**2.1. Unheated batch method**

Ion-exchanged forms of Na-clinoptilolite from the Bigadiç area were produced via the batch method, using solutions of 0.1N, 0.5N and 1N – with salts of Na+, K+, Ca2+ , Cr3+, Ag+ and 100

ml of deionized water. Five grams of 300-mesh clinoptilolite were poured into each solution and stirred gently, and then put in suspension for 72 hours at room temperature. Subsequently, the clinoptilolite-solution suspension system was filtered. After filtration, the clinoptilolite was washed eight times with deionized water at 98°C and dried at 110°C for 16h. [9, 10]

**Figure 1.** Cation positions in clinoptilolite.[3]

### **2.2. Heated batch methods**

Ion exchange is conducted using a heated/cooled back magnetic stirrer system. A 100 ml solution was prepared by mixing 5 g of 300 mesh clinoptilolite with deionized water kept at 98°C for 2h.

The clinoptilolite-solution suspension system was then filtered. After filtration, the clinoptilolite was washed eight times with deionized water at 98°C and then dried at 110°C for 16 h. [11, 12]

### **2.3. Ion exchange**

316 Ion Exchange Technologies

for 16h. [9, 10]

**Figure 1.** Cation positions in clinoptilolite.[3]

**2.2. Heated batch methods** 

98°C for 2h.

ml of deionized water. Five grams of 300-mesh clinoptilolite were poured into each solution and stirred gently, and then put in suspension for 72 hours at room temperature. Subsequently, the clinoptilolite-solution suspension system was filtered. After filtration, the clinoptilolite was washed eight times with deionized water at 98°C and dried at 110°C

Ion exchange is conducted using a heated/cooled back magnetic stirrer system. A 100 ml solution was prepared by mixing 5 g of 300 mesh clinoptilolite with deionized water kept at The process of ion exchange occurs between the AZA cation in solution and BZB\* cation in the zeolite, and can be formulated as follows:

$$\mathbf{Z} \mathbf{B} \mathbf{A}^{\mathsf{Z}} \mathbf{A} + \mathbf{Z} \mathbf{A} \mathbf{B}^{\mathsf{Z}} \mathbf{B}^\* \leftrightarrow \mathbf{Z} \mathbf{B} \mathbf{A}^{\mathsf{Z}} \mathbf{A}^\* + \mathbf{Z} \mathbf{A} \mathbf{B}^{\mathsf{Z}} \mathbf{B}^\*$$

where ZA and ZB show the valences of the cations, and AZB\* and BZB\* show the cations in the zeolite structure.

Ion-exchange reactions are stoichiometric, graphical representations of equilibrium concentrations of exchangeable ions in both solutions; the structure of zeolite may be ascertained from ion-exchange isotherms.

Before an ion-exchange isotherm may be obtained, equilibrium of ion exchange must be reached. In zeolites A, X, and Y with low framework densities, the equilibrium of exchange between one valence ions (such as Na+ and K+) is obtained in approximately one week. In zeolite structures with high framework densities, the equilibrium of exchange among high valence ions is obtained in a few months.

After the time of equilibrium is defined, this procedure could be utilized in order to plot an isotherm. Zeolites react with a solution containing ions of both AZA and BZB. Although the relative amounts of ions AZA and BZB might vary, solutions must have a constant total normality (N). According to the condition of equinormality, total ionic intensities of any solution in the system of the zeolite/solution must be constant before and after ionexchange reactions.

The ionic intensity of any solution is

$$\mathbf{I} = (1/2)\boldsymbol{\Sigma}\boldsymbol{\Sigma}\boldsymbol{\Sigma}\boldsymbol{\Sigma}^2$$

where Ci are the concentrations of opposing ions in ion-grams per liter, and Zi are the valences of opposing ions.

Because of the distribution of AZA and BZB between the phases, the solution and solid phases in equilibrium must be analyzed. Thus, a plot of the equivalent fraction of ion in solution (As) versus equivalent fraction of the same ion in zeolite (AZ\* ) isotherm may be obtained.

