Ind. Eng. Chem. Res. 2009, 48, 1051–1058
1051
Sorption of Nitrobenzene from Aqueous Solution on Organoclays in Batch and Fixed-Bed Systems Hasmukh A. Patel,† Hari C. Bajaj,† and Raksh V. Jasra*,‡ Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research Institute (Council of Scientific & Industrial Research, CSIR), G.B. Marg, BhaVnagar-364 002, Gujarat, India, Research and DeVelopment Centre, Reliance Industries Limited, Vadodara Manufacturing DiVision, Vadodara-391 346, Gujarat, India
Organoclays were synthesized using different quaternary ammonium salts namely, stearyldimethylbenzylammonium chloride, dioctadecyldimethylammonium chloride, and hexadecyltrimethylammonium bromide and employed as a sorbent for sorption of nitrobenzene from aqueous solution. Among the organoclays studied, stearyldimethylbenzylammonium as organic modifier was found to have highest sorption capacity and was further used in fixed-bed sorption study. The effect of flow rate, sorbent particle size, feed concentration, temperature, and the amount of organic modifier in organoclay on sorption of nitrobenzene were studied. The column parameters required for the design of the fixed-bed sorption systems such as time for primary sorption zone to move up its length, total time required for establishment of primary sorption zone, rate at which the exchange zone is moving up/down through the bed, fractional capacity, the height of the exchange zone, percentage of the total column saturated at breakthrough and breakthrough capacity were evaluated on the basis of breakthrough curves. Desorption of nitrobenzene was also carried out by water as elution solvent. The Yoon-Nelson model was used to depict the breakthrough behavior for sorption of nitrobenzene on organoclay in the fixed-bed system. 1. Introduction Removal of organic pollutants from contaminated wastewater is critical to ensuring the safety of water supplies worldwide. Nitroaromatic compounds are widely used as pesticides, explosives, solvents, and intermediates in the synthesis of dyes, plastics and other chemicals.1,2 Most of these compounds have a global toxicological concern. These environmental contaminants are commonly found in the subsurface soil and pose a potential threat to human health.3 Therefore, a variety of wastewater treatment technologies such as adsorption, ozonation, and advanced oxidation processes have been employed for the purification of nitrobenzene contaminated water. Activated carbon served as most efficient adsorbent for nitrobenzene adsorption. However, it is flammable and difficult to regenerate.4 Thus alternative adsorbent for nitrobenzene removal is desired. Adsorption of organic contaminants from water on different layered and porous inorganic materials and its organic derivatives have been used for years.5,6 Recent development of photocatalytic degradation of organic contaminants in wastewater using TiO2 as photocatalyst has also been the thrust area for tackling environmental problems.7 The environment at the montmorillonite (MMT, smectite group clay) surface is hydrophilic in nature due to hydration of inorganic cations on the exchange site. As a result, MMT is ineffective as a sorbent for nonionic organic compounds in the presence of water. A unit layer of MMT is formed by the bonding through oxygen bridges of one alumina sheet composed of octahedrons between two silica sheets composed of tetrahedrons. These three-layer units are stacked one above another with oxygens in neighboring layers adjacent to each other, with * To whom correspondence should be addressed. E-mail: rvjasra@ gmail.com,
[email protected]. Tel.: +91 265 6693935. Fax: +91 265 6693934. † Central Salt and Marine Chemicals Research Institute. ‡ Reliance Industries Limited.
