Chapter 1

General Introduction

1

Introduction

Analytical chemistry is the backbone of science because of its fundamental

importance in today‟s information society. Analytical science is the term given to the

science of detection and measurement. We see the use and benefits of it in everyday life

from the tests performed to check the purity of medicines, daily monitoring of industrial

wastes and analysis in the forensic laboratory. It is basically concerned with the study of

matter in order to reveal its composition, structure and extent. Because these fundamental

understanding are very necessary for preliminary study of every chemical inquiry.

Analytical chemistry is used to obtain information and solve problems in many different

chemical areas which are essential in both theoretical and applied chemistry (practical

aspect of chemical, bio-chemical and microbiological analysis). Owing to accurate data

obtained for a trained analytical scientist, the demand of analytical chemistry is increasing

day by day.

Early analytical chemistry was mainly focused on identification of elements,

compounds and discovering their attributes. Discovery gave way to systematic analysis

which took a giant step forward with the invention in the 1850‟s of the first instrument for

chemical analysis–flame emissive spectrometry–by Robert Bunsen, a German chemist

who is better known for his invention of the Bunsen burner, and his colleague Gustav

Kirchoff, a German physicist who is known for coining the name "black body" radiation

in 1862. Modern analytical chemistry covered main aspect as identification,

quantification, elucidation of structure, separation of different elements in natural and

artificial materials by ion-exchangers. It also focused on improvements in experimental

design, chemometrics and the creation of new measurement tools to provide better

chemical information. Separation process has very important applications in various

fields namely medicine, agriculture and environmental analysis. It involves both classical

and instrumental techniques.

CLASSICAL (Wet methods) INSTRUMENTAL

Classical gravimetric analysis Optical methods

Classical volumetric analysis Separation Methods

Electroanalytical Methods

2

The use of classical methods in the separation of metal ions is carried out by

precipitation, extraction, distillation and qualitative analysis by colour, odour or melting

point. Quantitative analysis is achieved by measurement of weight or volume.

Instrumental methods use an apparatus to measure physical quantities of the analyte such

as light absorption, fluorescence and conductivity.

Chemical analysis is an important part of many exciting scientific projects being

carried throughout the world because on the basis of this analysis we are able to know the

properties of materials of our interest. The major areas in which chemical analysis plays

an important role are:

a) Chemical analysis of air and water is required to identify and quantitate the

pollutant which is a necessary step in determining safe level of pollutants.

b) Medicines rely heavily on chemical analysis to diagnose illness properly

and to monitor the progress of patients.

c) Chemical analysis of soil and plants is used to determine the nutrients

which must be added to the soil to increase the productivity.

d) It is also used to indicate the quality of its product and to help developing

new sources and new forms of energies.

The entire chemical industry uses chemical analysis as a method for checking and

ensuring the quality of many synthetic products which we rely upon to make life more

comfortable and enjoyable. So it is clear that analytical chemistry is an exciting field with

a distinguished history and a bright future.

Separation of materials is accomplished by using electrophoresis and ion-

exchange chromatography. Amongst, them ion-exchange chromatography is considered

to be most versatile and particularly well suited and helpful method in sorption of metal

ions of similar properties. Ion-exchangers are particularly suited for the removal of

chemical impurities for several reasons: ion-exchangers have high capacity and also

specificity for the impurities like metal ions that are found in low concentration. They are

thermally stable and readily regenerated. Selective ion-exchangers exhibit the high

selectivity towards the specific species even in the presence of large concentration of

other species. Ion-exchangers have been widely used for the removal of heavy toxic metal

ions from waste water which is untreated or partially treated by product of various

industries. Year by year the literature on ion-exchangers is increasing which show the

great importance of these substances. Furthermore, not only the applications of ion

exchange materials increasing but the new ion-exchange materials also afford new

3

opportunities for both chemists and analysts. Many natural and synthetic substances have

the capability of ion-exchange.

An ion-exchange reaction may be defined as the reversible interchange of ions

between a solid phase (the ion-exchanger) and the solution phase, the ion-exchanger

being insoluble in the medium in which the exchange is carried out. According to the

charge of the exchangeable ions the material may be classified as:

1. Cation exchangers

2. Anion exchangers

3. Amphoteric ion-exchangers

Cation exchangers: - Those which carry exchangeable cations

M- A

+ + B

+ M

- B

+ + A

+

Anion exchangers: - Those which carry exchangeable anions

M+ A

- + B

- M

+ B

- + A

-

Amphoteric ion-exchangers: - Those which are capable of exchanging both cation and

anion.

The efficiency of an ion-exchanger depends on the following fundamental properties:

Equivalence of exchange

Selectivity preference of the exchanger for one ion relative to another

Donnan exclusion- the ability of the resin to exclude ions under most conditions

but not un-dissociated substances

Screening effect- the inability of very large ions or polymer to be absorbed to an

appropriate extent.

Difference in migration rates of absorbed substances down a column-primarily a

reflection of differences in affinity.

Ionic mobility restricted to the exchangeable ions and counter ions only.

Miscellaneous-swelling surface area and other mechanical properties.

