Modified coconut shell fibers: A green and

0 downloads 0 Views 1MB Size Report
Dec 29, 2011 - G Model. CEJ 8851 1–11. Chemical Engineering Journal xxx (2012) xxx–xxx. Contents ..... MCB and raw coconut powders by using 50 mg of each sample in. 139 ..... methyl group's vibrations of ligninocellulose present in the solids,. 288 ..... 5.325. R2. 0.722. 0.761. 0.768. 0.771. 0.585. 0.637. 0.633. 0.666.
Our reference: CEJ 8851

P-authorquery-v9

AUTHOR QUERY FORM Journal: CEJ

Please e-mail or fax your responses and any corrections to: E-mail: [email protected]

Article Number: 8851

Fax: +353 6170 9272

Dear Author, Please check your proof carefully and mark all corrections at the appropriate place in the proof (e.g., by using on-screen annotation in the PDF file) or compile them in a separate list. Note: if you opt to annotate the file with software other than Adobe Reader then please also highlight the appropriate place in the PDF file. To ensure fast publication of your paper please return your corrections within 48 hours. For correction or revision of any artwork, please consult http://www.elsevier.com/artworkinstructions. Any queries or remarks that have arisen during the processing of your manuscript are listed below and highlighted by flags in the proof. Click on the ‘Q’ link to go to the location in the proof. Location in article Q1 Q2 Q3 Q4 Q5 Q6

Query / Remark: click on the Q link to go Please insert your reply or correction at the corresponding line in the proof Please confirm that given names and surnames have been identified correctly. The country name has been inserted for the affiliations. Please check, and correct if necessary. Please check the telephone/fax number of all author, and correct if necessary. Please check the hierarchy of the section headings. Please note that all equations have been rekeyed as they were in picture format (or) they were corrupted. Please check that they are correct. To maintain sequential order, Eq. (17) has been changed to Eq. (16). Please check, and correct if necessary.

Thank you for your assistance.

G Model

ARTICLE IN PRESS Chemical Engineering Journal xx (2012) xxx–xxx

Contents lists available at SciVerse ScienceDirect

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

Graphical Abstract

Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions

Chemical Engineering Journal xx (2012) xxx–xxx

Ari Clecius A. de Lima, Ronaldo F. Nascimento, Francisco F. de Sousa, Josue M. Filho, Alcineia C. Oliveira∗ Adsorption isotherms for nitrate ions.

CEJ 8851 1

G Model

ARTICLE IN PRESS Chemical Engineering Journal xx (2012) xxx–xxx

Contents lists available at SciVerse ScienceDirect

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

Highlights

Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions

Chemical Engineering Journal xx (2012) xxx–xxx

Ari Clecius A. de Lima, Ronaldo F. Nascimento, Francisco F. de Sousa, Josue M. Filho, Alcineia C. Oliveira∗  Removal of inorganic anions from aqueous solution through batch process.  Characterizations by full factorial design, FTIR, elemental analysis, SEM and XRD.  Kinetics of adsorption and Freundlich, SIPS, Redlich–Peterson and Temkin models.  Modified coconut powder was efficient to remove nitrate, sulfate and phosphate.

CEJ 8851 1

ARTICLE IN PRESS

G Model CEJ 8851 1–11

Chemical Engineering Journal xxx (2012) xxx–xxx

Contents lists available at SciVerse ScienceDirect

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

Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions

1 2

3

Q1

4 5

Q2

Ari Clecius A. de Lima a,1 , Ronaldo F. Nascimento a,1 , Francisco F. de Sousa b,2 , Josue M. Filho b,2 , Alcineia C. Oliveira a,∗ a b

6

Universidade Federal do Ceará, Campus do Pici-Bloco 940, Brazil Universidade Federal do Ceará, Campus do Pici-Bloco 922, Departamento de Física, Fortaleza, Ceará, Brazil

7

a r t i c l e

8

i n f o

a b s t r a c t

9

Article history: Received 18 October 2011 Received in revised form 29 December 2011 Accepted 4 January 2012

10 11 12 13 14 15

The powder of green coconut shell (Coco nuscifera L.) was chemically modified and used to remove inorganic anions from aqueous solution through batch process. The solid was modified with ammonium quaternary salt (2-hidroxypropyltrimethyl ammonium chloride) and characterized by a full factorial design. The FTIR, elemental analysis, SEM and X-ray measurements were performed. FTIR analysis indicated that the coconut bagasse interacted with NH2 groups of the surfactant. Initial anion concentration, pH and adsorbent dosage were investigated in this study, as well as the kinetics of adsorption and isotherms for the modified coconut bagasse. Kinetics of adsorption was examined by means of three kinetic models, i.e., pseudo-first-order, pseudo-second-order and intraparticle diffusion models. Pseudosecond-order kinetic model showed good agreement with the experimental data. Data on equilibrium were evaluated by using Langmuir, Freundlich, SIPS, Redlich–Peterson, Temkin models. It was observed that the experimental data fits well to Langmuir, SIPS, and Redlich–Peterson equations. The results indicated that the modified coconut powder exhibited potential application for removal of nitrate, sulfate and phosphate from aqueous solutions. © 2012 Published by Elsevier B.V.

20

Keywords: Coconut powder Modifications Quaternization Anions adsorption

21

1. Introduction

22

The increasing levels of chloride, fluoride, sulfate and nitrate ions in drinking and groundwater due to natural and anthropogenic activities has been recognized as one of the major problems worldwide [1–5]. This imposes a serious threat to human health and environmental issues. Thus, a renewed interest in the ions removal from domestic and industrial wastewaters has been greatly increased [1–16]. Moreover, technologies for ions removal from water are of great relevance in waste treatment processes, which aim to achieve efficient strategies to obtain acceptable levels of disposal of the aforesaid ions. Therefore, new research strategies for removal of SO4 2− , Cl− , NO3 − , F− and PO4 3− anions, such as precipitation [1–3], ion exchange [1,2,11], biologic and membrane processes [3–6], agro chemical [8] have been developed. According to the findings, these separation techniques suffer of drawbacks such as low binding capacity, depending on the composition of the solution.

16 17 18 19

23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Q3

∗ Corresponding author. Tel.: +55 85 3366 90 42; fax: +55 85 3366 99 80. E-mail address: [email protected] (A.C. Oliveira). 1 Tel.: +55 85 3366 90 42; fax: +55 85 3366 99 80. 2 Tel.: +55 85 3366 90 08; fax: +55 85 3366 90 08.

