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Anion-exchange equilibria in alkaline media
Analytica Chimlca Actct Elsevier Publishing Company, Amsterdam P r i n t e d in T h e N c t h e r l a n d s
ANION-EXCHANGE
473
EQUILIBRIA
IN A L K A L I N E
MEDIA
I~.OLAgD F. HIRSCH AND JOHN D. ]?ORTOCK* Departmet,t of Chemistry, Seton Hall Uuiversity. .7outh Orange, N.J. 07079 ( U . S . A . ) (Received September 29th, 1969)
KRAUS AND z'NI~LSON1 m a d e e x t e n s i v e s t u d i e s of t h e a b s o r p t i o n of m e t a l s f r o m hydrochloric acid solutions by anion exchangers. Since their pioneering work, m a n y o t h e r m e d i a h a v e b e e n s t u d i e d , i n c l u d i n g h y d r o f l u o r i c a c i d 2, nitric a c i d 3, a n d s u l f u r i c a c i d 4, as well as m i x t u r e s of t h e s e acids w i t h o r g a n i c s o l v e n t s 5. R e l a t i v e l y little a t t e n t i o n has been p a i d to a n i o n e x c h a n g e f r o m a l k a l i n e m e d i a . A few s t u d i e s h a v e d e a l t w i t h t h e g r o u p ¥ I B a n d g r o u p V I I B e l e m e n t s in t h e i r h i g h e s t o x i d a t i o n s t a t e s . M e t h o d s h a v e b e e n d e v e l o p e d b a s e d on a n i o n e x c h a n g e f r o m h y d r o x ide s o l u t i o n s to s e p a r a t e p e r r h e n a t e ~ n d m o l y b d a t e Q, p e r t e c h n e t a t e a n d m o l y b d a t e 7, a n d p e r r h e n a t e a n d t u n g s t a t e s. O t h e r w o r k has b e e n c o n c e r n e d w i t h s e p a r a t i o n of n o n - m e t a l s s u c h as f l u o r i d e a n d p h o s p h a t e 0, iodide, i o d a t e a n d p e r i o d a t O 0, b o r a t e a n d s i l i c a t e it, a n d sulfite, s e l e n i t e a n d t e l l u r i t e v-'-. A m o r e c o m p l e t e s t u d y of a n i o n e x c h a n g e f r o m h y d r o x i d e m e d i a h a s b e e n r e p o r t e d .by TAK1URA AND TAKINO t3. T h e y d e t e r m i n e d s e l e c t i v i t y c o e f f i c i e n t s for s e v e r a l s i n g l y - c h a r g e d a n i o n s i n t o a s t r o n g l y basic a n i o n e x c h a n g e r in t h e h y d r o x i d e form. The selectivity coefficients represent the concentration equilibrium constants for the r e a c t i o n A - o x t . s o I tl + O H
-ros in = A-rcs|
n + on-ox
t. s o l n
T h i s p a p e r r e p o r t s a c o m p r e h e n s i v e s t u d y of a n i o n e x c h a n g e of t h e e l e m e n t s f r o m s o d i u m h y d r o x i d e solutions. C o m m o n a n i o n s a n d m o s t m e t a l ions w h i c h are soluble in h i g h l y a l k a l i n e s o l u t i o n s w e r e i n c l u d e d . I n s t e a d of d e t e r m i n i n g s e l e c t i v i t y c o e f f i c i e n t s , t h e d i s t r i b u t i o n ratios, D , w e r e m e a s u r e d D
=
[ E'
(I)
w h e r e E r e p r e s e n t s a n e l e m e n t in a p a r t i c u l a r o x i d a t i o n s t a t e or c h e m i c a l form. a n d [E'] r e p r e s e n t s t h e t o t a l a n a l y t i c a l c o n c e n t r a t i o n of E in t h e g i v e n phase. D i s t r i b u t i o n r a t i o s a r e s p e c i f i e d for f i x e d c o n c e n t r a t i o n s of s o d i u m h y d r o x i d e in t h e e x t e r n a l solut i o n (o.Io, 1.oo a n d IO.O F s o d i u m h y d r o x i d e i n t h i s s t u d y ) a n d t h e r e f o r e m a y be m o r e u s e f u l t h a n s e l e c t i v i t y coefficients in d e v i s i n g a n a l y t i c a l s e p a r a t i o n p r o c e d u r e s . EXPERIMENTAL
Equipment All of t h e l a b o r a t o r y w a r e used t o store, m e a s u r e or t r a n s f e r s o l u t i o n s w a s m a d e of e i t h e r p o l y e t h y l e n e or p o l y p r o p y l e n e . D r a i n a g e of s o l u t i o n s f r o m t h e s e c o n t a i n e r s * Prosent kddress: Diamond-Shamrock Corp., I~'orth Arlington, ~N'.J., U.S.A.. Anal. Chim. Acta, 49 (x97o) 473-479
474
R. F. I-HRSCFI, J . D. P O R T O C K
is c o m p l e t e , s i n c e t h e p l a s t i c s u r f a c e s are n o t w e t t e d b y a q u e o u s s o l u t i o n s . T h i s a l l o w s u s e of t h e c o n t a i n e r s w i t h v a r i o u s s o d i u m h y d r o x i d e c o n c e n t r a t i o n s w i t h o u t r e c a l i b r a t i o n . A 5o-ml g r a d u a t e d c y l i n d e r w a s c a l i b r a t e d for u s e in all d i l u t i o n s a n d v o l u m e t r i c t r a n s f e r s . I t w a s f o u n d a c c u r a t e a n d r e p r o d u c i b l e t o b e t t e r t h a n + o.I ml.
D~, box A carbon dioxide-free a t m o s p h e r e was a t t a i n e d by working inside a d r y box, c o n t i n u o u s l y f l u s h e d w i t h d r y , CO.a-free n i t r o g e n . A p a i r of small b l o w e r fans a i m e d a t a t r a y filled w i t h i n d i c a t i n g s o d a l i m e s e r v e d t o i n s u r e t h e a b s e n c e of c a r b o n d i o x i d e .
Reagents Boiled, d e i o n i z e d w a t e r w a s u s e d t h r o u g h o u t . T h e s o d i u m h y d r o x i d e s o l u t i o n s w e r e p r e p a r e d f r o m J. T. B a k e r 5 0 % R e a g e n t , s t a n d a r d i z e d a g a i n s t s t a n d a r d h y d r o c h l o r i c a c i d s o l u t i o n a n d s t o r e d in p o l y e t h y l e n e b o t t l e s . All o t h e r r e a g e n t s w e r e of t h e highest purity available, usually r e a g e n t grade.
Resin A m b e r l y s t A-29 ( R o h m a n d H a a s , P h i l a d e l p h i a , Pa.), a m a c r o r e t i c u l a r resin in t h e c h l o r i d e form, w a s c h o s e n b e c a u s e it is r e p u t e d to h a v e h i g h r e s i s t a n c e t o m e c h a n i c a l a t t r i t i o n a n d e x c e l l e n t s t a b i l i t y in h i g h l y a l k a l i n e s o l u t i o n s , b e i n g s u p e r i o r in t h e s e r e s p e c t s to c o n v e n t i o n a l gel resins ta. T h e b e a d s w e r e u n s i z e d b u t a p p e a r e d t o be m o s t l y in t h e 2 o - 5 o m e s h r a n g e . T h e resin was c o n v e r t e d to t h e h y d r o x i d e f o r m b y p l a c i n g a s l u r r y of t h e m a t e rial in a c o l u m n a n d p a s s i n g several b e d v o l u m e s of I F s o d i t t m h y d r o x i d e t h r o u g h t h e b e a d s a t a flow r a t e of t w o b e d v o l u m e s p e r h. T h e resin w a s t h e n w a s h e d w i t h w a t e r u n t i l t h e e f f l u e n t w a s n e u t r a l , a n d d r i e d for 3 d a y s i n t h e n i t r o g e n a t m o s p h e r e . A p o r t i o n of t h e p r o d u c t w a s d r i e d a t IiO ° to d e t e r m i n e t h e m o i s t u r e c o n t e n t of t h e r e s i n dried at room temperature. T h e e x c h a n g e c a p a c i t i e s a n d d e g r e e s of c o n v e r s i o n t o t h e h y d r o x i d e f o r m of e a c h b a t c h of a n i o n e x c h a n g e r w e r e d e t e r m i n e d b y s t a n d a r c l m e t h o d s 15. T h e c a p a c i t y w a s 2.7-2.8 m e q ] g r e s i n in all cases. SLx b e d v o l u m e s of t h e s o d i u m h y d r o x i d e s o l u t i o n p r o d u c e d 75% conversion to the h y d r o x i d e form, while ten bed v o l u m e s were requirect t o r e a c h 9 o % c o n v e r s i o n . H o w e v e r , b a t c h e s c o n v e r t e d to d i f f e r e n t d e g r e e s w i t h i n t h e 7 5 - I o o % r a n g e g a v e s i m i l a r r e s u l t s for s e v e r a l t e s t ions.
