KINETICS AND EQUILIBRIUM STUDIES OF - CiteSeerX

R. Venckatesh et. al. / International Journal of Engineering Science and Technology Vol. 2(6), 2010, 2040-2050

KINETICS AND EQUILIBRIUM STUDIES OF ADSORPTION OF DIRECT

RED-28 ONTO PUNICA GRANATUM CARBON

R.VENCKATESH

Department of Chemistry, Government Arts College, Udumalpet – 642 126, Tamilnadu, India [email protected]

T.AMUDHA

Department of Science and Humanities, R.V.S.College of Engineering and Technology, Coimbatore, India [email protected]

RAJESHWARI SIVARAJ

Department of Biotechnology, Karpagam University, Coimbatore-641 021, Tamilnadu, India [email protected]

M.CHANDRAMOHAN

Department of Science and Humanities, PARK Engineering College, Coimbatore, Tamilnadu, India [email protected]

M.JAMBULINGAM

Department of Chemistry, P.S.G.Arts and Science College, Coimbatore – 641 014, Tamilnadu, India

Abstract : An experimental study has been conducted on the adsorption of Direct red-28 dye using activated carbon prepared from Punica granatum (Pomegranate rind) by chemical activation with sulphuric acid. BET surface area of the activated carbon was determined as 1075.6 m2.g-1 and SEM observations showed the amorphous nature of the carbon. Adsorption kinetics, equilibrium and thermodynamics were investigated as a function of initial dye concentration, temperature and pH. First order Lagergren, pseudo-second order and Elovich kinetic models were used to test the adsorption kinetics. Results were analyzed by the Langmuir, Freundlich, Tempkin and fractional power isotherm models. Based on regression coefficient, the equilibrium data was found to fit well to the Langmuir equilibrium model than other models. Response surface method using the Box-Behnken design of experiments gives a mathematical model for the adsorption of the dyestuff. Keywords : Adsorption, Direct red - 28, Punica granatum, Kinetics, Equilibrium 1. Introduction One of the major problems concerning textile wastewater is colored effluent. The discharge of color waste is not only damaging the aesthetic nature of receiving streams but also it may be toxic to aquatic life. The color in the effluent is mainly due to unfixed dye. The concentration of unused dyes in the effluent depends upon the nature of dyes and dyeing process underway at the time [1]. Inefficiency of dyeing process results in 10-25% of all dye stuffs being lost directly to the wastewater. Although the textile dyes contribute only a small portion of the total volume of discharged wastewater after the dyeing process, yet they make it deeply colored [2].

Most of the commercially used dyes are resistant to biodegradation and photo-degradation and even oxidizing agents. Unless and otherwise properly treated, these dyes can significantly affect photosynthetic activity in aquatic life due to reduced light penetration and may also be toxic to certain forms of aquatic life due to the presence of metals and chlorides in them. Considerable work has been carried out on the removal of dye from wastewater [2-6] aerobic granules [7], rice husks [8], pineapple stem waste [9], cedar sawdust and crushed brick [10], nitric-acid treated water hyacinth [11], yellow passion fruit peel [12] are used in the treatment of textile wastewater. Many physical and chemical treatment methods including adsorption, coagulation, precipitation, filtration, electrodialysis, membrane separation and oxidation have been used for the treatment of dye containing effluents. Further, the adsorption process provides an attractive alternative treatment, especially if the adsorbent is inexpensive and readily available.

The present work was undertaken to explore the feasibility of finding a low cost effective adsorbent, Pomegranate rind for the treatment of Direct red - 28 dye from aqueous solution as a function of initial concentration, temperature, particle size of the adsorbent, dosage and pH by batch mode adsorption studies and to report the applicability of various kinetic models for the chosen dye by the adsorbent in a controlled system.