The ion-exchange isotherm indicates the relative preferences of any ion within the zeolite structure. Besides, the separation factor of ion A within the zeolite structure is

$$\alpha = (\mathbf{A}z^\ast / \mathbf{B}z^\ast)(\mathbf{m}\_\mathbf{B}\mathbf{/}\mathbf{m}\_\mathbf{A})$$

where AZ\* ve BZ\* are equivalent fractions of ions A and B in zeolite, respectively, and mA and mB are the concentrations of ions in solutions in mole/liter. The total of the equivalent fractions of AZ\* and BZ\* must equal 1. On the basis of ion selectivity, if α >ZA/ZB , the zeolite prefers AZA ions; if α=ZA/ZB, the zeolite has no preference; and if α < ZA/ZB , the zeolite prefers BZB ions. [13, 14]

### **2.4. Ion-exchange rate**

XRF analyses were conducted on 0.1N-, 0.5N- and 1N-modified forms of solid-phase Naclinoptilolite, and especially the values of exchangeable and other cations differed greatly from values of the natural form (Table 1). The numbers of atoms in the unit cell were calculated with the knowledge that the unit cell includes 72 oxygen atoms. The numbers of atoms calculated and the following formula were used:

$$\chi\_{\text{form}} = \left[1 - (\text{A}\_{\text{form}} / \text{A}\_{\text{natural}})\right] \times 100 \text{ }$$

where Xform = the ion-exchange rate of the forms and the number of atoms in the unit cell of the same form, and Anatural = the number of atoms in the unit cell of the natural form.

### **2.5. Rate of ion selectivity**

The rate of ion selectivity, as termed by us, is different from the ''ion selectivity'' of the ionexchanged forms; this rate is calculated from the percentages of ions in the structure, and thus is similar to the rate of ion exchange. For Na+, K+, Ca2+ and Mg2+ (exchangeable cations) forms, this quantity may be calculated using

αform = [(Aform/Anatural) -1] x100

and for non-exchangeable cations such as Co3+, Cd +, Cr3+, Ag+ forms using

$$\alpha\_{\text{form}} = \text{A}\_{\text{form}} \times 100$$

where αform is the ion-selectivity rate of the ionic form, and Aform and Anatural are the numbers of atoms in the unit cells of the ion-exchanged form and the natural form, respectively.

## **3. Results and discussion**

### **3.1. Rate of ion exchange**

The results of chemical analyses and the numbers of atoms in the unit cells of natural and Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+ and Ag+ modified forms of clinoptilolite are given in Tables 1 and 2. As shown in the chemical formula of clinoptilolite, the numbers of atoms in the unit cell were calculated with the knowledge that the unit cell includes 72 oxygen atoms (Table 2).

Tables 3 and 4 were derived from data given in Table 2. Ion-exchange rates and the ordering of ion-exchange rate for unheated and heated methods applied to Na-clinoptilolite from Bigadiç-Balkesir (Turkey) are given in Tables 3 and 4.



fractions of AZ\* and BZ\*

prefers BZB ions. [13, 14]

**2.4. Ion-exchange rate** 

**2.5. Rate of ion selectivity** 

**3. Results and discussion** 

**3.1. Rate of ion exchange** 

(Table 2).

forms, this quantity may be calculated using

Bigadiç-Balkesir (Turkey) are given in Tables 3 and 4.

atoms calculated and the following formula were used:

must equal 1. On the basis of ion selectivity, if α >ZA/ZB , the zeolite

prefers AZA ions; if α=ZA/ZB, the zeolite has no preference; and if α < ZA/ZB , the zeolite

XRF analyses were conducted on 0.1N-, 0.5N- and 1N-modified forms of solid-phase Naclinoptilolite, and especially the values of exchangeable and other cations differed greatly from values of the natural form (Table 1). The numbers of atoms in the unit cell were calculated with the knowledge that the unit cell includes 72 oxygen atoms. The numbers of

Xform= [1 – (Aform/ Anatural)] x 100 where Xform = the ion-exchange rate of the forms and the number of atoms in the unit cell of

The rate of ion selectivity, as termed by us, is different from the ''ion selectivity'' of the ionexchanged forms; this rate is calculated from the percentages of ions in the structure, and thus is similar to the rate of ion exchange. For Na+, K+, Ca2+ and Mg2+ (exchangeable cations)

αform = [(Aform/Anatural) -1] x100

αform = Aformx100 where αform is the ion-selectivity rate of the ionic form, and Aform and Anatural are the numbers of atoms in the unit cells of the ion-exchanged form and the natural form, respectively.

