Actinide Chemistry

19 Actinide Chemistry in Saturated Potassium Fluoride Solution

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CONRAD E. THALMAYER and DONALD COHEN Argonne National Laboratory, Argonne, Ill. Absorption spectra have been obtained for certain actinide ions which are soluble in saturated KF solution: U(IV), Np(IV), Np(V), Np(VI), and Am(III). Oxidation-reduction reactions of neptunium have been studied. Four new com plex fluorides have been prepared and identified by x-ray powder patterns: α-K NpF , β -Κ ΝpF , KNpO F , and K NpO F . Three additional complex fluorides, of Np(III), Np(V), and U(VI), have been prepared but not identified. 2

3

2

6

1

2

6

2

2

5

/ C o n c e n t r a t e d salt solutions are a class of solvent w h o s e properties h a v e ^

h a r d l y b e g u n to b e a p p r e c i a t e d . T h e r a t i o of w a t e r to salt i n these

m e d i a is so l o w t h a t the p r i m a r y h y d r a t i o n n u m b e r ( the n u m b e r of w a t e r m o l e c u l e s a b o u t e a c h i o n ) m u s t b e f a r l o w e r t h a n i n d i l u t e solutions. A s a t u r a t e d D 0 s o l u t i o n of K F , f o r e x a m p l e , w h i c h is 1 2 . 4 M w i t h a d e n s i t y 2

of 1.563, has o n l y 3.4 moles of D 0 p e r m o l e of K F w h i l e p e r h a p s e i g h t 2

moles of w a t e r p e r m o l e of K F (4)

are r e q u i r e d f o r t h e p r i m a r y h y d r a

t i o n sphere i n a d i l u t e s o l u t i o n . T h e e n h a n c e d c o m p l e x f o r m a t i o n w h i c h necessarily results m a y l e a d to a c h e m i s t r y different f r o m aqueous c h e m istry. A s p r e y a n d P e n n e m a n ( 3 ) h a v e r e p o r t e d that A m

4 +

is b o t h stable

a n d s o l u b l e i n saturated N H F , R b F , a n d K F . 4

T h i s s t u d y is c o n c e r n e d w i t h t h e c h e m i s t r y of t h e actinides i n s a t u rated

K F solution.

T h e areas

examined

are s o l u b i l i t i e s , a b s o r p t i o n

spectra, o x i d a t i o n - r e d u c t i o n reactions, a n d s o l i d c o m p o u n d s that c a n b e produced

i n this m e d i u m .

T h i s p a p e r reports w o r k w i t h n e p t u n i u m

w h i c h is essentially c o m p l e t e , a n d also i n c l u d e s w o r k w i t h u r a n i u m a n d americium.

Experimental T h e fluoride solvent w a s p r e p a r e d b y d i s s o l v i n g B a k e r a n d A d a m s o n reagent g r a d e K F i n 9 9 . 8 % D O f o r t h e n e p t u n i u m studies a n d i n H 0 s

2

256

In Lanthanide/Actinide Chemistry; Fields, P., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

19.

T H A L M A Y E R

A N D C O H E N

Potassium

Fluoride

257

Solution

f o r the u r a n i u m a n d a m e r i c i u m w o r k . A s e a c h n e w b o t t l e of K F w a s u s e d , t h e a b s o r p t i o n s p e c t r u m of its s o l u t i o n w a s m e a s u r e d . S o m e bottles of K F h a d to b e d i s c a r d e d because of a n i m p u r i t y w h i c h c a u s e d a n u l t r a v i o l e t a b s o r p t i o n . D 0 solutions w e r e u s e d to enable s p e c t r a l m e a surements to b e m a d e i n the near i n f r a r e d r e g i o n . T h e s a t u r a t e d K F s o l u t i o n i n D 0 is 1 2 . 4 M a n d i n H 0 is 1 2 . 6 M . T h e neptunium was purified b y an anion column, a n d alpha pulse analysis r e v e a l e d n o other species t h a n N p . T h e u r a n i u m solutions w e r e p r e p a r e d f r o m reagent grade u r a n i u m n i t r a t e h e x a h y d r a t e . A l p h a p u l s e analysis of t h e a m e r i c i u m s h o w e d i t to c o n t a i n 4 7 % A m and 53% A m b y activity. T h e reactions w e r e c a r r i e d o u t i n b o r o s i l i c a t e glass, q u a r t z , a n d p o l y c a r b o n a t e containers. T h e r e w a s v e r y l i t t l e attack u p o n the glass b y fluoride i o n . N a F w a s f o u n d as a n i m p u r i t y i n o n l y one or t w o p r e p a r a tions, a n d this p r o b a b l y w a s c a u s e d b y a h i g h h y d r o g e n i o n c o n c e n t r a t i o n . S p e c t r a w e r e m e a s u r e d w i t h a C a r y 14 spectrophotometer or a B e c k m a n I R - 1 0 . T h e x - r a y studies w e r e m a d e w i t h a 9 - c m . B r a d l e y - J a y c a m e r a w i t h c o p p e r K r a d i a t i o n a n d a n i c k e l filter. 2