Indeed, ion exchange using resins, electrodialysis, and adsorption using activated alumina are non-selective because they develop unwanted by-products [6]. Among various methods used for ions removal from water, the adsorption processes are attractive and offers satisfactory results for the removal of SO4 2− , Cl− and NO3 − ions, in terms of cost, simplicity of design and operation [1,7]. Various conventional and non-conventional adsorbents have been evaluated for the removal of ions from groundwater, as shown elsewhere [1,17–20]. Active carbon is the most used adsorbent; however its low efficiency makes the use of carbon derivates in waste treatment unfeasible for the removal of the abovementioned ions. Hence, the replacement of active carbon by biomass-based adsorbents is aimed, provided that less environmental impact and low-cost technologies could be achieved [18–27]. Specifically, in Brazil about 1,860,697 t of coconut was produced in 2011, being 85% of this biomass by-product discarded in the environment [9,26]. From the environmental point of view, the disposal of this material as bulky wastes is a great problem which may lead to environmental and toxicological issues. Although the industrial use of coconut water and mesocarp is of great commercial interest in Northwestern Brazil, the widespread use of coconut shell is hampered by its short deterioration time, so that its use is limited to 1% by the industries [26]. New effluent treatment technologies have been developed in order to meet the legal requirements

1385-8947/$ – see front matter © 2012 Published by Elsevier B.V. doi:10.1016/j.cej.2012.01.037

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61

G Model CEJ 8851 1–11

ARTICLE IN PRESS A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx

2

regarding effluent disposal as well as reduce the operating costs of such processes [1,10,12]. In this context, modification of natural adsorbent (e.g., rice and sugar cane bagasses, shrimp waste, bench sawdust) has been studied for removal of ions, especially, phosphates, sulfates or nitrates [12,21,28]. It is well known that ligninocellulose material quaternization influences on the adsorption of anions from aqueous solution [22,23]. Upon using ligninocellulose, the anions present in the wastewaters could be adsorbed physical or chemically on the modified coconut solid bagasse surface by the new functional sites introduced in the modified coconut bagasse. This will enable the removal of the anions from the aqueous solutions, in particular PO4 3− , SO4 2− and NO3 − . Coconut shell has been investigated in the metal ions removal from solution aqueous [10], however, few studies have been devoted to the anions removal using this kind of adsorbent. In the present study, a new derivative obtained by the reaction between ammonium quaternarium salt (-chloride 2hydroypropyltrimethylammonium chloride) and coconut bagasse was used as low-cost adsorbent. The material was characterized by the physicochemical techniques and applied in the studies of batch adsorption. Adsorption isotherms and ion exchange modeling equilibria are widely studied to predict the relative affinities of ions and their distribution in the adsorbent-solution system during the purification process [2]. Thus, we use adsorption isotherms to investigate the removal of PO4 3− , SO4 2− and NO3 − anionic species from aqueous solutions by a modified coconut adsorbent through the Langmuir, Freundlich, SIPS, Redlich–Peterson, and Temkin single-component adsorption isotherms. The sorption parameters and the fitting of the models are determined by nonlinear regression and discussed.

62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91

92

2. Experimental

93

2.1. Modification of coconut shell surface

113

Coconut shell raw material was provided by Embrapa Agroindústria Tropical (CNPAT, Brazil). According to Carrijo [26], the material was processed in a blender (Arno) to obtain the powder. The powder was then pressed into a PRH steel mill to remove the excess of water. After sieving the product, both powder and fiber were obtained. Finally, the coconut powder was washed with water and dried at room temperature whereas the fiber was used for handicrafts production. Prior to the chemical modification, the dried coconut powder was pretreated with 400 mL of a 1% calcium carbonate solution (CaCO3 , Vetec). Then, the solid was washed thoroughly and dried in an oven at 60 ◦ C for 2 h. The powder was chemically modified by adding 1.2 mL of a 5 mol L−1 sodium hydroxide solution (NaOH, Vetec) per gram of bagasse, followed by rest for 1 h. About 1 mL of 3-chloride 2-hydroypropyltrimethylammonium chloride solution (Quat 188, Down Chemistry, 69%) was added to the treated powder bagasse under room pressure in order to favor a stronger interaction between the reactants and the coconut bagasse. The abovementioned methodology was used to modify the surface of the adsorbent, by removing the lignocelluloses constituents [26].

114

2.2. Modified coconut powder characterizations

94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112

115 116 117 118 119 120 121

Q4

Both raw and modified coconut powder (MCB) were characterized by Elemental Analysis, X-Ray Diffraction (XRD), N2 adsorption–desorption measurements, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Scanning Electron Microscopy (SEM). Elemental analysis was carried out in a CHN 2400 device (PerkinElmer) (2400 model, Perkin Elmer) at University of São Paulo, Brazil.

The samples were treated in oxygen atmosphere to remove the halogen and sulfur compounds, prior to analysis. XRD experiments (DMAXB model, Rigaku) were carried out using CuK␣ radiation, 40 kV and 25 mA. Crystal structures were determined using wide-angle diffraction patterns in the 2 = 2◦ –25◦ range. Surface area and pore volume were determined by analysis of nitrogen adsorption–desorption isotherms in a Asap 2000, Micromeritics equipment. The raw and modified coconut powders (MCB) were pretreated overnight at 150 ◦ C under vacuum. Specific surface areas were calculated by using the BET equation. IR spectra of the solids were obtained by a Prestige FTIR spectrometer (Shimadzu, Japan) in the 500–4000 cm−1 range. About 1 mg of the powdered fiber was mixed with 200 mg of vacuumdried IR grade KBr and submitted to a pressure of 8 t. TGA experiments were carried out using a TGA/DSC 50 device (Shimadzu, Japan). The measurements were performed on both MCB and raw coconut powders by using 50 mg of each sample in an aluminum pan. The experiment was performed under air flow in the 27–1000 ◦ C range, using a heating rate of 5 ◦ C min−1 . A XMU Tecsan (Vega) SEM microscope was used to characterize morphological aspects of the coconut bagasse. Previously, the samples were sputtered with gold to have a conductor material. The solids were then ultrasonically dispersed in acetone and one drop of the suspension was evaporated on a carbon-coated copper grid. Zeta potential analyses were performed by using 0.1 g of the MCB in 50 mL anions solution. The samples were placed in vials and the pH values were adjusted with either 0.1 mol L−1 chloride acid solution or 0.1 mol L−1 sodium hydroxide solution. Samples were taken from the supernatants. A Zetasizer Nano ZS instrument (Malvern, GBR) was used to measure the zeta potentials of all samples. 2.3. Preparation of the anions solutions

2.4. Adsorption studies

124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154

156 157 158 159 160

161

Preliminary experiments showed that the adsorption of the raw coconut bagasse is meaningless. Therefore, the experiments were performed with the MCB solid, as follows: about 10 mL aliquots of anions solutions ranging from 20.0 to 1000.0 mg L−1 were added to 0.1 g of the modified coconut powder adsorbent. To ensure that the equilibrium was totally reached, the solution was stirred during 4 h and the pH was adjusted with sodium citrate/citric acid buffer. The temperature is kept at 25 ◦ C. After the 4 h of equilibrium time, the concentration of the adsorbed anions was measured by ion chromatography by using a chromatograph (DIONEX, IC3000) coupled to an electrical conductivity detector (model AS40). The column possessing 30 cm × 4.0 mm I.D. was used at 30 ◦ C and 1917 psi and potassium hydroxide was the mobile phase. The amount of adsorbed anions (mg g−1 ) was calculated from the concentrations, before and after adsorption, as follows: Q5 (Ceq − C0 ) × V m

123

155

Nitrate, sulfate and phosphate anions solutions were obtained from sodium nitrate, sodium sulfate and sodium phosphate (CARLO ERBA), respectively, and were used as adsorbates. The solutions containing the abovementioned anions were prepared by dilution of multi-component stock solution at pH 7.

q=

122

(1)

where C0 and Ceq are the initial and final anions concentration in the solution (mg L−1 ), respectively. V is the solution volume (L) and m is the dry mass of the modified coconut powder (g).

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

162 163 164 165 166 167 168 169 170 171 172 173 174 175 176

177

178 179 180

ARTICLE IN PRESS

G Model CEJ 8851 1–11

A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx Table 1 Elemental analysis result.

