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US2847274A - Sulfide method plutonium separation - Google Patents

Sulfide method plutonium separation Download PDF

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US2847274A
US2847274A US25075A US2507548A US2847274A US 2847274 A US2847274 A US 2847274A US 25075 A US25075 A US 25075A US 2507548 A US2507548 A US 2507548A US 2847274 A US2847274 A US 2847274A
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plutonium
solution
precipitate
separating
uranyl
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Robert B Duffield
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G56/00—Compounds of transuranic elements
    • C01G56/004—Compounds of plutonium

Definitions

  • thename of'theelement is used to designate the element generically, eitherxin its element state or combined in ateompoundunless other wise indicated by the sense in which it is used, for. example by a specific designation, such as -metal? or.elemental.
  • Natural uranium is composed of. three. isotopesnamely, U U and U3 the. latter being present in! excess of 99% of the whole.
  • U is.subjected-to the action of slow or thermal neutrons.aiourthLisotope
  • U2 is produced havingahalf-life.ofttwentyethree. minutes which undergoes beta decay. to Np which in..turn
  • plutonium producedas
  • the procedure employed to recover that element must be highly efficient in order to be at all practicable.
  • it is highly desirable to separate the fission products from the plutonium since these have exceedingly important uses as therapeutic agents and are also used as radioactive tracers in chemical, medical, and industrial research.
  • An additional object of this invention is to provide' a convenientand efiicient method of recovering plutonium from impurities commonly associated therewith in neu-' tron-irradiated uranium.
  • the present invention involve'sthe treatment of'plutonium in a lower state of oxidation; -with "a soluble'sulfide in the presence ofa'source-of uranylions.
  • the plutonium which is contained in an aqueous, alkaline solution, is contacted with a soluble sulfidecompound, whereby a precipitate is formed whicheontains-a substanti'al'part of the plutonium present.
  • The-precipitate is separated from the solution, thus effectively separatingthe plutonium from such impurities as are soluble in thelsolution under these conditions;
  • the preeipitate isithenrdissolved by treatment withan'aqueous soluti'omco'ntaining carbonate ion in eXcess of that stoichiometrically .re quired to form a soluble carbonate :complex withi-the uranium and the plutonium contained in the precipitate.
  • This treatment brings the plutonium and uranium into solution, but does not affect the fission product sulfides which are not soluble in anexcess carbonate solution; for example, the eerie sub-group rare earth" sulfides;
  • the solution is then centrifuged, thus separating th'eiplutonium from these insoluble fission product sulfides;
  • this'pro'cess' comprises the treatment of plutonium, contained inan aqueousalk'aline solution, in a reduced state,,i. e.', the'tri-i ortetravalent state.
  • This solution maybe formedby; dissolving neutron-irradiated uranium in nitric "acid and'ithen'converti'ng the solution to the alkaline state .by' addition of "analkali hydroxide.
  • the solution formedin this "manner will'contain the plutonium in very'small' concentration, uranyl ions and fission products:
  • Theplutonium-containing solution isthen treated with a soluble sulfide, and preferably' hydrogen sulfide, whereby; aninsoluble "precipitate is formed.”
  • This precipitate contains' theuranium; plutonium, andthose fission products "present; which'ifo'rminsoluble sulfidesin alkaline solution.
  • The'fissionproducts
  • the advantages of the process of this invention are readily apparent. It provides a simple method for separating plutonium from solutions in which the plutonium is contained in small concentrations. It also provides a novel method of separating plutonium from such contaminating elements, normally associated with plutonium in neutron-irradiated uranium, as form soluble sulfides in an aqueous alkaline solution. It further provides a method of separating plutonium from the contaminating elements, the sulfides of which are insoluble in an excess carbonate solution. The separation method is a simple one, which does not require the use of any highly corrosive reagents and efl'iciently separates plutonium from some of the most highly radioactive fission products.
