This article was downloaded by: [York University Libraries]On: 10 August 2014, At: 12:34Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Solvent Extraction and Ion ExchangePublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/lsei20

Lamellar Inorganic Ion Exchangers. H+/M2+ (M=Ca,Cu) Ion Exchange in γ-Titanium Phosphate by UsingAcetate Salts.Celia Alvarez a , Ricardo Llavona a , Josè R. Garcia a , Marta Suàrez a & Julio Rodrìguez aa Departamento de Quimica Inorgànica. Facultad de Quìmica , Universidad de Oviedo ,OVIEDO, SPAINPublished online: 12 Mar 2007.

To cite this article: Celia Alvarez , Ricardo Llavona , Josè R. Garcia , Marta Suàrez & Julio Rodrìguez (1986) LamellarInorganic Ion Exchangers. H+/M2+ (M=Ca, Cu) Ion Exchange in γ-Titanium Phosphate by Using Acetate Salts., Solvent Extractionand Ion Exchange, 4:6, 1209-1222, DOI: 10.1080/07366298608917919

To link to this article: http://dx.doi.org/10.1080/07366298608917919

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

SOLVENT EXTRACTION AND I O N EXCHANGE, 4 ( 6 ) , 1 2 0 9 - 1 2 2 2 ( 1 9 8 6 )

Lamellar Inorganic Ion Exchangers.

H+/M~+ (M=Ca.Cu) Ion Exchange in

r-Titanium Phosphate by Using Acetate Salts.

Celia Alvarez, Ricardo Llavona, Jose R. Garcia

Marta SuLrez and Julio Rodriguez*

Departamento de Quimica Inorghica. Facultad de

Quimica. Universidad de Oviedo. OVIEDO. SPAIN.

ABSTRACT

Exchange isotherms and pH curves at 25.0, 40.0,

55.0 and 80.0•‹C are obtained. The hydrolysis degree

and the amount of metallic phosphate precipitated are

determined. The evolution of the solids is followed by

X-ray diffraction. The substitution increases with

temperature, reaching at 80.0•‹C the 70% (ca2+) and the

90% (cu2+). The results are compared with those

obtained by using (CaC12 + HC1). (CaC12 + Ca(OH)2) or

(CuS04 + H2S04) solutions.

INTRODUCTION

Crystalline forms of the titanium bis (monohy-

drogen orthophosphate) show lamellar structure and ion

Copyright @ 1986 by Marcel Dekker, lnc. 0736-6299/86/0406-1209$3.50/0

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

1210 ALVAREZ E T A L .

exchange p r o p e r t i e s ( 1 - 5 ) . Y - T i p h a s a b a s a l s p a c i n g

o f 11.6A ( 6 ) and m o n o c l i n i c symmetry w i t h t h e l a t t i c e

p a r a m e t e r s : a = 5 . 2 9 , b=6 .44 , c=23.948, and 6 =103 .g0 ( 7 ) .

When t h e b e h a v i o u r o f i o n exchange m a t e r i a l s

t owards a l k a l i n e e a r t h c a t i o n s o f f i r s t row t r a n s i t i o n

m e t a l s i s s t u d i e d , t h e a t t a i n m e n t o f h i g h s u b s t i t u t e d

p h a s e s is u s u a l l y d i f f i c u l t as a consequence o f t h e

low s o l u b i l i t y o f t h e h y d r o x i d e s o f t h e s e e l e m e n t s and

t h e p r e s e n c e o f h y d r o l y s i s r e a c t i o n s which mask t h e

i o n exchange r e s u l t s ( 8 - 1 2 ) .

