Recovery and Purification of Cesium-137 from Purex Waste Using

35 Recovery and Purification of Cesium-137

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch035

from Purex Waste Using Synthetic Zeolites LANE A. BRAY and HAROLD T. FULLAM Battelle Northwest, Richland, Wash. 99352 The recovery and purification of cesium-137 from Purex acid waste using a synthetic zeolite has been studied. Zeolite capacity and selectivity for cesium were determined. Stability of the synthetic zeolite to high radiationfieldsand chemical attack was adequately demonstrated. Kilocurie quantities of cesium-137 of 98+% chemical purity were prepared using zeolite ion exchange. T n the reprocessing of n u c l e a r fuels, d i s p o s i t i o n of the r a d i o a c t i v e waste A

is a serious p r o b l e m . A t H a n f o r d , the P u r e x process is u s e d to r e p r o -

cess spent f u e l . T h e r a d i o a c t i v e fission p r o d u c t s l e a v e the process as a n aqueous

n i t r i c a c i d stream.

C u r r e n t waste m a n a g e m e n t

p l a n n i n g at

H a n f o r d calls for the s e p a r a t i o n of the s t r o n t i u m - 9 0 a n d cesium-137 f r o m the a c i d waste, w i t h subsequent p a c k a g i n g a n d l o n g - t e r m storage of e a c h element

as i n d i v i d u a l

compounds

i n s m a l l h i g h - i n t e g r i t y containers.

C e s i u m c h l o r i d e a n d s t r o n t i u m f l u o r i d e w e r e selected as the o p t i m u m compounds

for storage.

T h e final storage sites h a v e not b e e n

yet, b u t salt m i n e s are a possible choice.

selected

I n t e r i m storage ( 3 0 - 5 0 y e a r s )

w i l l b e i n concrete canyons o n the H a n f o r d R e s e r v a t i o n . T h e A t l a n t i c R i c h f i e l d H a n f o r d C o . ( A R H C O ) operates the P u r e x P l a n t at H a n f o r d for the U S A E C , a n d has r e s p o n s i b i l i t y for d e s i g n , c o n s t r u c t i o n , a n d o p e r a t i o n of Northwest Laboratory

the W a s t e P a c k a g i n g P l a n t .

( P N L , operated

for

M e m o r i a l I n s t i t u t e ) has r e s p o n s i b i l i t y for

the

The

USAEC

developing

by

the

Pacific Battelle

technology

r e q u i r e d for the p a c k a g i n g p l a n t . F o r c e s i u m , the waste p a c k a g i n g process calls for the s e p a r a t i o n of the c e s i u m f r o m t h e a c i d waste, p u r i f i c a t i o n to r e m o v e m e t a l l i c c o n t a m i nants, c o n v e r s i o n to a n h y d r o u s c h l o r i d e , a n d subsequent

encapsulation

i n d o u b l e - w a l l e d m e t a l cans. T h e c e s i u m c u r r e n t l y is separated f r o m the a c i d waste b y p h o s p h o t u n g s t i c a c i d p r e c i p i t a t i o n a n d p a r t i a l l y p u r i f i e d 450 In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

35.

Recovery

BRAY AND F U L L A M

and Purification

b y i o n e x c h a n g e u s i n g a n i n o r g a n i c exchanger

451

of Cesium-137 AW-500

(a

synthetic

zeolite p r o d u c e d b y the L i n d e D i v i s i o n of the U n i o n C a r b i d e C o r p . ) . T h e p a r t i a l l y p u r i f i e d c e s i u m p r o d u c t f r o m the A W - 5 0 0 c o l u m n contains l a r g e amounts of s o d i u m a n d p o t a s s i u m , a n d a d d i t i o n a l p u r i f i c a t i o n is r e q u i r e d before the c e s i u m is c o n v e r t e d to the c h l o r i d e for p a c k a g i n g . I n o r g a n i c i o n e x c h a n g e w a s selected as the best m e t h o d for o b t a i n i n g the n e e d e d p u r i f i c a t i o n . T h e c e s i u m p r o d u c t stream f r o m t h e A W - 5 0 0 c o l u m n after c o n c e n t r a t i o n for a m m o n i a r e m o v a l is a c a r b o n a t e s o l u t i o n h a v i n g the a p p r o x i Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch035

