Kinetic analysis of 2,4,5-trichlorophenol adsorption onto acid-activated montmorillonite from aqueous solution

International Journal of Mineral Processing 100 (2011) 72–78

Contents lists available at ScienceDirect

International Journal of Mineral Processing j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / i j m i n p r o

Kinetic analysis of 2,4,5-trichlorophenol adsorption onto acid-activated montmorillonite from aqueous solution Hassina Zaghouane-Boudiaf ⁎, Mokhtar Boutahala Laboratoire de Génie des Procédés Chimiques (LGPC), Département de Génie des Procédés, Faculté de Technologie, Université Ferhat Abbas, Sétif 19000, Algeria

a r t i c l e

i n f o

Article history: Received 17 April 2010 Received in revised form 21 April 2011 Accepted 30 April 2011 Available online 15 May 2011 Keywords: Acid-activated montmorillonite 2,4,5-trichlorophenol Adsorption Isotherms Kinetic models

a b s t r a c t This study has investigated the potential use of acid-activated montmorillonite (AMt) as adsorbent for the removal of 2,4,5-trichlorophenol (2,4,5-TCP) from aqueous solution. The kinetics of adsorption were studied in a batch system. Important parameters which affect the adsorption, such as pH of solution, the mass of acidactivated montmorillonite, temperature and initial TCP concentration have been investigated. The increase in adsorbent mass, pH and temperature resulted in a lower TCP loading per unit weight of the acid-activated montmorillonite, but an increase of adsorption was observed when initial concentration of 2,4,5-TCP increases. The effect of different adsorption parameters was fitted to the pseudo-first-order, pseudo-secondorder and the intraparticle kinetic models. The linear regression method was used to obtain the relative parameters. According to the error analysis, it was found that the pseudo-second-order kinetic model was better to predict the experimental results. The value of activation energy was calculated as 47.7 kJ/mol. The result obtained indicates that the adsorption is assigned to a physisorption. © 2011 Elsevier B.V. All rights reserved.

1. Introduction The activated carbon is a widely used adsorbent due to its high adsorption capacity, high surface area, microporous structure, and high degree of surface reactivity, but there are some problems with its use. The high cost and recovering problems of activated carbon particles from treated water are of disadvantage. In recent years, increasing concern over pollution of water courses arising from different anthropogenic activities has resulted in a growing demand of low cost adsorbents. Clays such as sepiolite, zeolite and bentonite are being considered as alternative low-cost adsorbents. Some studies (Naseem and Tahir, 2001; Özcan et al., 2004; Witthuhn et al., 2005; Gonen and Rytwo, 2006; Bhattacharyya and Sen Gupta, 2007; Koyuncu, 2008; Shu et al., 2010) illustrated the importance of clay materials modified by chemical or physical processes as adsorbents for removal of organic pollutants, pesticides and heavy metals from water and wastewater. The modification of mineral clay using an inorganic acid, which is referred to as “acid activation”, is an example of one of these chemical processes. Bentonite is a natural mineral clay that is found in many places in the world. It is predominantly montmorillonite clay, a non-pollutant material and one of the most important natural adsorbents. It has a privileged place in the purification of water (Bouras et al., 2002; Arfaoui et al., 2005; Hamdi and Srasra, 2007). High specific surface

⁎ Corresponding author. E-mail address: [email protected] (H. Zaghouane-Boudiaf). 0301-7516/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.minpro.2011.04.011

area, chemical and mechanical stabilities, layered structure, high cation exchange capacity (CEC), tendency to hold water in the interlayer sites, and the presence of Brønsted and Lewis acidity have made clays excellent adsorbent materials (Al-Asheh et al., 2003; FuChuang et al., 2004). The chemical nature and pore structure of bentonite generally determine their adsorption ability (Espantaleón et al., 2003; Min-Yu and Su-Hsia, 2006; Okada et al., 2006). The objective of this study was to prepare an acid-activated montmorillonite which retains the layered morphology but which develops a high specific surface area and still has the ability to adsorb organic molecules. The most significant mechanism in the activation of natural bentonite is cation exchange by H + ions (Babaki et al., 2008). During the activation process, a considerable amount of cations was substituted by hydrogen cations which increase the specific surface area (Özcan and Özcan, 2004). These transformations in the bentonite give rise to significant changes in the cation exchange capacity (CEC), and chemical and mineralogical characteristics of the bentonite (Komadel and Madejová, 2006). The acid activation improves the adsorption properties of the clay by increasing the number of active sites (Min-Yu and Su-Hsia, 2006). Some studies have focused on organic clays (Özcan et al., 2004; Witthuhn et al., 2005; Gonen and Rytwo, 2006), but the modification processes are too complicated to be produced on a large scale. Hence the simpler acidification process is an alternative method to enhance the adsorption capacity of the clays. In this study the ability of acid-activated montmorillonite to remove the 2,4,5-trichlorophenol (2,4,5-TCP) by adsorption has been studied.

