plutonium ion exchange processes/67531/metadc869324/...anion exchange provides higher separation of...

PLUTONIUM ION EXCHANGE PROCESSES Proceedings of the U S-UK Technical Exchange Meeting, Oak Ridge National Laboratory, April 25-27, 1960

February 1961 [OTI Issuance Date]

Oak Ridge National Laboratory Oak Ridge, Tennessee

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‘

TID- 76 07

CHEMICAL SEPARATIONS PROCESSES FOR PLUTONIUM AND URANIUM

PLUTONIUM I O N EXCHANGE PROCESSES

Proceedings of the

US-UK Technical Exchange Meeting

Oak Ridge National Laboratory

April 23-27, 1960

Issuance Date: February 1961

OAK RIDGE NATIONAL LABORATORY APRIL 25, 26, AND 27, 1960

CONTENTS

7’ I

I

................................................ 1.0 Abstract 1

2.0 Introduction 1

3.0 Ekchange Applications ................. 3. L. Ryan 2

............................................ Chemistry of Plutonium i n Anion

4 .O Continuous Anion Exchange Processing of Plutonium: Hanford Engineering and Operating Experience .............. W. H. Swi-rY; 21

Exchange Contactors A . M. P h t t 33

Plant Ion Exchange D. A . Orth 44

5 .O Engineering Development of Ion ................... 6.0 Objectives of Savannah River .................... 7.0 Cation Exchange Process f o r ............................. Plutonium H. J. Groh 42

Plant Ion Ekchange D. A. Orth 34 8.0 .Operation of Savannah River .................... 9.0 Isolat ion of Plutonium by

Cation Exchange a t ORNL ............... R. E . Brooksbank 60

10.0 Amine Extraction of Plutonium and Related Metals .................... C . F. Coleman 64

11.0 Production Experience with Recovery of Uranium from Reduction Residues by Anion Exchange i n a Higgins Contactor ....... N. J. Se t t e r 74

iii

' 1

i)

1.0 ABS!T!RACT

Information i s presented on the process chemistry of plutonium i n In the cation exchange system both cation and anion exchange systems.

plutonium i s sorbed from a 0.25 M n i t r i c acid solution;,uranium i s eluted with 0.2 M sulfur ic acid;-followed by plutonium elut ion with 5.7 M n i t r i c aciz . t o G i n t a i n plutonium i n the t r iva len t s t a t e . system plutonium a s PU,(NO3)g i s sorbed from a 7 M n i t r i c acid solution with the-meta-llurgical impurities passing on through the ion exchange bed. The ion exchange processes a re carried out i n both fGed beds and continuous column equipment. 15 in . deep and 10 in . diameter- by- 5 in . deep. The €Eggins ty-pe continuous ion exchange contactor has been operated with the anion exchange system fo r about two years, and there i s now development work i n progress on other types of continuous ion exchange columns a s possible replacements f o r the Higgins uni t . The contactors under development include two moving packed-bed vcontactors, one moving f luidized bed d i f f e ren t i a l contactor, and,l moving fluidized bed multistage contactor,

Information i s a l so reported on the use of amine extraction t o

Hy-droxyl.amine su l fa te i s present i n a l l solutions I n the anion exchange

The plutonium i s then eluted with 0.26 M n i t r i c acid.

Fixed beds -are;used-that*are 7 in . diameter by

replace ion exchange f o r plutonium product purif icat ion and on the use of a large scale Higgins continuous ion exchange contactor for recovery of uranium by anion exchange,

2.0 INTRODUCTION

Ion exchange processes have been used f o r the f i n a l concentration and purif icat ion of the plutonium product from the Pwrex process and a l s o f o r the recovery of plutonium from metallurgical wastes. plutonium product from the Purex t r i b u t y l phosphate solvent extraction process contains 0 . 1 t o 1.0 g of plutonium per l i t e r along with some f i s s ion products (ruthenium, zirconium, and niobium) and corrosion products ( i ron and nickel) . venient method f o r concentrating the plutonium t o 10 t o 50 g / l i t e r and removes both the f i s s ion and corrosion products. change procedure has been used a t Hanford i n continuous ion exchange equipment.

The

The ion exchange process provides a con-

The anion ex-

A t Savannah River both cation and anion exchange procedures

1

a r e used i n conventional f ixed beds. change i n fixed beds and proposes t o use anion exchange i n a new ins ta l la t ion . Anion exchange provides higher separation of plutonium from impurities, but both systems have been very successfully used. Continuing development work i n t h i s f ie ld i s being carried on t o provide improved continuous ion exchange equipment and t o develop an amine solvent extraction method a s an al ternat ive t o ion exchange.

Oak Ridge has used cation ex-

The ear ly work i n the development of ion exchange processes f o r plutonium was based on a batch cation exchange procedure and has been successfully used i n plant scale operation. Later developments using the anion exchange system i n continuous ion exchange contactor equipment has a l so been successfully used on a plant scale. exchange process has been found t o be more desirable f o r the concen- t r a t ion of large volumes of d i lu t e solutions when moderate decontamina- t i o n and low waste losses a r e desired, while anion exchange i s readily adapted t o concentrated acid and s a l t solutions and provides higher decontamination.

The cation

3.0 CHEMISTRY OF PLUTONIUM IN ANION EXCHANGE APPLICATIONS .T. L. Ryan

Plutonium, l ike a l l quadrivalent actinides, i s readily sorbed on anion exchange resins from n i t r a t e solutions. The e f fec ts of temperature and solution concentrations on the dis t r ibut ion of plutonium between Dowex-l X-4 and n i t r a t e solutions a r e indicated i n Fig. 3.1. The d is t r ibu t ion coefficient i s higher a t low temperatures and i n calcium n i t r a t e than i n n i t r i c acid solutions. However, the be t t e r kinetics of higher temperatures and acid solutions more than compensate f o r the poorer equilibrium re la t ions a t these conditions. From ni t r&c acid solutions, the maximum dis t r ibu t ion coefficients a t 25OC and 60 C a r e obtained a t 7.5 and 7.0 M acid, respectively. The sorbed species within the r e s in i s Pu(N03)g-(Proof of t h i s statement i s contained i n an a r t i c l e accepted f o r publication by J. Phys. Chem. ).

The r e s in loading r a t e s increase with temperature (Fig. 3.2). A s the temperature i s increased from 25OC, the breakthrough curve moves toward the right because the diffusion rates in to the regin a r e increasing. movement of the breakthrough curve toward the l e f t a t the flow r a t e and feed composition shown i n Fig. 3.3. This i s because the equilibrium i s sh i f t ing and the plutonium capacity of the bed i s decreasing. these data and r e s in s t a b i l i t y considerations, it was conc ludedE . -O- t o 6OoC i s the optimum temperature a t which t o load a plutonium n i t r a t e anion exchange column. the same general behavior i s obtained with most strong base resins .

However, increasing the temperature beyond 60 C resu l t s i n

From

----_--.,"..-.--- The data shown were obtained w i t h Le- Dowex-1, ,----- but

For the higher cross-linked resins there was a notable drop i n t h e diffusion coefficient a s the r e s in became loaded (Fig. 3.4).

2

.

9

V

b

g Pu/gResin (Dry Nitrate Form) g Pu/ml Solution K D =

e

/-

4 / /'

#- 8

0-

0 V

1 o3

HN03 at 25OC

#*----a -I

HN03 at 60°C 0

0 0

0 0

0 0

0

0 0

3 . 0 4 .0 5 . 0 6.0 7.0 8.0 9 . 0 10.0 Nitrate Molarity

Fig. 3.1. Distribution coefficients of Pu(IV) on Dowex-1, X-4 (50-100 mesh) from nitr ic acid and calcium nitrate.

3 3

3 2 0

d 2 8 0

d

.r(

v)

0,

E 240

6( al id l.4

4-2

CJ

2 2 0 0

r; E , k 160

h

id

M \

2 y 120

M d

id z

d o

40

Feed: 1.0 g P u / l , 7 . 2 M HNO3

/

1 I I I I I 1 1 1 I I I I I I I I I I I 1 I I I I l l 0 1.0

Fig. 3.2. Plutonium absorption rates on Dowex-1, X-4 (50-100 mesh).

4

10 100 Time - Minutes

1000

L

0"

N

00 F

9

m

m

N

4

0

0

0

0

0

0

0

0

0

0

09

/3

5

0 0 0

hJ

0 0

In

4 z 1 0

u 0

a

,-i

c,

gt

2

E

E 1

.r(

c, 1

3

0

0

rn

0

+.

9%

oa,

E

0 >o

0

L

*s

0

v u v) .

N

E

F r a c t i o n of E q u i l i b r i u m P u A b s o r p t i o n , F

Fig. 3.4. Variation of plutonium absorption diffusion coefficient i n Dowex-1 wi th fraction of equilibrium attained.

6

b

Actually the drop was more severe than i s jndicated i n the f igure because the points on these curves a re mean coeff ic ients measured up t o tha t loading. the resin, making diffusion i n the beads more d i f f i c u l t . Most res ins lose a t l e a s t 50% of the i r water during loading. several commercial anion resins a r e compared i n Fig. 3.5.

This e f f ec t i s believed t o be due t o loss of water by

The loading rates of

Uranium can compete with the plutonium f o r r e s in capacity i f it i s present i n large amounts i n the loading solution and lower the plutonium loading (Fig. 3.6). The plutonium stream tha t i s concentrated by ion exchange a t Ilanford has oiily t race concentrations of uranium, and t h i s does not i n t e r f e re with plutonium loading.

Plutonium m y be desorbed from anion resins with d i lu t e n i t r i c acid solutions. hydrolysis i n the r e s in phase occurs. 0.35-0.75 M i n n i t r i c acid, depending on the r e s in used, i s suff ic ient . ' The desorpxion r a t e s of commercial res ins vary considerably (Figs. 3.7 and 3.8). e f fec t on the concentration of the plutonium product from the ion exchange system (Fig. 3.9). Elution from the higher cross linked resin, Dowex-1 X-8 i s slower than from Dovex-1 X - 4 . f ac tors a t reasonable flow ra t e s a r e s in with good e lu t ion kinet ics i s need-ed.

However, the acid concentration must not be too low, a s Normally an e lu t ing solution

The elut ion kinet ics and e lu t ion flow rate have a marked

For hi@ concentration

Largely because of i t s good kinet ics a t elevated temperature, $e-F-kit.SK was selected a s the best commercial r e s in f o r the plutonium n i t r a t e anion exchange process. This r e s in shows remarkable e lu t ion kinetics, and with it high product concentration ca'n be'o5Wined (Fig. 3.10). Several equilibrium reki t ions a r e involved i n the elut ion

K = 0.34

With constant r e s in loading Rn-4 E( N O ? ) q and RNO are constant and the equilibrium constant of react ion ( ) ecomes: 3

J 3 Substi tuting concentrations for a c t i v i t i e s ,

Also,

K* = Cm03+ . CNo; 3 3 C

- 3+ + 4c 4+ 'NO; - 'HNO 3 + 3 C p u ~ ~ 3 Pu

7

300

250 - (20-50 m e s h )

200.-

Permut i t SK Dowex 21K Dowex 1, X - 4 .- (20-50 m e s h ) . - (20-50 m e s h )

Amber l i te IRA - 4 0 0

fi .r(

0) CI Duolite A-42 LC Amberli te IRA-40 1 rd .- (20-50 m e s h ) (20-50 m e s h )

(d k 00

Duolite A-101 Dowex 3 (20-50 m e s h Pe rmut i t S - 1

1.0 10 100 1.0 10 100 1.0 10 100 Time - Minutes

Fig. 3.5. Plutonium absorption rates with various commercial anion b

exchange resins.

8

104

I

40

32

Plutonium Held Constant at 0.4 g m s / l

-

. I I I I I I I 0 40 a0 120 160 200 240 280 3 ,

I- . I I I I I I I 0 40 a0 120 160 200 240 280 3 ;

g U/g P u in Feed

Fig. 3.6. Variation o f Dowex-1, X-4 (50-100 mesh) resin capacity at 6OoC with changes i n uranium to plutonium feed concentration ratio.

9

0

4 I

.o t-

-0

9

1

$

0

2 -

m

0

m 0

I -0

2

z Fl

-0

4

N

0

-N

x 3-

-0

4

a

I111 I I

I 1

I 1

0

10

-I

b

0

0

w

Fra

ctio

n o

f P

luto

niu

m R

emai

nin

g o

n R

esin

0

w

I I

I I

11

11

1

I I

I I

I Il

l 0

0

+.

