Studies on Synthetic Inorganic Ion-Exchangers and Ligand Exchangers

X- A^^~l

SUMMARY

Thesis Submitted for the Degree of

Doctor of Philosophy in

CHEMISTRY

by TABASSUM KHAN

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

ALIGARH (INDIA)

August, 1992

o

SUMMARY

The thesis entitled "Studies on synthetic inorganic

ion-exchangers and ligand exchanges" is comprised of six

chapters. The first chapter introduces the subject of ion

exchange and ligand exchange on materials mainly of inorganic

rigin. The literature survey on the related work done and

the importance of work has been summarized in this chapter.

The matter has been presented as a review for this particular

chapter. To cover the matter in a concise manner the

description has been presented in tabular form whereever

possible. The survey of the literature has been made on the

basis of recent available journals and chemical abstracts.

Certain fundamental points of importance are mentioned.

The second chapter entitled "Mechanism of Exchange

on Linde Molecular Sieve (13X) Comprises the studies of

kinetics on linde molecular sieve (13X) a synthetic

zeolite. The exchanger has been taken in Na form and

kinetics of exchange reactions of Mg , Ca and Sr has

been performed on this exchanger. Ut values at four

different temperatures 5% 25°, 45° and 65°C with ± 1°C

variation have been determined and corresponding Bt values

have been plotted as a function of temperature. The

mechanism is found to be particle diffusion control.

Interruption test has also been applied to decide the

mechanism of exchange. The rate of exchange is directly

proportional to temperature (t) and inversely proportional

to the concentration. Various parameters like effective

diffusion coefficient (Di), diffusion coefficient (Do),

energy of activation (Ea) and entropy of activation (zlS )

have been calculated.

The Di values have been calculated from the B and r

values by the formula

r\ • • • • \ X /

TV

Plots of -log Di against 1/T give the Do values as

intercept and the Ea values as slopes. The entropies of

activation have been calculated by the equation (2).

Do.h ^ s " 2 = -^ •••• (2)

2.72d^ KT R

The third chapter deals with the equilibrium studies

for the sorption of Ag on tin thioglycolate a chelating

material . The rate of sorption is fast at the start and

slows down reaching to a maximum value after 24 hrs. The

equilibrium studies were performed by batch process, shaking

for a period of 24 hrs. Sorption isotherms were obtained by

plotting X/m vs Ce. These plots show the variation of

sorption with the increasing temperature. Regression

coefficient (R) values for Langmuir equation and Freundlich

equation show that sorption of Ag on tin thioglycolate

obeys Langmuir equation because R approaches to unity in

this case and not in Freundlich equation. Equilibrium

constant for adsorption were obtained and various

thermodynamic parameters viz'^H, •^S, O-Q are computed using

least square method on VAX~11 computer. For the physical

characterization of this material IR studies were performed.

Thus it was concluded that the sorption of Ag on tin

thioglycolate is physiosorption not cheraisorption. An

attempt has been made to give the tentative structure for

this exchange material which helps in the elucidation of

mechanism of sorption.

The fourth chapter deals with the ion exchange

equilibrium of "some alkaline earth metal ions on Linde

Molecular Sieve (13X) a synthetic zeolite type material.

This resin functions weakly in the acidic medium.

Thermodynamics of alkaline earth metal ions were studied on

this resin in sodium form. A simple approach has been made

using a batch process for equilibrium based on the mass

action law modified in terms of activities. Thermodynamic

equilibrium constant (Ka) was calculated by Gaines and

Thomas method after normalising the Xw values as Xj, never

approaches 1 in the present studies.

The isotherms plotted indicate that the bivalent

cations are preferred by the resin than the Na ion. The

thernodynamic parameters, '^G" , H° and AS" have been

evaluated.

The mechanism of exchange studies was also done on

sodium stannosilicate. Thus the fifth chapter describes the

kinetics of exchange on sodium stannosilicate an analogue of

zeolite. The exchanger has been taken in Na^ form and

kinetics of exchange reaction of Cd , Cu , Pb and Ag

ions has been performed on this exchanger. Experimental and

theoretical approaches have been used to show the rate of

diffusion through the particle. Different kinetic and

thermodynamic parameters have been calculated under the

conditions favouring a particle diffusion control mechanism.

"Bf'technique has been used to calculate these parameters.

The sixth chapter deals with Distribution studies of

some metal ions in nonaqueous medium on Linde Molecular

Sieve (13X) and sodium stannosilicate. The distribution

^ - r XT-2+ r 2+ w 2+ „,2+ „ 2+ . + ..3+ „,2 + studies of Ni , Co , Mn , Cd , Zn , Ag , Al , Pb ,

Mg , Ca , Ba and Sr were carried out in aqueous

organic - NaNO^ media and aqueous organic - HNO^ media. The

results indicate that as the percentage of methanol

decreases the Kd values increase for all the metal ions

studied. This variationis because of the fact that . the

mobility of counter ions is based on the polarity of the

so lu t ion . 1^547

Studies on Synthetic Inorganic Ion-Exchangers and Ligand Exchangers

Thesis Submitted for the Degree of

Doctor of Philosophy in

CHEMISTRY

by TABASSUM KHAN

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

ALIGARH (INDIA)

August, 1992

^V^-' - - > >

T^^Gl JSLl'l

T4567

aiECKED 199^-5:

Jaijilislt Jy. (Kitiiuil M.sc, pfi.n.

FUAOFR IN c i i rw in rnY

nrrARTMHNT or niFMisTUY ALIGAHH MUSLIM UNIVtHSITY

ALIGARH-10?001 INDIA

CERTIFICATE

This is to certify that the work embodied in this

thesis entitled "Studies on Synthetic Inorganic ion

exchangers and Ligand exchangers"j is original, carried

out by MISS TABASSUM KHAN under my supervision and is

suitable for submission for the award of Ph.D., degree

in Chemistry of this University.

( J.P. Rawat )

ACKNOWLEDGEMENT

I express my gratitude ar.d indehtness to Dr. J.P. Rauat for his

excellent advice and guidance.

I am thankful to Prof. M.A.Beg Chairman^ Department of

Chemistry, A.M.U., Aligarh for providing research facilities

I .am indebted to my hushand SEUEB, for his encouraging

attitude towards my work.

A word of thxmks to all my teachers especially Dr. Anees

Ahmadj, my lab colleague Mr. Omar, and my friends Fabeha, Tauseef &

Faisal. I praise Dilshazid for his timely and much needed help.

Thanks are also due to U.S. Sharma, for the typing of this

work.

Last but not the least to my family who made it possible

to com(plete this work.

(TABASSUM KHAN)

C O N T E N T S

1. L i s t of Pub l i ca t ions

2. L i s t of Tables

3 . L i s t of Figures

4 . CHAPTEai-I

5. CHAPTER-II

CHAPTER-III

CHAPTER-IV

INTRODUCTION

References

Mechanism of Exchange on linde molecular sieves {13X)

Introduction

Experimental

Results

Discussion

References

(i)

(ii)

(vi)

1

44

65

66

69

88

99

Equilibrium studies for the sorption of Ag on tin thioglycolate - A chelating material

Introduction 102

Experimental 104

Results 107

Discussion 129

References 134

Ion exchange equilibria of alkaline earth metal ions with sodium ion on linde molecular sieve (13X)

Introduction 136

Experimental 139

8. CHAPTER-V

Results 140

Discussion 153

References 160

Mechanism of exchange on sodium stannosilicate

Introduction 163

Experimental 165

Results 167

Discussion 191

References 200

CHAPTER-VI Distribution studies of some metal ions in non-aqueous ff?ediunr an linde molecular sieve (13X) and sodium stannosilicate

Introduction

Experimental

Results

Discussion

References

203

205

207

208

219

LIST OF PUBLICATIONS

1. Mechanism of exchange on linde molecular sieve (13X).

Chemical & Environmental Research (press).

2. Equilibrium studies for the sorption of Ag on tin

thioglycolate - A cheating material.

Colloids and surfaces (Comm.).

3. Ion exchange equilibria of alkaline earth metal ions

with sodium ion on linde molecular sieve (13X).

React. Polym. Ion. Exch. Sorbents (Comm.).

4. Mechanism of exchange on sodium stannosilicate.

Solvent Extn. Ion Exch., (Comm.).

5. Distribution studies of some metal ions in nonaqueous

medium on linde molecular sieve (13X) and sodium

stannosilicate.

J. of Ind. Chem. Soc. (Comm.).

11

LIST OF TABLES

CHAPTER - I

INTRODUCTION

Table 1 : Thermodynamic studies on various ion

exchange materials 22

Table 2 : Certain oxides, inorganic ion exchangers and

ion exchange resins used as adsorbents 37

CHAPTER - II

Mechanism of exchange on linde molecular

sieves (13X)

Table 1 : Ion exchange capacity of linde sieve (13X) 69

for alkaline earth metal ion.

Table 2 : Interruption test for Mg - Na exchange on

linde molecular sieve (13X) at 25^1°C. 69

Table 3 : U(t) and Bt values as a function of time for

Mg on linde molecular sieve (13X) at

different temperatures. 72

Table 4 : U(t) and Bt values as a function of time for

Sr on linde molecular sieve (13X) at

different temperature. ^^

Table 5 : U(t} and Bt values as a function of time for

Ca on linde molecular sieves {13X) at

different temperature. 78

Table 6 : U(t) and Bt values as a function of concen-2+ + tration for Mg -Na exchange on linde

molecular sieve {13X) at 25+l°C. 84

Table 7 : B values as a function of temperature and

concentration. 91

Ill

2 Table 8 : Values of D.(m /sec) of various ions at

different temperatures on linde molecular

sieves (13X). 93

Table 9 : Diffusion coefficient, energy of activation

and entropy of activation of migrating ions

on linde molecular sieves (13X) in Na form. 94

CHAPTER - III

Equilibrium studies for the sorption of Ag

on tin thioglycolate - Achelating material.

Table 1 : Adsorption of Ag on exchanger, fitting of

Freundlich equation at different

temperatures for a constant particle size. 114

Table 2 : Fitting of Freundlich equation for different

particle size at 25JH1°C. 117

Table 3 : Adsorption of Ag on exchanger, fitting of

Langumuir equation. 120

Table 4 : Fitting of Langmuir equation for different

particle size at 25+_l°C. 125

CHAPTER - IV

Ion exchange equilibria of alkaline earth

metal ions with sodium ion on linde

molecular sieve (13X).

Table 1 : Equivalent fractions of Mg , selectivity

coefficient and thermodynamic equilibrium

constants for Mg -Na exchange on linde

molecular sieve (13X). 141

Table 2 : Equivalent fractions of Sr , selectivity

coefficients and thermodynamic equilibrium

constants for Sr -Na exchange on linde

molecular sieve (13X). ^^^

IV

Table 3 : Thernodynamic paraneters for Mg -Na

exchange on linde molecular sieve (13X) at

constant ionic strength. 151

Table 4 : Thernodynamic paraneters for Sr -Na

exchange on linde molecular sieve (13X) at

constant ionic strength. 152

Table 5 : Hypothetical thermodynamic data on zero

loading on the ion exchange resin for Mg . 158

CHAPTER - V

Mechanism of exchange on sodium

stannosilicate

Table 1 : Ion exchange capacity of sodium

stannosilicate. 167

Table 2 : Interruption test for Mg -Na exchange on

sodiun stannosilicate at 25j l°C. 169

Table 3 : Ut and Bt values as a function of time for

Cd" on sodium stannosilicate at different

temperatures. 171

Table 4 : Ut and Bt values as a function of time for

Pb" on sodium stannosilicate at different

temperatures. 174

Table 5 : Ut and Bt values as a function of time for

Cu~^ on sodium stannosilicate at different

temperature. 177

Table 6 : Ut and Bt values as a function of time for

Ag on sodium stannosilicate at different

te-;peratures. 180

Table 7 : Ut and Bt values as a function of particle

size for Cu -Na exchange on sodium

stannosilicate. 183

2

Table 8 : Values of Di (m /sec) of various cations at

different temperatures on sodium

stannosilicate. 194

Table 9 : Diffusion coefficient, energy of activation 2+ 2 + and entropy of activation of Cu , Pb ,

Ag and Cd on sodium stannosilicate in Na

forn. 195

CHAPTER - VI

Distribution studies of some metal ions in

non aqueous medium on linde molecular sieves

(13X) and sodium stannosilicate.

Table 1 : Kd values of metal ions in aqueous organic

solvent - O.IM NaNO2-0.02M metal ions on

linde molecular sieve (13X). 209

Table 2 : Kd values of metal ions in aqueous - organic

solvents (.02M HNO^) and 0.025 M metal ions

on sodium stannosilicate (Na forn).

Methanol + HNO3 (1:1). 215

Table 3 : Kd values of metal ions in aqueous - organic

solvent - (0.02M to 0.2M HNO3) and 0.025 M

metal ions on sodium stannosilicate (Na

forn) Methanol + HNO3 (1:1). 217

vi

LIST OF FIGURES

CHAPTER - II

Mechanism of exchange on linde molecular

sieves(13X)

Figure 1 : Effect of an interruption test on the rate

of Mg -Na exchange on linde sieve (13X). 70

Figure 2 : Rate of exchange of Mg at different

temperature on linde sie/e (13X). 74

Figure 3 : Rate of exchange of Sr at different

temperatures on linde sieve (13X). 77

Figure 4 : Rate of exchange of Ca at different

temperatures on linde sieve (13X). 80

Figure 5 : Effect of temperature on the rate of

Mg -Na exchange on linde sieve (13X). 81

Figure 6 : Effect of temperature on the rate of

Sr -Na exchange on linde sieve (13X). 82

Figure 7 : Effect of temperature on the rate Ca -Na

exchange on linde sieve (13X). 83

Figure 8 : Influence of concentration on the rate of

Mg -Na exchange at 25°C on linde sieve

(13X). 86

Figure 9 : Effect of concentration on the rate of

Mg -Na exchange on linde sieves (13X). 87

Figure 10 : Plot of B Vs 1/c for Mg . 92

Figure 11 : Log D against 1/T K for Mg^^. 96

Figure 12 : Log D against 1/T K for Ca^^. 97

Vll

Figure 13 : Log D^ against 1/T K for Sr^^. 98

CHAPTER - III

Equilibrium studies for the sorption of

Ag on tin thioglycolate-A cheating

material.

Figure 1 : Plot of F(t) Vs. time (Rate of sorption of

Ag""). 109

Figure Ha) : IR spectra of tin thioglycolate

(unadsorbed). 110

(b) : IR spectra of tin thioglycolate (adsorbed). Ill

Figure 3 : Plot of x/m Vs Ce at different temperatures

for the same particle size. 112

Figure 4 : Plot of x/m Vs. Ce for different mesh size

(microns) at 30H^1°C. 113

Figure 5 : Langmuir adsorption isotherms of Ag on tin

thioglycolate at different temperatures for

the same particle size. 121

Figure 6 : Langmuir adsorption isotherms of Ag on

different mesh size (Microns) of tin

thioglycolate at 30^1°C. 128

CHAPTER - IV

Ion exchange equilibria of alkaline earth

metal ions with sodium ion on linde

molecular sieve (13X).

Figure 1 : Ion exchange isotherms of Mg -Na exchange

on linde molecular sieve (13X). 143

Vlll

Figure 2 : Ion exchange isotherms of Sr -Na" exchange

on 1-inde molecular sieve (13X). 146

Figure 3 : In of selectivity coefficient Vs equivalent

fraction of Mg in exchanger phase. 147

Figure 4 : In of selectivity coefficient versus 2 + equivalent fraction of Sr in exchanger

phase. 1 8

Figure 5 : Plot of In Ka Vs 1/T for alkaline earth

metal ion Mg . 149

Figure 6 : Plot of In Ka vs 1/T for alkaline earth

metal ion Sr . 150

CHAPTER - V

Mechanism of exchange on sodium stanno-

silicate.

Figure 1 : Effect of an interruption on the rate of

Cu -Na exchange on sodium stannosilicate. 168

Figure 2 : Rate of exchange of Cd at different

temperatures on sodium stannosilicate. 173

Figure 3 : Rate of exchange of Cu at different

temperatures on sodium stannosilicate. 179

Figure 4 : Rate of exchange of Pb at different

temperature on sodium stannosilicate. 176

Figure 5 : Rate of exchange of Ag at different

temperatures on sodium stannosilicate. 182

Figure 6 : Effect of temperature on the rate of

Cd ^-Na^ exchange on sodium stannosilicate. 185

IX

Figure 7 : Effect of temperature on the rate of

Cu -Na exchange on sodlu::; stannosilicate. 186

Figure 8 : Effect of temperature on the rate of

Pb -Na exchange on sodiun stannosilicate. 187

Figure 9 : Effect of temperature on the rate of

Ag -Na exchange on sodiun stannosilicate. 188

Figure 10 : Influence of particle size on the rate of

Cu^-Na^ exchange at 30^1°C. 189

Figure 11 : Influence of particle size on the rate of

Cu -Na"*" exchange at 30j^l°C on sodium

stannosilicate. I^Q

Figure 12 : Plot of log Di vs l/T on Cd . 196

Figure 13 : Plot of log Di vs l/T on Ag^^ 197

Figure 14 : Plot of log Di vs l/T on Cu j gg

Figure 15 : Plot of log Di vs l/T on Pb '^ 199

CHAPTER - VI

Distribution studies of some metal ions in

non aqueous medium on linde molecular sieve

(13X) and sodium stannosilicate.

Figure 1 : Plots of Kd vs % of methanol on linde

molecular sieve (13X). 210

Figure 2 : Plots of Kd vs % of r.ethanol on linde

molecular sieve (13X). 211

Figure 3 : Plots of Kd vs % of methanol on linde •o

molecular sieve (13X). 212

Figure 4 : Plots of Kd vs \ of methanol on linde

nolecular sieve (13X). 213

Figure 5 : Plots of Kd vs \ of methanol on linde

molecular sieve (13X). 214

Figure 6 : Plots of Kd vs different metal ion on

sodium stannosilicate. 216

Figure 7 : Plots of Kd vs nitric acid concentration on

sodium stannosilicate. 218

INTRODUCTION

Nowadays the ion-exchange has come to be recognized

as an extremely valuable analytical technique. All over the

world numerous plants are in operation for developing the

separations of inorganic, organic and biochemical mixtures.

Nearly 140 yrs. ago an English land owner Thompson engaged an

York analyst named spence to investigate the loss of ammonia-

from manure heaps. He discovered a technique familiar to many

of us for treating water by process such as "softening" and

"high purity" condensate polishing.

This discovery of calcium displacement by ammonia

using a natural ion-exchanger soil was the beginning of the

technology.

Ca(Soil) + (NH^)^SO^ ^ " (Soil) NH^+ CaSO^ ... (1)

Spence reported his discoveries to the Royal Agricultural

Society in 1850. These were rapidly confirmed by another

2 agricultural chemist, G.T. Way who described this new

phenomenon as "base exchange".

2

It was Way who included the first synthetic

aluminosilicate base exchanger. He laid down the foundation

of modern ion exchange theory and technology vrith remarkable

completeness. However it was 50 yrs. later in 1905, that

3 Cans in Germany softened water on an industrial scale using

a natural or synthetic aluminosilicate material called

zeolite. The Can's patents were used universally during the

next 30 yrs.

In 1934 two new types of materials were invented.

The first was a sulphonated coal developed in Germany and the

second was a phenol-formaldehyde polymer 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

demineralisation process possible. This has, since becor.e the

most used and important application of ion-exchanger.

The material produced by Adams & Holmes, though

relatively unstable by today's standards, found considerable

industrial applications. Progress was so rapid that the first

industrial scale demineralisation plant in the world was

built in Great Britain by 1937.

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

universities, 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.