H. Zaghouane-Boudiaf, M. Boutahala / International Journal of Mineral Processing 100 (2011) 72–78

2. Experimental 2.1. Materials The bentonite used in this study was obtained from Hammam Boughrara (West Algeria). Its chemical composition was found to be as: 69.4% SiO2, 1.1% MgO, 14.7% Al2O3, 0.8% K2O, 0,3% CaO, 1.2% F2O3, 0.5% Na2O, 0.2% TiO2, 0.05% As, 11% loss of ignition (Khalaf et al., 1997). Its cation exchange capacity (CEC) is 0.97 meq/g (Aliouane et al., 2002). Sodium chloride (analytical grade); sulfuric acid (H2SO4, 98 wt.%) and 2,4,5-trichlorophenol (purity of N99%) were purchased from Sigma-Aldrich Chemicals.

73

initial and final concentrations of TCP in the liquid phases. All experiments were run in triplicate to ensure reproducibility. The TCP uptake by AMt was calculated by the following equation: qt =

ðC0 −Ct Þ:V m

ð1Þ

where qt in (mg/g) is the amount of adsorbed TCP at time t; V the volume of solution (L), C0 and Ct are the initial and at time t TCP concentration respectively (mg/L) and m is the mass of adsorbent (g). 3. Results and discussion

2.2. Sample preparation

3.1. FTIR analysis

The NaMt was prepared with a procedure similar to that of reported by Khalaf et al. (1997). 30 g of crude bentonite was mixed with 1 L of 1 M NaCl solution and stirred for 24 h. After three successive treatments, the homoionic bentonite was dialyzed in deionized water until it was free of chloride. Then it was separated by centrifugation to eliminate all other solid phases (quartz, cristobalite and felspath) (Boutahala and Tedjar, 1993). The montmorillonite fraction (b2 μm) was recovered by decantation and dried at 80 °C. A sample of 10 g of NaMt was treated drop by drop under mechanical stirring with a 1.0 M H2SO4 solution at 363 K for 6 h in a flask under reflux. The resulting activated clay was centrifuged and washed with distilled water several times till it was free of SO42− as indicated by the AgNO3 test and was then dried at 353 K for 24 h. Acid-activated montmorillonite noted AMt, was then stored for further use in the adsorption tests.

In order to obtain complementary evidence for the intercalation of hydrogen ions into the silicate lattice, FTIR spectra were recorded in the region of 400–4000 cm − 1 (Fig. 1). FTIR spectroscopy is very sensitive to modification of the clay structure upon acid treatment. As protons penetrate into the clay layers and attack the OH groups, the resulting dehydroxylation connected with successive dissolution of the central atoms can be readily followed by changes in the characteristic absorption bands, attributed to vibrations of OH groups and/or octahedral cations. The bands at 3440 and 1648 cm − 1 for water of hydration show a significant decrease in AMt. The intensity of hydroxyl stretching bands at 3623 cm − 1 also reduces after the acid treatment. It is due to the removal of octahedral cations causing the loss of water and the hydroxyl groups linked to them. This may be an acceptable evidence for the acid activation occurring on the bentonite. The SiO-stretching band (1089 cm − 1) for AMt occurs at the same position as that of NaMt, but its intensity decreases. In NaMt the bands at 522 and 464 cm − 1 result from the Si\O\Al (where Al is an octahedral cation) and bending vibrations, respectively. After the acid treatment the Si\O\Al vibration was only observed at 473 cm − 1. The bending vibration of Si\O\Si was not observed (or very small). It is the most sensitive indication of the remains of the layers after acid dissolution (Madejová et al., 1998).

