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Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions
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Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions Ihssane Belbachir, Benamar Makhoukhi∗ Laboratory of Separation and Purification Technologies, Tlemcen University, BP119, Algeria
a r t i c l e
i n f o
Article history: Received 26 June 2016 Revised 5 September 2016 Accepted 13 September 2016 Available online xxx Keywords: Bentonite Dyes Isotherm Kinetic Adsorption Wastewater
a b s t r a c t The aim of the present work was to investigate the adsorption of synthetic textile dyes, such as Bezathren-Blue, Bezathren-Green and Bezathren-Red onto sodium bentonite (Bt-Na+ ). Adsorption experiments were performed under batch process, to assess the performance of Bt-Na+ for the removal of Bezathren-dyes, using initial dyes concentrations, pH of solution, contact time and temperature as variables. According to results, the uptake of Bezathren-dyes by Bt-Na+ was rapid and the maximum sorption was observed at lowest pH. The maximum uptake capacities (qm ) for Bezathren-Blue, Bezathren-Green and Bezathren-Red were 35.08 mg/g, 32.88 and 48.52 mg/g respectively. Different types of adsorption isotherms and kinetic models were used to describe the Bezathren-dyes adsorption behavior. The experimental results fitted Freundlich model and the pseudo-second order kinetic models well. The results suggested that Bt-Na+ is suitable as a sorbent material for recovery and adsorption of Bezathren dyes from aqueous solutions. © 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Synthetic dyes are extensively used in different processing industries such as textile leather, printing, cosmetic, drug and food [1]. Based on their structure, synthetic dyes can be classified into 20–30 groups. But, the largest class of synthetic dyes in the color index is acid dyes, and this class of dyes is anionic compounds and mostly is azo, anthraquinone or triarylmethane group. Anthraquinone based dyes account for about 15% of colorants and have structures based on quinines. These dyes are very resistant to degradation and its color will fade away for a long time [2]. Dyes removal from industrial wastewater is an environmental issue, due to their high organic loads, low biodegradability, toxicity, mutagenicity and carcinogenicity; even in low concentrations, color imparts an anesthetic appearance to water [3]. The selection of adequate methods for effective removal of dyes from wastewaters depends on many factors: the dye chemical structure, specific behavior at different pH values, concentration in wastewater etc. Various physical, chemical and biological processes are used for dyes removal: coagulation-flocculation, precipitation, biodegradation, adsorption, ion exchange, membrane processes, chemical oxidation and solvent extraction [4,5]. However, all these conventional methods are not comparable to adsorption technique in term of efficiency, operating cost, process flexibility and ease of ∗
Corresponding author. E-mail address: [email protected] (B. Makhoukhi).
operation. Further all these techniques were found to be inefficient and incompetent because of the fairly high solubility and stability of the dyes toward light, oxidizing agents and aerobic digestion. A comprehensive survey indicates that adsorption technique was the most appropriate and efficient one [6]. A large number of studies have been dedicated to finding suitable and cheap adsorbents for the treatment or removal of dyes from water and wastewater. The conventional adsorbent is the activated carbon but many other low cost adsorbents such as sepiolite, kaolinite, montmorillonite, smectite, bentonite, zeolite and alunite have been investigated for this purpose [7–13]. Some of clay minerals possess a high adsorption capacity toward several classes of dyes and their adsorption capabilities are comparable to those activated carbons. From the recent studies of the adsorption of dyes using clay minerals it can be seen that some of natural clay minerals (mostly is montmorillonite/bentonite) show significant dye removal capacities; while others still need modification in order to enhance its adsorption capacities [14]. The adsorption performance of clay minerals and its modified forms also depend strongly on class of dye. Many of natural clay minerals have a high adsorption capacity for binding basic (cationic) dyes but often hardly to remove dyes from other groups or classes of dyes [15]. In this regard, montmorillonite-rich materials like bentonites exhibit highly interesting properties, e.g. high specific surface area, cation-exchange capacity (CEC), porosity, and tendency to retain water or other polar and non-polar compounds [16]. The
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Please cite this article as: I. Belbachir, B. Makhoukhi, Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2016.09.042
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Bentonite is the clay mineral used in this study. It is clay mainly composed of montmorillonite which is a 2:1 type aluminosilicate. Bentonite has the capacity to exchange these cations with the ones present in aqueous solutions of organic or inorganic salts. This property is mainly responsible for the great adsorbent power of bentonite, especially toward ions in solution. The bentonite was chosen for this work because of its natural abundance and low cost, compared with other clay types, bentonite has excellent adsorption properties and possesses adsorption sites available within its interlayer space as well as on the outer surface and edges [17]. Therefore, bentonite has recently been employed in many separation applications with or without modification [18]. The aim of the present work is to investigate the possibility of Bt-Na+ as an adsorbent for removal of Bezathren dyes (Anthraquinone based dyes), which is, namely Red, Blue and Green, from aqueous solution by adsorption. Effects of pH and temperature on the adsorption process are also investigated. The adsorption capacity of Bezathren dyes with Bt-Na+ was carried out using two kinetic models, which are the pseudo-second order and pseudo-first order. Finally, the experimental data were compared using two isotherm equations, which are Langmuir and Freundlich.
Dyes solutions at 10 0 0 ppm were prepared by dissolving of dyes powder (0.1 g) in 100 mL of distilled water. On a Analytik Jena Specord 210 Plus UV–vis spectrophotometer, these compounds absorbed at wavelength (λmax ) 600.0 nm for Bezathren-Blue, 630.0 nm for Bezathren-Green and 510.4 nm for Bezathren-Red.
2. Experimental
Adsorption (% ) =
2.1. Bentonite sample The natural bentonite used in this study was obtained from deposits in the area of Maghnia (west of Algeria); it was supplied by ENOF Ltd. Company (Algeria). The chemical composition was found to be as follows: 62.48% SiO2 , 17.53% Al2 O3 , 1.23% Fe2 O3 , 3.59% MgO, 0.82% K2 O, 0.87% CaO, 0.22% TiO2 , 0.39% Na2 O, 0.04% As, 13.0% loss on ignition at 950 °C. The mineralogical analysis showed that the native crude clay mineral contains preponderantly Montmorillonite (86 wt.%); the clay composition also includes Quartz (10%), Cristoballite (3.0%) and Beidellite (less than 1%) [16,19]. The bentonite was purified according to the method published in a previous study [14] and it was put in sodic form as follow: an amount of bentonite was dispersed in NaCl solution (1 M) with a 1/5 mass ratio and after agitation for 2 h, the solid was separated by centrifugation (rotational speed equal to 60 0 0 rpm for 15 min), this operation was repeated three times. The solid was washed three times with distilled water and it was dried at 40 °C for three days. The chemical composition of purified bentonite (Bt-Na+ ) was found to be as follows: 64.7% SiO2 , 18.1% Al2 O3 , 0.95% Fe2 O3 , 2.66% MgO, 0.8% K2 O, 0.61% CaO, 0.2% TiO2 , 1.43% Na2 O, 0.05% As, 10.0% loss on ignition [20,21]. The cation-exchange capacity (CEC) of bentonites was determined according to the ammonium acetate saturation method and was found to be 70 meq per 100 g of dry natural-Bt and 98 meq per 100 g of dry Bt-Na+ . The BET specific surface area increase from 50 m2 /g in natural-Bt to 95 m2 /g in Bt-Na+ [16,22]. 2.2. Dyes solutions Bezathren dyes used in this study are classified as an anthraquinone dyes (Schema 1). They were provided from SOITEX Company (Tlemcen–Algeria). - Bezathren-Blue: Dinaphthol [2,3-a:2 ,3 -h] phenazine-5,9,14, 18(6H,15H)-tetraone (C28 H14 N2 O4 ); MW: 442.10 g/mol, Log P : 2.68, C Log P : 7.60. - Bezathren-Red: 1, 4-diamino-2-methoxyanthracene-9,10-dione (C15 H12 N2 O3 ); MW: 268.27 g/mol, Log P : 0.69, C Log P : 2.92. - Bezathren-Red: 1, 4-bis (p-tolylamino) anthracene-9,10-dione (C28 H22 N2 O2 ); MW: 418.49 g/mol, Log P : 6.32, C Log P : 9.32.
