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Use of grape pomace as a biosorbent for the removal of the Brown KROM KGT dye
Accepted Manuscript Use of grape pomace as a biosorbent for the removal of the Brown KROM KGT dye
Ana Paula de Oliveira, Aparecido Nivaldo Módenes, Maria Eduarda Bragião, Camila L. Hinterholz, Daniela E.G. Trigueros, Isabella G. de O. Bezerra PII: DOI: Reference:
S2589-014X(18)30035-5 doi:10.1016/j.biteb.2018.05.001 BITEB 33
To appear in: Received date: Revised date: Accepted date:
19 March 2018 2 May 2018 2 May 2018
Please cite this article as: Ana Paula de Oliveira, Aparecido Nivaldo Módenes, Maria Eduarda Bragião, Camila L. Hinterholz, Daniela E.G. Trigueros, Isabella G. de O. Bezerra , Use of grape pomace as a biosorbent for the removal of the Brown KROM KGT dye. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Biteb(2017), doi:10.1016/j.biteb.2018.05.001
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ACCEPTED MANUSCRIPT Use of grape pomace as a biosorbent for the removal of the Brown KROM KGT dye
Ana Paula de Oliveira2*, Aparecido Nivaldo Módenes1, Maria Eduarda Bragião1, Camila L.
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Hinterholz1, Daniela E. G. Trigueros1, Isabella G. de O. Bezerra1
645,
Jd.
Santa
Maria,
85903-000,
Toledo,
PR,
Brazil,
e-mail:
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Faculdade
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¹Postgraduate Program of Chemical Engineering, West Paraná State University, Rua da
[email protected]. 2*
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Academic Department of Chemical Engineering (DAENQ), Federal University of
Technology - Paraná (UTFPR), Linha Santa Bárbara, s/nº, CEP: 85601-971, Francisco
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Beltrão-PR, Brazil, e-mail: [email protected].
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ABSTRACT
In this paper, the removal capacity of grape pomace was evaluated removing the KROM
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Brown KGT dye. Initially, batch adsorption tests were conducted to evaluate the operating parameters, which indicated 2.0 as initial pH, particle size between 0.14-1.4 mm and
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temperature of 25 °C, for initial dye concentration of 100 mg L-1. Based on these operating conditions, kinetic and adsorption equilibrium data were obtained. The resulting equilibrium time was 12 hours. The kinetic model of pseudo first order was the one that best represented the experimental data. The adsorption equilibrium data suggest a process of monolayers, according to the Langmuir model, with a maximum biosorption capacity of 180.2 ± 3.2 mg g1
. The thermodynamic data suggest a thermodynamically favorable and exothermic process.
ACCEPTED MANUSCRIPT Based on the results, it was found that the grape pomace has potential to be used as biosorbent in wastewater treatment systems containing dyes.
Key words: biosorption, dye, grape pomace, industrial organic waste.
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1. INTRODUCTION
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Industries facing the textile and leather dyeing are characterized by high consumption of water and application of dyes. As a result of losses in the production process, large volumes
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of wastewater are generated, which require proper treatment (Yu et al., 2015). The presence of synthetic dyes in water bodies makes the penetration of light very difficult, and
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consequently affects much of the photosynthetic activity and the development of aquatic organisms (Bakheet et al., 2013; Anastopoulos e Kyzas, 2014). The class of dyes of greatest
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interest in these industrial sectors corresponds to the azo group, which are characterized by
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the presence of one or more –N=N– groups bound to aromatic rings which make them toxic and with low biodegradability ratio (Kunz et al., 2002). To minimize the effect on the impacts
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caused by the dye discharge into water bodies, many wastewater treatment techniques have been investigated, such as: biodegradation (Mona et al., 2011), electrochemical techniques
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(Módenes et al., 2012), adsorption (Zhou et al., 2014), membrane filtration (Kebria et al., 2015), advanced oxidation processes (Manenti et al., 2015), among others. As a highlight, the biosorption process can be mentioned as a promising technique that has high efficiency in the removal of dyes, is economically viable and is of simple operation (Srinivasan e Viraraghavan, 2010, Módenes et al., 2011). Currently, researches facing the biosorption process study have been employing various materials of natural origin, in order to develop new alternative biosorbents. Among them we
ACCEPTED MANUSCRIPT can mention the orange peel (Noreen e Bhatti, 2014), rice straw (El-Bindary et al., 2014), banana pseudostem (Módenes et al., 2015), banana peel (Thuan et al., 2017), sugarcane bagasse (Yu et al., 2015), bamboo shell (Zhang et al., 2015), among others. In addition, the use of agricultural and industrial by-products in the adsorption is interesting because of its contribution to the proper disposal of the waste, as well as the obtainment of low cost
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biomasses (Rangabhashiyam et al., 2013; Xue et al., 2016).
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Among the industrial organic waste, the waste generated in the production of wine can be a
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promising biosorbent. This, in turn, has a composition consisting of shells, seeds and some grape stalks, being generated in large amounts, which becomes a problem of ecological
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management (Zhu et al., 2015). Conventionally, the grape pomace has been used for the fertilization of its own fruit culture, methanisation or energy production and animal feed
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(Soto et al., 2008; Brahim et al., 2014). However, the disposal of the pomace or its use for composting is harmful to the environment, because it takes a significant time to decompose
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(Ping et al., 2012).
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Studies involving the use of raw grape bagasse for dyes biosorption are still scarce in the literature. Some examples of work using this type of biomass are directed to the treatment of
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wastewater containing drug components (Villaescusa et al., 2011, Antunes et al., 2012) and heavy metals (Farinella et al., 2007, Chand et al., 2009).
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The objective of this study was to evaluate the potential use of grape pomace in the removal of the Brown KROM KGT dye in an aqueous solution. A chemical characterization of biosorbent and the determination of the appropriate operating parameters were performed, as well as a kinetic, thermodynamic and equilibrium study to which the main kinetic and literature equilibrium models were adjusted.
2. MATERIAL AND METHODS
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2.1. The Dye
The dye used was Brown KROM KGT, provided by a tannery from Toledo - Paraná. This dye corresponds to the azo group with molar mass of 413 g mol-1.
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Initially, a dye stock solution (1500 mg L-1) was prepared, which was subsequently diluted
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and adjusted the pH using NaOH solution (1 M) and H2SO4 (1 M), for the experiments.
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2.1.1. UV-Vis analysis
The molecular absorbance spectrum of the dye solution at 100 mg L-1 was measured in order
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to identify the wavelength of maximum absorption using the UV-Vis spectrophotometry technique (Shimadzu, Model UV 1800). A value of A438 nm was found for the solution.
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To determine the final concentration of the dye solution, a calibration curve was built
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(R²=0,999), which relates the initial concentration of the dye solution corresponding to the absorbance obtained by UV - Vis spectrophotometry at A438 nm. Further, a set of diluted
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Brown KROM KGT dye solutions (10–300 mg L-1) was used to calibrate the UV–Vis
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spectrophotometer.
2.2. Biosorbent
The grape pomace used was collected in a winery in the city of Toledo - Paraná. Initially, the biomass was washed with distilled water and dried at 45 °C until constant mass. Then it was mechanically milled and the size fractions between 0.14 and 1.4 mm were selected.
ACCEPTED MANUSCRIPT 2.3. Biosorbent characterization
The grape pomace was characterized by determining the point of zero charge (pHpzc) and
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2.3.1. Determination of the point of zero charge (pHpzc)
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using the Infrared Fourier Transform Spectroscopy (FTIR).
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The zero charge point (pHpcz) of the biosorbent is an important feature for understanding the adsorption process. This parameter correspond to the pH at which the surface charge of the
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biosorbent is null.
According to Davranche et al. (2003), the surface of the material presents either positive,
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negative or zero charge according to the pH of the solution in which it is found, being able to behave as an anion or cation exchanger. The adsorption of cations is favored at a pH>pHpcz,
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whereas the anion adsorption is favored at a pH
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To determine the pH where the surface charge of the biosorbent is zero (pHpzc), the methodology described by Davranche et al. (2003) was used.
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We employed two flasks initially containing a suspension of 5 g of adsorbent and 100 ml NaNO3 (0.1 mol L-1). Then one suspension was titrated with HNO3 (0.1 mol L-1) and the
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other with NaOH (0.1 mol L-1) in the pH range between 2 and 12. The total surface charge of the adsorbent was calculated according to Equation 1.
q
C A C B OH H CS
(1)
where q is the net surface charge of the biosorbent (M), the variables CA and CB are the concentrations of acid and base (M), respectively; [OH-] and [H+] are the concentrations of
ACCEPTED MANUSCRIPT these ions in the suspension (M) and Cs is the concentration of the adsorbent in the suspension (g L-1).
2.3.2. FTIR analysis
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The absorption spectroscopy analysis in the Fourier Transform Infrared (IR Frontier model,
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brand Perkin Elmer) was performed to determine the functional groups on the surface of the adsorbent. The FTIR spectra of the grape pomace before and after the adsorption of the dye
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Brown KROM KGT were obtained to evaluate possible changes resulting from the process.
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Analyses were performed using the method of KBr pellets, which were prepared by homogeneously mixing and milling 1 mg of the sample and 100 mg of KBr by pressing in a 5
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ton die, both previously dried at 105°C. The FTIR spectrum was obtained in the range of
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2.4. Pigmentation assay
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4000-450 cm-1 with resolution of 4 cm-1.
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In order to assess the possible release of pigment from the grape pomace in the solution,
to 10).
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adsorption experiments were conducted using distilled water at different initial pH values (1
An amount of 0.25 g of biosorbent and 50 mL distilled water were mixed and maintained under constant stirring at a speed of 90 rpm and at a controlled temperature of 25 °C. After a period of 24 hours, the samples were centrifuged (3000 rpm, 10 min) and the absorbance of the residual liquid phase was determined by UV-Vis spectrophotometry at A438nm.
