EP0064877B1 - Procédé avec membranes liquides pour la récupération de l'uranium - Google Patents

Procédé avec membranes liquides pour la récupération de l'uranium Download PDF

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Publication number
EP0064877B1
EP0064877B1 EP82302373A EP82302373A EP0064877B1 EP 0064877 B1 EP0064877 B1 EP 0064877B1 EP 82302373 A EP82302373 A EP 82302373A EP 82302373 A EP82302373 A EP 82302373A EP 0064877 B1 EP0064877 B1 EP 0064877B1
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Prior art keywords
uranium
emulsion
feed
wppa
phase
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German (de)
English (en)
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EP0064877A1 (fr
Inventor
Robert Paul Cahn
Paul Louis Valint, Jr.
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ExxonMobil Technology and Engineering Co
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Exxon Research and Engineering Co
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
    • C22B60/02—Obtaining thorium, uranium, or other actinides
    • C22B60/0204—Obtaining thorium, uranium, or other actinides obtaining uranium
    • C22B60/0217—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes
    • C22B60/0252—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes treatment or purification of solutions or of liquors or of slurries
    • C22B60/026—Obtaining thorium, uranium, or other actinides obtaining uranium by wet processes treatment or purification of solutions or of liquors or of slurries liquid-liquid extraction with or without dissolution in organic solvents