2.3. Adsorption and procedure The method of adsorption used for this study, was carried out by a mixture of 10 mL of Blue and Green dyes solutions of known concentration (C0 = 50 ppm), and 0.05 g of our Bt-Na+ and 15 mL of Red dye solution with 0.03 of Bt-Na+ in Erlenmeyer with stopper, under vigorous stirring (700 rpm) at room temperature (20 ± 2 °C). Both liquid and solid phases were separated by centrifugation; the liquid phase was measured by the UV–visible spectrometer. The amount of adsorbed dyes at various equilibrium times (qt , mg/g) was calculated using following relationship:
qt (mg/g ) =
ci − ct ×V W
(1)
The percentage removal of dyes was calculated using following equation:
Ci − Ce × 100 Ci
(2)
where Ci , Ct and Ce (mg/L) are the initial, time t and equilibrium dyes concentrations, respectively; V and W are the liquid volume (L) and the weight of dried used adsorbent (g). 2.6. Characterization techniques The chemical composition of the bentonites was determined by X-ray fluorescence spectroscopy (Philips PW 3710) and XRD patterns of bentonites were collected on a Philips X-Pert diffractometer. Thermogravimetric analyses of bentonite (TGA) was performed using a Perkin Elmer TGA-7 thermogravimetric analyzer at a heating rate of 15 °C/min from 40 to 800 °C under nitrogen atmosphere (at 20 ml/min) in order to evaluate the thermal stability of our bentonite. IR spectrum was obtained with a Perkin Elmer 16PC spectrometer Model Fourier transform infrared spectrometer. 3. Results and discussion 3.1. Characteristic results of Bt-Na+ 3.1.1. FTIR analysis of the Bt-Na+ The IR spectrum of Bt-Na+ (Fig. 1) reveals the presence of characteristic absorption bands of clay such as bands corresponds to Si-O, Si-O-M, and M-O-H (M = Al, Fe or Mg) existing between anions and cations located in octahedral and tetrahedral sheets, and OH groups. For example, bands between (3620–3640 cm−1 ) can be associated to stretching vibrations of O–H groups coordinated to Al and Mg atoms (3640 cm−1 ) or two Al atoms (3620 cm−1 ) in octahedral sheets of bentonite; For the band centered at 1027 cm−1 , it characterizes the Si–O stretching vibrations; the stretching vibrations bands of Si–O–MVI (M= Al, Mg, and Fe) located in octahedral sheets appears at 400–550 cm−1 range [19,20]. For MVI –OH bands (MVI = Al, Mg, and Fe): AlVI –OH vibrations occur at 920 cm−1 , sharing of the OH group between Fe and Al in octahedral sheets can move this peak until about 815–915 cm−1 , in the case of our sample of Bt-Na+ , the peak appears at 913 cm−1 . 3.1.2. TG analysis of the Bt-Na+ For the dried Bt-Na+ curve (Fig. 2), 9.5% mass-loss was recorded at the temperature range of 30–200 °C and 4.75% mass-loss appeared at 350–800 °C. The first is due to desorption of water molecules, which were adsorbed onto the cations in the bentonite
Please cite this article as: I. Belbachir, B. Makhoukhi, Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2016.09.042
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Scheme 1. Structures of Bezathren dyes.
Fig. 1. FTIR spectra of Bt-Na+ .
the broad and weak bands around 700 °C can be assigned to the structural water released during the dehydroxylation/dehydration process [23].
Fig. 2. TGA (DTG) curves of Bt-Na+ .
interlayer. The second is related to the removal of water molecules from the crystal lattice, with one alumina octahedral sheet sandwiched between two silica tetrahedral sheets. Between 200 and 800 °C, CO, CO2 and water are released in addition to Cl2 [23]. The presence of carbon and sulfur is attributed to organic contamination in bentonite, sulfur is released as SO2 at temperatures above 700 °C and the presence of (Cl) is attributed to NaCl traces in the Bt-Na+ . It must be noted that the peak at 160 °C in the DTA curve corresponds to bonded water which according to the literature is associated with the Brönsted acid sites [20]. On the other hand,
3.1.3. XRD results of the Bt-Na+ The X-ray diffraction pattern of Bt-Na+ was compared to that of the natural bentonite, as illustrated by (Fig. 3). It clearly appears that the clay mineral crystallinity of Bt-Na+ was not diminished upon purification. Fig. 3 shows the XRD pattern of natural bentonite and Bt-Na+ was exhibiting the reflection peak occurred at 6.1° and 6.7°, respectively. The interlayer spacing distance of the ˚ respectively. bentonites was found to be 14.5 A˚ and 13.2 A, The decrease in the interlayer spacing of Bt-Na+ was due to cationic exchange of Ca2+ , Mg2+ and K+ cations, replaced by Na+ cations which have a smaller atomic radius. The X-ray diffraction pattern of bentonites confirms that bentonite was purified. We observed the disappearance of some characteristic reflection peak of crystalline phases of impurities especially that of quartz located at 2θ = 26.8°. Also, we observed the intensification of some reflection peak localized at 2θ = 5.7 and 28°.
3.2. Dye adsorption over Bt-Na+ In this study different parameters were examined: contact time, effect of initial pH, initial concentration of dyes, and effect of temperature.
Please cite this article as: I. Belbachir, B. Makhoukhi, Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2016.09.042
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Fig. 3. XRD patterns for bentonites before and after purification: (0 0 1) basal peak (1) Natural bentonite; (2) Bt-Na+ .
will be greater if the volume of the molecules is small [14]. Therefore, if the size of the dye molecules is larger, the saturation of the adsorption sites in the bentonite will be faster. The geometric calculations performed by Gausian software shown the following sizes for the dyes molecules: BezathrenRed (277.28 A˚ 3 ), Bezathren-Green (141.22 A˚ 3 ) and Bezathren-Blue (313.49 A˚ 3 ). The Bezathren-Blue molecule is the larger compared to other dyes. Consequently, saturation of adsorption sites in bentonite is faster. 3.2.2. Adsorption kinetics model In an attempt to express the mechanism of dyes adsorption onto the Bt-Na+ , the following kinetic model equations are used to analyze the adsorption experimental data for determination of the related kinetic parameters.
Fig. 4. Removal of Bezathren-dyes by sodic bentonites as a function of time 1: Blue dye, 2: Green dye, 3: Red dye.
