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LosAlamosLosAlamos,

.aboratoryNew Mexico 87545

An AffirmativeAction/Equal Opportunity Employer

This workwas supportedby the US Departmentof Energy,Office of NuclearMaterialsProduction.

EditedbyMaryJ.Mann

Thisreportwassubmittedon November26, 1986.

DISCLAIMER

This reporrwaspreparedas an accountof worksponsoredbyan agencyof the United StatesGovernment.Neithcrthc United StatesGovernment nor any agencythereot noranyoftheiremployees, makesanywarranty,expressor implied,or assumesany legalliabilityor responsibilityfor the accuracy,completeness,oruscfulnessofany information, apparatus. product, or processdisclo~d, or representsthat its usewouldnot infringeprivatelyownedrights.Referenceherein to any spcciiiccommercialproduct, process,or servicebytrade name. trademark, manufacturer,or otherwise,does not necessarilyconstitute or implyitsendorsement,recommendation,or favorins by the United StatesGovernment or any agencythereof.Theviewsand opinions ofauthors expressedhereindo not necessarilystate or reflectthoseof the United StatesGovemmentorany agencythereof.

LA-10906

Uc-4 and UC-10Issued:May 1987

Improved Recovery and Purificationof Plutoniumat Los Alamos

UsingMacroporousAnion Exchange Resin

S. FredricMarsh

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IMPROVED RECOVERY AND PURIFICATION OF PLUTONIUM AT LOS ALAMOSUSING MACROPOROUS ANION EXCHANGE RESIN

by

S. Fred.ric Marsh

ABSTRACT

For almost 30 years, Los AlamoRNational Laboratory has used anionexchange in nitric acid as the major aqueous process for the recoveryand purificationof plutonium. One of the few disadvantagesof this sys-tem is the particularly slow rate at which the anionic nitrato complexof Pu(IV) equilibrateswith the reain. The Nuclear Materials ProcessTechnology Group at Los Alamos recently completed an ion exchangedevelopment program that focused on improving the slow sorption ki-neticsthat limits this process. A comprehemiveinvestigationof modernanion exchangeresinsidentifiedporosity and bead size as the propertiesthat most influenceplutonium sorption kinetics. Our study found thatsmall beads of macroporousresinproduceda dramatic increasein pluto-nium processefficiency.The Rocky Flats Plant has already adopted thisimproved ion exchange technology, and it currently is being evaluatedfor use in other DOE plutonium-processingfacilities.

INTRODUCTION

Nearly three decadeshave passed since Ryan andWheelwrightcompleted their extensivestudyl of theanion exchangebehavior of plutonium in nitric acid.Shortly thereafter, Faris2 measured the distributioncoefficientsof 60 elements on anion exchange resinfrom nitric acid. The data of Faria (Fig. 1) con.tlrmthat anionexchangein nitric acid is a nearlyidealays-tem for plutonium, as no metal ion is more stronglysorbed than Pu(IV), and few other ions show evenmoderate sorption from nitric acid. The nuclear in-dustry quickly adopted this anion exchange system,and it is now the major aqueousprocess used to re-cover and puri~ plutonium.

One of the few disadvantagesof this system is theparticularlyslow rate at which the hexanitratocom-plex of Pu(IV) equilibrateswith the resin. Sorptionisso slow, in fact, that Ryan and Wheelwrightestimatedthat finalequilibriumwouldrequireseveral months Amore recentstudy by Streat3reportedthat 547 hourawas requiredfor complete sorptionof plutoniumontoa singleresinbead.

Boyd, Adamaon,and Myera4identiiledthree rate-controllingmechanismsfor such anion exchangeays-tema. These are (1) filmgradientdiffiion at the resinbead surface,(2) difision withinthe resinmatrix, and(3) chemicalreactionat the exchangesite. Ryan andWheelwright found that plutoniumsorptionwaslim-ited by the second rat~controlling mechanism,diffu-sionwithinthebead. Earlyattemptsto overcomeslow

1

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diffusionwithin the beads led to the use of low cross-linkedresinwhoselargerporeapresentedfewerphysi-cal obstructionsto the large [Pu(N03)6]= ions. Smallresin beads also have been used to improve sorptionkineticsbecausedifision within the bead is inverselyproportionalto the squareof the bead radius.s

Early investigatorsagreedthat the need for anionexchangeresinof high porosity could best be met atthat timeby usinga gel-typeresinof lowcross-linkage,such as Dowex 1x4. Consequently,the gel-type resinof low cross-linkagespecifiedin theseearlystudieswasquicklyadoptedfor usein thestandardprocessingpro-ceduresused by the nuclear industry. Although thisresinhasworkedreasonablywellfor more thana quar-ter of a century, slow sorption kinetics remainedthemajor limitationof the process.