Definitions

  • This invention relates to a process for recovering uranium from aqueous solution. More particularly, this process relates to an improved emulsion extraction process for recovering uranium from a WPPA feed solution which comprises adding excess oxidizing agent to the feed. Still more particularly, this invention relates to an improved process for recovering uranium from a WPPA feed solution containing uranyl cations which comprises adding excess oxidizing agent to the feed before or while it is contacted with the emulsion extractant.
  • WPPA wet process phosphoric acid
  • the uranium is extracted from the WPPA by contacting the WPPA with an extractant which is an oily, water-immiscible material consisting of a mixture of di-2-ethylhexyl phosphoric acid (D2EHPA) and trioctylphosphine oxide (TOPO) dissolved in an oily, organic liquid such as' kerosene.
  • D2EHPA di-2-ethylhexyl phosphoric acid
  • TOPO trioctylphosphine oxide
  • the amount of uranium that the oily extractant can contain is limited by equilibrium conditions. This is quite low and is generally less than one gram of uranium per liter of extractant.
  • the uranium enriched extractant is then separated from the WPPA and contacted with an aqueous solution containing a reducing agent such as ferrous ions in an acid such as phosphoric acid, to convert the uranium to tetravalent U(IV) ions.
  • a reducing agent such as ferrous ions in an acid such as phosphoric acid
  • the U(IV) ions are relatively insoluble in and are not re-extracted by the D2EHPA/TOPO-containing oil.
  • This step results in stripping the uranium from the oily extractant into the aqueous reducing solution and the aqueous reducing solution is then further processed to recover the uranium.
  • at least two different extraction operations are required.
  • Extraction efficiency is defined as the ratio of the uranium concentration in the oily extractant to the uranium concentration remaining in the WPPA feed at extraction equilibrium conditions.
  • Low extraction efficiency means that large quantities of expensive D2EHPA/TOPO extractant must be used and circulated with high concomitant losses of expensive reagents.
  • large, expensive contacting vessels and settling tanks and pumps are required to handle large amounts of oily extractant.
  • Another drawback of this process is due to the fact that as the temperature increases, the extraction efficiency decreases. For example, a report issued by the Oak Ridge National Laboratories (cf.
  • the WPPA is produced at a temperature of about 60°C which means that the acid must be cooled down to about 40°C before being extracted or additional extraction stages must be used to maintain satisfactory extraction efficiency at the higher temperature. This naturally necessitates additional equipment and the use of considerable amounts of energy to cool the WPPA down to an economically viable extraction temperature.
  • This emulsion process comprises contacting a uranium containing WPPA feed with globules of a water-in-oil emulsion comprising microdroplets of an aqueous interior phase dispersed in an oily, continuous exterior phase containing at least one transfer agent for selectively transferring the uranium from the feed into the interior phase of the emulsion wherein the valence of the uranium species is changed, thereby trapping the uranium in the emulsion.
  • the uranium-enriched emulsion is then separated from the feed, the emulsion is broken and the uranium is recovered.
  • the uranium is present in the WPPA feed as uranyl ion
  • the exterior phase contains a mixture of D2EHPA and TOPO as selective transfer agents for the uranyl ion
  • the interior phase of the emulsion contains a reducing agent which changes the uranyl to U(IV) ions, thereby trapping the uranium in the interior phase of the emulsion as uranous ions.
  • excess oxidizing agent is meant oxidizing agent in an amount greater than that initially added to the WPPA feed, if necessary, in order to ensure that all of the uranium in said feed is in the uranyl or hexavalent form and that any iron in the feed is in the ferric or trivalent form.
  • this invention is an improvement in an emulsion process for recovering uranium from a WPPA feed solution wherein the uranium ions initially are oxidised by adding an oxidising agent to said feed solution in order to ensure that all uranium is present in the hexavalent form, said process comprising (a) contacting, preferably, at a temperature of from about 30 to 100°C, 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 WPPA feed solution, 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 solution to interior phase of the emulsion wherein said uranyl ion is reduced to the tetravalent U(IV) ion to form
  • the total amount of excess oxidant to be added will, of course depend on the feed and emulsion compositions and also on the process conditions. In general, the minimum amount of excess oxidant added to the feed will be that amount just in excess of that stoichiometrically needed to oxidize any U(IV) and ferrous ions that transfer back to the WPPA feed (due to leakage and/or breakage of the emulsion) to uranyl and ferric ions, respectively. The so-formed uranyl ions are then reextracted by the emulsion.
  • oxidizing agent used in the process of this invention.
  • suitable oxidizing agents include chlorates, persulfates and peroxides such as hydrogen peroxide.
  • Contacting of the WPPA feed and emulsion is generally done in a countercurrent manner in a plurality of stages, each stage comprising at least one mixing zone and a settling zone, the mixing zone containing suitable means for mixing the WPPA feed with the emulsion.
  • suitable mixing means includes turbine and propeller mixers, static mixers, wire mesh, ultrasonic vibrations, etc. It is well-known that countercurrent extraction in a plurality of stages results in better extraction efficiency and requires less extracting agent or emulsion than a single.stage. It is preferred that each stage contains a plurality of co-current mixing zones or compartments.
  • this leakage reduces the overall efficiency of the process by putting uranium back into the feed and by introducing iron into the feed which later requires that more oxidant be used to maintain the uranium in the feed in the hexavalent (uranyl) form.
  • the interior phase of the emulsion will be a phosphoric acid solution containing ferrous ions and the oily, water and feed-immiscible exterior phase of the emulsion will be a mixture of D2EHPA/TOPO in an aliphatic hydrocarbon which also contains a surfactant for forming and stabilizing the emulsion.
  • the D2EHPA/TOPO in the exterior phase transports the U022+ cations from the WPPA feed into the interior phase of the emulsion wherein the uranium is stripped from the D2EHPA/TOPO by the phosphoric acid and reduced to U(IV) ions by the ferrous ions and is thereby trapped in the emulsion.
  • emulsions of the type disclosed in U.S. 3,779,907 are suitable for use in the process of this invention.
  • These emulsions are referred to liquids include substantially aliphatic hydrocarbons such as kerosene and paraffinic hydrocarbons such as Norpar 13, SK-100, Low Odor Paraffin Solvent (LOPS) and Solvent Neutral 100 (S-100N), which are available from Exxon Chemical Company. ("Norpar” and "Exxon” are registered Trade Marks, at least in the United Kingdom).
  • the hydrocarbon may contain one or more other hydrocarbons, halogenated hydrocarbons or higher oxygenated compounds such as alcohols, ketones, acids or esters as long as the emulsion is stable and the exterior phase is immiscible with both the aqueous feed solution and aqueous interior phase and permits transferring the uranium from the feed to the interior phase of the emulsion.
  • the exterior phase of the emulsion will contain from about 60-98 weight % of this hydrocarbon liquid, preferably from about 75-95% and most preferably from about 85-95 weight %.
