Actinide Separations - American Chemical Society

1 Neptunium (V) Anionic Exchange in Sulfate-Sulfuric A c i d Solutions J. REGO, J. GARRISON, and R. CARVER

Downloaded by 211.103.180.34 on August 25, 2015 | http://pubs.acs.org Publication Date: April 16, 1980 | doi: 10.1021/bk-1980-0117.ch001

Lawrence Livermore Laboratory, Livermore, CA 94550

The purpose of this study was to investigate the anionic ex change behavior of neptunium(V) in sulfate-sulfuric acid, because neptunium is often present as a contaminant during the separation of other actinides (1). Sulfuric acid systems are seldom utilized in industrial processes, but are often used as part of a labora tory analytical procedure. Literature on neptunium in HClO , HCl, HCl-HF, and HNO is quite complete, but the information on the H SO system is sketchy at best. There is one report (2) that neptunium(V) is adsorbed strongly on Dowex 2 resin from 0.1 Ν to 1 Ν H SO . Our measurements indicate that there is very l i t t l e adsorption of Np(V) on Dowex 1 resin even at low concentrations of sulfate-sulfuric acid. We believe the differences in chemical structure of the two resins are not sufficient to explain the dis parity in adsorption. 4

3

2

4

2

4

Experimental 237N traced with 239N ( t ½ = 2.35 days) was used to measure the amounts of Np adsorbed on anion exchange resin. The 239N was selected because of availability and convenience in detection. The 239N tracer was prepared by extraction from a Am solution into thenoyltrifluoroacetone (TTA). The Np in the organic TTA was washed three times with 1 Ν HCl-0.4 Ν HI. The Np was then back -extracted into 9 Ν HCl. p

p

p

243

p

The (V) o x i d a t i o n s t a t e f o r a l l Np s o l u t i o n s was achieved by d i g e s t i n g w i t h d i l u t e HNO3 b e f o r e b o i l i n g t o near dryness with H2S0^ and d i l u t i n g t o 0.1 Ν s u l f u r i c a c i d (3., £) · F i v e standard s o l u t i o n s o f i n c r e a s i n g concentrations o f ^ S O ^ were prepared: 0 . 0 5 , 0.1, 0 . U , 0 . 8 , and h.2 N. From each o f these s o l u t i o n s s i x a l i q u o t s were taken. To f i v e o f these a l i quot s a weighed and i n c r e a s i n g amount o f Na2S0l| was added. A measured amount o f 3 Ï N p t r a c e d with 3 9 N was added t o a l l s i x aliquots. The concentrations o f the s u l f u r i c a c i d ranged from 0 . 0 5 Ν t o k.2 N. The t o t a l s u l f a t e c o n c e n t r a t i o n ranged from 0 . 0 5 Ν t o 8 N. 2

2

p

0-8412-0527-2/80/47-117-003$05.00/0 © 1980 American C h e m i c a l Society In Actinide Separations; Navratil, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

ACTINIDE SEPARATIONS


4

The f i n a l s o l u t i o n s were mixed and then added t o weighed amounts of anion exchange r e s i n i n a 15-ml c e n t r i f u g e cone. The r e s i n had been prepared from commercial Dowex-1 ( l χ 8 ) , c h l o r i d e form, t h a t had been graded f o r p a r t i c l e s i z e by s e l e c t i n g the f r a c t i o n w i t h a s e t t l i n g r a t e o f 30-70 mm/min. The r e s i n was f i r s t converted t o the hydroxide form by washing w i t h d i l u t e NaOH, r i n s i n g with water, and then converted t o s u l f a t e form by washing w i t h d i l u t e H2S01;. The r e s i n was a i r - d r i e d at room temperature b e f o r e use. Each mixture o f r e s i n and neptunium s u l f a t e s o l u t i o n was mixed by mechanical shaking and was allowed t o e q u i l i b r a t e over n i g h t . T h i s time i n t e r v a l i s l o n g , compared t o the d u r a t i o n o f an a n a l y t i c a l procedure. The l i q u i d was then f i l t e r e d away from the r e s i n , and the r e s i d u a l r a d i o a c t i v i t y o f a measured a l i q u o t of the l i q u i d was compared t o an i d e n t i c a l s o l u t i o n t h a t had not been added t o any anion exchange r e s i n . The r a d i o a c t i v i t y meas urements were performed i n an end-window Nal c r y s t a l counter s h i e l d e d w i t h l e a d . The a c i d i t y o f each s o l u t i o n was measured by t i t r a t i o n w i t h a standard base. R e s u l t s and D i s c u s s i o n The neptunium a d s o r p t i o n on the r e s i n was c a l c u l a t e d from the measurements o f 39Np not adsorbed according t o the f o l l o w i n g equation: 2

[Total K

d

2

3

% p -

=

2 3 9 N

P(

)1/g

l i q u i d

m

resin

239 ^(liquid/

1 1 1 1

Values f o r the c a l c u l a t e d K^'s are l i s t e d i n Table 1. Where rep l i c a t e measurements were made, t h e i n d i v i d u a l r e s u l t s are r e p o r t ed. A computer was used t o generate a graph o f the data ( F i g . l ) . Neptunium(V) e x i s t s as a neptunyl i o n and e i t h e r hydrates or complexes (3., h) as shown below: Np

5 +

Np0 I f s u l f a t e complexing Np0

2

+ 20 " 5 Np0 + 2

+ 2

+ 6H 0 * Np0 2

2

(H 0)g 2

o c c u r s , the f o l l o w i n g process i s p r e d i c t e d : + 2

+ nHSO^"" $ Np0

1

2

2

(SO^)^ "" ^

+ nH

+

T h i s process has been s t u d i e d u s i n g spectrophotometry and o x i d a t i o n p o t e n t i a l s h i f t , and no formation o f a s u l f a t e complex has been found (j[).

