Ind. Eng. Chem. Res. 2006, 45, 5165-5171
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Removal of Crystal Violet from Wastewater by Activated Carbons Prepared from Rice Husk Kaustubha Mohanty, J. Thammu Naidu, B. C. Meikap,* and M. N. Biswas Department of Chemical Engineering, Indian Institute of Technology (IIT), Kharagpur, Dist: Midnapur(W), West Bengal, Pin - 721 302, India
Adsorption onto activated carbons is a potent method for the treatment of dye-bearing effluents because it offers various advantages. In this study, activated carbons, prepared by a new technique from low-cost rice husk by sulfuric acid and zinc chloride activation, were used as the adsorbent for the removal of crystal violet, a basic dye, from aqueous solutions. The effects of various experimental parameters, such as adsorbent dosage and size, initial dye concentration, pH, contact time, and temperature, were investigated in batch mode. The kinetic data were well fitted to the Lagergren, pseudo-second-order, and intraparticle diffusion models. It was found that intraparticle diffusion plays a significant role in the adsorption mechanism. The isothermal data could be well described by the Langmuir and Freundlich equations. The maximum uptakes of crystal violet by sulfuric acid activated (RHS) and zinc chloride activated (RHZ) rice husk carbon were found to be 64.875 and 61.575 mg/g of adsorbent, respectively. The results indicate that RHS and RHZ could be employed as low-cost alternatives to commercial activated carbon in wastewater treatment for the removal of basic dyes. Introduction The removal of color from dye-bearing effluents is a major problem because of the difficulty in treating such wastewaters by conventional treatment methods.1-3 Most dye-containing effluents from various industrial branches, mainly dye manufacturing and textile finishing, are discharged into river streams. Even in low concentrations, dyes affect aquatic life and the food web. Because many organic dyes are harmful to human beings, the removal of color from process or waste effluents is environmentally important. Adsorption is a widely used method for the treatment of industrial wastewaters containing colors, heavy metals and other inorganic and organic impurities.1,3,5-6 The advantages of adsorption are its simplicity of operation, low costs (compared to other separation processes), and absence of sludge formation. Textile industries are the major consumers of water, and they release a fair amount of color in their effluents. Liquid-phase adsorption has been used effectively for the removal of dye from wastewater.1,6 Activated carbon is the most widely used adsorbent for this purpose because of its extensive surface area, microporous structure, high adsorption capacity, and high degree of surface reactivity. The high cost of activated carbon sometimes makes its use limited.7,8 This has led to a search for alternative materials that are relatively inexpensive and, at the same time, provide reasonable adsorption efficiencies. In addition, adsorption will become inexpensive if the sorbent used is composed of inexpensive material and does not require any expensive additional pretreatment steps. To date, a number of low-cost, commercially available adsorbents have been tried for dye removal. These include coal fly ash, wood, silicagel, agricultural wastes, de-oiled soya, red mud, bagassee fly ash, bottom ash, and cotton wastes.7-14 However, as the adsorption capacities of the above adsorbents are not large, new adsorbents * To whom correspondence should be addressed. Tel.: +91-3222283958. Fax: +91-3222-282250. E-mail:
[email protected],
[email protected].
