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SEPARATIONS Adsorption Study for Removal of Basic Red Dye Using Bentonite Q. H. Hu,† S. Z. Qiao,† F. Haghseresht,‡ M. A. Wilson,§ and G. Q. Lu*,† ARC Centre for Functional Nanomaterials, School of Engineering, The UniVersity of Queensland, St Lucia, QLD 4072, Australia, Integrated Mineral Technology Holdings Ltd., Brisbane, Australia, and The UniVersity of Western Sydney, Richmond Campus, Locked Bag 1797, Penrith South DC 1797, NSW, Australia
Colored wastewater poses a challenge to the conventional wastewater treatment techniques. Solid-liquid phase adsorption has been found to be effective for the removal of dyes from effluent. In this paper, the ability of bentonite as an adsorbent for the removal of a commercial dye, Basic Red 2 (BR2), from an aqueous solution has been investigated under various experimental conditions. The adsorption kinetics was shown to be pseudo-second-order. It was found that bentonite had high adsorption capacity for BR2 due to cation exchange. The adsorption equilibrium data can be fitted well by the Langmuir adsorption isotherm model. The effect of the experimental parameters, such as temperature, salt, and pH was investigated through a number of batch adsorption experiments. It was found that the removal of dye increased with the increase in solution pH. However, the change of temperature (15-45 °C) and the addition of sodium chloride were found to have little effect on the adsorption process. The results show that electrostatic interactions are not dominant in the interaction between BR2 and bentonite. It was found that the adsorption was a rapid process with 80-90% of the dye removed within the first 2-3 min. Bentonite as an adsorbent is promising for color removal from wastewater. Introduction Industrial wastewaters generated by textile, paper, carpet, and printing industries contain a high concentration of colored organic, often toxic compounds. It has been reported that there is a large amount of residual dyes remaining in wastewater in the dyeing process, especially for reactive dyes. It is estimated that an average of 30% of applied reactive dyes end up in effluent in the alkaline dye bath because their hydrolyzed form has no affinity for textile fabrics.1 In some situations, the concentration may be as high as 800 mg/L.2 Due to the toxic nature of most dyes to plants and micro-organisms, colored wastewater cannot be discharged without adequate treatment. Even if they are non-toxic, such wastewater obstructs light penetration and, therefore, decreases the efficiency of photosynthesis in aquatic plants and raises the chemical oxygen demand (COD).3 Hao et al.4 reported that cationic dyes are tested to be more toxic than anionic dyes. Chromium-based dyes can release, into the water, chromium ions which are carcinogenic in nature.5 As dyes are designed to resist breakdown with time and exposure to sunlight, water, soap, and oxidizing agent, they cannot be easily removed by conventional wastewater treatment processes due to their complex structure and synthetic origins.6 Dye removal has been an important but challenging area of wastewater treatment. To remove dyes and other colored contaminants from wastewaters, several physical, chemical, and biological methods have been developed, such as membrane separation, floccula* To whom correspondence should be addressed. Tel: 61 7 33653885. Fax: 61 7 33656074. E-mail:
[email protected]. † The University of Queensland. ‡ Integrated Mineral Technology Holdings Ltd. § The University of Western Sydney.
