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Adsorption Kinetics and Isotherms for the Removal of Zinc Ions from Aqueous Solutions by an Ion-Exchange Resin.

Byline: BAYBARS ALI FIL, RECEP BONCUKCUOGLU, ALPER ERDEM YILMAZ AND SERKAN BAYAR

Summary: The capacity of ion exchange resins, Dowex HCR-S, for removal of Zinc from aqueous solution was investigated under different conditions such as initial solution pHs, stirring speeds, temperatures, initial concentrations and resin dosages. Adsorption equilibrium isotherms were analyzed by Langmuir, Freundlich, Temkin, Elovich, Khan, Sips, Toth, Radke-Praunstrzki, Koble-Corrigan, models. Khan model was found to show the best fit for experimental data. The experimental kinetic data were analyzed using the first-order, second-order, Elovich and intra-particle kinetic models and the second-order kinetic model described the ion exchange kinetics accurately for Zn (II) ions. Thermodynamic activation parameters such as [?]G , [?]S and [?]H were also calculated.

Keywords: Zinc, ion exchange, Dowex HCR-S, kinetics, isotherm.

Introduction

High concentrations of heavy metals in the environment are mostly due to uncontrolled wastewater discharge. It is often the discharge of industrial wastewaters from plating, metal finishing and rinsing manufacturing processes. Some industries of organic compounds such as pesticides, pigments metal additives; petroleum refining and pulp industries produce large amounts of solid and liquid waste that contains different types and quantities of heavy metals [1, 2].

There are various methods for the removal of heavy metals in the literature. Some of them are chemical precipitation [3], ion exchange [4], adsorption [5], biosorption [6] and electrocoagulation [7] such methods can be sorted.

Ion-exchange method is one of the most effective methods used in removing heavy metals from waste water. This method is used in the ion exchange resins can be used again due to chemical or physical, this method has not changed and is very economical compared to other methods. The stabilization treatment of this waste always includes the operation of their removal and possible recycling in the process using ion exchangers. The synthetic resins [4, 8, 9] have recently become recognized as an improved material for removal of heavy metals from wastewaters, contaminated surface and groundwater using ion exchange process.

The aim of our study, strongly acidic cation exchange resin DOWEX HCR-S using a batch system, aqueous solutions of different initial conditions for the equilibrium curves of Zn+2 to achieve metal removal and the maximum adsorption capacity is to find experimentally.

Results and Discussion

Effect of pH

Effect of Stirring Time and Initial Metal Concentration

A series of agitation time studies for zinc ions have been carried out with the initial metal concentration from 25 to 1000 mg/L at 293 K. Fig. 2 showed that the amount of the sorbed Zn (II) ions onto strongly acidic cation-exchanger increased with time. The agitation time necessary to reach equilibrium was 15 min. The sorption capacities (qt) increased from 11.712 to 124.232 mg/g with the increase in initial concentration from 25 to 1000 mg/L. The equilibrium uptake in the case of Dowex HCR-S occurred after 60 min. The sorption capacities of the resin were equal to 11.712, 22.205, 42.888, 65.457, 85.764, and 124.232 mg/g for the zinc solutions having initial concentration of 25, 50, 100, 250, 500 and 1000 mg/L, respectively [11, 12].

Effect of Temperature

A plot of the zinc exchange as a function of temperature (293, 313, 333 and 353 K) was shown in Fig. 3. The results revealed that the metals exchange slightly increased with increasing temperature at 293 K 65.457 mg/g; 313 K 68.225 mg/g; 333 K 70.662 mg/g and 353 K 74.100 mg/g). The exchange of metal at higher temperatures was found to be greater than that at a lower temperature. Therefore, the exchange capacity should largely depend on the chemical interaction between the functional groups on the resin surface and the adsorbate, and should increase as the temperature rises. This can be explained by an increase in the diffusion rate of the adsorbate into the active sites. At higher temperatures the resin might contribute to the exchange of Zn (II) as diffusion is an endothermic process [13].

Effect of Resin Dosage

The effect of the amount of resin on sorption of Zn (II) ions was investigated. For this purpose, the resin amounts were taken between 0.25 and 2.00 g/500 ml. The results in Fig. 4 showed that the retention of Zn (II) ions increased with increasing of resin amount but sorption density decreased and then attained equilibrium. It is readily understood that the number of available sorption sites increases by increasing the resin amount, therefore results in the increase of removal efficiency for Zn (II) ion. The decrease in sorption density can be attributed to the fact that some of the sorption sites remain unsaturated during the sorption process; whereas the number of available sorption sites increases by an increase in resin amount and this results in an increase in removal efficiency [14, 15].

