EQUILIBRIUM AND KINETIC STUDIES

Environmental Engineering and Management Journal

October 2011, Vol.10, No. 10, 1579-1587

http://omicron.ch.tuiasi.ro/EEMJ/

“Gheorghe Asachi” Technical University of Iasi, Romania

ADSORPTION OF Pb (II) FROM AQUEOUS SOLUTION ONTO LEWATIT FO36 NANO RESIN: EQUILIBRIUM AND KINETIC STUDIES Mehdi Ahmadi1,2, Pari Teymouri2, Azra Setodeh3, Mohamad Sedigh Mortazavi3, Alireza Asgari4

1 Environmental Technology Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran Department of Environmental Health Engineering, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran 3 Department of Environmental Engineering, Islamic Azad University, Bandar Abbas Branch, Bandar Abbas, Iran 4 Department of Environmental Health Engineering, Tehran University of Medical Sciences, Tehran, Iran

2

Abstract This investigation focused on the adsorption of Pb (II) onto Lewatit FO 36 resin from aqueous solutions. The effects of initial metal concentration, contact time, pH of solution were factors that affected the adsorption of Pb (II). Adsorption kinetic was better explained by the pseudo second order type 1 kinetic model that was confirmed by the values (R2>0.986). The Langmuir, Freundlich, Temkin and BET adsorption models were used for the equilibrium studies and Freundlich isotherm better described the adsorption equilibrium. According to the Langmuir isotherm the maximum adsorption capacity of Pb (II) onto Lewatit FO 36 was 62.5 mmolg-1at pH 7 and 0.04 gL-1 resin dosage and 15min contact time. Key words: adsorption, isotherm, kinetics, lead (II), lewatit FO 36 Received: December, 2010; Revised final: May, 2011; Accepted: May, 2011

1. Introduction Because of non-biodegradability of heavy metals in the environment and their harmfulness to living organisms, their removal becomes so important with regard to protection of ecosystem and human health (Anayurt et al., 2009; Sari et al., 2007a). Human activities in urban, industrial and mining areas contaminate water with heavy metals (Sato et al., 2007). Lead (II) as a toxic heavy metal has the tendency to accumulate in blood, soft tissues and mineralizing tissues like bones and poses serious health hazards such as anemia and damage to kidney, lung, brain and central nervous system (Chandara et al., 2005). Different industries such as batteries, cables, plastics, fuel and explosive manufacturing use Pb (II) and discharge their Pb (II) contained effluent in aquatic environment (Uluozlu et al., 2008). There are strict legislations on heavy metals discharge in the environment and accessing to water 

with minimum heavy metal concentration (Sheng et al., 2009). Therefore, various methods are used for heavy metal removal from aqueous solutions such as chemical precipitation, ion exchange, solvent extraction, membrane processes, reverse osmosis, evaporation and adsorption (Bulgariu et al., 2010; Caramalău et al., 2009; Modher et al., 2009; Sari et al., 2007b; Kicsi et al., 2010). However technical and economic factors such as higher operational cost, requiring additional chemicals, high energy consumption, and residual metal sludge disposal sometimes limit the application of these processes (Balan et al., 2010; Modher et al., 2009; Sari et al., 2007c). Ion exchange, because of its simple and safe application, is an attractive method among the others (Bulai et al., 2009; Popa et al., 2010). This process also can be effective, if the ion exchanger is cheap (Gode and Moral, 2008). Chelating resins, which have ligands for selectively bonding heavy metal ions, are generally used for removal of these ions

Author to whom all correspondence should be addressed: e-mail: [email protected]; Phone:+989126779273