2.5. Preliminary tests
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Preliminary tests were based on the investigation of operational parameters such as initial pH of the solution (1 to 10), particle size of the biosorbent (0.14 - 0.18, 0.18 - 0.59, 0.59 – 1.4 and 0.14 to 1.4 mm) and the adsorption temperature (25, 40 and 55 °C). Adsorption experiments were performed in batch system and in duplicate. In 125 ml
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Erlenmeyer flasks, 0.25 g of biosorbent and 50 ml of dye solution Brown KROM KGT, with
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initial concentration of 100 mg L-1 were added. The mixture was held under constant stirring
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(90 rpm) on an orbital shaker table at a controlled temperature for 24 h. After this period of contact, aliquots of the solution were separated from the adsorbent by centrifugation at 3000
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rpm for 10 min. The analysis of the final concentration of the dye present in solution was performed by UV - Vis spectrophotometry at A438 nm.
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For the adsorption studies evaluating the influence of the initial pH of the solution, particle size between 0.14 and 1.4 mm was used at 25 oC. In the tests related to the influence of
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temperature, particle size between 0.14-1.4 mm was used with the initial pH resulted from the
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previous test. And for the influence of the particle size, the tests were based on the initial temperature and pH indicated in the previous tests.
q
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Equation 2.
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The amount of dye adsorbed by the pomace was calculated as the mass balance described in
(C 0 - C)V m
(2)
where q (mg g-1) is the amount of dye adsorbed by the pomace, C0 and C (mg L-1) are the initial and final concentrations of dye in the solution, respectively, V (mL) is the solution volume and m (g) is the sorbent mass used in each test.
ACCEPTED MANUSCRIPT 2.6. Kinetic study
The kinetic study was carried out by adsorption experiments performed in the best operating conditions indicated in the preliminary tests. An amount of 0.25 g of adsorbent and 50 ml of dye solution with an initial concentration of
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100 mg L-1 were mixed. The mixture was stirred constantly at 90 rpm under controlled
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temperature.
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Samples were collected at preset intervals between 5 min and 36 h. At the end of each test, solution aliquots were taken, which were submitted to centrifugation. Then, the dye
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concentrations were determined by UV - Vis spectrophotometry (A438 nm). The adsorption
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capacity of the grape pomace is determined by the mass balance expressed in Equation 2.
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2.6.1. Kinetic parameters determination
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The evaluation of the kinetics of dye adsorption by grape pomace was performed by the pseudo first order, pseudo second order and Elovich models.
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The kinetic model of pseudo first order, described by Lagergren (1898), is shown in Equation
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3, which characterizes the process of adsorption by occupying an active site of the adsorbent.
q(t) q eq (1 e k1t )
(3)
where q (t) and qeq correspond to the color removal ability in time t and at equilibrium (mg g1
), respectively, and k1 refers to the rate constant (h-1).
The model of pseudo second order, which requires chemisorption, is shown in Equation 4 (Ho and McKAY, 1998).
ACCEPTED MANUSCRIPT q(t)
2 q eq k2 t
(4)
1 q eq k 2 t
where k2 is the rate constant (mg g-1 h-1). In Equation 5 the model of Elovich is shown, which is suitable for chemical adsorption
1 1 ln a ln t
(5)
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q(t)
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processes in systems with heterogeneous surfaces (Chien and Clayton, 1980).
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where α is the adsorption rate (mg g-1 h-1) and β is a parameter related to the activation energy
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(mg g-1).
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2.7. Equilibrium study
Again, the ratio of 0.25 g of adsorbent to 50 mL of dye solution was used with stirring at 90
to 1500 mg L-1.
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rpm and temperature controlled. The initial concentration of the solution was varied from 10
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After 24 h of contact, the samples were centrifuged and the determination of the residual dye concentration was realized by UV-Vis spectrophotometry at A438.
2.7.1. Equilibrium parameters determination
Based on the ratio between the adsorption capacity of the grape pomace and the equilibrium concentration, the equilibrium data were evaluated by isotherm models commonly employed in the study of biosorption that enable the assessment of the nature of the adsorption process.
ACCEPTED MANUSCRIPT The Langmuir and Freundlich isotherms are shown in Equations 6 and 7, respectively.
q eq
q maxbC eq
(6)
1 bC eq
q eq k F C eq
(7)
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1/ n
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where qmax (mg g-1) corresponds to the maximum dye adsorption capacity, qeq (mg g-1) to the equilibrium dye adsorption capacity, Ceq (mg L-1), b (L mg-1) to the Langmuir constant, kF (L) to the Freundlich constant in (dimensionless) a constant that characterizes the adsorption
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1
intensity.
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The Langmuir isotherm indicates a monolayer adsorption on an homogeneous surface, with energy identical adsorption sites (Langmuir, 1918) while the Freundlich isotherm indicates
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multilayer adsorption in systems with heterogeneous surfaces (Freundlich, 1906).
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In the literature, some empirical modifications of these isotherms can be found and are presented in Table 1, where qmax (mg g-1) corresponds to the maximum capacity of the dye
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adsorption, qeq (mg g-1) to dye the adsorption capacity in the equilibrium, Ceq (mg L-1) to the dye concentration at the equilibrium, b (L mg-1) is the Langmuir constant, kF (L-1) is the
adsorption.
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Freundlich constant and n (dimensionless) is a constant that characterizes the intensity of the
From the models shown in Table 1, the constants KRP, aRP, bS, NS, bT and nT are the adjustable parameters of the models, being KRP, nS and nT values between 0 and 1. Another isotherm used was the Temkin, which may be considered suitable for monolayer chemisorption process, being represented by Equation 8 (Temkin, 1981).
ACCEPTED MANUSCRIPT q eq B ln( k T ) B ln( C eq )
(8)
where kT (L mg-1) is the bound equilibrium constant and B (dimensionless) is the constant of the model that takes into account the heat of adsorption.
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The Dubinin - Radushkevich isotherm is characterized by allowing the distinction of physical or chemical adsorption, additionally considering the effect of temperature. This isotherm is
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similar to the Langmuir model, however, it does not assume homogeneous surface or constant
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2 1 q max exp RT ln 1 Ceq
(9)
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q eq
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potential energy and it is represented by Equation 9 (Radushkevich and Kolganov, 1967).
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where β is the adsorption energy constant (mol2 kJ-2), T is the temperature (K) and R is the
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ideal gas constant (8.314 J mol-1 K-1).
By means of Equation 10, the Dubinin - Radushkevich constant, β, is related to the average energy of sorption (E), which is characterized by the free energy involved in the transfer of 1
E
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mole of solute from the solution to the surface of the adsorbent (Dotto et al., 2011).
1 2
(10)
2.8. Thermodynamic study
The evaluation of the thermodynamic parameters of the sorption process was performed through the temperature effect analysis and equilibrium constants.
ACCEPTED MANUSCRIPT Therefore, the change in the Gibbs free energy (ΔG°), the change in the enthalpy (ΔH°) and the change in the entropy (ΔS°) system were evaluated. The relationship between these energies can be represented by Equation 11 (Kumar et al., 2008).
G H TS
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(11)
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The Gibbs energy variation indicates the degree of spontaneity of the adsorptive process. Positive values for this parameter indicate a non-spontaneous process, and the negative values
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are characteristic of spontaneous processes, or thermodynamically favorable process where
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the adsorbate has high affinity with the adsorbent. As reported by Kumar et al. (2008), the ΔG
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° can be determined by Equation 12.
(12)
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G RT ln k L
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where kL is the thermodynamic equilibrium constant, T is the absolute temperature of the system (K) and R is the universal gas constant.
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However, kL is related to the activity coefficient and ionic strength of the solute in the medium. When considering the small ionic strength in organic compounds, such as the dyes,
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this property is discarded. Thus, the kL constant can be reasonably approximated by the affinity constant of the Langmuir isotherm (Liu, 2009). However, this approach considers the activity coefficient equal to unity, which has validity for neutral or weakly charged adsorbates. The thermodynamic parameters ΔH° and ΔS° are determined by the linear fit of ΔG° as a function of the temperature, which can be estimated by the Van't Hoff relationship presented in Equation 13 (Wang, 2012).
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ln k L
S H R RT
(13)
As reported by Wang et al. (2005) and Wang (2012) positive values of ΔH° indicate
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endothermic adsorption process, and negative values are characteristic of exothermic processes, promoting the release of energy. Moreover, the enthalpy variation values between -
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40 and -800 kJ mol-1 characterizes the chemical adsorption process, whereas in the range of 0
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and -40 kJ mol-1 it represents the physical adsorption heats (Wang, 2012, El-Bindary et al. 2014, Monte Blanco et al., 2017).
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The negative ΔS° parameter suggests the decrease of randomness at the solid/liquid interface
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due to interactions between the adsorbent and adsorbate. If the difference of entropy is positive it indicates that there is an increase in the system disorder in the solid/liquid interface
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during the adsorption of the dye (Zhang et al., 2011, Zhang et al., 2015).
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3. RESULTS AND DISCUSSIONS
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3.1. Biosorbent characterization
3.1.1. Determination of the point of zero charge (pHpzc)
The pHpcz value of the biosorbent grape pomace was obtained from the evaluation of the net surface charge of the adsorbent as a function of the initial pH of the solution, as shown in Figure 1.
ACCEPTED MANUSCRIPT It was observed in Figure 1 that the net surface charge of grape pomace decreases with increasing pH. The pHpcz at which the net surface charge of the grape pomace is zero was observed at pH 3.0. The grape pomace surface has a predominantly positive character based on the behavior of net surface charge, at pH values below 3.0. On the other hand, at pH values greater than 3.0, the
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biosorbent presented negative net charge.
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Considering that at pH values below pHpcz, the surface of the adsorbent was positively
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charged it is suggested the sorption of pollutants with an anionic character through electrostatic attraction. In contrast, the adsorption of substances having cationic characteristics
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presented as negatively charged (pH> 3.0).
