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Treatment influence on green coconut shells for removal of metal ions: pilot-scale fixed-bed column a
b
a
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Giselle S. C. Raulino , Carla B. Vidal , Ari Clecius A. Lima , Diego Q. Melo , Juliene T. b
Oliveira & Ronaldo F. Nascimento
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Department of Hydraulic and Environmental Engineering, Federal University of Ceará, Rua do Contorno, S/N Campus do Pici, Bl. 713 – CEP: 60451-970, Fortaleza, CE, Brazil b
Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Rua do Contorno, S/N Campus do Pici, Bl. 940 – CEP: 60451-970, Fortaleza, CE, Brazil Published online: 27 Feb 2014.
To cite this article: Giselle S. C. Raulino, Carla B. Vidal, Ari Clecius A. Lima, Diego Q. Melo, Juliene T. Oliveira & Ronaldo F. Nascimento (2014) Treatment influence on green coconut shells for removal of metal ions: pilot-scale fixed-bed column, Environmental Technology, 35:14, 1711-1720, DOI: 10.1080/09593330.2014.880747 To link to this article: http://dx.doi.org/10.1080/09593330.2014.880747
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Environmental Technology, 2014 Vol. 35, No. 14, 1711–1720, http://dx.doi.org/10.1080/09593330.2014.880747
Treatment influence on green coconut shells for removal of metal ions: pilot-scale fixed-bed column Giselle S. C. Raulinoa , Carla B. Vidala , Ari Clecius A. Limaa , Diego Q. Melob , Juliene T. Oliveirab and Ronaldo F. Nascimentob∗ a Department of Hydraulic and Environmental Engineering, Federal University of Ceará, Rua do Contorno, S/N Campus do Pici, Bl. 713 – CEP: 60451-970, Fortaleza, CE, Brazil; b Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Rua do Contorno, S/N Campus do Pici, Bl. 940 – CEP: 60451-970, Fortaleza, CE, Brazil
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(Received 2 July 2013; accepted 3 January 2014 ) This work investigates copper, nickel and zinc ion biosorption in single- and multi-component systems in a fixed-bed column using green coconut shells (CS). Approximately 85% of biosorbents are in a particle size ranging from 0.25 to 2 mm. Operational parameters selected include a flow rate of 200 mL min−1 and a bed height of 100 cm, which were selected for a shorter execution time and good adsorption capacity. Empty-bed contact time and Thomas models were applied, showing a good fit with the experimental data. The column adsorption capacity increased after the green CS powder was treated in a column with NaOH at a concentration of 0.1 mol L−1 . The highest values of adsorption capacities founded were 0.69, 0.45 and 0.39 mmol L−1 for Cu(II), Ni(II) and Zn(II), respectively, using green CS treated inside a column with NaOH of 0.1 M. The pH and chemical oxygen demand were monitored in the treatment solution and indicated that the adjustment of these parameters is necessary before disposal of these solutions. A study of desorption using an acid solution was carried out for recovery of metal ions. Keywords: biosorption; green coconut shells; metal ions; wastewater; biosorbent treatment
1. Introduction Heavy metal ions are known to be toxic and carcinogenic to living organisms. They are not degradable and can accumulate in the environment where they manifest their toxicity. Because of its mobility, metal ions are very difficult to trace when they are introduced into the ecosystem, and the ultimate destination of these metal ion species is frequently unknown.[1–3] Among the processes for removing toxic metals from aqueous effluents are chemical precipitation, flocculation, carbon adsorption, ion exchange, reverse osmosis and electrodialysis.[3–7] These methods present disadvantages, including high cost or production of sludge with a high metal concentration which is difficult to dispose of.[8,9] Adsorption using low-cost materials is emerging as an economically attractive potential treatment for toxic metal removal and recovery.[2,8] Lignocellulosic materials are examples of low-cost materials with excellent mechanical properties that may originate from agricultural or industrial waste.[2,9] Due to the high organic matter content and the large volume of these agricultural or industrial wastes, the improper disposal of these materials can contaminate water bodies and soil.[8,10] Many of
∗ Corresponding
author. Email: [email protected]
© 2014 Taylor & Francis
these agricultural or industrial waste materials have been investigated for potential use as a biosorbent, including carrot waste, peanut shells, rice, nuts and crushed sugar cane, among others.[2,8,11–14] One problem with the use of lignocellulose-containing materials for wastewater treatment is the high tannin content. These compounds add colour to water, an undesirable characteristic in the effluent.[8,10] Some studies of metal ion removal with lignocellulosic materials proposed treatments of these lignocellulosic materials to increase their adsorption capacity.[6,9,15–18] However, the quality of the final solutions resulting from these treatments is not monitored, and the solutions are not treated further. The aim of this work was to investigate the treatment influence on green coconut shells (CS) using a fixed-bed system for the removal of metal copper, nickel and zinc ions in aqueous solution. The adsorption capacity of the treated biosorbent was determined in singleand multi-component solutions and equilibrium modelling of Thomas and empty-bed contact time (EBCT) was applied. The treatment solutions were monitored for pH and COD.