The purposeof our investigationwasto identify,byevaluatinga widevarietyof commerciallyavailablean-ion exchangeresins,the resinbest suited for process-ing plutoniumin nitric acid. Major variablesincludedresin structure, resin porosity, resin bead size, nitricacid concentration,and dynamic contact time.

REAGENTS

Nitric Acid

The reagent-gradenitric acid usedthroughoutthisstudy was diluted z-isneeded using single distilledwater.

Anion ExchangeResin

Gel-typeDowex 1x4 and macroporousDow MSA-1resins were obtained from the Dow Chemical Com-pany,Midland,Michigan.

MacroporousIRA-900and IRA-938resinswereob-tained from Rohm & Haas, Philadelphia,Pennsylva-nia.

MacroporousLewatitMP-500-FK (40- to 70-mesh)resin, manufacturedby BayerAG in the FederalRe-public of Germany,wasobtainedfrom Mobay Chemi-cal Company,Pittsburgh,Pennsylvania.

2

EXPERIMENTAL

Assay Technique

We used a wrist-action shaker, shown in Fig. 2,to achievedynamic batch contacts. Liquid scintilla-tion viala, also shown in Fig. 2, contained a meas-uredweightof dry, nitrate-formresinand a measuredvolume of solution. Each solution initiallycontained2Wpu, 2S7U,~d 241AMin a selectedconcentrationof nitric acid. After completion of the first dynamiccontact period, we removed a measured portion ofthe aqueousphase for assay. The dynamic contactswerequickly resumedand continueduntil completionof the second contact period, when we removed an-other aqueousportion for assay. This procedurewasrepeateduntilall scheduledcontact periodswerecom-pleted.

Aqueous portions were in all cases assayed bygamma spectrometry, which allowed us to measureand compare each portion of resin-contactedsolutionwith an identicalvolumeof uncontactedsolution. Thedifferencebetweenthesetwo measurementsrepresentsthe quantity of the selected radioisotopesorbed onthe resin. Gamma spectrometricassaywas based onthe 59.5-keV,129-keV,and 208-keVgamma-raypeakaof 241Am, 239Pu,and 237U,respectively,as shown inFig. 3. The oxidation states of these three actinidesimmediatelybefore the resin contact were Am(III),Pu(IV), andU(VI). Any changein oxidationstatedur-ing the contact periods is unlikely.

Dynamiccontact periods rangedfrom 3 minutesto3 hours. Becausethe sorption kinetics of plutoniumin this system is particularlyS10W,3we have no rea-sonto believethat thedistributioncoefficient(Kd) val-ues measuredafter 3-hourcontacts even approximate

Fig. 2. Apparatus used for small-scale dynamic contact studies of anion exchange resins.

3

Fig. & Gamma spectrum showing the specific energieaused to assay americium, plutonium, and uranium.

Kd values at equilibrium. These measurementsdo,however,allow us to compare all resinaon an identi-cal baaisduringshort time periodathat simulatethebrief residencetime of an aqueoussolutionas it flowsthrougha stationarybed of anionexchangeresin.

Computation of Kd Valuea

We computeddistributioncoefficientsfor eachcon-tact period as follows:

Kd = concentrationof elementper milliliterof wetrwinconcentrationof elementper milliliterof solution“

In practice,Kd valueawerecalculatedby the equa-tion:

4

‘d=(AtilA’)($Or%)

whereAt is the activityof the actinideinitiallyin the liquid,Al is the actinideactivi~ in the liquidafter contact,VI is the liquidvolume,V. is the volumeof wet resin,andW, is the weightof dry resin.

Becauseeachresin/acidcombinationwasusedfor aseriesof sequentialcontact measurements,the liquid-to-resinratio changedas eachaqueousportion wasre-movedfor assay.We correctedfor this changingratio,as wellas for the decreasein the total activityremain-ing in a vial afterthe removalof eachaqueousportion.