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is enhanced at a pH greater than pHpcz because, in this case, the surface of the adsorbent was
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3.1.2 FTIR analysis
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By the analysis of the FTIR spectra, the characterization of the functional groups present in the grape pomace structure was made, before and after the dye adsorption process at the
in Figure 2.
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concentration of 100 mg L-1 initial pH of 2.0 and particle size mixture. The spectra are shown
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In Figure 2, it appears that the main spectral bands identified in the grape pomace structure can be attributed to vibrations in the stretching N-H and asymmetric O-H at 3400 cm-1, C-H stretch indicated by bands in the range of 2925 and 1739 cm-1 (Mona et al., 2011; Ping et al., 2014), and according to Pala et al. (2014) in the 1740 cm-1 region, the presence of C=O stretching from carboxylic groups and esters is indicated. As reported by Danish et al., peak at around 1600 cm−1 and at 1700 cm−1 evidence the presence of aromatic ring with carboxylate groups.
ACCEPTED MANUSCRIPT The bands observed in the range 1450 to 1612 cm-1 can be related to the C=C stretching of aromatic groups, lignin and C-H vibration from CH2 and CH3 (Manara et.al., 2014; Pala et al., 2014). Another band observed in the FTIR spectrum of the grape pomace was at 1035 cm-1 and it may be attributed to C-O stretching (Ping et al., 2014). In the scale enlargement in the range between 1400 and 1800 cm-1, shown as a detail in
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Figure 2, one can observe some subtle changes in the spectra after the dye adsorption. Small
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changes were observed in the peaks shape as well as a band displacement at 1739-1745 cm-1,
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1641-1646 cm-1, 1518-1533 cm-1 and 1452-1456 cm-1. These changes may indicate that the
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functional groups assigned to these bands are involved in the dye adsorption process.
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3.2. Pigmentation test
The pigmentation test was performed to evaluate the occurrence of detachment of the grape
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pomace pigments that could interfere with the solution absorbance values. The results of the
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tests performed in distilled water at different initial pHs are shown in Table 2. It is observed in Table 2 that the solutions of initial pH above 2.0 had their pH changed during
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the time of contact between the biosorbent and distilled water, indicating final pH between 5.0 and 7.5. In this pH range of the medium, the net surface charge of the grape pomace ranges
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from zero to mildly negative.
According to Drosou et al. (2015), the phenolic compounds responsible for the natural pigmentation of the waste from wine production are the anthocyanins. These are characterized as highly unstable and easily liable to deterioration by environmental factors such as light, pH and temperature molecules. They are stable at acidic pH because pHs greater than 4.0 can degrade anthocyanins (Xu et al., 2015).
ACCEPTED MANUSCRIPT In this context, the increase in the initial pH may degrade this type of substance to alter the color of the residual solution. Due to the effect of initial pH it was necessary to take into account the effect of release of pigments in the solution and the interference that this causes in the absorbance values of the dye solution after contact with the biosorbent was corrected by
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using the zero in the experimental tests.
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3.3. Preliminary tests
In the study of the influence of the initial pH on the Brown KROM KGT dye adsorption
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process, the response that changes in the initial pH of the solution promoted in terms of removal ability was evaluated and the results are shown in Table 3.
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It is observed in Table 3, that there was a significant decrease in the amount of dye adsorbed for initial pH values above 2.0. By evaluating the results at pH values above 2.0, it is
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observed that the final pH of the solution has values around 6.6, which may alter the
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conditions of electrostatic interactions of the surface with the solution at pH of the liquid phase above the pHpcz (3.0).
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The best removal capacity was attributed to the initial pH 2.0 (20.0 ± 0.1 mg g-1). Considering the information obtained for the pHpcz (Figure 1), it can be said that in the best adsorption
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condition, the net charge on the surface of grape pomace presented a positive character. This suggests that the dye Brown KROM KGT, may have anionic characteristics, enabling the attraction between biosorbent and adsorbate. Similar behavior was also reported by El Bindary et al. (2014), which state that the high adsorption capacity of dye onto biosorbent in highly acidic solutions is due to the strong electrostatic interactions between its adsorption site and dye anion.
ACCEPTED MANUSCRIPT Carboxylic, amino, amide, esters groups are the major binding sites identified by the analysis of the FTIR spectra for adsorption of the dye in the grape pomace. These groups can be ionized when the pH varies. At low pH values, the surface sites are protonated, and the surface becomes positively charged, while the ionizable groups lose their protons and the surface becomes negatively charged at high pH values. Thus, it is suggested that surface
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protonation occurs with a positive net charge at surface, as a function of the increase of the
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dye adsorption with the reduction of pH, specifically for pHs lower than 3.0 (pHpcz).
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When investigating the adsorption temperature, in conditions of particle size between 0.14 and 1.4 mm, initial pH 2.0, the parameter of interest was varied at 25, 40 and 55 °C, and the
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removability values were 20.0 ± 0, 1 mg g-1, 19.9 ± 0.1 mg g-1 and 19.4 ± 0.4 mg g-1, respectively. Thus, it can be stated that there is considerable influence of temperature on the
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removal of dye in solution with an initial concentration of 100 mg L-1, the variation being less than 5%. Considering this fact, the room temperature of 25 °C was used in the experiments.
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In the evaluation of the influence of particle size with adsorption tests with initial pH 2.0 and
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room temperature, it was observed that for the granulometric fractions 0.14 - 0.18, 0.18 - 0.59 and 0.14 - 1.4 mm, the dye removal capacity was about 20 mg g-1, with a variation of less
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than 5%. However, for the particle diameter range from 0.59 to 1.4 mm, the adsorption capacity was reduced (15.6 ± 0.3 mg g-1), possibly due to the heterogeneity of size of the solid
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particles, and to the presence of higher amount of grape seeds, which for this specific particle size remained whole. Thus, the preliminary tests indicated the use of granulometric mixture (0.14 - 1.4 mm), since it enables good removability, without the need for excessive grinding of the adsorbent and the best use of the biosorbent. The adsorption capacity obtained for the initial pH 2.0, mixture of all granulometric fractions and room temperature corresponds to a removal rate of approximately 94%.
ACCEPTED MANUSCRIPT 3.4. Kinetic study
In Figure 3 the experimental data of the adsorption kinetics obtained for the grape pomace are shown. The kinetic models of pseudo-first order, pseudo-second order and Elovich were adjusted for the evaluation of the experimental data.
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The kinetic behavior, which can be seen in Figure 3, showed high removal rates early in the
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process, reaching the equilibrium at around 12 h, with removal around 93%. Among the evaluated models, it appears that the model of pseudo first order was the one that best fit to
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the experimental data (R2 = 0.9958), with an adsorption capacity of 19.9 ± 0.2 mg g-1, as
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shown in Table 4.
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3.5. Equilibrium study
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In Figure 4, the equilibrium data obtained for the adsorption process at temperatures of 25, 35
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and 45 °C are presented, considering the adjustment of the Langmuir isotherm. Isotherms commonly used in adsorption studies were fitted to the experimental equilibrium
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data for the temperatures 25, 35 and 45 °C, and the model parameters are shown in Table 5. As seen in Table 5, the Langmuir isotherm was the one that best fit to the equilibrium data
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(R2 = 0.9930, 0.9960 and 0.9976) with maximum adsorption capacity around 180, 190 and 213 mg g-1 for the temperatures 25, 35 and 45 °C respectively. Thus, it is suggested that the dye adsorption is monolayer, with a homogeneous surface. El-Bindary et al. (2014) further emphasize that in the Langmuir model it is assumed that each dye molecule occupies a specific active site, which is unavailable for the adsorption process. Based on the hypotheses of the model, the adsorbent presents a finite capacity to capture the adsorbate, being this the maximum capacity of saturation (qmax), with values presented in
ACCEPTED MANUSCRIPT Table
5.
Despite the slight increase in the removal capacity as a function of temperature increase, the room temperature was chosen as working condition. Considering that the constants from the models of Redlich-Perterson (g), Sips (ns) and Toth (nT), which correspond to the heterogeneity of the solid, were equal to 1, the models are
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reduced to the Langmuir model, as shown in Table 5.
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The adjustment of the Dubinin - Radushkevich model to the experimental data also brought
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additional information on the forms of physical or chemical adsorption, additionally considering the effect of temperature.
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Based on Eq. (10), the mean sorption energy, E (kJ mol-1), was determined to be useful for obtaining information on the mechanisms of the adsorption process. If the E value is between
1
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8 and 16 kJ mol-1, the adsorption is classified as chemistry. On the other hand, if E <8 kJ mol, it can be suggested that the physical adsorption process occurs (Matouq et al., 2015).
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According to data from Table 5, it can be observed that for the three temperatures evaluated,
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the mean sorption energy value was lower than 8 kJ mol-1. Thus, it is suggested that the
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sorption mechanism for the grape pomace involves the process of physical adsorption.
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3.6. Thermodynamic study
The estimation of the thermodynamic parameters was performed based on Equations 11 and 13, and the values of ΔG°, ΔH° and ΔS° are shown in Table 6. In Table 6, it is observed that the variation in the Gibbs free energy for the different temperatures resulted in negative values, which suggests a thermodynamically favorable process. It is also observed in Table 6 that the negative value of ΔH°, between 0 and -40 kJ mol-1, suggests an exothermic process and the physical nature of the dye adsorption.
ACCEPTED MANUSCRIPT The physical nature of the adsorption process was also indicated by the average adsorption energy obtained through the Dubinin - Radushkevich isotherm, indicating that the adsorption has a low potential barrier. The positive value of ΔS° indicates an increase in the degree of disorganization (randomness) at the liquid-solid interface during the sorption process.
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According to Wang (2012), the positive entropy variation may also indicate some structural
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changes in the adsorbate and adsorbent and a good affinity of the adsorbent for the dye. The
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author further adds that the relationship between the increase in dye adsorption and the increase in temperature may be linked to an increase in the intra-particle diffusion rate of
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adsorbate, since diffusion is an endothermic process.
