US3000695A

US3000695A - Compounds and compositions containing plutonium

Info

Publication number: US3000695A
Application number: US637485A
Authority: US
Inventors: Glenn T Seaborg
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-12-27
Filing date: 1945-12-27
Publication date: 1961-09-19
Anticipated expiration: 1978-09-19

Description

United States Patc 3,000,695 COMPOUNDS AND COMPOSITIONS CONTAINING PLUTONIUM Glenn T. Seaborg, Chicago, Ill., assignor to the Umte States of America as represented by the United States Atomic Energy Commission N Drawing. Filed Dec. 97, 1945, Ser. No. 637,485

44 Claims. (Cl. 23-145) This invention relates to a new chemical element of atomic number 94, to novel compounds and compositions thereof, and to methods for their reduction and oxidation.

The term element 94 is used throughout this specification to designate the element having atomic number 94. Element 94 is also referred to in this specification as plutonium, symbol Pu. Likewise, element 93 means the element having atomic number 93, which is also referred to as neptunium, symbol Np. Reference herein to any of the elements is to be understood as denoting the element generically, whether in its free state, or in the form of a compound, unless otherwise indicated by the context.

The apparent discovery of transuranic elements was first announced by Enrico Fermi in 1934. At that time, Fernn' stated that the bombardment of uranium with neutrons gave beta activities which he attributed to transuranic elements of atomic number 93 and possibly higher. From 1934 to 1938 other workers, notably Hahn and Curie extended this work. But in 1939, Hahn discovered that the elements which he and others had believed to be transuranic elements were in fact radioactive elements of intermediate atomic weights produced by the fission of uranium. Hahns results were subsequently confirmed, and a great many other fission products in addition to those first found by Hahn were discovered and identified. Such products were all of lower atomic weight than uranium, generally of atomic numbers in the middle of the periodic system.

So far as is known, prior to about June 1940, no positive evidence was found indicating the existence of any transuranic element. However, in June 1940, E. McMillan and P. Abelson published in the Physical Review, 57, 1185 (1940) their discovery that a 2.3 day activity produced by the bombardment of uranium with neutrons was an isotope of element 93, probably 93*. Although it was assumed that the initial product of the beta decay of the 93 isotope of 2.3 day half-life would be a nucleus of atomic number 94, there was no proof that any such 94 nucleus could have more than an ephemeral existence before undergoing spontaneous disintegration. McMillan and Abelson found no evidence of the production of any daughter product from their 93 isotope, and, in fact did not even obtain the 93 isotope itself in pure or useful form.

One phase of the present invention which is especially useful in plutonium recovery processes relates to methods for the control of the state of oxidation of plutonium. An object of this phase of the invention is to provide means for attaining a plurality of oxidation states of plutonium. Another object of this phase of the invention is to provide methods for oxidizing plutonium from a lower to a higher valence state, and for reducing plutonium from a higher to a lower valence state. A further object is to provide means for stabilizing lower and higher oxidation states of plutonium in aqueous solutions of plutonium ions. Additional objects and advantages of this phase of the present invention will be evident from the following description.

In accordance with the present invention it has been found that plutonium is chemically unlike osmium in many respects and is probably a member of a second rare earth group, the actinide series. It has further been discovered that plutonium, unlike a number of other members of this series, possesses a plurality of valence states. Plutonium has at least four valence states, including +3, +4, +5, and +6. In 0.5 M1.0 M aqueous hydrochloric acid the oxidation-reduction potentials are of the following magnitudes:

As may be seen from the above couples, the stability of the higher oxidation states is dependent on the hydro- 'gen ion concentration. In moderately acidic solutions the Pu+ ion is generally very unstable and disproportionates to Pu+ and Pu The Pu+ ion is capable of disproportionating to the Pu+ ion and the PuO ion, and in dilute aqueous hydrochloric acid this disproportionation may take place to a considerable extent. The Pu+ disproportionation is opposed, however, by

increase in hydrogen ion concentration and by the presence of ions which tend to complex or otherwise stabilize the Pu+ ion. The effect of additional ions in hydrochloric acid solutions is illustrated by the following potentials for the Pu+ Pucouple:

1.0 M HCl O.97 V. 1.0 M HCl--0.1 M H PO -0.80 v. 1.0 M HCl-LO M HF 0.53 v.

Generally the anions of slightly ionized acids tend to complex the Pu+ ion to a much greater extent than the anions of highly ionized acids. Thus, Pu+ is only slightly complexed by C10 3 Cl, and N0 1 it is complexed to a much greater extent by and it is very strongly complexed by PO F C H 0 and 0 0 In addition to the complexing effect of the anions of the acids employed as solvents for plutonium, certain of these acids may also serve as oxidizing agents. However, at room temperatures, or moderately elevated temperatures, and in the absence of oxidation catalysts, the rate of oxidation by the acid is often so low that this effect may be ignored. Thus, the Pu+ ion is stable for considerable periods of time in perchloric acid, although under proper conditions, the latter is capable of oxidizing Pu+ to PuO It is therefore desirable to control the state of oxidation of the plutonium by the use of oxidizing agents and reducing agents which have rapid reaction rates under the conditions employed for processing the solutions.

The Pu ion may suitably be oxidized to the Pu0 ion by the addition of an active oxidizing agent having an oxidation-reduction potential substantially more negative than the oxidation-reduction potential of the Pu+ PuO couple in the particular solution employed. The following are representative potentials for this couple:

1.0 M HCl 1.0 v. 1.0 M HNO -1.1v. 1.0 M H2804 1.3 V.

oxidizing agents having adequate oxidation-reduction potentials for use in such solutions may be chosen by reference to tables such as the table of standard oxidation-reduction potentials given in the Reference Book 3 of Inorganic Chemistry by Latimer and Hildebrand (The MacMillan Company, New York, 1934).

It is generally desirable to effect purification and concentration of plutonium in nitric acid solutions. Examples of oxidizing agents for use in such solutions are bromates, permanganates, dichromates, silver-catalyzed peroxydisulfates, and ceric compounds. To effect the oxidation, a quantity of oxidizing agent at least equivalent to the amount of plutonium is added to the solution, and the resulting mixture is digested at a moderately elevated temperature for a sufficient period of time to insure complete oxidation of the plutonium. In most cases, this digestion may suitably be effected at 60-80 C. for 15-60 minutes. In order to maintain the plutonium in the hexavalent state for considerable periods of time after oxidation, it is desirable to employ an excess of oxidizing agent to serve as a holding oxidant. This is especially true if an acid solution is to be processed in ferrous metal equipment, or under other conditions permitting subsequent reduction of the plutonium.