4

Historically speaking, the use of solid absorbing substances to improve water

quality has been recorded since ancient times. The earliest of the references were found in

the Holy Bible, which says „Moses‟ succeeded in preparing drinking water from brackish

water by an ion-exchange method [1] to remove the salts bearing minerals containing

sodium, calcium and magnesium. Aristotle [2] stated that the sea water loses part of its

salts content when percolated through certain sands. In 1623, Francis Bacon and Hales

described a method for removing salts by filtration and desalination from sea water. The

idea that the sorbents can be employed in technical application for studying adsorption

came at the end of 18th

century in 1790 when Lowitz purified sugar beet juice by passing

it through charcoal. As experimental information increased, De Saussure drew the first

qualitative conclusions at the beginning of 19th

century. Gazzeri (1819) discovered that

clay retained dissolved fertilizer particle. Sprengel (1826) stated that humus frees certain

acids from soil. Fuchs (1833) pointed out that the lime frees potassium and sodium from

some clay. By middle of 19th

century sufficient experimental observations and

information had been collected but principle of ion-exchange had not yet been

discovered. Thomson 1845 [3] and Way [4] in 1850 led the foundation of ion-exchange

by base exchange in soil. They observed that when soils are treated with ammonium salts,

ammonium ions are taken up by the soil and an equivalent amount of calcium and

magnesium ions are released. During 1850 to 1855 the agro chemist Way demonstrated

the following mechanism to be one of the ion-exchange methods, involving complex

silicates presence in the soil. As described by Way the process observed by the Thomson

could be formulated:

Ca-soil + (NH4)2SO4 NH4-Soil + CaSO4

Eichorn [5] demonstrated that exchange process is reversible in naturally

occurring zeolites having the structure of aluminosilicates. Aluminium based synthetic

zeolite was first prepared in 1903 by Harms and Rumpler [6] to purify the beet syrup.

Gans [7] succeeded in utilizing the synthetic aluminium silicates ion-exchangers for

industrial purpose like softening of water and also for treating sugar solutions. According

to the Lamberg and Weigner [8, 9] the materials responsible for the phenomenon were

mainly clays, zeolites, gluconites and humic acids. The first application of synthetic

zeolites for collection and separation of ammonia from urine was made by Follin and Bell

[10]. Due to the limitation in the applications of natural and synthetic silicates in various

5

industrial applications an attempt had developed to meet the demands of the industries. A

revolution in the field of ion-exchange underwent in 1930s when Adam and Holmes [11]

observed that the crushed phonograph records exhibit ion-exchange properties. This lead

to investigation to develop synthetic ion exchange resins. These resins were developed

and improved by the formal I.G. Farben industries in Germany followed by the

manufactures in U.S.A and U.K., which proved very effective for separation, recoveries,

the ionization catalysis etc.

An ion-exchanger may be organic or inorganic depending on the nature of the

matrix of which it is made up. Ion-exchangers are usually insoluble solid substances

(large molecular poly electrolytes having porous structures) or immiscible liquids (in case

of liquid ion-exchangers) which can take up ions of positive or negative charge from an

electrolyte solution and released other ions of like charge into the solution in an

equivalent amount. Revival of interest in inorganic ion-exchange materials has largely

stemmed from the fact that the materials can be used under condition unfavourable

towards organic resins. Organic resins are usually stable in a wide pH range while

inorganic materials differ widely in this respect. The insoluble salts of polyvalent metals

are highly stable even in highly concentrated acids.

The thermal stability of ion-exchangers depends on the type of resin skeleton, its

degree of cross linking, type of ionogenic and their counter ions. Polymer materials of

organic resin break down at elevated temperatures, with a concomitant decrease in their

exchange capacity. In contrast inorganic ion-exchangers are highly stable at elevated

temperature. Their resistant towards heat and ionizing radiations make their attractive

alternative towards certain ions while organic resins are highly sensitive to exposure to

high radiation doses which cause significant changes in their capacity and selectivity.

Inorganic ion-exchangers have good applications in the treatment of industrial, radio-

active wastes and processing of radio-isotopes in nuclear technology. Analysis of rocks,

minerals alloys and pharmaceutical products have also been made by using these

materials. These materials also had other important and advantageous of ions such as high

selectivity and ion-exchange capacity. However, the last few decades have seen great

upsurge in the field of inorganic ion-exchangers about their synthesis, characterization

and analytical applications in various fields.

Kraus et al. [12, 13] at Oak Ridge national laboratory and C. B Amphlett [14, 15]

in United Kingdom did the excellent work on these materials in the initial stages. The

work up to 1963 has been summarized by Amphlett [16] in the classical book „Inorganic

6

ion-exchanger‟. The later work up to 1970 has been condensed by Pekareck and Vesely

[17], Clearfield [18, 19], Alberti [20, 21], Walton [22, 23], Torracca [24, 25] and Abe [26,

27] have also worked on aspects of synthetic inorganic ion-exchangers. In India Qureshi

and co-workers [28, 29] have prepared number of such inorganic materials and studied

their ion-exchange behaviour during the last 15 years. Other groups that were engaged in

the field of research and whose work is of significant interest are Anil K. De at

Shantiniketan and Tandon at Rorkee. Some important uses of inorganic ion-exchangers

are:

The treatment of waste water and air pollution.

Separation of metal ions.

Separation of organic compounds.

The preparation of fuel cells.

The preparation of artificial kidney machines.