tion-coagulation, adsorption, ozonatioin, and aerobic or anaerobic treatment.7 Some of these approaches are effective only if the amount of dyeing effluent is small; some of them produce a large amount of sludge which causes disposal problems, thus increasing the operation cost.8 After the chemical treatment, some toxic byproducts are still hazardous to the environment.9 In fact, many dyes are generally resistant to biodegradation due to their complex aromatic molecular structure.10 Therefore, no one specific treatment process seems to be able to completely decolorize all types of colored wastewater.4 Among these processes, adsorption has been found to be an effective and cheap technique for removing dyes and having wide potential applications.11 Adsorption is a complex phenomenon and involves passive separation of the adsorbate from an aqueous/ gaseous phase onto the solid phase. It occurs between two phases in transporting pollutants from one phase into another.12 It has been reported that many different types of adsorbents are effective in removing color from aqueous effluent. The most commonly used adsorbent in industrial wastewater treatment systems is activated carbon because it has a large specific surface area, although it is a bit expensive to run such systems.13 Natural phyllosilicates, commonly known as clays considering their particle size, such as bentonite, have the potential to act as alternative low-cost adsorbents because they are naturally available and possess unique physiochemical properties. Bentonite consists of layers of two tetrahedral silica sheets sandwiching one octahedral alumina sheet. Due to the isomorphous substitution of the silicon ions by aluminum or ferric cations in the tetrahedral sheets, and the aluminum ions by magnesium or ferrous cations in the octahedral sheets, bentonite has net negative charges on its layer lattice. To maintain the electrical neutrality, other cations external to the lattice, like sodium or calcium ions, are commonly present in the interlayer
10.1021/ie050889y CCC: $33.50 © 2006 American Chemical Society Published on Web 11/19/2005
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Figure 1. Structure of Basic Red 2. Table 1. Mineral Analysis of Bentonite (% by Weight) SiO2
Al2O3
MgO
Fe2O3
Na2O
CaO
K2O
TiO2
others
65
16.28
3.98
3.75
1.75
0.75
0.29
0.27
0.09
region. When clay is in contact with water, these chargecompensating cations can be exchanged or replaced by others present in the bulk of the suspension.14-16 The application of bentonite as an adsorbent is largely based on its ability to exchange cations. Previous studies show that the modified bentonite obtained by replacing the inherent clay inorganic cations with suitable quaternary amine cations or surfactant to remove organic contaminants from aqueous solution can affect the capacity of the bentonite to exchange.17-19 Thus, Wang et al.20 compared the adsorption properties of basic dyes onto Camontmorillonite and Ti-montmorillonite and found that Camontmorillonite possessed larger adsorption capacity than Timontmorillonite because Ca2+ is easier to be displaced by ion exchange. Ozcan et al.21 reported that the removal of acid dyes was promoted using sulfuric acid-activated bentonite compared with untreated bentonite. Bouberka et al.22 used pillared and surfactant-activated bentonite for treating effluent containing acid dye; they showed that the modified clays displayed higher adsorption capacity than the original clay toward the anionic dye in an acidic environment. However, there has been little work on the adsorption mechanism of dyes in bentonite or similar clays. Mohammad23 concluded that the mechanism of basic dye adsorption by natural clay is initially controlled by the thickness of the boundary layer. Hence, in this paper, the use of bentonite in removing a commercial dye Basic Red 2 (C20H19ClN4, Figure 1) from aqueous solution has been studied with the aim of understanding the process. The monolayer equilibrium adsorption capacity was estimated using an adsorption isotherm technique. The effects of various adsorption conditions, such as temperature, salt concentration, and initial pH value of the dye solution, have been studied. The changes of the bentonite surface properties induced by dye adsorption have been characterized using nitrogen adsorption and X-ray diffraction (XRD) techniques. Experimental Materials and Methods Materials. Adsorbent. The adsorbent used in this work was bentonite supplied by Integrated Mineral Technology Holdings Ltd. (IMT) Australia. It was used without any further purification. Its cation-exchange capacity (CEC) is 75 mequiv/100 g and its mineral compositions as oxide are given in Table 1. The bentonite point of zero charge pHpzc of 10.02 was obtained following the method suggested by Haghseresht et al.24 Adsorbate. One commercial dye, namely, Basic Red 2 (BR2) (Figure 1), having a color index number of 50240, molecular weight of 350.85, and maximum wavelength λmax of 520 nm (Sigma-Aldrich),25 was selected as the adsorbate. Methods. Calibration CurVe. To determine the dye concentration in the solution, a calibration curve was first obtained using a UV-Vis spectrophotometer (JASCO V550). The maximum absorbance of 520 nm was confirmed by scanning the BR2 aqueous solution over the spectral range of 450-600 nm. A series of BR2 solutions with predetermined concentration
Figure 2. Effect of adsorbent concentration on the removal of BR2.