3

Sum of the squares of the errors (ERRSQ) [29], Eq. (2):

Adsorbent

%C

%H

%N

Raw coconut bagasse Modified coconut bagasse

39.17 35.56

5.73 6.47

1.5 0.27

ERRSQ =

p 

(qe − qcal )2

217

(2)

Hybrid fractional error function (HYBRID) [25], Eq. (3):

194

The effect of pH on the adsorption studies was also investigated and did not have any significant impact on the adsorption rate of the anionic species under study. Also, MCB adsorbent was reused at least three times, in order to know its adsorption efficiency by using a 50 mg L−1 of nitrate, sulfate and phosphate anions solution. To investigate the feasibility of anions removal, recyclability studies of MCB were performed by treating the modified solid with hydrochloric acid, after the third cycle of anions removal (C3). Thereafter, the pH was adjusted to 2 and the solid was thoroughly washed with ultra pure water to eliminate the chloride ions. In addition, experimental data were applied to the models of Langmuir, Freundlich, SIPS, Redlich–Peterson and Temkin adsorption isotherms.

195

2.5. Full factorial design analyses

181 182 183 184 185 186 187 188 189 190 191 192 193

218

i=1



100  (qe − qcal ) P−n qe p

HYBRID =



219

2

(3)

220

i=1

Marquardt’s percent standard deviation (MPSD) [26], Eq. (4): MPSD =

p    qe − q cal

i=1

221

2

(4)

qe

Qui-quadrado (2 ), Eq. (5): 2 =

p   i=1

(qe − qcal ) qe

222

223

 2 (5)

where qe is the observation from the batch experiment i; qcal is the estimate from the isotherm; n is the number of observations in the experimental isotherm and P is the number of parameters in the regression model. The smaller function value indicates the best curve fitting; however, due to difference in scale among the error functions, it is necessary to normalize error functions (SNE) to perform the accurate [29–31].

224

225 226 227

200

The adsorption of nitrate, sulfate, and phosphate anions was carried out by means of a full factorial design. 23 essays were performed, and the responses obtained were used to analyze the effects of each variable on the adsorption of the anions. The variables and levels considered are displayed in Table 1.

201

2.6. Kinetic adsorption studies

3. Results and discussion

232

3.1. Physicochemical characterization of the coconut powder

233

208

The kinetic adsorption study of the anions was performed with each anion individually, by using a 100 mg L−1 solution. Approximately, 0.5 g of the adsorbent was added to 100 mL of each anion solution and kept under stirring for 24 h at pH 7. The kinetic adsorption of the anions was evaluated using the kinetic models, as follows: Pseudo-first order model, Pseudo-second order kinetic model and intraparticle diffusion kinetic model.

209

2.7. Non-linear regression analysis

196 197 198 199

202 203 204 205 206 207

210 211 212 213 214 215 216

3.1.1. Structural characterizations by DRX, FTIR and TGA analyses The characterization of both raw and modified coconut bagasse (MCB) is intended to verify the well succeeded modification of the solid surface by the quaternization process, as well as to evaluate the efficiency of the MCB toward the adsorption process. Before quaternization treatment, the amounts of ca. 39.2, 5.3 and 1.5%, respectively, for carbon, hydrogen and nitrogen are obtained by elemental analysis in the raw coconut bagasse. After the chemical modification, the amounts of the referred chemical entities increased, suggesting that the introduction of these elements on the overall composition of the solid has been achieved. The steps of the quaternization consist of successive chemical reactions such as epoxide formation (reaction (I)), interaction between the lignin cellulose and sodium hydroxide (reaction (II)) and the reaction between the epoxide and the lignin cellulose material (reaction (III)) [25]:

All the model parameters were evaluated by non-linear regression using Excel 2007 software (Microsoft, USA). The optimization procedure requires an error function to be defined in order to be able to evaluate the fit of the equation to the experimental data [24]. The correlation coefficient (R2 ), sum of the squares of the errors (ERRSQ), hybrid fractional error function (HYBRID), Marquardt’s percent standard deviation (MPSD) and qui-quadrado (2 ), were obtained as follow: HO

O

CH3

+

Cl

N H3C

Cl

+

Na

H3C

CH3

OH

O O

-

+

N

-

R

R

+

OH

NaOH

HCL (dil.)

+

+ N Cl

H3C

R R

CH3

-

CH3

O

229 230 231

234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249

Cl

CH3 Cl

-

CH3

O HO

Na

228

-

(I)

250

(II)

251

(III)

252

H3C +

N

CH3 Cl

-

CH3

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

ARTICLE IN PRESS

G Model CEJ 8851 1–11

A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx

4

a

Raw coconut bagasse

160

6 140

5

% weight loss

Intensity(ua)

120

100

80

4

3

60

2 40

1 20 2

4

6

8

10

12

14

16

18

20

22

0

2θ (degree)

b

100

200

300

400

500

600

700

800

900

800

900

o

Temperature ( C) MCB

160

6 140

5

% Weight loss

Intensity (ua)

120

100

80

4

3

60

2

40

20 2

4

6

8

10

12

14

16

18

20

22

2θ (degree)

253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276

1 0

100

200

300

400

500

600

700

Temperature (°C)

Fig. 1. XRD patterns of the (a) raw coconut powder and (b) modified coconut powder (MCB).

Fig. 2. Thermogravimetric analysis curves of the non-modified and modified coconut bagasses.

The abovementioned reactions describe the adopted experimental procedure which is used for the modification of MCB and the increased nitrogen content indicated that nitrogen groups were introduced into the adsorbent material. Additionally, Fig. 1 shows that the modification of the coconut bagasse does not result in changes in the amorphous feature of the solid, and this is a clear indication of the structural stability of the MCB. Indeed, the TGA analysis of the samples (Fig. 2) displayed distinct curves. The non-modified coconut bagasse has the first weight loss centered in 100 ◦ C, which is assigned to concomitant loss of volatile compounds and vaporization of physisorbed water [32]. The second event, from 150 to 350 ◦ C, is related to the residual ligninocellulose polymer decomposition at moderated temperatures [32], whereas the following event is a progressive weight loss and finally the stabilization of the solid is about 800 ◦ C. On the contrary, the MCB powder has three events of weight loss in temperatures higher than those of the non-modified coconut bagasse. The first event is centered at 100 ◦ C and is attributed to the loss of physisorbed water, as aforesaid and further confirmed by FTIR and N2 adsorption–desorption measurements. This could explain the slightly higher temperature range compared to that of the raw coconut bagasse. A minor weight loss (13%) in the 100–300 ◦ C range is observed and this could be related to the

decomposition of the quaternizant agent with no interaction with the solid surface, due to the large excess of the quaternizant agent used. The intensity of the third event (at 350 ◦ C) reveals that a strong interaction between the OH superficial groups of the solid and the quaternizant agent occurred. A condensation reaction has probably occurred on the coconut adsorbent solid surface; as a consequence, after eliminating the water, the stabilization of the solid has been achieved at 600 ◦ C. Fig. 3 shows the stretching of the O H and C H groups at 3379 and 2990 cm−1 , respectively [33]. These vibrations are found in both solids and were attributed to physisorbed water and to methyl group’s vibrations of ligninocellulose present in the solids, in agreement with the TGA results. In case of MCB, FTIR bands are shifted to higher frequencies, e.g., 3462 and 2908 cm−1 , which indicates the occlusion of water in the pores of the solid. This is a sound proof of the ligninocellulose polymer structure modification, which is consistent with the TGA and elemental analysis results. Additional bands appear in MCB at 2095 and 1466 cm−1 and these vibrations are attributed to the quaternary methyl ammonium groups of the quaternizant agent [33]. The solid lattice vibrations are also shown at lower frequencies (e.g., 1050–902 cm−1 ).