0

r-1

r-1

0

72

64

5 t

4E $4

2 bo

‘ 4c 2

E .r( c, d

32

U u +J rb 9 24 ci

16

8

C 0 1.0 2.0 3.0

Eluate Volume (Bed Volumes)

Fig. 3.9. Elution of plutonium by 0.25 M nitric acid.

12

4.0

b

64

56

48 d

;z 40

.rl U

rb I 4

al

0

0)

3

2 32

: ; 24

ij

0

16

8

0 0

T e m p . : 6OoC

Bed Depth: 44 cm

Flow Rate: 0 . 6 5 m l . /min, c m 2

1 . 0 2 .0 3 . 0 Eluate Volume (Bed Volumes)

4.0

Fig. 3.10. Elution of plutonium from Permutit SK (20-50 mesh) by 0.60 M " 0 3 ,

flto600c elut ion with 0.25 M HNO3 of Dowex 1 X-4 (50-100 mesh) loaded a t 50 C gives 63 g of p l u t o n i L per l i t e r . Solving eq. 3 using eqs . 2 and 5 gives KE = 0.26. tained f o r various r e s in loadings aIF: shown i n Fig. 3.11. The curves a r e calculated from the open points using equilibrium relat ions shown above.

The m x i m product concentrations t h a t can be ob-

One of the chief advantages of plutonium concentration by anion exchange i s the separation from metal l ic impurities t h a t can be obtained (Table 3.1). The f ac to r shown f o r sodium i s probably low because the experiments were carried out i n glass equipment.

Besides the metall ic impurities from corrosion and sa l t i ng i n e a r l i e r phases of the Purex process, anion exchange gives considerable decontamination from uranium and f i s s i o n products (Tables 3.2 and 3.3). With only n i t r i c acid washes, the decontamination factors from zirconium- niobium a r e not so high a s m y be desired. believed t o be due t o co l lo ida l niobium held within the bed. Trace concentrations of f luoride ion (0.01 N) help remove the niobium from the bed (Figs. 3.12 and 3.13). The izn A l 3 + may be added t o complex the F' and decrease corrosion and plutonium losses without greatly 3ecreasing the decontamination. However, with high f luoride concentrations plutonium losses become s igni f icant .

The remaining a c t i v i t y i s

Chemical r e s in damge i n hot n t t r i c ac id solutions appears t o be largely autocatalyt ic due t o n i t r i t e formation. i s destroyed completely i n stagnant n i t r i c acid i n approximately 14 days. However, l i t t l e damage i s observed i n a flowing stream where the n i t r i t e ions a r e constx3ntly being washed away. High radiat ion doses also damage the resin, as a r e s u l t of n i t r i t e fornaation from n i t r i c 'acid radiolysis . Permutit SK i s considered the most r e s i s t an t r e s in t o both chemical and radiat ion a t t a c k (Table 3.4).

A t 6OoC Dowex-1 X-4

m e r e s in has a l i f e expectancy i n the p lan t of approximately 100 days' operating t i m e . A t this point the res in becomes suf f ic ien t ly s o f t t o be d i f f i c u l t t o force through the co?tinuous column.

A t very high loadings a white prec ip i ta te has been observed i n the product solutions i f the r e s in has been allowed t o stand loaded for some t i m e . exchange process, and under n o m 1 operating conditions i s not formed. It does not appear i f Np-237 i s subst i tuted f o r plutonium, and thus m y come from r e s in degradation by alpha i r rad ia t ion .

Tnis prec ip i ta te does not seem t o in te r fe re with the ion

14

80

70

6 0

50

40

30

20

10

0 0 0.5 1.0

" 0 3 Molari ty 1 . 5

1 .oo

10-1

10-2

10-4

- P u Absorbed from 7.2M "03 -

W a s h Cycle 7.2M "03, 0.01M HF - -

W a s h Cycle 7.2M I N 6 3 c----------l

Elu - t ion Sycle 7

0 3 6 9 12 15 18 2 1 24 27 30 33 36 Column Volumes of Effluent Solution

( W a s h a n d Elution Cycles)

39 42

V

b

Fig. 3.12. The effect of the addition of fluoride to the wash solution.

16

I I I I I I 1 I I I I I I I I I I 1 I I I 1 I I I I I I I I I

17

Column Volumes of Effluent Solution ( W a s h and Elution Cycles)

Fig. 3.13. Direct fluoride wash of loaded resin.

Table 3 .l. Separa-tion of Plutollium from Metcllic Impurities by Anion Exchange a t 60°C

2 Coluinn: 'dash:

90 c m x 0.28 cm ; resin, Dovex-1 X-4, 50-100 mesh 15 bed srolumes 7.2 - M n i t r i c acid, 10 ml/~n.sq cm

Coqosit ion, ppm of PU Decoiitamina t i on Element Feed Product Fa c'cor

100,000 e >50,000 A 1 100,000 <13 >7,700 Ca 100,000 <5 X O , 000 C r 100,000 5 20,000 cu 100,000 10 10,000 Fe 2 , 000,000 45 44 , 000

A g

xo, 000 K 100,000 <5 <1 >loo, 000 Li 100 , 000

100,000 20 5 7 000 Ym 10,000 2 5,000 Mg

Na 10 , 000 20 5 00 100,000 <lo >lo, 000 N i

0 Table 3.2. Separation of Plutonium f r o m Uranium a t 60 C

Feed and msh flow rate: Resin: Dowex-1 X-4 , 50-100 mesh

18-20 ml/min.sq cm

TiJash solution: 16 C O ~ W V O ~ W ~ ~ S

Product Solution

Pu Conc, tamination g/ li te r Factor

Feed Solution U Decon-

Pu Conc, u/m g/ li t e r Ratio

0.80 1 0.40 61 0.41 103

0.11 1440 0.63 294

4* 5 47.3 3.6 x iolc

36 *3 4.8 x io6

43 .o 4.5 x 10

5.6 lo5 46.5 6.8 x 10 3.27

* Only 4 column volumes of wash used with a U/Pu r a t i o of 1 i n feed. b

18

h I

Table 3.3. Effect of Washing Agent on Fission Product Removal

Bed depth: 110 cm; resin, Permutit SK, 30-50 mesh Operating temperature: 0

6OoC except i n e lut ion cycle of Run 2, which was a t 25 C

Wash Cycle Elution Cycle Avg Avg Flow Flow Fu Fission Product

Colwan Rate Rate, Product Pu Decontamination Product Purity

No. of Wash Solution sq ern sq em g / l i t e r Factor Zr-Nb Ru-Rh Z r - N b Ru-Rh Run Volumes Vash & / m i n e ml/min* Conc, Conc Factor ( y pc/Pu c r ) X l O i l

0.2

0.2

1,210 13,000 i o 1 34 7.2 - M HNO3 5.3 1.2 50 E O

2 34 7.2 M mo3 5.0 0 *9 41 98 5,400 27,000 4.5

3 14 7.2 M HN03

0.01-M HF3 7.2 M-mO 5.2

18 7.2 E HXO

- 3 6 2.4 49 26,000 39,000 0.05 0.05 77

4 30 7.2 M HNO 0.01-M HF3

6 7.2 M-H.NO 5.4 2.3 50 77 164,000 15,000 0.04 0.05 - 3

Table 3.4. Plutonium Capacity of @--irradiated Anion Exchange Resins

I r radiat ion temperature : 25OC

Resin

Resin Capacity t o 50% Breakthrough

Radiation a t 6ooc, g Pu/ l i te r $I of Capacity of M i t r a t e - of Unirradiated

x kv%l 10 r form Resin Resin

Dowex 1 X-4, 50-100 mesh

2.03

Amberlite IRA-401, 0 *5 20-50 mesh 1.6

2 .o 3 -5 4 -5

D O ~ X 21-K, 50-100 mesh

Permutit SK, 20-50 mesh

1.0 1.8 3 -0 4 .O

1.0 2.6 3 *4 5 .o

65

55 53 46 44 23

76 63 52 - 72 72 65 -

5 1

85 82 71 68 35

63 53 43 - 100 100 90 -

- I

20

4.0 CONTINUOUS ANION EXCHANGE PROCESSING OF PLUTONIUM: HANFORD ENGLNEmING AND OPERATING EXPERJ3NCE

W. H. Swift

The Hanford Purex Plant, s tar ted up i n 1956, vas discussed by I r i sh a t - t h e f irst U.S.-U.K. Interchange (1). The process described i s the outgrowth of an i n i t i a l f lex ib le design followed by several years of aggressive plant improvement e f for t , a small face t of which i s the use of continuous anion exchange f o r plutonium concentration.

A t s tartup, the plant could best be described a s a three-cycle process,. i n t ha t both uranium and plutonium were processe-d- through 'three cycles of solvent ex t9c t ion . A t t ha t time, evaporative concen- t r a t ion with simultaneous steam stripping was used a s the f i n a l step f o r both products. Unique features of the Hanford Purex Plant a r e i t s continuous, a s opposed t o batch, nature and reliance on safe geometry design f o r c r i t i c a l i t y control of the plutonium processing equipment a s opposed t o concentration control.

Shortly a f t e r plant startup, it became apparent t ha t the f i n a l plutonium evaporator equipment would be a continuing trouble-maker r

1. Corrosion r a t e s were such tha t 304L s ta in less s t e e l tube bundles f a i l ed regularly a f t e r 50 days' service.

2 Plutonium polymer f o m t i o n (Figs. 4.1 and 4.2) was a constant problem ( 2 ) . -

3. Siliceous deposits were d i f f i c u l t t o control because of the high concentration factors required.

_ b

!These problems provided much of the incentive f o r i n s t a l l a t ion of the continuous ion exchange process, which was s t a r t e d up i n January 1958.

In 1958, the plant was converted t o two cycles of solvent extrac- \

t i on f o r both uranium and plutonium, and anion exchange replaced the plutonium evaporation system. be used t o backcycle aqueous raffinates from the f inal uranium and plutonium cycles and from the plutonium anion exchange system (Fig. 4.3).

This change freed equipment, which could

In 1956, development work undertaken a t Hanford was necessarily limited by the f a c t that only one continuous contactor design (Higgins) and one ion exchange process (cat ion) had reached a s t a t e of development sui table f o r immediate application. p i l o t plant studies were undertaken t o evaluate contactor hydraulics. Bench-scale laboratory studies included continuous plutonium reduction chemistry and feed adjustment studies and 1-in.-dia continuous contactor work.

Nonradioactive fu l l - s i ze

21

- \

CT

00

90

8 0

70

6 0

5 0

4 0

30

20

IO STABLE COLLI

STABILITY LINE \

S I

/

"03 STOCK SOLUTION

- B

LINE FOR Pu 2.5M

CALCULATED (CO

0 0.1 0.2 0.3 0.4 0.5 0.6 0

dPLETE 1

- M "03

Fig. 4.1. effect of acidity.

Stability of Pu(IV) nitrate solutions at room temperature:

22

24

W

z 0

2

0

a, V

x

V

I 0 3

'X

!?!

- c

3

L

. . . . .. . . . .

The development work with plutonium solutions indicated tha t continuous feed preparation (i .e. reduction) was not p rac t i ca l with the common eas i ly handled reductants. Reduction kinet ics with hydroxylamine su l fa te (used i n batch work by ORNL and SRP) was much too slow, and the po ten t i a l f o r polymer formation w5th Hanford plutonium levels was readi ly apparent. sui table .

Other reductants were investigated but none were

The bench scale work w i t h a 1-in.-dia continuous contactor showed that , although the cation exchange process could be mde t o work i n a Higgins contactor, extremely careful control was necessary t o prevent the autocatalyt ic oxidation of plutonium and subsequent gas f o m t i o n i n the r e s in bed. The continuous contactor would not to le ra te gassing. With t h i s background on the cation exchange process, the advent of the snion exchange process vas welcomed.

Table 4.1 gives a qua l i ta t ive comparison of the cation and anion exchange processes a s seen from the viewpoint of the Hanford application.

