Ind. Eng. Chem. Res. 2009, 48, 3261–3267
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APPLIED CHEMISTRY Synthesis of N-Methylimidazolium Functionalized Strongly Basic Anion Exchange Resins for Adsorption of Cr(VI) Lili Zhu,†,‡ Yinghui Liu,†,‡ and Ji Chen*,† Key laboratory of Rare Earth Chemistry and Physics, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China, and Graduate School of Chinese Academy of Sciences, Beijing 100049, China
N-Methylimidazolium functionalized strongly basic anion exchange resins in the Cl- form (RCl) and SO42form (R2SO4) were synthesized and employed for adsorption of Cr(VI) from aqueous solution. FT-IR and elementary analysis proved the structures of anion exchange resins and the content of functional groups. The gel-type strongly basic anion exchange resins had high thermal stability according to TGA and good chemical stability under the experimental conditions. The adsorption behaviors of Cr(VI) on RCl and R2SO4 were studied using the batch technique. It was shown that adsorption equilibrium was reached rapidly within 60 min. The adsorption data for RCl and R2SO4 were consistent with the Langmuir isotherm equation. The maximum adsorption capacities of RCl and R2SO4 were 132 and 125 mg/g, respectively, with almost all active sites fully occupied. RCl and R2SO4 could be used in the wide pH range 1-12 and were very suitable to remove Cr(VI) at a low concentration level. They also showed great preference to Cr(VI) compared to the other counterions. RCl was easily regenerated using the mixed solution of 0.3 mol/L NaOH and 0.3 mol/L NaCl, and retained nearly 100% of its orginal capacity during four cycles. 1. Introduction Chromium is a metal that requires much attention to deal with it in wastewater and solid waste treatment. The effluents of many industries, such as those of tanning, electroplating, paints, textiles, dyes, fertilizers, and photography contain hexavalent chromium, Cr(VI). As we known, Cr(VI) compounds are toxic pollutants in water and soil, suspected carcinogenic materials, and very harmful to human health. Compared to other toxic heavy metals, Cr(VI) oxyanions are quite soluble in the aqueous phase over almost the entire pH range and mobile in the natural environment.1,2 Therefore, Cr(VI) is often found as a contaminant in water and needs to be treated to reduce and eliminate it. In many cases, the concentration of Cr(VI) in wastewater was low or trace, generally lower than 100 mg/L, with high concentration of counterions, such as Cr(VI)containing cooling water 5-20 mg/L,3 plating wastewater 47 mg/L,4 contaminated groundwater from a shallow aquifer 95 mg/L,5 and drinking water 0.5-3.0 mg/L.6 The traditional methods to remove Cr(VI) from aqueous solutions are chemical precipitation, reduction, liquid-liquid extraction, adsorption, and ion exchange. Currently, a wide range of cost-effective biosorbents7-9 has been used. However, the biosorbents, in their natural form, are soft and easy to agglomerate or to form a gel, and the binding sites are not readily available for adsorption.7 Another problem is the regeneration and recovery of useful materials making them unattractive for wide commercial applications.10 Imidazole functionalized sol-gel adsorbent11 and the modified mesoporous SBA-15 containing amino and imidazole groups12,13 were also reported for separa* To whom correspondence should be addressed. Tel.: +86 431 8526 2646. Fax: +86 431 8526 2646. E-mail:
[email protected]. † Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. ‡ Graduate School of Chinese Academy of Sciences.
