Kinetic, Isotherm and Thermodynamic Modeling of Sorption of Acid Orange 7 on To Balsamodendroncaudatum Wood Waste Activated Carbon

Kinetic, Isotherm and Thermodynamic Modeling of Sorption of Acid Orange 7 on To Balsamodendroncaudatum Wood Waste Activated Carbon

1. Sivakumar 1*, S. Karthikeyan2 and C. Kannan3

   1* Department of Chemistry, Angel College of Engineering and Technology, Tirupur, TamilNadu, India.

   2 Department of Chemistry,Chikkanna Government Arts College,Tirupur, TamilNadu, India.

   . 3Department of Chemistry, Manonmaniam Sundaranar University, Tirunelveli, TamilNadu, India.

   Abstract – Balsamodendron caudatum wood waste activated carbon (BAC) has the ability to adsorb the dye stuff from aqueous solution. The inappropriate disposal of dyes in waste water constitutes an environmental problem and can cause damage to the ecosystem. Present investigation deals with the utilization of BAC waste as adsorbent for the removal of Acid Orange 7 dye from its aqueous solutions. The investigation indicates that adsorption is influenced by initial dye concentration, contact time, dye solution pH, thermodynamic parameters such as the free energy, enthalpy, entropy and adsorption temperature have been investigated in the present study. A Kinetic study of dye followed the pseudo-first- order, pseudo second-order and Elovich models respectively. Equilibrium isotherms for the adsorption of Acid Orange 7 on BAC were analyzed by the Freundlich and Langmuir isotherm equations. Results show that the pseudo first order kinetic model was found to correlate the experimental data well.

   Keywords: BAC ; Adsorption ; Acid Orange 7; kinetics ; isotherm; low-cost adsorbents; aqueous solution.

   INTRODUCTION

   Water is essential to all forms of life. It serves as a medium, catalyst and (or) participant in all the chemical reactions occurring in our environment. In nature, a number of regulatory mechanisms play an important role in controlling the physico-chemical properties of important as well as the number and types of its biological populations. Irrespective of origin, it always contains a complex mixture of organic and inorganic substances most of which are of natural origin resulting from complex interaction between water, soil and underlying geological status. Biological and microbiological process occurring in soil and water. Suspended and colloidal mineral matter, plant detritus, algae and protosozoa are also frequently found.

   Activated carbon with large surface area, micro porous character and chemical nature of their surface have made them potential adsorbents for removal of dyes from industrial wastewater. The adsorptive properties of active carbon for removal of pollutants are well documented (Macias et al., 1993). Adsorption of hazardous soluble chemicals from wastewater in to surface of a solid adsorbent has provided a new dimension to wastewater technology (Benefield et al., 1982). One of the major challenges associated with adsorption by activated carbon is its cost effectiveness. Hence research of recent past mainly focused on utilizing waste materials as alternatives to activated carbon. Bamboo (Ahmad et al., 2009 ) , sugar cane bagasse ash (Kanawade et al., 2011), bone char (Alvin et al., 2010), fly ash(Sell et al., 1994), peat moss( Allen and McKay 2001; Chen et al.,2001), ipomoea carnia stem waste (Karthikeyan et al., 2007) , jujuba seeds (Somasekhara Reddy et al., 2012) and potatoes and egg Husk ( Hila et al., 2012), are some of the waste materials which have been fruitfully tried for this purpose.

   1. EXPERIMENT

      1. Adsorbent

         Balsamodendron caudatum wood waste was obtained from various regions of Erode & Tirupur Districts, Tamil Nadu, India. The study of Balsamodendron caudatum wood waste material is used as adsorbent is expected to be economical, environmentally safe and it has practical importance.To develop adsorbents, the material was first ground and washed with doubly distilled water and then dried. The dried material thus obtained was treated with hydrogen peroxide (30%W/V) at room temperature for about 24 hrs to oxidize the adhering organic matter. The resulting material was thoroughly washed with doubly distilled water and then subjected to the temperature of 120°C for the moisture removal.