were used for the measurement of a calibration curve. A linear relationship between the absorbance and BR2 concentration was obtained. Adsorbent Concentration. To determine the appropriate amount of adsorbent used in adsorption experiments, various amounts of bentonite were brought into contact with the dye solution at a fixed initial concentration of 200 mg/L. After the equilibrium was attained, the residual dye concentration was determined. As shown in Figure 2, the dye residual concentration decreases with the increase of adsorbent concentration until a plateau is reached. Adsorption Equilibrium Studies. Various dye solutions with different initial concentration, in the range of 50-450 mg/L, were prepared by diluting a stock dye solution. A sufficient amount of bentonite, 1.5 g/L, was brought into contact with known volumes (50 mL) of dye solutions. The bottles were sealed and agitated in a thermostatic shaker at a desired temperature, normally at 30 °C unless otherwise stated, for 1 h, which was found to be sufficient to reach equilibrium. After equilibrium was reached, each sample withdrawn was filtrated through a 0.45 µm membrane filter to remove any particles. The residual dye concentration of BR2 was then determined. Adsorption Kinetics. Adsorption kinetics study was carried out in order to test the relationship between contact time and BR2 dye uptake. Dye solutions (1000 mL) with different initial concentrations of 100, 150, and 200 mg/L were prepared and maintained at 30 °C, prior to the experiment. Bentonite was then added into the dye solution while being constantly stirred. Samples were withdrawn at different time intervals. Effect of Adsorption Parameters. To examine the effect of temperature, adsorption experiments were conducted at 15, 30, and 45 °C, respectively. The influence of the initial pH was observed by adjusting the pH value of the dye solutions to 4, 7, and 11 by using 0.5 M HCl or 0.5 M NaOH prior to the experiments. Sodium chloride was used to investigate the effect of salt at nine different salt concentrations (NaCl between 0 and 1 M). These were achieved by changing one parameter at a time while maintaining the others constant. Characterization of Bentonite. The X-ray diffraction (XRD) patterns of bentonite and its loaded BR2 samples were measured on a Rigaku Miniflex instrument with cobalt KR radiation at 30 kV and 15 mA to identify the changes of its structure during the adsorption process. The loaded BR2 samples were obtained following the normal equilibrium isotherm study. BR2-unsat denotes bentonite unsaturated with BR2 collected before the saturation level was reached; similarly, the BR2-sat sample was obtained after the saturation. Nitrogen ad-/desorption isotherm was measured at 77 K with Autosorb-1 (Quantachrome, USA). The bentonite sample was degassed overnight at 200 °C prior to the adsorption measurements. The specific surface area was
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Figure 3. Kinetics of BR2 uptake by bentonite, initial dye concentration at 100, 150, and 200 mg/L, respectively.
Figure 4. Pseudo-second-order adsorption kinetics of BR2 uptake by bentonite.
calculated by the Brunauer, Emmett, and Teller (BET) equation using the adsorption data in the relative pressure of 0.05-0.25. Results and Discussion Adsorption Kinetics. It is seen from Figure 3 that the adsorption of BR2 is initially a rapid process with approximately 80-90% of the dye onto the bentonite surface within the first 2-3 min, indicating a high affinity between the BR2 molecules and the bentonite surface. Following this phase, the adsorption process slows, suggesting a gradual equilibrium, possibly due to intraparticle diffusion of BR2 molecules. Finally, the saturation is reached, showing the final equilibrium, beyond which no further adsorption takes place at approximately 30 min. These results complement those obtained by Al-Asheh et al. with methylene blue and bentonite.26 For the lower initial dye concentration, the adsorption rate is even faster and the dye removal percentage is higher, showing dye removal increases with the decrease of initial dye concentration when the adsorbent concentration is constant. The Lagergren Equation, pseudo-first-order model, has been used to describe dye adsorption kinetics,27 but here a pseudosecond-order model developed by Ho et al.28 fits the adsorption kinetics data better. The pseudo-second-order equation is presented in eq 1,
1 1 t ) + t qt kq 2 qe
(1)
e
where qe and qt are the amount of dye adsorbed per unit mass of adsorbent at equilibrium and time t (mg/g) and k is the pseudo-second-order rate constant. Linear plots of t/qt against t (Figure 4) show the application of the pseudo-second-order equation for the adsorption system in which the equilibrium adsorption capacity corresponding to the given initial dye concentration can be calculated from the slope of the straight line. With the increase of initial dye concentration from 100 to 200 mg/L, the adsorption capacity increases from 125 to 239 mg/g, indicating that dye removal content depends on the initial dye concentration when the adsorbent amount is constant. The regression coefficients of 0.999 are extremely high, which indicates a good compliance with the pseudo-second-order model for the adsorption mechanism. Equilibrium Isotherm. From the shape of the equilibrium isotherm, the characteristics of the adsorption system and the
Figure 5. Adsorption equilibrium isotherm of BR2 on bentonite at 30 °C.
