73 Sustain. Environ. Res., 25(2), 73-81 (2015) Batch and fixed bed studies: Removal of copper(II) using chitosan-coated kaolinite beads from aqueous solution I-Ping Chen,1 Chi-Chuan Kan,2 Cybelle Morales Futalan,3 Mary Jane C. Calagui,4 Shiow-Shyung Lin,1 Wan Chi Tsai5 and Meng-Wei Wan1,* 1 Department of Environmental Engineering and Science Chia Nan University of Pharmacy and Science Tainan 71710, Taiwan 2 Institute of Hot Spring Industrial Chia Nan University of Pharmacy and Science Tainan 71710, Taiwan 3 Department of Environmental Engineering University of the Philippines-Diliman Quezon City 1101, Philippines 4 College of Chemical Engineering Cagayan State University Cagayan 3500, Philippines 5 Department of Medical Laboratory Science and Biotechnology Kaohsiung Medical University Kaohsiung 80708, Taiwan Key Words: Breakthrough curve, chitosan, fixed bed, groundwater, kaolinite ABSTRACT In this study, Cu(II) removal under batch and fixed-bed conditions using chitosan-coated kaolinite (CCK) was investigated. The surface morphology of CCK was characterized using scanning electron microscopy. Batch experiments showed that 1:20 chitosan to kaolinite ratio can provide satisfactory Cu(II) removal. Kinetics study revealed that adsorption is best described by pseudo-second order equation (R2 > 0.99). The isotherm data of Cu(II) adsorption using different ratios of CCK fitted well with Langmuir model (R2 > 0.98). The Langmuir constant, qmL has the following values of 11.2, 9.4 and 8.9 mg g-1 for 1:5, 1:10 and 1:20 chitosan to kaolinite ratio. In fixed bed studies, Cu(II) uptake increases and longer breakthrough time are attained as pH becomes more acidic. In addition, about 93% of Cu(II) removal from real groundwater system was attained using 2 g CCK. INTRODUCTION Copper, an essential mineral needed by the human body, is generated by several anthropogenic sources such as cooling water systems, mining, fungicide manufacturing, metal electroplating and finishing [1]. An increase in Cu(II) intake can cause health problems like Wilson’s disease, gastrointestinal disturbance, vomiting, and lesions in the central nervous system [2,3]. In addition, heavy metal contamination in surface water and groundwater will further prevent any beneficial use of the water bodies. Among the physicochemical treatment for heavy metal removal, adsorption has the ability to remove contaminants in wastewater with high solute loading *Corresponding author Email: [email protected] and even at dilute concentrations [4]. However, using commercialized adsorbent such as activated carbon is considered to be expensive, which leads to high operational costs [5]. On the other hand, chitosan has been proven to have the highest metal chelating capacity among natural adsorbents [6]. Chitosan, polyβ(1→4)-2-amino-2-deoxy-ᴅ-glucose, is produced through deacetylation of chitin using a strong alkaline solution [7]. Due to its hydrophilicity, it becomes soft and gel-like in aqueous media [4]. In addition, it easily swells and crumbles and has a low specific surface area [1,8]. Modification could be applied to chitosan in order to improve its chemical and mechanical properties. Physical modification such as coating chitosan on a support material would enhance the accessibility of 74 Chen et al., Sustain. Environ. Res., 25(2), 73-81 (2015) its binding sites and improve its mechanical stability [9,10]. Clay materials are made up of the colloidal fraction (< 2 μm) from soils, sediments and rocks [11]. They are abundant, cheap and have relatively large surface areas [12], which makes clay minerals an attractive support or immobilization material for chitosan. Kaolinite has a 1:1 aluminosilicate structure, which is the most abundant phyllosilicate mineral found from weathered soils [13]. Recent studies have been carried out on chitosan-bentonite or chitosanmontmorillonite composites in the removal of tannic acid [14], heavy metals [15-20], tungsten [21] and dyes [22]. Only a few batch studies have been performed on chitosan-coated kaolinite (CCK) in the removal of copper [23]. In addition, no fixed bed studies or studies utilizing real groundwater have been carried out on copper removal using CCK. In continuation of the work made by Kan et al. [23] the removal of Cu(II) using CCK from aqueous solution under batch and fixed bed conditions was studied. The effect of initial concentration and ratio of chitosan to kaolinite on Cu(II) removal and adsorption capacity was investigated. Kinetic experimental data were analyzed using pseudo-first and pseudo-second order equation. Equilibrium data were evaluated using Langmuir and Freundlich isotherm. Fixed bed studies examined the effect of pH on the shape of the breakthrough curve. MATERIALS AND METHODS 1.Chemicals (FTIR, Jusco FTIR-410) with a disc composing of 1:10 ratio of sample to KBr. 3.Preparation of CCK Beads The procedure applied is similar to the method used by Wan et al. [9] with slight modifications, where the chitosan to kaolinite weight ratio (5:100, 5:50, 5:25) was varied. In order to prepare 1:20 chitosan to kaolinite ratio, chitosan (5 g) was dissolved in 5% (v/v) HCl by stirring at 300 rpm for 2 h. Kaolinite (100 g) was added into the chitosan solution and stirred for another 3 h. Drop wise addition of 1 N NaOH was carried out to precipitate chitosan onto kaolinite particles. CCK beads were washed with deionized water and dried in an oven (Channel Precision Oven model DV452 220V) for 24 h at 65 °C. CCK beads with heterogeneous size range of 0.35-0.71 mm were used throughout the study. 4.Comparative Study of Different Adsorbents Adsorption of Cu(II) using chitosan, kaolinite and CCK (1:20, 1:10, 1:5) was carried out using batch experiments. About 2.5 g adsorbent and 30 mL Cu(II) solution were agitated using a reciprocal shaker bath (YIH BT350) for 4 h with initial pH 4 at 25 °C. The Cu(II) residual was analyzed using inductively-coupled plasma spectrometry (ICP-OES Perkin Elmer Optima DV2000). The adsorption capacity, q e (mg g -1) is computed using Eq. 1: qe = (C0 − Ce ) V m (1) Low molecular weight chitosan (75-85% deacytelation degree) and kaolinite (Al2Si2O5OH4) were procured from Sigma Aldrich. CuSO4 (99% purity), NaOH (99% purity) and HCl (37% fuming) were purchased from Merck (Germany). where V is the volume of solution (mL), m is the mass of adsorbent (g), C0 and Ce is the initial and equilibrium Cu(II) concentration (mg L-1). 2.Instrumentation Kinetic studies were carried out by placing 2.5 g adsorbent in contact with 30 mL Cu(II) solution under agitation speed of 50 rpm at 25 °C. Samples were taken at pre-determined time intervals (15 to 240 min). Equilibrium studies were performed by agitating 2.5 g adsorbent and 30 mL Cu(II) solution using 50 rpm at 25 °C for 24 h under varying initial concentrations (100 to 2000 mg L-1). The average pore diameter and surface area of chitosan, kaolinite and CCK were measured utilizing a BET multipoint technique and gas adsorption surface analyzer (GEMINI 2360 Micrometrics) using the adsorption-desorption isotherm of N2 at 77 K. The surface morphology of chitosan, kaolinite and CCK was analysed with a scanning electron microscopy (SEM, S-3000N Hitachi) under a vacuum running at 20 kV and using a tungsten filament. The samples were coated with a thin layer of gold (10 nm) using a sputter coater. CCK beads before and after Cu(II) adsorption were analysed using fourier transform infrared spectroscopy 5.Kinetic and Isotherm Studies 6.Fixed Bed Study Fixed bed experiment was performed using a UPVC column with internal diameter of 3 cm and length of 30 cm. The fixed bed was packed with 9 g CCK (1:20) and bed height of 3 cm. The fixed bed Chen et al., Sustain. Environ. Res., 25(2), 73-81 (2015) was operated in a downflow mode, where 200 mg L-1 Cu(II) solution was pumped at the top of column under constant flow rate of 5 mL min-1. The initial solution pH was adjusted in the range of pH 3 to 4 using 0.1 M HCl or 0.1 M NaOH. The adsorption capacity at breakthrough point, qbrk is described as when Cu(II) in effluent reaches 10% of influent concentration. It is given by: (2) where M is