mate c o m p o s i t i o n : Rb+ NH +-

Cs - > 1 0 0 0 curies/liter Cs+0.3M Na+2.0M K+1.0M

1 3 7

0.004ΑΓ 0.0024M

4

pH-

10.7

R a d i o a c t i v e heat generation ~ 6 w a t t s per liter P a c k a g i n g r e q u i r e m e n t s d i c t a t e t h a t the p u r i t y of the c e s i u m c h l o r i d e b e at least 95 w t % .

E a r l i e r w o r k at P N L b y M e r c e r a n d others ( I , 2 )

using a nonradioactive cesium solution indicated that i o n exchange using the s y n t h e t i c zeolite Z e o l o n ( 3 )

( p r o d u c e d b y the N o r t o n C o . )

offered

the best c h a n c e of o b t a i n i n g the r e q u i r e d c e s i u m p u r i f i c a t i o n . A c c o r d i n g l y , a series of experiments w a s c a r r i e d out i n a P N L H i g h L e v e l R a d i o chemical

Facility

(hot

cell)

to

purify

radioactive

cesium

solution

o b t a i n e d f r o m the A W - 5 0 0 c o l u m n . T h e s o l u t i o n w a s d i l u t e d t h r e e - f o l d p r i o r to l o a d i n g o n the Z e o l o n c o l u m n . T w o Z e o l o n c o l u m n s w e r e u s e d i n the s t u d y : one w a s a 1.9-cm. d i a m e t e r c o l u m n c o n t a i n i n g 40 m l of exchanger

(L/D =

7 ) , and the

s e c o n d w a s a 5-cm d i a m e t e r c o l u m n c o n t a i n i n g 1000 m l of (L/D =

10).

T h e s m a l l c o l u m n was u s e d to evaluate the

exchanger

performance

of the Z e o l o n exchanger, w h i l e the s e c o n d w a s u s e d to p r e p a r e

large

q u a n t i t i e s of h i g h - p u r i t y c e s i u m s o l u t i o n for f u r t h e r processing. T h e o p e r a t i o n of e a c h c o l u m n w a s essentially i d e n t i c a l . F i r s t t h e c o l u m n w a s l o a d e d w i t h the c e s i u m f e e d at the rate of 2 c o l u m n v o l u m e s p e r h o u r ( 2 C v / h r ) . T h e c o l u m n t h e n w a s s c r u b b e d w i t h 8 C v of a 0 . 1 5 M ( N H ) C O - 0 . 1 M N H O H s o l u t i o n at 2 C v / h r . 4

2

3

was e l u t e d w i t h a 3 M ( N H

4

4

) C0 -2M 2

3

NH OH 4

N e x t the c o l u m n

s o l u t i o n at 2

Cv/hr.

F i n a l l y , the c o l u m n w a s w a s h e d w i t h 4 C v of w a t e r b e f o r e the next l o a d i n g cycle. D o w n f l o w w a s u s e d for a l l c o l u m n operations, a n d the c o l u m n t e m p e r a t u r e w a s m a i n t a i n e d at a p p r o x i m a t e l y 25 ° C .

E a c h column vol

u m e of effluent w a s a n a l y z e d for c e s i u m b y i n - c e l l g a m m a energy analysis. T h e entire eluent effluent w a s c o m b i n e d after e a c h r u n a n d s a m p l e d for s o d i u m , p o t a s s i u m , a n d r u b i d i u m analysis b y flame p h o t o m e t r y .

In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

452

MOLECULAR SIEVE ZEOLITES

1

Variations i n c o l u m n operating conditions were l i m i t e d because of the h i g h cost i n v o l v e d i n h o t c e l l operations.

