Environ. Sci. Technol. 2005, 39, 4628-4632
Adsorption of Fluoride on Zirconium(IV)-Impregnated Collagen Fiber XUE-PIN LIAO AND BI SHI* The Key Laboratory of Leather Chemistry and Engineering of Ministry of Education, Sichuan University, Chengdu 610065, People’s Republic of China
A novel adsorbent, zirconium(IV)-impregnated collagen fiber, was prepared. Zr(IV) was uniformly dispersed in collagen fiber, mainly through chemical bonds, and was able to withstand the extraction of water. This adsorbent is effective for the removal of fluoride from aqueous solutions. The adsorption capacity was 2.29 mmol/g at pH ) 5.5 when 5.00 mmol/L fluoride solution was adsorbed by use of 0.100 g of adsorbent, and the extent of removal was 97.4% when the adsorbent dose was 0.300 g. The adsorption isotherms were well fitted by the Langmuir equation, and the maximum adsorption capacities calculated by the Langmuir equation were close to those determined by experiment. The adsorption capacity increased with rising temperature. These facts imply that the mechanism of chemical adsorption might be involved in the adsorption process of fluoride on the absorbent and that fluorides are adsorbed in the form of monolayer coverage on the surface of the adsorbent. The adsorption kinetics of fluoride onto Zr(IV)-impregnated collagen fiber could be described by Lagergren’s pseudo-first-order rate mode. The investigation on desorption indicated that this adsorbent is easily regenerated by use of dilute NaOH solution.
Introduction Fluoride pollution in the environment can occur due to natural reasons and human activities. Fluoride frequently exists in minerals and it can be leached out due to erosion by rainwater, thereby allowing it to contaminate ground and surface water. On the other hand, fluoride contamination occurs in a wide range of industrial wastewater produced from aluminum and steel production, metal finishing and electroplating, glass and semiconductor manufacturing, ore beneficiation, and fertilizer operation (1). Fluoride in drinking water may be a double-edged sword depending on its concentration and total amount ingested. The presence of fluorine in drinking water is beneficial to the production and maintenance of healthy bones and teeth when its content is within permissible limits, while excessive intake of fluoride causes dental or skeletal fluorosis, which is a chronic disease manifested by mottling of teeth in mild cases and softening of bones and neurological damage in severe cases (2). According to World Health Organization (WHO) norms, the upper limit of fluoride concentration in drinking water is 0.5-1.0 mg/L (3). The methods of chemical precipitation (4, 5), ion exchange (6), adsorption (7, 8), and electrolysis (9) have been studied * Corresponding author phone: +86-028-85405508; +86-028-85405237; e-mail:
[email protected]. 4628
9
fax:
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 12, 2005
for defluoridation of water. Among these methods, precipitation and adsorption are two important techniques used for fluoride removal from aqueous solution. Precipitation processes with iron, aluminum, calcium, and lanthanum salts have been widely used. The method of precipitation is simple and economical, but the final concentration of fluoride in water greatly depends on the solubility of precipitated fluoride and precipitation reagents and therefore often results in supplementary difficulties of eliminating excess chemicals. Comparatively, adsorption seems to be the most attractive method for the removal of fluoride. Different adsorbents have been successfully used for the removal of fluoride, including activated alumina (7, 8), activated carbon (10, 11), bone charcoal (12), synthetic ion exchangers (6), and other materials (2, 13). Recently, considerable work has been conducted in developing new adsorbents loaded with metal ions for the purpose of adsorptive removal of fluoride (14). The metal ions adsorbed onto porous adsorbents or carrier materials have shown promising results. It has been reported that the adsorption capacity of fluoride on aluminum-impregnated carbon is 3-5 times higher than that of plain activated carbon (15). The extent of removal of fluoride ion by adsorption of lanthanum-impregnated silica gel was more than 99.9% at neutral pH from an initial concentration of 0.55 mmol/L (16). In addition, the adsorbents that use rare earth elements are attracting more and more attention because of their selective affinity to F-, high adsorption capacity, little pollution, and easy operation (17). For example, lanthanum(III)-loaded polymer matrices (18), lanthanum oxide-coated silica gel (19), La3+-impregnated cross-linked gelatin (17), and CeO2-TiO2/SiO2 surface composites were documented and exhibited effectiveness for the removal of fluoride ion. Collagen fiber, an abundant natural biomass, comes from the skin of animals and has been traditionally used as raw material in leather manufacturing. The collagen molecule is composed of three polypeptide chains with triple-helical structure, and they are aggregated through hydrogen bonds to form collagen fiber (20). Collagen fiber is water-insoluble but is a hydrophilic material. According to the principles of leather manufacturing, collagen fiber that has abundant functional groups is capable of chemically reacting with many kinds of metal ions, such as Cr(III), Al(III), Zr(IV), etc. (21). Therefore, collagen fiber is ready to be used as a carrier of metal ions. In the present study, a novel adsorbent was prepared by impregnating zirconium(IV) on collagen fiber, and its adsorption behavior in removing fluoride from water was investigated.
