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Adsorption of zinc and toluene by alginate complex impregnated with zeolite and activated carbon
Current Applied Physics 9 (2009) 694–697
Contents lists available at ScienceDirect
Current Applied Physics journal homepage: www.elsevier.com/locate/cap
Adsorption of zinc and toluene by alginate complex impregnated with zeolite and activated carbon Jae-Woo Choi a, Ki-Seok Yang b, Dong-Ju Kim a,*, Cheol Eui Lee c a
Department of Earth and Environmental Sciences, Korea University, Seoul 136-713, Republic of Korea SK Gas Corporation, Seoul 110-110, Republic of Korea c Department of Physics and Institute for Nano Science, Korea University, Seoul 136-713, Republic of Korea b
a r t i c l e
i n f o
Article history: Received 2 June 2008 Accepted 4 June 2008 Available online 24 June 2008 Keywords: Adsorption Alginate complex Zinc Toluene Removal efficiency
a b s t r a c t In this study, a novel alginate complex was developed for removal of mixed contaminants containing both organic and inorganic compounds. The alginate complex was generated by impregnating synthetic zeolite and powdered activated carbon (PAC) into alginate gel bead. The adsorption of zinc and toluene as target contaminants onto the alginate complex was investigated by performing both equilibrium and kinetic batch tests. Equilibrium tests showed that adsorption of two contaminants followed Langmuir isotherm and that the alginate complex was capable of removing zinc (maximum binding energy b = 4.3 g/kg) and toluene (b = 13.0 g/kg) best compared to other adsorbents such as granular activated carbon (GAC), zeolite, and alginate impregnated with PAC (AG–AC bead). These values were higher than those of any other adsorbents for each contaminant. It was further revealed from kinetic tests that removal efficiency of zinc and toluene was 54% and 86% for the initial solution concentrations of 250 mg/L, respectively. This indicates that the alginate complex developed in this study can be used as promising adsorbents for simultaneous removal of organic and inorganic compounds from industrial wastewater or groundwater containing mixed contaminants. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction Industrial wastewater often contains both organic and inorganic compounds such as aromatic hydrocarbons and heavy metals since the latter comes from industrial use of organic compounds containing metal additives in the petroleum and organic chemical industries. Heavy metal ions should be removed from wastewater before disposal since they are highly toxic even at low concentrations and therefore sources of great concern in aquatic environment. Aromatic compounds such as toluene are used as raw materials in many chemical productions and solvents in manufacturing processes. These compounds are carcinogenic and their presence in water stream even at low concentrations poses significant environmental risks. So far a considerable effort has been made for removal of these compounds. For instance, removal of heavy metals was attempted using various adsorbents such as chitosan [1,2], zeolite [3–5], and clay [6] among which zeolite was found the cost efficient adsorbent [7]. For removal of aromatic compounds, many attempts were made via adsorption process using various adsorbents. To date the most widely used adsorbent is activated carbon for removal of organic compounds such as phenol, benzene and toluene. Adsorption of phenol [8], benzene and * Corresponding author. Tel.: +82 2 3290 3177; fax: +82 2 3290 3189. E-mail address: [email protected] (D.-J. Kim). 1567-1739/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2008.06.008
toluene [9,10] on activated carbon was studied to investigate the structure of activated carbon. However, for simultaneous removal of both organic and inorganic compounds from industrial wastewater, complex adsorbents other than these materials are needed. Therefore in this study we attempted to develop a new adsorbent, alginate gel bead impregnated with zeolite and activated carbon for removal of mixed industrial contaminants. In order to examine the adsorption capacity of the alginate complex, both equilibrium and kinetic batch studies were performed. 2. Materials and methods 2.1. Preparation of alginate complex beads All chemicals of sodium alginate, granular activated carbon (GAC), powdered activated carbon (PAC) and calcium chloride were obtained from Sigma Aldrich, Korea except for synthetic zeolite which was purchased from Jishim tech. Korea. The type of synthetic zeolite was zeolite A that exhibits the LTA (Linde Type A) structure. It has a three-dimensional pore structure with pores running perpendicular to each other in the x, y, and z planes, and is made of secondary building units 4, 6, 8, and 4–4. The pore diameter is 4.2 Å and defined by an eight member oxygen ring. This leads into a larger cavity of minimum free diameter 11.4 Å. The cavity is surrounded by eight sodalite cages (truncated octahedra)
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J.-W. Choi et al. / Current Applied Physics 9 (2009) 694–697
