nonpermeable form.

Phosphate rock is converted to phosphoric acid by reaction with sulfuric acid.

The phosphoric acid created by this process is referred to as Wet Process Phosphoric Acid or WPPA. The reaction with sulfuric acid simultaneously solubilizes the uranium present in the phosphate rock. The concentration of the uranium present in the phosphate rock ranges from about 100--200 ppm. The current processes for recovery of the uranium-containing ions present in the WPPA involve a two-step, multistage procedure. In the first step, the uraniumcontaining ions, primarily UO2++, is removed from the WPPA by an extractant. In the second step, the uranium-containing species is then separated from the extractant by a stripping agent. (cf. Solvent Extraction of Uranium from Wet Process Phosphoric Acid. F. J. Hurst, D. J. Crouse, and K. B. Brown, Report from Oak Ridge National Laboratory, April, 1969).

A number of problems exist in these current processes. One such problem is caused by phase separation. Kerosene, the solvent normally utilized in these processes, will not fully separate from the phosphoric acid phase resulting in an incomplete uranium recovery. In addition, the extractant efficiency of these processes is relatively low. (This efficiency is measured by the amount of uraniumcontaining ions in the extraction component vs. the amount of uranium-containing ions in the aqueous feed phase). Finally, the phosphoric acid, resultant from the reaction of the phosphate rock with the sulfuric acid, must be cooled down to at least 40"C before the uranium-containing ions may be extracted by this process, since the current processes lose their operating efficiency above this temperature.

For example, in the report from the Oak Ridge National Laboratories cited above, it was found that the solvent extraction of uranium from WPPA using a combination of 0.2M di(2-ethylhexyl)phosphoric acid and 0.05 trioctylphosphine oxide was adversely affected by a temperature increase. The extraction efficiency decreased from about 7 to 1 as the temperature was increased from 20 to 60"C.

Further, there was a 50% decrease in efficiency (i.e. from 2.0 to 1.0) as the temperature was increased from 40 to 600 C.

In U.S. Pat. No. 3,779,907, liquid membranes utilizing certain liquid ion exchange compounds are disclosed. It is not disclosed, however, that this type of liquid membrane composition retains a high extraction efficiency at a temperature where the liquid ion exchange compound itself has lost extraction efficiency when utilized outside the liquid membrane environment.

It has now been unexpectedly discovered that water-in-oil type emulsions comprising a surfactant-containing exterior phase, which exterior phase contains a transfer agent that selectively transports uranium-containing ions and an interior phase comprising components that require the uranium-containing ions from the transfer agent and change the values of the uranium in said uranium-containing ions to a second valency state and convert these uranium-containing ions into a nonpermeable form, are especially effective in removing these uranium-containing ions from WPPA. The liquid membrane compositions of the present invention solve the above problems experienced by the prior art. These emulsion compositions eliminate the phase separation difficulties of the prior art. In addition, where the extractant efficiencies of the prior art's processes were about 2-3, the extractant efficiency of the present invention ranges from about 50 to 1000. Finally, there is no need to cool down the phosphoric acid resultant from the reaction of phosphate rock with sulfuric acid. Where current processes cannot operate efficiently, e.g. at temperatures in the range of about 55--80"C, the compositions of the present invention efficiently remove uranium-containing ions from Wet Process Phosphoric Acid.

The exterior phase of the emulsion will comprise one or more surfactants, a transfer agent and a solvent. The exterior phase is designed to be immiscible with both the aqueous solution of WPPA and the aqueous interior phase of the emulsion. The exterior phase is permeable to the uranium-containing ions which results from the formation of the phosphoric acid from the phosphoric rock.

The transfer agent of the emulsion's exterior phase may be a liquid ion exchange compound for transferring uranium-containing ions. The liquid ion exchange compounds exhibiting this characteristic are trioctylphosphine oxide (TOPO); dialkyl esters of phosphoric acid of the general formula:

wherein R is an alkyl group from C4-C10 inclusive and the chemical composition is soluble in oil such as dif2-ethylhexyl)phosphoric acid (D2EHPA); mono-alkyl esters of phosphoric acid of the general formula

wherein R is an alkyl group from C4-C10 inclusive and the chemical composition is oil soluble such as monodecylphosphoric acid. These liquid ion exchange compounds may be utilized either separately or in conjunction with one another as constituents of the extraction component of the present invention.