T h e operating conditions

u s e d f o r t h e h o t c e l l tests w e r e selected o n t h e basis of tests c a r r i e d o u t using a nonradioactive cesium solution. T w e n t y - o n e exchange cycles w e r e c a r r i e d o u t u s i n g t h e 4 0 - m l c o l u m n . C e s i u m b r e a k t h r o u g h curves w e r e o b t a i n e d f o r R u n s 2, 7, a n d 20 (see F i g u r e 1 ) . I n e a c h case, a 5 % C s b r e a k t h r o u g h o c c u r r e d at t h e 10th c o l u m n v o l u m e of feed.

T h i s corresponds

to a c e s i u m l o a d i n g of 1.25


m i l l i e q u i v a l e n t s p e r g r a m of d r y Z e o l o n at 5 % b r e a k t h r o u g h a n d shows that t h e Z e o l o n is q u i t e stable to r a d i a t i o n a n d c h e m i c a l attack, a n d little loss of c e s i u m c a p a c i t y s h o u l d result f r o m e x t e n d e d use.

I

I

1

2

I

ι

I

I

I

t

5

t

t

10

1

L_J

15

COLUMN VOLUMES OF FEED

Figure

1.

Cesium

breakthrough

curve

for Zeolon

exchanger,

Cycle 20 D e c o n t a m i n a t i o n factors

(DF's)

for sodium, potassium, a n d r u

b i d i u m w e r e o b t a i n e d at v a r i o u s l o a d i n g levels u s i n g t h e 4 0 - m l c o l u m n . T h e results o b t a i n e d ( T a b l e I ) s h o w that f o r s o d i u m a n d p o t a s s i u m t h e D F ' s decreased w i t h i n c r e a s e d c o l u m n l o a d i n g . F o r r u b i d i u m , t h e D F is essentially i n d e p e n d e n t o f c o l u m n l o a d i n g . T h e data presented indicate that l o w cesium loadings should b e used i n order to o b t a i n h i g h s o d i u m a n d p o t a s s i u m D F ' s . H o w e v e r , f r o m o p e r a t i n g considerations, t h e l o a d i n g l e v e l s h o u l d b e as h i g h as possible


35.

Recovery and Purification

BRAY AND F U L L A M

Table I.

Effect of Cesium Loading on N a , K , and R b Decontamination Decontamination

Factors

Element

6 Cv Feed

7 Cv Feed

9 Cv Feed

Na Κ Rb

216 39 2.5

85 25 3.5

31 9 2.5

Table II. Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 1, 2015 | http://pubs.acs.org Publication Date: August 1, 1974 | doi: 10.1021/ba-1971-0101.ch035

453

of Cesium-137

Comparison of D F ' s Obtained in 40- and 1000-Ml Columns at 6 C v Feed Loading

Element

Jfi-Ml

Na Κ Rb Table III.

Column

1000-Ml

216 39 2.5

Column

600 87 9

D F ' s for N a , K , and R b Using a Nonradioactive Feed Solution Decontamination

Factors

Element

2 Cv Feed

6 Cv Feed

8 Cv Feed

Na Κ Rb

1.3 4 1

160 88 4

1000 7

to r e d u c e t h e n u m b e r of exchange cycles r e q u i r e d . S i x c o l u m n v o l u m e s of f e e d p e r c y c l e w a s selected as t h e m i n i m u m l o a d i n g l e v e l w h i c h w o u l d be acceptable i n a plant operation. T h r e e runs w e r e m a d e i n t h e 1000-ml c o l u m n u s i n g a l o a d i n g of 6 C v of f e e d p e r r u n . T h e d e c o n t a m i n a t i o n factors o b t a i n e d i n t h e l a r g e c o l u m n w e r e s i g n i f i c a n t l y better t h a n those o b t a i n e d i n t h e 4 0 - m l c o l u m n ( T a b l e I I ) , p o s s i b l y because of decreased w a l l effects a n d t h e greater l e n g t h - t o - d i a m e t e r ratio.