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SO Na3

NH 2NH 2

SO Na3

N = N N = N

2. Materials and Methods 2.1 Adsorbent The Pomegranate rind was cut into small pieces, dried in sunlight until the moisture was partially evaporated and was further dried in a hot air oven at 333K for 24 hours until the residual moisture was completely evaporated. This dried material was kept in desiccators before it was used as a source material for the preparation of adsorbent. The dried material was mixed with concentrated H2SO4 (ratio 1:1) and kept at room temperature overnight. Then it was washed with doubled distilled water for more than 5 times to remove the excess acid if any, and kept in hot air oven at 383K for 12 hours and soaked in 2% sodium carbonate overnight, drained and was carefully taken in an iron vessel, covered with a tight fitting lid to avoid contact with atmospheric air, and that was placed in a muffle furnace and the temperature was gradually raised up to 823K and the vessel kept at the same temperature for an hour. After cooling, the material was taken out and ground well by using ball mill and then crushed and sieved 125-250BSS mesh number, preserved in air tight vessel for further studies on adsorption kinetics. 2.2 Adsorbate The Direct Red-28 dye used in the present study was procured from Hindustan Ciba Geigy, Mumbai, India. 1000 mg of the dye was accurately weighed and made up to 1000 ml with double distilled water. All the reagents used were of analytical grade. 3. Results and Discussion The characteristics of the activated carbon prepared from pomegranate rind had been subjected to various characterization parameters and the results are shown in Table1. The surface area and the total pore volume were determined using B.E.T method (Fig.1) and the surface morphology of the activated carbon was observed with SEM (Model: Joel JSM 6360) (Fig.2). The X-ray Diffraction study of activated carbon was carried out using Rotoflux X-ray Diffractometer 20KW/20A, Model 10.61 with a Microprocessor recorder. The amorphous nature of the activated carbon was determined by using intensity of the observed rays with respect to scattering angle (2) (Fig.3).

Structure of Direct Red-28 The results indicated that the removal of dyes increased (mg.g-1) progressively with contact time and attained saturation after equilibrium time. The equilibrium time was dependent on the initial dye concentrations for all the dyes at all the range of concentrations used in the study. Also perusal of the results indicated that with increase in dye concentration the percent removal decreased but the amount of dye adsorbed/ unit weight of the carbon (mg.g-1) increased in all the range of concentrations tested suggesting that the dye removal using adsorption technique is concentration dependent. Similar results have been reported by various authors using low cost adsorbents [4,13,14]. This may be explained as, at a given constant adsorbent dosage, the decrease of adsorption with increase in initial concentration of dye solution may be due to lack of adsorbent surface area and the available sites for adsorption becomes fewer for adsorption [15]. Also the formation of second layer of the dye molecules is highly hindered at higher initial concentration of the dye, due to the repulsive interaction between adsorbed and unadsorbed dye molecules present on the solid surface and in solution, respectively [16]. The curves were found to be single, smooth and continuous, leading to saturation, indicating the possibilities of formation of monolayer coverage of dye on the outer surface of the adsorbent. 3.1 Adsorption rate constants Many attempts have been made to formulate a general expression describing the kinetics of sorption on solid surfaces for liquid-solid phase sorption systems. The pseudo-first order equation was first represented by Lagergren [17] for the adsorption of oxalic acid and malonic acid on to charcoal. 3.2 Pseudo – First Order Equation The pseudo-first order equation of Lagergren is generally expressed as follows,

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dq / dt = Kad (qe qt) (1)

Table 1. Characteristics of activated carbon

S.No Parameters Value1. pH solution 6.5 2. Moisture content (%) 4.18 3. Ash content (%) 2.22 4. Decolorizing power (mg/g) 155.9 5. Ion-exchange capacity (milliequi/g) 0.046. Surface area (m2/g) 1075.67. Pore volume (cm3/g) 0.185 8. Pore size (Ao) 250.2 9. Apparent Density (g/l) 0.45 10. Particle size (BSS) 125 11. Volatile matter (%) 5.612. Fixed carbon (%) 88.013. Calcium (%) 16.0 14. Sodium (mg/g) 7.0 15. Potassium (mg/g) 13.0 16. Iron (mg/g) 0.02 17. Water soluble matter (%) 2.0 18. HCl soluble matter (0.25N) (%) 7.0 19. Phenol number, mg 11.2 20. pHpzc 6.2 21. Yield (%) 87.8 22. Porosity (%) 89.22 23. Specific Gravity, S 1.35 24. Conductivity, mS/cm 0.62 25. Bulk density, ζ g/cm3 0.824

Fig. 1 BET isotherm of activated carbon Fig. 2 SEM photographs of activated carbon with dye

Where qe and qt are the sorption capacity at equilibrium and at time, ‘t’ and Kad is the rate constant of pseudo–first order sorption (per min). After integration and applying boundary condition t = 0 to t = t and q = 0 to q = qt, the integrated form of equation (1) becomes,

log (qe qt ) = log qe [ Kad / 2.303 t (2) Where, qe - Amount of dye adsorbed (mg.g-1) at equilibrium

qt - Amount of dye adsorbed (mg.g-1) at time, (t)