interaction between adsorbate and adsorbent can be estimated.29 The Langmuir isotherm model has been used to describe the experimental data well in the adsorption of BR2 by bentonite. The Langmuir constants Q0 and b can be estimated from the linear form Langmuir equation,
Ce Ce 1 + ) qe Q0b Q0
(2)
where Ce is the equilibrium dye concentration in solution and Q0 and b are the Langmuir constants related to the monolayer adsorption (saturation) capacity and surface energy, respectively, which can be determined from the intercept and the slope of the Ce/q versus Ce linear plot. The application of the Langmuir equation assumes that the adsorption is monolayer coverage and the adsorption site is homogeneous. The adsorption equilibrium isotherm of BR2 on bentonite at 30 °C is presented in Figure 5. The solid line in the plot shows the fitting result using the Langmuir adsorption equation. From the isotherm, there is a sharp initial rise (type I isotherm), suggesting a high affinity between the dye and the adsorbent surface.30 The saturation level of the isotherm is reached at the very low equilibrium concentration of approximately 5 mg/L and the high adsorption capacity of 274 mg/g, indicating a high degree of irreversibility of the adsorption system.31 The adsorption behavior is also reflected by the corresponding Langmuir constants which are listed in Table 2. The very high correlation coefficient (r2) of 0.999 indicates that the Langmuir model
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Table 2. Langmuir Adsorption Isotherm Constants dye
temperature (°C)
Q0
b
r2
BR2
15 30 45
269 274 273
3.00 3.54 2.97
0.999 0.999 0.999
represents the experimental data considerably well, indicating the adsorption of BR2 on the bentonite surface as a monolayer coverage. Changes in Adsorbent Surface Properties. Nitrogen adsorption-desorption isotherms of bentonite before and after adsorption of BR2 are compared in Figure 6. There are considerable differences between these two isotherms, although they all represent type II adsorption isotherm with type H3 hysteresis loops which are characteristics of slit-like pore materials. The obvious hysteresis loop can be seen on the bentonite isotherm, suggesting the occurrence of capillary condensation and the existence of mesopores. After adsorption, the hysteresis loop nearly disappears, possibly due to the filling of organic dye molecules. However, the pore structure of material seems not to change. The adsorption capacity of bentonite decreases dramatically after the adsorption of BR2 due to the occupancy of the adsorption site by dye molecules. The BET surface area of bentonite also drops considerably during the adsorption process, from 47.73 to 21.38 m2/g. Figure 7 highlights the XRD powder patterns comparison of bentonite before and after the adsorption of BR2 dye. The results show that the bentonite basal spacing changes after the adsorption of BR2 (Table 3). This can be explained by the fact that dye molecules expanded the bentonite interlayer. To further prove this, the orientation of BR2 dye on the bentonite surface was investigated. The three dimensions of BR2 molecule was estimated using Weblab ViewerPro, which are 13.1 Å in x-axis length, 9.2 Å in y-axis, and 4.0 Å in z-axis, respectively. Considering the changes of bentonite d spacing (which is obtained by subtracting 9.6 Å, the thickness of a single silicate layer of bentonite,32 from basal spacing) during the adsorption process, from 6.04 Å for the BR2-unsat sample and to 8.18 Å for the BR2-sat sample (Table 3), dye molecules may enter the interlayer space and lie down with the amino group bound to bentonite internal surface before the saturation level is reached, whereas after the saturation is attained, dye molecules are probably orientated at some tilt angles with respect to the
Figure 7. XRD patterns of bentonite before and after adsorption. Table 3. XRD Results of Bentonite before and after the Adsorption of BR2
material
diffraction angle (2θ)
basal spacing (Å)
d-spacing (Å)
bentonite BR2-unsat BR2-sat
7.1 6.6 5.8
14.54 15.54 17.68
5.04 6.04 8.18
bentonite surface and intercalated into the interlayer surface. Combining the obtained adsorption results, if the surface area is divided by the saturation adsorption capacity of bentonite, each dye molecule could only occupy about 10 Å2; it would be expected that the dye molecule seems more favorable to be attached with some tilt angles on the bentonite surface when the saturation is reached. Kaneko et al.33 in their investigation of the interaction of a cationic dye with montmorillonite found that the orientation the dye on the montmorillonite surface was in a narrow angle range of 68-71°. This is consistent with our assumptions. Adsorption Mechanism. There are many factors that may influence the adsorption behavior, such as dye structure and adsorbent surface properties. Basic Red 2 is a cationic type dye having an amino group in its structure. In aqueous solution, it dissociates a positive ammonium cation. H2O
R4N+Cl 798 R4N+ + Cl-
(3)
where R stands for the rest of the dye structure (see Figure 1). Although natural bentonite has an overall neutral charge, it has excess negative charges on its crystal lattice due to the isomorphous substitution. These kind of negative charges are compensated for by exchangeable cations from the external medium. When bentonite is placed in water, the exchangeable cations, such as sodium ions, diffuse away from the solid surface, leaving the clay surface with negative charges.15 The presence of negative charges on the surface of clay layers has the tendency to attract dye cationic ions. H2O
Figure 6. Nitrogen adsorption isotherms of bentonite before and after the adsorption of BR2.
