Macauba palm (Acrocomia aculeata) cake from biodiesel processing: An efficient and low cost substrate for the adsorption of dyes

Macauba palm (Acrocomia aculeata) cake from biodiesel processing: An efficient and low cost substrate for the adsorption of dyes

Chemical Engineering Journal 183 (2012) 152–161 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: ww...

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Chemical Engineering Journal 183 (2012) 152–161

Contents lists available at SciVerse ScienceDirect

Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej

Macauba palm (Acrocomia aculeata) cake from biodiesel processing: An efficient and low cost substrate for the adsorption of dyes Sara S. Vieira, Zuy M. Magriotis ∗ , Nadiene A.V. Santos, Maria das Grac¸as Cardoso, Adelir A. Saczk Departamento de Química, Universidade Federal de Lavras, 37.200-000, Lavras, MG, Brazil

a r t i c l e

i n f o

Article history: Received 1 September 2011 Received in revised form 9 December 2011 Accepted 12 December 2011 Keywords: Macauba palm cake Adsorption Methylene Blue Congo Red

a b s t r a c t The potential of natural and heat-treated Macauba palm cake as adsorbent for the removal of Methylene Blue (MB) and Congo Red (CR) from solution has been investigated. Equilibrium adsorption was attained in <7 h and the process was favored at pH 5.0 for MB and pH 6.5 for CR with an adsorbent (g):adsorbate (mL) ratio of 1:200 and an initial concentration of adsorbate of 25 mg L−1 . The maximum adsorption capacities of the natural and heat-treated materials were, respectively, 25.80 and 32.30 mg g−1 for MB, and 32.00 and 20.30 mg g−1 for CR. The isotherm model proposed by Sips represented most adequately the adsorption of MB and CR. The adsorptions of the dyes were best described in terms of a pseudo secondorder reaction. Thermodynamic parameters such as Ho , So and Go were calculated. The adsorption process was found to be endothermic and spontaneous. Macauba palm cake is adequate for the removal of waste dye from industrial effluents by virtue of its abundance, low cost and efficiency of adsorption. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Industrial dyeing processes are believed to be responsible for the release of around 100,000 tons of dye per annum, and a significant proportion of this effluent ends up contaminating water bodies and watercourses. Some of this industrial waste is highly toxic and carcinogenic to humans and animals, and can also inhibit photosynthesis in plants. Alongside these harmful consequences, the pollution caused by waste dye is visually displeasing [1]. Since, by their very nature, synthetic dyes are chemically stable, traditional methods have often proven to be ineffective in removing these species from the environment. A number of different technologies have been applied to the treatment of dye effluents, and these include coagulation, flocculation, advanced oxidation processes and adsorption. Such methods need to be economically viable and environmentally friendly while, at the same time, the final concentrations of contaminants in the treated effluents must comply with the standards imposed by governmental regulatory agencies. Adsorption technology is often employed for the removal of organic pollutants from wastewaters, and activated carbon (AC) is the material most commonly applied for this purpose. However, AC is non-selective and relatively expensive [2], and for this

∗ Corresponding author. Tel.: +55 35 38291889; fax: +55 35 38291812. E-mail addresses: saraufl[email protected] (S.S. Vieira), [email protected]fla.br (Z.M. Magriotis), [email protected] (N.A.V. Santos), [email protected]fla.br (M.d.G. Cardoso), [email protected]fla.br (A.A. Saczk). 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.12.047

reason a number of non-conventional materials have recently been assessed, including clays [3–5] and residues from agro-industrial processes [6–10]. Agricultural lignocellulosic residues offer many advantages over AC since they originate from abundant, cheap and renewable sources. In this context, a number of studies have demonstrated that the pressed cake from oil-rich species can be employed for the adsorption of lead (olive oil cake [11]), copper (mustard oil cake [12]), chromium and cadmium (Jatropha oil cake [13,14]), as well as for the removal of Methylene Blue (oil palm fiber [15]). In order to satisfy the ever-increasing demand for cleaner and renewable sources of energy, the production of biodiesel by transesterification of vegetable oils is escalating at a remarkable rate. The process typically involves pressing raw plant material in order to obtain the crude oil, and this generates considerable quantities of residual cake composed mainly of cellulose, hemicelluloses and lignin. It is estimated that for each ton of seed, about half a ton of cake cellulose is generated. The production of biodiesel increases every year, with this increment in the production, the volume of waste generated can become a major environmental issue and the disposal of this byproduct (agro-industrial residue) should be studied. So, one of the key problems to be solved by the biodiesel industry concerns the adequate disposal of this residue. If it were possible to use this type of waste as an alternative adsorbent material for the removal of organic pollutants from industrial effluent, the cost of clean-up treatment would be significantly reduced. In this context, the aim of the present study was to investigate the potential application of Macauba palm [Acrocomia aculeata (Jacq.) Lodd. ex Mart.; Arecaceae] cake as an adsorbent for

