INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 6, 2011

INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 6, 2011 2011 Satish Patil et al., licensee IPA- Open access - Distributed under Creative Commons Attribution License 2.0 Research article ISSN 0976 4402 Kinetics of adsorption of crystal violet from aqueous solutions using different natural materials Satish Patil 1, Vaijanta Deshmukh 2, Sameer Renukdas 2, Naseema Patel 2 1 -Department of Chemistry, A.P.Science College, Nagothane 402106 (MS), India. 2- Research guide, Department of Chemistry, Yashwant Mahavidyalaya, Nanded 431602 (MS), India. sdpatil72@gmail.com doi:10.6088/ijes.00106020007 ABSTRACT Adsorption studies of Crystal Violet (CV) on different natural materials were carried out by batch experiments. The parameter studied includes initial dye concentration, adsorbent dose, ph, contact time, agitation speed, particle size of adsorbent and temperature. The linear regression coefficient R 2 was used to elucidate the best fitting isotherm model. All isotherm models, Langmuir (R 2 = 2 to 9), Temkin (R 2 = 0.973 to 8) and Freundlich (R 2 = to 8 and n = 1.886 to 2.294) were found to be best fitting models. The monolayer (maximum) adsorption capacities (q m ) were found to be between 142.857 to 250 mg/g for natural adsorbents under study. Lagergen pseudo -second order model best fits the kinetics of adsorption. The correlation coefficient R 2 for second order adsorption model has very high values of R 2 for all absorbents (R 2 8) and q e(the) values are in good agreement with with q e(exp) showed that adsorption of CV on these natural materials follwed second order kinetics and chemosorption playing role in rate determining step. Intra particle diffusion plot showed boundary layer effect and larger intercepts indicates greater contribution of surface sorption in rate determining step. ph was found to be an important factor in controlling the adsorption of cationic dye. Adsorption of CV on adsorbents was found to increase on increasing ph, increasing temperature and decreasing particle size. Thermodynamic analysis showed that adsorption was favourable and spontaneous, endothermic physical adsorption and increased disorder and randomness at the solid- solution interface of CV with biosorbents. Mangrove plant leaf powder was found have excellent adsorption capacity towards CV than other natural materials under study. Keywords: Adsorption isotherm, Crystal violet (CV), biosorbents, kinetic and thermodynamic parameters. 1. Introduction Textile industry uses large volumes of water in wet processing operations and thereby, generates substantial quantities of wastewater containing large amounts of dissolved dyestuffs and other products, such as dispersing agents, dye bath carriers, salts, emulsifiers, leveling agents and heavy metals 1. Majority of this dyes are synthetic in nature and are usually composed of aromatic rings in their structure, inert and non-biodegradable when discharged into waste streams. Colored dyes are not only aesthetic, carcinogenic but also hinder light penetration and disturb life processes of living organisms in water. Therefore, the removal of such colored agents from aqueous effluents is necessary. Crystal violet (CV), a basic dye, is most widely used for the dyeing of cotton, wool, silk, nylon, paper, leather etc., among all other dyes of its category. In fact, basic dyes, such as crystal violet, are the Received on December, 2010 Published on March 2011 1123