Can's recognized the practical utility of the ion

exchange phenomena 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 aluminosilicates may confer ion-

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

ferrous aluminosilicate analogue to the zeolites, possesses

exchangeable potassium with considerable capacity. The first

aluminosilicates were synthesized by Harms and Rumpler

1903. General formula for the synthetic aluminosilicate can

be written as

Na20, Al^O^. nSi02

where n = 1-12

Gallium and Germanium analogues have been prepared

e.g. gallogermanate and alurainogermanate, silicates of

. 1 . . S ,. , 9 , .10 _, . 11, zirconium, titanium, bismuth, ferric and zinc have also been

prepared.

Ion exchange is considered as a reversible process

in which cations or anions are exchanged stoichioraetrically

between the ion exchanger and solution phases, when they are

placed in close contact v 7ith each other. When an ion

exchanger in counter ion'A'form is placed in a solution of

another counter ion'3' then the ion exchange process may be

written as

A + B ; ^ B + A ... (2)

where the barred quantities refer to the exchanger phase and

unbarred to the solution phase.

Cation exchange in soils are of great importance as

12 it can alter the availability of several micronutrients . A

study of cation exchange in soils may give an idea about the

13 14

capability of the soils to store and supply the nutrients

to the plants. These studies are useful in relation to plant

growth because the metal ions may increase the supply of 12

some nutrients in plants while decrease the others , The

exchange behaviour of heavy metals in soils has been

investigated by Lagerwerff and Brower . Amphlett and 16 McDonald ' studied the ion exchange equilibria of clay

mineral fraction of a soil from English lower greensand

series.

The clay minerals comprise a complex series of

aluminosilicate structure. Aluminosilicate back bone of the

clays, is composed of an alternating parallel, two dinensional

layers formed by silicate tetrahedra and alurainate

tetrahedra . The disposition of these layers and the extent

and nature of isonorphous substitution 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 having

similar structures but showing different degrees of

isomorphous substitution. They swell appreciably in water

when the concentration of interlayer cations is high. The

18 clay possesses a well defined affinity series and in

general the affinity for cations increases in the order of

decreasing hydrated ionic radii. Clay minerals can be used

as an ion exchange media, particularly when one is concerned

with specificity, cheapness or stability towards radiation

or high temperature water. After some preliminary treatment

montmorillonite may be used for the treatment of radioactive

v;aste solutions. Verraiculite needs no preparation for this

purpose.

The first claim to have synthesized a zeolite^dates

back from 1812 when Devilla reported the production of

levyne (levynite) by heating a potassium silicate with

19 sodium aluminate in a sealed glass tube. Breck lists many

similar early claims but those produced prior to

availability of XRD relied upon mineralogical identification

(via optical and chemical analysis) often on raicrocrysta-

lline products.

The first synthesis reliably characterized by

chemical analysis, optical properties and XRD are those

carried out by Professor R.M. Barrer and co-workers around

1940. However, it is the work carried out in the union

carbide laboratories (1949 ), culminating in the report by

Milton, Breck and others of the synthesis of zeolite A

(reported in 1956), that is generally regarded as the first

example of the synthesis of a completely characterized new

zeolitic structure unknown in nature. Very singificant

feature in this work was the fact that it was carried out

under mild hydrothermal conditions ( <100°C), at atmospheric

pressure and with high water concentrations:

Last 30 yrs. have seen many systematic studies of

zeolite synthesis both to generate a new structure and to

clarify their modes of formation in the laboratory and in

nature. As computer predictions say that there are

numerous conceiviable zeolitic structures it seems that

studies will continue for a little while longer. Some of the

zeolites with completely regular structure have been

20-29 prepared by several workers . Sodium gallosilicate has

30 been prepared by Selbin and Mason . Gallocarbonates have

been prepared by reacting together solutions sodium gallate

31 32

and sodium bicarbonate . Amonium tungstosilicate has been

prepared for chromatographic separation of UO from Cs ,

Eu , La and Bi . Ferrosilicate and other sodium

metallosilicates have also been synthesized. Synthesis of a

layered aluminophosphate molecular sieve (A1P0,-CJ by Long 35 et al. . The high temperature synthesis of Caesium alumino

Of. silicate by Dimitrijevic and Coworkers

Alumino silicophosphate molecular sieve crystalline

composition exhibiting the ion exchange properties and can

easily be converted to catalytically active material was

37 prepared by Van Ballmoos and Coworkers . Kawamura and

Coworkers prepared aluminoborosilicate containing alkaline

earth metal. Room temperature synthesis and characterization

of a new ZnPO and ZnAso sodalite open frameworks has been

39 done by Nenoff and Others

Zeolites are hydrated aluminosilicate minerals

discovered in 1756 by Cronstedt. He observed that the

crystals of these minerals visibly lost water when heated and

therefore he named them as zeolites (meaning boiling

stones in greek). Later, it was noticed that zeolites

possess the properties of reversible water loss, ion

exchange and sorption of molecules differentially. The

structure of zeolites are build up of AlO; and SiO,

tetrahedra which have their oxygen' atoms in common.

Depending upon the structure and type of bonding, zeolites

may exist as fibrous, lamellar or rigid three dimensional

structures. Zeolites with three dimensional structures have

been extensively studied by Barrer . Their frameworks are

open with channels and interconnecting cavities in the

aluminosilicate lattice. The negative charge due to AlO/

grouping is balanced by alkali or alkaline earth metal ions,

which are present as counter ions in the channels of the

lattice framework. These counter ions can be replaced by

other cations.

Barrer distinguished three categories of molecular

sieves according to the minimum diameters of the

interstitial channels. The development of linde molecular

sieves synthesized and studied by Breck and others in

recent years has made it possible to use such process on an

43 industrial scale . Saha studied the use of natural and

synthetic zeolites for fractionation sorption and catalysis.

The narrow, rigid and strictly uniform pore

structure of the zeolites gives them a pronounced "sieve

action" on a molecular scale. Large cations such as 44

quaternary ammonium ions and large nonelectrolyte

molecules ' ' which are larger than the openings in

crystal frame work are completely excluded, whereas small

molecules are sorbed or exchanged. Even inorganic cation

such as Cs is partially or completely excluded by several

zeolites ^' -*' . A wide range of chromatographic separa­

tions can be achieved by choosing a suitable zeolite and its

cationic form. For e.g. Cs has been separated from other

48 alkali metals on analcite

Selectivity in the zeolites have been studied by

Barrer . In the absence of ionic sieve action in zeolites,

selectivity towards certain ions may still exist due to

differing thermodynamic affinities. Basic sodalites can be

used under suitable condition for the recovery of silver in

quantitative analysis, while the mineral clinoptilolite may

be employed to remove trace concentration of sodium and has

been tested as an adsorbent for the treatment of low

49 activity radioactive waste solution . Synthetic

223 ultramarines have been used to separate Fr from its

actinium parent and other activities .

When zeolites are exposed to water vapour at

elevated temperatures and/or pressures they are experiencing

conditions close to those under which they are formed in

nature- Under these circunstances they mimic the natural

progression to a more stable and less porous phase. Studies

of hydrothermal stability are of great importance to the

regeneration processes used in association with the use of

10

synthetic zeolites as catalysis, r.olecular sieves and drying

agents. Zeolites have a low resistance to mineral acids and

indeed both A and X readily dissolve in even a nodest

molarity of hydrochloric acid. The ease of dissolution can

be linked to the ready removal oi aluminium from tetrahedral

site fraie works, where Si:Al is 1 - 2. The leached

aluminium readily hydrolyses to a variety of species in

which the metal is hexacoordinated. However, ion exchange

phenomenon may be utilized in the preparation of H form of

the zeolites. For example, H form analcite is prepared by

treating silveranalcite with an aqueous solution of halide

of a metal ion which is too large to enter the structure of

analcite ' . A precipitate of silver halide is formed in the

solution. The metal ion and hydroxide ion remain in the

solution and analcite in H form is obtained.

Zeolite structures have proved to be remarkably

resistant to radiation. On prolonged exposure to high

neutron and "^ doses, the effect on zeolite matrix is

negligible. The first use of zeolites as catalysts occurred

in 1959 when zeolite v as used as an isomerization catalyst

by Union Carbide. More important was the first use of

zeolite X as a cracking catalyst in 1962, based upon earlier

work by Plank and Rosinki. They noted that relatively small

amounts of zeolites could usefully be incorporated into the

then-standard silica/alumina or silica/clay catalysts. The

11

use of zeolites in this way as promoters for petroleum

cracking (i.e. the production of petrol from crude oils)

greatly improved their performance. The resultant saving

from this improvement can be measured in billions of pounds

per annum in the present economy. The major employment of

zeolites is as acid cracking catalysts. As such they account

for over 99% of the worlds petrol production from crude

oil s.

In recent journals the ion exchange of alkyl tin

cations into zeolites Y, L, sodiummordenite and hydrogen

mordenite is reported and it is shown that the resultant

materials are catalytical1y active for the dehydration of

pentan-1-ol. Similar zeolites as catalysis studies have been

A K 1 51-66 done by many workers

Nok , uses are appearing as phosphate substitutes in

detergent builders, in water purification apparatus as fertilisers,

as soil conditioners and as dietary supplement for catties.

Limitations of zeolites and clays in their stability

in acids led to the discovery of some stable ion exchange

materials. In 1931 Kullgren observed that .sulfite

cellulose works as an ion exchanger for the determination of

copper. In 1935 Adams & Holmes found ion exchange properties

in crushed phonograph.

12

This interesting discovery led the inventors to the

synthesis oJ: organic ion exchange resins which had much

69 better properties . These resins were stable towards acids

and easy to handle. Since then these organic ion exchangers

have been used both in laboratories and industries for

separations, recoveries of metals, deionization of water,

concentration of electrolytes and elucidating the mechanism

of a great many 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 presence 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 exchangers 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 radiation, they can be used

advantageously in reactor technology. Inorganic ion exchange

z*

13

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

electrodes . The ion selective electrodes have now become

an important tool for solving various analytical

Ki 71-73 problems

In order to understand the applications and to

improve upon them, systematic and fundamental studies are

being persuaded on these materials. It was shown by Russe

that columns containing finely divided zirconium phosphate

supported on silica wool could be used to separate uranium

and plutonium from fission products by ion exchange process.

Various inorganic ion exchangers reported upto 1964 have

been excellently reviewed in a monograph of Amphlett

entitled "Inorganic Ion Exchangers". Literature data on a

new series of synthetic inorganic ion exchangers has been

76 compiled by lonescu . Representative types of inorganic ion

exchangers have been reviewed by Ito and Abe''. The

theoriticaL aspects of ion exchange in the inorganic ion

exchangers have been described by Marinsky'" . The work done

till 1970 has been summarized by Pekarek and Vesely'°*"^

under the following categories:

1. Hydrous oxides.

14

2. Acidic salts of polyvalent metals

3. Salts of heteropoJy acids

4. Insoluble ferrocyanides

5. Synthetic aluniinosilicates

6. Materials with chelating groups

7. Electron and Redox exchangers

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

sulphLdcs, alkaline earth sulphates.

Marinsky and Walton edited the reviews on the

applications of inorganic ion exchangers. The synthesis and

application of inorganic ion exchangers have been reviewed Q 3-QQ

by Walton . Recent literature on these materials has

89 been covered by clearfield in his manograph in 1982.

90 Recently Sarkar B. and Basu S. have done some

studies on zirconium tungstate ion exchanger a new inorganic

91 ion exchanger. Costantino, U. and Others prepared a new

ion exchanger zirconium phosphate phosphite a more facile

exchanger for large and hydrated cations.

Conventional ion exchangers are practically inso­

luble cross linked polymers that contain either basic or

acidic functional groups in a high concentration. These func­

tional groups are tightly attached to the polymer matrix and

are commonly introduced into basic solid copolymer by a

substitution reaction. Practice however has proved this

method to be sojdoni applicable in the synthesis ol a

chelating resin.

Above a]I the resin should have in addition to the

demanded selectivity, sufficient mechanical and chemical

stability especially towards acids and bases which are used

for the regeneration of the resin. In the practical

performance of separation, dimensions of the column and the

amount of resin required should be as small as possible,

consequently resin should have an effective exchange

capacity of at least 1 meq/gm (referred to the air dried

material). According to considerations given by Gregor et

92 al. the following properties are required for a chelating

agent that is to be incorporated as a functional group into

an ion exchange resLn.

1. The chelating agent should yield a resin gel of

sufficient stability or it should be capable of being

incorporated by substitution into a polymer- matrix.

2. The chelating molecule must possess sufficient chemical

stability so that during the synthesis of the rosin the

functional structure is not changed by polymerization

or any other reaction.

3. The steric structure of the chelating molecule should

16

be compact so that the formation of the chelate rings

will not be hindered by the matrix.

4. Because the agents forming relatively stable complexes

are at least tridentate. It is necessary that the

ligand groups of the chelating molecule be situated

appropriately so that the specific arrangement of the

ligand will be preserved in the resin.

Recently a number of chelating ion exchangers have

'been synthesized to encourage the applications of ion

exchange to a broader range of separation and for the

93 -109 recovery of certain metal ions selectively . The

selectivity of the most complexing agents predominantly

depends on their ability to form chelates with certain

metal ions. For this purpose the development of complexing

ion exchangers have taken place where the complexation

equilibrium will play an important role. Gold and

110 Gregor prepared a chelating resin with aromatic nitrogen

as the only functional group. The number of chelating ion

exchangers with nitrogen and oxygen as donor atom is

Hi 112 comparatively much large. Many workers ' prepared

such materials by fixing ligands to the CA\r^ nucleus of the

crosslinked polystyrene. The number of such materials

utilized for analytical applications is small. Nevertheless

many different chelating resins have been prepared. The

17

main difficulty in their use is restriction of effective

simpler means and chemical stability of these materials.

Although a number of chelate ion exchange resins have come

in wide use but no comparative study exists on inorganic

ion exchangers containing such groups.

1. The utility of the ion exchange material can be

developed on the basis of the following studies. Distribu­

tion of counter ions between the exchanger and the solution

phases.

2. Thermodynamics

3. Kinetics, and

4. Analytical applications.

The affinity of an ion exchanger for a counter ion

A is given quantitatively by the distribution coefficient,

Kd which is defined as-

No. of meg of A in exchanger phase g , s Kd = -\ ... I J j

No. of meq of A in solution phase ml

The distribution of an ion between the exchanger

and solution phases is a direct measure of selectivity.

Usually, the ion exchanger takes up certain ions in

preference to the other counter ions present in the

solution. The selectivity is an important factor for the

study of separations and it may depend mainly on -

18

1. Donan potentia]

2. Sieve action, and

3. Complex formation

The distribution coefficient is a practical guide

to the separation procedure. By determining Kd values under

varying experimental conditions, it is possible to select

most suitable conditions for separating small amounts of

vairous ions. The general use of distribution coefficient

is made in the elution technique used in separations. The

rate at which ions move in an ion exchange column depends

on their distribution coefficient values. The ratio of the

distribution coefficients of two different ions at low

concentrations is called the separation factor which can be

used to evaluate the ease of separating the two ions.

The thermodynamic study is of course the study of

chemical equilibria. Rigorous thermodynamics however gives

an inherently abstract treatment devoid of the mechanical

or microscopic images which would lead one to a feeling of

greater intimacy and understanding of the phenomena. The

most successful treatments have been based on the model

which incorporates observed physical characteristics. In

case of organic exchangers the most successful models take

into account the swelling observed when the resin change

the environment or the ionic form.

19

In one approach attempts have been made to

correlate the activities with some measurable quantities

113 with the thermodynamic equation. Cans gave the first

quantitative formulation of ion exchange equilibria using

the law of mass action in its simplest form which was

extended by Kiel land . A suitable choice of the general

115 treatment was given by Gains and Thomas . However Gregor

was ab)e to relate selectivity to hydrated ionic volumes in

his semiquantitative model. Rigid structure, negligible

swelling pressure and a differential selectivity has made

the study simple on inorganic ion exchangers. When an

exchanger in counter ion A form is placed in a solution of

counter ion B there will be an equilibrium set up for the

distribution of A and B between the exchanger and the

solution phase according to their selectivity for the

exchanger phase. At equilibrium this exchange process may

be represented as

A + B (aq) ; ^ = ^ B + A (aq) ... (4)

where bar represents the ion in the exchanger phase. For

the sake of convenience the effect of co-ions on the

equilibrium may be neglected. The thermodynamic equilibrium

constant for the above reaction may be written as

Ka = l i iA-= i i j jALx tS^jA ,31

20

where -V represents the activity coefficients in the

exchanger phase and f is the activity coefficient in the

solution phase. Thermodynamic equilibrium constant is

particularly used to find out the free energy changes of

the ion exchange processes by the expression

A G = -RT InKa (6)

The ionic selectivity is governed by lowering of free

energy of the system which gives the information about the

preferential uptake of the counter ions by the exchanger ,

Ka values at different temperatures give the value of

enthalpy change. Changes in the number and the strength of

the bonds involved in the ion exchange reaction is directly

related to enthalpy changes. The ion exchange reaction

(eq. 4) provides that structural changes within the

exchanger are small , the most important factor influencing

the entropy of equally charged ions will be expected,

results from changes in liberation entropy may also play an

important role and the overall entropy will reflect changes

in randomness in the ion exchange reaction the driving

force being the tendency for the system to go to the most

probable i.e., the most random state.

The ion exchange equilibria of alkali metal ions 1 -ic

was studied by Larsen and Vissers and Gal and

11 7 Ruvarac on amorphous zirconium phosphate of various

21

composit'-ions and properties. Ion exchange thermodynamic

studies have been extended on more defined semi-crystalline -1 1 8 — 1 28

and crystalline zirconium phosphate for alkali cation

Similar studies have also been reported on hydrous zirconia

129 acting as anion exchanger by Nancollas

Thermodynamic studies for alkali metals on ferric-

1 30 131 132 antimonate ' , niobiumarsenate zirconium triethyl

133 134

amine , thorium tetracyclohexamine were made in our

laboratories. Some of the equilibrium studies on different

ion exchange materials with various systems and their

parameters are given in table 1.

The thermodynamics of anion exchange on the ion

exchange materials have also been studied. The reversibility

of Br -NO^ exchange on hydrous zirconia was demonstrated by

Kraus , Ruvarac studied the thermodynamics of CI and

2-SO, from solution on NO^ form of hydrous zirconia at

25-80°C. The use of mixed solvent systems like

methanol-water system changes the value of c G, AH, AS on

1 fi 3 hydrous zirconia and hence the selectivity coefficient is

1 fsL. affected. Misakard and Mikhail studied the thermodynamics

of N0~-C1~, NO~-Br~, N0~-SCN" exchange on hydrous

ceria.

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- 0 C CO

+ m

O 1

+ ( N

V-i

CO

• +

U3

o 1

-t-^

<u 00 c CO

x: o X cu

-1-

(/5

o 1

-1-co

>-

CU

00 c CO

x; CJ X tu

+ -1-

CNJ

<u u^

Xl c CO

H-co

2 1

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H

n

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2 1

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cu 00 c CO

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2

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1

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r\

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1

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1^

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r J

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1 -1-

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4-1

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c • H

H

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CM eg (N CN

i n CM CN IN

00 CM

en CM

o en c-)

25

Although thermodynamic studies of ion exchange help

in investigating the conditions at equilibrium, but it

does not provide any information about the mechanism of

change from one state to the other and the time required

thereon. The kinetics of exchange takes these factors into

consideration.

Kinetics depends on the surface area of the ion

exchange particles. Thus where diffusion rate or kinetics

are of importance, particle size and macro porosity of the

exchanger become important parameters. The kinetics of a

simple homogeneous chemical reaction are governed by their

differential rate of reaction depending on the

disappearance of product or formation of reactant with

time.

AX + BY .' ^ Product

Rate = K. X^. Y^

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

concentrations of the reacting species. The powers A and B

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

respectively.

