Studies on Synthetic Inorganic Ion - ExchangeOand Ligand Exchangers

DISSBRTA'TION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS

FOR THE AWARD OF THE DEGREE OF

iHasiter of ^fjiloistopl)? IN

Chemistry

E 'Sd fe

BY

Tabassum Khan

'"vn->5,-*t^

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

ALIGARH (INDIA) March 1990

A . 2 * ' iM§^*

I*' - . . . . • • ! « K ^

. ^ • - j * ' *

1 4 NGv 1990

n'

DS1539

^agdidk ^ . ^awat M.SC' Ph.D.

READER IN CHEMISTRY

Ph. Office: 6515

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

ALIGARH-202002 INDIA

Dated

C E R T I F I C A T E

This is to certify that the work embodied in this

dissertation entitled "Studies on Synthetic Inorganic lon-

Exchangerg and Llgand Exchangers" is original, carried out

by Miss. Tabassum Khan under my supervision and is suitable

for submission for the award- of iVI.Phil. degree in Chemistry

of th is University.

(J.P. Rawat)

A C K N O W L E D G E M E N T

I wish t o express my deep sense of g r a t i t u d e and

indeb tedness t o Dr . J . P . Rawat f o r h i s e x c e l l e n t adv ice

and a b l e gu idance . He was a source of i n s p i r a t i o n

th roughout t h e e n t i r e cou r se of t h i s s t u d y .

I am very much thank fu l t o P rof , S.A.A. Z a i d i ,

Chairman, Department of Chemistry, Al iga rh Muslim

U n i v e r s i t y , Al igarh fo r p rov id ing me a l l r e s ea r ch

f a c i l i t i e s .

I a l s o wish t o thank my l a b c o l l e a g u e s Mis s . Archana

Agarwal, Mr. A. Aziz and my f r i e n d s Fabeha, Tauseef ,

Sangeeta D i d i , Arshad Bhai , Wasif Bha i , Di l shad and

Zubai r for t h e i r f r i e n d l y coope ra t ion throughoirt:.

Thanks a r e a l s o due t o Mr. H.S , Sharma, for t h e

t yp ing of t h i s work.

L a s t but not t h e l e a s t t o my dear p a r e n t s , b r o t h e r s

and s i s t e r s for t h e i r p a t i e n c e and s t i m u l a t i n g i n t e r e s t

in t h e p e r s u a l of my r e sea r ch endeavour .

(TABASStm KHAN)

C O N T E N T S

I . Acknov/ledaerttents

Page

I I . L i s t of Tab les 1 1

I I I , L i s t of F igu re s 111

IV. CHAPTER - I

Introduction

References

1

26

V. CHAPTER - I I

Mechanism of Exchange on Linde molecular s i e v e s (l3x)

I n t r o d u c t i o n

Experimental

Results

Discussion

References

33

34

37

56

66

LIST OF TABLES P a g e

T a b l e 1. I o n Exchange c a p a c i t y of L l n d e s i e v e

(13X) f o r a l k a l i n e e a r t h m e t a l i o n , 37

2+ 4-T a b l e 2 , I n t e r r u p t i o n t e s t f o r Mg -Na

exchange one L i n d e H o l e c u l a r s i e v e

(IBX) a t 2 5 ° + l ° C . 37

Table 3. u(t) and Bt values as a function of

time for Mg on Linde Molecular sieve

(13X) at different temperatures. 46

Table 4. u{t) and Bt values as a function of 2+ time for Sr on Linde Molecular

sieves (l3x) at different temperature. 50

Table 5. u(t) and Bt values as a function of 2+ time for Ca on Llnde Molecular sieves

(13X) at different temperature. 52

Table 6, u(t) and Bt values as a function of 2+ +

concentration for Mg -Na exchange on Linde Molecular sieve (l3x) at 25°+l°C. 54

Table 7, B values as a function of temperature

and concentration 59 2

Table 8, Value of Di (m /sec) of various ions

at different temperatures on Linde

Molecular sieves (13X), 61

Table 9, Diffusion coefficient, energy of

activation and entropy of activation

of m.igrating ions on Linde Molecular

sieves (l3x) in Na form 62

LIST OF FIGURES

Page

Figure 1. Effect of an interruption test on the 2+ +

rate of Mg -Na exchange on Linde

s i e v e s (13X)

2+ F i g u r e 2 . Rate of exchange of Mg a t d i f f e r e n t

t empe ra tu r e on Linde s i e v e (l3x)

2+ Figure 3, Rate of exchange of Sr at different

temperatures on Linde sieves (13X) 2+ Figure 4, Rate of exchange of Ca at different

temperatures on Linde sieves (13X)

Figure 5.. Effect of temperature on the rate of 2+ +

Mg -Na exchange on Linde sieve (l3x)

38

40

41

42

43

Figure 6,

Figure 7,

Figure 8.

Figure 9,

F i g u r e 10,

F i g u r e 11 ,

F i g u r e 12,

F i g u r e 13.

Ef fec t of t empera tu re on t h e r a t e of 2+ + Sr -Ma exchange on Linde s i e v e (l3x)

Ef fec t of t empera tu re on t h e r a t e of

Ca -Na exchange on Linde s i e v e (l3x)

I n f l u e n c e of c o n c e n t r a t i o n on t h e r a t e 2 -f- -I- o

of fig -Na exdiance a t 25 C on Linde s i e v e (l3xi ,

E f fec t of c o n c e n t r a t i o n on t h e r a t e of 2 4* -4-

Mg -Na exchange on Linde s i e v e s ( l3x)

P l o t of Bvs 1/C fo r Mg " a t 25°C,

o 2+

Log Do a g a i n s t l/T K for Mg •

Log Do a g a i n s t l / r°K for Ca " .

Log Do a g a i n s t l / r °K for Sr "*".

44

45

49

60

63

64

65

CHAPTER - I

I N T R O D U C T I O N

Now-a-days the ion-exchange has come to be recog­

nized as an extremely valuable ana ly t i ca l technique . All

over the world numerous p lan t s are in operat ion for deve­

loping the separat ions of inorganic , organic and b io ­

chemical mixtures . Nearly 140 yrs ago an English landowner

H.S, Thomas engaged an York analyst named Spence t o inves­

t i g a t e the l o s s of ammonia from manure heaps. He discovered

a technique fami l ia r to many of us for t r e a t i n g water by

process such as "Softening" and "high pur i ty condensate

po l i sh ing .

This discovery of calcium displacement by ammonia

using a na tu ra l ion-exchanger so i l was the beginning of

the technology

Ca(soil) + (NH ) QSO^ ' ( soi l ) NH + CaSO^

Spence reported h i s d iscover ies t o the Royal Agr icul tura l

Society in 1850, These were rapidly confirmed by another 2

ag r i cu l tu ra l chemist, G,T, Way , who described t h i s new phenomenon as "base exchange".

I t was Way who included the f i r s t synthet ic alumino

s i l i c a t e ion-exchanger. He l a i d down the foundation of

modern ion exchange theory and technology with remarkable

completeness. However i t was 50 yrs l a t e r , in 1905, t h a t 3

Cans in Germany softened water on an i n d u s t r i a l scale

•2

using a natural or synthetic aluminosilicate material called

zeolite. The Gans* patents were used universally during the

next 30 yrs.

In 19 34 two new types of materials were invented.

The first was a sulphonated.coal developed in Germany and

the second was a phenol-formaldehyde invented by Adams

and Holmes at the national physical laboratories in England.

The virtually simultaneous development of relatively stable

synthetic cation and anion exchangers made the deminera-

lisation process possible. This has since became the most

used and important application of ion-exchange.