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Table 1 Properties and characteristics of Methylene Blue and Congo Red. Generic name

Methylene Blue

Congo Red

Chemical name (IUPAC)

3.7-bis(dimethylamino)-phenothiazin-5-ium chloride

CAS number C.I. Chemical formula Molecular weight (g mol−1 ) max (nm)

61-73-4 52015 C16 H18 ClN3 S 319.85 668

Sodium 3.3 -(1E.1 E)-biphenyl-4.4 -diylbis(diazene-2.1diyl)bis(4-aminonaphthalene-1-sulfonate) 573-58-0 22120 C32 H22 N6 Na2 O6 S2 696.66 500

Chemical structure

the removal of the synthetic dyes Methylene Blue (MB) and Congo Red (CR) from aqueous solution. The equilibrium biosorption data were evaluated by Langmuir, Freundlich and Sips isotherm models. The pseudo-first order, pseudo-second order and intraparticle diffusion models were used for determining of the adsorption kinetics. Thermodynamic parameters such as Ho , So and Go were also determined.

the required pH (in the range 2–11) and sedimented/conditioned for 2 h at 22 ◦ C in 250 mL conical flasks containing sodium nitrate solution (0.002 mol L−1 ) as supporting electrolyte. Potentials were measured using a Zeta Meter (Staunton, VA, USA) System 3.0+ ZM3-D-G instrument: the applied tension varied between 75 and 200 mV, and zeta potentials were expressed as the mean values of 20 repetitions.

2. Materials and methods 2.3. Adsorption experiments 2.1. Preparation of dye solutions and adsorbent The dilute solutions of dyes employed in the adsorption studies were prepared from stock solutions containing 5000 mg L−1 of either MB or CR (Table 1). The natural pH values of the dye solutions were approximately 5.0 and 6.5, respectively, and these were adjusted (where necessary) by the addition of either 0.02 mol L−1 potassium hydroxide or 0.02 mol L−1 hydrochloric acid. Macauba palm cake was dried for 24 h in an air oven at 40 ◦ C, reduced to a powder and sieved (40–60 mesh) to yield the experimental material Macauba cake in natura (MCN). A portion of MCN (50 g) was heated at 130 ◦ C for 24 h, cooked in type II water (300 mL) to remove soluble phenolic compounds, washed with type II water, and finally dried for 3 h in an air oven at 90 ◦ C [16,17] to yield the experimental material Macauba cake thermally treated (MCT). 2.2. Characterization of adsorbents An Elementar Analysensysteme (Hanau, Germany) vario MICRO cubeTM was employed to determine the percentages of C, H, N, S and O (by difference) in MCN. Thermogravimetric analyses were performed using a Shimadzu (Kyoto, Japan) model DTG-60AH thermomechanical analyzer and were carried out under a nitrogen atmosphere in the temperature range of 25–900 ◦ C at a heating rate of 10 ◦ C min−1 . The Fourier transform infrared spectra (FTIR) of adsorbents (in the form of KBr pellets) were measured using a Digilab Excalibur (Randolph, MA, USA) FTS 3000 series spectrometer in the range 400–4000 cm−1 at a resolution of 4 cm−1 . Microscopic observations and electron micrographs were made using a Nano Technology Systems (Carl Zeiss, Oberkochen, Germany) model Evo® 40 VP SEM. For the purpose of determining zeta potentials, adsorbents were finely ground (particle size < 37 ␮m), the suspensions adjusted to

