Removal of lead and zinc ions from aqueous solution

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The study showed that at at low metal concentrations the zeolite samples .... Figures 3a and 3b show the changes in the pH values and removal efficiencies with.

161

Int. J. Environmerıt and Pollution, Vol.19, No. 2, 2003

Removal of lead and zinc ions from aqueous solution using Amasya zeolites from Turkey Nevzat Beyazit* and İbrahim Peker Department of Environmental Engineering, Faculty of Engineering. Cumhuriyet University, 58140 Sivas, Turkey

Osman Nuri Ergun Department of Environmental Engineering, Faculty of Engineering, Ondokuzmayıs University, Samsun. Turkey Abstract: This paper deals with the removal of Pb2* and Zn2+ ions from aqueous solutions using zeolitic minerals containing 45 wt.% clinoptilolite and 35 wt.% mordenite. The effects of partide size, zeolite/solution ratio, stirring time, and metal ion concentration on Pb2+ and Zn2+ removal were examined. The study showed that at at low metal concentrations the zeolite samples exhibited optimum efficiency at metal concentration around 22 mg/1 for both Pb2+ and Zn2+, and Pb2+ ions were much more preferred by zeolites. More than 98% of the removal was achieved in the first five minutes for Pb2+, whereas the Zn2+ removal efficiency was around 90% for the same time. Pb2r and Zn2+ adsorption capacities related to Langmuir isothenns were found to be 34.48 and 19.49 mg/g, respectively. In summary, it can be concluded that metal ions such as Pb2+ and Zn2+ can be removed with approximately 100% efficiency from aqueous solutions and wastcwater containing similar ions using Amasya zeolites. Keywords: Amasya, clinoptilolite, mordenite, Pb2+, removal, zeohte, Zn2+. Reference to this paper should be made as follows: Beyazit, N., Peker, î. and Ergun, O.N. (2003) ‘Removal of lead and zinc ions from aqueous solution using Amasya zeolites from Turkey’, Int. J. Environmerıt and Pollution, Vol. 19, No. 2, pp. 160-170.

1

Introduction

Heavy metals are very toxic elements and their discharge into receiving waters has detrimental effects on human health and the environment (Maliou et al., 1992). The removal of heavy metal cations from aqueous solutions and wastewaters can be achieved by several processes, such as chemical preparation, adsorption on activated carbon, solvent extraction, ultrafiltration, or ion-exchange by synthetic or natural materials. Of

* Corresponding author: e-mail: [email protected] cumhuriyet.edu.tr. Copyright © 2003 Inderscience Enterprises Ltd.

Removal o f lead and zinc ionsfrom aqueous solution using Amasya zeolitiesl62 these methods, ion-exchange is considered attractive because of the relative simplicity of application (Blanchard et al., 1984). Zeolites are the fırst known natural material which can be used as an ion exchanger (Ames, 1960; Blanchard et al., 1984; Inglezakis et al., 2001; Kesraoui-Ouki and Kavannagh, 1997; Maliou et al., 1992; Semmens and Martin, 1988). Many industries, such as metal fınishing, mining and mineral Processing, coal mining and oil refining, have problems associated with heavy metal contamination of process waters and run-off waters. For instance, new approaches and technologies must be developed to assist in the removal of metal ions from process vvaters and wastewaters. In such cases a selective cation exchanger, such as natural zeolites, may provide an economical means of removing mixed heavy metal from effluents (Kesraoui-Ouki and Kavannagh, 1997). This paper presents a comprehensive section of the paper by Beyazıt (2001) related to the removal of Pb2+ and Zn2+ ions from aqueous solutions using natural zeolites collected from the Amasya-Doğantepe region in Turkey.

2

Material and methods

2.1 Sample collection and preparation The samples containing zeolitic tuffs were collected from the Amasya region in Turkey. According to Yalçın (1997), this basin contains approximately 1.5 million tonnes of zeolitic minerals. The samples were broken and sieved into the following mesh partide sizes: -10+18, -18+20, -20+30, -30+35, -35+40 and -40+50.* They were washed with distilled water to remove very fine particles from their surfaces. A complete chemical analysis of the zeolites is given in Table 1. Prior to the experiments, the washed zeolite samples were dried at 105°C for two hours and stored until required for use. According to X-ray diffraction analysis results, the zeolitic tuffs consisted of 45 wt.% clinoptilolite, 35 wt.% mordenite and 20 wt.% quartz plus feldspar (Beyazıt, 2001).