Experimental Procedures Materials. Collagen fiber was prepared according to the procedures in our previous work (22). In brief, bovine skin was cleaned, limed, split, and delimed according to the procedures of leather processing in order to remove noncollagen components. Then the skin was treated with an aqueous solution of acetic acid (concentration 16.0 g/L) three times to remove mineral substances. After the pH of the skin was adjusted to 4.8-5.0 with acetic acid-sodium acetate buffer solution, the skin was dehydrated by absolute ethyl alcohol, dried in a vacuum to moisture content e10.0%, ground, and sieved. As a result, the collagen fiber was obtained with particle size of 0.1-0.25 mm, moisture e12.0%, ash content e0.3%, and pH ) 5.0-5.5. The proper moisture content (8.0-12.0%) is essentially important to the stability of triple-helical structure of collagen. 10.1021/es0479944 CCC: $30.25
2005 American Chemical Society Published on Web 05/10/2005
Zr(SO4)2 was a commercial product (Shichuan Ting Jiang Fine Chemicals Co. Ltd., China), and the content of ZrO2 was 31.5 wt %. The other chemicals were all analytical reagents. Impregnation of Zr(IV) on Collagen Fiber. Collagen fiber (15.0 g) was suspended in 400 mL of distilled water at room temperature for 24 h. The pH of the distilled water was preadjusted to 1.7-2.0 by HCOOH and H2SO4. Then, 20.0 g of Zr(SO4)2 was added and the reaction proceeded at 30 °C with constant stirring for 4 h. The proper amount of NaHCO3 solution (15% w/w) was gradually added within 2 h in order to increase the pH of the solution to 4.0-4.5 and then the reaction proceeded continuously at 40 °C for another 4 h. When the reaction was completed, the product was collected by filtration, washed with distilled water, and vacuum-dried at 50 °C for 12 h, and then the adsorbent of the Zr(IV)impregnated collagen fiber was obtained. The content of Zr(IV) in residual solution after impregnation reaction was determined by means of atomic absorption spectrophotometry (AA7000, Peking East-West Electronic Technology Institute, P. R. China). Effect of pH on Adsorption Capacity. Stock solution of sodium fluoride was prepared with deionized water and further diluted to desired concentrations for practical use. Zr(IV)-impregnated collagen fiber adsorbent (0.100 g) was suspended in 100 mL of F- solution in which the concentration of F- was 5.00 mmol/L. The initial pH values of the F- solutions were adjusted to 3.5-11.4 with 0.1 M NaOH or 0.1 M HNO3. The adsorption experiments were conducted by constant shaking at 303 K for 24 h. At the end of adsorption, the concentration of F- in residual solution was analyzed by fluoride selective electrode determination. The adsorption capacities at different initial pH values were obtained by mass balance calculation. The content of Zr(IV) in residual solutions after adsorption was also determined by means of atomic absorption spectrophotometry. Effect of Adsorbent Dose on Removal Extent of Fluoride. Different dose of adsorbent were suspended in 100 mL F- solutions in which the concentration of F- was 5.00 mmol/L. The adsorption procedures were the same as described for the effect of pH on adsorption capacity. Adsorption Isotherms. Adsorbent (0.100 g) was suspended in F- solutions in which the concentrations of F- were 1.00, 2.00, 3.00, 4.00, and 5.00 mmol/L, respectively. The adsorption procedures were the same as described for the effect of pH on adsorption capacity. Adsorption Kinetics. The procedures for adsorption kinetics investigations were similar to those for adsorption isotherms, but the concentration of F- during adsorption process was analyzed at a regular interval. Desorption Studies. Adsorbent (0.100 g) was suspended in 100 mL of fluoride solution (5.00 mmol/L), and the adsorption was conducted with constant shaking at 303 K for 24 h. Then the solution was filtered and the adsorbent was transferred to 100 mL of distilled water with varying pH adjusted with 0.1 M NaOH or 0.1 M HNO3. Desorption studies were conducted by constant shaking at 303 K for 0.5 h, and the fluoride amount desorbed into the solution was determined. All the adsorption experiments above were conducted twice and it was found that the errors for all tests were less than 5%. Therefore, the average values of two tests were used as adsorption data.