The ion exchange compounds described above are selective to the most abundant uranium-containing ions resulting from the WPPA process. Those expert in the art believe that this uranium-containing ions has the formula UO2++. Further, to ensure that most of the uranium in WPPA exists in the U+6 state, i.e. as UO2++, an oxidizing agent should be added to the WPPA feed solution, e.g. NaCIO3.

However, it is not intended to be limited to the particular uranium-containing ion named in this specification. The WPPA process conducted in a phosphoric acid medium may also contain an anionic uranium-containing ions such as [UO2PO41- and the chemical analogues of this compound. To remove it from the WPPA solution, the WPPA should be contacted with a separate emulsion containing transfer agent selective for the transfer of such anionic uranium-containing ions, a transfer agent selective for the transfer of such anionic uranium-containing ions, expert in the art, such amine-containing liquid ion exchange compounds include primary amine-containing liquid ion exchange compounds (e.g. Primene), tertiary amine-containing liquid ion exchange compounds (e.g. Alamine), and quaternary amine liquid ion exchange compounds (e.g. Aliquat). (The word 'Primene' is a registered Trade Mark). Those skilled in the art can select other liquid ion exchange compounds selective for the removal of such anionic uranium-containing ions. It should be further noted that if WPPA is subjected to a reducing medium before the transfer of the uranium-containing species, a different form of uranium ion will be present in the WPPA from those described above. Those expert in the art believe that the form of uranium existing under such conditions is U+4.

Consequently when the WPPA is subjected to such a reducing medium, the transfer agent of the present invention should comprise compounds selective to the removal of U+4 from the WPPA. Octylphenylphosphoric acid (OPPA) is such a compound. This compound, however, is not selective for the removal of UO2++ The extraction component of the present invention will usually comprise from 3 to 30 O by weight of the exterior phase of the emulsion, preferably from 520%, and most preferably from 1W16 ' by weight.

In a preferred embodiment the transfer agent comprises from 1018% by weight of the exterior phase, preferably from 1216%, with the extraction component comprising a combination of di(2-ethylhexyl)phosphoric acid (D2EHPA) and trioctylphosphine oxide (TOPO) in the molar ratio of 1/6 to 6/1, preferably 2/1 to 5/1 D2EHPA/TOPO.

As noted above, the exterior phase also includes a surfactant component.

Since the present invention contemplates water-in-oil type emulsions, the surfactants utilized in the present invention must promote the formation of this type of emulsion. The surfactants utilized will be of the oil-soluble type. In general, the surfactants must have low solubility in both the aqueous feed solution and the interior phase of the emulsion. In addition, the surfactant preferably promotes the permeability of the uranium-containing ions of interest through the membrane.

Finally, and most important, the surfactants utilized in the present invention should be chosen to achieve a proper balance of emulsion stability and the rate of ion transfer across the membrane.

Specific surfactants which may be used include anionic, cationic, or nonionic surfactants.

The following anionic surfactants may be utilized in the present invention: Carboxylic acids, including fatty acids, rosin acids, tall oil acids, branched alkanoic acids, etc.

Sulfuric acid esters, including alcohol sulfates, olefin sulfates, etc.

Alkane and alkaryl sulfonates, including alkyl benzene sulfonates, alkyl naphthalene sulfonates, etc.

Phosphoric acid esters, including mono and dialkyl phosphates.

The following cationic surfactants may be used in the present invention: Quaternary amine salts.

Nonionic surfactants are the preferred surfactant type for the practice of the present invention. A useful group of nonionic surfactants include polyethenoxyether derivatives of alkyl phenols, alkylmercaptans and alcohols, e.g.

sorbitol, pentaerythritol, etc.

Particular nonionic surfactants for use in the present process include compounds having the general formula:

wherein R10 may be C8H17, CgH19 or C1oH2l and m is an integer varying from 1.5 to 8.