The material produced by Adams & Holmes, though

relatively unstable by today* s standards, found considera­

ble industrial applications. Progress was so rapid that the

first industrial scale demineralisation plant in the world

was built in Great Britain by 19 37,

4 There followed the separate D'Alelio and McBurney

inventions of sulphonated crosslinked polystyrene cation

exchangers and the corresponding aminated polymeric anion-

exchangers. Thus very highly stable, cross-linked polymers

were used for the past 45 yrs. While active research into

new materials occupies resin manufacturers and the univer­

sities, there are no signs that polystyrene based polymers

will be replaced in the forseable future. The polymeric

ion exchangers which are commercially available are based

mainly on cross-linked polystyrene, A limited number of

acrylic based resins are used for specific applications.

Gans recognized the practical utility of the ion-

exchange phenomenon for water softening using natural and

synthetic zeolites and clays, A close identification of

the ion exchange properties of soils with clay fractions

has been achieved. Other alumino silicates may confer ion-

exchange properties in certain soils e.g. glauconite, a

ferrous aluminosilicate analogous to the zeolites, posse­

sses exchangeable potassium with considerable capacity.

General formula for the synthetic aluminosilicate can be

written as:

Na20. AI2O3, nSi03

where n = 1-12

Gallium and Germanium analogs have been prepared

5 e.g. gallogermanate and aluminogermanate silicates of

6 ^.. . 7 , . .,8 ^ .9 ^ . 10 V, zirconium , titanium , bismuth , ferric and zinc have

also been prepared.

The clay minerals comprise a complex series of

aluminosilicate structure. The aluminosilicate back-bone

of the clays is composed of alternating, parallel, two

dimensional layers formed from silicate tetrahedra and

11 aluminate octahedra , The disposition of these layers

and the extent and nature of isomorphous substitution

f

within them determine to a great extent the chemical and

physical properties of the clay.

Exchange in clay minerals is non~stoichiometric

and the capacity may vary appreciably among minerals hav-

ipg similar structures but showing different degrees of

isomorphous substitution.

Limitations of zeolites and clays in their stabi­

lity in acids led to the discovery of some stable ion

12

exchange materials. In 19 31 Kullgren observed that

sulfite cellulose works as an ion-exchanger for the deter­

mination of copper. In 19 35 Adams & Holmes found ion-

exchange properties in crushed phonograph. This interesting discovery led the inventors to

the synthesis of organic ion exchange resins which had

13 much better properties • These resins were stable towards

acids and easy to handle. The structure can be varied as

desired, therefore the difficulties observed with zeolites

and clays were removed by introduction of resins. Since

then these organic ion exchangers have been used both in

laboratories and industries for separations, recoveries

of metals, deionization of water, concentration of electro­

lytes and elucidating the mechanism of a great many

14 reactions , The application of these ion-exchange resins

progressed so rapidly that the theory lagged behind and

could not follow the experiments.

The application of organic ion exchangers are also

limited under certain conditions i.e. they are unstable

in aqueous systems at high temperatures and in the pres-

cence of the ionizing radiations. Thus organic and inorganic

ion exchangers can be used complementary to each other.

There has been a revived interest in inorganic ion-exchan­

gers in recent decades, as they are unaffected by ionizing

radiations and are also insensitive to higher temperatures.

The structure of these inorganic ion exchangers, is stiff,

therefore they are more selective and suitable for the

separation of ions on the basis of their different sizes.

Being stable towards ionizing radiations, they can be used

advantageously in reactor technology. Inorganic ion exchange

membranes have been used recently because of their ability

to withstand higher temperatures and their high selectivity

for certain ions.

The selectivity of inorganic ion exchangers have

been utilized for the preparation of ion selective elect-

15 rodes , The ion selective electrodes have now became an

1 fi— 1 R

important tool for solving various analytical problems

In order to understand the applications and to

improve upon them, systematic and fundamental studies are

being persuaded on these materials. This new interest in

inorganic ion exchangers may be said to have begun in 1943,

19 It was shown by Boyd that columns containing finely

divided zirconium phosphate supported on silica wo©l

could be used to separate uranium and plutonium from

fission products by ion exchange process. In addition to

zirconium phosphate many other similar substances may be

prepared by oxides of element of group IV with more acidic

oxides of elements of group V and VI of the periodic table.

Inorganic ion exchangers also find applications in

20—21 21 22 the analysis of alloys and silicate rocks * sepa-

23 24 ration of metal from drugs ' and in the detection of

iron and molybdenum '

The inorganic ion exchangers have found numerous

important analytical applications as categorized below:

1. Water pollution control

2. Separation of one ion from the other on a small ion

exchanger

(a) Removal of interfering ions

(b) Possibility of group separation

(c) Purification of samples.

3. Ion exchange paper chromatographic separation

4. Electrophoresis

5. Ion exchange for gas chromatography

6. Solid state separations

7. Specific spot test

8, Use of ion exchange beads to locate the end point in

titration

9, Use of ion selective electrode

10, Standard solutions can De prepared

11, Formation constants of complexes can be determined

12, They can be used as acid and base catalysts.

The water pollution is increasing day by day. However,

the methods based on ion-exchange are becoming of promising

success when applied to this field.

Purification on a large scale can be made by passing

the sample solution through the ion exchanger beds which

take up certain materials in preference over others. The

exchanger bed can be regenerated into a suitable form by

27 conventional methods

Ion exchange has resolved the most difficult problem

in chemical tnalysis i.e. separation of typical components

having similar enough properties. Column chromatography is

valuable, since the substances separated are collected

quantitatively. Ion exchangers can separate the micro ( <( 1-

mg quantities) as well as the macro ( 1-g quantities)

samples. Because of the macro application, ion exchangers

can also be used on industrial scale. Ion exchange chroma­

tography has played an important role in the isolation and

identification for the concentration and extraction of the

28—33 most important metals and of the new transuranium elements

34 and has even been used for enrichment of isotopes / organic

substances such as amino acids / alcohol , carbonyl com-

37 pounds etc. have also been separated in ion-exchange

column. As far as practical applications are concerned,

organic resins/ are by far the most important ion exchangers.

The more recent application of ion exchange resin includes

the collection of Selenium(IV) ppb level of aluminium

40 pre concentration of Cobalt

Ion exchange have been used with success in food

industry. The ion processing of wine is commonly practised

by large manufacturers in the U.S.A. It is worth recording

that the use of strong acid cation exchange resins in the

H form and one in Na form produces a wine low in potassium,

while removing calcium responsible for instability, and at

the same time iron, copper and other undesirable metals are

conveniently reduced.

The use of weak acid cation resins for the removal

of permanent hardness (alkalinity) is practised by the

brewing industry (dealkalisation) for the production of

feed water suitable for "light beers", "bitter" and 'longer*.

The production of sweeteners highlights the versatility of

ion exchange in the processing of food.

No application of ion exchangers would be complete

without reference to the use of ion exchangers as carriers

for plant nutrients.

Thus after 140 yrs researchers are endeavouring to

utilise ion-exchange technology in the place where it was

originally discovered. Ion exchangers are broadly classi­

fied into

1. Natural Ion Exchangers

2. Synthetic Ion Exchangers

Of these synthetic ion exchangers are further classified

into

1. Synthetic organic ion exchangers

2, Synthetic inorganic ion exchangers

A large number of synthetic inorganic substances

has been described which exhibit ion-exchanging properties.

These materials may be divided into the following main

groupsJ

1. Hydrous oxides

2. Acidic salts of multivalent metals

3. Salts of heteropoly acids

4. Insoluble ferrocyanide

5. Synthetic aluminosilicates

6. Materials with chelating groups

7. Electron and Redox exchangers

10

8, Certain other substances e.g. synthetic apatites, sulphi­

des, alkaline earth sulphates.

During the last 20 yrs great progress has been made

in the development and study of the basic properties of

these materials.