The results of chemical analyses and the numbers of atoms in the unit cells of natural and Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+ and Ag+ modified forms of clinoptilolite are given in Tables 1 and 2. As shown in the chemical formula of clinoptilolite, the numbers of atoms in the unit cell were calculated with the knowledge that the unit cell includes 72 oxygen atoms

Tables 3 and 4 were derived from data given in Table 2. Ion-exchange rates and the ordering of ion-exchange rate for unheated and heated methods applied to Na-clinoptilolite from

and for non-exchangeable cations such as Co3+, Cd +, Cr3+, Ag+ forms using

the same form, and Anatural = the number of atoms in the unit cell of the natural form.


UHBM: unheated batch method; HBM: heated batch method

**Table 1.** Chemical analyses of natural and Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+, Ag+ modified forms of clinoptilolite.



Ion-Exchange Forms

UHBM: unheated batch method; HBM: heated batch method

Molecules

**Table 1.** Chemical analyses of natural and Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+, Ag+ modified forms of

Atoms

0.1N Na+ 23.98 4.84 0.23 1.02 0.64 0.98 0.55 - - - -- 28.00 4.95 0.5N Na+ 24.40 4.92 0.21 0.69 0.56 1.95 0.78 - - - -- 25.80 4.96 1N Na+ 24.80 4.99 0.22 0.59 0.51 1.93 1.16 - - - - 23.86 4.97

0.1N Na+ 23.82 4.79 0.22 1.18 0.82 0.86 0.64 - - - - 28.19 4.97 0.5N Na+ 24.54 4.91 0.23 1.16 0.78 0.81 0.70 - - - - 25.07 5.00 1N Na+ 24.33 4.88 0.24 0.73 0.60 0.74 2.18 - - - - 25.74 4.99

0.1N K+ 24.28 4.88 0.22 1.02 0.65 1.22 0.29 - - - - 26.71 4.98 0.5N K+ 24.00 4.83 0.19 0.61 0.51 2.64 0.07 - - - - 28.00 4.97 1N K+ 23.73 4.71 0.18 0.54 0.49 2.92 0.09 - - - - 24.53 5.04

0.1N K+ 24.15 4.85 0.22 1.34 0.65 0.78 0.31 - - - - 27.19 4.98 0.5N K+ 24.20 4.85 0.22 0.91 0.71 1.86 0.12 - - - - 26.75 4.99 1N K+ 24.54 4.94 0.17 0.22 0.30 3.96 0.08 - - - - 25.42 4.97

