Ammon Sorp

731

Adsorption of Ammonium Ions onto a Natural Zeolite: TranscarpathianClinoptilolite

Mariya Lebedynets1,2, Myroslav Sprynskyy1,3, Iryna Sakhnyuk3, Radoslaw Zbytniewski1,Roman Golembiewski4 and Boguslaw Buszewski1* (1) Department of Environmental Chemistry andEcoanalytics, Faculty of Chemistry, Nicolaus Copernicus University, 7 Gagarina Str., 87-100 Torun, Poland. (2)Department of Ecological and Engineering Geology and Hydrogeology, Faculty of Geology, Ivan Franko Lviv NationalUniversity, 4 Grushevsky Str., 79005 Lviv, Ukraine. (3) Department of Oil and Gas Hydrogeology, Hydrogeochemistryand Hydrosphere Protection, Institute of Geology and Geochemistry of Combustible Minerals, Ukrainian NationalAcademy of Sciences, 3a Naukova Str., 79053 Lviv, Ukraine. (4) Department of Fundamentals of Chemistry, Faculty ofChemistry, Nicolaus Copernicus University, 7 Gagarina Str., 87-100 Torun, Poland.

(Received 16 January 2004; revised form accepted 31 May 2004)

ABSTRACT: A study was carried out of ammonium ion sorption from syntheticaqueous solutions by Transcarpathian clinoptilolite, a natural zeolite, understatic conditions. The main physical properties of the clinoptilolite and the basicparameters of its porous structure were determined. Values of the specific surfacearea and of the pore volume occupied by sorbed substances were calculated usingthe relative moisture content established and the maximum sorption capacityexhibited towards ammonium ions as well as a nitrogen adsorption/desorptionmethod. Ammonium ion sorption by the zeolite appeared to be complete within24 h for all fraction sizes, initial NH+4 ion concentration and adsorbate volumes.The amounts of NH+4 ions sorbed increased with increasing initial NH+4 concentrationand decreasing adsorbate volumes, with the maximum sorption capacity exhibitedby the clinoptilolite being 0.64 mequiv/g. The sorption effectiveness decreasedsomewhat with increasing fraction size. The Langmuir and Freundlich models wereapplied to the data obtained from the batch studies with the first model exhibitingthe more satisfactory correlation coefficient value (0.996 and 0.959, respectively).

INTRODUCTION

The pollution of surface and ground waters by mineral forms of nitrogen is quite common, withthe loss from irrigated cropland and untreated industrial, municipal and agricultural wastewaterstreams providing the sources of environmental pollution of an anthropogenic character. Elevatedlevels of nitric compounds in natural waters not only complicate the use of freshwater resources,but also have a negative influence on the ecological state of water and the surrounding objects.The most effective natural process for reducing the content of nitrate(V) ions in water, i.e. thestable form of nitrogen in surface and sub-surface waters under oxidation conditions, is dilutionwith fresh water. However, this process is often impossible in sub-surface aquifers due to rechargesources, filtration velocities and water volumes. Hence, the prevention of nitrogen pollution by theremoval of ions from wastewater is a necessary stage of a great importance.NH4

+

*Author to whom all correspondence should be addressed. E-mail: [email protected].

AST 22(9)_61 05/01/05 3:08 pm Page 731

732 M. Lebedynets et al./Adsorption Science & Technology Vol. 22 No. 9 2004

Among the technologies for ion control are processes such as air stripping, breakpointchlorination, nitrification/denitrification, adsorption by activated coal, chemical coagulation andion exchange (Tsitsishvili et al. 1985). The advantages of the latter process became more obviouswhen effective, low-cost materials were used as exchangers.