adsorbent mass of fixed bed (g), mbrk is the total amount of Cu(II) adsorbed by column at breakthrough point (mg), Q is the flow rate (mL min-1) and tb is time at breakthrough (min). The adsorption capacity at exhaustion (qexh) corresponds to amount of Cu(II) contained in fixed bed when effluent reaches 90% of influent concentration. It is computed using [5]: q exh m = exh M (3) where mexh is the total quantity of Cu(II) adsorbed by column until exhaustion. It is calculated using Eq. 4: (4) where te is exhaustion time (min), and Ct is the effluent concentration (mg L-1) at time t. The treated effluent volume is calculated using Eq. 5: (5) Veff = Q te The length of mass transfer zone or MTZ, Zm could be calculated using Eq. 6: tb Zm = Z 1 − te (6) where Z is the bed height (cm). The total amount of Cu(II), mtotal (g) applied to the column and total solute removal percentage can be calculated using Eqs. 7 and 8 [24]: mexh %removal = mtotal 100 (7) (8) 7.Adsorption of Cu(II) from Groundwater Batch experiments were performed using aqueous solution and real groundwater. Groundwater was obtained from a monitoring well located in Chia Nan University of Pharmacy and Science (Taiwan). The chemical composition of the groundwater is listed in 75 Table 1. The pH of the aqueous solution was adjusted to pH 8.12, which is similar to the pH of groundwater. Both aqueous solution and groundwater were spiked with 3 mg L-1 Cu(II) and the removal capacity of CCK (1:20) was studied under varying adsorbent mass. RESULTS AND DISCUSSION 1. Surface Morphology As shown in Fig. 1, the SEM micrograph revealed that the texture of CCK (1:20) is denser and shows sign of aggregation in comparison to the surface of chitosan and kaolinite. The aggregated structure could be attributed to the hydroxyl and amine groups of chitosan forming hydrogen bonds with the silicate hydroxylated edge groups of kaolinite [25]. 2. Surface Area Analysis In Table 2, the surface area, pore volume and average pore diameter of chitosan, kaolinite and CCK are listed. Based from the International Union of Pure and Applied Chemistry classifications, the pore diameters are divided into three categories: macropores (d > 50 nm), mesopores (2 nm < d < 50 nm) and micropores (d < 2 nm). The results show that chitosan, kaolinite and CCK are mesoporous materials. From Table 2, chitosan exhibited the least surface area whereas kaolinite provided the largest surface area. In comparison to chitosan, physical modification such as coating chitosan onto kaolinite led to an improvement of the surface area and pore volume. However, the properties of CCK such as surface area, pore volume Table 1. Chemical characteristics and background composition of groundwater Parameter Value pH 8.12 -1 Conductivity (µS cm ) 2480 Eh (mV) 75 Dissolved oxygen (mg L-1) 1.4 Alkalinity (ppm as CaCO3) 680 Total organic carbon, TOC (mg L-1) 5.2 Ion species: Total arsenic (µg L-1) 11.9 Chloride (mg L-1) 246 Sulfate (mg L-1) 34 -1 Nitrate (mg L ) 0 Phosphate (mg L-1) 1.6 -1 Potassium (mg L ) 34 Calcium (mg L-1) 24 -1 Sodium (mg L ) 625 Heavy metals: Iron (mg L-1) 0.51 Manganese (mg L-1) 0.15 Lead (mg L-1) 0.37 -1 Nickel (mg L ) 0.68 Copper (mg L-1) 3.0 76 Chen et al., Sustain. Environ. Res., 25(2), 73-81 (2015) 4. Effect of Initial Concentration Fig. 1. SEM micrographs of (a) kaolinite, (b) chitosan and (c) CCK (1:20). Table 2. Surface area and pore characteristics of adsorbent beads analyzed by BET N2 adsorption-desorption analysis Adsorbent Chitosan Kaolinite CCK Surface area (m2 g-1) 0.04 6.8 4.1 Pore volume (m3 g-1) < 0.0001 0.0108 0.0070 Average pore diameter (nm) 11.5 5.2 5.0 and average pore diameter decreased in comparison to kaolinite. It implies that individual kaolinite particles are not coated by chitosan. Instead, aggregates of kaolinite were coated by the chitosan polymer. The results are similar to the study of Monvisade et al. [22], where decrease of pore volume of chitosan intercalated montmorillonite was attributed to the blocking of montmorillonite pores upon coating with chitosan [22]. 