         One portion of the above material was soaked well with H2 SO4 solution for a period of 24 hours. At the end of 24 hrs the excess of H2 SO4 solution were decanted off and air-dried. Then the materials were placed in the muffle furnace carbonized at 120-130°C. The dried materials were powdered and activated in a muffle furnace kept at 800°C for a period of 60 minutes. After activation, the carbon of obtained were washed sufficiently with large volume of water to remove free acid, Then the obtained material was washed with plenty of water to remove excess of acid, dried then to desired particle size. The resulting carbon named as BAC.

      2. Preparation of aqueous dye solution

         The details of dye used and its characteristics are presented in Table.1, respective structure is shown in the Figure1 (International Color Index, 1998). The stock solutions of the dye (1000 mg/L) were prepared by dissolving 1 g of respective dye in one litre of water without any further treatment, which

         were kept in dark coloured glass bottles. For batch study, an aqueous solution of this dye was prepared from stock solutions in deionized water. NaOH and HCl solutions were used as buffers for pH studies.

         Table 1 Characteristics of the dye used

         Class Sample Generic name

         C.I. No. max nm Fw

         Acid AO7 Acid Orange7

         715510 484 350.32

         -O

         O

         S

         Na+

         O

         N

         HO

         N

         Fig. 1 Structure of Acid Orange 7

      3. Amount of dye adsorbed

         The formula used to find the Amount of dye adsorbed, Qe , was as shown below:

         Q C 0 C V

         e M

         (1)

         Qe (mg/g) is the amount of dye adsorbed at equilibrium, V (L), isthe volume of the solution dye, Co (mg/L) is the initial dye concentration, C (mg/L) is the dye concentration at any time and M (g) is the adsorbent dosage.

         The percentage of removed anionic dye (R %) in solution was calculated using eqn. (2)

         % Removal

         C 0 C t

         100

         (2)

         C 0

         The initial concentration of Acid Orange 7 pH and temperature was investigated by varying any one parameters and keeping the other parameters constant

      4. The pseudo first order equation

         The pseudo first – order equation (Lagergren 1898) is generally expressed as follows.

         dqt dt

         k1(qe

         qt )

         (3)

         where,

         qe and qt are the adsorption capacity at equilibrium and at time t., respectively (mg g-1), k1 is the rate constant of pseudo first order adsorption (l min-1).

         After integration and applying boundary conditions t =0 to t = t and qt= 0 to qt = qt, the integration form of equation (3) becomes.

         log(qe

         qt )

         log(qe ) k1 t

         2.303

         (4)

         The value of log (qe qt) were linearly correlated with t. The plot of log (qe qt) Vs t should give a linear relationship from which k1 and qe can be determined from the slope and intercept of the plot, respectively.

      5. The pseudo second order equation.

         The pseudo second order adsorption kinetic rate equation is expressed as (Ho et al. 2000)

         t

         dqt dt

         k2 (qe

         q )2

         (5)

         where, k2 is the rate constant of pseudo second order adsorption (g. mg-1. min-1). For the boundary

         conditions t = 0 to t = t and qt = 0 to qt = qt, the integrated form of equation (5) becomes.

         1

         q e qt

         1

         q

         k t (6)

         e

         Which is the integrted rate law for pseudo second order reaction. Equation (6) can be rearranged to obtain equation (7), which has a linear form.

         t 1

         q k q 2

         1 (t)

         q

         (7)

         t 2 e e

         If the initial adsorption rate h (mg g-1 min-1) is

         2

         h k qe 2

         (8)

         Then Equations. (7) And (8) become:

         t 1 1 t

         qt h qe

         (9)

         The plot of (t/qt) and t of equation (7) should give a linear relationship from which qe and k2 can be determined form the slope and intercept of the plot, respectively.

      6. The Elovich equation

      The Elovich model equation is generally expressed (Chien and Clayton 1980) as

      dqt

      d t

      exp qt

      (10)

      where, is the initial adsorption rate (mg.g-1 min-1), is the adsorption constant (g. mg-1) during any one experiment.