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2. Materials and methods 2.1. Biosorbent The green CS (Cocos nucifera) was supplied by Embrapa Tropical-CE (EMBRAPA/CE – Brazil) in its powdered form with particle sizes less than 5 mm. To study the distribution of biosorbent particle sizes, a mass of 90.0017 g of biosorbent was weighed and placed at the top of a sieving tower composed of sieves for various particle sizes (5-2/2-0.84/0.84-0.25/0.25-0.15/0.15-0.106/0.1060.075/0.075-0.062/0.062-0.045/below 0.045 mm), overlapping in a descending manner. The tower was then stirred for 15 min. The fractions retained in the different sieves were weighed carefully.[19] 2.2. Chemicals and solutions For the adsorption study, the synthetic solutions of Cu(II), Ni(II) and Zn(II) (Carlo Erba, Italy) were prepared from the following salts: Cu(NO3 )2 · 3H2 O, Zn(NO3 )2 · 6H2 O and Ni(NO3 )2 · 6H2 O, analytical grade (VETEC, São Paulo, Brazil). The reagents sodium hydroxide (Merck, São Paulo, Brazil) and nitric acid (VETEC, São Paulo, Brazil) were used. Single- and multi-component solutions of metal ions (copper, zinc and nickel) were prepared in concentrations of approximately 200 mg L−1 of Cu(II), Ni(II) and Zn(II) from their respective salts in water (from Water Supply Company). The water was untreated to prepare a synthetic sample as similar to a real effluent as possible. A large volume of solution was used in each experiment (approximately 70 L). The characteristics of the water used in this work were measured and are described as follows: pH = 7.12; conductivity = 631 μS cm−1 ; calcium = 16.8 mg L−1 ; magnesium = 21.87 mg L−1 ; chloride = 137.55 mg L−1 ; hardness = 132 mg L−1 and total dissolved solids: 305 ppm. Solutions of NaOH (0.1 mol L−1 ) and HNO3 (0.1 mol L−1 ) were used in the treatment of the biosorbent, and a solution of HNO3 (0.5 mol L−1 ) was used as an eluent for metal ions adsorbed on the material. 2.3. Adsorption column The adsorption studies were performed in a fixed-bed system after treatment with different solutions (NaOH (0.1 mol L−1 ), HNO3 (0.1 mol L−1 ) or water). A peristaltic pump (model Watson-Marlow Sci-Q 323) was used to control the flow rate on the poly(vinyl chloride) (PVC) column (100 and 160 cm × 62 cm ID) filled with the biosorbent. The solution was pumped through the column in an upward flow. All experiments occurred at room temperature (27 ± 2◦ C). The apparent density (ρap ) of the bed was determined by American Society for Testing and Materials Method D2854, and the apparent volume (Vap ) for a given mass was calculated. The packing density (ρE ) (the ratio between the total mass of particles (ML ) and the volume of the empty
column (VL ) was used to calculate the porosity (ε) of the bed, according to Equation (1)): ε =1−
VL − Vap ρE = , ρap VL
(1)
where ρE is the packing density, ρap is the apparent density, VL is the total volume (internal) of the empty column and Vap is the total volume of the bed particles (apparent volume). The maximum adsorption capacity of the biosorbent is given by Equation (2) [19]: [(C0 /MM) × Fm ] t=x 1 − C Q= dt, (2) ms C0 t=0 where Q is the maximum adsorption capacity (mmol g−1 ), C0 is the initial concentration of the solution, MM is the molar mass, C is the concentration of adsorbate at a certain volume, ms is the mass of biosorbent (g), Fm is the volumetric flow (L min−1 ) and t is the time (min). 2.4.