a thickness of 1 nm. Stacking of the layers leads to a regular van der Waals gap between them called the interlayer or gallery. Although the basal spacing is 1.2-1.3 nm at ambient condition, it can be modified with respect to amount of hydrophilic or organophilic groups situated at gallery. Isomorphic substitution within the layer (either in octahedral or tetrahedral site) by Mg2+, Fe2+, or Al3+ generates negative charges that are normally counterbalanced by hydrated alkali or alkaline earth cations (Na+, K+, Ca+, Li+) residing in the interlayer.8,9 Because of the relatively weak forces between the layers (due to the layered structure), intercalation of various molecules, an even polymer, between the layers is facile. The ion-exchange reaction between quaternary ammonium cations and MMT results into organoclays and has two consequences; first, the gap between the single sheets is widened, enabling organic cations chain to move in between them, and second, the surface properties of each single sheet are changed from being hydrophilic to hydrophobic or organophilic.10,11 Therefore, organic derivatives of MMT (organoclay) with different types of organic modifiers are more effective than their unmodified counterparts in the sorption of organic contaminants from water. Organoclay sorbs organic contaminants through adsorption or partitioning phenomenon, depending on the structure of the organic cation that has been exchanged on the MMT and nature of organic contaminants (polar or nonpolar) present in the wastewater.12-14 Boyd et al.15 reported the adsorption mechanism of various substituted nitrobenzene on K+, Na+, Mg2+, Ca2+, and Ba2+ exchanged smectite clay and concluded that the potential for adsorption of substituted nitrobenzene by K+-smectite is determined largely by the additive interactions of the -NO2 groups and the secondary substituent with interlayer K+ ions. Zhu et al.16,17 have described that the sorption of polar organic contaminants onto organoclays resulted nonlinear isotherm, mainly governed by adsorption and other specific interaction while sorption of nonpolar contaminants followed partition phenomenon. Pernyeszi et al.18 have studied the adsorption of
10.1021/ie800953g CCC: $40.75 2009 American Chemical Society Published on Web 12/18/2008
1052 Ind. Eng. Chem. Res., Vol. 48, No. 2, 2009
2,4-dichlorophenol on organoclay/aquifer materials in static and flow conditions. Farkas et al.3 have studied arrangement of nitrobenzene in the interlayer space of the hexadecylpyridiniumMMT, which resulted in a monolayer at low concentration of pollutant by replacing water molecules and bilayer orientation with the alkyl chain solvated by the pollutant. There are many reports on the sorption of nitrobenzene as a contaminant in wastewater on organoclays in a static (batch experiments) condition. In this work, we report the detailed study of the sorption of nitrobenzene from aqueous solution, by organoclays in a fixed-bed system. The objective of the present research is to study the effect of size of sorbent, flow rate of sorbate solution, temperature of the sorption, and concentration of sorbate and sorbent with different amounts of organic modifier exchanged in MMT in a fixed-bed column. Desorption of nitrobenzene from organoclays in a fixed bed is also studied. 2. Experimental Section
Figure 1. Schematic representation of the fixed-bed experimental setup (bed length 50 mm, bed diameter 5 mm).