2~rocedure A l i q u o t s of a s t o c k s o l u t i o n of t h e e l e m e n t b e i n g s t u d i e d w e r e d i l u t e d w i t h v a r i o u s a m o u n t s of s o d i u m h y d r o x i d e a n d w a t e r . A 25.o-ml p o r t i o n of e a c h d i l u t e d s o l u t i o n w a s m i x e d w i t h a 2-g s a m p l e of t h e resin ( w e i g h e d e x a c t l y ) in a c a p p e d b o t t l e . T h e m i x t u r e w a s s w i r l e d a t f r e q u e n t i n t e r v a l s for 2 h t o e n s u r e t h a t e q u i l i b r i u m w a s reached. T h e solution w a s t h e n s e p a r a t e d f r o m t h e resin b y d e c a n t a t i o n or f i l t r a t i o n t h r o u g h glass wool. T h i s s o l u t i o n , a n d also a ~ o r t i o n of t h e s o l u t i o n w h i c h h a d n o t c o n t a c t e d t h e resin, w e r e t h e n a n a l y z e d for t h e i o n u n d e r c o n s i d e r a t i o n .
Analytical techniques Radioisotopic tracers to. T h e r a d i o i s o t o p e s o b t a i n e d ( N e w E n g l a n d N u c l e a r A n a l . Ghim, A c t a , 49 ( I 9 7 o ) 4 7 3 - 4 7 9
ANION-EXCHtXNGE
EQUILIBRIA
IN
ALIC~LINE
475
MEDIA
C o r p . , I s o - S e r v e D i v i s i o n of C a m b r i d g e N u c l e a r Corp., N u c l e a r S c i e n c e a n d E n g i n e e r i n g C o r p . , a n d B a i r d - A t o m i c ) w e r e all s p e c i f i e d b y t h e s u p p l i e r to b e of a t l e a s t 9 9 % radiochemical purity. ~ , - E m i t t e r s w e r e a s s a y e d in a 5 - c m d i a m e t e r N a I ( T l ) c r y s t a l w e l l , w i t h a B a i r d A t o m i c M o d e l 135 s c a l e r - t i m e r . I s o t o p e s e m i t t i n g o n l y f l - r a d i a t i o n w e r e a s s a y e d b y l i q u i d s c i n t i l l a t i o n in a N u c l e a r - C h i c a g o M o d e l 7 o 3 P s y s t e m ( t h e s e p a r a t e s t a n d a r d r u n a t e a c h s o d i u m h y d r o x i d e c o n c e n t r a t i o n e l i m i n a t e d t h e treed f o r q u e n c h c o r r e c t i o n s ) o r b y G e i g e r c o u r x t i n g w i t h t h e B a i r d - A t o m i c M o d e l 135 s c a l e r - t i m e r a n d a thin-window detector tube. A t o m i c absorption x7. A P e r k i n - E l m e r M o d e l 29o s p e c t r o p h o t o m e t e r w i t h a i r a c e t y l e n e f l a m e w a s u s e d f o r all m e a s u r e m e n t s , e x c e p t f o r silicon, w h i c h w a s d e t e r mined on a Perkin-Elmer Model 3o3 Spectrophotometer with a nitrous oxide-acetylene flame. Ion-sensitive electrodes. A C o r n i n g M o d e l IO pH m e t e r w a s u s e d to m e a s u r e p o t e n t i a l s a g a i n s t a S . C . E . F l u o r i d e ion w a s d e t e r m i n e d b y d i r e c t p o t e n t i o m e t r y w i t h t h e O r i o n R e s e a r c h M o d e l 94-09 F l u o r i d e E l e c t r o d e 1~. O t h e r d i r e c t m e a s u r e m e n t s w e r e m a d e w i t h t h e O r i o n R e s e a r c h M o d e l 9 2 - 8 1 P e r c h l o r a t e E l e c t r o d e t U , '-'0. I n all ca_ses a l i q u o t s o f t e s t s o l u t i o n s w e r e n e u t r a l i z e d w i t h n i t r i c o r a c e t i c a c i d a n d m a d e u p to a definite volume before the measurement. Separate calibration curves were made u p for each ion a t each s o d i u m h y d r o x i d e c o n c e n t r a t i o n . T h e r e s u l t s can t h e r e f o r e be considered concentration distribution ratios, consistent with the results obtained by using the other measurement techniques. Titrations "-~. A r g e n t o m e t r i c t i t r a t i o n s w e r e c a r r i e d o u t w i t h a s t a n d a r d s i l v e r nitrate solution to the potentiometric end-point. Chelometric titrations were carried out with standard EDTA solution to visual indicator end-points ; the aluminum determ i n a t i o n w a s a b a c k - t i t r a t i o n w i t h zinc. I o d o m e t r i c t i t r a t i o n s w e r e c a r r i e d o u t w i t h sodium thiosulfate solutions standardized against potassium iodate. Vanadate was t i t r a t e d b y s t a n d a r d i r o n ( I I ) s u l f a t e solution'-' o. Speclrophotometry. A B e c k m a n D U S p e c t r o p h o t o m e t e r w a s u s e d . B o r a t e w a s m e a s u r e d b y t h e c a r m i n e m e t h o d 2s, a n d n i t r a t e b y d i r e c t s p e c t r o p h o t o m e t r y a t 22o llmo.4.
RESULTS
. .I
AND
DISCUSSION
The distribution m e a n s o f eqn. (2) :
r a t i o s ( e q n . I) a r e c a l c u l a t e d f r o m t h e e x p e r i m e n t a l
A r/w D .'= s/-------V A
data by
(2)
w h e r e A r a n d A s a r e t h e a m o u n t s of t h e g i v e n s p e c i e s in t h e r e s i n a n d e x t e r n a l s o l u t i o n , r e s p e c t i v e l y , w is t h e n e t d r y w e i g h t ( c o r r e c t e d f o r m o i s t u r e c o n t e n t ) of r e s i n t a k e n , a n d V is t h e v o l u m e of s o l u t i o n c o n t a c t e d b y t h e resin. S i n c e i n m o s t c a s e s t h e c o n c e n t r a t i o n o f t h e s p e c i e s in t h e resin w a s d e t e r m i n e d b y d i f f e r e n c e , t h e c a l c u l a t i o n s a r e b e s t r e p r e s e n t e d b y e q n . (3) :
D =
(AI--As)/w
(3)
As/V A n a l . Ghim. Acta, 49 (I97o)
473-479
476 TABLE
R.F.
Re Cl
I)IS'rRIBUTION
Chemical form
RATIOS
FROI~I A Q U E O U S
SODIUM
IIYDROXIDI'~
.'1 n a l y t i c a l t e c h n i qtte a
Logarithm o . 1 o 1:
f . o o 1 ~"
1 o . o 1:
ReO.t CIO,t-
ISE l SI~
3.96 4.20 3-7 ° 3-1 o 2.54 3- 68 2.2,t 2.1o 3.23 z.89 t .54 t. 04 t.97 I.o,t -~ o
4.o6 3.4o 3.34 3.28
2.54 b 2.76b 2.o 4 2.20
2.26
2 .or
2. oo t .75 t.54 1.49 r.3,t , .04 t. o o 0.68 0.53 o.I 8
1
t-
AgT
Tc N l Br C Mo CF S Br S C TI CI Se V Co I F C Zn
TcO.t NO:t1O4BrOaCNM o O a 'aC r O , i 2S a13rSO,t zAcetate TI(1) CISeO:3~VOaCo(If) IOaFCO:,"-Zn(ll)
Si Mg AI Cu l~b
S i O a 'aMg '-'-+ A l ~+ C u 'a+ P b ''+ PO,taAsO,2Borate C a ~+ Cs + K + M n ( l l)
GM Sp 1SE IT AgT AA /kA AgT AgT LS LS OM AgT S liT S IT ISE LS S AA. AA AA EDTA AA S G1VI 1T Sp EDTA S AA S
P As ;13 Ca Cs K MIX
J . D. P O R T O C K
I
ANION-]':XCIIANGE
!:h, m e n t
ItlRSCH,
of distribution
ratio in NaOH
x.oo
o.15
1,28 0.56 0.42 0.75 0.32 1.25 o.,14 0.38 0.38 0.23
o. I I 0.08 o.o8 o.oo o.oo < o < o < o < o
t. 56" i .o3 t.o8 <: o -< o ~.23 t. 2 0 0.78 <2_ o < o ~ o o . lo < o < o -< o o.30 < o < o < o < o
< o < o --" < o < o < o < o < o <: o < o __e
< o 0.4 2 o . 18 0.08 <: o < o < o < o < o < o < o
,~ A A ~--- a t o m i c : t b s o r p t i o n ; AgT ~ argentometric titration; EDTA = EDTA titration; G1H = Goigcr-Muller counter; ISE = potontiometry with ion-selective electrode;' I T == i o d o n x e t r i c titrattion; LS = liquid scintillation counter; I¢T = direct redox titration; S = ~al(T1) crystal scintillation counting; Sp ~- spcctrophotomctr y. " 5.o F I~aOH, electrode response unsatisfactory in ease of Io.o F NaOH. u insoluble.