I n o r d e r t o a v o i d t h e p r e c i p i t a t i o n o f m e t a l l i c

p h o s p h a t e s , C l e a r f i e l d and Hagiwara ( 1 3 ) have u s e d i n

t h e exchange o f a l k a l i n e e a r t h c a t i o n s i n a -ZrP

s o l u t i o n s o f m e t a l l i c a c e t a t e s . I n t h i s p a p e r t h e

b e h a v i o u r o f Y - t i t a n i u m p h o s p h a t e i n t h e H + / M ~ +

(M=Ca,Cu) i o n exchange is d e s c r i b e d when M(CH3-C00)2

s o l u t i o n s a r e u s e d . For t h e s a k e o f b r e v i t y t h e

v a r i o u s i o n i c fo rms a r e s i m p l y i n d i c a t e d by t h e i r

c o u n t e r i o n s ( u n d e r a b a r ) and w a t e r c o n t e n t w h i l e t h e

i n t e r l a y e r d i s t a n c e s a r e r e p o r t e d i n p a r e n t h e s e s .

EXPERIMENTAL

Reagents. A l l c h e m i c a l s used were o f r e a g e n t g r a d e .

The y-Tip w a s o b t a i n e d by u s i n g 16.5M H3P04 and r e f l u x

t i m e o f 1 0 d a y s as p r e v i o u s l y d e s c r i b e d ( 1 4 ) .

Analytical Procedures. pH-measurements were made i n a

C r i s o n model 501 pH-meter e q u i p p e d w i t h g l a s s and

s a t u r a t e d c a l o m e l e l e c t r o d e s . The r e l e a s e d p h o s p h a t e

g r o u p s were measured s p e c t r o p h o t o m e t c i c a l l y ( 1 5 ) u s i n g

a P e r k i n Elmer , model 200. Calc ium i o n s i n s o l u t i o n

were d e t e r m i n e d c o m p l e x o m e t r i c a l l y by a d d i t i o n o f EDTA

( 1 6 ) and by a tomic a b s o r p t i o n s p e c t r o s c o p y i n a P e r k i n

Elmer model 372. Cu i o n s i n s o l u t i o n were d e t e r m i n e d

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

LAMELLAR INORGANIC I O N EXCHANGERS

FIGURE 1.- H+/M'+ exchange isotherms at 25.0 (0). 40.0 (0). 55.0 (v) and 80.0•‹C (a): M=Ca (a) and M=Cu (b).

iodometrically (16) and by differential pulse polaro-

graphy using a Metron model E-506. The diffractometer

used was a Philips model PV 1050/23 (A=1.5418&, 28

scan rate 0.125-2 deg/min, chart speed 2cm/min).

Ion Exchange Studies. The exchanger was equilibrated

with M(CH3-C00)2 (M=Ca,Cu) solutions at 25.0, 40.0,

55.0 and 80.0•‹C following the procedure described by

Clearfield et a1.(17). The solid was present in the

solution in an approximate -ratio of 400mL:lg (M=Ca) or

250mL:lg (M=Cu). Equilibration time was 48 hours.

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

ALVAREZ ET AL.

FIGURE 2.- H + / M ~ + p H curves at ' 25.0 (0) , 40.0 (0) , 55.0 (v) and 80.0•‹C (e ) : M=Ca (a) and M=Cu (b).

RESULTS

H + / M ~ + exchange i so the rms a r e p l o t t e d i n Figu-

r e 1. It is seen t h a t t h e r e t e n t i o n i n c r e a s e s wi th t h e

working tempera ture , be ing p r a c t i c a l l y q u a n t i t a t i v e

under 1 . 5 (M=Ca) and 3.0 meq/gy-Tip (M=Cu). The las t

pH o f t h e s o l u t i o n s is p l o t t e d i n F igure 2.