tion of Cr(VI) from aqueous solution. These adsorbents could be regarded as weakly basic ion exchangers, which showed strong affinity to Cr(VI) at pH 2 but had a very low adsorption amount at neutral and basic pH values for the demand of protonation. Ion exchange technology has been widely used for various separation processes and is recognized as an efficient and simple method to remove Cr(VI) from water.1,14-16 The main advantages of ion exchange are high selectivity to Cr(VI) compared to other counterions, less sludge volume produced, and recovery of metal of value and reused.14 Moreover, there is no functional group or extractant loss compared to solvent extraction.17 Weakly basic anion exchange resins can only remove Cr(VI) at acidic pH values, but strongly basic anion exchange resins can remove Cr(VI) in the entire pH range, which fits better the process in practice. Various structures of strongly basic anion exchangers including quarternary amines and pyridine structures were studied.2,18-20 In recent years, ionic liquids have been studied extensively as alternative green solvents in separation processes.21-25 In order to overcome some drawbacks of ionic liquids, such as high viscosity, large amounts used, and difficulties of separation and recovery, ionic liquids were supported on solid supports.26-30 Generally, the cationic parts of ionic liquids, such as alkylimidazole, were supported on resins or silica supports via covalent bonds. The new supported ionic liquids with imidazole groups or zwitterionic imidazolium chloride could be regarded as a new type of anion exchangers. They have the ability to adsorb inorganic or organic anions from aqueous solution. For example, N-methylimidazolium anion exchange stationary phase based on N-methylimidazolium immobilized on silica was used for high-performance liquid chromatographic separations of inorganic anions.31
10.1021/ie801278f CCC: $40.75 2009 American Chemical Society Published on Web 02/17/2009
3262 Ind. Eng. Chem. Res., Vol. 48, No. 7, 2009
Figure 1. Schematic illustration of the preparation of RCl and R2SO4.
In this paper, we synthesized polymer supported ionic liquids by successfully anchoring N-methylimidazole on Merrifield resins. The modified resins with different anionic forms were examined as strongly basic anion exchange resins for adsorption of Cr(VI) from aqueous solution. These resins could adsorb Cr(VI) in the entire pH range, superior to imidazole functionalized adsorbents,11-13 which were most effective only at acidic pH values. Moreover, almost all exchange sites of the anion exchange resins were easily accessible with high adsorption capacity even at low Cr(VI) concentration. Their adsorption rates were relatively rapid, and the resins were easily regenerated. The resins showed great preference to Cr(VI) over the other competing ions, and the polymer supported Cr(VI) ion containing ionic liquid was obtained after exchange. The factors that influenced the adsorption capacity and adsorption equilibrium were also investigated. 2. Experimental Section 2.1. Reagents. Merrifield resin (3.5 mmol of Cl/g, 1% DVB, 200-400 mesh) was purchased from Tianjin Nankai Hecheng Science & Technology Co., Ltd. (China). N-Methylimidazole was purchased from Aldrich (USA). The stock solution of Cr(VI) was prepared from potassium dichromate (K2Cr2O7) of primary standard grade. The other chemicals were analytical grade reagents. 2.2. Methods. Fourier transform infrared (FT-IR) analysis was conducted with a Bruker VECT OR 22/N spectrometer (Germany). Thermogravimetric analysis (TGA) was determined by a thermal analysis instrument (SDTQ600, TA Instruments, USA) from room temperature to 800 °C in air at a heating rate of 10 °C min-1. Elementary analysis was performed by VarioEL. The concentrations of anions were determined by ion chromatography (Dionex ICS-1500). UV-visible spectra were measured with a Shimadzu UVmini-1240 spectrophotometer. 