The ion exchange process is however quite different

in many respects from such simple chemical reactions. In

the first case it concerns a reaction which involves the

26

transport of ions from solution to exchanger and vice versa

i.e. ion exchange process constitutes a solid phase in

aqueous solutions and hence is heterogeneous. Secondly in

dilute solutions there is effectively no electrolyte

preparation into the exchanger and hence the co-ions has no

part to play in the overall reaction mechanism, and thirdly

the electroneutrality is maintained every time, hence the

exchange process is stoichiometric. This coupling of flows

of the entering and leaving ions simplifies the treatment

of ion exchange kinetics.

For an exchanger in 'A' form placed in a solution

with 'B' as counter ion, following steps may be considered.

1. Migration of counter ion 'A' from exchanger to the

adhering film of the particle.

2. Migration of 'A' from film to solution.

3. Chemical reaction between 'A' and 'B'.

4. Migration of 'B' from solution to film.

5. Migration of 'B' from film to the particle.

Since the slowest step is the rate determining

step hence all the above steps are considered. Thus three

distinct type of kinetic process may be considered in an

ion exchange process.

27

(a) The film diffusion control (FDC) i.e. interdiffusion

of counter ions in the adherentfi]m.

(b) Particle diffusion control (PDC) i.e. interdiffusion

of counter ions in the ion exchanger itself.

(c) Chemical reaction control between two types of counter

ions.

It is important to note that till now all the

kinetic studies were found to depend either on film

diffusion or on particle diffusion and not on the chemical

exchange reaction. Furthermore, the rate determining step

also depends upon the experimental conditions.

1 fi S

Nachod and Wood have made the first serious

attempts on kinetic studies of ion exchange. They have

studied the reaction rate with which ions from solutions

are removed by the solid ion exchanger or conversely the

rate with which the exchangeable ions are released from the

exchanger. Later on Boyd et al. have studied kinetics of

metal ions on the resin beads and have given a clear

understanding about the particle and film diffusion

phenomenon which govern the ion exchange.

Reichenberg confirmed that at high concentration

the rate is independent of ingoing ion (particle diffusion

control ) Harvie studied the kinetics of Na' -H

28

exchange on crystalline zirconium phosphate. The exchange

rate is initially fast and then becomes slow suggesting a

change in crystal structure. Fuga and Kikindai studied the

; kinetics of ion exchange between alkali metals and zirconium

antimonate in H form at 25°C. They found that the rate of

reaction increases with the atomic number of the cation.

170 Costantino et al. have studied the self diffusion of

Na and K ions on micro crystal of Zr (NaPO/) 3H2O and

Zr(KPO,).3HpO and modified Picks equation to take into

account the non-uniformity of the particle size. The equation

obtained have been employed in a study of self diffusion rate

of Na and K ions in the above exchange.

Some work on kinetics has also been done in our

laboratories. A kinetic study of exchange of cations Ag ,

alkaline earth metals, Y and Th was made on tantalum

171 arsenate . It was a particle diffusion control mechanism.

The kinetic study of Ag , Zn , Cd , Hg , La and Th

172 ions on Fe(IIl) antimonate has been made at different

temperatures,. Here again the mechanism is particle diffusion

control. Various kinetic parameters have been evaluated, much

of the kinetic studies have been done on the synthetic

173 organic ion exchange resins by Junge et al. and

188

29

Modelling of the kinetic processes on ion exchanger

swelling during the reaction was studied by Rodin, V.N.;

189 Volzhinskii, A.I. and Co-workers and they observed that

the non-uniform swelling of the polymeric matrix leads to the

formation of stresses having a strong effect on diffusion

190 process. Evmiridis, Nicholaus & Co-worker studied the

spectrophotometric method for rate determination of the ion

exchange process in solid-liquid heterogenous system

containing NaX, NaA and CaA zeolites. The method can

selectively monitor specific metal ions in the presence of

others. The method can also be used with HPLC to allow the

determination of the metal ions that are eluted. Kinetics of

Na -H ion exchange in concentrated buffer solutions of

sodium borate and boric acid was done by Koloini, T. and

191 192 Others . Helfferich and Friedrich studied the Models and

Physical reality in ion exchange kinetics.

Solid liquid interactions have always been of

interest for many workers because of the diversity of the

phenomena involved and immense application in chemistry and

re]ated sciences.

When a solution containing some solute is brought

into contact with a solid, some of the solute is taken up by

the solid,, The phenomena of the uptake of a solute by a

solid is referred to as "Sorption". In sorption the solute

30

molecules are sorbed either by the inner frame work of the

solid in contact with the solution or by its surface only.

So when the solute is adsorbed by the surface only the

process is called "Adsorption" and when the solute is

adsorbed by the solid to inner layer the process is called

as "Absorption".

Adsorption is a fundamental natural process. It is

one of the most fascinating areas of chemistry since the

molecules on the surface have an environment different from

those in the bulk of the material, the surface energy is

193 different from the energy of the bulk . Concentration of

the molecules of a gas or a liquid on the surface of the

solid is termed as adsorption. This process is different

from absorption which results from the penetration of one

component throughout the body of another.

The adsorbing material is called as adsorbate and

the underlying material is called "adsorbent" or substrate.

Adsorption is of great importance in the field of

agriculture, industries and analytical chemistry.

Adsorption of pollutants by soil, of dyes by wool and

cotton and of impurities by insoluble precipitates are well

known examples. Similarly adsorption indicators and

adsorption chromatography are also well known in the

chemical analysis. Another important application of

adsorption is in catalysis. A surface can catalyse numerous

31

reactions depending upon the configuration of the adsorbed

molecuJe and the nature of the adsorbent. A study of

adsorption phenomena helps us in understanding the process by

means of a molecular model.

The photoelectron spectroscopy method such as

el ectronspectropscopy for chemical analysis can be applied to

reveal some of the bonding properties of the adsorbed

species. In surface studies this is normally referred to as

photoemission spectroscopy. Infrared absorption spectra can

be obtained by using I.R. transparent material and a

technique that involves the internal reflection.

Adsorption is of two types physical and chemical.

The physical adsorption is called as "physisorption" and

chemical adsorption as "chemisorption". In the former the

molecules are adsorbed to a solid surface. In case of

physical adsorption there is a vander waal's interaction

between the surface and the adsorbed molecule. These are weak

types of interaction and the amount of energy released when a

molecule is physisorbed is of the order of 25 KJmol i.e.

the enthalpy of condensation. This energy can be absorbed by

the vibration of the lattice and is dissipated as heat. A

molecule bouncing across the surface will loose its

kinetic energy and stick to the surface resulting in the

rise in temperature of the system, i.e. heat is

evolved. In chemisorption which is shortening of

32

chemical adsorption the molecules stick to the surface as a

result of the formation of chemical bonds, usually covalent

bonds, and tend to find the site that increases their

coordination number with the temperature. Thus the energy

of attachment is greater than is that of physical sorption

-I and is in the range of 200 KJ mol

For a spontaneous process chemisorption must be

exothermic (barring the exceptional case). This can be

explained as follows:

For a spontaneous process AG should be negative.

As the species is adsorbed there is reduction in its

transl ational freedom so A S is also negative. Hence A H

must be negative if AG = AH + TAS is to be negative and a

negative A H value corresponds to the exothermic process.

A formal distinction between the chemisorption and

phystsorption was formerly the magnitude of the entalpy of

adsorbed ion. AH for physisorption is rarely more negative

than about -25 KJ mol while that for chemisorption is

usually more negative and sometimes much more negative than

-40 KJ mol . Plotting of adsorption isotherms is the most

convenient way of studying and understanding the nature of

adospriton taking place in a particular system. The

isotherms are obtained by plotting the amount adsorbed

against the equilibrium concentration at any instant at a

33

particular temperature. Based on these factors adsorption

isotherms can be divided into four main classes and

thereafter into subgroups. The main classes are as follows.

a) Langmuir isotherm or L curves.

b) S. type of isotherms.

c) High affinity isotherm or H curves.

d) Constant partition or C curves.

Langmuir isotherms indicate that molecules are

adsorbed flat at the surface or sometimes vertically

oriented with strong intermolecular attraction. This is the

best known isotherm. These curves occur in majority of

cases of adsorption from dilute solution and for cases of

the other types appear to have been previously recorded.

The initial slope depends on the rate of change of site

availability with increase in solute adsorbed. As more

solute is taken up, there is progressively less chance that

a bombarding solute molecule will find a suitable site on

which it can be adsorbed. The initial curvature shows that

as more sites in the substrate are filled it becomes

increasingly difficult for a bombarding solute molecule to

find out a vacant site available. This implies either that

the adsorbed solute molecule is not vertically oriented or

that there is no strong competition from the solvent. The

type of systems which give this curve have one of the

following characteristics.

34

(1) The adsorbed molecules ai-e most likely to- be adosrbed

flat e.g. resorcinol on alumina (2) If adsorbed end on they

encounter little solvent competition e.g. high polar solute

on substrate or systems with monofunctional ionic

substances with strong intermolecu!ar attraction.

S. type curves indicate the vertical, orientation

of the adsorbed molecule at the surface.

High affinity curves are given by solutes adsorbed

as ionic micelles and by high affinity ions exchanging with

low affinity ions.

And lastly the constant partition curves or the

linear curves are obtained when the solUte penetrates into

the solid more readily than does the solvent.

Nearly, all sufficiently complete curves have

either a plateau or an infliction (knee). Those which do

not have plateau or knee are clearly incomplete ie. surface

saturation is not reached probably because of experimental

difficulties.

The different models for adsorption applicable to

both gases and liquids, are available in literature. They

are however being discussed in brief as follows:

35

(I) Langmuir Mode]

Langniuir proposed

Ce/Am = 1/K x 1/b + (1/b). Ce

where Ce is the equi] ibrium concentration and Am is the

amount adsorbed per specified amount of adsorbent. K is the

equilibrium constant and b is the amount of adsorbate

required to form a monolayer. Hence a plot of Ce/m Vs Ce

should be a straight line, with a slope equal to 1/b and

1/K. l/b as intercept.

(II) Freundlich Model

Accord i ng to Lli i s model

A 1/ r. 1 /n Am = K Ce

In Am = InK + 1/n In Ce

where al1 the terms have the usual significance and n is an

empirical constant. Thus a plot of In Am Vs Ce should give

a straight line with a slope equal to 1/n and intercept

gives the value of InK.

This model deals with the multilayer adsorption of

the substance on the adsorbent.

(III) BET Model

This model was given by Brunaur Emmet and Teller

for a multilayer adsorption.

36

(IV) Temkin Mode]

This mode] dea]s with the adsorption of so]ute on

the adsorbents with the assumption that there are a number

of energetical Jy unequal adsorption sites present in the

adsorbent.

The adsorbents which have been commonly studied are

alumina, silica, carbon and cellulose. These were mainly

used for the adsorption of hydrocarbon, alcohol, phenols,

organic acids, dyes, pesticides and pollutants etc.

Literature survey shows that even inorganic ion exchangers

and organic synthetic resins have also been used for many

adsorption studies Table 2. Adsorption equilibrium of NH^

at NaCarA zeolitic molecular sieve studied by Spindler and

215 Coworkers

The ion exchange materials have found a number of

important analytical applications. An introductory

description on the application of natural and synthetic ion

exchangers have been given by Kuroda . The analytical

applications of ion exchange continue to increase at an

exponential rate. Newer and Newer areas of application are

actively sought day after day. Ion exchange has found its

application in -

1. VJater pollution control - purification of water

2. Removal of interfering ions.

o •H C CO C O u o c

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37

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40

3. Recovery of precious inetaJs.

4. Preparation of deionized water.

5. Water softening.

6. Determination of totaJ salt content of a solution.

7. Separation of metal ions.

8. Separation of organic and biologically important

substances.

9. Concentration of trace constituents.

10. Sepecific spot tests.

11. Location of end point in titration.

12. Gas chromatography, electrophoresis and solid state

separations.

13. Preparation of ion selective electrodes.

14. Preparation of ion exchanger and fuel cells

15. They can be used as acid and base catalysts.

Water pollution is increasing day by day. However,

the methods based on ion-exchange are becoming of promising

success v;hen 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 conventional

methods.

41

Ion exchange has resolved the most difficult problem

in chemical analysis i.e. separation of typical components

having similar enough properties. Ion exchange chromatography

has played an important role in the isolation and

identification - of the concentration and extraction - of the

most important metals and of the new transuranium

217-222 elements and has even been used for enrichment of

9 9 '5 9 9/ isotopes , organic substances such as amino acids ,

O T r 99fi

alcohol 5 carbonyl compounds etc. They have also been

separated in ion exchange column. The more recent application

of ion exchange resin Includes the collection of

2 27 228 Sclenium(IV) ppb level of aluminium pre concentration

229 230 of cobalt . M.B. , Evans, and J.K., Haken studied the dispersion and selectivity indexes in gas chromatography.

t

231 Bowling, Evans & Co-worker studied the

Gas-liquid chromatography in qualitative analysis and also

the study of the dependence of the retention behavior of

polyoxyethylene glycol columns on the nature of the support

and phase loading. Similarly many more Studies in gas

232 233 chromatography have been done by Evans & Co-workers '

Ion exchange has been used with success in food

industry. The ion processing of wine is commonly practised by

large manufacturer in the U.S.A. It is worth recording that

the use of strong acid cation exchange resins in the H form

42

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 (dealkyllzation) for the production of feed

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

production of sweetner 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.

A recent application of ion exchangers has emerged

as their use in the preparation of fuel cells. Ion exchanger

fuel cells have many advantages over others such as their low

cost, pollution free operation, regenerative nature and easy

reaction conditions. However very few literature is available

on the ion exchanger fuel cells. A cation exchange membrane

234 electrolyte has been used by Fugita et al. for the

235 preparation of a fuel cell. Mucoyama et al . used a

strongly acid cation exchanger resin for this purpose. A

fibrous ion exchanger sheet has also been used for the

236 preparation of the fuel cell

43

237 2'hao & Co-workers studied the method for

recovering Mo from industrial effluent by a new type of ion

238 exchanger resin. Zhu and Co-workers studied the

application of accelerative effect to the separation of

uranium isotopes by cationic ion exchange.

Ion exchange resin for extraction of gold from

alkaline leaching slurries was done by Hester and

n^u 239 Others

The present work was carried out to study mechanism

of ion exchange on a synthetic inorganic ion exchanger 1inde

molecular sieve (13X) by the kinetic studies for rare earth

2+ 2+ 2+ + metal ions: Ca , Mg and Sr -Na exchange systems, to

calculate the parameters like diffusion coefficient, energy

of activation and entropy of activation. The work was

undertaken to thermodynamic studies on the 1inde molecular

sieve (13X), to equilibrium studies for the sorption of Ag

on tin thioglycolate a chelating material to calculate the

thermodynamic parameters like AH, AS and A G using a

VAX-11 computer.

The work was also carried out on a zeolite type

exchanger, sodium stannosilicate mainly to study the

mechanism of ion exchange and distribution studies has been

carried out of some metal ions in non-aqueous medium on 1inde

molecular sieves (13X) and sodium stannosilicate.

44

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56

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57

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59

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Ramankov, P.G.; Zh. Prikl. Khim.; 62(9), 2004-10

(1989)

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60

191. Koloini, T.; Plazl, I.; Zumer, M.; Chem. Eng. Commun.;

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E.S.; Simanova, S.A.; Zh. Prikl. Khim.; 57(7),

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64

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27 Dec. 1989 Appl. 89/2733, 14 Apr. (1989).

65

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

earlier in 1940's by Nachod & VJood then by Nan Col las &

Paterson'", since then much of the kinetic work has been done

on inorganic ion exchangers mainly zeolites. Kinetics of the

vapour adsorption of Cc - C.r. n-alkane and Cyclohexane on 3

zeolite (analogous to ZMS 5) vv'as investigated by dynamic

process. Desorption kinetics of C^ - C.^ alkanes & C^H^

were studied from zeolite CaA and NaX. The kinetic studies

of oxygen sorption of Ce ion was studied on linde sieves

13X . Ragimov et. al . studied kinetics of crystallization

and ion exchange properties of an L - D zeolite, Werling

et. al . applied the math model to study the kinetics of

adsorption and desorption process of 2 commercial molecular

8-17 sieves. Similar kinetic studies were done by others on

zeolites .

This chapter deals with the kinetic studies of Mg ,

Ca and Sr on Linde sieves 13X. Experimental and theore­

tical approaches have been used to show the rate of

diffusion through the particle. Various parameters like Do,

Ea and A S"have also been calculated.

66

EXPERIMENTAL

Reagents and Chemicals:

Linde Adsorbent Molecular sieves (13X ) in Na" form

were used (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 0.05 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 \'3as determined by the

1 8 method proposed by Dyal and Hendricks . For this purpose

1.0 gm of the exchanger \<ias taken in an aluminium box. It

was dried at 25j l°C in an air oven and kept in a dessicator

over P7O1-. A constant weight of this dried sample was

recorded. After that the exchanger was rinsed with ethylene

glycol dropwise with the help of pipette. Excess of

67

ethylene glycol was evaporated in an air oven at 60_+l°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.

Surface area

Wt. of ethylene glycol retained by exchanger (g)

Wt. of dried exchanger x 0.00031

KINETIC MEASUREMENTS:

Conditions approaching infinite bath technique were

used to perform the kinetic measurement on linde sieves with

particles of mean radius 0.125 um were used unless

stated other wise. 50 ml fractions of the metal ion solution

(Mg , Ca and Sr ) were shaken with 500 mg of the

exchanger in Ha form in several stoppered conical flasks at

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

different time intervals. Supernatant liquid was immediately

removed and analyzed for its metal ion content. The alkaline

earth metal ions were determined by titrating with EDTA

using Eriochrome black T as an indicator.

INTERRUPTION TEST:

21 For performing the interruption test , eleven

stoppered conical flask were taken. In each flask 50 ml

Mg solution was taken and thermostated at room temperature

(25°C). To each flask 0.5 g of exchanger was added and after

68

the specific time interval the solution was separated from

the exchanger beads. The first reading was taken after 2

minutes. 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 supernatant solution was determined

at various time intervals again.

69

RESULTS

The results of ion exchange capacity of Linde sieve (13X)

for alkaline earth metal ion are summarized in table 1.

Table 1. Ion exchange capacity of Linde sieve (13X)

Metal ion Taken as Capacity meq/g

Mg nitrate 1.2

Ca nitrate 2.2

Sr nitrate 4.0

Interruption Test:

Interruption test was performed for Mg - Na

exchange on Linde sieves (13X) in Na form. The u(t)

(fractional attainment of equilibrium) values as a function

of time before and after interruption of 10 minutes at

25+_l°C are given in table 2 and are plotted in Fig. 1.

Table 2: Interruption test for Mg - Na exchange on Linde

Molecular sieves (13X) at 25 + 1°C

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

1 2 0.2765

2 5 0.2978

3 10 0.4680

70

c

£

E

z o UJ o z < I o X

+ o z

I +

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o LU

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z o z o t—

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71

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

4

5

6

7

8

9

10

11

20

40

10 Minutes

0

10

20

40

60

80

Intel rruption

0.5950

0.6808

0.6808

0.8290

0.9000

0.9140

0.9140

0.9140

Effect of Temperature:

In order to see the effect of temperature the

kinetics was performed for Mg , Ca and Sr at four

different temperatures viz. 5°, 25°, 45° and 65 +_ 1°C. u (t)

values as a function of time are calculated and the

corresponding Bt values are taken as tabulated by

1 9 Reinchenberg . The results are given in table 3, 4 and 5.

The results of u (t) Vs time at different temperatures for

the above mentioned cations are plotted in Fig. 2, 3 and 4.

While the results of Bt Vs time are plotted in Fig. 5, 6

and 7.

72

Effect of Concentration :

The diffusion studies were performed on Mg for

different concentrations The results of u (t) and Bt as

function of different concentrations at 25 +_ 1°C are given in

table 6. The Bt values as a function of time for Mg - Na

exchange at 25 +_ 1°C for five different concentrations are

plotted in Fig. 9.