in w h i c h A t is t h e a m o u n t of t h e s p e c i e s in t h e e x t e r n a l s o l u t i o n b e f o r e it w a s b r o u g h t in c o n t a c t w i t h t h e resin. T h e r e s u l t s a r e s u m m a r i z e d in T a b l e I. T h e species a r e l i s t e d in t h e o r d e r of t h e l o g a r i t h m s of t h e i r d i s t r i b u t i o n c o e f f i c i e n t s in I.OO F s o d i u m h y d r o x i d e . V a l u e s of log D less t h a n o a r e n o t g i v e n as t h e y a r e l a c k i n g in p r e c i s i o n a n d n o t a n a l y t i c a l l y significant. T h e w i d e r a n g e of v a l u e s of t h e d i s t r i b u t i o n r a t i o s is s i m i l a r t o t h a t f o u n d i n o t h e r m e d i a x-5. S e v e r a l possibilities a r e s u g g e s t e d for s e p a r a t i o n s of ions or g r o u p s of ions: n i t r a t e f r o m p h o s p h a t e , b r o m a t e f r o m i o d a t e , zinc f r o m c a l c i u m . Anal. Chim..'lcla,
49 (197o) 473-479
ANION-EXCKANGE
EQUILIBRIA
IN ALKALINE
477
MEDIA
Specific c o m p a r i s o n s w i t h p r e v i o u s l y p u b l i s h e d d a t a c a n be m a d e i n t w o ins t a n c e s . T h e s e l e c t i v i t y o r d e r i n d i c a t e d b y t h e s e l e c t i v i t y c o e f f i c i e n t s of TAXlURA AND TA KIN O 13 c a n be c o m p a r e d w i t h t h e s e l e c t i v i t i e s o b s e r v e d in t h e v a r i o u s s o d i u m h y d r o x i d e s o l u t i o n s u s e d in this w o r k . T h i s c o m p a r i s o n is p r e s e n t e d in T a b l e II. E x c e p t for b r o m a t e a n d b r o m i d e , t h e r e s u l t s of t h e t w o s t u d i e s a r e similar. TABLE
II
SELECTIVITY
ORDERS
FOR
T A K I U R A AND T A K I N O to Tiffs work: o. t F NaOl-[ Tliis work: t.o F NaOH T h i s w o r k : 1o 1: N a O F I
TABLE
ANION
EXCIIANGE
IN
ALl{ALINE,
SOLUTIONS
B O o - ---~ F - < A s O o . - < I O n - < B r O 3 - ~ C I - < C N - < N O n - < B r - < I B O o . - ~_. A s O z - < F - - < I O : F < CI - < B r - < C N - < . B r O a - < N O n - - < l B O 2 - ~__ A s O z ' - < F-" _ I O n - < C I - < S B r - < ~ C N - < B r O : l - < N O : v < l BOe- _ AsOz- _ IOa-
1I1
DISTRIBUTION
RATIOS
FOR
I,ERRHI.2.NATE
AND
MOLYBDATE
IN SODIUM
I.[YDItOXIIJE
log D f o r p e r r h e m , te
log 1) f o r molybdate
T h i s worh
Literature '~
T h i s worh
o. l o .5
3.96
3.95
t .o
.1.o6
3.78
5.0 to.o
z .54
2.95 2.oo
CN.o.(1:)
Lite~'atto'e '~
3.23 2.48
3.00 z.9o
1.49
2 .o8
0.38 --0.26
1.65 x.65
T h e d a t a of FISHER AND MELOCHE 6 are s h o w n in T a b l e I I I . T h e a g r e e m e n t b e t w e e n t h e d i s t r i b u t i o n r a t i o s for p e r r h e n a t e is s a t i s f a c t o r y b u t t h e r e is s i g n i f i c a n t d i s a g r e e m e n t in t h e case of m o l y b d a t e . T h e m o l y b d a t e d i s t r i b u t i o n d a t a in this w o r k give a s t r a i g h t line w h e n log D is p l o t t e d a g a i n s t log Cr¢~olt, a n d t h e slope of t h i s line is 1.8, w h i c h is close to t h e v a l u e of z p r e d i c t e d for a n " i d e a l " e x c h a n g e i n v o l v i n g a d o u b l y c h a r g e d a n i o n in t r a c e c o n c e n t r a t i o n a n d a s i n g l y c h a r g e d a n i o n in m a c r o c o n c e n t r a t i o n 25. T h e a g r e e m e n t m a y be f o r t u i t o u s , h o w e v e r , for t h e slopes of t h e l o g log p l o t s for m o s t of t h e o t h e r species s t u d i e d do n o t fit t h e p r e d i c t i o n . I t is possible t h a t t h e d i f f e r e n c e s b e t w e e n t h e d a t a o b t a i n e d in t h i s s t u d y a n d t h o s e of t h e o t h e r w o r k e r s are d u e t o t h e use of t h e m a c r o r e t i c u l a r resin in this w o r k . DISC0"SSION
T h e r e s u l t s m a y be i n t e r p r e t e d b y c o n s i d e r i n g t h e t y p e of species a c t u a l l y p r e s e n t in e a c h c a s e a n d t h e e x t e n t of i n t e r a c t i o n b e t w e e n t h e species a n d the a q u e o u s s o l u t i o n o u t s i d e t h e resin. I o n - w a t e r i n t e r a c t i o n s a n d t h e effects of t h e ion on t h e e x t e r n a l w a t e r s t r u c t u r e h a v e b e e n s h o w n to b e of c o n s i d e r a b l e i m p o r t a n c e in d e t e r m i n i n g s e l e c t i v i t y orders for i o n - e x c h a n g e resins a~. T h e first t y p e i n c l u d e s t h o s e m e t a l c a t i o n s w h i c h do n o t f o r m anionic c o m p l e x e s r e g a r d l e s s of t h e h y d r o x i d e c o n c e n t r a t i o n a n d t h e r e f o r e r e m a i n in solution as c a t i o n s a n d a r e n o t a b s o r b e d b y t h e resin. E x a m p l e s h e r e w o u l d b e t h e alkali m e t a l s a n d t h e alkaline earths. A n a l . C h i m . A c t a , 4 9 (x97o) 4 7 3 - 4 7 9
478
R. Iv. H I R S C H , J. D. PORTOCK
Type two includes those metal cations formingmat high p~i--anionic hydroxide complexes which are not ~bsorbed into the resin to any great extent. Among the m e m b e r s of t h i s g r o u p a r e A I ( I I I ) , S i ( I V ) , C o ( I I ) , A s ( I I I ) , a n d Z n ( I I ) . All p r e c i p i t a t e f r o m a p p r o x i m a t e l y n e u t r a l s o l u t i o n s , b u t r e d i s s o l v e in h i g h l y a l k a l i n e m e d i a . T h e n e u t r a l h y d r o x i d e s or o x i d e s are o n l y w e a k l y a c i d i c ; t h u s t h e a n i o n i c c o m p l e x e s a r e n o t a t all acidic. T h e r e a s o n w h y t h e s e h y d r o x y a n i o n s are n o t a b s o r b e d b y t h e resin, t h e r e f o r e , p r o b a b l y is t h a t t h e a n i o n i c c o m p l e x e s a r e h y d r o g e n b o n d e d t o t h e w a t e r m o l e c u l e s in t h e e x t e r n a l s o l u t i o n . T h u s t h e y a r e n o t " r e j e c t e d " b y t h i s p h a s e i n t o t h e resin. A t h i r d t y p e i n c l u d e s t h e s m a l l a n d m e d i u m sized a n i o n s of t h e n o n - m e t a l l i c e l e m e n t s , s u c h as fluoride, c h l o r i d e , sulfide, a c e t a t e , a n d c a r b o n a t e . T h e s m a l l e s t of t h e s e ions are h y d r a t e d a n d t h e r e f o r e h a v e s m a l l v a l u e s of D. As t h e ions i n c r e a s e in size, t h e e x t e n t of h y d r a t i o n d e c r e a s e s a n d t h e d i s t r i b u t i o n r a t i o i n c r e a s e s . T h e r e is n o s h a r p b o u n d a r y s e p a r a t i n g t h i s g r o u p f r o m t h e n e x t one. T h e final t y p e i n c l u d e s t h e a n i o n s of t h e v e r y a c i d i c o x y a c i d s , w h i c h are c o m p l e t e l y d i s s o c i a t e d in a l k a l i n e s o l u t i o n . T h e y h a v e n o c h a n c e of h y d r o g e n b o n d i n g t o t h e w a t e r s t r u c t u r e a n d a r e c o m p l e t e l y " r e j e c t e d " i n t o t h e i o n - e x c h a n g e resin p h a s e . E x a m p l e s of t h i s t y p e are p e r c h l o r a t e , p e r r h e n a t e , p e r i o d a t e , m o l y b d a t e a n d c h r o m a t e . V e r y large s i m p l e a n i o n s , s u c h as i o d i d e , also b e l o n g in t h i s g r o u p b e c a u s e of t h e i r size, low charge density, and inability to interact strongly with water. T h e a u t h o r s t h a n k Dr. EUGENE T. McGUINNESS for his a i d w i t h t h e l i q u i d s c i n t i l l a t i o n c o u n t i n g , Mr. HENRY STOBER for m a k i n g t h e a t o m i c a b s o r p t i o n m e a s u r e m e n t s on t h e silicon s a m p l e s , a n d t h e I o n E x c h a n g e D e p a r t m e n t , R o h m a n d H a a s C o r p o r a t i o n , for f u r n i s h i n g s a m p l e s of t h e i r m a c r o r e t i c u l a r a n i o n e x c h a n g e r s . SUMMARY