2.3. Synthesis of the Strongly Basic Anion Exchange Resins. The synthesis route proceeded according to the modified method.32 A 5.0 g sample of Merrifield resin in 30 mL of DMF was stirred for 2 h. Then, 1.65 g of N-methylimidazole was added and the mixture was stirred for no less than 36 h at 80 °C. The resin was filtered and washed with ethanol. The resin in 30 mL of ethanol was stirred for another 24 h at 65 °C. The resin was filtered and dried in a vacuum to afford N-methylimidazolium functionalized anion exchange resin in the Cl- form denoted as RCl. A schematic illustration of the preparation procedure is shown in Figure 1. The N-methylimidazolium functionalized anion exchange resin in the SO42- form was denoted as R2SO4. It was prepared by shaking RCl with 1 mol/L Na2SO4 solution. This procedure was repeated three times, and nearly no Cl- was determined in the aqueous phase by ion chromatography. The R2SO4 resin was filtrated and washed with deionized water many times to remove excessive SO42-. The chemical stability of RCl was studied by contacting 0.1 g of RCl with 5 mL of different aggressive media including 0.1 mol/L HCl (pH 1.0), 0.01 mol/L NaOH (pH 12.0), 1 mol/L NaOH, and 10 wt % H2O2 at 50 °C for 24 h, respectively. After contact, the resin was centrifuged and washed with deionized
water. Then the resin was regenerated with 2 wt % HCl, followed by washing with deionized water to remove excessive acid. The adsorption capacity loss was determined by contacting 0.01 g of treated resin with 15 mL of 100 mg/L Cr(VI) solution and shaking for 1 h. 2.4. Adsorption Studies Using Batch Method. The sorption kinetics experiments were carried out by shaking 0.01 g of dried resin (RCl or R2SO4) and 15 mL of Cr(VI) solution at the initial concentration of 100 mg/L for different time intervals from 10 to 150 min. The concentration of Cr(VI) was determined spectrophotometrically by the diphenylcarbazide (DPC) method.33 The amount of adsorbed Cr(VI) was calculated by a mass balance between the initial and equilibrium concentrations. The effect of pH on the uptake of Cr(VI) was studied by contacting 0.01 g of dried resin and 15 mL of Cr(VI) solution (100 mg/L) at pH 1-12 and shaking for 1 h. To adjust the pH, 1 mol/L HCl and 1 mol/L NaOH were used. The adsorption isotherm experiments were determined by placing 0.01 g of dried resin and 15 mL of Cr(VI) with desired concentrations (50-160 mg/L) and shaking for 1 h. The effect of counterions (Cl-, SO42-, NO3-) on the adsorption of Cr(VI) was carried out at initial Cr(VI) concentration of 100 mg/L. The solutions of NaCl, Na2SO4, and NaNO3 were used at different concentrations from 0 to 100 mmol/L. The adsorption experiments were carried out by shaking 0.01 g of dried resin and 15 mL of Cr(VI) solution containing Cl-, SO42-, or NO3-, respectively. 2.5. Resin Regeneration and Reusability. A 0.1 g sample of RCl was shaken with 85 mL of a Cr(VI) solution of 100 mg/L for 1 h to reach equilibrium. The Cr(VI)-loaded RCl resin (mainly RHCrO4) was separated by filtration and rinsed with a small quantity of deionized water to remove the unsorbed Cr(VI). The Cr(VI)-loaded RCl resin was dried at 60 °C in a vacuum for 24 h. Then 0.01 g of dried Cr(VI)-loaded RCl resin was shaken with 15 mL of NaCl, NaOH, or their mixed solution for 1 h. The amount of released Cr(VI) was also determined by the diphenylcarbazide (DPC) method.33 A 0.01 g sample of RCl was shaken with 15 mL of a Cr(VI) solution of 100 mg/L for 1 h. The Cr(VI)-loaded RCl resin was centrifuged and regenerated by 15 mL of 0.3 mol/L NaOH and 0.3 mol/L NaCl mixed solution, and washed with deionized water. Then it was equilibrated with 15 mL of 2.0 wt % hydrochloric acid. The resin was washed with deionized water to remove excessive acid and dried at 60 °C. Then 0.01 g of regenerated RCl was shaken with 15 mL of a Cr(VI) solution of 100 mg/L for 1 h in the next cycle. The adsorption/desorption operation was repeated four times. All adsorption experiments were studied at an initial pH of Cr(VI) solution prepared without change (pH 4.6) except for the pH experiment, and each experiment was carried out at 25 °C. All batch experiments were conducted in duplicate under the same conditions, and the relative error between duplicates was less than 5%. The results were reported as mean values. 3. Results and Discussion 3.1. Characterization of the Strongly Basic Anion Exchange Resins. The anion exchange resin in the Cl- form (RCl) was synthesized by successfully anchoring N-methylimidazole on the Merrifield resin. The SO42- ionic form anion exchange resin (R2SO4) was attained by contacting RCl with 1 mol/L Na2SO4 solution. The FT-IR spectra of RCl, R2SO4, and Merrifield resin are shown in Figure 2. The characteristic band at 1263 cm-1, -CH2- bending vibration of -CH2Cl, is found in the Merrifield resin but not found in RCl and R2SO4. The
Ind. Eng. Chem. Res., Vol. 48, No. 7, 2009 3263
Figure 2. FT-IR spectra of (a) Merrifield resin, (b) RCl, and (c) R2SO4.