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

on Linde Molecular sieve (13X) at different

temperatures.

Time (min) u (t) Bt

Mg - Na exchange at S'C

2 0.291 0.086

5 0.236 0.052

10 0.236 0.052

20 0.277 0.073

40 0.236 0.052

60 0.236 0.052

80 0.380 0.157

100 0.416 0.188

120 0.347 0.122

Mg " - Na^ exchange at 25°C

2 0 .323 0 .107

5 0.382 0.157

73

Time (min) u (t) Bt

To 0.367 0.139

20 0.397 0.167

40 0.557 0.382

60 0.622 0.522

80 0.470 0.259

100 0.470 0.259

120 0.720 0.798

Mg2+- Na^ exchange at 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 0.691 0.703

80 0.721 0.790

100 0.770 0.985

120 0.720 0.798

Mg2+- Na" exchange at SS'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 2.160

80 0.805 1.126

100 0.864 1.460

120 0.898 1.700

74

+-

140

Time (min )

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

75

Table 4: u (t) and Bt values as a function of time for Sr

on Linde Molecular sieves (13X) at different

temperature

Time (min) U (t) Bt

Sr2'* -Na" exchange at 5''C

2 0o265 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

Sr2+-Na" exchange at ZS'C

2 0.090 ' 0.007

5 0.196 0.034

10 0.330 0.114

20 0.409 0.177

40 0.651 0.5921

60 0.800 1.100

80 0.680 0.675

100 0.790 1.073

120 0.770 0.985

76

Time (min) U (t) Bt

2+ +

Sr -Na exchange at 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

Sr -Na exchange at GS'C

2 0.232 ' 0.052

5 0.214 0.042

10 0.660 0.479

20 0.571 0.419

40 0.660 0.620

60 0.870 1.521

80 0.840 1.340

100 0.840 1.340

120 0.946 2.320

77

10 20 30 40 50 60 70 80 90 100 110 120 130

T ime ( m in )

FIG.3 RATE OF EXCHANGE OF S r 2 + A T DIFFERENT TEMPERATURE ON LINDE SIEVES 13 X .

T^547

78

Table 5: u (t) and Bt values as a function of time for Ca

on Linde Molecular sieves (13X) at different

temperature

Time (min) u (t) Bt

Ca -Na exchange at 5°C

2 0.291 0.086

5 0.291 0.086

10 0.375 0.148

20 0.291 0.086

40 0.330 0.110

60 0.440 0.222

80 0.52C 0.332

100 0.450 0.232

120 0.472 0.259

Ca -Na exchange at 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 0.3820

79

Time (min) U (t) Bt

Ca -Na* exchange at 45°C

2 0.420 0.199

5 0.449 0.220

10 0.420 0.199

20 0.550 0.382

40 0.623 0.522

60 0.681 0.675

80 0.681 0.675

100 0.720 0.798

120 0.811 1.170

Ca -Na exchange at 65°C

2 0 .326 1.0760

5 0 .134 0.0156

10 0 .364 0 .1391

20 0 .365 0 .1391

40 0 .730 0 .8320

60 0 .615 0.5000

80 0.850 1.4000

100 1.000 OO

120 0.923 2.0300

80

10 20 30 40 50 60 70 60 90 100 HO 120 130 140

Time ( mm )

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

81

o LO

VD

C3 0 0 LO 1/1 U^ •J- (VI O

X m

LJ > UJ

LU O

LU O

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u.

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o UJ

< a. LU X

z o

CL

UJ

u. o

UJ u, u. UJ

o u.

>8

84

Table 6: u(t) and Bt values asafunction of concentration for

2+ + Mg -Na exchange on Linde Molecular sieve {13X) at

25 + 1°C

Time (min) U (t) Bt

With concentration .002 M

5 0.303 0.092

10 0.378 0.148

20 0.530 0.348

40 0.757 0.905

With concentration .005 M

5 0.215 0.042

10 0.359 0.130

20 0.441 0.222

40 0.503 0.301

With concentration .01 M

5 0.180 0.030

10 0.310 0.099

20 0.380 0.157

40 0.456 0.234

With concentration .02 M

5 0.151 0.021

10 0.272 0.073

20 0.321 0.107

40 0.391 0.107

85

Time (min) U (t) Bt

With concentration .04 M

5 0.127 0.013

10 0.170 0.027

20 0.340 0.122

40 0.352 0.130

86

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88

DISCUSSION

From table 1 it is evident that the Linde sieve 13X

shows a considerable ion exchange capacity for alkaline

earth metal ions and varies from 1.2 to 4 meq g . The ion

exchange capacity varies according to the following order

Mg < Ca < Sr

That is Sr having lowest hydrated ionic radii is exchanged

to the maximum extent.

The surface area of the Linde sieve 13X determined

1 8 by Dyal and Hendricks method was found to be 483.87

2 -1 m gm

Rate of exchange studies show that in the beginning

the rate of exchange increases and after sometime it becomes

constant indicating the attainment of steady state.

20 According to Boyd et al . mainly two potential

diffusion processes are considered, "particle diffusion"

where the interdiffusion of counter ions takes place within

the ion exchanger itself and "film diffusion" where the

interdif fusion of the counter ion is in the adherent film.

Particle diffusion control (PDC) phenomenon is favoured by

high metal ion concentration, relatively large particle size

of the exchanger and vigorous shaking of the exchanging

mixtures,under these conditions the fractional attainment of

89

equilibrium with time is given by the following expression

C - C. u (t) o t

C^ r

where C , C^ and C ^ are concentration of the ions in the o' t CO

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

21 2 +

control . This test was applied for Mg ions where

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

reimmeision and hence the rate should be controlled by

particle diffusion. This is because the concentration

gradients disappear in the particle during the interruption

and on reimmersion are much greater than before at the

surface. Therefore the experimental conditions were choosen

accordingly to explain the particle diffusion mechanism.

Kinetic parameters were obtained by using the equation 20 developed by Boyd et. al. and improved by Riechenberg.

The u (t) values at different time intervals and

different temperatures obtained for Mg , Sr and Ca ,

+ -Na , 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

90

ions is rapid initially then it becomes slow and finally

reaches a constant value with increase of time. The results

22 are analogous with that of Heitner and Markovits

As the particle diffusion is the rate determining

step the following equation is valid

,(t) -1--^ \ --P -f ^'^ .... (2) 71^ n=l n^

u p TT^ Pi where B = (3) r

where r is the radius of the particle, D^ is the effective

diffusion coefficient of two exchanging ions inside the

23 resin phase and t is the time. The typical Bt Vs t plots

at four different temperatures, 5°, 25°, 45° and 65°C for

Mg , Sr and Ca -Na exchange given in figures (5 to 7)

show that the rate of exchange is directly proportional to

temperature. In all cases the plots of Bt Vs t are linear,

passing through the origin. This further indicates that the

rate determining step is diffusion through the particle at

all temperatures studied.

Concentration has a marked influence on the rate of

exchange. A plot of Bt versus t for five different

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

inversely proportional to the concentration (this statement

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

91

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 than this value the B

value is nearly constant. B values are given in table 7.

From the Bt versus t plots, B values were calculated. From

the values of B and knowing the radius of the particle the

values of the effective diffusion coefficient D. controlling

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

D-j are given in table 8. A plot of log Di versus l/T K (Fig.

11 to 13) shows a linear relationship.

Table 7: B values as a function of temprature and concen­

tration

Cation Concentration ^-^ ( i n M o l a r i t y ) ^ ' ^ (25°C)

Mg^^ 0 .002 2 . 3 X 10"^

0 .005 2.08x 10"^

0.010 1.27x 10"^

0 .020 0 .875x10"^

0 .040 0 .67x 10"^

92

2.1

2 . 0

1 6

m 1-2

1.0

0.0

U G

0 U

0.2

100 200 300 400 500

l/C Cone. ( m o l e ' M

600

FIG.10 PLOT OF B VS. I /C FOR M g 2 * AT 2 5°C .

93

2 Table 8: Value of Dj (m /sec) of various ions at different

temperatures on Linde Molecular sieves (13X)

Cation 5° 25° 45° 65°

Mg^^ 2.768x10'^^ 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 activation Ea, for the diffusion process

was obtained from the slope of a linear plot of log Dj

versus 1/T K assuming the Arrhenius equation.

D^ = Do exp (- Ea/RT) 4(a)

On extrapolating the plot of Jog D;i_ versus l/T K (Fig. 11 to

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

in the following equation 4(b) gives entropy of activation,

AS"

Do = 2.72 d^ KT/h exp ( A S ' V R ) 4(b)

where d is the ionic jump distance assumed equal to

"10 -7^

5x10 m, K is the Boltzman constant equal to 1.38x10

JK mole , h is planck's contant equal to 6.6x10

Joule sec. T was taken as 273 K, R is the gas constant

-1 -1 '" equal to 8.3lJouleK mol . The values of Do and AS are given in table 9.

94

Table 9: Diffusion coefficient, energy of activation and

entropy of activation of migrating ions on Linde

Molecular sieves (13X) in Na form

2 -1 Migrating Do, m S

ion

Ea,

kJ mole

A S

J deg mole

Mg

Ca

Sr

2 +

2 +

2 +

1.995x10 -9

7.943x10 •10

7.94 xlO -11

17.728

14.984

13.163

•62.90

-76.6245

-89.768

Thus the value of A S support the order of the

extent of exchange of these ions. That is, Sr is exchanged

to the maximum value because of lowest entropy change and

Mg to the lowest value due to maximum entropy value. The

Do values of these ions suggest that probably ions migrate

inside the exchanger in unhydrated form. Further the Ea

values are parallel to the values of hydration number of the

ions. This means energy is required for the dehydration of

these alkaline earth metals.

On the basis of these results we can suggest that

probably the following mechanism is involved in the exchange

of magnesium, calcium and strontium ion on linde sieve (13X)

zeol ites.

95

The ions shed some of the water of hydration at the

surface of bead, enter into the pore, and diffuse inside the

exchanger upto the exchange site in unhydrated form. At

exchange sites they are exchanged as such without creating

any hinderance in the matrix of the zeolite. Though this is

a limited bath system, it may be considered to follow the

infinite solution volume conditions because CV >> C V and

C and C are the metal ion concentrations in the solution and

the exchanger phases respectively, and V and V are the

volumes of these phases.

96

m

in m

in

rsi

o

o (M

1 O — X

V—

m 2r <

<

o o

. S ^ UJ T"^ & 0 1 -

97

I

X

— • - ?

P o o

^ - s 2 uj yn^ 6 01 -

98

+ (Nl

a: o u.

m 1 O '~ X

—

1— to z — < o <

•>< i o o o

m

o U-

L-s ^u j Y0_6o| -

99

REFERENCES

1. Nachod, F.C. and Wood, W. , J. Am. Chem. Soc, 66, 1380

(1944).

2. Nancollas, G.H. and Paterson, R., J. Inorg. Nucl. Chem.,

22, 259 (1961).

3. Grigoliya, E.L. and Rusiya, E.A., Soobshch. Akad. Nauk.

Gruz, 122(1), 109-12 (1986).

4. Evs;eev, L.N., Seballo, A.A. and Plachenov, T.G., Zh.

Prikil. Khim, 50(8), 1815-20 (1977).

5. Tempere, J.F., Bozon-Verduraz, F., Delajosse, D. and

Cornu, 0., Mater. Res. Bull., 12(9), 871-9 (1977).

6. Ragimov, N.G., Ganbarov, D.M., Alieva, Sh. A. and Mamedov,

Kh.S., Dokl. Akad. Nauk. AZ, 35(5), 48-52 (1979).

7. Werling, K. and Wimmerstedt, R., Chem. Eng. Sci., 35(8),

1783-6 (1980).

8. Mitra, N.K., Ghatak, S. and Mitra, S., J. Chem., 19A(3),

195-9 (1980).

9. Barrer, R.M., Zeolites 5th 1980 Proc. Int. Conf., 273-90

(1980).

10. Costa, E. , Sotelo Sacho, J.L., Gutierrez Carreras, M.L.

and Uguina Zamorano, M.A., An. Quim. Ser., 76(2), 282-8A

(1980).

100

11. Kocirik, M., Smutik, M., Bezus, A. and Zikanova, A.,

Collect, Czech. Chem. Commun, 45(12), 13392-40 (1980).

12. Buelow, M. , Struve, P. and Mietk, W., Z. Phys. Chem.

267(3), 613-16 (1986).

13. Kang, T. , Uh, Y.S., Kim, Y.M. and Seo, G., Hwahak,

Konghak, 25(3), 313-18 (1987).

14. Borowiak, M.A. and Berak, J.M., Zeolity Synt.

Tchzastosow, Ratal., Pr. Semin. Szk, 30-8 (1974).

15. Solomakha, V.N. and Ilin, V.G., Adsorbtsiya Adsorbenty,

5, 37-42 (1977).

16. Wolf, F., Golz, C. and Pilochowski, K., Z. Phys. Chem.,

257(6), 1148-52 (1976).

17. Kiezel, L., Liszka, M., Rutowski, M. and Gryta, M., J.

Chem. Soc. , Chem. Commun., (2), 34-5 (1977).

18. Dyal, R.S. and Hendricks, S.B.; Trans. 4th Inter. Congr.

Soil Sci., 2, 71 (1950).

19. Reichenberg, D. , J. Am. Chem. Soc, 75, 589 (1953).

20. Boyd, G.E., Adamson, A.W. and Myers, L.S., J. Am. Chem.

SCO., 67, 2836 (1947).

21. Kressman, T.R.E. and Kitchner, J.A., Discussion Faraday

Soc., 7, 90 (1949).

22. Carla-Heitner-Wirguin and Markovits, G., J. Phys. Chem.,

67„ 2263 (1963).

CHAPTER - III

EQUILIBRIUM STUDIES FOR THE SORPTION OF Ag" ON

TIN THIOGLYCOLATE -A CHELATING MATERIAL

102

INTRODUCTION

Recently ]igand ion exchangers are receiving

considerable attention. The use of complexing agent

increases the selectivity for exchange between a liquid

and a solid phase. The solution behaviour is influenced by

the chemical reaction between the metal ion and the

complexing agent. In the complexing tendency the 1igand

ion exchange behaviour is similar to the complexing agent,

which can accept and release the metal ion in the

solution.

Many organic ion exchange resin based chelating

ion exchanger have been synthesized and utilized. However,

the possibility of using an inorganic based chelate ion

exchanger has not been explored to a great extent.

Hydroxides of Sn , Zr , Al chelate resins ' fi -J

with oxime , pyridinium tungstoarsenate , stannic

8 9 diethanolamine , Titanium diethanolamine , Thorium

triethanolamine , Zirconium triethanolamine , Aluminium

1 ? 11-16 triethanolamine and others were used as 1igand

exchangers.

To develop the materials of this kind a new

chelate ion exchanger tin thioglycolate has been

synthesized. This material shows great affinity towards

2+ + Hg and Ag by the formation of a complex with

thioglycolate.

103

Mercury has received a great deal of attention in

the field of environmental pollution, organic and inorganic

compounds of mercury are very toxic in nature, particularly

in water. Macchi et al.-^^, Gladkov"^^, Sraith" , Maeda^"^ &

21 Terada successfully tried the chelate exchangers to remove

the mercury from waste water.

To understand the behaviour of complex formation,

the sorption of Ag on tin thioglycolate has been studied in

detail. The thermodynamic parameters viz. AH, AS and AG

vv'ere computed using least square method on VAX-11 computer.

IR study has been reported for the physical characterization

of the material and elucidation of mechanism of sorption.

104

EXPERIMENTAL

Reagents: Thioglycolic acid (Loba, India) and stannic

chloride (Loba, India) were used to prepare the exchanger.

All other chemicals used were of analytical grade.

Different concentrations of silvernitrate ranging

from 0.025 M to 0.30 M were made in buffer solution of pH

5.6.

Apparatus: An electric temperature controlled shaker (Sico)

was used for shaking. While IR studies were performed on

IR-20 spectrophotometer.

Synthesis: O.IM solution of thioglycolic acid was mixed

with O.IM solution of stannic chloride in the ratio of 3:6:

1. The product was heated till boiling, so that the

precipitation was complete. The precipitate was kept

standing for 24 hrs at room temperature. After that it was

filtered, washed and dried in a temperature controlled

electric oven at 40^^1°C. The exchanger was broken down into

small particle by immersing in water. It was washed and

dried again at 40^1°C.

Adsorption studies: Equilibrium isotherms were determined by

contacting a constant mass (0.2 gm) of exchanger with the

metal solution (0.025 to 0.30 M)in the stoppered conical

105

flasks and agitated in the shaker at constant temperature.

Equilibrium isotherms were determined for two variables.

(1) Variation of adsorbent particle size (0.355, 0.250,

0.1150,<( 0.150) .

(2) Variation of temperature of the metal solution at

constant particle size i.e., 10°C, 30°C, 45°C and

65°C.

The system was contacted for a period of 24 hrs to

ensure equilibrium after which it was filtered and the

concentration of metal solution was determined by KSCN

titration using Ferric Alum indicator.

Data Treatment: The results were treated for the fitting of

Freundlich and Langmuir isotherms. The equations are as

fol1ows.

(a) Freundlich equation

/ ^ ^ 1/n X/m = K C^ ' (1)

or In x/m = In K + i In C

b) LangmuiT equation

C 1 , e r 1

= — i - + C ] (2) x/m b K 6

106

where

C = Equilibrium concentration of Ag in gm/litre.

b = maximum amount of substance needed in gms per

gram of the adsorbent for the monolayer

formation.

x/m = Amount of Ag uptake in grams per gram of the

exchanger

(C - Cg ) X 6.354 x/m =

500

where C and C are the initial and the final concentrations o e

of the metal ion at equilibrium.

107

RESULTS

Sorption capacity: To determine the sorption capacity

0.5 gni of the exchan",er was shaken with 20 ml of O.IM

solution of Ag for 24 hrs, after which the unsorbed cation

left in the supernatant solution was determined and

sorption capacity was calculated as 0.46 meq/gm.

Rate of Sorption: The rate of sorption of Ag was

determined by batch process where 20 ml of O.IM AP

solution was shaken thoroughly with 0.2 gn of the exchanger

in stoppered conical flasks. After appropriate intervals of

time, the contents of the flasks were filtered and titrated

against KSCN. The amount of Ag sorbed was calculated by

the difference in the initial and final amount of the metal

left after shaking. The corresponding results are plotted

in Fig. 1.

Infra-red analysis: IR analysis of Tin thioglycolate sample

was performed using KBr disc technique Fig. 2. The sorption

isotherms for the sorption of Ag on tin thioglycol ate at

different temperatures are plotted in Fig. 3 while for

different particle size at constant temperature are plotted

in Fig. 4.

Both Freundlich and Langmuir isotherm equations

were applied for the sorption of Ag on this exchanger. In

108

order to test the validity of Freundlich equation values of

In x/m from the best fit line by the method of least

squares are given in table la to Id and 2a to 2d, for

different temperatures at constant particle size and for

different particle size at constant temperature

respectively. The statistical parameters are given in tables

le and 2e respectively for Langmuir equation to be tested

the values of x/m, C , C /(x/m) at different temperatures

at constant particle size and for different particle sizes

at constant temperature are summarized in tables 3a to 3e

and 4a to 4d and statistical parameters are given in

tables 3f and 4e respectively. Plots of C /(x/m) Vs C are

presented in Fig. 5 and 6 respectively.

109

1 O r

^ 5 6 7

T im i in ( hours )

Fig 1 Plot of F ( t ) vs t ime (Rate of sorption of Ag*)

24

110

o u m a o O < z

O o

o o 00

o r-

o o CO

O o Ol

o o o •— o o

o 1 '^

o o

• ro

o o

- -1 •"

o o

~ in

o o

~ VO

O o

~ r-

O O

~ CO

O O

~ en

" O o

~ o rM

O O

"• in (N

O o o rn

O O

" tn n

O O O

—d-J-

1

2 o Q; Ul

2

Z UJ

> < ?