Natural 24.60 4.95 0.21 1.25 0.70 0.75 0.33 - - - - 25.15 4.97

Si Al Fe Ca Mg K Na Co Cd Cr Ag H Si/Al

 0.1N Cd2+ 69.21 11.90 0.83 2.87 2.06 1.78 0.19 - 0.61 - - 10.66 100.11 HBM 0.5N Cd2+ 67.65 11.51 0.65 2.85 1.33 1.91 0.20 - 2.30 - - 11.59 99.99 1N Cd2+ 64.45 10.92 0.52 2.33 1.11 2.08 0.18 - 5.61 - - 12.81 100.01 0.1N Cr3+ 68.39 11.65 0.88 3.28 1.27 1.65 0.56 - - 0.65 - 11.67 100.00 UHBM 0.5N Cr3+ 68.76 11.74 0.79 3.00 1.25 1.66 0.55 - - 0.98 - 11.26 99.99 1N Cr3+ 68.70 11.70 0.85 2.81 1.18 2.33 0.33 - - 0.87 - 11.23 100.00 0.1N Cr3+ 69.47 11.88 0.81 2.92 1.34 1.80 0.31 - - 0.66 - 10.81 100.00 HBM 0.5N Cr3+ 67.79 11.58 0.63 2.77 1.33 3.13 0.19 - - 1.76 - 10.83 100.01 1N Cr3+ 61.92 10.39 0.27 0.70 0.47 8.36 0.10 - - 5.64 - 12.15 100.00 0.1N Ag+ 69.44 11.86 0.74 2.62 1.20 2.82 0.32 - - - 0.22 10.79 100.01 UHBM 0.5N Ag+ 66.25 11.25 0.55 1.85 1.02 2.46 0.33 - - - 4.36 11.90 100.00 1N Ag+ 63.17 10.69 0.42 1.57 0.86 2.27 0.23 - - - 10.57 10.22 100.00 0.1N Ag+ 68.04 11.51 0.47 2.49 1.26 2.25 0.20 - - - 0.36 13.42 100.00 HBM 0.5N Ag+ 67.63 11.39 0.59 2.35 1.35 1.67 0.17 - - - 1.93 12.91 99.99 1N Ag+ 62.21 10.51 0.16 0.84 0.52 1.34 0.12 - - - 10.98 13.31 99.99

SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O Co2O3 CdO Cr2O3 Ag2O H2O Σ

Ion-Exchange Method

clinoptilolite.

Ion-Exchange Method

UHBM

HBM

UHBM

HBM

Ion-Exchange Forms

> **Table 2.** Numbers of atoms in the unit cells of natural and Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+, Ag+ modified forms of clinoptilolite.



Ion-Exchange Method

UHBM

HBM

UHBM

HBM

UHBM

HBM

UHBM

HBM

Ion-Exchange Forms

Ions Na+ K+ Ca2+ Mg2+ Fe3+

0.1N Na+ - - 18.40 8.57 - 0.5N Na+ - - 44.80 20.00 - 1N Na+ - - 52.80 27.14 -

0.1N Na+ - - 5.60 - - 0.5N Na+ - - 7.20 - - 1N Na+ - 1.33 41.60 14.29 -

0.1N K+ 12.12 - 18.40 7.14 - 0.5N K+ 78.79 - 51.20 27.14 9.52 1N K+ 72.72 - 56.80 30.00 14.29

0.1N K+ 6.06 - - 7.14 - 0.5N K+ 63.63 - 27.20 - - 1N K+ 75.76 - 82.40 57.14 19.05

0.1N Ca2+ - 2.67 - 2.67 - 0.5N Ca2+ 3.03 2.67 - 1.43 - 1N Ca2+ 66.67 - - - -

0.1N Ca2+ 54.55 - - 8.57 4.76 0.5N Ca2+ 63.64 - - - 9.52 1N Ca2+ 69.70 - - 7.14 4.76

0.1N Mg2+ - 4.00 4.80 - - 0.5N Mg2+ - 4.00 9.60 - - 1N Mg2+ - 6.67 12.80 - -

0.1N Mg2+ 57.58 - 8.00 - 4.76 0.5N Mg2+ 54.55 - 4.80 - - 1N Mg2+ 45.45 - 12.00 - 9.52 0.1N Co3+ 33.33 - 20.08 10.00 -

1N Co3+ 24.24 - 22.40 14.29 - 0.1N Co3+ 78.79 - 86.40 64.29 28.57

1N Co3+ 57.57 - 13.60 11.43 9.52 0.1N Cd2+ 18.18 - 20.80 10.00 4.76

1N Cd2+ 36.36 - 25.60 18.57 14.29 0.1N Cd2+ 60.61 - 12.80 - -

1N Cd2+ 60.61 - 28.00 14.29 33.33

UHBM 0.5N Co3+ 21.21 - 22.40 12.85 -

HBM 0.5N Co3+ 60.61 - 3.20 - 4.76

UHBM 0.5N Cd2+ 18.18 - 24.80 12.85 4.76

HBM 0.5N Cd2+ 57.58 - 12.80 - 14.29

**Table 3.** Ion-exchange rates for Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+, Ag+ modifiedforms compared to natural clinoptilolite.