In order to assess the efficacy of dye adsorption by MCN and MCT, batch experiments were performed in which different amounts of adsorbent samples were added to 10 mL aliquots of dye solution and the resulting mixtures maintained at room temperature (25 ± 1 ◦ C) on an orbital shaker (100 rpm). The supernatants were then separated by centrifugation (5 min at 1540 × g) and diluted as necessary such that the remaining concentrations of dye could be determined at 665 nm (MB) or at 500 nm (CR) using a Femto (São Paulo, Brazil) model 800 XI UV–vis spectrometer. UV scans were carried out for samples in which pH was changed, to investigate possible changes in the maximum absorption wavelength. No significant changes in the maximum wavelength were observed. The equilibrium time for the adsorption of dye by MCN and MCT was initially determined by a 24 h kinetic study with the following conditions: pH value of dye solution, 5.0 for MB and 6.5 for CR; initial dye concentration, 50 mg L−1 ; adsorbent (g):adsorbate (mL) ratio, 1:200 (corresponding to 0.05 g of adsorbent). Once the equilibrium time had been established, the effects of pH of dye solution (MB at pH 2.0, 5.0 and 10.0; CR at pH 6.5 and 10.0), initial concentration of dye (25, 50 and 100 mg L−1 ), and adsorbent (g):adsorbate (mL) ratio (1:200 and 1:1000 corresponding to 0.05 and 0.01 g of adsorbent respectively) on dye adsorption were determined. The percentage removal of dye (%R) was calculated from:

%R =

Co − Ct × 100 Co

(1)

where Co is the initial concentration of dye (mg L−1 ) and Ct is the concentration of dye (mg L−1 ) at time t. All assays were carried out in duplicate to ensure reproducibility of the results.

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0

50

MCT

40 30

60

0 -10

80

-20 -30

100 0

200

400

600

800

Transmittance (a.u.)

10

1528

3610

20

40

DTG (uV)

Mass loss (%)

20

3760

2853

1644

3430 2928

1041

MCN 1530

-40 1000

2858

3400

1646

1041

2928

Temperature (°C) 4000

Fig. 1. Direct (TG; —) and differential (DTG; · · ·) thermogravimetric curves.

3500

3000

2500

2000

1500

1000

500

-1

Wavenumber (cm ) Fig. 2. FTIR spectra of the Macauba palm cake in natura and of the thermally treated material.

2.4. Adsorption isotherms Adsorption isotherms for MCN, MCT and commercial AC (as control) were determined in the concentration ranges 10–1000 mg L−1 for MB and 10–3000 mg L−1 for CR, with the remaining parameters maintained at their optimized values. The effect of temperature on adsorption of dyes was studied at 25 ◦ C, 35 ◦ C and 45 ◦ C. All experiments were carried out in triplicate. Quantitative evaluation of the models was performed by comparison of the correlation coefficients (R). The amount of dye adsorbed per unit mass of adsorbent at equilibrium (Qe ; mg g−1 ) was determined from: Qe =

(Co − Ce )V m

(2)

where Co is the initial concentration of dye (mg L−1 ), Ce is the concentration of dye (mg L−1 ) at equilibrium, m is the mass of adsorbent (g), and V is the volume of solution (L). 3. Results and discussion 3.1. Characteristics of the absorbents The elemental composition of MCN was C 50.93%, O 40.68%, H 6.59%, N 1.60% and S 0.197%, indicating that the adsorbent material was rich in oxygen but contained only low levels of sulfur. The direct (TG) and differential (DTG) thermogravimetric curves

Fig. 3. Scanning electron microscopy for Macauba palm cake in natura (A and A ) and for the thermally treated material (B and B ).

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A

155

100

Removal of MB (%)

80

60

40

20

0 0

Fig. 4. Zeta potential of Macauba palm cake in natura (– – –) and of the thermally treated material (· · ·).

3.2. Influence of physicochemical parameters on adsorption The rates of adsorption of MB and CR as a function of time of contact with the absorbent are shown in Fig. 5A and B, respectively.

10

15

20

25

15

20

25

Time (h)

B

100

80

Removal of CR (%)