U) CD

a: o 0") o < z D

*— UJ t—

< _J o u >-

o

z t—

LL

o

< a: t—

UJ a tn

t—*

• — •

o PNl

o LL

(•/.) 3DNVi i lWSNVt i i

I l l

u

a UJ CO

2 U > <

Q UJ CD CC O (yi Q < UJ

(— < _J o >-_J o o

LL

o < Q: I— (J UJ

a

cc

O LL

(V.) 3 D N V i i m S N V a i

2 5 r

113

1.5 - •—•--• .355

05

e X

02

0 01 02 03 06

A.250

.05 06

Equilibrium concentration of Ag* ,Ce(gm/ l i t )

Fig.4 P l o t o f X / m v s Ce for dif ferent mesh size ( microns ) at 3011°C

114

Table 1

Adsorption of Ag on Exchanger, Fitting of Freundlich Equation

at different temperatures for a constant particle size.

(a) Studies at 10.00 degree celcius

m

0.70

1.00

1.35

1.70

1.70

1.90

1.70

1.97

1.77

1.77

1.85

C e

0.000

0.000

0.002

0.007

0.008

0.013

0.019

0.026

0.360

0.460

0.565

] n x/m

-0.356

0.000

0.300

0.530

0.530

0.641

0.530

0.680

0.573

0.573

0.615

In C e

-23.71

-23.71

- 5.99

- 4.89

- 4.82

- 4.30

- 3.95

- 3.63

- 3.32

- 3.07

- 2.87

1n x/m (mol)

-0.187

-0.187

0.483

0.524

0.527

0.547

0.560

0.572

0.584

0.593

0.601

112

E X

0 10 20 30 40 50 60

CeXlQ-^ Equ i l i b r i um concentrat ion of Ag* ,Ce ( g m / l i t . )

Fig.3 : Plots of X / m vs. Ce at d i f ferent temperatures for the some particle s ize.

115

(b) Studies at 30.00 degree celcius

^

0 .70

1.00

1.55

1.95

1.90

1.90

2 .10

2 .12

2 .20

2 .17

2 .27

C

0 .000

0 .000

0 .000

0 .005

0.006

0 .013

0 .015

0 .025

0 .031

0 .042

0 .052

^" \ .

- 0 . 3 5 6

0 .000

0 .438

0 .667

0 .641

0 .641

0 .741

0 .753

0 .788

0.777

0 .822

In C

- 2 3 . 7 1

- 2 3 . 7 1

- 7 .60

- 5.29

- 5 .11

- 4 .30

- 4 . 1 8

- 3 .68

- 3 .44

- 3 .17

- 2 .95

In x/m(mod)

- 0 . 1 9 2

- 0 . 1 9 2

0 .552

0 .659

0 .667

0 .705

0 .710

0 .733

0 .744

0.757

0 .767

(c) Studies at 45.00 degree celcius

0 .70

1.00

1.55

2 .00

2 .00

2.17

2 .25

2 .37

2 .47

2 .55

2 .75

0 .000

0 .000

0 .000

0 .004

0 .005

0 .010

0 .013

0 .022

0.029

0 .038

0 .047

- 0 . 3 5 6

0 .000

0 .438

0 .693

0 .693

0.777

0 .810

0 .865

0.906

0.936

1.011.

- 2 3 . 7 1

- 2 3 . 7 1

- 7 .60

- 5 .40

- 5 .29

- 4 .53

- 4 .28

- 3 .79

- 3 .54

- 3.26

- 3 .04

- 0 . 2 0 6

- 0 . 2 0 6

0.637

0 .752

0 .758

0 .798

0 .811

0.837

0 .850

0 .865

0.876

116

(d) Studies at 65.00 degree celcius

x/m

0.70

1.00

1.55

2.25

2.37

2.47

2.47

2.57

2.67

2.80

3.02

C

0.000

0.000

0.000

0.002

0.001

0.007

0.011

0.020

0.027

0.035

0.044

In x/m

-0.356

0.000

0.438

0.810

0.865

0.906

0.906

0.945

0.983

1.029

1.106

In C

-23.71

-23.71

- 7.60

- 6.21

- 6.68

- 4.86

- 4.46

- 3.88 -

- 3.61

- 3.33

- 3.10

In x/m(mod)

-0.203

-0.203

0.734

0.815

0.787

0.893

0.916

0.950

0.966

0.982

0.995

(e) Statistical Parameters at different temperatures

Temp. Regression Equilibrium 1nK 1/n

(°C) coefficient(R) const (K)

10 0.940 0.20339E+01 0.710 0.037

30 0.968 0.24699E+01 0.904 0.046

45 0.961 • 0.28172E+01 1.035 0.052

65 0.959 0.32431E+01 1.176 0.058

117

Table 2

Fitting of Freund]ich equation for different particle size at

25+1°C

(a) Studies for <0.15 um particle size

X /m

gra/gm

0.028

0.039

0.060

0.080

0.081

0.090

0.095

0.101

0.105

0.105

0.112

C e

gm/1it

0.000

0.000

0.001

0.004

0.004

0.010

0.012

0.021

0.027

0.037

0.047

1 n x/m

-3.575

-3.223

-2.813

-2.525

-2.503

-2.407

-2.353

-2.292

-2.253

-2.251

-2.189

In C e

-11.512

- 9.903

- 6.907

- 5.403

- 5.381

- 4.605

- 4.382

- 3.863

- 3.593

-3.283

- 3.057

In :< /n ( mod)

-3.529

-3.270

-2.787

-2.545

-2.541

-2.416

-2.380

-2.296

-2.535

-2.203

-2.167

118

(b) Studies for 0.1150 um particle size

x/m gm/gm

0.028

0.039

0.062

0.077

0.080

0.085

0.090

0.095

0.097

0.102

0.108

C e gm/lit

0.000

0.000

0.000

0.005

0.005

0.011

0.013

0.022

0.029

0.038

0.048

1 n x/m

-3.57

-3.22

-2.78

-2.56

-2.52

-2.46

-2.40

-2.35

-2.33

-2.28

-2.22

In C e

-11,51

- 9.90

- 7.60

- 5.24

- 5.29

- 4.48

- 4.28

- 3- 79

- 3.52

- 3.26

- 3.03

In x/m(mod)

-3.488

-3.248

-2.905

-2.555

-2.562

-2.442

-2.412

2.338

-2.298

-2.259

-2.226

(c) Studies for 0.250 urn pa r t i c l e s ize

0.028

0.039

0.059

0.071

0. 071

0.072

0.077

0.080

0.084

0.085

0.086

0.000

0.000

0.001

0.006

0.007

0.014

0.017

0.026

0.032

0.042

0.053

-3.57

-3.22

-2.83

-2.64

-2.63

-2.63

-2.56

-2.525

-2.47

-2.45

-2.45

-11.51

- 9.90

- 6.68

- 4.99

- 4.95

- 4.23

- 4.07

- 3.64

-3.41

- 3.16

- 2.92

-3.489

-3.289

-2.887

-2.677

-2.671

-2.581

-2.562

-2.507

-2.480

-2.448

-2.419

119

(d) Studies for 0.355 um particle size

x/m

gr.i/gm

0.650

0.900

1.400

1.950

1.550

1.525

1.525

1.575

1.650

1.775

1.750

gm/lit

0.000

0.001

0.002

0.005

0.009

0.017

0.021

0.030

0.037

0.046

0.057

In yj m

-0.430

-0.105

0.336

0.667

0.438

0.422

0.422

0.454

0.500

0.573

0.559

In C e

-7.600

-6.907

-6.214

-5.298

-4.656

-4.059

-3.863

-3.490

-3.290

3.079

2.856

In x./m ( mod )

-0.126

-0.014

0,097

0.246

0.350

0.447

0.479

0.539

0,571

0,606

0.642

(e) The S t a t i s t i c a l parameters for different Part ic l e s i z e at 25j|^l°C

Mesh size

yMm

Regression coefficient

(R)

Equilibrium constant

K

InK 1/n

<0.15

0.1150

0.250

0.355

0.997

0.992

0 .991

0 .809

0.18745E+00 -1.674 0.161

0.16969E+00 -1.774 0.148

0.12829E+00 -2.053 0.124

0.30195E+01 1.105 0.162

120

Table 3

Adsorption of Ag on Exchanger, Fitting of Langmuir equation

(a) Studies at 10.00 degree Celsius

x/m Cg Cg /f x/m) C^/( x/m ) ( mod )

( g r o / ] i t )

0 .000

0 .000

0 .001

0 .004

0 .004

0 .007

0 .010

0 .014

0 .019

0 .025

0.056

0 .700

1.000

1.350

1.700

1.700

1.900

1.700

1.975

1.775

1.775

1.850

0 .000

0 .000

0 .002

0.007

0 .008

0 .013

0 .019

0.026

0.036

0.046

0.056

0 .000

0 .000

0 .001

0 .004

0 .004

0.007

0 .011

0 .013

0 .020

0 .025

0 .030

121

(b) Studies at 30.00 degrees celcius

x/m

0 .700

1.000

1.550

1.950

1.900

1.900

2 .100

2 .125

2 .200

2 .175

2 .275

C e g m / l I t

0 .000

0 .000

0 .000

0 .005

0.006

0 .013

0 .015

0 .025

0 .031

0 .042

0 .052

C /^x/m) e

0 .000

0 .000

0 .000

0 .002

0 .003

0.007

0 .007

0 .011

0 .014

0 .019

0 .023

C /(x/m){mod) e

0 .000

0 .000

0 .000

0 .002

0 .003

0 .006

0 .007

0 .011

0 .014

0 .019

0 .023

(c) Studies at 45.00 degree celcius

0.700

1.000

1.550

2 .000

2 .000

2 .175

2 .250

2 .375

2 .475

2 .550

2 .750

0 .000

0 .000

0 .000

0 .004

0 .005

0 .010

0 .013

0 .022

0 .029

0 .038

0.047

0 .000

0 .000

0 .000

0.002

0 .002

0 .004

0.006

0 .009

0 .011

0 .015

0.017

0 .000

0 .000

0 .000

0 .002

0 .002

0 .004

0 .005

0 .008

0 .011

0 .014

0 .018

(d) Studies at 65.00 degree celcius

122

>V'm c e

gm/lit 0.000

0.000

0.000

0.002

0.001

0.007

0.011

0.020

0.027

0.035

0.044

C /(x e

0.000

0.000

0.000

0.000

0.000

0.003

0.004

0.008

0.010

0.012

0.014

C /(xlm) e (mod)

0 .700

1.000

1.550

2 .250

2 .375

2 .475

2 .475

2 .575

2 .675

2 .800

3 .025

0 .000

0 .000

0 .000

0 .001

0 .000

0 .003

0 .004

0.007

0 .009

0 .012

0 .015

(e) The thermodynamic parameters for adosprtion of Ag on

Temp (k)

283.00

303.00

318.00

338.00

InK

8.073

7.132

6.614

7.053

exchangi er

j/mol

-18994.65

-17967.43

-17487.98

-19822.44

J/K/mol

67.00

59.24

54.94

58.59

The enthalpy of the overall system at the temperature range

studied is AH° = -16.3286 J/K/mol

123

(f) Statistical parameter for Langmuir adsorption isotherm at

different temperature for constant particle size

Temperature (°C)

10

30

45

65

R

0.998

0.998

0.996

0.996

K

3206.702

1251.831

745.894

1157.387

1.833

2.250

2.679

2.911

Where R = Regression coefficient

b = Maximum amount of substance adsorbed per gram

of the adsorbate for the monolayer formation.

K = Equilibrium constant

124

m O X

Ce X 10^ Equilibrium concentration of Ag* ,Ce(gm/ l i t . )

Fig.5; Langmuir adsorption isotherms of Ag* on tin thioglycolote at different temperatures for the same particle size .

125

Table 4

Fitting of Langmuir equation for different particle size at

25+l°C

(a) Studies at <0.150 ura particle size

x/m

(gm/gm) (gm/lit)

Cg/(x/m)

(mod)

0.028

0 .039

0 .060

0 .080

0 .081

0 .090

0 .095

0 .101

0 .105

0 .105

0.112

0 .000

0 .000

0 .001

0 .004

0 .000

0 .010

0.012

0 .021

0 .027

0.037

0.047

0 .000

0 .001

0.016

0.056

0.056

0 .111

0 .131

0.207

0 .261

0.356

0 .419

0 .011

0.012

0 .020

0 .052

0 .053

0 .101

0 .124

0 .200

0 .259

0 .349

0 .434

126

(b) Studies at 0.1150 ;n« particle size

x/m

(gm/gm)

0 .028

0 .039

0 .062

0 .072

0 .080

0 .085

0 .090

0 .095

0 .097

0 .102

0 .108

( g m / l i t )

0 .000

0 .000

0 .000

0 .005

0 .005

0 .011

0 .013

0 .022

0 .029

0 .038

0 .048

Cjix/m)

0.000

0 .001

0 .018

0 .068

0 .061

0 .132

0 .152

0.236

0 .304

0 .375

0 .444

C / ( x / m )

(mod)

0 .013

0 .013

0 .018

0.062

0 .060

0 .019

0 .142

0 .225

0 .291

0 .373

0 .465

(c) Studies at 0.250 B particle size

0.028

0 .039

0 .059

0 .071

0 .071

0.072

0 .077

0 .080

0 .084

0 .085

0.086

0 .000

0 .000

0 .001

0.006

0 .007

0 .014

0.017

0.026

0.032

0.042

0 .053

0 .000

0 .001

0 .021

0 .095

0 .098

0 .201

0 .220

0 .328

0 .389

0 .493

0 .622

0 .013

0 .014

0 .027

0 .091

0 .094

0 .180

0 .209

0 .316

0 .391

0 .501

0 .630

127

(d) Studies at 0.355 um particle size

x/m (gm/gm)

0 .650

0 .900

1.400

1.950

1.550

1.525

1.525

1.575

1.650

1.775

1.750

C e ( g m / l i t )

0 .000

0 .001

0 .002

0 .005

0 .009

0 .017

0 .021

0 .030

0.037

0.046

0.057

C^/(x/m)

0 .000

0 .001

0 .001

0.002

0.006

0 .011

0 .013

0 .019

0 .022

0 .025

0 .032

(mod)

0 .001

0 .001

0 .001

0 .003

0.006

0 .010

0.012

0 .018

0 .022

0.027

0 .033

(e) Statistical parameters from Langmuir fit for different particle

size at constant temperature 25+l°C

Particle size ( >um )

R K 1/b

<0.150 0.998 774.40 9.003

0.1150 0.997 710.00 9.421

0.250 0,998 852.90 11.531

0.355 0.997 791.21 0.570

128

xie

0.7

0.6

0.5

O < .150 JLi

^ .1150JU

• . 2 5 0 i i i . 3 5 5 i i

0.02 0.03 0.04 0.05 0.06 0.07

E q u i l i b r i u m concent ra t ion of A g * , Ce ( gm / l i t . )

Fig GlLongmuir aclsorptionisothermsofAg*on different mesh size (Microns) of tin thioglycolate at 3011°C

129

DISCUSSION

The preliminary data for the rate of sorption of

Ag (Fig.. 1) on tin thioglycolate Indicate that initially

the rate of sorption is very fast and then it slows down

reaching to a maximum value after 24 hrs.

The results of Freundlich adsorption isotherm for

different temperature at a constant particle size and for

different particle size at a constant temperature are given

in table 1 and 2, while those of Langmuir adsorption

isotherms for both the variables are given in table 3 and 4

and plotted in Fig. 5&6. The regression coefficient (R)

(table le & 2e) of determination of the least squares fit

of the former equation for both the variables neither

approach unity nor do they show a consistency where as

those of Langmuir equation (table 3e & 4e) approach unity

as well as show consistency. It means that the Langmuir

equation is the best fit for the adsorption of Ag on tin

thioglycolate as compared to that of the Freundlich

equation with certain limitations. It appears that the

uptake of Ag is governed by physisorption and not

chemisorption phenomenon. The principal test to distinguish

between physisorption and chemisorption is the magnitude

of enthalpy of adsorption AH. For physisorption it is

generally less than 25 KJ mol where as for chemisorption

it is more than 25 KJ mol

130

The process of adsorption of Ag seems to be

spontaneous process over the entire temperature range. It

is indicated by the negative values of the free energy

change. Though, the spontaneousity is affected by the

temperature change, but the effect is very small. This

phenomenon is exothermic upto 45°C, but becomes endothermic

at GS'C. Thus, the Clausius - Claperyon equation is

obeyed between 10 to 45°C but not over the entire range of

studies.

The average enthalpy of adsorption at three

temperature range are as follows:

1. A H ^ , , = - 16.328 J/mole (10° to 65°C)

2. A H = - 33.256 J/mole (10° to 45°C)

3. A Hj^^o to 65°C) " -19.630 J/mole

These values of A H indicates that the process is

physiosorption and not chemisorption.

On the basis of the chemical structure of tin

thioglycolate one can expect the adsorption of Ag through

the following process.

1. Chelation Chemisorption process

2. Hydrogen bonding Physisorption process

3. Ion-exchange Physisorption process

131

On the basis of the above discussion, the

possibility of the first process is ruled out. The

probability of Hydrogen bond vanishes, because of electro­

positive nature of Ag .

Thus, the only possible mechanism of physisorption

of Ag on tin thioglycol ate is the ion exchange process,

which can be explained as follows.

'Ov

H \

H*0" C—CH2S>

H H

SCH2-C •OH

Sn

H*0~ C-CH2S'

0

H H \

K

^SCH2 — C

0 I I

OH*

H H

(©

Monovalent

132

C 1 Q ^ M

-"6:

2* 0 C

0 ^

Divalent

The entropy of the system is almost constant

throughout the process, which suggests the uniform

selectivity of the Ag by the adsorbent. The overall trend

of the thermodynamic parameters once again reflects that

the adsorption of Ag on tin thioglycolate is a physiso-

rption process.

The IR spectrum of tin thioglycolate (Fig. 2) also

confirms ion exchange behaviour of the adsorbent. The

-1 unadsorbed material shows a broad band around 3000 cm and

1600 cm ". This band is due to the presence of bond water

attached via hydrogen bonding to the surface thio groups as

shown below:-

0--

H/

: > • '

6+6-- -HSCH2-

5+6----HSCH2-

u

11 - c -

- C -II 0

- 0

- 0

\ s

0-

n

II - c -

- c -II 0

-CH2

-CH2

S H —

6-6+ SH—

H -0

133

On adsorption of Ag the band at 1600 cm

vanishes, while that of 3000 cm reduces to a sharp peak.

134

REFERENCES

1. Richards, R.J. and Fritz, J.S.; Anal. Chem.; 50(11),

1504 (1978).

2. Chow, F.K. and Grushka, E. ; Anal. Chem.; 50, 1346

(1978).

3. Vernon, P. and Nyo, K.M.; Sep. Sci. Technol .; 13(3),

273 (1978).

4. King, J.N. and Fritz, J.S.; J. Chromatogr.; 153(2), 507

(1978).

5. PhilLps, R.J. and Fritz, J.S.; Anal. Chem.; 50(11),

1504 (1978).

6. Suggi, A.; Ogana, N. and Hashizume, J.; Talanta, 26,

189 (1979).

7. Malik, W.U.; Srivastava, S.K. and Kumar, S.; Talanta.,

23, 323 (1976).

8. Rawat, J.P. and Iqbal, M.; Analidi. Chimica.; 431

(1981 ).

9. Rawat, J.P.; Iqbal, M. and Ali, S.; J. Ind. Chem. Soc;

185-88 (1984).

10. Rawat, J. P. and Alam, M. ; J. Ind. Chem. Soc; (In

Press ).