2.1. Materials. Bentonite lumps were collected from Barmer district of Rajasthan, India. Hexadecyltrimethylammonium bromide (HDTA) [CH3(CH2)15N(CH3)3 · Br], stearyldimethylbenzylammonium chloride (SDBA) {C6H5CH2N[(CH2)17CH3](CH3)2 · Cl}, and dioctadecyldimethylammonium chloride (DODA) {[(CH2)17CH3]2N(CH3)2 · Cl} were purchased from Sigma-Aldrich, USA. Nitrobenzene was obtained from s.d. fine chem. (INDIA) and was used as received. 2.2. Synthesis of Organoclays. MMT was purified by sedimentation technique as discussed earlier.19 The purified clay fractions were obtained by dispersing 150 g of bentonite lumps (R-MMT) in 10 L of deionized water (1.5% w/v) and was allowed to swell overnight. It was stirred (200 rpm) for 30 min. The supernatant slurry having desired clay particles size ( DODA 90 > HDTA 90. Thus, SDBA 90 has been used for the fixed-bed experiments. 3.4. Fixed-Bed Experiments. In the dynamic sorption studies, the sorbent (organoclay) was loaded in column with dimension of 50 mm length and 5 mm diameter, through which the aqueous solution of the nitrobenzene is passed. During its passage through the bed, the solution continuously meets a fresh part of the sorbent and tends to establish equilibrium. However, as the time of contact with a given part of the sorbent is limited, a true equilibrium is never attained.22,23 The U.S. Environmental Protection Agency (EPA) recommends that levels in lakes and streams should be limited to 17 parts of nitrobenzene per million parts of water (17 ppm) to prevent possible health effects from drinking water or eating fish contaminated with nitrobenzene.7 Thus, in the present study, breakthrough point is considered at 17 mg/L effluent concentration, and the exhaust times were taken at C/C0 ) 0.9. The breakthrough curves expressed in terms of C/C0 and time for sorption of aqueous nitrobenzene on organoclays are shown in Figures 5-9. From the breakthrough curves, important column parameters such as time for primary sorption zone to move up its length (tZ), total time involved for the establishment of primary sorption zone (tE), rate at which the exchange zone is moving up through the bed (Uz), fractional capacity (F), the height of the exchange zone (hZ), and percentage of the total column saturated at breakthrough (% S) are calculated on the basis of eqs 1-7.24-26 VE - VB Qw
(1)
VE Qw
(2)
hZ h ) tz tE - tf
(3)
h(tz) tE - tf
(4)
tz )
tE ) Uz )
hz )
Ind. Eng. Chem. Res., Vol. 48, No. 2, 2009 1055
tf ) (1 - F)tz SZ ) F) Smax
∫
VE
VB
Where kYN is the Yoon-Nelson rate constant (min-1). The values of kYN and t0.5 can be obtained from the slope and the intercept of the linear plot of ln(C/C0 - C) versus t. The experimental and calculated values of t0.5 (50% breakthrough) along with the Yoon-Nelson rate constant for sorption of aqueous nitrobenzene on organoclays in fixed-bed are listed in Table 1a and b. The experimental t0.5 for different breakthrough curves were obtained at C/C0 ) 0.5. The values of t0.5 obtained from model and experiments are comparable. The predicted breakthrough curves for feed rate of 0.6 mL/min, SDBA 90 of (-)60-(+) 100 mesh size, and feed concentration of 252 mg/L are almost fit with the experimental breakthrough. However, higher feed rate, concentration, and particle size, and organoclay with lower organic modifier (SDBA 50) are partially fitted with the experimental results. 3.4.1. Effect of Feed Rate. The measured breakthrough curves of nitrobenzene (461 mg/L) on the SDBA 90 (1 g) bed at different flow rates are shown in Figure 5. The breakthrough point (C/C0 at effluent concentration of 17 mg/L) occurs faster with increase of the flow rate. The important column behavior parameters are shown in Table 1a and b. The tZ and tE values are 408 and 583 min (0.6 mL/min); 295 and 370 min (1.0 mL/ min); and 193 and 233 (1.5 mL/min), respectively. In the case of SDBA 90 with particle size of (-)60-(+)100, the fractional capacities (F) of the column in the sorption zone from breakthrough point to continue to remove solute from solution are 0.92, 0.92, and 0.85, and the percent saturation values at breakpoint are 93.7, 93.1, and 85.4% for feed rates of 0.6, 1.0, and 1.5 mL/min, respectively. The rate of exchange zone increases with increase in the feed rate. The breakthrough
(5)
(C0 - C) dV
C0(VE - VB)
(6)