connected by their square faces in a cubic structure. The unit cell is symmetry. Zeolite A has a void volcubic (a = 24.61 Å) with Fm3c ume fraction of 0.47, with a Si/Al ratio of 1.0. It thermally decomposes at 700 °C. Formation of alginate complex is as follows. First, 5.0% sodium alginate solution was prepared by mixing 20 g of sodium alginate powder with 400-mL distilled water. After adding 4 g of each PAC and zeolite into 400-mL alginate solution, homogeneous mixing was performed for 20 h to yield 1% (w/v) alginate solution mixed with activated carbon and zeolite. The 1% alginate solution contained in a burette was then allowed to drop into a solution of 4% CaCl2 (500 mL) solution and thus forming 200 g of 4-mm spherical alginate complex beads. In order to compare with other type of alginate bead, alginate bead impregnated with powdered activated carbon only (AG–AC bead) was also formed using the same procedure except for addition of 4 g of zeolite to alginate solution. 2.2. Equilibrium adsorption test In order to determine the adsorption capacity of the alginate complex, and compare with those of other existing adsorbents such as granular activated carbon, zeolite and AG–AC bead, equilibrium batch tests were conducted. Twenty gram of complex beads and other adsorbents was allowed to react with each 80 mL of Zn(SO4)2 solutions (pH 6.7–6.8) with various initial zinc concentrations (50, 100, 300, 500, 700, 1000 mg/L) in 125 mL wide neck bottle using air shaker (140 rpm, 32 °C). For toluene adsorption, 280 ml solutions of five different initial concentrations (50, 100, 200, 500, 700 mg/L) were used to react with 8 g of adsorbents. At equilibrium (48 h), zinc and toluene solutions were analyzed by ICP-OES (Optima 2000 DV, Massachusetts) and HPLC (Young Lin, Seoul, Korea), respectively. 2.3. Kinetic adsorption test Kinetic batch tests were also performed to evaluate the adsorption capacity of alginate complex for each type of contaminants. Tests were initiated by placing 42 g of complex beads in 840 ml mixed solution (250 mg/L of aqueous zinc and toluene, respectively) in 1 L glass flask and allowed to react in an air shaker. After reaction, aqueous samples were analyzed at pre-determined times. 2.4. Modeling of kinetic adsorption
neous) and the Type-2 (kinetic), a is mass transfer rate from solution to Type-2 site, and b is defined as a limiting factor for S2(1) with its range 0 < b 6 1. The relative concentration curve (C/C0) of the aqueous phase versus time is characterized by four parameters, n1, n2, c; and b, where n1 and n2 are the relative fraction of mass adsorbed at Type-1 and Type-2 sites, respectively. 3. Results and discussion 3.1. Equilibrium adsorption The adsorption isotherms of various adsorbents for zinc obtained from the equilibrium batch tests are shown in Fig. 1. All of the isotherms resulted in a nonlinear curve with an asymptotic increase and therefore was fitted with the Langmuir adsorption model. Among the curves, GAC showed the lowest adsorption capacity while AG–AC bead exhibited a higher adsorption than GAC. This would be due to the contribution of alginate for adsorption of heavy metals since as a polysaccharide biopolymer it is well known to have a significantly high affinity to divalent metal ions [12]. The adsorption isotherm of zeolite showed a sharp increase of adsorbed concentration in the lower range of equilibrium concentration but it reached maximum capacity about 200 mg/L, whereas that of alginate complex extended the maximum capacity to a much higher value. This indicates that the binding energy (a) of zeolite for zinc seems to be very high compared to others since the steepness of the curve represents the extent of the binding energy (Table 1). In general, the highest adsorption capacity of alginate complex among the adsorbents is due to the contribution from the relatively high binding energy of zeolite in the low concentration range and the relatively high adsorption capacity of alginate in the high concentration range. The maximum adsorption capacity (b) of alginate complex was found to be 4.3 g/kg which is higher than those of any other adsorbents used in this study. This value is also higher than the values of 0.50 g/kg [13] and 2.70 g/kg [14] for adsorption capacity of natural zeolite clinoptilolite but slightly lower than that of 5.50 g/kg [14] for adsorption capacity of natural zeolite chabazite reported in the literature. The adsorption isotherm for toluene is shown in Fig. 2. Contrary to the case of zinc, zeolite showed the least adsorption capacity for toluene although its capacity was higher than that of GAC for zinc. GAC and AG–AC bead showed a similar capacity for toluene. This would be due to the role of activated carbon in adsorption of toluene. It is remarkable that the alginate complex showed the highest
In order to compare the adsorption capacity for different adsorbents (Alginate complex, zeolite, GAC, AG–AC bead), both equilibrium and kinetic adsorption models were used by introducing the Langmuir adsorption isotherm model (Eq. (1)) and three-stage kinetic model (Eq. (2)) [11] developed for adsorption of aqueous benzene as follows:
abC 1 þ aC
ð1Þ
where S and C are the adsorbed and aqueous concentrations, and a and b are the constants related with binding energy (L/mg) and the maximum adsorption capacity (mg/kg).