11. Rawat, J.P.; Alam, M. ; Singh B. and Aziz, H.M.A.; Bull.

Chem. Soc; 60(1), 2619 (1987),

135

12. Rawat, J.P. and Alam, M.; Anali, di. chimica.; 75(1-2),

87 (1985).

13. Hubicke, K.; Huhicka, H. and Tusink, S.; Mater. Sci.;

3(1-2), 53 (1977).

14. Vernon, F. and Eodes, H.; Anal. Chim. Acta.; 79, 229

(1975).

15. Qureshi, M. ; Kumar, V. and Zehra, N. ; J. Chromatogr.

(1977).

16. Varshney,K.G. and Naheed, S.; J. Inorg. Nuclear. Chem.;

39, 9075. (1977).

17. Macchi, G.; Marani, D.; Majone, M. and Coretti, M.R.;

Environ. Technol. lett. 6(4), 369, (1985).

18. Gladkov, S. Yu.; Churilova, N.A.; Malinina, G.V.;

Toroptseva, T.N. and Okhwakystin, N.I.; Chem. abstr.;

103, 1446644 (1985).

19. Smith, M.R. and Cochran, H.B.; U.S. US4, 578, 760.

20. Maeda, Hlronori, Egawa, Hiroaki.; J. AppI. Polym. Sci.;

29(7), 2281 (1984).

21. Terada, K.; Morimoto, K.; Keba, T. ; Bull. Chem. Soc.

Jpn.; (53), 1605 (1980).

CHAPTER - IV

ION EXCHANGE EQUILIBRIA OF ALKALINE EARTH

METAL IONS WITH SODIUM ION ON LINDE

MOLECULAR SIEVE (13X)

136

INTRODUCTION

Equilibrium studies on ion exchangers are being made

with great interest. Several theories for ion exchange

equilibria have been developed and tried on a number of ion

exchangers. Equilibria on synthetic organic resins have been

1 2 studied by several workers ' . The thermodynamics of ion

exchange on inorganic ion exchangers' is considerably

simplified as compared with the organic ion exchanger

resin, due to their rigid structure, little swelling and

relatively small changes in water content between different

cationic forms of the inorganic ion exchangers. The first

study of ion exchange equilibria on zirconium phosphate

deals with the Li -H , Na -H and K -H exchange Abe ' ,

t 7 ft Q ID

Amphlett , Nancollas ' , Costantino and Toracca

performed some admirable studies of ion exchange on

zirconium phosphate for alkali metal ions. Larsen and Cilley 11 made these studies on cerium phosphate . Ion exchange

isotherms for Li -K exchange were studied by Alberti and

12 13 Costantino on crystalline zirconium phosphate . Baetsle

reported the ion exchange equilibria for Rb , Cs , Sr ,

Ca 5 Ce and Eu with hydrogen ion on zirconium phosphate

both at micro and macro concentration levels in the

temperature range 5-71°C. Ion exchange equilibria for alkali

metal ions on zirconium phosphate have also been studied by

Ruvarac . The thermodynamics of ion exchange for alkali and

137

IS 1ft alkaline earth metal ions on ferric antimonate ' and

17 niobium arsenate have been made in our laboratories. Abe

1 8 and Furuki studied exchange equilibria of alkali metal

ions with hydrogen ion on tin antimonate. They also reported

the hypothetical thermodynamic data on"zero loading" on the

ion exchange reaction.

The thermodynamics of ion exchange on zeolites have

19-21 22 been extensively studied by Barrer , Dyer and

23 Frysinger . They studied the effect of temperature on ion

exchange equilibria with different zeolites in various

cationic forms. Several analogues of the zeolites have been

synthesized and studied by many workers '

Meunier studied the thermodynamic analysis of

solar-zeolite refrigeration system on (13X) and observed

that the latent heat of adsorption decreases by a factor of

two which does not occur in zeolite-water pair. But this

22

statement was contradicted by Chang and Roun and they

observed a factor of 1.5 determined from latent heat of

adsorption of synthetic zeolite-water pairs. 28

Coullet et al . , studied the solubility and

thermodynamic constants of dissolution of zeolites 4A and

13X in basic aqueous solutions of pH range 0.02M, O.IM and

0.50M sodium hydroxide (soln) and temp (25°, 60° & 80°C).

The obtained results allowed to calculate the thermodynamic

constants.

138

29 Abou] Magd et al. studied the equilibrium

coefficients for Cu(II)-H, Co(II)-H and Ni(II)-H exchange

systems on strongly cationic styrene-butadiene-phenol form

aldehyde resin exchangers in aqueous and aqueous acetone

media.

The present report describes the influence of

temperature on the equilibria of Mg -Na and Sr -Na

exchange on linde molecular sieve (13X) at a constant ionic

strength within the temperature range from 10°, 30° and

50°C. A simple approach has been applied and various

thermodynamic parameters are calculated.

139

EXPERIMENTAL

Reagents: Linde adsorbent molecular sieve (13X) (Union

Carbide Corporation) in Na form were used. All other

chemicals used were of A.R. grade.

Apparatus: An electric temperature controlled shaker (Sico)

pH-meter model Li-10 (India) were used for shaking and pH

measurements respectively.

Equilibrium studies:

The equilibrium experiments were performed using

batch technique. The solution (50 ml) containing sodium

nitrate and appropriate alkaline earth metal nitrate having

constant ionic strength O.IM was taken in a stoppered

conical flask. To this flask 0.2g of exchanger in sodium

form was added and shaken in a temperature controlled shaker

for 6 hrs at the required temperature. The supernatant

solution was then titrated with 0.05 molar EDTA solution for

the determination of the cations left.

140

RESULTS

The ion exchange isotherms for various cations at

different temperatures are plotted in Figures 1&2 and the

results of equivalent fractions of metal ions, selectivity

coefficients and thermodynamic equilibrium constants are

given in tables 1&2.

The plots of InKc versus equivalent fractions of

cations in exchanger phase are presented in figures 3&4. The

thermodynamic equilibrium constants calculated from these

plots are given in tables 1&2.

The values of enthalpy change A H° were obtained

from the plots of InKa versus 1/T presented in Figures 5&6

and free energy change AG° and entropy change A S° were

calculated using appropriate equations. The values of

various thermodynamic parameters are given in tables 3&4.

Hypothetical thermodynamic data at zero loading on ion

exchange reaction at 10°, 30° & 50+;l°C are given in table 5.

141

Table 1

Equivalent fractions of Mg , selectivity coefficient and thermo­

dynamic equilibrium constants for Mg -Na exchange on 1 inde

molecular sieve (13X)

S.No. XMg XMg Kc Ka

(a) Mg "'-Na at 10°C

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

1

2

3,

4,

5,

6,

7,

8.

9.

10.

0.063

0.121

0.181

0.254

0.318

0.318

0.526

0.628

0.742

0.860

0.036

0.092

0.170

0.241

0.320

0.413

0.509

0.613

0.729

0.850

0.116

0.300

0.500

0.616

0.687

0.681

0.780

0.830

0.850

0.880

<b) Mg^'^-Na'^at

0.333

0.530

0.580

0.710

0.816

0.850

0.890

0.930

0.933

0.940

2.740

5.107

9.471

12.185

12.503

12.000

9.147

8.410

4.503

1.850

30°

25.676

28.573

17.706

26.817

46.282

41.880

46.295

61.622

25.409

9.185

9.725x10^

10.7167x10^

Mg^^-Na* at SO^C

142

1.

2 .

3 .

4 .

5 .

6 .

7 .

8 .

9.

10 .

0 .012

0.147

0 .144

0 .230

0 .311

0.406

0 .509

0.606

0 .721

0.842

0 .533

0 .660

0 .770

0 .800

0 .870

0 .890

0 .900

0 .970

0 .970

0 .999

257 .80

37 .48

98 .42

68 .51

104 .23

84 .94

56 .64

366.89

153 .44

390.05

4 .270x10^^

143

en

I X

cn c

u X

rg

cn

c o u n)

c

> D cr

u

0 0.1 0.2 0.3 0.^ 0.5 0.6 0.7 0.8 0.9

Equivalent fraction of Mg^* in solution ( X Mg )

ig. 1'. Ion exchange isotherm of Mg2*- NQ* exchange on linde molecular sieve (13 X ) .

144

Table 2

Equivalent fractions of Sr , selectivity coefficients and

thermodynanic equilibrium constants for Sr -Na exchange on

]inde molecular sieve (13X)

S.No. XSr XSr Kc Ka

(a) Sr " -Na" at 10°C

1.

2.

3.

4.

5.

6.

7.

8.

9.

10

(b) Sr "'-Na"' at 30'

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

0.042

0.092

0 .150

0 .210

0 .290

0 .360

0 .460

0 .570

0 .690

0 .830

0 .15

0 .26

0 .30

0 .48

0 .53

0 .63

0 .65

0 .71

0 .73

0 .80

7.128

6 .685

4 .633

3.289

6 .553

8.227

5.285

4 .303

2 .191

1.094

3 .076x10^

0 .047

0 .100

0 .168

0 .233

0 .307

0 .393

0.492

0 .596

0 .713

0 .850

0 .18

0 .35

0 .50

0 .57

0 .69

0 .75

0 .78

0 .83

0.86

0 .85

8 .324

10 .543

13.979

12.230

16.706

17.677

13.280

12 .258

8 .754

1.571

15.735x10^

145

1 .

2 .

3 .

4 .

5 .

6 .

7 .

8 .

9.

10 .

(c) Sr ""-

0.040

0.050

0.105

0.170

0.243

0.323

0.419

0.638

0.655

0.800

-Na^ at 50°

0.23

0.53

0.69

0.75

0.82

0.88

0.91

0.91

0.95

0.96

14.043

59.992

1.897

76.409

93.780

136.255

142.217

36.258

108.502

65.244

12.684x10

146

en t: ro xz u >< CI c:

•

U)

u n

c. en

cr ui

0.0 0.1 0.2 0.3 OA 0.5 0.6 0.7 0.8 0.9

Equivalent fraction of Sr^* in solution (X Sr )

ig. 2 , Ion exchange isotherm of S r 2 * - N a * exchange on linde molecular sieve (13 X ),

147

00 01 02 03 04 05 06 07 08 0.9 10

X Mg

Fig 3 In of selectivity coefficient vs equivalent fraction of Mg2* in exchanger phase

148

u

c

0.0 0.1 0.2 0.3 0.4 0.5 0.5 0.7 0.8 0.9 1.0

X Sr

Fig.*!*: In of selectivity coefficient versus equivalent fraction of Sr2* in exchanger phase .

149

no

c

Fig S.PIot of In ka vs 1 /T for alkaline earfh metal ion Mg^*

150

3 0 31

1/yk X I C

Fig.5' Plot of In ko vs. WT for alkaline earth metal ion Sr^*

151

Table 3

The thermodynamic parameters for Mg -Na exchange on ] inde

molecular sieve (13X) at constant ionic strength

Thermodynamic Temperatures Parameters

10+1°C 30°C 50+l°C

InKa 2.60 3.92 6.78

AG° (Cal/mole) -1463.09 -2361.84 -4357.92

AS° (Cal/K/mole) 5.23 7.85 13.54

AH° (Cal/mole) 18.84

152

Table 4

Thermodynamic parameters for Sr -Na exchange on 1inde

molecular sieve (13X) at constant ionic strength.

Thermodynamic Temperatures

Parameters

10+1°C 30+l°C 50+l°C

In Ka 2 .38 3.12 4 .38

A G°(Ca l /mole ) - 1340 .72 - 1 8 8 2 . 3 7 - 2 8 1 6 . 8 8

A SMCal /K/mole ) 4 .76 6 .23 8 .74

A H°(Ca l /mole ) 9 .04

153

DISCUSSION

Linde molecular sieves (13X) in sodium form behaves

as weak cation exchanger. The ion exchange reaction with

bivalent metal ions on linde molecular sieve (13X) may be

written as

2 Na^ + M^^ ,;==r M^^ + 2Na^ (1)

Where the barred quantities refer to the exchanger phase

and the unbarred to the solution phase.

Ion exchange process being stoichiometric will

liberate an amount of sodium ion equivalent to the metal

ion taken by the exchanger. Such an exchange is plotted in

Figures 1&2 in the form of ion exchange isotherms. The

affinity for alkaline earth metal ions increases at higher

tempe ratures.

The selectivity coefficient values for alkaline

earth metal ion exchange with sodium form of linde

molecular sieve (13X) (equation 1) are calculated from the

1 - u- 30 relationship

(2) c

2 ^M' ^Na

- 2 ^Na M

2 y Na

y M

Where X^ and Xj, are the equivalent fractions of metal and

154

sodium ion respectively in the exchanger phase, Xw and X^

the equivalent fractions of metal and sodium ion

respectively in solution phase, y„ and y^, the activity,

coefficients of soium and metal ions respectively in the

solution phase. The activity coefficients of the cations in

the solution phase are calculated using Debye-Huckel

equation

- ^ogy. = ^ ^ ^ .... (3) 1 + li.a I \/ jd

where A and B are constants, a-j the ion size parameter, p.

the ionic strength and Z. the charge on the ion i. The

values of A, B and a j are taken from that given by Fresier

31 and Fernando

The values of selectivity coefficients are given in

tables 1&2 and plotted in Figures 3&4. These results

indicate that the value of K does not remain constant but c

varies with the equivalent fraction of alkaline earth metal

ion, Xw in the exchanger phase and hence the thermodynamic

equDibrium constant can be evaluated. The thermodynamic equilibrium constant Ka, is calculated from the expression

32 given by Gains and Thomas for the exchange involving

cations A and B with charges Z. and Z„ respectively. A

Ir InKa = Z^ - Zg + j InKc.d Xj . . . (4;

o

155

The magnitude of the charges A and B are known,

therefore the first term in equation (4) is readily

calculated. The second term is obtained by integrating below

the curve of In Kc as a function of Xw (Figures 3&4) . The

values of Ka are presented in tables 1&2. These results show

that alkaline earth metal ions are preferred to sodium ion

by the exchanger at all temperatures studied. However, the

degree of selectivity increases V7ith the increase in

temperature.

The standard free energy change A G ° for the

exchange process is calculated from the thermodynamic

equilibrium constant using equation.

R T A G° = - = . inKa (5

7 7

Where R is universal gas constant, T the absolute

temperature and Z„ ,Z„ the valencies of competing ionic

species the results of standard free energy change presented

in table 3&4 indicate that free energy change is negative

over all the temperatures during the exchange of alkaline

earth metal ion on sodium form of linde molecular sieve

(13X) and becomes more and more negative with the rise in

temperature in Mg as well as Sr ion exchange. Thus, the

spontaneity of the process increases with increase in temp­

erature.

156

The entropy of the two systems rises with

temperature indicating thereby the more stability of the

system from 10° to 50°C, On comparing the free change of the

two ions, it has been observed that it decreases with the

decrease in ionic radii, while reverse is true for the

entropy data. Thus, one can conclude that the ion exchange

process, in this case takes place in the unhydrated form. In

this way the exchange of Mg ion, having the ionic radii

2 + 0.65 A is more spontaneous than that of Sr which has ionic o

radii of 1.33 A.

Though the spontaneity of the process increases with

the decrease in ionic radii but the stability decreases. The

Mg ion exchanged material show higher values of entropy

data than that of the Sr ^ r j TU • i i • J • ,. found. This clearly indicates

that the ions get hydrated after being exchanged at the

exchange site.

Since the 1inde molecular sieves (13X) are zeolites

which has a rigid three dimensional structure and probably

the pore of the cavity is not sufficient to allow the entry

of the ions in the hydrated form, the ions enter into the

cavity in unhydrated form and get hydrated at the exchange

site.

These studies are very much similar to the findings

33 of Qureshi et al. for the exchange of alkali metals on the

zcolitic type niobium phosphate

157

They proposed, on the basis of the thermodynamic and

kinetic studies that the ions shed most of the water of

hydratation at the surface of the bead, then enter into the

pores in the unhydrated form, diffuse into the ion exchange

site and get hydrated after being exchanged. Since the

hydration of the counter ion takes place after being

exchanged, the exchange process is spontaneous but overall

system is less stable.

The findings reported here are very much similar to

the above model discussed.

The overall process in the two cases is endothermic

and the enthalpy of the exchange of Mg (18.85 cal/mole) is

double that of Sr , Probably this is the energy needed

mostly for the removal of hydration shell of the ions.

Hypothetical thermodynamic data in inifinitesimal

concentration are calculated for interpretation of the

selectivity of the alkaline earth metal ions in the trace

amounts of 1inde molecular sieve (13X). The values of

(lnKc)X|^ - 0 are obtained by extra polating to zero

loading of alkaline earth metal ions in Figures 3&4. From

these values the hyothetical thermodynamic data are

calculated by the similar treatment as for the overall

equilibrium constant. The accuracy of these values may be

higher than those of the latter hypothetical thermodynamic

158

Table 5

Hypothetical thermodynamic data on zero loading on the ion

2 + exchange r e s i n fo r Mg'

H y p o t h e t i c a l thermodynamic 10^1 °C 30j^l°C 50j^l°C d a t a

( In Kc) Xj - 0 0 .75 1.8 6 .3

( A G M X^ _ Q - 2 1 0 . 8 7 - 5 4 1 . 8 5 -2021 .67

(Ca l /mo le )

( A H°)X|^ - 0 0 0 0

(Ca l /mole )

( A S°) ^^ - 0 0 .745 1.788 6.259

(Ca l /K/mole)

for Sr 2+

( In Kc) Xj - 0 1.9 2 . 1 2 .35

( AG°)X^ - 0 - 5 3 4 . 2 0 - 6 3 2 . 1 6 -754 .116

(Cal /mole)

( A H°) Xj - 0

(Ca l /mole )

( A S°) Xj - 0 1.887 2.086 2 .334

(Cal /K/mole)

159

data on "zero loading" on the ion exchange reaction at 10

to 50^1°C are given table 5. The calculated (AH°)Xj^- 0

values indicate that there is no enthalpy change in the

reaction when alkaline earth metal ion concentration in the

exchanger phase approaches zero over the entire temperature

range.

160

REFERENCES

1. Kraus, K.A. and Raridon, R.J.; J. Phys. Chem.; 63,

1901 (1959).

2. Kraus, K.A.; Raridon, R.J. and Holcamb, D.L.; J.

Chromatogr. ; 3, 178 (1960).

3. Larsen, E.M. and Vissars, D.R.; J. Phys. Chem; 64,

1732 (1960).

4. Abe, M. ; Yoshigasaki, K. and Sugiura, T. ; J. Inorg.

Nuc]. Chem.; 42, 1753 (1980).

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6. Amphlett, C.B.; Eaton, P.; McDonald, L.A. and Miller,

A.J.; J. Inorg. Nucl. Chem.; 26, 297 (1964).

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Nucl. Chem.; 31, 3643 (1969).

8. Harkin, J.D.; Nancollas, G.H. and Paterson, R.; J.

Inorg. Nucl. Chem.; 26, 305 (1964).

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(1979).

10. Toracca, E.; J. Inorg. Nucl. Chem.; 31, 1189 (1969).

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Chem,, ; 36, 653 (1974).

161

13. Baetsle, L.H.; J. Inorg. Nucl. chem.; 25, 271 (1963).

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235 (1971).

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Chem.; 43, 2121 (1981).

16. Rawat, J.P. and Singh, B.; Bull. Chem. Soc. Jpn.; 57,

271 (1984).

17. Oureshi, M. ; Rawat, J.P. and Gupta, A.P.; J. Ind.

Chem. Soc; LVIII, 855 (1981).

18. Abe, M. and Furuki, N.; Solvent. Extn. Ion. exch.;

4(13), 547 (1986).

19. Barrer, R.M. and Meier, W.M.; Trans. Faraday. Soc;

55, 130 (1959).

20. Barrer, R.M. and Sammon, D.C.; J. Chem. Soc; 2839

(1955).