2

2

2 8 7


2 4 3

2 4 1

a

0.4

0.5

0.6

0.7

0.8

0.9

1.0

I.I

1.2

1.3

1.4

1.5

1.6

1.7

1.8

Wavelength, μ Figure

1.

Absorption

spectra of Np(VI) in saturated KF solution lMHClO (10, 13)

and in

h

in saturated KF in aqueous acid

Neptunium Absorption Spectra. T h e a b s o r p t i o n spectra of t h e v a r i o u s o x i d a t i o n states of n e p t u n i u m i n s a t u r a t e d K F are g i v e n i n F i g u r e s 1, 2, a n d 3.


258

LANTHANIDE/ACTINIDE CHEMISTRY


350

0.4

0.5

0.6

0.7

0.8

0.9

1.0

I.I

1.2

1.3

1.4

1.5

1.6

1.7

1.8

Wavelength, μ Figure

2.

Absorption

spectra of Np(V) in saturated KF solution lMHClO (10, 13)

and in

Jf


E a c h s p e c t r u m is c o m p a r e d w i t h the aqueous d i l u t e a c i d s p e c t r u m t a k e n from Sjoblom and H i n d m a n ( J O ) and Waggener

( 1 3 ) . T h e absorption

s p e c t r u m of N p ( V I ) is c h a r a c t e r i z e d b y a single p e a k at ΙΑβμ. It also exhibits t h e c h a r a c t e r i s t i c large a b s o r p t i o n i n the u l t r a v i o l e t r e g i o n , b u t i t does not s h o w a n y v i b r a t i o n a l fine structure. T h e s p e c t r u m of N p ( V ) is s i m i l a r to the aqueous

s p e c t r u m , w i t h the peaks u s u a l l y s m a l l e r i n

intensity. T h e major N p ( V ) p e a k at 0.983/x, e =

3 7 0 , is s h i f t e d to 1.004/x

a n d r e d u c e d i n i n t e n s i t y to a m o l a r a b s o r p t i v i t y of 1 0 4 . T h e N p ( I V ) s p e c t r u m is s i m i l a r to the aqueous s p e c t r u m , s h o w i n g m a n y sharp peaks. T a b l e I lists t h e m o l a r a b s o r p t i v i t i e s of t h e major peaks f o r t h e three o x i d a t i o n states of n e p t u n i u m i n s a t u r a t e d K F i n D

2

0 solutions.

We

consider t h e m o l a r a b s o r p t i v i t y for the N p ( V I ) p e a k accurate to 1 0 % , a n d t h e values f o r the N p ( V ) a n d N p ( I V ) peaks accurate to 5 % . S o l u b i l i t i e s . T h e s o l u b i l i t i e s of t h e several o x i d a t i o n states of n e p t u n i u m w e r e d e t e r m i n e d b y α-assay a n d a b s o r p t i o n spectra.

A concen

t r a t e d s o l u t i o n of n e p t u n i u m i n e a c h o x i d a t i o n state i n d i l u t e D C 1 w a s a d d e d to a l a r g e v o l u m e of the s a t u r a t e d K F s o l u t i o n . T h i s s o l u t i o n w a s h e a t e d a n d c o o l e d to i n s u r e e q u i l i b r i u m , a n d t h e n c e n t r i f u g e d .

The

s p e c t r u m of the s o l u t i o n w a s m e a s u r e d to check o n t h e valence state, a n d an α-assay w a s m a d e to measure the n e p t u n i u m c o n c e n t r a t i o n .



Figure

3.

Absorption

spectra of Np(IV) in saturated 1M HClO (10, 13)

KF solution

and in

u


Table I.