A preferred nonionic surfactant is Span 80, a fatty acid ester of anhydro sorbitol condensed with ethylene oxide. (The word 'Span' is a registered Trade Mark).

Various polyamine derivatives also are useful as surfactants within the scope of the present invention. The preferred polyamine derivatives are those having the general formula:

wherein R1, R2, R3, R4, R5, R6, R7 and Y are hydrogen, C1 to C20 alkyl, C6 to C20 aryl, C7 to C20 alkaryl radicals or substituted derivatives thereof; and x is an integer of from 1 to 100. More preferably R3, R4, R5, R8 and R7 are hydrogen, and x varies from 3 to 20.

The substituted derivatives previously mentioned are preferably oxygen, nitrogen, sulfur, phosphorus or halogen-containing derivatives.

In the most preferred polyamine derivative, R1 and R2 together form an alkyl succinic radical having the general formula

wherein n varies from 10 to 60, x varies from 3 to 10, R2, R4, R5, R6 and R7 are hydrogen, and y is hydrogen or oxygen-containing hydrocarbyl radicals having up to 10 carbons, e.g. acetyl, etc.

Short-chain fluorocarbons with polar groups are frequently soluble in hydrocarbon oils to function as surfactants. Long-chain fluorocarbons attached to a hydrocarbon chain of sufficient length are soluble in hydrocarbon oils.

The above surfactants can be utilized either alternatively or in conjunction with one another.

The most preferred surfactant component of the present invention comprises a compound having the formula

where m is an integer of about 40, giving said polyamine derivative a molecular weight of about 2,000. This polyamine derivative is referred to as ENJ-3029 and is available from Exxon Chemical Company.

Since those skilled in the art can select other surfactants that fulfill the requirements of the surfactant component in the present invention, these examples are presented solely as illustrations of the component and not limitations to the present invention. The following publications may be referred to for further examples: Surface Chemistry by Lloyd I. Osipow, Reinhold Publishing Company, New York (1962) Chapter 8; and Surface Activity, Moilliet et al, Van Nostrand Company, Inc. (1961) Part III.

The surfactant component of the present invention usually comprises from 0.2 to 10% by weight of the exterior phase of the emulsion, preferably from 0.5 to 5 , and most preferably from 2 to 5%.

In addition to the extraction and surfactant components, the exterior phase will also contain a water-immiscible solvent. The solvent must be liquid at the conditions under which the emulsion is used, and also must be capable, in conjunction with the surfactant component, of forming a stable water-in-oil emulsion with the aqueous interior phase. The solvent may be a hydrocarbon, a halogenated hydrocarbon, an ether, or a higher oxygenated compound such as an alcohol, a ketone, an acid or an ester. Preferably, the solvent is a hydrocarbon exhibiting the above-specified characteristics. In a preferred embodiment, an isoparaffinic hydrocarbon, such as Solvent Neutral 100, is utilized as the solvent component in the exterior phase. Solvent Neutral 100 (S-lOON) is an iso-paraffinic hydrocarbon lubricating oil available from Exxon Chemical Company. S-100N is characterized as having a viscosity of 100 SUS at 1000 F.

The solvent component of the present invention usually comprises from 60 to 96.8go by weight of the exterior phase of the emulsion, preferably from 7594.5%, and most preferably from 7988% by weight.

The aqueous interior phase of the present invention comprises a reactant capable of changing the valency of uranium, in the uranium-containing ions and converting the uranium-containing ions into a nonpermeable form, i.e. one that will not permeate out of the interior phase. This reactant should also exhibit limited permeability into the exterior phase, as well as limited reactivity with the components of the exterior phase and convert the particular uranium-carrying ions (e.g. UO2'+ or U+4 or [UO2PO4]-, etc.).

Examples of valency changing agents capable of converting the "stripped" UO2++ into a nonpermeable form are also well known in the art. For example, when the UO2++ is removed from the transfer agent in an acidic medium, i.e. when a valency changing agent such as phosphoric acid is utilized, a reducing agent can be selected from any composition capable of reducing the UO2++ ion to U+4 in this acidic medium. Examples of such reducing agents include a source of Fe++ or CR++ ions and VO2. It should be further noted that a catalyst may be added as a component in the interior phase to facilitate the above-described reduction reaction.

