US2864841A - Process for the recovery of plutonium - Google Patents

Description

PROCESS FOR THERECOVERY F PLUTONIUM Herbert A. Potratz, St. Louis, Mo., assgnor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application ()ctober 23, 1946 Serial No. 705,254

12 Claims. (Cl. 260-429.1)

This invention relates to a method for the recovery of plutonium from solutions containing the same. More particularly it is concerned with a method for separating plutonium in a substantially uranium free state from solutions containing uranium, fission products, and other impur1t1es commonly associated therewith wherein the urani- `um is concerted to a non-carriable or non-interfering state.

This is a continuation in'part of co-pending application U. S. rSerial No. 565,991, filed November 30, 1944, and any subject matterl appearing therein common to the subject matter disclosed herein is incorporated by reference;

It is known that when uranium is subjected to neutron bombardment there is formed in small quantities a new element having an atomic weight of 239 and atomic numberof 93, known asneptunium (symbol Np). This new elementby radioactive decay is transformed through a halfflife of 2.3 days to a further new element known as plutonium (symbol Pu) having an vatomic number of 94. The particular isotope of this second new element has a mass of 239. In addition, certain other elements are formed as a result of fission of the uranium 235 nucleus such elements being referred to as fission fragments or, including radioactive decay products thereof, as fission products. The fission fragments or products are radioactive isotopes which may be included in two general element groups, a light fission fragment comprising elements having atomic numbers from about 35 to 46 such as bromine, krypton, rubidium, strontium, yttrium, zirconium, columbium, molybdenum, masuriurn, ruthenium, rhenium and a heavy fragment comprising elements having atomic numbers from about 5 l to 60 such as antimony, tellurium, iodine, xenon, caesium, barium, lanthanum, cerium, praseodyrnium and neodymium. The fission fragments are usually present in radioactive form, ordinarily having a very short half-like, and by radioactive decay many of the fission fragments form other sho-rt lived products. As a result the radioactivity of the mass of uranium remains at a high and very dangerous level for some time following the neutron bombardment. It

is particularly desirable to separate the plutonium from r the radioactive fission products thereby remo-ving from the mass the radioactive materials and particularly the lightY elements suchas light metals having very short half-lives and consequently high radio-activities. Thus the product obtained by neutron bombardment comprises a major portion of uranium together with minor por-- tionsrarely in excess of one or two percentby weight of fission products and element 94 together with a smaller concentration of element 93. The recovery of element 94 in a concentrated form involves the separation of that element from such a product without excessive lloss of element 94.

The removal of fission products from plutonium is of particular interest since they retain their radioactivity for a substantial time after the neutron bombardment. Such radioactivity is so intense that it is exceedingly hazardous to personnel engaged in working therewith.

j 2,864,841 Patented Dec. 16, 1958 A further problernwhich isfrequently encountered involves the removal of impurities which may be present in plutoniumfconcentrates. Such impurities may comprise residual uranium and/or fission products and/ or agents used to assist in theseparation ofthe plutonium from the irradiateduranium and may include numerous lightelements 'including lithium,'magnesium, sodium, calcium, silicon, beryllium, etc.

It is an object ofthe present inventionV to eiect a relatively clean separation of the'plutonium from the uranium andi ssion products wherein said plutonium is removed from solutions containing uranium and fission products as impurities.

It is a further object of the present invention to provide a simple lmethod for removing plutonium from-aqueous solutions particularlyfrom other interfering substances.

In the process described' and claimed in the co-pending application referred to above plutonium is readily re`- moved from solutions containing fission products and uranium by addingan aqueoussolution of cupferron thereto, thereby forming a precipitate substantially of plutonium cupferride together with uranium as a contam'- inant. This plutonium is next extracted from the precipitate by contacting the' entire mixture of precipitate and mother liquor with several separate solutions of substantially'water immiscible solvents for the plutonium cupferride. Whilev this 'procedure functions very effectively to'remove the plutonium4 from such solutions it does not result inthe. procurement of a product' that is substantially free from uranium inasmuch as appreciable concentrations 'of the latter'tend4 to'follow Vtheplutonium through each stage'of the recovery process.

Ithas nowbeen discovered that plutonium can be recovered in a substantially uranium-free condition from solutionscontaining uranium yand other common impurities by adding ammonium carbonate to the initial plutonium-containing solution preferably in a slight excess over the amount required to neutralize said solution prior to the removal of theplutonium with cupferron. UnderV the above conditions the -uraniumvis` rendered noncarriable by cupferron thereby resulting in-the obtainment of substantially pure precipitate of plutonium cupferride.

