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Removal of Pb2+, Cu2+, and Fe3+ from battery manufacture wastewater by chitosan produced from silkworm chrysalides as a low-cost adsorbent
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REACTIVE & FUNCTIONAL POLYMERS
Reactive & Functional Polymers 68 (2008) 634–642
www.elsevier.com/locate/react
Removal of Pb2+, Cu2+, and Fe3+ from battery manufacture wastewater by chitosan produced from silkworm chrysalides as a low-cost adsorbent Alexandre Tadeu Paulino *, Lı´dia Brizola Santos, Jorge Nozaki 1 Universidade Estadual de Maringa´, Po´s-Graduacßa˜o em Quı´mica, Av. Colombo, 5790 CEP 87020-900 Maringa´, PR, Brazil Received 13 June 2006; received in revised form 4 May 2007; accepted 6 October 2007 Available online 1 November 2007
Abstract In this work, it was investigated the best ChSC deacetylation time (DT) for the removal of Pb2+ and Cu2+ from battery manufacture wastewater. Bath experiments were used to determine the best adsorption conditions. The best DT for Cu2+ removal was 180 min (92% deacetylation) and for Pb2+ removal was 90 min (80% deacetylation). The maximum adsorption capacities of Pb–ChSC and Cu–ChCS were 0.4247 mmol g1 and 1.5953 mmol g1, respectively, for contact time of 24 h, pH 5.0, particle size from 300 to 425 lm, and temperature of 20 ± 0.1 °C. Metal adsorption onto ChSC was evaluated by Langmuir and Freundlich isotherms. An experimental column packed with ChCS was used to remove Fe3+, Cu2+, and Pb2+ from battery wastewater. Experimental column results were obtained by plotting C/C0 against time. Metal adsorption onto ChSC in column was higher at pH 5.0 than pH 3.0. The results of this work support the use of ChSC in battery wastewater treatment. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Silkworm chrysalides; Low-cost adsorbent; Chitosan; Battery wastewater; Metals
1. Introduction All living beings are affected by the presence of heavy metals, which are frequently discarded in water flow near cities [1]. Many metals are essential for several organisms, from bacteria to even the human being; however, low concentrations are
*
Corresponding author. Tel.: +55 44 3261 4332; fax: +55 44 3261 4125. E-mail address: [email protected] (A.T. Paulino). 1 In memoriam.
required; otherwise, they may damage the biological systems [2]. Lead (Pb2+), one of the metals of interest in this work, may be found in the environment (atmosphere, water, soil, rocks and sediments) and in the biosphere. Lead may cause mental disturbance, retardation, and semi-permanent brain damage and it does not have an important biological activity. It is classified as a persistent environmental toxic substance and is toxic in even very small amounts, with a toxicity limit is <0.05 lg mL1 [3]. Another, copper (Cu2+), an abundant and naturally occurring element, it may be toxic if ingested in large amounts.
1381-5148/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2007.10.028
A.T. Paulino et al. / Reactive & Functional Polymers 68 (2008) 634–642
It participates in vegetable metabolism in two ways: in the synthesis of chlorophyll and in the activity of other enzymes. Although Cu2+ does not exist in chlorophyll, it is indispensable for vegetables and its lack may result in photosynthetic deficiencies and incapacity to produce seeds. It is also a constituent of enzymes responsible for the catalysis of oxidation–reduction reactions. The lack of Cu2+ in animal diet may lead to anemia, diarrhea, and nervous disturbances. On the other hand, the excessive ingestion of this element may result in vomit, cramps, convulsion, and even death [4]. Iron (Fe3+), the third metal of interest, and Cu2+ are essential micronutrients for animals and plants. However, they become toxic at high levels. Fe3+, the fourth most abundant element on the earth crust, is present in a variety of rocks, soils, and minerals. This element is important for the biosphere due to its essential role in photosynthesis and because it is a phytoplankton growth limiting nutrient in some parts of the ocean [5]. Fe3+ is also an important active center in a wide range of proteins such as oxidases, reductases, and dehydrases [6]. Battery manufacture wastewater contains high amounts of Fe3+, Pb2+, and Cu2+ and may not be disposed to the environment without previous treatment. In recent years, solid adsorbents have been widely used for the removal of heavy metals and dyes in low-cost wastewater treatment [7–10]. Low-cost adsorbents may be used as an alternative large scale wastewater treatment procedure [11– 13]. Chitosan is a polysaccharide obtained by deacetylation of chitin (copolymer b-(1,4)-D-glucosamin and b-(1,4)-N-acetyl-D-glucosamin), which is abundant in nature, principally in shells of crustaceans, terrestrial invertebrates, and fungi [14]. New sources for the production of chitin and chitosan have been explored, thus making the treatment of industrial wastewater at a cost lower than that using chitin and chitosan obtained from crustaceans possible [15]. The aim of this work was to remove metals such as Pb2+, Cu2+, and Fe3+ from battery manufacture wastewater using chitosan obtained from silkworm chrysalides (ChSC) as a low-cost adsorbent. The best conditions for the removal of Pb2+ and Cu2+ from aqueous solutions were determined at various pHs, contact times, and deacetylation times (DT). The uptake of Fe3+, Pb2+, and Cu2+ from battery manufacture wastewater was carried out by adsorption and desorption process in ChSC-packed column [16].
635
2. Materials and methods 2.1. Production of chitin and ChSC Silkworm chrysalide samples were kindly supplied by Cocamar silk spinning (Cooperativa Agroindustrial, Maringa´, PR, Brazil). The samples were lyophilized and triturated in an automatic knife crusher. A portion of silkworms was carefully weighed and treated with HCl 1.0 mol L1 (1:15 w/v) at 90 °C for 1 h under constant stirring for demineralization. The residues were filtered out and treated with NaOH 1.0 mol L1 (1:10 w/v) at 70 °C for 2 h under constant stirring for deproteination. The residues were filtered out and washed up to the neutralization of chitin [15]. The chitin obtained in the previous experiment was weighed and deacetylated with 40% NaOH/ NaHB4 (0.250 g NaHB4 and 300 mL 40% NaOH) at 110 °C for five different times under constant stirring. The solid produced was filtered and washed several times until pH 7.0 ± 0.2 was reached [15]. The adsorption DTs studied were: 30, 90, 120, 180, and 240 min. 2.2. Acetylation degree of ChSC ChSC samples were submitted to nuclear magnetic resonance spectroscopy (1H NMR model Varian, Mercury plus BB spectrometer) to determine the acetylation degree (AD). The solid ChSC samples were dissolved in diluted CD3COOD solution. Deacetylation degree (DD) may be associated to AD in Eq. (1), which describes the percent correlations between AD and acetyl groups in the polymer chain. ACH3 % AD ¼ 100 ð1Þ 3AH2 where ACH3 is the signal area corresponding to the hydrogen bound to CH3 groups, and AH2 is attributed to the signal area corresponding to the hydrogen bound to carbon-2 of the glucosamin group [17,18]. 2.3. X-ray powder diffraction of chitin and ChSC ChSC samples were submitted to XRD (X-ray powder diffraction) analyses and the results were compared with those of commercial chitosan (Across Organics Chitosan). X-ray diffractograms of powdered samples were obtained using a Bruker AXS D8 Advance X-ray diffractometer under operation conditions of 40.0 kV and 30.0 mA with Cu
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˚ . The slit parameters Ka1 radiation at k 1.54184 A used were: Divergence 1.0°, scatter 1.0° and receiving 0.3 mm. The scanning parameters were: Axis h – 2h ranging from 2.0 to 40.0, speed 5.0 min1, sampling pitch 0.05°, and preset time of 0.60 s. The crystallinity index (CrI) was determined by CrI020 = (I020 – Iam) X 100/I020, where I020 is the maximum intensity below 13° and Iam is the intensity of amorphous diffraction at 16°. Another crystallinity index was expressed as CrI110 using the maximum intensity at 20° [19]. 2.4. Determination of Pb2+ and Cu2+ by voltammetric method
ChSC. MilliQÒ water, 50 mL, was used to prepare 100 mg L1 solutions of Pb2+ and Cu2+ (Merck) in two separate flasks. The pH of the metal solutions was fixed at 5.0 and the solutions were stirred at 250 rpm. The temperature was 20.0 ± 0.1 °C, and particle size ranged from 300 to 425 lm. The adsorbent/adsorbate ratios (qe mg g1) were obtained by the difference between initial and final metal concentrations in solution. Particle size was selected through granulometric sieve (Granutest). [20]. The adsorption capacity (qe mg g1) was calculated according to the following equation: qe ¼
C 0 C eq V m
ð2Þ
The quantitative determination of adsorbed Pb2+ and Cu2+ and remaining in solution was carried out on an Autolab potentiostat/galvanostat (GPES). The method used was square wave voltammetry with a three-electrode system; hanging mercury drop working electrode (HMDE), Ag/AgCl reference electrode, and graphite electrode as support. Metal concentrations were determined from an analytical curve that correlates adsorption to metal concentrations. Volumes of 20 mL of appropriate supporting electrolyte and 100 lL of samples were placed in the cell for each analysis. The electrolytic solutions used in this procedure were prepared as follows: Amounts of 1000 mg L1 of Pb2+ and Cu2+ standards (Merck) were diluted to appropriate low concentration of 0.1 mol L1 HCl for Pb2+ evaluation and 0.1 mol L1 KNO3 for Cu2+ evaluation.