Certain components utilized for the removal of UO2++ may also function as valency changing components for UO2++. These include calcium carbonate, sodium carbonate, ammonium carbonate and hydrogen fluoride.

Suitable examples of agents that may be utilized in the removal of what is believed by those skilled in the art to be [UO2PO41- and its chemical analogues include carbonate, nitrate and chloride solutions in the presence of an acid catalyst. The carbonate component, nitrate component or chloride component in the presence of an acid catalyst will both remove and convert the uraniumcontaining ions in the interior phase. Thus, when such components are utilized, there is no need to include additional components in the interior phase.

Other suitable examples whicn oxidise the uranium-containing ion, e.g. U+4 to UO2++ are sulphuric acid, hydrochloric acid or phosphoric acid. Solutions of oxidizing agents, including sodium chlorate as well as various peroxide compositions.

The concentration of the valency changing agents in the aqueous interior phase used in the present invention is limited primarily by their solubility in the aqueous interior phase. Specific embodiments describing concentration limitations of particular components of the interior phase are given below to illustrate this general principle.

In the removal of UO2++ from an aqueous feed solution, an acid, e.g. sulfuric acid, hydrochloric acid or phosphoric acid, can range in concentration from 5-12, e.g. 5 to 8 moles/litre. The concentration of the reducing agent, which is used in conjunction with the acid is dependent upon its solubility in the interior phase of the emulsion. If FeCI2 is used, for example, its concentration would range from 835 g/litre, preferably from 1-25 litre, and most preferably from 14-20 g/litre.

When a carbonate composition is utilized in the interior phase in the removal of UO2++ from an aqueous feed solution, the concentration of said carbonate composition ranges from about 1-10 moles/litre, preferably from about 2-5 moles/litre.

In the removal of [UO2PO4]- and its chemical analogs from an aqueous feed solution, the valency changing agent comprising a carbonate, chloride or nitrate solution can range in concentration from 1 to 10 moles/litre, preferably from about 3 to 5 moles/litre. The pH of the carbonate, chloride or nitrate solution should range from 1--5.

When an acidic composition, e.g. sulfuric acid, hydrochloric acid or phosphoric acid, is utilized in the interior phase in the removal of U+4 from an aqueous feed solution, its concentration can range from 10--15 moles/litre, preferably from 12 to 14 moles/liter. The oxidizing agent, which is utilized in the interior phase in conjunction with the acidic stripping agent, again ranges in concentration according to its solubility in the emulsion's interior phase. For example, if NaClO3 is used, its concentration ranges from 1--10 g/litre of the interior phase, preferably from 3-6 g/litre.

The interior phase usually comprises from about 1580% by volume of the emulsion, preferably from 3070%, and most preferably from 40--604, by weight.

The weight ratio of exterior phase/interior phase (M/R) usually ranges from about 1/6 to 6/1, preferably from about 1/2 to 2/1.

The emulsions of the invention may be prepared by various methods. The interior phase of the emulsion containing the valency changing agent is emulsified with the components of the exterior phase of the emulsion in the concentration ranges specified above by the use of high speed stirrers, colloid mills, valve homogenizers, ultrasonic generators or mixing jets.

The emulsions may be contacted with the aqueous stream containing the WPPA by agitating a mixture of the emulsion and the aqueous stream together in a batch process; cocurrent contacting in a continuous flow reactor; counter-current contacting by bubbling said aqueous stream through a column containing said emulsion, or vice versa. In all of these procedures a difference in density between said aqueous stream and said emulsion is maintained in order to permit separation of the emulsion and the aqueous stream after contact. The weight ratio of the emulsion/feed solution (E/F) ranges from about 1/1 to 1/10, preferably from about 1/3 to 1/5.