**Table 4.** Ordering of ion-exchange rate for unheated and heated methods for Na-clinoptilolite from Bigadiç-Balkesir (Turkey)

The order of ion-exchange rate of Na+ and K+ forms is constant under both unheated and heated conditions. On the other hand, high ion-exchange rates occur under the effects of heating. The ion-exchange rate order of Ca2+, Mg2+, Co3+, Cd2+, Cr3+ and Ag+ forms changes upon heating, plus Fe3+ is leached from the structure. Although iron occurs as Fe3+ in the general order, Fe2+ was depleted instead of Fe3+ because Fe3+ cannot be depleted from the structure of clinoptilolite. Generally speaking, the ion-exchange process acts more on the surface of clinoptilolite than on its inner sites.[15]

Generally, the ion-exchange rate of the cations increases with increase in normality via application of both unheated and heated batch methods. Ion-exchange rates increase via the heating method compared to the unheated one. Forced-ion exchange occurs using the heated batch method as compared to natural ion exhange via the unheated method. The ion exchange of cations is controlled by cation valence, cation radius, ionization potential and the location of cations within pores.

The weak connection of the +1 valence of the Na+ cation to the structure of 10T is related to its low ionization potential, resulting in leaching -with a high ion-exchange rate- from its structure (Figure 1). The Mg2+ cation exhibits low depletion due to its having symmetrical binding to the structure of 8T, despite having the lowest ionization potential. Ca2+ is more depleted than Mg2+ because of the unsymmetrical binding of Ca2+ to the structure, although the ionization potential of Ca2+ is higher than that of Mg2+. The K+ cation is strongly bound between the 8T and 10T structures; therefore, it is only slightly depleted.


**Table 5.** Ionic radii and ionization potentials of exchangeable cations. [16]


surface of clinoptilolite than on its inner sites.[15]

the location of cations within pores.

The order of ion-exchange rate of Na+ and K+ forms is constant under both unheated and heated conditions. On the other hand, high ion-exchange rates occur under the effects of heating. The ion-exchange rate order of Ca2+, Mg2+, Co3+, Cd2+, Cr3+ and Ag+ forms changes upon heating, plus Fe3+ is leached from the structure. Although iron occurs as Fe3+ in the general order, Fe2+ was depleted instead of Fe3+ because Fe3+ cannot be depleted from the structure of clinoptilolite. Generally speaking, the ion-exchange process acts more on the

Generally, the ion-exchange rate of the cations increases with increase in normality via application of both unheated and heated batch methods. Ion-exchange rates increase via the heating method compared to the unheated one. Forced-ion exchange occurs using the heated batch method as compared to natural ion exhange via the unheated method. The ion exchange of cations is controlled by cation valence, cation radius, ionization potential and

The weak connection of the +1 valence of the Na+ cation to the structure of 10T is related to its low ionization potential, resulting in leaching -with a high ion-exchange rate- from its structure (Figure 1). The Mg2+ cation exhibits low depletion due to its having symmetrical binding to the structure of 8T, despite having the lowest ionization potential. Ca2+ is more depleted than Mg2+ because of the unsymmetrical binding of Ca2+ to the structure, although the ionization potential of Ca2+ is higher than that of Mg2+. The K+ cation is strongly bound

Exchangeable Cations Ionic Radii (Å) Ionization Potential (eV)

Na+ 0.99 5.13

K+ 1.37 4.34

Ca2+ 1.00 6.11 Mg2+ 0.57 7.64

Cr3+ 0.62 6.77 Ag+ 0.79 7.57

Co3+ 0.55 7.88 Cd2+ 0.78 8.99

Fe+2 0.63 7.90 Fe3+ 0.49 7.90

**Table 5.** Ionic radii and ionization potentials of exchangeable cations. [16]

between the 8T and 10T structures; therefore, it is only slightly depleted.


**Table 6.** The ion-selectivity rates of Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+ and Ag+ modified forms of clinoptilolite compared to natural clinoptilolite.