2.3.1. FTIR analysis The Fourier Transform Infrared Spectroscopy (FTIR) study was carried out using a Perkin Elmer FTIR spectrometer (Spectrum1000). FTIR spectra were recorded in the range of 400–4000 cm −1 with KBr pellet technique. The KBr pellets were prepared by mixing the clay sample using the KBr powder (around 1:100) and using a hydraulic press at the pressure of 10 tonnes. 2.3.2. Specific surface area The specific surface area was determined by nitrogen gas adsorption–desorption isotherms using a Quanta Chrome Autosorb1 instrument at 77 K. The measurements were made after degassing under vacuum at 180 °C for 6 h. The specific surface area (S.B.E.T) was calculated by the B.E.T method (Brunauer et al., 1938) and the pore size was determined by the B.J.H method using the adsorption and desorption isotherms, respectively (Barrett et al., 1951). The total pore volume was calculated from the maximum amount of nitrogen gas adsorption at the partial pressure (P/P0) of 0.999. 2.4. Kinetic studies Adsorption experiments were carried out in a batch equilibrium mode. The effects of pH (2(9)2–9), temperature (15; 25 and 35 °C), initial TCP concentration C0 (20; 50; 80 and 100 mg/L) and adsorbent mass (20; 30; 40 and 50 mg) were investigated. The pH was adjusted by adding a few drops of dilute NaOH or HCl. An amount of acidactivated montmorillonite was dispersed in 50 mL of TCP solution and stirred with an agitation speed of 100 rpm. After each time of contact, the pH of solution was measured (no significant change in pH was found ) a sample was removed and filtered. The TCP concentrations were determined using a UV-1700 UV spectrophotometer at 290 nm for dispersions at acidic pH values and at 310 nm for dispersions at alkaline pH values. The amount of TCP adsorbed was derived from the

3.2. Specific surface area The N2 adsorption–desorption isotherms of NaMt and AMt samples are shown in Fig. 2. We can see that the two samples are of type IV indicating that the samples have a mesoporous structure. Acid-activation markedly affected N2 adsorption characteristics of the

NaMt AMt

1.5

% Absorbance

2.3. Methods for material characterization

1.0

1648

0.5

3623

3440

464

0.0 4000

1033 3500

3000

2500

2000

1500

Wavelenght (cm-1) Fig. 1. FTIR spectra of NaMt and AMt.

1000

500

74

H. Zaghouane-Boudiaf, M. Boutahala / International Journal of Mineral Processing 100 (2011) 72–78

300

A

AMt

35

NaMt

250

200 25 150

qe (mg/g)

Vads (cm3/g)

30

100

20

50 15 0 0,0

0,2

0,4

0,6

0,8

1,0

10

P/P0 Fig. 2. N2 adsorption–desorption isotherms of NaMt and AMt.

5 1

2

3

4

5

6

7

8

9

10

pH

3.3. Effect of the solution pH To study the influence of the pH on the adsorption capacity of acidactivated montmorillonite (AMt), experiments were investigated using the pH varying from 2 to 9. In the first the uptake of TCP increased slowly with increasing the pH, reacted maximum for pH 4 and decreased (Fig. 3A). This result is comparable to those obtained by other authors (Radhika and Palanivelu, 2006; Hameed, 2007; Hameed et al., 2008). It was observed that the adsorption is highly dependent on the pH of the solution, which affects the surface charge of the adsorbent and the degree of ionization and speciation of the adsorbate. This was due to the chemical characteristics of the acidactivated-montmorillonite (AMt) with acidic pHpzc of 5. At a solution pH lower than the pHpzc, the total surface charge would be on average positive, whereas at a higher solution pH, it would be negative. The TCP uptake was the highest at lower pH where the pH was below the pKa of TCP (pKa of 2,4,5-TCP is 6.8). At acidic pH, the TCP was undissociated and the dispersion interactions predominated (Hamdaoui and Naffrechoux, 2007). The unionized species of halogenated organic compounds were high, which did not favor any repulsion between the acid-activatedmontmorillonite (AMt) surface and the molecular species of TCP, thereby increased the electrostatic attractions between the TCP molecules and the adsorption sites (Hameed et al., 2008). However, at basic pH, the ionized species of the 2,4,6-TCP are dominant, uptake was lower due to the electrostatic repulsions between the negative surface charge of AMt and the chlorophenolate anions and between chlorophenolate–chlorophenolate anions in the solution (Hamdaoui and Table 1 Structural parameters of samples.

NaMt AMt

B 30

qe (mg/g)

bentonite. After the activation the nitrogen uptake relatively increased. The BET surface areas (calculated at the relative pressure range of 0.05–0.30) of the samples were also determined. The acidactivation causes the formation of smaller pores in the solid particles resulting in a higher surface area of AMt. The pore size was obtained by applying the method of B.J.H to the desorption branch of the isotherms of nitrogen at 77 K. The BET surface area, the pore diameter, and the pore volume, for NaMt and AMt are presented in Table 1.