We haveelectedto expressKd in termsof wet-resinvolume, contra~ to the common practice of express-ing Kd in terms of dry-resinweight. Becausewateraccounts for ss much as two-thirds of the weight ofss-receivedresin,the proceduresusedto obtain “dry”resinmust be reproducibleand clearlydefined. Manypublishedstudiesspec~ “air-drying” to obtain “dry”resin. (Air-drying in Los Alamos, at 7400 feet with20% relative humidity, is likely to yield resin witha substantiallydifferentwater content from that ofresin air-driedat sea level with 90% relativehumid-ity.) Some investigatoradry their resin at elevatedtemperatures,otherause vacuum, and still others usesome combination of elevated temperatureand vac-uum. This assortmentof dryingprocedurescan makeit difficult, if not impossible, to reproduce publisheddata.

On the other hand, the volume of wet resinin wa-ter can be measuredeasily and reproducibly in anylaboratory by using equipmentno more elegantthana graduatedcylinder. Furthermore,when resin is se-lected for a given process, the relative performancemustbe predictedfor a columnof specifieddimensionsand volume. Wet-resinvolume thereforeseemsinher-entlymore usefulthan dry-resinweightfor comparingthe performanceof resins.

For these reasons, we have chosen to present ourmeasuredKd valuesin termsof the volumeof nitrate-form resin in water. However,for those who wish toconvert our Kd valuesto a dry-resinweight, we ob-tainedthe “Los Alamos air-dried”weightsper volumeof wet resin,and presentthem in Table L

TABLE I. RelationshipBetween Wet-Resin Volumeand Dry-ResinWeight

Air-driedweight ConversionResin (dry g/wet ml)’ factorb

Dowex 1x4 0.331 3.02Dow MSA-1 0.363 2.75IRA-900 0.342 2.92IRA-938 0.196 5.10LewatitMP-500-FK 0.305 3.29

Resins Studied

Becauseanionexchangein nitric acid continuestobe the major processusedto recoverandpuri~ pluto-nium at the Los Alamos PlutoniumFacility (TA-55),our initial efforts to improvethis process focused onovercomingtheslowsorptionkinetics. Ourexper”hnen-tal studies emphasizedmacroporouaresins, in whichthe styrene/divinylbenzenestructure is polymerizedin the presenceof an inert substancethat producesextra-largepores in the resultingpolymer. The con-trast betweenconventionalgel-typeresin and macro-poroua resin is shown in Figs. 4 and 5. These arescanningelectronmicrographsof thegel-typeresinfor-merly used and the macroporousresincurrentlyused,respectively.Note that thesurfaceof thegel-typeresinappearssolid, evenat 10,OOOXmagnification,wheressmacroporous resin clearly exhibits pore structure atthis samemagnification.

In our small-scalestudies,we evaluatedmany vari-eties of anion exchangeresin of both gel and macro-porous structure (Table II). The resins listed in Ta-ble II include an unusuallylarge number of poly-4-vinylpyridineresins, which gave occssiomdly rapid,but highly variable sorption kinetics for plutonium.The highly variable nature of the sorption data fortheseresinswas finallytraced to a linearpolymer im-purity that remained from the resin manufacturingprocess. Ratherthanfillmanypageswith descriptionsof resinsthat performedpoorly, we describehereonlythoseresinswhoseperformancequalifiesthem aacan-didates for plutoniumprocessing,and compare themto resinstraditionallyused in this process. Otherma-jor variablesstudiedin our investigationwereacidcon-centrationand dynamiccontact time.

Dowex 1x4. Gel-type Dowex 1x4 resinhad beenusedroutinelyfor recoveringand purifyingplutoniumat the Los Alamos Plutonium Facility for 25 yearsbefore 1984, when the performance of resin identi-fied and purchased as Dowex 1x4 from an interme-diate resinprocessordeterioratedto an unacceptablelevel. Consequently,the unacceptableresin was re-placed with macroporouaDow MSA-1 resin becausesmall-scalecolumn experimentshad demonstrateditssuperiorperformance.

‘Volume of nitrate-formresinin water.bDistributioncoefficientsreportedhereinmaY be rnUl-

tipliedby thesefactors to obtain Kd valuesper gramof “air-dried” resin.