brightest class of soluble dyes whose tinctorial values are very high; less than 1 mg/l of the dye produces an obvious coloration. Hence, it is needed to remove these dyes from textile effluent before it is discharged into receiving water bodies. The studies have been performed in order to remove color and other contaminations using various types of methods include adsorption 4, coagulation 5, nano-filtration and ozonalysis 6, membrane filtration 7, oxidation process 8 etc., in which adsorption is most useful due to its efficiency and visibility. Although, activated carbon adsorption appears to be the one of the most widely used techniques for dye removal, but in view of the high cost and regeneration problems, there has been a constant search for alternate low cost adsorbents. The adsorbents were prepared from natural materials such as plant roots, leaf and seed like neem leaf powder 10,11, gulmohar plant leaf powder 12, shells of hazelnut and almond 13, shells of lentil, wheat and rice 14, orange peel 15, Banana peel 16, guava leaf powder 17 used for removal of color. In the present study different leaf, fruit and bark materials were tested as adsorbents for adsorption of CV from wastewater. 2. Materials and methods 2.1 Adsorbents Adsorbents used in the present study are- 1. Mangrove plant (Sonneratia Apetala ) leaf powder ( MPLP) 2. Mangrove plant (Sonneratia Apetala ) fruit powder ( MPFP) 3. Mango ( Mangifera Indica) leaf powder (MLP) 4. Tamarind ( Tamarindus indica) fruit shell powder (TFSP) 5. Teak tree ( Tectona Grandis) bark powder (TTBP) 6. Almond tree (Terminialia cattapa) bark powder (ATBP) Mature materials of all above biosorbents were collected from Konkan region of Maharashtra state in India and washed thoroughly with distilled water to remove dust and other impurities. Washed materials were dried for 10 days in sunlight. Dried materials were grounded in a domestic mixer- grinder after removing non required parts separately. After grinding, the powders were again washed and dried. Different sized powders of each adsorbent were obtained by passing the powders through Jayant s sieves and stored in plastic bottle containers for further use. 2.2 Synthetic textile dye solution Crystal Violet (CV), a monovalent cationic basic dye with Molecular Formula C 25 H 30 N 3 Cl. In dye classification it is classified as C.I. 42555 and Class: basic dye 3. It has a molecular weight of 407.98 g/mol, used in this study was supplied by Merck, India. Structure of crystal violet molecule is, A stock solution of CV 1000 mg/l was prepared in double- distilled water and the experimental solutions of the desired concentration were obtained by successive dilutions. 1124

2.3 Methods Standard solution (5 mg/l) of the CV was taken and absorbance was determined at different wavelengths using Equiptronics single beam u.v. visible spectrophotometer to obtain a plot of absorbance verses wavelength. The wavelength corresponding to the maximum absorbance (λmax= 580 nm) as determined from the plot, was noted and this wavelength was used for measuring the absorbance in the present study. ph of solutions were adjusted using 1M HCl and 1M NaOH by Equiptronics ph- meter. The efficiency of adsorbents is evaluated by conducting laboratory batch mode studies. Specific amounts (25mg) of adsorbents were shaken in 25 ml aqueous solution of dye of varying concentration for different time periods at natural ph ( 7) and temperature ( 303K). At the end of pre-determined time intervals, adsorbent was removed by centrifugation at 10000 rpm and supernant was analyzed for the residual concentration of CV, spectrophotometrically at 580 nm wavelength. Also variation in ph, adsorbent dose, particle size, agitation speed and temperature were studied. 2.3.1 Effect of contact time 25 mg of adsorbent of 120 mesh size with 25 ml of dye solution was kept constant for batch experiments with an initial dye concentration of 200 mg/l (for MPLP, MPFP, MLP) and 125 mg/l (TFSP, TTBP, ATBP) were performed at nearly 303K on a oscillator at 230 rpm for 10, 20, 30, 40, 50,60 and 70 minutes at ph = 7. Then optimum contact time was identified for further batch experimental study. 2.3.2 Effect of adsorbent dosage Initial dye concentration of 400 mg/l were used in conjunction with adsorbent dose of 1, 2, 3, 4, 5, and 6 g/l. Contact time, ph, agitation speed, temperature and particle size of 60 minutes, 7, 230 rpm, 303K and 120 mesh respectively were kept constant. 2.3.3 Effect of initial dye concentration Initial dye concentration of 50, 75, 100, 125, 150, 175 and 200 mg/l were used in conjunction with adsorbent dose of 1 g/l. Contact time, ph, agitation speed, temperature and particle size of 60 minutes, 7, 230 rpm, 303K and 120 mesh respectively were kept constant. 1125