The preparation of ion selective electrodes.

Possibility of group separation.

Ion exchange as packing for gas chromatography.

Specific spot test.

Preparation of standard solutions.

They can be used as acid and base catalysts.

Formation constant of compounds can be determined.

On the basis of their salt composition Vesley et al. [30] classified inorganic ion-exchange

materials into the following main groups:

1. Hydrous oxides

2. Synthetic aluminosilicates

3. Salts of heteropolyacids

4. Metal ferrocyanides

5. Quadrivalent metal oxides (oxides of group IV with more acidic oxides of

group V and VI of the periodic table) or acidic salts of multivalent metals.

6. Double layered hydroxides

7

1. Hydrous oxides

They are of particular interest. A wide range of hydroxides exhibit excellent

selectivity with respect to certain elements or group of elements due to their amphoteric

nature. The amphoteric ion-exchange behaviour can be deducted by the following

mechanism.

M-OH M+ + OH

- (1)

M-OH M-O- + H

+ (2)

(M represent the central atom)

Eq. 1 is favoured in acidic condition when the substance functions as an anion exchanger,

while in alkaline condition Eq. 2 when the substance functions as cation exchanger.

The hydrous oxides may be divided into two main types:

(a) Particle hydrates

(b) Frame work hydrates

Particle hydrates are both cation and anion exchangers. Most of the metals of

group 3, 4, 13 and 14 form hydrous oxides. They are characterized by having a bulk

structure which resembles one of their ceramic oxides. Frame work hydrates are generally

formed by metals in group 5 and 15 in their higher oxidation states. The pyrochlore nature

of crystalline antimony(V)oxides exchanger was revealed by powder X-ray diffraction

which established the composition as (H3O)2 Sb2O6.nH2O [31].

2. Zeolites

Zeolites were first inorganic materials to be used for the removal of waste

effluents at large scale. These are microporous aluminosilicates minerals commonly used

as commercial sorbents. It is also known as “molecular sieves”. The chemical

composition of zeolites is expressed by the formula.

Mx/n [(AlO2)x (SiO2)y]zH2O

where M is the metal ion with valence n and y/x usually varies from 1 to 5.

There are two kinds of zeolites.

1. Natural

2. Synthetic

8

Synthetic and natural zeolites are hydrated aluminosilicates with synthetically

slacked alumina and silicate tetrahedra which result in an open and stable three

dimensional honey comb structure with a negative charge. The negative charge within the

pores is neutralized by positively charge ions (cations) such as sodium. Synthetic zeolite

can be classified into following groups. Faujasite, mordenite, Heulendite, Chabazite,

analcite, natrolite, phillipsite like zeolite and other zeolites. Other natural substances

having ion-exchange properties are glaunites. Thus, appetite is an anion exchanger.

The main advantages of synthetic zeolites when compared with naturally

occurring zeolites are that they can be engineered with a wide variety of chemical

properties, pore sizes and they are stable at high temperature but they have some

limitations too.

The main limitations of synthetic zeolites are:

They have relatively high cost compared to natural zeolites.

They have limited chemical stability at extreme pH ranges (either high or low)

Their ion specificity is susceptible to interference from similar size ions.

In India, a systematic investigation has been carried out to evaluate the

performance of locally available synthetic zeolite for the removal of cesium, strontium

and thorium from solution [32-34].

3. Salts of heteropolyacids

Salts of heteropolyacids have a general formula HmXY12O40.nH2O where m= 3, 4

or 5, X can be phosphoric, arsenic, silicon, germanium or boron and Y is one of the

elements such as molybdenum, tungsten or vanadium. The heteropoly acids with small

cation are relatively soluble where as those with larger cation are less soluble. Their

hydrolytic degradation occurs in strong alkaline solution. Smith and Robb [35] explored

the ion-exchange mechanism of this class. Quereshi and Qureshi et al. [36] have

presented the view on the applications of these materials in radiochemical separation

utilizing waste processing and fuel processing. The heteropolyacids exhibit high affinity

to heavy alkali metals, thorium and silver. The size of univalent ions of these elements is

suitable for retention in the crystal lattice of heteropolyacids.

9

4. Metal ferrocynides

They can be precipitated by mixing the metal salts solution with H4[Fe(CN)6],

Na4[Fe(CN)6] or K4[Fe(CN)6] solutions. The composition of such precipitate may depend

on the acidity, order of mixing and the initial ratio of reacting components. They have

high ion exchange capacity and are also known as scavengers for alkali metals. They are

easily prepared and useful in the separation of radioactive wastes and fissionable

materials [37] with less damage to radiation than their organic counter parts. Baetsley et

al. [38] studied ferrocyanide molybdate and determine its structure by X-ray studies.

They also used molybdenum and tungsten ferrocyanides for the separation of Cs-137 and

Sr-90 from fissionable products in acidic medium. Amine based metals ferrocyanides

were first introduced by Hahn and Clein [39], who prepared a cobalt amine ferrocyanide.

Later on Sn(II) and Sn(IV) ferrocyanides were prepared [40]. Insoluble ferrocyanides

have found various applications in analytical chemistry and in technological practice

because of their high selective ion-exchange characteristics and satisfactory chemical and

mechanical properties.