Results and Discussion Impregnation of Zr(IV) on Collagen Fiber. Figure 1 is the scanning electronic microscope (SEM) photo of Zr(IV)impregnated collagen fiber. It was obvious that Zr(IV) was uniformly impregnated into collagen fiber without piled Zr salt precipitate, which favors adsorption behavior of the absorbent. There was no Zr(IV) detected in the residual
FIGURE 1. SEM photo of Zr(IV)-impregnated collagen fiber.
FIGURE 2. Effect of pH on fluoride adsorption capacity (average values of two tests, error < 5%). solution of the Zr(IV) impregnation reaction, implying that the amount of Zr(IV) loaded on collagen fiber was approximately 0.42 g of ZrO2/g of collagen fiber. During the Zr(IV) impregnation process, the permeation of Zr(IV) and its combination with collagen fiber were predominantly determined by the pH of the solution. Therefore, the initial pH of the impregnation process was controlled at 1.8-2.0 in favor of the permeation of Zr(IV), and then the pH was increased to 4.0-4.5 to promote the combination of Zr(IV) with collagen fiber. It was reported that the Zr(IV) can chelate with the -COOH and -NH2 groups on the side chains of collagen peptide (21), and this combination could withstand washing when the pH is above 3.0. Effect of pH on Adsorption Capacity. Figure 2 shows the effect of pH on fluoride adsorption capacity of Zr(IV)impregnated collagen fiber. As the pH of the test fluoride solution increased from 3.5 to 11.4, the adsorption capacity of fluoride was changed; that is, it first increased to 2.29 mmol/g at pH 5.5 and then slightly decreased to 1.91 mmol/g at pH 10.0. After that, the adsorption capacity dramatically decreased and the adsorbent exhibited no adsorption of fluoride at 11.4. This is consistent with the results obtained for other metal ion-impregnated adsorbents (17). The quick reduction of the amount of fluoride adsorbed in the alkaline pH range should be attributed to competition of hydroxyl ions with fluoride for adsorption sites (23). The relatively lower adsorption of fluoride in the acidic range (pH < 5) may be due to the formation of weakly ionized hydrofluoric acid (24). VOL. 39, NO. 12, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
4629
TABLE 1. Langmuir Parameters of Fluoride Adsorbed on Zr(IV)-Impregnated Collagen Fiber
FIGURE 3. Effect of adsorbent dose on removal extent and adsorption capacity of fluoride (average values of two tests, error < 5%). (0) Adsorption extent vs adsorbent dose; (O) adsorption capacity vs adsorbent dose.
temp (K)
qmax(mmol/g)
b
R2
303 313 323
2.18 2.41 2.70
11.6 10.9 9.52
0.999 0.997 0.998
Effect of Adsorbent Dose on Extent of Removal of Fluoride. The effect of adsorbent dose on the extent of removal of fluoride at natural pH is shown in Figure 3. The amount of adsorbent significantly influenced the extent of fluoride adsorption. The extent of fluoride removal was 42.0% for 0.100 g of adsorbent, while it was greatly increased to 97.4% for 0.300 g of adsorbent. However, there was only a small change in the extent of fluoride adsorption when the adsorbent dose was over 0.300 g. For example, the removal extent was 98.2% for 0.400 g of adsorbent. Furthermore, the higher adsorbent dose will result in lower qe value at a fixed fluoride concentration (5.00 mmol/L), as shown in Figure 3. This is consistent with the argument that the surface sites of the adsorbent are heterogeneous (25). According to the surface site heterogeneity model, the surface is composed of sites with a spectrum of binding energies. At low adsorbent dose, all types of sites are entirely exposed and the adsorption on the surface is saturated faster, showing a higher qe value. But at higher adsorbent dose, the availability of higher energy sites decreases with a larger fraction of lower energy sites occupied, resulting in a lower qe value. The distribution coefficient KD can be employed to describe the binding ability of adsorbent surface for an element. The KD values (in liters per gram) of the adsorption were calculated as (26)
KD ) Cs/Cw
FIGURE 4. Plot of KD values as a function of adsorbent dose. The effect of pH (from 3.0 to 12.0) on Zr(IV) dissolution from Zr(IV)-impregnated collagen fiber was also investigated and no Zr(IV) was detected in the washing solutions, which indicated that the Zr(IV) could not be leached out in a wide pH range. But Zr(IV) would be released from collagen fiber if the pH was lower than 2.5. So it could be concluded that the optimum pH of the adsorption of fluoride on Zr(IV)impregnated collagen fiber should be 5.0-8.0. The natural pH of fluoride solutions used in our experiments were all in this range. Therefore, all the following adsorption experiments were conducted without adjusting the pH of fluoride solutions.