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Kad - Rate constant of adsorption, (per min) t - Agitation time (mins)

Fig. 3 XRD pattern of activated carbon

The Kad values have been calculated from the slope of the linear plots and are 2.53, 1.61, 1.38 and 1.15 respectively for different concentrations (10, 20, 30 and 40 mg.l-1) of the dyes studied. The rate constants observed are comparable with the values reported earlier [18]. Diffusive transport through the internal pores of the carbon and / or along the pore-wall surface (Intraparticle diffusion) adsorption or attachment of the solute particle at a suitable site on the carbon surface one or more of the above steps may be the rate controlling factor. 3.3 Intraparticle Diffusion (q) There is a possibility of transport of dye molecules from bulk into pores of the adsorbent besides adsorption at the outer surface of the adsorbent. The intraparticle diffusion rate constant can be given as follows [19].

q = Kp t ½ (3) Kp values for the adsorption of dyes are shown to be 0.15, 0.269, 0.421 and 0.45 mg.g-1.min-1/2 for the range of concentrations studied. Values of Kp generally increased with increase in dye concentration which shows that the adsorption rate is governed by the diffusion of the dye within the pores of the adsorbent. Similar results were reported for metal ion adsorption onto activated carbon cloths [20-21]. 3.4 Effect of carbon dose on dye adsorption The percent removal of the dyes increased with increase in carbon dosage and attained a plateau after a particular carbon dose for all the concentrations of the dyes studied .The observed increase in the percent removal of the dyes with increase in dose of the adsorbent is due to the increase of the surface area consequent to the increase in the number of carbon particles with more number of active sites for adsorption and saturation occurs as a result of non availability of dye molecules for adsorption[2,20,22]. This may also be due to the increase in effective surface area resulting from the conglomeration of the adsorbent especially at higher dosage of the adsorbent [23-24]. 3.5 Adsorption isotherm studies 3.5.1 Freundlich Equation An empirical relationship exists between the adsorption of solute to the surface of the adsorbent .This model could be effectively utilized to study the heterogeneity and surface energies.

The most common shape of the graph of amount of dye adsorbed per unit weight of adsorbent versus the concentration in the fluid in equilibrium is: These data often fit nicely the empirical equation proposed by Freundlich:

q = Kf C1/n (4)

Where, Kf and n are coefficients; q = weight adsorbed per unit weight of adsorbent; C = concentration in fluid Taking logs and rearranging:

log q = log Kf + 1/n log C (5) The constant Kf is an approximate indicator of adsorption capacity, while 1/n is a function of the strength of adsorption in the adsorption process. These constants can be evolved by linearising the above equation by adopting mathematical techniques [25].

It is learnt that, If n = 1 then the partition between the two phases are independent of the concentration. If the 1/n value is below one it indicates a normal adsorption. On the other hand 1/n being above one indicates

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cooperative adsorption [26]. The values of x/m and Ce observed from the adsorption experiments carried over by using Pomegranate rind activated carbon at 125-250 BSS mesh numbers of constant mass agitated with dyes of known concentrations at 300K up to the respective equilibrium periods are shown in Table 2. It was also observed from the earlier works of Wang [27], Nasar and Elgeundi [28], Choi and Cho [29], Manickavaskam [30] that the adsorption capacity and adsorption intensity of some other type of low cost adsorbents selected individually for different types of dyes increased with increase in temperature and increased with decrease in particle size. Similar pattern of results were reported [2,31] with carbonaceous and non-carbonaceous low cost adsorbents for different type of dyes as shown in Table 2. 3.5.2 Langmuir equation The Langmuir isotherm is valid for monolayer adsorption onto a surface containing a finite number of identical sites. The model assumes uniform energies of adsorption onto the surface and no transmigration of adsorbate in the plane of the surface.

Based upon these assumptions, Langmuir represented the following equation, qe = {(Q0 x b x Ce) / (1 + (b x Ce)} (6)

where, qe - is equal to the quantity of dye adsorbed in mg.g-1 of the adsorbent Q0 - The maximum quantity of dye adsorbed in mg.g-1 of the adsorbent,

b - The constant of Langmuir adsorption, Ce - The dye concentration at equilibrium in mg.l-1 Langmuir adsorption parameters are determined by transforming the Langmuir equation, which is in linear form. The linear plot of Ce/qe vs Ce showed that the adsorption followed Langmuir isotherm model and the values are tabulated in Table 2. The essential features of the Langmuir isotherm may be expressed in terms of equilibrium parameter RL, which is a dimensionless constant referred to as separation factor or equilibrium parameter [32].