T h e cesium solution from the large

column

w a s sufficiently l o w i n s o d i u m a n d p o t a s s i u m that a n a n h y d r o u s c e s i u m c h l o r i d e of 9 8 + % w a s o b t a i n e d o n f u r t h e r processing. S e v e r a l k i l o c u r i e s of t h e c h l o r i d e w e r e p r e p a r e d . It is of interest to c o m p a r e

results o b t a i n e d w i t h t h e r a d i o a c t i v e

c e s i u m f e e d w i t h results o b t a i n e d u s i n g s i m u l a t e d n o n r a d i o a c t i v e solutions.

feed

T w o n o n r a d i o a c t i v e solutions w e r e t e s t e d : one w a s a n i t r a t e

f e e d of p H 5.9; t h e second a c a r b o n a t e f e e d of p H 11.2. T h e c a t i o n c o m p o s i t i o n of e a c h s i m u l a t e d f e e d w a s t h e same as t h a t of r a d i o a c t i v e c e s i u m feed.

A 40-ml Zeolon column was used a n d the operating condi

tions w e r e s i m i l a r to those u s e d i n t h e r a d i o a c t i v e tests. I n t h e n o n r a d i o a c t i v e studies, the d e c o n t a m i n a t i o n factors f o r N a , +

K , a n d R b increased w i t h increasing cesium loading ( T a b l e I I I ) for +

+


454

MOLECULAR SIEVE ZEOLITES

1

b o t h the n i t r a t e a n d c a r b o n a t e f e e d solutions. I n a d d i t i o n , the c e s i u m c a p a c i t y of t h e exchanger d e c r e a s e d

s u b s t a n t i a l l y ( u p to 3 0 % )

with

e x t e n d e d use a n d also v a r i e d s u b s t a n t i a l l y f r o m l o t to lot ( F i g u r e 2 ) . H o w e v e r , lots of exchanger o b t a i n e d w i t h i n the past y e a r s h o w e d

more

consistent l o a d i n g b e h a v i o r . Reasons f o r t h e differences i n b e h a v i o r of the r a d i o a c t i v e a n d n o n -


r a d i o a c t i v e f e e d solutions are c u r r e n t l y u n d e r i n v e s t i g a t i o n .

0.6

1

10

15

20

25

LOADING CYCLES

Figure 2.

Variations in cesium capacity with exchanger lot and loading cycle

O n e p r o b l e m w a s e n c o u n t e r e d i n the e l u t i o n phase of t h e exchange cycle.

I n a b o u t 1 0 % of the cycles, c o m p l e t e e l u t i o n of the c e s i u m f r o m

t h e exchanger c o u l d not b e effected.

T h i s o c c u r r e d i n b o t h the r a d i o -

a c t i v e a n d n o n r a d i o a c t i v e tests. A n a l y s e s of exchanger samples f r o m the n o n r a d i o a c t i v e tests after 2 0 - 3 0 exchange cycles i n d i c a t e d t h a t t h e r e s i d u a l c e s i u m a m o u n t e d to 0.1-0.15 m i l h e q u i v a l e n t s p e r g r a m of changer.

ex-

T h i s a m o u n t e d to a b o u t 1 0 % of the i n i t i a l l o a d i n g c a p a c i t y of

the exchanger u n d e r process o p e r a t i n g c o n d i t i o n s . V a r i o u s e l u t i n g agents w e r e tested to r e m o v e the r e s i d u a l c e s i u m . O n l y h o t ( 7 0 ° C ) c o n c e n t r a t e d n i t r i c a c i d w a s effective i n s t r i p p i n g the c e s i u m f r o m the exchanger.


35.

BRAY

AND

FULLAM

Recovery

and

Purification

of

Cesium-137

455

Literature Cited (1) Mercer, B. W., Ames, L. L., "The Adsorption of Cs, Sr, and Ce on Zeolites from Multication Systems," USAEC Report HW-78461 (1963). (2) Nelson, J. L., Mercer, B. W., "Ion Exchange Separation of Cs from Alkaline Supernatant Solutions," USAEC Report HW-76449 (1963). (3) Norton Co., "Zeolon Synthetic Zeolites—Technical Data Sheet," Norton Co., Worcester, Mass.


RECEIVED February 4, 1970.


Recovery and Purification of Cesium-137 from Purex Waste Using

Recommend Documents