obtained by chemical activation are still under development. In this work, a new technique of chemical activation was used that had not previously been reported for the removal of dyes. Adsorption studies for dye removal were carried out using activated carbon made from unconventional sources as adsorbents.15-17 In general, these carbons will be as efficient in the adsorption of both organic and inorganic materials as the commercial activated carbons.18-20 This article reports on the preparation of activated carbons from rice husk, a byproduct of the rice milling industry, by sulfuric acid and zinc chloride activation to remove crystal violet from aqueous solution. Among the many available dyes, crystal violet (CV) is a well-known dye that is used in a variety of ways: as a biological stain; dermatological agent; veterinary medicine; additive to poultry feed to inhibit propagation of mold, intestinal parasites, and fungus; etc. It is also extensively used in textile dying and paper printing. However, crystal violet is also a mutagen and mitotic poison.21 We investigated the equilibrium and kinetic behavior of CV adsorption on the newly prepared activated carbons. The Langmuir and Freundlich equations were used to fit the equilibrium isotherm. The batchcontact-time method was used to measure the adsorption rate. Kinetic parameters were then evaluated. The results obtained here will be useful in further applications of these rice-huskbased activated carbons in color removal from wastewater. Experimental Section Preparation of the Activated Carbons. There are two different processes for the preparation of activated carbon: physical activation and chemical activation. In comparison to physical activation, chemical activation provides two important advantages. One is the lower temperature at which the process is performed. The other is that the global yield of chemical activation tends to be greater because burnoff char is not required. Among the numerous available dehydrating agents, zinc chloride, in particular, is a widely used chemical agent in the preparation of activated carbon. Knowledge of different variables during the activation process is very important in
10.1021/ie060257r CCC: $33.50 © 2006 American Chemical Society Published on Web 05/20/2006
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Table 1. Physicochemical Characteristics of Activated Carbons Prepared from Rice Husk property
RHS
RHZ
carbon yield (%) ash content (%) moisture content (%) bulk density (g/mL) BET surface area (m2/g) total pore volume (cm3/g) mean pore radius (Å)
36 3.0 4.28 0.84 681 0.526 24.2
32 3.3 5.62 0.78 578 0.463 22.6
controlling the porosity of carbon sought for a given application. Chemical activation by ZnCl2 improves pore development in the carbon structure, and because of the effect of chemicals, the yields of carbon are usually high.22 Rice husk collected from a nearby rice mill was washed with distilled water to remove water-soluble impurities and surfaceadhered particles and then oven-dried at 60 °C to remove the moisture and other volatile impurities. Then, part of the dried rice husk was soaked in concentrated H2SO4 in an amount sufficient to cover the raw material completely, agitated at 120 rpm in an incubator shaker for 30 min, and then left for 2 h. After being mixed, the slurry was subjected to vacuum-drying at 100 °C for 24 h. Chemical activation of the rice husk was performed with ZnCl2 as well. Ten grams of rice husk was well mixed with 100 mL of a concentrated solution that contained 10 g of ZnCl2. The mixing was performed at 50 °C for 1 h. After being mixed, the slurry was also subjected to vacuumdrying at 100 °C for 24 h. The resulting impregnated solids were placed in a stainless steel tubular reactor and heated (5 °C min-1) to a temperature of 300 °C under a nitrogen flow at a rate of 150 cm3 min-1 STP for 1 h. Nitrogen entering the reactor was first preheated to 250-300 °C in a preheater. The products were washed sequentially with 0.5 N HCl, hot water, and finally cold distilled water to remove residual organic and mineral materials and then dried at 110 °C. In all experiments, the heating rate and nitrogen flow were kept constant. The various physicochemical characteristics of the prepared activated carbons are reported in Table 1. Dye Used. CV, a basic dye, was used in the experiments. Chemically, crystal violet is known as hexamethyl pararosaniline chloride. The dye was of analytical reagent (AR) grade, supplied by Loba Chemie Pvt. Ltd., Mumbai, India. The chemical structure of the dye is shown below. A stock solution of crystal violet (1000 ppm) was prepared by dissolving the necessary amount of dye in tap water. Experimental solutions of the desired concentration were obtained by successive dilutions.