Neptunium may be oxidized by any of the oxidizing agents mentioned above, without the necessity of digestion at an elevated temperature. This greater rapidity of oxidation of neptunium at low temperatures may be utilized to effect preferential oxidation of neptunium without substantial oxidation of plutonium. The preferred oxidizing agent for this purpose is the bromate ion. At temperatures of 15-25 C. neptunium may be substantially completely oxidized by alkali metal bromates in nitric acid solutions, which contain ions such as 80.; ions to complex +4 plutonium, without appreciable oxidation of plutonium to the heXava-lent state. There is some evidence that bromate oxidation of plutonium may be catalyzed by cerium, and it is therefore desirable to effect the preferential oxidation of neptuniurn in ceriumfree solutions.

For the reduction of plutonium, reducing agents of adequate potential may be selected by reference to tables of standard potentials such as the table previously referred to. The reduction may suitably be effected by digestion at room temperature or slightly elevated temperatures. Digestion for 15 to 60 minutes at 15 to 35 C. will generally be satisfactory.

For the reduction of PuO or Pu+ to Pu, the reducing agent should have an oxidation-reduction potential substantially more positive than the oxidation-reduction potential of the Pu+ Pu+ couple in the solution employed. Thus, in 1.0 M HCl an active reducing agent having a potential more positive than 0.97 v. will be required, and in 1.0 M HNO;;, a potential more positive than 0.92 v. will be necessary. In order to maintain the plutonium in the +3 valence state for appreciable periods of time, it is desirable to maintain an excess of the reducing agent in solution.

In order to reduce PuO to Pu+ without reducing Pu+ to Pu, it is desirable to employ an active reducing agent having an oxidation-reduction potential substantially more positive than the oxidation-reduction potential of the Pu+ PuO couple, and substantially more negative than the oxidation-reduction potential of the Pu+ Pu+ couple, in the solution used. A wider selection of reducing agents of the desired potential will be available for use in solutions containing ions which complex the Pu+ ion than are available for use in solutions which are substantially free from complexing effects. Thus, in 1.0 M HCl and 1.0 M HCl1.0 M HF, the oxidation-reduction potentials are approximately:

It may be seen that in the solution containing fluoride ion, reducing agents such as hydrogen peroxide and ferrous iron, which have oxidation-reduction potentials of O.68 v. and .0.74 v. respectively, will reduce PuO only to Pu+ whereas in the solution without fluoride ion to complex the Pu+ ion, these reducing agents will tend to reduce the plutonium to the +3 state. A reducing agent, such as sulfur dioxide, having an oxidation-reduction potential of O.14 v. will tend to reduce the plutonium to the +3 state in either solution.

When employing the preferred solutions of plutonium in aqueous nitric acid, the reduction of PuO to Pu+ is preferably effected in the presence of a complexing ion, employing reducing agents having oxidation-reduction po tentials of the same magnitude as hydrogen peroxide and ferrous iron. However, it is also possible to use stronger reducing agents such as sulfur dioxide if any excess reducing agent is removed or destroyed after the initial reduction is effected. In any case, if Pu+ is desired, the hydrogen ion concentration should be sufficiently high to oppose the disproprotionation of Pu+ to Pu+ and PuO For this purpose, it is desirable to employ solutions having a pH not substantially above 2, and preferably considerably below 1. In the case of aqueous nitric acid solution, it is generally desirable to maintain a free acid concentration of at least 1M.

It will be apparent that the considerations discussed above will also apply to the oxidation of Pu+ to Pu+ without oxidizing Pu+ to PuO by the use of oxidizing agents having potentials intermediate the potentials of the two plutonium couples.

The plutonium oxidation and reduction processes described. above may be employed, if desired, for the simultaneous oxidation or reduction of both neptunium and plutonium. Such simultaneous oxidation or reduction will be attained provided equilibrium is reached. As previously pointed out, however, differential reaction rates may be utilized to attain one oxidation state for neptunium and another oxidation state for plutonium.

The solutions of plutonium ions of the various valence states described above are useful for the electro-deposition of plutonium, for the precipitation of plutonium compounds while leaving contaminating compounds in solution, and for the precipitation of contaminating compounds while leaving plutonium in solution.

The oxidation state of plutonium in aqueous solutions of the various plutonium cations may be determined in accordance with methods commonly used for the determination of the valence state of other metals in solution. Thus, the total plutonium in solution may be determined by quantitative gravimetric or radiometric analysis, and the percentage of any particular ion may then be determined by a suitable differential analysis, such as quantitative oxidation or reduction, polarographic analysis, or the like. Spectrophotometric analysis is especially advantageous for determining qualitatively or quantitatively the various plutonium ions in solution, in view of the sharp characteristic peaks in the absorption spectra for the different valence states. Representative molar extinction coefiicients for the Pu Pu, and PuO ions in aqueous inorganic acid solutions are given in the following tables:

Table 1 Pu+ in 1 M 1101 Wave length in A 4, 260 4, 560 4, 740 5, 050 5, 620 6, 010 6, 660 8, 000 9, 090

Table '5-Continued Table v2 Pu 111 1 M HNo,

Weave length in 4, 040 4, 220 4, 480 4, 760 5, 020 5, 460 6, 600 7, 080 8, 000 8, 550 Molar extinctlon eoetficient 27.0 24. 5 17.5 72. 5 8. 7 17. 31. 0 14.0 18. 9 13. 2

Table 3 Pu in 1 M H280 Wave length in A 4, 090 4, 360 4, 810 5, 480 6, 640 7, 200 8, 140 8, 510 Molarextinetioncoefficient 29. 2 28. 5 85.2 20.0 39. 6 21.0 27. 1 14.3

Table 4 P1102+ in 1 M HNO;

Wave length in A 4, 590 4, 700 5, 060 5, 220 6, 240 8, 310 9, 580 9, 870 Molarextinctioncoefficient. 15.0 14. 0 14.0 14.0 10.0 171.0 23.0 17.0

The suitability of various anions for the precipitation of insoluble plutonium compounds will depend on the oxidation state of the plutonium and on the nature of the aqueous solvent from which the precipitation is to be made. I have found that the anions which are suitable for the precipitation of an insoluble compound of hi valent or tetravalent plutonium fromany solution suitably comprise the anions which may be used to precipitate an insoluble compound of trivalent or tetravalent cerium from the same solvent. In the same manner that the solubility of the lower valence states of plutonium parallels that of cerium, the solubility of hexavalent plutonium corresponds to that of hexavalent uranium.