### **3.2. Rate of ion selectivity**

Table 6 shows the ion-selectivity rates of Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+ and Ag+ modified forms compared to natural clinoptilolite. Entrance of the cation into the structure depends on the ion-selectivity rate, that is, the ion-selectivity coefficient of cations. The rate of ion selectivity is controlled by cation valence, cation radius, ionization potential, pore size and location of the cation within the pore. Entrance of the cation into the structure increases with increasing normality and heating (Table 6). Monovalent cations such as K+, Na+ and Ag+ predominantly enter the structure of Na-clinoptilolite; these cations have relatively low ionization potentials. These cations are followed by other cations, such as Ca2+, Mg2+, Co3+, Cd2+ and Cr3+.


**Table 7.** Global experimental ion-selectivity order for modified clinoptilolite.

The ordering of ion-selectivity rates via application of unheated and heated methods is as follows:

Unheated: K+>Na+>Ag+>Co3+>Cd2+>Cr3+>Ca2+>Mg2+

Heated: Na+>K+> Co3+>Ag+> Cr3+>Cd2+> Mg2+>Ca2+

The ordering rate obtained via the unheated batch method is consistent with the results given in the global literature; conversely, this order changes upon heating via application of the heated batch method.

Moreover, the order of the ion-selectivity rates, namely

$$\mathrm{Na^{+} > Ag^{+} > K^{+} \approx NHl^{+} > Cd^{2+} > Ca^{2+} > Cr^{3+} > Mg^{+2} > Co^{3+}}$$

was also determined for the Gördes Na-clinoptilolite.[17, 18]. Other results are given in Table 7.

### **4. Conclusions**

326 Ion Exchange Technologies

Ion-Exchange Forms

clinoptilolite compared to natural clinoptilolite.

**3.2. Rate of ion selectivity** 

Cd2+ and Cr3+.

follows:

the heated batch method.

Ions

Na+ K+ Ca2+ Mg2+ Co3+ Cd2+ Cr3+ Ag+

 0.1N Cr3+ - - - - - - 18 - HBM 0.5N Cr3+ - - - - - - 50 - 1N Cr3+ - - - - - - 163 - 0.1N Ag+ - - - - - - - 4 UHBM 0.5N Ag+ - - - - - - - 83 1N Ag+ - - - - - - - 211 0.1N Ag+ - - - - - - - 7 HBM 0.5N Ag+ - - - - - - - 35 1N Ag+ - - - - - - - 213

**Table 6.** The ion-selectivity rates of Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+ and Ag+ modified forms of

Table 6 shows the ion-selectivity rates of Na+, K+, Ca2+, Mg2+, Co3+, Cd2+, Cr3+ and Ag+ modified forms compared to natural clinoptilolite. Entrance of the cation into the structure depends on the ion-selectivity rate, that is, the ion-selectivity coefficient of cations. The rate of ion selectivity is controlled by cation valence, cation radius, ionization potential, pore size and location of the cation within the pore. Entrance of the cation into the structure increases with increasing normality and heating (Table 6). Monovalent cations such as K+, Na+ and Ag+ predominantly enter the structure of Na-clinoptilolite; these cations have relatively low ionization potentials. These cations are followed by other cations, such as Ca2+, Mg2+, Co3+,

Selectivity Order References Pb2+>NH4+>Ba2+>Cu2+>Zn2+>Cd2+>Co2+ [19] Pb2+>Cd2+>Cs2+>Cu2+>Co2+>Cr3+>Zn2+>Ni2+>Hg2+ [20] Pb2+>Ag+>Cd2+>Zn2+>Cu2+>Na+ [21] Pb2+>Cu2+>Cd2+>Zn2+>Cr3+>Co2+>Ni2+ [22]

The ordering of ion-selectivity rates via application of unheated and heated methods is as

Unheated: K+>Na+>Ag+>Co3+>Cd2+>Cr3+>Ca2+>Mg2+

Heated: Na+>K+> Co3+>Ag+> Cr3+>Cd2+> Mg2+>Ca2+ The ordering rate obtained via the unheated batch method is consistent with the results given in the global literature; conversely, this order changes upon heating via application of

**Table 7.** Global experimental ion-selectivity order for modified clinoptilolite.

Ion-Exchange Method