2.3.4 Effect of ph Initial P H of dye solutions were adjusted to 3, 4.3, 7, 9 and 11 for 100 mg/l concentration. Contact time, adsorbent dose, agitation speed, temperature and particle size of 60 minutes, 1 g/l, 230 rpm, 303K and 120 mesh respectively were kept constant. 2.3.5 Effect of particle size Three different sized particles of 120, 120 85 and 85 60 mesh were used in conjunction with 150 mg/l dye concentration. Contact time, adsorbent dose, agitation speed, temperature and ph of 60 minutes, 1 g/l, 230 rpm, 303K and 7 respectively were kept constant. 2.3.6 Effect of agitation speed 100, 170 and 230 rpm agitation speeds were used in conjunction with initial dye concentration of 150 mg/l. Adsorbent dose, ph, temperature, contact time and particle size of 1 g/l, 7, 303K, 60 minutes and 120 mesh respectively were kept constant. 2.3.7 Effect of temperature 303K, 313K and 323K temperatures were used in conjunction with 200 mg/l dye concentration. Contact time, adsorbent dose, agitation speed, particle size and ph of 60 minutes, 1 g/l, 230 rpm, 120 mesh and 7 respectively were kept constant. 3. Results and Discussions 3.1 Effect of contact time Effect of contact time on adsorption of CV is presented in Figures 1 and 2. Uptake of CV was rapid in first 10 minutes and after 60 minutes amount of dye adsorbed was almost constant. The dye uptake process appears to be rapid in first 10 minutes and nearly 40 to 70% of total dye uptake appears to have been adsorbed in this duration depending upon the adsorption ability of different adsorbents. The initial rapid phase may also be due to the increased number of vacant sites available at the initial stage. Later on the process becomes relatively slower and equilibrium conditions are reached within 50 to 60 minutes. At this point, the amount of the dye desorbing from the adsorbent is in a state of dynamic equilibrium with the amount of the dye being adsorbed onto the adsorbents. The time required to attain this state of equilibrium is termed the equilibrium time, and the amount of dye adsorbed at the equilibrium time reflects the maximum adsorption capacity of the adsorbent under those operating conditions.therefore, further batch experiments were carried out at 60 minutes optimum contact time. The mechanism of adsorption was investigated by pseudo - first order, pseudo- second order, Natarajan and Khalaf first order, Bhattacharya and Venkobachar first order, Intraparticle diffusion and models. The Lagergen (Singh et al., 1998) pseudo- first order rate expression is given as log (q e - q t ) = log q e (k 1 / 2.303) t (1) 1126

Where q e and q t are amounts of dye adsorbed (mg /g) on adsorbent at equilibrium and at time t, respectively and k 1 is rate constant of pseudo first order adsorption (min -1 ). The slope and intercept values of plot log (q e - q t ) against t, Figures 3 was used to determine pseudo first order rate constant (k 1 ) and theoretical amount of dye adsorbed per unit mass of adsorbent q e(the), respectively. q e(the) were compared with the q e(exp) values in Table(1). q e(exp) values do not agree with calculated values i.e. q e(the) values. This shows that the adsorption of the CV onto adsorbents under study is not the first-order kinetics (Ho and Mckay, 1999). The Langergen pseudo- second order kinetic model (Ho and Mckay, 1999) is given as t/q t = 1/(k 2 q e 2 ) + t/q e (2) Where k 2 is rate constant of second order adsorption (g /mg/ min). The slopes and intercepts of plot of t/q t against t, Figure 4, were used to determine q e(the) and k 2 respectively. The pseudo second order parameters, q e(the), h and k 2 obtained from the plot are represented in Table (1). Where h is initial adsorption rate (mg g -1.min), h = k 2 q e 2. The second order rate constant (k 2 ) was 0.00112 to 0.002564 mg/gm /min and in addition the experimental and theoretical equilibrium uptake values i.e. q e(exp) and q e(the) were found to have good agreement between them and the highly linear plot with correlation coefficient (R 2 8) for all the adsorbents showed that pseudo second order adsorption equation of Langergen fit well with whole range of contact time and dye adsorption process appears to be controlled by chemisorptions playing a significant role in the rate determining step. This indicates the adsorption of CV on these adsorbents is second order kinetics. Figure 1: Effect of contact time on adsorption of CV. 1127