      To simplify the Elovich equation, assumed t >> t and by applying the boundary conditions qt = 0 at t = 0 and qt=qt at t = t Eq (10) becomes;

      1 1

      qt = ln ( ) + ln t (11)

      If Acid Orange 7 adsorption fits the Elovich model a plot of qt vs ln t should yield a linear relationship with slope of (1/ ) and an intercept of (1/ ) In )

   2. RESULTS AND DISCUSSION

2.1 Characterization of adsorbent

Physico-chemical characterizations of the adsorbents were presented in Table 2.

Table 2 Characteristics of the Activated Carbon BAC

Parameter BAC

pH

Surface area (m2/g) pH zpc

6.5

458

4.2

The surface area of the BAC was measured through N2 adsorption at 77K using a NOVA1000, Quanta chrome Corporation. The pH of BAC was measured by a PHS-3C pH meter. pH of zero charge (pHpzc) of the samples was determined using pH drift method (Fariaa et al., 2004). The surface area of the BAC obtained from the N2 equilibrium adsorption isotherms was found to be 458 m2/g. The results of pH drift experiment, from which the pHpzc of BAC studied in this test was found to be 4.2.

1. Effect of pH

   From the set of experiments conducted to find the effect of pH on adsorption phenomenon, it was observed that pH influences BAC surface dye binding sites and the dye chemistry in water. Figure 1 shows the amount of dye adsorbed, qe using acid activated absorbent at initial pH value. In this experiment, the initial dye concentration was fixed at 20 mg/L. From the shake flask experiments, better colour removal of the dye, Acid Orange 7, was observed at pH of 6.5 .The uptake of Acid Orange 7was found to be optimal at pH 6.5 with the maximum dye uptake of 81.6 mg/g . In the pH range of 5.5 to 8.0 a decreasing trend in qe values was observed. Identically, the qe values were found to decrease in the alkaline pH range of 7.0 – 10.1. Similar results are reported (Low et al. 1995).

   120

   100

   80

   60

   40

   20

   0

   2

   3

   4

   5pH

   6

   7

   8

   9 10

   qe mg/g

   Fig. 2 Impact of pH on equilibrium uptake of Acid Orange 7 sorption onto BAC. M, 100 mg; V, 50 ml; C0 20 mg/L; temperature, 30°C).

2. Effect of adsorbent dosage

   The effect of quantity of acid treated BAC on the amount of color adsorbed was studied by agitating 50 ml of 20 mg/L dye solution with amount of sorbent addition was 100 mg. All these studies were conducted at room temperature and at a constant speed of 200 rpm. An increase in % colour removal was observed with an increase in adsorbent dosage.

3. Effect of initial dye concentration and contact time

   For conducting the kinetic studies, the dye is agitating at equal time intervals were used. Contact time experiments were carried out by agitating with 50 ml of dye solutions whose concentrations viz. 20 mg/L, 40 mg/L and 60 mg/L at an optimum pH of 6.5 witp00 mg of BAC at room temperature. The speed of agitation was maintained constant at 200 rpm. The colour reduction profiles were obtained using the absorbance measurements.

   100

   % of Dye removal vs Initial Dye Concentration, mg/L Amount Adsorbed vs Initial Dye Concentration, mg/L

   100

   90 90

   Amount Adsorbed, mg/g

   80 80

   % of Dye removal

   70 70

   60 60

   50 50

   40

   40

   30

   30

   20

   20

   10

   10

   0

   0 10 20 30 40 50 60 70 80

   Initial Dye Concentration, mg/L

   Fig. 3 Effect of Initial Concentration of Acid Orange 7 Solution

4. Effect of Temperature on kinetic rate constant and rate parameters

   Adsorption experiment was carried out with fixed initial dye concentration (20mg/L) at pH 6.5 and at different temperature viz. 30 °C. 45 °C and 60 °C. The analysis of the data in (Table 3) reveals that the influence of temperature of the dye has very little influence on the pseudo second order rate constants. The table 3 also reveals that the influence of the temperature of dye on Elovich and pseudo first order rate constant is neither appreciable nor little. It is obvious that the adsorption of dye on the BAC waste activated carbon is best described by first order rate equation with regression coefficient value is greater than 0.98.