The natural zeolites are cheap materials which are readily available in large quantities in manyparts of the world. These have become especially important in the purification of water(Misaelides et al. 2003). Being a natural zeolite with a representative unit-cell formula of(Na3K3)(Al6Si30O72)24H2O, a void volume of 34%, channel dimensions of 3.9 5.4 and acation-exchange capacity of 2.16 mequiv/g, clinoptilolite seems to be the most attractive materialfor the removal of ions from drinking water and wastewater because of its ion selec-tivity and good performance towards ion sorption at low temperatures (Tsitsishvili et al.1985; Mumpton 1999). An additional advantage is the ability to use -saturated zeolite as anitrogen fertilizer without regeneration rather than the toxic admixtures normally present insewage. This reduces nitrogen loss from irrigated soils, decreases the number of nitrogen appli-cations to crops and prevents sub-surface water pollution (Tsitsishvili et al. 1985). Because of itspreference for large cations, including , clinoptilolite is used for the removal of ionsfrom municipal sewage effluent as well as in agricultural and aqua-cultural applications.

Large-scale cation-exchange processes using natural zeolites were first developed by Ames(1967) and Mercer et al. (1970) who demonstrated the effectiveness of clinoptilolite for extract-ing ions from municipal and agricultural waste streams (Mumpton 1999). Various aspects of

ion removal from aqueous solutions by clinoptilolite have been investigated by manyresearchers. Thus, the removal of ions from municipal wastewater was studied by Koon andKaufman (1975) and Ershov et al. (1985), while Polyakov et al. (1979) studied the same processfrom livestock farm wastewater. Gaspard et al. (1983) examined the ion removal character-istics from drinking water of clinoptilolite. Schoeman (1986) evaluated NNH+4 removal fromunderground mine water by South African clinoptilolite (Pratley) and compared it with Hectorclinoptilolite from the USA. Demir et al. (2002) studied the capacity of Bigadi clinoptilolite(Turkey) for removing ions from synthetic aqueous solutions under varying conditions.Murphy et al. (1978) investigated the ion-exchange ability of clinoptilolite tuffs from various USAdeposits towards to ions. Nikolina (1979) analyzed the cation-exchange capacity of clinop-tilolite derived from various deposits in the USSR (Dzegvi, Georgia; Transcarpathian deposits ofthe Ukraine; Noembryan, Armenia). From the results of these two studies, it was concluded that the cation-exchange capacity of clinoptilolite from different sources towards ion removalvaried by up to 1.7-times. In addition, Haralambous et al. (1992) compared the capacities of naturaland synthetic zeolites towards ion removal from aqueous solution.

Zeolites remove ions from aqueous solutions by exchange with cations or by adsorptionin the pores of aluminosilicate systems. Thus, ion exchange prevails when the ion concen-tration is equal to or lower than the concentration of exchangeable cations in the zeolite. Similarly,the adsorption process begins to predominate as the ion content of the system increases(Jorgensen et al. 1976). The cation-exchange capacity of clinoptilolite tends to increase with anincrease in the relative content of alkaline metal cations but is independent of the alkaline-earthcation content of the mineral (Nikolina 1979). Tsitsishvili et al. (1985) and Demir et al. (2002)established that the effectiveness towards ion removal increases as the zeolite particle sizedecreases.

The cation-exchange capacity depends on the presence of other cations in the aqueousphase and the initial ion concentration (Ames 1967; Polyakov et al. 1979; Gaspard et al.1983; Lin and Wu 1996; Singh and Prasan 1997; Kithome et al. 1998; Demir et al. 2002).

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+NH4

+

NH4+NH4

+

NH4+

NH4+

NH4+NH4

+

NH4+

AST 22(9)_61 05/01/05 3:08 pm Page 732

Adsorption of Ammonium Ions onto Natural Zeolite: Transcarpathian Clinoptilolite 733

Because of the high selectivity of zeolites towards the potassium ion, it is the main competitor inthe removal of ions from aqueous solutions by clinoptilolite (Polyakov et al. 1979; Mumpton1999). The amounts of ions sorbed by clinoptilolite increase as the initial concentrationof ions increases in the system, with ion adsorption and desorption by zeolites beingdiffusion-controlled (Kithome et al. 1998). Since ion exchange is an endothermic process, anincrease in temperature tends to increase the effectiveness of natural zeolites towards the removalof ions (Nikolina 1979; Lin and Wu 1996). The pH value is also an important factor in thecation-exchange purification of water, because only the ionized form of ammonium can beremoved by the cation-exchange process. Hence, for optimum operations, the pH of the aqueoussolution must be maintained at or below 7 (Tsitsishvili et al. 1985; Demir et al. 2002). Kithomeet al. (1998) established that the amount of ions sorbed by clinoptilolite increased as the pHwas increased from 4 to 7.