Ahmadi et al./Environmental Engineering and Management Journal 10 (2011), 10, 1579-1587

from the aqueous solutions or wastewater (Gode and Pehlivan, 2003). In recent years, a number of commercial resin are used for heavy metals removal, such as Lewatit Mono plus SP112 (Dizge et al., 2009), Lewatit MP 64, Lewatit MP500 (Pehlivan and Cetin, 2009), Amberlite IR-120 (Manuel et al., 2008), Amberlite IRC-748 (Dinu and Dragan, 2008), Lewatit CNP-80 (Pehlivan and Altun, 2007), Lewatite S-100 (Bedoui et al., 2008; Gode and Pehlivan, 2006), Amberlite IRC-718 and IR-120 (Lee et al., 2006), Carboxymethyl-chitosan (Sun et al., 2006), Chelex100, Lewatit MP62 (Gode and Pehlivan, 2003). Among resins cross linked polystyrene polymers are commonly used (Pehlivan and Altun, 2007). Nanoscale iron particles are new generation of effective environmental cleanup technologies (Zhang, 2003). Lewatit FO 36 is a polystyrene-based and macro porous resin, which the inner surface of the pores is covered by a nano–scaled film of iron oxide. Oxyanions such as arsenate or arsenite, HPO42-, HSbO42-, SCN-, etc., ions are bounded by a specific, reversible reaction involving hydroxyl-group on the iron oxide surface. It has to be mentioned that the weakly basic anion exchange group in the resin is still active and can react in the specific way, known for this kind of functional group (Lewatit, 2008). Polymer resin based iron oxide doped adsorbents, are regenerable and bleeding of fine iron oxide particle does not happen. They have high mechanical strength, so they are easily backwashed or pumped in suspension. Macro pore bead, due to its sponge like structure that causes more stress relief, gives this resins better physical stability. Furthermore, as a result of building up fines, no blocking of resin bed happens. The optimized pore structure cause fast ion exchange kinetics, which make it proper for the treatment of electroplating effluents. Meanwhile, gel resins usually are more efficient and effective. They are suitable for lots of applications like treatment of the solutions containing metal salts (Lewatit, 2008; Rafati et al., 2010). The objective of this work is to study the feasibility of using Lewatit FO 36, Polystyrene based resin doped with FeO (OH) nano particles, as adsorbent for lead(II) removal from aqueous solutions, using batch technique under various conditions of pH, contact time and initial concentration of Pb (II). Different isotherm models were used to the equilibrium data. Adsorption mechanisms of Pb (II) ions were also estimated by kinetic studies. 2. Experimental 2.1. Characteristics of the adsorbent Lewatit FO 36 was used in this experiment as adsorbent. The physical and chemical characteristics of this resin are shown in Table 1.

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Table1. The physical and chemical characteristics of Lewatit FO 36 Characteristics Ionic form as shipped Functional group Matrix Structure Operating pH-range Bed size Capacity Appearance Uniformity coefficient Density Regenerate

Value Neutral FeO(OH) Cross linked polystyrene Macro porous 4-11 0.35 mm 1.5 g L-1 Brown, Opaque 1.1 1.25 g ml-1 NaOH+NaCl (with a mass-ratio of 1:1)

2.2. Pb(II) adsorption All chemicals used in this study were of analytical reagent grade and were supplied from Merck Chemical Company, Germany. All dilutions were carried out by using double deionized water. A pH meter (Metrohm Model 747: Switzerland) was used for measuring pH value of solutions. Agitation was carried out by a magnetic stirrer (Model CAGAlpha 5054: India). A flame atomic absorption spectrophotometer (Model GBC 932 AA: Korea) was used for Pb (II) determinations and all measurements were performed in an air/acetylene flame. The batch method was used to study the adsorption of Pb (II) on Lewatit FO 36. Experiments were carried out at room temperature (24±1C) in a 1L beaker containing 500ml of test solution. Stock solution of the lead ion under study were prepared by dissolving an appropriate weight of pure Pb (NO3)2 salt in distilled water. Important parameters affecting the nanosorption such as contact time, Pb (II) initial concentration and pH were studied. Adsorbate /adsorbent ratio was chosen 24mMg-1, so 0.25g of nanosorbent was added to flasks contained 6mM of Pb (II); and was shaken for the contact time varied from 1-10 min. Initial pH of synthetic solution was arranged on 7. The time required for obtaining equilibrium condition was estimated in this way. For investigating initial metal effect on adsorption, constant amount of nanosorbent was then added to initial Pb (II) concentration varied from 0.4-6mM and other parameters were constant, too. Nanosorption experiments for studying the effect of pH were conducted by using a solution having 3mM of Pb (II) and 0.125 g of nanosorbent. 0.1M HCl and 0.1M NaOH were used for adjusting pH at 4-8. After filtering the contents of flask by 0.45μ membrane filter, the filtrate was analyzed for Pb(II) concentration by flame AAS. Concentration of metal ions adsorbed at time (t), per unit of adsorbent qt was obtained using Eq. (1): (1) qt  [(C0 - C) V]/M where qt is the amount of metal ions adsorbed onto the unit amount of the nanosorbent (mg g−1). C0 and C are the concentrations of the metal ions in the initial solution (mg L−1) and after nanoosorption,