Hydrous oxides;

The adsorptive properties of hydrous oxides, such as

alumina, silica and ferric oxide have been known for many

years and it has been established that the adsorption of

ion by them is presumably by ion exchange. In that sense

the hydrous oxides are of particular interest because most

of them can function both as cation and anion exchangers,

and under certain condition, both cation and anion exchange

can occur simultaneously. These substances are mostly ampho­

teric and there dissociation may be schematically represented

as follows:

M - OH ;;;; ' *" M**" + OH" (i)

M - OH ^ " M - 0 + H"*" ( i i )

(M r e p r e s e n t s c e n t r a l atom)

A l a r g e number of compounds of t h i s t y p e have been

41-43 s t u d i e d in r ecen t yea r s , some more e x t e n s i v e l y than

o t h e r s , wi th p a r t i c u l a r a t t e n t i o n t o deeper knowledge of

t h e adso rp t i on mechanism as wel l as t o t h e i r a p p l i c a t i o n in

11

c h e m i c a l p r o c e s s i n g of r a d i o a c t i v e m a t e r i a l s and i n w a t e r

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

Hydrous o x i d e s of b i v a l e n t m e t a l s :

2+ T h i s g roup of e x c h a n g e r s i n c l u d e s h y d r o x i d e s of Be ,

2+ 2+ Mg f Zn and t h e i r m i x t u r e s w i t h f e r r i c h y d r o x i d e s and

h y d r o u s a l u m i n a .

H y d r o u s o x i d e s of t e r v a l e n t m e t a l s :

T h e s o r p t i o n p r o p e r t i e s of p s e u d o m o r p h i c i o n h y d r o ­

x i d e s were s t u d i e d wi th r e s p e c t t o i t s i s o e l e c t r i c p o i n t ,

44 which was found a t pH 7 , 1 - 7 . 2 . A p p l i c a t i o n i n c l u d e t h e

45 46 f o l l o w i n g s e p a r a t i o n on h y d r o u s a l u m i n a C l - B r - I , Mo - T c /

S and P from w a s t e w a t e r # and some t h i n l a y e r c h r o -

. 50 m a t o g r a p h i c s e p a r a t i o n .

Hydrous o x i d e s of q u a d r i v a l e n t e l e m e n t s ;

A s y s t e m a t i c s t u d y h a s been made of t h e i o n - e x c h a n g e

p r o p e r t i e s of q u a d r i v a l e n t i o n o x i d e s such a s S iO^/ SnO_,

T i O p , ThOj* ' 2 ^ 2 ^ " ^ Mn02. S t a n n i c o x i d e h y d r o u s , s t a n n i c

o x i d e i s p r e p a r e d by t h e a c i d i f i c a t i o n of sodium s t a n n a t e

s o l u t i o n .

T i t a n i u m o x i d e : P r e p a r e d by mix ing t i t a n y l o x a l a t e o r T i c l 4

51 s o l u t i o n w i t h sodium h y d r o x i d e s ,

Thor ium o x i d e : P r e p a r e d by m i x i n g t h o r i u m n i t r a t e s o l u t i o n

52 w i t h a l k a l i ' s i n v a r i o u s i n i t i a l r a t i o of t h e r e a c t a n t s

2

Zirconium oxide: Prepared by mixing zirconium s a l t so lu t ions

with a l k a l i s .

M anganese dioxide; Prepared by mixing KMnO . and MnSo. solu-o 53 t i on at 90",

Hydrous oxides of quinquevalent and sexivalent metals:

1, Antimonic acid

2, Phospho antimonic acid

Acidic S a l t s of Multivalent Metals:

A wide range of compounds of t h i s type have been

described as ion exchangers. Among the metals s tudied have

zirconium, thorium, t i tan ium, cer ium(iv) , t i n ( I V ) , aluminium,

i r o n ( I I I ) , chromium(lll) , uranium(VI) e t c . and the anion

employed include phosphate, a rsenate , antimonate, vanadate,

molybdate, t ungs t a t e , t e l l u r a t e , s i l i c a t e , oxala te e t c .

Acidic s a l t s of quadrivalent metals:

These substances have been the most in t ens ive ly

studied group of synthet ic inorganic ion exchangers.

Zirconium s a l t s : Zirconium phosphate, a rsenate and antimonate,

zirconium molybdate and t u n g s t a t e .

Thorium s a l t s : Thorium molybdate, t i tanium s a l t s , cerium

s a l t s , s tannic s a l t s .

13

other Acidic S a l t s ; Chromiumphosphate, t r ipolyphosphate .

Stannous polyphosphate: Exhibits electron-exchange 5 4 3-f- •¥

proper t i e s , reducing l2# 5'e and Ag .

Z e o l i t e s : The sub j ec t of ion exchange in z e o l i t e s has

been studied for well over a hundred years mainly because

of the importance of z e o l i t e s in the chemistry of s o i l s .

Zeol i tes are hydrated a luminos i l ica te minerals d i s ­

covered in 1756 by c rons ted t . He observed t h a t the c r y s t a l s

of these minerals v i s i b l y l o s t water when heated, and

the re fo re he named them as zeo l i t e s (meaning b o i l i n g ' s t o n e s

in Greek), Later , i t was noticed t h a t z e o l i t e s possess the

p rope r t i e s of r eve r s ib le water l o s s , ion exchange and

sorpt ion of molecules d i f f e r e n t i a l l y . The s t r u c t u r a l

s tud ies showed tha t these m.aterial have three dimensional

s t r uc tu r e s containing Sio.& AlO. un i t s r e su l t i ng in a

h ighly porous framework. In ce r t a in minerals poros i ty was

even upto 50% of the t o t a l c rys t a l volume. The pores are

in the form of channels & cav i t i e s containing the mobile

ca t ions and water molecules which are responsible for t he

cat ion exchange and water losses r e spec t ive ly . The minerals

can be represented by the empirical formula.

M 2/nO.Al203. X 3102* ^ ^2°

Where n i s the cation valency, X ^ 2 and Y i s a function

of poros i ty R,M. Earrer has s tudied the fundamental aspects

of zeolite chemistry for over thirty years and contributed

greatly to our \inderstending of this subject.

In early 1940*s he suggested the catalytic activity

of zeolites and molecular sieves in various process used by

the petroleum refining industry. An interest was then

developed for the synthetic methods of preparing pure

zeolites.

Many synthetic species have been reported since the

discovery of well known synthetic species A, X and Y by the

workers at the tinion carbide laboratories.

Just prior to this discovery union carbide corpora­

tion, U.S.A., had developed a method for the production of

Linde Molecular sieves on a commercial basis.

These two factors have led to the virtual monopoly

in the use of zealites as catalysts in petroleum cracking.

In the production of specific catalysts ion exchange

processes are required. Much interest has therefore, deve­

loped in the structure, position of the cations and the

fundamental aspects of ion exchange in these materials.

Like the clays the zeolites possess a well defined

crystal structure. Depending upon the structure and type

of bonding, zeolites may exist as fibrous, lamellar or

rigid three dimensional structures. The third type with

covalent bonding in three dimensions has been extensively

l o

s tudied for i t s ion exchange proper t i es by Barrer and h i s

55

co-workers when the s t r uc tu r e of t he z e o l i t e s are exami­

ned in d e t a i l , i t i s seen t h a t polyhedra are stacked in

such a way tha t t he re are channels pene t ra t ing in to the

i n t e r i o r of the l a t t i c e . The channels may e i t h e r be i n t e r ­

sec t ing or non- in te rsec t ing , and they may e i the r pass

completely through the l a t t i c e or terminate within i t .

Within the l a t t i c e the re may also be approximately spher ica l

c a v i t i e s , which may be connected to the ex t e r io r by such

channels . Exchangeable ca t ions , non s t r u c t u r a l anions and

any water molecules are located within these c a v i t i e s .

