CA1191696A - Liquid membrane process for uranium recovery - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved emulsion extraction process for recovering uranium from a WPPA feed solution containing uranyl cations wherein the WPPA feed is contacted with a water-in-oil emulsion which extracts and captures the uranium in the emulsion, wherein the improvement comprises adding excess oxidizing agent to the WPPA feed before or during the time that the feed is contacted with the emulsion. This results in both higher levels of uranium extraction and higher concentrations of uranium in the emulsion.

Description

6~6 BACKGROUND OF THE INVENTI_

2 Field of the Invention

3 This invention relates to an improved process

4 for recovering uranium from aqueous solution. More particularly, this process relates to an improved emulsion 6 extraction process for recovering uranium from a WPPA feed 7 solution wherein the improvement comprises adding excess 8 oxidizing agent to the feed. Still more particularly, 9 this invention relates to an improved process for recover-ing uranium from a WPPA feed solution containing uranyl 11 cations, wherein the improvement comprises adding excess 12 oxidizing agent to the feed before or while lt is con-13 tacted with the emulsion extractant.
14 Background of the Disclosure Recovering uranium as a by-product from wet 16 process phosphoric acid is well-known in the art. Phos-17 phate rock is mined primarily to produce a high-phosphate 18 containing fertilizer, the first step of which involves 19 digesting the rock in sulfuric acid to produce a phos-phoric acid solution which is ~nown in the art as wet 21 process phosphoric acid (WPPA). This WPPA contains 22 uranium which can be recovered before the acid is further 23 processed for making fertilizer. This uranium is present 24 in the acid primarily as U022+ cations referred to in the art as uranyl ions, wherein the uranium is in the 26 hexavalent, +6 state. In known processes for recovering 27 uranium from WPPA, the uranium is extracted from the WPPA
28 by contacting the WPPA with an extractant which is an 29 oily, water-immiscible material consisting of a mixture of di-2-ethylhexyl phosphoric acid (D2EHPA) and trioctylphos-31 phine oxide (TOPO) dissolved in an oily, organic liquid 32 such as kerosene. The amount of uranium that the oily 33 extractant can contain is limited by equilibrium condi-3~ tions. This is quite low and is generally less than one gram of uranium per liter of extractantO The uranium 36 enriched extractant is then separated from the WPPA
37 and contacted with an aqueous solution containing a 38 reducing agent such as ferrous ions in an acid such as , ~k, 1 phosphoric acid, to convert the uranium to tetravalent 2 U(IV~ ions. The U(IV) ions are relatively insoluble in 3 and are not re-extracted by the D2EHPA/TOPO-containing 4 oil. This step results in strippin~ the uranium from the oily extractant into the aqueous reducing solution and the 6 aqueous reducing solution is then further processed to 7 recover the uranium. Thus, at least two different extrac-8 tion operations are required. Typical of the prior art g which teaches the recovery of uranium from WPPA by first contacting the acid with an oily extractant containing 11 D2EHPA/TOPO, separating the uranium-enriched extractant 12 from the uranium-reduced feed and then stripping the 13 uranium from the uranium-enriched extractant with an 1~ aqueous reducing solution of ferrous ions in phos~oric acid are U.S. Patents 3,711,591 and 3,737,513, 16 Unfortunately, this well-known and commercially 17 practiced process for recovering uranium from WPPA suffers 18 from many disadvantages, among which is a relatively low 19 extraction efficiency ranging from about 1 to about 7O
Extraction efficiency is defined as the ratio of the 21 uranium concentration in the oily extractant to the 22 uranium concentration remaining in the WPPA feed at extrac-23 tion equilibrium conditions. Low extraction efficiency 24 means that large quantities of expensive D2EHPA/TOPO
extractant must be used and circulated with high concomit-2~ ant losses of expensive reagents. Additionally large, 27 expensive contacting vesseis and settling tanks and pumps 28 are required to handle large amounts of oily extractant.
29 Another drawback of this process is due to the fact that as the temperature increases, the extraction efficiency 31 decreases. For example, a report issued by the Oak Ridge 32 National Laboratories (cf. Solvent Extraction of Uranium 33 from Wet Process Phosphoric _cid, F. J. Hurst, D. J.