the resins. According to elementary analysis of RCl (74.26 wt % C, 7.22 wt % N, 6.44 wt % H), the content of mimCl in RCl was calculated to be 2.58 mmol/g. On the basis of elementary analysis of R2SO4 (67.11 wt % C, 6.46 wt % N, 7.70 wt % H), the content of the methylimidazolium sulfate (mim(SO4)1/2) group in R2SO4 was calculated to be 2.31 mmol/g. The decomposition temperature of RCl and R2SO4 is 220 °C according to thermogravimetric analysis, and they are relatively thermal stable. The chemical stability of RCl was studied by determining the chemical resistance of the ionogenic groups and its general resistance to oxidation.34 RCl had good chemical stability in 0.1 mol/L HCl (pH 1.0), 0.01 mol/L NaOH (pH 12.0), and 10 wt % H2O2, and no adsorption capacity loss was observed. There was some degradation of RCl in 1 mol/L NaOH at 50 °C for 24 h, and about 15% loss of adsorption capacity was observed. That may be due to the Hoffmann degradation of quaternary ammonium hydroxides.34 Some properties and specifications of RCl and R2SO4 are shown in Table 1. 3.2. Adsorption Kinetics of Cr(VI). The scatter plot of Figure 3 shows the effect of shaking time on the removal of Cr(VI) by the resins. The adsorption rates of RCl and R2SO4 for Cr(VI) were very rapid in the first 10 min, and then increased slowly with shaking time. The adsorption equilibriums were attained at 60 min for RCl and 50 min for R2SO4. The pseudo-first-order and pseudo-second-order kinetic models were used to investigate the adsorption kinetic mechanism by fitting the experimental data obtained from the batch method. The pseudo-first-order model of Lagergren35,36 is expressed as log(qe - qt) ) log qe -
Figure 3. Pseudo-first-order and pseudo-second-order kinetic model for Cr(VI) adsorption on RCl and R2SO4. Adsorption conditions: initial Cr(VI) concentration, 100 mg/L; resin amount, 0.01 g; volume of Cr(VI) solution, 15 mL; pH 4.6.
type matrix functional group ionic form decomposition temperature max adsorption capacity (mg/g)
qt ) qe(1 - e-k1t)
(2)
The qe and k1 were calculated by plotting qt versus t. The pseudo-second-order model of Ho37,38 is given as
RCl
R2SO4
strongly basic anion exchange resin gel-type crosslinked polystyrene methylimidazolium Cl220 °C
strongly basic anion exchange resin gel-type crosslinked polystyrene methylimidazolium SO42220 °C
132
(1)
where qt and qe are the amounts of adsorbed Cr(VI) at time t and equilibrium, respectively. k1 is the rate constant of pseudofirst-order adsorption. It can be rearranged as
Table 1. Properties and Specifications of RCl and R2SO4 Anion Exchange Resins resin
k1 t 2.303
t 1 t ) + qt k q 2 qe
where k2 is the rate constant of pseudo-second-order adsorption. It can be rearranged as qt )
125
bands at 1572 and 1160 cm-1 for RCl and 1573 and 1164 cm-1 for R2SO4 are framework vibration and C-H in-plane bending vibration of the imidazolium ring. This indicates that Cl in the Merrifield resin was substituted by zwitterionic methylimidazolium chloride (mimCl) group. The band at 1114 cm-1 for R2SO4 is the characteristic band of SO42-, which implies Clexchanged with SO42-. The broad bands at 3401 cm-1 for RCl and 3413 cm-1 for R2SO4 are the physically adsorbed water of
(3)
2 e
qe2k2t 1 + qek2t
(4)
The qe and k2 were attained by plotting qt versus t. Figure 3 and Table 2 show the fitted results according to the pseudo-first-order and pseudo-second-order models. It could be seen that both the pseudo-first-order and pseudo-second-order models fitted the data well, yielding high regression values. However, the regression value of the pseudo-second-order model was a little higher than that of the pseudo-first-order model. The qe calculated from the pseudo-second-order model fitted the experimental data very well, especially for RCl anion