The cations under go ion exchange i f a channel of

s u i t a b l e dimensions i s avai lable along which i t can diffuse

to the external so lu t ion , even then i t w i l l only exchange

with ions which themselves have a diameter compatible with

the channel diameter. Apart from s t r u c t u r a l considera t ions

t he ava i lab le space may be fur ther l imi ted by t h e prescence

of water molecule or of anions within the channels. The

z e o l i t e s can be used as molecular s i e v e s .

The porous s t ruc tu re of the z e o l i t e s makes i t poss i ­

b le to use them for the sorption of gases and vapours at

su i t ab l e temperatures provided t h a t t h e dimensions of

channel and cav i t i e s are su i t ab le owing to the r i g id s t r u c ­

t u r e and the ease with which the channel dimensions may be

1(}

varied by varying the ionic form of the zeolite, their

specificity towards gaseous absorption may be varied almost

56 at will . By careful choice of the particular zeolite and

of its cationic composition it is possible to effect a wide

range of chromatographic separations,

57 Barrer distinguished three categories of molecular

sieves according to the minimum diameters of the inter­

stitial channels. The development of linde molecular sieves

58 synthesised and studied by Breck and Barrer m recent

years has made it possible to use such process on an indus-

59 trial scale. Saha studied the use of natural and synthetic

zeolites for fractionation sorption and catalysis.

Ion sieve properties can arise in zeolite either

because channel diameters.-are too small to permit the

passage of certain cations, or because v?hen the cations

concerned are above a certain size, the cavity dimensions

are inadequate to accomodate the number of cations corres­

ponding to the number of available exchange sites. In either

case the zeolite tends to behave as a semipermeable memb­

rane, and very clean separation may be possible between

certain pairs of ions, Barrer studied the separation of

Cs from other alkali metals by the ion sieve action of

analcite.

1/

Zeol i tes in H form can not be prepared by treatment

of the z e o l i t e with acid s ince the anionic framework i s

chemically \instable and breaks down with the p r e c i p i t a t i o n

of hydrated s i l i c a , leaving aluminixim in so lu t ion . For

t h i s purpose, s i l v e r ana l c i t e i s t r e a t e d with an aqueous

so lu t ion of t he ha l ide of a cat ion which i s too long to

enter t he s t r u c t u r e .

Ag X + M"*" + Hal" + H2O A ^ a l 4 + M"*" + OH" + KX

The solution must contain no cations vAiich can enter the

lattice and in addition the cations originally present in

the exchanger should form an insoluble compound with the

anion present in the solution.

Selectivity in the zeolites has been studied by

Barrer . In the absence of extreme effects due to ion

sieve action, the zeolites display marked selectivity

towards certain ions due to differing thermodynamic affini­

ties. The affinity varies rather unpredictably and is

strongly dependant in some cases on the cationic composi­

tion of the exchanger.

The reason for these striking selectivity patterns

are not yet established, still, use may be made of them in

a number of instances. Basic sodalites can be used under

suitable condition for the recovery of silver in quantita­

tive analysis, whil^ the mineral clinoptilolite may be

18

employed to remove trace concentration of sodium and has

been tested as an absorbent for the treatment of low

activity radioactive waste solution

Now the preparation of zeolitic products has been

studied beginning with several basic ones. To investigate

calcium/magnesium ion exchange the authors measured exchange

capacity before and after treatment. The exchange modifica­

tion was effected by transformation into other zeolitic

products. This was accomplished with concentrated solution

of sodium hydroxide and stirring. The basic substances used

were Tierrade lebrija, natural chabazite, kaoline and ben-

tonite.

Although ion-exchange molecular sieve zeolites play

key catalytic role in the petroleum industry'- hitherto there

has been no report of tin exchange in zeolite. But in recent

journals the ion exchange of alkyl tin cations into zeolites

y, L, sodium mordenite and hydrogen mordenite is reported

and it is shown that the resultant materials are catalytica-

lly active for the dehydration of penton-:!-ol.

The zeolites achieved importance only through their

catalytic application in petroleum cracking.

Now, uses are appearing as phosphate substitutes in

detergent builders, as fertilisers as soil conditioners and

as dietary supplents for catties.

19

A recent application of zeolite selectivity involves

the use of a synthetic ultramarine to separate the Francium

isotope Fr from its actiniiim parent and other activities

The highly charged cation ^^\c, " Th, -"- Po and ^'^'^Ph are

223 207 223 strongly absorbed, while Fr, Tl and Ra pass through the column and may subsequently be separated from each other.

In order to understand the analytical applications

and in order to improve upon them, systematic and fundamental

studies are being persued of these materials.

Ion exchange is a reversible, stoichiometric exchange

between the ions in the mobile liquid phase and the ion on

the exchange sites on the stationary phase.

The exchange of univalent ions may be represented by

the following equation

where R and S refer to the cation being in the resin phase

and solution phase respectively. Since the reaction reaches

the equilibrium position, an equilibrium expression in terms

of concentrations can be written as

' " MR M S

where the square brackets are for equilibrium concentrations.

The properties of ion exchanger, facilitates the

selection of the correct ion exchanger for a particular

9 u

problem. The more important properties are colour/ density,

mechanical strength, particle size, capacity, selectivity,

amount of cross-linking, swelling porosity surface area;

and chemical resistance.

Ion exchange capacity is one of the most fundamental

characterization of any ion exchange material. For a strong

ion exchanger, the capacity can readily be determined by

direct titration, various types of capacities can be expre­

ssed in different manners. Majority of the synthetic inor­

ganic ion exchangers behave as a weak ion-exchanger and,

therefore, the direct titration is not reliable. In this

case ion exchange capacity is determined by replacement of

hydrogen ions from the exchanger phase by the counter ions

of a neutral salt solution and equilibrium ion exchange

capacity is determined by pH titrations.

The ion exchange material must be studied for chemical

stability in acidic and basic media to check its limitations.

Separation of inorganic mixtures to a more or less

extent are based on one of the three different principles.

1, At low concentration the extent of exchanger is directly

proportional to the valency of the exchanging ion.

2, At constant valence the extent of exchange is directly

proportional to the atomic number at low concentration.

2i

3 . The ex t en t of exchange h i g h l y depends upon t h e forma­

t i o n of complexes.

D i s t r i b u t i o n c o e f f i c i e n t Kd may be de termined t o

c a l c u l a t e t h e s e p a r a t i o n f a c t o r which may be r ega rded as

a measure of p o s s i b l e s e p a r a t i o n ,

- 1 Amount of ion (A) P r e s e n t i n exchanger phase q Kd — —1

Amotint of ion (A) p r e s e n t i n s o l u t i o n phase ml

The gene ra l use of d i s t r i b u t i o n c o e f f i c i e n t i s made

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

which ions move in ion-exchange chromatography i s p ropor ­

t i o n a l t o 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 . I t i s a l s o

p o s s i b l e t o s e p a r a t e a t r a c e q u a n t i t y of a metal from a

macro amoiont of ano ther metal i o n .

Theory of ion exchange and t h e unde r ly ing mechanism

invo lved in t h e exchange p rocess can be under s tood by t h e

knowledge of thermodynamics and k i n e t i c s r e s p e c t i v e l y .

The thermodynamic s tudy i s t h e s tudy of chemical

e q u i l i b r i a , R e g o r o u s thermodynamics g ives an i n h e r e n t l y

a b s t r a c t t r e a t m e n t devoid of t h e mechanical or mic roscop ic

images which would l e a d one t o a f e e l i n g of g r e a t e r i n t i -fi 3

macy and understanding of the phenomena. Cans gave the

f i r s t quan t i t a t i ve formulation of ion exchange e q u i l i b r i a

using the law of mass action in i t s simplest form which 64 was extended by Kielland ,

22

The particular use of the thermodynamic equilibrium

constant is made to find out the free energy changes of

the ion exchange process, usually by the expression.