34 Crouse and K. B. Brown, Report from Oak Ridge National Laboratory, April, 1969) disclosed that the extraction 36 efficiency decreased from about 7 to about 1 when the 37 extraction temperature increased only from about 20C to 9:~L6~36 1 60C when uranium was extracted from WPPA using a solu-2 tion of 0.2M D2EHPA and 0.5M TOPO in kerosene as the 3 extractant~ At a temperature of 40C the extraction 4 efficiency was 2. As a consequence, commercial processes must either operate at a temperature no higher than about 6 40C or include more extraction stages to maintain a 7 higher efficiency at the higher temperatures. ~he WPPA is 8 produced at a temperature of about 60C which means that 9 the acid must be cooled down to about 40C before being extracted or additional extraction stages must be used to 11 maintain satisfactory extraction efficiency at the higher 12 temperature. ThiS naturally necessitates additional 13 equipMent and the use of considerable amounts of energy to 14 cool the WPPA down to an economically viable extraction temperature~
16 ~t is known to use an emulsion process for 17 recovering uranium from uranium-bearing WPPA streams.
18 This emulsion process comprises contacting a uranium 19 containing WPPA feed with globules of a water-in-oil emulsion comprising microdroplets of an aqueous interior 21 phase dispersed in an oily, continuous exterior phase 22 containing at least one transfer agent for selectively 23 transferring the uranium from the feed into the interior 24 phase of the emulsion wherein the valence of the uranium species is changed, thereby trapping the uranium in the 26 emulsion. The uranium-enriched emulsion is then separated 27 from the feed, the emulsion is broken and the uranium is 28 recovered.
29 In a preferred embodiment of this process, the uranium is present in the WPPA feed as uranyl ion, the 31 exterior phase contains a mixture of D2EHPA and TOPO as 32 selective transfer agen~s for the uranyl ion and the 33 interior phase of the emulsion contains a reducing agent 34 which changes the uranyl to U(IV) ions, thereby trapping the uranium in the interior phase of the emulsion as 36 uranous ions.
37 SUMM~RY OF THE INVENTION
38 It has now been discovered that the liquid 3g membrane emulsion extraction process known in the art is 69~i 1 improved if excess oxidizing agent is added to the uranyl 2 ion-containing WPPA feed before and/or while the feed is 3 contacted with the emu]sion. By excess oxidizing agent is 4 meant oxidlzing agent in an amount greater than that initially added to the WPPA feed, if necessary, in order 6 to insure that all of the uranium in said feed is in the 7 uranyl or hexavalent form and that any iron in the feed is 8 in the ferric or trivalent form.
9 It is known in the art to initially oxidize or add oxidizing agent to t~)e WPPA feed in order to insure 11 that all of the uranium is present therein as uranyl 12 cations before contacting the feed with an extracting 13 agent. In the liquid membrane extraction process, we have 14 discovered that by adding to the feed excess oxidizing agent or oxidizing agent beyond that needed to initially 16 insure that the uranium in the feed is in the hexavalent 17 state, one will obtain greater levels of uranium extrac-18 tion and achieve higher levels of extracted uranium in the 19 emulsion. Thus, this invention is an improvement to a liquid membrane emulsion process for recovering uranium 21 from a WPPA feed containing uranyl cations which comprises 22 the steps of (a) contacting, at a temperature of from 23 between about 30 to 100C, said WPPA feed with a water-in-24 oil emulsion comprising (i) an aqueous interior phase dispersed in (ii) an oily exterior phase immiscible with 26 both said interior phase and said WPPA feed solution, 27 said interior phase comprising an acid solution containing 28 a reducing agent and said exterior phase comprising a 29 surfactant-containing hydrocarbon solution of D2EHPA and TOPO which transfer the uranyl ion from the WPPA solution 31 to the interior phase of the emulsion wherein said uranyl 32 ion is reduced to the tetravalent U(IV) ion to form 33 a uranium-rich emulsion, (b) separating the uranium rich 34 emulsion from the WPPA solution, and (c) recovering the uranium from the emulsion, wherein the improvement com-36 prises adding excess oxidant to the WPPA feed before 37 and/or during contacting the WPPA with the emulsion. In a 38 preferred embodiment the contacting will take place in a 39 plurality of zones.