Although it is not intended to be bound by theory, it is believed that when the emulsion is contacted with the aqueous feed solution which contains the uraniumcontaining ions, the uranium-containing ions permeates through the "liquid membrane" of this emulsion, i.e. into the exterior phase of the emulsion, where the transfer agent "attaches" to it and "carries" it through to the interior phase. There the uranium-containing ions are removed from the transfer agent and converted to a different valancy and into a form that will not permeate out of the interior phase of the emulsion. The transfer agent recycles into the exterior phase where it may again perform its function. Due to this recycling of the transfer agent, i.e. by removing the uranium-containing ions from it, the transfer efficiency of the invention ranges from about 90% to 99.9%.

The emulsion is then separated from the aqueous solution containing the WPPA, which is now depleted in the uranium-containing ions, and optionally the emulsion is cycled to a recovery area, where it may be regenerated. For example.

the emulsion may be broken, the surfactant, solvent and transfer agent reused for making a fresh emulsion, and the valency-changing agent regenerated for reuse.

The removal of the uranium-containing ions from the WPPA solution may be efficiently performed at any temperature in the range of 25 to 800 C, preferably from 40 to 70"C, most preferably from about 55 to 65"C. This removal may also be performed at any pressure at which the emulsion and the feed solution are fluid and stable. For convenience ambient pressures are used in the Examples.

The following Examples are submitted to illustrate and not to limit the invention.

Example 1 In the following runs Us2++ was removed from the WPPA solution using an emulsion of the following composition: Exterior phase=0.18M D2EHPA, 0.05M TOPO, 5 wt % ENJ-3029 (surfactant), 80% of Solvent Neutral 100: Interior phase=5M H3PO4 plus 2 wt % FeCI2. The above-identified components of the emulsion's interior and exterior phase were emulsified and then contacted with the WPPA solution. This emulsification and contacting were performed in a separation zone provided with a mixer. These runs were conducted at room temperature (approximately 20"C) and at one atmosphere pressure. The emulsion-to-feed ratio, E/F, was 1/2. The membrane- (i.e. exterior phase)-to-interior phase reagent ratio was 2/1 by weight. In these test runs the same emulsion was reused each time with just fresh feed added. All the uranium analyses were done by X-ray. The separation results are summarized in Table I.

TABLE I Separation Results" U charged (ppm) Mixing U in Feed U in Emulsion This cycle Total Time (ppm) ppm g E Cycle 1 200 200 0 200 0 0 15 1 100(2) 0 0.03'2" 100 Cycle 2 1000 1200 0 1000 100 15 2 800(2) 0.3'2' 400 Cycle 3 1000 2200 0 1000 1000 15 - 2 Cycle 5 1000 4200 0 1000 3200 15 100 4100'3' 1.5'3' 36 Cycle 7 1000 6200 0 1000 5000'3 > 15 42 6000(3' 2.1'3' 150 Estimated capacity of system: > l5 g/l of internal phase of emulsion.

(1) Same emulsion reused each time: fresh feed added; all analyses by X-ray; uranium as UO2+2 (2) Could not be determined accurately; probably a minimum value (3) Estimated by difference After 15 minutes of mixing in each run, a drastic reduction occurred in the amount of uranium present in the feed. The estimated capacity of the system was greater than 15 grams of U/liter of interior phase. The extractant efficiencies of these runs ranged from 36400.

Table II presents a direct comparison between a commonly used uranium extraction method of the prior art and that of the present invention. The solvent extraction data representing the prior art is taken from data presented in a report made by the Oak Ridge National Laboratory titled Solvent Extraction of Uranium from Wet Process Phosphoric Acid, by F. J. Hurst, D. J. Crouse, and K. B. Brown, April, 1969.

The transfer agent utilized in the solvent extraction runs of the prior art comprised D2EHPA and TOPO in the amounts specified in Table II. The solvent used in the solvent extraction runs was n-dodecane. The composition of the liquid membrane used was the following: Exterior phase: the amount of D2EHPA and TOPO specified in Table II, 5% ENJ-3029 (Surfactant), and the balance was Solvent Neutral 100; Interior phase: SMH3PO4 plus 12 grams/liter Fe++.

The liquid membrane was made and contacted with the WPPA solution as described in Example 1. All the uranium analyses for the liquid membrane extractions were done by X-ray.