  • Example I A 0.5 M potassium hydroxide solution was prepared in a volume of about cc. To this solution was added 0.5 mg. of potassium diuranate obtained from neutronirradiated uranium, containing a tracer quantity of 50- year plutonium in the tetravalent state. Hydrogen sulfide was then passed into the solution for ten minutes. The uranyl precipitate thus formed was then separated from the solution by centrifugation. The precipitate and the supernatant solution were analyzed and it was found the plutonium had carried with the precipitate to the extent of 81% with 12% of the plutonium unaccounted for and the balance remaining in the supernatant solution.
  • Example 11 A 0.5 mg. sample of the uranyl precipitate obtained in the manner described in the preceding example was introduced into 5 cc. of a 0.5 M potassium hydroxide solution. This solution was then made 0.5 M in K CO and 0.6 M in NH OH. The precipitate was digested for about thirty minutes in this solution, which treatment efiected the dissolution of the greater part of the precipitate. The balance of the undissolved precipitate was then separated from the solution by centrifugation and the precipitate and solution analyzed by radiometric methods. The solution was found to contain 91% of the plutonium contained in the original precipitate with 6% remaining in the undissolved precipitate and 3% unaccounted for.
  • the process of separating plutonium from contaminants normally associated therewith in neutron-irradiated uranium which comprises treating an aqueous alkaline solution containing plutonium values and contaminants normally associated therewith, said plutonium having a Valence state less than +5, in the presence of a source of 'uranyl ions, with a soluble sulfide, whereby a plutoniumcontaining uranyl precipitate is formed, separating said precipitate from the solution, treating said precipitate with an aqueous solution containing carbonate ion in excess, whereby the plutonium is dissolved away from the fission product sulfides insoluble in excess carbonate, and separating said insoluble fission product sulfides from the plutonium-containing solution.
  • the process of separating plutonium from contaminants normally associated with plutonium in neutronirradiated uranium which comprises treating said plutonium contained in an aqueous alkaline solution in the tetravalent state, with a soluble sulfide whereby a plutonium-containing precipitate is formed, separating said precipitate from the solution, treating said precipitate with an aqueous solution containing carbonate ion in excess, whereby the plutonium is dissolved away from the fission product sulfides insoluble in excess carbonate, and separating said insoluble fission product sulfides from the plutonium-containing solution.
  • the process of separating plutonium from an aqueous alkaline solution in which plutonium is contained in very dilute concentration, in a valence state less than +5, which comprises treating said plutonium with a soluble sulfide in the presence of a source of uranyl ions, whereby a plutonium-containing uranyl precipitate is formed, and separating said plutonium-containing uranyl precipitate from the solution.
  • the process of separating plutonium from a contaminant whose sulfide is soluble in an aqueous alkaline solution and which is normally associated with plutonium in neutron-irradiated uranium which comprises treating said plutonium contained in an aqueous alkaline solution in a valence state less than +5, in the presence of a source of uranyl ions, with a soluble sulfide whereby a plutoniumcontaining uranyl precipitate is formed, and separating said precipitate from the solution which contains said contaminant.

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Description

SULFIDE METHOD PLUTON-IUIVI ISEBARATION Robert B. Dumeld, Champaign, 111., assignor to-tlt'e United States of America as represented by-the United'States Atomic Energy Commission No Drawing. Application May 4,'194'8 Serial No. 25,075
6 Claims. c1. 23-1455 This invention is concernedwith .a.method..for.separat-- ing plutonium from impurities normally associated:there-- with in neutron-irradiated uranium.
In this specification and claims .thename of'theelement is used to designate the element generically, eitherxin its element state or combined in ateompoundunless other wise indicated by the sense in which it is used, for. example by a specific designation, such as -metal? or.elemental.
