________________________________ Introduction _________________________________
CHAPTER 1
INTRODUCTION
1.1. Ion exchange
Ion exchange is an elegant separation technique that allows different ionic
materials to be selectively retained on an ion exchange material. In the last decades, ion
exchangers have been used extensively in the chemical decontamination process for
metal ion recovery, regeneration of decontaminants and removal of the formulation
chemicals from the coolant. Today it is used on an incomparably wider scale and is an
integral part of many new technical and industrial processes.
The literature review shows that the materials used as inorganic ion exchangers
have become an established class of materials of great analytical importance. There are
suggestions found in the Bible and in writings by the ancient Greeks that put forward
knowledge of desalting brackish waters. In 1623, Francis Bacon brought the intentional
use of ion exchange. Thompson and Way in 1850 described the exchange of calcium
and magnesium ions of certain types of soils for potassium and ammonium ions1. In
1858, Eichorn demonstrated that the exchange processes in soils was reversible2 and in
1859 Boedecker proposed an empirical equation describing establishment of
equilibrium on inorganic ion exchange sorbents. Lemberg, in 1876, also confirmed the
reversibility and calculated the reversibility of the process. In the 20th century, the
majority of chemists believed that the ‘base exchange’ in soils was nothing but a sort of
absorption.
Strong supports to ion exchange came out with the synthesis of materials from
clay, sand and sodium carbonate by Gans3. Gans developed the basis for the synthesis
and technical application of inorganic cation exchangers at the beginning of the 20th
century. He termed the amorphous cation exchangers based on aluminosilicate gels as
‘permutites’, which were the first commercially available ion exchangers. Gans
demonstrated the first practical application of synthetic zeolite as water softener4. Later
zeolite development progressed to the replacement of aluminosilicate with zirconium
phosphate. Folin and Bell developed an analytical method based on these materials for
the separation of ammonia5 in 1917. Between 1930s and 1940s, inorganic ion exchange
1
,________________________________ Introduction _________________________________
sorbents were replaced by the new organic ion exchangers in almost all fields. The
observation of Adams and Holmes that crushed phonograph records exhibit ion
exchange properties6 eventually resulted in the development of synthetic ion exchange
resins in 1935.
Due to the breakdown of organic resins in aqueous systems at high temperatures
and in the presence of high ionizing radiation doses, they had limited applications.
There was a resurgence of interest in inorganic exchangers in the 1950s. Pioneering
work was carried out in this field by the research team at the Oak Ridge National
University led by Kraus7 and by the English team led by C. B. Amphlett. The first
monograph that is also of historical importance was written by Amphlett, one of the
first research workers in the development of modern inorganic sorbents, in 1964. It
describes the beginning of the rapid development of this subject8. Further extensive
research and study of inorganic ion exchanger sorbents were carried out in the 1960s
and 1980s. Barrer wrote an excellent monograph on contemporary zeolites and clay
minerals. In the 1980s, Clearfield et al. made a great contribution to the understanding
of the structure and mechanism of sorption processes on the acidic salts of multivalent
metals and hydrous oxides9. In the last two decades, intense research has continued on
the synthesis of a number of new ‘organic-inorganic’ composite materials.
There are a number of books dealing with ion exchangers. The most important
among them were written by Kunin10, Helfferich11, Reiman and Walton12 and
Inczedy13. Samuelson wrote the first book on the analytical applications of ion
exchangers14. The technical practice of column operation in analytical chemistry was
introduced by White who used a synthetic zeolite as a reagent for amine15. Frederick C.
Nachod published a book regarding the theory and applications of ion exchangers16.
Reviews related to ion exchangers were published by different scientists like Pekareck
and Vesely17, Clearfield18, Walton19, Torracca20 and Abe21. The first analytical
application of organic ion exchanger is connected with the name of Kullgren22.
Extensive studies on synthetic inorganic ion exchangers have proved their
potential in solving diverse problems of environmental and analytical chemistry.
Inorganic ion exchangers of double salts, based on tetravalent metal acid (TMA) salts
often exhibit much better ion exchange behaviour as compared with its single salts23.
An interest of inorganic as well as composite ion exchange materials in ion exchange
2
, ________________________________ Introduction _________________________________
operations in industries is increasing day by day as their field of applications is
expanding.
1.2. The process of ion exchange
The process of ion exchange became established as an analytical tool in
laboratories and in industries, as it was studied mainly by practical chemists interested
in effects and performance. When the exchanger is in contact with an electrolyte, these
ions can be exchanged for a stoichiometrically equivalent amount of other ions of the
same sign24. Basically the ion exchange process consists of contact between the
exchanger and the medium in which the exchange takes place. A typical ion exchange
reaction may be represented as;
̅̅̅̅
𝐴𝑋 + B(aq) → ̅̅̅̅
𝐵𝑋 + A(aq)
where A and B taking part in ion exchange are the replaceable ions and X is the
structural unit (matrix) of the ion exchanger. The bar indicates the exchanger phase and
(aq) represents the aqueous phase.
(-) Matrix with fixed charge A and B counter ions
Initial state Equilibrium state
Figure 1.1: Schematic representation of ion exchange process within a solution. A
cation exchanger containing counter ions ‘A’ is placed in a solution containing
counter ions ‘B’ (left). The counter ions are redistributed by diffusion until
equilibrium is attained (right)
Ion exchange resembles adsorption, in both cases; a dissolved species is taken
up by a solid. The characteristic difference between the two is that the ion exchange in
contrast to sorption is a stoichiometric process. However, in the case of sorption of a
3
CHAPTER 1
INTRODUCTION
1.1. Ion exchange
Ion exchange is an elegant separation technique that allows different ionic
materials to be selectively retained on an ion exchange material. In the last decades, ion
exchangers have been used extensively in the chemical decontamination process for
metal ion recovery, regeneration of decontaminants and removal of the formulation
chemicals from the coolant. Today it is used on an incomparably wider scale and is an
integral part of many new technical and industrial processes.
