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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
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67
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