Pseudo-first order model (PFO). The linear form of the pseudo-first order rate equation by Lagergren is expressed as [25]:
Ln (qe − qt ) = Ln qe − k f × t 3.2.1. Effect of contact time (kinetics study) The adsorption of dyes on Bt-Na+ was studied as a function of contact time and results are shown in Fig. 4. As seen, the adsorption of dyes increases rapidly with increasing time. The time needed for sodic bentonite to adsorb the maximum of BezathrenBlue is 15 min (47.80%, 5.334 mg/g) and 45 min to adsorb the maximum of Bezathren-Green (29.40%, 2.94 mg/g) and BezathrenRed (11.53%, 2.86 mg/g), and then tended to keep constant after this time. In most liquid phase adsorption system, the efficiency of adsorption is dependent on the pH of the system, the variation of pH leads to the variation of surface charge of the adsorbent and the degree of ionization of the dyes molecules [24]. In order to estimate the solubility of dyes, the partition-coefficient (Log P) was measured as follow: Bezathren-Red (Log P : 0.69), BezathrenGreen (6.32) and Bezathren-Blue (2.68). From these results, the Bezathren-Green has a hydrophobic character and present a less solubility in water compared to other dyes. The Bezathren-Red is the more soluble in water amongst the three dyes. The time needed for bentonite to adsorb the maximum of Bezathren-Blue is 15 min and it is 45 min to adsorb the maximum of other dyes. In our previous study we have shown that the adsorption capacity is inversely proportional to size of molecule dye. The diffusion of dye molecules in the pores and layers of bentonite
(3)
Pseudo-second order model (PSO). The linear form of the pseudosecond order rate equation is given as [26]:
t 1 t = + qt qe ks q2e
(4)
where qt (mg/g) is the amount of adsorbate adsorbed at time (t), qe (mg/g) the adsorption capacity at equilibrium, kf (min−1 ) is the rate constant of the PFO model and t (min) is the time. Ks is the pseudo-second order adsorption rate constant (g/mg/min). It was observed that the pseudo-second order model agreed with the experimental data better than the pseudo-first order model for the adsorption of dyes (Table 1). High correlation coefficients are obtained when employing the pseudo-second order model (R2 ≥ 0.9995) and the calculated equilibrium adsorption capacity is similar to the experimental data, and this indicated that the adsorption of Bezathren-dyes onto Bt-Na+ is controlled by chemical adsorption (chemisorption) involving valence forces through sharing or exchange electrons between sorbent and sorbate. In chemical adsorption, it is assumed that the adsorption capacity is proportional to the number of active sites occupied on the adsorbent surface [14]. Pseudo-first order and pseudo-second order models for adsorption onto Bt-Na+ .
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Table 1 Pseudo-first order and pseudo-second order models for adsorption onto Bt-Na+ .
Bezathren-Blue Bezathren-Green Bezathren-Red
qe (exp.)
Pseudo-first order
Pseudo-second order
5.33 mg/g 2.94 mg/g 2.86 mg/g
R2 = 0.854 qe (calc) = 3.249 mg/g K1 = 5.194 min−1 R2 = 0.527 qe (calc) = 0.675 mg/g K1 = 0.0685 min R2 = 0.802 qe (calc) = 1.542 mg/g K1 = 0.042 min
R2 = 0.999 qe (calc) = 5.385 mg/g K2 = 0.761 min R2 = 0.999 qe (calc) = 3.039 mg/g K2 = 0.225 min R2 = 0.999 qe (calc) = 2.942 mg/g K2 = 0.108 min
Fig. 5. Kinetic plots for the adsorption of dyes onto Na-Bt, 1: Blue, 2: Green, 3: Red.
Fig. 6. Removal of Dyes solution by sodic bentonite as a function of initial pH 1: Blue, 2: Green, 3: Red.
3.2.3. Effect of pH The variations of pH medium were one of the most important factors affecting the concentration and dyes recovery procedure, which was related to the formation of soluble dyes complexes and subsequently their stabilities in aqueous solutions [27] (Fig. 5). The adsorptions of dyes by sodic bentonite were studied at different pH value ranged from 1.1 to 6.73 and the results are show in Fig. 6, it is seen that the adsorption decreases with increasing of initial pH. It reaches a maximum value around pH 1.4 for Bezathren-Red (100%), pH 1.5 for Bezathren-Green (98.7%) and pH 2.35 for Bezathren-Blue (100%). 3.2.4. Effect of initial dye concentration In order to demonstrate the effect of the initial concentration on the adsorption, experiments were carried out at different initial dyes concentrations ranging from 20 to 500 mg/L (Fig. 7). Fig. 7 shows that by increasing the initial concentration in solution, the amount of adsorbed dyes gradually increases (Fig. 8). The Bezathren-Blue uptake increases from 3.554 to 35.08 mg/g,
Fig. 7. Removal of dyes by sodic bentonite as a function of concentration 1: Blue, 2: Green, 3: Red.
the Bezathren-Green uptake increases from 2.16 to 32.88 mg/g and the Bezathren-Red uptake increases from 2.86 to 48.52 mg/g, with increasing the initial concentration from 40 to 500 ppm. The increase in initial dye concentration enhances the interaction force, that it is necessary to overcome the resistances to the mass transfer between adsorbate and the adsorbent [28]. However, as the initial concentration of dyes increased, most of the available sorption sites became occupied, leading to a decrease in the removal efficiency, this is why this increase starts to ease off after 300 ppm of initial dyes concentrations. 3.2.5. Isotherm adsorption The Langmuir and Freundlich isotherms are the equations most frequently used to represent the data on adsorption from solution. Langmuir and Freundlich isotherms are represented by the following equations [29,30]:
Ce Ce 1 = + qe qm qm KL
(5)
Please cite this article as: I. Belbachir, B. Makhoukhi, Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2016.09.042
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Fig. 8. Isotherms plots for the adsorption of dyes onto Na-Bt 1: Blue, 2: Green, 3: Red. Table 2 Isotherm parameters for dyes adsorption onto Bt-Na+ .
Bezathren-Blue Bezathren-Green Bezathren-Red
Ln qe = Ln KF + n Ln Ce
qm (exp.), mg/g
Langmuir isotherm
Freundlich isotherm
5.334 2.94 2.86
R2 = 0.785 qm (calc.) = 83.33 mg/g KL = 0.0025 (L/mg) R2 = 0.620 qm (calc.) = 100 mg/g KL = 0.0 0 08 (L/mg) R2 = 0.518 qm (calc.) = 66.66 mg/g KL = 0.0012 (L/mg)
R2 = 0974 KF = 0.330 n = 1.196 R2 = 0.997 KF = 0.050 n = 0.884 R2 = 0.988 KF = 0.025 n = 0.776
(6)
where Ce is the equilibrium concentration of dye (mg/L), qe is the amount of dye adsorbed on the bentonite (mg/g), KL is the Langmuir adsorption constant (L/mg), qm is the maximum amount of dye that can be adsorbed by the sodic bentonite, KF is the Freundlich adsorption constant, and n is a constant that indicates the capacity and intensity of the adsorption. The experimental data were modeled according to Langumir and Freundlich isotherms, and the evaluated constants were given in Table 2. It was clear that Freundlich isotherm described better with a higher correlation coefficient (R2 ≥ 0.974) in comparison with that of Langmuir (R2 ≤ 0.785), this results confirm the existence of interactions between adsorbed molecules. Isotherm parameters for dyes adsorption onto Bt-Na+ 3.2.6. Thermodynamic parameters The effect of temperature on the adsorption of dyes by sodic bentonite at initial pH and concentration of 50 ppm was studied. The thermodynamic parameters, namely the enthalpy (H) and entropy (S) associated with the adsorption process could be obtained from the slope and intercept of the Vant Hoff plot. ln Kc versus 1/T using the following equation [31]:
Ln Kd =
S R
−
H RT
(7)
where Kd is the distribution coefficient, T is the temperature in Kelvin, and R is the gas constant (8.314 J/mol K). Distribution coefficient (Kd , mL/g) is also computed using the following equation [31]:
Kd (mL/g ) =
Ci − Ce V × Ce m
(8)
where Ci and Ce are the initial and equilibrium concentrations of dyes (mg/L) in solution. m is the weight of the adsorbent (g), V is the volume of the aqueous phase (mL). Fig. 9 shows adsorbed percent (%) of dyes onto Bt-Na+ as a function of the temperature. Thermodynamic data for adsorption of dyes onto Bt-Na+
Fig. 9. Removal of Bezathren-dyes by sodic bentonite as a function of temperature 1: Blue, 2: Green, 3: Red.