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4. CONCLUSION
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Based on the results obtained in preliminary tests, it can be concluded that the adsorption of
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the dye by the grape pomace with initial dye concentration of 100 mg L-1 is strongly influenced by the initial pH of the solution, being the best results observed for initial pH of
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2.0. It was verified that the particle size and the temperature of the medium do not significantly affect the dye adsorption capacity, and thus the particle size between 0.14-1.4
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mm and the temperature of 25 °C were used. When evaluating the adsorption kinetics, it was observed that the equilibrium time was about 12 h following the pseudo-first order model. At the equilibrium study, the Langmuir isotherm was the one that best represented the process with maximum adsorption capacity of 180.2 ± 3.2 mg g-1 at 25 °C, indicating monolayer adsorption and homogeneous surface. The thermodynamic parameters determined for the adsorption process is question indicated that it is favorable, exothermic and accompanied by an increase in the randomness at the solid/liquid interface. Thus, it is concluded that the grape
ACCEPTED MANUSCRIPT pomace showed potential application as a biosorbent in the treatment of industrial waste containing dyes. Based on the data obtained for the batch system, the study of the adsorption of this dye by the grape pomace should be continued by means of bed column adsorption studies. In this way, the process is evaluated in a continuous system in order to determine other pertinent parameters of operation. Finally, after performing the study on a laboratory
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scale, it should be replicated to the pilot scale, maintaining the experimental conditions that
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provided the best results for the reduced scale. In this way, it is sought the approximation of
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an industrial process as a polishing process for the treatment of large volumes of waste.
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Acknowledgments
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The authors thank CNPQ and Araucaria Foundation for the financial support of this study.
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5. REFERENCES
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ACCEPTED MANUSCRIPT Matouq, M., Jildeh, N., Qtaishat, M., Hindiyeh, M., Al Syouf, M. Q. 2015. The adsorption kinetics and modeling for heavy metals removal from wastewater by Moringa pods. J. Environ. Chem. Eng., 3, 775–784. Módenes, A.N., Espinoza-Quiñones, F.R., Alflen, V.L., Colombo, A., Borba, C.E. 2011. Utilização da macrófita Egeria densa na biossorção do corante reativo 5G. Engevista, 13, 160166.
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Módenes, A.N., Espinoza-Quiñones, F.R., Borba, F.H.; Manenti, D.R. 2012. Performance evaluation of an integrated Photo-Fenton – Electro coagulation process applied to pollutant removal from tannery effluent in batch system. Chem. Eng. J., 197, 1–9.
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Monte Blanco, S. P. D., Scheufele, F. B., Módenes, A. N., Espinoza-Quiñones, F. R., Marin, P., Kroumov, A. D., Borba, C. E., 2017. Kinetic, equilibrium and thermodynamic phenomenological modeling of reactive dye adsorption onto polymeric adsorbent. Chem. Eng. J., 307, 466–475.
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Noreen, S. E Bhatti, H.N. 2014. Fitting of equilibrium and kinetic data for the removal of Novacron Orange P-2R by sugarcane bagasse. J. Ind. Eng. Chem., 20, 1684-1692.
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Pala, M., Kantarli, I.C., Buyukisik, H.B., Yanik, J. 2014. Hydrothermal carbonization and torrefaction of grape pomace: A comparative evaluation. Bioresour. Technol., 161, 255–262.
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Radushkevich, L.V., Kolganov, V.A. 1967. Experimental Study of the Deposition of Flowing Highly Dispersed Aerosolson Thin Cylinders. Institute of Physical Chemistry; Academy of Sciences of the USSR; Moscow; U.S.S.R. Received. Rangabhashiyam, S., Anu, N., Selvaraju, N. 2013. Sequestration of dye from textile industry wastewater using agricultural waste products as adsorbents. J. Environ. Chem. Eng., 16, 629641. Redlich, O., Peterson, D.L. 1959. A useful adsorption isotherm. J. Phys. Chem., 63, 1024– 1026. Sips, R. 1948. Combined form of Langmuir and Freundlich equations. J. Chem. Phys., 16, 490–495. Soto, M.L., Moure, A., Domínguez, H., Parajo, J.C. 2008. Charcoal adsorption of phenolic compounds present in distilled grape pomace. J. Food Eng., 84, 156–163.
ACCEPTED MANUSCRIPT Srinivasan, A. E Viraraghavan, T. 2010. Decolorization of dye wastewaters by biosorbents: A review. J. Environ. Manage., 91, 1915–1929. Temkin, D.E. 1981. Interface kinetics in the growth of two. Component Crystals. J. Cryst. Growth, 52, 299–310. Thuan, T.V., Quynh, B.T.P., Nguyen, T.D., Ho, V.T.T., Bach, L.G. 2017. Response surface methodology approach for optimization of Cu2+, Ni2+ and Pb2+ adsorption using KOHactivated carbon from banana peel, Surfaces and Interfaces, 6, 209–217.
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Toth, J. 1971. State equations of the solid gas interface layer. Acta Chim. Hung., 69, 311–317.
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Villaescusa, I., Fiol, N., Poch, J., Bianchi, A., Bazzicalupi, C. 2011. Mechanism of paracetamol removal by vegetable wastes: the contribution of p–p interactions, hydrogenbonding and hydrophobic effect. Desalination, 270, 135–142.
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Wang, S.B., Boyjoo, Y., Choueib, A., Zhu, Z.H. 2005. Removal of dyes from aqueous solution using fly ash and red mud. Water Res., 39, 129-138.
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Wang, L. 2012. Application of activated carbon derived from ‘waste’ bamboo culms for the adsorption of azo disperse dye: Kinetic, equilibrium and thermodynamic studies. J. Environ. Manage., 102, 79-87.
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Xu, H., Liu, X., Yan, Q., Yuan, F., Gao. F. 2015. A novel copigment of quercetagetin for stabilization of grape skin anthocyanins. Food Chem., 166, 50-55.
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Xue, L., Zhang, P., Shu, H., Chang, C. C., Wang, R., Zhang, S. 2016. Agricultural Waste. Water Environ. Res., 88, 1334-1373.
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Yu, J., Zhu, J., Feng, L., Chi, R. 2015. Simultaneous removal of cationic and anionic dyes by the mixed sorbent of magnetic and non-magnetic modified sugarcane bagasse. J. Colloid Interface Sci., 451, 153-160.
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Zhang, Z., Moghaddam, L., O’hara, I.M., Doherty, W.O.S. 2011. Congo Red adsorption by ball-milled sugarcane bagasse. Chem. Eng. J., 178, 122–128.
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Zhang, Y., Ou, J., Duan, Z., Xing, Z., Wang, Y. 2015. Adsorption of Cr (VI) on bamboo barkbased activated carbon in the absence and presence of humic acid. Colloids Surf., A, 481, 108116. Zhou, Z., Lin, S., Yue, T., Lee, T. 2014. Adsorption of food dyes from aqueous solution by glutaraldehyde cross-linked magnetic chitosan nanoparticles. J. Food Eng., 126, 133-141. Zhu, F., Du, B., Zheng, L., Li, J. 2015. Advance on the bioactivity and potential applications of dietary fibre from grape pomace. Food Chem., 186, 207-212.
ACCEPTED MANUSCRIPT TABLES Table 1. Empiric modifications of the Langmuir and Freundlich isotherms. Model Aplication Redlich-Peterson1 Hterogenous surface
Sips2
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Langmuir-Freundlich combination
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Toth3
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Multilayers in heterogenous surfaces
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Font: 1[35, 36, 37] Redlich and Peterson (1959); 2Sips (1948); 3Toth (1971).
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Table 2. Effect of the biosorbent pigmentation on the distilled water at different pH. pHinitial pHfinal q (mg g-1) 1.0 1.5 3.0 ± 0.4 2.0 2.1 1.8 ± 0.3 4.0 5.2 10.9 ± 1.0 6.1 7.5 6.7 ± 1.2 8.1 6.8 5.6 ± 0.4 10.0 5.7 7.1 ± 0.3
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Table 3. Effect of the pH in the capacity of the dye adsorption with initial concentration of 100 mg L -1 (T = 25°C, 90 rpm, t = 24 h, granulometric mixture). pHinitial pHfinal q (mg g-1) 1.0 1.2 19.0 ± 0.2 2.2 2.1 20.0 ± 0.1 4.0 6.7 1.3 ± 0.3 6.1 6.6 2.0 ± 0.7 8.2 6.6 1.3 ± 0.4 10.0 6.8 1.0 ± 0.4
Table 4. Estimated parameters of kinetic models and fitting parameters for dye sorption data. Model Pseudo-first order
Adjusted parameters qe (mg g-1) 19.9 ± 0.2 -1 k1 (h ) 0.88 ± 0.03
Pseudo-second order
qe (mg g-1) k2 (g mg-1 h-1)
21.5 ± 0.42 0.056 ± 0.01
Elovich
a (mg g-1 h-1) b (g mg-1)
91.2 ± 32 0.29 ± 0.03
ACCEPTED MANUSCRIPT Table 5. Adjusted values of modelling parameters for a set of tested isotherm models representing equilibrium adsorption data
Toth
Temkin
DubininRadushkevich
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Sips
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Redlich-Peterson
35 °C 190.5 ± 3.5 0.016 ± 0.001 0.9960 14.14 ± 2.4 2.4 ± 0.2 0.9616 3.09 ± 0.2 0.016 ± 0.001 1 0.9960 190.5 ± 3.5 0.016 ± 0.001 1 0.9960 190.5 ± 3.5 0.016 ± 0.001 1 0.9960 22.65 ± 2.9 1.11 ± 0.5 0.7961± 0.5 153.2 ± 9.7 3.71 ± 1.1 0.37 0.8981
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Freundlich
25 °C 180.2 ± 3.2 0.024 ± 0.001 0.9930 19.6 ± 3.6 2.9 ± 0.3 0.8884 4.37 ± 0.2 0.024 ± 0.001 1 0.9930 180.2 ± 3.2 0.024 ± 0.001 1 0.9930 180.2 ± 3.2 0.024 ± 0.001 1 0.9930 30.71 ± 1.6 0.43 ± 0.06 0.9502 151.2 ± 7.1 1.84 ± 0.3 0.52 0.9182
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Langmuir
Parameters qmax(mg g-1) b (L mg-1) R² kF(L-1) n R² krp (L g-1) arp (L mg-1) g R² qm (mg g-1) ks (L mg-1) ns R² qm(mg g-1) bt(L mg-1) nT R² B (adim) kT (L mg-1) R² qm(mg g-1) β (mol2kJ-2) E (kJ mol-1) R²
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Isotherms
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Table 6. Values of the thermodynamic parameters. ΔG ΔH ΔS T (K) (kJ mol-1 K-1) (kJ mol-1 K-1) (J mol-1 K-1) 298 -22.83 308 -22.57 -16.23 21.62 318 -23.28
45 °C 213.6 ± 2.9 0.0161 ± 0.0008 0.9976 15.1 ± 3.3 2.4 ± 0.2 0.9422 3.44 ± 0.13 0.0161± 0.0008 1 0.9976 213.6 ± 2.9 0.0161 ± 0.0008 1 0.9976 213.6 ± 2.9 0.0161 ± 0.0008 1 0.9976 35.10 ± 2.15 0.370 ± 0.06 0.9562 173.1 ± 9.1 3.60 ± 0.90 0.37 0.9210
ACCEPTED MANUSCRIPT FIGURE CAPTIONS Figure 1. Distribution of the net surface charge of the grape pomace as a function of pH.