The following plutonium compounds are insoluble in water, the term insoluble being used to designate solubilities of less than 0.01 mol per liter:

It is generally desirable to precipitate plutonium compounds from acidic aqueous solutions, and especially from aqueous inorganic acid solutions. Representative solubilities of trivalent and tetravalent plutonium compounds in solutions of various acids and of various acid concentrations are given in the following table:

Table 5 Trivalent plutonium Solubility Compound Aqueous solvent (mg. Pu/

liter) 1.0 M 69 1.0 M 49 1.0 M 37 0.2 M 25 0.6 M 7 0.6 M 28 0.8 M 20 0.8 M 66 0.8 M 210 0.8 M 23 0.8 M 120 0.8 M 900 Tetravalent plutonium Solubility 5 Compound Aqueous solvent (mg. Pu/

liter) Fluoride 0.1-2.0 M HNO3+0.52.0 M HF- 350-700 Ptgassum double 0.52.0 M HNO;+0.5-2.0 M HF. 10-50 mm e. Lanthanum 0.5-2.0 M HNO;+0.52.0 M HF- 20-70 10 double fluoride.

date 24 84 73 103 4 11 15 47 95 32 15 11 a 14 25 20 29 1 i 25 23 I 4 63 550 12 16 29 30 72 710 HNOa+3.1% H202 70 l. HNO3+5.4% H20 50 1.0 M HNO3+7.5% H202".-- 20 0.01 M Na2SO4+HrSO4, pH 5.4. 0. 02 0.01 M Nazs04+H2sO pH 4 1. O. 2 0.01 M Na2SO4+H2S04, pH 3.7- 0. 5 0.01 M N82SO4+H2SO4, pH 3.0. 1. 2 0.01 M NazSO4-i-HzSO4, pH 2.5-. 20. 9 1.0 M N3ZSO4+H2SO4, H 6.3---. 1.1 1.0 M Na2SO4+HzS04, D 5 1 l 16 1.0 M NaZSO4-I-HQSO4, pH 4.2 217 40 1.0 M N ZSOA-I-H2SO4: PH 3.6.... 300 1.0 M Na2SO4+HzSO4, pH 3.2 355 0.1 M NaClO4+HO104, pH 1.3.- 8. 0 0.1 M N aClO4+HOlO4, pH 1.6- 4. 2 0.1 M N aOlO4+HGlO4, pH 1.8 2.1 0.1 M NaO10l+HOlOo P 2.2. 1. 0 0.1 M NaO1O4+HOlO4, pH 3.1- 0. 4 0.1 M NaOlO4+HOlO4, pH 4.1- 0.3 0.1 M NaO1O4+H0lO4, pH 5.0 0. 2

Anion Cations which form soluble compounds Fluoride Cs, Rb, Zr, Nb-+ Ag. Orthophosphate Cs, Rb. Iodate Cs; Rb, La, Coi and other rare earths.

The reduction of plutonium is illustrated in the following example by way of its preoipitationon a carrier.

EXAMPLE 1 7 An 8.6 N sulfuric acid solution was prepared containing lanthanum sulfate in a concentration of approximately 430 mg. per liter and plutonium in tracer concentration. To this solution was added about 2.1 times its volume of a saturated aqueous solution of sulfur dioxide, and the mixture was allowed to stand at room temperature for 25 minutes to effect reduction of any hexavalent plutonium. The sulfuric acid concentration of the resulting solution was about 2.8 N and the lanthanum sulfate concentration was about 139 mg. per liter. About 27% by volume of 48% aqueous hydrofluoric acid was then added to the solution and the resulting lanthanum fluoride precipitate was separated by centrifuging. Analyses for alpha radiation showed that the precipitate contained 93% of the plutonium which was present in the original solution.

The following example illustrates the direct precipitation of an insoluble plutonium compound, without a carrier, from a solution derived from a preceding carrier precipitate after reduction of the plutonium by the process of this invention.

EXAMPLE 2 A mixture of hydroxides comprising 88.2% by weight of lanthanum hydroxide, 9.9% plutonium hydroxide and 1.9% potassium hydroxide, was dissolved in 2.03 times its Weight of 16 N nitric acid. Approximately 3.22% by weight of concentrated sulfuric acid (sp. gr. 1.84) was added to the resulting solution, which was then diluted with water to form a solution 0.8 N with respect to nitric acid and 0.2 N with respect to sulfuric acid. The plutonium concentration of this solution was 8.25 g. per liter. The solution was heated to 60 C. and 50% by volume of 30% aqueous hydrogen peroxide was added over a period of one hour. The resulting slurry was digmted for an additional hour at room temperature, after which the plutonium peroxide (probably a basic peroxidic sulfate) was separated by filtration. The precipitate was then dissolved in 16 N nitric acid, sulfuric acid was added, and the solution diluted to 0.8 N HNO -0.2 N H SO Plutonium peroxide was then reprecipitated and separated by filtration as before. The reprecipitated product, which was free from lanthanum, amounted to 99% of the plutonium originally present in the lanthanum hydroxide mixture.

In order to remove fission products by precipitation for the purpose of decontaminating plutonium, the plutonium is maintained in solution in the hexavalent state while precipitating a carrier for the contaminating cations. The carrier for this procedure may suitably comprise a carrier for trivalent or tetravalent plutonium, and such a carrier is highly advantageous when employed alternatively as a carrier for reduced plutonium and as a carrier for contaminants from a solution containing oxidized plutonium. In such a combination procedure, contaminants which were carried with reduced plutonium in one step of the process may be carried away from oxidized plutonium in a succeeding step employing the same carrier. Conversely, contaminants which would be carried with reduced plutonium on a given carrier may first be carried, on that carrier, away from oxidized plutonium.