25

20

15

20

25

Pore diameter ´ (A˚)

82.5 396.5

0.085 0.434

41.6 43.8

40

45

50

Naffrechoux, 2007). Besides, there might be competition between the OH− ions and the ionic species of TCP. The possible mechanism is the interactions between protonated aluminol and silanol groups in bentonite and hydrophobic 2,4,5-TCP molecules. Silica and alumina functional groups on bentonite surface may be protonated as the solution pH lies below its pHpzc, again due to the presence of free H + ion in the solution. The protonation and deprotonation of silica can be described as (Kubilay et al., 2007) þ

þ

Si−OH + H →Si−OH2 −

Pore volume (cm3 N2g g−1)

35

Fig. 3. Adsorption of TCP onto AMt (A) effect of pH; (B) effect of adsorbent weight.

−

Si−OH + OH →SiO

Surface area (m2 g−1)

30

adsorbent mass (mg)

−

+ OH :

Furthermore, the aluminol groups on bentonite surface were also protonated in the form of AlOH 2+ when pHsol b pHpzc of AMt or in the form of AlO − when pHsol N pHpzc due to deprotonation mechanism (Bajpai and Sachdeva, 2002). During the process, interactions

H. Zaghouane-Boudiaf, M. Boutahala / International Journal of Mineral Processing 100 (2011) 72–78

between protonated aluminol groups in bentonite and unprotonated 2,4,5-TCP molecules also take place. An increase in the TCP adsorption was observed. When the pH of the solution increases, the adsorbent surface becomes negatively charged and does not favor the adsorption of TCP which is also negatively charged. On the other hand, it is well known that the solubility of chlorophenols in water increases with increasing pH, in this case the adsorption of TCP onto AMt reduced (Ku and Lee, 2000; Yousef Rushdi and El-Eswed, 2009). 3.4. Effect of adsorbent mass The adsorption of TCP on AMt was studied by changing the mass of adsorbent (20, 30, 40 and 50 mg). The experiments were kept at pH 4; temperature of 25 ± 2 °C and initial TCP concentration of 100 mg/L. As seen from Fig. 3B, the amount adsorbed per unit mass showed a decrease. The decrease in adsorption density may be due to a large adsorbent amount which effectively reduces the unsaturation of the adsorption sites and correspondingly, the number of such sites per unit mass comes down resulting in comparatively less adsorption at higher adsorbent amount (Shukla et al., 2002). On the other hand, it was found that the increase in the adsorbent weight from 20 to 50 mg increased the removal of TCP from 12 to 15%. This effect can be attributed to increased surface area and the adsorption sites (Bilgili, 2006; Hameed, 2007; El Nemr et al., 2009). 3.5. Effect of contact time and initial TCP concentration on the adsorption As can be seen from Fig. 4, when the equilibrium time was increased, the amount of adsorption was not drastically increased. The adsorption of TCP occurred very quickly from the beginning of the experiments and the maximum adsorption of TCP was sequestered within 10 15 10–15-min for all tests. The rapid adsorption at the initial contact time is due to the availability of the positively charged surface of the AMt for adsorption of molecule TCP in the solution at pH 4. The later slow rate of TCP adsorption probably occurred due to the electrostatic hindrance as well as the slow pore diffusion of the solute ions into the bulk of the adsorbent. The equilibrium was found to be nearly 20 min when the maximum TCP adsorption onto AMt was reached. It can be said that beyond this there is almost no further increase in the adsorption and it is thus fixed as the equilibrium time. It can be said also that the TCP ions were adsorbed by the exterior surface of the adsorbent. When the adsorption of exterior surface of the adsorbent reacted saturation, the TCP ions entered into the 35 30

qt (mg/g)