5. Acidic salts of multivalent metals

Acidic salts of multivalent metals forms by mixing the solutions of the salts of III

and IV groups elements of periodic table with the more acidic salts. These salts acting

generally as cation exchangers which are gel like micro crystalline materials and possess

high chemical, thermal and radiation stability.

6. Double layered hydroxides

Layered structures (α-layered) were found among the acid salts of tetravalent

metals. The α-layered material has been generally prepared by refluxing the amorphous

materials in concentrated phosphoric acid (10-14M) for few days. The degree of

crystallinity increases with increase of the refluxing time and concentration of phosphoric

acid as in case of α-zirconium phosphate.

A new class of exchangers has been developed by incorporation of bidentate or

polydentate ligands on the ion exchange matrix known as chelating ion-exchangers. Ion-

exchange resin containing chelating groups show superior selectivity. The affinity of a

particular metal ion for certain chelating resin depends mainly on the nature of the

chelating group and the selective behaviour of the resin which is largely based on the

different stabilities of the metal complexes formed on the resin under various pH

conditions. Chelating resin can be considered as special type of ion-exchangers. These

10

materials usually exhibit an ability to coordinate counter ions in addition to the ability for

simple ion-exchange interactions. A number of chelating ion-exchangers have been

developed by the incorporation of ligands on the resins [41-43] sorbed on porasil is

capable of separating metal ions at trace level. Nabi et al. have modified exchange resin

by incorporating chelating agents such as bromophenol blue [44], congo red [45], crystal

violet [46], tolidine blue [47].

Some important synthetic inorganic ion-exchangers based on two or three

components along with their composition, ion-exchange capacity and selectivity of metal

ions have been reported in Table 1.1 and Table 1.2

11

Table 1.1 Two-component ion exchange materials with their properties

S.No Ion exchange Materials Type Composition Empirical Formula IEC(meqg1) Selectivity References

1 Aluminium antimonate A Al/Sb=4.20 - 1.14 Ag+, UO2

2+, Ba

2+ 48

2 Aluminium oxide C - - - - 49

3 Aluminium vanadate A - (Al2O3)n.(V2O5)n - - 50

4 Aluminium silicate A - - - - 51

5 Aluminium

tripolyphosphate A

Al/P=0.50-

0.66 - 2.50 - 52

6 Aluminium metatungstate - - - - - 53

7 Antimonic acid A - Sb2O5.4H2O 1.28 Li+, Na

+, K

+, Ta

5+ 54

8 Antimony molybdate - - - - - 55

9 Antimony phosphate - - Sb(HPO4)2.H2O - Cd2+

, Hg

2+ 56

10 Antimony silicate C - Sb2O5(H2SiO3)6.nH2O - Rh+ 57

11 Antimony ferrocyanide A - - - Sr2+

58

12 Antimonysulphide

(Hydrous)