  • the oily, water immiscible external phase of the emulsion will contain one or more oil soluble surfactants for forming and stabilizing the emulsion, but which will not prohibit transfer of the uranium through the exterior phase to the interior phase.
  • Suitable surfactants may be selected from among oil soluble anionic, cationic, and nonionic surfactants.
  • Surfactants that have been found to be particularly suitable for use in the process of this invention include various derivatives of polyisobutylene succinic anhydride (PIBSA) which includes, but is not limited to polyamine derivatives thereof for example those having the general formula: wherein
  • a particular PIBSA polyamine derivative surfactant that has been found to be useful in the process of this invention is one wherein R, and R 2 taken together to form an alkyl succinic radical and wherein the surfactant is a compound having the general formula: wherein m is an integer generally ranging of about 10-60 and more preferably 40, thereby giving said preferred polyamine derivative a molecular weight of about 2000.
  • This surfactant will generally comprise from about 0.2 to 10 weight % of the exterior phase of the emulsion, preferably from about 0.5 to 5 weight % and still more preferably from about 1-3 weight %.
  • the external phase of the emulsion must contain an agent capable of transferring the uranium from the aqueous feed, through the oily external phase to the interior phase.
  • Transfer agents found suitable for transferring cationic uranium species containing hexavalent uranium (i.e. UO 2 2+ ) through the external phase to the internal phase include a mixture of oil soluble dialkyl esters of phosphoric acid and trialkyl-phosphine oxide.
  • the transfer agent will comprise from between about 1-30 wt. % of the exterior phase of the emulsion, preferably from about 2-18 wt. % and most preferably from about 2-6 wt. %.
  • the transfer agent comprises a combination of D2EHPA and TOPO they will be in said exterior phase in a molar 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 D2EHPA/TOPO.
  • the interior phase of the emulsion will be an aqueous acid solution containing a reagent capable of changing the valence state of the uranium transferred through the oily, external phase to trap the uranium being removed from the aqueous feed where it is in the +6 valence state.
  • This interior phase will be an aqueous acid solution containing a reducing agent to reduce the uranium to a +4 valence state.
  • suitable reducing agents include acid solutions of ferrous or chromous ions such as an aqueous solution of ferrous sulfate in phosphoric acid wherein the concentration of the ferrous ion ranges from about 8-50 grams per liter, preferably from 10 to 40 g/liter and wherein the concentration of the phosphoric acid ranges from about 3-12 moles/liter and more preferably from about 5-8 moles/liter.
  • the following reaction is believed to occur when reducing (UO 2 2+ ) with acidic ferrous sulfate: It is important that the concentration of phosphoric acid in the internal phase be approximately the same as in the feed in order to avoid excessive swelling and ultimately destruction of the emulsion.
  • the internal phase may be prepared from the WPPA feed by adding iron thereto.
  • the interior phase will comprise from about 15-80 volume percent of the emulsion, preferably from 30-70 and most preferably from 33-60 volume percent, i.e., the volume ratio of the oily exterior or membrane phase to the aqueous interior phase of the emulsion will range from about 6/1 to 1/4, more preferably from about 2/1 to 1/2, and still more preferably from about 2/1 to 1/1.
  • the emulsions used in this invention may be prepared by any of the well known methods.
  • a solution comprising the components of the oily exterior phase is mixed with an aqueous solution which will form the interior phase under high shear conditions attained by the use of high speed stirrers, colloid mills, homogenizers, ultrasonic generators, mixing jets, etc.
  • the excess oxidizing agent can be added to the WPPA feed before it enters the extraction train, or it may be added in stages throughout the extraction sequence, or both. Thus, a portion of the excess may be added to the feed before it is contacted with the emulsion, with the remainder added at one or more points along the extraction train. Alternatively it may all be added to the feed prior to its being contacted with the emulsion or it may all be added to the feed at one or more points of the extraction train.
  • uranyl ion (U0 2 H ) was laboratory batch extracted from an actual sample of central Florida WPPA comprising a 5.2 M solution of H 3 P0 4 containing 130 ppm of uranium as UO Z ++.
  • the emulsion used to extract the uranium had the following composition:
  • the WPPA was filtered through a 1 m cartridge filter to remove the solid gypsum and some organics as solids.
  • the WPPA 1500 mL, was then added to the resin kettle of 10 cm I.D. fitted with four 1 cm vertical baffles and four evently spaced marine propellers of 5.1 cm diameter. The temperature was increased to and controlled at 60 ⁇ 1°C with external heating.tape and a Thermowatch controller.
  • the liquid membrane emulsion was prepared in a Waring blender at 10,000 ppm for 4 min. using 333 ml of.membrane and 167 ml of internal aqueous phase.
  • the emulsion, 125 ml, for a feed to emulsion ratio of 12, was added to the resin kettle. Mixing at 600 rpm was then begun and was t 0 for measurement of contact time. In the first run, only 0.068 grams of ammonium persulfate oxidant was added to the kettle which was just enough to ensure that all of the uranium and iron in the WPPA feed were in the +6 and +3 valence state, respectively.
  • Samples of the dispersion were taken during agitation through a stopcock in the bottom of the resin kettle at various contact times. These samples were allowed to phase separate and aliquots of the raffinates were analyzed for uranium content. At the completion of extraction, a sample emulsion was coalesced to isolate internal phase for uranium analysis by X-ray fluorescence spectroscopy.
  • the internal phase of the liquid membrane will contain tetravalent uranium, as U(IV) ion, to a loading in a range of about 6 to 12 g/L. Therefore, extraction of uranium from the WPPA was done with a preloaded emulsion whose internal phase contained 10 g/L of uranium as U +4 .
  • the experimental conditions were the same as in Example 1.
  • the results given in Table II show that no extraction was observed without added oxidant, whereas with added oxidant 47% of the uranium was extracted after 25 minutes contact time.
  • extraction was also carried out in a continuous contacting system comprising one extraction stage which contained five cocurrent, cascading mixing compartments.
  • Each compartment was a cube of one liter capacity containing a marine propeller mixer.
  • Pretreated WPPA and fresh LM emulsion were fed into the first compartment wherein a dispersion of LM emulsion in the continuous WPPA phase was formed by the shear of the marine propeller-stirrer contained in each compartment.
  • the resultant dispersion cascaded through each successive compartment by overflow after a finite contacting period.
  • the dispersion overflowed from the last compartment into a settler to allow disengagement and separation of the loaded LM emulsion from the WPPA raffinate phase.
  • WPPA was oxidized in polyethylene lined, 55 gal (250 I) drums with hydrogen peroxide and pumped through a 1 m polypropylene cartridge in line filter to a 3 I vessel.
  • This vessel was a preheater which increased the temperature of the pretreated WPPA to 60-70 0 C.
  • the acid was then fed via a peristaltic pump (all fluids were transferred with peristaltic pumps) to the continuous contacting system described above.
  • Samples of raffinate from each mixing compartment were analyzed for uranium content by inductively coupled ion plasma emission spectroscopy.