Adsorption of Pb (II) from aqueous solution onto lewatit FO36 resin: equilibrium and kinetic studies

respectively. V is the volume of the aqueous phase (L−1) and M is the amount of the nanosorbent (g). The mathematical equations using in experiments are shown in Table 2. 3. Results and discussions 3.1. Effect of pH on Pb (II) adsorption Acidity of aqueous solution is an important controlling parameter in heavy metals adsorption. Solubility of metal ions and ionization state of functional groups of adsorbent are affected by solution pH (Aydın et al., 2008; Kaçar et al., 2002). The effect of solution pH on lead (II) adsorption on the Lewatit FO 36 was investigated at different pH values in the range of 4-8 and the results are shown in Fig.1. Because of precipitation of Pb (II) at pH above 8, experiments were not carried out at these pH values. Moreover, investigations were not conducted at pH lower than 4, Because Lewatit FO 36 should never be exposed to solutions with these values of pH, otherwise its iron oxide will be dissolved and washed out and the resin will lose its functionality (Lewatit, 2008). As it is clear from Fig.1, nanosorption was increased gently by increasing of pH until pH 7 and sharply after this pH. Maximum adsorption capacity achieved at pH 8. At lower pH values, H+ ions is competing with metal ions for binding sites of adsorbent, thus positive charge of adsorbent’s surface by protons resulting in less adsorption of metal ions (El-Ashtoukhy et al., 2008; Matos and Arruda, 2003). By contrast, increasing of pH and reduction of electrostatic repulsion especially in alkaline solutions (pH>7), as a result of lower ionic

comparison and reducing of the metal solubility at these pH values, causes an increased metal adsorption (Matos and Arruda, 2003; Sari et al., 2007a). The similar results were obtained by different researchers on other adsorbents (Modher et al., 2009; Paul et al., 2006; Sari et al., 2007b; Shibi and Anirudhan, 2006). Due to little difference between nanosorption efficiency of Pb (II) at pH 7 and 8, (49% and 53%, respectively) and because of the natural pH of water, pH 7 was selected for further experiments. 3.2. Effect of contact time on Pb(II) adsorption The contact time is the other important factor which affects heavy metal adsorption. The effect of contact time on lead (II) adsorption on the Lewatit FO 36 was investigated at 1-10 min range and the results were shown in Fig. 2. The Pb (II) removal decreased with time. The results show that agitation time necessary to reach equilibrium was 6 min.This equilibrium time is less than other studies (Guo et al., 2006; O’Connell et al., 2006). 3.3. Effect of initial concentration on Pb(II) adsorption The initial Pb (II) concentrations tested were 6,5,4,3,2,1,0.6 and 0.4 mM. As it is shown in Fig. 3, the equilibrium sorption capacities (qe) of Pb (II) onto Lewatit FO 36 increase from 8.45 to 51mmol g-1 by increasing of initial concentration of Pb (II) from 0.4 to 6 mM, respectively. So removal of ions is concentration dependent. In fact, high driving force for mass transfer can be the reason for this behavior (Aydın et al., 2008).