Fig. 4. Scanning electron micrograph of gel-type Dowex

lx4 resin (10,OOOXmagnification).

Fig. 5. Scanning electron micrograph of macroporoua DowMSA-1 reain (10,OOOXmagnification).

TABLE II. Anion ExchangeResinsTested at Los Alamos

Manufacturer Resin Comments

Dow ChemicalCo. Dowex 1x4 strong base, gel-typeDowex 11 strongbase, gel-typeDow MSA-1 strong base, macroporousDow A-1 weakacid, iminodiacetate,chelating

Rohm& Haas IRA-99 weakbase, macroporouaIRA-900 strong base, macroporousIRA-904 strongbase, macroporousIRA-91O strongbase, macroporousIRA-938 strongbase, macroporousIRA-958 strong base, macroporous

DiamondShamrock Duolite ES-63 intermediateacid, phosphonate,chelatingDuoliteES-467 weakacid, aminophosphonate,chelating

Sybron Chemical Ionac A-580 strongbase, pyridiniumpolymer

Reilly Chemical P-4VP strong base, poly-4-vinylpyridine,more than20 combinationsof porosity and cross-linkage

BayerAG (Germany) LewatitMP-500-FK strong base, macroporoua

6

Whetherthe observedunacceptableperformanceofDowex 1x4 resultedfrom manufacturingproblems orfromalterationor mislabelingby the intermediatesupplier has not been established.To minimizethe pos-sibility of mislabelingor alterationof resin after itsmanufacture,weobtainedthe resinausedin thisstudydirectlyfrom the producerwheneverpossible.

To further minimize the possibility of generatingmisleadingdata from questionableDowex 1x4 resin,we used for this study a several-year-oldportion ofDowex 1x4 that representedthe acceptableperform-ancetypicalof manyyearaof operationat Los Alamos.

Dow MSA-1. Dow MSA-1, like Dowex 1x4, isa strong-baseanion exchangeresin that incorporatestetraalkylammoniumexchange groups on styrene/divinylbenzenecopolymer beads. The highly signifi-cant ‘differencebe~weenthese two resina= that‘DowI

MSA-1resinispolymerizedin a mannerthat producesthe macroporousstructureshownin Fig. 5.

Amberlite IRA-900. AmberliteIRA-900 was ofparticularintereat,as its manufacturer,Rohm & Haas,deilnesit to be the equivalentof Dow MSA-1.

Amberlite IRA-938. Because Amberlite IRA-938 has by far the largestpore structureof any resinstudied, the diffusion-controlledrate of exchangewasexpectedto be rapid. This, in fact, was the case. Un-fortunately, the highly porous structure of IRA-938contributesdirectly to its low mechanicalstrength. Ascanningelectronmicrograph(SEM) of IRA-938 resin(Fig. 6) showsthat the interlockingsolid structure ofother resina(Figs. 4 and 5) is lacking. Instead,IRA-938 appears to be an agglomerationof microspherethat are approximately10pm in diameter. (Note alsothat the SEM shown in Fig. 6 was taken at tenfoldlowermagnificationthan the SEMSshown in Figs. 4and 5.)

IRA-938 resin is so fragile that it literally disin-tegratedduring the relativelygentle agitation of thewrist-actionshakerusedin our dynamiccontacts. Theultrafineresin particles that remainedsuspended inthe aqueousphasemade reliableassayof the aqueousphase impossible. Becausethe continuousdisintegra-tion of suchfragileresinin a plantprocesswouldcauseexcessivelossof plutoniumto wastestreamsand plug-gingof proceasvalvesand filters,we considerIRA-938resinunsuitablefor plant processuse at Los Alamos.

Fig. 6. Scanning electron micrograph of Amberlite IRA-938 resin (10,OOOXmagnification).

Lewatit MP-500-FK. Lewatit MP-500 is amacroporous,strong-baseanion exchangeresin,man-ufacturedby BayerAG in theFederalRepublicof Ger-many,that is similarin structureto Dow MSA-1 andAmberlite IRA-900. This resin is attractive becauseit is availableas 40- to 70-meshsphericalresinbeads,designatedLewatitMP-500-FK. All domestic sourcesof macroporousstrong-baseanionexchangebeada,bycontrast,supply only a coarse20- to 50-meshrange.