Molar Absorptivities for the Major Absorption Peaks of Neptunium Ions in Saturated K F Solution

Oxidation State Np(VI) Np(V)

Np(IV)

Wavelength,

microns

c

1.460 1.004 1.034 1 122 0^9661 0.7987 0.7282 0.6936

30 104 26 25 57 43 41 40

N p ( I I I ) is not sufficiently s o l u b l e to p e r m i t o b s e r v a t i o n of its spect r u m . If one assumes a m o l a r a b s o r p t i v i t y of 2 5 for the 0.790/x N p ( I I I ) p e a k t h e n the s o l u b i l i t y m u s t be less t h a n 0 . 0 0 0 2 M .

N p ( I V ) , with a

s o l u b i l i t y of 0 . 0 2 M is the most s o l u b l e o x i d a t i o n state. s o l u b l e species is N p ( V ) w i t h a s o l u b i l i t y of 0 . 0 0 9 M .

T h e next m o s t

T h e s o l u b i l i t y of

N p ( V I ) is almost a factor of ten less, b e i n g 0 . 0 0 1 M . T h e s o l u b i l i t y for a f r e s h l y p r e p a r e d s o l u t i o n of the N p ( V ) is 0 . 0 0 9 M .

species

Sometimes the s o l u b i l i t y decreased w i t h t i m e , a n d i n t w o


260

LANTHANIDE/ACTINIDE CHEMISTRY

weeks a s o l u t i o n w o u l d b e at o n l y one-tenth the o r i g i n a l c o n c e n t r a t i o n . S i n c e this decrease i n s o l u b i l i t y d i d not a l w a y s occur,

i t cannot

be

a t t r i b u t e d to s u p e r s a t u r a t i o n . T h i s p h e n o m e n o n m a y b e c o r r e l a t e d w i t h the h y d r o g e n i o n c o n c e n t r a t i o n of the s o l u t i o n , w h i c h w a s not c a r e f u l l y controlled. Oxidation-Reduction

Reactions.

T h e v a r i o u s o x i d a t i o n states

of

n e p t u n i u m i n the K F s o l u t i o n w e r e o b t a i n e d b y a d d i n g the n e p t u n i u m , w h i c h h a d b e e n a d j u s t e d to the d e s i r e d v a l e n c e state i n d i l u t e a c i d , to Downloaded by UCSF LIB CKM RSCS MGMT on August 25, 2014 | http://pubs.acs.org Publication Date: June 1, 1967 | doi: 10.1021/ba-1967-0071.ch019

the K F s o l u t i o n . O b s e r v a t i o n s w e r e m a d e of the effect of a n u m b e r of p o t e n t i a l l y u s e f u l o x i d i z i n g a n d r e d u c i n g agents

upon

the

oxidation

state of the n e p t u n i u m . T h e v a l e n c e states of the n e p t u n i u m ions, I V , V , a n d V I , w e r e d e t e r m i n e d b y a b s o r p t i o n spectra.

D u r i n g the r e d u c t i o n

to the I I I state, the s o l u t i o n color d i s a p p e a r e d , a n d a p u r p l e s o l i d w a s produced. Table II. Np(VI)

Oxidation-Reduction Reactions of Neptunium Ions in Saturated K F Solution

--> Np(V) NaBH H 0 Na S0 NaN0 NH OH ·HCl H (Pt) -» Np(IV) NH9OH · H C l H (Pt) NaN0

Room temperature Slow, even w i t h heating R a p i d , w i t h heating Slow Rapid Rapid

4

2

2

2

3

2

2

2

Np(V)

W i t h heating Slow, w i t h heating Slow, even with heating Rapid

2

2

Np(IV)

--»

so

2

Np(III) Li(Hg) Mg(Hg) Np(IV) --» Np(V) H 0 NaOCl Na Xe0 Np(V) -» Np(VI) 0 KMn0 Na XeO (NH ) S O NaOCl 2

W i t h heating Rapid

2

4

R a p i d , w i t h heating

6

R a p i d , w i t h heating W i t h heating Slow, even with heating W i t h heating W i t h heating

3

4

4

e

4

2

2

s

T h e results of this s t u d y , g i v e n i n T a b l e I I , s h o w a b e h a v i o r q u i t e different f r o m that i n aqueous a c i d . H 0 2

a n d to o x i d i z e N p ( I V )

to N p ( V ) .

was f o u n d to r e d u c e N p ( V I )

2

S0

2

rapidly reduced

Np(V)

to

N p ( I V ) , b u t a large a m o u n t of K F s a l t e d out, a n d a y e l l o w a d d i t i o n


19.