25

75

adsorbent pores and adsorbed by the interior surface of the particles. In this way, the contact time is very long. Also, the effect of initial TCP concentration in the solution on the capacity of adsorption on AMt was studied and shown in Fig. 4. Adsorption experiments were carried out with a constant mass of adsorbent (20 mg), pH (4.0), temperature (25 °C) and at different initial concentrations of TCP. The amount of TCP adsorbed per unit mass of adsorbent increased from 9 to 33 mg/g with increase in TCP concentration from 20 to 100 mg/L indicating that the initial TCP concentration plays an important role in the adsorption of TCP onto acid-activated montmorillonite. Increasing the initial TCP concentration would increase the mass transfer driving force and therefore the rate at which TCP molecules pass from the bulk solution to the particle surface (Hameed, 2007). 3.6. Effect of temperature on TCP adsorption The uptake of TCP by AMt decreases with increasing temperature, the amount of TCP adsorbed per unit mass of adsorbent decreased from 35 to 29.5 mg/g when temperature increases from 288 to 308 K (figure not showed) which indicates that the adsorption of TCP on AMt is controlled by an exothermic process. A similar trend was also observed by Hameed (2007) with 2,4,6-trichlorophénol adsorption by activated clay and Bilgili (2006) with 4-chlorophenol adsorption onto XAD-4 resin. This is partly due to a weakening of the attractive forces between TCP and adsorbent sites (Hameed, 2007) and when temperature increases, solubility of TCP increases and its adsorption decreases. 3.7. Kinetic models To identify the correct mechanism, several models must be checked for suitability and consistency over a broad range of the system parameters. Three kinetic models are used to fit the experimental data and can be summarized as follows. 3.7.1. Pseudo-first-order kinetics model The pseudo-first-order kinetic adsorption model was suggested by Lagergren (1898) for the sorption of solid/liquid systems and can be expressed in integrated and linear form using the following equation: lnðqe −qt Þ = lnqe −k1 t

ð3Þ

where k1 is the rate constant of adsorption (min −1), qe and qt are the adsorption loading of TCP (mg/g) at equilibrium and at time t (min), respectively. If the pseudo-first-order kinetics is applicable, a plot of ln (qe − qt) versus t should provide a straight line from which k1 and predicted qe can be determined from the slope and intercept of the plot, respectively (figure not showed). 3.7.2. Pseudo-second-order kinetic model The pseudo-second-order kinetic model (Ho and McKay, 1999) is expressed as:

20 15

t 1 1 = + t qt qe k2 q2e

10 C0 (mg/L)

5

where k2 (g/mg min) is the rate constant of pseudo-second-order adsorption. Plotting t/qt against t (Fig. 5 and Fig. 6), a straight line is obtained and the rate constant k2 as well as qe can be calculated.

20 50 80

0

ð4Þ

100

0

20

40

60

80

100

t (min) Fig. 4. Kinetic adsorption of TCP onto AMt for various initial TCP concentrations.

3.7.3. Intraparticle diffusion model The adsorbate species are most probably transported from the bulk of the solution into the solid phase through intraparticle diffusion/ transport process, which is often the rate-limiting step in many adsorption processes, especially in a rapidly stirred batch reactor

76

H. Zaghouane-Boudiaf, M. Boutahala / International Journal of Mineral Processing 100 (2011) 72–78

12

10

35 C0 (mg/L)

25

qt (mg/g)

8

t/qt

30

20 50 80 100

6

4

20 15 10 C0 (mg/L)

2

5

20 50 80 100

0

0

0 0

20

40

60

80

2

4

100

t (min)

(McKay, 1983). The possibility of intraparticular diffusion was explored by using the intraparticle diffusion model, which is commonly expressed by the equation proposed by Weber and Morris (1962): 0:5

ð5Þ

+ C:

Eq. 5 is an empirically found functional relationship, where uptake varies almost proportionally with t 0.5 rather than with the contact time t, ki is the intraparticle diffusion rate (mg/g min 0.5) obtained from the slope of the straight line of qt versus t 0.5. Fig. 7 shows that plots of qt against (t 0.5) consist of two or three separate linear regions, which confirms that intraparticle diffusion is not the only process involved in this system, since a simple linear plot would be observed if these were the case (Lazaridis and Asouhidou, 2003). Ho (2003) has shown that if the intraparticle diffusion is the sole rate-limiting step, it is essential for the qt versus t 0.5 plots to pass through the origin, which is not the case in Fig. 7. Where three linear regions are observed, it has been suggested that the first one can be attributed to external surface

3,5

Temp. (K) 288

3,0

298 308

2,5

t/qt

8

10

Fig. 7. Intraparticle diffusion plots of adsorption of 2,4,5-TCP on AMt.