Batch Sorption Procedure. Adsorption kinetic and equilibrium studies were conducted using the bottle-point isotherm technique by placing a known quantity of the adsorbent in each of several conical flasks containing 200 mL of an aqueous solution of dye with a predetermined concentration. The final adsorbent concentration thereby achieved was 5 g/L, unless otherwise stated. After such solution preparation, each bottle
was shaken vigorously in a temperature-controlled incubator shaker for specific time intervals until equilibrium was reached. The samples were withdrawn from the shaker after regular intervals of time, filtered, and analyzed spectrophotometrically (Thermo Spectronic, Waltham, MA) at a wavelength of 586 nm to determine the residual dye concentration in the solution. The kinetics of adsorption was determined by analyzing the adsorptive uptake of the dye from aqueous solution at different time intervals. Three different initial concentrations of dye, viz., 50, 150, and 250 ppm, were used for the kinetic study. Equilibrium isotherms for adsorption onto the selected carbons were determined using sample dosages of 0.4 g of adsorbent per 200 mL of aqueous solution for initial dye concentrations in the range of 10-100 ppm. For these experiments, the bottles were shaken, at constant temperature (25 °C) and agitation speed (120 rpm), for the minimum contact time required to attain equilibrium, as determined from the kinetic measurements detailed above. The influence of pH was studied by adjusting the reaction mixture to different initial pH values and analyzing the residual color at the equilibrium contact time. The pH values were adjusted with dilute sulfuric acid and sodium hydroxide solutions. The amount of dye adsorbed onto the activated carbons, qe (mg/g), was calculated according to:
qe )
(Co - Ce)V W
(1)
where Co and Ce are the initial and equilibrium liquid-phase concentrations of dye, respectively (ppm); V is the volume of the solution (L), and W is the weight of the adsorbent (g). Results and Discussions Effect of Contact Time. To determine the equilibration time for the maximum uptake of crystal violet, the adsorption on RHS and RHZ was studied for three different initial concentrations as a function of contact time, and the results are shown in Figure 1. These experiments were performed with an adsorbent dose of 5 g/L at the natural pH of the solution. It can be concluded that the rate of dye uptake on activated carbon is higher during the initial stages and gradually decreases and becomes almost constant after a period of 120 min for both RHS and RHZ. RHS has a higher adsorption capacity than RHZ at equilibrium. The dye uptake versus time curve is single, smooth, and continuous leading to saturation, suggesting the possible monolayer coverage of the dye on the surface of the adsorbent.23 Adsorption Kinetics. The kinetics of adsorption was studied for its possible importance in the treatment of dye-containing industrial effluents. Numerous kinetic models have been proposed to elucidate the mechanism by which pollutants are adsorbed. The mechanism of adsorption depends on the physical and/or chemical characteristics of the adsorbent, as well as on the mass-transport process. To investigate the mechanism of dye adsorption, two kinetic models were considered as follows: Lagergren Model. Lagergren24 proposed a pseudo-first-order kinetic model. The integral form of the model is
log(qe - q) ) log qe -
Kad t 2.303
(2)
where q is the amount of dye adsorbed (mg g-1) at time t (min), qe is the amount of dye adsorbed at equilibrium (mg g-1), and Kad is the equilibrium rate constant of pseudo-first-order
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Figure 2. Crystal violet uptake by rice-husk-based carbons according to the Lagergren model.
Figure 1. Effect of contact time on uptake of crystal violet dye.
adsorption (min-1). This model has been successfully applied to describe the kinetics of many adsorption systems. Pseudo-Second-Order Model. Adsorption kinetics for some systems can also be described by a pseudo-second-order reaction.25 The linearized-integral form of this model is
t 1 1 ) + t q K q 2 qe
(3)
2 e
where K2 is the pseudo-second-order rate constant of adsorption (mg g-1 min-1). The applicability of the Lagergren and pseudo-second-order models can be examined by linear plots of log(qe - q) vs t and t/q vs t, respectively, as shown in Figures 2 and 3, respectively. To quantify the applicability of each model, the correlation coefficient, R2, was calculated from these plots. The linearity of these plots indicates the applicability of the two models. However, the correlation coefficients, R2, shows that the pseudosecond-order model, an indication of a chemisorption mechanism, fits the experimental data slightly better than the pseudofirst-order model. The first-order and second-order rate constant for RHS were found to be greater than those for RHZ. The rate constants along and correlation coefficients for three different initial concentrations of crystal violet are reported in Table 2. If the movement of the solute from the bulk liquid film surrounding the adsorbent is ignored, the adsorption process for porous solids can be separated into three stages, viz., (1) mass transfer (boundary-layer diffusion), (2) sorption of ions onto sites, and (3) intraparticle diffusion. In many cases, there is a possibility that intraparticle diffusion will be the rate-limiting step, which is normally determined using the equation proposed by Weber and Morris26
qe ) kpt1/2 + C
(4)
Figure 3. Crystal violet uptake by rice-husk-based carbons according to the pseudo-second-order model.