The cation-exchange capacity of clinoptilolite is influenced significantly by chemical and phys-ical pretreatment and the loading or regeneration of the zeolite (Murphy et al. 1978; Nikolina1979; Polyakov et al. 1979; Klieve and Semmens 1980; Tarasevich et al. 1985; Ershov et al. 1985;Demir et al. 2002). In addition, Eshov et al. (1985) have investigated the adsorption propertiesof Transcarpathian natural zeolites towards ammonium compounds in aqueous solutions andanalyzed the use of the Transcarpathian clinoptilolite for extracting cations from Kievsewage. The same zeolite sorbent from the Sokyrnytsya deposit has been used as a filter inthe purification unit of the water station system in the Polonne Khmelnitsky region (Tarasevichet al. 1985).

The purpose of the present work was to investigate the sorption characteristics of the naturalzeolite, Transcarpathian clinoptilolite, towards ions under static conditions. The main phys-ical properties of as-extracted clinoptilolite samples and their basic porous structure parameterswere determined. The equilibrium parameters for the sorption of ions from synthetic aqueoussolutions by Transcarpathian clinoptilolite have been established.

EXPERIMENTAL

Samples and chemicals

Clinoptilolite rock samples from the Sokyrnytsya deposit (Transcarpathian region, Ukraine) con-taining 7075% clinoptilolite were used in the study. Quartz, calcite, biotite, muscovite, chloriteand montmorillonite were found to be the main contaminants of such samples. The characteristicsof the zeolite adsorbent used are listed in Table 1. It will be noted that the exchange cations wereCa2+, Mg2+, Na+ and K+, with the latter being the most prevalent (Valter et al. 1975). The clinop-tilolite samples were ground in a metal mortar and divided by mechanical sieves into thefollowing size fractions: 0.10.16; 0.160.25; 0.250.315; 0.3150.5; 0.51.0; and 1.02.0 (mm).Each fraction was washed with distilled water to remove any turbidity. Then, one part of everyfraction was dried at room temperature (air-dried) while the other parts of two fractions (0.51.0and 0.160.315 mm) were dried at 110C for 2.5 h to remove any adsorbed water. Finally, theclinoptilolite samples were stored in a desiccator before use.

Ammonium chloride stock solution (1000 mg/l ) was prepared by dissolved NH4Cl (A.R.grade) in deionized water. Synthetic samples of aqueous solution were prepared by adding appro-priate amounts of NH4Cl stock solution to deionized water to obtain ion concentrations of 5, 10, 20, 40, 50, 100, 200 and 400 mg/l, respectively.

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+NH4

+NH4

+NH4

+

AST 22(9)_61 05/01/05 3:08 pm Page 733


Tests of physical properties

The relative moisture content of the clinoptilolite was determined by drying the rock samples at 110C to constant weight (as determined by thermometric methods). The specific gravity was determined by picnometric methods with a measurement error of 0.02 g/cm3. The volumedensity of the dried rock was analyzed by hydrostatic weighing after preliminary treatment with paraffin, the porosity being calculated from the determined values of the specific gravity andvolume density.

Sorption kinetics

Six replicate amounts of each size fraction of the air-dried clinoptilolite (0.5 g) were placed indi-vidually into 50 ml of a 10 mg/l NH4Cl contained in 330-ml volume glass tubes. Each tube wasshaken separately. Samples were then taken periodically (after 0.5, 1, 2, 4, 8, 16, 24 and 48 h),filtered and the ion concentration in the aqueous phase determined.