Figure 2. FTIR spectrum of the grape pomace (a) before and (b) after the adsorption of the dye with initial concentration of 100 mg L-1.
(pHinitial = 2.0, T = 25°C, granulometric mixture, 90 rpm).
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1
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Figure 3. Kinetic data for the process of dye adsorption with initial concentration of 100 mg L-
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Figure 4. Equilibrium data and Langmuir profile for the Brown KROM KGT adsorption at
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the temperatures of (a) 25, (b) 35 e (c) 45 °C (pHinitial = 2.0, granulometric mixture, 90 rpm).
ACCEPTED MANUSCRIPT Highlights
Use of grape pomace waste for removal of dye, suggesting an adequate management of this type of waste.
Possibility for treatment of effluent generated in the dyeing of leather using a lowcost process.
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Evaluation of the appropriate operating parameters of the system by different kinetic and
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Characterization of the evaluated biosorbent material.
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equilibrium models.
Figure 1
Figure 2
Figure 3
Figure 4
Ana Paula de Oliveira, Aparecido Nivaldo Módenes, Maria Eduarda Bragião, Camila L. Hinterholz, Daniela E.G. Trigueros, Isabella G. de O. Bezerra PII: DOI: Reference:
S2589-014X(18)30035-5 doi:10.1016/j.biteb.2018.05.001 BITEB 33
To appear in: Received date: Revised date: Accepted date:
19 March 2018 2 May 2018 2 May 2018
Please cite this article as: Ana Paula de Oliveira, Aparecido Nivaldo Módenes, Maria Eduarda Bragião, Camila L. Hinterholz, Daniela E.G. Trigueros, Isabella G. de O. Bezerra , Use of grape pomace as a biosorbent for the removal of the Brown KROM KGT dye. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Biteb(2017), doi:10.1016/j.biteb.2018.05.001
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ACCEPTED MANUSCRIPT Use of grape pomace as a biosorbent for the removal of the Brown KROM KGT dye
Ana Paula de Oliveira2*, Aparecido Nivaldo Módenes1, Maria Eduarda Bragião1, Camila L.
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Hinterholz1, Daniela E. G. Trigueros1, Isabella G. de O. Bezerra1
645,
Jd.
Santa
Maria,
85903-000,
Toledo,
PR,
Brazil,
e-mail:
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Faculdade
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¹Postgraduate Program of Chemical Engineering, West Paraná State University, Rua da
[email protected]. 2*
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Academic Department of Chemical Engineering (DAENQ), Federal University of
Technology - Paraná (UTFPR), Linha Santa Bárbara, s/nº, CEP: 85601-971, Francisco
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Beltrão-PR, Brazil, e-mail: [email protected].
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ABSTRACT
In this paper, the removal capacity of grape pomace was evaluated removing the KROM
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Brown KGT dye. Initially, batch adsorption tests were conducted to evaluate the operating parameters, which indicated 2.0 as initial pH, particle size between 0.14-1.4 mm and
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temperature of 25 °C, for initial dye concentration of 100 mg L-1. Based on these operating conditions, kinetic and adsorption equilibrium data were obtained. The resulting equilibrium time was 12 hours. The kinetic model of pseudo first order was the one that best represented the experimental data. The adsorption equilibrium data suggest a process of monolayers, according to the Langmuir model, with a maximum biosorption capacity of 180.2 ± 3.2 mg g1
. The thermodynamic data suggest a thermodynamically favorable and exothermic process.
ACCEPTED MANUSCRIPT Based on the results, it was found that the grape pomace has potential to be used as biosorbent in wastewater treatment systems containing dyes.
Key words: biosorption, dye, grape pomace, industrial organic waste.
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1. INTRODUCTION
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Industries facing the textile and leather dyeing are characterized by high consumption of water and application of dyes. As a result of losses in the production process, large volumes
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of wastewater are generated, which require proper treatment (Yu et al., 2015). The presence of synthetic dyes in water bodies makes the penetration of light very difficult, and
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consequently affects much of the photosynthetic activity and the development of aquatic organisms (Bakheet et al., 2013; Anastopoulos e Kyzas, 2014). The class of dyes of greatest
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interest in these industrial sectors corresponds to the azo group, which are characterized by
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the presence of one or more –N=N– groups bound to aromatic rings which make them toxic and with low biodegradability ratio (Kunz et al., 2002). To minimize the effect on the impacts
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caused by the dye discharge into water bodies, many wastewater treatment techniques have been investigated, such as: biodegradation (Mona et al., 2011), electrochemical techniques
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(Módenes et al., 2012), adsorption (Zhou et al., 2014), membrane filtration (Kebria et al., 2015), advanced oxidation processes (Manenti et al., 2015), among others. As a highlight, the biosorption process can be mentioned as a promising technique that has high efficiency in the removal of dyes, is economically viable and is of simple operation (Srinivasan e Viraraghavan, 2010, Módenes et al., 2011). Currently, researches facing the biosorption process study have been employing various materials of natural origin, in order to develop new alternative biosorbents. Among them we
ACCEPTED MANUSCRIPT can mention the orange peel (Noreen e Bhatti, 2014), rice straw (El-Bindary et al., 2014), banana pseudostem (Módenes et al., 2015), banana peel (Thuan et al., 2017), sugarcane bagasse (Yu et al., 2015), bamboo shell (Zhang et al., 2015), among others. In addition, the use of agricultural and industrial by-products in the adsorption is interesting because of its contribution to the proper disposal of the waste, as well as the obtainment of low cost
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biomasses (Rangabhashiyam et al., 2013; Xue et al., 2016).
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Among the industrial organic waste, the waste generated in the production of wine can be a
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promising biosorbent. This, in turn, has a composition consisting of shells, seeds and some grape stalks, being generated in large amounts, which becomes a problem of ecological
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management (Zhu et al., 2015). Conventionally, the grape pomace has been used for the fertilization of its own fruit culture, methanisation or energy production and animal feed
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(Soto et al., 2008; Brahim et al., 2014). However, the disposal of the pomace or its use for composting is harmful to the environment, because it takes a significant time to decompose
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(Ping et al., 2012).
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Studies involving the use of raw grape bagasse for dyes biosorption are still scarce in the literature. Some examples of work using this type of biomass are directed to the treatment of
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wastewater containing drug components (Villaescusa et al., 2011, Antunes et al., 2012) and heavy metals (Farinella et al., 2007, Chand et al., 2009).
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The objective of this study was to evaluate the potential use of grape pomace in the removal of the Brown KROM KGT dye in an aqueous solution. A chemical characterization of biosorbent and the determination of the appropriate operating parameters were performed, as well as a kinetic, thermodynamic and equilibrium study to which the main kinetic and literature equilibrium models were adjusted.
2. MATERIAL AND METHODS
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2.1. The Dye
The dye used was Brown KROM KGT, provided by a tannery from Toledo - Paraná. This dye corresponds to the azo group with molar mass of 413 g mol-1.
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Initially, a dye stock solution (1500 mg L-1) was prepared, which was subsequently diluted
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and adjusted the pH using NaOH solution (1 M) and H2SO4 (1 M), for the experiments.
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2.1.1. UV-Vis analysis
The molecular absorbance spectrum of the dye solution at 100 mg L-1 was measured in order
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to identify the wavelength of maximum absorption using the UV-Vis spectrophotometry technique (Shimadzu, Model UV 1800). A value of A438 nm was found for the solution.
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To determine the final concentration of the dye solution, a calibration curve was built
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(R²=0,999), which relates the initial concentration of the dye solution corresponding to the absorbance obtained by UV - Vis spectrophotometry at A438 nm. Further, a set of diluted
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Brown KROM KGT dye solutions (10–300 mg L-1) was used to calibrate the UV–Vis
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spectrophotometer.
2.2. Biosorbent
The grape pomace used was collected in a winery in the city of Toledo - Paraná. Initially, the biomass was washed with distilled water and dried at 45 °C until constant mass. Then it was mechanically milled and the size fractions between 0.14 and 1.4 mm were selected.
ACCEPTED MANUSCRIPT 2.3. Biosorbent characterization
The grape pomace was characterized by determining the point of zero charge (pHpzc) and
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2.3.1. Determination of the point of zero charge (pHpzc)
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using the Infrared Fourier Transform Spectroscopy (FTIR).
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The zero charge point (pHpcz) of the biosorbent is an important feature for understanding the adsorption process. This parameter correspond to the pH at which the surface charge of the
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biosorbent is null.