where C0 and Ceq are initial and equilibrium concentrations (mg L1), respectively, m is the adsorbate weight and V is the solution volume.
2.5. Determination of Fe3+ by FAAS measurements
3. Results and discussion
The quantitative determination of Fe3+ was carried out on a FAAS (CGAA 7000 ABC Spectrometer with air:acetylene flame and deuterium background correction). The concentrations of adsorbed metal and remaining in solution were determined through analytical curve. The Fe3+ standards used in analytical curve construction were prepared as follows: 1 mg mL1 Fe3+ (Merck) were diluted in 1000 mL of water to a final concentration of 1000 mg L1. Successive dilutions were carried out to prepare the analytical curve.
3.1. XRD analyses and deacetylation degree of ChSC
2.6. Bath experiments for the determination of the best adsorption conditions Bath adsorption experiments were conducted in a 125 mL Erlenmeyer to which was added 50 mg of
2.7. Column experiments for Fe3+, Pb2+, and Cu2+ removal from wastewater A column with 5 cm i.d. and 30 cm long was used. Amounts of 50 mg of ChSC were introduced at the bottom of the column and wastewater with Fe3+, Pb2+, and Cu2+ was passed through a column at a fixed flow rate. Downstream column wastewater samples were collected at different intervals of time and Fe3+ measurements were obtained by FAAS and Pb2+ and Cu2+ by GPES. The samples were collected until column and metal equilibrium were reached.
Fig. 1 shows the XRD results of chitin and ChSC. Chitin and chitosan are polymorphic forms occurring as a form in shrimp, crab shell waste, and silkworm chrysalides [15,21]. Processing adjustments based on the DD of chitin are frequently required to allow the quick preparation of chitosan. A relationship between the analyses of the crystalline structure by XRD and DD was proposed by Zhang [22]. According to the results shown in Fig. 1, CrI020 decreases when DD increases; therefore, it was supposed that commercial chitosan has higher DD than that of ChSC (90 min deacetylation). The DD of ChSC after 90 min of reaction with 40% NaOH/NaHB4 (0.250 g NaHB4 and 300 mL 40% NaOH) was 80% and that of commercial chitosan was 88%.
A.T. Paulino et al. / Reactive & Functional Polymers 68 (2008) 634–642
1400
Intensitity (%)
observed a significant increase in adsorption at pH between 4.5 and 5.5. The best pH interval, from 5.0 to 5.5, was chosen for the adsorption studies of Pb2+ and Cu2+ onto ChSC.
ChSC 90 min Chitosan standard Chitin from silkworm
(110)
1600
1200 1000
637
(020)
3.3. Best DT for ChSC removal of Pb2+ and Cu2+ from wastewater
800 600
Fig. 3a and b show the best DT (% deacetylation or DD) for ChSC in the adsorption studies of Pb2+ and Cu2+, respectively. Fig. 3a shows that the best DT of ChSC for the removal of Pb2+ from wastewater using bath experiments was 90 min with 80% deacetylation, the one which resulted in the largest removal of metal. The decrease in maximum adsorption capacity at higher DT was attributed to the biopolymer degradation, and the decrease in the molar mass and amino groups. Fig. 3b shows the best DT for Cu2+ removal using bath experiments. The best DT, the one that removed the largest amount of Cu2+, was 180 min with 92% deacetylation. The DT for the removal of Cu2+ was higher than that of Pb2+, which was attributed to the stabilization of the complex formed between NH2, OH, and HN A COOH groups and the metallic ions. Inter- and intramolecular chelation must be considered in adsorption studies of chitin, chitosan, and heavy metals [23]. Four interaction situations between metallic cations and NH2, OH, and COOH groups were considered. In form 1, the metallic cations may bind to two different NH2 groups of chitosan, or NH in the case of chitin. In form 2, the metallic cations may bind to one NH2 and one O6 of the second polysaccharide. In form 3, the metallic cations may bind to two O3 of the polysaccharide,
400 200 5
10
15
20
25
30
35
40
2θ (º) Fig. 1. X-Ray powder diffractograms of chitin from silkworm chrysalides, pure ChSC, and comparison with that of commercial chitosan (across organics chitosan).
3.2. pH effect on the adsorption of Pb2+ and Cu2+ onto ChSC Fig. 2a shows the precipitation of Pb2+ and Cu2+ in aqueous solution by pH changes using bath experiments. Fig. 2b shows the amounts of Pb2+ and Cu2+ adsorbed onto ChSC as a function of pH. At high pH, the metal ions precipitate as hydroxides and maximum adsorption capacity decreases. On the other hand, although Pb2+ and Cu2+ do not precipitate as hydroxides at low pH, they compete with H+ ions in solution for the basic NH2 groups of ChSC. In this condition, most NH2 groups are in the form of NHþ 3 . As it is not possible to establish interactions with any metal, a reduction of adsorption capacity follows. Otherwise, it was
a
100
Cu2+
140
mg metal / g ChSC
Concentration (mg L-1)
160
120 Pb2+
100 80 60 40
b
Cu2+
90 80
Pb2+
70 60 50 40
20 30
0 3
4
5
6
7
3.0
8
(pH)
3.5
4.0
4.5
5.0
5.5
6.0
(pH) 2+
2+
Fig. 2. Effect of pH changes on the precipitation of Pb and Cu in aqueous solutions (a) and on the adsorption of Pb2+ and Cu2+ (b) onto ChSC. Experimental parameters were: particle size from 300 to 425 lm, temperature of 20.0 ± 0.1 °C, and 250 rpm stirring.