A F = - RT InKa

where AF is change in free energy, from the Ka values at

different temperatures, the enthalpy change in the system

may be evaluated.

Although thermodynamic studies of ion exchange

help in investigating the conditions at equilibrium, but

it does not provide with any information about the mecha­

nism of change from one state to the other and the time

required there on. The kinetics of exchange takes these

factors into consideration.

The kinetics depends on the surface area of the

ion exchange particles. Thus vhere diffusion rate of kine­

tics are of importance, particle size and macroporosity

of the exchanger became important parameters. The kinetics

of a simple homogeneous chemical reaction is governed by

their differential rate of reaction depending on the dis­

appearance of product or formation of reactant with time,

A X + B Y ^ Product

Rate = K. X^. y^

where K is the rate constant and (X) and (Y) are the

concentrations of reacting species. The power A and B

23

are the orders of the reaction with respect to X and Y

respectively.

Ion exchange Kinetics involve three types of

processes,

1, Interdiffusion of counter ions in the adherent film.

2, Interdiffusion of counter ions with in the ion

exchanger particles themselves, and

3, Chemical exchange reaction.

I t i s important to note t h a t of a l l the s tud ies on

ion exchange k ine t i c s which have appeared in the l i t e r a ­

t u r e to date , none of them has been shown by chemical

exchange r e a c t i o n s .

65 Nachod and Wood made the f i r s t ser ious attempt

on the k ine t i c s tudies of ion exchange. They s tudied the

react ion r a t e with which ions from solut ion are removed

by the so l id ion exchanger or conversely t he r a t e with

which the exchangeable ions are re leased from the exchan-fifi

ger . Later on Boyd, et, a l . s tudied k ine t i c s of metal

ions on the res in beads and gave a c l ea r understanding

about the p a r t i c l e and film diffusion phenomena which

govern the ion exchange.

en Reichenberg confirmed that at a concentration

the rate independant of ingoing ion (particle diffusion

+ + control). Kancollas studitd the kinetics of Na - H

exchange on crystalline zirconium phosphate.

24

C o n s t a n t i n o , et,. a l . h a v e s t u d i e d t h e s e l f d i f f u -

s i o n of Na and K i o n s on m i c r o c r y s t a l s of Zr(NaHPC^) .3H2O

and Zr(KPO^) • 3H2O and m o d i f i e d F i c k s e q u a t i o n t o t a k e

i n t o accoxint t h e n o n - u n i f o r m i t y of t h e p a r t i c l e s i z e .

Some work on k i n e t i c s h a s a l s o been done i n o u r

l a b o r a t o r i e s , A k i n e t i c s t u d y of exchange of c a t i o n s Ag ,

3+ 4+ a l k a l i n e e a r t h m e t a l s ^ Y , and Th was made on t a n t a l u m

a r s e n a t e •

Much of t h e k i n e t i c s t u d i e s h a v e a l s o been done on

69 t h e s y n t h e t i c o r g a n i c i o n exchange r e s i n s by J u n g e e t a l ,

, ^. 70 -73 and o t h e r s .

The v a r i o u s i n o r g a n i c i o n e x c h a n g e r s r e p o r t e d u p t o

74 1963 , h a v e been summarized by Amph le t t i n h i s c l a s s i c a l

book , " I n o r g a n i c I o n - E x c h a n g e r s " , The r e l e v a n t work from

1962 t o 1970 h a s been r e v i e w e d by P e k a r e k and V e s e l y .

M a r i n s k y h a s summar ized t h e t h e o r e t i c a l a s p e c t s of exchange

77 i n i n o r g a n i c i o n exchange m a t e r i a l s , The s y n t h e s i s and

i p p l i c a t i o n of i n o r g a n i c i o n e x c h a n g e r s h a v e b e e n r e v i e w e d

7R—83 by Wal ton ~ . R e c e n t r e v i e w s on t h e a p p l i c a t i o n of i o n

84 8S

exchange h a v e been e d i t e d by M a r i n s k y and Wal ton .

R e c e n t l i t e r a t u r e on t h e s e m a t e r i a l s h a s b e e n c o v e r e d by

c l e a r f i e l d i n h i s monograph i n 1982

To u n d e r s t a n d t h e mechanism of i o n e x c h a n g e on a

s y n t h e t i c z e a l i t e l i n d e s i e v e l 3 X by t h e k i n e t i c s t u d i e s

23

2+ 2+ 2+ +

f o r r a r e ea r th metal i o n s : Ca , Mg + Sr - Na exchange

sys t ems . The p a r t i c l e d i f f u s i o n c o n t r o l l e d mechanism i s

conf i rmed. The s t a n d a r d en tha lpy change ^ S a c t i v a t i o n

energy and o t h e r parameters a re de te rmined .

26

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CHAPTER - II

"MECHANISM OF EXCHANGE ON LINDE

MOLECULAR SIEVES (13X)

•5 3

INTRODUCTION

The study of kinetics of ion exchange ascertains the

use of possible rate laws the rate determining step and

mechanism of ion exchange process. Diffusion process plays

the main role in simple ion exchange systems rather than

chemical factors. Though kinetic studies were started much 1

e a r l i e r i n 1940's by Nachod & Wood then by Nan Col l as & 2

P a t e r s o n , s i n c e then much of t h e k i n e t i c work has been

done on i n o r g a n i c ion exchangers mainly z e o l i t e s . K i n e t i c s

of t h e vapour a d s o r p t i o n of Cn - C.^ n - a lkane and Cyclo-3

hexane on z e o l i t e (analogous t o ZMS 5) was i n v e s t i g a t e d by 4

dynamic p r o c e s s . Desorpt ion k i n e t i c s of Cg - C^^ a lkanes&

CgHg were s t u d i e d from z e o l i t e CaA and NaX, The k i n e t i c

s t u d i e s of oxygen s o r p t i o n of Ce ion was s t u d i e d on l i n d e

s i e v e s l3x , Ragimov e t , a l . s t u d i e d k i n e t i c s of c r y s t a ­

l l i z a t i o n and ion exchange p r o p e r t i e s of an L - D z e o l i t e , 7

Werl ing e t , a l , a p p l i e d t h e math model t o s tudy t h e k i n e t i c s

of a d s o r p t i o n and d e s o r p t i o n p roces s of 2 commercial molecular 8— 1 7

s i e v e s . S i m i l a r k i n e t i c s t u d i e s were done by o t h e r s " on

z e o l i t e s ,

2+ Th i s c h a p t e r dea l s with t h e k i n e t i c s t u d i e s of Mg ,

2+ 2+

Ca and Sr on Linde s i e v e s l 3 x . Experimental and t h e o r i -

t i c a l approaches have been used t o show t h e r a t e of d i f f u ­

s i on through t h e p a r t i c l e . Var ious parameters l i k e Do, Ea

and A S have a l s o been c a l c u l a t e d .

3'f

EXPERIMENTAL

Reagents and Chemicalst

Linde Adsorbents Molecular sieves (l3x) in Na form

supplied by union carbide corporation. All other chemicals

were of reagent grade.

Ion Exchange Capacity?

Exchange capacity for alkaline earth metal ions was

determined by titrimetric method. For this purpose 0.5 gm

of the exchanger was taken in a conical flask. To this

flask 50 ml of .05 molar solution of aqueous alkaline

earth metal nitrate was added and it was shaken for 48

hours at 25 + 1 C in a temperature controlled SICO shaker.

The supernatent liquid was titrated with 0.1 molar EDTA

solution for determining the metal ions left.