- - - - - 59

13 Bismuth tungstate A Bi/W=0.50 - 0.50 Pb2+

60

14 Bismuth nitrate A - - - - 61

12

15 Bismuth tellurate A Te/Bi=0.70 Bi4(H2TeO6)3.nH2O 3.20 - 62

16 Bismuth silicate A - - 3.30 - 63

17 Cerium vanadate A - CeO2.2V2O5.4H2O - - 64

18 Cerium antimonite A Sb/Ce=0.30 - 1.23 Hg2+

, Cu2+

,Tl+ 65

19 Cerium arsenate C As/Ce=2.0 Ce(HAsO4)2.2H2O 4.30 Li+, Na

+, K

+, Cs

+ 66

20 Cerium molybdate A Mo/Ce=2.3-

8.2

- 0.96 Pb2+

67

21 Cerium oxide A H2O/CeO2=3.0 - 0.99 Cu2+

66

22 Cerium oxide (Hydrous) C CeO2/H2O=2.5 - - - 68

23 Cerium tellurite A - - - - 69

24 Cerium tungstate A Ce/W=0.49 - - Al3+

, Hg+ 70

25 Cobalt antimonite A Co/Sb=1.3 - 0.89 Bi3+

71

26 Cobalt ferrocyanide A - - - Ag+ 72

27 Copper ferrocyanide A - - - - 73

28 Copper phosphate A - - - - 74

29 Chromium phosphate A P/Cr=0.6-1.0 Cr2O2HPO4Cr2O3(HPO4)2 5.90 Li+, Na

+, K

+, Rb

+,

Cs+

75

30 Chromium arsenate A As/Cr=1.98 Cr2O3(H3AsO4)4.3H2O 0.63 Zr4+

, Hf4+

76

13

31 Chromium molybdate A Mo/Cr=1.90 Cr2O3(H2MoO4)4.8H2O 0.34 Pb2+

, Ca2+

77

32 Chromium tungstate A W/Cr=1.92 Cr2O3(H2WO4)4.11H2O 0.02 Th4+

, Hf4+

78

33 Chromium antimonite A Sb/Cr=2.95 Cr2O3.3Sb2O5.22H2O 0.42 Co2+

, Pb2+

79

34 Chromium tellurate A Te/Cr=0.20 - - - 80

35 Chromium ferrocyanide A Cr/Fe=0.33 K6Cr2[Fe(CN)6]3.16H2O 2.65 Li+, Na

+, K

+, Ca

2+ 81

36 Ferric phosphate A P/Fe=2.00 FeH(HPO4)4.nH2O 0.77 Pb2+

, Eu3+

, Ca2+

82

37 Ferric arsenate A As/Fe=1.33 - 0.80 Li+, Na

+, K

+ 83

38 Ferric silicate A - - 0.20-1.60 Zn2+

, Cd2+

, Cr3+

,

Al3+

84

39 Ferric antimonite A Sb/Fe=2.40 - 0.80 Cd2+

85

40 Ferric tungstate A Fe/W=1.0 - 0.84 Ce4+

86

41 Ferric ferrocyanide A - - 3.60 Cs+ 57

42 Germanium(IV)phosphate C - Ge(HPO4)2.H2O 7.80 - 87

43 Hafnium phosphate C - Hf(HPO4)2.H2O 4.17 - 88

44 Hafnium arsenate A - HfAsO4 - - 89

45 Lead phosphate C - Pb(HPO4)2.H2O 4.79 - 87

46 Lead tungstate A W/Pb=2.50 - 1.0 Cu2+

90

14

47 Lead strontium phosphate A - - - - 91

48 Lead ferrocyanide A - Pb2 [Fe(CN)6] - Cs+, Co

2+ 92

49 Lanthanum tellurate A La/Te=0.66 La2(TeO4)3 1.61 - 93

50 Lanthanum oxalate A - - - - 94

51 Niobium phosphate A - - - - 95

52 Niobium arsenate A Nb/As=1.96 - 1.06 Cd2+

, Mn2+

, Al3+

96

53 Niobium vanadate A - - - Ce4+

, Eu3+

97

54 Niobium Antimonate S-C Nb/Sb=1.40 - 1.10 Mg2+

98

55 Niobium pentaoxide A - - - - 99

56 Stannic arsenate A Sn/As=1.84 - 0.79-0.94 Pb2+

, Al3+

, Fe3+

,

Ga3+

, In3+

100

57 Stannic phosphate A P/Sn=1.25 SnO2.0.62P2O5. nH2O 1.20-1.44 Li+, Na

+, K

+, Rb

+,

Cs+

101

58 Stannic tungstate A Sn/W=1.30 - 0.58 Ba2+

, Ca2+

, Sr2+

,

Mn2+

, Ni2+

, Co2+

102

59 Stannic antimonite A Sb/Sn=1.0 SnO2.Sb2O5.nH2O 0.75 Co2+

, Ni2+

103

60 Stannic oxide A - SnO2.nH2O 1.98 Cu2+

, Zn2+

, Co2+

,

Fe3+

, Ni2+

, Mn2+

104

61 Stannic molybdate A Sn/Mo=1.0 - 1.0 Pb2+

105

62 Stannic silicate A Sn/Si=4.0 - - Cu2+

, Pb2+

, Cr3+

106

15

63 Stannic selenite A Sn/Se=1.33 (SnO4)(OH)2(SeO3)3.6H2O 0.75 Li+, Na

+, K

+, La

3+ 107