9~i 2 The total amount of excess oxidant to be 3 added will, of course depend on the feed and emulsion 4 compositions and also on the process conditions. In general, the minimum amount of excess oxidant added 6 to the feed will be that amount stoichiometrically 7 needed to oxidize any U(IV) and ferrous ions that transfer 8 back to the WPP~ feed (due to leakage and/or breakage of 9 the emulsion) to uranyl and ferric ions, respectively.
The so-formed uranyl ions are then reextracted by the 11 emulsion. The exact amount of excess oxidizing agent used 12 will, of course, depend on both the amount of U(IV) and 13 ferrous ion going back into the feed and the amount of 14 uranium it is desired to extract from the WPPA. Any suitable oxidizing agents may be used in the process of 16 this invention. Illustrative, but non-limiting examples 17 of suitable oxidizing agents include chlorates, persul-18 fates and peroxides such as hydrogen peroxide.
19 Contacting of the WPPA feed and emulsion is generally done in a countercurrent manner in a plurality 21 of stages, each stage comprising at least one mixing zone 22 and a settling zone, the mixing zone containing suitable 23 means for mixing the WPPA feed with the emulsion. Illus-24 trative, but non-limiting examples of suitable mixing means includes turbine and propeller mixers, static 26 mixers, wire mesh, ultrasonic vibrations, etc. It is 27 well-known that countercurrent extraction in a plurality 28 of stages results in better extraction efficiency and 29 requires less extracting agent or emulsion than a single stage. It is preferred that each stage contain a plur-31 ality of co-current mixing zones or compartments. Employ-32 ing a plurality of smaller mixing zones in each stage as 33 opposed to a lesser number of larger zones enables one to 34 minimize the size of mixing equipment required to achieve a given amount of extrac~ion as those skilled in the art 36 will know based on the well known continuous-stirred-37 transfer-reactor (CSTR) theory.
38 When the feed and emulsion are contacted in 39 a mixing zone, a small amount of internal aqueous phase "36 1 of the emulsion leaks into the feed due to minor breakage 2 of the emulsion from the mixing shear and rupture caused 3 by internal phase swelling. Internal phase swelling is an osmotic ef~ect resulting from difference ln ion strength across the hydrocarbon membrane of the e~ulsion. Since 6 the internal aqueous phase of the emulsion contains both 7 e~tracted uranium in the tetravalent form and ferrous 8 ion reducing agent, this leakage reduces the overall 9 efficiency of the process by putting uranium back into the feed and by introducing iron into the feed which later 11 requires that more oxidant be used to maintain the uranium 12 in the feed in the hexavalent ~uranyl) form.
13 In a preferred embodiment of this invention, the 14 interior phase of the emulsion will be a phosphoric acid solution containing ferrous ions and the oily, water and 16 feed immiscible exterior phase of the emulsion will be a 17 mixture of D2EHPA/TOPO in an aliphatic hydrocarbon which 18 also contains a surfactant for forming and stabilizing 19 the emulsion. The D2E~IPA/TOPO in the exterior phase transports the U022~ cations from the WPPA feed into 21 the interior phase of the emulsion wherein the uranium is 22 stripped from the D2EHPA/TOPO by the phosphoric acid 23 and reduced to U(IV) ions by the ferrous ions and is 24 thereby trapped in the emulsion.
Essential to the successful operation of the 26 process of this invention is a suitable water-in-oil type 27 of emulsion. It has been discovered that emulsions of the 28 type disclosed in U~S. 3,779,907~ are s~ita~le for use 29 in the process of this invention. These emulsions are referred to liquids include substantially aliphatic 31 hydrocarbons such as kerosene and paraffinic hydrocarbons 32 such as Norpar 13*, SK-100*, Low Odor Paraf~in Solvent 33 (LOPS) and Solvent Neutral 100 (S-lOON) which are avail-34 able from Exxon Chemical Company. It is understood, of course, that the hydrocarbon may contain one or more 36 components selected from the group consisting of other 37 hydrocarbons, halogenated hydrocarbons~ higher oxygenated Trade Mark 1 compounds such as alcohols, ketones, acids and esters as 2 long as the emulsion is stable and the exterior phase is 3 immiscible with both the aqueous feed solution and aqueous ~ interior phase and permits transferring the uraniu~ from the feed to the interior phase of the emulsion. The 6 exterior phase of the emulsion will contain from about 7 60--98 weight % of this hydrocarbon liquid, preferably from 8 about 75-95% and most preferably from about 85-95 weight %.
9 As hereinbefore stated, the oily, water immis-cible external phase of the emulsion will contain one or 11 more oil soluble surfactants for forming and stabilizing 12 the emulsion, but which will not prohibit transfer of the 13 uranium through the exterior phase to the interior phase.
14 Suitable surfactants may be selected from among oil soluble anionic, cationic, and nonionic surfactants.
16 Surfactants that have been found to be particularly 17 suitable for use in the process of this invention include 18 various derivatives of polyisobutylene succinic anhydride 19 (PIBSA) which includes, but is not limited to various polyamine derivatives thereof having the general formula:

22 Rl_____N ~ ~ C - N ,------Y

24 _4 R6 _ x 25 wherein Rl, R2, R3~ R4~ R5~ R6, and R7 and Y are chosen 26 from the group consisting of hydrogen, Cl to C20 alkyl, 27 C6 to C20 aryl, C7 to C20 alkyaryl radicals and substi-28 tuted derivatives thereof; and x is an integer of from 1 29 to 100. R3, R4, R5, R6 and R7 are preferably hydrogen, with x preferably varying from 3 to 20. The substituted 31 derivatives are preferably selec~ed from the group con-32 sisting of oxygen, nitrogen, sulfur, phosphorus and 33 halogen-containing derivatives. Various PIBSA-polyamine 34 compounds that have been found useful in the practice of this invention include those taught in U.S. Patent No.
36 3,172,892. A particular PIBSA polyamine derivative 37 surfactant that has been found to be useful in the 38 process of this invention is one wherein Rl and R2 1 taken together to form an alkyl succinic radical and 2 wherein the surfactant is a compound having the general 3 formula:

4 CH3 ~ CH3`~ H O H O
H -C ~ C-CH2~ - C-C - N-(CH2 -CH2-N)4-C-CH3 CH3 H3 ~m H-C-C ~
7 H o 8 wherein m is an integer generally ranging of about 10-60 g and more preferably 40, thereby giving said preferred polyamine derivative a molecular weight of about 2000.
11 This surfactant will generally comprise from about 0.2 to 12 10 weight % of the exterior phase of the emulsion, prefer-13 ably from about 0.5 to 5 weight % and still more prefer-14 ably from about 1-3 weight %.
~5 As hereinbefore stated, the external phase of 16 the emulsion must contain an agent capable of transferring 17 the uranium from the aqueous feed, through the oily 18 external phase to the interior phase. Transfer agents 19 found suitable for transferring cationic uranium species containing hexavalent uranium (i.e. U022+) through the 21 external phase to the internal phase include a mixture of 22 oil soluble dialkyl esters of phosphoric acid and trialkyl-23 phosphine oxide. In particular, a mixture of di(2-ethyl-24 hexyl~ phosphoric acid (D2EHPA) and trioctylphosphine oxide (TOPO) are preferred for transporting uranyl (UO22~) 26 through the external phase of the emulsion. This mixture 27 will not transfer uranium species wherein uranium exists 28 in the +4 valence U (IV) state. In general, the transfer 29 agent will comprise from between about 1-30 wt. % of the exterior phase of the emulsion, preferably from about 31 2-18 wt. % and most preferably from about 2-6 wt. ~.
32 When the transfer agent comprises a combination of D2EHPA
33 and TOPO they will be in said exterior phase in a molar 34 ratio ranging from about 1/1 to 10/1, preferably from 2/1 to 8/1 and, more preferably from about 2/1 to 7/1 of 36 D2EHpA/Topo.