In carrying out a preferred embodiment of the-presentinvention a 20% uranylnitrate hexahydrate solution, prepared if desired by dissolving neutron irradiated uranium in nitric acid, is first subjected to the-action of a suitable reducing agent such as, for example, hydrogen peroxide, hydroxylamine hydrochloride, or the like, in order to reduce any `hexavalent plutonium which might be present to the +4 state. Thereafter a saturated solution of'ammonium carbonate is added until the resulting solution gives' a permanent alkaline reaction. Ordinarily an excess Vof lammonium carbonate in a concentration additional ammonium* carbonate said-precipitate goesV back into solution and under such conditions the uraniumV exists in ,awhighly soluble non-carriable state, probably in the form of a A complex.

In Vinstanceswhere there is some question as to whetheror not allof the uranium is in the hexavalent state lprior to the addition of ammonium carbonate an oxidizing agent which will not affect the valence of plutonium should be employed. Nitric acid is an example of a suitable oxidizing agent for this purpose. Also, when working with solutions in which at least a portion of the plutonium contained therein is in the -l-6 state, said solutions should be permitted to standY at least one-half hour after a suitable reducing agent has been added thereto. As examples of reducing agents suitable for this purpose there may be mentioned ferrous ion, hydroxylamine hydrochloride, iodide ion, and the like.

After the plutonium is removed from solution by the addition of cupferron, usually in the form of a dilute aqueous solution, to form a precipitate of plutonium cupferride after which a precipitate may be extracted from the resulting mixture by agitation with a substantially water immiscible organiccompound, i. e., a selective solvent for plutonium cupferride. Alternatively, the plutonium may be removed from such solutions by adding the cupferron thereto in the form of a dilute solution in the water immiscible liquid organic solvent for plutonium cupferride whereby the plutonium cupferride passes into the solvent layer as it is formed.

The substantially water immiscible organic solvents that may be employed in carrying out the process of the present invention are benzene, ethyl acetate, chloroform, carbon tetrachloride, aniline, hexyl alcohol, xylene, and the like.

The -water immiscible organic solvents as used in this invention extract the plutonium cupferride from aqueous solutions either by actual solution in the solvent or by preferential wetting by the solvent. In case of preferential wetting the plutonium cupferride may appear as a suspension or precipitate in the organic solvent owing to the fact that the plutonium cupferride is preferentially wetted by the solvent rather than by the water. It is to be understood throughout the present disclosure and appended claims that extraction by water immiscible organic solvents includes extraction by solvent action and/ or preferential wetting action.

' Formation of the plutonium cupferride may be effected by adding the cupferron or a solution thereof to the plutonium-containing solution and permitting the mixture to stand either with continuous or intermittent agitation for a suitable period of time, such as, for example, twenty-four toVforty-eight hours. Heating under such circumstances is generally unnecessary.

The present invention may be further illustrated by the specific example which follows:

Example To 5 ml. ofga 20% solution of uranyl nitrate prepared from neutron irradiated uranium, said uranyl nitrate solution having a plutonium concentration of 372 alpha counts per minute, were added 3 drops of an aqueous 20% hydroxylamine hydrochloride solution. The resulting mixture was agitated for a period of one-half hour after which suicient ammonium carbonate in the form of a saturated solution was added to bring the pH thereof up to a value of 8.0. Thereafter this soultion was extracted three times with 1 ml. of chloroform containing two drops of 6% cupferron, each extraction being carried out with fresh solvent. The resulting extracts were combined and filtered after which the filtrate was placed in a platinum crucible and evaporated to dryness. The residue was ignited in order to free the extracted material from organic matter and thereafter was analyzed for its plutonium content by use of a suitable alpha pulse counter. This analysis indicated that the plutonium recovered amounted to a total of 371.6 alpha counts per minute.

It is to be understood that the above example and.

tive thereof. Other substitutes for ammonium carbo-Y nate may be utilized to bring about the same results and the procedures herein set forth may be modified in numerous respects without departing from the broad embodiments of this invention. In general, it may be said that any modification or improvement that would normally occur to one skilled in the` art is to be considered as lying within the scope of this invention.

What is claimed is:

l. In a process for the separation of plutonium from 2. In a process for the separation of tetravalent plutonium from solutions containing that element together with hexavalent uranium and other impurities commonly associated therewith, the steps which comprise adding suicient ammonium carbonate to said solutions to render said solution alkaline, and thereafter contacting the resultant solution with cupferron dissolved in a substantially water immiscible organic liquid solvent for the plutonium cupferride.