Table 3 Thermodynamic data for adsorption of dyes onto Bt-Na+ .
Bezathren-Blue Bezathren-Green Bezathren-Red
H (KJ/mol)
S (J/mol K)
R2
−09,04 −08,96 −25,88
12.36 06.80 −52,75
0.959 0.950 0.985
The thermodynamic parameters of the adsorption of dyes on Bt-Na+ at the examined temperatures are presented in Fig. 10 and Table 3. It can be seen that the yield adsorption of dyes decreases with increasing temperature, this behavior indicates the exothermic nature of adsorption for all three dyestuffs onto Bt-Na+ , as supported by the negatives values of H. These results are contrary to the data given in the literature. This can be due to the energy released after the adsorption being higher than that needed to absorb the solvent molecules from the pores of bentonite clay [32]. Also, the positive values of S for both
Please cite this article as: I. Belbachir, B. Makhoukhi, Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2016.09.042
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Fig. 10. Plot Van’t Hoff plot for the adsorption of Bezathren-dyes onto sodic bentonite 1: Blue, 2: Green, 3: Red.
Bezathren-Blue and Bezathren-Green indicate that the randomness at the solid–liquid interface during the adsorption process increases, in contrast, in the case of Bezathren-Red the negative standard entropy change (S) suggests that the randomness in solid/solution interface decreased during the adsorption [32]. 4. Conclusion In this study, the adsorptions of Bezathren-dyes onto sodic bentonite were studied by batch tests conducted under various experimental conditions such as contact time, pH, initial dyes concentrations and temperature. The kinetic study shows that the process can be described by a pseudo-second order model and the adsorption of Bezathren-Blue achieves equilibrium quickly (15 min) compared to other dyes (45 min). Kinetics adsorption of Bezathren-dyes onto Bt-Na+ is controlled by chemical adsorption. The adsorption yields obtained onto bentonite are 100% (at pH 1.4 for Bezathren-Red and at pH 2.35 for Bezathren-Blue), it is equal to 98.7% (at pH 1.5 for Bezathren-Green). The equilibrium batch experiment data demonstrate that Bt-Na+ is effective adsorbent for the removal and recovery of Bezathren-dyes from aqueous solutions, with the maximum sorption capacity of 35.08 mg/g, 32.88 mg/g and 48.52 mg/g for Bezathren-Blue, Bezathren-Green and Bezathren-Red respectively, under the given experimental conditions. The results show that sodic bentonite could be employed as low-cost material for the removal of Bezathren dyes from effluents. References [1] Chinoune K, Bentaleb K, Bouberka Z, Nadim A, Maschke U. Adsorption of reactive dyes from aqueous solution by dirty bentonite. Appl Clay Sci 2016;123:64–75. [2] Ismadji S, Soetaredjo FE, Ayucitra A. Clay materials for environmental remediation. Heidelberg, New York: E-publiching Inc: Cham: Springer; 2015. p. 5–31. [3] Wan D, Li W, Wang G, Chen K, Lu L, Hu Q. Adsorption and heterogeneous degradation of rhodamine B on the surface of magnetic bentonite material. Appl Surf Sci 2015;349:988–96.
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[4] Asfaram A, Ghaedi M, Goudarzi A, Soylak M, Langroodi SM. Magnetic nanoparticle based dispersive micro-solid-phase extraction for the determination of malachite green in water samples: optimized experimental design. New J Chem 2015;39:9813–23. [5] Ozcan A, Omeroglu C, Erdogan Y, Ozcan AS. Modification of bentonite with a cationic surfactant: an adsorption study of textile dye reactive blue 19. J Hazard Mater 2007;140:173–9. [6] Suzuki M. Fundamentals of adsorption. 4th ed. Tokyo: Kodansha; 1993. [7] Santos SCR, Boaventura RAR. Adsorption of cationic and anionic azo dyes on sepiolite clay: equilibrium and kinetic studies in batch mode. J Environ Chem Eng 2016;4:1473–83. [8] Liu P, Zhang L. Adsorption of dyes from aqueous solutions or suspensions with clay nano-adsorbents. Sep Purif Technol 2007;58:32–9. [9] Gong R, Ding Y, Li M, Yang C, Liu H, Sun Y. Utilization of powdered peanut hull as biosorbent for removal of anionic dyes from aqueous solution. Dyes Pigm 2005;64:187–92. [10] Bulut Y, Akçay G, Elma D, Ersin Serhatli I. Synthesis of clay-based superabsorbent composite and its sorption capability. J Hazard Mater 2009;171:717–23. [11] Patil SP, Bethi B, Sonawane GH, Shrivastava VS, Sonawane S. Efficient adsorption and photocatalytic degradation of Rhodamine B dye over Bi2 O3 -bentonite nanocomposites: a kinetic study. J Ind Eng Chem 2016;34:356–63. [12] Zhang L, Hu P, Wang J, Huang R. Adsorption of Amido Black 10B from aqueous solutions onto Zr (IV) surface-immobilized cross-linked chitosan/bentonite composite. Appl Surf Sci 2016;369:558–66. [13] Li H, Leng Y, Tuo X. Research on adsorption and desorption behavior of Pu on bentonites for buffer backfill material. Procedia Environ Sci 2016;31:401–7. [14] Makhoukhi B, Djab M, Didi MA. Adsorption of Telon dyes onto bis-imidazolium modified bentonite in aqueous solutions. J Environ Chem Eng 2015;3:1384–92. [15] Özcan AS, Erdem B, Özcan A. Adsorption of acid blue 193 from aqueous solutions onto Na-bentonite and DTMA-bentonite. J Colloid Interface Sci 2004;280:44–54. [16] Didi MA, Makhoukhi B, Azzouz A, Villemin D. Colza oil bleaching through optimized acid activation of bentonite—a comparative study. Appl Clay Sci 2009;42:336–44. [17] Makhoukhi B, Didi MA, Moulessehoul H, Azzouz A, Villemin D. Diphosphonium ion-exchanged montmorillonite for Telon dye removal from aqueous media. Appl Clay Sci 2010;50:354–61. [18] Gupta VK, Sharma M, Vyas RK. Hydrothermal modification and characterization of bentonite for reactive adsorption of methylene blue: an ESI-MS study. J Environ Chem Eng 2015;3:2172–9. [19] Makhoukhi B, Didi MA, Villemin D. Modification of bentonite with diphosphonium salts: synthesis and characterization. Mater Lett 2008;62:2493–6. [20] Makhoukhi B, Villemin D, Didi MA. Preparation, characterization and thermal stability of bentonite modified with bis-imidazolium salts. Mater Chem Phys 2013;138:199–203. [21] Makhoukhi B, Didi MA, Villemin D, Azzouz A. Acid activation of Bentonite for use as a vegetable oil bleaching agent. Int J Fats 2009;60:343–9. [22] Makhoukhi B, Didi MA, Moulessehoul H, Azzouz A. Telon dye removal from Cu(II)–containing aqueous media using p-diphosphonium organo-montmorillonite. Med J Chem 2011;2:44–55. [23] Makhoukhi B, Villemin D, Didi MA. Synthesis of bisimidazolium–ionic liquids: Characterization, thermalstability and application to bentonite intercalation. J Taibah Univ Sci 2016;10:168–80. [24] Aghayan H, Mahjoub AR, Khanchi AR. Samarium and dysprosium removal using 11-molybdo-vanadophosphoric acid supported on Zr modified mesoporous silica SBA-15. Chem Eng J 2013;225:509–19. [25] Ho YS, McKay G. The kinetics of sorption of divalent metal ions onto sphagnum moss peat. Water Res 20 0 0;34:735–42. [26] Su J, Lin S, Chen Z, Megharaj M, Naidu R. Dechlorination of p-chlorophenol from aqueous solution using bentonite supported Fe/Pd nanoparticles: synthesis, characterization and kinetics. Desalin Water Treat 2011;280:167–73. [27] Özcan A, Öncü EM, Özcan AS. Adsorption of acid blue 193 from aqueous solutions onto DEDMA-sepiolite. J Hazard Mater 2006;129:244–52. [28] Rafatullah M, Sulaiman O, Hashim R, Ahmad A. Adsorption of copper (II), chromium (III), nickel (II) and lead (II) ions from aqueous solutions by meranti sawdust. J Hazard Mater 2009;170:969–77. [29] Langmuir I. The evaporation, condensation and reflection of molecules and the mechanism of adsorption. J Franklin Inst 1934;217:543–69. [30] Freundlich H. Colloid and capillary chemistry. London: Metheun; 1926. p. 883. [31] Gok C. Neodymium and samarium recovery by magnetic nano-hydroxyapatite. J Radioanal Nucl Chem 2014;301:641–51. [32] Sari A, Soylak M. Equilibrium and thermodynamic studies of stearic acid adsorption on Celtek clay. J Serb Chem Soc 2007;72:485–94.