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298

ARTICLE IN PRESS

G Model CEJ 8851 1–11

A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx

36

5

Raw coconut bagasse

Transmittance (%)

34 32 30 28 -CH 2990 cm

26 24 4500

-OH 3379 cm 4000

3500

3000

-1

-1

2500

2000

1500

1000

500

-1 wavenumber (cm )

MCB

22 20

Transmittance (%)

18 16

2095 cm

-1

14 12 10 8

1050 cm

6

-CH 2908 cm

4 -OH 3462 cm

2 4500

4000

3500

1466 cm

-1

3000

2500

-1

-1

2000

1500

-1

1000

500

-1 wavenumber (cm ) Fig. 3. (a) FTIR spectra of both the non-modified and the modified coconut bagasses. Fig. 4. (a) SEM image of raw coconut bagasse solid. (b) SEM image of the modified coconut bagasse.

301 302 303 304 305 306 307 308 309 310

311 312 313 314 315 316 317 318 319 320

3.1.2. Surface and morphological aspects of the solids The morphological aspects of the solids show that both materials are in flake-like form. In case of MCB, the chemical treatment degraded lignin and spaced the fibrils, probably due to sodium hydroxide (Fig. 4). As a result, the BET surface area slightly increases from 218 m2 g−1 to 221 m2 g−1 , respectively, for the raw and MCB solids. These results indicated that no drastic changes on the surface area are achieved. However, the pores diameters distribution shows that the MCB had mesopores, with no uniform size, as compared to that of the non-modified coconut bagasse. This confirms that the chemical treatment expanded the pores of the solid to incorporate the reactants. 3.1.3. Zeta potential determination The electrostatic potential on the surface is called zeta potential and gives the velocity of the particles in an electric field. The point where the plot passes through zero zeta potential is called the isoelectric point and is very important from a practical consideration. Since that ions may be specifically adsorbed on the surface of an adsorbent, two types of adsorption on surface should be considered, as follows: for cationic species, a positively charged surface is developed whereas anionic species gives a negatively charged surface. Therefore, a curve of zeta potential versus pH is positive at

low pH while at higher pH, either lower or negative values can be observed. The plot of zeta potential distribution is shown in Fig. 5 with a point of zero zeta potential at pH around 4.7, and this indicates a sufficient positive charge on solid surface.

Zeta Potential Distribution 1400000 1200000

Intensity (kcps)

299 300

1000000 800000 600000 400000 200000 0 -200

-100

0

100

200

Zeta Potential (mV) Record 1: coco pH4,76

Fig. 5. Potential Zeta plots.

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

321 322 323 324 325

ARTICLE IN PRESS

G Model CEJ 8851 1–11

A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx

6

Table 2 Factors studied for nitrate, sulfate, phosphate adsorption, at a confidence level of 95%. Factor

Name

(−)

(+)

A

Concentration solution of a 3-cholride 2hydroypropyltrimethylammonium chloride Temperature Pressure

1 mL

2 mL

60 ◦ C 720 mmHg

80 ◦ C 760 mmHg

B C

Fig. 6. Reuse and regeneration tests.

326 327 328 329

The pH solution was adjusted with a 0.1 mol L−1

of chloride acid and 0.1 mol L−1 of sodium hydroxide solution at pH 5. These conditions reveal an optimum adsorption capacity and adsorbent dose of ca.1 g L−1 for the solution.

353

3.1.4. Reuse and regeneration tests Fig. 6 shows the results of the reuse and recyclability experiments. The adsorption efficiency level of MCB was superior to 50% for all anions studied after the first cycle of anions solution removal (C1). Indeed, the experiments show that sulfate undergoes a great level of ions removal, being the adsorption efficiency greater than 95%. There was a marginal decrease in the adsorption capacity after the following cycles of reuse (i.e., C2 adsorption efficiency for sulfate was about 92%). A loss of 80% in sulfate adsorption capacity of MCB was observed, after three cycles and this effect was more pronounced in the case of nitrate and phosphate that experienced a very fast drop in the anions removal during the first uses. The regeneration data are also illustrated in Fig. 6. Regeneration procedure resulted in 30% of adsorption efficiency (RC1), as compared with that of the third cycle of reuse (C3). However, a successive regeneration of the solid resulted in the complete loss of adsorption capacity, after the second cycle of reuse (RC2) due to the physical degradation of the bioadsorbent. Despite the lesser reuse and recyclability capacity compared to that of anionic resins [1,2], the modified coconut bagasse is an abundant reagent for bioadsorption studies and can still be used as fertilizer for agriculture. Also, modified bioadsorbent is less expensive than the anion exchange resin, which requires pre-concentration of anions procedure.

354

3.2. Full factorial design

330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352

355 356 357

Among the factors studied for phosphate adsorption, at a confidence level of 95%, the effects of pressure and temperature were the major contributors to efficiency in preparing the solids (Table 2).

Although the concentration itself was found to be an insignificant factor, the efficiency of the preparation process is greatly affected by the temperature and pressure. The results also indicated that an increase in the quaternization degree is provided by an increased temperature (Table 3) due to the endothermic nature of the process. The degree of quaternization of the fiber under reduced pressure was probably favored by the formation of epoxide due to the vaporization of water. The following equations can be used to express the adsorption of nitrate (Eq. (6)), sulfate (Eq. (7)), and phosphate (Eq. (8)), anions by the MCB:

Constant C T P C×T C×P T×P C×T×P

Coef

SE coef

T

P

0.016 0.779 −0.642 0.028 −0.043 0.598 0.088

1.588 0.008 0.390 −0.321 0.014 −0.022 0.299 0.044

0.017 0.017 0.017 0.017 0.017 0.017 0.017 0.017

96.190 0.490 23.600 −19.450 0.860 −1.310 18.110 2.660

0.000 0.631 0.000 0.000 0.404 0.208 0.000 0.017

360 361 362 363 364 365 366 367 368

(6)

369

Y = 1.312 + 0.417T − 0.260P + 0.189T · P

(7)

370

Y = 1.129 + 0.337T − 0.376P − 0.118C · P + 0.224T · P

(8)

371

3.3. Isotherm studies

372

The equilibrium between the solute and the adsorbent surface is commonly represented by single-component adsorption isotherms, mostly considering the surface reaction: S + T ↔ ST

373 374 375

(IV)

376

where S represents the sorbent in its initial form, T is the aqueous phase species, and ST is the species T in the adsorbent phase. The isotherm models of Langmuir, Freundlich, Temkin, SIPS and Redlich–Peterson were used to describe the equilibrium between the anions sorbed onto the adsorbent in the solution as shown in Fig. 7. The isotherm constants, correlation coefficient (R2 ), Sum of the squares of the errors (ERRSQ), Hybrid fractional error function (HYBRID), Marquardt’s percent standard deviation (MPSD) and Qui-quadrado (2 ) of these models for sorption of anions on adsorbent at ambient temperature are shown in Table 4

377

3.3.1. Langmuir Isotherm The Langmuir model is semi-empirical and assumes that a monolayer adsorption phenomenon on a homogeneous surface is likely [28,34–36]. Considering Eq. (9) at equilibrium, the Langmuir

Sulfate

Effect

359

Y = 1.588 + 0.390T − 0.321P + 0.299T · P + 0.044T · P · C

Table 3 Estimated effects and coefficients. Nitrate

358

Phosphate

Effect

Coef

SE coef

T

P

0.162 0.834 −0.519 −0.004 −0.094 0.378 0.153

1.312 0.081 0.417 −0.260 −0.002 −0.047 0.189 0.076

0.052 0.052 0.052 0.052 0.052 0.052 0.052 0.052

25.140 1.550 7.990 −4.970 −0.040 −0.900 3.620 1.460

0.000 0.140 0.000 0.000 0.968 0.383 0.002 0.163

Effect

Coef

SE coef

T

P

0.141 0.674 −0.753 0.008 −0.236 0.447 0.114

1.129 0.071 0.337 −0.376 0.004 −0.118 0.224 0.057

0.038 0.038 0.038 0.038 0.038 0.038 0.038 0.038

29.440 1.840 8.790 −9.810 0.100 −3.080 5.830 1.490

0.000 0.084 0.000 0.000 0.921 0.007 0.000 0.157

T = temperature; P = pressure; C = concentration.