64 Stannic vanadate A Sn/V=1.0 [(SnOH)3V3O9.4H2O]n 0.85 Li+, Na

+, K

+ 108

65 Stannic ferrocyanide A Sn/Fe=3.0 [(SnO)3.(OH)3H4Fe(CN)6.3H2O]n 0.85 Na+, K

+, Ba

2+ 109

66 Tantalum pentaoxide A - - - - 110

67 Tantalum phosphate A - - - - 111

68 Tantalum arsenate A Ta/As=2.80 - 1.09 Na+, K

+, Ba

2+ 112

69 Tantalum antimonite A Ta/Sb=1.30 - 0.99 NH4+

, Na

+, K

+,

Vo2+

113

70 Tantalum selenite A Se/Ta=1.5 - 1.19 Fe3+

, Ba2+

114

71 Tantalum tungstate A - - 0.84 K+ 115

72 Thorium phosphate C Th/PO4=0.50 Th(HPO4)2.2H2O 0.77 Ca2+

, Sr2+

, Ba2+

116

73 Thorium tungstate A Th/W=2.0 Th(OH)2(HWO4)2.nH2O 0.46 Na+, K

+, Cs

+, Bi

3+,

Hg2+

, Vo2+

117

74 Thorium antimonite A Sb/Th=3.65 - 0.32 Cu2+

, Pb2+

118

75 Thorium oxide A - Th(OH)n.nH2O 2.00 Na+, Rb

+, Ca

2+,

Sr2+

119

76 Thorium arsenate C As/Th=1.53 Th(HAsO4)2.H2O 0.20 Li+ 120

77 Thorium molybdate A Th/Mo=0.5 - 0.75 Pb2+

, Fe3+

, Zr4+

121

16

78 Titanium arsenate A - Ti(HAsO4)2 2.5H2O TiO2.

0.5 As2O5.nH2O

1.0 Ba2+

, Sr2+

, Cd2+

,

Zn2+

, Cu2+

, Pb2+

122

79 Titanium antimonite A Sb/Ti=1.0-

1.36

- 0.70 Mg2+

, VO2+

, Zn2+

,

rare earth metals

123

80 Titanium tungstate A Ti/W=0.80 - 0.40-0.76 Cs+, Ca

2+, Cr

3+ 124

81 Titanium oxide A - TiO(OH)2.nH2O 2.00 Rb+, Cs

+, Co

2+ 119

82 Titanium molybdate A Mo/Ti=0.5-2.0 - 0.80-1.60 Na+, K

+, Ba

2+,

Pb2+

125

83 Titanium selenite A Ti/Se=1.39 - 0.78 Cd2+

126

84 Titanium vanadate A V/Ti=4.0 Ti3(V3O9.1.5H2O)4 0.68 Sr2+

127

85 Titanium tellurate A Te/Ti=2.06 - - - 80

86 Titanium ferrocyanide A Fe/Ti=2.00 - 1.40 Cs+ 128

87 Titanium silicate A Ti/Si=1.0 - 3.62 Li+, Na

+, K

+, Pb

2+,

Cr3+

129

88 Zirconium antimonite A - ZrO2.Sb2O5.nH2O - Na+, K

+, NH

4+,

Rb+, Cs

+, Li

+

130

89 Zirconium arsenate A As/Zr=1.53-

1.96

ZrO2.84As2O5.nH2O 4.30 Na+, K

+, Cs

+ 131

90 Zirconium ferrocyanide A Fe/Zr=0.63 - 0.96 NH4+

, Li+, Na

+,

Zn2+

132

91 Zirconium molybdate A Zr/Mo= 0.5-

2.0

- 2.18 - 133

17

92 Zirconium oxide A - ZrO2.4.7H2O 1.09 Ca2+

, Ba2+

134

93 Zirconium pyrophosphate A P/Zr=2.5-2.8 - - Cu2+

, Ni2+

, Ba2+

,

Ca2+

, Mg2+

, Fe3+

135

94 Zirconium hypophosphate A Zr/P=0.57 - - Multivalent metals 136,137

95 Zirconium selenite A Zr/Se=1.23 - 0.48 Ag+, Cu

2+, Au

2+ 138

96 Zirconium silicate A Zr/Si=0.5 - 3.18 Ag+, Ca

2+, Cu

2+,

Cr3+

, Th4+

139,140

97 Zirconium tellurate A - Zr(H2TeO6).4H2O 2.80 - 141,142

98 Zirconium oxalate C - Zr(OH)C2O4H 2.50 Alkali metals 143

99 Zirconium tungstate A Zr/W=1.0-

0.44

- - Alkali metals 144

100 Zirconium polyphosphate A - - - Na+, K

+, Li

+, Cs

+, (NH4

+ form)

Ba2+

, Co2+

, Cu2+

, Fe3+

(H+form)

145,146

101 Zinc silicate A Si/Zn=1.25 - 2.00 - 147

102 Zinc ferrocyanide A Zn/Fe=1.98 Zn2Fe(CN)6 6.10 - 148

103 Zinc phosphate A - - - - 149

A= Amorphous, C= Crystalline, S-C= Semi-crystalline

18

Table 1.2 Three-component ion exchange materials with their properties

S. No. Ion exchange materials Type Composition Empirical Formula IEC

(meqg-1

)