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Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions Ihssane Belbachir, Benamar Makhoukhi∗ Laboratory of Separation and Purification Technologies, Tlemcen University, BP119, Algeria
a r t i c l e
i n f o
Article history: Received 26 June 2016 Revised 5 September 2016 Accepted 13 September 2016 Available online xxx Keywords: Bentonite Dyes Isotherm Kinetic Adsorption Wastewater
a b s t r a c t The aim of the present work was to investigate the adsorption of synthetic textile dyes, such as Bezathren-Blue, Bezathren-Green and Bezathren-Red onto sodium bentonite (Bt-Na+ ). Adsorption experiments were performed under batch process, to assess the performance of Bt-Na+ for the removal of Bezathren-dyes, using initial dyes concentrations, pH of solution, contact time and temperature as variables. According to results, the uptake of Bezathren-dyes by Bt-Na+ was rapid and the maximum sorption was observed at lowest pH. The maximum uptake capacities (qm ) for Bezathren-Blue, Bezathren-Green and Bezathren-Red were 35.08 mg/g, 32.88 and 48.52 mg/g respectively. Different types of adsorption isotherms and kinetic models were used to describe the Bezathren-dyes adsorption behavior. The experimental results fitted Freundlich model and the pseudo-second order kinetic models well. The results suggested that Bt-Na+ is suitable as a sorbent material for recovery and adsorption of Bezathren dyes from aqueous solutions. © 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Synthetic dyes are extensively used in different processing industries such as textile leather, printing, cosmetic, drug and food [1]. Based on their structure, synthetic dyes can be classified into 20–30 groups. But, the largest class of synthetic dyes in the color index is acid dyes, and this class of dyes is anionic compounds and mostly is azo, anthraquinone or triarylmethane group. Anthraquinone based dyes account for about 15% of colorants and have structures based on quinines. These dyes are very resistant to degradation and its color will fade away for a long time [2]. Dyes removal from industrial wastewater is an environmental issue, due to their high organic loads, low biodegradability, toxicity, mutagenicity and carcinogenicity; even in low concentrations, color imparts an anesthetic appearance to water [3]. The selection of adequate methods for effective removal of dyes from wastewaters depends on many factors: the dye chemical structure, specific behavior at different pH values, concentration in wastewater etc. Various physical, chemical and biological processes are used for dyes removal: coagulation-flocculation, precipitation, biodegradation, adsorption, ion exchange, membrane processes, chemical oxidation and solvent extraction [4,5]. However, all these conventional methods are not comparable to adsorption technique in term of efficiency, operating cost, process flexibility and ease of ∗
Corresponding author. E-mail address: [email protected] (B. Makhoukhi).
operation. Further all these techniques were found to be inefficient and incompetent because of the fairly high solubility and stability of the dyes toward light, oxidizing agents and aerobic digestion. A comprehensive survey indicates that adsorption technique was the most appropriate and efficient one [6]. A large number of studies have been dedicated to finding suitable and cheap adsorbents for the treatment or removal of dyes from water and wastewater. The conventional adsorbent is the activated carbon but many other low cost adsorbents such as sepiolite, kaolinite, montmorillonite, smectite, bentonite, zeolite and alunite have been investigated for this purpose [7–13]. Some of clay minerals possess a high adsorption capacity toward several classes of dyes and their adsorption capabilities are comparable to those activated carbons. From the recent studies of the adsorption of dyes using clay minerals it can be seen that some of natural clay minerals (mostly is montmorillonite/bentonite) show significant dye removal capacities; while others still need modification in order to enhance its adsorption capacities [14]. The adsorption performance of clay minerals and its modified forms also depend strongly on class of dye. Many of natural clay minerals have a high adsorption capacity for binding basic (cationic) dyes but often hardly to remove dyes from other groups or classes of dyes [15]. In this regard, montmorillonite-rich materials like bentonites exhibit highly interesting properties, e.g. high specific surface area, cation-exchange capacity (CEC), porosity, and tendency to retain water or other polar and non-polar compounds [16]. The
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Bentonite is the clay mineral used in this study. It is clay mainly composed of montmorillonite which is a 2:1 type aluminosilicate. Bentonite has the capacity to exchange these cations with the ones present in aqueous solutions of organic or inorganic salts. This property is mainly responsible for the great adsorbent power of bentonite, especially toward ions in solution. The bentonite was chosen for this work because of its natural abundance and low cost, compared with other clay types, bentonite has excellent adsorption properties and possesses adsorption sites available within its interlayer space as well as on the outer surface and edges [17]. Therefore, bentonite has recently been employed in many separation applications with or without modification [18]. The aim of the present work is to investigate the possibility of Bt-Na+ as an adsorbent for removal of Bezathren dyes (Anthraquinone based dyes), which is, namely Red, Blue and Green, from aqueous solution by adsorption. Effects of pH and temperature on the adsorption process are also investigated. The adsorption capacity of Bezathren dyes with Bt-Na+ was carried out using two kinetic models, which are the pseudo-second order and pseudo-first order. Finally, the experimental data were compared using two isotherm equations, which are Langmuir and Freundlich.
