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Although a small portion of thisreport is not reproducible, it isbeing made available to expeditethe availability of information on theresearch discussed herein.

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REILLEXm HPQ: A NEW’, MA CR OPOROUS POL}’VIN}” LPYRIDINE RESI\

FOR SEPARATING PLUTONIUM USING NITRATE ANION EXCHANGE

S. Fredric Marsh, Nuclear Materials Process Technology Group,

Los Alamos National Laboratory, Los Alamos, Ncw Mexico 87545

ABSTRACT

Anion exchange in nitric acid is the major ●queous process used to

recover and purify plutonium from impure scrap materials. Most strong-

base anion exchange resins incorporate a styrenc-divinyl bcnzcnc copoly-

mer. A newly available, macroporous anion exchange resin based on &

copolymer of l-met hyl-4-viny\py ridine ●nd divinylbenzcne has been

evaluated. Comparative data for Pu(I!’) sorption kinetics arid capacit}

are presented for this aew resin and two other commonly used anion

exchange resins, The new r~s!n offers high capacity and rapid sorption

kinetics for Pu(l V) from nitric acid, ns well as greater stability to

chemical and radiolytic degradation.

IN~Ro~L lJ--JJQ~

Aliiun cxchangc in nitric ●cid is the major aqueous process used to

recover ●nd purify plutonium from impure scrap materials at the Los

A!amos Piutonium Facility Data from ● n early study by Faris and

Buchanan, Fig. l(l), show why this systcm is nearly ideal for processing

FIGURE 1.Distribution of elements from nitric ●cid onto strong-base anionexchange resin.(l)

plutonium; no metal ion is more strongly sorbed that ?u(l V), and few

other ions show even moderate sorptiou from nitric acid,

One of the few disadvaotagcs of the nitrate anion exchange sysfcm

is the particularly S1OWrote ●t which the anionic Pu(IV) nitrctn complex

equilibrates with the resin. As part of an earlier Los Alamos effor~ to

improve the slow kinetics that limit this process, more tltart 30 commerc-

ial and experimental ~nion cxchant: resins were evaluated Thsr study(2)

identified resin Porosily ●nd bead size ss the two properties that most

influence plutonium sorption kinetics, Based on these findin~s, grl-type

Dowcx- 1x4 resin previously used at ‘Los Alamos was replscecl with

macroporous Lcwatit~ MP-500-FK resin, which resulted in ● dramatic

improvement in process efficiency.(3)

‘ w SK, a gel-type resin no IongcrNearly 30 years -go, Pcrmut]t

produced, was reported to offer better sorp~ion and dcsorption kiuttics{4)

●nd capacity for plutonium than other resins avail ab!c Bi that time

Pertnutitm SK consist?d of ~oly-2-meth yl-5-vinylpyrid ine, rather than the

Polystyrene used for Dowexm, Lewatitw, ●nd most other strong-base

snion cxc~angc resins, in ●ddltlon to the /cportcd performance benefits of

Pcrm’; titm SK, pol}~inylp}ridine ●nion exchange resins have been reported

to offer greatly increased stability to chemical attack(6) and radio lytic

degra4stion.(7)

This expectation of iucrcascd safet) and pcrformarice I&d us to

●ctively seek a new commercial source of macroporous polyvinyl pyridinc

anion exchange resin. Subsequent interaction betwtcn Los Alamos National

l.,sborutory and Reilly Industries, Inc., s manufacturer of vinyl pyridinc poly -

mcrs, has resulted in a stew, macroporous anion exchange resin that consists

of ● copolymer of J-methyl-4-viny!pyridinc tad divinylbcnzc,lc.

A comps~lson of the chemical structures of this new polyvinylpyridlnc

w HPQ, and conventional polystyrene resin isresin. designated as Rcillcx .shown in Fig 2. in both structures a rauatcrnizcd nitrogen is the anion cx -

change site. In polysfyrenc rc:in, the quatcrnary ammonium group attaches

CONVENTIONAL NEW

POLYS”iWRENE P(WYVINYLPYRIDINE

RESIN RESIN

““cti&-cH* *“m

CH2I

CH3-iN6CH3

CH3

FIGL’RE 2 Comparstivc structure of :onvcntional polystyrene resin andocw Polyvinyl pyrldlnc resin

to the benzene ring, whereas polykinylpyridlnc resin is quatcrnizcd by

addition of a methyl group to the nitrogen in the pyridlnc ring.