T h e d i s t r i b u t i o n r a t i o s of a l a r g e n u m b e r of species a r e r e p o r t e d for a n i o n e x c h a n g e f r o m s t r o n g l y a l k a l i n e s o l u t i o n s . T h e s t r o n g l y basic m a c r o r e t i c u l a r a n i o n e x c h a n g e r , A m b e r l y s t A-29, w a s u s e d . T h e e l e m e n t s in t h e o x i d a t i o n s t a t e s s t u d i c d are classified b y t h e i r i o n - e x c h a n g e b e h a v i o r . T h e d e g r e e to w h i c h a s p e c i e s is a b s o r b e d b y t h e resin d e p e n d s o n w h e t h e r it e x i s t s in a n a n i o n i c f o r m a n d w h e t h e r it is h y d r a t e d o r f o r m s h y d r o g e n b o n d s w i t h t h e w a t e r in t h e a q u e o u s s o l u t i o n . W h i l e w o r k i n g w i t h h y d r o x i d e s o l u t i o n s p r e s e n t s s o m e p r a c t i c a l p r o b l e m s , t h e s i z e a b l e d i f f e r e n c e s in d i s t r i b u t i o n c o e f f i c i e n t s for s e v e r a l g r o u p s of ions m a y be a n a l y t i c a l l y useful. RI~SUMI~
O n a e x a m i n 6 les c o e f f i c i e n t s d e p a r t a g e o b t e n u s e n s o l u t i o n s f o r t e m e n t alcalines, en u t i l i s a n t u n d c h a n g e u r d ' a n i o n s , l ' A m b e r l y s t A-29, f o r t e m e n t b a s i q u e , m a c r o r 6 t i c u l a i r e . L e s 61dments a u x d e g r d s d ' o x y d a t i o n d t u d i ~ s s o n t classds s e l o n l e u r c o m p o r t e m e n t " 6 c h a n g e u r d ' i o n s " . Cela d ~ p e n d d e leur f o r m e a n i o n i q u e , s'ils s o n t h y d r a t 6 s ou s'ils f o r m e n t des l i a i s o n s h y d r o g ~ n e a v e c l ' e a u , en s o l u t i o n a q u e u s e . L e s d i f f 6 r e n c e s clans les c o e f f i c i e n t s d e p a r t a g e , p o u r p l u s i e u r s g r o u p e s d ' i o n s p r ~ s e n t e n t u n int~r~t d u p o i n t de vtte a n a l y t i q u e . A n a l . C h i m . :1eta,, 49 (I97 o) 4 7 3 - 4 7 9
A N I O N - E X C H A N G I ~ E Q U I L I B R I A IN A L K t k L I N E M E D I A
479
ZU SAMME N F A S S U NG
Fiir eine grosse A n z a h l v o n S p e z i e s w e r d e n ' d i e Verteilungsverlvaltnisse ffir d e n A n i o n e n a u s t a u s c h irl stark alkalischell L6sungen m i t g e t e i l t . E s w u r d e der stark basische, h o c h v e r n e t z t e A r f i o n e n a u s t a u s c h e r A m b e r l y s t A - z 9 verwertdet. D i e E l e m e n t e in dert urltersuchten O x i d a t i o n s s t u f e n w e r d e n auf Grund ihres I o n e n a u s t a u s c h verhalterts klassifiziert. D e r Grad, m i t w e l c h e m eine I o n e n a r t v o m I o n e n a u s t a u s c h e r harz absorbiert wird, h/ingt davort ab, ob sie in einer A n i o n e n f o r m e x i s t i e r t und ob sie h y d r a t i s i e r t ist oder \ V a s s e r s t o f f b r ~ c k e n mit d e m Wasser irt der w,tssrigen L 6 s u n g bildet. Wenrt auch das Arbeitert mit H y d r o x i d - L 6 s u n g e r t einige p r a k t i s c h e P r o b l e m e stellt, k 6 n n e n doch die z i e m l i c h grossert Urtterschiede i~l den V e r t e i l u n g s k o e f f i z i e n t e n ffir die verschiederlen Iorlengruppen a n a l y t i s c h v o n N u t z e n sein. REFEREI~CES I K . A. KRAUS AND F . "NELSON, Proc. II~teru. Co~f. Peaceful Uses At. Energy, Geneva, 1955, 7 (t956) I t 3 . 2 J . P . 17ARIS, H n a l . Chem., 32 (196o) 520. 3 J-l~- ]FARIS AND l{.. F . ]~UCHANAN, A n a l . Chem., 36 (1964) I t 5 7 . 4 F . •V. E . STII.ELO~.V AND C. j . c . I~OTHMA, A n a l . Chem., 39 (1967) 595. 5 J . ]~.ORlC.Isclq, i n D . C. ST'I~,VART AND H . A . ELION, Progress in N u c l e a r Energy, S e r i e s I X , l:~ergamon l:'ross, O x f o r d , t 9 6 6 , V'ol. 6, C h a p t e r 1. 6 S. A. FISHER AND V. ~'V. M~LOCtIE, A~ral. Chem., 24 (~952) t ~oo. 7 N. F . H A L L AND D . H . J o N ] t . s , J . A m . Chem. See., 75 (1953) 5787 • 8 H . OKUNO, M. HONDO' AND T. [SHIMORI, J a p a u A n a l y s t , 4 (1955) 386. 9 C. EGEIt AND J . L I P K E , A n a l . Chim. Acta., 2o (t959) 5.t8. i o M. L . GOOD, M . B . P U R D V AND T. H . I-IoEreING, J . [norg. 65, Nttcl. Chem., 6 ( t 9 5 8 ) 73. xr T. S U z u K I , J . Chem. Soc. J a p a n , Pure Chem. Sect. ( N i p p o ~ K a g a k u Z a s s h i ) , 82 (I96x 696. 12 A.. IGUCHI, 13ull. ~ h e m . Soc..]apart, 31 ( t 9 5 8 ) 748. 13 I{. TAKIURA AND Y. TAKINO, Japa$~ A n a l y s t , i o (1961) 483, 488, 493. 14 Amberlyst A-29 Technical Bttlleti,~, ]~.ohm a n d H a a s , I J h i l a d e l p h i a , I-'a., x967. x 5 R . ]q.UNIN', Io*~ Exchange Resi,zs, J o h n W i l e y , l ~ e w Y o r k , 1958, p. 34 t. 16 l{. T. OV'~RMAN AND H . t~I. CLARK, Radioisotope Tech~iques, M c G r a . w - H i l l , l'¢ew Y o r k I 9 6 o . x7 Analytical ~[ethods f o r ,'ltomi¢ ,,Ibsorpti0n Spectrophotometry, P e . r k i n - E l m e r , 2q'orwalk, C o n n . , t968. 18 J. J. LINGAN:E;, .'trial. Chem., 39 (1967) 8 8 I . i 9 [~[. J . ~BACZLIK AND R. J . DOBOlS, A,gal. Chem., ,to (1968) 685. 20 I{. U. H I R S C l t AND J . D . PORTOCK, A n a l . Letters, 2 ( t 9 6 9 ) 295. 2 I A. 1. VOGEL, Quantitative lnorg(odc ,4,~alysis, Johtx W i l e y , iN'ew Y o r k , x961. "2-2 H . R. G'RAD~2", i n I. M. KOL'rHOt~F AND P . J . ELVING, Treatise o1~ AnalyMcal Chetvistry, J o h n W i l c y - I n t e r s c i c n c o , I'~ew Y o r k , t 9 6 3 , Pa.rt: I I , V o l . 8, p. 2.26. 25 2:967 Book of A S T M Standards. A S T M , P h i l a d e l p h i a , P a . , 1967, V o l . 32, p. t 6 7 . 24 R. BASTIAN, R. ~,VEBERLING AND F. "PALILLA, A*zal. Chem., 29 ( r 9 5 7 ) t795. 25 R . i . DIAI~IOND ANt) D . C. WI-IITN:~.Y, i n J . A . 3'IARINSKY. [o*~ Excha~ge, Mttrcel D e k k e r , [rtc., N e w Y o r k , ~966, V o l . 1, C h a p t e r 8.