A.T. Paulino et al. / Reactive & Functional Polymers 68 (2008) 634–642
60 55 50 45 40 35 30 25 20 15 10 5 0
a
90 min 30 min 120 min 180 min 240 min
0
100
200
300
mgCu2+ / g ChSC
mg Pb2+/ g ChSC
638
85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5
400
b
180 min 240 min 120 min
90 min
30 min
0
100
200
(min)
300
400
(min)
Fig. 3. Effect of DT on the adsorption capacities of Pb2+ (a) and Cu2+ (b) by ChSC. Experimental parameters were: particle size from 300 to 425 lm, pH 5.0, temperature of 20.0 ± 0.1 °C, and 250 rpm stirring.
3.4. Maximum adsorption capacity for Pb–ChSC and Cu–ChSC Fig. 4 shows the maximum adsorption capacity for Pb2+ and Cu2+ onto ChSC using bath experiments. The maximum adsorption capacities of Pb– ChSC and Cu–ChCS were 87 mg g1 and 72 mg g1, respectively, at contact time 24 h, pH 5.0, particle size from 300 to 425 lm, 250 rpm stirring, and temperature of 20 ± 0.1 °C. The difference between the maximum adsorption capacities of Pb2+ and Cu2+ was attributed to factors such as ionic size, steric hindrance, coordination number, aggregation, different complex properties, hydrolysis constants, and electrostatic forces. As shown by morphologic analysis of previous works [20,21], the ChSC surface exhibits a larger porous morphology than that of chitosan obtained from crustaceans. In this condition, ChSC performed better in the removal of Pb2+ and Cu2+ from wastewater than chitosan from crustaceans did.
90 80
mg metals / g ChSC
and in form 4, the metallic cations bind to two O (either O6 or O3) of the different polysaccharides. Taking this into account, Cu2+ interacts more favorably with NH2 groups than with other groups such as OH and COOH. As a result, the largest amount of Cu2+ was removed from wastewater with sufficient ChSC deacetylation. On the other hand, Pb2+ may interact with either NH2 groups or OH and COOH groups. It was observed that ChSC with low DD supported the removal of a larger amount of Pb2+ from wastewater, while for the removal of Cu2+, it was necessary a DD higher than that for the removal of Pb2+.
70 60 Cu2+
50
Pb2+
40 30 20 0
20
40
60
80
100
(hours) Fig. 4. Maximum adsorption capacity of Pb2+ and Cu2+ by ChSC with DT 90 min, pH 5.0, particle size from 300 to 425 lm, 250 rpm stirring, and temperature of 20.0 ± 0.1 °C.
3.5. Langmuir and Freundlich equilibrium isotherms The Langmuir isotherm model assumes that adsorption occurs in a monolayer or that adsorption may only occur at a fixed number of localized sites on the surface with all adsorption sites identical and energetically equivalent. The Langmuir equation is based on the assumptions of a structurally homogeneous adsorbent and is described by the following equation: C eq C eq 1 ¼ þ qe Q0 Q0 b
ð3Þ
where Ceq is the adsorbent concentration at equilibrium (mmol L1), qe is the adsorption capacity of the adsorbate (mmol g1), and Q0 and b are Lang-
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muir constants related to adsorption capacity and adsorption energy. The plot of Ceq/qe vs. Ceq gives a straight line with slope 1/Q0 corresponding to complete monolayer coverage (mmol g1); the interception is 1/Q0b. The linear correlation coefficient (R2) values strongly support the fact that metaladsorbent adsorption data closely fit the model. The Freundlich equation is an empirical equation employed to describe heterogeneous systems characterized by the heterogeneity factor 1/n. Therefore, a plot of lnqe vs. lnCeq gives reversible adsorption and it is not restricted to the formation of a monolayer. This isotherm model is the most important multisite adsorption isotherm for heterogeneous surfaces and it is another form of Langmuir’s approach of adsorption on an amorphous surface. The amount of adsorbed material is the summation of adsorption on all sites [20]. The Freundlich model is described by the following equation: ln qe ¼ bF ln C eq þ ln k F
ð4Þ
where kF and n are characteristic constants of the adsorbent/adsorbate system and may be determined by linear fitting. Ceq is the concentration of the adsorbent in equilibrium (mmol L1), qe is the adsorption capacity of the adsorbate (mmol g1), and bF ¼ 1n. Fig. 5a–b shows the Langmuir and Freundlich isotherms, respectively, for Pb–ChSC and Fig. 6a–b shows the Langmuir and Freundlich isotherms, respectively, for Cu–ChSC. Table 1 summarizes the characteristic parameters of these isotherms. The Langmuir isotherm model shows that the Pb– ChSC bL values are higher than those of Cu–ChSC. Q0 values of Pb–ChSC and Cu–ChSC are different.
Different bL and Q0 values for the two metals are not an essential factor for the Freundlich model. The bL value of Cu–ChSC is 2.7640 L mmol1 and that of Pb–ChSC is 0.2019 L mmol1. The Q0 value of Pb–ChSC is 0.8773 mmol g1 and that of Cu–ChSC is 0.3533 mmol g1. It was noted that the adsorption energy of Cu–ChSC is higher than that of Pb–ChSC; this analysis was based on bL values, which were higher for Cu–ChSC than for Pb– ChSC. On the other hand, Q0 formation is supported by Pb–ChSC instead of Cu–ChSC. It suggests that our data fit better the Langmuir model than Freundlich’s. The R2 for Langmuir’s data suggest that Pb–ChSC adsorption is more favored than the Cu–ChSC one is. Different adsorption enthalpies may affect these data. In the case of the Freundlich’s model, kF is higher for Cu–ChSC than for Pb–ChSC, and bF values are also higher for Cu– ChSC than for Pb–ChSC. As the kF parameter is different for each metal-ChSC and both bF values are 0 6 bF 6 1, either electrostatic interaction or ion-exchange or a metal adsorption combined mechanism is supported. The R2 values are higher for Pb–ChSC than for Cu–ChSC, which is attributed to the better fit of Freundlich’s model comparatively to Langmuir’s. 3.6. Thermogravimetric and differentiate analyses Fig. 7a–b shows the thermogravimetric analysis (TGA) and the differential calculations, respectively, for pure ChSC, Pb–ChSC, and Cu–ChSC. The adsorption of metal ions such as Pb2+ and Cu2+ onto ChSC may decrease its thermal instability. It was observed that pure ChSC and metal-ChSC 0.024
a 10
b
0.022
ln qe (mmol g-1)
Ceq/qe (g L-1)
639
9 8 7
0.020 0.018 0.016 0.014 0.012
6
0.010 0.5
1.0
1.5
2.0
2.5
Ceq (mmol
3.0
L-1)
3.5
4.0
1.5
-1.0
-0.5
0.0
lnCeq (mmol
0.5
1.0
1.5
L-1)
Fig. 5. Langmuir (a) and Freundlich (b) isotherms for adsorption of Pb2+ onto ChSC. DT 90 min, particle size from 300 to 425 lm, pH 5.0, contact time 24 h, temperature of 20.0 ± 0.1 °C and 250 rpm stirring.
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18 16
a
0.064 0.062
ln qe (mmol g-1)
14
Ceq/qe (g L-1)
b
12 10 8 6 4
0.060 0.058 0.056 0.054 0.052 0.050
2 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
0.048 -1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
lnCeq (mmol L-1)
Ceq (mmol L-1)
Fig. 6. Langmuir (a) and Freundlich (b) isotherms for adsorption of Cu2+ onto ChSC. DT 90 min, particle size from 300 to 425 lm, pH 5.0, contact time of 24 h, temperature of 20.0 ± 0.1 °C and 250 rpm stirring.