Our initial small-scale evaluations of Rcillcx m HPQ resin show

that it provides Pu(IV) sorption hincti;s comparable or superior to that

obtained with Lcwatitm MP-500-FK resin, the best poiystyrcnc resin wc

had prcv]ousiy identified.(2) This resin also offers persuasive safety

advantages. Production-scale testing is currcrltly under way using

Rcillcxm HPQ resin in onc of our full-scale ion cxchangc systcm$.

BE AGE NT~

Reagent-grade nitric acid was diluted as nccdcd using deionized water

that had a rcsistivi!; of st least 17 megohms.

Dowcxm 1x4 gcl-:ypc, .@trong-base anion exchange resin, 50 to 100

mesh, was obtained from Dow Chemical Company, Midland, Michigan.

(A 50 to 60 mesh fractio.:, separated by dry-scrccning, was used in this

stud!. )

Lcwatitw MP-5WLFK macroporous, strong-base anion exchange rcs

40 to “IO mesh, was obtained from Mobay Chemical Corp., Pittsburgh,

Pr,n~sylvania. (A 50 to 60 mesh fraction, separated by dry-scrccning. was

used in this $tudy. )

n,

Rcillcxm HPQ macroporous, polyvinyl pyridinc anion cxch~ngc resin, 30

to 60 mesh, was obtained from Reilly I~dusirits, Inc., Indianapolis, Indiana.

(A 50 to 60 mesh fraction, xcparatcd by dry-screcn]ng, was used in this

sludy, j Specific properties of this ncw resin, ●s supplied by the

manufacturer, c~c:

C’hlo’idc exchange capacity - ().85 moles pcr Iitcr (in water)

Tots! cxchangc capacity in ●cid = 1.34 moles pcr Iitcr (in water)

Surface area = 75 square meters pcr gram

Functinilril groups quatcrnir.cd - 63%

~XPFRIMFNT.AL

Bes in Form co nvcr ~

As specified above, only 63% of the pyridinc r!ngs arc quatcrnizcd by

the addition of a methyl group. Howrvcr, the unquatcrnizecl nitrogen atoms

in the pyridinc rings readily acquire a proton in acid solution In either

case, a positive anion -cxchangc si(e results.

A two-step process was thcrcforc Ilscd to convert the as-rccciked,

chloride-form Rcillcxm HPQ rcsic to the desired nitrate form, Most of

the chloride ions were first displaced by passing two resin-bed volumes of

0.7 M aluminum nitrate solution through the resin-corrtaining column. This

was followed by four resin-bed volumes of 2 M nitric acid to complctc the

displacement of chloride and also to profooatc any unquatcrnizccl pyric!inr

rings,

Ii is essential that the rc:; in bcd bc given udcquatc free s~acc within

the column for expansion durirg this conversion, ●nd also thai both

solutions mrc passed through in En upflcw dircc[ion to keep the resin

cuspcndcd during the expected volume increase of - 1 1%.

as TcWS@K

Small-scale dynamic contact:; brtwccn resin and plutonium solutions of

specified compositions were cffcctcd for designated contact periods on a

wrist-action shaker. Measured portions of aqueous :oluti’.>n were removed

●fter each contact period for gamms spectromctric ●ssay. The 129-kc V

gamma-ray peak of Pu-239 was measured in all aqueous portions, both

before and after contact with the resin. The diffcrcncc bctwccn these two

mcasuk’cments rcprcscntcd the quantity of plutonium scrbcd on the resin. A

more detailed description of the cxpcrimcntal ●ssay tcchrriquc is prcscntcd

elscw’!’sere.(l!)