Table 2. Mathematical equation using in experiments Equilibrium isotherms models

Equations

Langmuir

Ceq/qe=1/KL qm + Ceq/qm

Freundlich

log qe=log kf+1/n log Ce

Temkin

qe=B ln(A)+B ln(Ce)

(BET) Brunauer, Emmett, Teller

C/(Cs-C)qe=1/Bqm+(KB1/Bqm)(C/Cs)

Lagergren pseudo-first order Type 1 Pseudosecond order Type 2 Pseudosecond order Type 3 Pseudosecond order Type 4 Pseudosecond order

log (qe-qt)=log (qe)-K1. t /2.303

Elovich

t/qt=1/k2qe2+1/qe×t 1/qt = 1/qe+(1/k2qe)(1/t) 1/t = (k2-qe2 /qt)-( k2-qe2 /qe) qt/t =k2qe2 – (k2qe2/qe)qt qt = 1/ln(á)+1/ln(t)

Plot

Calculated coefficient

Ce/qe vs. KL= slope/ intercept Ce qm =1/slope logqevs. n=1/slope; log Ce Kf=10intercept B=slope ; qe vs. A= Exp (inercept/slope) Ln(Ce) C/ (Csqm=1/(intercept + slope) C)qevs. KB=1+(slope/intercept) C/Cs Kinetics models log((qe-qt) qe=10intercept; vs. t k1=-2.303×slope qe=1/slope; t/qtvs. t k2=slope2/intercept qe=1/intercept; 1/qt vs.1/t k2=intercept2/slope qe=-slope/intercept; 1/t vs. 1/qt k2=intercept2/slope qe= -intercept/slope; qt /t vs. qt k=slope2/ intercept =1/slope; qt vs. ln(t) á=exp(intercept/slope-ln())

Eq.no 2 3 4 5

6 7 8 9 10 11

Reference (Aydın et al., 2008) (Aydın et al., 2008) (Kumar and Kirthika, 2009) (Sciban et al., 2007) (Dizge et al., 2009) (Dizge et al., 2009) (Dizge et al., 2009) (Dizge et al., 2009) (Dizge et al., 2009) (Dizge et al., 2009)

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Fig. 1. Effect of pH on the sorption of Pb (II) by Lewatit FO 36 (Initial concentration of Pb (II): 3mM; amount of resin: 0.125 g; stirring time 6 min)

Fig. 2. Effect of contact time on the ion exchange of Pb (II) using Lewatit FO 36; initial Pb (II) concentration 6 mM and amount of Lewatit FO 36: 0.25g, respectively in pH 7

Fig. 3. Effect of initial metal concentration at Pb (II) adsorption on Lewatit FO 36. Initial concentration of Pb (II): 0.4-6 mmol L-1; amount of resin: 0.02 g; pH 7

3.4. Equilibrium modeling Equilibrium sorption isotherm is used to describe adsorbent capacity and is one of the important parameters for adsorption system designing (Dizge et al., 2009; Sari and Tuzen, 2009).In this study several adsorption isotherms (Langmuir,