Figure 2: Effect of initial dye concentration and contact time on % removal of CV Figure 3: Pseudo first order plot of effect of contact time on adsorption of CV. Figure 4: Pseudo second order plot of effect of contact time on adsorption of CV. 1128

The linearized form of Natarajan and Khalaf first order kinetic equation is presented as log (C o /C t ) = (K /2.303) t (3) Where C o and C t are concentrations of CV (mg/l) at time zero and time t respectively. K is first order adsorption rate constant (min -1 ), which was calculated from slope of the plot log(c o /C t ) against t, Figure 5, Table (2). The lineaized form of Bhattacharya and Venkobachar first order kinetic equation is presented as log [ 1 U(T) ] = - (k /2.303) t (4) Where U (T) = [(C o -C t ) / (C o -C e )] C e is equilibrium MB concentration (mg/ l) K is first order adsorption rate constant (min-1) which was calculated from slope of the plot log [ 1 U(T)] against t, Figure 6, Table (2). Figure 5: Natarajan and Khalaf first order plot of effect of contact time on adsorption of CV. Figure 6: Bhattacharya and Venkobachar first order plot of effect of contact time on adsorption of CV. 1129

Natarajan and Khalaf first order and Bhattacharya and Venkobachar first order kinetic models does not fit well with whole range of contact time and is generally applicable for initial stage of adsorption Correlation coefficient values were high enough for all adsorbents for Natarajan and Khalaf (R 2 = 0.971 to 8) as well as Bhattacharya and Venkobachar (R 2 = 0.976 to 3) first order equations upto 50 minutes but once the equilibrium is reached amount of dye adsorbed remains constant and thus showed non linearity. Adsorption of the dye by adsorbent includes transport of solute from aqueous to surface of solid and diffusion of solute into the interior of pores, which is generally a slow and rate determining process. According to Weber and Morris, the intra particle diffusion rate constant (K i ) is given by the following equation q t = K i t 1/2 (5) K i (mg/ g /min 1/2 ) values, Table (2) can be determined from the slope of the plot q t against t 1/2, Figure 7 showed a linear relationship but they do not pass through origin. This is due boundary layer effect. The larger the intercept, the greater the contribution of surface sorption in rate determining step.. Initial portion is attributed to the liquid film mass transfer and linear portion to the intra particle diffusion. The linearized form of Elovich kinetic equation is presented as q t =1/ β [ln(αβ)] + ln t /β (6) Where α and β are the constants calculated, Table (2) from the intercepts and slopes of plot q t against ln t, Figure 8. The constant β is related to the extent of surface coverage. The simple Elovich modelis used to describe second-order kinetic, assuming that the actual solid surface is energetically heterogeneous. This Elovich kinetic model has R 2 = to 989 for adsorbents under study. Figure 7: Intra particle diffusion plot of effect of contact time on adsorption of CV 1130

Figure 8: Elovich plot of effect of contact time on adsorption of CV 3.2 Effect of adsorbent dosage The adsorption of CV was studied by varying the adsorbent dosage. The percentage of adsorption increased with increase in dosage of adsorbent but amount of dye adsorbed per unit mass of adsorbent decreased with increased in adsorbent dose from 1 to 6 g/l. Figures 9 and 10.As amount of adsorbent increases, number of active sides available for adsorption also increases thus % removal also increases but as all active sides may not be available during adsorption due to overlapping between the active sides themselves and thus amount adsorbed mg/g of adsorbent decreases. Thus, the adsorption of dye increased with the sorbent dosage and reached an equilibrium value after certain sorbent dosage (3 to 4 g/l) for most of the adsorbents. Figure 9: Effect of adsorbent dosage on % removal of CV 1131