h + (F - 1)hZ × 100 (7) h Where, VE and VB are total volume of wastewater treated to the point of exhaustion and to the point of breakthrough, respectively. Qw and h are wastewater flow rate and depth of bed. tf is time required for the exchange zone to initially form. C0 and C are initial and exhaustion solute concentration. Sz and Smax are amount of solute that has been removed by the sorption zone from breakthrough to exhaustion and amount of solute removed by the sorption zone if completely exhausted, respectively. The breakthrough capacity indicates the sorption capacity of organoclay to the breakthrough point and was measured by VBC0/W, where W is the weight of the sorbent. There have been several models used for the prediction of breakthrough. Srivastava et al.27 reported that the Yoon-Nelson model gave values of the time for 50% breakthrough point that were comparable to the experimental time. We have predicted breakthrough curve using the Yoon-Nelson model28 which is based on the assumption that the rate of decrease in the probability of sorption for each sorbate molecule is proportional to the probability of sorbate sorption and sorbate breakthrough on the sorbent. The equation for the 50% breakthrough concentration from a fixed bed of sorbent is % S)
ln(C/C0 - C) ) kYNt - t0.5kYN
(8)
Table 1. Column Behavior Parameters for Sorption of Nitrobenzene from Aqueous Solution on Organoclays a sorbent feed rate (mL/min) feed concentration (mg/L) sorbent size (ASTM mesh size) temperature (°C) VB (mL) VE (mL) tZ (min) tE (min) F hZ (cm) UZ (cm/h) %S breakthrough capacity (mg/g) t0.5, exp (min) t0.5, theor (min) kYN (min-1)
SDBA 90 0.6
105 350 408 583 0.92 3.7 0.55 93.7 48.4 379.1 382.4 0.0111
SDBA 90
1.0 461 (-)60-(+)100 27 75 370 295 370 0.92 4.3 0.87 93.1 34.6 210.1 215.3 0.0148
1.5
60 350 193 233 0.85 4.8 1.47 85.4 27.7 128.8 137.2 0.0174
1.0 461 (-)30-(+)60 27 30 450 420 450 0.88 5.3 0.75 87.2 13.8 164.5 162.3 0.0079
SDBA 90 1.0 252
763 (-)60-(+)100 27 110 60 420 550 310 490 420 550 0.82 0.8 4.3 5.4 0.82 0.66 84.5 78.9 27.7 44.8 219.2 232.7 248.4 233.6 0.0192 0.0086
b sorbent feed rate (mL/min) feed concentration (mg/L) sorbent size (ASTM mesh size) temperature (°C) VB (mL) VE (mL) tZ (min) tE (min) F hZ (cm) UZ (cm/h) %S breakthrough capacity (mg/g) t0.5, exp (min) t0.5, theor (min) kYN (min-1)
SDBA 50
SDBA 70 0.6 461 (-)60-(+)100 27
54 276 370 460 0.79 4.8 0.79 79.1 24.9 199.3 179.4 0.0075
75 399 540 665 0.9 4.4 0.49 91.5 34.6 312.1 345.3 0.0104
SDBA 90 1.0 461 (-)60-(+)100 17 80 450 370 450 0.87 4.6 0.74 88.4 36.9 248.1 239.8 0.0142
1056 Ind. Eng. Chem. Res., Vol. 48, No. 2, 2009
Figure 6. Effect of concentration of sorbate solution on breakthrough curve of sorption of nitrobenzene on SDBA 90 (sorption conditions: sorbent 1 g; bed length 50 mm; bed diameter 5 mm; flow rate 1 mL/min; temperature 27 °C; size of sorbent (-)60-(+)100 mesh size).
capacity of nitrobenzene sorption on SDBA 90 decreases with increase in the flow rate. This is due to fact that as the feed rate increases the sorbate gets lower contact time to diffuse into the sorbent particles. The column capacity was found to be higher than batch capacity as calculated by sorption isotherms. A higher capacity of column operations was established by a continuously large concentration gradient at the interface zone as it passed through the column, while the concentration gradient decreased with time in a batch isotherm test. 3.4.2. Effect of Feed Concentration. The effect of feed concentration is illustrated in Figure 6. The volume (VB) at the breakthrough point increases with decrease in the feed concentration. For feed concentrations of 252 and 763 mg/L, the values of tZ, tE, F, and % S are 310 and 490 min, 420 and 550 min, 0.82 and 8, 84.5 and 78.9%, respectively, as shown in Table 1a. The rate of exchange zone (Uz) decreases when increases the feed concentration. The breakthrough capacity also increases with increase in feed concentration since the equilibrium sorption isotherm is linear. The breakthrough capacity for feed concentration of 252 mg/L is around 50% of its equilibrium sorption capacity, and for 461 and 763 mg/L, it is 30 and 25% of its equilibrium sorption capacity. 