for MCN (Fig. 1) show that mass loss occurred at three different stages. The initial loss of mass at approximately 100 ◦ C was associated with the elimination of water and small volatile molecules, while the second reduction occurred between 300 and 350 ◦ C and was caused by the thermal degradation of cellulose and hemicelluloses. The final mass loss at approximately 500 ◦ C may be attributed to the degradation of lignin, which has a much higher thermal stability than either cellulose or hemicellulose polymers. The greatest rate of mass loss occurred at this temperature. The FTIR spectrum of MCN (Fig. 2) showed a broad peak at 3400 cm−1 related to hydroxyl groups. Also in Fig. 2, the appearance of vibrations between 3760–3610 cm−1 related to the presence of free and intramolecularly bonded OH is observed. For both materials, an absorption about 2928 cm−1 corresponding to symmetric and asymmetric stretching vibrations of CH2 groups is detected. A high intensity peak in 2858 cm−1 was observed for MCN. The peaks at 1646 (MCN) and 1644 (MCT) cm−1 correspond to the stretching vibration of the C C bonds and the small peaks found at 1530 cm−1 (MCM) and 1528 cm−1 (MCT) confirm the presence of aromatic C C bonds. The peak at 1041 cm−1 can indicate the presence of C C groups. The small peaks within the band 1300–1000 cm−1 were attributed to C O bonds from phenolic groups, while absorptions at 1041 cm−1 were associated with O CH2 groups [18]. These spectral details indicate that Macauba palm cake contains functional entities, such as phenolic OH groups, that can interact with cationic groups of MB [13,19]. Scanning electron microscopy of the Macauba palm cake in natura and thermally treated are shown in Fig. 3. These micrographs show the fibrous structure of the two biosorbents employed in this work. The zeta potential is a measure of the superficial charge of the adsorbent at a specific pH and indicates which type of ion would be adsorbed under such conditions. As shown in Fig. 4, MCN and MCT presented negative surface charges throughout the pH range studied (2.0–11.0) signifying that both adsorbents would exhibit a great affinity for cations. The negative charge present on the surface of lignocellulosic materials is associated with acidic entities such as carboxyl and phenolic OH groups. Interestingly, however, at any particular pH the charge on the surface of MCT was less negative than that of MCN suggesting that thermal treatment degraded a small proportion of these acidic groups.

5

60

40

20

0 0

5

10

Time (h) Fig. 5. The kinetics of adsorption (determined over a 24 h period) of Methylene Blue (MB, A) and Congo Red (CR, B) onto Macauba palm cake in natura (MCN, ) and onto the thermally treated material (MCT, ).

Initially, adsorption was rapid because of the ready availability of binding sites on the surface of the material, but after a relatively short period the rate of adsorption decreased and finally reached equilibrium as result of saturation of MCN and MCT surface sites. Equilibrium adsorption by MCN and MCT was achieved in less than 5 h for both MB and CR, hence adsorbent and adsorbate were left in contact for 7 h in subsequent experiments in order to ensure that equilibrium was fully attained. The pH of the adsorbate solution affects the adsorption capacity of the adsorbent through modification of the state of ionization of the binding groups, either increasing or decreasing competition between the protonated species and adsorbate molecules for the active sites. The optimal pH value for the adsorption process depends, therefore, on the chemical natures of the adsorbate and adsorbent. Hence, in order to maximize adsorption, preliminary tests were performed to determine the most favorable pH for the construction of isotherms. The effects of pH on the rates of adsorption of MB by MCN and MCT (Fig. 6A and B, respectively) were determined with an initial dye concentration of 25 mg L−1 and an adsorbent (g):adsorbate (mL) ratio of 1:200. In both cases, adsorption was improved when the pH of the dye solution was increased from 2 to 5 or 10. MCT