Fig. 5. Fit pseudo-second order of adsorption of 2,4,5-TCP on AMt at different concentrations.

qt = ki t

6

t0,5 (min0,5)

adsorption or an instantaneous adsorption stage, where the TCP molecules are transported to the external surface through film diffusion and its rate is very fast. The second region is due to a gradual adsorption stage, where the TCP molecules are entered into activated-montmorillonite particle by intraparticle diffusion through pore and the final stage to the adsorption reaction. The values of intercept C provide information about the thickness of the boundary layer, the resistance to the external mass transfer increases as the intercept increases. The constant C was found to increase from 7.52 to 29.86 mg/g with increase of TCP concentration from 20 to 100 mg/L, which indicates the increase of the thickness of the boundary layer and decrease of the chance of the external mass transfer and hence increase of the chance of internal mass transfer (El Nemr et al., 2009). Table 2 presents the results of fitting experimental data to the pseudo-first-order, the pseudo-second-order and intraparticle models. It can be seen from Table 2 that the correlation coefficient R 2 varies in the order: pseudo-second-order N pseudo-firstorder N intraparticle diffusion model under all experimental conditions, which indicates that the pseudo-second-order model is the most suitable in describing the adsorption kinetics of TCP on AMt. The experimental qe,exp values agree well with the calculated ones obtained from the pseudo-second-order kinetic model. The same result was found by Radhika and Palanivelu (2006); by Hameed (2007) in adsorption of 2,4,6-TCP onto activated bentonite and Hameed et al. (2008) in adsorption of 2,4,6-trichlorophenol on coconut husk-based activated carbon. The pseudo-second-order

2,0 Table 2 Adsorption parameters of kinetic for the adsorption of 2,4,5-TCP on AMt.

1,5

Pseudo-firstorder

1,0 T (K)

0,5 0,0 0

20

40

60

80

100

t (min) Fig. 6. Fit pseudo-second order of adsorption of 2,4,5-TCP on AMt at different temperatures.

C0

qe,exp

qe,

Pseudosecond-order

Intra-particle diffusion

k1

R2

qe,cal

k2

R2

ki

C

R2

0.048 0.080 0.040 0.043 0.024 0.024

0.867 0.914 0.948 0.928 0.966 0.752

8.64 17.43 27.53 33.25 34.75 29.46

0.048 0.045 0.039 0.032 0.021 0.076

0.999 0.999 0.999 0.999 0.999 0.999

0.16 0.10 0.25 0.26 0.52 0.11

7.52 16.71 24.40 29.86 29.65 28.30

0.910 0.889 0.903 0.879 0.511 0.971

cal

298 20 8.54 3.10 298 50 17.25 3.74 298 80 27.48 3.21 298 100 33.00 3.60 288 100 35.04 5.44 308 100 29.53 1.75

C0 (mg L−1), qe (mg g−1), k1 (min−1), k2 (g (mg min)−1), ki (mg g−1 min−1/2), C (mg g−1).

H. Zaghouane-Boudiaf, M. Boutahala / International Journal of Mineral Processing 100 (2011) 72–78

-2,4

References

-2,6

Y=15,98-5737,76X

R2 = 0,95

-2,8 -3,0

lnk2

77

-3,2 -3,4 -3,6 -3,8 -4,0 0,00325

0,00330

0,00335

0,00340

0,00345

0,00350

1/T (1/K) Fig. 8. Arrhenius plot for adsorption of 2,4,5-TCP onto AMt.

equation is based on the adsorption loading of the solid phase. Advantage of the pseudo-second-order model is that it predicts the behavior over the whole range of the adsorption process. The Arrhenius relationship was used to evaluate the activation energy of adsorption representing the minimum energy that reactants must have for the reaction to proceed. The pseudo-second-order rate constant is expressed as a function of temperature by the following equation:

lnk2 = lnA−

Ea RT

ð6Þ

where Ea is the Arrhenius activation energy of adsorption, A the Arrhenius factor, R the gas constant equal to 8.314 J/mol K and T is the operated temperature. A plot of lnk2 against 1/T gives a straight line (Fig. 8) with slope −Ea/RT. The range of 5–50 kJ/mol of activation energies indicates a physisorption mechanism while the range of 50 800 50–800-kJ/mol suggests a chemisorption mechanism (Özkaya, 2006). The result obtained in this study is 47.7 kJ/mol indicating that the adsorption is assigned to a physisorption.

4. Conclusion The present study showed that the amount of TCP uptake increased with increasing initial TCP concentration and contact time, and decrease with increasing temperature and solution pH. Also the adsorption efficiency of the 2,4,5-TCP onto the acid-activated montmorillonite was increased with increasing initial acid-activated montmorillonite amounts The maximum TCP adsorption onto AMt was rapidly attained within 20 min. Kinetic data tend to fit well in pseudo-second-order rate expressions. The study shows that acidactivated montmorillonite can be used as cheap, efficient and ecofriendly adsorbent for removing TCP from water and wastewaters.