According to Davranche et al. (2003), the surface of the material presents either positive,
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negative or zero charge according to the pH of the solution in which it is found, being able to behave as an anion or cation exchanger. The adsorption of cations is favored at a pH>pHpcz,
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whereas the anion adsorption is favored at a pH
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To determine the pH where the surface charge of the biosorbent is zero (pHpzc), the methodology described by Davranche et al. (2003) was used.
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We employed two flasks initially containing a suspension of 5 g of adsorbent and 100 ml NaNO3 (0.1 mol L-1). Then one suspension was titrated with HNO3 (0.1 mol L-1) and the
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other with NaOH (0.1 mol L-1) in the pH range between 2 and 12. The total surface charge of the adsorbent was calculated according to Equation 1.
q
C A C B OH H CS
(1)
where q is the net surface charge of the biosorbent (M), the variables CA and CB are the concentrations of acid and base (M), respectively; [OH-] and [H+] are the concentrations of
ACCEPTED MANUSCRIPT these ions in the suspension (M) and Cs is the concentration of the adsorbent in the suspension (g L-1).
2.3.2. FTIR analysis
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The absorption spectroscopy analysis in the Fourier Transform Infrared (IR Frontier model,
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brand Perkin Elmer) was performed to determine the functional groups on the surface of the adsorbent. The FTIR spectra of the grape pomace before and after the adsorption of the dye
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Brown KROM KGT were obtained to evaluate possible changes resulting from the process.
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Analyses were performed using the method of KBr pellets, which were prepared by homogeneously mixing and milling 1 mg of the sample and 100 mg of KBr by pressing in a 5
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ton die, both previously dried at 105°C. The FTIR spectrum was obtained in the range of
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2.4. Pigmentation assay
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4000-450 cm-1 with resolution of 4 cm-1.
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In order to assess the possible release of pigment from the grape pomace in the solution,
to 10).
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adsorption experiments were conducted using distilled water at different initial pH values (1
An amount of 0.25 g of biosorbent and 50 mL distilled water were mixed and maintained under constant stirring at a speed of 90 rpm and at a controlled temperature of 25 °C. After a period of 24 hours, the samples were centrifuged (3000 rpm, 10 min) and the absorbance of the residual liquid phase was determined by UV-Vis spectrophotometry at A438nm.
2.5. Preliminary tests
ACCEPTED MANUSCRIPT
Preliminary tests were based on the investigation of operational parameters such as initial pH of the solution (1 to 10), particle size of the biosorbent (0.14 - 0.18, 0.18 - 0.59, 0.59 – 1.4 and 0.14 to 1.4 mm) and the adsorption temperature (25, 40 and 55 °C). Adsorption experiments were performed in batch system and in duplicate. In 125 ml
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Erlenmeyer flasks, 0.25 g of biosorbent and 50 ml of dye solution Brown KROM KGT, with
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initial concentration of 100 mg L-1 were added. The mixture was held under constant stirring
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(90 rpm) on an orbital shaker table at a controlled temperature for 24 h. After this period of contact, aliquots of the solution were separated from the adsorbent by centrifugation at 3000
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rpm for 10 min. The analysis of the final concentration of the dye present in solution was performed by UV - Vis spectrophotometry at A438 nm.
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For the adsorption studies evaluating the influence of the initial pH of the solution, particle size between 0.14 and 1.4 mm was used at 25 oC. In the tests related to the influence of
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temperature, particle size between 0.14-1.4 mm was used with the initial pH resulted from the
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previous test. And for the influence of the particle size, the tests were based on the initial temperature and pH indicated in the previous tests.
q
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Equation 2.
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The amount of dye adsorbed by the pomace was calculated as the mass balance described in
(C 0 - C)V m
(2)
where q (mg g-1) is the amount of dye adsorbed by the pomace, C0 and C (mg L-1) are the initial and final concentrations of dye in the solution, respectively, V (mL) is the solution volume and m (g) is the sorbent mass used in each test.
ACCEPTED MANUSCRIPT 2.6. Kinetic study
The kinetic study was carried out by adsorption experiments performed in the best operating conditions indicated in the preliminary tests. An amount of 0.25 g of adsorbent and 50 ml of dye solution with an initial concentration of
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100 mg L-1 were mixed. The mixture was stirred constantly at 90 rpm under controlled
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temperature.
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Samples were collected at preset intervals between 5 min and 36 h. At the end of each test, solution aliquots were taken, which were submitted to centrifugation. Then, the dye
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concentrations were determined by UV - Vis spectrophotometry (A438 nm). The adsorption
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capacity of the grape pomace is determined by the mass balance expressed in Equation 2.
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2.6.1. Kinetic parameters determination
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The evaluation of the kinetics of dye adsorption by grape pomace was performed by the pseudo first order, pseudo second order and Elovich models.
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The kinetic model of pseudo first order, described by Lagergren (1898), is shown in Equation
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3, which characterizes the process of adsorption by occupying an active site of the adsorbent.
q(t) q eq (1 e k1t )
(3)
where q (t) and qeq correspond to the color removal ability in time t and at equilibrium (mg g1
), respectively, and k1 refers to the rate constant (h-1).
The model of pseudo second order, which requires chemisorption, is shown in Equation 4 (Ho and McKAY, 1998).
ACCEPTED MANUSCRIPT q(t)
2 q eq k2 t
(4)
1 q eq k 2 t
where k2 is the rate constant (mg g-1 h-1). In Equation 5 the model of Elovich is shown, which is suitable for chemical adsorption
1 1 ln a ln t
(5)
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q(t)
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processes in systems with heterogeneous surfaces (Chien and Clayton, 1980).
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where α is the adsorption rate (mg g-1 h-1) and β is a parameter related to the activation energy
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(mg g-1).
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2.7. Equilibrium study
Again, the ratio of 0.25 g of adsorbent to 50 mL of dye solution was used with stirring at 90
to 1500 mg L-1.
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rpm and temperature controlled. The initial concentration of the solution was varied from 10
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After 24 h of contact, the samples were centrifuged and the determination of the residual dye concentration was realized by UV-Vis spectrophotometry at A438.
2.7.1. Equilibrium parameters determination
Based on the ratio between the adsorption capacity of the grape pomace and the equilibrium concentration, the equilibrium data were evaluated by isotherm models commonly employed in the study of biosorption that enable the assessment of the nature of the adsorption process.
ACCEPTED MANUSCRIPT The Langmuir and Freundlich isotherms are shown in Equations 6 and 7, respectively.
q eq
q maxbC eq
(6)
1 bC eq
q eq k F C eq
(7)
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1/ n
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where qmax (mg g-1) corresponds to the maximum dye adsorption capacity, qeq (mg g-1) to the equilibrium dye adsorption capacity, Ceq (mg L-1), b (L mg-1) to the Langmuir constant, kF (L) to the Freundlich constant in (dimensionless) a constant that characterizes the adsorption
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1
intensity.
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The Langmuir isotherm indicates a monolayer adsorption on an homogeneous surface, with energy identical adsorption sites (Langmuir, 1918) while the Freundlich isotherm indicates
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multilayer adsorption in systems with heterogeneous surfaces (Freundlich, 1906).
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In the literature, some empirical modifications of these isotherms can be found and are presented in Table 1, where qmax (mg g-1) corresponds to the maximum capacity of the dye
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adsorption, qeq (mg g-1) to dye the adsorption capacity in the equilibrium, Ceq (mg L-1) to the dye concentration at the equilibrium, b (L mg-1) is the Langmuir constant, kF (L-1) is the
adsorption.
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Freundlich constant and n (dimensionless) is a constant that characterizes the intensity of the
From the models shown in Table 1, the constants KRP, aRP, bS, NS, bT and nT are the adjustable parameters of the models, being KRP, nS and nT values between 0 and 1. Another isotherm used was the Temkin, which may be considered suitable for monolayer chemisorption process, being represented by Equation 8 (Temkin, 1981).
ACCEPTED MANUSCRIPT q eq B ln( k T ) B ln( C eq )
(8)
where kT (L mg-1) is the bound equilibrium constant and B (dimensionless) is the constant of the model that takes into account the heat of adsorption.
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The Dubinin - Radushkevich isotherm is characterized by allowing the distinction of physical or chemical adsorption, additionally considering the effect of temperature. This isotherm is
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similar to the Langmuir model, however, it does not assume homogeneous surface or constant
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2 1 q max exp RT ln 1 Ceq
(9)
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q eq
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potential energy and it is represented by Equation 9 (Radushkevich and Kolganov, 1967).
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where β is the adsorption energy constant (mol2 kJ-2), T is the temperature (K) and R is the
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ideal gas constant (8.314 J mol-1 K-1).
By means of Equation 10, the Dubinin - Radushkevich constant, β, is related to the average energy of sorption (E), which is characterized by the free energy involved in the transfer of 1
E
AC
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mole of solute from the solution to the surface of the adsorbent (Dotto et al., 2011).
1 2
(10)
2.8. Thermodynamic study
The evaluation of the thermodynamic parameters of the sorption process was performed through the temperature effect analysis and equilibrium constants.
ACCEPTED MANUSCRIPT Therefore, the change in the Gibbs free energy (ΔG°), the change in the enthalpy (ΔH°) and the change in the entropy (ΔS°) system were evaluated. The relationship between these energies can be represented by Equation 11 (Kumar et al., 2008).
G H TS
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(11)
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The Gibbs energy variation indicates the degree of spontaneity of the adsorptive process. Positive values for this parameter indicate a non-spontaneous process, and the negative values
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are characteristic of spontaneous processes, or thermodynamically favorable process where
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the adsorbate has high affinity with the adsorbent. As reported by Kumar et al. (2008), the ΔG
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° can be determined by Equation 12.
(12)
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G RT ln k L
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where kL is the thermodynamic equilibrium constant, T is the absolute temperature of the system (K) and R is the universal gas constant.