The literature review shows that the materials used as inorganic ion exchangers
have become an established class of materials of great analytical importance. There are
suggestions found in the Bible and in writings by the ancient Greeks that put forward
knowledge of desalting brackish waters. In 1623, Francis Bacon brought the intentional
use of ion exchange. Thompson and Way in 1850 described the exchange of calcium
and magnesium ions of certain types of soils for potassium and ammonium ions1. In
1858, Eichorn demonstrated that the exchange processes in soils was reversible2 and in
1859 Boedecker proposed an empirical equation describing establishment of
equilibrium on inorganic ion exchange sorbents. Lemberg, in 1876, also confirmed the
reversibility and calculated the reversibility of the process. In the 20th century, the
majority of chemists believed that the ‘base exchange’ in soils was nothing but a sort of
absorption.
Strong supports to ion exchange came out with the synthesis of materials from
clay, sand and sodium carbonate by Gans3. Gans developed the basis for the synthesis
and technical application of inorganic cation exchangers at the beginning of the 20th
century. He termed the amorphous cation exchangers based on aluminosilicate gels as
‘permutites’, which were the first commercially available ion exchangers. Gans
demonstrated the first practical application of synthetic zeolite as water softener4. Later
zeolite development progressed to the replacement of aluminosilicate with zirconium
phosphate. Folin and Bell developed an analytical method based on these materials for
the separation of ammonia5 in 1917. Between 1930s and 1940s, inorganic ion exchange
1
,________________________________ Introduction _________________________________
sorbents were replaced by the new organic ion exchangers in almost all fields. The
observation of Adams and Holmes that crushed phonograph records exhibit ion
exchange properties6 eventually resulted in the development of synthetic ion exchange
resins in 1935.
Due to the breakdown of organic resins in aqueous systems at high temperatures
and in the presence of high ionizing radiation doses, they had limited applications.
There was a resurgence of interest in inorganic exchangers in the 1950s. Pioneering
work was carried out in this field by the research team at the Oak Ridge National
University led by Kraus7 and by the English team led by C. B. Amphlett. The first
monograph that is also of historical importance was written by Amphlett, one of the
first research workers in the development of modern inorganic sorbents, in 1964. It
describes the beginning of the rapid development of this subject8. Further extensive
research and study of inorganic ion exchanger sorbents were carried out in the 1960s
and 1980s. Barrer wrote an excellent monograph on contemporary zeolites and clay
minerals. In the 1980s, Clearfield et al. made a great contribution to the understanding
of the structure and mechanism of sorption processes on the acidic salts of multivalent
metals and hydrous oxides9. In the last two decades, intense research has continued on
the synthesis of a number of new ‘organic-inorganic’ composite materials.
There are a number of books dealing with ion exchangers. The most important
among them were written by Kunin10, Helfferich11, Reiman and Walton12 and
Inczedy13. Samuelson wrote the first book on the analytical applications of ion
exchangers14. The technical practice of column operation in analytical chemistry was
introduced by White who used a synthetic zeolite as a reagent for amine15. Frederick C.
Nachod published a book regarding the theory and applications of ion exchangers16.
Reviews related to ion exchangers were published by different scientists like Pekareck
and Vesely17, Clearfield18, Walton19, Torracca20 and Abe21. The first analytical
application of organic ion exchanger is connected with the name of Kullgren22.
Extensive studies on synthetic inorganic ion exchangers have proved their
potential in solving diverse problems of environmental and analytical chemistry.
Inorganic ion exchangers of double salts, based on tetravalent metal acid (TMA) salts
often exhibit much better ion exchange behaviour as compared with its single salts23.
An interest of inorganic as well as composite ion exchange materials in ion exchange
2
, ________________________________ Introduction _________________________________
operations in industries is increasing day by day as their field of applications is
expanding.
1.2. The process of ion exchange
The process of ion exchange became established as an analytical tool in
laboratories and in industries, as it was studied mainly by practical chemists interested
in effects and performance. When the exchanger is in contact with an electrolyte, these
ions can be exchanged for a stoichiometrically equivalent amount of other ions of the
same sign24. Basically the ion exchange process consists of contact between the
exchanger and the medium in which the exchange takes place. A typical ion exchange
reaction may be represented as;
̅̅̅̅
𝐴𝑋 + B(aq) → ̅̅̅̅
𝐵𝑋 + A(aq)
where A and B taking part in ion exchange are the replaceable ions and X is the
structural unit (matrix) of the ion exchanger. The bar indicates the exchanger phase and
(aq) represents the aqueous phase.
(-) Matrix with fixed charge A and B counter ions
Initial state Equilibrium state
Figure 1.1: Schematic representation of ion exchange process within a solution. A
cation exchanger containing counter ions ‘A’ is placed in a solution containing
counter ions ‘B’ (left). The counter ions are redistributed by diffusion until
equilibrium is attained (right)
Ion exchange resembles adsorption, in both cases; a dissolved species is taken
up by a solid. The characteristic difference between the two is that the ion exchange in
contrast to sorption is a stoichiometric process. However, in the case of sorption of a
3