The following example illustrates decontamination by an oxidation-reduction carrier cycle:

EXAMPLE 3 Plutonium was separated from the uranium and fission products contained in uranyl nitrate hexahydrate which had received 100 milliampere hours of neutron bombardment. The uranyl nitrate had been stored for approximately four weeks after bombardment, and it contained a substantial amount of 94 Pu but was practically free from 93 N The 94 Pu was separated by the following procedure:

Approximately 1053 parts by weight of the bombarded uranyl nitrate hexahydrate described above and approximately 30 parts by weight of thorium nitrate dodecahydrate were dissolved in suflicient nitric acid to produce a 8 solution 2 N with respect to nitric acid after the addition of 3186 parts by weight of a 0.35 M potassium iodate solution. incorporated as a tracer to give an a count of 10,000 per minute per m1. of the final mixture. The potassium iodate solution was then added, producing a solution having a uranium concentration of approximately 0.050 g. U per ml. This solution, containing the resulting thori um iodate precipitate, was allowed to stand for twenty minutes at room temperature.

The thorium iodate precipitate, containing the bulkofthe plutonium, was then filtered off and washed with a solution 1.0 M with respect to nitric acid and 0.1 M with respect to potassium iodate. The washed precipitate was dissolved in 1188 parts by weight of 12 N hydrochloric acid, 2198 parts by weight of 0.5 M sodium dichromate solution was added, and the resulting solution wasthen diluted with water to a concentration 2.4 N -with respect to hydrochloric acid and 0.1 M with respect to sodium dichromate. This solution was then digested for one half-hour at 65 C. to eliect oxidation of the Pu+ to Pu+ The Pu+ solution was then cooled to room temperature, after which 4248 parts by weight of 0.35 Mpotassium iodate solution was added, and the mixture was allowed to stand for twenty minutes at room temperature. The resulting thorium iodate precipitate, containing the bulk of the fission products, was filtered ofi and washed in the same manner as the first thorium iodate precipitate.

The distribution of the plutonium and fission products between the first thorium iodate precipitate, the first supernatant liquid, the second thorium iodate precipitate, and the second supernatant liquid, was determinedby measurement of the on, p, and '7 radiation omitted. For this purpose, blank determinations were first made on the original mixture, prior to the separation of the first thorium iodate precipitate. The oz count on this original mixture was taken to be that of the added 94 Pu Aliquots were analyzed for total {3 count, and for total [3 count corrected for the UX p count, by means of Geiger-Mueller counters and well known techniques. Aliquots of the two thorium iodate precipitates and of the two supernatant liquids were then analyzed for 5 and 7 activities in the same manner.

The plutonium content of the two thorium iodate precipitates and of the two supernatant liquids was recovered by an additional precipitation in each case, and the or activity of each of the precipitates was then determined. Since 94 Pu and 94 Pu have identical chemical properties, the distribution of 94 Pu as indicated by the a counts, also represented the distribution of the 94 Pu The distribution of uranium, plutonium, and fission products obtained by the above separation procedure is shown in the following table:

Table 6 Percentage of original substance The following example illustrates concentration of plutonium with respect to its carrier, as well as decontamination, in an oxidation-reduction carrier cycle:

EXAMPLE 4 Lanthanum fluoride, carrying plutonium as the only alpha-active component, and carrying beta-activecon Sufiicient radioactive plutonium, 94 Pu ,--was- 9 tamifiants, was dissolved in a mixture of nitric and sulfuric acids. The solution was evaporated until fumes of sulfur trioxide were evolved and was then cooled and diluted with water to 30 times the volume of the fuming 10 which differs from the plutonium carrier as to both cation and anion. I II a A t I EXAMPLES a A cerous fluoride precipitate carrying plutonium as solution A rnixtureof potassium peroxydisulfate and theIonlyvalphamcfive cqmponentfland cmyingvbetaacfive sllver filtrate a F of 20 to was then added contaminants, was subjected to radioactive analysis for the solution was d gested for 15 minutes toeffect oxidatotal alpha and beta radiation The precipitate was Q Plutomum to hexavalent f Hydro solved in nitric and sulfuricacids, the solution evaporated fluoric acid Was then added m a concentration in excess I to drynessi and the residue dissolved in aqueous nitric of the equivalent concentration of lanthium ion. After An excess of potassium bromatewas introduced digestion for 5 minutes the lanthanum fluoride precipitate and the bmmate ion, catalyzed by cerium, Ioxidized was P P y centll-fugmgplutonium from the tetravalent to the hexavalent state, The centrifugate was evaporated until fumes of sulfur A substantial opo ti nn f the Camus ion was Simulg tIlOXidG Were evolved, thus destroying the PfiIOXYdlSLlltaneously oxidized to eric i011, Thorium i011 and an fate and eifecting reduction of the plutonium to the tetraexcess of iodate ion-were then introduced to precipitate valent state, and the solution was then cooled and diluted mixed thorium and ceric iodates. This precipitate was with water. Lanthanum ion, an amount less than that in separated I by centrifuging and was dissolved and reprethe preceding precipitate, together with an excess of hycipi d addlflonal ihorlulu f G Q t drofluoric acid, were then introduced. The resulting Ian- 20 ThBICeIItYIfUgatBISIfI' 01.11 the two iodate P eclpltatiis were thanum fluoride precipitate was separated by centrifug- QP and evaporated W1th ooncentrated hydrochlonf ing, washed with dilute hydrofluoric acid, and dried. q resultmg m W5 cooled, and The ratios of plutonium to lanthanum fluoride carrier g g g i i g f i 3 g a in the initial material and in the final precipitate were deg q W i e 3 {3 e igg termined on the basis of alpha radiation and weight of F 5 non preplp 6 W5 separ y eel} n lanthanum It was found that the ratio of lutonium washed wlth dllute hydrofluonc acid and dned t I th fin 1 t 131 Radioactive analysis of the iodate precipitates showed g i i e .2 prficlpl a f 6 Ta them to be inactive with respect to alpha radiation, thus i mm a W ereas f f eta i indicating no by-product loss of plutonium. Analysis mation to carrier t o the final preclpltate as only 13% of the final plutonium-carrying cerous fluoride, precipitate of the ratio in the imtial material. I I showed it to contain only one third of the beta radia: e fqllowmg amp Illustrates an a p titm of the initial cerous fluoride precipitate. tron carrier cycle utilizing smiultaneous precipitation of Combinations of variousreducing and oxidizingagents two contarmnant carriers, one of which contains the same as applied to diiferent carrier precipitations are set forth cation element as the plutonium carrier and the other of in Tables 7 and 8.