Surface Area:

Surface area of the exchanger was determined by the

method proposed by Dyal and Hendricks. For t h i s purpose

1.0 gm of the exchanger was taken in an aluminium boX, I t

was dr ied at 25 + 1 C in an a i r oven and kept in a dessi~

cator over Pn^S* ^ constant weight of t h i s dr ied sample

was recorded. After t ha t t he exchanger was r insed with

ethylene glycol drop wise with the help of p i p e t t e . Excess

of ethylene glycol was evaporated in an, a i r oven at

3a

60 + 1 C and kept in a dessicator. Weight of this sample

was recorded till a constant value. The surface area was

calculated by using the formula.

Wt. of ethylene glycol retained by exchanger (g)

Surface area = VJt. of unhydrated dried exchanger x

.00031 KINETIC MEASUREMENTS;

Conditions approaching infinite bath technique were

used to perform the kinetic measurement linde sieves with

particles of mean radii .000125 meters were used unless

stated other wise. 50 ml fractions of the metal ion 2+ 2+ 2+ solution ( Mg • •, Ca and Sr ) were shaken with 500 mg of

the exchanger in Na form in several stoppered conical

flasks at the desired temperatures (25°, 45°, 65° and 5°C)

for different time intervals, Supernatent liquid was

immediately removed and analyzed for its metal ion content.

The alkaline earths v;ere determined by titrating with EHI'A

using Eriochrome black T as an indicator.

INTERRUPTION TEST;

For performinc interruption test eleven stoppered

2+

conical f lask v/ere taken. In each f lask 50 ml Mg solut ion

was taken and thermostated at room temperature (25 C) . To

each f lask ,5 g of exchanger was added and a f t e r the

speci f ic t ime in te rva l the solut ion was separated from the

exchanger beads. The f i r s t reading was taken af te r 2 minutes

36

After a specified time (40 min) , the exchanger particles

were removed and quickly separated from the adhering

solution. After a 10 min break they were reimmersed in

their respective solutions and the experiment continued.

The Mg content in the supernatent solution was deter­

mined at various time intervals again.

RESULTS

The r e s u l t s of ion ejtchange c a p a c i t y of Linde s i e v e (13X)

fo r a l k a l i n e ea r th metal ion a re summarized in T a b l e 1.

T a b l e 1. Ion exchange c a p a c i t y of Linde s i e v e (13X)

Metal ion Taken as Capac i ty meq/g

M g "*• nitrate 1.2

Ca "*" n i t r a t e 2.2

Sr n i t r a t e 4 ,0

I n t e r r u p t i o n T e s t ;

2+ +

I n t e r r u p t i o n t e s t was performed fo r Mg - Na

exchange on Linde s i e v e s (13X) in Na form. The u ( t )

( f r a c t i o n a l a t t a i n m e n t of equ i l ib r ium) v a l u e s as a func­

t i o n of t ime b e f o r e and a f t e r i n t e r r u p t i o n of 10 minutes

a t 25 + 1 C a r e g iven in t a b l e 2 and a r e p l o t t e d in F i g , 1, 2+ +

T a b l e 2 , I n t e r r u p t i o n T e s t for Mg - Na exchange on

Linde Molecular s i e v e s ( l3x) a t 25°+ 1°C

S,No. Time (minutes) u (t)

1 2 0.2765

2 5 0.2978

3 10 0.4680

4 20 0.5950

5 40 0.6808

-g 38

o 00

LJU

< I

X UJ

1 <r> O

t c

i o

1 CO

O

1 c

o

1 vo

o

1

in

O

1 -4-O

. •

n O

(NJ

6 o

-

o • ( ^

o vo

o 1/1

o

o

O

o

c

E

E

+ rsi en S L L O UJ J —

<

LU

i—

2 O 2 O (— CL

cc: cr LU • t - X Z en * — - 1 * —

Z I/) < UJ u. > o y I - I/)

UJ -J

o u.

( ; ) T i

39

S.No. Time (minutes) u ( t )

10 Minutes I n t e r r u p t i o n

6 0 0.6808

7 10 0 .8290

8 20 0.9000

9 40 0.9140

10 60 0.9140

11 80 0.9140

Ef fec t of t empera tu re t

I n o r d e r t o see t h e e f f e c t of t e m p e r a t u r e t h e

2+ 2+ 2+

k i n e t i c s was performed for Mg , Ca and Sr a t four

d i f f e r e n t t empera tu re s v i z . 5 , 25 , 45 and 65 + 1 C.

u ( t ) v a l u e s as a func t ion of t ime a r e c a l c u l a t e d and t h e 1 8

cor responding Bt va lues a r e taken as t a b u l a t e d by Reichenberg

The r e s u l t s a r e given i n t a b l e 3 , 4 and 5 . The r e s u l t s of

u ( t ) Vs t ime a t d i f f e r e n t t empera tures f o r t h e above

mentioned c a t i o n s a re p l o t t e d in F i g , 2^3 and 4 . While t h e

r e s u l t s of Bt Vs t ime a re p l o t t e d in F i g . 5,6 and 7 .

Ef fec t of C o n c e n t r a t i o n s :

2+ The d i f fu s ion s t u d i e s were perform.ed on Mg for

d i f f e r e n t c o n c e n t r a t i o n . The r e s u l t s of u ( t ) and Bt as

func t ion of d i f f e r e n t c o n c e n t r a t i o n a t 25 + 1 C a re given

/ • • " ,

140

Time (min )

FIG. 2. RATE OF EXCHANGE OF Mg2* AT DIFFERENT TEMPERATURE ON LINDE SIEVE 13 X .

4i

20 30 40 50 60 70 80 90 100 HO 120 »30

Time {m i r )

FIG.3. RATE OF EXCHANGE OF S r 2 * AT DIFFERENT TEMPERATURE ON LINDE SIEVES 13 X .

iZ

20 30 40 50 60 70 80 90 100 110 120 130 140

Time ( min )

FIG.4. RATE OF EXCHANGE OF Co^^AT DIFFERENT TEMPERATURE ON LINDE SIEVES 13 X .

43

X m

>

l/l

Q Z

z o UJ o z < X <J X LU

• o z

I +• (SI

u. o UJ

< a.

z o Q. 2 ui I —

LL

o t— o UJ u. u. u IT)

u.

^8

c £

a

X ro

(/) UJ > UJ

10

LJ Q Z

z o Ul o z < I X UJ • o z I

• rg

t -

(/) u. o LJ I — < cr LJJ

a U)

LL

o t -u UJ u. u. LU

o u.

;a

40

X en

CO UJ

> UJ 1/1

UJ Q

z

UJ o z < I CJ X UJ

+ o z

o

u. o UJ

< cc UJ

a s UJ

u. o

u. u. UJ

u.

;a

4B

in Table 6, The Et values as a function of time for Mg -Na

exchange at 25 + 1 C for five different concentration are

plotted in Fig, 9.