where qe (mg/g) is the amount adsorbed at time t, kp is the intraparticle rate constant (mg min0.5/g), and C is the intercept. qe was found to be linearly correlated with t1/2. The kp values were calculated using correlation analysis (Table 2). The R2 values are close to unity, indicating the appropriateness of the application of this model. This reveals the occurrence of an intraparticle diffusion process.26 The calculated values of kp are higher for the RHS-crystal violet system and lower for the RHZ-crystal violet system. The intraparticle diffusion plots are presented in Figure 4. The values of the intercept (Table 2) provide an idea of the boundary-layer thickness, i.e., the larger the intercept, the greater the boundary-layer effect.24 The
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Table 2. Kinetic Rate Constants for the Adsorption of Crystal Violet at Three Initial Concentrations onto Activated Carbons Prepared from Rice Husk activated carbon RHS parameter
RHZ
50 ppm 150 ppm 250 ppm 50 ppm 150 ppm 250 ppm
Kad (min-1) R2
0.0339 0.9932
Lagergren Model 0.0242 0.0324 0.0246 0.9781 0.9801 0.9332
0.0214 0.9994
0.0333 0.9918
K2 (mg/g min) R2
0.0281 0.9999
Pseudo-Second-Order Model 0.0079 0.0041 0.0023 0.9998 0.9998 0.9352
0.0073 0.9999
0.0043 0.9999
kp (mg min0.5/g) 0.2058 intercept 12.678 R2 0.9608
Intraparticle Diffusion Model 0.6097 1.1682 0.1961 34.842 52.662 12.066 0.9792 0.9904 0.8969
0.6921 32.945 0.9822
1.1533 49.657 0.9823
Figure 5. Effect of adsorbent dose on the removal of crystal violet.
Figure 4. Crystal violet uptake by rice-husk-based carbons according to the intraparticle diffusion model.
divergence in the value of the slope from 0.5 indicates the contribution of intraparticle diffusion as one of the rate-limiting steps, in addition to many other processes controlling the rate of adsorption, all of which might be operating simultaneously.27 Effect of Adsorbent Dose. The effect of adsorbent dose on the percentage removal of crystal violet for RHS and RHZ is shown in Figure 5. The percentage sorption followed the predicted pattern of increasing as the dosage was increased. The adsorption at the equilibrium time (120 min) increased from 56.6% to 96.6% as the RHS dose was increased from 1 to 6 g/L. In the case of RHZ, the adsorption increased from 48.6% to 93.5% for the same change in adsorbent dose. This might be due to the increase in the availability of surface-active sites resulting from the increased dose and conglomeration of the adsorbent.28 The further increase in the extent of removal of crystal violet was found to be insignificant above a dose of 5 g/L for both RHS and RHZ, which was fixed as the optimum dose of adsorbent in subsequent experiments.
Figure 6. Effect of particle size on the uptake of crystal violet.
Effect of Adsorbent Particle Size. The effect of adsorbent particle size on crystal violet uptake for four different particle sizes is shown in Figure 6. The results show that there is a gradual increase in adsorption with decreasing particle size. It is obvious that the smaller particles, which have higher solidliquid interfacial areas, will have the higher adsorption rates. A linear relationship exists between the amount of dye adsorbed and the particle size, as evidenced by the R2 values being close to unity (for RHS, R2 ) 0.9926, and for RHZ, R2 ) 0.9992). Similar observations have been reported previously for the adsorption of dyes.29
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Figure 7. Effect of temperature on crystal violet uptake, Co) 150 ppm, W ) 5 g/L.