Dyes solutions at 10 0 0 ppm were prepared by dissolving of dyes powder (0.1 g) in 100 mL of distilled water. On a Analytik Jena Specord 210 Plus UV–vis spectrophotometer, these compounds absorbed at wavelength (λmax ) 600.0 nm for Bezathren-Blue, 630.0 nm for Bezathren-Green and 510.4 nm for Bezathren-Red.
2. Experimental
Adsorption (% ) =
2.1. Bentonite sample The natural bentonite used in this study was obtained from deposits in the area of Maghnia (west of Algeria); it was supplied by ENOF Ltd. Company (Algeria). The chemical composition was found to be as follows: 62.48% SiO2 , 17.53% Al2 O3 , 1.23% Fe2 O3 , 3.59% MgO, 0.82% K2 O, 0.87% CaO, 0.22% TiO2 , 0.39% Na2 O, 0.04% As, 13.0% loss on ignition at 950 °C. The mineralogical analysis showed that the native crude clay mineral contains preponderantly Montmorillonite (86 wt.%); the clay composition also includes Quartz (10%), Cristoballite (3.0%) and Beidellite (less than 1%) [16,19]. The bentonite was purified according to the method published in a previous study [14] and it was put in sodic form as follow: an amount of bentonite was dispersed in NaCl solution (1 M) with a 1/5 mass ratio and after agitation for 2 h, the solid was separated by centrifugation (rotational speed equal to 60 0 0 rpm for 15 min), this operation was repeated three times. The solid was washed three times with distilled water and it was dried at 40 °C for three days. The chemical composition of purified bentonite (Bt-Na+ ) was found to be as follows: 64.7% SiO2 , 18.1% Al2 O3 , 0.95% Fe2 O3 , 2.66% MgO, 0.8% K2 O, 0.61% CaO, 0.2% TiO2 , 1.43% Na2 O, 0.05% As, 10.0% loss on ignition [20,21]. The cation-exchange capacity (CEC) of bentonites was determined according to the ammonium acetate saturation method and was found to be 70 meq per 100 g of dry natural-Bt and 98 meq per 100 g of dry Bt-Na+ . The BET specific surface area increase from 50 m2 /g in natural-Bt to 95 m2 /g in Bt-Na+ [16,22]. 2.2. Dyes solutions Bezathren dyes used in this study are classified as an anthraquinone dyes (Schema 1). They were provided from SOITEX Company (Tlemcen–Algeria). - Bezathren-Blue: Dinaphthol [2,3-a:2 ,3 -h] phenazine-5,9,14, 18(6H,15H)-tetraone (C28 H14 N2 O4 ); MW: 442.10 g/mol, Log P : 2.68, C Log P : 7.60. - Bezathren-Red: 1, 4-diamino-2-methoxyanthracene-9,10-dione (C15 H12 N2 O3 ); MW: 268.27 g/mol, Log P : 0.69, C Log P : 2.92. - Bezathren-Red: 1, 4-bis (p-tolylamino) anthracene-9,10-dione (C28 H22 N2 O2 ); MW: 418.49 g/mol, Log P : 6.32, C Log P : 9.32.
2.3. Adsorption and procedure The method of adsorption used for this study, was carried out by a mixture of 10 mL of Blue and Green dyes solutions of known concentration (C0 = 50 ppm), and 0.05 g of our Bt-Na+ and 15 mL of Red dye solution with 0.03 of Bt-Na+ in Erlenmeyer with stopper, under vigorous stirring (700 rpm) at room temperature (20 ± 2 °C). Both liquid and solid phases were separated by centrifugation; the liquid phase was measured by the UV–visible spectrometer. The amount of adsorbed dyes at various equilibrium times (qt , mg/g) was calculated using following relationship:
qt (mg/g ) =
ci − ct ×V W
(1)
The percentage removal of dyes was calculated using following equation:
Ci − Ce × 100 Ci
(2)
where Ci , Ct and Ce (mg/L) are the initial, time t and equilibrium dyes concentrations, respectively; V and W are the liquid volume (L) and the weight of dried used adsorbent (g). 2.6. Characterization techniques The chemical composition of the bentonites was determined by X-ray fluorescence spectroscopy (Philips PW 3710) and XRD patterns of bentonites were collected on a Philips X-Pert diffractometer. Thermogravimetric analyses of bentonite (TGA) was performed using a Perkin Elmer TGA-7 thermogravimetric analyzer at a heating rate of 15 °C/min from 40 to 800 °C under nitrogen atmosphere (at 20 ml/min) in order to evaluate the thermal stability of our bentonite. IR spectrum was obtained with a Perkin Elmer 16PC spectrometer Model Fourier transform infrared spectrometer. 3. Results and discussion 3.1. Characteristic results of Bt-Na+ 3.1.1. FTIR analysis of the Bt-Na+ The IR spectrum of Bt-Na+ (Fig. 1) reveals the presence of characteristic absorption bands of clay such as bands corresponds to Si-O, Si-O-M, and M-O-H (M = Al, Fe or Mg) existing between anions and cations located in octahedral and tetrahedral sheets, and OH groups. For example, bands between (3620–3640 cm−1 ) can be associated to stretching vibrations of O–H groups coordinated to Al and Mg atoms (3640 cm−1 ) or two Al atoms (3620 cm−1 ) in octahedral sheets of bentonite; For the band centered at 1027 cm−1 , it characterizes the Si–O stretching vibrations; the stretching vibrations bands of Si–O–MVI (M= Al, Mg, and Fe) located in octahedral sheets appears at 400–550 cm−1 range [19,20]. For MVI –OH bands (MVI = Al, Mg, and Fe): AlVI –OH vibrations occur at 920 cm−1 , sharing of the OH group between Fe and Al in octahedral sheets can move this peak until about 815–915 cm−1 , in the case of our sample of Bt-Na+ , the peak appears at 913 cm−1 . 3.1.2. TG analysis of the Bt-Na+ For the dried Bt-Na+ curve (Fig. 2), 9.5% mass-loss was recorded at the temperature range of 30–200 °C and 4.75% mass-loss appeared at 350–800 °C. The first is due to desorption of water molecules, which were adsorbed onto the cations in the bentonite
Please cite this article as: I. Belbachir, B. Makhoukhi, Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2016.09.042
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Scheme 1. Structures of Bezathren dyes.
Fig. 1. FTIR spectra of Bt-Na+ .
the broad and weak bands around 700 °C can be assigned to the structural water released during the dehydroxylation/dehydration process [23].