The Oak Ridge Solvent extraction was conducted as follows: the solvent, here n-dodecane, containing the amount of D2EHPA and TOPO Specified in Table II was added to the WPPA solution and mixed with rapid stirring. The mixing was stopped and the phases were separated after settling. This solvent extraction was performed three times for each run. All three solvent extraction phases resulting from a particular run were combined and tested for uranium content by fluorophotometric techniques.

All runs, both for the solvent extraction and liquid membrane, were performed at 40"C and ambient pressure. The results are summarized below.

TABLE II Comparison Of Uranium Extraction Performed By Solvent Extraction And The Liquid Membrane Compositions Of The Invention Acid Strength of H3PO4 Solvent Liquid Extractant in WPPA(M) (1) Extraction Membrane E E 0.36M D2EHPA/ 0.09M TOPO 0.1 - 800 0.18M D2EHPA/ 0.05M TOPO 1--2 150 400 0.18M D2EHPA/ 0.05M TOPO 3 12 1000 (1) Pure H3PO4 U concentration in Organic phase E = U concentration in Feed at Equilibrium As can be seen from Table II, the extraction efficiencies achieved by the liquid membrane compositions of the present invention are much greater, even as much as 800 times greater than three solvent extractions utilizing the identical liquid ion exchange component.

Example 2 In the following runs UO2++ was removed from an actual WPPA solution obtained from Red Water, Canada, at varying temperatures using an emulsion of the following composition: Exteriorphase:=0.50M D2EHPA, 0.12M TOPO, 5 wt % ENJ-3029 (Surfactant); the balance was Solvent Neutral-100; Interior phase H3PO4 plus 12 grams/liter Fe++. The above-identified components of the emulsion's interior and exterior phase were emulsified and contacted with the WPPA solution as in Example 1. These runs were performed at one atmosphere pressure. The concentration of the uranium in the actual WPPA was 197 ppm. Also sufficient NaClO3 (0.1 g/liter) was added to WPPA to ensure that all the uranium present would exist in the U+6 state. The membrane-to-interior phase reagent ratio was 2/1 by weight. The emulsion-to-feed ratio, E/F, was 1/1. The results of the runs are summarised in Table III.

TABLE III Effect Of Temperature On The Extraction Of Uranium From WPPA Utilizing A Liquid Membrane Composition Of The Invention Mixing Time % Uranium Temperature (Minutes) Extracted 25"C 2 10 75 20 88 40 92 40"C 2 58 5 83 10 90 20 90 60"C 2 75 5 95 10 95 20 95 Unlike the process of the prior art, a temperature increase in the WPPA solution increases the efficiency of the uranium removal, not decreases it. In fact, at 60"C, the temperature at which WPPA is normally encountered, 95% of the uranium was extracted in 5 minutes, while it took four times longer to extract 90% at 40"C. The process of the present invention is clearly superior to those of the prior art which require cooling the 60"C WPPA to about 40"C in order for these prior art processes to function efficiently. Highly efficient operability at a higher temperature and elimination of a cooling step clearly demonstrate the superiority of the present invention over the prior art.

WHAT WE CLAIM IS: 1. A water-in-oil emulsion capable of extracting uranium-containing ions from an aqueous feed solution containing uranium ions at a temperature in the range of 25"C to 800 C, which emulsion comprises an aqueous interior phase surrounded by a surfactant-containing exterior phase, said exterior phase being immiscible with the interior phase and comprising a transfer agent capable of transporting selectively the desired uranium-containing ions and a solvent for said transfer agent, said interior phase comprising a reactant capable of removing uraniumcontaining ions from the transfer agent and capable of changing the valency of uranium in said uranium-containing ions to a second valency state and converting said uranium-containing ions into a nonpermeable form.

2. An emulsion according to claim 1 wherein said aqueous interior phase ranges from 15 to 80 volume % of said emulsion, the balance being exterior phase.

3. An emulsion according to either of claims 1 and 2 wherein said exterior phase comprises 3 to 30% by weight of said transfer agent, 0.2 to 10% by weight of said surfactant and 60 to 96.8% by weight of said solvent.