As hereinbefore stated, the lnterior phase of 2 the emulsion will be an aqueous acid solution containing a 3 reagent capable of changing the valence state of the 4 uranium transferred through the oily, external phase to

5 trap the uranium being removed from the aqueous feed where

6 it is in the +6 valence state. This interior phase will

7 be an aqueous acid solution containing a reducing agent to

8 reduce the uranium to a +4 valence state. There should be g enough reducing agent present in the internal phase to 10 reduce the uranium ion transported therein. Illustrative, 11 but non-limiting examples of suitable reducing agents 12 include acid solutions of ferrous or chromous ions such as 13 an aqueous solution of ferrous sulfate in phosphoric acid 14 wherein the concentration of the ferrous ion ranges from 15 about 8-50 grams per liter, preferably from 10 to 40g/
16 liter and wherein the concentration of the phosphoric acid 17 ranges from about 3-12 moles/liter and more preferably 18 from about 5-8 moles/liter. The following reaction is 19 believed to occur when reducing (UO22+) with acidic 20 ferrous sulfate:

21 2Fe2 + UO2 + 4H+~ 2Fe3+ + U +2H2O
22 It is important that the concentration of phosphoric 23 acid in the internal phase be approximately the same 24 as in the feed in order to avoid excessive swelling and 25 ultimately destruction of the emulsion. As a matter 26 of convenience, the internal phase may be prepared from 27 the WPPA feed by adding iron thereto.
28 The interior phase will comprise from about 29 15-80 volume percent of the emulsion, preferably from 30 30-70 and most preferably from 33-60 volume percent, i.e., 31 the volume ratio of the oily exterior or membrane phase to 32 the aqueous interior phase of the emulsion will range from 33 about 6/1 to 1/9, more preferably from about 2/1 to 1/2, 34 and still more preferably from about 2/1 to 1/1.
The emulsions used in this invention may be 36 prepared by any of the well known methods. Thus, a 6~6 1 solution co~prising the components of the oily exterior 2 phase is mixed with an aqueous solution which will form 3 the interior phase under high shear conditions attained by 4 the use of high speed stirrers, colloid mills, homogen-izers, ultrasonic generators, mixing jets, etc.
6 As mentioned previously, the excess oxidi~ing 7 agent can be added to the WPPA feed before it enters the 8 extraction train, or it may be added in stages throughout g the extraction sequence, or both. Thus, a portion of the excess may be added to the feed before it is contacted 11 with the emulsion, with the remainder added at one or more 12 points along the extraction train. Alternatively it may 13 611 be added to the feed prior to its being contacted 14 with the emulsion or it may all be added to the feed at one or more points of the extraction train.
16 The invention will be more readily understood by 17 reference to the examples set forth below.

19 Example 1 In this example, uranyl ion (UO2++) was labor-21 atory batch extracted from an actual sample of central 22 Florida WPPA comprising a 5.2M solution of H3PO4 con-23 taining 130 ppm of uranium as UO2++. The emulsion used 24 to extract the uranium had the following composition:
25 External phase - 2.91 wt. % D2EHPA, 0.88 wt. % TOPO and 26 5 wt. % of a PIBSA-THAM surfactant of the type disclosed 27 in U.S. Patent No. 4,102,798, (made by reacting 1 mole of 28 PIBSA having a molecular weight of about 1,300 with 1.9 29 moles of tris-hydroxymethyl amino methane) in LOPS:
Interior Phase - a solution of 6M H3PO4 containing 30 g/l -31 of ferrous ion; and the volume ratio of exterior to 32 interior phase was 2/1.
33 The WPPA was filtered through a 1 m cartridge 34 filter to remove the solid gypsum and some organics as solids. The WPPA, 1500 mL, was then added to the resin 36 kettle of 10 cm I.D. fitted with four 1 cm vertical 37 baffles and four evenly spaced marine propellers of 5.1 cm 38 diameter. The temperature was increased to and controlled 1 at 60 ~ 1C with external heating tape and a Thermowatch 2 controller.
3 The liquid membrane emulsion was prepared in a 4 Waring blender at 10,000 ppm for ~ min. using 333 mL of membrane and 167 mL of internal aqueous phase. The 6 emulsion, 125 mL, for a feed to emulsion ratio of 12, 7 was added to the resin kettleO Mixing at 600 rpm was then 8 begun and was t = 0 for measurement of contact time. In