Table 4 .l. Plutonium Concentration and Decontamimtion: Comparison of Cation and Anion Exchange Processes

Cation Exchange Anion Exchange

Feed adjustment Coqlex Simple Vaste losses LOW’ Moderate Decontamination and Moderate High

Product acidity H i g h Low

pur i f ica t ion Chemical s t a b i l i t y Unstable Stable

Product concentration H i & Moderate Process temperature L O W Elevated

Process and Equipment Description

The basic chemistry of the anion exchange process has been re- viewed (3) . Figure 4.4 out l ines the process as used a t Hanford, -

The system receives solvent extract ion product stream (2BP) continuously. This solution i s roughly 0.5 M i n n i t r i c ac id and 0.05 M i n su l fu r i c acid, the l a t t e r used as a chemiTa1 s t r ipping agent f o r plutonium i n the 2B c o l m . s c i n t i l l a t i o n alpha monitor f o r determination of plutonium content. Sixty percent n i t r i c acid i s blended with the 2BP stream continuously

- The stream flows through a l iquid contact

t o yield a net 6-7 M n i t r i c acid feed. r e su l t s from t h i s axjustment.

A 2-fold increase i n volume After acid adjustment, the feed passes

I

25

26

€ e 7n V

X

al

C 0

K

U

.- E 3

C 0 3

n

.- c

- v) 3

0 .J K K

.- c

through a heat exchanger, where the %eqera ture i s raised t o c-70°C, and i s then introduced in to the XAF slab tank.

Feed t o the loading section i s pumped with aoremote-head diaphragm pwq and i s fed to the c o l m a t approximtely 60 C. The feed ra te i s of the order of 0.5 gpm. upward intermittently a s a dense bed through the 5.29-in.-dia by 6-ft- 3-in.-high loading section. A g a m absorption photometer (500 mc of Cs-137) continuously measures the plutonium loading of the res in a t a point several f e e t below the feed point. The plutonium concentration on the res in leaving -the loading section i s of the order of 30 t o 50 g per l i t e r of res in . The plutonium loss t o the ra f f ina te i s of the order of 0.5%, and t h i s stream i s recycled. tonium content by a continuous alpha-printer in-l ine monitor.

The res in (Permutit SK, 20-50 mesh) passes

It i s monitored f o r plu-

The loaded res in continues i t s ipward path through the scrub section, where it i s washed with approximtely 7 M n i t r i c acid a t a ra te of 5-10 ml/min.sq cm. Washed, loaded res in Then passes downward i n f ree f a l l and i s essent ia l ly dewatered by removal of a s l i p water stream (actual ly 7 M n i t r i c acid a s introduced by the XAS). The s l i p water i s recycled aiong m t h the X A W stream and condensate from the f i n a l evaporator. The res in then moves upward i n the 5.29-in.dia by 6-ft-3-in.-high elut ion column, where it i s contacted with 0.5-1.0 M n i t r i c acid for elution of plutonium. Plutonium leaves the XC col& a t a concentration of 30-50 g / l i t e r i n approximtely 1 M n i t r i c acid. Resin leaving the XC column has been stripped t o a p1ut'i;nium content of l e s s than 0.05 g / l i t e r and i s ready f o r return t o the XA column.

Eluted plutonium solution XCP passes through an absorptometer, where the attenuation of americium-241 gamma rays measures the plutonium content. Plutonium solution i s concentrated continuously i n a thermosyphon emporator t o concentrations ranging up t o 250 g of plutonium per l i t e r . cycled. ?"ne heat transfer surface of this vessel is of commercially pure A55 titanium, vacuum annealed. Because of the high f a i lu re ra tes experienced with s ta inless tube bundles (of the order of 55 days' l i f e expectancy), the use of titanium a s a material of construction f o r heat t ransfer surfaces has been act ively pursued a t Hanford. shows some of the fabrlcat ion de ta i l s used on small tube bundles such a s used i n the f i n a l plutonium evaporator (4) . excellent, with no fa i lures i n more than tw; years of service.

Condensed overheads from the evaporator a re re-

Figure 4.5

Performance has been

Figure 4.6 shows an a r t i s t ' s conception of the general layout of equipment i n the hood. Details of solution d is t r ibu tors and collectors a re shown i n Fig. 4.7. l i r e mesh s izes used ore 24 by 110 or 14 by 88.

Cr i t i ca l mss Control

With two exceptions, the ion exchange equipment has an "always- safe" geometry on a water-tamped basis, vhich permits essent ia l ly un- limited contact operation and mintenance. The two exceptions a r e the

27

12 Holes 1 1/4 c - c on Tr i angu la r P i tch

Ti tanium Tube Sheet F a c i n / C o m m e r c i a l A-55 8 1 / 2 " ;a I / Welded to Tubes . . x 5/32'' Th.

Tube Sheet 11" Dia. x 2" Th. Baffle Type 430 SS

a.

Steam Inlet 2 Sche d . 40 Pipe Type 304-L ss

Condensation Outlet

1" Sched 40 Pipe Type

" 304-L SS

+ "B" End Shell 6" Sched. 40 Pipe Type 430 SS TUBE SHEET DETAIL

Titanium Tube Sheet Fac ing

Melt C o r n e r by Shielded Iner t Gas / / A r c Welding P r o -

6' - 1 / 8 "

'IAA"

End

/ 1 A-

i / I c e s s

1.013" Dia. in Tube Sheet

Ti tanium Tube 1" O.D. x .075" Wall Comme r cia1 A - 5 5

ve s

L

Fig. 4.5. Titanium tube heat exchanger.

28

r 0 .- + e L t al V

C 0

V

a t

U

t 0

U

C

U

t 0

V

al -0

.- -I- .- E

+

E 3

K 0 3

Q

.- +

- al

0)

t

U I

V

X

Q)

t 0

C

U

.- 0)

.- u-

I

, , " . . , 1 /.. ...

Q XAF tank and the hood f loo r and sump. plutonium-contaminated r e s in i s r e s t r i c t ed by special procedures.

In addition, the handling of

The XAF tank i s a slab tank 2-5/8 in . thick ( inside) by 8 f t long and 5 f t high, fabricated t o l /h-in.-thick s ta in less s t e e l p l a t e . the exis t ing geometry within the hood, the XAF tank i s "always-safe," and maintenance or operation through ex is t ing glove ports adjacent t o the vessel adds a negligible amount of neutron reflection; consequently, no r e s t r i c t ions a re necessary when glove ports a r e used. The hood face i s 18 in . from the centerline of the vessel . However, if it becomes necessary t o enter the hood t o perform mintenance, the neutron re f lec- t i o n furnished b y the body must be considered.

With

The ion exchange hood sump can be regarded a s an i n f i n i t e s lab water-tamped on one side (bottom). provided by equipment located above the hood f loor . water-tamped on one s ide with an addi t ional water re f lec tor located 36 in . from the other surface (more re f lec t ion than i s actual ly present) i s "always-safe" up t o a thickness of 2.59 in . f loor , 1.5 i n . deep, const i tutes the low point of the swap and. mkes t h i s figure s t i l l more conservative.

Operating Experience

Additional neutron re f lec t ion i s An i n f i n i t e s lab

A trough i n the

The ion exchange system has now operated sa t i s f ac to r i ly f o r more Decontamination than two years with an on-stream eff ic iency of -95$.

fac tors f o r zirconium-niobium, the limiting contaminants, have gene- ra l ly ranged from 3 t o 5. These fac tors a r e considerably lower than those observed in"lsboradbry work, and t h i s f a c t i s believed pa r t ly due t o longitudinal mixing i n the packed bed and pa r t ly t o using fewer column volumes of wash solut ion (scrub) .

--"-"_I.

Product recovery has been generally good considering t h a t the recycle system permits to le ra t ion af losses up t o several percent. Generally, losses have been of the order of l e s s than 0.5%. qual i ty i s excellent. Aside from improvement i n decreased f i s s ion product ac t iv i ty , the metal l ic impurity content has been decreased more than 5-fold below t h a t resul t ing from d i r e c t evaporative concentra t i on .

Product

I n p lan t practice, usefu l r e s in l i f e has been of the order of ,~ 60 _- - t o 140 days of continuous operation, and the degraded r e s in is-removed *generally a t convenience. Degradation of the r e s in i s due t o chemical attack, radiolysis by plutonium alpha bombardment ( the effect ive dose rate t re s in loaded t o 50 g of plutonium per l i t e r i s of the order of 7 x 10 r /hr) , and mechanical a t t r i t i o n . t i o n a r e mechanical ra ther than chemical.

E The symptons of r e s in degrada-

32

L

1. E. R . I r i sh , "Description of Purex Plant Process," HW-60116 ( J A P r i l 30, 1959)

2 . A. Brunstad, "Polymerization and Precipitation of Plutonium( IV) i n Nitric fixid, 'I HW-54203 (Dec . 17, 1957).

3. J. L. Ryan and E. J. Wheelwright, "The Recovery, Purification and Concentration of Plutonium by Anion Exchange i n Nitr ic Acid," J34-55893 (Jan. 2, 1959).

4. R. W. W i r t a , "Fabrication of a Titanium Tube Keat Exchanger;" HW-51998 (Aug- 20, 1957)-

5 .O ENGINEERING DEVELOPMENT OF I O N EXCHANGE CONTACTOFS A . M. P l a t t

Considerable in te res t has developed i n the use of ion exchange i n the nuclear e n e r a f i e l d i n the last decade. Aside from the obvious use of providing demineralized coolant water for reactors, there a r e many potent ia l uses f o r a simple and rugged contactor i n separation f i e l d s Included a r e the separation and purif icat ion of fissionable and fertile m t e r i a l s ; the recovery of f i ss ion products from waste streams e i ther f o r indus t r ia l use or t o render the wastes l e s s toxic; and the recoveq of transuranic elements. overal l separations processing, a s i n the case of the mrex anion exchange uni t t ha t has been described by Swift, or may be the prime separation process a s i n the anticipated application i n the recovery of plutonium and uranium from spent PRTR f u e l elements.

These processes may be incidental t o the

Considerable e f fo r t has been expended i n developing continuous countercurrent contactors both within the Atomic Energy Commission's programs and by private industry. However, f e w designs adequate for high-level radiation use have been successfully demonstrated.

The --_ purpose -- _- - _-,, of 11 t h i s discussion i s t o c i t e the philosophy and objectives of contactor development work a t Hanford and t o summarize the s ta tus of t h i s work. Most of our work has, of necessity, been devoted t o the ,mechanical and hydraulic features of the contactors. We a re j u s t now cXppro;achi-@-*the poixt where we f e e l t ha t such features a r e suf f ic ien t ly developed tha t we can devote more e f f o r t t o process considerations and efficiency studies.

In establishing the philosophy and objectives of our ion exchange work, we have considered the strong and weak points of the two prime competitors of ion exchange, i . e . , solvent extraction and precipi ta t ion processes. To be competitive f o r the recovery and decontamination of a specific ion, the ion exchange system must have cer ta in features, namely:

33

a. The a b i l i t y t o sorb a specific ion without excessive waste losses.

b . The ab i l i t y , when loaded, of being scrubbed for removal of contami- nating ions without excessive waste loss.

c . The a b i l i t y t o allow elution of the desired ion.

d. The a b i l i t y t o process feeds containing par t iculate matter.

e. Dependability and ease of control.

f , Ease of operation and maintenance.

g. Continuous operation.

The batch fixed-bed columns long used successfully f o r water treatment o r purif icat ion of process solutions have few of the features j u s t enumerated, although f o r some specif ic applications they a re s t i l l highly recommended.

Engineering Parameters

Three features markedly d i f fe ren t ia te the contactor types selected by Hanford f o r development from t h e i r analogs i n gas-liquid and liquid- l iquid mss t ransfer systems. F i r s t , the equilibrium s i tua t ion i s quite different . For examgle, typ ica l dis t r ibut ion coefficients under favorable conditions f o r anion exchange of plutonium exceed those f o r solvent extraction by a fac tor of 100. When these favorable complexes a r e destroyed, the plutonium has l i t t l e a f f i n i t y f o r the res in and the d is t r ibu t ion coefficient drops t o essent ia l ly zero.

Second, i n ion exchange the resistance t o mass t ransfer i s i n the res in and i s mch greater than t h a t i n gas o r l iquid phases. diffusion coefficient f o r anions i n the res in i s about lom8 t o 10-9 sq cm/sec, whereas i n the l iquid phases and f o r some cation exchanges, it is about 10-5 sq cm/sec. solvent extraction, an ion exchange contactor would require about 1000 t o 10,000 times the in t e r f ac i a l t ransfer area per un i t volume and uni t driving force. Practically, the use of small-size res in par t ic les desirable for rapid solute t ransfer leads t o hydraulic d i f f i cu l t i e s i n the operation of ion exchange contactors.