A n a l . Chim. Acta, 49 (197o) 4 7 3 - 4 7 9
ANION-EXCHANGE
473
EQUILIBRIA
IN A L K A L I N E
MEDIA
I~.OLAgD F. HIRSCH AND JOHN D. ]?ORTOCK* Departmet,t of Chemistry, Seton Hall Uuiversity. .7outh Orange, N.J. 07079 ( U . S . A . ) (Received September 29th, 1969)
KRAUS AND z'NI~LSON1 m a d e e x t e n s i v e s t u d i e s of t h e a b s o r p t i o n of m e t a l s f r o m hydrochloric acid solutions by anion exchangers. Since their pioneering work, m a n y o t h e r m e d i a h a v e b e e n s t u d i e d , i n c l u d i n g h y d r o f l u o r i c a c i d 2, nitric a c i d 3, a n d s u l f u r i c a c i d 4, as well as m i x t u r e s of t h e s e acids w i t h o r g a n i c s o l v e n t s 5. R e l a t i v e l y little a t t e n t i o n has been p a i d to a n i o n e x c h a n g e f r o m a l k a l i n e m e d i a . A few s t u d i e s h a v e d e a l t w i t h t h e g r o u p ¥ I B a n d g r o u p V I I B e l e m e n t s in t h e i r h i g h e s t o x i d a t i o n s t a t e s . M e t h o d s h a v e b e e n d e v e l o p e d b a s e d on a n i o n e x c h a n g e f r o m h y d r o x ide s o l u t i o n s to s e p a r a t e p e r r h e n a t e ~ n d m o l y b d a t e Q, p e r t e c h n e t a t e a n d m o l y b d a t e 7, a n d p e r r h e n a t e a n d t u n g s t a t e s. O t h e r w o r k has b e e n c o n c e r n e d w i t h s e p a r a t i o n of n o n - m e t a l s s u c h as f l u o r i d e a n d p h o s p h a t e 0, iodide, i o d a t e a n d p e r i o d a t O 0, b o r a t e a n d s i l i c a t e it, a n d sulfite, s e l e n i t e a n d t e l l u r i t e v-'-. A m o r e c o m p l e t e s t u d y of a n i o n e x c h a n g e f r o m h y d r o x i d e m e d i a h a s b e e n r e p o r t e d .by TAK1URA AND TAKINO t3. T h e y d e t e r m i n e d s e l e c t i v i t y c o e f f i c i e n t s for s e v e r a l s i n g l y - c h a r g e d a n i o n s i n t o a s t r o n g l y basic a n i o n e x c h a n g e r in t h e h y d r o x i d e form. The selectivity coefficients represent the concentration equilibrium constants for the r e a c t i o n A - o x t . s o I tl + O H
-ros in = A-rcs|
n + on-ox
t. s o l n
T h i s p a p e r r e p o r t s a c o m p r e h e n s i v e s t u d y of a n i o n e x c h a n g e of t h e e l e m e n t s f r o m s o d i u m h y d r o x i d e solutions. C o m m o n a n i o n s a n d m o s t m e t a l ions w h i c h are soluble in h i g h l y a l k a l i n e s o l u t i o n s w e r e i n c l u d e d . I n s t e a d of d e t e r m i n i n g s e l e c t i v i t y c o e f f i c i e n t s , t h e d i s t r i b u t i o n ratios, D , w e r e m e a s u r e d D
=
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(I)
w h e r e E r e p r e s e n t s a n e l e m e n t in a p a r t i c u l a r o x i d a t i o n s t a t e or c h e m i c a l form. a n d [E'] r e p r e s e n t s t h e t o t a l a n a l y t i c a l c o n c e n t r a t i o n of E in t h e g i v e n phase. D i s t r i b u t i o n r a t i o s a r e s p e c i f i e d for f i x e d c o n c e n t r a t i o n s of s o d i u m h y d r o x i d e in t h e e x t e r n a l solut i o n (o.Io, 1.oo a n d IO.O F s o d i u m h y d r o x i d e i n t h i s s t u d y ) a n d t h e r e f o r e m a y be m o r e u s e f u l t h a n s e l e c t i v i t y coefficients in d e v i s i n g a n a l y t i c a l s e p a r a t i o n p r o c e d u r e s . EXPERIMENTAL
Equipment All of t h e l a b o r a t o r y w a r e used t o store, m e a s u r e or t r a n s f e r s o l u t i o n s w a s m a d e of e i t h e r p o l y e t h y l e n e or p o l y p r o p y l e n e . D r a i n a g e of s o l u t i o n s f r o m t h e s e c o n t a i n e r s * Prosent kddress: Diamond-Shamrock Corp., I~'orth Arlington, ~N'.J., U.S.A.. Anal. Chim. Acta, 49 (x97o) 473-479
474
R. F. I-HRSCFI, J . D. P O R T O C K
is c o m p l e t e , s i n c e t h e p l a s t i c s u r f a c e s are n o t w e t t e d b y a q u e o u s s o l u t i o n s . T h i s a l l o w s u s e of t h e c o n t a i n e r s w i t h v a r i o u s s o d i u m h y d r o x i d e c o n c e n t r a t i o n s w i t h o u t r e c a l i b r a t i o n . A 5o-ml g r a d u a t e d c y l i n d e r w a s c a l i b r a t e d for u s e in all d i l u t i o n s a n d v o l u m e t r i c t r a n s f e r s . I t w a s f o u n d a c c u r a t e a n d r e p r o d u c i b l e t o b e t t e r t h a n + o.I ml.
D~, box A carbon dioxide-free a t m o s p h e r e was a t t a i n e d by working inside a d r y box, c o n t i n u o u s l y f l u s h e d w i t h d r y , CO.a-free n i t r o g e n . A p a i r of small b l o w e r fans a i m e d a t a t r a y filled w i t h i n d i c a t i n g s o d a l i m e s e r v e d t o i n s u r e t h e a b s e n c e of c a r b o n d i o x i d e .
Reagents Boiled, d e i o n i z e d w a t e r w a s u s e d t h r o u g h o u t . T h e s o d i u m h y d r o x i d e s o l u t i o n s w e r e p r e p a r e d f r o m J. T. B a k e r 5 0 % R e a g e n t , s t a n d a r d i z e d a g a i n s t s t a n d a r d h y d r o c h l o r i c a c i d s o l u t i o n a n d s t o r e d in p o l y e t h y l e n e b o t t l e s . All o t h e r r e a g e n t s w e r e of t h e highest purity available, usually r e a g e n t grade.
Resin A m b e r l y s t A-29 ( R o h m a n d H a a s , P h i l a d e l p h i a , Pa.), a m a c r o r e t i c u l a r resin in t h e c h l o r i d e form, w a s c h o s e n b e c a u s e it is r e p u t e d to h a v e h i g h r e s i s t a n c e t o m e c h a n i c a l a t t r i t i o n a n d e x c e l l e n t s t a b i l i t y in h i g h l y a l k a l i n e s o l u t i o n s , b e i n g s u p e r i o r in t h e s e r e s p e c t s to c o n v e n t i o n a l gel resins ta. T h e b e a d s w e r e u n s i z e d b u t a p p e a r e d t o be m o s t l y in t h e 2 o - 5 o m e s h r a n g e . T h e resin was c o n v e r t e d to t h e h y d r o x i d e f o r m b y p l a c i n g a s l u r r y of t h e m a t e rial in a c o l u m n a n d p a s s i n g several b e d v o l u m e s of I F s o d i t t m h y d r o x i d e t h r o u g h t h e b e a d s a t a flow r a t e of t w o b e d v o l u m e s p e r h. T h e resin w a s t h e n w a s h e d w i t h w a t e r u n t i l t h e e f f l u e n t w a s n e u t r a l , a n d d r i e d for 3 d a y s i n t h e n i t r o g e n a t m o s p h e r e . A p o r t i o n of t h e p r o d u c t w a s d r i e d a t IiO ° to d e t e r m i n e t h e m o i s t u r e c o n t e n t of t h e r e s i n dried at room temperature. T h e e x c h a n g e c a p a c i t i e s a n d d e g r e e s of c o n v e r s i o n t o t h e h y d r o x i d e f o r m of e a c h b a t c h of a n i o n e x c h a n g e r w e r e d e t e r m i n e d b y s t a n d a r c l m e t h o d s 15. T h e c a p a c i t y w a s 2.7-2.8 m e q ] g r e s i n in all cases. SLx b e d v o l u m e s of t h e s o d i u m h y d r o x i d e s o l u t i o n p r o d u c e d 75% conversion to the h y d r o x i d e form, while ten bed v o l u m e s were requirect t o r e a c h 9 o % c o n v e r s i o n . H o w e v e r , b a t c h e s c o n v e r t e d to d i f f e r e n t d e g r e e s w i t h i n t h e 7 5 - I o o % r a n g e g a v e s i m i l a r r e s u l t s for s e v e r a l t e s t ions.