CðtÞ ð1 n1 Þð1 n1 bn2 Þ ¼ C0 ð1 n1 bn2 exp½ctÞ MS1 ð1Þ MS2 ð1Þ ; n2 ¼ ; n1 ¼ VC 0 VC 0
AG-AC bead GAC Zeolite Alginate complex
3000
C*(mg/kg)
S¼
4000
2000
1000
ð2Þ
c¼
ð1 n1 bn2 Þa bn2
ð3Þ
where C(t) and C0 is the aqueous concentrations at time t and initial stage, V is the solution volume, M is the mass of adsorbent, S1 ð1Þ and S2 ð1Þ are the adsorbed concentrations for the Type-1 (instanta-
0 0
200
400
600
800
1000
Ceq (mg/l) Fig. 1. Adsorption of zinc fitted with Langmuir isotherm on AG–AC beads, GAC, zeolite, alginate complex.
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J.-W. Choi et al. / Current Applied Physics 9 (2009) 694–697
Table 1 Adsorption constants of Langmuir isotherm for zinc and toluene Parameter
AG–AC bead
Zinc Toluene
GAC
Zeolite
Alginate complex
a (L/mg)
b (g/kg)
a (L/mg)
b (g/kg)
a (L/mg)
b (g/kg)
a (L/mg)
b (g/kg)
0.2 102 1.4 102
3.8 9.7
0.4 103 1.1 102
2.0 1.0
3.4 102 0.2 102
2.7 10.1
1.2 102 1.6 102
4.3 13.0
Table 2 Adsorption parameters of three-stage kinetic model (Eq. (2)) for zinc and toluene
Zinc Toluene
Fig. 2. Adsorption of toluene fitted with Langmuir isotherm on AG–AC beads, GAC, zeolite, alginate complex beads.
capacity (b = 13.0 g/kg) due to the contribution from both activated carbon and zeolite (Table 1). This value is lower than that (b = 122– 257 g/kg) obtained for treated activated carbon F-400Cox and F400Tox [10]. The much lower value of maximum capacity obtained in this study is due to the fact that only 0.16 g (one fiftieth) of activated carbon was contained in the complex bead of 8 g used in the batch test and even only the surface region of this portion can contribute to adsorption. 3.2. Kinetic adsorption The relative concentration of zinc and toluene as a function of time is shown in Fig. 3 when the mixed contaminants were allowed to simultaneously react with alginate complex and the re-
Relative concentration (C/C0)
1.2
Toluene Zinc
1.0
0.8
0.6
0.4
n1
n2
a
b
Removal rate (%)
0.07 0.06
0.92 0.93
7.7 8.2
0.51 0.86
54 86
lated parameters of three-stage kinetic model (Eq. (2)) are shown in Table 2. In general, two contaminants showed three distinct stages of adsorption; instantaneous, gradual and constant stage [11]. Overall removal rate of zinc amounted to 54% of which 7% was removed by instantaneous adsorption via surface exterior site while that of toluene was 86% with removal rate of 6% at the initial stage during 4d-reaction (Table 2). This indicates that more mass of aqueous toluene was removed via adsorption at the interior site. Based on these data, adsorption capacities of complex bead for zinc and toluene could be calculated for a given adsorbent-to-adsorbate ratio (1:20 for zinc and toluene). They were 2.7 g/kg, 4.3 g/kg on a bead basis, and 135 g/kg, 215 g/kg on each single material of zeolite and activated carbon, respectively. Adsorption capacity of these values for zinc is much higher than those from the literature and that for toluene approaches well the literature value given above. 4. Conclusions This study aimed at developing a new adsorbent for removing both organic and inorganic contaminants from solution. Batch type experiments were performed to test the adsorption capacity of newly developed alginate complex beads consisting of synthetic zeolite and powdered activated carbon. The following conclusions could be drawn from the experimental investigation: (1) The alginate complex beads developed in this study could remove simultaneously zinc and toluene from aqueous solution. (2) Maximum adsorption capacity of alginate complex for zinc and toluene obtained from Langmuir adsorption isotherm fitted to the equilibrium batch data was 4.3 g/kg and 13.0 g/kg, respectively, which were comparable with literature values. (3) Removal rates of alginate complex for zinc and toluene obtained from kinetic batch test were 54% and 86% of which about 90% occurred in a form of adsorption via interior site. (4) Adsorption capacity for zinc and toluene by kinetic test revealed that 135 g and 215 g could be removed per each kg of zeolite and activated carbon, indicating that the complex beads developed in this study can be utilized for treatment of wastewater containing both organic and inorganic chemical compounds.