The

Thus t o be kinet ical ly competitive w i t h

Third, a s i n any piece of engineering equipment, f l u id flow character is t ics through an ion exchange bed are important. and thus rest r ic ted, beds, the pressure drop i s a d i rec t function of the l iquid velocity and an inverse function of the square of the pa r t i c l e diameter. i n an increased pressure drop penalty. bed, increasing flow rates w i l l f i rs t cause f luidizat ion and s t i l l higher ra tes will e i the r cause concurrent flow of res in and l iquid o r

For packed,

Decreasing ‘the pa r t i c l e s i z e t o improve mass t ransfer resu l t s For flow through an unrestricted

34

pack the res in against the screens or barr ie rs i n the l iquid eff luent l ine.

The c r i t i c a l f luidizat ion velocity i s a function of the square of the pa r t i c l e diameter and the density difference between the par t ic le and the f lu id . mesh w i l l lower the f luidizat ion velocity about 9-fold. toward f luidizat ion i s fur ther aggravated by the low density differences between phases which ex is t i n some exchange systems. In cases where the l iquid acid concentration i s high and the res in l i gh t ly loaded, this density difference can drop t o near zero.

Decreasing the res in s ize from 20-50 mesh t o 50-100 This tendency

-- I

In summry, it i s apparent t ha t a compromise between desirable hydraulic and mass t ransfer character is t ics i s necessary. The res in , par t ic le s ize i s usually selected t o give reasonable t ransfer ra tes with reasonable pressure drops or f luidizat ion veloci t ies .

Contactor m e s

In many ion exchange processes, the sorption and elution cycles involve enough var ia t ion i n flow conditions that different contactor designs may be desirable f o r the two cycles. exchange contactors t ha t a r e considered of prac t ica l i q o r t a n c e m y be divided in to f ive basic designs: fluidized-bed column; ( c ) moving, packed-bed column; (d ) continuous, countercurrent, fluidized, d i f f e ren t i a l contactor; and (e) continuous, countercurrent, f luidized multistage contactor (mixer-sett ler) . Be- cause of the uncertainty of success with any development program, we have examined four contactors during the past few years: packed-bed contactors; one moving, fluidized-bed, d i f f e ren t i a l contactor; and one moving fluidized-bed, multistage contactor.

The possible types of ion

( a ) fixed, packed-bed column; (b ) fixed,

two moving,

Moving, Packed-bed Column

This type of uni t , of vhich the Higgins contactor i s a good example, i s characterized by a packed bed which i s moved e i ther continuously or semicontinuously and countercurrently t o the l iquid stream by some external driving force. The efficiency of t h i s un i t can approach tha t of a fixed bed, and it has the process advantage of a continuous countercurrent operation, namely high product concentration, low waste loss, and high decontamination efficiency. Since a new res in surface i s being continuously exposed t o the feed stream, the uni t can handle limited amounts of sol ids . i s tha t of effect ing sat isfactory r e s in movement.

The chief problem with t h i s type of un i t

The Higgins uni t has been described by others a t t h i s meeting, so I will confine my comments t o a modjfied j igg ler column (Fig. 5.1). This uni t i s an adaptation of the Australian uni t described by Arden and associates i n Paper 1096 of the 1958 Geneva Conference. Its pr inci- p a l features can be described by s t a r t i ng with introduction of the res in

35

i n to the sorption section. The res in moves downward, continuously and countercurrently t o l iquid flow, under the force of gravity and aug- mented by the pulse expansion. The resin i s removed from the column and moved to the elut ion cycle by the pulse coinpression cycle. s l i p l iquid carried with the resin i s pa r t i a l ly removed i n the de- watering chamber (returning t o the sorption column) and the res in flows by gravity in to and through the elution column. The l iquid streams a r e conventional a s t o type and point of entry.

The

The p r i m r y advantage of t h i s u n i t i s i t s simplicity. Very few moving par t s a r e involved, resul t ing i n a very re l iab le un i t . Since the bed moves essent ia l ly a s a plug, we ant ic ipate eff ic iencies approaching those of a fixed packed bed exchanger, although we have yet t o ver i fy t h i s f a c t . probably typ ica l of a l l un i t s t ha t do not use posit ive driving forces on the resin, t ha t is, a limited range and capacity, promulgated by the rather sensit ive hydraulic balances tha t must be maintained a t all times.

The primary disadvantages of t h i s un i t a r e

We have run a p i l o t h-in.-dia by 10-ft-high model of t h i s un i t under a ( t o date) limited s e t of operating conditions. tudes of 0.5 t o 1.0 in . and frequencies of 3 to 10 cycles/min have been used. res in movements up t o 20 gal/hr.sq f t have been secured.

Pulse amplj-

Aqueous flow ra tes up t o 200 gal/hr.sq f t have been used and

Very few efficiency data havc been collected since our experimental environs prohibi t the use of plutonium. We have made runs with thorium tracers which indicate recoveries i n the range 95-98$ a t a feed rate of 100 gal/hr.sq f t over the 5-ft-high sorption section.

Moving Fluidized Bed

The second contactor we have under development i s a moving fluidized-bed uni t (Fig. 5.2). A g a i n , t h i s un i t i s of Australian origin, f i r s t reported by Weiss i n the Australian Journal of Applied Science, 4:510-43 (1953). The operation of t h i s contactor i s analo- gous t o t h a t of a sieve-plate absorber.

The res in i s introduced in to the contactor through a standpipe. It progresses across the p la tes and through the downcomers under the act ion of a superimposed pulse. Resin i s removed from the 80lumn by a s luicing device and carried t o an appropriate e lut ion column. Liquid streams can be introduced a t intermediate points i n the contactor without d i f f i cu l ty . The apparatus a l so lends itself t o easy in s t a l l a t ion of a device f o r c lass i f ica t ion and bleed-off of r e s in between the elu- t ion and sorption columns. Since the contactor operates with an un- restrained res in bed, the throughputs a r e limited by f lu id iza t ion i n e i ther the downcomers or i n the zones between plates . provide good eff ic iencies with essent ia l ly trouble-free nonprogrammed operation. It a l so has the a b i l i t y t o process feeds containing sol id matter whose pa r t i c l e s i z e i s l e s s than tha t of the resin.

The uni t should

37

Q

Fig. 5.2. Continuous countercurrent differential contactor, Weiss design.

38

The aqueous and res in flow character is t ics of t h i s un i t a r e indicated on Fig. 5.3. Normal pulse amplitudes a re small, from 0 . 1 t o 0.2 in . , and pulse frequencies a re high, from 75 t o 300 cycles/min. have operated a t reasonable l iquid flow rates , up t o 200 gph/sq f t with l iquid/resin flow ra t ios a s low a s 2.

We

The chief disadvantages tha t we see i n t h i s un i t a r e pa r t i a l ly those of the j iggler , i . e . , sensit ive hydraulic balance, and no posi- t i ve driving force f o r res in movement; the more complex mechanical features such a s downcomers, e tc . ; and the lower inherent efficiency since the res in i s a t l ea s t pa r t i a l ly fluidized and does not completely f i l l the column.

Moving, Fluidized-bed, Stage Contactor

The th i rd contactor t ha t we have examined i s a multistage agitated- bed ion exchange ( m b i e ) contactor (Fig. 5.4). countercurrent t o the l iquid flow. The res in i s then violently f lu id iz - ed by the propellor ag i ta tor and finally leaves the stage under the impetus of a r e s in flow impeller. This sequence i s repeated through- out the contactor. The l iquid ex i t s through a screen a t the top of the un i t .

The res in i s injected

The p r i m r y advantages of the un i t include the a b i l i t y t o handle sol ids of any s ize reasonably smaller than the resin. a b i l i t y ex is t s t o handle sml l -pa r t i c l e res ins since the r e s in i s subject t o powered transfer, and the un i t has a high range of l iquid and res in flows coupled with high capacity.

An i n t r i n s i c

We have noted some interest ing f a c t s on power consumption i n t h i s un i t : A t high holdup, power requirements increase because a thick s lurry i s being handled. Surprisingly enough, th i s a l s o occurs a t l o w holdups, possibly because large quantit ies of l iquid m y be recirculat ing through the downcomers and separation plates .

there i s an optimum power input (Fig. 5.5) vs. res in holdup.

The same so r t of in formt ion i s shown i n Fig. 5.6 a s power input We have run t h i s u n i t vs. aqueous flow ra tes with holdup parameters.

a t aqueous flow ra tes up t o 400 gal/hr.sq f t ( i .e . , about 2 liters/min i n a 4-in.-dia column) with no limit evident on the max im throughput. The absence of res in flow parameters i s explained by the f a c t t ha t f o r the range of conditions we have examined t o date, including resin/l iquid flow rates of almost 1, the res in holdup appears t o great ly overshadow any possible e f fec t of variations i n r e s in flow.

In conclusion, I might note tha t we a r e optimistic about the out- come of our current development program. The advantages of successful moving bed operation a re roughly those associated with any continuous operation: a constant supply of a uniform quality product a t reduced investment i n space, capital , and labor.

39

6 c V

0

C 0

V

c

In In .- P a; ., 3

c

0

C

- rc .- In L In >

RESIN I N

RESIN "RESTRICT

RESIN F L O W

RESIN OUT @

Fig. 5.4. Mabie contactor.

41

Resinr P e r m t i t SK 20-50 mesh Aqpwus: 7.0 4

I I

0.6 Resin Holdup

0.8

Fig. 5.5. Effect of resin holdup on agitator power requirements in three-stage Mabie contactor.

I I

\ \

\

43

6 .O OBJECTIVES OF SAVANNAH RIVER PIANT ION EXCHANGE D. A. Orth

A t the Savannah River Plant two ion exchange processes a re used i n plutonium separation work: the Purex 2BP stream and anion exchange f o r recovery of plutonium from residues. Both a r e carried out i n batches i n small fixed beds of res in i n similar equipment and i n a "wet cabinet'' type of ins ta l la t ion . These a r e d i r ec t maintenance and operation systems.

cation exchange f o r concentration of / I

The cation exchange ins ta lk i t ions have several advantages. The 2BP stream already contains hydroxylamine, which was added t o a i d stripping from the solvent, and i s processed d i rec t ly with no fur ther feed adjustment. feed eff ic ient ly; on occasions, solutions with plutonium concentrations as Low a s 0.001 g / l i t e r have been processed without d i f f icu l ty . requiremGnt--of Grge volumes i s set primarily by the mixer-settler contactors used i n solvent extraction a t the Savannah River Plant. Nuclear safety i s maintained by s t r i c t control of concentrations i n the contactors, and the product s t r e a m has been i n the range 0.2-1.2 g / l i t e r on d i f fe ren t flowsheets, with much lower Concentrations a t s tar tup and shutdown. -&osses a r e suff ic ient ly ow t ha t recycle o r recovery of the column waste i s unnecessary; have been mintained f o r long periods of time, but t h i s low l eve l i s unnecessary, and process control conditions n o m l l y a r e relaxed u n t i l losses a r e i n the neighborhood of 0.01$, f o r eas ie r operation. important aspect of the cation exchange system i s the s u i t a b i l i t y of the product f o r subsequent precipi ta t ion processes; the s tabi l ized Pu3+ n i t r i c acid solution appears t o have unique advantages and gives superior pe r fomnce . a l terna t ive concentration -me-th_od,-but the advantages of cation exchange and the operating Sroblems with evaporators were both suf f ic ien t t ha t the evaporators were not installed. The improvement i n product quali ty includes separation from residual organic phase, fur ther separation from uranium, decontamination from f i s s ion products, and no additiQn of corrosion products.

The system i s able t o handle large volumes of d i lu t e

The

BS--down t o 0.0001%

An

Evaporation actual ly had been designed a s an

The physical construction of the cation exchange systems was in- fluenced by several other c r i t e r i a besides the ac tua l process operating conditions: (a ) they a r e i n a d i r ec t maintenance area; ( b ) the column feed system i s large because of the large volumes of d i lu t e solutions; ( c ) the column product and recycle tanks a r e small f o r nuclear safety; (d) although a few transfers a r e made by pump, plutonium solutions a r e fed t o the column system only by gravity t o avoid any poss ib i l i ty of excessive pressure; and (e ) there i s no inherent prejudice against batch operation, so no great e f f o r t has been made t o i n s t a l l continuous equipment. x

The anion exchange system is used f o r recovering plutonium from the miscellaneous solutions and sol ids generated during production of

44

2

3

plutonium metal from the cation exchange product. The fixed beds of anion exchange r e s in give excellent decontamination from the concentrated s a l t solution, a s the i n i t h l s tep i n the recovery operations.