RESULTS AND DISCUSSION

The large amount of data generatedin this studycan be presentedin many ways. Becauseplutoniumsorption kineticshas been the major limitationof thenitrate anion exchange process, we have chosen topresentour data in a mannerthat emphasizesdiffer-ences in sorptionkinetics.

General. As expected, americiumshowedno sig-nificant sorption on any of the resins studied fromany concentrationof nitric acid and thereforewss notincluded in the graphical presentationof measuredKd values. In all cases, uraniumequilibratedrapidlywith the resin, where= plutoniumsorption wss con-sistentlymuch slower. Finally,a comparisonof pluto-nium Kd valuesfor the shortestcontact time and thelongest contact time confirms that plutonium equili-brates more rapidly from dilute nitric acid, in agree-ment with calculatedpredictionsof James.G

Effect of Resin Bead Size. The effect of resinbead size on plutonium sorption kinetics (Fig. 7) isdemonstratedby comparing two different-sizefrac-tionsof thesameDowex1x4resin. The observedfasterkinetimof smallerbeadais in completeagreementwiththeory and was fully expected. However,the benefitsassociatedwithusingsmallerresinbeadareacha pointof diminishingreturnswhen the increasingresistanceto liquid flow eventuallyresultsin unacceptablyhigh

Effect of Resin Porosity. The effect of resinporosity on plutonium sorption kinetics (Fig. 8) isdemonstratedby comparing similar-sizefractions oftworesinsof differentporosity. Dowex1x4isa gel-typeresin, whereasDow MSA-1 is a macroporous resin.The relativeporositiesof these two resinsare shownin Figs. 4 and 5, respectively.

From the resultsof many small-scaleexperiments,we concludedthat an idealresinfor processingpluto-niumwould incorporateboth smallbead sizeand highporosity. Because small, sphericalbeada of macro-poroua resin were not available from any domesticmanufacturer,wedevelopedan in-househydraulicsys-tem capableof separatingcubic-foot quantitiesof 40-to 50-mesh beads from as-received 20- to 50-meshmacroporous resin. Use of a separated,smaller-sizefraction of macroporouaresin in our full-scaleplantprocessresultedin a dramaticimprovementin perfor-mance; the apparentcapacity of the resin for pluto-niumtripled,whilethe plutoniumcontentof the efflu-ent wastestreamdecreasedby a factor of 10.

liquidback-pressure.

/

100

uY

10

1

‘ DOWEX 1x4GEL-TYPE

40-50MESH

3 10 20 60

DYNAMIC CONTACT TIME (rein)

Fig. 7. Sorption of Pu(IV) from 7 M nitric acid as afunction of reainbead size.

100

13 10 20 60

DYNAMIC CONTACT TIME (rein)

/’ ///

DOW MSA-1 /’,/’MACROPOROUS z

40-50 MESH / I

,/’ /,/ /’

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40-50MESH

I I I I

Fig. 8. Sorption of Pu(IV) from 7 M nitric acid aa afunction of reain porosity.

8

Lewatit MP-500-FK Resin. Meanwhile,weattempted to find a foreign supplierof small, spher-ical beads of macroporousresin. We finallycontactedMobay ChemicalCorporation, a U. S. company thatrepresentsBayerAG in the FederalRepublic of Ger-many. Testingof Bayer’sLewatitMP-500-FK resininsmall-scaleexperimentsand iill-scale processeacon-firmedour expectation of significantlyfaster kineticswhen these smallerbeads are used. In Fig. 9, whichshowsplutoniumdistributiononto all threeresinaas afunctionof contact time, the highestcurvereflectsthesuperiorkineticsof the Lewatitresin.

The dramatic effect of dynamic contact time alsois demonstratedin Figa. 10 and 11. Figure 10 com-pares the distributioncoefficientsof Dowex 1x4 andLewatitMP-500-FK as a function of nitric acid con-centration,afl.era dynamic contact period of 3 hours.The curves for this relativelylong contact period arevirtuallyidentical.