Effect of flow rate and bed height
The biosorbent used was washed with water and dried at room temperature before its use in the column. The weight used is referred to the dry mass. Flow rates of 100, 200 and 300 mL min−1 with a bed height of 100 cm were studied. The column was filled with 480 g of biosorbent, and a multi-component synthetic solution was percolated through it. Two bed heights were studied: 100 and 160 cm, filled with 480 and 600 g of biosorbent, respectively. Multicomponent synthetic solution was percolated through the column at a flow rate of 200 mL min−1 . Aliquots of 50 mL of column effluent solution were collected every 10 min, and the residual concentrations of metal ions were analysed by atomic absorption spectrophotometry (AAS). 2.5. Treatment influence on biosorbent Two procedures were carried out: treatment of biosorbent outside the column and treatment of biosorbent inside the column. 2.5.1. Treatment outside the column In the first study, the coconut shells were used untreated (CS). A second study was conducted with the CS washed with water out of the column (CSWO). A mass of raw CS was placed in a container with water at a ratio of 1:3. This mixture was stirred for 1 h, filtered and then the biosorbent material was dried at room temperature. In the third study, the CS was washed with NaOH (0.1 mol L−1 ) out of the column (CSBO). A mass of biosorbent was placed in a container with a solution of NaOH (0.1 mol L−1 ) at a ratio of 1:3. This mixture was stirred for
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1 h, filtered, washed with water to remove the excess basic solution, filtered again and the material was then dried at room temperature. For the above-mentioned three studies, a multicomponent synthetic solution was percolated through the column under the following conditions: flow rate of 200 mL min−1 , initial concentration of metal ions 200 mg L−1 , 480 g of untreated or treated CS. Aliquots of 50 mL were collected every 10 min for obtaining the breakthrough curves. The concentrations of metal ions were determined for each aliquot collected.
2.5.2. Treatment in the column The column was filled with CS and washed: with water coconut shell washed with water inside the column (CSWI) and with NaOH (0.1 mol L−1 ) coconut shell washed with basic solution inside the column (CSBI). In the first study, 20 L of water was percolated through the column filled with 402 g of CS (CSWI). Fractions were collected every 10 min, and the pH and COD were determined to measure the residual organic matter. In the second study, 11 L of NaOH solution (0.1 mol L−1 ) was percolated through the column, filled with 402 g of CS powder (CSBI), at a flow of 150 mL min−1 . Then, water (20 L) was percolated through the column to remove the excess of basic species. Fractions were collected every 5 min, and the pH and COD were measured. For the above-mentioned two studies, a multicomponent synthetic solution at a concentration of 200 mg L−1 was percolated through the column (100 cm bed height) after treatments. Aliquots of 50 mL were collected every 10 min, and the pH and concentration of metal ions were determined. The per cent mass loss was calculated and was found to be 6% for treatment with water and 17% for treatment with NaOH. The adsorption capacities of materials treated inside the column were calculated considering the cited values of mass loss.
2.6. Breakthrough curves for single component Breakthrough curves for single-component solutions of metal ions (copper, nickel and zinc) were evaluated. First, the biosorbent was subjected to CSBI treatment. Then, the single-component synthetic solution of copper, nickel and zinc was percolated through the column. Aliquots of 50 mL were collected every 10 min and single-metal ion concentrations were determined.
2.7.