Acknowledgments The authors acknowledge the “Laboratoire Sciences Chimiques de Rennes. Equipe Organométalliques et Matériaux Moléculaires.” The authors are grateful to Prof. Lahcène Ouahab for his help in the characterization work. We would also like to thank Mr Yann Le Gal for the assistance with FTIR measurements, and his help.

Al-Asheh, S., Banat, F., Abu-Aitah, L., 2003. Adsorption of phenol using different types of activated bentonites. Sep. Purif. Technol. 33, 1–10. Aliouane, N., Hammouche, A., De Doncker, R.W., Telli, L., Boutahala, M., Brahimi, B., 2002. Investigation of hydratation and protonic conductivity of H-montmorillonite. Solid States Ionics 148, 103–110. Arfaoui, S., Frini-Srasra, N., Srasra, E., 2005. Application of clays to treatment of tannery sewages. Desalination 185, 419–426. Babaki, H., Salem, A., Jafarizad, A., 2008. Kinetic model for the isothermal activation of bentonite by sulfuric acid. Mater. Chem. Phys. 108, 263–268. Bajpai, A.K., Sachdeva, R., 2002. Study on the adsorption of hemoglobin onto bentonite clay surfaces. J. Appl. Polym. Sci. 85, 1607–1618. Barrett, E.P., Joyner, L.G., Halenda, P.H., 1951. The determination of pore volume and area distributions in porous substance. I. Computations from nitrogen isotherms. J. Am. Chem. Soc. 73, 373–380. Bilgili, M.S., 2006. Adsorption of 4-chlorophenol from aqueous solution by XAD-4 resin: isotherm, kinetic and thermodynamic analysis. J. Hazard. Mater. 137, 157–164. Bouras, O., Chami, T., Houari, M., Khalaf, H., Bollinger, J.C., Baudu, M., 2002. Removal of sulfacid brilliant pink from an aqueous stream by adsorption onto surfactantmodified Ti-pillared montmorillonite. Environ. Technol. 23, 405–411. Boutahala, M., Tedjar, F., 1993. Application of exchanged montmorillonite as protonic solid electrolyte. Solid States Ionics 61, 257–263. Brunauer, S., Emmet, P.H., Teller, E., 1938. Adsorption of gases in multimolecular layers. J. Am. Chem. Soc. 60, 309–319. El Nemr, A., Ola, A., Amany, El-Sikaily, Azza, K., 2009. Removal of direct blue-86 from aqueous solution by new activated carbon developed from orange peel. J. Hazard. Mater. 161, 102–110. Espantaleón, A.G., Nietoa, J.A., Fernández, M., Marsal, A., 2003. Use of activated clays in the removal of dyes and surfactants from tannery waste waters. Appl. Clay Sci. 24, 105–110. Fu-Chuang, H., Jiunn-Fwu, Lee, Chung-Kung, Lee, Huang-Ping, Chao, 2004. Effects of cation exchange on the pore and surface structure and adsorption characteristics of montmorillonite. Colloid Surf. A: Physicochem. Eng. Aspects. 239, 41–47. Gonen, Y., Rytwo, G., 2006. Using the dual-mode model to describe adsorption of organic pollutants onto an organoclay. J. Colloid Interface Sci. 299, 95–101. Hamdaoui, O., Naffrechoux, E., 2007. Modeling of adsorption isotherms of phenol and chlorophenols onto granular activated carbon. Part II. Models with more than two parameters. J. Hazard. Mater. 147, 401–411. Hamdi, N., Srasra, E., 2007. Remove of fluoride from acidic wastewater by clay mineral effect of solid–liquid ratios. Desalination 206, 238–244. Hameed, B.H., 2007. Equilibrium and kinetics studies of 2,4,6-trichlorophenol adsorption onto activated clay. Colloid Surf. A: Physicochem. Eng. Aspects 307, 45–52. Hameed, B.H., Tan, I.A.W., Ahmad, A.L., 2008. Adsorption isotherm, kinetic modeling and mechanism of 2,4,6-trichlorophenol on coconut husk-based activated carbon. Chem. Engin. J. 144, 235–244. Ho, Y.S., 2003. Removal of copper ions from aqueous solution by tree fern. Water Res. 37, 2323–2330. Ho, Y.S., McKay, G., 1999. Pseudo-second order model for sorption processes. Process. Biochem. 34, 451–465. Khalaf, H., Bouras, O., Perrichon, V., 1997. Synthesis and characterization of Alpillared and cationic surfactant modified Algerian bentonite. Microp. Mater. 8, 141–150. Komadel, P., Madejová, J., 2006. Chapter 7.1: acid activation of clay minerals. Develop. Clay Sci 1, 263–287. Koyuncu, Hülya, 2008. Adsorption kinetics of 3-hydroxybenzaldehyde on native and activated bentonite. Appl. Clay Sci. 38, 279–287. Bhattacharyya, K.G., Sen Gupta, S., 2007. Adsorptive accumulation of Cd (II), Co(II), Cu (II), Pb(II), and Ni(II) from water on montmorillonite: influence of acid activation. J. Colloid Interface Sci. 310, 411–424. Kubilay, S., Gurkan, R., Savran, A., Sahan, T., 2007. Removal of Cu(II), Zn(II) and Co(II) ions from aqueous solutions by adsorption onto natural bentonite. Adsorption 13, 41–51. Ku, Y., Lee, K.C., 2000. Removal of phenols from aqueous solution by XAD-4 resin. J. Hazard. Mater. 80, 59–68. Lagergren, S., 1898. About the theory of so-called adsorption of soluble substances. K. Sven. Vetenskapsakad. Handl. Band. 24, 1–39. Lazaridis, N.K., Asouhidou, D.D., 2003. Kinetics of sorption removal of Chromium (VI) from aqueous solutions by calcined Mg\Al\CO3 hydrotalcite. Water Res. 37, 2875–2882. Madejová, J., Bujdák, J., Janek, M., Komadel, P., 1998. Comparative FT-IR study of structural modifications during acid treatment of dioctahedral smectites and hectorite. Spectrochim. Acta A. 54, 1397–1406. McKay, G., 1983. The adsorption of dyestuff from aqueous solution using activated carbon: analytical solution for batch adsorption based on external mass transfer and pore diffusion. Chem. Eng. J. 27, 187–195. Min-Yu, T., Su-Hsia, L., 2006. Removal of basic dye from water onto pristine and HClactivated montmorillonite in fixed beds. Desalination 194, 156–165. Naseem, R., Tahir, S.S., 2001. Removal of Pb(II) from aqueous solutions by using bentonite as adsorbent. Water Res. 35, 3982–3986. Okada, K., Arimitsu, N., Kameshima, Y., Akira, N., Kenneth MacKenzie, J.D., 2006. Solid acidity of 2:1 type clay minerals activated by selective leaching. Appl. Clay Sci. 31, 185–193. Özcan, A.S., Özcan, A., 2004. Adsorption of acid dyes from aqueous solutions onto acidactivated bentonite. J. Colloid Interface Sci. 276, 39–46.