where Cs is the concentration of fluoride in solid particles (mmol/g) and Cw is the concentration of fluoride in water (mmol/L). As can be seen in Figure 4, the distribution coefficient KD increases with increasing adsorbent dose, which implies that the surface of Zr(IV)-impregnated collagen fiber should be heterogeneous. If the surface is homogeneous, the KD values at a given pH should not change with adsorbent concentration (25). Adsorption Isotherms. The adsorption isotherms of fluoride on the adsorbent, as shown in Figure 5a, indicate that the adsorption capacity increases with rising temperature and increasing equilibrium concentration of fluoride. The data were further analyzed by the Langmuir and Freundlich equations, and it was found that the Langmuir equation (eq 2) gives a satisfactory fitting to the adsorption isotherms,
FIGURE 5. Adsorption isotherms of fluoride on Zr(IV)-impregnated collagen fiber (average values of two tests, error < 5%). 4630
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 12, 2005
(1)
FIGURE 6. Adsorption kinetics of fluoride on Zr(IV)-impregnated collagen fiber (average values of two tests, error < 5%).
FIGURE 7. Effect of pH on desorption of fluoride from Zr(IV)impregnated collagen fiber.
as shown in Figure 5b and Table 1:
g-1 min-1). Based on the eq 4 and the experimental data of qt, qe and k2 can be determined from the slope and the intercept of the plot of t/qt against t. The intraparticle diffusion equation can be described as
Ce Ce 1 ) + qe qmaxb qmax
(2)
where qe and Ce are the amounts of fluoride adsorbed (mmol/ g) and bulk concentration (mmol/L), respectively, at equilibrium; qmax is the maximum fluoride adsorption (mmol/g); and b is the Langmuir coefficient relating to the strength of adsorption. The values of qmax calculated by the Langmuir equation fitting were all close to those actually determined at given temperatures. These facts suggest that the chemical adsorption mechanism might be involved in the adsorption process of fluoride on Zr(IV)-impregnated collagen fiber and that fluorides are adsorbed in the form of monolayer coverage on the surface of the adsorbent. Satisfactory fitting of the Langmuir model to the adsorption isotherms of fluoride on alum sludge (24), lanthanum oxide-coated silica gel (19), and rare earth oxides (23) has been reported, and the mechanism of adsorption was elucidated to be monolayer coverage of fluoride ion on the outer surface of the adsorbents. Adsorption Kinetics. To investigate the mechanism of adsorption, the pseudo-first-order adsorption, pseudosecond-order adsorption, and intraparticle diffusion models were used to test adsorption kinetics data. The pseudo-firstorder-rate expression of Lagergren is given as (27)
log (qe - qt) ) log qe -
k1 t 2.303
(3)
where qe and qt are the amount of fluoride adsorbed on adsorbent (mmol/g) at equilibrium and at time t (min), respectively, and k1 is the rate constant of pseudo-first-order adsorption (min). The pseudo-second-order rate model is expressed as (28)
1 1 t ) + t qt k q 2 qe
(4)
2 e
where k2 is the constant of pseudo-second-order rate (mmol
qt ) kit0.5
(5)
where ki is the intraparticle diffusion rate constant (mmol g-1 min-0.5), which can be determined by the slope of the straight-line portion of a plot of qt versus t0.5. Figure 6 shows the adsorption kinetics of fluoride on Zr(IV)-impregnated collagen fiber. The influence of initial fluoride concentration on adsorption capacity is not obvious due to the limitation of saturated adsorption capacity of the adsorbent. This fact is consistent with the study of the adsorption isotherms and thus further confirms the chemical adsorption mechanism of fluoride on Zr(IV)-impregnated collagen fiber. Table 2 lists the results of rate constant studies for different initial fluoride concentrations by the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The value of correlation coefficient R2 for the pseudo-first-order adsorption model is extremely high (>0.997), and the adsorption