Selectiviy References

1 Amine tin hexacyano ferrate - - - - 150

2 Ammonium dodeca

Molybdoantimonate C (NH4)3(Mo12 SbO40).11H2O - - 151

3 Ammonium

molybdophosphate C (NH4)3PMo12O40 1.57 - 152

4 Ammonium

tungstophosphate C (NH4)3PW12O40 0.66 - 153

5 Anilinium zirconium

phosphate - (ZrO2)2(C6H5NH2)2.HPO4.3.7H2O 1.87

Co2+

,Zn2+

,

Cd2+

,Hg2+

154

6 Anilinium tin phosphate - - - - 155

7 Chromium arsenophosphate A Cr:As:P=2:1:1 [Cr2O3.H3AsO4.H3PO4].nH2O - K+ 156

8 Cesium zirconium phosphate - - - - 157

9 Chromium arsenosilicate A 2 Cr2O3.2.5 As2O5. 3SiO2.nH2O - K+ 158

10 Cerium phosphosilicate A Ce:Si:P=2:5:4 (CeO2)2 (SiO2)3 (H3PO4)4.nH2O - - 159

11 Dipotassium tri-zinc

hexa cyano ferrate - - - - 160

19

12 Nickel aluminosilicate A - - - 161

13 Stannic arsenoborate A - 0.99 - 162

14 Stannic arsenosilicate - - - - 163

15 Stannic boratomolybdate A Sn:B:Mo=1:1:1 - 1.12 Zr4+

, Th4+

162

16 Stannic boratophosphate A - 1.10 - 164

17 Stannic boratosulphate A - 0.55 - 162

18 Stannic boratotungstate A - 1.15 - 162

19 Stannic iodophosphate - - - - 165

20 Stannic molybdophosphate - Sn:Mo:P=1:0.33:2 - - - 166

21 Tin(IV) arsenosilicate - - - Amino acid 167

22 Tin(IV) vanadopyrophsosphate M-C - 3.17 - 168

23 Tin(IV) tungstovanado

Phosphate - - - - 169

24 Tin(IV) tungstoselenate C Sn:Se:W=7:1:18 - 1.43 Ba2+

170

25 Titanium tungstophosphate - - - - 171

20

26 Titanium phosphate

ammonium tungstophosphate - - - - 172

27 Titanium tungstoarsenate - - - - 173

28 Titanium arsenosilicate - - - Pb2+

174

29 Titanium vanadophosphate - - - - 175

30 Titanium tungstovanadophosphate - - - Amines 176

31 Titanium phosphosilicate A - - Zr4+

, Nb5+

, Cs+ 177

32 Titanium aluminium silicate - - - Pb2+

178

33 Titanium molydophosphate - - - - 179

34 Titanium phosphate ammonium

phosphomolybdate - - - - 180

35 Titanium(IV) tungstosilicate C - 0.44 - 181

36 Zirconium hydrogen arsenate

hydrogen phosphate A Zr(HAsO4)(HPO4).H2O - - 182

37 Zirconium iodooxalate A Zr:IO3:C2O4H=2:1:3 (ZrO)2(IO3)(HC2O4)3.nH2O - - 183

38 Zirconium alumina

pyrophosphate - - - - 184

21

39 Zirconium arsenophosphate A Zr:As:P=2:1:1 (ZrO2)(H3AsO4)(H3PO4).nH2O - Rb+, Ag

+, Tl

+ 185,186

40 Zirconium arsenosilicate C - - Hg2+

187

41 Zirconiumphosphoantimonate - - - - 188

42 Zirconium phosphoborate - Zr:P:B=1:1:1 - - - 189

43 Zirconium pthalophosphate - - - - 190

44 Zirconium vanadophosphate - - - Li+, Na

+, NH4

+ 132

45 Zirconium sulphosalicylate S-C - - - 191,192

46 Zirconium phosphosilicate A - 2.2 Cs+ 193,194

47 Zirconium molybdophosphate - ZrH2MoO2.nH2O 1.6 - 195

48 Zirconium(IV) selenophosphate - (ZrO)5(OH)4(HSeO3)2(H2PO4).2H2O - - 196

49 Zirconium(IV) iodomolybdate - - - Hg2+

197

50 Zirconium(IV) iodophosphate - - 1.78 - 198

51 Zirconium titanium phosphate C Zr:Ti=3.25 ZrxTi1-x (HPO4)2.H2O 6.87 - 199-204

52 Zirconium molybdovanadate - Zr:V:Mo=1.68:1:0.088 - Li+, Na

+ 205

22

53 Zirconium tungstoarsenate A - - UO22+

, Cs+,Tl

+ 206

54 Zirconium(IV)tungstophosphate - Zr:W:P=18.8:25.4:4.3 1.00 Pb2+

207,208

55 Zirconium ceriumphosphate - - - - 209

56 Zirconium(IV) 4-amino 3-

hydroxy naphthalene sulphonate - - - Hg

2+ 210

57 Zirconium bis

(monooctyl)phosphate C - - - 211

58 Zirconium(IV) iodovanadate A Zr:IO3:VO3=2:1:3 (ZrO2)(IO3)(V3O9) 4.20 Electron

exchanger 212

59 Zirconium(IV) tunsgto-

molybdate A (ZrO)(OH)2(H2WO4)4(H2MoO4)3·8H2O 2.40 - 213

60 Acrylamide zirconium phosphate C - 2.26 - 214

A=Amorphous,C=Crystalline,S-C=Semi-crystalline,M-C=Micro-crystalline

23

Inorganic ion-exchangers have their own limitations. For instance, these materials

in general are reported to be not very much reproducible in behaviour and fabrication of

the inorganic adsorbents into rigid beads type media are not suitable for column

operation. Further they have generally less mechanical and chemical strength than the

organic counter part because of their inorganic nature. These drawbacks of organic resin

and inorganic adsorbents have compelled researchers to introduce new class of ion-

exchangers i.e. organic-inorganic hybrid ion-exchangers. These hybrid ion-exchangers

formed by the combination of inorganic materials and organic polymer are attractive for

the purpose of creating high performance or high functional polymeric materials. They

have been found useful in preparation of ion-selective electrodes and as packing materials

in chromatography. The transformation of inorganic ion-exchangers into composite ion-

exchange materials is the latest development in this discipline. These composite materials

have found numerous applications in the area of chemistry, biochemistry, engineering and

materials science [215]. The organic-inorganic hybrid materials prepared via the sol-gel

technique have attracted significant attention in the literature [216]. These hybrid

materials show the improvement in the granulometric properties that makes more suitable

for application in the column operation. The column operation suitability makes it more

convenient in regeneration of exhausted beds also. The binding of organic polymers

(polyaniline, polythiophene, polypyrrole, polyacrylonitrile, polymethylmethacrylate,

polyacrylicacid etc.) introduce better mechanical properties in the composite ion-

exchange materials. These sol-gel materials are also used in general areas e.g. chemical

sensors, chromatography and fabrication of selective material and in electrical and optical

applications. Some organic-inorganic composite ion-exchange materials have been

recently developed. Polyaniline Zr(IV)tungstophosphate has been synthesised by Gupta et

al. [217] for the selective separation of La3+

and UO22+

. Chand et al. reported polyacrylic

acid coated SiO2 as a new ion-exchange material. Beena Pandit et al. [218] have

synthesised such type of ion-exchange materials, i.e. o-chlorophenol Zr(IV)tungstate and

p-chlorophenol Zr(IV)tungstate. Khan et al. have reported polyaniline

Sn(IV)arsenophosphate [219] and polystyrene Zr(IV)tungstophosphate [220] used for the

selective separation of Pb2+

, Cd2+

and Hg2+

respectively, the ion-exchange kinetics of

M2+

-H+ exchange and adsorption of pesticide [221] have also been carried out on these

materials. These materials can be used as ion-exchange membrane and ion selective

electrodes. Styrene supported Zr(IV)phosphate hybrid material [222] and fibrous ion-

exchange materials such as polymethylmethacrylate, polyacrylonitrile, styrene and pectin