Effect of Stirring Speed

Stirring is an important parameter in adsorption phenomena, influencing the distribution of the solute in the bulk solution and the formation of external boundary film. Fig. 5 showed the adsorption rate of Zn (II) using resin at different stirring speed (200, 300, 400, 500 and 600 rpm) within contact time of 60 min. From the figure it is clear that with increasing stirring speed from 200 to 600 rpm, the maximum adsorption capacity of Zn (II) increases 50.267 mg/g to 70.778 mg/g at the end of 60 min of operation. The increasing in ion exchange capacity can be explained by the fact that increasing stirring speed reduced the film boundary layer surrounding ions, thus increasing the external film transfer coefficient, and hence the adsorption capacity, similar result is also reported in the literature [16].

Adsorption Isotherm, Kinetics, Activation Parameters

Adsorption Isotherms

The capacity of Dowex HCR-S for heavy metal can be determined by measuring equilibrium isotherms. Basically, adsorption isotherm is important to describe how adsorbate interacts with adsorbents. The relationship between the amount of adsorbate adsorbed on the adsorbent and the concentration of dissolved adsorbate in the liquid at the equilibrium can be given by the adsorption isotherms. These equations which are often used to describe the experimental isotherms were developed isotherm models in Table-1 [17-25]. In order to adapt for the considered system, an adequate model that can reproduce the experimental results obtained, equations of Langmuir, Freundlich, Elovich, Temkin, Sips, Khan, Toth, Koble-Corrigan and Temkin have been considered.

Table-1: Isotherm models equations.

Isotherm###Mathematical equations###References

Langmuir###qe = (qm KLCe) (1 + KLCe)###[17]

Freundlich###qe = KFCe m###[18]

Elovich###qe qm = KECe exp ([?]qe qm)###[19]

Temkin###q e = (RT b) ln (KT Ce)###[20]

Sips###qe = (qma aS Cc)/(1+bKCe)K###[21]

Khan###qe = (qmbKCe)/(1+bKCe)aK###[22]

Radke-Prausnitz###qe = (ARCeP )/(A + RCe P-1)###[23]

Koble-Corrigan###qe = (A Ce n)/(1 + B Ce n)###[24]

Toth###qe = (qmCe)/(KTo + Ce n)###[25]

Correlation coefficients and constants of the isotherm models were given in the Table-2 (two parameters) and Table-3 (three parameters). As can be seen from tables and figures (Fig 6-7), experimental results with the best fit Khan Isotherm. The capacity of the adsorption isotherm is fundamental, and plays an important role in the determination of the maximum capacity of adsorption.

Table-2: The data for two parameter isotherms.

###Langmuir Isotherm###Freundlich Isotherm

KL###0.023567###KF###13.35417

qm###110.6965###1/n###0.332789

R2###0.93905###R2###0.99291

###Temkin Isotherm###Elovich Isotherm

KT###0.794756###qm###628.0824

b###144.2953###KE###0.000835

R2###0.96940###R2###0.87515

Table-3: The data for three parameter isotherms

###Koble-Corrigan###The Radke-Prausnitz

Sips Isotherm###Isotherm###Isotherm

qm###8208.831###A###14.07774###A###44.88950

aS###0.001621###B###0.285073###R###14.99659

n###2.981729###n###0.036349###p###0.314727

R2###0.99291###R2###0.99335###R2###0.99329

Khan Isotherm###Toth Isotherm

qm###13.62126###qm###2.160679

bK###1.308449###KTo###0.284907

aK###0.684104###n###-0.122691

R2###0.99362###R2###0.99202

Adsorption Kinetics

The kinetics of ion-exchange for the treatment of heavy metal containing industrial effluents has already been operated. Numerous kinetic models explaining the mechanism by which pollutants are adsorbed have been suggested in Table-4 [26-29]. The kinetics of adsorption is important because this is what controls the efficiency of the process. Various kinetic models have been used and different systems use different models.

The feasibility of the pseudo-second-order models can be examined by the linear plot of t/qt versus t respectively, as were shown in Fig. 8-12. The correlation coefficient R2 showed that the pseudo- second-order model is indicative of a chemisorptions mechanism, which fit the experimental data slightly better than Elovich and the pseudo-first order models. In other words the ion exchange of Zinc can be approximated more favorably by the pseudo-second-order model. This model has been successfully applied to describe the kinetics of many adsorption systems. The calculated correlations were closer to unity for the second order kinetics model; therefore, the heavy metals adsorption kinetics could well be more favorably when approximated by a second- order kinetic model. The calculated k2 (g/mg min) R2 values were listed in Table-5.