3. In a process for the separation of plutonium from solutions containing that element together with uranium, iission products and other impurities commonly associated therewith, the steps which comprise contacting an acid l solution containing plutonium in the tetravalent state and uranium in the hexavalent state with a saturated aqueous solution of ammonium carbonate in an amount sufficient to render said solution slightly alkaline, thereafter contacting said alkaline solution with cupferron, and extracting the resulting mixture with a substantially water immiscible organic liquid solvent for the plutonium cupferride.

4. In a process for the separation of plutonium from solutions containing that element together with uranium,

f fission products, and other impurities commonly associated therewith the steps which comprise contacting an acid solution containing plutonium in the tetravalent state and uranium in the hexavalent state with a saturated aquesolution of ammonium carbonate in an amount sufficient to render said solution slightly alkaline, thereafter contacting said alkaline solution with cupferron and extracting the resulting mixture with chloroform.

5. In a process for the separation of plutonium from solutions containing that element together with uranium and other impurities commonly associated therewith, the steps which comprise contacting an acid solution containing plutonium in the tetravalent state and uranium in the hexavalent state with a saturated aqueous solution of ammonium carbonate in an amount not substantially in excess of 10% over that required to neutralize said solution, thereafter contacting said solution with cupferron and extracting the resulting mixture with a substantially water' immisicible organic liquid solvent for the plutonium cupferride.

6. The process of claim 5 in which the selective solvent is chloroform. ,5.

Y In a process for the separation of plutonium from solutions containing that element togetherwith uranium, fission products, and other impurities commonly associated therewith, the steps which comprise contacting an acid solution containing plutonium in the tetravalent state and uranium in the hexavalent state with a suicient quantity of ammonium carbonate to give a solution having a pH of about 8, thereafter contacting said solution with cupferron and extracting the resulting mixture with a substantially water immiscible organic liquid solvent for the plutonium cupferridetthus formed.

8. In a process for the separation of plutonium from solutions containing that element together with uranium, ssion products and other impurities commonly associated therewith, the steps which comprise contacting an acid solution containing plutonium in the tetravalent state and uranium in the hexavalent state with a suicient quantity of ammonium carbonate to give a solution having a pH of about 8, thereaftercontacting the resulting mixture with a solution comprising cupferron dissolved in a substantially water immiscible organic liquid solvent for the plutonium cupferride thus formed.

9. The process of claim 8 in which the selective solvent is chloroform.

10. In a process for the separation of plutonium from neutron irradiated uranyl nitrate hexa'nydrate solutions, the stepswwhich comprise contacting said solution with Vammonium carbonate in an amount sucient to render said solution slightly alkaline and thereafter extracting said alkaline solution with a solution containing cupferron dissolved in a substantially water immiscible organic liquid solvent for the plutonium cupferride thus formed.

11. In a process for the separation of plutonium from neutron irradiated uranyl nitrate hexahydrate solutions, the steps which comprise adding sufficient ammonium carbonate thereto to give a. solution having a pH of about 8 and thereafter contacting the resulting mixture with a chloroform solution of cupferron.

12. A process for the separation of plutonium from an aqueous alkaline ammonium carbonate solution containing plutonium values and uranium values, which com prises contacting said solution with cupferron so as to selectively form plutonium cupferride and separating said plutonium cupferride therefrom.

References Cited in the le of this patent UNITED STATES PATENTS Hixson et al. Aug. 13, 1940 OTHER REFERENCES Thornton et al.: Arn. J. Sci., 42, 151-54 (1916);

Y Chem. News, 114, 13-14 (1916).

Angeletti: Gazz. Chim. Ital.,'5l, I, 285-88 (1921).

Claims (1)

1. IN A PROCESS FOR THE SEPARATION OF PLUTONIUM FROM SOLUTIONS CONTAINING THAT ELEMENT TOGETHER WITH URANIUM, FISSION PRODUCTS AND OTHER IMPURITIES COMMONLY ASSOCIATED THEREWITH, THE STEPS WHICH COMPRISE CONTACTING AN ACID SOLUTION CONTAINING PLUTONIUM IN THE TETRAVALENT STATE AND URANIUM IN THE HEXAVALENT STATE WITH AMMONIUM CARBONATE IN AN AMOUNT SUFFICIENT TO RENDER SAID SOLUTION ALKALINE, THEREAFTER CONTACTING SAID ALKALINE SOLUTION WITH CUPFERRON AND EXTRACTING THE RESULTING MIXTURE WITH A SUBSTANTIALLY WATER IMMISCIBLE ORGANIC LIQUID SOLVENT FOR THE PLUTONIUM CUPFERRIDE.