[Na - clay] 798 [clay]- + Na+
(4)
R4N+ + [clay]- T R4N - clay
(5)
It is clear that the basic dye cation is exchanged with the exchangeable interlayer cation of bentonite, such as Na+, and
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Figure 8. Effect of temperature on the adsorption of BR2 at 15, 30, and 45 °C, respectively.
Figure 9. Effect of salt on the adsorption capacity, initial dye concentration at 50, 100, 200, and 250 mg/L, respectively.
is thus intercalated into the bentonite interlayer. So the driving force for the adsorption of BR2 is probably the cation exchange. Effect of Temperature. The effect of temperature on adsorption capacity was investigated by measuring the adsorption isotherms at various temperatures, namely, 15, 30, and 45 °C. The results are presented in Figure 8. The corresponding isotherm parameters obtained by fitting the experimental data to eq 2 are listed in Table 2. As can be seen with the increase of temperature from 15 to 30 °C, the adsorption capacity of BR2 increases slightly from 269 to 274 mg/g. This observation reveals that the adsorption process is slightly endothermic. This may be caused by the increased tendency of adsorbate ions to be adsorbed from the solution into the dye-clay interface. The adsorption capacity does not change as much when the temperature increases from 30 to 45 °C, suggesting the adsorption behavior is insensitive to the changes of temperature in this range. The overall temperature influence is weak for the adsorption of BR2, which probably indicates the low activation energy in the predominantly ionic system. Effect of Salt. A study of salt effect was carried out and the results are presented in Figure 9. In this study, the initial dye concentration was at 50, 100, 150, and 200 mg/L, respectively. For the certain dye solution, salt concentration was adjusted in the range from 0 to 1 M. Figure 9 shows that the addition of salt has a slight effect on the adsorption capacity. These results indicate that the presence of external electrolyte, such as sodium
Figure 10. Adsorption equilibrium isotherms with the effect of initial pH.
chloride, has a limited effect on the binding efficiency between bentonite and BR2. They also suggest that the electrostatic interaction between bentonite and BR2 does not play an important role in the adsorption of BR2 from aqueous solution because the external electrolyte should affect the adsorption behavior if the driving force of the adsorption is the electrostatic interaction. As discussed above, the adsorption of BR2 on bentonite is probably dominated by cation exchange because the cation exchange capacity is largely independent of the salt concentration.34 Effect of pH. In the present work, the effect of pH on the adsorption capacity was tested by varying the initial pH value of the dye solution. The pH value of each isotherm measurement was adjusted at 4, 7, and 11, respectively, prior to the adsorption experiment while other conditions were kept constant. The results as depicted in Figure 10 show that, as expected, the removal of dye increases in an alkaline environment. In an alkaline environment, there are possibly more negative charges present on the bentonite surface, although the permanent net negative charges on the bentonite surface generated by isomorphous substitution is independent of pH. In aqueous solution, the bentonite surface hydroxy site (M-OH), such as alumina, undergoes the protonation/deprotonation process.35 An alkaline environment gives rise to more negative charges on the bentonite hydroxyl groups. H+
H+
H2O + M-O- 79 98 M-H 79 98 M-OH2+ (6) OH
OH