Table 2. Pseudo-First-Order and Pseudo-Second-Order Kinetic Parameters for Cr(VI) Adsorption on RCl and R2SO4 pseudo first order
pseudo second order
resin
qe (mg g-1)
k1 (min-1)
R2
qe (mg g-1)
k2 (g mg-1 min-1/2)
R2
RCl R2SO4
130 117
0.26 0.19
0.998 0.991
133 122
0.0076 0.0039
0.999 0.998
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exchange resin. Therefore, the pseudo-second-order model could describe the adsorption kinetics of Cr(VI) on RCl and R2SO4 better. 3.3. Effect of pH on Cr(VI) Adsorption. In aqueous solution, Cr(VI) exists in different ionic forms dependent on both total Cr(VI) concentration and pH. Cr(VI) exists in five main forms in aqueous solution, and the equilibrium reactions for different Cr(VI) species are shown as follows:3 H2CrO4 h H+ + HCrO4HCrO4- h H+ + CrO42-
2-
2HCrO4 h Cr2O7
K1 ) 0.16
(5)
K2 ) 3.2 × 10-7
(6)
+ H2O
HCr2O7- h H+ + Cr2O72-
K3 ) 33.1 K4 ) 1.17 2-
(7) (8)
Cr4O132-,
have The other two forms of Cr(VI), Cr3O10 and been reported to exist at concentrations higher than 0.1 mol/L, and their concentrations are too low to be considered under the experimental conditions. The ion fractions of various Cr(VI) species at different pH values and the initial concentration of 100 mg/L are shown in Figure 4, according to the reported counting method.39 At the initial concentration of 100 mg/L and pH range from 1.0 to 6.3, HCrO4- was the dominant Cr(VI) species with an ion fraction higher than 0.6. There was also a small amount of Cr2O72- with the ion fraction from 0.02 to 0.06 in this pH range. When the pH value was lower than 0.8, H2CrO4 was the dominant Cr(VI) species with an ion fraction higher than 0.5. CrO42- dominated with an ion fraction higher than 0.5 when the pH value was above 6.5. The initial pH value of Cr(VI) solution had a strong effect on the adsorption behavior of RCl anion exchange resin, as shown in Figure 5. RCl could adsorb Cr(VI) in the pH range 1-12 due to the strongly basic anion exchange characteristic, and had good chemical stability in this pH range. RCl had an adsorption capacity greater than 100 mg/g in the pH range 1.0-6.3 because HCrO4-, as the dominant Cr(VI) species, would attack RCl and exchange with Cl- at a ratio of 1:1. Maximum adsorption was observed at pH 4.6, the initial pH value of Cr(VI) solution with a total concentration of 100 mg/ L, due to a 0.96 ion fraction of HCrO4- and less competitive anions in the system. H2CrO4 with an ion fraction higher than 0.05 at pH NO3- > SO42- > Cl-. With the anion exchange of RCl, polymer supported ionic liquids with different anion forms could be prepared. The polymer supported ionic liquids had tunable surface characteristics, such as hydrophilicity/hydrophobicity and polarity,43 through varying the length of alkyl chains and anions. RCl had different selectivity orders for anions due to different relative stabilities. RCl and R2SO4 showed a chemical bias toward exchanging HCrO4- preferentially over the other anions because of the lower hydration energy of HCrO4- (∆G° ) -184 kJ/ mol44) than the other counteranions. The resins became more hydrophobic and more stable than that before exchange. They may not be easily accessed by other anions with high hydration energy. Polymer supported Cr(VI) ion containing ionic liquid was obtained. NO3- was more effective in competing with HCrO4- adsorption on the resins than SO42- because NO3- was also a poorly hydrated anion and the hydration energy of NO3-
3266 Ind. Eng. Chem. Res., Vol. 48, No. 7, 2009
Figure 9. Desorption ratio of Cr(VI) from Cr(VI)-loaded RCl resin by different desorption solutions, NaCl, NaOH, and their mixture solution (mol ratio:1:1). Desorption conditions: Cr(VI)-loaded resin amount, 0.01 g; volume of desorption solution, 15 mL; shaking time, 1 h.