9 the first run, only 0.068 grams of ammonium persulfate oxidant was added to the kettle which was just enough to 11 insure that all of the uranium and iron in the WPPA feed 12 were in the +~ and +3 valence state, respectively. This 13 amount of oxidant was enough to give an initial concentra-14 tion of oxidant in the feed of O.OOlM. For run 2, 0.342 grams of oxidant were added initially tyielded initial 16 conc~ of oxidant of 0.005M) and another 0.342 grams after 17 10 minutes. In run 3, 0.342 grams were added initially, 18 followed by another 0.342 grams after 20 minutes.
19 Samples of the dispersion were taken during agitation through a stopcock in the bottom of the resin 21 kettle at various contact times. These samples were 22 allowed to phase separate and aliquots of the raffinates 23 were analyzed for uranium content. At the completion of 24 extraction, a sample emulsion was coalesced to isolate internal phase for uranium analysis by X-ray fluorescence 2~ spectroscopy.
27 The results of these runs are set forth in Table 28 I and illustrate a significant improvement in extraction 29 efficiency using the process of this invention.

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6~6 1 Example 2 2 In an actual commercial extraction operation, 3 the internal phase of the liquid membrane will contain 4 tetravalent uranium, as U(I~) ion, to a loading in a range of about 6 to 12 g/L. Therefore, extraction oE uranium 6 from the WPPA was done with a preloaded emulsion whose 7 internal phase contained 10 g/L of uranium as U~4. The 8 experimental conditions were the same as in Example 1.
9 The results given in Table II show that no extraction was observed without added oxidant, whereas with added oxidant 11 47% of the uranium was extracted after 25 minutes contact 12 time. These results demonstrate the significant and 13 surprising improvement provided by the addition of 14 oxidant during LM extraction of uranium.

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2 More related to commercial practices, extraction 3 was also carried out in a continuous contacting system conprising one extraction stage which contained five cocurrent, cascading mixing compartments. Each compart-6 ment was a cube of one liter capacity containing a marine 7 propeller mixer. Pretreated WPPA and fresh LM emulsion 8 were fed i~to the first compartment wherein a dispersion 9 of LM emulsion in the continuous WPPA phase was formed by

10 the shear of the marine propeller-stirrer contained

11 in each co~partment. The resultant dispersion cascaded

12 through each successive compartment by overflow after a

13 finite contacting period. Finally, the dispersion over-

14 flowed from the last compartment into a settler to allow

15 disengagement and separation of the loaded LM emulsion

16 from the WPPA raffinate phase.

17 Commercial WPPA was oxidized in polyethylene

18 lined, 55 gal. drums with hydrogen peroxide and pumped

19 through a 1 m polypropylene cartridge inline filter to a

20 3 L vessel. This vessel was a preheater which increased

21 the temperature of the pretreated WPPA to 60-70C. The

22 acid was then fed via a peristaltic pump (all fluids were

23 transferred with peristaltic pumps) to the continuous

24 contacting system described above.
The detailed conditions of the experiments 26 are given in Table III.
27 Samples of raffinate from each mixing compart-28 ment were analyzed for uranium content by inductively 29 coupled ion plasma emission spectroscopy.
AS seen from the results presented in Table III, 31 a similar improvement in extraction of uranium from WPPA
32 was obtained by the addition of oxidant to WPPA feed dur-33 ing extraction. In this case a 2.5M ammonium persulfa~e 34 solution was added to the fourth mixing compartment at a 35 flow rate of 0.2 ml/min. In Run 5, with no added oxidant, 36 the extraction efficiency at 50 min. contact time was 63%, 37 whereas, with added oxidant in Run 6, the extraction 38 efficiency was 68%. This significant improvement was 39 corraborated by the replicate experiment Run 7.

6~

3 Conditions:

4 feed - 30% P205 Central Florida WPPA, [U] - 130 g/g membrane - 3 wt. % surfactantal 2.91 6 wt. ~ DEHPA, 0.88 wt. % TOPO in Norpar-13 7 internal phase - 30 g/L Fe(II) in 6M H3PO4 8 ~/E - 10, M/IR - 2 g mixing rate - 500 rpm, temp. - 60C

U Extraction Efficiency at 11 Run (NH4)2S208 Various Contact Times, Min.b 12 No. M 10 20 30 40 50 14 6 0.005 39 50 57 64 68 7 ~.005 37 52 58 64 68 16 aA PIBSA-polyamine surfactant of the type disclosed 17 in U.S. 3,172,892 made by reacting 1.3 moles of PIBSA
18 of a molecular weight of 1,000 with 1 mole of tetra-19 ethylene pentamine.

b(NH4)2S2Og was added to fourth compartment.

