US2942968A - Method of separating uranium from alloys - Google Patents

Description

U ite. States Patent it LuSuanY.itQkiflbDut%4T -1Qm' toxfumaccecool below the melting temperature of the thorium-magnestummutechc $942968 (5896') led V tth bl h h han a L p :contento ecruci e, w ic YWas WTHOD atsolidpieceof metal contahfing'modistincnphases was machinedolf .in .a lathe, {and the centrakportion of each phase was removed and :Jcleaned. ,Samples :of .both assignorstothe United States of America astrepresented phases were zanalyzed, for u anium .by ten ammonium by theiUnitedStates Atomic EnergyCummission thiocyanatespectrophotometric method gandforuthorium t r i, gravimetricallyzby. oxalate preoipitation. TIPhewresults-of No Drawing Flled 1957 696389 these determinaticnstat various temperatures .=are comltremotChiotti "and Howard E. Shoemaker, Ames, Iowa,

10 Claims. 7 (Cl. 75-84. 1) piled in Table I.

Table Thisdnvention deals with therecovery of 15 mmmummssolved,

from metallicuranium-thorium mixtures part cua 'tliereentxlotilne lar from tor'alloys containing the in 9 t t t t comparatively small amounts. Mar-3% Mz:1 5% ure-Ms A number of, reactors, the. so-called breeder reactors, f use tho ium as breeding material, often in the .fqrmeof a blanket arranged aroundhthe fissicnable-fuelmaterial. 5 "55 "The breeding material captures and reacts withneutrons 110 t 80 not captured by the fissionablemateiial and form siUz 'd, 160 $33 a fissionable uranium isotope, by n, 7 reaction and sub- 2:3 Egg Egg sequent fl-decay. Such, reactors -using (thorium as blanlr 61 550 et materialaredescribed,for instance, in application 1 558 1 18 Seria1 No.'72l-,10 8' on -Fast Neutron ReactionSystern, 11 ,2' 1:450 filed by w'alter H. Zinn on'Jannary -9,"l-947. 1 5 4 3 131670 1 Operation ofwthese reactors is usually F discontinued at a point when the U -content is's below :1 percent :by 30 .Wei'ghttofthe-,neutron-reacted thorium mass. (Through ounthe app i ation per entages :given are percent by weight.) tQneaccount of this srnall-ratio-yof-Um -it-:is mill td ifi l l Y S 1 l an r ve t i ur ium LS whentahout 6'5 percentrma gnesium werestadded toi the tope. Aqueous methods using a solubn-p f ;th ;-ima di ftholqium inass ljshowfidianiaverage mhariumi:conitefitfibf rated metal have been used heretofore for this p p 0.91-3 percent, the content being somewhat lower when but these methods have the disadvantage that the uranithe h i content was 1 i th magnesium-rich um compounds obtained fromqtheseraqueous solutions phase, The balance of m uranium.rih phase was have to be converted to the metal for most reactors in fi u i Used- 1 ""ltwas also found that two liquid phases can be ob- EI'E'FYiSHaEIObleQFQf llihis illzlflMQ E i ifi p fi tained at a temperature lower than the melting point of Separating i m f l t. there of u anium by incorporating a further component, name- .W i 9 uranium is an dirwtlr a e-me '19 hnnmn, into the alloy. The quantity of the chroiQlT R- mium should be high enough to form the uranium-chro- "Ibis/315 p l this invention to PI :P 45 mium eutectic, which contains 5.2 percent of chromiess 'of-recovering-uranium from"thorium-uraniumimixi h ll f th iu present, B adding this tures, 0Y$ui 1h gl y QIA ZQJ J M a, "f amounti of chromium, the temperature at which two liqare obtained is reduced to about 860 (3., as ared with 1132 C. for pure uranium. The addiabout 5 percent of chromium, based on the total um content present in the alloy or metallic mixture, p the formation of a uranium-rich liquid phase These' data show that-theseparation'of' uranium from thorium :is" better :withlincreasing magnesium content and with decreasing temperature. V