Table 1 Langmuir and Freundlich isotherms for adsorption studies of Pb2+ and Cu2+ onto ChSC using bath experiment Metals
qe (mmol g1)
Langmuir isotherm for ChSC Pb2+ 0.4247 Cu2+ 1.5953 Metals
qe (mmol g1)
Freundlich isotherm for ChSC Pb2+ 0.4247 Cu2+ 1.5953
R2
pH
bL (L mmol1)
Q0 (mmol g1)
0.9695 0.9815
5.0 5.0
0.2019 2.7640
0.8773 0.3533
R2
pH
bF (L mmol1)
kF (L g1)
0.9976 0.9636
5.0 5.0
0.004830 0.005384
1.0372 1.1327
degrade in two stages. For pure ChSC, the first stage begins at 90 °C with 5.5% weight loss and the second begins at 300 °C, reaching maximum degradation at 350 °C with 45% weight loss. For Pb–ChSC, the first stage begins at 90 °C with 6.5% weight loss and the second one begins at 300 °C, with maximum degradation at 400 °C. For Cu–ChSC, the first stage begins at 250 °C and reaches maximum degradation at 350 °C. The TGA results of pure ChSC, Pb–ChSC, and Cu–ChSC indicate that Pb–ChSC is less stable than Cu–ChSC is. On the other hand, pure ChSC is as stable as the Pb–ChSC complex is. Fig. 7b shows the results previously discussed. The differential signs indicate that the order of degradation is: Pb–ChSC ffi pure ChSC > Cu–ChSC. 3.7. Removal of Fe3+, Pb2+, and Cu2+ from wastewater in column experiment Fig. 8a–b show the column experiment used in the removal of metals from battery wastewater. Fig. 8a shows a column with pure ChSC. Metals
such as Fe3+, Pb2+, and Cu2+ may interact with ChSC in different ways. After passing battery wastewater through the column, it was observed that the Cu–ChSC complex is blue as indicated at the bottom of the column in Fig. 8b. The Fe–ChSC complex is yellow as indicated at the top of the column and the Pb–ChSC complex is colorless. Fig. 8c shows the system used. The samples were run through the column by gravitational difference. 3.8. Breakthrough profiles Fig. 9a–b show the breakthrough profiles for metal adsorption at two different pHs, fixed ChSC mass (90 min deacetylation), and a given flow rate. The plot of C/C0 against time is given. The breakthrough curves become less sharp when the mass transfer rate decreases. An s-shape curve occurred when the mass transfer was finite. The metal uptake may be changed under different experimental conditions [24]. Metal uptake increased with the increase in pH, which was attributed to the competition
A.T. Paulino et al. / Reactive & Functional Polymers 68 (2008) 634–642
a
7 6
% weight
0.00
Pb-ChSC
differentiate
8
Pure ChSC
5 4 Cu-ChSC
3 2
641
b
-0.02 Cu-ChSC
-0.04 -0.06
Pb-ChSC
-0.08
Pure ChSC
1 100
200
300
400
500
600
100
Temperature ºC
200
300
400
500
600
Temperature ºC
Fig. 7. TGA curves (a) and differential calculation (b) of pure ChSC, Pb–ChSC, and Cu–ChSC.
Fig. 8. Column experiments for adsorption of Fe3+, Cu2+, and Pb2+ from battery manufacture wastewater. (a) Columns with pure ChSC (DD 80%), (b) ChSC (DD 80%) plus adsorbed metals, (c) system used in experiments.
1.0
b
a
0.8
0.8
0.6
0.6
0.4
C/C0
C/C0
1.0
Pb2+ Cu
0.2
Fe
0.4
Pb2+
2+
Cu2+
0.2
3+
0.0
Fe3+
0.0 0
200
400
600
mim
800
1000
1200
0
200 400 600 800 1000 1200 1400 1600
mim
Fig. 9. Breakthrough profiles for the removal of Fe3+, Cu2+, and Pb2+ from battery manufacture wastewater with ChSC-packed columns. (a) pH 3.0, (b) pH 5.0. Others experimental conditions for both conditions: Flow rate of 1 mL min1, adsorbent mass of 50 mg, particle size from 300 to 425 lm.
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between H+ and metal ions for ChSC amine groups. On the other hand, at pH higher than 6.0, the metals precipitate as hydroxides as well, as shown by results of a previous bath experiment for the removal of metals. The metal removal order was: Fe–ChSC > Cu–ChSC > Pb–ChSC at both pHs analyzed. The column regeneration for the recovery of metal ions as well as the use of biosorbent was performed running 0.1 mol L1 HCl for 20 min. 4. Conclusion Pure ChSC is an effective adsorbent for the removal of Fe3+, Cu2+, and Pb2+ from battery manufacture wastewater. Studies using bath experiments were carried out to analyze the appropriate DD of ChSC for the removal of Pb2+ and Cu2+ from battery wastewater. XRD analyses may be used to predict the amount of amine groups supported by pure ChSC. The best pure ChSC DDs obtained for the removal of Pb2+ and Cu2+ from battery wastewater are 80% (90 min ChSC deacetylation) and 92% (180 min ChSC deacetylation), respectively. The maximum adsorption capacities for Pb2+ and Cu2+ using pure ChSC with 80% and 92% DD were 72 mg g1 and 87 mg g1, respectively. Experimental conditions for these analyses were: pH 5.0, particle size from 300 to 425 lm, temperature of 20.0 ± 0.1 °C, and 250 rpm stirring. Langmuir model data suggest that adsorption is more favored for Pb–ChSC than for Cu–ChSC. Freundlich model data such as the kF parameter are different for each metal-ChSC and bF values are 0 6 bF 6 1, supporting either electrostatic interaction or ion-exchange or a metal adsorption combined mechanism onto ChSC. The thermal behavior of Pb–ChSC is on the same profile of pure ChSC. On the other hand, the thermal behavior of Cu–ChSC is higher than that of pure ChSC. Column experiments may be an alternative method for the removal of Fe3+, Cu2+, and Pb2+ from battery wastewater. Pure ChSC is suitable for the removal of heavy metals from battery wastewater. From the economic view point, it could be pointed out that the use of pure ChSC as a low-cost adsorbent of heavy metals such as Pb2+ may be a solution for industries to treat battery manufacture wastewater.