Effect of Temperature. Temperature is an important parameter for the adsorption process. A plot of the crystal violet uptake as a function of temperature (15, 25, and 40 °C) is shown in Figure 7. The results reveal that the dye uptake increased with increasing temperature for both RHS (from 39.33 to 41.4 mg/g) and RHZ (from 38.205 to 40.095 mg/g). The fact that the sorption increased as the temperature rose indicates that these systems are endothermic, which suggests that chemisorption took place; this can be attributed to the formation of hydrogen bonds between the adsorbate and the adsorbent. Therefore, the adsorption capacity should largely depend on the chemical interaction between the functional groups on the adsorbent surface and the adsorbate and should increase with temperature rising. This can be explained in that an increasing diffusion rate of the adsorbate into the pores of the adsorbent at higher temperature might contribute to the crystal violet adsorption, as diffusion is an endothermic process.30,31 Adsorption Isotherm Studies. The equilibrium removal of crystal violet was mathematically expressed in terms of adsorption isotherms. Several models have been used in the literature to describe the experimental data of adsorption isotherms. The Langmuir and Freundlich models are the most frequently employed models. In the present work, both models were used. The crystal violet sorption isotherm followed the linearized Freundlich model as shown in Figure 8. The relation between the metal uptake capacity of the adsorbent, qe (mg/g), and the residual metal ion concentration at equilibrium, Ce (ppm), is given by
1 ln qe ) ln k + ln Ce n
(5)
where the intercept, ln k, is a measure of adsorbent capacity and the slope, 1/n, is the sorption intensity. The isotherm data fit the Freundlich model well for both RHS and RHZ. The fact that the value of 1/n is less than 1 indicates a favorable adsorption.
Figure 8. Freundlich isotherms for the removal of crystal violet by adsorption onto two different activated carbons prepared from rice husk carbon.
The Langmuir equation relates the solid-phase adsorbate concentration (qe), or uptake, to the equilibrium liquid concentration (Ce) as follows
qe )
KLbCe 1 + bCe
(6)
where KL and b are the Langmuir constants, representing the maximum adsorption capacity for the solid-phase loading and the energy constant related to the heat of adsorption, respectively. It can be seen from Figure 9 that the isotherm data fit the Langmuir equation well for both RHS and RHZ. The observed statistically significant (at the 95% confidence level) linear relationships, as evidenced by the R2 values (close to unity), indicate the applicability of these two adsorption isotherms and the monolayer coverage on the adsorbent surface. The Freundlich and Langmuir isotherm constants, along with the correlation coefficients, are reported in Table 3. One of the essential characteristics of the Langmuir isotherm can be expressed by a separation factor, RL; which is defined as
RL )
1 1 + KLCo
(7)
where Co is the initial concentration of the dye (ppm). The value of RL (Table 3) indicates whether an isotherm is irreversible (RL ) 0), favorable (0 < RL < 1), linear (RL ) 1), or unfavorable (RL > 1). It can be seen that the adsorptions of crystal violet on RHS and RHZ are favorable.27,30 Effect of Initial pH on Adsorption. The effect of the initial pH of the dye solution on the amount of dye adsorbed was studied by varying the initial pH (2.5-10.8) at constant process parameters. The experiments were performed for an initial concentration of 150 ppm and an adsorbent dose of 5 g/L, and the results are shown in Figure 10. An increase in initial pH increases the amount of dye adsorbed. It is important that the
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Figure 9. Langmuir isotherms for the removal of crystal violet by adsorption onto two different activated carbons prepared from rice husk carbon. Table 3. Freundlich and Langmuir Parameters for the Adsorption Isotherms activated carbon parameter
RHS
RHZ
intercept (ln k) slope (1/n) R2
Freundlich Isotherm 4.0202 0.9545 0.9995
1.9485 0.8186 0.9896
KL (mg/g) b (L/mg) R2 RL
Langmuir Isotherm 11.175 0.0015 0.9997 0.0089
3.77 0.0044 0.9891 0.0253
maximum adsorption for both RHS and RHZ takes place at pH 10.8. The favorable adsorption at this basic pH can be attributed to the cationic nature of the dye. At acidic pH, the presence of excess H+ ions decreases the number of negatively charged adsorbent sites, and the increase in the number of positively charged surface sites probably does not favor the adsorption of these positively charged dye cations. An increase in pH increases the number of negatively charged surface sites on the adsorbent, which enhances the adsorption of positively charged dye ions. These results are in agreement with other literature reports.27,28 Conclusions The removal of crystal violet from aqueous solution using two rice-husk-based activated carbons has been investigated under different experimental conditions in batch mode. The adsorption of crystal violet was found to be dependent on the adsorbent surface characteristics, adsorbent dose and size, and initial dye concentration. Most of the dye was removed within 60 min of the start of every experiment. The kinetics of crystal violet adsorption nicely followed pseudo-first- and -second-order rate expressions and demonstrated that intraparticle diffusion plays a significant role in the adsorption mechanism. Fits to the Freundlich and Langmuir isotherm models were found to be linear, indicating the applicability of classical adsorption
Figure 10. Effect of pH on the adsorption of crystal violet onto rice-huskbased activated carbons.