where H+ and OH- refer to the potential determining ions. It can be seen that bentonite has some extra negative charges on its surface at the pH higher than its pHpzc; therefore, the electrostatic attraction between the negatively charged adsorption site and the positively charged dye is enhanced, resulting in more cationic dye being adsorbed. Conclusions Bentonite as a natural clay is able to remove dye, Basic Red 2, from wastewater very effectively. The adsorption kinetic studies show that the removal of BR2 is a rapid process and the adsorption process obeys the pseudo-second-order model, indicating cationic dye has a very strong affinity on the bentonite surface. It was found that the experimental isotherm data can be fitted well to the Langmuir equilibrium equation and bentonite has very high BR2 adsorption capacity of ap-
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proximately 274 mg/g at 30 °C. The effect of temperature on adsorption capacity is negligible in the range of 15-45 °C. The addition of salt has a slight influence on the adsorption capacity. The removal of dye increases in an alkaline environment. The study on adsorption mechanism shows that the adsorption of BR2 on bentonite is dominated by cation exchange but not electrostatic interaction. Acknowledgment Financial and in-kind support from the Australia Research Council and Integrated Mineral Technology Holdings Ltd. (IMT) Australia, ARC Centre for Functional Nanomaterials, are gratefully acknowledged. The authors would like to thank Chenghua Sun for the calculation of the molecular size of the BR2 dye. Literature Cited (1) Gahr, F.; Hermanutz, F.; Oppermann, W. Ozonation - an Important Technique to Comply with New German Laws for Textile Waste Water Treatment. Water Sci. Technol. 1994, 30, 255-263. (2) Steenkenrichter, I.; Kermer, W. D. Decolorizing Textile Effluents. J. Soc. Dyers Colourists 1992, 108, 182-186. (3) Ramakrishna, K. R.; Viraraghavan, T. Dye removal using low cost adsorbents. Water Sci. Technol. 1997, 36, 189-196. (4) Hao, O. J.; Kim, H.; Chiang, P. C. Decolorization of wastewater. Crit. ReV. EnViron. Sci. Technol. 2000, 30, 449-505. (5) Anliker, R.; Clarke, E. A.; Moser, P. Use of the Partition-Coefficient as an Indicator of Bioaccumulation Tendency of Dyestuffs in Fish. Chemosphere 1981, 10, 263-274. (6) Clarke, E. A.; Anliker, R. The Handbook of EnVironmental Chemistry; Hutzinger, O., Ed.; Springer-Verlag: Berlin, 1980; Vol. 3, p 181. (7) Slokar, Y. M.; Le Marechal, A. M. Methods of decoloration of textile wastewaters. Dyes Pigm. 1998, 37, 335-356. (8) Robinson, T.; McMullan, G.; Marchant, R.; Nigam, P. Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative. Bioresour. Technol. 2001, 77, 247-255. (9) Yang, Y. Q.; Wyatt, D. T.; Bahorsky, M. Decolorization of dyes using UV/H2O2 photochemical oxidation. Text. Chem. Color. 1998, 30, 27-35. (10) Pagga, U.; Taeger, K. Development of a Method for Adsorption of Dyestuffs on Activated-Sludge. Water Res. 1994, 28, 1051-1057. (11) Mitchell, M.; Ernst, W. R.; Lightsey, G. R. Adsorption of Textile Dyes by Activated Carbon Produced from Agricultural, Municipal and Industrial-Wastes. Bull. EnViron. Contam. Toxicol. 1978, 19, 307-311. (12) Ardizzone, S.; Gabrielli, G.; Lazzari, P. Adsorption of MethyleneBlue at Solid-Liquid and Water Air Interfaces. Colloids Surf. A 1993, 76, 149-157. (13) Sanghi, R.; Bhattacharya, B. Review on decolorisation of aqueous dye solutions by low cost adsorbents. Color. Technol. 2002, 118, 256269. (14) Worral, W. E., Ed. Clays: their nature, origin and general properties; Maclaren and sons Ltd: London, 1968. (15) Neumann, M. G.; Gessner, F. Encyclopedia of Surface and Colloid Science; Hubbard, A. T., Ed.; Marcel Dekker: New York, 2002; Vol., pp 307-321. (16) Avena, M. J. Encyclopedia of Surface and Colloid Science; Hubbard, A. T., Ed.; Marcel Dekker: New York, 2002; Vol., pp 37-63.