RL = 1 / (1+ b C0) (7) Where C0 is the initial concentration and ‘b’ is the constant related to the energy of adsorption (Langmuir Constant). The values of RL indicate the nature of the isotherm. In the present investigation, the value of RL was less than one which showed that the adsorption process was favourable. The results of present investigation were compared with the earlier reports [2, 6], which were carried out as adsorption studies by using different types of dyes and on low cost adsorbent. 3.6 Pseudo-second-order model The pseudo-second-order model [33] is represented by the following differential equation

dqt/dt = k2 (qe-qt)2 (8)

Where qe = Amount of dye adsorbed (mg.g-1 at equilibrium), qt = Amount of dye adsorbed (mg.g-1 at time t) k2 is the equilibrium rate constant of pseudo-second order (g.mg-1.min-1) adsorption. Integrating the above equation for the boundary condition t = 0 to t and qt = 0 to q, gives:

t/q = 1/k2qe2 +1/qe . t (9)

The slope and intercept of plot of t/q versus t were used to calculate the second-order rate constant k2 (Fig.4). The values of equilibrium rate constant (k2) are presented in Table 2. Similar phenomenon was observed for the adsorption of malachite green onto bentonite [34]. 3.7 Elovich equation The simple Elovich model equation is generally expressed by the following equation [34]

qt = α + β lnt (10) The slope and intercept of plot of qt vs. ln t (Fig.4) were used to calculate the values of the constants ‘α’ and ‘β’ as shown in Table 2. 3.8 The Harkins-Jura adsorption isotherm [35] This can be expressed as

1/qe2 = (B/A) - (1/A) log Ce (11)

Where B and A are the isotherm constants. The Harkins-Jura adsorption isotherm accounts to multilayer adsorption and can be explained with the existence of a heterogeneous pore distribution. 1/qe2 was plotted vs. log Ce (Fig.4) and the isotherm constants and correlation coefficients are summarized in Table 2. 3.9 Tempkin model Heat of adsorption and the adsorbent- adsorbate interaction on adsorption isotherms were studied by Tempkin and Pyzhev [36]. The Tempkin isotherm equation is given as

qe = RT/b ln (KTCe) (12)

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or qe = B ln KT + B lnCe (13)

Where A = KT; B = RT/b, T is the absolute temperature in K, R is Universal gas constant, 8.314J.mol-1.K-1, KT the equilibrium binding constant (mg-1) and B is related to the heat of adsorption [34,37]. A plot of qe versus ln Ce at studied temperature is given in Fig.4. The constants obtained for Tempkin isotherm are shown in Table 2. The Tempkin constant B shows that the heat of adsorption decreases indicating exothermic adsorption [34]. 3.10 Fractional power model The fractional power model [38] is a modified form of the Freundlich equation and can be expressed as

ln qt = ln a + b ln t (14) Where, qt the amount of the dyes sorbed by the adsorbent at time, ‘t’ and ‘a’ and ‘b’ are constants with b1. The function ‘a’ ‘b’ is also a constant, being the specific sorption rate at unit time, i.e., when t=1. The plot of ln t vs ln qt (Fig.4) showed the linear relationship and the computed constants ‘a’ and ‘b’ from the intercepts and slopes of the plots are presented in Table 2.

Table 2. Isotherm constants for various models at 300k

Models Concentration

mg l-1 Isotherm constants

K2 h R2

Pseudo second order

10 6.15 0.186 0.995 20 37.88 0.293 0.989 30 103.4 0.36 0.976 40 205.9 0.399 0.959

Elovich Model

α β R2 10 0.09 1.171 0.978 20 0.03 2.29 0.974 30 0.02 3.392 0.954 40 0.01 4.479 0.932

Fractional power model

a b R2 10 0.778 0.363 0.977 20 1.365 0.376 0.991 30 1.775 0.392 0.99 40 1.99 0.415 0.985