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However, kL is related to the activity coefficient and ionic strength of the solute in the medium. When considering the small ionic strength in organic compounds, such as the dyes,
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this property is discarded. Thus, the kL constant can be reasonably approximated by the affinity constant of the Langmuir isotherm (Liu, 2009). However, this approach considers the activity coefficient equal to unity, which has validity for neutral or weakly charged adsorbates. The thermodynamic parameters ΔH° and ΔS° are determined by the linear fit of ΔG° as a function of the temperature, which can be estimated by the Van't Hoff relationship presented in Equation 13 (Wang, 2012).
ACCEPTED MANUSCRIPT
ln k L
S H R RT
(13)
As reported by Wang et al. (2005) and Wang (2012) positive values of ΔH° indicate
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endothermic adsorption process, and negative values are characteristic of exothermic processes, promoting the release of energy. Moreover, the enthalpy variation values between -
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40 and -800 kJ mol-1 characterizes the chemical adsorption process, whereas in the range of 0
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and -40 kJ mol-1 it represents the physical adsorption heats (Wang, 2012, El-Bindary et al. 2014, Monte Blanco et al., 2017).
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The negative ΔS° parameter suggests the decrease of randomness at the solid/liquid interface
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due to interactions between the adsorbent and adsorbate. If the difference of entropy is positive it indicates that there is an increase in the system disorder in the solid/liquid interface
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during the adsorption of the dye (Zhang et al., 2011, Zhang et al., 2015).
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3. RESULTS AND DISCUSSIONS
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3.1. Biosorbent characterization
3.1.1. Determination of the point of zero charge (pHpzc)
The pHpcz value of the biosorbent grape pomace was obtained from the evaluation of the net surface charge of the adsorbent as a function of the initial pH of the solution, as shown in Figure 1.
ACCEPTED MANUSCRIPT It was observed in Figure 1 that the net surface charge of grape pomace decreases with increasing pH. The pHpcz at which the net surface charge of the grape pomace is zero was observed at pH 3.0. The grape pomace surface has a predominantly positive character based on the behavior of net surface charge, at pH values below 3.0. On the other hand, at pH values greater than 3.0, the
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biosorbent presented negative net charge.
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Considering that at pH values below pHpcz, the surface of the adsorbent was positively
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charged it is suggested the sorption of pollutants with an anionic character through electrostatic attraction. In contrast, the adsorption of substances having cationic characteristics
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presented as negatively charged (pH> 3.0).
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is enhanced at a pH greater than pHpcz because, in this case, the surface of the adsorbent was
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3.1.2 FTIR analysis
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By the analysis of the FTIR spectra, the characterization of the functional groups present in the grape pomace structure was made, before and after the dye adsorption process at the
in Figure 2.
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concentration of 100 mg L-1 initial pH of 2.0 and particle size mixture. The spectra are shown
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In Figure 2, it appears that the main spectral bands identified in the grape pomace structure can be attributed to vibrations in the stretching N-H and asymmetric O-H at 3400 cm-1, C-H stretch indicated by bands in the range of 2925 and 1739 cm-1 (Mona et al., 2011; Ping et al., 2014), and according to Pala et al. (2014) in the 1740 cm-1 region, the presence of C=O stretching from carboxylic groups and esters is indicated. As reported by Danish et al., peak at around 1600 cm−1 and at 1700 cm−1 evidence the presence of aromatic ring with carboxylate groups.
ACCEPTED MANUSCRIPT The bands observed in the range 1450 to 1612 cm-1 can be related to the C=C stretching of aromatic groups, lignin and C-H vibration from CH2 and CH3 (Manara et.al., 2014; Pala et al., 2014). Another band observed in the FTIR spectrum of the grape pomace was at 1035 cm-1 and it may be attributed to C-O stretching (Ping et al., 2014). In the scale enlargement in the range between 1400 and 1800 cm-1, shown as a detail in
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Figure 2, one can observe some subtle changes in the spectra after the dye adsorption. Small
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changes were observed in the peaks shape as well as a band displacement at 1739-1745 cm-1,
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1641-1646 cm-1, 1518-1533 cm-1 and 1452-1456 cm-1. These changes may indicate that the
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functional groups assigned to these bands are involved in the dye adsorption process.
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3.2. Pigmentation test
The pigmentation test was performed to evaluate the occurrence of detachment of the grape
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pomace pigments that could interfere with the solution absorbance values. The results of the
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tests performed in distilled water at different initial pHs are shown in Table 2. It is observed in Table 2 that the solutions of initial pH above 2.0 had their pH changed during
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the time of contact between the biosorbent and distilled water, indicating final pH between 5.0 and 7.5. In this pH range of the medium, the net surface charge of the grape pomace ranges
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from zero to mildly negative.
According to Drosou et al. (2015), the phenolic compounds responsible for the natural pigmentation of the waste from wine production are the anthocyanins. These are characterized as highly unstable and easily liable to deterioration by environmental factors such as light, pH and temperature molecules. They are stable at acidic pH because pHs greater than 4.0 can degrade anthocyanins (Xu et al., 2015).
ACCEPTED MANUSCRIPT In this context, the increase in the initial pH may degrade this type of substance to alter the color of the residual solution. Due to the effect of initial pH it was necessary to take into account the effect of release of pigments in the solution and the interference that this causes in the absorbance values of the dye solution after contact with the biosorbent was corrected by
PT
using the zero in the experimental tests.
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3.3. Preliminary tests
In the study of the influence of the initial pH on the Brown KROM KGT dye adsorption
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process, the response that changes in the initial pH of the solution promoted in terms of removal ability was evaluated and the results are shown in Table 3.
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It is observed in Table 3, that there was a significant decrease in the amount of dye adsorbed for initial pH values above 2.0. By evaluating the results at pH values above 2.0, it is
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observed that the final pH of the solution has values around 6.6, which may alter the
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conditions of electrostatic interactions of the surface with the solution at pH of the liquid phase above the pHpcz (3.0).
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The best removal capacity was attributed to the initial pH 2.0 (20.0 ± 0.1 mg g-1). Considering the information obtained for the pHpcz (Figure 1), it can be said that in the best adsorption
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condition, the net charge on the surface of grape pomace presented a positive character. This suggests that the dye Brown KROM KGT, may have anionic characteristics, enabling the attraction between biosorbent and adsorbate. Similar behavior was also reported by El Bindary et al. (2014), which state that the high adsorption capacity of dye onto biosorbent in highly acidic solutions is due to the strong electrostatic interactions between its adsorption site and dye anion.
ACCEPTED MANUSCRIPT Carboxylic, amino, amide, esters groups are the major binding sites identified by the analysis of the FTIR spectra for adsorption of the dye in the grape pomace. These groups can be ionized when the pH varies. At low pH values, the surface sites are protonated, and the surface becomes positively charged, while the ionizable groups lose their protons and the surface becomes negatively charged at high pH values. Thus, it is suggested that surface
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protonation occurs with a positive net charge at surface, as a function of the increase of the
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dye adsorption with the reduction of pH, specifically for pHs lower than 3.0 (pHpcz).
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When investigating the adsorption temperature, in conditions of particle size between 0.14 and 1.4 mm, initial pH 2.0, the parameter of interest was varied at 25, 40 and 55 °C, and the
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removability values were 20.0 ± 0, 1 mg g-1, 19.9 ± 0.1 mg g-1 and 19.4 ± 0.4 mg g-1, respectively. Thus, it can be stated that there is considerable influence of temperature on the
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removal of dye in solution with an initial concentration of 100 mg L-1, the variation being less than 5%. Considering this fact, the room temperature of 25 °C was used in the experiments.
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In the evaluation of the influence of particle size with adsorption tests with initial pH 2.0 and
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room temperature, it was observed that for the granulometric fractions 0.14 - 0.18, 0.18 - 0.59 and 0.14 - 1.4 mm, the dye removal capacity was about 20 mg g-1, with a variation of less
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than 5%. However, for the particle diameter range from 0.59 to 1.4 mm, the adsorption capacity was reduced (15.6 ± 0.3 mg g-1), possibly due to the heterogeneity of size of the solid
AC
particles, and to the presence of higher amount of grape seeds, which for this specific particle size remained whole. Thus, the preliminary tests indicated the use of granulometric mixture (0.14 - 1.4 mm), since it enables good removability, without the need for excessive grinding of the adsorbent and the best use of the biosorbent. The adsorption capacity obtained for the initial pH 2.0, mixture of all granulometric fractions and room temperature corresponds to a removal rate of approximately 94%.
ACCEPTED MANUSCRIPT 3.4. Kinetic study
In Figure 3 the experimental data of the adsorption kinetics obtained for the grape pomace are shown. The kinetic models of pseudo-first order, pseudo-second order and Elovich were adjusted for the evaluation of the experimental data.
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The kinetic behavior, which can be seen in Figure 3, showed high removal rates early in the
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process, reaching the equilibrium at around 12 h, with removal around 93%. Among the evaluated models, it appears that the model of pseudo first order was the one that best fit to
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the experimental data (R2 = 0.9958), with an adsorption capacity of 19.9 ± 0.2 mg g-1, as
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shown in Table 4.
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3.5. Equilibrium study
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In Figure 4, the equilibrium data obtained for the adsorption process at temperatures of 25, 35
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and 45 °C are presented, considering the adjustment of the Langmuir isotherm. Isotherms commonly used in adsorption studies were fitted to the experimental equilibrium
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data for the temperatures 25, 35 and 45 °C, and the model parameters are shown in Table 5. As seen in Table 5, the Langmuir isotherm was the one that best fit to the equilibrium data
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(R2 = 0.9930, 0.9960 and 0.9976) with maximum adsorption capacity around 180, 190 and 213 mg g-1 for the temperatures 25, 35 and 45 °C respectively. Thus, it is suggested that the dye adsorption is monolayer, with a homogeneous surface. El-Bindary et al. (2014) further emphasize that in the Langmuir model it is assumed that each dye molecule occupies a specific active site, which is unavailable for the adsorption process. Based on the hypotheses of the model, the adsorbent presents a finite capacity to capture the adsorbate, being this the maximum capacity of saturation (qmax), with values presented in
ACCEPTED MANUSCRIPT Table
5.