isotherms to this adsorbate-adsorbent system. The uptake of crystal violet was greatly affected by the solution pH. Commercial activated carbons are usually expensive, so that regeneration is essential, whereas these activated carbons prepared from rice husk are inexpensive, so regeneration is not necessary. The data reported here should be useful for the design and fabrication of an economically favorable treatment process using batch or stirred-tank flow reactors for the removal of crystal violet from dilute industrial effluents. Nomenclature b ) Langmuir constant (L/mg) C ) intercept of eq 4 Ce ) equilibrium phenol concentration (ppm) Co ) initial concentration of dye(ppm) k ) measure of adsorbent capacity K2 ) pseudo-second-order rate constant for adsorption (mg-1 g min-1) Kad ) equilibrium rate constant for pseudo-first-order adsorption (min-1) kd ) rate constant for intraparticle diffusion (mg g-1 min-1/2) KL ) Langmuir constant (mg/g) kp ) intraparticle rate constant (mg min0.5/g) 1/n ) sorption intensity RL ) separation factor q ) amount of dye adsorbed in time t (mg/g) qe ) amount of phenol adsorbed at equilibrium (mg/g) t ) time (min) V ) volume of the solution (L) W ) weight of the adsorbent (g) Literature Cited (1) McKay, G. Adsorption of dyestuffs from aqueous solutions with activated carbon. Part I. Equilibrium and batch contact time studies. J. Chem. Technol. Biotechnol. 1982, 32, 759.
Ind. Eng. Chem. Res., Vol. 45, No. 14, 2006 5171 (2) McKay, G. Waste colour removal from textile effluents. Am. Dyest. Rep. 1979, 68, 29. (3) Malik, P. K. Use of activated carbons prepared from sawdust and rice-husk for adsorption of acid dyes: A case study of Acid Yellow 36. Dyes Pigm. 2003, 56, 239. (4) Nigarn, P.; Banat L. M,; Singh, D. Marchant R. Microbial process for decolourisation of textile effluents containing azo, diazo and reactive dyes. Process Biochem. 1996, 31, 435. (5) Walker, G. M.; Hansen, L.; Hanna, J. A.; Allen, S. J. Kinetics of a reactive dye adsorption onto dolomitic sorbents. Water Res. 2003, 37, 2081. (6) Allen. S. J.; Mckay, G.; Porter, F. J. Adsorption isotherm models for basic dye adsorption by peat in single and binary component systems. J. Colloid Interface Sci. 2004, 280, 322. (7) Mckay, G.; Prasad, G. R.; Mowli, P. R. Equilibrium studies for the adsorption of dyestuff from aqueous solutions by lowcost materials. Water Air Soil Pollut. 1986, 29, 273. (8) Khare, S. K.; Panday, K. K.; Srivastava, R. M.; Singh, V. N. Removal of Victoria blue from aqueous solution by flyash. J Chem. Technol. Biotechnol. 1987, 38, 99-104. (9) Mittal, A.; Krishnan, L.; Gupta, V. K. Removal and recovery of malachite green from wastewater using an agricultural waste material, deoiled soya. Sep. Purif. Technol. 2005, 43, 125. (10) Mittal, A.; Kurup, L.; Gupta, V. K. Use of waste materialssbottom ash and de-oiled soyasas potential adsorbents for the removal of amaranth from aqueous solutions. J. Haz. Mater. 2005, 117, 171. (11) Gupta, V. K.; Mohan, D.; Sharma, S.; Sharma, M. Removal of basic dyes (rhodamine B and methylene blue) from aqueous solutions using bagasse fly ash. Sep. Sci. Technol. 2000, 35, 2097. (12) Gupta, V. K.; Mittal, A.; Krishnan, L.; Gajbe, V. Adsorption kinetics and column operations for the removal and recovery of malachite green from wastewater using bottom ash. Sep. Purif. Technol. 2004, 40, 87. (13) 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. (14) Gupta, V. K.; Ali, I.; Saini, V. K. Suhas. Removal of rhodamine B, fast green and methylene blue from wastewater using red mudsAn aluminum industry waste. Ind. Eng. Chem. Res. 2004, 43, 1740. (15) Howlader, M. M.; Hossain, Q. S.; Chowdhury, A. M. S.; Mustafa, A. I.; Mottalib, M. A. Activated carbon from Krishnachura fruit (Delonix regia) and caste seed (Ricinus communis L.). Ind. J. Chem. Technol. 1999, 6, 146. (16) Mohanty K.; Jha, M.; Meikap, B. C.; Biswas, M. N. Preparation and Characterization of Activated Carbons from Terminalia Arjuna Nut with Zinc Chloride Activation for the Removal of Phenol from Wastewater. Ind. Eng. Chem. Res. 2005, 44, 4128.