Harkins Jura plot

- A B R2

37.037 3.037 0.901

Freundlich plot

Kf n R2 10 0.94 1.91 0.93 20 1.36 1.68 0.89 30 2.3 1.78 0.88 40 2.52 1.56 0.89

Langmuir plot - Qo (mg/g) B (l/mg) R2

100 112.2 0.998

Tempkin plot - A B P R2

0.07051 8.856 281.64 0.973

3.11 Box – Behnken methodology and design of experiments

Response surface method using the Box-Behnken design [39] of experiments gives a mathematical model for the adsorption of dyestuff. In the present study the effect of several factors influencing the dye adsorption such as pH, particle size and temperature have been considered as the critical variables designated as X1, X2 and X3 respectively and statistical design was used to determine the optimal levels of adsorption studies. The low, middle and high level of each variable pH (4, 6.5 and 9.2), particle size (<125, 125-250 and 250-500 BSS mesh number) and temperature (300, 318 and 330K) were designated as -1, 0 and +1 respectively (Table 3). For the three significant independent variables X1, X2 and X3, the mathematical relationship of the response M on these variables can be approximated by the quadratic model equation

M = A0 + A1X1 + A2X2 + A3X3 + A11X1 + A22X22+ A33X3

2 + A12X1X2 +A13X1X3 + A23X2X3 (15) Where M is the predicted response, A0 is constant, X1 is pH, X2 is particle size and X3 is Temperature, A1, A2, A3 are linear coefficients, A12, A13 and A23 are cross product quadratic coefficients. For the Box-Behnken Box

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and Hunter [40], design of three independent variables, a total of 15 experiments were necessary to estimate the 10 coefficients of the model [41] and the results for the linear coefficients and quadratic cross product coefficients were listed in Table 4. The summary of the analysis of variance (ANOVA) is listed in Table 5.

Fig.4 Direct Red - 28 adsorption at 300k and a particle size of 250 – 500 BSS mesh

(a) Pseudo second order plots; (b) Elovich plots; (c) Harkins Jura plots; (d) Tempkin plots (e) Fractional

power plot (f) Effect of pH

From the ANOVA, it was found that quadratic regression and quadratic square regression was significant at the confidence level of >98% for all the adsorption systems studied. This indicates that the selected variance (Temperature, pH and Particle size) have a combined effect on the adsorption of dyes by the adsorbents. The theoretical values of dye adsorption on adsorbents by the Box-Behnken model at each experimental point are summarized as the theoretical values was 240.8, 237, 281.1, 316.1, 186.2, 229.7, 314.4, 302.2, 162.1, 230.2, 270.9, 322, 277.7, 277.7, 277.4 and 229.3, 226, 267.8, 301.1, 177.3, 218.8, 299.4, 287.8, 154.3, 219.3, 258.1, 306.7, 264.5, 264.5, 264.2 with experimentally observed values and it was found that there was a close agreement between the experimental values and the theoretical values. 3.11.1 Effect of Contour Plot The effect of variables was analyzed and plots were obtained to assess the effect of each factor graphically. From the contour plots, it has been found that there is a gradual increase in adsorption of dyes with increase in temperature from the lower level 300K (Coded value -1) to the middle level 318K (Coded value–0) and there is

a b

cd

e f

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no further increase to adsorption even if the temperature is increased to 330K (Coded value +1). Similarly, the adsorption increases with respect to the particle size of Pomegranate rind activated carbon from 250-500, 125-250 and <125BSS mesh numbers (Coded value -1, 0 and +1) (Fig.5). It is also revealed that the basic dye adsorption increases with decrease in pH value .Similar types of result were reported by Syed shabudeen [41].

Table 3. Box-Behnken design for three independent variables

Trial No. pH Particle Size

(BSS mesh No.) Temperature

(K)