2.2 Reagents For ali experimental studies, stock lead and zinc solutions were prepared with their nitrate and chloride salts, Pb(N03)2 and CuCl2, respectivelv, in distilled water. The bufifer solutions for pH calibration were prepared wıth KH2P 04, KHCjIijO* and Na2HP04, respectively. The glassware was washed with concentrated 1:1 nitric acid (HN03) before and after use in the experiments.

* These values are the sizes of the zeolite samples used in this study (for example, -10+18 mesh means that it is betvveen 2 and 1 mm. Similarly: -18+20 = 1-0.84 mm; -20+30 = 0.84-0.59; -30+35 = 0.59-0,50; -35+40 = 0.50-0.42; -40+50 = 0.42-0.30.

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Table 1

Chemical composition of zeolite samples (Beyazıt, 2001).

Oxides

% weight

Elements

ppm

Si02 Ti02 Al203 U 'e20 3a MnO MgO CaO Na20 k 2o P2O5 LOIb

70.27 0.19 12.90 1.38 0.02 1.71 2.05 3.21 1.49 0.04 6.57

Total

99.43

Cr Ni Co Cu Pb Zn Rb Ba Sr Ga Nb Zr Y Th

8 1 4 13 26 54 106 137 1470 15 7 182 16 25

a Total Fe, bLoss on ignition at 1000°C.

2.3 Analytical methods Ali solutions, standards and dilutions were made using distilled water. The initial and final metal concentrations were analysed using an atomic absorption spectrofotometer (Perkin-Elmer 2380). The pH values were measured with a digital pH meter (Jenway 3010). Ali solutions containing metal ions were acidified to pH 2 by the addition of 0.1 M of HN03 before analysis using atomic absoıption spectrometry.

2.4 Lead and zinc removal studies Zeolites were used in their natural form during the removal studies. The contact of zeolite samples with solutions containing metal ions was provided by mixing in a mechanical six-pedal stirrer at 200 rotations per minute. A known weight of sample was stirred with 100 mİ of lead and zinc solutions in beakers. These studies were carried out at four different stages. In the first stage, the effect of partide size ranging from -10+18 to -40+50 mesh on removal was investigated. The other experimental conditions were selected to be 15 minutes for the stirring time and 30 g/l for the zeolite/solution ratio. In the second stage, the zeolite/solution ratio, which provided the maximum removal efficiency for a constant zeolite partide size, was determined. In the third stage, the optimum stirring time was determined for the same purpose. Finally, the changes in removal effidendes at different initial metal concentrations were investigated. Ali the data obtained for Pb2+ and Zn2+ were evaluated by comparison of the amount removed from the solutions and these data were plotted on the same graphs to enable a comparison of their efficiencies. Experimental conditions are listed under each figüre. The adsorbed metal concentrations were calculated from the difference between the total initial metal concentration and the final metal concentration.

Removal o f lead and zinc ions from agueous solution using Amasya zeolities\6A

3

Results and discussion

3.1 Effect o f partide size on Pb2+and Zn2+ removal The final pH values and removal efficiencies obtained for various partide sizes are indicated in Figures la and lb, respectively. As seen in these figures, the removal efficiencies increased with decreasing partide size. The increase in percentage of metal ions removed is due to the availability of a greater surface/volume ratio for smaller particles. The pH values increased when the efficiencies increased, which is due to the hydrolysis of zeolitic minerals. The graph clearly shows that Pb2+ is much more preferred by zeolites than Zn2+. This is in agreement with the previously reported results of Semmens and Martin (1988) and Maliou et al. (1992). In other words, partide size has a significant impact on Zn2+ removal since Zn2+ ions were less preferred.

Förticte Size (rTEsh)

Partide Size (mesh)

Figüre 1 Effect of partide size on Pb2+ and Zn2+removal: the variation of pH values versus partide size (top); and the variation of removal efficiencies versus partide size (bottom).