Natural uranium is composed of. three. isotopesnamely, U U and U3 the. latter being present in! excess of 99% of the whole. When. U is.subjected-to the action of slow or thermal neutrons.aiourthLisotope, U2 is produced havingahalf-life.ofttwentyethree. minutes which undergoes beta decay. to Np which in..turn
decays further by beta radiation .with. ahalflifeofjtwor and three-tenths days to yield. plutonium... In addition. to the formationof Pu there arezsimultaneously produced vother. elements of lower atomicweight .knownasfission they quickly transform themselves into isotopes-of these various elements having longer half-lives. Themesulting' materials are commonly knownasfission products... The various radioactive. fission .products have half-livesranging from. a fraction of a second to. thousands ofiyears. Those having half-lives whichare .very shortunaybesubstantially eliminated by aging. the material for areasonable period before handling. Those-withvery longhalflives do not have sufficiently intensenradiationsto endanger personnel protected by moderateshie'ldingn on the other hand, the fissionv products. having haltllives ranging from a few days to a few'years havedangerously intense radiations which cannot .beelirninatedi'bypaging for practical storage. periods. These products are-chiefiy radioactive isotopes of Te,-.I, Cs, Ba,.La,-Ce,.Sr',v Zi", Cb, and Rh.
It may be readily seen that plutonium, producedas" generally set forth-above, is contaminated with,.considerable quantities of uranium and fission products. In fact, the plutonium constitutes onlyxa'veryxminorfportion of the irradiated mass, i. e., less.than-.=1% thereof. .Intview 6Q of such a low concentration of plutonium;imtheiirradiatedi metal it becomes apparent that the procedure employed to recover that element must be highly efficient in order to be at all practicable. In addition to the recovery of the plutonium, it is highly desirable to separate the fission products from the plutonium, since these have exceedingly important uses as therapeutic agents and are also used as radioactive tracers in chemical, medical, and industrial research.
It is an object of this invention to provide a method of separating plutonium from an aqueous solution in which the plutonium is contained in a small concentration.
An additional object of this invention is to provide' a convenientand efiicient method of recovering plutonium from impurities commonly associated therewith in neu-' tron-irradiated uranium. V
Broadly, the present invention"involve'sthe treatment of'plutonium in a lower state of oxidation; -with "a soluble'sulfide in the presence ofa'source-of uranylions. The plutonium which is contained in an aqueous, alkaline solution, is contacted with a soluble sulfidecompound, whereby a precipitate is formed whicheontains-a substanti'al'part of the plutonium present. The-precipitate is separated from the solution, thus effectively separatingthe plutonium from such impurities as are soluble in thelsolution under these conditions; The preeipitate isithenrdissolved by treatment withan'aqueous soluti'omco'ntaining carbonate ion in eXcess of that stoichiometrically .re quired to form a soluble carbonate :complex withi-the uranium and the plutonium contained in the precipitate. This treatment brings the plutonium and uranium into solution, but does not affect the fission product sulfides which are not soluble in anexcess carbonate solution; for example, the eerie sub-group rare earth" sulfides; The solution is then centrifuged, thus separating th'eiplutonium from these insoluble fission product sulfides;
In its preferred embodiment, this'pro'cess' comprises the treatment of plutonium, contained inan aqueousalk'aline solution, in a reduced state,,i. e.', the'tri-i ortetravalent state. This solution maybe formedby; dissolving neutron-irradiated uranium in nitric "acid and'ithen'converti'ng the solution to the alkaline state .by' addition of "analkali hydroxide. The solution formedin this "manner will'contain the plutonium in very'small' concentration, uranyl ions and fission products: Theplutonium-containing solution isthen treated with a soluble sulfide, and preferably' hydrogen sulfide, whereby; aninsoluble "precipitate is formed." This precipitate contains' theuranium; plutonium, andthose fission products "present; which'ifo'rminsoluble sulfidesin alkaline solution. The'fissionproducts,
such .as S1", Te, Rb, and Cs, whichi'form" soluble" sulfides inalkaline solution, will remain in'solution andhythe separation of the insoluble plutonium-eontainingprecipitate from the solution, the plutonium'will b"e"efi'ective1y freed from this type of fission products; Separation of'the precipitate may be effected by any'of 'the"usual'methods,