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was more efficient in the removal of MB (≈95% of dye removed at equilibrium) compared with MCN (≈85% removal). This superior performance may be associated with an increase in the number of active sites on the surface of the adsorbent since thermal treatment eliminates the soluble organic compounds present in the raw material that are responsible for reducing the adsorption capacity of lignocellulose [20]. This hypothesis is supported by the changes observed in the infrared spectra (Fig. 2). At pH 2.0, the low efficiency of removal of MB by MCN and MCT (≈50 and 60%, respectively) may be explained by the decrease in the negative charge under these conditions, as indicated by the zeta potential. In view of the above findings, the remaining isotherms for MB were measured at pH 5.0, since this is the natural pH of the dye solution. The adsorption of CR was favored at pH 6.5 in comparison with pH 10 but, in contrast to the results obtained with MB, the efficiency of the adsorbent MCN (54% removed; Fig. 6C) was higher than that of MCT (34% removed; Fig. 6D). The adsorption of an anionic dye generally decreases with an increase in pH, and this phenomenon is associated not only with the negative charge on the surface of the adsorbent but also with excess OH− ions in the solution that compete for the adsorption sites [21]. The adsorption of CR was not investigated at pH 2.0, however, because at this pH the color of the solution changed and the wavelength of maximum absorption was altered. In view of the above findings, the remaining isotherms for CR were measured at pH 6.5. With the initial MB concentration set at 25 mg L−1 , increasing the adsorbent (g):adsorbate (mL) ratio from 1:1000 (0.01 g of adsorbent) to 1:200 (0.05 g of adsorbent) produced an enhancement in the efficiency of dye adsorption by MCN from 57 to 78% (Fig. 7A), and by MCT from 80 to 92% (Fig. 7B). In the case of CR, the removal efficiency of MCN increased from 45 to 55% (Fig. 7C), while that of MCT increased from 17 to 34% (Fig. 7D). Clearly, increasing the relative amount of adsorbent employed enhanced the number of active sites present, thus improving removal efficiency. In view of these findings, the remaining isotherms were measured at an adsorbent (g):adsorbate (mL) ratio of 1:200. When the initial concentration of MB was increased from 25 to 50 mg L−1 , the removal efficiency of MCN diminished from 76 to 55% (Fig. 8A) and that of MCT decreased from 92 to 83% (Fig. 8B). A further increase in the initial concentration of MB to 100 mg L−1 gave rise to a reduction in the removal efficiency of MCN to 49%, and of MCT to 63%. These effects were likely caused by the rapid saturation of the active adsorbent sites. In the case of CR, the removal efficiency of MCN decreased when the initial concentration of dye was increased (Fig. 8C), whereas that of MCT was not significantly altered (Fig. 8D). The removal efficiencies of the two adsorbents were compared under optimized conditions, i.e. an initial dye concentration of 25 mg L−1 , an adsorbent (g):adsorbate (mL) ratio of 1:200, and pH 5.0 for MB or pH 6.5 for CR. The removal of the cationic dye MB was more efficient in the presence of MCT than in the presence of MCN (Fig. 9A), while the opposite was the case for CR (Fig. 9B).

Qe = KF Ce1/nF Qe =

(4)

Qm KS Ce1/nS 1 + KS Ce1/nS

(5)

where Qe is the amount of dye adsorbed (mg g−1 ) at equilibrium, Qm is the maximum adsorption capacity of a monolayer (mg g−1 ), KL is the Langmuir constant (L mg−1 ), Ce is the concentration of dye at equilibrium (mg L−1 ), KF (mg1−(1/nF ) L1/nF g−1 ) is the Freundlich constant relating to the relative capacity of adsorption (mg g−1 ), nF is a constant relating to the intensity of adsorption, KS is the 1/nS Sips adsorption constant (L mg−1 ) , and 1/nS is the Sips exponent (non-dimensional). The Langmuir isotherm assumes that adsorption occurs on a homogeneous monolayer surface containing sites with uniform energy, whereas Freundlich isotherm presupposes that adsorption occurs on a heterogeneous surface containing exponentially distributed sites. The Sips isotherm combines the two preceding isotherms, following the Langmuir principle at high concentrations of adsorbate and the Freundlich principle at low concentrations of adsorbate. Table 2 demonstrates that the Langmuir [22] and Sips [24] equations provided the best models for the adsorption of MB and CR onto MCN and MCT. The applicability of these two isotherms to the dyes adsorption shows that both monolayer adsorption and heterogeneous energetic distribution of active sites on the surface of the adsorbent are possible. According to the classification of the IUPAC, these isotherms are type I, i.e. they characterize adsorption onto monolayers and indicate a great affinity between adsorbate and adsorbent. The maximum adsorption capacity (Qm ) of MCT with respect to MB was greater than that of MCN (32.30 and 25.80 mg g−1 , respectively), whereas the Qm of MCN with respect to CR was larger than that of MCT (32.00 and 20.30 mg g−1 , respectively; Table 2). The Qm values for Macauba palm cake were, however, well within the range published for other plant residues (Table 3). Although the Qm value of AC was somewhat greater than those of MCN and MCT (Table 2), it is important to emphasize that the Macauba palm cake preparations were either untreated or subjected to an inexpensive heating process. Therefore, the comparative disadvantage of MCN and MCT in relation to AC does not reduce the value of Macauba palm cake as an alternative cleanup material for contaminated wastewaters since the material is plentiful and cheap in comparison with AC. 3.4. Kinetic characteristics of the adsorbents The kinetic parameters of adsorption of MB and CR by MCN and MCT were determined under optimized conditions. Data were analyzed using pseudo-first order [35], pseudo-second order [36] and intraparticle diffusion [37] models represented mathematically by the respective non-linear equations: Qt = Qe (1 − e−k1 t )