Column regeneration
After CSBI treatment and column saturation with multielement synthetic solution, the metal ion desorption was
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carried out with HNO3 solution (0.5 mol L−1 ). The concentration of metal ions was analysed by an AAS, model GBC 933 plus, in an air-acetylene flame. 2.8. Fixed-bed column modelling In this study, Thomas and EBCT models were used to predict the performance of the column. 2.8.1. Empty-bed contact time In some systems on a real scale where default behaviour is not observed, the breakthrough curve depends on the column length. This dependence can be determined by performing experiments on a pilot-scale column at the same flow rate, varying the lengths of the biosorbent bed. The breakthrough times are then determined from the rupture concentration. The EBCT is a measure of how much time a parcel of fluid spends in the column, on the basis that the column contains no solid packing.[19,20] The EBCT is represented by Equation (3). Another important parameter is the biosorbent usage rate (BUR), that is, the ratio between the weight of biosorbent in the column and the amount of liquid passed into the column at the time of breakthrough (Equation (4)).[19] EBCT (min) =
VL × Asec , H
(3)
where VL is the total volume of the empty column (mL), H is the hydraulic loading and Asec is the bed cross-sectional area. ML , (4) Biosorbent usage rate = Vb where ML is the total mass of biosorbent inside the column (g) and Vb is the volume of treated solution at the breakthrough point (L). 2.8.2. Thomas model This model assumes a behaviour of continuous flow and uses the Langmuir isotherm for equilibrium and the reversible second-order kinetics reaction. The Langmuir isotherm is applicable for favourable and unfavourable adsorption conditions. Traditionally, the Thomas model is used to determine the maximum adsorption capacity of biosorbent in continuous systems. The Thomas model is expressed by Equation (5).[20–23] C kt (q0 mc − C0 Ve ) 1 . (5) = C0 1 + exp Fm The adsorption capacity of the bed (q0 ) and the coefficient (Kt ) may be obtained from the intercept and slope, respectively, of a curve obtained by plotting ln(C/C0 − 1) as a function of t or Ve from the breakthrough point (Cb ) until the
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exhaustion point (Cx ). The linearized form of the Thomas model is given by Equation (6): ln[(C0 /C) − 1] =
K t q0 ms − Kt C0 t, Fm
(6)
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where C is the adsorbate concentration at a determinate volume (mg L−1 ); C0 is the initial solution concentration (mg L−1 ); Kt is the Thomas rate constant (mL mg−1 min−1 ); q0 is the maximum solid phase concentration (mg g−1 ), i.e. the maximum adsorption capacity; ms is the amount of biosorbent (g); Fm is the volumetric flow rate (L min−1 ); and Ve is the effluent volume (L). 3. Results and discussion 3.1. Characterization of the biosorbent bed The contact surface between the biosorbent and the liquid phase as well as the biosorbent particle size plays an important role in the phenomenon of adsorption.[4,24] Green CS powder was submitted to a particle size determination. Approximately 85% of the biosorbent was in a particle size ranging from 0.25 to 2 mm. Rosa et al.,[25] performing the same type of analysis, found a value of 78% at the same particle size range. Sousa et al.,[18] studying the removal of metal ions Cu(II), Ni(II), Zn(II), Pb(II) and Cd(II) by green CS powder, found no significant effect on removal efficiency for metals studied in the particle size ranging from 0.15 to 0.25 mm. The results of determination of some physical properties of the biosorbent bed are described below for the bed heights of 100 and 160 cm, respectively: apparent density, 0.188 g cm−3 for both; packing density, 0.159 and 0.124 g cm−3 ; particle volume of 2553 and 3191 cm3 ; and porosity of the bed of 0.154 and 0.338. 3.2.