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

378 379 380 381 382 383 384 385 386 387

388 389 390 391

ARTICLE IN PRESS

G Model CEJ 8851 1–11

A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx

7

Table 4 The isotherm constants, correlation coefficient (R2 ), error function values of the models for sorption of anions on adsorbent at room temperature. Nitrate

392 393

394

395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422

Sulfate

Phosphate

HYBRID

2

MPSD

Redlich–Peterson 101.193 Qmax 0.007 KRP 2 1.175  2 R 0.982 SNE 3.532

33.776 0.029 1.000 0.973 2.385

26.497 0.044 0.961 0.969 2.556

24.060 0.045 0.944 0.965 2.639

21.728 57.084 0.945 0.789 3.996

21.608 47.850 0.944 0.789 3.990

21.606 176.574 0.945 0.789 3.997

21.525 13.693 0.944 0.789 3.979

8.058 5.176 0.580 0.843 1.526

8.664 3.905 0.592 0.841 1.525

2.089 2.843 0.370 0.643 4.000

9.191 3.104 0.602 0.836 1.554

SIPS Qmax Ks 2 R2 SNE

33.735 0.029 1.058 0.974 3.877

35.294 0.025 0.924 0.971 3.100

35.956 0.025 0.891 0.970 3.326

34.926 0.025 0.934 0.971 3.151

31.912 0.135 0.708 0.897 1.561

31.320 0.096 0.879 0.918 1.247

32.156 1.212 0.414 0.748 4.000

35.267 0.642 0.318 0.836 2.522

319.509 0.001 0.674 0.836 3.942

285.226 0.001 0.698 0.832 3.956

678.170 0.000 0.512 0.840 3.864

678.170 0.000 0.481 0.833 3.911

Langmuir Qmax KL R2 SNE

34.282 0.028 0.974 3.801

33.744 0.029 0.973 3.760

33.266 0.033 0.972 3.849

32.368 0.032 0.970 3.888

31.206 0.074 0.935 0.261

31.219 0.073 0.935 0.261

29.396 4.108 0.036 4.000

31.231 0.073 0.935 0.261

209.332 0.002 0.822 2.274

200.576 0.002 0.819 2.246

158.605 0.004 0.648 4.000

193.236 0.003 0.809 2.298

Freundlich 1/nf Kf R2 SNE

0.308 5.151 0.852 2.984

0.414 2.896 0.782 1.942

0.381 3.750 0.804 2.118

0.510 1.760 0.630 2.819

0.054 21.733 0.789 3.362

0.056 21.596 0.789 3.357

0.055 21.644 0.789 3.358

0.063 20.619 0.744 4.000

0.423 7.880 0.843 3.882

0.412 8.366 0.841 3.877

0.423 7.901 0.843 3.905

0.402 8.876 0.836 3.940

Temkin B KT R2 SNE

5.751 0.605 0.940 3.470

5.421 0.669 0.936 2.916

5.609 0.672 0.939 2.945

5.017 0.714 0.911 3.472

2.011 8637.869 0.752 1.476

2.062 6148.864 0.740 1.540

2.862 111.812 0.328 4.000

2.057 6155.100 0.738 1.558

48.985 0.019 0.831 3.866

46.909 0.021 0.829 3.844

48.904 0.020 0.831 3.883

45.155 0.023 0.822 3.928

ERRSQ

ERRSQ

HYBRID

parameter qe represents the equilibrium constant and can be expressed as:

qe =

qo · b · Ce (1 + bCe ) (mg g−1 )

(9)

(mg L−1 )

where qe and Ce is the metal concentration in solution at equilibrium; qo is the maximum amount of the metal per unit mass of sorbent to form a complete monolayer on the surface bound at high Ce and b is a constant related to the affinity of the binding sites (L mg−1 ). The average values for qo were 33.7, 31.2, 200 mg g−1 for nitrate, sulfate and phosphate, respectively (Table 4). Application of Langmuir model to sorption of nitrate at 30 ◦ C, initial concentration of 100 mg L−1 , pH 2.5 and agitation speed of 180 rpm is shown in Fig. 6. According to the findings [2], the shape of the Langmuir adsorption isotherms of the nitrate anion suggests a favorable and spontaneous sorption of the solutes. The MCB curves of nitrate, reach a plateau corresponding to qo and lower energy while the sulfate and phosphate exhibit a very progressive adsorption process and do not attain the plateau within the concentration range of the study. The Langmuir isotherms fit well with the experimental results (R2 > 0.90). It is interesting to note that the error functions were applied to represent the experimental data. SNE values (e.g., hybrid error function) are lower than that of the experimental data and this suggests that the surface of the sorbent was homogenous. Indeed, all sites are energetically equivalent and there is no interaction among the sorbed molecules, probably. This result is in a good agreement with those led with biosorbents (Table 5). Although a direct comparison of adsorbent with other reported biosorbents is difficult due to the varying experimental conditions employed, it can be observed that the adsorbent studied had reasonable sorption efficiency for nitrate, sulfate and phosphate.

2

MPSD

ERRSQ

HYBRID

2

MPSD

Therefore, it can be noteworthy that the adsorbent had considerable potential for the removal of nitrate ions from aqueous solution. 3.3.2. Freundlich isotherm The Freundlich isotherm is an empirical equation employed to describe heterogeneous systems. This isotherm does not predict any saturation of the sorbate; thus, infinite surface coverage is predicted mathematically, indicating a multilayer adsorption on the surface. The Freundlich equation is expressed as: qe = Kf · Ce

1/n

(10)

where qe is the adsorbed equilibrium amount (mg g−1 ); Ce is the equilibrium concentration of the adsorbate (mg L−1 ). Kf and 1/n are the Freundlich constants related to adsorption capacity and intensity of adsorption, respectively. The estimated parameters of the models have been evaluated by regression analysis and the results are shown in Table 4. Among the adsorption isotherm models studied, the Freundlich model had not satisfactory correlation coefficients (R2 < 0.800) for describing the biosorption of anions studied onto adsorbent. HYBRID error function values are in general higher than those of the other models, being the nitrate an exception. The values of Kf and 1/n were Table 5 Comparison of sorption capacities for anions studied for various biosorbents. Agro-industrial residue

Adsorption capacity, mg g−1

Anion

Reference

Wheat Sugar cane bagasse Rice husk Sugar cane bagasse QA 52 (Anionic resin) Shrimp waste

22.99 19.2 80.6 86.8 43.7 156

Phosphate Sulfate Nitrate Nitrate Phosphate Sulfate

[12] [17] [10] [18] [19] [19]

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

423 424 425

426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443

ARTICLE IN PRESS

G Model CEJ 8851 1–11

A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx

8

is dissociation parameter. The SIPS model reduces to the Langmuir model, when  = 1 [38]. 3.3.4. Redlich–Peterson isotherm model The three-parameter Redlich–Peterson model is used to represent the adsorption equilibria in large concentration ranges (Eq. (12)): qe =

qmax KRP Ce 1 + KRP Ce ˇ

(12)

where qmax and KRP are Redlich–Peterson isotherm constants [39]. For sulfate adsorption, the models of SIPS and Redlich–Peterson represented well the experimental data, with R2 values upper to 90%. In case of phosphate, the Redlich–Peterson isotherm had good agreement with the experimental data (Fig. 6). Also, the lowest value for the hybrid error function (e.g., R2 ) results in the SIPS model

Fig. 7. Adsorption isotherms (a) nitrate, (b) sulfate and (c) phosphate.