For Fb2+ and Zn2+ removal, the optimum partide size was -18+20 and -40+50 mesh, respectively. The observed differences between Pb2+ and Zn2+ removal might be the result of various factors. such as hydration energies and ionic radius, which influence the selectivity of zeolite for metal ions. The hydration energies for Pb2+ and Zn2+ ions

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are -357.8 and -484.6 kcal/g ion, respectively (Semmens and Martin, 1988). Thtıs, Pb2+ ions with the largest hydration energy prefers the zeolite phase, and Zn2+ with the lowest hydration energv prefers the solution phase where it may satisfy its hydration requirements. The other factor that prevents a material being adsorbed by a zeolite is the size of the ions. If the ion size is greater than that of the pore, the species will be excluded. The hydrated radii of Zn2+ and Pb2+ ions are 4.3 and 4.01Â, respectively (Senunens and Seyfarth, 1978). Therefore, except for initial concentrations, for same experimental conditions, different removal efficiencies for Pb2+ and Zn2+ were obtained. The removal efficiencies for different partide sizes were found to be 85.62, 99.69, 99.51, 99.69, 99.51, 99.69, 99.75, 99.88% for Pb2+ and 51.45, 71.91, 71.98, 78.93, 85.88, 89.29% for Zn2+. These lead -10+18, -18+20, -20+30, -30+35, -35+40 and 40+50 sizes, respectively for both Pb and Zn. The initial pH values of Pb2+ and Zn2\ which were 4.70 and 5.60 respectively, ranged from 6.44-7.30 and 5.90-6.88, respectively.

3.2 Effect o f zeolite/solution ratio on Pb2+ and Zn2+removal As can be seen in Figüre 2a, the pH values increased during the removal studies. Pb2+ removal efficiencies were approximately 100% for ali zeolite/solution ratios and Zn2+ removal efficiencies ranged from 70-99%. In other words, the differences bet\veen removal efficiencies for Pb2+ and Zn2+ at different zeolite/solution ratios between 5-50 g/l were 1.36 and 29.41%, respectively. Figüre 2b shovvs the change of zeolite/solution ratios versus removal efficiencies for both Pb2‘ and Zn2+. The zeolite/solution ratio has a significant impact on metal removal by zeolites, since this ratio increases with the surface area/volume ratio of the particles, which provides much more contact betvveen the ions and zeolites. During the removal studies, the pH values for Pb2+ and Zn2+ solutions increased from 4.70 and 5.60 to 6.44-7.30 and 5.90-6.88, respectively. According to these graphs, the zeolite/solution ratio has no significant effect on the removal of Pb2+ under conditions selected for this stage. The removal efficiencies for 5 and 10 g/l zeolite/solution ratios vvere 66 and 89%, and the efficiencies for 15-50 g/l zeolite/solution ratios ranged between 96 and 99%. In addition to these results, 15 g/l of the ratio seems to be an optimum value to provide enough removal for 100 mİ of the solutions.

3.3. Effect o f stirring time on Pb2+and Zn2+removal Figures 3a and 3b show the changes in the pH values and removal efficiencies with regards to stirring time. According to these graphs, the time required to reach equilibrium for Zn2+ was determined to be 240 minutes, however, more than 90% of the removal was achieved in the first 5 minutes, whereas Pb2+ removal efficiencies were approximately 99-100% in most cases. When the stirring time for Zn2+ increased from 5 to 10 minutes, the removal efficiency increased from 90 to 94%. In other words, only 4% increase was observed. In addition to this, when the stirring time was increased from 15 to 60 minutes, the increase in removal efficiencies was only 3%. The pH values (5.28 for Pb2+ and 6.14 for Zn2+) ranged between 6.42-6.66 and 6.40-6.66, respectively.

Removal o f lead and zinc ionsfrom aqueous solution using Amasya zeolitiesl66

Zeolite/Solution Ratio (g/L)

Zeolite/Solution Ratio (g/L)

Figüre 2 Effect of the zeolite/solution ratio: the variation of pH values versus zeolite/solution ratio (top); and the variation of removal efficiencies versus zeolite/solution ratio (bottom).