   Table 3 The adsorption kinetic model rate constants for BAC at different Temperature

   Adsorbent

   Initial Temperature

   Pseudo first order

   2

   k 1

   Pseudo Second order

   2

   k 2 h

   Elorich Model

   		min- 1	– 1			1
   300C 0.0163	0.9587	0.0006	0.3798	0.9833	0.1906	0.8594	0.9610
   BAC 450C 0.0082	0.8576	0.0300	5.3046	0.3019	0.1734	0.4287	0.9211
   600C 0.0234	0.6016	0.0012	0.1556	0.6156	0.1793	0.4637	0.9223

   g r2

   l min- 1

   r g mg- 1

   mg g- 1 r

   min- 1 mg g-

5. Isotherm

   The Langmuir, Freundlich isotherms are the most frequently used two parameter models in the literature describing the non-linear equilibrium between amount of dye adsorbed on the acid treated BAC (qe) and equilibrium concentration of solution (Ce) at a constant temperature

   (30°C). The Langmuir equation, which is valid for monolayer sorption onto a homogeneous surface with a finite number of identical sites.

6. Langmuir Model

   The Langmuir model was developed based on the assumption of the formation of a monolayer of the adsorbate species onto the surface of the particle of the adsorbent. It has also been assumed that the surface sites are completely energetically homogeneous. But in the true sense, the adsorbent surface is

   energetically heterogeneous (Langmuir, 1918). The study of the Langmuir isotherms is essential in assessing the adsorption efficiency of the adsorbent. This study is also useful in optimizing the operating conditions for effective adsorption. In this respect, the Langmuir isotherm is important, though the restrictions and the limitations of this model have been well recognized.

   This model is the most widely used two-parameterequation, generally expressed in the form by the following equation

   1 1 . Ce

   qe Qo K L Qo

   (12)

   where,

   qe = the amount of dye removed at equilibrium (mg/g) Ce = the equilibrium concentration of dye (mg/L)

   Q0 = the Langmuir constant, related to the adsorption capacity (mg/g)

   b = the Langmuir constant, related to the energy of adsorption (L/mg) KL = direct measure of the intensity of the sorption (L / mg)

   Ce/qe was plotted against Ce using linear regression analysis, as shown in Fig. 3. The constants Q0 and KL were determined fro the intercept and slope of the linear plots, respectively. As shown in Table 5, the Qo from the Langmuir isotherm were 44.05 mg/g for Acid Orange 7. The values of KL it could be concluded that adsorptions of acid dye (KL = 0.08926). The essential characteristic of Langmuir equation can be expressed in terms of a dimensionless separation factor RL (Wang et al., 2005).

   The essential characteristics of Langmuir isotherm can be expressed in terms of a dimensionless parameter, RL, which is defined by RL = 1/1+ bC0, where, C0 is the initial dye concentration (mg/L) and b is the Langmuir constant (L/mg). The parameter indicates the shape of isotherm as given in Table 4.

   Table 4 Parameters for types of isotherm

   RL Type of isotherm

   RL > 1 Unfavourable

   RL = 1 Linear

   0 < RL < 1 Favourable

   RL = 0 Irreversible

   In the present research work, the investigator aims at determining how well the Langmuir model can be applied to the chosen adsorbate adsorbent system.

   RL = (1/1+KLC0) (13)

   Table 5 Equilibrium isotherm constants at 30°C.

   Freundlich isotherm

   Langmuir isotherm

   Kf(mg/g) n R2 KL l/mg qo mg/g R2

   5.0354 0.6186 0.9871 0.08926 44.052 0.9933

   where,

   C0 = (mg /L) is the initial dye concentration. RL= the nature of the adsorption process.