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Freundlich, Temkin and BET) are selected for fitting the data to examine the relationship between adsorbed (qe) and aqueous concentrations of metal ions (Ce) at equilibriums. All isotherm equations evaluated from the linear plots which are presented in Fig. 4(a), (b), (c) and (d), as well as Table 2, Eqs. (2) - (5), and their calculated parameters are listed in Table 3. Langmuir model assumes monolayer adsorption of solute with no interaction between adsorbed ions (Wang and Chen, 2009). In Langmuir isotherm formula, qe is the equilibrium metal ion concentration on the adsorbent (mg g-1), Ce is the equilibrium solute concentration in the solution, qmax and b are Langmuir constants related to maximum sorption capacity (monolayer capacity) (mg g-1), and bonding energy of adsorption (mg-1), respectively. In Table 4, qm of the of Lewatit FO 36 resin for lead (II) sorption is compared with other adsorbents reported in the literatures. The adsorption capacity of Lewatit FO 36 for lead (II) is more than that of other adsorbents, so it has very good potential for removing Pb (II) from aqueous solutions. Freundlich model is used for heterogeneous surfaces (Ayari et al., 2007). Parameters in Freundlich isotherm are defined as follows: Kf is adsorption equilibrium constant; relating the adsorbent capacity and 1/n is parameter relating the adsorption intensity and is the slope of log qe vs. log Ce plot. As Table 3 reveals Freundlich isotherm was fitted well with the equilibrium data (R2>0.967). It is discussed as occurrence of initially occupation of stronger binding sites and by increasing degree of these site occupations decreasing in the binding straights occurs (Vijayaraghavan and Yun, 2008). Moreover, as it is clear in Table 3, the n value is greater than 1, which is representative of favorable condition for adsorption of lead (II) in this study (Dizge et al., 2009). The Temkin isotherm model assumes that with coverage, adsorbate–adsorbent interaction causes linearly reduction in heat of adsorption of all the molecules in the adsorbed layer. Moreover, in this model a uniform distribution of binding energies up to a maximum binding energy is happened. The Temkin constants, B and A, reveal heat of adsorption and maximum binding energy, respectively, which increasing temperature causes the former value raising and falling of the latter (Inbaraj et al., 2008). BET (Brunauner, Emmett, and Teller) model is based on multilayer sorption of solute, assuming that Langmuir isotherm is used for each layer (Modher et al., 2009; Wang and Chen, 2009). Cs in BET formula is the saturation concentration of the adsorbed component; kB a constant representative of the energy of interaction between the metal ions and the adsorbent surface, and qm is a constant indicating the amount of metal ions adsorbed forming a complete monolayer.


Table 3. Langmuir, Freundlich, Temkin and BET isotherm parameters Langmuir isotherm qmm KL R2 (mmol g-1) (mmol-1) 62.5 0.281 0.923

Freundlich isotherm Kf n R2 (mmol-1) 2.15 25.58 0.967

Temkin isotherm

BET isotherm qm kB R2 (mmol g-1) 1601 62.46 0.923

2

B

A

R

10.56

17.759

0.885

Table 4. Maximum adsorption capacity of different status for lead (II) sorption Adsorbent Manganese Oxide-coated sand (MOCS) Manganese oxide-coated crushed brick Siderite Palygorskite clay Cross-linked Starch Phosphate Carbamate 8-hydroxy quinoline-immobilized bentonite Turkish kaolinite clay Celtek clay Expanded perlite Clay/poly(methoxyethyl)acrylamide (PMEA) Oxidizedmultiwalledcarbon nanotubes Nano-hydroxyapatite particles Lewatit FO 36

Maximum sorption capacity for Pb (II) (mmol.g-1) 0.029 0.03 0.05 0.503 2.01 0.69 0.15 0.087 0.065 0.391 0.01 1.17 62.5

References (Boujelben et al., 2009) (Boujelben et al., 2009) (Erdem and Ozverdi, 2005) (Chen and Wang, 2007) (Guo et al., 2006) (Ozcan et al., 2009) (Sari et al., 2007a) (Sari et al., 2007b) (Sari et al., 2007d) (Solener et al., 2008) (Xu, et al., 2008b) (Zhang et al., 2009) Present study

(a)

(b)

(c)

(d)

Fig. 4. (a) Langmuir, (b) Freundlich, (c) Temkin and (d) BET isotherm plots for adsorption of Pb (II) onto Lewatit FO 36 resin (adsorbent dosage, 0.04g.L-1; contact time: 6min; pH 7)

3.5. Kinetic modeling Kinetic studies were used to investigate the sorption mechanism and its rate controlling steps, which contain transport and chemical reaction processes (Febrianto et al., 2009). In order to

investigate the adsorption mechanism, the rate constant of adsorption for lead (II) ions was determined using six kinetic models: the lagergren pseudo-first order (Eq. 6), four types of pseudosecond order (Eqs. 7-10), Elovich (Eq. 11), respectively (Table 2). Fig. 5a shows the log (qe−qt)