444 445 446 447 448 449

found to be 2.89 and 0.41, respectively, and this indicates that the adsorption of nitrate onto the modified coconut shell was favorable at the studied conditions. However, compared to the R2 values obtained from the Langmuir model (R2 > 0.900), it can be noted that the Langmuir isotherm model is superior to that of fitted from the equilibrium data.

454

3.3.3. SIPS isotherm model SIPS isotherm model considers the adsorption capacity as limited by high adsorbate concentrations [37]. This model is similar to that of Langmuir, except from the fact that there is a parameter, which represents the heterogeneous system (Eq. (11)):

455

qe = qmax

450 451 452 453

456 457 458

(Ks Ce )

1 + (Ks Ce )

(11)

where Ce (mg L−1 ) is the equilibrium concentration in the liquid phase. qe is the total adsorption capacity at equilibrium. Qmax is the maximum adsorbent capacity, and Ks is the adsorption constant. 

Fig. 8. Kinetics parameters for (a) nitrate, (b) sulfate and (c) phosphate.

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

459 460

461 462 463 464

465

466 467 468 469 470 471

ARTICLE IN PRESS

G Model CEJ 8851 1–11

A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx

9

Table 6 Kinetic parameters, correlation coefficient (R2 ), error function values of the models for sorption of anions on adsorbent at ambient temperature. Nitrate

472

474 475 476 477 478 479

Phosphate

HYBRD

2

MPSD

ERRSQ

HYBRD

2

MPSD

ERRSQ

HYBRD

2

MPSD

Pseudo first order 22.932 qe 1.824 Kf 2 R 0.928 SNE 3.805

22.613 1.916 0.922 3.728

22.551 2.109 0.906 3.88

22.149 2.021 0.909 3.784

40.322 4.606 0.934 3.959

40.359 4.553 0.931 3.931

40.369 4.569 0.932 3.936

40.397 4.504 0.928 3.965

36.634 2.438 0.871 3.793

35.342 2.684 0.847 3.655

35.712 2.79 0.84 3.706

33.536 3.037 0.78 3.88

Pseudo second order 25.621 qe 0.091 Kf 0.947 R2 SNE 2.403

25.493 0.091 0.946 2.407

25.275 0.1 0.941 2.47

25.124 0.094 0.942 2.444

43.763 0.191 0.937 0.648

43.842 0.187 0.938 0.645

43.942 0.187 0.939 0.646

43.877 0.184 0.939 0.648

44.08 0.061 0.913 2.206

42.917 0.067 0.905 2.181

43.014 0.069 0.903 2.203

43.015 0.069 0.903 2.202

7.283 7.252 0.761 7.373

7.383 7.809 0.768 7.633

7.87 6.286 0.771 7.848

13.779 23.342 0.585 3.555

14.908 22.127 0.637 3.489

14.749 22.693 0.633 3.525

15.939 21.059 0.666 3.584

22.657 7.37 0.927 2.015

23.704 6.298 0.931 1.949

23.085 7.133 0.93 2.004

24.763 5.325 0.931 2.029

Intra-particle diffusion 6.531 kWM 8.663 C 0.722 R2 SNE 7.859

473

Sulfate

ERRSQ

values of 83.3%. The exponents of SIPS (e.g., ) and Redlich–Peterson (e.g., ˇ) isotherm are close to the unity for nitrate and sulfate. This is in agreement with the Langmuir model, being the phosphate adsorption an exception. The constants obtained by Redlich–Peterson (KRP ) and SIPS (Ks ) for nitrate and sulfate are close to zero (Table 4), indicating that the adsorption and desorption rates are very close, however, the adsorption process is favored.

485

3.3.5. Temkin isotherm model Temkin and Pyzhev considered the effects of some indirect sorbate/adsorbate interactions on adsorption isotherms and suggested that the heat of adsorption of all the molecules in the layer would decrease linearly with coverage due to the physiochemical interactions (Eq. (13)):

486

qe =

480 481 482 483 484

RT (ln KT Ce ) = B(ln KT Ce ) b

(13)

501

where B = RT/b; b is the Temkin constant related to heat of sorption (J mol−1 ); A is the Temkin isotherm constant (L mg−1 ), R is the gas constant (8.314 J mol−1 K−1 ) and T the absolute temperature (K). Therefore, by plotting qe versus ln Ce enables one to determine the constants A and b. The constants A and B are listed in Table 4. The Temkin model estimated the heat of adsorption at room temperature and the B coefficient is 5.42 for nitrate while that of phosphate and sulfate are 48.9 and 2.06, respectively. Among the error functions used in the algorithm, a hybrid error function resulted in the lowest value sum of the standard error. By comparing the maximum adsorption capacity of nitrate and sulfate, the former had a higher adsorption capacity due to its smaller ionic radius of hydration (e.g., 300 pm for NO3 − compared to 400 pm for SO4 2− ). This is a sound proof that an ease adsorption on the sites assets is due to lower steric hindrance of nitrate ions.

502

3.4. Kinetic adsorption

487 488 489 490 491 492 493 494 495 496 497 498 499 500

503 504 505 506 507

508 509 510 511

The kinetic studies predict the progress of adsorption, however, the determination of the adsorption mechanism is also important for design purposes. In order to investigate the adsorption kinetics of the anions on the adsorbent, pseudo-first order, pseudo-second order, and intraparticle diffusion models were used. 3.4.1. Pseudo-first and second order models The kinetics of anions adsorption was studied to verify the adsorption mechanism. The first-order rate expression of Lagergren (14) and pseudo-second order rate (15) expressions were applied

in this study [22]. Fig. 8 shows the biosorption kinetics for pseudo first-order rate equation of nitrate, sulfate and phosphate on the adsorbent. The initial phase of biosorption is fast such that almost 60 to 80% of the anions are adsorbed within 120 min. Lagergren [40] suggested that a pseudo first-order rate equation for sorption of solutes from a liquid solution is represented as follows: log(qe − qt ) = log qe −

k1 ×t 2.303

(14)

where qe is the adsorption capacity at the equilibrium; qt is the individual capacity in a given time. k1 and k2 are the pseudo-first and pseudo-second order rate constants, respectively, and t is the time in minutes. The value of the sorption rate constant (k1 ) for NO3 − biosorption by adsorbent was determined from the plot of log(qe − qt ) against t. Although the correlation coefficient value is higher than 0.98, the experimental qe value do not agree with the calculated one, obtained from the linear plot (Table 6). This result indicated that the anions biosorption system do not follow a first-order reaction. Another model for the analysis of sorption kinetics is pseudo second-order. This model proposed by Ho and McKay [41] can be used to explain the sorption kinetics. The model is based on the assumption that the biosorption follows a second order chemisorption. The pseudo-second order model can be expressed as: t 1 1 = + ×t qt qe k2 q2e