The turan'iumnich Iphase's formed in these experiments,

It was 'found t-hat uranium is very little solubleminitail m-r chnma naiu ahmiu all and e e less soluble in puremagnesium. It was alsoTound that; .Q011l7 7 versely, he aa s nl t leht b e i The various=solubilities or uranium in pure magnesium! v ries and inthree magnesiumghprium alloysmgntaining {5535 con ng from 0.2 to 0.6 percent of thorium when and 16 percent' of ithorium, respectively, were ldeter ff eq brated with a magnesium-thorium alloy containing mined. In thesetests uranium Was.. ,jalways present-in m j Sarto percent of magnesium. While the addin' xc amount in order to make sure that the magi tion' of chromium has the great advantage of a lower sium-ri eh phases were saturated in uranium. Narious-de-:""separation temperature, it has the disadvantage of revices were used for this purpose, one being, for instance, iring;; an additional step, namely, that of uraniumla lel m c uc bl int whic thol ompqnc ts were 7, omium separation if chromium-free uranium is deintroduced and held tunder an atmosphere Eof argonifgas. -fillislret l. separation can be carried out by any proc- The, crucible sealed, by,-we1ding, and thersealed crug lcnown in the art; it does not form part of this invencible wast enclosed in a welded jacket of stainlessnsteel; T ttion; the assemblynwasvithen heated in an oscillating resist: V, "Ihe process of this invention for the separation of ance f n nace rotated back and fonth through ur nilllflgflom thorium contained in a metallic mass (the an are of'about 180 C. once about every 50 S QQQdS-I 5 ,te Ieniass is to comprise metallic mixtures and alloys) For solubility ndeterrninations, up t 0; 8 00 ,Q, rotation t thus'comprises adding magnesium to the mass in a quanwas carried out-for '2 hours, whiletor those at temperaijjjjfltyntoeflobtain a content of from 48 to percent by lures i 800 Mi 1.21 9 .C- l lgi'ettlll sztim iiwxe le-t v.uieit-llitin the mixture; melting the mixture; agitating the molten mixture; allowing the mixture to settle whereby duced to from l5to l0 The content of the crucible was then allowed tosettle, for phase separation T1 1 .-';t;W hases, a thorium-containing magnesium-rich phase for about the same time as rotation had been ca iedout and: ,uranium-rich phase are formed; and separating said and then either quenchedbr permitted tofurna ce-cool; two phases.

i The preferred magnesium content is about 58 percent,

' because then the magnesium-thorium eutectic is formed ing the mixture to about 1150 C. when both phases are I in the liquid state and the uranium-rich phase settles at the bottom, then cooling to below 585 C., preferably to room temperature, whereby the uranium-rich phase and the magnesium-thorium alloy solidify and finally separating the uranium from the alloy by mechanical means. Under these conditions the uranium-rich phase is obtained in one solid piece.

Or else, and this is the preferred method, the separation is carried out in two stages, namely, a preseparation and a final separation. Preseparation is effected by maintaining the reaction mass at a temperature above the melting point of the magnesium-thorium alloy but below the melting point of uranium, suitably just about above 585 C. in the case of the magnesium-thorium eutectic, and decanting the bulk of the liquid magnesium-thorium alloy away from a residue comprising the 'solid'uranium-rich particles and the remainder of the magnesium-thorium alloy; recovery of the uraniumfrom the residue is then carried out according to the methods given below. In the case of using a preseparation step less uranium is lost with the magnesium-thorium alloy on account of the lower temperature-used and the lower uranium solubility at lower temperatures.-

The residue, according to this invention, can be processed by two methods. One method comprises cooling of the residue to below the melting point of the magnesium-thorium alloy preferably to room temperature for solidification and separation of the solid uraniumrich phase from the solid remainder of magnesiumthoriurn alloy by mechanical means. According to the 4 other method, the residue which then has a temperature of about 585 C. is heated to above the melting point of uranium, which is about 1132 C., preferably to about 1150 C., whereby the heavy liquid uranium-rich phase, which contains less than one percent of thorium, separates and settles at the bottom of the container; the masses are then cooled to room temperature. In this case the use of the high temperature for melting the uranium does not involve a considerable uranium loss because the bulk of the magnesium-thorium alloy has been removed so that there is very little of the magnesiumthorium alloy left for dissolving uranium. The solid onepiece uranium phase is then separated from the solid onepiece magnesium-thorium alloy by mechanical means.

If chromium is added, it is preferably incorporated to the residue, that is, after the bulk of the magnesiumthorium alloy has been removed by decanting. The quantity of chromium is preferably 5.2 percent by Weight based on the total amount of uranium present. The mass is then heated toa temperature within the range from 860 to 900 C., whereby the uranium-chromium eutectic settles at the bottom while the magnesium-thorium alloy collects above it. Cooling to room temperature and separation by mechanical means complete the separation.

Separation by mechanical means can either be carried out by hitting the metallic mass with a hammer whereby the two solid pieces fall apart, or by removing the magnesium-thorium alloy by lathing; the latter is preferred when there is very little magnesium-thorium alloy present with the uranium-rich phase. For further cleaning the uranium piece can be immersed in dilute nitric acid whereby any magnesiumrthorium alloy still adhering to the surface is dissolved? The thorium content of the uranium phase, which is always less than one percent, can then be reduced further by repeating the process with pure magnesium whereby the thorium is dissolved in the magnesium but very little uranium is taken up.

Table II Mixing Settling Average chemical analyses Conditions Conditions Typical charge grams I Time, Time, Mg-rlch U-rich mine. O. mine. O. phase, wt. phase, wt.

percent percent 1,000 00-120 800 {gSfiEg- 1,000 120-180 B800 {@fifi-S 1,000 00-240 1.000 {@fgjfl:

1 000 Til-32.0.... 1:200 10 1,200 Th-1.2.

1.200 -10 1.200 Th32.0. 'Ih-0.85.