3.4.3. Effect of Size of Sorbent. The size of the sorbent plays an important role in the fixed-bed system as shown in Figure 7. SDBA 90 with (-)30-(+)60 and (-)60-(+)100 mesh size was used in this study for column sorption. The breakthrough point of nitrobenzene occurs slowly in SDBA 90 with fine particle size compared to coarser particle size. This is due to the faster diffusion of nitrobenzene in SDBA 90 with fine particles, and thus, it can have a high breakthrough capacity (34.6 mg/g) compared to coarser particles of SDBA 90 which is having breakthrough capacity of 13.8 mg/g. The tZ, tE, F, and % S values are 420 min, 450 min, 0.88, and 87.2 respectively. The rate of exchange zone is 0.8 cm/h. This explains that the percent saturation is higher in finer as compared to coarser particle size. The height of exchange zone (hZ) is also higher (5.3 cm) while the sorption study carried out using (-)30-(+)60 mesh sized particles. The hZ for (-)60-(+)100 mesh sized particles is 4.3 cm. The rate of exchange zone is decreases with decrease in size of the SDBA 90. 3.4.4. Effect of Amount of Organic Moiety Exchanged in MMT. The organic modification of MMT substantially increases the sorption capacity of nonpolar organic contaminants from wastewater. To illustrate this effect, organoclay with
Figure 7. Effect of particle size of SDBA 90 on breakthrough curve of sorption of nitrobenzene (sorption conditions: sorbent 1 g; bed length 50 mm; bed diameter 5 mm; sorbate concentration 461 mg/L; temperature 27 °C; flow rate: 1 mL/min).
Figure 8. Effect of amount of organic moiety exchanged with MMT on breakthrough curve of sorption of nitrobenzene on SDBA 90 (sorption conditions: sorbent 1 g; bed length 50 mm; bed diameter 5 mm; flow rate: 1.0 mL/min; sorbate concentration 461 mg/L; temperature 27 °C; size of sorbent (-)60-(+)100 mesh size).
different amounts of organic moiety (SDBA 70 and SDBA 50) were synthesized and employed for the sorption of aqueous nitrobenzene in the fixed-bed system as shown in Figure 8. The breakthrough point of nitrobenzene appears faster on sorbent with lower organic modifier. The tZ and tE values are 470 and 460 min (SDBA 50) and 540 and 665 min (SDBA 70), respectively. The fractional capacity (F) and % S decrease while hZ and UZ increase with decrease in the amount of organic modifier in sorbent. The % S for SDBA 70 and SDBA 50 is 91.5 and 79.1, respectively. The breakthrough capacity also decreased with decrease in the amount of organic moiety in organoclay, on the order of 44.6 mg/g for SDBA 90, 34.6 mg/g for SDBA 70, and 24.9 mg/g for SDBA 50. 3.4.5. Effect of Temperature and Desorption. The temperature of the sorption medium is also an important parameter for designing a fixed-bed sorption setup. The temperature effect on breakthrough curve was studied at 27 °C (room temperature) and 17 °C. We have also tried to get data at higher temperature (37 °C), but failed, due to swelling as well as breaking of organoclay particles at higher temperature which blocked the column and substantially reduced the effluent flow rate. The tZ and tE values are 370 and 450 min at 17 °C. The saturation at
Ind. Eng. Chem. Res., Vol. 48, No. 2, 2009 1057
the breakthrough characteristics for the sorption of nitrobenzene on the organoclays. Acknowledgment We thank The Director, Central Salt & Marine Chemicals Research Institute, Bhavnagar, for taking keen interest in this work and also providing the facilities. H.A.P. thanks Mr. Sunil A. P. for helpful discussion. We also thank Council of Scientific & Industrial Research (CSIR), New Delhi, for funding under the Network Project. Literature Cited
Figure 9. Effect of temperature on breakthrough curve of sorption of nitrobenzene on SDBA 90 (sorption conditions: sorbent 1 g; bed length 50 mm; bed diameter 5 mm; flow rate: 1.0 mL/min; sorbate concentration 461 mg/L; size of sorbent (-)60-(+)100 mesh size) and desorption using water at a temperature of 27 °C.