21 CEach 10 min. of contact time represented one mixer 22 compartment.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An emulsion process for recovering uranium from a WPPA feed solution containing uranium ions in the hexavalent form wherein excess oxidizing agent is added to said WPPA solution, said process comprising:
(a) contacting said WPPA feed with a water-in-oil emulsion comprising (i) an aqueous interior phase dispersed in (ii) an oily exterior phase immiscible with both said interior phase and said feed, said interior phase comprising an acid solution containing a reducing agent and said exterior phase comprising a surfactant-containing hydrocarbon solution of D2EHPA and TOPO which transfer the uranyl ion from the WPPA feed to the interior phase of the emulsion wherein said hexavalent uranium ion is reduced to tetravalent uranium ion to form a uranium-rich emulsion.
(b) separating the uranium-rich emulsion from the WPPA feed; and (c) recovering the uranium from the emulsion.

2. The process of claim 1 wherein said interior phase acid solution comprises phosphoric acid and wherein said interior phase comprises from about 15-80 volume percent of said emulsion.

3. The process of claim 2 wherein said phos-phoric acid solution in said interior phase is at a concentration of from 3-12 moles per liter.

4. The process of claim 3 wherein the concen-tration of said phosphoric acid solution in said interior phase is substantially the same as the concentration of phosphoric acid in said WPPA solution.

5. The process of claim 4 wherein said sur-factant is a polyamine derivative of polyisobutylene succinic anhydride and has the general formula:

wherein R1, R2, R3, R4, R5, R6, and R7 and Y are chosen from the group consisting of hydrogen, C1 to C20 alkyl, C6 to C20 aryl, C7 to C20 alkyaryl radicals and substi-tuted derivatives thereof; and x is an integer of from 1 to 100.

6. The process of any of claims 1, 3, or 5 wherein said feed/emulsion contacting is carried out in a plurality of contacting zones.

7. The process of claim 1, 3 or 5 wherein said feed/emulsion contacting is carried out in a plurality of contacting zones and wherein R3 through R7 are hydrogen and x varies from 3 to 20.

8. An improved emulsion process for recovering uranium from a WPPA feed which contains uranyl ions, said process comprising:
(a) contacting, in a plurality of contact-ing zones, said WPPA feed with a water-in-oil emulsion comprising (i) an aqueous interior phase dispersion in (ii) an oily exterior phase immiscible with both said interior phase and said feed t said interior phase compris-ing an acid solution containing a reducing agent and said exterior phase comprising a nonionic surfactant-containing hydrocarbon solution of D2EHPA and TOPO which transfer the uranyl ion from the WPPA solution to the interior phase of the emulsion wherein said uranyl ion is reduced to U(IV) ion to form a uranium-rich emulsion, (b) separating the uranium-rich emulsion from the WPPA solution, and (c) recovering the uranium from the emul-sion;

wherein the improvement comprises adding excess oxidant to the WPPA solution.

9. The process of claim 8 wherein said excess oxidizing agent is added to said feed prior to its con-tacting said emulsion.

10. The process of claim 8 wherein said feed is sequentially contacted with said emulsion in a plurality of contacting stages or zones and said oxidizing agent is added to said feed after it has initially contacted said emulsion.

11. The process of claim 10 wherein a portion of said excess oxidizing agent is added to said feed prior to its being contacted with said emulsion.

12. The process of any of claims 9, 10 or 11 wherein said surfactant is a polyamine derivative of PIPSA.

13. The process of claim 9, 10 or 11 wherein said surfactant is a polyamine derivative of PIPSA and the concentration of the phosphoric acid in said interior phase is about the same as the con-centration of phosphoric acid in the WPPA feed solution.

14. The process of claim 9, 10 or 11 wherein said surfactant is a polyamine derivative of PIPSA and said interior phase is pre-pared from said WPPA feed solution, with the concentration of the phosphoric acid in said interior phase being about the same as the concentration of phosphoric acid in the WPPA feed solution.