3. FTIR Analysis The FTIR spectra of the CCK before and after Cu(II) adsorption of EBT are shown in Fig. 2 and Table 3. The hydroxyl (-OH) stretching vibration is attributed to the band at 3674 cm-1. The bands at 948 and 835 cm-1 correspond to the -Si-OH and -Al(OH)3 stretching vibrations. In the amine functional groups, the peak at 3412 cm-1 indicates -N-H2 stretching while band around 1047 cm-1 is attributed to -C-N stretching. On the other hand, the peak at 1657 cm-1 refers to the -N-H2 stretching in amide group. After Cu(II) adsorption, the peaks at 3412 and 1047 cm -1 shifted to higher wavelength of 3426 and 1070 cm -1 that indicates the -NH 2 and -C-N groups were involved in the removal of Cu(II). Meanwhile, the peak at 1657 cm-1 shifted to lower wavelength of 1550 cm-1, which indicates that -NH2 from amide functional group is also involved in the adsorption of Cu(II). However, there were no significant changes or shifts observed in the region of 3674, 948 and 835 cm-1, which implies that hydroxyl groups are not involved in the removal of Cu(II). Figure 3 shows the adsorption capacity and percent removal of adsorbents under varying initial concentration. The percent Cu(II) removal was observed to decrease with increasing initial concentration, which is caused by saturation of binding sites at higher concentration. On the other hand, adsorption capacity increases as initial concentration was increased from 100 to 2000 mg L -1. A high concentration gradient serves as an important driving force that will help overcome the mass transfer resistance of Cu(II) between liquid and solid phases [26]. Among the adsorbents, chitosan and kaolinite provided the highest and lowest removal efficiency and adsorption capacity, respectively. It was observed that CCK beads have better removal efficiency and adsorption capacity than kaolinite, where increasing the amount of chitosan coated on kaolinite would result in removal efficiency similar to that of chitosan. 5. Effect of pH In Fig. 4, the effect of pH on the Cu removal efficiency and adsorption capacity of CCK on Cu(II) removal is illustrated. As the pH was decreased from 7 to 2, the Cu(II) removal efficiency and adsorption capacity were observed to decrease. This could be due to the higher amount of H+ present in acidic solution, which competes with Cu(II) for the binding sites of CCK. In addition, a lower pH indicates that more amine groups become protonated (-NH 3 + ), where positively charged amine groups exert an electrostatic repulsive force to the approaching Cu(II) ions on the CCK surface. 6. Kinetics Study In order to determine the rate of Cu(II) uptake of CCK beads, kinetic models such as pseudo-first order and pseudo-second order equation were applied to the experimental data. The pseudo-first order equation is given by Eq. 9: log(qe − qt ) = log qe − k 1t 2.303 (9) where qe and qt refer to Cu(II) adsorbed by CCK (mg Table 3. FT-IR analysis of CCK (before and after copper adsorption) Frequency (cm-1) IR peak Before adsorption After adsorption Differences 1 3674 3674 0 2 3412 3426 +14 3 1657 1550 -107 4 1047 1070 +23 6 948 945 -3 7 835 834 -1 Assignment -O-H stretching -N-H2 stretching -N-H2 bending -C-N stretching -Si-OH stretching -Al(OH)3 stretching Chen et al., Sustain. Environ. Res., 25(2), 73-81 (2015) 77 Fig. 4. Effect of pH on the percent (%) removal and adsorption capacity of CCK in the removal of Cu(II) from aqueous solution. Fig. 2. FT-IR spectra of pure CCK and CCK loaded with Cu(II). This indicates that the rate-determining step of Cu(II) adsorption onto CCK is chemisorption. The pseudosecond order rate constant k2 obtained for CCK (1:20) is slightly lower than the values for CCK (1:10, 1:5). This implies that rate of adsorption is slightly higher for CCK (1:5, 1:10) over CCK (1:20), which led to better adsorption capacity. 