Figure 10: Effect of adsorbent dosage on amount adsorbed (mg/g) of CV. 3.3 Effect of initial dye concentration Percentage sorption decreased but amount of CV adsorbed per unit mass of adsorbent (mg /g) increased with increase in CV concentration from 50 to 200 mg /l, Figures 11 and 12. The initial concentration provides an important driving force to overcome all mass transfer resistances of the CV between the aqueous and solid phases. Therefore, a higher initial dye concentration of dye will enhance the sorption process. Figure 11: Effect of initial dye concentration on adsorption of CV. 1132

Figure 12: Effect of initial dye concentration on % removal of CV The Freundlich equation was employed for the adsorption of CV onto the adsorbents. The isotherm was represented by log q e = log K f + 1/n log C e (7) Where q e is amount of CV adsorbed at equilibrium (mg/g), C e is the equilibrium concentration of CV in solution (mg/l), K f and n are constant incorporating factors affecting the adsorption capacity and intensity of adsorption respectively. The plots of log q e vs log C e showed good linearity (R 2 = to 8 ) indicating the adsorption of CV obeys the Freundlich adsorption isotherm, Figure 13. Figure 13: Freundlich isotherm plot of effect of initial dye concentration on adsorption of CV The values of K f and n given in the Table (3). Values of n between 1 to 10 indicates an effective adsorption (Potgeiter, et al., 2005) while higher values of K f represents an easy uptake of adsorbate from the solution (Mahvi, et al., 2004). The Langmuir isotherm was represented by the following equation C e / q e = 1/ (q m b) + C e /q m (8) 1133

Where q m is monolayer (maximum) adsorption capacity (mg/g) and b is Langmuir constant related to energy of adsorption (1/mg). A linear plots of C e / q e vs C e suggest the applicability of the Langmuir isotherm Figure 14 (R 2 = 2 to 8). The values of q m and b were determined slop and intercepts of the plots, Table (3). Figure 14: Langmuir isotherm plot of effect of initial dye concentration on adsorption of CV. The essential features of the Langmuir isotherm can be expressed in terms of dimensionless constant separation factor, R L, which is defined by the following relation given by Hall 20 R L = 1/ (1+bC o ) (9) Where C o is initial CV concentration (mg/l). R L values lies between 0.05749 to 0.308737 indicates favorable adsorption (Table 5). The Temkin isotherm is given as q e = B ln A + Bln C e (10) Where A (1/g) is the equilibrium binding constant, corresponding to the maximum binding energy and constant B is related to heat of adsorption. A linear plots of q e against ln C e, Figure 15 enables the determination of the constants B and A from the slope and intercept, Table (3). 3.4 Effect of ph ph is one of the important factors in controlling the adsorption of dye on adsorbent. The adsorptions of CV from 100mg /l concentration on given adsorbents were studied at ph 3, 4.3, 7, 9 and 11. The amount of dye adsorbed per unit mass of adsorbent at equilibrium (q e ) increased with increased in ph. The results, as depicted in Figure 16, reveal that the dye uptake increases with the ph and it attains almost saturation value as the ph of the solution becomes 7 to 11, The observed finding may be explained on the basis of the fact that when the ph of the solution is quite low i e. 3.0, the presence of excess H+ ions compete with the cationic dye molecules in the solution and preferably occupy the binding sites available in the sorbent particles. As the ph of the sorbate solution increases number of H+ ions decreases 1134

thus making the adsorption process more favorable.in the vicinity of ph value of 11.0, optimum dye uptake is obtained. Similar results have also been reported elsewhere. Figure 15: Temkin isotherm plot of effect of initial dye concentration on adsorption of CV Figure 16: Effect of ph on adsorption of CV from initial concentration of 100 mg/l. 3.5 Effect of particle size Adsorption of CV on three sized particles 120, 120 85 and 85 60 mesh of adsorbent was studied for 100 mg/l concentrations of CV. The results of variation of these particle sizes on dye adsorption are shown in Figure 17. It can be observed that as the particle size increases the adsorption of dye decreases and hence the percentage removal of dye also decreases. This is due to larger surface area that is associated with smaller particles. For larger particles, the diffusion resistance to mass transfer is higher and most of the internal surface of the particle may not be utilized for adsorption and consequently amount of dye adsorbed is small. 1135