Acknowledgments We thank CAPES (Brazil), CNPq (Brazil), Fundacßa˜o Araucaria-PR (Brazil) for the financial support and Cocamar (Cooperativa Agroindustrial de Maringa´) Maringa´/PR Brazil for silkworm chrysalide samples. References [1] S. Davydova, Microchem. J. 79 (2005) 133–136. [2] A.T. Paulino, J.A.A. Tessari, E.M. Nogami, E. Lenzi, J. Nozaki, Bull. Environ. Contam. Toxicol. 75 (2005) 42–49. [3] E. Merian, M. Anke, M. Ihnat, M. Stoeppler, Metals and their compounds in the environment: occurrence, analysis and biological relevance, John Wiley & Sons, New York, 2004. [4] B. Murphy, B. Hathaway, Coord. Chem. Rev. 243 (2003) 237–262. [5] W.S. Wan Ngah, S.Ab. Ghani, A. Kamari, Biores. Technol. 96 (2005) 443–450. [6] H.J. Hapke, In: E. Merian (Ed.), VCH Weinheim, New York, (1991) pp. 469–479. [7] A.T. Paulino, M.R. Guilherme, A.V. Reis, G.C. Campese, E.C. Muniz, J. Nozaki, J. Coll. Interf. Sci. 301 (2006) 55–62. [8] V.K. Gupta, A. Mittal, V. Gajbe, J. Coll. Interf. Sci. 284 (2005) 89–98. [9] C. Gee´rente, P.C. Mesnila, Y. Andre`s, J.-F. Thibault, P. Le Cloirec, Reac. Func. Polym. 46 (2000) 135–144. [10] R. Coskun, C. Soykan, M. Sacßak, Reac. Func. Polym. 66 (2006) 599–608. [11] V.K. Gupta, S. Sharma, Ind. Eng. Chem. Res. 42 (2003) 6619–6624. [12] W.S. Wan Ngah, C.S. Endud, R. Mayanar, Reac. Func. Polym. 50 (2002) 181–190. [13] S.S. Gupta, K.G. Bhattacharyya, J. Coll. Interf. Sci. 295 (2006) 21–32. [14] J. Synowiecki, N.A. Al-Khateeb, Crit. Rev. Food Sci. Nutr. 43 (2003) 145–171. [15] A.T. Paulino, J.I. Simionato, J.C. Garcia, J. Nozaki, Carbohydr. Polym. 64 (2006) 98–103. [16] V.W.D. Chui, K.W. Mok, C.Y. Ng, B.P. Luong, K.K. Ma, Environ. Inter. 22 (1996) 463–468. [17] R.A.A. Muzzarelli, F. Tanfani, G. Scarpini, G. Laterza, J. Biochem. Biophys. Method. 2 (1980) 299–306. [18] R.H. Chen, H-D. Hwa, Carbohydr. Polym. 29 (1996) 353– 358. [19] A.B.V. Kuma, M.C. Varadaraj, R.G. Lalithac, R.N. Tharanathan, Biochem. Biophys. Acta 1670 (2004) 137–146. [20] A.T. Paulino, F.A.S. Minasse, M.R. Guilherme, A.V. Reis, E.C. Muniz, J. Nozaki, J. Coll. Interf. Sci. 301 (2006) 479– 487. [21] J.I. Simionato, A.T. Paulino, J.C. Garcia, J. Nozaki, Polym. Inter. 55 (2006) 1243–1248. [22] Y. Zhang, C. Xue, Y. Xue, R. Gao, X. Zhang, Carbohydr. Res. 340 (2005) 1914–1917. [23] A.L. Debbaudt, M.L. Ferreira, M.E. Gschaider, Carbohydr. Polym. 56 (2004) 321–332. [24] Z. Zulfadhly, M.D. Mashitah, S. Bhatia, Environ. Pollut. 112 (2001) 463–470.
REACTIVE & FUNCTIONAL POLYMERS
Reactive & Functional Polymers 68 (2008) 634–642
www.elsevier.com/locate/react
Removal of Pb2+, Cu2+, and Fe3+ from battery manufacture wastewater by chitosan produced from silkworm chrysalides as a low-cost adsorbent Alexandre Tadeu Paulino *, Lı´dia Brizola Santos, Jorge Nozaki 1 Universidade Estadual de Maringa´, Po´s-Graduacßa˜o em Quı´mica, Av. Colombo, 5790 CEP 87020-900 Maringa´, PR, Brazil Received 13 June 2006; received in revised form 4 May 2007; accepted 6 October 2007 Available online 1 November 2007
Abstract In this work, it was investigated the best ChSC deacetylation time (DT) for the removal of Pb2+ and Cu2+ from battery manufacture wastewater. Bath experiments were used to determine the best adsorption conditions. The best DT for Cu2+ removal was 180 min (92% deacetylation) and for Pb2+ removal was 90 min (80% deacetylation). The maximum adsorption capacities of Pb–ChSC and Cu–ChCS were 0.4247 mmol g1 and 1.5953 mmol g1, respectively, for contact time of 24 h, pH 5.0, particle size from 300 to 425 lm, and temperature of 20 ± 0.1 °C. Metal adsorption onto ChSC was evaluated by Langmuir and Freundlich isotherms. An experimental column packed with ChCS was used to remove Fe3+, Cu2+, and Pb2+ from battery wastewater. Experimental column results were obtained by plotting C/C0 against time. Metal adsorption onto ChSC in column was higher at pH 5.0 than pH 3.0. The results of this work support the use of ChSC in battery wastewater treatment. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Silkworm chrysalides; Low-cost adsorbent; Chitosan; Battery wastewater; Metals
1. Introduction All living beings are affected by the presence of heavy metals, which are frequently discarded in water flow near cities [1]. Many metals are essential for several organisms, from bacteria to even the human being; however, low concentrations are
*
Corresponding author. Tel.: +55 44 3261 4332; fax: +55 44 3261 4125. E-mail address: [email protected] (A.T. Paulino). 1 In memoriam.
required; otherwise, they may damage the biological systems [2]. Lead (Pb2+), one of the metals of interest in this work, may be found in the environment (atmosphere, water, soil, rocks and sediments) and in the biosphere. Lead may cause mental disturbance, retardation, and semi-permanent brain damage and it does not have an important biological activity. It is classified as a persistent environmental toxic substance and is toxic in even very small amounts, with a toxicity limit is <0.05 lg mL1 [3]. Another, copper (Cu2+), an abundant and naturally occurring element, it may be toxic if ingested in large amounts.
1381-5148/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2007.10.028
A.T. Paulino et al. / Reactive & Functional Polymers 68 (2008) 634–642
It participates in vegetable metabolism in two ways: in the synthesis of chlorophyll and in the activity of other enzymes. Although Cu2+ does not exist in chlorophyll, it is indispensable for vegetables and its lack may result in photosynthetic deficiencies and incapacity to produce seeds. It is also a constituent of enzymes responsible for the catalysis of oxidation–reduction reactions. The lack of Cu2+ in animal diet may lead to anemia, diarrhea, and nervous disturbances. On the other hand, the excessive ingestion of this element may result in vomit, cramps, convulsion, and even death [4]. Iron (Fe3+), the third metal of interest, and Cu2+ are essential micronutrients for animals and plants. However, they become toxic at high levels. Fe3+, the fourth most abundant element on the earth crust, is present in a variety of rocks, soils, and minerals. This element is important for the biosphere due to its essential role in photosynthesis and because it is a phytoplankton growth limiting nutrient in some parts of the ocean [5]. Fe3+ is also an important active center in a wide range of proteins such as oxidases, reductases, and dehydrases [6]. Battery manufacture wastewater contains high amounts of Fe3+, Pb2+, and Cu2+ and may not be disposed to the environment without previous treatment. In recent years, solid adsorbents have been widely used for the removal of heavy metals and dyes in low-cost wastewater treatment [7–10]. Low-cost adsorbents may be used as an alternative large scale wastewater treatment procedure [11– 13]. Chitosan is a polysaccharide obtained by deacetylation of chitin (copolymer b-(1,4)-D-glucosamin and b-(1,4)-N-acetyl-D-glucosamin), which is abundant in nature, principally in shells of crustaceans, terrestrial invertebrates, and fungi [14]. New sources for the production of chitin and chitosan have been explored, thus making the treatment of industrial wastewater at a cost lower than that using chitin and chitosan obtained from crustaceans possible [15]. The aim of this work was to remove metals such as Pb2+, Cu2+, and Fe3+ from battery manufacture wastewater using chitosan obtained from silkworm chrysalides (ChSC) as a low-cost adsorbent. The best conditions for the removal of Pb2+ and Cu2+ from aqueous solutions were determined at various pHs, contact times, and deacetylation times (DT). The uptake of Fe3+, Pb2+, and Cu2+ from battery manufacture wastewater was carried out by adsorption and desorption process in ChSC-packed column [16].