(17) Bhatnagar, A.; Jain, A. K. A comparative adsorption study with different industrial wastes as adsorbents for the removal of cationic dyes from water. J. Colloid Interface Sci. 2005, 281, 49. (18) O ¨ zacar, M.; Sengil, A. Adsorption of metal complex dyes from aqueous solutions by pine sawdust. Bioresour. Technol. 2005, 96, 791795. (19) Rengaraj, S.; Banumathi, A.; Murugesan, V. Preparation and characterization of activated carbon from agricultural wastes. Ind. J. Chem. Technol. 1996, 1, 13. (20) Mohanty, K.; Jha, M.; Meikap, B. C.; Biswas, M. N. Removal of chromium (VI) from dilute aqueous solutions by activated carbon developed from Terminalia arjuna nuts activated with zinc chloride. Chem Eng. Sci. 2005, 60, 3049. (21) Au, W.; Pathak, S.; Collie, C. I.; Hsu, T. S. Cytogenic toxicity of gentian violet (crystal violet) on mammalian cells in vitro. Mutat. Res. 1978, 58, 269. (22) Ahmadpour, A.; Do, D. D. The preparation of activated carbon from macadamia nutshell by chemical activation. Carbon 1997, 35, 1723. (23) Namasivayam, C.; Renganathan, K. Removal of Cd(II) from wastewater by adsorption on “waste” Fe(III)/Cr(III) hydroxide. Water Res. 1995, 29, 1737. (24) Lagergren, S. About the theory of so-called adsorption of soluble substances. Kungliga SVen. Vetenskapsakad. Handl. 1989, 24, 1. (25) Ho, Y.; Wase, D.; Forster, C. F. Kinetic studies of competitive heavy metal adsorption by sphagnum moss peat. EnViron. Technol. 1996, 17, 71. (26) Weber, W. J., Jr. Physicochemical Processes for Water Quality Control; Wiley-Interscience: New York, 1972. (27) Nagarethinam, K.; Mariappan, M. S. Kinetics and mechanism of removal of methylene blue by adsorption on various carbonssA comparative study. Dyes Pigm. 2001, 51, 25. (28) Garg, V. K.; Moirangthem, A.; Kumar, R.; Gupta, R. Basic dye (methylene blue) removal from simulated wastewater by adsorption using Indian Rosewood sawdust, a timber industry waste. Dyes Pigm 2004, 63, 243. (29) Deo, N.; Ali, M. Adsorption by a new low cost material: congo red 1 and 2. Indian J. EnViron. Prot. 1997, 17, 328. (30) Ho, Y.; Chiang, T.; Hsueh, Y. Removal of basic dye from aqueous solution using tree fern as a biosorbent. Process Biochem. 2005, 40, 119. (31) Qi, J.; Li, Z.; Guo Y.; Xu, H. Adsorption of phenolic compounds on micro- and mesoporous rice husk-based active carbons materials. Chem Phys. 2004, 87, 96.
ReceiVed for reView March 3, 2006 Accepted March 27, 2006 IE060257R