1,200 15 1,200 101-340-.-. Til-0.68.

1,000 10 1,200 Til-34.0-.-- Th-0.84.

1,200 10 1,200 Th-3.0..-- Hr-0.8.

'Ih-30 Til-0.4. 000 00-120 900 u-0.053 11-035.v

Or-0.13..... (Jr-5.6.

I Uranium shavin gs b Sample furnace-cooled from temperature indicated.

Aro-melte dell y. Y a Sample quenched instead or Iumace-cooled, from temperature indicated.

In view of the high reactivity of the metals involved, it is advisable to carry out the separation process under the exclusion of air; this is best accomplished by operating in an inert atmosphere of helium or argon gas.

The magnesium-rich phase can be processed by distillation for the separation of the magnesium from the thorium.

A number of uranium-thorium separations were carried out using a technique similar to that employed for the determination of the solubilities and described above. The conditions and results togetherwith the compositions of the mixtures melted are compiled in Table II.

The balance of the magnesium-rich phase in each of the above examples was magnesium and that of the uranium-rich phase uranium. The experiments show that a good separation is accomplished by the process of this invention.

It will be understood that this invention is not to be limited to the details given herein, but that it may be modified within the scope of the appended claims.

What is claimed is: v I

1. A process of recovering uranium from metallic uranium-thorium mixtures, comprising adding magnesium to the mass in a quantity to obtain a content of from 48 to 85 percent by weight; melting and forming a magnesium-thorium alloy at a temperature of between 585 and 800 C.; agitating the mixture; allowing the mixture to settle whereby two phases, a thorium-containing magnesium-rich liquid phase and a solid uraniumrich phase are formed; and separating said two phases.

2. The'process of claim 1 wherein the phases are separated by heating to about 1150 C. whereby both phases are melted and the uranium-rich phase settles at the bottom, "then cooling both phases to room temperature for solidification, and separating the uranium-rich phase from the magnesium-thorium phase by mechanical means.

3. The process of claim 1 wherein a phase preseparation is first carried out by heating the phases to above the melting point of the magnesium-thorium alloy, but below the melting point of the uranium and decanting the bulk of the magnesium-thorium alloy away from a residue containing the remainder of the magnesium-thorium alloy and solid particles of the uranium-rich phase.

4. The process of claim 3 wherein magnesium is added in a quantity of about 58 percent and the preseparation temperature is about 585 C.

5. The process of claim 3 wherein said residue is cooled.

to room temperature whereby the uranium-rich phase and the remainder of the magnesium-thorium alloy solidify and the phase is separated from the remainder by mechanical means.

6. The process of claim 3 wherein said residue is heated to about 1150 C. until the uranium-rich phase is melted and has settled at the bottom, it is then cooled to room temperature and the uranium-rich phase is separated from said remainder of the alloy by mechanical means.

7. The process of claim 3 wherein from 5 to 5.2 percent of chromium, based on the quantity of uranium, is added to the residue, the mixture thus obtained is heated to from 860 to 900 C. until a liquid light magnesiumthorium alloy has separated from a liquid heavy uraniumchromium eutectic, the alloy and the eutectic are then cooled to room temperature and separated by mechanical means. V

8. The process of claim 1 wherein melting is carried out in an inert atmosphere.

9. The process of claim 1 wherein magnesium is added to the separated uranium-rich phase whereby a further decontamination from any thorium still present with the uranium is obtained.

10. A process of recovering uranium from metallic uranium-thorium mixtures, comprising adding magnesium in a quantity to obtain a content of about 58 percent in the mixture and about 5.2 percent of chromium based on the uranium present in the mass; heating the mixture to about 900 C. and agitating it for thorough contacting; allowing the mixture to settle whereby two phases, a thorium-containing magnesium-rich phase and a uraniumchromium eutectic phase are formed; and separating said two phases.

References Cited in the file of this patent Lawroski: Survey of Separation Processes, P/ 823, 7

International Conference on the Peaceful Uses of Atomic Energy, v01. 9, pages 580-582 (1956). i

Finniston et al.: Metallurgy and Fuels, Progress in Nuclear Energy, vol. 5, McGraw-Hill Book Co., N.Y. (1956), pages 169, 212, 253.

Claims (1)

1. A PROCESS OF RECOVERING URANIUM FROM METALLIC URANIUM-THORIUM MIXTURES, COMPRISING ADDING MAGNESIUM TO THE MASS IN A QUANTITY TO OBTAIN A CONTENT OF FROM 48 TO 85 PERCENT BY WEIGHT, MELTING AND FORMING A MAGNESIUM-THORIUM ALLOY AT A TEMPERATURE OF BETWEEN 585 AND 800*C., AGITATING THE MIXTURE, ALLOWING THE MIXTURE TO SETTLE WHEREBY TWO PHASES, A THORIUM-CONTAINING MAGNESIUM-RICH LIQUID PHASE AND A SOLID URANIUM-RICH PHASE ARE FORMED, AND SEPARATING SAID TWO PHASES.