The select ion of an ion exchange process r ea l ly r e s t s on the design requirements and c r i t e r i a . Generally speapdng, cation exchange i s most desirable f o r concentration from a large volume of d i lu t e solu- t i o n when moderate decontamination and low waste losses are required. For t h i s case, the complex feed adjustment and slower exchange r a t e s of anion exchange pose several disadvantages: ( a ) the already large volumes of feed must be doubled for acid adjustment t o greater than 6 M n i t r i c acid, ( b ) n i t r i t e must be added f o r valence adjustment, (c7 the columns must be operated hot fo r reasonable exchange r a t e s t o be achieved, ( d ) the same u n i t throughput requires e i the r more equipment or f a s t e r flows, with attendant higher feed pressures on the hot, strong n i t r i c acid solution, ( e ) the higher losses require t h a t plutonium be recovered from the waste or t h a t much longer columns (with attendant higher feed pressures) be used, ( f ) f o r economic reasons, the large amount of n i t r i c acid must be recovered from the waste. On the other hand, anion exchange i s extremely valuable when plutonium‘ must be recovered and decontaminated from concentrated ac id and sa l t solutions. These solutions generally a r e smller i n volume than tke m i n process streams, and higher l o s s can be tolerated i n recovery operations which generally involve only a f r ac t ion of the main stream.

7.0 CATION EXCHANGE PROCESS FOR PLUTONIUM H. J. Groh

The primary purpose of the cation exchange process i n use a t SRP is t o concentrate the d i lu t e plutonium solution from the Purex solvent

cessing. A concentration of the order of 50- t o 100-fold i s accomplished i n the ion exchange step. A s a secondary purpose, the plutonium i s fur ther decontaminated from the res idua l uranium and f i s s i o n products and other metall ic impurities l e f t over from the solvent extraction process.

extraction process in to a sa t i s fac tory feed f o r the subsequent pro- _-

“$e basic process chemistry i s described here.

The or ig ina l cation exchange process used a t Savannah River was developed a t ORNL by Overholt, Tober, Orth, and others. This process has been modified s l igh t ly by fu r the r work a t Savannah River Iaboratory by Tober and Burney, and by experience gained through more than six years of successful operation i n the p lan t . Most of the information has been published by Tober (2nd Geneva Conference on Peaceful Uses of Atomic Energy).

Resin Chemistry

The properties required f o r a good cation exchange r e s in a re : ( a ) rapid exchange of ions; (b ) low resis tance t o flow a t high flow

45

r a t e s i n a packed column; ( e ) small change i n volume during the process cycle; and (d) good s t a b i l i t y toward physical and chemical deteriora- t ion. ments t o an acceptable degree.

Compromises a r e obviously necessary t o sa t i s fy a l l these require- The Dowex cation exchange resins of the

---sulfonic acid type have sa t i s f i ed most of these requirements. ~ - . 50-XI2 and, more recently, Dowex 5OW-XI2 have been used very success-

Dowex

fu l ly i n our plant. polystyrene-divinylbenzene beads with concentrated sulfur ic acid a t high temperature. Some batches have been found t o contain 3 t o 6$ of weakly acidic exchange s i t e s , but t h i s has not been found t o af2ect i t s process pe r fomnce . The Dowex 5OW series i s prepared by sulfonation with chlorosulfonic acid a t a lower temperature. Essentially a l l the s i t e s a r e strongly ionized sulfonic acid groups. superior bead or par t i c l e strength.

The Dowex 50 ser ies i s prepared by sulfonation of

This resin has a

The Dowex resins a re available with various degrees of cross- linkage of the polymer chain, varied by the proportion of $Lyiql- benzene i n the polymer. The 12% cross-linked res in has been found most sat isfactory i n the plutonium process. rates and does not swell and shrink excessively. Figure 7.1 shows the

r e s in shrinks about 10% over the range of ac id i t i e s used i n the pmcem A t lower cross-linking than about 8% the volume change of the res in i s excessive for use i n compressed beds, and a t higher cross-linking the exchange ra tes become too slow f o r high productivity operation.

I_ _ - _ --- It provides rapid exchange

--shrinkage of 8 and 12% cross-linked resins i n n i t r i c acid. The 12%

The bead s ize found most sat isfactory f o r compressed bed operation i s i n the 50- t o 100rmesh range. exchange r a t e s without causing a n excessive pressure drop a t high flow ra tes .

These s m l l p a r t i c l e s provide rapid c-- -

The exchange capacity of Dowex 5OW-Xz i s 2.3 equivalents per l i t e r of res in . pU( 111) per l i t e r . t h i s value i s never attained, but loadings of the order of 140 g/l i ter , representing about 75% of the theore t ica l capacity, a r e eaa-obtainFd-. The capacity of Dowex 5OW res in i s adequate t o allow a re la t ive ly large batch of plutonium t o be processed readily even i n equipment sized f o r nuclear safety.

A t complete saturation, the r e s in can sorb 185 g of Under p rac t i ca l operating conditions, of course,

The Dowex 50 resins have good chemical s t a b i l i t y i n ,ni t r ic acid systems, and the physical deter iorat ion of the res in beads i s not severe. the r a t e of degradation of the r e s in by the.-alpha par t ic les emitted by plutonium. Figure 7;2-~hows t h e loss-of capacity of the res in a f t e r exposure t o Pu-239 a t a saturation of 7% f o r a period of 470 days. The resins with the highest i n i t i a l cross-linking a re I most _-_- res i s tan t _-__----- t o damge. The volume of %he exposed res in increases; therefore, cross-linkages a re broken. volumes of the resin.

A point of par t icu lar concern i n the plutonium process i s L----

- These capacit ies a re based on the i n i t i a l

After 470 days' exposure, Dowex 50-XI2 expanded

46

EFFECT OF HNO, CONCENTRATION ON RESIN SHRINKAGE

Fig. 7.1

* CIPICITIES I R E BASED ON INITIIL WUNE ff TWt RESIN

' 0 "0 100 200 300 400 500

W E C T OF AL PHA RADIATION ON E XCHANGE CAPACITY OF 'DOWEX' so RESIN

Fig. 7.2

47

about 40%. the usefu l l i f e of the r e s i n i s about one year.

These changes a r e r e a l l y not severe, and i n p lan t service

Typical Process Flowsheet

Figure 7.3 i s a generalized ion exchange flowsheet f o r plutonium. No spec i f ic dimensions o r volumes a r e given; Orth's paper discusses the d e t a i l s of the design of the r e s i n bed and some typ ica l operating data . The flowsheet assumes the use of f ixed, compressed beds of r e s i n with provision f o r e i t h e r upflow or downflow of solutions. The basic process consis ts of four sequent ia l s teps: elution, product elution, and reconditioning. The volumes of the streams a r e given here i n bed volumes, which i s defined a s the volume of the l iqu id phese i n a pwclred column of res in . equal t o 50% of the packed r e s in volume. For example, with a 2 - l i t e r packed bed, the bed volume would be 1 l i t e r and the Teed volume 140 l i t e r s .

feed sorption, uraaiun

This i s approximtely

- !J%e f i r s t s tep i s sorption of t he plutonium i n the t r i v a l e n t state from d i l u t e n i t r i c ac id solut ion on the cat ion exchange r e s in i n i t i a l l y i n the hydrogen form. The column can be operated a t low enough satura- t i o n of the r e s i n t h a t the sorpt ion e f f luen t contains negl igible amounts of plutonium. In the next s tep the uranium and the bulk of the zirconium-niobium a r e se lec t ive ly e lu ted w i t h d i l u t e sulfur ic acid solut ion. There i s a net downward movement of t he plutonium, depending on the volume of e luant used, but the conditions can be controlled so that th i s e f f luen t will a l s o c o n t a b negl igible amounts of plutonium. In the next s tep the plutonium i s eluted with r e l a t ive ly strong n i t r i c ac id containing sulfamic ac id . The plutonium product solut ion contains 50-60 g of plutonium per l i t e r . Roughly 20% of the plutonium i s l e f t i n the bed a f t e r the product cut . The column i s reconditioned with d i l u t e n i t r i c ac id containing some reductant, and about half the remaining plutonium i s recycled t o the next feed batch. About 10% re - m i n s i n the column a s a heel .

Plutonium Somtion

The d i l u t e plutonium product solut ion from the solvent extract ion f l r o c e s s contains plutonium i n the range 0.2-1.2 g / l i t e r , hydroxylamine

sulfate a t about 0.025 M concentration, & - i e s T s e d i n the solvent ex t rac t ion s t r ipp ing sorution, n i t r i c ac id a t about 0.25 M, and residual uranium from the solvent ex t rac t ion separation i n var iab lz quant i t ies , a rou@i average being 0.1% of the plutonium concentration. product a c t i v i t y i s variable, and there a r e t r ace quant i t ies of corro- s ion products. va len t state. The reduction of plutonium by hydroxylamine su l f a t e i n n i t r i c ac id solut ion less concentrated than 0.75 Mis essen t i a l ly com- p l e t e i n 4 h r when 0.025 M excess reductant i s present. hydroxylammonium ions are-sorbed on the resin, and an appreciable quant i ty i s eluted \iith the plutonium. The presence of 0.2-0.4 - M

The f i s s i o n

The plu.tonium i s e s sen t i a l ly completely i n the tri-

The excess

48

Q

. - I C ' I

Feed Absorlstion

Feed

1 4 0 bed volumes 1 g P u / l i t e r

0.025 M (NH30H),S04 20 ~ml/(cm2)(min)

0 .25 M HNO,

Re c yc 1 e

Dowex

50-100 mesh 50w -xi 2

25Oc s p = 80%

I- Ab s o r p t i on Was t e

1 4 1 bed volumes o.ooz$ Pu

FIGURE 7.3 TYPICAL FLOWSHEET F O R PROCESSING PLUTONIUM

I I ,, 41

Uranium E l u t i o n Product E l u t i o n Recondi t ion ing

Ur a n i um E l u t r i a n t

5-20 bed volumes D i splBc ement Product Re c o n d i t i o n in&

Recycle wi th f e e d

- c u t c u t E f f l u e n t 0 . 2 M H2SO4

0.05 M ",OH 2 ml/(cm2)(min) 2 .5 bed volumes 1 bed volume 2 bed

10 % Pu A vo 1 ume s 55 g P u / l i t e r I T

P u r i f i c a t i o n Waste

5-20 bed volumes U

ZP-Nb

U 10% Pu

7- Product E l u t ri a n t

3 bed volumes 5.7 M HNO,

0 . 4 ml/(crn')(min) 0 .3 M NHZSOSH

L i-'

Recondi t ion ing

S o l u t i o n 2 .5 bed volumes

0.1 M HNO, 0.05 M (NH30H),S0, I

i i 1

i 1

I I

1

hydroxybmonium ion i n the product has been measured.

The prac t ica l capacities of the cation exchange resin f o r plutonium and hydroxylamonium ions can be discussed by a convenient terminology used a t SRF'. centage of the t o t a l exchange capacity of the res in u t i l i zed i n sorp- t i on of a specific ion, and designated a s Sp f o r plutonium, and Sh for hydroxylamonium ion. For example, Sp = 70% means t h a t the composition of the solution i n contact with the res in i s such t h a t a t equilibrium 70% of the exchange capacity i s saturated with plutonium ions. Sp i s thus a function only of the composition of the solution i n contact with the resin.

The capacit ies a re expressed a s the per-

These a re referred t o a s "par t ia l capacities,"

If the exchange reaction f o r plutonium with hydrogen-form res in i s writ ten

F'~(111) + 3HR = 3H+ + PUR3

a t e qui l i b rium

For a given degree of saturation of the res in with plutonium, the term (PUR )/(HR)3, which involves only the res in phase, w i l l be approximtely consLnt . related i n such a way t ha t (H')3/(Pu( III)) = a constant. between t h i s constant and Sp is shown i n Fig. 7.4. used t o c a l c u h t e the equilibrium capacit ies f o r Pu(II1) and "30" ions i n n i t r i c acid solutions up t o 1 M concentration centrations of the acid and the cation, It has been useful i n corre- l a t ing the experimental data, and it gives a simple method of indica- t i ng the e f fec t of smll differences i n the feed solution comosition on the equilibrium capacity of the resin.