Batch experiments

The sorption of ions by a given clinoptilolite sample was studied using the batch equilibriummethod in four phases. In the first phase, six replicate amounts of each size fraction of the air-driedclinoptilolite (0.5 g) were shaken singly with 10, 25, 50 and 100 ml of NH4Cl solutions of 50, 20,10 and 5 mg/l concentration, respectively. After 24 h, the ion concentration in the aqueousphase was determined after filtration of each sample. In the second phase of the study, six repli-cate amounts of each size fraction of the air-dried clinoptilolite (0.5 g) were shaken singly with50 ml of 10, 20, 40, 100, 200, 400 and 1000 mg/l NH4Cl solutions with the ion concentra-tion in the aqueous phase being determined after 24 h following filtration of each sample. In thethird phase of the experiment, four replicate amounts of two fractions (0.51.0 and 0.160.315mm) of air-dried and 110C-dried samples of clinoptilolite (0.5 g) were shaken singly with 50 mlof 40 mg/l NH4Cl solution with the ion concentration in the aqueous phase being determinedafter 24 h following filtration of each sample.

Chemical analysis

The ion concentration in the aqueous phase was determined using the standard Nesslerreagent method employing a Perkin-Elmer 402 UV spectrophotometer. The sensitivity of the

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

TABLE 1. Characteristics of the TranscarpathianClinoptilolite Studied (Valter et al. 1975)

Property Value

Maximum SiO2 content 70%SiO2/Al2O3 ratio 10Thermal stability up to 650700CStatic water-storage capacity 9.03%Relative moisture content 10.19%Exchange cation content 53.5 mmol/100 g

AST 22(9)_61 05/01/05 3:08 pm Page 734

method was 0.1 g/ml, the measurement error ranged from 0.1 to 0.2 g/ml while the repro-ducibility error was 0.10.5 g/ml.

Evaluation of sorption parameters and modelling

The specific surface area of the clinoptilolite was calculated using the relative moisture content ofthe original rock sample as determined by thermometric methods, while the maximum sorptioncapacity towards ions was evaluated via the following expression (Dubinin 1985) assumingmonolayer adsorption:

(1)

where S is the specific surface area of the sorbent (m2/g); Am

is the monolayer capacity of thesorbed molecules expressed as mmol/(g sorbent); is the area occupied by one sorbed moleculeof water in the monolayer (m2); and N0 is Avogadros number.

The pore volume of sorbent occupied by water molecules at room temperature was also calcu-lated on the basis of the relative moisture of the sorbent as determined in this study by thermometricmethods via the expression:

(2)

where W is the pore volume occupied by water molecules at room temperature (cm3); W0 is thevolume of one water molecule (cm3) [W0 = 4/3r3, where r is the radius of a water molecule (cm)];N0 is Avogadros number; and M is the amount of water occupying the sorbent porous volume asdetermined by thermometric methods (mmol/g).

The pore volume of the sorbent occupied by ions was also calculated employing themaximum sorption capacity towards ions as determined in this study using equation(2), where W is the pore volume occupied by ions at the maximum sorption capacity (cm3);W0 is the volume of one ion (cm3) [W0 = 4/3r3, where r is the radius of the ion (cm)];N0 is Avogadros number; and M is the amount of ions occupying the porous volume of thesorbent at the maximum sorption capacity (mmol/g).

The equilibrium ion adsorption from aqueous solution was determined from the formula:

(3)

where q is the amount of ions sorbed at equilibrium [mg/(g sorbent)]; C0 is the initialconcentration of ions (mg/l); C

eis the equilibrium concentration of ions (mg/l); V is

the volume of solution from which adsorption occurs (l); and m is the adsorbent mass (g).The sorption effectiveness was calculated from the following formula:

(4)

where E is the sorption effectiveness (%); me

is the mass of ions sorbed at equilibrium (mg);and m0 is the initial mass of ions in the aqueous solution(mg).NH4+

NH4+

E m me= 100 0/

NH4+NH4

+NH4

+

q C C V me= ( )0 /NH4

+

NH4+

NH4+NH4

+NH4

+NH4

+NH4

+

W W N M= 0 0

S A Nm= 0

NH4+


AST 22(9)_61 05/01/05 3:08 pm Page 735


The adsorption of ions was evaluated by means of the first-order kinetic, Langmuir,Freundlich and linear models. The first-order kinetic model may be expressed by the followingequation:

(5)

where C is the ion concentration in the aqueous phase (mg/l) after time t (h); C0 is the ini-tial concentration of ions (m); and K1 is the velocity constant.

The Langmuir equation may be written as:

(6)

where KL (KL = aM) and a are the Langmuir model parameters while M is the adsorptionmaximum, all other symbols having been explained already.