The results also defined that an intra-particle diffusion mechanism played a significant role in the adsorption process, while the adsorption rate was controlled by a film-diffusion step.

Activation Parameters

The activation energy was calculated from the linearized Arrhenius Eq (3).

equation

where Ea is activation energy (kJ/mol); k2 is the rate constant of sorption (g/mol s); k0 is Arrhenius factor, which is the temperature independent factor (g/mol s); Rg is the gas constant (J/K mol); and T is the solution temperature (K). The slope of plot of ln k2 versus 1/T was used to evaluate Ea, which was found to be 10.091 kJ/mol for Zinc exchange, respectively (Fig 13).

equation

Free energy ([?]G), enthalpy ([?]H ) and entropy ([?]S ) of activation can be calculated by Eyring equation[30]:

equation

where kb and h are Boltzmann's and Planck's constants, respectively. According to Eq. (4), a plot of ln(k2/T) versus 1/T should be a straight line with a slope [?][?]H /Rg and intercept (ln(kb/h) + [?]S /Rg). [?]H and [?]S were calculated from slope and intercept of line, respectively (Fig. 14). Gibbs energy of activation may be written in terms of entropy and enthalpy of activation:

[?] G = [?] H [?] T .[?] S (5)

It was calculated at 313 K from Eq. (5). It was found that the values of the free energy ([?]G ), enthalpy ([?]H ) and entropy ([?]S ) of activation for Zinc were 57.782 kJ/mol, 7.423 kJ/mol and [?]0.1719 kJ/mol K, respectively. The results were shown in Table-6.

Table-4: Kinetic models equations.

Kinetic model###Mathematical equations###References

pseudo-first order###In(qe - qt) = 1nqe -k1t###[26]

rate model

pseudo-second-order###t/qt = [1/k2qe2]+(1/qe)t###[27]

rate model

Elovich model###qt = b In (ab) + b 1nt###[28]

Intra Particle model###qt = kdif t 1/2 + C###[29]

Experimental

Ion exchange experiments were carried out in a batch process by using synthetic aqueous metal solution. The heavy metal solutions of Zn (II) chloride (Analytical grade from Sigma Co) were prepared in double-distilled water. Synthetic Dowex HCR S/H in hydrogen form was obtained from Fluka Co. The properties of Dowex HCR S/H were given in Table-7.

Table-7: Properties of Dowex HCR-S resin.

Parameters Value

Type Strong acid cation

Change capacity 1.8 meq/ml

Particul size 300 um - 1200 um

pH 0 - 14

Max. oper.

temperature 100 oC

Ionic form H+

Ionic density 1.22 g/cm3

Physical form Uniform particle size spherical beads

The parameters chosen in the experiments were initial pH of the solution, contact time, adsorbent dosage, stirring speed, solution temperature and initial metal ion concentration, whose ranges were given in Table-8.

Table-8: Experimental parameters

Parameter###Study Ratio

Initial zinc concentration

mg/L###25,50, 100, 250, 500 and 1000

Adsorbent dosage (g/500 ml) 0.25, 0.50, 1.00, 1.50 and 2.00

pH###3.0, 4.0, 5.0, and 6.0

Stirring speed (rpm)###200, 300, 400, 500 and 600

Solution temperature (K)###293, 313, 333 and 353

A batch system was used for removing by the exchange reaction of zinc from wastewater. The temperature of the reactor was controlled with a HAAKE D8 thermostat connected to reactor.

Experimental set up was seen Fig. 15. The amount of metal adsorbed (mg g-1), (qe), onto Dowex HCR S/H was calculated from the mass balance equation as follows:

equation

where Co and Ce are the initial and equilibrium liquid phase concentrations of metal solution (mg L-1), respectively; V the volume of metal solution (L), and m the mass of resin amount used (g). Kinetic experiments were made by using 500 mL of zinc solutions of various concentrations. Samples were taken at different time intervals and remaining metal concentrations were analyzed. The rate constants were calculated using conventional rate expressions. Following formula was used to determine adsorbed metal concentration qt:

equation

where qt (mg g-1) is the adsorption capacity at time t, Co (mg L-1) is the initial metal concentration, Ct (mg L-1) is the concentration of metal ions in solution at time t, V (L) is the volume, and m (g) is the amount of the resin.

Table-5: Kinetics data calculated for ion exchange of Zn (II) on Dowex HCR-S/H.