In Actinide Separations; Navratil, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


2.1

0.58

0.58

0.1T

0.15

0.09

0.08

0.06

1999

1971+

198U

2009

2008

206l

2113

2090

1 g

0.25

0.25

0.06

0.06

0.02

0.02

0.0

The

0.1^

2167

2298

0.1+

2196

sample was 2320 c t s / m i n / m l .

0

O.U

2259

0.U o.i

0.5 0.5

2335

0.5

2185

t o each

0.76

0.68

0.8U

U.Uo 0.8

2U89 0

2U26

0 0.9 2Ul3

0

0 0.9 2395 0 0.18

6

1+.U5

2396 0 1.0 2377

0.06

0.6

2296

0.8

0.2

2058

1.07

0

0

0 U.U5 0.18 1.0 2259

0

0.5

0.7

23Ul

0.2

21lU

1.06

0 21+70

l.U 2U01

0.2k

0.92

2239

0.9

0.6

20U0

1.23

0 U.7I+ 2U52

2385

0.9!+

0

0 U.83

6.20 21+66

0 6.06

0

0 8.02

D

2U0U

K

2317

Normality Total Sulfate

U.2 Ν

l.U

2278

0.8

0.1+

2068

1.22

2.5

0.13

1 +

2378

0.12

0.9

1+.8

NP Count Rate

2

H S0

0

227U


0.86 Ν

2.8

0.18

Np Count Rate

2

E S0l

2373

2.1

1.05

k.k

NormalityTotal Sulfate

O.Ul Ν

0.30

2215

2256

0.05

U.l

2156

I^SO^ Np Count Rate

0.12 Ν


1 +

Np Count Rate

2

H S0

20k6

0.98

0.87

available

2.1

2031

1 g

Np a c t i v i t y

U.O

2

Weight Na S0i

2056

0.05 Ν

2 g

|

]x


2

E S0

Np Count Rate

Acid Cone.

D a t a f o r Measured a n d C a l c u l a t e d

TABLE I



ACTTNIDE SEPARATIONS

Figure 1. Ν ρ (V) adsorption in total sulfate


1.

REGO E T A L .

Np(V) Anionic

Exchange

7

Conclusion The most s i g n i f i c a n t d i f f e r e n c e between Dowex 1 and Dowex 2 r e s i n i s i n t h e order o f s e l e c t i v i t y o f the hydroxide i o n . A l l other mechanical v a r i a b l e s between the two r e s i n s , such as pore s i z e , shrinkage, c a p a c i t y and water content, are n e g l i g i b l e d i f erences. We conclude that these d i f f e r e n c e s are i n s u f f i c i e n t t o e x p l a i n t h e d i s p a r i t y o f adsorption o f neptunium. We have measured the adsorption o f Np(V) on Dowex 1 anion exchange r e s i n from s o l u t i o n s o f s u l f u r i c a c i d that had i n c r e a s ing amounts o f s u l f a t e s a l t s added. We found that Np(V) d i d not adsorb s i g n i f i c a n t l y at any a c i d o r s u l f a t e concentrations. The measured K D S are l a r g e s t at low concentrations o f s u l f a t e and s u l f u r i c a c i d . The Kp's decreased as both the s u l f a t e o r s u l f u r i c a c i d concentrations increased.


?

Literature Cited 1.

Carver, R.; Dupzyk, R., Lawrence Livermore Lab. Internal Rept. NCDTN-78-1, 1978.

2. Wish, L . ; Rowall, Μ., U.S. Naval Radiological Defense Lab. Rept. USNRDL-TR-117, NS-081-001, 1956. 3. Burney, G.; Harbour, R., "Radiochemistry of Neptunium," U.S. AEC Technical Information Center, Oak Ridge, TN, NAS-NS-3060, 1974. 4. Mikhailov, V., "Analytical Chemistry of Neptunium," Halsted Press, NY, 1973. 5. Ai-Niaimi, N.; Wain, Α.; McKay, H., J . Inorg. Nuc. Chem., 1970, 32, 2331. 6.

Sjoblom, R.; Hindman, J., J. Am. Chem. Soc., 1951, 73, 1744.

RECEIVED

June 27, 1979.

Work performed under the auspices of the U.S. Department of Energy by the Lawrence Liver more Laboratory under contract number W-7405-eng-48.


Actinide Separations - American Chemical Society

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