0.2
0.0 0
1
2
3
Acknowledgements 4
Time (day) Fig. 3. Adsorption of zinc and toluene on alginate complex beads fitted with kinetic adsorption model (Eq. (2)).
This work was supported by Korea University Grant and by the Korea Ministry of Education, Science and Technology (NRL Program R0A-2008-000-20066-0 and KRF-2007-314-C00129).
J.-W. Choi et al. / Current Applied Physics 9 (2009) 694–697
References [1] [2] [3] [4] [5] [6] [7]
G. McKay, H.S. Blair, A. Findon, Ind. J. Chem. 28A (1989) 356. C.P. Huang, Y.C. Jung, M.R. Liu, J. Hazard. Mater. 45 (1996) 265. V.J. Inglezakis, H. Grigoropoulou, J. Hazard. Mater. B 112 (2004) 37. A.H. Oren, A. Kaya, J. Hazard. Mater. B 131 (2006) 59. A.M. El-Kamash, A.A. Zaki, M.A.E. Gellel, J. Hazard. Mater. B 127 (2005) 211. T. Undaybeytia, E. Morillo, C. Maqueda, Clays Clay Miner. 31 (1996) 485. S. Babel, T.A. Kurniawan, J. Hazard. Mater. B 97 (2003) 219.
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[8] M.W. Jung, K.H. Ahn, Y. Lee, K.P. Kim, J.S. Rhee, J.T. Park, K.J. Paeng, Microchem. J. 70 (2001) 123. [9] A.A.M. Daifullah, B.S. Girgis, Colloids Surf. 214 (2003) 181. [10] N. Wibowo, L. Setyadhi, D. Wibowo, J. Setiawan, S. Ismadji, J. Hazard. Mater. 146 (2007) 237. [11] J.W. Choi, N.C. Choi, S.J. Lee, D.J. Kim, J. Colloid Interface Sci. 314 (2007) 367. [12] T. Gotoh, K. Matsushima, K.I. Kikuchi, Chemosphere 55 (2004) 135. [13] M.J. Zamzow, B.R. Eichbaum, Sep. Sci. Technol. 25 (1990) 1555. [14] S.K. Ouki, M. Kavanagh, Waste Manage. Res. 15 (1997) 383.