Thus a t a given Sp, the concentrations of H+ and Pu(II1) a re The re la t ion

This figure can be

a t various con-

The operation of a cation exchange cycle with plutonium i n the t r iva len t instead of te t ravalent s t a t e i s desirable f o r several rea sons :

1. The r e s in has a greater capacity f o r Pu(II1) than f o r PU(IV).

2. Pu( 111) w i l l be desorbed from the res in i n strong n i t r i c acid more readily than Pu(IV) and therefore will give higher product concentrations.

3. Pu(IV) complexes with sulfate and losses would be high with sulfur ic acid eluant for uranium and f i s s ion product decontamina- t ion.

4. Pu(II1) i s the n o m 1 s t a t e of the plutonium i n the solvent extraction product and i t s use without adjustment i s simple and cheap.

I I I \ \

-FRACTION OF TOTAL CAPACITY USE0 BY INDICATED CATION, X-

140

100

0

10

L 2

K z

8 1

Y

E' c- Y 3 b 0 1 z P

z 0

I-

K z Y y o 01

SP z 75% 35 om EWTRWT 5 7 Y mq* O J Y m,**

. 2 h n , fWWRATE 0 5 nl/lnln-cm21

I E D V O W * 0 47 X VOLWE OF RESIN IN C O W

I

0.001 10 20 30 40 x) 60 70 80 90 100 110 120 130

I l l / j j / 1 j j 1 1 1 1 -QUANTITY OF Pu IN FEED IEPUILIBRIUM CAPACITY OF BED * l O 0 Y . G

DATA FOR CALCULATION OF RESIN CAPACITIES FOR PU*~&(U~)AND (NhOH) EFFECT OF W R A T E ON CONCENTRATION OF Pu IN EFFLUENT

Fig. 7.5 Fig. 7.4

I20

I10

100

90

80

70

60

0 .

40 I I I I

VOLUME OF PROOUCT. REO MWMES

EFFECT OF BED DEPTH ON CONCENTRATKIN OF Pu IN PRODUCT

Fig. 7.6

Sorption of Pu(II1) by Dowex 50W i s rapid. high a s 60 mg/min.sq cm can be used with low losses. t i c e rates i n the range 20-30 mg/min,sq cm a r e used. losses are, of course, a function of the feed flow ra te . shows breakthrough curves f o r plutonium on a bed of Dowex 50-x8, a t various flow rates. If breakthrough i s defined a s the point a t which the loss i n the eff luent i s 1% of the feed concentration, a t a n o m 1 operating r a t e of 30 ml/min.sq cm the res in can be loaded t o 903 of i t s equilibrium capacity, t ha t i s , 90% of the Sp value, before breakthrough occurs,

Mass flow ra t e s a s In ac tua l prac- The eff luent

Figure 7.5

(The curve applies f o r any concentration f o r which Sp = 7546).

Uranium Elution

Uranium and plutonium a r e separated i n the sorption step because Pu(II1) i s more strongly sorbed than uranium and it displaces uranium from the res in bed. l y with d i lu te sulfur ic acid. volume of the eluant and on the su l fur ic acid concentration. In the laboratory, separation factors a s high a s 900 were obtained when 0.25 - M H2SO4 was used. The higher concentrations of sulfur ic acid have the disadvantage of. spreading the plutonium band, resul t ing i o a less concentrated product cut.

Most of the remaining uranium i s eluted selective- The amount of separation depends on the

The decontamination from residual f i s s ion products i s an important par t of the process, par t icular ly from zirconium-niobium. t o 65% of the ruthenium i n the feed i s not sorbed and appears i n the eff luent . Most of the sorbed ruthenium i s eluted with the plutonium product, and therefore decontamination factors a re 2-3. Most of the

, zirconium-niobium i n the feed i s sorbed, but good decontamination from these f i s s ion products i s obtained i n the uranium elut ion step. The

* behavior i s reasonably consistent, and the uranium eluant volume can be ta i lored t o meet ziie required DF. Tne DF's f r o m zirconium-niobium range from 5 t o 50 i n the su l fa te elution. f o r zirconium-niobium decontamination. Its use was tes ted unsuccess- f u l l y a t SIip during one short period. contamination of the product w i t h a c t i v i t y removed from the walls of the s ta in less s t e e l equipment by the fluoride. probably be used under some coiiditions, but it has never been considered necessary i n our process.

Normally 50

Fluoride ion has been used

The r e su l t s were obscured by

A fluoride wash could

Product Elution i

The plutonium i s eluted with strong n i t r i c acid containing

eluant does not contain a s t ab i l i ze r such a s sulfamic acid, vigorous oxidation w i l l occur during the elut ion w i t h the evolution of gases i n the res in bed. This gassing can be suff ic ient ly vigorous t o dis- rupt the packed bed and permit solutions t o channel through the resin. The gas formed i s almost pure nitrogen i f the oxidation i s slow, but during rapid oxidation a mixture of nitrogen and nitrogen oxides i s

L r ' su l fan ic acid t o prevent oxidation of Pu(II1) t o pU( IV) . If the

52

formed. oxidation produces nitrous acid, which i s a catalyst f o r the Pu( 111)- n i t r i c acid reaction. The function of the sulfamic acid is t o react with nitrous acid as rapidly as it i s formed so tha t the oxidation of PU( 111) i s slow.

The oxidation of Pu(I1I) i n n i t r i c acid i s au toca ta ly t ic . The

- ; After elution the Pu(II1) i s slowly oxidized inothe concentrated

product solution. In a typical laboratory run a t 25 C with eluate containing 50 g of Pu(II1) per l i t e r , 4.7 M HN03, 0.3 M sulfamic acid, and 0.3 M hydroxylamine n i t ra te , the P u ( I I 1 ~ was oxidizzd a t a r a t e of aboux 5% per day u n t i l about 40% was i n the te t ravalent state; then the rate decreased t o l e s s than 0.5% per day. been added t o the product i n the laboratory t o hold the Pu(II1) i n th i s s ta te , e.g. ascorbic acid, aminoguanidine sulfate , and ni t ro- acetanil ide. i n the t r iva len t s t a t e f o r several days.

Various s t ab i l i ze r s have

In moderate concentrations they can hold the plutonium

During elution the plutonium concentration i n the eff luent f a l l s of€ rapidly a s conlplete e lut ion of the plutonium i s approached. eff luent m y be collected i n whatever fractions a r e desired. t o obtain an average concentration of 50-60 g / l i t e r i n the groduct Traction, it i s necessary t o leave a f a i r l y large heel. After the product f ract ion has been collected, e i the r by observing the color of the eff luent o r by collecting a predetermined volume, the reconditioning wash m y be begun and the strong acid displaced can be collected a s recycle.

The I n order

A number of variables i n the elut ion step a f f ec t the concentration of plutonium i n the eluate. Unfortunately, fac tors that increase the concentration, such a s the use of stronger n i t r i c acid i n the eluant, and longer band lengths and higher saturation of plutonium on the resin, a l so tend t o increase the amount of gassing i n the column. Some idea of the interdependence of these fac tors can be obtained from the following examples :

( a ) 6 M eluant (5.7 M n i t r i c acid + 0.3 M sulfamic acid) can be used sa'Tely, without excessive gas formatyon, i n a column saturated with plutonium t o a band depth of 25 cm.

(b ) The 6 M eluant could not be used, however, i n a column containing 35 cm zf res in loaded t o Sp = 7'5%; the m a x i m usable was 5 I M.

( c ) 7 M eluant (6.7 M n i t r i c acid + 0.3 - M sulfamic acid) could not be ussd even i n a 1T-cm column.

Some typica l e lut ion data from laboratory runs a r e shown i n Fig. 7.6. The concentrations were s ignif icant ly higher when going from 5 t o 10 t o 15 cm but gains were small vhen the depth was increased beyond 15 cm.

53

The concentration of plutonium i n the eluate decreases a s the flow Both the peak and the average concen- r a t e of the eluant i s Increased.

t ra t ions suffer i f r a t e s higher than 0.5 ml/min.sq cm a re used. slower than t h i s do not of fe r any s ignif icant advantage.

Rates

Reconditioning Wash

The last portion of the eluant i s displaced from the column with I the d i lu t e reconditioning solution. This solution contains only

enough acid t o prevent formation of plutonium polymers and some‘ reduc- t an t t o prevent oxidation.

The f i r s t portion i s passed through the column slowly t o complete elution. plutonium i s recycled w i t h the reconditioning eff luent .

Then the r a t e i s increased t o save time. About 10% of the

8.0 OPERATION OF SAVANNAH RIVER PLANT I O N EXCHANGE D. A . Orth

___- I

The Savannah River Plant has used shallow beds of Dowex 50 cation f

- - -. :

exchange res in successfully f o r concentration of the Purex 2BP solutions. Although longer columns might allow larger batch s izes with attendant fewer operations, they a l so lead d i r ec t ly t o problems with oxidation of the plutonium during elution. The l imitat ion i n height actual ly i s a blessing i n disguise because column diameters can be increased while minta in ing nuclear safety, and the large cross-sectional area gives greater t o t a l throughput.

-“8.1) and have r e s in beds 13 o r 15.5 in . deep ( i n two s l igh t ly different designs); the r e s i n volumes a r e 8.2 and 9.8 liters, respectively. spring-loaded porous p la te maintains a packed bed of res in . A co l la r on the plate, with 20 mils’ clearance from the column wall, maintains alignment, and t h i n wipers of p l a s t i c around the p la te prevent r e s in leakage. In another ins ta l la t ion , a larger instantaneous throughput

To m i n t a i n nuclear safety, the in te rna l height of these units i s limited and the resul t ing res in bed is 5 i n . deep, w i t h a volume of 6.7 liters. Two such columns (separated adequately f o r safety) a r e operated i n ser ies t o serve a s a single unit with an effect ive res in depth of 10 in . The sat isfactory performance of these shallow beds i l l u s t r a t e s graphically the rapid exchange i n the cation exchange system and the excellent dis t r ibut ion efficiency of a compressed bed of f ine resin.

--’

The or ig ina l columns a r e 7 in . dia (Fig.

A

-‘-is obtained w i t h columns of 10 in . dia (Fig, 8.2).

The cation exchange un i t s a r e operated with downflow loading and The simple wash cycles and upflow elut ion and reconditioning cycles.

countercurrent operation has various advantages, which are particularly important i n systems such a s the one here where the dis t r ibut ion coeff ic ient f o r Pu3+ i n the n i t r i c ac id - sulfamic acid eluant s t i l l i s i n favor of the resin. They apply t o almost any ion exchange process and a r e the determining fac tors i n the success of t h i s specif ic

.

Q 54

,

" SS Perforated

(3) 1/16" Air Mat

Lead Shieldmg. 3" Thick

Diameter - 7 inches

Bed Depth - 13 t o 15.5 inches

Resin Volume - 8.2 t o 9.8 l i t e r s

U

R E S I N COLUMN NO. 1

FIG. 8.1

55

R E S I N COLUMN NO. 2

FIG 8.2

I tem

1 2 3 4 5 6 7 8 9

10 1 1 12 13 14 15

- Description

Expanded Polyethylene Foam

Column Top Polyethylene Coated Cadmium Plate "Teflon" Wiper Rings Metal Wiper Springs Stainless Steel Follower Plate Spring Column Body Column Bottom Top Screen Top Support Plate Screen Sup ort Plate (Top) Wiper Hol 8 er Bottom Support Plate Bottom Screen Screen Support Plate (Bottom)

Diameter - 10 inches

Bed Depth - 5 inches

Resin Volume - 6.7 l i t e r s

t I

. . . ..

plutonium cat ion exchange system; cocurrent los,ding and e lu t ion a r e s i q l y not f eas ib l e here.