The Freundlich equation may be written as:

(7)

where KF and n are empirical constants, with all other symbols having been explained already.The linear model may be considered as similar to the Freundlich equation with the parameter n

being set equal to unity:

(8)

where Kd is called the partition coefficient.The goodness-of-fit of the model to the experimental data was checked by comparison of the

correlation coefficient R2 and the standard error SE. The CurveExpert 1.37 freeware program wasused in all the calculations with the confidence level set at 95%.

RESULTS AND DISCUSSION

The following results were obtained on the basis of our measurements of the physical propertiesof the original sorbent: relative moisture content of clinoptilolite sample, 6.18%; specific gravity,2.38 g/cm3; volume density of dried rock, 1.68 g/cm3; and porosity, 29.4%.

The progress of the sorption process was followed until sorption equilibrium had been attained.Sorption of ions appeared to be complete on all six samples within 24 h. The correspondingkinetic data for air-dried clinoptilolite of fraction size 0.51.0 mm are depicted in Figure 1.

The results demonstrate that the first 50% of the ions were sorbed during the first 7 h, witha further ca. 40% being sorbed during the next 17 h and the extraction process being virtuallycomplete after 24 h. The difference between the rate of ion removal during the first 7 h andthat in the following period may be connected either with different mechanisms for the processover these stages (ion exchange and adsorption) or with the different localization of adsorptioncentres (on the surface or within the internal porous structure, respectively).

The direct dependence of sorption on the initial ion concentration in solution and the indi-rect dependence on the adsorbate volume may be explained by increasing diffusion control of

NH4+

NH4+

NH4+

NH4+

q K Cd e=

q K C nF en

= < 1

q K C aCL e e = +( )/ 1

NH4+

NH4+

C C K t= ( )0 1exp

NH4+

AST 22(9)_61 05/01/05 3:08 pm Page 736


adsorption with increasing concentration gradient. The corresponding data for air-dried clinop-tilolite of 0.51.0-mm fraction size are listed in Table 2.

The sorption ability of the air-dried clinoptilolite and of the sample dried at 110C towardsions decreased somewhat as the fraction size of the sorbent increased (Figure 2). The more

effective ion adsorption by the finest fraction of clinoptilolite may have been due toincreased accessibility of the internal pore structure in the smallest particles.

In contrast to the sorption capacity, the relative effectiveness of ion sorption by clinop-tilolite decreased with increasing initial ion concentration in the solution (Table 3). Themaximum sorption capacity of the air-dried clinoptilolite towards ions as evaluated at an ini-tial ion concentration of 1000 mg/l was 11.6 mg (0.64 mequiv) per gram of sorbent.

The data listed in Table 4 demonstrate the insignificant growth in ion sorption as thedrying temperature of the clinoptilolite was increased from 20C to 110C, probably as a result ofthe partial removal of water sorbed in the porous structure. Because of the different nature of thesorbed substances, the values for the specific surface area and the occupied porous volume of the sorbent calculated for water and ions varied over a wide range (Table 5).

The plots of the experimental data for the sorption of ions onto clinoptilolite of 0.160.315-mm fraction size using equations (5), (6) and (7), respectively, depicted in Figures 3 and 4

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

TABLE 2. Influence of Adsorbate Volume and Initial Ion Concentration on IonAdsorption onto Clinoptilolitea

Adsorbate Initial conc. of Sorption Amt. of ionsvolume (ml) NH+4 ions (mg/l) effectiveness (%) sorbed (mg/g)10 50 95.2 0.9525 20 88.1 0.8850 10 79.0 0.79

100 5 53.3 0.53aFraction size, 0.51.0 mm.

NH4+

NH4+NH4

+

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50 60Time (h)

Amt.

of N

H+4

ions

sor

bed

(mg/g

)

Figure 1. Sorption kinetics of NH+4 ions onto air-dried clinoptilolite (fraction size, 0.51.0 mm).