3.4

Effect o f initial concentration on Pb2+ and Zn2' removal

At this stage, 14 different concentrations of metal solutions were tried and the changes in pH values and removal efficiencies are presented in Figures 4a and 4b. The graphs sho\v that high selectivities were obtained for Pb2, and slightly lower values for Zn2+. İn addition, even if the concentrations of metal solution were relatively high, Pb2+ ions could be effectively removed. For example, when the Pb2" concentration were at 284.54 mg/1, 85% of removal efficiency was achieved. Similarly, at 293 mg/1 of Zn2+, the achieved value was only 39%. Pb2+ ions were removed with highest efficiencies between 4.47-185 mg/1 concentrations, whereas for Zn2+ the values which obtained the highest efficiency was 5.63-78.59 mg/L.

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Stirring Time (min.)

Stirring Time (min.)

Figüre 3 Effect of stirring time: the variation of pH value versus stirring time (top); and the variation of removal efficiencies versus stirring time (bottom).

3.5 Adsorption isotherms The heavy metal removal from aqueous solution or wastewater using zeolilites is attributed to the mechanisms of both ion exchange and adsorption. The amount of an ion adsorbed and/or exchanged by these processes is calculated by adsorption isotherms. Within this context, to detennine the capacity of ion exchange and/or adsorption of zeolite samples for both Pb2+ and Zn2+, isotherms were generated using both Langmuir and Freundlich equations, with better correlation calculated for the Langmuir equation. Based on this equation, Langmuir constants related to adsorption capacity and energy of adsorption, which is expressed in terms of ‘a’ and b \ respectively, were calculated (Tchobanoglous and Burton, 1991). In this section of the study, ‘a’ and ‘b’ were calculated from the slope and intercept of the plots and were found to be 34.48 and 19.49 mg/g, respectively for Pb2+, and 0.043 and 0.013 1/mg for Zn2+, respectively. On the other hand, the adsorption capacities of zeolites for Pb2+ and Zn2+ ions were 34.48 and 19.49 mg/g, respectively. The isotherm data and constants are given in Table 2. The equilibrium constant related to the Langmuir isotherm is expressed in term of a dimensionless constant, RL (RL (Namasivayam and Yamuna, 1999) is defined as follovvs:

Removal o f lead and zinc ions from agueous solution using Amasya zeolities\6&

Pb initial pH Pb final pH Zn initial pH - a - Zn final pH

100 200 300 400 500 600 700 800 900 1000 1100 İnitial Concentration (mg/L)

İnitial Concentration (mg/L)

Figüre 4 Effect of initial concentration: the variation of pH value versus initial concentration (top); and the variation of removal efficiencies versus initial concentration (bottom).

=-

1

l+ * c

The Rh values obtained by using the above equation, together with the other constants are shown in Table 2. As can be seen in the table, ali RL values were between 0 and 1, indicating favourable adsorption for ali the initial concentrations of metal ions studied. In addition, Table 2 indicates that the adsorbed amount of metal ion increased with increasing amount of metal ion concentration while the percentage removal decreased. These increases were much more for Pb2+ than Zn2+. Langmuir plots for the adsorption of both Pb2+ and Zn2+ are shown in Figures 5 and 6, respectively.

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N. Beyazit, İ. Peker and O.N. Ergun

Table 2

isotherm data for lead and zinc adsorption.

Metal ion

C0 (mg/1)

Ce (mg/1)

xlm (mg/g)

CJ{x!m'f (g/L)



Pb2+

89.43 185.82 284.54 371.65 435.53 598.12 882.66

6.15 11.61 40.65 87.11 145.18 325.19 528.44

8.32 17.42 24.38 28.45 29.03 27.29 35.42

0.73 0.66 1.66 3.06 5.00 11.91 14.91

0.206 0.111 0.075 0.058 0.050 0.037 0.025

Zn2+

78.59 168.20 293.32 377.42 469.21 797.40 1012.78

7.41 74.59 177.43 213.32 342.04 820.48 820.48

7.11 9.36 11.58 16.41 12.71 19.23 19.23

1.04 7.97 16.58 12.99 26.91 42.66 42.66

0.536 0.350 0.236 0.194 0.162 0.082 0.082

a data taken from Tchobanoglous and Burton (1991).

"î,

O

100

200

400

300 Ce (mg/L)

Figüre 5 Langmuir plot for the adsorption of lead.

y = 0.0513x + 44434 R2= 0.9505

400

500

Ce (rT^L) Figüre 6 Langmuir plot for the adsorption of zinc.