45 such: as 'centrifugation, decantation; or'filtration. Following the separation of the precipitate; it may be washed with water and then treated with a soluti'dn'containing carbonate ion in excess. The plutonium in its lower oxidation-statesforms a very stable complexwith'carbonate 0ion and .the carbonate solution thus will effectively dissolve the. plutonium. Uranyl ion is dissolvedinth'e same way. and so is also brought into solution; Certain'of the fission products which form insoluble sul'fi'des, notably cerium, lanthanum, and the other members" of theceric 5 sub-group of the rare earth, are insoluble' nexcesscarbonate, so these willremain in the solid form as the sulfides, in the presence .of the excess carbonate-solution. These undissolved sulfides may be separated 'frorn thies'olution by, eentrifugation, filtration, or'decantation': This step, will elfectively'separate" the plutonium from the greater portion of theremaining"contaminants: Plutonium may then be separated from the uranyl ion-containing solution by any of the usual methods, such as precipitation with a lanthanum fluoride or bismuth phosphate carrier. The process of this invention has been described as applied to the separation of plutonium contained in solution in such small concentration that it must be precipitated with an auxiliary precipitate. The process may be directly precipitated. In case the plutonium is present in such concentration the procedure for separating the plutonium is the same as that previously set forth, except that the precipitation of the plutonium may be carried out in a solution which does not contain uranyl ions.
The advantages of the process of this invention are readily apparent. It provides a simple method for separating plutonium from solutions in which the plutonium is contained in small concentrations. It also provides a novel method of separating plutonium from such contaminating elements, normally associated with plutonium in neutron-irradiated uranium, as form soluble sulfides in an aqueous alkaline solution. It further provides a method of separating plutonium from the contaminating elements, the sulfides of which are insoluble in an excess carbonate solution. The separation method is a simple one, which does not require the use of any highly corrosive reagents and efl'iciently separates plutonium from some of the most highly radioactive fission products.
Now that this invention has been broadly described, it may be further illustrated by the following specific examples.
Example I A 0.5 M potassium hydroxide solution was prepared in a volume of about cc. To this solution was added 0.5 mg. of potassium diuranate obtained from neutronirradiated uranium, containing a tracer quantity of 50- year plutonium in the tetravalent state. Hydrogen sulfide was then passed into the solution for ten minutes. The uranyl precipitate thus formed was then separated from the solution by centrifugation. The precipitate and the supernatant solution were analyzed and it was found the plutonium had carried with the precipitate to the extent of 81% with 12% of the plutonium unaccounted for and the balance remaining in the supernatant solution.
Example 11 A 0.5 mg. sample of the uranyl precipitate obtained in the manner described in the preceding example was introduced into 5 cc. of a 0.5 M potassium hydroxide solution. This solution was then made 0.5 M in K CO and 0.6 M in NH OH. The precipitate was digested for about thirty minutes in this solution, which treatment efiected the dissolution of the greater part of the precipitate. The balance of the undissolved precipitate was then separated from the solution by centrifugation and the precipitate and solution analyzed by radiometric methods. The solution was found to contain 91% of the plutonium contained in the original precipitate with 6% remaining in the undissolved precipitate and 3% unaccounted for.
It will be apparent to those skilled in the art that various modifications in the present invention exist. In general, it may be said that any process for the isolation of plutonium, wherein the plutonium is separated from an alkaline solution either directly or together with a uranyl sulfide carrier, is to be considered as lying within the scope of the present invention.
What is claimed is:
1. The process of separating plutonium from contaminants normally associated therewith in neutron-irradiated uranium, which comprises treating an aqueous alkaline solution containing plutonium values and contaminants normally associated therewith, said plutonium having a Valence state less than +5, in the presence of a source of 'uranyl ions, with a soluble sulfide, whereby a plutoniumcontaining uranyl precipitate is formed, separating said precipitate from the solution, treating said precipitate with an aqueous solution containing carbonate ion in excess, whereby the plutonium is dissolved away from the fission product sulfides insoluble in excess carbonate, and separating said insoluble fission product sulfides from the plutonium-containing solution.