During t he i on exchange p roces s a smal l hydroly-

sis of t h e Y-Tip, i n c r e a s i n g a s t h e same time as

tempera ture , t a k e s p l a c e . The rnaximun v a l u e s reached

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

LAMELLAR INORGANIC ION EXCHANGERS 1213

i n t h e sys tems s t u d i e d a r e c l o s e t o 5% when t h e

t empera tu re i s 80.0•‹C. A t 25.0•‹C t h e h y d r o l y s i s i s

61.5%. Small amounts o f p r e c i p i t a t e d m e t a l l i c phospha-

t e a r e d e t e c t e d from t h e a n a l y s i s o f t h e phosphate

g roups i n t h e e q u i l i b r i u m s o l u t i o n s and from t h e

a n a l y s i s o b t a i n e d when H C 1 is added (pH=l ) ( 1 8 ) . By

c a l c u l a t i n g t h e h y d r o l y s i s and t h e phosphate p r e c i p i -

t a t i o n ( 1 9 ) i t i s p o s s i b l e t o r e f e r t h e d a t a p l o t t e d

i n F i g u r e 1 t o t h e p e r c e n t a g e o f exchange w i t h r e s p e c t

t o t h e non hydrolyzed Y-Tip ( F i g . 3 ) .

X-ray p a t t e r n s o f some of t h e most s i g n i f i c a n t

samples s t a b i l i z e d i n a i r a t room tempera tu re a r e

shown i n F i g u r e s 4 and 5 . The r e f l e c t i o n s at 13.18.

(M=Ca) and 12.48. (M=Cu) cor respond t o t h e i n t e r l a y e r

d i s t a n c e o f a new c r y s t a l l i n e phases which i n t e n s i t y

i n c r e a s e s when t h e s u b s t i t u t i o n p r o g r e s s e s . A d e t a i l e d

s t u d y o f t h e zone o f t h e i n t e r l a y e r d i s t a n c e a l l o w s u s

t o e v a l u a t e (by c u t t i n g o u t t h e peak a r e a s and

weighing them) t h e r e l a t i v e i n t e n s i t y of t h e r e f l e c -

t i o n s cor responding t o t h e exchange phases w i t h

r e s p e c t t o t h a t o f t h e x . 2 ~ ~ 0 (11.68.) phase ( F i g . 6 ) .

DISCUSSION

Calcium ion exchange. I n t h e s t u d y o f t h e H + / c ~ 2+

system i n Y-Tip by u s i n g (CaC12 + H C 1 ) o r (CaC12 + Ca(OH)2) s o l u t i o n s , two phases a r e observed i n t h e

f i r s t s t a g e of t h e exchange (from 0 t o 35-37.5%

s u b s t i t u t i o n ) : t h e i n i t i a l phase FTFi. 2H20 (11.6A) and

an exchange phase w i t h i n t e r l a y e r d i s t a n c e o f

13.1-13.48. 1 9 ) . Higher c o n v e r s i o n s , even s a t u r a -

t i o n , a r e reached wi thou t l a r g e m o d i f i c a t i o n i n t h e

i n t e r l a y e r d i s t a n c e o f t h e s o l i d . The p r o c e s s can be

schemat ized as:

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

ALVAREZ ET AL.

70

60

50

40

30

20

10 Z 0 V) a 9 90 -.-.-.-a Z 8 80

' 70 v - v - - v - v - v -

60 o+~-o-o-o-o-

50 -0-0-0-0-0-04-

LO

30

20

10

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2

M ~ ' ADDED (rneqlg &Tip)

FIGURE 3 . - H+/M*+ exchange isotherms corrected by the hydrolysis e f f e c t at 25.0 (0). 40.0 (0). 55.0 ( v ) and 80.0•‹C ( 0 ) : M=Ca ( a ) and M=Cu ( b ) .

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

LAMELLAR INORGANIC ION EXCHANGERS

ANGLE , 2 8

FIGURE 4.- X-ray patterns o f the H + / c ~ ~ + exchanged s o l i d s (T=80.0•‹C) dried i n a i r a t room temperature ( a ) and de ta i l ed study o f the zone of the inter layer distance (b).

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

ALVAREZ ET AL.

90% cS' A lLl LO 35 30 25 2 0 15 10 5 8.5 8 0 7.5 7.0 6.5 6.0

ANGLE, 2 6

FIGURE 5 . - X-ray patterns o f the H + / c u ~ + exchanged s o l i d s (T=80.0DC) d r i e d . i n a i r at room temperature (a) and detai led study o f the zone o f the inter layer distance (b).