3.6 Effect of agitation speed The sorption is influenced by mass transfer parameters. The amount adsorbed at equilibrium was found to increase with increased in agitation speed from 100, 170 and 230 rpm of an oscillator from 150 mg/l initial CV solution. Figure 18. Figure 17 Effect of particle size on % removal of CV. Figure 18: Effect of agitation speed on adsorption of CV. This is because with low agitation speed the greater contact time is required to attend the equilibrium. With increasing the agitation speed, the rate of diffusion of dye molecules from bulk liquid to the liquid boundary layer surrounding the particle become higher because of an enhancement of turbulence and a decrease of thickness of the liquid boundary layer. 3.7 Effect of temperature Temperature has important effects on adsorption process. Adsorption of CV at three different temperatures (303K, 313K and 323K) onto biosorbents was studied for 200 mg/l initial CV concentration. The results, as depicted in Figure 19, clearly indicate that dye uptake increases with temperature. This may be explained on the basis of the fact that increase in temperature enhances the rate of diffusion of the adsorbate molecules across the external boundary layer and in the internal pores of the adsorbent particles as a result of the reduced viscosity of the 1136

solution. In addition, the mobility of sorbate molecules also increases with temperature, thereby facilitating the formation of surface monolayers. Changing the temperature will change the equilibrium capacity of the adsorbent for particular adsorbate. Thermodynamic analysis: Thermodynamic parameters such as change in free energy ( G) (J/mole), enthalpy ( H) (J/mole) and entropy ( S) (J/K/mole) were determined using following equations K o = C solid /C liquid (11) G = -RTlnK o (12) G = H - T S lnk o = - G/RT lnk o = S/R - H/RT (13) Where K o is equilibrium constant, C solid is solid phase concentration at equilibrium (mg/l), C liquid is liquid phase concentration at equilibrium (mg/l), T is absolute temperature in Kelvin and R is gas constant. G values obtained from equation (12), H and S values obtained from the slope and intercept of plot ln K o against 1/T, Figure 20 presented in Table (4). The negative value of G indicates the adsorption is favourable and spontaneous. G values increases with increase in temperature. Figure 19: Effect of temperature on adsorption of CV The low positive values of H indicate endothermic nature of adsorption. The positive values of S indicate the increased disorder and randomness at the solid solution interface of CV with the adsorbent. The adsorbed water molecules, which were displaced by adsorbate molecules, gain more translational energy than is lost by the adsorbate molecules, thus allowing prevalence of randomness in the system. The increase of adsorption capacity of the adsorbent at higher temperatures was due to enlargement of pore size and activation of adsorbent surface. 1137