Contents lists available at ScienceDirect
Current Applied Physics journal homepage: www.elsevier.com/locate/cap
Adsorption of zinc and toluene by alginate complex impregnated with zeolite and activated carbon Jae-Woo Choi a, Ki-Seok Yang b, Dong-Ju Kim a,*, Cheol Eui Lee c a
Department of Earth and Environmental Sciences, Korea University, Seoul 136-713, Republic of Korea SK Gas Corporation, Seoul 110-110, Republic of Korea c Department of Physics and Institute for Nano Science, Korea University, Seoul 136-713, Republic of Korea b
a r t i c l e
i n f o
Article history: Received 2 June 2008 Accepted 4 June 2008 Available online 24 June 2008 Keywords: Adsorption Alginate complex Zinc Toluene Removal efficiency
a b s t r a c t In this study, a novel alginate complex was developed for removal of mixed contaminants containing both organic and inorganic compounds. The alginate complex was generated by impregnating synthetic zeolite and powdered activated carbon (PAC) into alginate gel bead. The adsorption of zinc and toluene as target contaminants onto the alginate complex was investigated by performing both equilibrium and kinetic batch tests. Equilibrium tests showed that adsorption of two contaminants followed Langmuir isotherm and that the alginate complex was capable of removing zinc (maximum binding energy b = 4.3 g/kg) and toluene (b = 13.0 g/kg) best compared to other adsorbents such as granular activated carbon (GAC), zeolite, and alginate impregnated with PAC (AG–AC bead). These values were higher than those of any other adsorbents for each contaminant. It was further revealed from kinetic tests that removal efficiency of zinc and toluene was 54% and 86% for the initial solution concentrations of 250 mg/L, respectively. This indicates that the alginate complex developed in this study can be used as promising adsorbents for simultaneous removal of organic and inorganic compounds from industrial wastewater or groundwater containing mixed contaminants. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction Industrial wastewater often contains both organic and inorganic compounds such as aromatic hydrocarbons and heavy metals since the latter comes from industrial use of organic compounds containing metal additives in the petroleum and organic chemical industries. Heavy metal ions should be removed from wastewater before disposal since they are highly toxic even at low concentrations and therefore sources of great concern in aquatic environment. Aromatic compounds such as toluene are used as raw materials in many chemical productions and solvents in manufacturing processes. These compounds are carcinogenic and their presence in water stream even at low concentrations poses significant environmental risks. So far a considerable effort has been made for removal of these compounds. For instance, removal of heavy metals was attempted using various adsorbents such as chitosan [1,2], zeolite [3–5], and clay [6] among which zeolite was found the cost efficient adsorbent [7]. For removal of aromatic compounds, many attempts were made via adsorption process using various adsorbents. To date the most widely used adsorbent is activated carbon for removal of organic compounds such as phenol, benzene and toluene. Adsorption of phenol [8], benzene and * Corresponding author. Tel.: +82 2 3290 3177; fax: +82 2 3290 3189. E-mail address: [email protected] (D.-J. Kim). 1567-1739/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2008.06.008
toluene [9,10] on activated carbon was studied to investigate the structure of activated carbon. However, for simultaneous removal of both organic and inorganic compounds from industrial wastewater, complex adsorbents other than these materials are needed. Therefore in this study we attempted to develop a new adsorbent, alginate gel bead impregnated with zeolite and activated carbon for removal of mixed industrial contaminants. In order to examine the adsorption capacity of the alginate complex, both equilibrium and kinetic batch studies were performed. 2. Materials and methods 2.1. Preparation of alginate complex beads All chemicals of sodium alginate, granular activated carbon (GAC), powdered activated carbon (PAC) and calcium chloride were obtained from Sigma Aldrich, Korea except for synthetic zeolite which was purchased from Jishim tech. Korea. The type of synthetic zeolite was zeolite A that exhibits the LTA (Linde Type A) structure. It has a three-dimensional pore structure with pores running perpendicular to each other in the x, y, and z planes, and is made of secondary building units 4, 6, 8, and 4–4. The pore diameter is 4.2 Å and defined by an eight member oxygen ring. This leads into a larger cavity of minimum free diameter 11.4 Å. The cavity is surrounded by eight sodalite cages (truncated octahedra)
695
J.-W. Choi et al. / Current Applied Physics 9 (2009) 694–697