Fig. 2. TGA (DTG) curves of Bt-Na+ .
interlayer. The second is related to the removal of water molecules from the crystal lattice, with one alumina octahedral sheet sandwiched between two silica tetrahedral sheets. Between 200 and 800 °C, CO, CO2 and water are released in addition to Cl2 [23]. The presence of carbon and sulfur is attributed to organic contamination in bentonite, sulfur is released as SO2 at temperatures above 700 °C and the presence of (Cl) is attributed to NaCl traces in the Bt-Na+ . It must be noted that the peak at 160 °C in the DTA curve corresponds to bonded water which according to the literature is associated with the Brönsted acid sites [20]. On the other hand,
3.1.3. XRD results of the Bt-Na+ The X-ray diffraction pattern of Bt-Na+ was compared to that of the natural bentonite, as illustrated by (Fig. 3). It clearly appears that the clay mineral crystallinity of Bt-Na+ was not diminished upon purification. Fig. 3 shows the XRD pattern of natural bentonite and Bt-Na+ was exhibiting the reflection peak occurred at 6.1° and 6.7°, respectively. The interlayer spacing distance of the ˚ respectively. bentonites was found to be 14.5 A˚ and 13.2 A, The decrease in the interlayer spacing of Bt-Na+ was due to cationic exchange of Ca2+ , Mg2+ and K+ cations, replaced by Na+ cations which have a smaller atomic radius. The X-ray diffraction pattern of bentonites confirms that bentonite was purified. We observed the disappearance of some characteristic reflection peak of crystalline phases of impurities especially that of quartz located at 2θ = 26.8°. Also, we observed the intensification of some reflection peak localized at 2θ = 5.7 and 28°.
3.2. Dye adsorption over Bt-Na+ In this study different parameters were examined: contact time, effect of initial pH, initial concentration of dyes, and effect of temperature.
Please cite this article as: I. Belbachir, B. Makhoukhi, Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2016.09.042
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Fig. 3. XRD patterns for bentonites before and after purification: (0 0 1) basal peak (1) Natural bentonite; (2) Bt-Na+ .
will be greater if the volume of the molecules is small [14]. Therefore, if the size of the dye molecules is larger, the saturation of the adsorption sites in the bentonite will be faster. The geometric calculations performed by Gausian software shown the following sizes for the dyes molecules: BezathrenRed (277.28 A˚ 3 ), Bezathren-Green (141.22 A˚ 3 ) and Bezathren-Blue (313.49 A˚ 3 ). The Bezathren-Blue molecule is the larger compared to other dyes. Consequently, saturation of adsorption sites in bentonite is faster. 3.2.2. Adsorption kinetics model In an attempt to express the mechanism of dyes adsorption onto the Bt-Na+ , the following kinetic model equations are used to analyze the adsorption experimental data for determination of the related kinetic parameters.
Fig. 4. Removal of Bezathren-dyes by sodic bentonites as a function of time 1: Blue dye, 2: Green dye, 3: Red dye.
Pseudo-first order model (PFO). The linear form of the pseudo-first order rate equation by Lagergren is expressed as [25]:
Ln (qe − qt ) = Ln qe − k f × t 3.2.1. Effect of contact time (kinetics study) The adsorption of dyes on Bt-Na+ was studied as a function of contact time and results are shown in Fig. 4. As seen, the adsorption of dyes increases rapidly with increasing time. The time needed for sodic bentonite to adsorb the maximum of BezathrenBlue is 15 min (47.80%, 5.334 mg/g) and 45 min to adsorb the maximum of Bezathren-Green (29.40%, 2.94 mg/g) and BezathrenRed (11.53%, 2.86 mg/g), and then tended to keep constant after this time. In most liquid phase adsorption system, the efficiency of adsorption is dependent on the pH of the system, the variation of pH leads to the variation of surface charge of the adsorbent and the degree of ionization of the dyes molecules [24]. In order to estimate the solubility of dyes, the partition-coefficient (Log P) was measured as follow: Bezathren-Red (Log P : 0.69), BezathrenGreen (6.32) and Bezathren-Blue (2.68). From these results, the Bezathren-Green has a hydrophobic character and present a less solubility in water compared to other dyes. The Bezathren-Red is the more soluble in water amongst the three dyes. The time needed for bentonite to adsorb the maximum of Bezathren-Blue is 15 min and it is 45 min to adsorb the maximum of other dyes. In our previous study we have shown that the adsorption capacity is inversely proportional to size of molecule dye. The diffusion of dye molecules in the pores and layers of bentonite
(3)
Pseudo-second order model (PSO). The linear form of the pseudosecond order rate equation is given as [26]:
t 1 t = + qt qe ks q2e
(4)
where qt (mg/g) is the amount of adsorbate adsorbed at time (t), qe (mg/g) the adsorption capacity at equilibrium, kf (min−1 ) is the rate constant of the PFO model and t (min) is the time. Ks is the pseudo-second order adsorption rate constant (g/mg/min). It was observed that the pseudo-second order model agreed with the experimental data better than the pseudo-first order model for the adsorption of dyes (Table 1). High correlation coefficients are obtained when employing the pseudo-second order model (R2 ≥ 0.9995) and the calculated equilibrium adsorption capacity is similar to the experimental data, and this indicated that the adsorption of Bezathren-dyes onto Bt-Na+ is controlled by chemical adsorption (chemisorption) involving valence forces through sharing or exchange electrons between sorbent and sorbate. In chemical adsorption, it is assumed that the adsorption capacity is proportional to the number of active sites occupied on the adsorbent surface [14]. Pseudo-first order and pseudo-second order models for adsorption onto Bt-Na+ .
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Table 1 Pseudo-first order and pseudo-second order models for adsorption onto Bt-Na+ .
Bezathren-Blue Bezathren-Green Bezathren-Red
qe (exp.)
Pseudo-first order
Pseudo-second order
5.33 mg/g 2.94 mg/g 2.86 mg/g
R2 = 0.854 qe (calc) = 3.249 mg/g K1 = 5.194 min−1 R2 = 0.527 qe (calc) = 0.675 mg/g K1 = 0.0685 min R2 = 0.802 qe (calc) = 1.542 mg/g K1 = 0.042 min
R2 = 0.999 qe (calc) = 5.385 mg/g K2 = 0.761 min R2 = 0.999 qe (calc) = 3.039 mg/g K2 = 0.225 min R2 = 0.999 qe (calc) = 2.942 mg/g K2 = 0.108 min
Fig. 5. Kinetic plots for the adsorption of dyes onto Na-Bt, 1: Blue, 2: Green, 3: Red.
Fig. 6. Removal of Dyes solution by sodic bentonite as a function of initial pH 1: Blue, 2: Green, 3: Red.