breakthrough point and fractional capacity are 88.4% and 0.87, respectively, which are lower than dynamic sorption measurement carried out at room temperature. The height of exchange zone is 4.6 cm, which is higher than the dynamic sorption at room temperature. These parameters show that at 17 °C, even though the equilibrium breakthrough capacity is higher the diffusion of nitrobenzene is slower than that at room temperature sorption which can be seen as the broader breakthrough curve given in Figure 9. The organoclay column is generally dumped as solid waste after sorption of organic contaminants from wastewater. As stated earlier, the phenomenon involved in sorption of nitrobenzene over organoclay is partitioning. Elution of sorbate with simultaneous chemical regeneration by suitable solvent has been tried by passing water through the column. Desorption of nitrobenzene were carried out in situ at room temperature after sorption of aqueous nitrobenzene at 27 °C temperature as shown in Figure 9. A volume of 375 mL of water is sufficient for the almost complete desorption of nitrobenzene, at the water flow rate of 1 mL/min. It is clear that a cyclic process for the recovery of nitrobenzene is feasible by using two or more sorbent column in parallel, in which one column is in the sorption cycle while the second one is used in regeneration cycle. 4. Conclusions In summary, sorption of nitrobenzene in dynamic conditions is a technologically important study for wastewater treatment. The phenomenon involved in sorption of nitrobenzene over organoclay is partition rather than adsorption. The presence of benzyl functionalities in organoclay can increase the sorption capacity of aromatic organic contaminants. The sorption capacity of organoclay is in the order of SDBA 90 > DODA 90 > HDTA 90. The breakthrough capacity is increases when the dynamic sorption carried out using finer particles of SDBA 90 and slower feed rate (0.6 mL/min.) at 27 °C. The broader breakthrough curves are obtained for higher particle size of SDBA 90. The important column parameters which are useful for designing a column, have evaluated for the sorption of nitrobenzene on organoclay from breakthrough curves. Desorption of nitrobenzene from organoclay is also possible. For 50% breakthrough time, the predicted values from the Yoon-Nelson model are comparable to the experimental time. The present work provided a simple and easy-to-follow method for analyzing
(1) Upson, R. T.; Burns, S. E. Sorption of nitroaromatic compounds to synthesized organoclays. J. Colloid Interface Sci. 2006, 297, 70–76. (2) Chatterjee, A.; Ebina, T.; Iwasaki, T.; Mizukami, F. Intermolecular reactivity study to scale adsorption property of para- and meta-substituted nitrobenzene over 2:1 dioctahedral smectite. J. Chem. Phys. 2003, 118 (22), 10212–10220. (3) Farkas, A.; Dekany, I. Interlamellar adsorption of organic pollutants in hydrophobic montmorillonite. Colloid Polym. Sci. 2001, 279, 459–467. (4) Qin, Q.; Ma, J.; Liu, K. Adsorption of nitrobenzene from aqueous solution by MCM-41. J. Colloid Interface Sci. 2007, 315, 80–86. (5) Patel, H. A.; Somani, R. S.; Bajaj, H. C.; Jasra, R. V. Nanoclays for polymer nanocomposites, paints, inks, greases and cosmetic formulations, drug delivery vehicle and wastewater treatment. Bull. Mater. Sci. 2006, 29, 133–145. (6) Alther, G. Using organoclays to enhance carbon filtration. Waste Manage. 2002, 22, 507–513. (7) Tayade, R. J.; Kulkarni, R. G.; Jasra, R. V. Photocatalytic degradation of aqueous nitrobenzene by nanocrystalline TiO2. Ind. Eng. Chem. Res. 2006, 45, 922–927. (8) Grim, R. E. Applied Clay Mineralogy; McGraw-Hill Book Co: New York, 1962. (9) Theng, B. K. G. The Chemistry of Clay-organic Reactions; John Wiley & Sons: New York, 1974. (10) Lagaly, G. Characterization of clays by organic compounds. Clay Miner. 