capacities calculated by the model are close to those determined by experiments. However, the values of R2 for the pseudo-second-order and intraparticle diffusion adsorption models are not satisfactory. Therefore, it can be concluded that the pseudo-first-order adsorption model is more suitable to describe the adsorption kinetics of fluoride on Zr(IV)-impregnated collagen fiber. Similar phenomena had also been observed in the adsorption of fluoride on lanthanum-impregnated silica gel (16), activated alumina (11), and aluminum-complexed amino phosphonic acid-type resins (29). Desorption Studies. The results of desorption studies are shown in Figure 7. Fluoride was difficult to leach out in the acidic pH range. But as the pH increased to 9.0, the adsorbed fluoride started to leach into the solution, and more than 97.0% of the adsorbed fluoride could be desorbed within 30 min at pH 11.5. This result is consistent with the study
TABLE 2. Comparison of First- and Second-Order Adsorption and Intraparticle Diffusion Rate Constants first-order kinetic model initial concn (mmol/L)
qe.exp (mmol/g)
k1 × 103 (min-1)
qe.cal (mmol/g)
4.00 5.00
2.04 2.16
4.99 7.70
2.13 2.44
second-order kinetic model
intraparticle diffusion model
R2
k2 × 104 (g/mmol‚min)
qe.cal (mmol/g)
R2
ki (mmol/g‚min)
R2
0.999 0.997
8.76 7.00
3.50 3.78
0.968 0.954
0.106 0.113
0.968 0.956
VOL. 39, NO. 12, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
4631
of the effect of pH on the adsorption capacity. Further tests should be done to determine the exact life cycle of the adsorbent. To further understand the properties of this new adsorbent, investigations of the relationship between adsorption capacity and the amount of Zr(IV) impregnated, column adsorption, and regeneration properties should be carried out.
Acknowledgments We acknowledge the financial support provided by National Major Research Plan (pilot) of China (2004CCA06100), National Natural Science Foundation of China (20476062) and National Science Fund for Distinguished Young Scholars (20325619).
Literature Cited (1) Paulson, E. G. Reducing fluoride in industrial wastewater. Chem. Eng. 1977, 84 (22), 89-94. (2) Fan, X.; Parker, D. J.; Smith, M. D. Adsorption kinetics of fluoride on low cost materials. Water Res. 2003, 37, 4929-4937. (3) World Health Organization. Guidelines for Drinking Water Quality; WHO: Geneva, Switzerland, 1993. (4) Huang, C. J.; Liu, J. C. Precipitate flotation of fluoride-containing wastewater from a semiconductor manufacturer. Water Res. 1999, 33 (16), 3403-3412. (5) Yang, M.; Zhang, Y.; Shao, B.; Qi, R.; Myoga, H. Precipitative removal of fluoride from electronics wastewater. J. Environ. Eng. 2001, 127 (10), 902-907. (6) Ku, Y.; Chiou, H. M.; Wang, W. The removal of fluoride ion from aqueous solution by a cation synthetic resin. Sep. Sci. Technol. 2002, 37 (1), 89-103. (7) Ku, Y.; Chiou, H. M. The adsorption of fluoride ion from aqueous solution by activated alumina. Water, Air, Soil Pollut. 2002, 133 (1-4), 349-360. (8) Bishop, P. L.; Sansoucy, G. Fluoride removal from drinking water by fluidized activated alumina adsorption, J. Am. Water Works Assoc. 1978, 70 (10), 554-559. (9) Amor, Z.; Bariou, B.; Mameri, N.; Taky, M.; Nicolas, S.; Elmidaoui, A. Fluoride removal from brackish water by electrodialysis. Desalination 2001, 133 (3), 215-223. (10) Li, Y. H.; Wang, S. G.; Zhang, X. F.; Wei, J. Q.; Xu, C. L.; Luan, Z. K.; Wu, D. H. Adsorption of fluoride from water by aligned carbon nanotubes. Mater. Res. Bull. 2003, 38 (3), 469-476. (11) Sivasamy, A.; Singh, K. P.; Mohan, D.; Maruthamuthu, M. Studies on defluoridation of water by coal-based sorbents. J. Chem. Technol. Biotechnol. 2001, 76 (7), 717-722. (12) Rao, A. V.; Nemade, P. D.; Alappat, B. J. Removal of fluorides from water using low cost adsorbents. Water Sci. Technol.: Water Suppl. 2002, 2 (1), 311-317. (13) Cengeloglu, Y.; Kir, E.; Ersoz, M. Removal of fluoride from aqueous solution by using red mud. Sep. Purif. Technol. 2002, 28 (1), 81-86.