Repetit ion af the cycle, i n continuous p lan t operation, leads t o steady-state conditions i n which losses, product concentrations, and decontamination f ac to r s a r e s tab i l ized . Steady state i s characterized by severa l conditions. sorption and the decontamination wash i s balanced by the movement up during elution, and, with no ne t movement down, losses r e m i n low. The a c t u a l load t h a t can be held by the column i s fixed by the r e s i n satura- t i o n a t the feed a c i d i t y and plutonium concentration, with an allowance for a clean s t r ipp ing sect ion a t the bottom of the column. The losses, 8.t any point short of breakthrough of the saturated band, a r e determined mostly by the t r a c e r d i s t r ibu t ion coefficient* i n the s t r ipp ing sect ion. The volume l i m i t t h a t can be put through the column when the feed i s so d i l u t e t h a t sa tura t ion i s very low also i s determined by the t r a c e r d i s t r ibu t ion coeff ic ient . This volume limit, and the r e l a t i v e volumes of sorption and e lu t ion solutions f o r low losses i n steady-state opera- t ion, can be calculated since the dis tance a d i l u t e band of plutonium on the r e s i n would t r a v e l under equilibrium conditions i s proportional t o the volume throughput divided by the t r a c e r d i s t r ibu t ion coef f ic ien t . For m i n i m t i m e cycles i n a c t u a l operation, flow r a t e s considerably €as t e r than equilibrium rates are used, and these cause a spread during movement of plutonium up and down the column so t h a t increases i n the calculated volume of eluant a r e required t o maintain low losses .

The movement of plutonium down the column during

-, The conditions under which the various processing s teps have been \

The volume changes re fer red .-/ car r ied on a r e summarized i n Table 8.1. t o a r e the free l iqu id i n the column and experimentally a r e 5O$ of the physical i n t e r n a l volume. The var ia t ions i n 2BP composition represent conditions t h a t individually were standard f o r mixer-settler operation for extended periods of time. The lower batch s i ze l i m i t on the 7-in.- dia columns represents conservative s ta r tup conditions t ha t were dis- carded- i n favor of grea te r throughput. ac tua l ly i s set by the gravi ty feed and the pressure drop i n the equipment, bu t f a s t e r flow rates would not be pa r t i cu la r ly desirable i n any case. A s s t a t ed previously, the losses a r e p r i m r i l y a m t t e r of choice and compromise with maxim throughput. The volume of the sul- f u r i c ac id wash used i n the p lan t i s set on a s l i d ing scale according t o the amount of uranium and zirconium-niobium i n the 2BP, and severa l intermediate volumes of wash (6, 12, or 18 vo l changes) m y be used. Since the su l fu r i c acid solut ion does move the plutonium down the column t o some extent, increases i n the wash volume a l s o require some increases i n t h e e lu t ion volume t o m i n t a i n low losses . flow r a t e s require la rger e lu t ion volumes, and the var ia t ion shown indi- cates t he range from small washes and slow rates t o la rge washes and f a s t rates. The concentration of t he product f r ac t ion and, correspond- ingly, t he f r ac t ion i n the recycle stream, a r e la rge ly a mtter of

*% a s resin/aqueous.

The m a x i m flow rate l i s t ed

Also, f a s t

57

Table 8.1. Operating Experience

Sorption

2BP composition 0.025 -0.05 N hydroxylamine su l f a t e 0.2-0.6 N €EO3 0.2-1.2 g ~u3-8- per l i t e r

Sorption batch 350-775 g i n 7-in.-dia u n i t 750-850 g i n lO-in.-dia u n i t

Flow r a t e

Losses (sorpt ion + €$SO4 wash) 10 t o 10-1 $

UP t o 20 rd/min.sq cm

-4

Sulfur ic Acid Wash*

Concentration 0.25 M b e t t e r decontamination 0.19 E - lower loss 2-3 d/min.sq cm Rate

Uranium DF, low U conc 4-20 with no wash, 30-80 with 25 v o l

100 and up

Up t o 10 with no wash, 10-70 with 25 vol changes

2-4 with no wash*

changes High u COllC

DF from Zr-Nb

From Ru

Product Elution

E lua n t vo 1

Product conc selected 50-70 g / l i t e r

1.6-4.0 vol changes

Recycle 2-15$

Elution rate 0.2-0.5 d /min .sq cm

Reconditioning rate 0.2-0.8 d /min .sq cm

* The wash a l so contains 0.05 - M I!E$OH.1/2 %SO4.

w The DF from Ru i s obtained during sorption, l a t h no addi t iona l DF during %shin&.

58

.. . . -. . . . . . . . . . . . . -. . . . . . . . - . . . . . - - . . . . . . . - . . -

choice. The concentrations shown were compatible with the plant preci- p i t a t ion processes. t i o n vas observed during development work, but it occurs extremely seldom i n the plant; there i s l t t t l e oxidation i f the peak concentra- t i o n i s l e s s tha.n 130 g l l i t e r , and conditions which could- give t h i s a r e avoided.

Uncontrolled oxidation of p1u.toniu-m during elu-

The Dowex 50 or 5OW resin, 50-100 mesh, i s graded hydraul ical ly i n a r i s i n g stream of water t o separate both f i n e and coarse p a r t i c l e s . Even a few percent of f i nes increases the pressure d-rop grez.tly, while coarser r e s i n has unsat isfactory exchange propert ies . The 2BP i s f i l t e r e d througn s in te red s t e e l f i l t e r s t o keep sludge from t'ne colmrs. The columns /- generally ._ must _._ be ... changed a f t e r a year of service; the pressure drop increases from fractured beads, and the exchange capacity decreases a s a r e s u l t of plutonium alpha radiat ion. Another character- i s t i c of these-q&g.units i s t h a t the product eluant volume must be increased t o maintain-low losses . Tkte heel i s stripped from the c o l m before extended shutdown periods and before the column i s removed; 10 volume changes of product eluant generally i s su f f i c i en t . If the u n i t s contain too much rad ia t ion f o r d i r ec t handling, accumulated f i s s i o n products m y be removed with oxal ic acid solut ion ( a f t e r a hee l e lu t ion only). jammed follower p la te , and t h i s happens very seldom i f the column i s assembled properly. If f a i l u r e occurs with the bed i n the expanded condition, the bed i s f lu id ized during e lu t ion and gives low product concentrations. If the bed i s compressed and the jammed p la t e does not allow it t o expand, r e s i n i s forced pas t the r e t a ine r s . Any gas i n the r e s i n bed would in t e r f e re with f l u i d flow and exchange; hence every e f f o r t i s made t o exclude gas. The columns have an ever-open vent, s o t h a t gas introduced with the feed can escape without going through the bed; the column ef f luent l i n e s a l s o a r e arranged so t h a t the colwnns w i l l not drain accidental ly . Some gassing occurs from radio lys i s of water and reactions of the reducing agents when a loaded column remi s idle . For such cases, a s well as f o r known introductions of gas or Fu", a refr igerated wash of d i l u t e n i t r i c acid and hydroxylamine eliminates the g i s and reduces the plutonium t o Pu3'.

The only f a i l u r e t h a t can occur i n t'nese s inple un i t s i s a

4+ The anion exchange recovery of Pu from residues i s carr ied out i n similiiir types of equipment t o t i e cat ion exchange operation. How- ever, the loading k ine t ics for anion exchange a r e poorer, so the feed i s heated and only the longer 7-in.-dia columns can be used. Tie great advantage of the anion exchange process here i s the high decontamination f ac to r s t h a t can be obtained; f ac to r s of 10 have been observed f o r many of the common metal l ic ions such a s calcium, magnesium, and aluminum. The l i f e of the anion exchange res ins has been considerably shor te r than f o r the cation; three months i s considered a good l i f e . The anion exchange r e s i n becomes so s o f t t h a t it f a i l s t o move %he pressure p b t e during elution, when the r e s i n expands, and i s de- formed instead. This cha rac t e r i s t i c type of f a i l u r e i s manifested a s a sudden increase i n pressure drop a t a set stage of e lut ion, and i s a s igna l t h a t the colwnn must be changed.

"_ l__l... .- --. ',

4

59

9.0 ISOLATION OF PLUTONIUM BY CATION EXCHANGE AT ORNL R. E . Brooksbank

-_ '-

ORNL Metal Recovery P i lo t Plant since December 1953 t o concentrate the IIBP plutonium product. t o 1200 g of plutonium per day (Fig. 9 .1) .

A plutonium cation exchange system has been i n operation a t the ' ! The ins t a l l a t ion i s capable of handling 1000

, The column i s mintained a t room temperature except during uranium

elution, plutonium elution, and column reconditioning. i 'cycles the solutions a re cooled t o 10 C t o prevent gassing i n the column. The resin, Dovex 5O-lZY, i s changed approximately once per year a.lthough t h i s probably i s more often than required. Plutonium losses t o the eff luent have averaged appraximtely 0.001$. The unit , i n addition t o concentrating the product, a l so provides "back-up" decontamination capabi l i t ies . have been approximately 3 and 5, respectively. The plutonium product . h2.s a high concentration of an element rrith a op t ica l spectrum l ine near aluminum (Table 9.1), possibly thorium.

During these 0

:

Decontamination factors for gross f3 and y

The equipment ins ta lk i t ion includes three res in columns i n pa ra l l e l +- (Fig. 9.2). The same auxi l iary equipment services a l l three columns.

The surge pot i n the IlBP l ine j u s t upstream from the f i l t e r serves a s a warning when the column starts t o become plugged so tha t the stream can be diverted t o another column. Allowing the uranium and plutonium eluants t o enter through the vent l ines has simplified the piping system required for elut ing and loading the c o l m s i n different direc- t ions . eluate i s sent t o the product tank a s long a s the density reading indi- cates t ha t the plutonium concentration i s suff ic ient ly high. t i r e plutonium processing system i s completely enclosed and i s operated with remote valves although d i rec t mintenance i s used. i s constructed of types 347 and 309 ELL! s ta in less s t ee l .

The density of the eluate i s measured continuously, and the '

The en-

The equipment

The ion exchange column i s 7 in . dia and 18 i n . high (Fig. 9 .3 ) . The res in depth i s approximately 14 in . p la te covered with a 125 mesh s ta in less s t e e l screen keeps the bed compressed. A fluorothene "wiper blade'' keeps res in from slipping past the p la te . t ions than any other un i t i n the Metal Recovery Plant.

A spring-loaded pressure

This un i t has given less trouble during plant opera-

The plutonium product i s transferred eventually t o shipping containers.

60

1 I c

I t 1 ' 1 1 I l l I l l I l l 1 1 1 I l l

u ELUTRIANTI

4.5 M, HNO3 eO.01 g U/LITER

UNCLASSIFIED ORN L- LR-Dwg . 47686

WLUTE PRODUCl 60 LITERS

3.0 LITER/HR

I I B P I 7.6 LITERS/HR 6.0 g Pu/LITER 0.05 M, HYE 0.25 M HNO3

7-15 LITERS/HR 500a c/m/mI "03, HYE,

PARTITION COLUMN

3 LITERS/HR 0. I M HNO3 0. I M NH2SO3H

l o o c I Pu ELUTRIANT IO LITERS 3 LITERSIHR 5.7 M, HNO3 0.3 M NH2SO3H IO" c

FIG 9.1 Pu ISOLATION METAL RECOVERY PLANT

1

VENT f l

S E PAR ATOR

U 4 ELUTRIANT-

&SURGE POT

TO PARALLEL) COL'S. 2 a 3

N0.I RESIN ........... ............ ............. ............. ............ ............ .......... ............. ............. ............ ............ ............. 8 ??%!! /i. ............ ............ ............ ............. I ............ ............ DOWEX 50 ............

I 7 IN. DIA. /

UNCLASSIFIED 0 RNL -LR-Dwg.

47685

r P u ELUTRIANT

L

P FROM COL'S. 2 ai3

:4 +TO I B

COL. 1 FIG 9.2 SIMPLIFIED

TO SHIPPING BOTTLE

EQUIPMENT FLOWSHEET

62

UNCLASSIFIED ORNL-LR-Dwg. 47687

125 MESH SCREEN

MACHINED SURFACE

7.8 LITERS DOWEX50

LINKED, 100 MESH RESIN: 12% CROSS-

FLANGES ARE

F I G 9.3 METAL RECOVERY RESIN COLUMN

Table 9.1. Ionic lmpurities i n Typical Plutonium Product

Ion PPm pu Ion PPm pu

None detected A 1* 200 M g

B <lo Mn <10

Ca None detected N i 50

C r 100 T i <lo

cu <lo

Fe 250

Z r <lo

U e 5 0

* See tex t .

10.0 AMINE EXTRACTION OF PLUTONIUM AND €EXATED METATS C . F. Coleman

Since purif icat ion and concentration of plutonium by anion exchange resins have been demonstrated, workers i n several different laboratories have begun studying the use of amine solvents, which a re known t o be capable of extracting anions. another s i t e f o r recovery of plutonium, and s ignif icant concentration factors a re possible. str ipping requires e i ther reduction t o Pu(II1) o r use of a complexing r agent such a s su l fa te o r oxalate. In some applications, however, t h i s

Lis not desirable.