Table 3. u(t) and Bt values as a function of time for

2+ Mg on Linde Molecular sieve (13X) at different

temperatures

Time (min) u (t) Bt

Mg -Na exchange at 5 C

2

5

10

20

40

60

80

100

120

2

5

10

20

40

60

80

100

120

0 . 2 9 1

0 .236

0 .236

0 ,277

0 .236

0 .236

0 .380

0 .416

0 . 3 4 7

2+ + o Mg -Na e x c h a n g e a t 25 C

0 . 3 2 3

0 . 3 8 2

0 . 3 6 7

0 . 3 9 7

0 . 5 5 7

0 . 6 2 2

0 .470

0 . 4 70

0 . 7 2 0

0 .086

0 . 0 5 2

0 .052

0 . 0 7 3

0 .052

0 . 0 5 2

0 . 1 5 7

0 . 1 8 8

0 . 1 2 2

0 . 1 0 7

0 . 1 5 7

0 . 1 3 9

0 . 1 6 7

0 . 3 8 2

0 . 5 2 2

0 . 2 5 9

0 . 2 5 9

0 . 7 9 8

47

Time (min) u ( t ) Bt

Mg "'"-Na'*' e x c h a i g e a t 45°C

2 0 .229 0 .047

5 0 .163 0 .024

10 0 .475 0 .259

20 0 .475 0 .259

40 0 ,573 0 .419

60 0 . 6 9 1 0 . 7 0 3

80 0 . 7 2 1 0 . 7 9 0

100 0 .770 0 .985

120 0 .720 0 . 7 9 8

Mg -Na exchange a t 65°C

2 0 .186 0 .030

5 0 .254 0 .062

10 0 .525 0 .332

20 0 .356 0 .136

40 0.694 0 .703

60 0 .932 2 . 1 6 0

80 0 .805 1.126

100 0.864 1.450

120 0 .698 1.700

4S

i n

m ro

Z < X o X LU

c E

+ C7>

u, o LU I —

< cr iU

o 2 O

LL O

LU

LU D _ j

X

UJ > LU

(/)

LU Q

Z o o

CM

00

d r*

6 lO

6 in

6 V *

6 ro

6 rvj

6

00

o LL

( n n

45

c

e

z o UJ o z < I o X

+ o z

I

+ f M

o LJJ

< a: u X

z o

z o

X m

to O ixl

o t—

o LU L L

L L

LU

cn

O L L

> UJ

to

LU Q Z

>a

Tab le 4 , u ( t ) and Bt v a l u e s as a func t ion of t ime fo r 2+

Sr on Linde Molecular s i e v e s ( l3x) a t d i f f e r e n t t empera tu re

Time (min) u ( t ) Bt

Sr^'''-Na'*' exchange a t 5°C

2 0,265 0.067

5 0.278 0.073

10 0.278 0.073

20 0.367 0,1391

40 0.405 0.177

60 0.556 0.382

80 0.560 0.400

100 0.470 0.259

120 0.620 0.522

Sr^"*'-Na'^ exchange a t 25°C

2 0.09 0.007

5 0.196 0.034

10 0.33 0.114

20 0.409 0.177

40 0.651 0.5921

60 0.800 l.lOO

80 0.680 0,675

100 0.790 1.073

120 0,770 0,985

5i

Time (min) u ( t ) Bt

S r -Na exchange a t 45 C

2 0 .122 0 .013

5 0 .280 0 .079

10 0.350 0 .130

20 0.350 0.130

40 0 .438 0 .210

60 0.877 1 .540

80 0 .770 0 .985

100 0 .870 1 .500

120 0 .890 1 .700

S r -Na exchange a t 65 C

2 0.232 0 .052

5 0.214 0.042

10 0.66 0 0 .479

20 0 .571 0.419

40 0.66 0 0.620

60 0 .870 1 .521

80 0.84 0 1.34 0

100 0.84 0 1.34 0

120 0.946 2 . 3 2 0

52

T a b l e 5 , u ( t ) and Bt v a l u e s as a f u n c t i o n of t i m e f o r 2

Ca + on L i n d e M o l e c u l a r s i e v e s ( l 3 x ) a t

d i f f e r e n t t e m p e r a t u r e

Time (min) u ( t ) Bt

2+ + o Ca -Na exchange a t 5 C

0 . 2 9 1

0 . 2 9 1

0 . 3 7 5

0 . 2 9 1

0 .330

0 .4400

0 .5200

0 .4500

0 .472

0 . 0 8 6

0 . 0 8 6

0 . 1 4 8

0 . 0 8 6

0 .110

0 . 2 2 2

0 . 3 3 2

0 .232

0 .259

2

5

10

20

40

60

80

100

120

Ca -Na e x c h a n g e a t 25 C

2 0 .075 0 .0044

5 0 .139 0 .0156

10 0 .139 0 .0156

20 0 .236 0 .0520

40 0 .247 0 .0570

60 0 .550 0 .3820

80 0 .590 0 .4500

100 0 .450 0 .2340

120 0 .550 0 . 3 8 2 0

53

Time (min) u ( t ) Bt

Ca " '-Na" exchange a t 45°C

2 0 .420 0 . 1 9 9

5 0 .449 0 . 2 2 0

10 0 .420 0 .199

20 0 .550 0 .382

40 0 . 6 2 3 0 .522

60 0 . 6 8 1 0 . 6 7 5

80 0 . 6 8 1 0 , 6 7 5

100 0 .720 0 . 7 9 8

120 0 . 8 1 1 1.170

Ca ' '-Na"*" e x c h a n a e a t 65°C

2 0 .326 1.0760

5 0.134 0 .0156

10 0.364 0 . 1 3 9 1

20 0 .365 0 . 1 3 9 1

40 0 .730 0 .8320

60 0 .615 0 .5000

80 0 .85 1 .4000

100 1.00 OC

120 0 .923 2 . 0 3 0 0

54

T a b l e 6 , u ( t ) and Bt v a l u e s as f u n c t i o n of c o n c e n t r a t i o n

2+ + f o r Mg -Na e x c h a n g e on L i n d e M o l e c u l a r s i e v e

(13X) a t 25 + 1°C

Time (min) u ( t ) Bt

With c o n c e n t r a t i o n ,002 M

5 0 . 3 0 3 0 . 0 9 2

10 0 . 3 7 8 0 . 1 4 8

20 0 .530 0 . 3 4 8

40 0 .757 0 . 9 0 5

With c o n c e n t r a t i o n . 005 M

5 0 . 2 1 5 0 . 0 4 2

10 0 .359 0 . 1 3 0

20 0 . 4 4 1 0 .222

40 0 .503 0 . 3 0 1

With c o n c e n t r a t i o n , 0 1 M

5 0 .180 0 .030

10 0 .310 0 .099

20 0 .380 0 .157

40 0 .456 0 .234

With c o n c e n t r a t i o n . 02 M

5 0 . 1 5 1 0 . 0 2 1

10 0 .272 0 . 0 7 3

20 0 . 3 2 1 0 .107

40 9 . 3 9 1 0 .107

55

Time (min) u ( t ) Bt

With c o n c e n t r a t i o n .04 M

5 0.127 0.013

10 0.170 0.027

20 0.340 0.122

40 0.352 0.130

5S

DISCUSSION

From table 1 it is evident that the Linde sieve

l3x shows a considerable ion exchange capacity for

alkaline earth metal ions and varies from 1.2 to 4 1

meg g~ • The ion exchange capacity is in the order of

decreasing hydrated ionic radii of the alkaline earth

metal ions i.e.

Mg " <Ca^"^<.Sr^'^

The surface area of the Linde s ieve 13X determined

2 -1 by Dyal and Hendricks method was found t o be 483.87 m gm .

Rate of exchange s tudies show t h a t in t he beginn­

ing the r a t e of exchange increases and a f t e r sometime i t

becames constant ind ica t ing the attainment of steady

s t a t e .

19 According to Boyd et al. mainly two potential

diffusion processes are considered, "particle diffusion"

\%here the interdiffusion of counter ions takes place

within the ion exchanger itself and "film diffusion"

where the interdiffusion of the counter ion is in the

adherent film. Particle diffusion control (PDC) phenomenon

is favoured by high m.etal ion concentration, relatively

large particle size of the exchanger and vigorous shaking

of the exchanging mixtures under these conditions the

57

f rac t iona l attainment of equilibrixom with time i s given

by the following expression

u (t) = C - C ect

where C / C. and C^ are concentration of the ions in the

exchanger at time 0, t and infinite (i.e. at equilibrium)

The interruption test is the best experimental test

for distinguishing between particle and film diffusion

control • Thus this test was applied for Mg ions.