Table 7 Preceding First pluto- Matathe- Fission prod- Reducing Second pluto- Metathev Final solution nium carrier sizing Subsequent solution oxidizing agent not carrier agent niurn carrier sizing solution precipitate agent precipitate precipitate agent (ZIO)3(PO4)2 Hi0i (ZIO)H(PO4)2 Aq HNot LaFs HzCzOi U(C204)2 Aq HNO; LeFt+oeFi so o H 1. LEKCZOOa-F LaF Th(IOa)4 L8.2(C1O4)3 Ce(IO Aq GEE; UO4.XHZO Aq H01. CGF H102"... LaFa NaOH Aq HNOs ThE Laz(C204)3 Aq HNOa T11F4 (ZIO)3(PO4)7 Aq HNOQ oet(P0i)i. ThF4 NaOH Aq H01. (ZlO)a(PO4)2. LaFa (Zr0)3(Poi)i. NaOH (ZI'O)3(PO4)Z Table 8 First pluto- Metathe- First fission Second i'ission n v Second pluto- Metathee Preceding niurn carrier sizing Subsequent Oxidizing product product Reducing nium carrier sizing Final solution precipitate agent solution agent carrier carrier agent precipitate agent solution precipitate precipitate I e A nNot A HNO3 KMHO4 Lari (ZI'O)3(PO4)2. H2o2- (ZIO)3(PO4)2 Aqfirioi Aq.HOl Aq.HO1 OB(NOa)4 LaF; CeFi B20204- C1(Cz04)a AQ.HNO3 Aq. HNOs.. Kfaszgfta- LaFs 20 Th04.XHzO

g AQ-HNOs Aq.(NH4)2CzO4 1194(02093--- La(OH)3 Aq.HC1. Aq.HNO3 LaP T Hi0i. Th(IO3)4 Aq.HNO Aq. HN03 s02 UO4.XH20- AQ.HN03 Aq. HNO3 sot-.. Tum Aq. HCL- Cez(C20i)a Aq. HSIOH- 112C204- T (CRO-l)fl. Aq.HC1 Thump"... 0' Kiortotmq zr0)'t(P0i)t. H20204. Aq. HO Th(IO )4 Kioriotm. L3PO4 20 m. Aq.HNOa ThF4. K ig ia- I C6(I03)4. s0i... o

g v Aq. HOL. U(C204)2 Ar I lNgfi Kioriotim (ZlO)3(PO4)2- OeFt.. soi,

I Aq.HNOs tzrontroni 2 2 7 mod... zto)t Poi i s0i Aq. H01-.. ZIO(IO3)2- K2C12O7 Z1O(IO )2 11202.... Aq.HO1- ZIO(IO3)Z Kfig g- LaFi Hi0i.

- In the recovery of plutoniumfrom neutron irradiated uranium by the decontamination and concentrationprocedures previously described, a precipitate may finally be obtained which consists of a single carrier and a substantially pure plutonium compound having the same anion as the carrier. Such a precipitate desirably has a low carrierto-plutonium ratio, e.g. 100/1 or lower. When a precipitate of this character is dissolved in a minimum quantity'of an aqueous inorganic acid, substantially pure oxygenated compounds of plutonium may be precipitated from the resulting solution.

The term oxygenated compound of plutonium, as used herein and in the appended claims, signifies a compound having at least one oxygen atom directly bonded to .a plutonium atom. Plutonium peroxide and'the various basic peroxidic salts of'tetravalent plutonium are examples of plutonium compounds having directly bound oxygen. These compoundsmay be precipitated from acidic solutions of tetravalent or hexavalent plutonium by the addition of a suitable peroxide, preferably hydrogen peroxide. The resulting hydratedprecipitattes are commonly mixtures of compounds having different ratios of oxy groups, peroxy groups, and acid anions, with the result that the over-all ratios are generally non-integral. Representative products of this class are shown below:

2.54(c1) 0.45 ('0=) 0.482.297. 120 Pu(O")2.61(SO4=)O.14(N0a)O.19(O=)0.46-1.65H2O Such products may contain hydrated compounds of the following types:

The following example illustrates the preparation of a basic peroxidic plutonium nitrate-sulfate:

EXAMPLE 6 A lanthanum fluoride-plutonium fluoride precipitate containing about 25% by weight of plutonium tetrafluoride is fumed with concentrated sulfuric acid until no further hydrogen fluoride is evolved. The material is then dissolved in aqueous nitric acid to form a solution 1.0 N with respect to nitric acid and 0.1 M with respect to sulfuric acid, having a lanthanum concentration of about 37.1 g. per liter, and a plutonium concentration of about 13.2 g. per liter. Aqueous hydrogen peroxide (30% H by weight) is then added over a period of one hour, at 20 C., in an amount such that the final solution contains 10% H 0 by weight. The slurry is then digested for one hour at 20 C. and filtered. The product thus obtained is a blue-green solid corresponding to an empirical formula It is readily soluble in acids and is useful for the preparation of other plutonium compounds.

Plutonium hydroxides and the various basic salts of tetravelent plutonium are additional examples of plu- 1'2 tonium compounds having directly boundoxygen. Compounds of this class may be precipitated by neutralizing acidic solutions of trivalent or tetravelent plutonium. The resulting products are obtained as hydrated precipitates comprising mixtures of different compounds such that the over-all ratio of hydroxide ion to acid anion is usually non-integral. Such mixtures may be represented by empirical formulas such as If such precipitates are dried without washing, Partial dehydration of the hydroxide, or transformation toa hydrated oxide structure may occur, and the mixtures may then be represented by empirical formulas such as 2( s)x' 2 and PuO (SO -yH 0 where x and y may be, but usually will notbe, integers.

Such products derived from tetravalent plutonium may contain compounds of the following types:

If an initial precipitate of the type described above is thoroughly washed or digested in alkali, substantially pure hydroxide is obtained. On drying the resulting hydroxide, even at moderately elevated temperatures, it is transformed at least partially to the hydrated oxide. The following example illustrates a suitable procedure for the preparation of this compound:

EXAMPLE 7 A basic peroxidic plutonium nitrate-sulfate precipitate, prepared as in Example 6, is dissolved in 16 N nitric acid *and diluted with water to form a solution having a nitric This compound is soluble in aqueous solutions having a pH of at least 7.0 to the extent of less than 2 mg. of plutonium per liter. It is readily soluble in strong acids and is useful for the preparation of other plutonium compounds.