2~rocedure A l i q u o t s of a s t o c k s o l u t i o n of t h e e l e m e n t b e i n g s t u d i e d w e r e d i l u t e d w i t h v a r i o u s a m o u n t s of s o d i u m h y d r o x i d e a n d w a t e r . A 25.o-ml p o r t i o n of e a c h d i l u t e d s o l u t i o n w a s m i x e d w i t h a 2-g s a m p l e of t h e resin ( w e i g h e d e x a c t l y ) in a c a p p e d b o t t l e . T h e m i x t u r e w a s s w i r l e d a t f r e q u e n t i n t e r v a l s for 2 h t o e n s u r e t h a t e q u i l i b r i u m w a s reached. T h e solution w a s t h e n s e p a r a t e d f r o m t h e resin b y d e c a n t a t i o n or f i l t r a t i o n t h r o u g h glass wool. T h i s s o l u t i o n , a n d also a ~ o r t i o n of t h e s o l u t i o n w h i c h h a d n o t c o n t a c t e d t h e resin, w e r e t h e n a n a l y z e d for t h e i o n u n d e r c o n s i d e r a t i o n .
Analytical techniques Radioisotopic tracers to. T h e r a d i o i s o t o p e s o b t a i n e d ( N e w E n g l a n d N u c l e a r A n a l . Ghim, A c t a , 49 ( I 9 7 o ) 4 7 3 - 4 7 9
ANION-EXCHtXNGE
EQUILIBRIA
IN
ALIC~LINE
475
MEDIA
C o r p . , I s o - S e r v e D i v i s i o n of C a m b r i d g e N u c l e a r Corp., N u c l e a r S c i e n c e a n d E n g i n e e r i n g C o r p . , a n d B a i r d - A t o m i c ) w e r e all s p e c i f i e d b y t h e s u p p l i e r to b e of a t l e a s t 9 9 % radiochemical purity. ~ , - E m i t t e r s w e r e a s s a y e d in a 5 - c m d i a m e t e r N a I ( T l ) c r y s t a l w e l l , w i t h a B a i r d A t o m i c M o d e l 135 s c a l e r - t i m e r . I s o t o p e s e m i t t i n g o n l y f l - r a d i a t i o n w e r e a s s a y e d b y l i q u i d s c i n t i l l a t i o n in a N u c l e a r - C h i c a g o M o d e l 7 o 3 P s y s t e m ( t h e s e p a r a t e s t a n d a r d r u n a t e a c h s o d i u m h y d r o x i d e c o n c e n t r a t i o n e l i m i n a t e d t h e treed f o r q u e n c h c o r r e c t i o n s ) o r b y G e i g e r c o u r x t i n g w i t h t h e B a i r d - A t o m i c M o d e l 135 s c a l e r - t i m e r a n d a thin-window detector tube. A t o m i c absorption x7. A P e r k i n - E l m e r M o d e l 29o s p e c t r o p h o t o m e t e r w i t h a i r a c e t y l e n e f l a m e w a s u s e d f o r all m e a s u r e m e n t s , e x c e p t f o r silicon, w h i c h w a s d e t e r mined on a Perkin-Elmer Model 3o3 Spectrophotometer with a nitrous oxide-acetylene flame. Ion-sensitive electrodes. A C o r n i n g M o d e l IO pH m e t e r w a s u s e d to m e a s u r e p o t e n t i a l s a g a i n s t a S . C . E . F l u o r i d e ion w a s d e t e r m i n e d b y d i r e c t p o t e n t i o m e t r y w i t h t h e O r i o n R e s e a r c h M o d e l 94-09 F l u o r i d e E l e c t r o d e 1~. O t h e r d i r e c t m e a s u r e m e n t s w e r e m a d e w i t h t h e O r i o n R e s e a r c h M o d e l 9 2 - 8 1 P e r c h l o r a t e E l e c t r o d e t U , '-'0. I n all ca_ses a l i q u o t s o f t e s t s o l u t i o n s w e r e n e u t r a l i z e d w i t h n i t r i c o r a c e t i c a c i d a n d m a d e u p to a definite volume before the measurement. Separate calibration curves were made u p for each ion a t each s o d i u m h y d r o x i d e c o n c e n t r a t i o n . T h e r e s u l t s can t h e r e f o r e be considered concentration distribution ratios, consistent with the results obtained by using the other measurement techniques. Titrations "-~. A r g e n t o m e t r i c t i t r a t i o n s w e r e c a r r i e d o u t w i t h a s t a n d a r d s i l v e r nitrate solution to the potentiometric end-point. Chelometric titrations were carried out with standard EDTA solution to visual indicator end-points ; the aluminum determ i n a t i o n w a s a b a c k - t i t r a t i o n w i t h zinc. I o d o m e t r i c t i t r a t i o n s w e r e c a r r i e d o u t w i t h sodium thiosulfate solutions standardized against potassium iodate. Vanadate was t i t r a t e d b y s t a n d a r d i r o n ( I I ) s u l f a t e solution'-' o. Speclrophotometry. A B e c k m a n D U S p e c t r o p h o t o m e t e r w a s u s e d . B o r a t e w a s m e a s u r e d b y t h e c a r m i n e m e t h o d 2s, a n d n i t r a t e b y d i r e c t s p e c t r o p h o t o m e t r y a t 22o llmo.4.
RESULTS
. .I
AND
DISCUSSION
The distribution m e a n s o f eqn. (2) :
r a t i o s ( e q n . I) a r e c a l c u l a t e d f r o m t h e e x p e r i m e n t a l
A r/w D .'= s/-------V A
data by
(2)
w h e r e A r a n d A s a r e t h e a m o u n t s of t h e g i v e n s p e c i e s in t h e r e s i n a n d e x t e r n a l s o l u t i o n , r e s p e c t i v e l y , w is t h e n e t d r y w e i g h t ( c o r r e c t e d f o r m o i s t u r e c o n t e n t ) of r e s i n t a k e n , a n d V is t h e v o l u m e of s o l u t i o n c o n t a c t e d b y t h e resin. S i n c e i n m o s t c a s e s t h e c o n c e n t r a t i o n o f t h e s p e c i e s in t h e resin w a s d e t e r m i n e d b y d i f f e r e n c e , t h e c a l c u l a t i o n s a r e b e s t r e p r e s e n t e d b y e q n . (3) :
D =
(AI--As)/w
(3)
As/V A n a l . Ghim. Acta, 49 (I97o)
473-479
476 TABLE
R.F.
Re Cl
I)IS'rRIBUTION
Chemical form
RATIOS
FROI~I A Q U E O U S
SODIUM
IIYDROXIDI'~
.'1 n a l y t i c a l t e c h n i qtte a
Logarithm o . 1 o 1:
f . o o 1 ~"
1 o . o 1:
ReO.t CIO,t-
ISE l SI~
3.96 4.20 3-7 ° 3-1 o 2.54 3- 68 2.2,t 2.1o 3.23 z.89 t .54 t. 04 t.97 I.o,t -~ o
4.o6 3.4o 3.34 3.28
2.54 b 2.76b 2.o 4 2.20
2.26
2 .or
2. oo t .75 t.54 1.49 r.3,t , .04 t. o o 0.68 0.53 o.I 8
1
t-
AgT
Tc N l Br C Mo CF S Br S C TI CI Se V Co I F C Zn
TcO.t NO:t1O4BrOaCNM o O a 'aC r O , i 2S a13rSO,t zAcetate TI(1) CISeO:3~VOaCo(If) IOaFCO:,"-Zn(ll)
Si Mg AI Cu l~b
S i O a 'aMg '-'-+ A l ~+ C u 'a+ P b ''+ PO,taAsO,2Borate C a ~+ Cs + K + M n ( l l)
GM Sp 1SE IT AgT AA /kA AgT AgT LS LS OM AgT S liT S IT ISE LS S AA. AA AA EDTA AA S G1VI 1T Sp EDTA S AA S
P As ;13 Ca Cs K MIX
J . D. P O R T O C K
I
ANION-]':XCIIANGE
!:h, m e n t
ItlRSCH,
of distribution
ratio in NaOH
x.oo
o.15
1,28 0.56 0.42 0.75 0.32 1.25 o.,14 0.38 0.38 0.23
o. I I 0.08 o.o8 o.oo o.oo < o < o < o < o
t. 56" i .o3 t.o8 <: o -< o ~.23 t. 2 0 0.78 <2_ o < o ~ o o . lo < o < o -< o o.30 < o < o < o < o
< o < o --" < o < o < o < o < o <: o < o __e
< o 0.4 2 o . 18 0.08 <: o < o < o < o < o < o < o
,~ A A ~--- a t o m i c : t b s o r p t i o n ; AgT ~ argentometric titration; EDTA = EDTA titration; G1H = Goigcr-Muller counter; ISE = potontiometry with ion-selective electrode;' I T == i o d o n x e t r i c titrattion; LS = liquid scintillation counter; I¢T = direct redox titration; S = ~al(T1) crystal scintillation counting; Sp ~- spcctrophotomctr y. " 5.o F I~aOH, electrode response unsatisfactory in ease of Io.o F NaOH. u insoluble.