3.3. Adsorption isotherms of the adsorbents

Qt =

The adsorption isotherms of MCN and MCT for the removal of MB and CR under optimized conditions are shown in Fig. 10A and B, respectively, together with the isotherm obtained using commercial AC. The data obtained were fitted to the isotherm models of Langmuir [22], Freundlich [23] and the combined model of Sips [24] represented mathematically by the respective non-linear equations: Qe =

Qm KL Ce 1 + KL Ce

(3)

(6)

Qe2 k2 t 1 + Qe k2 t

(7)

Qt = kdif t 1/2 + C

(8) (mg g−1 )

where Qt is the amount of dye adsorbed at time t (h), Qe is the amount of dye adsorbed (mg g−1 ) at equilibrium, k1 (h−1 ) and k2 (g mg−1 h−1 ) are, respectively, the pseudo first-order and second-order rate constants, kdif (g mg−1 h−1/2 ) is the intraparticle diffusion constant, and C is a constant relating to layer thickness. The results relating to kinetic behavior (Table 4) reveal that the adsorption of MB and CR can best be described as a pseudo secondorder reaction controlled by the interaction between the molecules

S.S. Vieira et al. / Chemical Engineering Journal 183 (2012) 152–161

A

100

100

B

80

Removal of MB (%)

Removal of MB (%)

80 60 40 pH 5 pH 10 pH 2

20

60 40 pH 5 pH 10 pH 2

20 0

0 0

1

2

3

4

5

6

7

0

8

1

2

3

Time (h)

4

5

6

7

8

Time (h)

D

100

100 80

80

Removal of CR (%)

Removal of CR (%)

C

157

60 40 20

pH 6,5 pH 10

0 0

1

2

3

4

5

6

7

60 40 20

pH 6,5 pH 10

0

8

0

1

2

3

Time (h)

4

5

6

7

8

Time (h)

Fig. 6. Influence of pH value on the adsorption of Methylene Blue (MB) and Congo Red (CR) by Macauba palm cake in natura (MCN; A and C) and by the thermally treated material (MCT; B and D).

A

B

100

80

Removal of MB (%)

80

Removal of MB (%)

100

60 40 20

1:200 1:1000

0

60 40 20

1:200 1:1000

0 0

1

2

3

4

5

6

7

8

0

1

2

3

100

Removal of CR (%)

80 60 40 20

D

100

Removal of CR (%)

C

4

5

6

0

80 60 40

1:200 1:1000

0

1

2

3

4

Time (h)

8

20

1:200 1:1000

0

7

Time (h)

Time (h)

5

6

7

8

0

1

2

3

4

5

6

7

8

Time (h)

Fig. 7. Influence of adsorbent:adsorbate ratio on the adsorption of Methylene Blue (MB) and Congo Red (CR) by Macauba palm cake in natura (MCN; A and C) and by the thermally treated material (MCT; B and D).

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Fig. 8. Influence of initial concentration of adsorbate on the adsorption of Methylene Blue (MB) and Congo Red (CR) by Macauba palm cake in natura (MCN; A and C) and by the thermally treated material (MCT; B and D).

A

B

100

80

Removal of CR (%)

80

Removal of MB (%)

100

60 40 20

MCT MCN

0

60

40

20

MCT MCN

0 0

1

2

3

4

5

6

7

8

0

1

Time (h) Fig. 9. Optimized conditions for the adsorption of Methylene Blue (MB, A; pH 5, 1:200, 25 mg L in natura (MCN) and onto the thermally treated material (MCT).

4

5

6

7

8

B 100

80

80

) and Congo Red (CR, B; pH 6.5; 1:200; 25 mg L−1 ) onto Macauba palm cake

adsorbent

)

)

A100

40 CA MCT MCN

20

Qe(mgadsorbateg

-1

60

-1

adsorbent

3

Time (h) −1

Qe(mgadsorbateg

2

60 40 20

CA MCT MCN

0

0 0

200 400 600 800 1000 1200 1400 1600 -1

Ce(mgL )

0

500

1000 1500 2000 2500 3000 3500 -1

Ce(mgL )

Fig. 10. Adsorption isotherms at optimized conditions of MB (A) and CR (B) onto MCN, MCT and activated carbon (AC).