The procedure of the above example may be modified by saturating the solution with sulfur dioxide prior to neutralizing with ammonium hydroxide. In such case the product obtained is the trivalent plutonium hydroxide. This compound is a blue solid which is readily soluble in acids and soluble in 5 N ammonium hydroxide to the extent of about 0.09 g. of plutonium per liter. This compound, as well as the tetravalent hydroxide is particularly useful for the production of other plutonium compounds.

Ignition of the hydrated oxides of plutonium results in complete dehydration to the corresponding oxides. Partial dehydration takes place at temperatures only slightly above room temperature, but it is desirable to heat the material to a temperature in the range of 500- 1000 C. to effect complete dehydration. The following example illustrates the production of plutonium dioxide.

EXAMPLE 8 Tetravalent plutonium hydroxide prepared as in Example 6, is ignited to constant weight in a mufiie furnace at about 850 C. The resulting compound, P is a crystalline solid appearing green by reflected light and yellow by transmitted light. It is soluble in strong mineral acids. The crystalline structure is face-centered cubic, with four molecules per unit cell and a lattice constant of 5.386:0.002A. The calculated density is 11.44.

Plutonium dioxide may also be prepared by the ignition of the plutonium nitrates or the basic peroxidic plutonium nitrates at temperatures above 300 C., and preferably at a temperature in the range of 500-1000 C.

The various soluble salts of plutonium may be prepared by dissolving plutonium hydroxide in the acid having the desired cation, adjusting the oxidation state of the plutonium in the resulting solution, and evaporating to crystallize out the desired compound. The insoluble salts may be prepared in a similar manner by dissolving plutonium hydroxide in an acid which forms a soluble salt, adjusting the oxidation state of the plutonium, incorporating the cation of the desired insoluble salt, and separating the resulting precipitate. The following examples illustrate the preparation of representative plutonium salts:

EXAMPLE 9 Tetravalent plutonium hydroxide is dissolved in 16 N nitric acid and the resulting solution is evaporated until the tetranitrate crystallizes out. The product is obtained as a highly hydrated lemon yellow crystalline material corresponding to the formula Pu(NO -xH O. This compound is very soluble in water and in dilute acids. A concentration as high as 2.5 M in 1.7 N nitric acid is obtainable, although this solution may be somewhat super-saturated at room temperature.

EXAMPLE 10 Tetravalent plutonium hydroxide is dissolved in 16 N nitric acid, diluted to l N nitric acid, and heated to 75- 100 C. until spectrophotometric analysis indicates complete oxidation of the plutonium to the hexavalent state. The solution is then cooled and concentrated by evaporation under high vacuum until plutonyl nitrate crystallizes out. The product is yellow to orange in color, with a pink tinge, and corresponds to the formula It is extremely soluble in water (ca. 500 g. Pu per liter). Treatment with various organic solvents results in solution of PuO (N in the organic phase.

EXAMPLE 11 Trivalent plutonium hydroxide is dissolved in concentrated hydrochloric acid and the resulting solution is evaporated in a stream of hydrogen chloride until PuCl -6H O crystallizes out as a blue solid. This compound is deliquescent and melts at 94-96 C. It may be dehydrated in vacuo (less than -1'mrn. Hg pressure) at room temperature to the monohydrate, PuCl -H O. The monohydrate may be slowly transformed to an-' hydrous PuCl at 70 C. in a high vacuum (10 mm. Hg pressure). The anhydrous trichloride is more conveniently prepared, however, by heating the hexahydrate slowly to 250 C. in a stream of hydrogen chloride.

PuCl is a blue-green colored solid which is readily soluble in water to form purple colored solutions. The solid is stable with respect to air oxidation at room temperature but is converted to PuO on heating in air to 400 C. The crystalline structure of the trichloride is hexagonal with two molecules per unit cell. The lattice constants are a =7.38Oi0.00l A. and a =4.238i-O.00l A.

and the calculated density is 5.70.

14 EXAMPLE 12 The procedure of Example 11 is modified by substituting hydrobromic acid for hydrochloric acid and substituting hydrogen bromide for hydrogen chloride in the,

drying operation. The final product, anhydrous plutonium tribromide, is a blue-green crystalline compound having the following properties:

Melting Point-654 0.:4". Crystalline Structure:

orthorhombic. Four molecules per unitcell. Lattice constants: a =12.57 -0.0 5 A. a =4.11- -0.03 A. a =9.13i0.04 A.

Calculated density6.69.

EXAMPLE 13 The calculated density is 4.89. E

The hydrated tetrafluoride may be dehydrated at 350 C. in a stream of hydrogen fluoride to yield the anhydrous compound. PuF is a yellow to pale brown crystalline compound which is soluble in hot concentrated sulfuric acid or nitric acid. The crystalline structure is mono! clinic with 12 molecules per unit cell. The lattice constants are: A

The calculated density is 7.0.

EXAMPLE 14 The procedure of Example 13 is modified by saturating the hydrochloric acid solution with sulfur dioxide prior to incorporating the hydrofluoric acid. The resulting precipitate is plutonium trifluoride, which is separated from the supernatant solution and dried at 300 C. in a stream of hydrogen fluoride. The resulting product is anhydrous PuF a crystalline solid of purple toblack color having "a melting point of 1141 C.i7. The crystalline structure is hexagonal with two molecules per unit cell. The lattice constants are:

a =4.087:0.001 I A. a =7.240i0.001 A.

The calculated density is 9.32. 7 7 l Plutonium trifluoride may be dissolved by fuming with I EXAMPLE 15 Tetravalent plutonium hydroxide is dissolved in 16 N nitric acid and the resulting solution is diluted to about 2 N HNO Potassium nitrate is then added in excess of the equivalent plutonium nitrate concentration and a potassium-plutonium double fluoride is precipitated by the addition of hydrofluoric acid. The composition 1 d of the final solution from which the precipitation is made is approximately 1.8 N HNO 0.5 N KNO -3.0 N HF The precipitate is a pale green material corresponding to the empirical formula KPuF -xH O. After drying in vacuo at room temperature the product is obtained as an anhydrous crystalline compound conforming to the formula KPuF The crystalline structure is rombohedral with six molecules per unit cell. The lattice constants are:

Other double fluorides may be prepared by substituting other alkali metals or ammonia for the potassium in the above example.