2. The process of claim 1 in which the soluble sulfide is hydrogen sulfide.
3. The process of separating plutonium values from contaminants normally associated with plutonium in neutron-irradiated uranium, which comprises treating an aqueous alkaline solution containing said plutonium values in a valence state less than +5, fission product values and a source of uranyl ions with a soluble sulfide, whereby a uranyl precipitate containing said plutonium values and insoluble fission product values is formed, separating said precipitate from the solution which contains fission product sulfides which are soluble in alkaline solution, treating said precipitate with an aqueous solution containing hydroxide ions and carbonate ions in excess of the amount stoichiometrically required to form a soluble carbonate complex with the uranyl and plutonium ions in said precipitate whereby the plutonium is dissolved away from the fission product sulfides insoluble in excess carbonate, and separating said insoluble fission product sulfides from the solution containing said plutonium values and said uranium values dissolved therein.
4. The process of separating plutonium from contaminants normally associated with plutonium in neutronirradiated uranium, which comprises treating said plutonium contained in an aqueous alkaline solution in the tetravalent state, with a soluble sulfide whereby a plutonium-containing precipitate is formed, separating said precipitate from the solution, treating said precipitate with an aqueous solution containing carbonate ion in excess, whereby the plutonium is dissolved away from the fission product sulfides insoluble in excess carbonate, and separating said insoluble fission product sulfides from the plutonium-containing solution.
5. The process of separating plutonium from an aqueous alkaline solution in which plutonium is contained in very dilute concentration, in a valence state less than +5, which comprises treating said plutonium with a soluble sulfide in the presence of a source of uranyl ions, whereby a plutonium-containing uranyl precipitate is formed, and separating said plutonium-containing uranyl precipitate from the solution.
6. The process of separating plutonium from a contaminant whose sulfide is soluble in an aqueous alkaline solution and which is normally associated with plutonium in neutron-irradiated uranium, which comprises treating said plutonium contained in an aqueous alkaline solution in a valence state less than +5, in the presence of a source of uranyl ions, with a soluble sulfide whereby a plutoniumcontaining uranyl precipitate is formed, and separating said precipitate from the solution which contains said contaminant.
References Cited in the file of this patent Seaborg et al.: Journal of the American Chemical Society, vol. 70, pages 1128-1134 1948). Report submitted March 21, 1942.

Claims (1)

1. THE PROCESS OF SEPARATING PLUTONIUM FROM CONTAMINANTS NORMALLY ASSOCIATED THEREWITH IN NEUTRON-IRRADIATED URANIUM, WHICH COMPRISES TREATING AN AQUEOUS ALKALINE SOLUTION CONTAINING PLUTONIUM VALUES AND CONTAMINANTS NORMALLY ASSOCIATED THEREWITH, SAID PLUTONIUM HAVING A VALENCE STATE LESS THAN +5, IN THE PRESENCE OF A SOURCE OF URANYL IONS, WITH A SOLUBLE SULFIDE, WHEREBY A PLUTONIUMCONTAINING URANYL PRECIPITATE IS FORMED, SEPARATING SAID PRECIPITATE FROM THE SOLUTION, TREATING SAID PRECIPITATE WITH AN AQUEOUS SOLUTION CONTAINING CARBONATE ION IN EXCESS, WHEREBY THE PLUTONIUM IS DISSOLVED AWAY FROM THE FISSION PRODUCT SULFIDES INSOLUBLE IN EXCESS CARBONATE, AND SEPARATING SAID INSOLUBLE FISSION PRODUCT SULFIDES FROM THE PLUTONIUM-CONTAINING SOLUTION.
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