500

600

Removal o f lead and zinc ionsfrom aqueous solution using Amasya zeolitiesllO

4

Conclusions

The study revealed that Ptr+ and Zn2+ ion removal efficiencies exceeding 98% could be achieved with zeolites taken from Amasya region in Turkey. and the selectivity sequence of these metal ions is as follows: Pb2+> Zn2+. The results also ındicated that the final pH values of metal ion solutions constantly increased during the removal studies whiclı were mainly due to the hydrolysis of zeolitic minerals. Based on this knovvledge, removal studies must be done at optimum pH values in which no precipitation of metal ions can be detected. According to the results of ali the experiments, the optimum values for Pb2+ and Zn2+, by which highest efficiencies were obtained, related to partide size, zeolite/solution ratio, stirring time and initial metal concentration were found to be as follows: -10+18 mesh, 5 g/l, 15 minutes, 22 mg/1 for Pb2+, and -40+50 mesh, 20 g/L 120 minutes, 21 mg/1 for Zn2+. After 120 minutes of stirring time, it was observed that desorption occured during Pb2+ removal studies since ion exchange is a process in which reversible reactions occur. Adsorption capacities of the zeolites used in this study, for Pb2+ and Zn2+ ions were found to be 34.48 and 19.49 mg/g respectively, and it was determined that the adsorption constants were convenient for favourable adsorption conditions (İ?L) related to the Langmuir adsorption equation.

5

Acknowledgements

The authors wish to thank to Cumhuriyet University Research Çenter, Sivas, Turkey.

References Ames, L.L. (1960) ‘The eation sieve properties of clinoptilolite’, The American Mineralogist, Vol. 45, pp. 689-700. APHA, AWWA (1995) Standard Methods fo r the Examination of Water and Wastewater, Fifth Edition, American Public Health Association/American Water Works Association, Washington DC, USA. Beyazıt, N. (2001) ‘Investigation of removal of heavy metal pollution in wastewaters with natural zeolite (clinoptilolite)’, PhD. thesis, Graduate School of Natural and Applied Sciences, Sivas, Turkey, 95 pp. Blanchard, G., Maunaye, M. and Martin, G. (1984) ‘Removal of heavy metals from waters by means of natural zeolites’, WaterSci. Tech., Vol. 18, pp. 1501-1507. Inglezakis, V.J., Papodeas, M.D. and Loizidou, M.D. (2001) ‘Effect of pretreatment on physical and ion exchaııge properties of natural clinoptilolite’, Environmental Technology, Vol. 22, pp. 75-82. Kesraoui-Ouki, S. and Kavannagh, M. (1997) ‘Performance of natural zeolites for the treatment of mixed metal-contaminated effluents’, Waste Management and Research, Vol. 15, pp. 383-394. Maliou, E., Malamis, M. and Sakellarides, P.O. (1992) ‘Lead and cadmium removal by ion exchange’, WaterSci. Tech., Vol. 25, pp. 133-138. Namasivayam, C. and Yamuna, RT. (1999) ‘Studies on chromium (IH) removal from aqueous solution by adsorption onto biogas residual slurry and its application to tannery wastewater treatment’, Water Air and Soil Pollution, Vol. 113, pp. 371-384.

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Semmens, M.J. and Seyfarth, M. (1978) ‘The selectivity of clinoptilolite for certain heavy metals’, Natural Zeolites, Occurrence, Properties, Use, Pergamon Press, 546 pp. Semmens, M.J. and Martin, W.P. (1988) ‘The influence of pretreatment on the capacity and selectivity of clinoptilolite for metal ions’, WaterRes. Tech., Vol. 2, pp. 537-542. Tehobanoglous, G. and Burton, F.L. (1991) Wastewater Engineering Treatment, Disposal and Reuse, Third Edition, Metcalf & Eddy, Inc., Vol. 2, 1334 pp. Yalçm, H. (1997) ‘EosenYaşlı denizaltı volkanizması ile ilişkili iç kuzey anadolu zeolit oluşumları’, Cumhuriyet Üniversitesi Mühendislik Fakültesi Dergisi, Seri A-Yerbilimleri, Vol. 14, pp. 43-56.

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