EXAMPLE 16 solution is approximately 14.6 mg. per liter.

EXAMPLE 17 Tetravalent plutonium hydroxide is dissolved in 16 N nitric acid and the resulting solution is diluted nearly to 1.0 M HNO Orthophosphoric acid is then added in an amount sufiicient to produce a solution. The resulting white precipitate after drying in vacuo at room temperature conforms to the empirical formula This compound is isomorphic with the corresponding ceric and thorium phosphates. It is soluble in 0.6 M H PO -1.O M HNO;; to the extent of about 19 mg. Pu per liter.

EXAMPLE 18 The procedure of Example 17 is modified by saturating the nitric acid solution with sulfur dioxide prior to incorporating the phosphoric acid. In this case the dried precipitate is a violet colored crystalline compound which conforms to the empirical formula PuPO -xH O. It is soluble in 0.6 M H3PO4-LO M HNO solution to the extent of about 28 mg. Pu per liter. The crystalline structure of this compound is hexagonal, with three molecules per unit cell. The lattice constants are:

The calculated density is 6.04.

EXAMPLE 19 Tetravalent plutonium hydroxide is dissolved in aqueous sulfuric acid to form .a solution approximately 2 M with respect to H 50 and approximately 0.4 M with respect to Pu(SO About 40 percent by volume of methyl alcohol is added to the sulfuric acid solution and the mixture is allowed to stand for 16 hours. Approximately 7 percent by volume of concentrated sulfuric acid is then added, with agitation, and the precipitate is separated from the supernatant solution. The product is a pink crystal- 16 line solid which on analysis was found to conform to the formula PU(SO4)24H20.

Metallic plutonium may be produced by reduction of any of the plutonium halides with active metals such as the alkali and alkaline earth metals.

Metallic plutonium and the various plutonium compounds which have been described above are extremely useful for the production of atomic energy. Pu in the metallic state, or in the form of any of the compounds previously described, can undergo nuclear fission in a selfsustaining neutronic chain reaction. The critical size of a single mass of plutonium metal for self-sustaining chain.

reaction is of the order of 10 kg. The critical size of a single mass of fused plutonium trichloride is of the order of 25 kg., and the critical sizes for the other. compounds described above will lie between that of the metal and that of the itrichloride. When the plutonium or plutonium compound is dispersed in a neutron-slowing material, termed a moderator, the critical mass for self-sustaining chain reaction becomes very much less than. for the pure material. Under optimum conditions, the critical mass of plutonium may be as low as 200 grams. This quantity of plutonium in a single mass of material should not be exceeded Without providing adequate neutron-absorbing safety devices.

Plutonium or mixtures of plutonium and other fissionable isotopes may be utilized for the production of atomic energy in neutronic reactors in accordance with the disclosure of copending application Serial No. 634,311, filed December 11, 1945, by Emilio Segre, Joseph W. Kennedy, and Glenn T. Seaborg and granted as US. Patent No. 2,908,621 on October 13, 1959. In such utilization, metallic plutonium may be dispersed in a solid moderator such as graphite in a lattice structure, or any of the plutonium compounds described above may be employed as solutions or dispersions in a liquid moderator such as deuterium oxide.

Metallic Pu and Pu and all of the compounds of these isotopes are also useful as sources of alpha radiation. In conjunction with ot-n reacting elements such as beryllium, they may also be employed as neutron sources.

It is to be understood that this aspect of the present invention is not limited to the specific compounds and methods of preparation which have been described above by way of illustration. Other analogous compounds and equivalent methods of preparation are included inthe scope of this phase of the invention. Also, the particu lar oxidizing and reducing agents, processes, and solutions discussed herein are merely illustrative and are not to be construed as limiting the scope of the present invention. Other oxidizing and reducing agents having the required potentials may be utilized instead of those specifically mentioned, and the procedures may be modified in numerous respects, as will be evident to those skilled in the art.

What is claimed is:

1. A process for controlling the oxidation state of plutonium in an aqueous solution containing plutonium ions, which comprises incorporating in said solution an agent of the class consisting of oxidizing agents selected from the group consisting of bromate, permanganate, ceric ions, dichromate and peroxydisulfate plus silver cation and reducing agents selected from the group consisting of hydrogen peroxide, ferrous ions, sulfite ionsand sulfur dioxide.

2. A process for oxidizing plutonium from a lower oxidation state to a higher oxidation state in an aqueous inorganic acid solution containing plutonium ions, which comprises incorporating in said solution an oxidizing agent selected from the group consisting of bromate, permanganate, ceric ions, dichromate and peroxydisulfate plus silver cation and digesting the resulting mixture at a moderately elevated temperature until the oxidation reaction is substantially complete.

3. A process of oxidizing plutonium from an oxidation state not greater than +4 to an oxidation state of +6 in an aqueous nitric acid solution containing plutonium ions, which comprises incorporating in said solution an oxidizing agent selected from the group consisting of bromate, permanganate, ceric ions, dichromate and peroxydisulfate plus silver cation and digesting the resulting mixture at a temperature of 60 to 80 C. for 15 to 45 minutes.

4. The process of claim 3 in which the oxidizing agent is an alkali metal dichromate.

5. The process of claim 3 in which the oxidizing agent is a silver catalyzed alkali metal peroxydisulphate.

6. A process for reducing plutonium from a higher oxidation state to a lower oxidation state in an aqueous inorganic acid solution containing plutonium ions, which comprises incorporating in said solution a reducing agent selected from the group consisting of hydrogen peroxide, ferrous ions, sulfite ions and sulfur dioxide and digesting the resulting mixture at a moderately elevated temperature until the reduction reaction is substantially complete.

7. A process for reducing plutonium from an oxidizing state of +6 to an oxidation state not greater than +4 in an aqueous nitric acid solution containing plutonium ions, which comprises incorporating in said solution a reducing agent selected from the group consisting of hydrogen peroxide, ferrous ions, sulfite ions and sulfur dioxide and digesting the resulting mixture at to 35 C. for 15 to 60 minutes.