1981, 16, 1–21. (11) Patel, H. A.; Somani, R. S.; Bajaj, H. C.; Jasra, R. V. Preparation and characterization of phosphonium montmorillonite with enhanced thermal stability. Appl. Clay Sci. 2007, 35, 194–200. (12) Redding, A. Z.; Burns, S. E.; Upson, R. T.; Anderson, E. F. Organoclay sorption of benzene as a function of total organic carbon content. J. Colloid Interface Sci. 2002, 250, 261–264. (13) Beall, G. W. The use of organo-clays in water treatment. Appl. Clay Sci. 2003, 24, 11–20. (14) Bergaya, F.; Theng, B. K. G.; Lagaly, G. Handbook of Clay Science; Elsevier Publication: The Netherlands, 2006; p 625. (15) Boyd, S. A.; Sheng, G.; Teppen, B. J.; Johnston, C. T. Mechanisms for the adsorption of substituted nitrobenzenes by smectite clays. EnViron. Sci. Technol. 2001, 35, 4227–4234. (16) Zhu, L.; Gren, X.; Yu, S. Use of cetyltrimethylammonium bromidebentonite to remove organic contaminants of varying polar character from water. EnViron. Sci. Technol. 1998, 32, 3374–3378. (17) Zhu, L.; Li, Y.; Zhang, J. Sorption of organobentonites to some organic pollutants in water. EnViron. Sci. Technol. 1997, 31, 1407–1410. (18) Pernyeszi, T.; Kasteel, R.; Witthuhn, B.; Klahre, P.; Vereecken, H.; Klumpp, E. Organoclays for soil remediation: Adsorption of 2,4dichlorophenol on organoclay/aquifer material mixtures studied under static and flow conditions. Appl. Clay Sci. 2006, 32, 179–189. (19) Patel, H. A.; Somani, R. S.; Bajaj, H. C.; Jasra, R. V. Synthesis and characterization of organic bentonite using Gujarat and Rajasthan clays. Curr. Sci. 2007, 92 (7), 1004–1009. (20) Vaia, R. A.; Teukolsky, R. K.; Giannelis, E. P. Interlayer Structure and Molecular Environment of Alkylammonium Layered Silicates. Chem. Mater. 1994, 6, 1017–1022. (21) Xi, Y.; Frost, R. L.; He, H. Modification of the surfaces of Wyoming montmorillonite by the cationic surfactants alkyl trimethyl, dialkyl dimethyl, and trialkyl methyl ammonium bromides. J. Colloid Interface Sci. 2007, 305, 150–158. (22) Goyal, M.; Singh, S.; Bansal, R. C. Equilibrium and dynamic adsorption of methylene blue from aqueous solutions by surface modified activated carbons. Carbon Sci. 2004, 5 (4), 170–179.
1058 Ind. Eng. Chem. Res., Vol. 48, No. 2, 2009 (23) Attia, A. A.; Girgis, B. S.; Fathy, N. A. Removal of methylene blue by carbons derived from peach stones by H3PO4 activation: Batch and column studies. Dyes Pigments 2008, 76, 282–289. (24) Gupta, V. K.; Mohan, D.; Suhas; Singh, K. P. Removal of 2-aminophenol using novel adsorbents. Ind. Eng. Chem. Res. 2006, 45, 1113–1122. (25) Gupta, V. K.; Srivastava, S. K.; Mohan, D. Equilibrium uptake, sorption dynamics, process optimization and column operations for the removal and recovery of malachite green from wastewater using activated carbon and activated Slag. Ind. Eng. Chem. Res. 1997, 36, 2207–2218. (26) Adak, A.; Bandyopadhyay, M.; Pal, A. Fixed bed column study for the removal of crystal violet (C. I. Basic Violet 3) dye from aquatic environment by surfactant-modified alumina. Dyes Pigments 2006, 69, 245– 251.
(27) Srivastava, V. C.; Prasad, B.; Mishra, I. M.; Mall, I. D.; Swamy, M. M. Prediction of Breakthrough Curves for Sorptive Removal of Phenol by Bagasse Fly Ash Packed Bed. Ind. Eng. Chem. Res. 2008, 47, 1603– 1613. (28) Yoon, Y. H.; Nelson, J. H. Application of gas adsorption kinetics. I. A theoretical model for respirator cartridge service time. Am. Ind. Hyg. Assoc. J. 1984, 45, 509–516.
ReceiVed for reView June 17, 2008 ReVised manuscript receiVed October 30, 2008 Accepted November 4, 2008 IE800953G