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

LAMELLAR INORGANIC I O N EXCHANGERS

FIGURE 6.- Variation of the relatfve2)ntensity of the reflection corresponding to the H /M exchange phase against that of the E . 2 ~ ~ 0 (11.6A) phase when the solids are dried in air at room temperature: M=Ca (a) and M=Cu (b).

where x=0.35, y=0.15, X=Y=13.4, Z=13.0 from Alberti et

a1.(12) or x=0.375, y=0.125, X=Y=Z=13.1 from Alvarez

et a1.(19).

When calcium acetate solutions are used in ion

exchange experiments, conversions higher than 50% are

reached (Fig. 3). The reflection corresponding to the

Y-Tip does not desappear in the 35-37% conversion

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

1218 ALVAREZ ET AL.

r a n g e , be ing main ta ined a lmos t u n t i l t h e 50%. ( F i g s . 4

and 6 a ) .

The use of (CaC12+HC1) s o l u t i o n s l e a d s t o t h e

f o r m a t i o n o f an unique exchange phase: H1. 2sCa0. 37

3.5H20 ( l 3 . l A ) . Assuming t h a t t h e molar c o n c e n t r a t i o n

o f t h e c r y s t a l l i n e phases i n a mix ture i s a l i n e a r

f u n c t i o n o f t h e i r r e l a t i v e i n t e n s i t y i n X-ray d i f f r a c -

t i o n ( 2 0 , 2 1 ) t h e r a t i o o f p r o p o r t i o n a l i t y f a c t o r s o f

t h e two phases p r e s e n t i n samples d r i e d i n a i r i s

c a l c u l a t e d ( 1 9 ) : f H / f -=1.15. I n F i g u r e 6 a 1 2sCa0 37 Y -HH

t h e c o n t i n o u s l ine ' s r eparesen t t h e p l a c e o f t h e

e x p e r i m e n t a l p o i n t s i f o n l y a 37.5% s u b s t i t u t i o n phase

( l e f t l i n e ) o r 50% ( r i g h t l i n e ) w a s formed d u r i n g t h e

i o n exchange p r o c e s s i n a c e t a t e medium. I n t h e l a t t e r

c a s e , a s i m i l a r i t y between t h e behav iour a g a i n s t X-ray

d i f f r a c t i o n o f t h e 50% phase and t h e 37.5% phase is

assumed. The exper imenta l s i t u a t i o n is i n t e r m e d i a t e

between bo th assumpt ions s o t h a t t h e s imoul taneous

f o r m a t i o n of b o t h phases o c c u r s . Moreover, t h e

c o n s t a n t i n c r e a s e i n t h e pH when t h e exchange

p r o g r e s s e s ( F i g . 2 a ) seems t o i n d i c a t e t h e absence o f

a d e f i n i t e exchange p r o c e s s . The c o n v e r s i o n s h i g h e r

t h a n 50% might be a t t r i b u t e d t o t h e f o r m a t i o n o f

p h a s e s f u l l y s u b s t i t u t e d .

Copper ion exchange. When t h e H + / c u ~ + system i n Y-Tip

is s t u d i e d by u s i n g (CuS04+H2S04) ( 1 9 ) one o b s e r v e s

t h e c o e x i s t e n c e of t h e Y-Tip w i t h a h a l f exchanged

phase: H C U ~ . ~ . ~ . ~ H ~ O (12.4A). Using moderate concen-

t r a t i o n s of CuS04 s o l u t i o n s c o n v e r s i o n s h i g h e r t h a n