8. The process of claim 7 in which the reducing agent comprises the sulphite ion.

9. The process of claim 7 in which the reducing agent is incorporated by saturating the solution with sulphur dioxide.

10. A process for controlling the oxidation state of plutonium in an aqueous solution containing plutonium ions, which comprises providing in said solution suflicient oxidizing agent selected from the group consisting of bromate, permanganate, ceric ions, dichromate and peroxydisulfate plus silver cation to maintain the plutonium in an oxidation state of +6.

11. A process for controlling the oxidation state of plutonium in an aqueous solution containing plutonium ions, which comprises incorporating in said solution a suflicient amount of a reducing agent selected from the group consisting of hydrogen peroxide, ferrous ions, sulfite ions and sulfur dioxide to maintain the plutonium in an oxidation state of +3.

12. A process for controlling the oxidation state of plutonium in an aqueous solution containing plutonium ions, which comprises reducing any hexavalent plutonium in said solution to an oxidation state not greater than +4 with a reducing agent selected from the group consisting of hydrogen peroxide, ferrous ions, sulfite ions and sulfur dioxide, maintaining said solution free from excess reducing agent, and providing in said solution an anion which complexes tetravalent plutonium, said anion being selected from the group consisting of fluoride anion, acetate anion, oxalate anion and sulfate anion.

13. The process of claim 12 in which the anion is the sulphate ion.

14. The process of claim 12 in which the anion is the fluoride ion.

15. A composition of matter consisting essentially of an aqueous solution containing trivalent plutonium ions.

16. A composition of matter consisting essentially of an aqueous solution containing tetravalent plutonium ions.

17. A composition of matter consisting essentially of an aqueous solution containing ions of hexavalent plutonium.

18. A composition of matter consisting essentially of an aqueous solution containing tetravalent plutonium ions and anions of an incompletely ionized acid selected from 18 the group consisting of sulfate, fluoride, acetate and oxalate anions.

19. A composition of matter consisting essentially of an aqueous solution containing tetravalent plutonium ions and sulphate ions.

20. A composition of matter consisting essentially of an aqueous solution containing tetravalent plutonium ions and fluoride ions.

21. A composition of matter consisting essentially of an aqueous solution containing hexavalent plutonium ions and an oxidizing agent selected from the group consisting of bromate, permanganate, ceric ions, dichromate and peroxydisulfate plus silver cation.

22. A composition of matter consisting essentially of an aqueous solution containing hexavalent plutonium ions and dichromate ions.

23. A composition of matter consisting essentially of an aqueous solution containing hexavalent plutonium ions, silver ions, and peroxydisulphate ions.

24. A composition of matter consisting essentially of an aqueous solution containing trivalent plutonium ions and a reducing agent selected from the group consisting of hydrogen peroxide, ferrous ions, sulfite ions. and sulfur dioxide.

25. A composition of matter consisting essentially of an aqueous solution containing plutonium ions and sulphite ions.

26. A composition of matter consisting essentially of an oxide of plutonium haw'ng the formula PuO 27. A composition of matter comprising plutonium dioxide, having the empirical formula PuO' 28. A composition of matter consisting essentially of a basic peroxidic compound of plutonium of the formula P11207- 29. A composition of matter consisting essentially of a basic peroxidic plutonium nitrate having the formula 2 e( s)2- 30. A composition of matter consisting essentially of a plutonium salt of an inorganic acid having the formula 2 5( s)2- 31. A composition of matter consisting essentially of a plutonium salt of an inorganic oxy acid having the formula PH(OH)2(NO3)2.

32. A composition of matter consisting essentially of a nitrate of plutonium having the formula Pu( OH) N0 33. A composition of matter comprising a nitrate of tetravalent plutonium having the empirical formula PI1(NO3)4'JCH20.

34. A composition of matter comprising plutonyl nitrate having the empirical formula PuO (NO -xH O.

35. A composition of matter comprising tetravalent plutonium iodate having the empirical formula Pu(IO 36. A composition of matter consisting essentially of a phosphate of plutonium having the formula PuPO 37. A composition of matter comprising tetravalent plutonium orthophosphate having the empirical formula 3( 4)4- 38. A composition of matter consisting essentially of a sulfate of plutonium having the formula PuO SO 39. A composition of matter comprising tetravalent plutonium sulfate having the empirical formula Pu(SO 40. A composition of matter consisting essentially of a halide of plutonium having the formula PuX wherein X is a halogen selected from the group consisting of fluorine, chlorine and bromine.

41. A composition of matter comprising trivalent plutonium chloride having the empirical formula =PuCl 42. A composition of matter comprising trivalent plutonium fluoride having the empirical formula PuF 43. A composition of matter comprising tetravalent plutonium fluoride having the empirical formula PuF 44. A composition of matter comprising trivalent plutonium bromide having the empirical formula PuBr (References on following page) References Cited in 3h? file of this patent UNITED STATES PATENTS Thompson et a1. Mar. 19, 1957 OTHER REFERENCES Seaborg et al.: The Actinide Elements, pages 371- 433; published by McGraW-Hill Book Co., N.Y. (1954), Article by Cunningham.

Seaborg et al.: The Transuranium Element. 'Published by the McGraw-Hill Book Co., N.Y. (1954).

Articles by: Hamaker et al., pages670, 671, 673, 674 and 681; Abraham et al., pages 741, 757; Anderson, pages 796-800; Mooney et al., page 442; Zachariasen (I), pages 1463 and 1464; Zachariasen (II), pages 1477 and 1485.

Seaborg et al.: The Actinide Elements, pages 250. Published by McGraW-Hill Book Co., N.Y., 1954.

Seaborg et al.: The Transuranium Elements. Published by McGraw-Hill Book Co., N.Y., 1949 pages 25- 38 (Article prepared March 19, 1942).

Claims

1. A PROCESS FOR CONTROLLING THE OXIDATION STATE OF PLUTONIUM IN AN AQUEOUS SOLUTION CONTAINING PLUTONIUM IONS, WHICH COMPRISES INCORPORATING IN SAID SOLUTION AN AGENT OF THE CLASS CONSISTING OF OXIDIZING AGENTS SELECTED FROM THE GROUP CONSISTING OF BROMATE, PERMANGANATE, CERIC IONS, DICHROMATE AND PEROXYDISULFATE PLUS SILVER CATION AND REDUCING AGENTS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN PEROXIDE, FERROUS IONS, SULFITE IONS AND SULFUR DIOXIDE.