.Of ~JS~ Q)g~

Distribution coefficient (Kd) values were calculated to rcprcscnt the

concentration of plut~niurrr pcr millllltcr of wet resin (nitrate-form in

water) u. :d by the concentration 6~ pluioniurn pcr milliliter of solution

This diff~ts from the common prscticc of calculating Kd values from the

weight of dry resin, rather than the volume of wet resin. We feel that

resin volume is a more useful parsmcter because process columns contain a

given volume of wet resin. rather than a measured dry weight, For readers

who prefer to work with values calculated from dry resin weight, those Kd

values ●re higher than ours by ●pproximately I factor of 3.

Distribution coefficients for Pu(IV) were measured ●s a function of

dynamic contact time for various resin loadings. As expected, measured Kd

values decrease as the quantity of plutonium per volume resin increases, as

seen in Fig. 3. (A solution-to-resin volume ratio of 10 was used for these

1000

100

IIII

10

1

I I 1111111 1 ‘T 111 TTT—

Pu p.r Iit.r *n

-—- 20 #arw Pu por Iitor rwn

. . . . . . . . 40 gmnw Pu por Iitor rosin

------- $0 @smS Pu por IRor row- SW*n W gm.ms Pu p W rwln

- I-R- 100 grams Pu por Iitor twin

1 loDynamic CWtact Period (ml%s)

FIGURE 3. Sorption of Pu(IV) on Reillr Am HPQ ●nion cxchauge resinfrom 7 M nitric ●cid at a function oif Nutoniurn loading.

cxpcrimcnts. The concentration of plutonium in each cxpcrimcnt was

therefore l/i O of the specified plutonium quantity. For example, a

plutonium solution concentration of 10 grams pcr Iitcr was used for the

experiment that resulted in 100 grams of plutonium loading per liter resin )

The observed faster kinrtics for lower resin loading lCVCIS is

attributed to the rapid sorptiou of small quantities of Pu(IV) by highly

accessible ion exchange sites on or near the surface of tnc resin beads. As

the quantity ot” plutonium increases, the competition for exchange sites also

increases. This competitive process requires Pu(I\’) ions to migrate prog-

ressively deeper within the resin bead to find available cxchangc sites, a

significantly slower process than when ions cxch, angc only at sites on or

near the surface.

Comparisons of Kd curves for different resins are therefore valid only

when quantities of plutonium pcr resin volume ●re identical. Accordingly,

wc have measured and reported the sorption kinetics of Pu(l V) from 7 M

nitric ●cid on Reillexm l-iPQ, Lcwatitm MP-500-FK, and Dowcxm 1x4

resins only undcl such equivalent plutonium-loading conditions. The effect

of resin bead size differences was eliminated by using dry-scrccned, 50 to

60 mesh resin in all cas~s.

sta ncc to N itric AC di

Most conventional strong-base ●nion exchange resins incorporate a

polymer of styrenc and divinylbcnzcnc. Because these styrene polymers can

react violently with nitric acid under certain conditions, their safe usc

requires strict ●voidance of conditions known to be hazardous. Potential

safety hazards associated with using ion exchange resins in nitric acid

systems have &en ●ddressed by Calmon.(8) Avoiding conditions that could

result in violent reactions between organic polymers and nitric acid

obviously is given an especially high priority within the nuclear industry.

Vinyl pyridinc polymers arc known to bc unusually resistant to attaci,

by nitric ●cid. Marston(6 ttributes the diffcrcncc in reactivity of poly-

styrene ●nd polyvinyl pyridinc to the fact that polystyrene is especially

susceptible to clectrophilic aromatic substitution, whereas the electron

deficiency of the aromatic system makes polyvirylpyridinc quite resistant to

such substitution.

Polyvinyl pyridinc resins arc thcrcforc cxpcctcd to bc s]gn]ficant!>

safer than polystyrene resins; howc~er, caution is always encouraged when

one combines organic polymers and nitric acid. In the specific case of

Rcillcxm HPQ resin, only about 70% of the polymer is vinylpyridinc; the

remaining 30% is divinylbcrizcnc, whose chemical stability is considerably

lower.