Amines a re being used a t

Unless the amine concentration i s very low,

Degradation of the amines due t o i r rad ia t ion o r chemical e f fec ts i s not considered a serious problem. Amines a re subject t o oxidation damage, which i s often induced by radiation, but the degradation products appear t o be soluble i n the aqueous phase. min ta ins i t s properties because of t h i s "self-cleaning" effect .

Therefore the solvent

i -- ' and f i s s i o n products have been d-etermined (Table 10.1).

The d i s t r ibu t ion coef f ic ien ts f o r the n i t r a t e s of severa l ac t in ides These measure-

ments were mde i d t h typ ica l solvents from each class, bu t they a r e not representative of a l l solvents from each class; major differences i n s t ruc ture give differences a s grea t a s those shown between classes . Typical solvents ava i lab le from each c l a s s a r e l i s t ed i n Table 10.2. Systematic studieg with these solvents have shovn the e f f ec t s of solu--) t i o n concentrations, solvent concentration, and oxidation state on the plutonium and neptunium d i s t r ibu t ion coef f ic ien ts (Figs . 10.1 through) 10.6).

Table 10.1. Typical Extractions from Ni t r i c Acid

-0.3 M extractant* 2 ,M HN03, -

NP( m 0.1 50 200

Pu( 111) <o .01 <o .01 0.05 0.1

sm( 111) 10-5

* Pr imry , secondary, t e r t i a r y amine; quaternary amonium.

65

I 0 4

I o3

I o2

5 - I 3 n v

Ow" IO

I

0 I I I I l l 1

Io-'

I I I I I I

x Aliquat 336 i n xylene 8-104 i n Amsco - 8% TDA

# B - I O i n xylene o TlOA i n Amsco - 8Yo TDA V Ditridecyl i n Amsco x LA-1 i n xylene

)r; NBHA i n xylene 4 Primene JM i n Amsco - 5% TDA

- A S-24 i n Amsco

Q

UNCLASSIFI ED OR N L -LR- DW G . 53093

1 [NO3] =

6 M(HN03 + N a N 0 3 )

..

H N 0 3 (EQUILIBRIUM), M

Q Fig. 10.1. Plutonium(1V) extraction by 0.1 Mamines: effect of n i t r ic acid and sodium nitrate concentrations. Amine class: (Q) quaternary ammonium, (3) tertiary, (2) secondary, (I) primary amine. Plutonium(1V) stabilized with 0.04-0.1 M N a N 0 2 . Amsco 125- 82, TDA = branched primary tridecanol.

66

13

c

..

I o2

IO

5 - I 3 a v

ouo I

Io-'

UNCLASSIFIED 0 R N L - LR - DW G . 5 3 094

Q

h v

- 8% IZ TlOA i n xylene

0 Primene JM in Amsco A NBHA in Amsco - 2%

A

/ 2MHNO9

TDA

- 5% T DA

T DI

AMINE CONCENTRATION, M

Fig. 10.2. Plutonium extraction by amines from nitric acid solutions: effect of amine concentration. Amine class: (Q) quaternary ammonium, (3) tertiary, (2) secondary, (1) primary amine. Plutonium(1V) stabilized with 0.04-0.1 ICI NaN02. 67

UNCLASSIFIED ORNL-LR-DWG. 53095

I O

I

lo-’

n p. = 10-2 W

I 0-3

I o-L

0.1 M Reagents:

0 8-104 i n Amsco - 8% TDA o TIOA i n Amsco - 8% TDA

c .e .@’

0. rJ TIOA i n xylene D.

XNBHA i n xylene ,0* do 0 Primene JM i n Amsco - .‘ .****

5% TDA Q. #

#* - v S-24 i n Amsco #

0 0.

4 #

v v 3 on- 4 4 ---- . .. , . . ,

1 4’ ,’

/

0.1 I IO H N 0 3 (EQUILIBRIUM), M

Fig. 10.3. PIutonium(III) and Pu(IV) extraction by 0.1 Mamines: effect of nitric acid concentration. Amine class: (Q) quaternary ammonium, (3) tertiary, (2) secondary, (1) primary amine. Plu- tonium reduced with 0.03 Mferrous sulfamate plus 0.05 Mexcess sulfamic acid, or oxidized with Ago .

68

103

10

A

e 3 IO-' W

OwU

lo-*

10-3

UNCLASSI FI ED ORNL-LR-DWG. 53096

0 0.1 M TIOA in Arnsco - 8% TDA xO.1 MTIOA in xylene H0 .3 MTIOA in xylene x 0 . 3 MTLA in xylene

0.3 MAlarnine 336 in xylene

-

0 -

/ ./' ,'-

0 -

Unsalted HNO Solutions 3 -

0.01 0. I I H NO3 (EQUI LI BRI UM), 1CI

Fig. 10.4. Extraction by tertiary amines from solutions of Pu(lll) Plutonium in nitric acid with and without aluminum nitrate salting.

reduced with 0.03 M ferrous sulfamate plus 0.05 M excess sulfamlc acid.

69

U NCLASSI FI ED ORNL-LR-DWG. 53097

io4

lo3

IO2

IO 9 - I 3 L1 v

I O w U

Io-‘

I o-2

1 Primene JM/Amsco-

/ TDA, H2S04 Pr i me ne JM/x y I e ne, 0.5 M H2SO4 2.0 M (NH4)2S04/

)I(

t

3 M S04,pH -0.7, NBHA/ Amsc0~3 M H2S04

N-benzyl-1 -undecyl -lauryl/ A //A~sco, 3 M H ~ S O ~

\ 3 M SO4, pH - 0.7, ditridecyl/ Amsco-TDA, 3 M H 2 S 0 4

A / Ami ne S-24/Amsco, 3 M SO4, pH - 0.7

Tri -iso-octyl/Amsco, 3 M SO4, pH - 0.7

0.00 I 0.01 0. I I IO

AMINE CONCENTRATION, M .

Fig. 10.5. Extraction of Pu(IV) from sulfuric acid and acidic sulfate solutions Diluents: xylene, Amsco 125-82, or

For primary amine extraction, plutonium re- by primary, secondary, and tertiary amines. 95% Amsco 1 2 5 - 8 2 4 % tridecanol. duced with hydroxylamine sulfate, reoxidized and stabilized at (IV) with 0.5 M N a N 0 2 .

0 Others stabilized at (IV) with 0.1 - 0.5 M N a N 0 2 .

70

___ __ _ _ - - __ - ~~~- - - _ _ _ _

UNCLASSIFIED

lo3

4 O2

I

10

E: 1

lo-'

0.1 1.0 10 0.01 A, 0, [HNO,] ( M I ; 0, A, [NO;] ( M )

Fig. 10.6. Neptunium(lV) extraction by 0.1 hf tri-iso-actylamine: Effect of nitr ic ac id concentration. Diluent: xylene. From 6. Weaver and D. E. Horner "Distribution Behavior of Neptunium and Plutonium between Acid Solutions and Same Organ Extractants," Chern. Eng. Data, 5, 260(1960).

71

Table 10.2. Ident i f icat ion and Sources of Some of the Typical Amines

Primary Amine

Primene J M (Rohm and 3aas Co.) trialkylmethylamine; R + R 1 + R" = 17-23 carbon atoms

%N-C( R ) ( R ' )R1'

Secondary Amines

Ditridecylamine (Union Carbide Chem. Co. ) "tridecyl" = mixture of 13-carbon alkyls from tetrapropylene

m- ( - C H ~ C H ~ C H ~ -C lo~21 l2 U-1, h b e r l i t e IA-1, previously Amine 9D-178 (Rohm and N-dodecenyl(triaUrylmethyl)amine, R + R 1 + R" = 11-14

CI$CH:CHC€$CCH2CCH 9 I 3 CH3 6h3

S-24, Amine S-24 (Union Carbide Chem. Co.) b i s ( 1- isobutyl- 3,5 -dime thylhexy1)amine

Haas C O . ) carbon atoms

m- C%CHC%CHCH3

C%CHCH -CH

1 3 CH3

L NBHA, N-benzylheptadecylamine (Union Carbide Chem. Co. )

N-benzyl- 1- ( 3 -e thylpentyl) -4-e thyloc tylamine

CH-C%CH2CHC%CH CH 2 3

C 5 C H 3

N-Benzyl-1-undecyllaurylamine (Amour Chemical Division)

72

P

TQ.ble 10.2. contd.

N-

Secondary Amines ( contd. )

-CH CH CHCH2CHCH 2 21 1 3

3 CH3 CH3

IT-Benzyl- 1-unde cyl laurylmine contd .

nlamine 336 (General M~US, k c . ) s t r a igh t chain a w l s , pr incipal ly oc ty l and decyl

I-

Quaternary Ammonium

B-104, Experimental Quaternary B-104 ( R o b and Haas C o . ) Dimethyl-didodecenylammoniwn

r - CH CH , 3 1 3

CH3 CH3

(CH ) -IT-( -C%CH :CHC%CC%CCH ) 3 2 1 I 3 2

I f

Aliquat 336 (General Mills, Inc.) Trialkylmethylamonim, s t m i g h t chain a w l s , pr incipal ly oc ty l and decyl

73

11.0 PRODUCTION EXPERIENCE WITH RECOVEFX OF. UPA_NIJM FROM REDUCTION RESIDUES BY ANION EXCHANGE IN A HIGGTNSTONWCTOR

N. J. Se t te r

Although t h i s paper i s not on plutonium ion exchange, it was of par t icular i n t e re s t because it describes the operation of the largest Higgins contactor i n use. i n a published"report, Y-3257, and will not be discussed i n d e t a i l here. The column used was 60 f t high and or iginal ly had a E-in.-dia loading section 33 f t high. Later it became desirable t o process di- lu te solutions from metal scrap dissolutions, andl the loading section was enlarged t o 211. in . dia . This allowed the volume throughput t o be increased t o approximately 2000 gal/hr .

-1- ---_ Most of the infomation i n the paper appears -

In processing reduction residues, the feed was largely sol id MgF2. Typical analyses of the metallic content of the residues showed the following content by weight: 20-25% Mg, 15% Ca, lO$ U. This m t e r i a l was crushed, calcined, and pulverized before being leached with sul- f u r i c acid. Mmganese dioxide was added t o oxidize the uranium t o the -6 state and the slag was leached for 2 hr. The mterial was f i l t e r e d t o remove the I@@ and Cas04 solids remining, and the f i l t r a t e was pumped t o the Higgins column for uranium recovery. ,The op t ions used i n the E-in.-dia column a re summrized iz-%ble 11.1. & s i Z used was 16-20 mesh Dowex 2 1 K . i n the loading &5Etion was approximtely 4 hr . t o be enough time f o r the res in t o become completely loaded.

The The residence t i m e for the res in

This i s not believed

One especially interest ing point about the operation of t h i s column was tha t a f t e r e lut ion the res in was passed in to a wash section i n which water was passed up the column with suff ic ient velocity t o remove res in smaller than 20 mesh. This separation was not e f f i c i en t enough t o remove a l l broken a.nd undersized resin, and some res in larger than 20 mesh was los t , but a steady s t a t e was reached under which fresh res in could be fed t o the column and f ines removed continuously so tha t the res in bed averaged 3 0 % &O mesh.

After leaving the column the uranium was precipitated with NH4OH and removed by a rotary vacuum f i l t e r containing a nylon cloth screen. The f i l t r a t e contained only 1 t o 2 ppm uranium.

The system i s being adapted t o operate on a uranium n i t r a t e sys tem .

74

. 0

Table 11.1. Operatiiig Conditions i n =-in. -dia Sorption Column

33-13 Bed 22-f't Bed Normal hBx No .nm 1 M8.X

Feed (2 v o l $ so l ids ) , gph

Feed scrub (0.25 M - SOk), gph

Feed wash, gph

Tota l solut ion flow, gph gph/sq ft

Feed/resin vol ratio

Resin rate, gph

Run in te rva l , min

Pulse in te rva l , sec

Resin movement per pulse, ga l

Pressure drop, p s i

Resin holdup t i m e , hr

2lco

30

102

372 475

5.33/1

45

3

10

2.5

37.5

4.3

330

30

102

4-62 590

7.33/1-

45

3

10

2.5

30

2 -9

75

plutonium ion exchange processes/67531/metadc869324/...anion exchange provides higher separation of...

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