T H A L M A Y E R

compound

A N D

(7)

Potassium

C O H E N

was

formed

which

Fluoride

severely

261

Solution l i m i t e d this

reaction's

usefulness. T h e s t a b i l i t y of e a c h o x i d a t i o n state is greater i n K F s o l u t i o n t h a n i n aqueous a c i d . I n aqueous s o l u t i o n N p ( I V ) is easily o x i d i z e d to N p ( V ) , and

care is necessary

i n storing a N p ( I V )

true i n saturated K F . W e

found

s o l u t i o n , b u t this is

that d i s p r o p o r t i o n a t i o n of

not

Np(V)

o c c u r r e d o n l y u p o n a d d i n g the aqueous N p ( V ) to the K F s o l u t i o n . A t


most, 1 0 % of the N p ( V ) w o u l d d i s p r o p o r t i o n a t e .

H o w e v e r , once p r e -

p a r e d , the N p ( V ) i n the K F s o l u t i o n w a s v e r y stable. Solid Compounds. fluoride

complexes

T h e l i t e r a t u r e ( 2 , 5, 8, 9, 12)

on solid actinide

is extensive, a n d m a n y n e w c o m p o u n d s

are b e i n g

p r e p a r e d . F o r e x a m p l e , T h o m a , F r i e d m a n , a n d P e n n e m a n ( 12 ) r e p o r t e d the first p r e p a r a t i o n of c o m p l e x alkali

fluorides

fluorides

formed between U F

a n d the

3

K F , R b F , a n d C s F . T h i s section s u m m a r i z e s the w o r k

w h i c h was p e r f o r m e d

c o n c e r n i n g the s o l i d c o m p o u n d s

resulting from

n e p t u n i u m i n saturated K F s o l u t i o n . Table III.

X - R a y Powder Pattern for x ( K F ) · y ( N p F ) 3

Intensity

Sin B

VW

0.0373 0.0565 0.0613 0.1120 0.1185 0.1725 0.2249 0.2425 0.2863 0.3404 0.3972 0.5112 0.5658 0.6249

2

vs vs

VVW M VS M VVW VVW VW W VVW VVW VVW NP(III).

A p u r p l e s o l i d was p r o d u c e d w h e n N p ( I I I ) i n d i l u t e D C 1

( w h i c h h a d b e e n p r e p a r e d b y h y d r o g e n r e d u c t i o n ) was a d d e d to a s a t u rated K F s o l u t i o n . T h i s s o l i d was v e r y sensitive to o x i d a t i o n a n d c h a n g e d to a green s o l i d after t w o w a t e r washes. T h e a b s o r p t i o n s p e c t r u m of the purple compound

s h o w e d that the n e p t u n i u m is i n the I I I state.

The

x - r a y p o w d e r p a t t e r n for this c o m p o u n d , g i v e n i n T a b l e I I I , has not yet been indexed. U F

3

It is not i s o m o r p h o u s w i t h the recently p r e p a r e d 3 K F ·

(12). NP(IV).

Two

solid compounds

state h a v e b e e n p r e p a r e d .

c o n t a i n i n g n e p t u n i u m i n the I V

If the p u r p l e N p ( I I I ) c o m p o u n d is o x i d i z e d


262

LANTHANIDE/ACTINIDE

CHEMISTRY

b y w a s h i n g , t h e c o l o r changes to g r e y or d u l l green. T h r e e s u c h p r e p a r a tions of this s o l i d h a v e g i v e n t h e same x-ray d i f f r a c t i o n pattern. A s s h o w n i n T a b l e I V , this p a t t e r n is i n d e x e d as f a c e - c e n t e r e d c u b i c a - K N p F , 2

isomorphous w i t h

fluorite-type

A vs. sin 0 p l o t a = 2

«-K ThF 2

6

and «-K UF 2

6

6

F r o m an

(14).

5.905A., w h i c h is i n excellent a g r e e m e n t w i t h t h e

value extrapolated f r o m the isomorphs.


Table I V .

a

Partial" X - R a y Powder Pattern for

Actinide Chemistry

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