635
2. Materials and methods 2.1. Production of chitin and ChSC Silkworm chrysalide samples were kindly supplied by Cocamar silk spinning (Cooperativa Agroindustrial, Maringa´, PR, Brazil). The samples were lyophilized and triturated in an automatic knife crusher. A portion of silkworms was carefully weighed and treated with HCl 1.0 mol L1 (1:15 w/v) at 90 °C for 1 h under constant stirring for demineralization. The residues were filtered out and treated with NaOH 1.0 mol L1 (1:10 w/v) at 70 °C for 2 h under constant stirring for deproteination. The residues were filtered out and washed up to the neutralization of chitin [15]. The chitin obtained in the previous experiment was weighed and deacetylated with 40% NaOH/ NaHB4 (0.250 g NaHB4 and 300 mL 40% NaOH) at 110 °C for five different times under constant stirring. The solid produced was filtered and washed several times until pH 7.0 ± 0.2 was reached [15]. The adsorption DTs studied were: 30, 90, 120, 180, and 240 min. 2.2. Acetylation degree of ChSC ChSC samples were submitted to nuclear magnetic resonance spectroscopy (1H NMR model Varian, Mercury plus BB spectrometer) to determine the acetylation degree (AD). The solid ChSC samples were dissolved in diluted CD3COOD solution. Deacetylation degree (DD) may be associated to AD in Eq. (1), which describes the percent correlations between AD and acetyl groups in the polymer chain. ACH3 % AD ¼ 100 ð1Þ 3AH2 where ACH3 is the signal area corresponding to the hydrogen bound to CH3 groups, and AH2 is attributed to the signal area corresponding to the hydrogen bound to carbon-2 of the glucosamin group [17,18]. 2.3. X-ray powder diffraction of chitin and ChSC ChSC samples were submitted to XRD (X-ray powder diffraction) analyses and the results were compared with those of commercial chitosan (Across Organics Chitosan). X-ray diffractograms of powdered samples were obtained using a Bruker AXS D8 Advance X-ray diffractometer under operation conditions of 40.0 kV and 30.0 mA with Cu
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˚ . The slit parameters Ka1 radiation at k 1.54184 A used were: Divergence 1.0°, scatter 1.0° and receiving 0.3 mm. The scanning parameters were: Axis h – 2h ranging from 2.0 to 40.0, speed 5.0 min1, sampling pitch 0.05°, and preset time of 0.60 s. The crystallinity index (CrI) was determined by CrI020 = (I020 – Iam) X 100/I020, where I020 is the maximum intensity below 13° and Iam is the intensity of amorphous diffraction at 16°. Another crystallinity index was expressed as CrI110 using the maximum intensity at 20° [19]. 2.4. Determination of Pb2+ and Cu2+ by voltammetric method
ChSC. MilliQÒ water, 50 mL, was used to prepare 100 mg L1 solutions of Pb2+ and Cu2+ (Merck) in two separate flasks. The pH of the metal solutions was fixed at 5.0 and the solutions were stirred at 250 rpm. The temperature was 20.0 ± 0.1 °C, and particle size ranged from 300 to 425 lm. The adsorbent/adsorbate ratios (qe mg g1) were obtained by the difference between initial and final metal concentrations in solution. Particle size was selected through granulometric sieve (Granutest). [20]. The adsorption capacity (qe mg g1) was calculated according to the following equation: qe ¼
C 0 C eq V m
ð2Þ
The quantitative determination of adsorbed Pb2+ and Cu2+ and remaining in solution was carried out on an Autolab potentiostat/galvanostat (GPES). The method used was square wave voltammetry with a three-electrode system; hanging mercury drop working electrode (HMDE), Ag/AgCl reference electrode, and graphite electrode as support. Metal concentrations were determined from an analytical curve that correlates adsorption to metal concentrations. Volumes of 20 mL of appropriate supporting electrolyte and 100 lL of samples were placed in the cell for each analysis. The electrolytic solutions used in this procedure were prepared as follows: Amounts of 1000 mg L1 of Pb2+ and Cu2+ standards (Merck) were diluted to appropriate low concentration of 0.1 mol L1 HCl for Pb2+ evaluation and 0.1 mol L1 KNO3 for Cu2+ evaluation.
where C0 and Ceq are initial and equilibrium concentrations (mg L1), respectively, m is the adsorbate weight and V is the solution volume.
2.5. Determination of Fe3+ by FAAS measurements
3. Results and discussion
The quantitative determination of Fe3+ was carried out on a FAAS (CGAA 7000 ABC Spectrometer with air:acetylene flame and deuterium background correction). The concentrations of adsorbed metal and remaining in solution were determined through analytical curve. The Fe3+ standards used in analytical curve construction were prepared as follows: 1 mg mL1 Fe3+ (Merck) were diluted in 1000 mL of water to a final concentration of 1000 mg L1. Successive dilutions were carried out to prepare the analytical curve.
3.1. XRD analyses and deacetylation degree of ChSC
2.6. Bath experiments for the determination of the best adsorption conditions Bath adsorption experiments were conducted in a 125 mL Erlenmeyer to which was added 50 mg of
2.7. Column experiments for Fe3+, Pb2+, and Cu2+ removal from wastewater A column with 5 cm i.d. and 30 cm long was used. Amounts of 50 mg of ChSC were introduced at the bottom of the column and wastewater with Fe3+, Pb2+, and Cu2+ was passed through a column at a fixed flow rate. Downstream column wastewater samples were collected at different intervals of time and Fe3+ measurements were obtained by FAAS and Pb2+ and Cu2+ by GPES. The samples were collected until column and metal equilibrium were reached.
Fig. 1 shows the XRD results of chitin and ChSC. Chitin and chitosan are polymorphic forms occurring as a form in shrimp, crab shell waste, and silkworm chrysalides [15,21]. Processing adjustments based on the DD of chitin are frequently required to allow the quick preparation of chitosan. A relationship between the analyses of the crystalline structure by XRD and DD was proposed by Zhang [22]. According to the results shown in Fig. 1, CrI020 decreases when DD increases; therefore, it was supposed that commercial chitosan has higher DD than that of ChSC (90 min deacetylation). The DD of ChSC after 90 min of reaction with 40% NaOH/NaHB4 (0.250 g NaHB4 and 300 mL 40% NaOH) was 80% and that of commercial chitosan was 88%.
A.T. Paulino et al. / Reactive & Functional Polymers 68 (2008) 634–642
1400
Intensitity (%)
observed a significant increase in adsorption at pH between 4.5 and 5.5. The best pH interval, from 5.0 to 5.5, was chosen for the adsorption studies of Pb2+ and Cu2+ onto ChSC.
ChSC 90 min Chitosan standard Chitin from silkworm
(110)
1600
1200 1000
637
(020)
3.3. Best DT for ChSC removal of Pb2+ and Cu2+ from wastewater
800 600
Fig. 3a and b show the best DT (% deacetylation or DD) for ChSC in the adsorption studies of Pb2+ and Cu2+, respectively. Fig. 3a shows that the best DT of ChSC for the removal of Pb2+ from wastewater using bath experiments was 90 min with 80% deacetylation, the one which resulted in the largest removal of metal. The decrease in maximum adsorption capacity at higher DT was attributed to the biopolymer degradation, and the decrease in the molar mass and amino groups. Fig. 3b shows the best DT for Cu2+ removal using bath experiments. The best DT, the one that removed the largest amount of Cu2+, was 180 min with 92% deacetylation. The DT for the removal of Cu2+ was higher than that of Pb2+, which was attributed to the stabilization of the complex formed between NH2, OH, and HN A COOH groups and the metallic ions. Inter- and intramolecular chelation must be considered in adsorption studies of chitin, chitosan, and heavy metals [23]. Four interaction situations between metallic cations and NH2, OH, and COOH groups were considered. In form 1, the metallic cations may bind to two different NH2 groups of chitosan, or NH in the case of chitin. In form 2, the metallic cations may bind to one NH2 and one O6 of the second polysaccharide. In form 3, the metallic cations may bind to two O3 of the polysaccharide,
400 200 5
10
15
20
25
30
35
40
2θ (º) Fig. 1. X-Ray powder diffractograms of chitin from silkworm chrysalides, pure ChSC, and comparison with that of commercial chitosan (across organics chitosan).