connected by their square faces in a cubic structure. The unit cell is symmetry. Zeolite A has a void volcubic (a = 24.61 Å) with Fm3c ume fraction of 0.47, with a Si/Al ratio of 1.0. It thermally decomposes at 700 °C. Formation of alginate complex is as follows. First, 5.0% sodium alginate solution was prepared by mixing 20 g of sodium alginate powder with 400-mL distilled water. After adding 4 g of each PAC and zeolite into 400-mL alginate solution, homogeneous mixing was performed for 20 h to yield 1% (w/v) alginate solution mixed with activated carbon and zeolite. The 1% alginate solution contained in a burette was then allowed to drop into a solution of 4% CaCl2 (500 mL) solution and thus forming 200 g of 4-mm spherical alginate complex beads. In order to compare with other type of alginate bead, alginate bead impregnated with powdered activated carbon only (AG–AC bead) was also formed using the same procedure except for addition of 4 g of zeolite to alginate solution. 2.2. Equilibrium adsorption test In order to determine the adsorption capacity of the alginate complex, and compare with those of other existing adsorbents such as granular activated carbon, zeolite and AG–AC bead, equilibrium batch tests were conducted. Twenty gram of complex beads and other adsorbents was allowed to react with each 80 mL of Zn(SO4)2 solutions (pH 6.7–6.8) with various initial zinc concentrations (50, 100, 300, 500, 700, 1000 mg/L) in 125 mL wide neck bottle using air shaker (140 rpm, 32 °C). For toluene adsorption, 280 ml solutions of five different initial concentrations (50, 100, 200, 500, 700 mg/L) were used to react with 8 g of adsorbents. At equilibrium (48 h), zinc and toluene solutions were analyzed by ICP-OES (Optima 2000 DV, Massachusetts) and HPLC (Young Lin, Seoul, Korea), respectively. 2.3. Kinetic adsorption test Kinetic batch tests were also performed to evaluate the adsorption capacity of alginate complex for each type of contaminants. Tests were initiated by placing 42 g of complex beads in 840 ml mixed solution (250 mg/L of aqueous zinc and toluene, respectively) in 1 L glass flask and allowed to react in an air shaker. After reaction, aqueous samples were analyzed at pre-determined times. 2.4. Modeling of kinetic adsorption
neous) and the Type-2 (kinetic), a is mass transfer rate from solution to Type-2 site, and b is defined as a limiting factor for S2(1) with its range 0 < b 6 1. The relative concentration curve (C/C0) of the aqueous phase versus time is characterized by four parameters, n1, n2, c; and b, where n1 and n2 are the relative fraction of mass adsorbed at Type-1 and Type-2 sites, respectively. 3. Results and discussion 3.1. Equilibrium adsorption The adsorption isotherms of various adsorbents for zinc obtained from the equilibrium batch tests are shown in Fig. 1. All of the isotherms resulted in a nonlinear curve with an asymptotic increase and therefore was fitted with the Langmuir adsorption model. Among the curves, GAC showed the lowest adsorption capacity while AG–AC bead exhibited a higher adsorption than GAC. This would be due to the contribution of alginate for adsorption of heavy metals since as a polysaccharide biopolymer it is well known to have a significantly high affinity to divalent metal ions [12]. The adsorption isotherm of zeolite showed a sharp increase of adsorbed concentration in the lower range of equilibrium concentration but it reached maximum capacity about 200 mg/L, whereas that of alginate complex extended the maximum capacity to a much higher value. This indicates that the binding energy (a) of zeolite for zinc seems to be very high compared to others since the steepness of the curve represents the extent of the binding energy (Table 1). In general, the highest adsorption capacity of alginate complex among the adsorbents is due to the contribution from the relatively high binding energy of zeolite in the low concentration range and the relatively high adsorption capacity of alginate in the high concentration range. The maximum adsorption capacity (b) of alginate complex was found to be 4.3 g/kg which is higher than those of any other adsorbents used in this study. This value is also higher than the values of 0.50 g/kg [13] and 2.70 g/kg [14] for adsorption capacity of natural zeolite clinoptilolite but slightly lower than that of 5.50 g/kg [14] for adsorption capacity of natural zeolite chabazite reported in the literature. The adsorption isotherm for toluene is shown in Fig. 2. Contrary to the case of zinc, zeolite showed the least adsorption capacity for toluene although its capacity was higher than that of GAC for zinc. GAC and AG–AC bead showed a similar capacity for toluene. This would be due to the role of activated carbon in adsorption of toluene. It is remarkable that the alginate complex showed the highest
In order to compare the adsorption capacity for different adsorbents (Alginate complex, zeolite, GAC, AG–AC bead), both equilibrium and kinetic adsorption models were used by introducing the Langmuir adsorption isotherm model (Eq. (1)) and three-stage kinetic model (Eq. (2)) [11] developed for adsorption of aqueous benzene as follows:
abC 1 þ aC
ð1Þ
where S and C are the adsorbed and aqueous concentrations, and a and b are the constants related with binding energy (L/mg) and the maximum adsorption capacity (mg/kg).
CðtÞ ð1 n1 Þð1 n1 bn2 Þ ¼ C0 ð1 n1 bn2 exp½ctÞ MS1 ð1Þ MS2 ð1Þ ; n2 ¼ ; n1 ¼ VC 0 VC 0
AG-AC bead GAC Zeolite Alginate complex
3000
C*(mg/kg)
S¼
4000
2000
1000
ð2Þ
c¼
ð1 n1 bn2 Þa bn2
ð3Þ
where C(t) and C0 is the aqueous concentrations at time t and initial stage, V is the solution volume, M is the mass of adsorbent, S1 ð1Þ and S2 ð1Þ are the adsorbed concentrations for the Type-1 (instanta-
0 0
200
400
600
800
1000
Ceq (mg/l) Fig. 1. Adsorption of zinc fitted with Langmuir isotherm on AG–AC beads, GAC, zeolite, alginate complex.