4632
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 12, 2005
(14) Luo, F.; Inoue, K. The removal of fluoride ion by using metal(III)-loaded Amberlite resins. Solvent Extr. Ion Exch. 2004, 22 (2), 305-322. (15) Leyva Ramos, R.; Ovalle-Turrubiartes, J.; Sanchez-Castillo, M. A. Adsorption of fluoride from aqueous solution on aluminumimpregnated carbon. Carbon 1999, 37 (4), 609-617. (16) Wasay, S. A.; Haron, M. J.; Tokunaga, S. Adsorption of fluoride, phosphate, and arsenate ions on lanthanum-impregnated silica gel. Water Environ. Res. 1996, 68 (3), 295-300. (17) Zhou, Y. M.; Yu, C. X.; Shan, Y. Adsorption of fluoride from aqueous solution on La3+-impregnated cross-linked gelatin. Sep. Purif. Technol. 2004, 36 (2), 89-94. (18) Fang, L.; Ghimire, K. N.; Kuriyama, M.; Inoue, K.; Makino, K. Removal of fluoride using some lanthanum(III)-loaded adsorbents with different functional groups and polymer matrices. J. Chem. Technol. Biotechnol. 2003, 78 (10), 1038-1047. (19) Ma, G. P.; Liu, Z. R.; Zhao, C. L. Study on the removal of fluoride by using lanthanum oxide-coated silica gel. Zhongguo Huanjing Kexue (Chin. Environ. Sci.) 1999, 19 (4), 345-348. (20) Friess, W. Collagen-biomaterial for drug delivery. Eur. J. Pharm. Biopharm. 1998, 45 (2), 113-136. (21) Evans, N. A.; Milligan, B.; Montgomery, K. C. Collagen crosslinking: new binding sites for mineral tannage. J. Am. Leather Chem. Assoc. 1987, 82 (4), 86-95. (22) Liao, X. P.; Zhang, M. N.; Shi, B. Collagen fiber immobilized tannins and their adsorption of Au(III). Ind. Chem. Eng. Res. 2004, 43, 2222-2227. (23) Raichur, A. M.; Basu, M. J. Adsorption of fluoride onto mixed rare earth oxides. Sep. Purif. Technol. 2001, 24, 121-127. (24) Sujana, M. G.; Thakur, R. S.; Rao, S. B. Removal of fluoride aqueous solution by using alum sludge. J. Colloid Interface Sci. 1998, 206, 94-101. (25) Das, D. P.; Das, J.; Parida, K. Physicochemical characterization and adsorption behavior of calcined Zn/Al hydrotalcite-like compound (HTlc) towards removal of fluoride from aqueous solution. J. Colloid Interface Sci. 2003, 261, 213-220. (26) Sigg, L. In Aquatic Surface Chemistry: Chemical Processes at the Particle-Water Interface; Stumm, W., Ed.; John Wiley and Sons: New York, 1987; 325 pp. (27) Chiou, M. S.; Li, H. Y. Adsorption behavior of reactive dye in aqueous solution on chemical cross-linked chitosan beads. Chemosphere 2003, 50, 1095-1105. (28) McKay, G.; Ho, Y. S. Pseudo-second-order model for sorption processes. Process Biochem. 1999, 34, 451-465. (29) Bhatt, D. B.; Bhatt, P. R.; Prasad, H. H.; Popat, K. M.; Anand, P. S. Removal of fluoride ion from aqueous bodies by aluminium complexed amino phosphonic acid type resins. Indian J. Chem. Technol. 2004, 11 (3), 299-303.
Received for review December 19, 2004. Revised manuscript received March 31, 2005. Accepted April 5, 2005. ES0479944