Resin dosage###Temperature###Initial metal###a###bg###h=k 2X qe2###k2x10 3###R2###k1###R1###k2###R2 2

(g/500 ml)###(K)###concentration###pH###Stirring speed###mg g-1###mg-1###R2###k1###R2###mg g-1###g mg-1###mg g-1###2###mg g-1

###(mg L-1)###(rpm)###min-1###min-1###min-1###min-1###min-1/2###min-1/2

1.00###293###250###6.0###400###51.522###0.079###0.978###0.1061###0.983###22.523###0.0047###0.996###12.690###0.991###2.620###0.800

1.00###303###250###6.0###400###76.657###0.081###0.971###0.0921###0.958###29.326###0.0058###0.998###13.288###0.981###2.181###0.850

1.00###313###250###6.0###400###137.213###0.086###0.945###0.0888###0.917###41.494###0.0079###0.999###13.648###0.941###1.620###0.907

1.00###323###250###6.0###400###353.616###0.097###0.942###0.0826###0.896###52.910###0.0094###0.999###14.248###0.896###1.742###0.910

1.00###293###25###6.0###400###8.545###0.447###0.992###0.1007###0.979###3.397###0.0223###0.994###2.057###0.978###0.693###0.892

1.00###293###50###6.0###400###13.550###0.223###0.989###0.0942###0.979###6.124###0.0112###0.994###4.408###0.966###1.222###0.932

1.00###293###100###6.0###400###23.356###0.117###0.990###0.0807###0.990###10.965###0.0057###0.994###8.430###0.985###2.261###0.933

1.00###293###250###6.0###400###51.522###0.079###0.978###0.1061###0.983###22.523###0.0047###0.996###12.690###0.991###2.620###0.800

1.00###293###500###6.0###400###87.456###0.063###0.943###0.0784###0.906###37.175###0.0047###0.998###18.962###0.945###2.527###0.967

1.00###293###1000###6.0###400###358.180###0.055###0.962###0.0666###0.902###62.500###0.0040###0.997###19.438###0.880###4.337###0.981

0.25###293###250###6.0###400###120.536###0.046###0.981###0.0710###0.963###38.314###0.0023###0.993###19.887###0.858###7.502###0.952

0.50###293###250###6.0###400###118.122###0.061###0.991###0.0778###0.987###32.051###0.0031###0.994###14.150###0.991###5.586###0.924

1.00###293###250###6.0###400###51.522###0.079###0.978###0.1061###0.983###22.523###0.0047###0.996###12.690###0.991###2.620###0.800

1.50###293###250###6.0###400###57.414###0.094###0.970###0.1095###0.992###22.883###0.0064###0.997###11.050###0.933###1.985###0.824

2.00###293###250###6.0###400###58.352###0.097###0.962###0.1448###0.982###24.938###0.0076###0.998###11.202###0.947###1.508###0.678

1.00###293###250###6.0###200###31.373###0.096###0.966###0.1288###0.996###15.221###0.0053###0.994###10.031###0.999###1.862###0.715

1.00###293###250###6.0###300###47.837###0.088###0.970###0.1043###0.984###21.505###0.0057###0.997###11.851###0.992###1.886###0.795

1.00###293###250###6.0###400###51.522###0.079###0.978###0.1061###0.983###22.523###0.0047###0.996###12.690###0.991###2.620###0.800

1.00###293###250###6.0###500###68.467###0.079###0.970###0.1079###0.981###28.409###0.0056###0.998###13.554###0.970###2.225###0.785

1.00###293###250###6.0###600###99.414###0.081###0.964###0.0970###0.949###34.247###0.0064###0.998###13.271###0.981###1.886###0.779

1.00###293###250###3.0###400###66.040###0.061###0.964###0.0801###0.907###17.986###0.0041###0.994###11.926###0.980###2.980###0.831

1.00###293###250###4.0###400###89.345###0.068###0.961###0.1020###0.963###19.120###0.0042###0.995###12.487###0.989###2.803###0.826

1.00###293###250###5.0###400###110.057###0.068###0.970###0.0862###0.964###37.879###0.0050###0.998###12.665###0.992###2.727###0.831

1.00###293###250###6.0###400###53.205###0.058###0.973###0.1043###0.991###26.385###0.0034###0.996###12.690###0.991###2.620###0.800

Conclusion

Dowex HCR S/H resin was a tender of removing zinc from an aqueous solution. It was found that the rate constant of ion exchange increased by increasing initial concentration, stirring speed, pH and temperatures. The adsorption data correlated well with Khan adsorption isotherm model. The results of this research evidence that the second-order kinetic model mechanism played a significant role in the ion exchange of Zn (II) by Dowex HCR S/H resin.