in w h i c h A t is t h e a m o u n t of t h e s p e c i e s in t h e e x t e r n a l s o l u t i o n b e f o r e it w a s b r o u g h t in c o n t a c t w i t h t h e resin. T h e r e s u l t s a r e s u m m a r i z e d in T a b l e I. T h e species a r e l i s t e d in t h e o r d e r of t h e l o g a r i t h m s of t h e i r d i s t r i b u t i o n c o e f f i c i e n t s in I.OO F s o d i u m h y d r o x i d e . V a l u e s of log D less t h a n o a r e n o t g i v e n as t h e y a r e l a c k i n g in p r e c i s i o n a n d n o t a n a l y t i c a l l y significant. T h e w i d e r a n g e of v a l u e s of t h e d i s t r i b u t i o n r a t i o s is s i m i l a r t o t h a t f o u n d i n o t h e r m e d i a x-5. S e v e r a l possibilities a r e s u g g e s t e d for s e p a r a t i o n s of ions or g r o u p s of ions: n i t r a t e f r o m p h o s p h a t e , b r o m a t e f r o m i o d a t e , zinc f r o m c a l c i u m . Anal. Chim..'lcla,
49 (197o) 473-479
ANION-EXCKANGE
EQUILIBRIA
IN ALKALINE
477
MEDIA
Specific c o m p a r i s o n s w i t h p r e v i o u s l y p u b l i s h e d d a t a c a n be m a d e i n t w o ins t a n c e s . T h e s e l e c t i v i t y o r d e r i n d i c a t e d b y t h e s e l e c t i v i t y c o e f f i c i e n t s of TAXlURA AND TA KIN O 13 c a n be c o m p a r e d w i t h t h e s e l e c t i v i t i e s o b s e r v e d in t h e v a r i o u s s o d i u m h y d r o x i d e s o l u t i o n s u s e d in this w o r k . T h i s c o m p a r i s o n is p r e s e n t e d in T a b l e II. E x c e p t for b r o m a t e a n d b r o m i d e , t h e r e s u l t s of t h e t w o s t u d i e s a r e similar. TABLE
II
SELECTIVITY
ORDERS
FOR
T A K I U R A AND T A K I N O to Tiffs work: o. t F NaOl-[ Tliis work: t.o F NaOH T h i s w o r k : 1o 1: N a O F I
TABLE
ANION
EXCIIANGE
IN
ALl{ALINE,
SOLUTIONS
B O o - ---~ F - < A s O o . - < I O n - < B r O 3 - ~ C I - < C N - < N O n - < B r - < I B O o . - ~_. A s O z - < F - - < I O : F < CI - < B r - < C N - < . B r O a - < N O n - - < l B O 2 - ~__ A s O z ' - < F-" _ I O n - < C I - < S B r - < ~ C N - < B r O : l - < N O : v < l BOe- _ AsOz- _ IOa-
1I1
DISTRIBUTION
RATIOS
FOR
I,ERRHI.2.NATE
AND
MOLYBDATE
IN SODIUM
I.[YDItOXIIJE
log D f o r p e r r h e m , te
log 1) f o r molybdate
T h i s worh
Literature '~
T h i s worh
o. l o .5
3.96
3.95
t .o
.1.o6
3.78
5.0 to.o
z .54
2.95 2.oo
CN.o.(1:)
Lite~'atto'e '~
3.23 2.48
3.00 z.9o
1.49
2 .o8
0.38 --0.26
1.65 x.65
T h e d a t a of FISHER AND MELOCHE 6 are s h o w n in T a b l e I I I . T h e a g r e e m e n t b e t w e e n t h e d i s t r i b u t i o n r a t i o s for p e r r h e n a t e is s a t i s f a c t o r y b u t t h e r e is s i g n i f i c a n t d i s a g r e e m e n t in t h e case of m o l y b d a t e . T h e m o l y b d a t e d i s t r i b u t i o n d a t a in this w o r k give a s t r a i g h t line w h e n log D is p l o t t e d a g a i n s t log Cr¢~olt, a n d t h e slope of t h i s line is 1.8, w h i c h is close to t h e v a l u e of z p r e d i c t e d for a n " i d e a l " e x c h a n g e i n v o l v i n g a d o u b l y c h a r g e d a n i o n in t r a c e c o n c e n t r a t i o n a n d a s i n g l y c h a r g e d a n i o n in m a c r o c o n c e n t r a t i o n 25. T h e a g r e e m e n t m a y be f o r t u i t o u s , h o w e v e r , for t h e slopes of t h e l o g log p l o t s for m o s t of t h e o t h e r species s t u d i e d do n o t fit t h e p r e d i c t i o n . I t is possible t h a t t h e d i f f e r e n c e s b e t w e e n t h e d a t a o b t a i n e d in t h i s s t u d y a n d t h o s e of t h e o t h e r w o r k e r s are d u e t o t h e use of t h e m a c r o r e t i c u l a r resin in this w o r k . DISC0"SSION
T h e r e s u l t s m a y be i n t e r p r e t e d b y c o n s i d e r i n g t h e t y p e of species a c t u a l l y p r e s e n t in e a c h c a s e a n d t h e e x t e n t of i n t e r a c t i o n b e t w e e n t h e species a n d the a q u e o u s s o l u t i o n o u t s i d e t h e resin. I o n - w a t e r i n t e r a c t i o n s a n d t h e effects of t h e ion on t h e e x t e r n a l w a t e r s t r u c t u r e h a v e b e e n s h o w n to b e of c o n s i d e r a b l e i m p o r t a n c e in d e t e r m i n i n g s e l e c t i v i t y orders for i o n - e x c h a n g e resins a~. T h e first t y p e i n c l u d e s t h o s e m e t a l c a t i o n s w h i c h do n o t f o r m anionic c o m p l e x e s r e g a r d l e s s of t h e h y d r o x i d e c o n c e n t r a t i o n a n d t h e r e f o r e r e m a i n in solution as c a t i o n s a n d a r e n o t a b s o r b e d b y t h e resin. E x a m p l e s h e r e w o u l d b e t h e alkali m e t a l s a n d t h e alkaline earths. A n a l . C h i m . A c t a , 4 9 (x97o) 4 7 3 - 4 7 9
478
R. Iv. H I R S C H , J. D. PORTOCK
Type two includes those metal cations formingmat high p~i--anionic hydroxide complexes which are not ~bsorbed into the resin to any great extent. Among the m e m b e r s of t h i s g r o u p a r e A I ( I I I ) , S i ( I V ) , C o ( I I ) , A s ( I I I ) , a n d Z n ( I I ) . All p r e c i p i t a t e f r o m a p p r o x i m a t e l y n e u t r a l s o l u t i o n s , b u t r e d i s s o l v e in h i g h l y a l k a l i n e m e d i a . T h e n e u t r a l h y d r o x i d e s or o x i d e s are o n l y w e a k l y a c i d i c ; t h u s t h e a n i o n i c c o m p l e x e s a r e n o t a t all acidic. T h e r e a s o n w h y t h e s e h y d r o x y a n i o n s are n o t a b s o r b e d b y t h e resin, t h e r e f o r e , p r o b a b l y is t h a t t h e a n i o n i c c o m p l e x e s a r e h y d r o g e n b o n d e d t o t h e w a t e r m o l e c u l e s in t h e e x t e r n a l s o l u t i o n . T h u s t h e y a r e n o t " r e j e c t e d " b y t h i s p h a s e i n t o t h e resin. A t h i r d t y p e i n c l u d e s t h e s m a l l a n d m e d i u m sized a n i o n s of t h e n o n - m e t a l l i c e l e m e n t s , s u c h as fluoride, c h l o r i d e , sulfide, a c e t a t e , a n d c a r b o n a t e . T h e s m a l l e s t of t h e s e ions are h y d r a t e d a n d t h e r e f o r e h a v e s m a l l v a l u e s of D. As t h e ions i n c r e a s e in size, t h e e x t e n t of h y d r a t i o n d e c r e a s e s a n d t h e d i s t r i b u t i o n r a t i o i n c r e a s e s . T h e r e is n o s h a r p b o u n d a r y s e p a r a t i n g t h i s g r o u p f r o m t h e n e x t one. T h e final t y p e i n c l u d e s t h e a n i o n s of t h e v e r y a c i d i c o x y a c i d s , w h i c h are c o m p l e t e l y d i s s o c i a t e d in a l k a l i n e s o l u t i o n . T h e y h a v e n o c h a n c e of h y d r o g e n b o n d i n g t o t h e w a t e r s t r u c t u r e a n d a r e c o m p l e t e l y " r e j e c t e d " i n t o t h e i o n - e x c h a n g e resin p h a s e . E x a m p l e s of t h i s t y p e are p e r c h l o r a t e , p e r r h e n a t e , p e r i o d a t e , m o l y b d a t e a n d c h r o m a t e . V e r y large s i m p l e a n i o n s , s u c h as i o d i d e , also b e l o n g in t h i s g r o u p b e c a u s e of t h e i r size, low charge density, and inability to interact strongly with water. T h e a u t h o r s t h a n k Dr. EUGENE T. McGUINNESS for his a i d w i t h t h e l i q u i d s c i n t i l l a t i o n c o u n t i n g , Mr. HENRY STOBER for m a k i n g t h e a t o m i c a b s o r p t i o n m e a s u r e m e n t s on t h e silicon s a m p l e s , a n d t h e I o n E x c h a n g e D e p a r t m e n t , R o h m a n d H a a s C o r p o r a t i o n , for f u r n i s h i n g s a m p l e s of t h e i r m a c r o r e t i c u l a r a n i o n e x c h a n g e r s . SUMMARY