(17) Smith, J. A.; Galan, A. Sorption of Nonionic Organic Contaminants to Single and Dual Organic Cation Bentonites from Water. EnViron. Sci. Technol. 1995, 29, 685-692. (18) Zhu, L. H.; Li, Y. M.; Zhang, J. Y. Sorption of organobentonites to some organic pollutants in water. EnViron. Sci. Technol. 1997, 31, 14071410. (19) Bae, J. H.; Song, D. I.; Jeon, Y. W. Adsorption of anionic dye and surfactant from water onto organomontmorillonite. Sep. Sci. Technol. 2000, 35, 353-365. (20) Wang, C. C.; Juang, L. C.; Hsu, T. C.; Lee, C. K.; Lee, J. F.; Huang, F. C. Adsorption of basic dyes onto montmorillonite. J. Colloid Interface Sci. 2004, 273, 80-86. (21) Ozcan, A. S.; Ozcan, A. Adsorption of acid dyes from aqueous solutions onto acid-activated bentonite. J. Colloid Interface Sci. 2004, 276, 39-46. (22) Bouberka, Z.; Kacha, S.; Kameche, M.; Elmaleh, S.; Derriche, Z. Sorption study of an acid dye from an aqueous solutions using modified clays. J. Hazard. Mater. 2005, 119, 117-124. (23) Mohammad, S. E. Adsorption Kinetics of Cationic Dyestuffs on to Natural Clay. Adsorp. Sci. Technol. 1996, 13, 295-303. (24) Haghseresht, F.; Nouri, S.; Lu, G. Q. M. Effects of carbon surface chemistry and solution pH on the adsorption of binary aromatic solutes. Carbon 2003, 41, 881-892. (25) Green, F. J., Ed. The Sigma-Aldrich Handbook of Stains, Dyes, and Indicators; Aldrich Chemical Co.: Milwaukee, WI, 1990. (26) Al-Asheh, S.; Banat, F.; Abu-Aitah, L. The removal of methylene blue dye from aqueous solutions using activated and non-activated bentonites. Adsorpt. Sci. Technol. 2003, 21, 451-462. (27) Walker, G. M.; Weatherley, L. R. Kinetics of acid dye adsorption on GAC. Water Res. 1999, 33, 1895-1899. (28) Ho, Y. S.; Chiang, C. C.; Hsu, Y. C. Sorption kinetics for dye removal from aqueous solution using activated clay. Sep. Sci. Technol. 2001, 36, 2473-2488. (29) Wong, Y. C.; Szeto, Y. S.; Cheung, W. H.; McKay, G. Equilibrium studies for acid dye adsorption onto chitosan. Langmuir 2003, 19, 78887894. (30) Giles, C. H.; Macewan, T. H.; Nakhwa, S. N.; Smith, D. Studies in Adsorption. 11. A System of Classification of Solution Adsorption Isotherms, and Its Use in Diagnosis of Adsorption Mechanisms and in Measurement of Specific Surface Areas of Solids. J. Chem. Soc. 1960, 3973-3993. (31) McKay, G.; Blair, H. S.; Gardner, J. R. Adsorption of Dyes on Chitin. 1. Equilibrium Studies. J. Appl. Polym. Sci. 1982, 27, 3043-3057. (32) Zhu, H. Y.; Ding, Z.; Barry, J. C. Porous solids from layered clays by combined pillaring and templating approaches. J. Phys. Chem. B 2002, 106, 11420-11429. (33) Kaneko, Y.; Iyi, N.; Bujdak, J.; Sasai, R.; Fujita, T. Effect of layer charge density on orientation and aggregation of a cationic laser dye incorporated in the interlayer space of montmorillonites. J. Colloid Interface Sci. 2004, 269, 22-25. (34) Theng, B. K. G., Ed. The Chemistry of Clay-Organic Reactions; Adam Hilger Ltd.: London, 1974. (35) Johnson, S. B.; Franks, G. V.; Scales, P. J.; Boger, D. V.; Healy, T. W. Surface chemistry-rheology relationships in concentrated mineral suspensions. Int. J. Miner. Process. 2000, 58, 267-304.
ReceiVed for reView July 30, 2005 ReVised manuscript receiVed October 24, 2005 Accepted October 24, 2005 IE050889Y