(∆G° ) -314 kJ/mol) was lower than that of (∆G° ) -1103 kJ/mol).45 Moreover, the imidazolium ring exhibited strong hydrogen bond interaction between the C2-H of the imidazolium ring and the N of NO3-. 3.6. Resin Regeneration and Reusability. The Cr(VI)loaded anion exchange resins were usually regenerated with NaCl, NaOH, or their mixed solution.15,16,19,46 In order to evaluate the ability of resin regeneration, the Cr(VI)-loaded RCl resin was desorbed by different concentrations of NaCl, NaOH, or their mixed solution. The desorption ratio (%) of Cr(VI) from the resin was calculated from eq 14. SO42-
desorption ratio (%) ) amount of Cr(VI) desorbed to desorption solution × 100 (14) amount of Cr(VI) sorbed on resin The desorption ratios of different concentrations of desorption solutions are shown in Figure 9. The desorption ratio increased with increasing concentration of desorption solution. Under the same conditions, NaOH solutions had a higher desorption ratio than NaCl solutions. However, they could not completely desorb Cr(VI) from the resin even though the concentration was 1 mol/ L. A 0.6 mol/L 1:1 (mol ratio) NaOH and NaCl mixed solution, which was 0.3 mol/L NaOH and 0.3 mol/L NaCl mixed solution, could completely desorb Cr(VI) from Cr(VI)-loaded RCl resin. Therefore, the mixed solution of 1:1 NaOH and NaCl had better desorption ability than individual NaOH and NaCl solutions. The efficiency of resin regeneration was improved because NaOH could transform the resin from the HCrO4- form to the CrO42- form and there was a reversal of selectivity between CrO42- and Cl- at high brine concentration.6,46 To evaluate the reusability of the resin after regeneration, RCl was used successively through four adsorption/desorption cycles. The adsorption amounts of Cr(VI) on RCl were 131, 130, 130, and 131 mg/g, respectively, during the four adsorption cycles. RCl had almost no loss of adsorption amount during four cycles. RCl was stable in multiple adsorption/desorption operations, and could be regenerated and reused repeatedly. 4. Conclusion The polymer supported ionic liquids with methylimidazolium chloride or sulfate functional groups could be regarded as strongly basic anion exchange resins and used for Cr(VI) adsorption from aqueous solution. The structures of anion exchange resins in the Cl- form (RCl) and the SO42- form
(R2SO4) were confirmed. Both resins had good chemical stability and high adsorption capacities in a wide pH range 1-12. They also had high thermal stability. The adsorption equilibriums were achieved rapidly within 60 min for RCl and 50 min for R2SO4. Both the pseudo-first-order and pseudo-second-order kinetic models could describe the adsorption kinetics of Cr(VI) on RCl and R2SO4 well, but the pseudo-second-order model described it better. RCl had the maximum adsorption capacity at pH 4.6. The adsorption data for RCl and R2SO4 were consistent with the Langmuir isotherm equation. The maximum adsorption capacities for RCl and R2SO4 were 132 and 125 mg/g, respectively. Nearly all active sites were easily accessible and fully used. RCl was easily regenerated by a mixed solution of 0.3 mol/L NaOH and 0.3 mol/L NaCl. RCl had almost no loss of adsorption capacity during four cycles. From these results, it could be concluded