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Table 2 Adsorption parameters for the dyes Methylene Blue and Congo Red adsorbed onto Macauba palm cake in natura (MCN), onto the thermally treated material (MCT) and onto activated carbon (AC) fitted according to three different isotherm models. Isotherms

Methylene Blue

−1

Qm Exp. (mg g

)

Langmuir Qm (mg g−1 ) KL (L mg−1 ) R Freundlich nF KF (mg1−(1/nF ) L1/nF g−1 ) R Sips Qm (mg g−1 ) 1/nS Ks (L mg−1 ) nS R

Congo Red

MCN

MCT

25.80

32.30

27.75 0.023 0.9898

33.06 0.099 0.9881

3.39 3.99 0.9908

4.83 9.07 0.9586

39.65 0.064 1.87 0.9957

34.93 0.176 1.4 0.9922

AC

MCN

MCT

AC

79.85

32.00

20.30

68.34

92.40 9.95 × 10−3 0.9923

34.87 0.0168 0.9558

24.45 0.0017 0.9263

90.13 0.0013 0.9775

5.05 7.90 0.8916

2.73 1.13 0.9364

2.107 1.64 0.9657

33.07 0.0021 0.656 0.9602

56.44 0.0120 2.06 0.9375

2.44 6.09 0.9977 217.9 2.10 × 10−2 1.89 0.9983

85.25 7.3 × 10−4 0.9205 0.9778

Qm , maximum adsorption capacity of a monolayer; KL , Langmuir constant; nF , intensity of adsorption constant; KF , Freundlich relating to the relative capacity of adsorption; KS , Sips adsorption constant; ns , Sips exponent; R, correlation coefficient. Table 3 A comparison of published maximum adsorption capacities of various plant materials and those established for Macauba palm cake in the present study. Adsorbent

Dye

Maximum adsorption capacity (Qm ) mg g−1

Reference

Brazilian-pine fruit shell NaOH-modified rejected tea Pyracantha coccinea berries Coffee husks Macauba palm cake Desert plant (Salsola vermiculata) Wheat shells N.O-carboximetil-quitosana Jute stick powder Cattail root Macauba palm cake Waste orange peel Cashew nut shell

MB MB MB

252 (in natura) 529 (carbonized) 242.1 127.5 90.1 27.75 (in natura) 33.06 (thermally treated) 23 (in natura) 53 (pyrolysed) 16.3 330.6 35.7 34.6 34.9 (in natura) 24.75 (thermally treated) 22.44 5.14

[25] [9] [26] [27] Present study [28] [29] [30] [31] [32] Present study [33] [34]

MB MB MB CR CR CR CR CR CR

of dye and the functional groups distributed on the surface of MCN and MCT. 3.5. Thermodynamic studies The determination of thermodynamic parameters, namely enthalpy of adsorption (Ho ), Gibb’s free energy of adsorption (Go ) and entropy of adsorption (So ), is important because they Table 4 Kinetic parameters for the adsorption of Methylene Blue and Congo Red onto Macauba palm cake in natura (MCN) and onto the thermally treated material (MCT). Parameter

denote features on the final state of the system. In addition, the calculation of these parameters allows us to know if the process is favorable or not under the thermodynamic point of view, the spontaneity of the system and if the adsorption process occurs with absorption or release of energy. The change in standard Gibb’s free energy (Go ), enthalpy (Ho ) and entropy (So ) of adsorption were calculated using the following equations and the values are given in Table 5. Go = −RT ln KL ln KL = −

S o H o + RT R

(9) (10)

Methylene Blue

Congo Red

MCN

MCT

MCN

MCT

Pseudo first-order reaction 3.81 Qe (mg g−1 ) 4.08 k1 (h−1 ) 0.9945 R

4.54 3.35 0.9711

3.23 1.28 0.9808

1.74 0.95 0.9370

Pseudo second-order reaction 3.90 Qe (mg g−1 ) 3.35 k2 (g mg−1 h−1 ) 0.9990 R

4.77 1.35 0.9889

3.60 5.05 0.9874

2.00 0.63 0.9644

where R is the ideal gas constant (8.314 J mol−1 K−1 ), T is the temperature (K), KL is the Langmuir constant (L mol−1 ). The negative values of Go for both dyes confirm the spontaneity of MB and CR adsorption onto MCN and MCT. The positive values found for Ho indicate the endothermic nature of the adsorption process. The positive values of So indicate increased randomness at the solid/solution interface during the MB and CR adsorption process and good affinity of biosorbents towards MB and CR dyes [38].