1. -1 -1 0

2. +1 -1 0

3. -1 +1 0

4. +1 +1 0

5. -1 0 -1

6. +1 0 -1

7. -1 0 +1

8. +1 0 +1

9. 0 -1 -1

10. 0 +1 -1

11. 0 -1 +1

12. 0 +1 +1

13. 0 0 0

14. 0 0 0

15. 0 0 0

Table 4. Parameter estimate co-efficient of the Box-Behnken model

Variable coefficient

A0 A1 A2 A3 A11 A22 A33 A12 A13 A23

Direct Red-28 245.6 9.01 32.98 30.43 3.91 -1.19 -8.33 0 -11.2 -10.2

Table 5. ANOVA for Box-Behnken Model for the adsorption of dyes

Source Sum of Squares

Degrees of Freedom

Mean Square F

value Model Error

Cor. Total Root MSE

C.V

41792.7 298.3 42091 6.50 0.18

4 6 10

10448.1 49.71

2.92

R- Squared Adj R-Squared

0.993 0.988

3.12 Effect of pH Solution pH is an important factor controlling the surface charge of the adsorbent and the degree of ionization of the materials in the solution [33]. The % removal for the dye, Direct red-28, decreased with increase of pH. The similar trend of results was reported for colour removal [42,43]. As surface charge density decrease with an increase in the solution pH, the electrostatic repulsion between the positively charged sites and the activated carbon is lowered, and a change in its polarity, which might have developed electric double layer around the adsorbent [44] may result in an increase in the rate of adsorption. At lower pH values the surface of the activated carbon becomes positively charged and this facilitates sorption of cationic dye molecules, probably by exchange sorption which may be the reason for increased adsorption of Direct red-28, at lower pH [34]. 3.13 Mechanism of Adsorption The adsorption pathway indicated that the kinetic rate of adsorption was as important as the final equilibrium distribution in analysis. The adsorbent properties including surface area, particle size, surface functional groups, surface polarity and pore size distribution may influence adsorption parameters. The porous adsorbent particles (activated carbon) have multi disperse structure. The multi disperse structure consisting of macro pores, which open directly to the external surface and an extensive system of micro pores that branch off from the macro

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pores. For typical adsorbents, the specific area of the micro pores usually amounts to atleast 90% of the total surface area.

Fig. 5 Response surface plot for the adsorption of Direct red - 28

Solutions related variables including pH, solubility, molecular weight, molecular size, polarity and chain length of the sorbate and the presence of the other species in solution may alter the adsorption system conditions or may compete directly with the compounds for sites of adsorbents. If the rate of the adsorption reaction is controlled by external diffusion, then the size of the adsorbent particle is important in design variable. When pore diffusion is the rate-limiting step, the internal pore diameter of carbon as compared to the molecular size of the adsorbate and the adsorption capacity of the adsorbent are additional key design factors. The relationship between steric size of the dye molecule, structure charge, surface area and size of the pores has been discussed by Peter Samaras [45].

The adsorption of Direct red-28 having giant molecular structure depends on the meso and macropores directly connected to the external surface that yields in comparatively less adsorption.

Model : Quadratic

Response : R1

Constants : P. Size

Variables

X – pH

Y – Temperature

Model : Quadratic

Response : R1

Constants : Temp.

Variables

X – pH

Y – P. Size

Model : Quadratic

Response : R1

Constants : pH

Variables

X – Temperature

Y – P. Size

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3.14 Desorption studies Desorption studies help to elucidate the nature of adsorption and recycling of the spent adsorbent and the dye.For desorption studies of the spent adsorbent by water (neutral pH), 1M H2SO4 and 1M NaOH solution shows no desorption while the dyes are desorbed at insignificant level with 1M CH3COOH. It is observed that the adsorption mechanism of the dyes Direct red-28, adsorbed on pomegranate rind carbon is predominantly by chemisorption and to a lesser extent ion exchange and active adsorption. According to spectroscopic measurements, -OH groups mainly appear to be the main cause for this secondary force of interaction physisorption because the molecules containing oxygen and nitrogen will prefer this type of adsorption and also partly centre for chemisorptions [2]. In the present study, desorption of dye from the spent adsorbent was significant by using organic solvents [22]. 4. Conclusions Experiments were conducted to investigate the potential of Punica granatum activated carbon as sorbent for the removal of Direct red-28 from aqueous solutions. Effects of the experimental conditions on the performance of the Punica granatum activated carbon as sorbents was studied and the sorption data were fitted by Langmuir and Freundlich models. The % removal for the dye, Direct red-28, decreased with increase of pH. A pseudo second-order mechanism was confirmed for the sorption kinetics. Punica granatum activated carbon presented a great potential as an inexpensive and easily available alternative adsorbent for the removal of Direct red-28 in wastewater treatments. Response surface method using the Box-Behnken design of experiments gives a favorable mathematical model for the adsorption of the dyestuff. References [1] G.McMullan, C.Meehan, A.Conneely, N.Kirby, T.Robinson, P.Nigam, I.M.Banat, R.Marchant, W.F.Smyth, (2001): Microbial

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