50% a r e n o t r eached . I n X-ray d i f f r a c t i o n , t h e r a t i o

o f t h e p r o p o r t i o n a l i t y f a c t o r s o f t h e two phases

p r e s e n t i n samples d r i e d i n a i r is fHr/f -=1.16. 0 . 5 Y -HH

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

LAMELLAR INORGANIC ION EXCHANGERS 1219

When s o l u t i o n s o f copper a c e t a t e a r e u s e d , t h e

s u b s t i t u t i o n reached i n c r e a s e s w i t h t h e working

t empera tu re from 53% a t 25.0•‹C u n t i l 90% a t 80.0•‹C

( F i g . 3 b ) . X-ray d i f f r a c t i o n ( F i g . 5 ) shows t h e

appearance o f a band at 12.48, cor responding t o t h e

i n t e r l a y e r d i s t a n c e o f a new c r y s t a l l i n e phase which

c o n c u r s w i t h t h e band d e t e c t e d when (CuS04+H2S04)

s o l u t i o n s a r e used. I n F i g u r e 6b, t h e r e l a t i v e

i n t e n s i t y o f t h i s r e f l e c t i o n w i t h r e s p e c t t o t h a t of

t h e y-Tip is p l o t t e d . The c o n t i n u o u s l i n e i n d i c a t e s

t h e p l a c e cor responding t o t h e e x p e r i m e n t a l p o i n t s i f

o n l y one phase o f 50% of c o n v e r s i o n was formed d u r i n g

t h e i o n exchange p r o c e s s . T h i s i s t h e s i t u a t i o n when

t h e working t e m p e r a t u r e s a r e 25.0 and 40.0•‹C. The

samples o b t a i n e d a t 55.0•‹C s l i g h t l y t end t o s h i f t

towards t h e r i g h t ( i n t h e p l o t t i n g ) . This t r e n d i s

v e r y s t r o n g e r a t 80.0•‹C. The t empera tu re f a c i l i t a t e s

t h e appearance of h i g h l y s u b s t i t u t e d p h a s e s which a r e

formed s i m o u l t a n e o u s l y t o t h e h a l f exchanged phase . It

might be expec ted t h a t t h e s u b s t i t u t i o n was completed

a t t h e b o i l i n g t empera tu re o f t h e s o l u t i o n . A t 80.0•‹C

t h e r e f l e c t i o n s cor responding t o t h e Y-Tip desappear

when t h e convers ion exceeds t h e 75%. X-ray p a t t e r n of

90% exchanged phases s t a b i l i z e d i n a i r is very similar

t o t h e cor responding t o t h e h a l f exchanged phase i n

t h e s e c o n d i t i o n s . The i n t e r l a y e r d i s t a n c e (12.4A)

remains u n a l t e r e d such as t h e r e s t of t h e r e f l e c t i o n s

excep t two: 2 .93 and 2.518, and two new r e f l e c t i o n s

which a p p e a r at 3 .08 and 2.88A.

The fo rmat ion of t h e h a l f exchanged phase is an

endothermic p r o c e s s (8H0=35.5 kJ mol - l ) ( 1 9 ) and as

might be expec ted t h e f o r m a t i o n o f t h e f u l l exchanged

phase w i l l be a more endothermic p r o c e s s because an

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

1220 ALVAREZ ET AL.

2+ . i n c r e a s e on t h e Cu c o n t e n t wi thout mod i f i ca t i on i n

t h e i n t e r l a y e r d i s t a n c e of t h e m a t e r i a l , l e a d s t o and

i n c r e a s e i n t h e r e p u l s i o n s t r e n g h t s . The i n c r e a s e i n

temperature w i l l f a c i l i t a t e t h e aproximat ion of t he

equ i l i b r i um c o n s t a n t s of bo th p roces se s which became

t o s imoul taneous ly be produced ( 2 2 ) .

The format ion of b u f f e r s o l u t i o n a l l ows t h e

v a l u e s of t he last pH ( F i g . 2b) t o be h i g h e r than

t hose of t h e equ i l i b r i um when (CuS04+H2S04) s o l u t i o n s

a r e used , t hus f a c i l i t a t i n g t h e i n c r e a s i n g of t he

exchange.