Intraparticle diffusion kdif (g mg−1 h−0.5 ) R

0.32 0.9429

1.15 0.9503

0.67 0.9823

3.6. Specific surface area of the adsorbents

0.20 0.8758

Qe , the amount of dye adsorbed at equilibrium; k1 , pseudo first-order rate constant; k2 , pseudo second-order rate constant; kdif , intraparticle diffusion constant; R, correlation coefficient.

Calculation of the specific surface area of adsorption using MB as probe molecule has been applied to AC and to clay materials [39].

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Table 5 Thermodynamic parameters for the adsorption of MB and RC on MCN and MCT. Biosorbent

Dye

Temp. (K)

Qm (mg g−1 )

KL (L mg−1 )

Go (kJ mol−1 )

Ho (kJ mol−1 )

So (J mol−1 )

MCN

AM

298 308 318

27.87 24.89 33.94

0.0175 0.0290 0.0344

−21.50 −23.12 −24.75

26.76

161.96

MCT

AM

298 308 318

28.54 27.36 28.65

0.0634 0.0727 0.0810

−24.58 −25.73 −26.88

9.66

114.90

MCN

VC

298 308 318

39.13 45.22 72.88

0.0104 0.0154 0.0165

−22.15 −23.51 −24.86

18.31

135.77

MCT

VC

298 308 318

21.04 50.30 54.26

0.0078 0.0146 0.0193

−21.43 −23.35 −25.27

35.83

192.15

Qm , maximum adsorption capacity of a monolayer; KL , Langmuir constant; Go , Gibb’s free energy of adsorption; Ho , enthalpy of adsorption; So , entropy of adsorption.

Values for the specific surface area of the adsorbent were calculated from: S = Qm

NA MB MMMB

(11)

where Qm is the maximum adsorption capacity (mg g−1 ), NA is the Avogadro number (6.022 × 1023 mol−1 ), MMMB is the molecular mass of MB (319.85 g mol−1 ) and  MB is the area occupied by a single adsorbed MB molecule (130 A˚ 2 ). Considering the experimental results and that the area occupied by an adsorbed molecule of this dye is 130 A˚ 2 , the specific surface area of the adsorbents MCN, MCT and AC were estimated according to Eq. (9) to be 63, 79 and 196 m2 g−1 . 4. Conclusions Natural and heat-treated Macauba palm cakes were more efficient at adsorbing MB in comparison with CR. The natural cake showed somewhat higher adsorption efficiency for CR compared with its heat-treated counterpart but was less efficacious for MB. Heat treatment eliminated compounds from the natural cake that could hinder the adsorption of MB. Among the economical and technical advantages offered by Macauba palm cake for the removal of waste dye from industrial effluents are abundance and low cost together with rapidity in the adsorption process. Acknowledgments The authors wish to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico for scholarships awarded to SSV and NAVS. The authors are grateful to Prof. P.R.M. Viana for valuable assistance with zeta potential analysis. References [1] S. Vanhulle, M. Trovaslet, E. Enaud, M. Lucas, S. Taghavi, D. Van der Lelie, B. Van Aken, M. Foret, R.C. Onderwater, D. Wesenberg, S.N. Agathos, Y.J. Scheneider, A.M. Corbisier, Decolorization, cytotoxicity, and genotoxicity reduction during a combined ozonation/fungal treatment of dye-contaminated wastewater, Environ. Sci. Technol. 15 (2008) 584–589. [2] G. Crini, Non-conventional low-cost adsorbents for dye removal: a review, Bioresour. Technol. 97 (2006) 1061–1085. [3] M. Roulia, A.A. Vassiliadis, Sorption characterization of a cationic dye retained by clays and perlite, Microporous Mesoporous Mater. 116 (2008) 732–740. [4] Z.M. Magriotis, P.V.B. Leal, P.F. Sales, R.M. Papini, P.R.M. Viana, Adsorption of etheramine on kaolinite: a cheap alternative for the treatment of mining effluents, J. Hazard. Mater. 184 (2010) 465–471. [5] C. Xia, Y. Jing, Y. Jia, D. Yue, J. Ma, X. Yin, Adsorption properties of congo red from aqueous solution on modified hectorite: kinetic and thermodynamic studies, Desalination 265 (2011) 81–87. [6] F. Deniz, S. Karaman, Removal of Basic Red 46 dye from aqueous solution by pine tree leaves, Chem. Eng. J. 170 (2011) 67–74.

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