AST 22(9)_61 05/01/05 3:08 pm Page 737


0

2

4

6

8

0.10.16 0.160.315 0.3150.5 0.51.0 1.02.0

Fraction size (mm)

Amt.

of N

H 4+ io

ns s

orbe

d (m

g/g)

Figure 2. Effect of fraction size of clinoptilolite on its sorption capacity towards ions.NH 4+

TABLE 3. Influence of Initial Ion Concentration in the Aqueous Solution on theSorption Capacity of the Air-dried Clinoptilolitea

Initial ion Initial amt. of Sorption Amt. of ionsconc. (mg/l) ions in solution (mg) effectiveness (%) sorbed (mg/g)

10 0.5 89.9 0.920 1 88.2 1.840 2 84.6 3.4

100 5 68.9 6.8200 10 48.2 9.6400 20 28.0 11.2

1000 50 11.7 11.6aFraction size, 0.16 0.315 mm.

NH4+NH4

+NH4+

NH4+

TABLE 4. Influence of Thermal Treatment of Clinoptilolite onNH+4 Ion Sorption

Samples Sorption Amt. of ionseffectiveness (%) sorbed (mg/g)

Clinoptilolite dried at 20CFraction size, 0.160.315 mm 87.3 3.50Fraction size, 0.51.0 mm 83.4 3.34

Clinoptilolite dried at 110CFraction size, 0.160.315 mm 89.1 3.56Fraction size, 0.51.0 mm 85.8 3.44

NH4+

AST 22(9)_61 05/01/05 3:08 pm Page 738


TABLE 5. Values of the Structural Parameters of Air-dried Clinoptilolite asCalculated from the Adsorption of Water and Ions

Parameter Water adsorption NH+4 ion adsorption

Specific area (m2/g) 113.09 32.53Porous volume (cm3/g) 0.0227 0.0071

NH4+

0

2

4

6

8

10

0 10 20 30 40 50 60Time (h)

Conc

. of N

H+4

ions

in s

olut

ion

(mg/I

)

Figure 3. Sorption of ions with time as described by the first-order kinetic model: , experimental data;, first-order kinetic model.

NH 4+

0

2

4

6

8

10

12

14

0 200 400 600 800 1000

Amt.

of N

H+4

ions

sor

bed

from

sol

utio

n (m

g/g)

Equilibrium conc. of NH+4 ions in solution (mg/l)

Figure 4. Sorption isotherm for ions as described by the Langmuir and Freundlich models: , experimental data;, Langmuir model; , Freundlich model.

NH 4+

AST 22(9)_61 05/01/05 3:08 pm Page 739


indicate that the first-order kinetic, Langmuir and Freundlich models gave good fits to the data incontrast to the situation with the linear model. The values of the parameters KL, a, M, KF, n, Kdand K1 as well as the corresponding correlation coefficients (R2) and standard errors (SE) are pre-sented in Table 6 where they are compared with the data for the Langmuir and Freundlich modelparameters obtained for ion sorption onto Bigadi (Turkey) clinoptilolite obtained by Demiret al. (2002). The maximum adsorption value obtained for the Transcarpathian clinoptilolite wasca. twice as large as the corresponding value for the Bigadi clinoptilolite, as calculated from thebatch experimental results of Demir et al. (2002).

CONCLUSIONS

The time necessary to achieve adsorption equilibrium for ions from aqueous solution ontoTranscarpathian clinoptilolite was 24 h irrespective of the fraction size, initial ion concen-tration in the solution and the adsorbate volume. The first-order kinetic model provided a gooddescription of ion sorption by clinoptilolite. The amounts of ions sorbed increased withincreasing initial ion concentration and decreasing adsorbate volume, thereby demonstratingthe importance of diffusion in the adsorption process. The maximum sorption capacity of

NH4+

NH4+NH4

+

NH4+

NH4+

NH4+

TABLE 6. Model Parameters for the Sorption of Ions by Clinoptilolite

Models Transcarpathian Raw Bigadi clinoptilolite,clinoptilolite, Ukraine Turkey (Demir et al. 2002)

First-order kinetic

K1 0.109 R2 0.965 SE 0.804

LangmuirKL 0.636 0.440a 0.055 0.085M 11.652 R2 0.996 0.992SE 0.438

FreundlichKF 2.510 0.608n 0.245 0.537R2 0.959 0.956SE 1.457

LinearKd 0.017 R2 0.238 SE 4.880

NH4+

AST 22(9)_61 05/01/05 3:08 pm Page 740

Transcarpathian clinoptilolite for the removal of ions from aqueous solution attained at aninitial ion concentration of 1000 mg/l was 11.6 mg (0.64 mequiv) per gram of sorbent.