Conspicuous on Calmon’s list of the potentially most dangerous

conditions involving resin and nitric acid arc high concentrations of nitric

acid and high tcmpcraturcs.(8) To evaluate the new resin under worst-

casc conditions, WC intentionally violated both of these safety precautions

by subjecting a portion of nitrate-form Reillex m HPQ resin to boiling,

concentrated nitric acid, under reflux, for 3 hours. Although a small

●mount of N02 was observed during this period, there was no indication of

any wigorous reaction. The weight of the post-treatment, air-dried resin

agreed closciy with the initial weight of air-dried resin, which was addi-

tional evidence that no significant resin decomposition had occurred.

Although rcfluxing the resin in concentrated nitric acid caused the

initially white Rcillexw HPQ resin to acquire a slight yellow color, there

was no significant change in the surface ●ppearance, even at 10, OOOX.

Moreover, thermal decomposition profiles of acid-refluxed and untreated

Reillcxw HPQ resin (both air-dried in nitrate form), as determined by

thermogravimetric ●nalysis in an argon ●tmosphere, were found to be nearly

identical (Fig. 4).

These similar thermal decomposition profiles for treated and untreated

Rcillcxm HPQ resin further confirm the ●bscncc of significant resin alter-

●tion by the treatment. A thermal decomposition profile of Lewatitm h4P-

500-FK resin ●lso was measured and is included in Fig. 4. The initial

decomposition of R.ci

resin. was unexpected,

position of resin in a

aqueous nitric acid.

Icxw resin at a lower temperature than LewatitTM

although there is no reason to expect thermal dccom-

dry argon atmosphere to simulate its reactivity in

—m

1~~–

.--. w-

00 “

-3~&

gtio–m8a=40 mReam0.. -t.p

--- ‘-- Treated Reiliexw Resinz

— Untreated ROilie# Raw10“

ot-l I 1 I 1 i

lcm)

Twperature (Z)

FIGURE 4. Thermal decomposition profiles of (]) nitric ●cid-refluxedReillcxw, (2) untreated nitrate-form Rcillcxw HPQ resins, ●nd (3)nitrate-form Lcwstitw MP-500-FK resin.

To further determine whether resin refluxed in nitric acid had

survived without

Pu(IV) from 7 M

determined from

per liter of resin

resin loaded also

significant damage, the capacity of treated resin for

nitric acid was measured, Capacities were experimentally

batch contacts, in which the Pu(IV) quantity of 182 grams

exceeded the totkl resin capacity. The rate at which the

was determined in these experiments by assay-ing the

solution for nonsorbed plutonium ●fter dynamic contact periods of 0.5, 1, 3,

5, and 8 hours.

Figure 3 shows the measured capacities of DowexW 1x4, Lewatitm

MP-500-FK, and Reillcxm HPQ resin before and after the rcfluxing nitric

acid treatment. Not only was there no loss in capacity of the treated resin

for Pu(IV) from nitric acid, relative to untreated resin, there was a

substantial increase!

‘“~ ’’’’”-l140

120

100

60

60

40

20

1.....................................”*

●.*.“

-------- -------- ----0

l--

t--

-

t

1~.e-”

-#”.& ●e

-/●0

●/.0

.0●/ ~-”..-.. knmUtmMP-50&FK

,// ---- Trutod RoiliexmHPO

l--●

— ROWX%PQ

1

-

o! 1 I I I 1 1 J ! I I I

o 2 4 e e 10 12

- Comcl POfiu3(~fq

FIGURE 5. Metsured capacities of various ●nion exchange resins for Pu(IV)

from 7 M nitric ●cid.

Because this increase in resin capacity was unexpected, wc repeated

the PU(IV) sorption kinetics s~udks using resin that hsd been refluxcd in

concentrated nitric scid. Figures 6 through 11 present comparative

distribution coefficients of Pu(lV) from 7 M nitric ●cid on Dowexm 1x4,

Lcwatitm MP-500-FK, and trctitcd and untretitcd Rcillcxw HPQ for total

plutonium loadings of 10, 20, 40, 60, 80, and 100 grams per liter ~esin,

respectively.

.