78

H. Zaghouane-Boudiaf, M. Boutahala / International Journal of Mineral Processing 100 (2011) 72–78

Özcan, Safa A., Bilge, Erdem, Adnan, Özcan, 2004. Adsorption of Acid Blue 193 from aqueous solutions onto Na–bentonite and DTMA–bentonite. J. Colloid Interface Sci. 280, 44–54. Özkaya, B., 2006. Adsorption and desorption of phenol on activated carbon and a comparison of isotherm models. J. Hazard. Mater. B 129, 158–163. Radhika, M., Palanivelu, K., 2006. Adsorptive removal of chlorophenols from aqueous solution by low cost adsorbent—kinetics and isotherm analysis. J. Hazard. Mater. 138, 116–124. Shukla, A., Zhang, Y.H., Dubey, P., Margrave, J.L., Shukla, S.S., 2002. J. Hazard. Mater. 95, 137–152. Shu, Yuehong, Li, Laisheng, Zhang, Qiuyun, Wu, Honghai, 2010. Equilibrium, kinetics and thermodynamic studies for sorption of chlorobenzenes on CTMAB modified bentonite and kaolinite. J. Hazard. Mater. 173, 47–53.

Weber, W.J., Morris, J.C., 1962. Proc. Int. Conf. : Water Pollution Symposium, vol. 2. Pergamon, Oxford, pp. 231–266. Witthuhn, B., Klauth, P., Klumpp, E., Narres, H.D., Martinius, H., 2005. Sorption and biodegradation of 2,4-dichlorophenol in the presence of organoclays. Appl. Clay Sci. 28, 55–66. Yousef Rushdi, I., El-Eswed, Bassam, 2009. The effect of pH on the adsorption of phenol and chlorophenols onto natural zeolite. Colloid Surf. A: Physicochem. Eng. Aspects 334, 92–99.