21. Barrer, R.M. and Falconer, J.D.; Proc Roy. Soc.

(London). A231, 227 (1956) .

22. Dyer, A. and Ahmad, Z.B.; Ion Exch. Technol.; 32, 519

(1984).

23. Fry&inger, G.R.; Nature, 194, 351 (1962).

24. Lok,. B.M.T. and Messina, C.A.; Union Carbide

Corporation, 16 May (1984).

162

25. Selbin, J. and Mason, R.B.; J. Inorg. Nucl. Chem.; 20,

222 (1961).

26. Meunier, F.; J. Sol. Energy, Eng.; 108(3), 257 (Eng)

(1986).

27. Chang, S.C; Roux, J.A.; J. Sol. Energy,Eng.; 108(3),

257 (1986).

28. Coullet, Philppie.; Guth, Jean fouise., way, Raymond.;

Bull. Minerak.; 103(3-4), 330-5 (1980).

29. Aboul Magd, A.S.; Kamal, F.H.; Asian, J. Chem.; 2(2),

191-9 (1990).

30. Barrer, R.M. and Townsend, R.P.; J.C.S. Faraday II,

72, 661 (1976).

31. Freiser, H, and Fernando, Q. ; "Ionic Equilibria in

Analytical Chemistry", Wiley, New York (1966).

32. Gains, G.L. and Thomas, H.C.; J. Chem. Phys.; 21, 714

(1953).

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U.S.A.; 4, 823-827 (1986).

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163

INTRODUCTION

As ion exchange has been proved to be an important

field for analytical and industrial purposes, mainly after

1940, and in the last two decades, an interest has been

developed in theoretical behaviour of ion exchange. A study

of kinetics of ion exchange will ascertain, in the real

sense, the applicability of possible rate laws, rate

determining step and the mechanism of the ion exchange

system. Sculze recognized that rate determining step in

ion exchange is interdiffusion of counter ions rather than

a chemical exchange reaction between the two counter ions.

The first serious attempt on the ion exchange kinetics was

2 3 made by Nachod and Wood and Nancol1 as & Paterson .

Some other studies on kinetics of ion exchange on

4-9 inorganic ion exchangers have also been reported . The

kinetics of ion exchange on zeolites have also been

10 extensively studied, Yao & Coworkers studied the

kinetic reaction of NaY zeolite with LnCK. Average kinetic

energy of methane in Na ZSM 5 zeolite by neutron inelastic

11 scattering were done by Jobic

The kinetics of crystallization of tetragonal (B„)

and Cubic (B. ) modification of zeolite NaP from freshly

prepared aluminosilicate gel was done by katovic and

others

164

Crystallization kinetics of zeolites ZK-19 in

complex aluminosilicate systems was done by Babaeu &

others ". Lee, Ting Yuch & others studied the kinetics of

Lanthanum-NaY zeolite. Several analogues of the zeolites

15-25 have been synthesized and studied by many workers

The present work in this chapter describes the

mechanism of exchange on sodium stannosilicate, an analogue

of the zeolites. Experimental and theoretical approaches

have been used to show the rate of diffusion through the

particles. Different kinetic and thermodynamic parameters

have been calculated under the conditions favouring a

particle diffusion control mechanism. Bt technique has

been used to calculate these parameters.

165

EXPERIMENTAL

Reagents and chemicals: Stannic chloride pentahydrate

(Reachim) and sodium metasilicate (Loba) were used. All

other chemicals used were of A.R. grade.

Synthesis of sodium stannosilicate:

Sodium stannosilicate was synthesized by mixing

0.1 M sodium meta silicate solution with 0.1 M sodium

stannate solution (freshly prepared) in a volume ratio 1:1.

This mixture was refluxed for 24 hrs and the resulting

white precipitate was allowed to settle overnight. It was

then filtered and dried at 60 +^ 1°C in an air oven. The

dried product was broken into small granules by simply

immersing in distilled water. These granules were washed

several times with distilled water and dried at 60 +_ 1°C.

To convert the exchanger in Na form it was kept in 1 molar

sodium nitrate solution overnight.

Kinetic measurements:

Conditions approaching infinite bath technique were

used to perform the kinetic measurement on sodium

stannosilicate. The exchanger was finally ground and sized

by standard sieves to get particles of different mesh sizes

0-25, 23-35, 35-45). Particles of mesh size 25-35 were

166

used for various kinetic studies unless otherwise stated.

Solutions of cations (0.005 M) at constant ionic strength

were thermostated at the required temperature (10°, 25°,

45° and 65°C) for different time intervals. A weighed

amount of the exchanger (0.2 gm) was added and the flasks

were thoroughly shaken at the specified temperatures. After

appropriate intervals the contents of the flasks were

immediately removed and analysed for its metal ion content.

INTERRUPTION TEST:

For performing the interruption test eleven

stoppered conical flasks were taken. In each flask 20 ml of

2 + Cu solution was taken and thermostated at room

temperature (25j^l°C). To each flask 0.2 gm exchanger was

added and after the specific time intervals the solution

was separated from the exchanger beads. 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

2 + solutions and the experiment recontinued. The Cu content

in the supernatant solution was determined at various time

intervals again.

167

RESULTS

The results of ion exchange capacity of sodium

stannosi]icate for four different metal ions are summarized

in table 1.

Table 1

Ion exchange capacity of sodium stannosilicate

Metal ion Taken as Exchange capacity -1

meq g

Cd " nitrate 1.10

Cu nitrate 1.20

Pb^^ nitrate 1.20

Ag nitrate 2.25

INTERRUPTION TEST:

Interruption test was performed for Cu - Na

exchange on sodium stannosilicate in Na form. The Ut

(fractional attainment of equilibrium) values as a function

of time before and after interruption of 10 minutes at

25+l°C are given in table 2 and are plotted in Fig. 1.

168

en c J: u K

c o

-•-•

u

0 5 10 15 20 25 30 35 ^0 ^5 50 55 60

Time in ( min )

Fig 1 • Effect of on interruption on the rate of Cu^* -Na* exchange on sodium stannosilicate.

169

Table 2

Interruption test for Mg -Na exchange on sodium stanno-

silicate at ZS+l^C

S.No. Time (min) Ut

1 2 0.560

2 5 0.636

3 10 0.670

4 15 0.784

5 20 0.818

10 minutes interruption

6 0 0.818

7 2 0.850

8 5 0.897

9 10 0.909

10 15 0.954

11 20 0.954

Effect of temperature:

In order to see the effect of temperature the

2+ 2+ 2+ +

kinetics was performed for Cd , Cu , Pb and Ag at four

different temperatures viz. 10°, 25°, 45° and 65j l°C. Ut

values as a function of time are calculated and the

corresponding Bt values are taken as tabulated by

170

27 Reichenberg . The results are given in tables 3, A, 5 and

6. The results of Ut Vs time at different temperatures for

the above mentioned cations are plotted in Fig. 2, 3, 4

and 5. While the results of Bt Vs time are plotted in

Figs. 6, 7, 8 and 9.

Effect of Particle Size:

The effect of particle size on the kinetics of ion

exchange for three different particle sizes viz. 701.04 cm,

495.3 cm and 350.52 cm were performed. The results of Ut

and Bt values as a function of particle size for Cu -Ma

exchange at 25j l°C are given in table 7. The Ut values as a

function of time are plotted in Fig. 10 and the values of

Bt Vs t are plotted in Fig. 11.

171

Table 3

Ut and Bt values as a function of time for Cd on sodium

stannosilicate at different temperatures

jl^Q Initial value Final value Ut Bt (m moles) (m moles)

Cd -Na^ exchange at 10+1°C

1

2

5

10

15

20

40

60

CO

13 .2

13 .2

13 .2

13 .2

13 .2

13 .2

13 .2

13 .2

13 .2

1

2

5

10

15

20

40

60

CO

16 .4

16 .4

16 .4

16 .4

16 .4

16 .4

16 .4

16 .4

10 .4

11 .74

11 .74

10 .30

9.30

8 .40

7.30

5 .80

4 .70

0 .80

0 .117

0 .117

0 .233

0 .314

0.387

0 .475

0.596

0 .685

1

0 .011

0 .011

0.052

0 .099

0.157

0 .259

0 .458

0 .675

-

Cd^*-Na^ exchange at 25+1°C

13 .04

13 .04

11.16

10 .00

8.80

7.90

•5 .30

3.60

0 .40

0 .210

0 .210

0 .301

0 .400

0 .473

0 .530

0 .691

0 .800

1

0 .042

0.042

0 .092

0.177

0 .299

0 .348

0 .703

1.120

-

172

1

2

5

10

15

20

40

60

CO

18 .4

1 8 . 4

1 8 . 4

18 .4

18 .4

18 .4

1 8 . 4

18 .4

18 .4

1

2

5

10

15

20

40

60

CO

19 .2

19 .2

19 .2

19 .2

19 .2

19 .2

19 .2

19 .2

19 .2

Cd ^-Na^ exchange at 45+1°C

15 .0

14 .0

12 .0

10 .4

9 ,3

8 .1

5.2

0 .92

0

0 .181

0 .234

0 .347

0 .431

0 .490

0.555

0 .712

0 .950

1

0 .030

0 .052

0 .122

0 .210

0 .287

0.382

0 .765

2 .500

—

Cd^'^-Na^ exchange at 65+l°C

14 .4

13 .5

11 .6

10 .0

8.7

7 .5

4 . 8

3.6

0

0 .250

0 .296

0 .395

0 .479

0 .546

0 .609

0 .750

0.812

1

0 .057

0 .086

0 .167

0 .259

0 .365

0 .479

0 .905

1.171

_

173

l O r

en c n s: u X

c o

•4-'

u

5 10 15 20 25 30 35 40 45 50 55 60 65 70

Time in ( min )

Fig 2 Rate of exchange of Cd2*a t d i f fe ren t t e m p e r a t u r e s on sodium stannosi l icate

174

Table 4

Ut and Bt values as a function of time for Pb on sodium

stannosilicate at different temperatures

Time Initial value Final value Ut Bt (m moles) (m moles)

Pb -Na^ exchange at 10+1"C

1

2

5

10

15

20

40

60

CO

18.0

18.0

18.0

18.0

18.0

18.0

18.0

18.0

18.0

16.3

16.3

14.7

13.1

12.5

11.9

9.9

8.7

2.8

0.110

0.110

0.217

0.320

0.361

0.406

0.532

0.611

1

0.011

0.011

0.042

0.107

0.139

0.177

0.348

0.500

-

Pb^^-Na^ exchange at 25+1°C

1

2

5

10

15

20

40

60

no

18.4

18.4

18.4

18.4

18.4

18.4

18.4

18.4

18.4

15.6

14.3

13.0

10.6

10.3

9.3

6.8

4.8

0

0.152

0.222

0.293

0.423

0.440

0.490

0.630

0.739

1

0.021

0.047

0.086

0.199

0.222

0.287

0.545

0.832

_

175

Pb ^-Na^ exchange at 45+l°C

1

2

5

10

15

20

40

60

CO

18.0

18.0

18.0

18.0

18.0

18.0

18.0

18.0

18.0

13.5

13.5

12.2

9.5

9.1

8.2

5.4

3.6

0

0.25

0.25

0.32

0.47

0.49

0.54

0.70

0.80

1

0.062

0.062

0.107

0.259

0.287

0.365

0.734

1.120

Pb " -Na exchange at 65+l°C

1

2

5

10

15

20

40

60

CO

16.4

16.4

16.4

16.4

16.4

16.4

16.4

16.4

16.4

11.8

10.1

10.8

9.0

7.7

6.3

3.9

2.4

0

0.28

0.38

0.34

0.45

0.53

0.61

0.76

0.85

1

0.079

0.157

0.122

0.234

0.348

0.500

0.947

1.404

~

176

5 10 15 20 25 30 35 ^0 45 50 55 60 65 70

Time in ( min )

Fig 3:. Rate of eychange of Pb^* at different t stannosilicGte. emperature on sodiunn

177

Table 5

Ut and Bt values as a function of time for Cu on sodium

stannosilicate at different temperatures

j g Initial value Final value Ut Bt (m moles ) (m moles )

7+ + Cu -Na exchange at 10+1°C

1

2

5

10

15

20

40

60

CO

20.0

20.0

20.0

20.0

20.0

20.0

20.0

20.0

20.0

1

2

5

10

15

20

40

60

CO

20.8

20.8

20.8

20.8

20.8

20.8

20.8

20.8

20.8

16.4

16.2

15.4

14.1

12.8

12.2

10.0

8.4

1.2

0.191

0.202

0.244

0.318

0.382

0.414

0.531

0.617

1

0.034

0.038

0.057

0.099

0.157

0.188

0.348

0.500

-

Cu^^-Na^ exchange at IS+l'C

15.8

15.1

14.7

13.52

11.8

10.6

8.3

6.4

0

0.240

0.274

0.293

0.350

0.432

0.490

0.600

0.692

1

0.057

0.073

0.086

0.130

0.210

0.287

0.479

0.703

-

178

Cu -Na exchange at 45j l°C

1

2

5

10

15

20

40

60

CO

20.0

20.0

20.0

20.0

20.0

20.0

20.0

20.0

20.0

15.0

14.4

13.4

11.8

10.6

9.3

6.5

3.8

0.2

0.252

0.282

0.333

0.414

0.474

0.540

0.681

0.818

1

0.062

0.079

0.114

0.188

0.259

0.365

0.675

1.171

Cu -Na exchange at 65j l°C

1

2

5

10

15

20

40

60

CO

20.0

20.0

20.0

20.0

20.0

20.0

20.0

20.0

20.0

13.8

14.0

13.2

11.0

9.4

8.2

5.0

3.2

0.1

0.311

0.301

0.341

0.452

0.532

0.592

0.753

0.844

-

0.099

0.092

0.122

0.234

0.348

0.458

0.905

1. 340

-

179

c ft

u K

c o

• • - •

(J

65^ 45'

10'

10 15 20 25 30 35 40 45 50 55 60

Time ( min )

Fig 4:Rate of exchonge of Cu*^ at d i f ferent temperatures on sodium stannosil icate.

180

Table 6

Ut and Bt values as a function of time for Ag on sodium

stannosi]icate at different temperatures

Time

1

2

5

10

15

20

40

60

oo

Ini (m

tia] va'

moles)

11.2

11.2

11.2

11.2

11.2

11.2

11.2

11.2

11.2

1 ue

Ag^

Final value (m moles )

-Na"*" exchange at

9.9

9.5

8.6

7.5

7.1

6.0

4.7

3.8

0.2

10

Ut

+ 1*'C

0.118

0.154

0.236

0.336

0.372

0.472

0.590

0.672

1

Bt

0.011

0.021

0.052

0.114

0.148

0.259

0.458

0.647

-

Ag -Na exchange at 25j l°C

1

2

5

10

15

20

40

60

CO

10.4

10.4

10.4

10.4

10.4

10.4

10.4

10.4

10.4

8.6

8.3

7.2

6.6

5.7

5.5

4.1

3.6

1

0.191

0.223

0.340

0.404

0.500

0.521

0.670

0.787

1

0.034

0.047

0.122

0.177

0.301

0.332

0.647

1.028

—

181

Ag -Na exchange at 45+1"C

1

2

5

10

15

20

40

60

OD

11.6

11.6

11.6

11.6

11.6

11.6

11.6

11.6

11.6

8.9 0.236 0.052

8.6 0.263 0.067

7.2 0.385 0.157

6.5 0.447 0.222

5.2 0.561 0.400

4.8 0.596 0.458

3.1 0.745 0.868

2.2 0.824 1.224

0.2 1

+ ,. + Ag -Na exchange at 65j l°C

1

2

5

10

15

20

40

60

OQ

11.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

8.6

7.2

6.3

5.7

4.5

3.9

2.0

1.3

0

0.272

0.345

0.427

0.481

0.590

0.645

0.818

0.881

1

0.073

0.122

0.199

0.275

0.458

0.569

0.171

1.623

-

182

cn c m

JZ u

C

g u

5 10 15 20 25 30 35 40 45 50 55 60

Time ( mm )

Fig.5;Rate of exchange of A g * at d i f f e r e n t t e m o e r a t u r e s on sodium s tannos i l i ca te .

183

Table 7

Ut and Bt values as a function of particle size for

Cu -Na exchange on sodium stannosilicate

Time Initial value Final value Ut Bt

(m moles ) (m mol es)

for particle size 701.04 Cm

1

2

5

10

15

20

40

60

CO

21.2

21.2

21 .2

21.2

21.2

21.2

21.2

21.2

21.2

19.6

18.9

17.8

16.7

15.8

14.6

14.0

12.1

7.2

0.114

0.164

0.242

0.321

0.385

0.471

0.514

0.650

1

0.011

0.024

0.057

0.107

0.157

0.259

0.316

0.594

-

for particle size 495.3 Cm

1

2

5

10

15

20

40

60

OO

20.4

20.4

20.4

20.4

20.4

20.4

20.4

20.4

20.4

17.6

16.1

15.8

14.7

13.8

12.6

10.3

9.1

5.2

0.184

0.282

0.302

0.375

0.434

0.513

0.664

0.743

1

0.030

0.079

0.092

0.148

0.210

0.316

0.620

0.868

-

for particle size 350.52 Cm

184

1

2

5

10

15

20

40

60

CO

20 .0

20 .0

20 .0

20 .0

2 0 . 0

20 .0

20 .0

20 .0

2 0 . 0

14 .6

14 .2

12 .0

11 .2

9 .8

6 .8

5 .4

3 .4

0

0 .27

0 .29

0 .40

0 .44

0 . 5 1

0 .66

0 .73

0 .83

1

0 .073

0.086

0 .177

0 .222

0 .316

0 .479

0.832

1.280

_

185

m

Fig 5' Ef fect of temperature on the rote of C d ^ * - N a * exchange on sodium Stannosil icote

186

03

0 5 10 15 20 25 30 35 UQ 45 50 55 60 65 70 75 80 85 90

Time in ( min)

Fig 7 Ef fect of temperature on the rate of Cu* 2 _ Ma • e)(ci-,ange on sodium stannosidcot

187

P 2

O 10 en O

QO

O r-O

«3

o LO

o ^ o

n O

(N O

a

188

m

5 10 15 20 25 30 35 40 45 50 55 60 65 70

Time in ( min )

Fig .9 :Ef fGC- to f tempera turGonthera teofAg '^ -Na '^ exchange on sodium stannosilicQte.

189

a\ c m r u (J

C

o u

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

- • - 350.52 Cm - i - 495.3 Cm -O- 701.04 Cm

10 15 20 25 30 35 40 45 50 55 60

Time ( mm )

Fig. 10 : Inf luence of part icle size on the rate o f C u * 2 - N a * exchange at 301 1°C

190

QO

'•5 r

1 u

1-3

1 2

1 1

1 0

0.9

0.8

0.7

06

0.5

0.4

0.3

02

0 1

• 0

-•- 350,52 Cm -A- 495.3 C m

10 15 20 25 30 35 40 45 50 55 60 65 70

Time ( mm )

F i g .n Inf luence of part icle s i z e o n t he ra te of C u * ^ - N a * exchange at 3 0 ! 1°C on sodium stonnosil icate. *

191

DISCUSSION

From table 1 it is evident that the sodium stanno-

silicate shows a considerable ion exchange capacity for

Cd , Cu' ' , Pb and Ag ions. It varies from 1 to 2.25

meq/gm. For Ag the capacity is exceptionally high. It may

be because of its high selectivity.