Thermodynamically parameters were evaluated for zinc ions and showed that the ion exchange of the zinc ions is endothermic in nature. The positive value of [?]H showed that adsorption was favorable at higher temperature and the presence of possible chemisorptions phenomenon. The positive values of the Gibbs free energy change ([?]G ) confirm that the ion-exchange process was not spontaneous whereas the negative values of the entropy ([?]S ) confirm that the decreased randomness at the solid-solute during ion-exchange process.

References

1. A. Benhammou, A. Yaacoubi, L. Nibou and B. Tanouti, Journal of Colloid and Interface Science, 282, 320 (2005).

2. D. Demirezen, A. Aksoy and K. Uruc, Chemosphere, 66, 553 (2007).

3. M. M. Matlock, B. S. Howerton and D. A. Atwood, Journal of Hazardous Materials, 84, 73 (2001).

4. N. H. Shaidan, U. Eldemerdash and S. Awad, Journal of the Taiwan Institute of Chemical Engineers, In Press, Corrected Proof.

5. Y. I. Khattak, S. K. Uddin and S. U. Din, Journal of the Chemical Society of Pakistan, 17, 190 (1995).

6. N. Jamil, Journal of the Chemical Society of Pakistan, 31, 362 (2009).

7. D. Sud, G. Mahajan and M. P. Kaur, Bioresource Technology, 99, 6017 (2008).

8. R. K. Misra, S. K. Jain and P. K. Khatri, Journal of Hazardous Materials, 85, 1508 (2011).

9. X. J. Hu, J.-S. Wang, Y.-G. Liu, X. Li, G.-M. Zeng, Z.-l. Bao, X.-X. Zeng, A.-W. Chen and F. Long, Journal of Hazardous Materials, 185, 306 (2011).

10. L.-C. Lin and R.-S. Juang, Chemical Engineering Journal, 132, 205 (2007).

11. A. Agrawal and K. K. Sahu, Journal of Hazardous Materials, 137, 915 (2006).

12. A. Amrane, M. Chabani and A. Bensmaili, Chemical Engineering Journal, 125, 111 (2006).

13. A. Agrawal, K. K. Sahu and B. D. Pandey, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 237, 133 (2004).

14. S. Rengaraj, C. K. Joo, Y. Kim and J. Yi, Journal of Hazardous Materials, B102, 257 (2003).

15. I. H. Lee, Y.-C. Kuan and J.-M. Chern, Journal of the Chinese Institute of Chemical Engineers, 38, 71 (2007).

16. S. Lu, S. W. Gibb and E. Cochrane, Journal of Hazardous Materials, 149, 208 (2007).

17. I. Langmuir, Journal of The American Chemical Society, 1361 (1918).

18. H. M. F. Freundlich, The Journal of Physical Chemistry 57, 385 (1906).

19. S. Y. Elovich and O. G. Larionov, Translated from Izvestiya Akademii Nauk SSSR, Otdelenie Khimicheskikh Nauk, 2, 209 (1962).

20. M. I. Temkin, Zhurnal Fizicheskoi Khimii, 15, 296 (1941).

21. R. Sips, Journal of Chemical Physics, 16, 490 (1948).

22. A. R. Khan, R. Ataullah, and A. Al-Haddad, Journal of Colloid and Interface Science, 194, 154 (1997).

23. C. J. Radke and J. M. Prausnitz, Industrial and Engineering Chemistry Fundamentals, 11, 445 (1972).

24. R. A. Koble and T. E. Corrigan, Industrial and Engineering Chemistry Research, 44, 383 (1952).

25. J. Toth, Acta Chimica Academiae Scientiarum Hungaricae, 69, 311 (1971).

26. Y. S. Ho and G. McKay, Trans Institution of Chemical Engineers, 76B, 332 (1998).

27. Y. S. Ho, D. A. J. Wase, and C. F. Forster, Water South Africa, 22, 219 (1996).

28. G. McKay, Y. S. Ho and J. C. Y. Ng, Separation and Purification Methods, 28, 87 (1999).

29. T. Furusawa and J. M. Smith, AIChE Journal, 20, 88 (1974).

30. K. Laidler and J. H. Meiser, Houghton Mifflin New York, p. 852 (1999).

Ataturk University, Faculty of Engineering, Department of Environmental Engineering, 25240, Erzurum, Turkey. baybarsalifil2@gmail.com
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Author:Fil, Baybars Ali; Boncukcuoglu, Recep; Yilmaz, Alper Erdem; Bayar, Serkan
Publication:Journal of the Chemical Society of Pakistan
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Date:Aug 31, 2012
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