Figure11, however,comparesthesesametwo resinsaftera dynamiccontactperiodof only 15minutes.Thesuperiorityof the Lewatitresinis clearlyapparentforthis shorter contact period that simulatesthe actualresidencetime of feed solutionflowingthrough a fiLll-scale anion exchange column. These two resinaare

100

ux

10

1

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/“/ /’/~LEWATIT /

MP-500-FK DOW MSA-1MACROPOROUS / ‘,/

MACROPOROU:40-70 MESH / 40-50 MESH

//

‘ /’

/’ /’

/

/’/’

DOWEX 1x4GEL-TYPE

50-100 MESH

I 13 10 20 60

DYNAMIC CONTACT TIME (rein)

Fig. 9. Sorption of Pu(IV) from 7 ~nitric acid on gel-typeDowex 1x4, macroporous Dow MSA-1, and macroporousLewatit MP-500-FK resins.

100

ux

/

//’

t4k%%_;:K /

/

40-70 MESH

/

/

OOWEX 1x460-100 ME3H

1 ! I , 13 4 5 6 7

NITRIC ACID MOLARITY

Fig. 10. Sorption of Pu(IV) on Dowex 1x4 and LewatitMP-500-FK resins, as a function of nitric acid concentrwtion, for a 3-hour dynamic contsct period.

L

100 -

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10

LEWATIT ,/-MP-500-FK40-70 MESH,N’

//

//

‘7

OOWEX 1x45OX1OO MESH

I , ,3 4 56 7

NITRIC ACID MOLARITY

Fig. 11. Sorption of Pu(IV) on Dowex lx4 and LewatitMP-500-FK resins, sa a function of nitric acid concentra-tion, for a 15-minute dynamic contact period.

9

compared as a function of dynamic contact time foronly 7 Mnitric acid in Fig. 12. The fallacyin the com-mon practice of usingpublished “equilibrium”distri-butioncoefficientvaluesto predictplutoniumbehavioris readilyapparent.

Uranium/Plutonium Separation. Uraniumequilibratedmuch more rapidly than plutoniumwithall resinsstudied. The combinationof rapid sorptionand consistentlylow uraniumdistributioncoefficientsresultain thesimilarcurveafor Dowex1x4andLewatitMP-500-FKshownin Fig. 13.

Becausethe Lewatitresin greatly affects the sorp-tion kineticsof plutonium,whereasit affectsthe sorp-tion kinetics of uranium only slightly, macroporousLewatitresinalsoprovidessignificantlyincreasedsep-aration factors between uranium and plutonium, asshownin Fig. 14.

Summary. Lewatit MP-500-FK resin offers ad-vantagesfor plutonium processing in every categorythat we can measure.When comparedwith the otherre9instested, Lewatit resin costs less, offers greatercapacity for plutonium, loads faster, elutesfaster (allof which result in greatly increasedthroughput), andyieldsa plutoniumproduct of higherpurity. Further-more, 10SSof plutoniumto the effluentwastestreamissignificantlyiower.

Ii

100

ux

10

LEWATITMP-500-FK /40-70 MESH

/’/

//

//

iiDOWEX 1x4

50-100 MESH

JI L

3 10 20 60 180

DYNAMIC CONTACT TIME (rein)

Fig. 12. Sorption of Pu(IV) from 7 ~ nitric acidon Dowex Ix4 and Lewatit MP-5CJCLFKreains, se afunction of dynamic contact time.

100

wx

10

LEWATITMP-soO-FK40-70 MESH

-——.—-—-—

DOWEX 1x450-100 MESH

/1 , { ,,1 I I I 1 I 1 Ill II , ,

3 10 20 60 1s0

DYNAMIC CONTACT TIME (rein)

Fig. 19. Sorption of U(VI) from 7 ~nitric acid on Dowexlx4 and Lewatit MP-500-FK resins, aa a function of dy-namic contact time.

/

LEWATITMP-500-FK

/

40-70 MESH ///’

,/DOWEX 1x4

/’ 60-100 MESH

/’

/“

,, 13 10 20 60 180

DYNAMIC CONTACT TIME (rein)

Fig. 14. Pu(IV)/U(VI) separation factora from 7 ~nitricacid on Dowex lx4 and Lewatit MP-50CJ-FKreains, se afunction of time.