24

based Ce(IV)phosphate, Th(IV)phosphate and Zr(IV)phosphate [223] have been reported

by Varshney et al. have numerous analytical applications. These hybrid ion exchangers

have good ion exchange capacity, higher stability, reproducibility and selectivity for

specific heavy metal ions indicate its useful environmental applications.

The real utility of composite ion-exchangers depends largely on its ion-exchange

characteristics namely ion-exchange capacity, nature of ionogenic groups, elution

behaviour, chemical stability, distribution coefficients and on structural studies such as

FTIR, X-ray, TGA-DTA, SEM, TEM and analytical applications.

Ion-exchange capacity:

The capacity of an ion-exchanger describes the quantity of uptake of

exchangeable ions under the specific conditions. The theoretical capacity of ion

exchanger is often higher than the apparent capacity which strongly depends on solution

concentration and pH. In addition the framework of the exchanger may create

circumstances in which the access of larger ions and hydrated cations is prevented and

therefore the experimentally obtained maximum uptake may not represent theoretical

capacity. Generally the ion exchange capacity is determined by non-equilibrium process

i.e. using column.

pH titrations:

To determine the nature of the ionogenic group of the ion exchanger, pH titrations

were performed. It also helps in determining the number of replaceable H+ ions per

molecule of material. In this way it helps in establishing whether the exchanger is

monofunctional, bifunctional or polyfunctional.

Elution behaviour:

The elution of H+ ions from the column depends on the concentration of eluent.

The optimum concentration of eluent necessary for maximum elution of H+ ions depends

on the nature of ionogenic group present in the exchanger, which in turn depends upon

the pKa values of the acids used in its preparation.

25

Distribution coefficients:

It is the measure of the functional uptake of metal ions competing for H+ ions

from a solution by ion-exchange material. It is defined as follows:

solution of mL / ions metal of equivalent milli

exchanger-ion of g / ions metal of equivalent millidK mL g

-1

M

V

F

F-I

dK mL g

-1

where I is the initial amount of the metal ion in the solution phase, F is final amount of

metal ion in the solution phase after treatment with the exchanger, V is the volume of the

solution (mL) and M is the amount of ion exchanger taken (g). The sorption of metal ions

involves the ion-exchange of the H+ ions in exchanger phase with that of metal ions in

solution phase as given below-

2R-H+

+ M2+

R2-M2+

+ 2 H+

Exchanger phase Solution phase Exchanger phase Solution phase

Chemical stability:

Chemical stability of synthetic ion-exchanger plays an important role in their

analytical applications. It establishes whether the material can sustain in particular solvent

or not during operation.

Structural studies:

With the development of modern analytical instruments it becomes easy to

understand the chemistry of ion-exchange materials. FTIR (Fourier Transform Infrared

Spectroscopy) is a molecular characterization technique that provides information about

the chemical makeup of materials. This technique provides a rapid means of identifying

substances. X-ray analysis determines the crystal structure and lattice spacing. The

thermogravimetric and differential thermal analyses are important techniques that

record the changes in the chemical composition of the material at different temperatures.

SEM (Scanning Electron Microscopy) has emerged as a powerful tool as it gives

topographic images and helps in microstructure analysis. TEM (Transmission Electron

26

Microscopy) forms a major analysis method in a range of scientific fields. This analysis

was carried out to know the particle size of composite ion exchange material.

Composite ion-exchange materials have applications in the following disciplines.

(1) Electro dialysis [224]

(2) Hydrometallurgy [225]

(3) Catalysis [226]

(4) Redox system [227]

(5) Effluent treatment [228]

(6) Water softening [229, 230]

(7) Separation and preconcentration of metal ions [231]

(8) Nuclear separation [232]

(9) Conducting polymer [233]

(10) Ion-exchange fibre [234]

(11) Ion selective electrode [235]

This thesis comprises of five chapters including general (chapter 1) introduction

which presents a critical review of the existing literature pertaining to inorganic and

composite ion exchangers. Chapters 2 to 5 deal with the synthesis, characterization and

analytical applications of composite cation exchange material for the separation of toxic

metal ions which are potential pollutants in the environment. Composite materials exhibit

properties entirely different from parent components. These materials possess good ion-

exchange capacity, high thermal, chemical stability along with reproducibility and also

found to be selective for heavy toxic metal ions. These materials have been characterized

by using various analytical techniques namely FTIR, TGA-DTA, XRD, SEM, TEM and

elemental analysis. The analytical applications of the composite materials have been

explored by achieving some analytically important separations of metal ions. The

specificity of these materials for Pb2+

and Hg2+

make them useful for the removal of these

toxic metals from industrial effluents.

27

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