I n good agreement w i th C l e a r f i e l d and Hagiwara

( 1 3 ) appa ren t l y a c e t a t e i on is s u f f i c i e n t l y s t r o n g

base t o i n i t i a t e exchange and then main ta in p H v a l u e s

high enough t o ach ieve h igh metal l oad ings . From t h i s

f a c t , t h e use of m e t a l l i c a c e t a t e s o l u t i o n s wi thout

t h e a d d i t i o n of hydroxide which l e a d t o h igh hydroly-

sis of t h e exchanger is a d v i s a b l e when phases o f ' h igh

s u b s t i t u t i o n a r e r equ i r ed .

REFERENCES

1.- V . Veseley and V . Pekarek, T a l a n t a , 19, 219

(1972 ) .

2.- A. C l e a r f i e l d , G.H. Nancol las and R . H . B l e s s ing ,

Ion Exchange and Solven t E x t r a c t i o n , v o l . 5 , J.A.

Marinsky and Y . Marcus, Eds. , Marcel Dekker, New

York (1973) .

3 . - G . A l b e r t i and U . Cos t an t i no , J . Chromatogr.,

102 , 5 (1974) . - 4.- G . A l b e r t i , Acc. Chem. Res s . , 11, 163 (1978) .

5 . - Inorganic Ion Exchange M a t e r i a l s , A. C l e a r f i e l d ,

Ed., CRC P r e s s , Boca Ratbn, FL (1982) .

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

LAMELLAR INORGANIC I O N EXCHANGERS 1221

6.- S. Allulli, C. Ferragina, A. La Ginestra, M.A.

Massucci and N. Tomassini, J. Inorg. ~uc'l. Chem.,

39, 1043 (1977). - 7.- E. Kobayashi and S. Yamazaki, Bull. Chem. Soc.

Jpn., 56, 1632 (1983). 8.- G. Alberti, U. Costantino and M. Pelliccioni, J.

Inorg. Nucl. Chem., 35, 1327 (1973). 9.- A. Clearfield and Z. Djuric, J. Inorg. Nucl.

Chem., 41, 885 (1979).

10.- B.F. Alfonso, M. Suhrez, J.R. Garcia and J.

Rodriguez, Mat. Chem. Phys., 10, 393 (1984). 11.- A. Clearfield and J.M. Kalnins, J. Inorg. Nucl.

Chem., 40, 1933 (1978). 12.- G. Alberti, U. Costantino and M.L. Luciani, J.

Chromatogr., - 201, 175 (1980).

13.- A. Clearfield and H. Hagiwara, J. Inorg. Nucl.

Chem., 40, 907 (1978). 14.- R. Llavona, J.R. Garcia, M. Subrez and J.

Rodriguez, Thermochim. Acta, 86, 281 (1985). 15.- O.B. Michelsen, Anal. Chem., 9, 60 (1957). 16.- M. Kolthoff, E.B. Sandell, E.J. Meehan and S.

Bruckenstein, Quantitative Chemical Analysis,

Nigar, Buenos Aires (1972).

17.- A. Clearfield, A. Oskarsson and C. Oskarsson, Ion

Exch. Membr., 1, 91 (1972). 18.- J.R. van Wazer, Phosphorus and its Compounds,

Interscience, New York (1958).

19.- C. Alvarez, R. Llavona, J.R. Garcia, M. Suhrez

and J. Rodriguez, in preparation.

20.- J.R. Garcia, M. Subrez, C.G. Guarido and J.

Rodriguez, Anal. Chem., 56, 193 (1984). 21.- R. Llavona, M. Sukrez, J.R. Garcia and J.

Rodriguez, Anal. Chem., 2, 547 (1986).

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014

1222 ALVAREZ ET AL.

2 2 . - M . Suhrez, J.R. Garcia and J . Rodriguez, J . Phys .

Chem., 88, 159 ( 1 9 8 4 ) .

R e c e i v e d by E d i t o r

A u g u s t 20, 1986

Dow

nloa

ded

by [

Yor

k U

nive

rsity

Lib

rari

es]

at 1

2:34

10

Aug

ust 2

014