4. An emulsion according to any one of the preceding claims wherein said desired uranium-containing ion is UO2++, and said transfer agent comprises trioctylphosphine oxide, an oil-soluble dialkyl ester of phosphoric acid of the general formula

wherein R is an alkyl group of from C4-C10 inclusive of an oil-soluble mono-alkyl ester of phosphoric acid of the general formula

wherein R is an alkyl group of from C4-C10 inclusive.

5. An emulsion according to claim 4 wherein the amount of said transfer agent is from 10 to 18% by weight of said exterior phase and said transfer agent comprises a combination of di(2-ethylhexyl)phosphoric acid (D2EHPA) and trioctylphosphine oxide (TOPO) in the molar ratio of 1/6 to 6/1, D2EHPA/TOPO.

6. An emulsion according to any one of the preceding claims wherein said interior phase comprises a solution of ferrous chloride in phosphoric acid.

7. An emulsion according to claim 6 wherein said interior phase comprises H3PO4 in a molar concentration ranging from 5 to 8 moles/litre and FeCI2 ranging in concentration from 8 to 25 litre 8. An emulsion according to any one of claims 1 to 3 wherein said transfer agent comprises a mixture of dialkyl phosphoric acid and a trialkylphosphine oxide.

9. An emulsion according to claim 8 wherein said transfer agent is a mixture of di(2-ethylhexyl)phosphoric acid and trioctylphosphine oxide.

10. An emulsion according to any one of the preceding claims wherein said surfactant has the general formula:

wherein m is an integer of about 40.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. at 40"C. The process of the present invention is clearly superior to those of the prior art which require cooling the 60"C WPPA to about 40"C in order for these prior art processes to function efficiently. Highly efficient operability at a higher temperature and elimination of a cooling step clearly demonstrate the superiority of the present invention over the prior art. WHAT WE CLAIM IS:

1. A water-in-oil emulsion capable of extracting uranium-containing ions from an aqueous feed solution containing uranium ions at a temperature in the range of 25"C to 800 C, which emulsion comprises an aqueous interior phase surrounded by a surfactant-containing exterior phase, said exterior phase being immiscible with the interior phase and comprising a transfer agent capable of transporting selectively the desired uranium-containing ions and a solvent for said transfer agent, said interior phase comprising a reactant capable of removing uraniumcontaining ions from the transfer agent and capable of changing the valency of uranium in said uranium-containing ions to a second valency state and converting said uranium-containing ions into a nonpermeable form.

wherein R is an alkyl group of from C4-C10 inclusive.

7. An emulsion according to claim 6 wherein said interior phase comprises H3PO4 in a molar concentration ranging from 5 to 8 moles/litre and FeCI2 ranging in concentration from 8 to 25 litre

8. An emulsion according to any one of claims 1 to 3 wherein said transfer agent comprises a mixture of dialkyl phosphoric acid and a trialkylphosphine oxide.

wherein m is an integer of about 40.

11. An emulsion according to any one of the preceding claims wherein said

solvent in said exterior phase is a hydrocarbon.

12. A process for the extraction of uranium-containing ions from an aqueous solution comprising uranium-containing ions which comprises contacting said solution with an emulsion according to any one of the preceding claims, whereby said uranium-containing ions permeate into said exterior phase, are carried through said exterior phase by said transfer agent, undergo valency change and are converted into said nonpermeable form and said exterior phase is immiscible with said aqueous solution.

13. A process according to claim 12 wherein said aqueous solution comprising uranium-containing ions is wet process phosphoric acid (WPPA).

14. A process according to claim 13 wherein the uranium ions are in a +6 valency state.

15. A process according to any one of claims 12 to 14 wherein said contacting takes place at a temperature ranging from 250C to 800 C.

16. A process according to claim 15 wherein said temperature ranges from 55"C to 65"C.

17. An emulsion according to claim 1 substantially as hereinbefore described with reference to the Examples.

18. A process for the extraction of uranium-containing ions from WPPA according to claim 13 substantially as hereinbefore described with reference to the Examples.

19. Uranium ions whenever extracted by the process according to any one of claims 12 to 16 and 18.