10

TECHNOLOGY TRANSFER

Soon afterwe sharedthis improvedanionexchangetechnology’ with Rocky Flats Plant personnel, theyperformedan independentcomparisonsof macrop~rous resinswith the IRA-938 resin formerly used atRocky Flats. Their resultscordlrmedthe Los Alamosconclusionthat LewatitMP-500-FK resinfar outper-forms all others tested. Of particular interestis theRocky Flats finding that Lewatit MP-500-FK resin,when compared with IRA-938 resin, provides essen-tiallytwicethecapacityfor plutonium,whileit alsoal-lowsthe sorbedplutoniumto be elutedin half the vol-ume. As this report is being written, SavannahRiverand Hanford personnel also are evaluatingLewatitMP-500-FK for use at those facilities.

CONCLUSIONS

1. High-porosity,macroporousanionexchangeresinsorbs the anionic nitrato complex of plutoniummorerapidly than does gel-type resin. Macroporouaresinthereforeis preferredfor processingplutonium.

2. Smallresinbeads of strong-baseanion exchangeresin sorb the anionic nitrato complex of plutoniummore rapidly than do large resin beada. Small resinbead size is thereforepreferredfor processingpluto-nium.

3. Either small, sphericalbeads of gel-type resinor large beads of macroporous resin may be pur-chased from domestic manufacturers, but none of-fers the combination of macroporous resin in smallbeadsize. LewatitMP-500-FKresin,manufacturedbyBayer AG in the FederalRepublic of Germany,com-bines high porosity and small bead size. This 40- to70-mesh, macroporouaresin is primarily responsiblefor the dramatic improvementin performanceand ef-ficiencythat we haveattainedin our plutoniumanionexchangeprocess at Los Alamos.

4. Amberlite IRA-938, which offers by far thelargest pore size of the resins studied, equilibratesrapidly with the plutonium complex. However, thehighly porous structure contributes directly to thepoor mechanicalstrength that causes IRA-938 resinto fractureunder relativelygentleagitation. The se-vere problems that can result from resin disintegrat-ing into a finesuspensionof microparticlesmakethis

resin unsuitablefor process use. (The relativemer-its of IRA-938 resinhave become academic,as Rohm& Haas has recently discontinuedproduction of thisresin.)

5. Uraniumequilibratesrapidlywith allresinsstud-ied from all concentrationsof nitric acid; however,Kdvalues of uranium are consistentlymuch lower thanthose of plutonium.

6. Because macroporous resin offers more rapidsorptionof plutonium,but not of uranium,whencom-pared with gel-type resin, there is an increasedsep-aration factor between these two actinides. In-plantprocess use of Lewatit MP-500-FK resin at the LosAlamosPlutoniumFacilityhasdemonstratednot onlya dramaticincreasein processefficiencyand through-put, but also a significantimprovementin productpurity.

7. The in-plant performance of most anion ex-changeresinsis best when the resin is new and grad-ually deterioratesthereafteras the resin is degradedby chemicaland radiolyticprocesses. An unexpectedbonusof LewatitMP-500-FKresinis that its perform-ance actually improvedduring the first eight monthsof routine in-plantprocess use. The capacity of thisresinfor plutoniumnoticeablyincreased,whilethevol-ume of elutingsolutionrequiredto recoverthe sorbedplutoniumsimultaneouslydecreasedby 25%. The ex-planationfor this improvedperformance,althoughnotcurrentlyunderstood,is being investigated.

ACKNOWLEDGMENTS

The Los Alamos Plutonium Facility at TA-55 isunique in that it combines plutonium research andproductionwithinthesameorganization.Sucha com-binationallowsus to rapidlytest and evaluateprocessimprovementideasand to quicklyincorporatethe bestof theseinto our routineoperations. A major shareofthe credit for the recentdramaticimprovementin plu-tonium processingefficiencythereforebelongs to keymembersof the production team who are responsiblefor convertingpromisingresearchideas into the real-ity of major production improvements. I gratefullyacknowledgethe essentialcontributionsof Tim Gal-legos, Jeff Hatchell, Bill McKerley, Arch Nixon, andWillard Williams.

REFERENCES

1.

2.

3.

4.

J. L. Ryan and E. J. Wheelwright, “The Re-covery, Purification, and Concentrationof Pluto-nium by Anion Exchange in Nitric Acid,” U. S.Atomic Energy Commissionreport HW-55893(del)(1959).

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