3.2. pH effect on the adsorption of Pb2+ and Cu2+ onto ChSC Fig. 2a shows the precipitation of Pb2+ and Cu2+ in aqueous solution by pH changes using bath experiments. Fig. 2b shows the amounts of Pb2+ and Cu2+ adsorbed onto ChSC as a function of pH. At high pH, the metal ions precipitate as hydroxides and maximum adsorption capacity decreases. On the other hand, although Pb2+ and Cu2+ do not precipitate as hydroxides at low pH, they compete with H+ ions in solution for the basic NH2 groups of ChSC. In this condition, most NH2 groups are in the form of NHþ 3 . As it is not possible to establish interactions with any metal, a reduction of adsorption capacity follows. Otherwise, it was
a
100
Cu2+
140
mg metal / g ChSC
Concentration (mg L-1)
160
120 Pb2+
100 80 60 40
b
Cu2+
90 80
Pb2+
70 60 50 40
20 30
0 3
4
5
6
7
3.0
8
(pH)
3.5
4.0
4.5
5.0
5.5
6.0
(pH) 2+
2+
Fig. 2. Effect of pH changes on the precipitation of Pb and Cu in aqueous solutions (a) and on the adsorption of Pb2+ and Cu2+ (b) onto ChSC. Experimental parameters were: particle size from 300 to 425 lm, temperature of 20.0 ± 0.1 °C, and 250 rpm stirring.
A.T. Paulino et al. / Reactive & Functional Polymers 68 (2008) 634–642
60 55 50 45 40 35 30 25 20 15 10 5 0
a
90 min 30 min 120 min 180 min 240 min
0
100
200
300
mgCu2+ / g ChSC
mg Pb2+/ g ChSC
638
85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5
400
b
180 min 240 min 120 min
90 min
30 min
0
100
200
(min)
300
400
(min)
Fig. 3. Effect of DT on the adsorption capacities of Pb2+ (a) and Cu2+ (b) by ChSC. Experimental parameters were: particle size from 300 to 425 lm, pH 5.0, temperature of 20.0 ± 0.1 °C, and 250 rpm stirring.
3.4. Maximum adsorption capacity for Pb–ChSC and Cu–ChSC Fig. 4 shows the maximum adsorption capacity for Pb2+ and Cu2+ onto ChSC using bath experiments. The maximum adsorption capacities of Pb– ChSC and Cu–ChCS were 87 mg g1 and 72 mg g1, respectively, at contact time 24 h, pH 5.0, particle size from 300 to 425 lm, 250 rpm stirring, and temperature of 20 ± 0.1 °C. The difference between the maximum adsorption capacities of Pb2+ and Cu2+ was attributed to factors such as ionic size, steric hindrance, coordination number, aggregation, different complex properties, hydrolysis constants, and electrostatic forces. As shown by morphologic analysis of previous works [20,21], the ChSC surface exhibits a larger porous morphology than that of chitosan obtained from crustaceans. In this condition, ChSC performed better in the removal of Pb2+ and Cu2+ from wastewater than chitosan from crustaceans did.
90 80
mg metals / g ChSC
and in form 4, the metallic cations bind to two O (either O6 or O3) of the different polysaccharides. Taking this into account, Cu2+ interacts more favorably with NH2 groups than with other groups such as OH and COOH. As a result, the largest amount of Cu2+ was removed from wastewater with sufficient ChSC deacetylation. On the other hand, Pb2+ may interact with either NH2 groups or OH and COOH groups. It was observed that ChSC with low DD supported the removal of a larger amount of Pb2+ from wastewater, while for the removal of Cu2+, it was necessary a DD higher than that for the removal of Pb2+.
70 60 Cu2+
50
Pb2+
40 30 20 0
20
40
60
80
100
(hours) Fig. 4. Maximum adsorption capacity of Pb2+ and Cu2+ by ChSC with DT 90 min, pH 5.0, particle size from 300 to 425 lm, 250 rpm stirring, and temperature of 20.0 ± 0.1 °C.
3.5. Langmuir and Freundlich equilibrium isotherms The Langmuir isotherm model assumes that adsorption occurs in a monolayer or that adsorption may only occur at a fixed number of localized sites on the surface with all adsorption sites identical and energetically equivalent. The Langmuir equation is based on the assumptions of a structurally homogeneous adsorbent and is described by the following equation: C eq C eq 1 ¼ þ qe Q0 Q0 b
ð3Þ
where Ceq is the adsorbent concentration at equilibrium (mmol L1), qe is the adsorption capacity of the adsorbate (mmol g1), and Q0 and b are Lang-
A.T. Paulino et al. / Reactive & Functional Polymers 68 (2008) 634–642
muir constants related to adsorption capacity and adsorption energy. The plot of Ceq/qe vs. Ceq gives a straight line with slope 1/Q0 corresponding to complete monolayer coverage (mmol g1); the interception is 1/Q0b. The linear correlation coefficient (R2) values strongly support the fact that metaladsorbent adsorption data closely fit the model. The Freundlich equation is an empirical equation employed to describe heterogeneous systems characterized by the heterogeneity factor 1/n. Therefore, a plot of lnqe vs. lnCeq gives reversible adsorption and it is not restricted to the formation of a monolayer. This isotherm model is the most important multisite adsorption isotherm for heterogeneous surfaces and it is another form of Langmuir’s approach of adsorption on an amorphous surface. The amount of adsorbed material is the summation of adsorption on all sites [20]. The Freundlich model is described by the following equation: ln qe ¼ bF ln C eq þ ln k F
ð4Þ
where kF and n are characteristic constants of the adsorbent/adsorbate system and may be determined by linear fitting. Ceq is the concentration of the adsorbent in equilibrium (mmol L1), qe is the adsorption capacity of the adsorbate (mmol g1), and bF ¼ 1n. Fig. 5a–b shows the Langmuir and Freundlich isotherms, respectively, for Pb–ChSC and Fig. 6a–b shows the Langmuir and Freundlich isotherms, respectively, for Cu–ChSC. Table 1 summarizes the characteristic parameters of these isotherms. The Langmuir isotherm model shows that the Pb– ChSC bL values are higher than those of Cu–ChSC. Q0 values of Pb–ChSC and Cu–ChSC are different.