O Q

According to Boyd et al . mainly two potential

diffusion processes are considered, "particle diffusion"

where 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 metal ion concentration, relatively large particle

size of the exchanger and vigorous shaking of the

exchanging mixtures, under these conditions, the fractional

attainment of equilibrium with time is given by

The amount of exchange at time (t)

The amount of exchange at infinite time (equilibrium)

The interruption test is the best experimental

approach for distinguishing between film and particle

9 r diffusion control phenomenon . Therefore, this test was

applied for Cu ions. Results are summarized in table 2

and plotted in Fig. 1. These results show an enhanced rate

192

after 10 minutes of interruption which indicates a

momentary exchange after reimmersion and hence the rate

should be controlled by particle diffusion. This is because

the concentration gradient disappears in the particle

during the interruption and on reimmersion are much greater

than before at the surface. Thus, on this basis, it was

concluded that the mechanism of exchange is controlled by

particle diffusion and hence the experimental conditions

were set to explain this phenomenon. The equations

27 developed by Boyd et al . and improved by Reichenberg to

calculate the kinetic parameters.

The Ut values at different time intervals and

different temperatures obtained for Cd , Cu , Pb and

Ag -Na exchange are plotted in Fig. 2 to 5. These results

show that the rate of exchange is directly proportional to

the temperature. These curves also reveal that the uptake

of ions is rapid initial 1y, then it becomes slow and finally

reaches a constant value with increase of time. These

29 results are analogous with that of Heitner and Markovits

As the particle diffusion is the rate determining

step the following equation is valid.

CO 2 - > e X p (-n Bt)

Ut = 1 - — n ^ ^- 1 6_ 2

' n.l

193

where B = 7\ di

.2 (2

r is the radius of the particle, D- is the effective

diffusion coefficient of two exchanging ions inside the

30 resin phase and t, is the time. The typical Bt vs t plots

at four different temperatures viz. 10°, 25°, 45° and 65°C

for Cd , Cu , Pb and Ag -Na exchange given in figures

6 to 9 show that the rate of exchange is directly

proportional to temperature. In all cases the plots of Bt

vs t are linear passing through the origin. This further

indicates that the rate determining step is diffusion

through the particle at all temperatures studied. Particle

size also has a marked effect on the rate of exchange. The

Ut values for Cu -Na exchange on exchanger particle of

different sizes are plotted in Fig. 10. While the results of

Bt vs t are given in table 7 and plotted in Fig. 11.

Equation(2) is used for the calculation of

diffusion coefficient (Dj^). The results of Di are given in

table 8.

194

Table 8

2 Values of D-^ (m /sec) of various cations at different

temperatures on sodium stannosilicate

Cations 10^1°C 25j l°C 45 + l°C 65j l°C

Pb^^ 3.641x10"^ 5.5037x10"^ 7.450x10""^ 9.090x10"^

Cu^^ 3.3106x10"^ 4.8008x10"^ 6.5732x10"^ 8.796x10"'^

Ag^ 4.41095x10"^ 6.62139x10"^ 8.277x10"^ 10.34x10"^

Cd "" 4.760 x 10"^ 7.323x10"^ 8.277x10"^ 9.106x10"^

The linear relationship between -log Di vs

(l/T) K (Fig. 12 to 15) enables the calculation of energy

of activation (Ea) from the Arrhenius equation.

D = Do exp ( - Ea/RT) (3)

The energy of the cation diffusion process reflects

the ease with which cation can pass through the exchanger.

The values of energy of activation are given in table 9. On

extrapolating the plot of -log D^ vs (l/T) K (Figs. 12 to

15) log Do value can be calculated. Substitution of these

values in equation (4) gives the entropy of activation

(AS").

195

Do = 2.72 d^ KT/h exp (AS"'7R) (4)

where d is the ionic jump distance assumed to be 5x10 cm.

-23 -1 -1 K is the Boltzman constant equal to 1.38x10 J K mole ,

h, is the planck's constant equal to 6.6x10 J. Sec.

T, is the absolute temperature equal to 273 K,

-1 -1 R is the gas constant equal to 8.31 J K mole

The values of Do and A S are given in table 9.

Table 9

Diffusion coefficient, energy of activation and entropy of

r- ^, 2+ ^2+ . + , ^ ,2+ ,.

activation of Pb , Cu , Ag and Cd on sodium

stannosilicate in Na form.

C a t i o n s

Pb2 '

Cu2*

Ag*

Cd2*

Do t 2 - 1 , (m sec )

0 .1148

0 .1071

0.0316

7.24x10"-^

(K

Ea

J /mo le )

13 .40

5.16

9.57

0 .58

(J

,

AS

deg mol e)

85 .58

85 .03

74.87

62 .68

196

- I ^

O

c o

fM ^

1 O

X t—

r -

1/1 >

o en O

_o

C7>

LL

m I I

( ^_:)is ^w ) iQ 5o| -

197

-3

-5 2

Fig 13 Plot of log Di vs 1/^ on A g *

198

6

o

Fig U Plot of log Di vs 1/^ on Cu*^

199

i/i

O cn o

J- X 10~^k' ' '

Fig 15 Plot of log Di vs 1, on Pb^*

200

REFERENCES

1. Sculze, G.; Physik, Chem.; 89, 168 (1915).

2. Machood, F.C. and Wood, W. ; J. Am. Chem. soc; 66, 1350

(1944).

3. NanCollas, G.H. and Paterson, R.; J. Inorg. Nucl .

Chem.; 22, 259 (1961).

4. Thind, P.S. and Gandhi, J. S. ; J. Solid State Chem.;

60(2), 165 (1985).

5. Trai, F. and Huang, T.; Chem. Eng. J.; 30(1), 39

(1985).

6. Froclich, P.; Teor Prokt. Sorbtsionnykl . Prolsessor,

14, 19 (1981).

7. Dyer, A. and Gill, G.S.; J. Inorg. Nucl. Chem.; 39, 665

(1977).

8. Singh, N.J. and Tandon, S.N.; Ind. J. Chem.; 29A, 441

(1981).

9. Varshney, K.G. and Premadas, A.; Ind. J. Chem.; 29A,

441 (1981).

10. Yao, Huqing.; Chen, Guodong.; Kong, Qingzhen. Shiyou

Xuebo Shiyou Jiangong.; 7(1), 103-8(Ch) (1991).

11. Jobic, H.; Chem. Phys. Ictt.; 170(2-3). 217-22 (Eng)

(1990).

201

12. Katovic, Andrea; Subotic, D.; Smit, Ivan,; Despotovic,

L.A.; Zeolites.; 10(7), 634-41 (Eng) (1990).

13. Babaeu, M.K.; Ganbarov, D.M.; Mamedov, Kh.S.; IZV.

Akad. Nauk SSR, Neorg. Mater. 26(4), 856-600 (Russ)

(1990).

14. Lee, T.Y.; Tsangsheng, Lu.; Chem, Shiamn Horng.; Chao,

Kuei, Jung., Ind. Eng. Chem. Res.; 29(10), 2024 (Eng)

(1990).

15. Veshtort, V.Z.; Shingel, I.A.; Savchits, M.F.;

Egiazarov, Yu. G.; Zavod. Lab. 55(10), 6-8 (Russ)

(1989) .

16. Joshi, P.N.; Kotasthane, A.N.; Shiralkar, V.P.;

Zeolites.; 10(6), 598-602 (Eng) (1990).

17. Dadyburjos, Dady B.; Bellare, A.; J. Catal. ; 126(1),

261-6 (Eng) (1990).

18. Schoellner, R.; Franke, T.; Hoffman, J.K.L.; Argyelan,

J.; Kutics, K.; Chem. Tech. (Leipzig) 42(6), 260-3

(Ger) (1990).

19. Manos, G. ; Hofmann, H.; Chem. Ing-Tech.; 62(9), 744-7

(Gcr) (1990).

20. Palermo, A.; Loeffler, D.G.; Thermochim. Acta.; 159,

171-6 (Eng) (1990).

21. Dai, Xing.; Huuxue Fanying Gongcheng Yu Gongyi.; 5(3),

79-84 (Ch) (1989).

202

22. Kocirik, M. ; Zikanova, A.; Struv, P.; Bulow, M. ; Z.

Phys. Chem. (Leiping), 271(1), 43-50 (Eng) (1990).

23. Gao, Yuqing; Guan, W.; Dong, Q.; Shlyou Xuebo, Shi you

Jiagong.; 5(3), 1-6 (Ch) (1989),

24. Hu, Hsin C ; Lee, Ting Y.; Ind. Eng. Chem. Res.; 29(5),

749-59 (Eng) (1990).

25. Haag, W.O.; Dessau, R.M.; Lago, R.M.; Stud. Surf. Sci.

Catal.; 60, 255-65 (Eng) (1991).

26. Kressman, T.R.E. and Kitchener, J.A.; Disc. Faraday

See.; 7, 90 (1949).

27. Reichenberg, D.; J. Am. Chem. Soc; 75, 589 (1953).

28. Boyd, G.E.; Adamson, A.W. and Myers, L.S.; J. Am. Chem.

Soc.; 69, 2836 (1947).

29. Carla-Heitner - Wirguin and Markovits, G.J.; Phys.

Chem.; 67, 2263 (1963).

30. Barrer, R.M.; Bartholomov, R.F. and Rees, L.V.C.; J.

Phys. Chem. Solids.; 21, 12 (1961).

CHAPTER - VI

DISTRIBUTION STUDIES OF SOME METAL IONS IN NON­

AQUEOUS MEDIUM ON LINDE MOLECULAR SIEVE (13X)

AND SODIUM STANNOSILICATE

203

INTRODUCTION

A number of complexing agents have been made for

eJution of some divalent ions in aqueous solution on cation

exchange resin column . They showed that the addition of

organic solvents to water medium modifies the affinities of

metal ions towards ion exchangers given a condition that is

widely different from that in the absence of solvent.

Moreover in some cases, the distribution coefficient values

of metal ions increases with chain length of organic

sol vents.

An extended method for analytical evaluation of

distribution coefficients on selective inorganic ion

exchangers have been studied by Tsuji and Kamareneni .

Aboul Magd and co workers have done the distribu­

tion studies of some metal ions in nitric acid nonaqueous

mixtures on organic zeolite cation exchanger. They studied

the cation-exchange characteristic of Ni , Cu , Co ,

Mg , Zn and Cd ions in nitric acid solutions eluting

with different proportions of organic solvent on synthetic

organic zeolite cation exchange resin (Amberlite IR-I ).

Distribution studies of some metal ions in water

"7 111 edium has already been done on sodium stannosilicate .

204

The distribution ratios for different metal ions have

revealed that the exchanger is specific towards Ag .

The aim of the present work is to evaluate the

values of the distribution coefficients for some divalent

ions using 1inde molecular sieves (13X) and on the analogue

of the zeolite sodium stannosilicate in methanol - water

systems.

205

EXPERIMENTAL

Reagents: Linde Adsorbent Molecular sieve (13X) in Na form

(Union Carbide Corporation) were used.

Tin (IV) chloride pentahydrate (SnCl, 5H2O)

(Reachim) and sodiummetasil icate (Na^SiO^. 5H^0) (Loba)

were used.

All other chemicals used were of A.R. grade.

Apparatus: An electric temperature controlled shaker (Sico)

was used for shaking.

Preparation of solutions: Stock solutions of Ni , Co ,

>, II ^,11 „II , 1 AiIII null ^,11 ^11 „II ,

Mn , Cd , Zn , Ag , Al , Pb , Mg , Ca , Ba and

Sr were prepared by dissolving their nitrates in water as

well as in organic solvents.

In case of sodium stannosilicate different

concentration of HNO^ were prepared.

Determination of the various elements

Most of the elements investigated were determined

titrimetrical1y using EDTA-disodium salt as the titrant,

KSCN was used for .the titration of Ag .

206

The indicators used were eriochrome black T, Pan-

indicator, xy]enoJ -orange and Ferric A] um in prescence of o _ -| n

suitable buffer solutions

Determination of Kd values

(i) On Linde Molecular Sieve (13X)

The distribution study was carried out in a 100 ml

glass stoperred flask containing the dry resin (0.2 gm )

and 0.02 M metal ion solution in aqueous and aqueous^ organic-

NaNO^ (0.1 M) media. Batches were equilibriated by shaking

Cor 24 hrs. All the experiments were carried out at

25+ 1°. Each batch was analysed for the same metal ion.

The column sorption procedure was the same as reported

1- 4,11 earller '

(ii) Studies on Sodium Stannosi] icate

In this case 0.2 gm of dry resin and 0.025 M of

metal ion solution (20 ml) in aqueous and aqueous organic -

HNOo media was taken. Each solution contained different

concentrations of HNO^ (0.02, 0.05, 0.1, 0.15 and 0.2 M)

The values of distribution coefficient Kd were

calculated using the relation.

, mequiv . metci 1/g dry resin

mequiv. metal/ml of solution

207

RESULTS AND DISCUSSION

The results of Kd values of certain metals on 1inde

molecular sieves {13X) in the mixture of non-aqueous

solvent with aqueous NaNO^ solution, summarized in table 1,

indicate that as the percentage of methanol decreases the

Kd values increase for all the metal ions studied. This

variation is because of the fact that the mobility of

counter-ions is based on the polarity of the solution. A

higher mobility will result in a more polar medium. Thus

when the concentration of methanol decreases the medium

becomes more polar and hence the Kd value increase. These

results may further be compared with the help of Fig.

1 to 5. These figures also show the selectivity of the

various metal ions studied.

These results also show the feasibility of some

important separations, for e.g. Ag and Pb show a

remarkable difference in their selectivities Fig. 4; Cd

and Mn Fig.2; Ni and Co (Fig. 1).

The studies in mixed organic inorganic systems were

made on a synthetic inorganic exchanger of zeolite type,

sodium stnnnosilicate. Kd values of some metal ions

presented in table 2 and plotted in Fig. 6 indicate that

sodium stannosilicate shows a differential selectivity

with different metal ions in methanol aqueous system.

208

The variation of Kd values with the addition of an

acid (HNO^), results summarized in table 3, indicate that

as the concentration of HNO^ increases the Kd values

decrease sharply. This is because sodium stannosilicate is

a weak cation exchanger and hence has a high affinity

towards H ions,as a result in competition of metal ion and

H ions, H ion are preferred when the number of H ions

increases and Kd value for the metal ion decreases. These

results presented in Fig. 7 are all in accordance with the

above theoretical behaviour.

Sodium stannosilicate has a very high affinity for

Ag in such systems and therefore this can be used for the

selective uptake of Ag ions. These results are also in

accordance with the studies made in aqueous system .

Although the non-aqueous systems seem to get some fruitful

results^but there theoretical interpretation is not an easy

affair because of the effect of various other interaction,

such as swelling pressure, polarity, steric hinderance,

ionization, temperature etc.

209

Table - 1

Kd v a l u e s of metal ions in aqueous o r g a n i c s o l v e n t -O.IM

NaNO^ - 0.02M metal i o n s on 1inde mo lecu l a r s i e v e {13X)

Methanol

I (V/V)

50 .00

44 .40

37.50

28 .52

16.66

0 .00

50.00

44 .40

37.50

28.52

16.66

0 .00

50.00

44 .40

37 .50

28 .50

16.66

0 .00

Ni2^

372.72

550.00

1200.00

1344.00

2066.00

4233.33

Zn

207.04

563.63

567.00

668 .71

670 .00

1091.36

Mg2*

237.21

240.00

261.36

278.02

280.95

300.8 7

Kd v a l u e s of

Co2^

414 .28

416 .25

642.30

880 .00

899 ,20

1740.00

Al3^

70.00

81 .81

92.97

99.47

100.00

150.00

r 2 + Ca

406 .25

676.05

685 .53

691.428

750.00

962.50

Mn2^

314 .63

388.96

411 .63

495 .66

522.85

557 .14

Ag*

212.98

912.00

1820.00

3160.00

3555.50

3950.00

Ba2^

300.00

424 .615

598.18

636.92

760.00

854 .54

2 +

1150.00

1785.00

1920.00

2430.00

2667.27

900.00

Pb2^

203 .15

430 .71

605 .00

624 .34

1560.00

1975.00

c 2 + Sr

115 .00

585.00

586.60

588.25

715.86

700.00

210

50r

O

T3

•/. of Methanol

Fig 1 Plots of kd vs 7o of methanol on linde molecular sieve (13x)

211

^Or

(SI

O

"O

-O- Mn

•/. of Methanol

Fig 2 Plots of k d v s Vo of methano l on linde molecular sieve (13x )

212

O

f

>

^Or

30

20

C^ , o _ _ , 0-1 - o - i - . - Q , ,

0 10 20 30 40 50 60

V. of Methanol

Fig 3 Plots of kd vs % of methanol on linde molecular sieve (13 X

213

4 0 i -

o

1/1

3

nl > • D

- • - Ag*

- o - Pb^*

•/, of Methanol

Fig.^ . Plots of kd vs. % of methanol on linde moleculor sieve (13 X )

214

i Mq2*

10 20 30 AO

V, of Methanol

Fig 5 '. Plots of kd VS. V« of methanol on linde molecular sieve (13 X 1

215

Table - 2

Kd values of metal ions in aqueous organic solvents

(0.02 M HNO^) and 0.025M metal ions on sodium stanno

silicate (Na" form) Methanol + HNOo (1:1)

S.No. Metal ion Kd value

1. Mg^^ 400

2. Ca" * 250

3. Ba '' 340

4. Sr^^ 340

5. Ag2+ 2700

6. Pb"'' 200

7. Ni "" 130

8. Co "" 300

9. Mn^^ 150

10. Cd^^ 50

.00

216

Oi

2 > X)

AOO

300

200 -

100

Mg _L -L Ca Ba Ni Co Sr Ag Pb

Different metal ion

Fig.6. Plots of kd vs d i f f e ren t meta l ion on sodium stonnosi l icate

Mn Cd

217

Table 3

Kd vaJues of metal ions in aqueous organic solvent -(0.02 M

to 0.2 M HNO-,) and 0.025 M metal ions on sodium stanno-

silicate (Na^ form) Methanol + HNO^ (1:1)

Cone. HNO^

0.02

0.05

0.1

0.15

0.2

of used

Ag^

2700.00

460.00

300.00

300.00

115.00

Kd Values

Mg^^

400.00

53.84

25.00

17.64

15.26

of

Ca2^

2500.00

160.00

30.00

18.18

18.18

Sr

0.000

340.00

37.50

22.22

10.00

Ba2^

0.000

833.33

86.00

40.00

40.00

218

2700

2100

1500

900V

700

• o

400/

300

200

100

J L ^ ^ - ^ ^ ^ f - ^ ^ ^ J I I '

00 002 OO'i 006 008 01 0 12 O.l'i 016 0 18 02

Cone of HNO3

Fig 7. Plots of kd vs nitric ocid concentration on sodium stonnosilicote

219

REFERENCES

1. Hassam, E.A., Aboul-Magd, A.S., Kamal , F.H., EL-Hadi,

M.F. and Ismail, N.M., Indian J. Chem. Sect A, 20, 598

(1981).

2. Korkisch, J. and Kla], E., Talanta, 16, 377 (1967).

3. Hassan, E.A., Salama, J.Y., EL-Hadi, M.F. and Aboul-

Magd, A.S., Pak. J. Sci. Ind. Res., 24, 56 (1931).

4. Tistiovch, I.K., Golubko, D.P., Fisenko, A.Z. and

Timesteeva, I. Yu., Zh. Prikl. Khim., 51, 1934 (1987).

5. Tsuji, M. , Kaiiiareneni, S., Sep. Sci. Techno]., 27(6),

813-21 (1992).

6. Aboul-Magd, A.S., Kamal, G.M., EL-Saied, Hassan, E.A.

and Mousa, A.A., J. Indian Chem. Soc., 67, 195-198

(1990).

7. Rawat, J.P. and Ansari, A.A., Bull. Chem. Soc. Jpn.,

63 (1990).

8. Vogel , A.I., "A Text Book of Quantitative Inorganic

Analysis", 3rd ed., Longman Green, London, (1966).

9. Irving, H., "Compl exo:netric Titration", Methuen,

London, (1957).

10. "Standard Methods for the Examination of Water and

Waste water", American Public Health Association,

(1966).