(15)

The plot of t/q versus t gives a straight line with slope of 1/q2 and intercept of 1/K2 (qe )2 There is no need to know any parameter beforehand and the grams of solute sorbed per gram of sorbent at equilibrium (q2 ) and sorption rate constant (k2 ) can be evaluated from the slope and intercept, respectively. Fig. 8 shows the biosorption kinetics for pseudo second-order rate equation of nitrate, sulfate and phosphate on the adsorbent. The values of the parameters k2 , calculated q2 , experimental qe and the correlation coefficients are presented in Table 6. The theoretical q2 value also agreed very well with the experimental qe value, indicating the pseudo second-order kinetics. In addition, the correlation coefficient for the second-order kinetic model was 0.98, which suggest the applicability of this kinetic equation and the second-order nature of the sorption process of anions on adsorbent. Similar phenomena have been observed in the biosorption of the anions on others adsorbents (Table 6).

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

512 513 514 515 516 517 518

519

520 521 522 523 524 525 526 527 528 529 530 531 532 533 534

535

536 537 538 539 540 541 542 543 544 545 546 547 548 549 550

ARTICLE IN PRESS

G Model CEJ 8851 1–11

A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx

10 551 552 553 554 555 556 557

3.4.2. Intra-particle diffusion In order to gain insight into the mechanisms and rate controlling steps affecting the kinetics of adsorption, the kinetic experimental results were fitted to the Weber’s intra-particle diffusion [42]. The kinetic results were analyzed by the intra-particle diffusion model Q6 to elucidate the diffusion mechanism, which model is expressed as: qt = kid t

1/2

+C

(16)

577

where C is the intercept and kid is the intra-particle diffusion rate constant (mg g−1 min1/2 ), which can be evaluated from the slope of the linear plot of qt versus t1/2 , as shown in Fig. 8. The C values provide information about the thickness of the boundary layer; as the interception is larger, the boundary layer effect is greater [43]. If intra-particle diffusion occurs, then qt versus t1/2 will be linear and if the plot passes through the origin, then the rate limiting process is only due to the intra-particle diffusion. Otherwise, some other mechanism along with intra-particle diffusion is also involved. As shown in Fig. 8, the linear line do not pass through the origin and this deviation from the origin near saturation might be due to the difference in the mass transfer rate in the initial and final stages of adsorption [44]. This means that the pore diffusion is not the only rate limiting mechanism in the adsorption process. It has been reported [45,46] that if the intra-particle diffusion is the sole rate-limiting step, it is essential for the qt versus t1/2 plots to pass through the origin, which is not the case in this study. It may be concluded that surface adsorption and intra-particle diffusion are concurrently operating during the anions-adsorbent interactions [32,47].

578

4. Conclusions

579

599

The modified coconut powder bagasse was characterized by physiochemical techniques and efficiently removed anions from aqueous solutions. The MCB adsorption capacity is close to that of the commercial resins, with the additional advantages of being a low cost material, has no toxicological issue and can be applied as complementary treatment sewage tertiary treatment. The adsorption of nitrates and sulfates are favorable whereas the adsorption of phosphate is difficult. Equilibrium data were evaluated by using Langmuir, Freundlich, SIPS, Redlich–Peterson, Temkin nonlinear models. It was observed that the experimental data fits well to Langmuir, SIPS, and Redlich–Peterson equations, being the Langmuir model an accurate model to predict q0 . Adsorption kinetics was examined in terms of three kinetic models, i.e., pseudo-firstorder, pseudo-second-order and intraparticle diffusion models. Pseudo-second-order kinetic model showed good agreement with the experimental data. Despite the low adsorption constant as well as the lesser recyclability capacity compared with anionic resins, the modified coconut bagasse is an abundant reagent for bioadsorption studies and can still be used as fertilizer for agriculture. The adsorbent material can also be tested for other anions and anionic dyes.

600

Acknowledgements

601

This work was supported by CAPES, FUNCAP and CNPQ (Process no.: 576591/2008-4 and 306114/2008-9).

558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576

580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598

602

603 604 605 606 607 608 609 610

References [1] A. Bhatnagar, E. Kumar, M. Sillanpää, Fluoride removal from water by adsorption—a review, Chem. Eng. J. 171 (2011) 811–840. [2] J. Dron, A. Dodi, Comparison of adsorption equilibrium models for the study of Cl, NO3 and SO4 2− removal from aqueous solutions by an anion exchange resin, J. Hazard. Mater. 190 (2011) 300–307. [3] C.T. Benatti, C.R.G. Tavares, E. Lenzi, Sulfate removal from waste chemicals by precipitation, J. Environ. Manage. 90 (2009) 504–511.