The effectiveness of ion sorption by the clinoptilolite samples decreased somewhat as thefraction size of the solid particles increased from 0.10.16 to 1.02.0 mm. The Langmuir andFreundlich adsorption models were applied to the data obtained from the batch studies. TheLangmuir isotherm which assumes the formation of an adsorption monolayer gave a more adequatevalue for the correlation coefficient compared to that for the Freundlich isotherm.

ACKNOWLEDGMENTS

One of us (M.L.) wishes to thank Kasa Mianowskiego (Warsaw, Poland) for a scholarship.

REFERENCES

Ames, Jr., L.L. (1967) Proc. 13th Pacific Northwest Industrial Waste Conf., Washington State Univ.,Pullman, WA, USA, p. 135.

Demir, A., Gnay, A. and Debik, E. (2002) Water S.A. 28, 329.Dubinin, M.M. (1985) Proc. Conf. Geology, Physical-Chemical Properties and Utilization of Natural

Zeolites, Tbilisi, p. 79. Ershov, A.Z., Jariomenko, L.V., Alekberova, V.V., Lebeda, L.V. and Bajrak, V.V. (1985) Proc. Conf. Geology,

Physical-Chemical Properties and Utilization of Natural Zeolites, Tbilisi, p. 339. Gaspard, M., Neveu, A. and Martin, G. (1983) Water Res. 17, 279.Haralambous, A., Maliou, E. and Malamis, M. (1992) Water Sci. Technol. 25, 139.Jorgensen, S.E., Libor, O., Lea Graber, K. and Barkacs, K. (1976) Water Res. 10, 213. Kithome, M., Paul, J.W., Lavkulich, L.M. and Boomke, A.A. (1998) Soil Sci. Soc. Am., J. 62, 622. Koon, J.H. and Kaufman, W.J. (1975) J. Water Pollut. Control Fed. 47, 448. Lin, S.H. and Wu, C.L. (1996) Ind. Eng. Chem., Res. 35, 553.Mercer, B.W., Ames, Jr., L.L., Trouhil, C.J., Van Slyke, W.J. and Dean, R.B. (1970) J. Water Pollut.

Control Fed. 42, 95.Misaelides, P., Zamboulis, D. and Stcker, M. (2003) Microporous Mesoporous Mater. 61, 1. Mumpton, F.A. (1999) Proc. Natl. Acad. Sci. USA 96, 3463.Murphy, C., Hrycyk, O. and Gleason, W. (1978) in Natural Zeolites. Occurrence, Properties, Use, Pergamon

Press, Oxford, p. 471.Nikolina, V.Ja. (1979) in Prirodnyje Tseolity, Mecniereba, Tbilisi, p. 190. Polyakov, V.Ye., Tarasevich, Yu.I., Medvyedyev, M.I., Rozenfeld, A.L. and Smirnov, O.P. (1979) Khim.

Technol. Vody 1, 19.Schoeman, J.J. (1986) Water S.A. 12, 73.Singh, G. and Prasan, B. (1997) Water Environ. Res. 69, 157.Tarasevich, Yu.I., Kravcheno, V.A., Rudenko, G.G. and Polykov, V.E. (1985) Proc. Conf. Geology, Physical-

Chemical Properties and Utilization of Natural Zeolites, Tbilisi, p. 349. Tsitsishvili, G.V., Andronikashvili, T.G., Kirov, G.N. and Filizova, L.D. (1985) Prirodnyje Tseolity,

Khimia, Moscow.Valter, A.A., Maslyakevych, Ya.V., Gamarnyk, Ye.A., Bobonych, F.M., Dyomenko, D.P. and Pysanskyj, A.I.

(1975) Geol. J. 35, 55.

NH4+

NH4+

NH4+


AST 22(9)_61 05/01/05 3:08 pm Page 741

Documents

Ammon Sorp