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Claims (9)

1. Procédé en émulsion pour récupérer l'uranium d'une solution de charge d'acide phosphorique obtenu par voie humide, procédé dans lequel on oxyde initialement les ions uranium en ajoutant un oxydant à ladite solution de charge pour faire en sorte que la totalité de l'uranium soit présent sous forme hexavalente, ledit procédé consistant:
(a) à mettre en contact ladite charge d'acide phosphorique avec une émulsion du type eau dans huile comprenant (i) une phase intérieure aqueuse dispersée dans (ii) une phase extérieure huileuse non-miscible tant à ladite phase intérieure qu'à ladite charge, ladite phase intérieure comprenant une solution dans un acide contenant un réducteur, et ladite phase extérieure comprenant une solution, dans un hydrocarbure contenant un tensio-actif, de D2EHPA (acide di-2-éthylhexylphosphorique) et de TOPO (oxyde de trioctylphosphine), qui transfèrent l'ion uranyle de la charge d'action phosphorique à la phase intérieure de l'émulsion, dans laquelle ledit ion uranium hexavalent est réduit en ion uranium tétravalent pour former une émulsion riche en uranium;
(b) à séparer l'émulsion riche en uranium de la charge d'acide phosphorique obtenu par voie humide, et
(c) à récupérer l'uranium de l'émulsion, caractérisé en ce qu'on ajoute à la solution d'acide phosphorique avant et/ou pendant que la charge est en contact avec la solution, un oxydant introduit en une quantité supérieure à la quantité nécessaire pour faire initialement en sorte que l'uranium se trouvant dans la charge se présente à l'état hexavalent et en une quantité suffisante pour que la totalité du fer éventuellement présent dans la charge se trouve à l'état trivalent.
2. Procédé selon la revendication 1, dans lequel ladite solution d'un acide dans la phase intérieure comprend de l'acide phosphorique, et dans lequel ladite phase intérieure compte pour environ 15-80% en volume de ladite émulsion.
3. Procédé selon la revendication 2, caractérisé en ce que la solution d'acide phosphorique dans ladite phase intérieure se présente à une concentration de 3 à 12 moles par litre.
4. Procédé selon l'une ou l'autre des revendications 2 ou 3, dans lequel la concentration de la solution d'acide phosphorique dans ladite phase intérieure est pratiquement la même que la concentration de l'acide phosphorique dans ladite solution d'acide phosphorique obtenu par voie humide.
5. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel ledit tensio-actif est un dérivé polyaminique de l'anhydride polyisobutylènesuccinique.
6. Procédé selon la revendication 5, dans lequel ledit dérivé polyaminique de l'anhydride polyisobutylènesuccinique a la forme générale
Figure imgb0009
dans laquelle R1, R2, R3, R4, Rs, R6 et R7 et Y sont identiques ou différents et sont chacun l'hydrogène, un radical alkyle en Ci à C2o, aryle en C6 à C20, alcaryle en C7 à C20, ou leurs dérivés substitués; et x est un entier de 1 à 100.
7. Procédé selon la revendication 6, dans lequel R3 à R7 sont chacun l'hydrogène, et x varie de 3 à 20.
8. Procédé selon l'une quelconque des revendications 1 à 7, dans lequel ladite mise en. contact de la charge et de l'émulsion s'effectue dans plusieurs zones de contact.
9. Procédé selon l'une quelconque des revendications 1 à 8, dans lequel ledit oxydant est ajouté à ladite charge après la mise en contact initiale de cette charge avec ladite émulsion.
EP82302373A 1981-05-11 1982-05-10 Procédé avec membranes liquides pour la récupération de l'uranium Expired EP0064877B1 (fr)