Results are summarized in table 2 and plotted in Fig, 1,

These results show an enhanced rate after 10 min of

interruption which indicates a momentery exchange rate

after reimmersion and hence the rate should be controlled

by particle diffusion. This is because the concentration

gradients disappear in the particle during the interrup­

tion and on reimmersion are much grater than before at

the surface. Therefore the experimental conditions were

chocsenaccordingly to explain the particle diffusion

mechanism kinetic parameters were obtained by using the

equation developed by Boyd et. al. and improved by

Riechenberg.

The u (t) values at different time intervals and

pj. 2+ 2+ + different temperatures obtained for Mg'' , Sr and Ca -Na ,

53

exchange are plotted in Fig, 2 to 4) , These results show

that the rate of exchange is directly proportional to the

temperature. The curves also reveal that the uptake of

ions is rapid initially than it becames slow and finally

reaches to a constant value with the increase of time.

The results are analogous with that of Heitner and

21 Markovits

As the particle diffusion is the rate determining

step the following equation is valid

u ( t ) = l - ^ ^^Pi-"^ ^ ^ (2) n=l

2 -. where B = ^ ^"^ (3)

r

where r is the radius of the particle, Di is the effective

diffusion coefficient of two exchanging ions inside the

22

res in phase and t i s the t ime. The t yp i ca l Bt Vs t p lo ts

at four d i f ferent temperatures 5° 25* ''5° anc 65 C for

Kg , Sr and Ca " -Na exchange given in f igures (5 to 7)

show t h a t the r a t e of exchange i s d i r e c t l y proport ional to

temperature. In a l l cases the p lots of Bt Vs t are l i n e a r

passing through the o r i g i n . This fur ther ind ica tes that the

r a t e determining step i s through the p a r t i c l e at a l l

temperatures s tudied.

5d

Concentration has a marked influence on the rate

of exchange. A plot of Bt versus t for five different

concentration (Fig. 9 Table 6) shows that the rate is

inversely proportional to the concentration (this statment

is better explained by plot B versus 1/C)• From the Bt

versus t plots B values were calculated and a plot of B

against 1/C was prepared (Fig, 10) , which shows that rate

is inversely proportional upto a particular concentration

-3 5x10 M and at a concentration lower then this value the B

value is nearly constant, B values are given in Table 7.

From the Bt versust plots, B values were calculated. From

the values of B and knowing the radii of the particle the

values of the effective diffusion coefficient Di. Contro­

lling the rate of exchange can be calculated by eq (3)

values of Di are given in Table 8. A plot of log Di versus

I/r K (Fig. 11 to 13) shows a linear relationship.

Table 7, B values as a function of temperature and

concentration

C a t i o n

Mg2+

C o n c e n t r a t i o n

( i n M a l a r i t y )

0 .002

0 .005

0 ,010

0 .020

0 .040

B, S"^ (25°C)

2 , 3 X 10"^

2.08X 10"^

1.27X 10'"^

0 . 8 7 5 x 1 0 " ^

0 . 6 7 x lO'"^

^0

100 200 300 400 500

l /C Cone, (mole" ' ' )

FIG.10. PLOT OF B VS. I /C FOR Mg2+ AT 25°C .

600

51

2 Tab le 8, Value of Di (m / s e c ) of va r ious ions a t d i f f e r e n t

t empera tu res on Linde Molecular s i e v e s (l3x)

Cat ion 5° 25° 45° 65°

Mg "*" 2.768xl0'"-^^ 2.10322x10""-^^ 3,24972x10*"^^ 4.01608x10"-^^

Sr^"^ 1.171x10"-^^ 2.103 x lO"" " 3.510 x lO"^^ 4.532 x lO""" ^

Ca '*' 9.301x10""-^'^ 1.608 x lO"" " 2.632 x lO""^^ 4.5069x lO""^^

Energy of a c t i v a t i o n Ea^ fo r the d i f f u s i o n p rocess

was o b t a i n e d from t h e s l o p e of a l i n e a r p l o t of log Do

ve r sus l/T K assuming t h e Arrhenium e q u a t i o n .

Di = Do exp (- Ea/RT)

on extrapolating the plot of log Di versus l/r°C (Fig. 11

to 13) , log Do can be calculated. Substitution of these

values in the following equation (4) gives entropy of *

activation, ^S

Do = 2.72 d KT/h exp ( 4 S A )

where d i s t h e i o n i c jump d i s t a n c e assumed equal t o

-10 -23 5 X 10 m, K i s t h e Boltzman cons tan t equal t o 1.38x10

- 1 - 1 -3A JK mole , h i s the plancJc's cons tan t equal t o 6.6x10 .

'-1 J o u l e s e c . T was taken as 273""K, R i s t h e gas cons t an t equal - 1 - 1 *

t o 8.31 J o u l e K mole . The va lue s of Do and AS a re given in Table 9.

62

Table 9, Diffusion coefficient, energy of activation and

entropy of activation of migrating ions on Linde

Molecular sieves (l3x) in Na form

M i g r a t i n g i o n

Mg2+

Sr2+

Ca2+

Do, U? S'-"-

1 .995x10 ' ^

7 .94 xlO"-^-^

7 . 9 4 3 x 1 0 " ^ °

Ea ,

kJ mole

17 .728

13 .163

14 ,984

*

- 1 - 1 J cleg mole

- 6 2 . 9 0

- 8 9 . 7 6 8

- 7 6 . 6 2 4 5

As conditions of the present system are approaching

to infinite bath conditions cv^^ cv (where c and c are the

metal ion concentration in the solution and the exchanger

phase respectively. While V and ^ are the volume of these

phases) therefore, the equation applicable to an infinite

bath can be used here.

63

X o

+

O

:^ o

en z

<

< o Q O o

LL

1 1 1 4-1

in 1 1 1 1

en 1

O

T 1 1

n

1 1

l^-s 2 JU OQ 6 o i -

64

b*::

oo 1 O '~ X

0

(--^

+ (VI

O o a: o u. ^ 0 1— - V

1— CO

z < v'> <

o o o o

^ - S ^UU OQ 6 0 )

65

I O

X o

+ (Nl

l_

a. o u. ) ^ o

z <

< o Q

O O

m

O U.

^-S ^UJ OQ 601 -

66

REFERENCES

1 , Kachod, F . C . and VJood/ W,, J . Am. Chem. S o c , _6_6, 1380

(1944) .

2 , N a n c o l l a s , G.K. and P e t e r s o n / R . , J . I n o r g . N u c l . Chem./

22/ 259/ (1961) .

3 , G r i g o l i y a / E . L . and R u s i y a , E . A . , S o o b s h c h . Akad. Nauk.

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Mamedov/ K h . S . , D o k l . Akad. Nauk. PZ, 3 5 ( 5 ) / 4 8 - 5 2 /

(1979) .

7 , W e r l i n g / K. and Wiramerstedt / R . / Chem, E n g . S c i . / 3 5 ( 8 ) /

1783-6/ (1980) .

8 , M i t r a / N . K . , Gha tak / S . and H i t r a / S . , j , Chem. , 19A(3) ,

195-9 / (1980) .

9 , B a r r e r / R .M. , Z e o l i t e s 5 th 1980 P r o c . I n t . Conf . /

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282-8 A, (1980) .

67

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C o l l e c t , Czech . Chem, Corraiiun, 45(12) , 13392-40 ( 1 9 8 0 ) .

1 2 . Buelow, M, , S t r u v e , P . eand M i e t k , W., Z . P h y s , Chem.

267(3) , 6 1 3 - 1 6 , (1986) .

1 3 . Kang, T , , uh , Y . S . , Kim, Y.K. and S e o , G , , Hwahak,

Konghak, 25(3) , 313-18 ( 1 9 8 7 ) ,

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