Different bL and Q0 values for the two metals are not an essential factor for the Freundlich model. The bL value of Cu–ChSC is 2.7640 L mmol1 and that of Pb–ChSC is 0.2019 L mmol1. The Q0 value of Pb–ChSC is 0.8773 mmol g1 and that of Cu–ChSC is 0.3533 mmol g1. It was noted that the adsorption energy of Cu–ChSC is higher than that of Pb–ChSC; this analysis was based on bL values, which were higher for Cu–ChSC than for Pb– ChSC. On the other hand, Q0 formation is supported by Pb–ChSC instead of Cu–ChSC. It suggests that our data fit better the Langmuir model than Freundlich’s. The R2 for Langmuir’s data suggest that Pb–ChSC adsorption is more favored than the Cu–ChSC one is. Different adsorption enthalpies may affect these data. In the case of the Freundlich’s model, kF is higher for Cu–ChSC than for Pb–ChSC, and bF values are also higher for Cu– ChSC than for Pb–ChSC. As the kF parameter is different for each metal-ChSC and both bF values are 0 6 bF 6 1, either electrostatic interaction or ion-exchange or a metal adsorption combined mechanism is supported. The R2 values are higher for Pb–ChSC than for Cu–ChSC, which is attributed to the better fit of Freundlich’s model comparatively to Langmuir’s. 3.6. Thermogravimetric and differentiate analyses Fig. 7a–b shows the thermogravimetric analysis (TGA) and the differential calculations, respectively, for pure ChSC, Pb–ChSC, and Cu–ChSC. The adsorption of metal ions such as Pb2+ and Cu2+ onto ChSC may decrease its thermal instability. It was observed that pure ChSC and metal-ChSC 0.024
a 10
b
0.022
ln qe (mmol g-1)
Ceq/qe (g L-1)
639
9 8 7
0.020 0.018 0.016 0.014 0.012
6
0.010 0.5
1.0
1.5
2.0
2.5
Ceq (mmol
3.0
L-1)
3.5
4.0
1.5
-1.0
-0.5
0.0
lnCeq (mmol
0.5
1.0
1.5
L-1)
Fig. 5. Langmuir (a) and Freundlich (b) isotherms for adsorption of Pb2+ onto ChSC. DT 90 min, particle size from 300 to 425 lm, pH 5.0, contact time 24 h, temperature of 20.0 ± 0.1 °C and 250 rpm stirring.
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18 16
a
0.064 0.062
ln qe (mmol g-1)
14
Ceq/qe (g L-1)
b
12 10 8 6 4
0.060 0.058 0.056 0.054 0.052 0.050
2 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
0.048 -1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
lnCeq (mmol L-1)
Ceq (mmol L-1)
Fig. 6. Langmuir (a) and Freundlich (b) isotherms for adsorption of Cu2+ onto ChSC. DT 90 min, particle size from 300 to 425 lm, pH 5.0, contact time of 24 h, temperature of 20.0 ± 0.1 °C and 250 rpm stirring.
Table 1 Langmuir and Freundlich isotherms for adsorption studies of Pb2+ and Cu2+ onto ChSC using bath experiment Metals
qe (mmol g1)
Langmuir isotherm for ChSC Pb2+ 0.4247 Cu2+ 1.5953 Metals
qe (mmol g1)
Freundlich isotherm for ChSC Pb2+ 0.4247 Cu2+ 1.5953
R2
pH
bL (L mmol1)
Q0 (mmol g1)
0.9695 0.9815
5.0 5.0
0.2019 2.7640
0.8773 0.3533
R2
pH
bF (L mmol1)
kF (L g1)
0.9976 0.9636
5.0 5.0
0.004830 0.005384
1.0372 1.1327
degrade in two stages. For pure ChSC, the first stage begins at 90 °C with 5.5% weight loss and the second begins at 300 °C, reaching maximum degradation at 350 °C with 45% weight loss. For Pb–ChSC, the first stage begins at 90 °C with 6.5% weight loss and the second one begins at 300 °C, with maximum degradation at 400 °C. For Cu–ChSC, the first stage begins at 250 °C and reaches maximum degradation at 350 °C. The TGA results of pure ChSC, Pb–ChSC, and Cu–ChSC indicate that Pb–ChSC is less stable than Cu–ChSC is. On the other hand, pure ChSC is as stable as the Pb–ChSC complex is. Fig. 7b shows the results previously discussed. The differential signs indicate that the order of degradation is: Pb–ChSC ffi pure ChSC > Cu–ChSC. 3.7. Removal of Fe3+, Pb2+, and Cu2+ from wastewater in column experiment Fig. 8a–b show the column experiment used in the removal of metals from battery wastewater. Fig. 8a shows a column with pure ChSC. Metals
such as Fe3+, Pb2+, and Cu2+ may interact with ChSC in different ways. After passing battery wastewater through the column, it was observed that the Cu–ChSC complex is blue as indicated at the bottom of the column in Fig. 8b. The Fe–ChSC complex is yellow as indicated at the top of the column and the Pb–ChSC complex is colorless. Fig. 8c shows the system used. The samples were run through the column by gravitational difference. 3.8. Breakthrough profiles Fig. 9a–b show the breakthrough profiles for metal adsorption at two different pHs, fixed ChSC mass (90 min deacetylation), and a given flow rate. The plot of C/C0 against time is given. The breakthrough curves become less sharp when the mass transfer rate decreases. An s-shape curve occurred when the mass transfer was finite. The metal uptake may be changed under different experimental conditions [24]. Metal uptake increased with the increase in pH, which was attributed to the competition
A.T. Paulino et al. / Reactive & Functional Polymers 68 (2008) 634–642
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Fig. 8. Column experiments for adsorption of Fe3+, Cu2+, and Pb2+ from battery manufacture wastewater. (a) Columns with pure ChSC (DD 80%), (b) ChSC (DD 80%) plus adsorbed metals, (c) system used in experiments.
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Fig. 9. Breakthrough profiles for the removal of Fe3+, Cu2+, and Pb2+ from battery manufacture wastewater with ChSC-packed columns. (a) pH 3.0, (b) pH 5.0. Others experimental conditions for both conditions: Flow rate of 1 mL min1, adsorbent mass of 50 mg, particle size from 300 to 425 lm.
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between H+ and metal ions for ChSC amine groups. On the other hand, at pH higher than 6.0, the metals precipitate as hydroxides as well, as shown by results of a previous bath experiment for the removal of metals. The metal removal order was: Fe–ChSC > Cu–ChSC > Pb–ChSC at both pHs analyzed. The column regeneration for the recovery of metal ions as well as the use of biosorbent was performed running 0.1 mol L1 HCl for 20 min. 4. Conclusion Pure ChSC is an effective adsorbent for the removal of Fe3+, Cu2+, and Pb2+ from battery manufacture wastewater. Studies using bath experiments were carried out to analyze the appropriate DD of ChSC for the removal of Pb2+ and Cu2+ from battery wastewater. XRD analyses may be used to predict the amount of amine groups supported by pure ChSC. The best pure ChSC DDs obtained for the removal of Pb2+ and Cu2+ from battery wastewater are 80% (90 min ChSC deacetylation) and 92% (180 min ChSC deacetylation), respectively. The maximum adsorption capacities for Pb2+ and Cu2+ using pure ChSC with 80% and 92% DD were 72 mg g1 and 87 mg g1, respectively. Experimental conditions for these analyses were: pH 5.0, particle size from 300 to 425 lm, temperature of 20.0 ± 0.1 °C, and 250 rpm stirring. Langmuir model data suggest that adsorption is more favored for Pb–ChSC than for Cu–ChSC. Freundlich model data such as the kF parameter are different for each metal-ChSC and bF values are 0 6 bF 6 1, supporting either electrostatic interaction or ion-exchange or a metal adsorption combined mechanism onto ChSC. The thermal behavior of Pb–ChSC is on the same profile of pure ChSC. On the other hand, the thermal behavior of Cu–ChSC is higher than that of pure ChSC. Column experiments may be an alternative method for the removal of Fe3+, Cu2+, and Pb2+ from battery wastewater. Pure ChSC is suitable for the removal of heavy metals from battery wastewater. From the economic view point, it could be pointed out that the use of pure ChSC as a low-cost adsorbent of heavy metals such as Pb2+ may be a solution for industries to treat battery manufacture wastewater.
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