7. Isotherm Study In this study, Langmuir and Freundlich models are applied to the equilibrium data. The Langmuir model assumes occurrence of monolayer coverage and no transmigration of adsorbate takes place on the adsorbent surface [28]. The Langmuir equation is given as: qe = Fig. 3. Behavior of Cu(II) in terms of percent removal and adsorption capacity using chitosan, kaolinite and CCK (1:5, 1:10, 1:20). g-1) at equilibrium and time t, and k1 is the pseudo-first order kinetic rate constant (min-1) [27]. The pseudo-second order equation is shown in Eq. 10: t 1 k 2 qe t = + 2 q q t e (10) where k2 (g mg-1 min-1) is the rate constant [7]. As shown in Table 4, the adsorption of Cu(II) using CCK correlates well with pseudo-second order equation due to high correlation coefficient values (R2 > 0.991). In addition, a good agreement was observed between theoretical qe values generated by the pseudosecond order equation and experimental q e values. qmaxb Ce 1 + b Ce (11) where q max is the maximum adsorption capacity of Cu(II) at complete monolayer coverage (mg g-1) and b refers to the affinity of Cu(II) to the binding sites (mL mg-1) [29]. The linearized form is provided in Eq. 12: 1 1 1 = + qe qmax b qmaxCe (12) The Freundlich model is based on assumption of reversible adsorption of a heterogeneous system [7]. It is given by Eq. 13: 1 log qe = log K F + log Ce n (13) where KF and n are Freundlich constants that refer to the adsorption capacity (mg g -1) and heterogeneity factor, respectively. Based from Table 5, CCK beads of ratio 1:20, 1:10 and 1:5 correlated well with the Langmuir model given 78 Chen et al., Sustain. Environ. Res., 25(2), 73-81 (2015) Table 4. Kinetic parameters of Cu(II) adsorption using CCK (1:20), CCK (1:10) and CCK (1:5) Pseudo-first order Pseudo-second order Experimental qe k2 Adsorbent C0 (mg L-1) -1 2 -1 k1 (min ) R qe (theo) R2 qe (theo) (mg g ) (g mg-1 min-1) CCK (1:20) 100 1.2 0.19 0.64 2.4 0.12 0.99 1.3 500 5.4 0.16 0.74 2.9 0.10 0.99 5.3 1000 8.5 0.10 0.77 4.0 0.07 0.99 8.8 2000 9.4 0.09 0.60 4.1 0.07 0.99 9.5 CCK (1:10) 100 1.2 0.21 0.61 2.6 0.14 0.99 1.4 500 6.0 0.19 0.62 3.1 0.12 0.99 6.1 1000 11 0.15 0.76 3.8 0.08 0.99 11 2000 13 0.12 0.56 4.3 0.09 0.99 14 CCK (1:5) 100 1.2 0.21 0.62 3.3 0.14 0.99 1.4 500 6.0 0.19 0.72 3.9 0.13 0.99 6.3 1000 12 0.17 0.76 4.5 0.09 0.99 12 2000 23 0.10 0.64 5.6 0.06 0.99 23 by high correlation coefficient values (R 2 > 0.987). Based on qmax, the order of adsorption is in the order: CCK (1:5) > CCK (1:10) > CCK (1:20). It is observed that as the amount of chitosan coated on kaolinite increases, qmax value increases as well. In terms of Langmuir coefficient, b, CCK (1:5) and CCK (1:20) provided the highest and lowest value, respectively. The coefficient b describes affinity of Cu(II) to the binding sites of CCK, indicating that Cu(II) has high affinity to be adsorbed onto CCK (1:5) over CCK (1:20) due to higher number of binding sites available on CCK (1:5). A dimensionless constant separation factor, R L could be calculated from Langmuir isotherm model, given by: (14) The values of RL would indicate whether isotherm is irreversible (RL = 0), favorable (0 < RL < 1), linear (RL = 1) or unfavorable (RL > 1). Based from Table 5, the RL values indicate that Cu(II) adsorption onto CCK, irrespective of the amount of chitosan in kaolinite, is favorable. Table 6 lists the adsorption capacity of CCK, modified chitosan forms and other biosorbents. In this study, CCK attained a good maximum adsorption capacity, which is higher in comparison to bentonite, chitosancoated sand, chitosan immobilized on bentonite, coconut shell, bark and sugarcane [20,30-32]. 8. Fixed-bed Study The effect of initial solution pH on the shape of the breakthrough curve is shown in Fig. 5. The flow rate, initial inlet concentration and bed height are kept constant at 5.0 mL min-1, 200 mg L-1 and 3 cm. An increase in initial pH from 3 to 4, the time to reach breakthrough and exhaustion was observed to increase as well. The breakthrough curve becomes steeper at pH 4, resulting in a quick exhaustion of the fixed bed. A longer breakthrough and exhaustion time of 70 and 130 min was observed to occur under pH 3 while shorter breakthrough and exhaustion times at 40 and 110 min took place at pH 4. Table 7 lists the calculated column