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vs. t plots taking into account the Pb (II) initial concentration for Lagergren pseudo-first order kinetic using Lewatit FO 36 resin in sorption experiments. The rate constants k1 were calculated from the slope of Fig. 4a. The R2values are found 0.924 (Table 5). From Table 2, it can be seen that the calculated equilibrium capacities (qe,cal) according to the Lagergren pseudo-first order rate expression are not in good agreement with the values of experimental capacities (qe,exp). Fig. 5b-e shows the plots of t/qe vs. t, 1/qt vs. 1/t, 1/t vs. 1/qt and qt/t vs. qt for type 1-4 of the pseudo second order expressions, respectively. These plots were used to calculate K2, the pseudo second order kinetic constant, and qe. Table 5 compares these calculated constants according to four linear forms of the pseudo second Order kinetic models at initial Pb (II) concentration of 6 mM and as it is obvious from

this table, the obtained K2, qe,cal and R2 were different for these models and pseudo second order type 1 was the one with high correlation (0.986). Moreover qe,cal are closer to qe, exp values. Therefore it can be concluded that the pseudo-second order type 1 model can be fitted for adsorption of Pb (II) on onto Lewatit FO 36 and chemisorption controls the adsorption process (Dizge et al., 2009). Fig. 5f represents qt versus ln (t) plot which gives a linear relationship for the applicability of the Elovich kinetic model. This model expresses the chemisorption on heterogeneous solid surface active sites (Lugo-Lugo et al., 2009; Pérez Marín et al., 2009). In Elovich model α is initial adsorption rate and is related to rate of chemisorption,  is desorption constant and is related to surface coverage (Nadeem et al., 2009).

(a)

(b)

(c)

(d)

(e)

(f)

Fig. 5. The fitting of different kinetic models for Pb (II) sorption on Lewatit FO36 resin for 6 mM initial concentration of Pb(II): (a) pseudo-first order; (b),(c), (d), (e) Type 1-4 pseudo-second order, respectively; (f) Elovich model

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High value of constant α tells that chemisorption reactions took place and by taking account of  and R2 values, we can say that Elovich model can be fitted for experimental data. Table 5. The kinetic parameters for lead (II) sorption onto Lewatit FO 36 resin Kinetic models Pseudo-first order

Type 1 pseudosecond order




Elovich

Coefficient K1 (L g-1) qeexp. (mmol g-1) qecal. (mmol g-1) R2 K2(g mmol-1min-1) qeexp. (mmol g-1) qecal. (mmolg-1) R2 K2 (g mmol-1min-1) qeexp. (mmol g-1) qecal. (mmol g-1) R2 K2 (g mmol-1min-1) qeexp. (mmol g-1) qecal. (mmol g-1) R2 K2 (g mmol-1min-1) qeexp. (mmol g-1) qecal. (mmol g-1) R2 Á



R2

Value 0.86 6.48 12.85 0.925 0.077 6.48 7.87 0.986 0.04 6.48 9.17 0.979 0.04 6.48 9.28 0.979 0.046 6.48 8.86 0.867 9.14 0.56 0.914

4. Conclusions This study focused on the adsorption of lead(II) onto Lewatit FO36 resin from aqueous solutions. The initial metal concentration, contact time and pH of solution were factors that affected the adsorption of Pb(II). Adsorption kinetic was better explained by the pseudo second order type1 kinetic model (R2>0.986). The Freundlich model better described the adsorption equilibrium. The maximum adsorption capacity of Pb(II) onto Lewatit FO36 was 62.5 mmol g-1 at pH 7, 0.04 g L-1 resin dosage and 6min contact time. It can be concluded that Lewatit FO36 resin is an effective adsorbent for Pb (II) removal from aqueous solutions. Acknowledgements The authors are grateful for financial support of this project by Iran Nanotechnology Initiative Council.

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