At each of these six levels of plutonium loading, the treated resin

exhibits equivalent or faster sorption kinetics for Pu(IV) than was ob:ained

with untreated resin. Furthermore, in almost every case the sorption kinet-

ics of Pu(IV) on treat~ ~ Rcillcxw HPQ resin is superior to the kifietics of

the other three resins tested. This is particularly significant because

Lewatitw MP-500-FK resin was found to offer !hc fastest kinetics of more

than 30 resins evaluated in a previous study.(2)

lmo E I ( !l .!,’ Ill;

..1i;

~,:,:::]

11 lW

OFluw Wmt (~)

FIGURE 6. Sorption of Pu(IV) onvarious anion exchange resins from7 M nitric scid (Pu l-ding - 10 8rsmsper liter resin).

Ft

/,/

./,0

L=1 10U

m 031d’-u(~)

FIGURE 7. Sorption of Pu(lV) tinvqrio~~ anion exchange resins from7 M nitric acid (Pu loading -20 gramsper liter resin).

~ved PL~,,

The unexpected improvement in resin capacity and sorption kinetics

was discussed with Charles Mxrston, the senior research chemist who devel-

oped this resin in collaboration with Donald McQuigg at Reilly Indusr,-ies,

Inc. Marston suagested that refluxlng HPQ resin in concentrated nitric acid

could cause oxidativc cleavage of some alkyl aromatic cross-linking ~roups,

SS evidcnccd by the production of FJ02. Cleavage of some of the divinyl -

bcnxcne cross-linking groups would relax the resin network structure by

lowering the cross-l inkins dcnsiti and ●now the resin beads to expand.

two I I I 1 , 1111 I I 1 1 I I Id.4

----- TroaBrYRdtox%Po

— n#D, %PQ. . . . . . . MWMP-WFK ●.

/

----- omnx-114 ... . .,..’

.. . I,..,.. ” I

,.,,., ,/’

,.., ./,..

.“ ,.. ,/,. /.,

/’,.,/’

... /’./.

/’./.

t 1,L I I! II III 1 1 I I 11111

m CadLbxr(IwMn)100

FIGURE 8. Sorption of Pu(IV) onvarious ●nion exchange resins from7 M nitric ~cid (Pu loading = 40 gramsper liter resin).

----- TmRasox”t@O

— hmox %m..... .. ~wwolwu—-. ~m,,~

‘Eiizi=7

t 1

1 ImOvnu= cA’PutM(~)

FIGURE 10. Sorption of Pu(lV) onvarious anion e~change resins from7 M nitric ●cid (PLJ Ioadin# m 80 gramsper Iitcr resin).

FIGURE 9. Sorption of Pu(IV) onvar’ous ●nion exchange resins from7 M nitric scid (Pu loading = 60 graper liter resin).

ms

1

FIGURE 11. Sorption of Pu(IV) onvarious snion exchan~e resins from7 M nitric ●cid (Pu Iosding - 100grams per liter resin)

This explanation is in accord with an observed increase in wet resin

vclume of approximately 10%. The more open structure of expanded beads

should make interior anion exchange s:tes mare accessible, which would

explain the increased resin capacity and improved sorption kinetics.

K~. .

on

Because Rcillexm HPQ retin exhibits Pu(IV) sorption kinetics

able or superior to that of Lewatitm MP-500-FK, we also comparcci

compar -

thc

elution of Pu(l V) from these two resins using dilute nitric acid as the

eluant. In all cases, l-milliliter portions of resin were tested in columns of

‘l-millimeter diameter, using gravity flow for loading and clution.

Fig,lre 12 presents Pu(IV) clution profiles from Reillexm resin using

eluants of 0.35, 0.40. 0.45, 0.50, and 0.60 M nitric acid. The elution profile

~a--m

15

Ii25

0

— lWlexm0.35 M Nitric Acid““- ReiUexmOAO M IWric kid— Reillexm0.45 M Nitric Acxd--” RetllexmO.SO M Nitric Aad-- W@xw0.60 M Nttnc Aczd-.. ~lWO.~ M NdrNti

.