parameters such as qbrk, qexh, % removal, Zm and Veff. As the pH becomes more acidic from pH 4 to 3, the Veff was observed to increase. Correspondingly, the parameters such as qbrk, qexh and % removal increased while Zm decreased at pH 3. However, other studies about chitosan and its derivatives regarding the effect of pH show that Cu(II) Table 5. Langmuir and Freundlich parameters and correlation coefficient of CCK beads Langmuir Adsorbent b qmax R2 RL 1/n CCK (1:20) 1.78 8.9 0.99 0.0033 0.20 CCK (1:10) 2.25 9.4 0.99 0.0044 0.25 CCK (1:5) 3.01 11 0.98 0.0056 0.38 Table 6. Comparison of the adsorption capacity of Cu(II) ions onto various bioadsorbents Adsorbent Adsorption capacity (mg g-1) CCK 8.9 Bentonite 7.9 Coconut shell 2.6 CCB (chitosan-coated bentonite) 12.2 CIB (chitosan immobilized on bentonite) 9.9 CCS (chitosan-coated sand) 8.8 Kudzu, bark 8.2 Sugar cane 0.3 Freundlich KF 2.20 3.02 3.72 R2 0.96 0.93 0.98 Reference This study [29] [30] [19] [31] [20] [30] [30] Chen et al., Sustain. Environ. Res., 25(2), 73-81 (2015) Fig. 5. Breakthrough curves of Cu(II) under different initial solution pH (pH 3-4). Table 7. Column parameters of CCK under varying initial solution pH Initial Veff qb qe % Cu(II) Zm pH (mL) (mg g-1) (mg g-1) removal (cm) pH 3 650 7.3 9.9 69 1.38 pH 4 550 4.2 6.3 52 1.91 *Bed height = 3 cm; Q = 5 mL min-1; C0 = 200 mg L-1 removal using grafted chitosan with poly(acrylamide) [33], chitosan coated PVC beads [4] and H 2 SO 4 modified chitosan [7] decreases as the pH becomes more acidic. In this study, pH 3 showed better Cu(II) removal and adsorption capacity over pH 4. This could be attributed to excess Cl- ions present, where HCl was added to adjust to pH 3. A high Cl- concentration could lead to formation of Cu(II) complexes, where Cl- acts as a bridging ligand, connecting two or more Cu(II) together [9]. Complex formation of Cu(II) causes an increase in removal and adsorption capacity since each binding site of CCK would retain more than one Cu(II) ion. 9.Adsorption of CCK (1:20) in Real Groundwater Figure 6 shows the Cu(II) removal capacity of CCK from groundwater and aqueous solution under varying adsorbent mass. In both aqueous solution and groundwater, removal of Cu(II) increases with increasing mass of adsorbent from 0.02 to 2 g, due to greater number of available binding sites on CCK. The maximum removal of > 99 and 93% was achieved using 2 g CCK for aqueous solution and groundwater, respectively. At pH 8.12, the removal of Cu(II) in aqueous solution and real groundwater could be attributed due to a combination of Cu(OH)2 precipitation and adsorption of Cu(II) by CCK beads. 79 Fig. 6. Percentage removal of Cu(II) using CCK (1:20) from aqueous solution and real groundwater system. Experiments were carried out without the addition of CCK, where precipitation is attributed in removing 17 and 22% of Cu(II) in aqueous solution and groundwater, respectively. However, it could be observed that the percentage removal of Cu(II) was higher in aqueous solution in comparison to the groundwater. This is attributed to background cations present in groundwater such as Pb(OH)+, Ni2+, Mn2+ and Fe(OH)2+ that could compete for the available binding sites on CCK. CONCLUSIONS Results of the study showed that CCK (1:20) can be used as an adsorbent in removing Cu(II) under batch and fixed bed conditions. The kinetic data correlated well with the pseudo-second order equation, signifying chemisorption as the rate-determining step. Isotherm data were best described using the Langmuir model. The adsorption capacity for Cu(II) under varying chitosan to kaolinite ratio can be arranged in the order: 1:5 > 1:10 > 1:20. 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J., 152(2-3), 440-448 (2009). Discussions of this paper may appear in the discussion section of a future issue. All discussions should be submitted to the Editor-in-Chief within six months of publication. Manuscript Received: December 5, 2013 Revision Received: March 24, 2014 and Accepted: June 3, 2014
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