Table 1: Effect of contact time on adsorption of CV Adsorbe nt MPLP MPFP MLP TFSP TTBP ATBP Initial CV Conc. (mg/l ) 200 200 200 125 125 125 q e(exp ) (mg/ g) 155 149 136 78 107. 5 91 Pseudo -first order model K 1 (min -1 ) 0.03684 8 0.04375 7 0.03915 1 0.05296 9 0.05527 2 0.05296 9 q e(the) (mg/g ) 52.72 3 56.23 4 44.77 1 48.75 3 42.75 6 32.73 4 R 2 3 2 0.976 9 0.976 1 q e(exp) (mg/g ) 155 149 136 78 107.5 91 Pseudo -second order model K 2 (g/mg/ min) 0.0012 0.00112 5 0.00112 5 0.00130 1 0.00182 9 0.00256 4 q e(the) (mg/g) 166.666 7 166.666 7 166.666 7 90.9090 9 125 100 h (mg/g. min) 33.3333 3 31.25 31.25 10.7526 9 28.5714 3 25.6410 3 R 2 8 8 8 8 9 9 Table 2: Effect of contact time on adsorption of CV Adsorb ent MPLP MPFP MLP TFSP TTBP ATBP Initial CV Conc. (mg/l) Intra particle diffusion model K i (mg/g /min 1/ 2 ) A (mg/g) 200 4.37 147.4 R 2 0.97 7 α (mg/g/mi n) Elovich Model β (g.mg -1 ) 24.87802 0.052083 200 5.466 126.2 0.97 25.04753 0.052521 200 5.822 89.47 125 5.385 36.14 125 4.551 72.57 125 3.618 62.97 5 0.95 6 0.94 5 0.95 2 19.63572 0.063776 35.39472 0.067705 R 2 3 6 1 8 Natarajan and Khalaf model K (min-1) 0.011515 0.011515 0.006909 0.009212 15.62773 0.079936 0.018424 12.15542 0.100422 9 0.006909 R 2 7 8 8 4 8 0.97 1 Bhattacharya and Venkobachar model K (min-1) 1.077804 0.971866 1.110046 0.467509 0.918897 1.020229 R 2 3 2 0.97 6 9 0.97 6 1 Adsorbent Table 3: Effect of initial dye concentration on adsorption of CV Freundlich isotherm parameters Langmuir isotherm parameters Temkin isotherm parameters K f n R 2 q m b R 2 A B R 2 MPLP 28.379 2.17865 200 0.08197 8 0.81427 42.24 8 MPFP 19.724 1.88679 2 250 0.08163 9 0.45746 46.85 4 MLP 18.197 2.06612 6 200 0.03876 7 0.41629 39.39 5 TFSP 13.614 2.1645 4 142.857 0.03302 7 0.30269 31.58 7 TTBP 26.122 2.1692 3 200 0.07042 7 0.71371 41.45 8 ATBP 19.86 2.29358 8 166.667 0.04478 2 0.49422 34.21 0.973 1138

Figure 20: Von t Hoff plot of effect of temperature on adsorption of CV Table 4: Equillibrium constants and thermodynamic parameters for the adsorption of CV Adsorbe nt Ko G (J/mole) H 303K 313K 323K 303K 313K 323K (J/mole) S (J/K/mol e) MPLP 3.34783 4 5.15385-3043.9-3607.5-4403.4 17509.3 67.7258 MPFP 2.8835 3.21053 3.84262-2667.8-3035.4-3615 11639.6 47.1321 MLP 2.07692 2.27869 2.63636-1841.2-2143.2-2603.2 9677.5 37.9285 TFSP 1.12766 1.28571 1.46914-302.66-653.99-1033 10750 36.4818 TTBP 3 3.84262 5.66667-2767.6-3503.1-4658.1 25798.3 94.0313 ATBP 1.75862 2.07692 2.63636-1422.1-1902 -2603.2 16428.5 58.8132 Table 5: Dimensionless Separation Factor (R L ) calculated from Langmuir constant (b) Initial CV Conc. (mg/l) MPLP MPFP MLP TFSP TTBP ATBP 50 0.196136 0.196792 0.340368 0.377216 0.22119 0.308737 75 0.139904 0.140405 0.255951 0.287646 0.159198 0.229437 100 0.108731 0.109135 0.205086 0.23245 0.124347 0.182548 125 0.088919 0.089256 0.171086 0.195027 0.102015 0.151573 150 0.075213 0.075503 0.146757 0.167983 0.086483 0.129584 175 0.065169 0.065423 0.128485 0.147525 0.075055 0.113167 200 0.05749 0.05772 0.11426 0.13151 0.0663 0.10044 4. Conclusions The objective of this paper was utilization of different natural materials as adsorbents for the removal of crystal violet. Langmuir, Temkin as well as Freundlich were found to be best fitting models with respect to R 2 values. The monolayer (maximum) adsorption capacities (q m ) were found to be 142.857 to 250 mg/g for natural adsorbents under study. Lagergen 1139