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US262394 1981-05-11

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JP (1) JPS589823A (fr)
CA (1) CA1191696A (fr)
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ZA (1) ZA823194B (fr)

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GB0218820D0 (en) 2002-08-14 2002-09-18 Antenova Ltd An electrically small dielectric resonator antenna with wide bandwith
US8226910B2 (en) * 2008-07-31 2012-07-24 Urtek, Llc Extraction of uranium from wet-process phosphoric acid
US8883096B2 (en) 2008-07-31 2014-11-11 Urtek, Llc Extraction of uranium from wet-process phosphoric acid
CN103045869B (zh) * 2012-12-27 2014-07-30 北京大学 一种利用浊点萃取技术从水相中富集铀、钍的方法

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US3779907A (en) * 1970-04-13 1973-12-18 Exxon Research Engineering Co Liquid membrane process for the separation of aqueous mixtures
GB1596410A (en) * 1976-12-27 1981-08-26 Exxon Research Engineering Co Liquid membranes and process for uranium recovery therewith
FR2457258A1 (fr) * 1979-05-22 1980-12-19 Rhone Poulenc Ind Perfectionnement au procede de recuperation de l'uranium d'un acide phosphorique impur

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
INDUSTRIAL AND ENGINEERING CHEMISTRY; PROCESS DESIGN AND DEVELOPMENT, vol.11, no.1, 1972, American Chemical Society, Washington D.C. (US) F.J. HURST et al.: "Recovery of uranium from wet-process phosphoric acid", pages 122-128 *
JOURNAL OF INORGANIC & NUCLEAR CHEMISTRY, vol.40, no.1, 1978, Pergamon Press, (GB) F.T. BUNUS et al.: "Synergic extraction of uranium from phosphate solutions with Di-(2ethylhexyl) phosphoric acid and Tri-n-octylphospine oxide", pages 117-121 *

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DE3268504D1 (en) 1986-02-27
EP0064877A1 (fr) 1982-11-17
ZA823194B (en) 1983-04-27
CA1191696A (fr) 1985-08-13
JPS589823A (ja) 1983-01-20

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