T h e d i s t r i b u t i o n r a t i o s of a l a r g e n u m b e r of species a r e r e p o r t e d for a n i o n e x c h a n g e f r o m s t r o n g l y a l k a l i n e s o l u t i o n s . T h e s t r o n g l y basic m a c r o r e t i c u l a r a n i o n e x c h a n g e r , A m b e r l y s t A-29, w a s u s e d . T h e e l e m e n t s in t h e o x i d a t i o n s t a t e s s t u d i c d are classified b y t h e i r i o n - e x c h a n g e b e h a v i o r . T h e d e g r e e to w h i c h a s p e c i e s is a b s o r b e d b y t h e resin d e p e n d s o n w h e t h e r it e x i s t s in a n a n i o n i c f o r m a n d w h e t h e r it is h y d r a t e d o r f o r m s h y d r o g e n b o n d s w i t h t h e w a t e r in t h e a q u e o u s s o l u t i o n . W h i l e w o r k i n g w i t h h y d r o x i d e s o l u t i o n s p r e s e n t s s o m e p r a c t i c a l p r o b l e m s , t h e s i z e a b l e d i f f e r e n c e s in d i s t r i b u t i o n c o e f f i c i e n t s for s e v e r a l g r o u p s of ions m a y be a n a l y t i c a l l y useful. RI~SUMI~
O n a e x a m i n 6 les c o e f f i c i e n t s d e p a r t a g e o b t e n u s e n s o l u t i o n s f o r t e m e n t alcalines, en u t i l i s a n t u n d c h a n g e u r d ' a n i o n s , l ' A m b e r l y s t A-29, f o r t e m e n t b a s i q u e , m a c r o r 6 t i c u l a i r e . L e s 61dments a u x d e g r d s d ' o x y d a t i o n d t u d i ~ s s o n t classds s e l o n l e u r c o m p o r t e m e n t " 6 c h a n g e u r d ' i o n s " . Cela d ~ p e n d d e leur f o r m e a n i o n i q u e , s'ils s o n t h y d r a t 6 s ou s'ils f o r m e n t des l i a i s o n s h y d r o g ~ n e a v e c l ' e a u , en s o l u t i o n a q u e u s e . L e s d i f f 6 r e n c e s clans les c o e f f i c i e n t s d e p a r t a g e , p o u r p l u s i e u r s g r o u p e s d ' i o n s p r ~ s e n t e n t u n int~r~t d u p o i n t de vtte a n a l y t i q u e . A n a l . C h i m . :1eta,, 49 (I97 o) 4 7 3 - 4 7 9
A N I O N - E X C H A N G I ~ E Q U I L I B R I A IN A L K t k L I N E M E D I A
479
ZU SAMME N F A S S U NG
Fiir eine grosse A n z a h l v o n S p e z i e s w e r d e n ' d i e Verteilungsverlvaltnisse ffir d e n A n i o n e n a u s t a u s c h irl stark alkalischell L6sungen m i t g e t e i l t . E s w u r d e der stark basische, h o c h v e r n e t z t e A r f i o n e n a u s t a u s c h e r A m b e r l y s t A - z 9 verwertdet. D i e E l e m e n t e in dert urltersuchten O x i d a t i o n s s t u f e n w e r d e n auf Grund ihres I o n e n a u s t a u s c h verhalterts klassifiziert. D e r Grad, m i t w e l c h e m eine I o n e n a r t v o m I o n e n a u s t a u s c h e r harz absorbiert wird, h/ingt davort ab, ob sie in einer A n i o n e n f o r m e x i s t i e r t und ob sie h y d r a t i s i e r t ist oder \ V a s s e r s t o f f b r ~ c k e n mit d e m Wasser irt der w,tssrigen L 6 s u n g bildet. Wenrt auch das Arbeitert mit H y d r o x i d - L 6 s u n g e r t einige p r a k t i s c h e P r o b l e m e stellt, k 6 n n e n doch die z i e m l i c h grossert Urtterschiede i~l den V e r t e i l u n g s k o e f f i z i e n t e n ffir die verschiederlen Iorlengruppen a n a l y t i s c h v o n N u t z e n sein. REFEREI~CES I K . A. KRAUS AND F . "NELSON, Proc. II~teru. Co~f. Peaceful Uses At. Energy, Geneva, 1955, 7 (t956) I t 3 . 2 J . P . 17ARIS, H n a l . Chem., 32 (196o) 520. 3 J-l~- ]FARIS AND l{.. F . ]~UCHANAN, A n a l . Chem., 36 (1964) I t 5 7 . 4 F . •V. E . STII.ELO~.V AND C. j . c . I~OTHMA, A n a l . Chem., 39 (1967) 595. 5 J . ]~.ORlC.Isclq, i n D . C. ST'I~,VART AND H . A . ELION, Progress in N u c l e a r Energy, S e r i e s I X , l:~ergamon l:'ross, O x f o r d , t 9 6 6 , V'ol. 6, C h a p t e r 1. 6 S. A. FISHER AND V. ~'V. M~LOCtIE, A~ral. Chem., 24 (~952) t ~oo. 7 N. F . H A L L AND D . H . J o N ] t . s , J . A m . Chem. See., 75 (1953) 5787 • 8 H . OKUNO, M. HONDO' AND T. [SHIMORI, J a p a u A n a l y s t , 4 (1955) 386. 9 C. EGEIt AND J . L I P K E , A n a l . Chim. Acta., 2o (t959) 5.t8. i o M. L . GOOD, M . B . P U R D V AND T. H . I-IoEreING, J . [norg. 65, Nttcl. Chem., 6 ( t 9 5 8 ) 73. xr T. S U z u K I , J . Chem. Soc. J a p a n , Pure Chem. Sect. ( N i p p o ~ K a g a k u Z a s s h i ) , 82 (I96x 696. 12 A.. IGUCHI, 13ull. ~ h e m . Soc..]apart, 31 ( t 9 5 8 ) 748. 13 I{. TAKIURA AND Y. TAKINO, Japa$~ A n a l y s t , i o (1961) 483, 488, 493. 14 Amberlyst A-29 Technical Bttlleti,~, ]~.ohm a n d H a a s , I J h i l a d e l p h i a , I-'a., x967. x 5 R . ]q.UNIN', Io*~ Exchange Resi,zs, J o h n W i l e y , l ~ e w Y o r k , 1958, p. 34 t. 16 l{. T. OV'~RMAN AND H . t~I. CLARK, Radioisotope Tech~iques, M c G r a . w - H i l l , l'¢ew Y o r k I 9 6 o . x7 Analytical ~[ethods f o r ,'ltomi¢ ,,Ibsorpti0n Spectrophotometry, P e . r k i n - E l m e r , 2q'orwalk, C o n n . , t968. 18 J. J. LINGAN:E;, .'trial. Chem., 39 (1967) 8 8 I . i 9 [~[. J . ~BACZLIK AND R. J . DOBOlS, A,gal. Chem., ,to (1968) 685. 20 I{. U. H I R S C l t AND J . D . PORTOCK, A n a l . Letters, 2 ( t 9 6 9 ) 295. 2 I A. 1. VOGEL, Quantitative lnorg(odc ,4,~alysis, Johtx W i l e y , iN'ew Y o r k , x961. "2-2 H . R. G'RAD~2", i n I. M. KOL'rHOt~F AND P . J . ELVING, Treatise o1~ AnalyMcal Chetvistry, J o h n W i l c y - I n t e r s c i c n c o , I'~ew Y o r k , t 9 6 3 , Pa.rt: I I , V o l . 8, p. 2.26. 25 2:967 Book of A S T M Standards. A S T M , P h i l a d e l p h i a , P a . , 1967, V o l . 32, p. t 6 7 . 24 R. BASTIAN, R. ~,VEBERLING AND F. "PALILLA, A*zal. Chem., 29 ( r 9 5 7 ) t795. 25 R . i . DIAI~IOND ANt) D . C. WI-IITN:~.Y, i n J . A . 3'IARINSKY. [o*~ Excha~ge, Mttrcel D e k k e r , [rtc., N e w Y o r k , ~966, V o l . 1, C h a p t e r 8.
A n a l . Chim. Acta, 49 (197o) 4 7 3 - 4 7 9