[4] J. Xiao, C. Zhu, D. Sun, P. Guo, Y. Tian, Removal of ammonium-N from ammonium-rich sewage using an immobilized Bacillus subtilis AYC bioreactor system, J. Environ. Sci. 23 (2011) 1279–1285. [5] K. Goh, T. Lim, Z. Dong, Application of layered double hydroxides for removal of oxyanions: a review, Water Res. 42 (2008) 1343–1368. [6] R. Malaisamy, A. Talla-Nwafo, K.L. Jones, Polyelectrolyte modification of nanofiltration membrane for selective removal of monovalent anions, Sep. Purif. Technol. 77 (2011) 367–374. [7] U.S. Orlando, A.U. Baes, W. Nishijima, M. Okada, Preparation of agricultural residue anion exchangers and its nitrate maximum adsorption capacity, Chemosphere 82 (2002) 1041–1046. [8] J.G. Ferreira, J.H. Andersen, A. Borja, S.B. Bricker, J. Camp, M. Cardoso da Silva, E. Garcés, A. Heiskanen, C. Humborg, L. Ignatiades, C. Lancelot, A. Menesguen, P. Tett, N. Hoepffner, U. Claussen, Overview of eutrophication indicators to assess environmental status within the European Marine Strategy Framework Directive, Estuar. Coast. Shelf. Sci. 93 (2011) 117–131. [9] A.L. Cazetta, A.M.M. Vargas, E.A. Nogami, N.H. Kunita, M.R. Guilherme, A.C. Martins, T.L. Silva, J.C.G. Morais, V.C. Almeida, NaOH-activated carbon of high surface area produced from coconut shell: kinetics and equilibrium studies from the methylene blue adsorption, Chem. Eng. J. (2011), doi:10.1016/j.cej.2011.08.058. [10] F.W. Sousa, M.J. Sousa, I.R.N. Oliveira, A.G. Oliveira, R.M. Cavalcante, P.B.A. Fechine, V.O.S. Neto, D. Keukeleire, R.F. Nascimento, Evaluation of a low-cost adsorbent for removal of toxic metal ions from wastewater, J. Environ. Manage. 90 (2009) 3340–3344. [11] X. Xu, Q. Li, B. Gao, Q. Yue, Q. Zhong, Q. Li, Preparation of new types of anion exchange resins from agricultural by-products and their utilization in the removal of various toxic anions from solutions, Chem. Eng. J. 167 (2011) 104–111. [12] L.H. Wartelle, W.E. Marshall, Quaternized agricultural by-products as anion exchange resins, J. Environ. Manage. 78 (2006) 157–162. [13] K.F Lam, K.L. Yeung, G. McKay, An investigation of gold adsorption from a binary mixture with selective mesoporous silica adsorbents, J. Phys. Chem. B 110 (2006) 2187–2194. [14] X.Q Chen, K.F. Lam, K.L Yeung, Selective removal of chromium from different aqueous systems using magnetic MCM-41 nanosorbents, Chem. Eng. J. 172 (2011) 728–734. [15] K.F Lam, K.L. Yeung, G. Mckay, Efficient approach for Cd2+ and Ni2+ removal and recovery using mesoporous adsorbent with tunable selectivity, Environ. Sci. Technol. 41 (2007) 3329–3334. [16] K.F Lam, C.M. Fong, K.L Yeung, Separation of precious metals using selective mesoporous adsorbents, Gold Bulletin 40 (2007) 192–198. [17] J.A. Laszlo, Preparing an ion exchange resin from sugarcane bagasse to remove reactive dye from wastewater, Text. Chem. Color. 28 (1996) 13–17. [18] S.A. Moreira, A.G. Oliveira, F.W. Sousa, R.F. Nascimento, E.S. Brito, Remoc¸ão de metais de soluc¸ão aquosa usando bagac¸o de caju, Quim. Nova 32 (2009) 1717–1722. [19] D. Sud, G. Mahajan, M.P. Kaur, Agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions—a review, Bioresour. Technol. 99 (2008) 6017–6027. [20] X. Xu, B. Gao, W. Wang, Q. Yue, Y. Wang, S. Ni, Adsorption of phosphate from aqueous solutions onto modified wheat residue: characteristics, kinetic and column studies, Colloids Surf. B 70 (2009) 46–52. [21] D.R. Mulinaria, M. Lucia, C.P. Silva, Adsorption of sulphate ions by modification of sugarcane bagasse cellulose, Carbohydr. Polym. 74 (2008) 617–620. [22] I. Simkovick, Preparation of anion exchangers from beech sawdust and wheat straw, Ind. Crop. Prod. 10 (1999) 167–173. [23] J.A. Laszlo, Biodegradability of quaternized, crosslinked sugarcane bagasse, Chem. Mater. Sci. 6 (1994) 73–78. [24] Z. Ma, Q. Li, Q. Yue, B. Gao, W. Li, X. Xu, Q. Zhong, Adsorption removal of ammonium and phosphate from water by fertilizer controlled release agent prepared from wheat straw, Chem. Eng. J. 171 (2011) 1209–1217. [25] S. Pal, D. Mal, R.P. Singh, Cationic starch: na effective flocculating agent, Carbohydr. Polym. 59 (2005) 417–423. [26] O.A. Carrijo, R.S. Liz, N. Makishima, Fibra da casca do coco verde como substrato agrícola, Hortic. Bras. 20 (2002) 533–535. [27] X.Q Chen, K.F. Lam, S.F. Mak, K.L Yeung, Precious metal recovery by selective adsorption using biosorbents, J. Hazard. Mater. 186 (2011) 902–910. [28] V. Boonamnuayvitaya, Removal of heavy metals by adsorbent prepared from pyrolyzed coffee residues and clay, Sep. Purif. Technol. 35 (2004) 11. [29] A. Gunay, E. Arslankaya, I. Tosun, Lead removal from aqueous solution by natural and pretreated clinoptilolite: adsorption equilibrium and kinetics, J. Hazard. Mater. 146 (2007) 362–371. [30] Y.S. Ho, J.F. Porter, G. Mckay, Equilibrium isotherm studies for the sorption of divalent metal ions onto peat: copper, nickel and lead single component systems, Water Air Soil Pollut. 141 (2002) 1–33. [31] S.J. Allen, G. Mckay, J.F. Porter, Adsorption isotherm models for basic dye adsorption by peat in single and binary component systems, J. Colloid Interface Sci. 208 (2004) 322–333. [32] M. Hashem, M. Refaie, A. Hebeish, Crosslinking of partially carboxymethylated cotton fabric via cationization, J. Cleaner Prod. 13 (2005) 947–954. [33] R.M. Silverstein, G.C. Bressler, T.C. Morril, Spectrometric Identification of Organic Compounds, 5th ed., John Wiley & Sons, New Jersey, 2005. [34] J. Eastoe, J.S. Dalton, Dynamic surface tension and adsorption mechanisms of surfactants at the air water interface, Adv. J. Colloid Interface Sci. 85 (2000) 103.

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696

G Model CEJ 8851 1–11

ARTICLE IN PRESS A.C.A. de Lima et al. / Chemical Engineering Journal xxx (2012) xxx–xxx

697 698 699 700 701 702 703 704 705 706 707 708 709 710

[35] G. Vazquez, et al., Adsorption of heavy metal ions by chemically modified pinus pinaster bark, Bioresour. Technol. 48 (1994) 251. [36] G.S. Chauhan, S. Chauhan, S. Kumar, A. Kumari, Study in the adsorption of Fe2+ and NO3 - on pine needles based hydrogels, Bioresour. Technol. 99 (2008) 6464. [37] R. Sips, On the structure of a catalyst surface, J. Chem. Phys. 16 (1948) 490– 494. [38] M. Chabani, A. Amrane, A. Bensmaili, Equilibrium sorption isotherms for nitrate on resin Amberlite IRA 400, J. Hazard. Mater. 165 (2009) 27–33. [39] O. Redlich, D.L. Peterson, A useful adsorption isotherm, J. Phys. Chem. 63 (1959) 1024. [40] S. Lagergren, Zur theorie der sogenannten adsorption geloester stoffe, Veternskapsakad Handlingar 24 (1898) 1. [41] Y.S. Ho, G. McKay, The kinetics of sorption of basic dyes from aqueous solutions by sphagnum moss peat, Can. J. Chem. Eng. 76 (1998) 822.

11

[42] W.J. Weber Jr., J.C. Morris, Kinetics of adsorption on carbon from solution, J. Sanit. Eng. Div. Proceed. Am. Soc. Civil Eng. 89 (1963) 31. [43] D. Kavitha, C. Namasivayam, Experimental and kinetic studies on methylene blue adsorption by coir pith carbon, Bioresour. Technol. 98 (2007) 14. [44] K. Mohanty, D. Das, M.N. Biswas, Adsorption of phenol from aqueous solutions using activated carbons prepared from Tectona grandis sawdust by ZnCl2 activation, Chem. Eng. J. 115 (2005) 121. [45] Y.S. Ho, Removal of copper ions from aqueous solution by tree fern, Water Res. 37 (2003) 2323. [46] G. Crini, H.N. Peindy, F. Gimbert, C. Robert, Removal of C.I. Basic Green 4 (Malachite Green) from aqueous solutions by adsorption using cyclodextrinbased adsorbent: kinetic and equilibrium studies, Sep. Purif. Technol. 53 (2007) 97. [47] S.J. Allen, Q. Gan, R. Matthews, P.A. Johnson, Comparison of optimised isotherm models for basic dye adsorption by kudzu, Bioresour. Technol. 88 (2003) 143–152.

Please cite this article in press as: A.C.A. de Lima, et al., Modified coconut shell fibers: A green and economical sorbent for the removal of anions from aqueous solutions, Chem. Eng. J. (2012), doi:10.1016/j.cej.2012.01.037

711 712 713 714 715 716 717 718 719 720 721 722 723 724 725