696
J.-W. Choi et al. / Current Applied Physics 9 (2009) 694–697
Table 1 Adsorption constants of Langmuir isotherm for zinc and toluene Parameter
AG–AC bead
Zinc Toluene
GAC
Zeolite
Alginate complex
a (L/mg)
b (g/kg)
a (L/mg)
b (g/kg)
a (L/mg)
b (g/kg)
a (L/mg)
b (g/kg)
0.2 102 1.4 102
3.8 9.7
0.4 103 1.1 102
2.0 1.0
3.4 102 0.2 102
2.7 10.1
1.2 102 1.6 102
4.3 13.0
Table 2 Adsorption parameters of three-stage kinetic model (Eq. (2)) for zinc and toluene
Zinc Toluene
Fig. 2. Adsorption of toluene fitted with Langmuir isotherm on AG–AC beads, GAC, zeolite, alginate complex beads.
capacity (b = 13.0 g/kg) due to the contribution from both activated carbon and zeolite (Table 1). This value is lower than that (b = 122– 257 g/kg) obtained for treated activated carbon F-400Cox and F400Tox [10]. The much lower value of maximum capacity obtained in this study is due to the fact that only 0.16 g (one fiftieth) of activated carbon was contained in the complex bead of 8 g used in the batch test and even only the surface region of this portion can contribute to adsorption. 3.2. Kinetic adsorption The relative concentration of zinc and toluene as a function of time is shown in Fig. 3 when the mixed contaminants were allowed to simultaneously react with alginate complex and the re-
Relative concentration (C/C0)
1.2
Toluene Zinc
1.0
0.8
0.6
0.4
n1
n2
a
b
Removal rate (%)
0.07 0.06
0.92 0.93
7.7 8.2
0.51 0.86
54 86
lated parameters of three-stage kinetic model (Eq. (2)) are shown in Table 2. In general, two contaminants showed three distinct stages of adsorption; instantaneous, gradual and constant stage [11]. Overall removal rate of zinc amounted to 54% of which 7% was removed by instantaneous adsorption via surface exterior site while that of toluene was 86% with removal rate of 6% at the initial stage during 4d-reaction (Table 2). This indicates that more mass of aqueous toluene was removed via adsorption at the interior site. Based on these data, adsorption capacities of complex bead for zinc and toluene could be calculated for a given adsorbent-to-adsorbate ratio (1:20 for zinc and toluene). They were 2.7 g/kg, 4.3 g/kg on a bead basis, and 135 g/kg, 215 g/kg on each single material of zeolite and activated carbon, respectively. Adsorption capacity of these values for zinc is much higher than those from the literature and that for toluene approaches well the literature value given above. 4. Conclusions This study aimed at developing a new adsorbent for removing both organic and inorganic contaminants from solution. Batch type experiments were performed to test the adsorption capacity of newly developed alginate complex beads consisting of synthetic zeolite and powdered activated carbon. The following conclusions could be drawn from the experimental investigation: (1) The alginate complex beads developed in this study could remove simultaneously zinc and toluene from aqueous solution. (2) Maximum adsorption capacity of alginate complex for zinc and toluene obtained from Langmuir adsorption isotherm fitted to the equilibrium batch data was 4.3 g/kg and 13.0 g/kg, respectively, which were comparable with literature values. (3) Removal rates of alginate complex for zinc and toluene obtained from kinetic batch test were 54% and 86% of which about 90% occurred in a form of adsorption via interior site. (4) Adsorption capacity for zinc and toluene by kinetic test revealed that 135 g and 215 g could be removed per each kg of zeolite and activated carbon, indicating that the complex beads developed in this study can be utilized for treatment of wastewater containing both organic and inorganic chemical compounds.
0.2
0.0 0
1
2
3
Acknowledgements 4
Time (day) Fig. 3. Adsorption of zinc and toluene on alginate complex beads fitted with kinetic adsorption model (Eq. (2)).
This work was supported by Korea University Grant and by the Korea Ministry of Education, Science and Technology (NRL Program R0A-2008-000-20066-0 and KRF-2007-314-C00129).
J.-W. Choi et al. / Current Applied Physics 9 (2009) 694–697
References [1] [2] [3] [4] [5] [6] [7]
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