pseudo -second order model best fits the kinetics of adsorption. The correlation coefficient R 2 8 for second order adsorption model and q e(the) values are consistent with q e(exp) showed that pseudo second order adsorption equation of Langergen fit well with whole range of contact time. Intra particle diffusion plot showed boundary layer effect and larger intercepts indicates greater contribution of surface sorption in rate determining step. Adsorption was found to increase on increasing ph, increasing temperature and decreasing particle size. G, H and S values showed favourable, spontaneous, endothermic physical adsorption with increased disorder and randomness at the solid- solution interface of CV with biosorbents. Adsorption capacities of different adsorbents towards CV were found to be of the order of MPLP > MPFP > TTBP > MLP > ATBP > TFSP. These adsorbents have excellent adsorption capacity compared to many other non conventional adsorbents. They can be used as a low cost attractive alternative for costly activated carbon. 5. Rererences 1. E. Weber, N.L. Wolfe, 1987. Enviorn. Toxical Chem., 6 : pp 911 920. 2. R. shivaraj, C. Namasivayam, K. Kardirvelu, 2001.Waste Manage., 21 : pp 105-110 3. K. C. Chen, J.Y.Wu. C. C. Huang, Y.M.Liang, S.C.J. Hwang, 2003. J. Biotechnol., 101: pp 241 252. 4. Mckay G.1982. J.Chem. Technol. Biotechnol, 32: pp 759-772. 5. S. Sheshadri, P. L, Bishop, A. M. Agha,1994. Waste Manage, 15 : pp 127-137. 6. M. Arami, N. Yousefi Limaee, L. M. Mahmoodi, N.S. Tabrizi. 2005. J. Collide interface Sci., 288: pp 371-376. 7. R. Reid, 1996. J. Soc. Dyres Colour., 112: pp 103-109. 8. C. B. Chandran, D. Singh, P. Nigam,2002. Appl. Biochem. Biotechnol.,102: pp 207-212. 9. T. Robinson, B. Chandran, P. Nigam, 2002. Enviorn. International, 28: pp 29-33. 10. P Nigam, G. Armour, R. M. Banat, D. Singh, R. 2002. Marchant, Bioresour. Technol.72: pp 219-226. 11. Y.S. Ho., T. H. Chiang, Y. M. Hsuch,2005. Process Biochem., 40: pp 119-124. 12. Weber W.J. 1967. Principle and Application of Water Chemistry, edited by Faust S.D. and Hunter J. V. Wiiley, New York. 13. Arivoli S., Venkatraman B., Rajachandrasekar T. and Hema M. 2007. Res. J. Chem. Enviorn., 17: pp 70. 14. Arivoli S., Kalpana K., Sudha R. and Rajachandrasekar T. E.2007. J. Chem., 4: pp 238.. 1140

15. Renmin G., Yingzhi S., Jian C., Huijun L., hao Y.2005. Dyes and pigments, 67 : pp 179. 16. Vadivelan V., Vasnthkumar K. 2005. J. Colloid Inter. Sci., 286: pp 91. 17. Singh A.K., Singh D.P., Pandey K.K., and Singh V. N.,1988. Wollastonite as adsorbentfor removal of Fe (II) from water, J. Chem. Technol., 42: pp 39. 18. Y.S.Ho and G. Mckay, 1999. Water Res., 33: pp 578-584. 19. Potgeiter J., Potgeiter Vermaak S., Kalibatonga P., 2005. Heavy metals removal from solution by Palygorskite clay. Minerals Engineering. 20. Hall K. R. Eagleton L.C.,Acrivos A., Vermeulen T. 1966. Ind. Eng. Chem. Fund.,5. 21. W. J. Weber Jr., J. C. Morris, 1963. Kinetics of adsorption on carbon from solutions, J. Sanitary Eng. Div. ASCE, 89: pp 31-60. 1141