3.2.3. Effect of pH The variations of pH medium were one of the most important factors affecting the concentration and dyes recovery procedure, which was related to the formation of soluble dyes complexes and subsequently their stabilities in aqueous solutions [27] (Fig. 5). The adsorptions of dyes by sodic bentonite were studied at different pH value ranged from 1.1 to 6.73 and the results are show in Fig. 6, it is seen that the adsorption decreases with increasing of initial pH. It reaches a maximum value around pH 1.4 for Bezathren-Red (100%), pH 1.5 for Bezathren-Green (98.7%) and pH 2.35 for Bezathren-Blue (100%). 3.2.4. Effect of initial dye concentration In order to demonstrate the effect of the initial concentration on the adsorption, experiments were carried out at different initial dyes concentrations ranging from 20 to 500 mg/L (Fig. 7). Fig. 7 shows that by increasing the initial concentration in solution, the amount of adsorbed dyes gradually increases (Fig. 8). The Bezathren-Blue uptake increases from 3.554 to 35.08 mg/g,
Fig. 7. Removal of dyes by sodic bentonite as a function of concentration 1: Blue, 2: Green, 3: Red.
the Bezathren-Green uptake increases from 2.16 to 32.88 mg/g and the Bezathren-Red uptake increases from 2.86 to 48.52 mg/g, with increasing the initial concentration from 40 to 500 ppm. The increase in initial dye concentration enhances the interaction force, that it is necessary to overcome the resistances to the mass transfer between adsorbate and the adsorbent [28]. However, as the initial concentration of dyes increased, most of the available sorption sites became occupied, leading to a decrease in the removal efficiency, this is why this increase starts to ease off after 300 ppm of initial dyes concentrations. 3.2.5. Isotherm adsorption The Langmuir and Freundlich isotherms are the equations most frequently used to represent the data on adsorption from solution. Langmuir and Freundlich isotherms are represented by the following equations [29,30]:
Ce Ce 1 = + qe qm qm KL
(5)
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Fig. 8. Isotherms plots for the adsorption of dyes onto Na-Bt 1: Blue, 2: Green, 3: Red. Table 2 Isotherm parameters for dyes adsorption onto Bt-Na+ .
Bezathren-Blue Bezathren-Green Bezathren-Red
Ln qe = Ln KF + n Ln Ce
qm (exp.), mg/g
Langmuir isotherm
Freundlich isotherm
5.334 2.94 2.86
R2 = 0.785 qm (calc.) = 83.33 mg/g KL = 0.0025 (L/mg) R2 = 0.620 qm (calc.) = 100 mg/g KL = 0.0 0 08 (L/mg) R2 = 0.518 qm (calc.) = 66.66 mg/g KL = 0.0012 (L/mg)
R2 = 0974 KF = 0.330 n = 1.196 R2 = 0.997 KF = 0.050 n = 0.884 R2 = 0.988 KF = 0.025 n = 0.776
(6)
where Ce is the equilibrium concentration of dye (mg/L), qe is the amount of dye adsorbed on the bentonite (mg/g), KL is the Langmuir adsorption constant (L/mg), qm is the maximum amount of dye that can be adsorbed by the sodic bentonite, KF is the Freundlich adsorption constant, and n is a constant that indicates the capacity and intensity of the adsorption. The experimental data were modeled according to Langumir and Freundlich isotherms, and the evaluated constants were given in Table 2. It was clear that Freundlich isotherm described better with a higher correlation coefficient (R2 ≥ 0.974) in comparison with that of Langmuir (R2 ≤ 0.785), this results confirm the existence of interactions between adsorbed molecules. Isotherm parameters for dyes adsorption onto Bt-Na+ 3.2.6. Thermodynamic parameters The effect of temperature on the adsorption of dyes by sodic bentonite at initial pH and concentration of 50 ppm was studied. The thermodynamic parameters, namely the enthalpy (H) and entropy (S) associated with the adsorption process could be obtained from the slope and intercept of the Vant Hoff plot. ln Kc versus 1/T using the following equation [31]:
Ln Kd =
S R
−
H RT
(7)
where Kd is the distribution coefficient, T is the temperature in Kelvin, and R is the gas constant (8.314 J/mol K). Distribution coefficient (Kd , mL/g) is also computed using the following equation [31]:
Kd (mL/g ) =
Ci − Ce V × Ce m
(8)
where Ci and Ce are the initial and equilibrium concentrations of dyes (mg/L) in solution. m is the weight of the adsorbent (g), V is the volume of the aqueous phase (mL). Fig. 9 shows adsorbed percent (%) of dyes onto Bt-Na+ as a function of the temperature. Thermodynamic data for adsorption of dyes onto Bt-Na+
Fig. 9. Removal of Bezathren-dyes by sodic bentonite as a function of temperature 1: Blue, 2: Green, 3: Red.
Table 3 Thermodynamic data for adsorption of dyes onto Bt-Na+ .
Bezathren-Blue Bezathren-Green Bezathren-Red
H (KJ/mol)
S (J/mol K)
R2
−09,04 −08,96 −25,88
12.36 06.80 −52,75
0.959 0.950 0.985
The thermodynamic parameters of the adsorption of dyes on Bt-Na+ at the examined temperatures are presented in Fig. 10 and Table 3. It can be seen that the yield adsorption of dyes decreases with increasing temperature, this behavior indicates the exothermic nature of adsorption for all three dyestuffs onto Bt-Na+ , as supported by the negatives values of H. These results are contrary to the data given in the literature. This can be due to the energy released after the adsorption being higher than that needed to absorb the solvent molecules from the pores of bentonite clay [32]. Also, the positive values of S for both
Please cite this article as: I. Belbachir, B. Makhoukhi, Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2016.09.042
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I. Belbachir, B. Makhoukhi / Journal of the Taiwan Institute of Chemical Engineers 000 (2017) 1–7
Fig. 10. Plot Van’t Hoff plot for the adsorption of Bezathren-dyes onto sodic bentonite 1: Blue, 2: Green, 3: Red.
Bezathren-Blue and Bezathren-Green indicate that the randomness at the solid–liquid interface during the adsorption process increases, in contrast, in the case of Bezathren-Red the negative standard entropy change (S) suggests that the randomness in solid/solution interface decreased during the adsorption [32]. 4. Conclusion In this study, the adsorptions of Bezathren-dyes onto sodic bentonite were studied by batch tests conducted under various experimental conditions such as contact time, pH, initial dyes concentrations and temperature. The kinetic study shows that the process can be described by a pseudo-second order model and the adsorption of Bezathren-Blue achieves equilibrium quickly (15 min) compared to other dyes (45 min). Kinetics adsorption of Bezathren-dyes onto Bt-Na+ is controlled by chemical adsorption. The adsorption yields obtained onto bentonite are 100% (at pH 1.4 for Bezathren-Red and at pH 2.35 for Bezathren-Blue), it is equal to 98.7% (at pH 1.5 for Bezathren-Green). The equilibrium batch experiment data demonstrate that Bt-Na+ is effective adsorbent for the removal and recovery of Bezathren-dyes from aqueous solutions, with the maximum sorption capacity of 35.08 mg/g, 32.88 mg/g and 48.52 mg/g for Bezathren-Blue, Bezathren-Green and Bezathren-Red respectively, under the given experimental conditions. The results show that sodic bentonite could be employed as low-cost material for the removal of Bezathren dyes from effluents. References [1] Chinoune K, Bentaleb K, Bouberka Z, Nadim A, Maschke U. Adsorption of reactive dyes from aqueous solution by dirty bentonite. Appl Clay Sci 2016;123:64–75. [2] Ismadji S, Soetaredjo FE, Ayucitra A. Clay materials for environmental remediation. Heidelberg, New York: E-publiching Inc: Cham: Springer; 2015. p. 5–31. [3] Wan D, Li W, Wang G, Chen K, Lu L, Hu Q. Adsorption and heterogeneous degradation of rhodamine B on the surface of magnetic bentonite material. Appl Surf Sci 2015;349:988–96.
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Please cite this article as: I. Belbachir, B. Makhoukhi, Adsorption of Bezathren dyes onto sodic bentonite from aqueous solutions, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2016.09.042