that both RCl and R2SO4 were possible to be used as effective Cr(VI) adsorbents from aqueous solution. Acknowledgment This project was supported by the National Natural Science Foundation of China (50574080) and the Distinguished Young Scholar Foundation of Jilin Province (20060114). We also thank the anonymous referees for their useful comments. Literature Cited (1) Zhao, D.; SenGupta, A. K.; Stewart, L. Selective Removal of Cr(VI) Oxyanions with a New Anion Exchanger. Ind. Eng. Chem. Res. 1998, 37, 4383. (2) Gode, F.; Pehlivan, E. Removal of Cr(VI) from aqueous solution by two Lewatit-anion exchange resins. J. Hazard. Mater. 2005, 119, 175. (3) Sengupta, A. K.; Clifford, D. Chromate ion exchange mechanism for cooling water. Ind. Eng. Chem. Fundam. 1986, 25, 249. (4) Kumar, R.; Bishnoi, N. R.; Garima; Bishnoi, K. Biosorption of chromium(VI) from aqueous solution and electroplating wastewater using fungal biomass. Chem. Eng. J. 2008, 135, 202. (5) Mukhopadhyay, B.; Sundquist, J.; White, E. Hydro-geochemical controls on removal of Cr(VI) from contaminated groundwater by anion exchange. Appl. Geochem. 2007, 22, 370. (6) Korngold, E.; Belayev, N.; Aronov, L. Removal of chromates from drinking water by anion exchangers. Sep. Purif. Technol. 2003, 33, 179. (7) Boddu, V. M.; Abburi, K.; Talbott, J. L.; Smith, E. D. Removal of Hexavalent Chromium from Wastewater Using a New Composite Chitosan Biosorbent. EnViron. Sci. Technol. 2003, 37, 4449. (8) Park, D.; Yun, Y. S.; Jo, J. H.; Park, J. M. Biosorption process for treatment of electroplating wastewater containing Cr(VI): Laboratory-scale feasibility test. Ind. Eng. Chem. Res. 2006, 45, 5059. (9) Kratochvil, D.; Pimentel, P.; Volesky, B. Removal of trivalent and hexavalent chromium by seaweed biosorbent. EnViron. Sci. Technol. 1998, 32, 2693. (10) Mohan, D.; Singh, K. P.; Singh, V. K. Removal of hexavalent chromium from aqueous solution using low-cost activated carbons derived from agricultural waste materials and activated carbon fabric cloth. Ind. Eng. Chem. Res. 2005, 44, 1027. (11) Park, H. J.; Tavlarides, L. L. Adsorption of Chromium (VI) from Aqueous Solutions Using an Imidazole Functionalized Adsorbent. Ind. Eng. Chem. Res. 2008, 47, 3401. (12) Li, J.; Wang, L.; Qi, T.; Zhou, Y.; Liu, C.; Chu, J.; Zhang, Y. Different N-containing functional groups modified mesoporous adsorbents for Cr(VI) sequestration: Synthesis, characterization and comparison. Microporous Mesoporous Mater. 2008, 110, 442. (13) Li, J.; Qi, T.; Wang, L.; Liu, C.; Zhang, Y. Synthesis and characterization of imidazole-functionalized SBA-15 as an adsorbent of hexavalent chromium. Mater. Lett. 2007, 61, 3197. (14) Rengaraj, S.; Yeon, K. H.; Moon, S. H. Removal of chromium from water and wastewater by ion exchange resins. J. Hazard. Mater. 2001, 87, 273. (15) Gala´n, B.; Castan˜eda, D.; Ortiz, I. Removal and recovery of Cr(VI) from polluted ground waters: A comparative study of ion-exchange technologies. Water. Res. 2005, 39, 4317. (16) Chanda, M.; Rempel, G. L. Selective chromate recovery with quaternized poly(4-vinylpyridine). React. Polym. 1993, 21, 77.
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ReceiVed for reView August 22, 2008 ReVised manuscript receiVed January 7, 2009 Accepted January 9, 2009 IE801278F