Despite the slight increase in the removal capacity as a function of temperature increase, the room temperature was chosen as working condition. Considering that the constants from the models of Redlich-Perterson (g), Sips (ns) and Toth (nT), which correspond to the heterogeneity of the solid, were equal to 1, the models are
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reduced to the Langmuir model, as shown in Table 5.
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The adjustment of the Dubinin - Radushkevich model to the experimental data also brought
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additional information on the forms of physical or chemical adsorption, additionally considering the effect of temperature.
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Based on Eq. (10), the mean sorption energy, E (kJ mol-1), was determined to be useful for obtaining information on the mechanisms of the adsorption process. If the E value is between
1
MA
8 and 16 kJ mol-1, the adsorption is classified as chemistry. On the other hand, if E <8 kJ mol, it can be suggested that the physical adsorption process occurs (Matouq et al., 2015).
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According to data from Table 5, it can be observed that for the three temperatures evaluated,
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the mean sorption energy value was lower than 8 kJ mol-1. Thus, it is suggested that the
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sorption mechanism for the grape pomace involves the process of physical adsorption.
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3.6. Thermodynamic study
The estimation of the thermodynamic parameters was performed based on Equations 11 and 13, and the values of ΔG°, ΔH° and ΔS° are shown in Table 6. In Table 6, it is observed that the variation in the Gibbs free energy for the different temperatures resulted in negative values, which suggests a thermodynamically favorable process. It is also observed in Table 6 that the negative value of ΔH°, between 0 and -40 kJ mol-1, suggests an exothermic process and the physical nature of the dye adsorption.
ACCEPTED MANUSCRIPT The physical nature of the adsorption process was also indicated by the average adsorption energy obtained through the Dubinin - Radushkevich isotherm, indicating that the adsorption has a low potential barrier. The positive value of ΔS° indicates an increase in the degree of disorganization (randomness) at the liquid-solid interface during the sorption process.
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According to Wang (2012), the positive entropy variation may also indicate some structural
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changes in the adsorbate and adsorbent and a good affinity of the adsorbent for the dye. The
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author further adds that the relationship between the increase in dye adsorption and the increase in temperature may be linked to an increase in the intra-particle diffusion rate of
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adsorbate, since diffusion is an endothermic process.
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4. CONCLUSION
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Based on the results obtained in preliminary tests, it can be concluded that the adsorption of
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the dye by the grape pomace with initial dye concentration of 100 mg L-1 is strongly influenced by the initial pH of the solution, being the best results observed for initial pH of
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2.0. It was verified that the particle size and the temperature of the medium do not significantly affect the dye adsorption capacity, and thus the particle size between 0.14-1.4
AC
mm and the temperature of 25 °C were used. When evaluating the adsorption kinetics, it was observed that the equilibrium time was about 12 h following the pseudo-first order model. At the equilibrium study, the Langmuir isotherm was the one that best represented the process with maximum adsorption capacity of 180.2 ± 3.2 mg g-1 at 25 °C, indicating monolayer adsorption and homogeneous surface. The thermodynamic parameters determined for the adsorption process is question indicated that it is favorable, exothermic and accompanied by an increase in the randomness at the solid/liquid interface. Thus, it is concluded that the grape
ACCEPTED MANUSCRIPT pomace showed potential application as a biosorbent in the treatment of industrial waste containing dyes. Based on the data obtained for the batch system, the study of the adsorption of this dye by the grape pomace should be continued by means of bed column adsorption studies. In this way, the process is evaluated in a continuous system in order to determine other pertinent parameters of operation. Finally, after performing the study on a laboratory
PT
scale, it should be replicated to the pilot scale, maintaining the experimental conditions that
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provided the best results for the reduced scale. In this way, it is sought the approximation of
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an industrial process as a polishing process for the treatment of large volumes of waste.
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Acknowledgments
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The authors thank CNPQ and Araucaria Foundation for the financial support of this study.
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Mona, S., Kaushik, A., Kaushik, C.P. 2011. Biosorption of reactive dye by waste biomass of Nostoc linckia. Ecol. Eng., 37, 1589–1594.
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Monte Blanco, S. P. D., Scheufele, F. B., Módenes, A. N., Espinoza-Quiñones, F. R., Marin, P., Kroumov, A. D., Borba, C. E., 2017. Kinetic, equilibrium and thermodynamic phenomenological modeling of reactive dye adsorption onto polymeric adsorbent. Chem. Eng. J., 307, 466–475.
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Noreen, S. E Bhatti, H.N. 2014. Fitting of equilibrium and kinetic data for the removal of Novacron Orange P-2R by sugarcane bagasse. J. Ind. Eng. Chem., 20, 1684-1692.
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ACCEPTED MANUSCRIPT TABLES Table 1. Empiric modifications of the Langmuir and Freundlich isotherms. Model Aplication Redlich-Peterson1 Hterogenous surface
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Langmuir-Freundlich combination
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Multilayers in heterogenous surfaces
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Font: 1[35, 36, 37] Redlich and Peterson (1959); 2Sips (1948); 3Toth (1971).
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Table 2. Effect of the biosorbent pigmentation on the distilled water at different pH. pHinitial pHfinal q (mg g-1) 1.0 1.5 3.0 ± 0.4 2.0 2.1 1.8 ± 0.3 4.0 5.2 10.9 ± 1.0 6.1 7.5 6.7 ± 1.2 8.1 6.8 5.6 ± 0.4 10.0 5.7 7.1 ± 0.3
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Table 3. Effect of the pH in the capacity of the dye adsorption with initial concentration of 100 mg L -1 (T = 25°C, 90 rpm, t = 24 h, granulometric mixture). pHinitial pHfinal q (mg g-1) 1.0 1.2 19.0 ± 0.2 2.2 2.1 20.0 ± 0.1 4.0 6.7 1.3 ± 0.3 6.1 6.6 2.0 ± 0.7 8.2 6.6 1.3 ± 0.4 10.0 6.8 1.0 ± 0.4
Table 4. Estimated parameters of kinetic models and fitting parameters for dye sorption data. Model Pseudo-first order
Adjusted parameters qe (mg g-1) 19.9 ± 0.2 -1 k1 (h ) 0.88 ± 0.03
Pseudo-second order
qe (mg g-1) k2 (g mg-1 h-1)
21.5 ± 0.42 0.056 ± 0.01
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a (mg g-1 h-1) b (g mg-1)
91.2 ± 32 0.29 ± 0.03
ACCEPTED MANUSCRIPT Table 5. Adjusted values of modelling parameters for a set of tested isotherm models representing equilibrium adsorption data
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35 °C 190.5 ± 3.5 0.016 ± 0.001 0.9960 14.14 ± 2.4 2.4 ± 0.2 0.9616 3.09 ± 0.2 0.016 ± 0.001 1 0.9960 190.5 ± 3.5 0.016 ± 0.001 1 0.9960 190.5 ± 3.5 0.016 ± 0.001 1 0.9960 22.65 ± 2.9 1.11 ± 0.5 0.7961± 0.5 153.2 ± 9.7 3.71 ± 1.1 0.37 0.8981
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25 °C 180.2 ± 3.2 0.024 ± 0.001 0.9930 19.6 ± 3.6 2.9 ± 0.3 0.8884 4.37 ± 0.2 0.024 ± 0.001 1 0.9930 180.2 ± 3.2 0.024 ± 0.001 1 0.9930 180.2 ± 3.2 0.024 ± 0.001 1 0.9930 30.71 ± 1.6 0.43 ± 0.06 0.9502 151.2 ± 7.1 1.84 ± 0.3 0.52 0.9182
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Langmuir
Parameters qmax(mg g-1) b (L mg-1) R² kF(L-1) n R² krp (L g-1) arp (L mg-1) g R² qm (mg g-1) ks (L mg-1) ns R² qm(mg g-1) bt(L mg-1) nT R² B (adim) kT (L mg-1) R² qm(mg g-1) β (mol2kJ-2) E (kJ mol-1) R²
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Isotherms
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Table 6. Values of the thermodynamic parameters. ΔG ΔH ΔS T (K) (kJ mol-1 K-1) (kJ mol-1 K-1) (J mol-1 K-1) 298 -22.83 308 -22.57 -16.23 21.62 318 -23.28
45 °C 213.6 ± 2.9 0.0161 ± 0.0008 0.9976 15.1 ± 3.3 2.4 ± 0.2 0.9422 3.44 ± 0.13 0.0161± 0.0008 1 0.9976 213.6 ± 2.9 0.0161 ± 0.0008 1 0.9976 213.6 ± 2.9 0.0161 ± 0.0008 1 0.9976 35.10 ± 2.15 0.370 ± 0.06 0.9562 173.1 ± 9.1 3.60 ± 0.90 0.37 0.9210
ACCEPTED MANUSCRIPT FIGURE CAPTIONS Figure 1. Distribution of the net surface charge of the grape pomace as a function of pH.
Figure 2. FTIR spectrum of the grape pomace (a) before and (b) after the adsorption of the dye with initial concentration of 100 mg L-1.
(pHinitial = 2.0, T = 25°C, granulometric mixture, 90 rpm).
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Figure 3. Kinetic data for the process of dye adsorption with initial concentration of 100 mg L-
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Figure 4. Equilibrium data and Langmuir profile for the Brown KROM KGT adsorption at
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the temperatures of (a) 25, (b) 35 e (c) 45 °C (pHinitial = 2.0, granulometric mixture, 90 rpm).
ACCEPTED MANUSCRIPT Highlights
Use of grape pomace waste for removal of dye, suggesting an adequate management of this type of waste.
Possibility for treatment of effluent generated in the dyeing of leather using a lowcost process.
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Evaluation of the appropriate operating parameters of the system by different kinetic and
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Characterization of the evaluated biosorbent material.
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equilibrium models.
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