0 1 2 3 4 5

Resin W Vdumcts of Ehant

FIGURE l?. Comparison of Pu(lV) elution profile~ from Rcillex- HPQresin using eluants O( 0.35, 0.40, 0.45, 0.50, 0.55, rnnd 0.60 M nitric acid,and from Le-lttitw M;- X30-FK resin using only ●n eluant of 0.35 M nitricacid

of Lewatitm resin using only 0.35 M nitric acid is presented for

comparison. Note that the elution is consistently sharper and more

complete in a smaller volume with Rcillexm resin, even when higher

concentrations of nitric acid are used as the eluant. This indicates that

the purified plutonium product can be recovered at hjghei concentration in

a smaller volume from Rcillcxw resin. The improved elution is particlllarly

sil]nificant because clution of Pu(IV) with dilute nitric acid is much faster

from Lewatitw resin than from any other resin previously testtd.

lU~MMUWQR

Another major safety advantage expected from Rcillexm HPQ resin is

increased resistance to radiolytic degradation. According to Gangwcr et

●l.,(7) ‘These resins with pyridinc exchange groups are more stable to

ionizing radiations than ●ll other types of synthetic organic ion exchangers

that have been examined for radiation-induced chemical changes,” Our

near-term plans include a comparison of the radiolytic stability of

Rcillcxw HPQ resin with several other macroporous and gel-type poly-

styrene resins commonly used in the nuclear industry.

A newly available, macroporous ●nion exchange resin based on a

copolymer of l-methyl -4-vi nylpyridinc ●nd divinylbcnzcne has been

evalua[cd. This new rcsln offers high capacity and rapid sorption kinetics

for Pu(lV) from nitric acid, as well as greater resistance to c5emical attack

by nitric ●cid. Significantly greater resistance to radiolytic degradation

●tso is expected, based on published studies of similar polyvinyl pyridinc

resins.

ACK NoWLE~ GtvlENT~

The author gratefully acknowledges the outstanding technical contrib-

utions of Charles R. Marston, Donald McQuigg (the ori~linal developer of

the Rcillexm family of polymers), and Richard D. Johnston, all of Reilly

Industries, Inc.. as well as the exceptional cooperation of ReJlly Industries,

Inc.* The collaboration between Reilly ●nd Los Alamos represents a model

for effective interaction between our national laboratories ttnd private

industry.

The author also is grateful to Anthony C. Muscatcllo for his assistance

during the elution experiments, and to Larry R. Avens for thcrmogravimct -

ric analyses of various anion exchange resins,

1. J. P. Faris and R. F. Buchanan, Applications of Anion-Exchange

Spectrographic Procedures in Nitric Acid Medium, U. S. Atomic Energy

C~mmission report TID-7606 (1960), pp. 165-J 94.

2. S. F. Marsh, Improved Recovery and Purification of Plutonium at Los

Alamos Using Macroporous Anion Exchange Resin, Los Alamos National

Laboratory report LA-10906 (May 1987).

3. S. F. Marsh and 1’. D. Gallegos, The Influence of Plutonium

Concentration and Solution Flow Rate on the Effective Capacity of

Macroporous Anion Exchange Resin, Los Alamos National Laboratory report

LA-1099O (July 1987).

4 J, L. Ryan, Plutonium Ion Exchange Proccsscs, Procccdings of the [1S.

LJK Technical Exchange Meeting, oak Rldgc National Laboratory. April 25-

27, 1960, V. S, Atomic Energy Commission report TII)-7607 (1961), pp. 2-20

—.....———— .-. .—.— .—— —

● Reilly Industries, Inc., 1500 S Iibbs Avenue, Indianapolis, IN 40241, wss

((,rmcrly known ●$ Rciliv Tar & Chcmi(al Corp

5. G. Callcri, A. Geoffroy, F. Franssen, and M Demonic, Study of the

Kinetics of’ Loading P~(IV) on Pcrmutit SK Resin from 7.2 M Nitric Acid,

Eurochemic Technical Report No. 120 (NP-12345) (1961).

6. C. R. Marston, Reilly Industries, Inc., l~dianapolis, Indiana, private

communication, November 1988.

7. T. E. Gangwcr, M Goldstein, and K. K. S. Pillay, Radiation Effects on

Ion Exchange Materials, Brook haven National Laboratory report BNL-50781

(1977), p. 88.

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