   The calculated RL values of acid dye is found to be between 0.3767, 0.3385 and 0.3450 for dye

   Ce/qe, g/L

   concentrations viz. 20 mg/L, 40 mg/L and 60 mg/L, respectively (data not shown). The magnitude of the RL values, i.e., 0 < RL <1, indicated the favorable adsorption of each of the dye under consideration.

   0.70

   0.60

   0.50

   0.40

   0.30

   0.20

   0.10

   0.00

   0

   20

   Ce, mg/L

   60

   80

   40

   Fig. 4 Langmuir plot for Acid Orange 7 sorption onto BAC. M, 100 mg; V, 50 ml; C0, 20 mg/L; pH, 6.5; temperature, 30°C ).

7. Freundlich Model

   At Equilibrium conditions, the adsorbed amount, qe can also be predicted by using the Freundlich equation (Freundlich, 1926).

   qe = kf Ce1/n (14)

   where,

   qe = dye concentration in solid at equilibrium (mg/g)

   Ce = dye concentration in solution at equilibrium (mg/L) kf = measure of adsorption capacity

   n = adsorption intensity

   A logarithmic form of the above equation is

   log qe =log kf + (1/n) log Ce (15)

   The values of n and kf were determined from the plot log Ce vs log qe .

   where, kf is the indication of the adsorbent capacity and 1/n is a measure of surface heterogeneity, ranging between 0 and 1, becoming more heterogeneous as its value gets closer to zero.The Freundlich equation predicts that the dye concentration on the adsorbent will increase so long as there is an increase in the dye concentration in the liquid. The experimental evidence indicates that an isotherm is reached at a limiting value of the solid phase concentration. The equation itself does not have any real physical significance. Freundlich isotherm fitted well to the data with correlation coefficient value 0.9871. The calculated Freundlich isotherm constants at 30°C are as shown in Table 5. The value of Freundlich exponent n = 1.6165 lying in the range of 1 – 10, indicate favorable adsorption.

8. Adsorption Thermodynamics

The speed of a reaction or the reaction rate can be calculated from the knowledge of kinetic studies. But the changes in reaction that can be expected during sorption process require the brief idea of thermodynamic parameters. The three main thermodynamic parameters include, enthalpy of adsorption (H), free energy change (G) due to transfer of unit mole of solute from solution to the solid liquid interface and entropy (S) of adsorption.

The thermodynamic parameters obtained for the adsorption systems were calculated using the following equation (Inbaraj and Sulochana 2002).

K C Ae

c C

(16)

e

G RT ln K c

(17)

log K c

S

2.303R

H

2.303RT

(18)

KC is equilibrium constant, CAe is the solid phase concentration at equilibrium, Ce is residual concentration at equilibrium, R is gas constant (J/mole) and T is the temperature in Kelvin. H and S was obtained from the slope and intercept of Vant Hoff plot (1/t Vs ln Kc ). Table 6 gives the value

of G, S and H for the adsorption of BAC. The negative values of free energy change ( G) indicate the feasibility and spontaneous nature of adsorption of BAC. The positive value of S is due to the increased randomness during the adsorption of adsorbents.

Table 6 Thermodyanamic parameters forAcid Orange 7, BAC adsorption.

G (J mol-1) H S Adsorbent

1. CONCLUSIONS

   Adsorption of anionic dye on the BAC was found to be dependent on the pH, (The optimal pH of Acid Orange 7 was 6.5), temperature and concentration for adsorbent. Thermodynamic parameters obtained for the adsorbent accounts for feasibility of the process at each concentration. Adsorption equilibriums were reached within 102 min contact time for anionic dye used in this test. Thermodynamic parameters obtained for the adsorbent accounts for feasibility of the process at each concentration. The kinetics of Acid Orange7 adsorption on adsorbent was found to follow a pseudo first -order rate equation. An equilibrium isotherm for the adsorption of Acid Orange7 on BAC was analyzed by the Freundlich, and Langmuir isotherm equations. Result showed that the Freundlich isotherm best-fit the Acid Orange7 adsorption.

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