Effect of flow rate and bed height
The experimental and theoretical breakthrough curves obtained for flow rates (100, 200 and 300 mL L−1 ) are shown in Figure 1.[26] The breakthrough and exhaustion volume (chosen, respectively, as 5% and 90% of initial concentration for all three metal ions) observed are larger for copper than for zinc and nickel, due to higher affinity of Cu(II) by biosorbent surface, and a larger time period is required to reach the exhaustion volume, in contrast for Ni(II) and Zn(II). Gao et al. [27] found a similar behaviour in Cu(II), Ni(II), Cd(II) and Zn(II) removal by oxidized carbon nanotubes. According to them, the removal process is related to such factors as the surface chemistry of the adsorbent, the initial concentration of ions, the components in the adsorption system and the ratio of the metal ion species in solution and the redox reactions on the carbon surface involving metals might affect negatively the amount adsorbed.[27]
The results shown in Table 1 revealed that with increase in flow rate (100–300 mL min−1 ), the adsorption capacity decreased for Cu, Ni and Zn ions. Higher adsorption capacity values of 0.23 mmol g−1 for Cu(II), 0.07 mmol g−1 for Ni(II) and 0.07 mmol g−1 for Zn(II) were obtained for a flow rate of 100 ml min−1 . On the other hand, when flow velocity increased three times, the percentage removal decreases at 26.0%, 28.5% and 29.5%, respectively, for each metal ion. A similar trend was observed by Shahbazi et al. [28] in Pb(II), Cu(II) and Cd(II) removal by functionalized mesoporous silica. According to them, this is because metal ions leave the column before the equilibrium stage can be achieved by reducing the performance of the column. In contrast, Revathi et al. [3] observed that by increasing the flow rate, the adsorption capacity and Thomas constant were increased using the Ceralite IR 120 ion exchange resin for the removal of Ni(II),Cu(II) and Zn(II) ions from synthetic electroplating rinse water solutions. It is known that the increase in the flow rate implies a reduction in the hydraulic retention time (HRT) of metal ions inside the column. According to Cooney,[19] HRT is a typical parameter of design and operation of bed fixed columns, and the usual residence times on column range from 15 to 30 min. Larger residence times can lead to a decrease in the solute removal, while shorter times do not allow an effective contact interaction to occur between the sorbent and sorbate.[5,19] It is important that HRT be higher than equilibrium time that is determined in batch experiments, allowing a time of contact large enough between the adsorbent and adsorbate. In this study, the HRT decreased from 30 to 10 min when the flow rate increased from 100 to 300 mL min−1 . According to results obtained by the breakthrough curves, the flow rate of 200 mL min−1 was chosen for the following studies because it provided high adsorption capacity and the HRT. The Thomas model was applied to the experimental data (continuous line, nonlinear (NL) model and dashed line, linear model, in Figure 1). A linear plot of ln[(C0 /C) − 1] versus Ve to data located in the range 0.05 < /C0 < 0.90 allowed a previous determination of the kinetic coefficient, Kt , and the adsorption capacity of the bed, q0 , according to Equation (6). NL regression analysis was performed using Equation (5). The sum of the squares of the errors (SSE) was examined for every experimental data set, and the parameters of Kt and q0 were determined for the lowest error values in each case by adjusting and optimizing the functions themselves using the solver add-in for Microsoft Excel® . The values of Kt and q0 obtained for the lowest error values are given in Table 1. Except for copper, the Thomas model represented the flow rate data well. In general, the theoretical and experimental maximum adsorption capacities were closed. The increase in the flow rate resulted in an increase in the Thomas rate constant and a decrease in the maximum
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Figure 1. Comparison of experimental and theoretical breakthrough curves for metal ions at varied flow rates of (a) 100 mL min−1 , (b) 200 mL min−1 and (c) 300 mL min−1 (NL, nonlinear; L, linear). Adapted from.[26]
adsorption capacity for metals studied with an initial metal concentration of 200 mg L−1 . According to Shahbazi et al.,[28] this occurs due to difference of metal ion radius size as it passes through the column.
The NL regression analyses better represented the data than linear (L) regression analyses. From Table 1, it can be seen that the errors for NL were lower than L, showing a better fit.
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Table 1. Parameters by linear (L) and NL regression analysis with Thomas model for metal ions Cu(II), Ni(II) and Zn(II) for the three flow rates (CSWO treatment). Kt (mL min−1 mg−1 ) Metalion
Flow rate (mL min−1 )
L
NL
100 200 300 100 200 300 100 200 300
0.102 0.091 0.292 0.462 1.008 3.478 0.412 1.203 2.716
0.113 0.270 0.299 0.460 1.141 3.464 0.410 1.119 1.991
Cu(II) Ni(II) Zn(II)
q0 (mmol g−1 ) Theoretical L NL Experimental 0.242 0.258 0.191 0.075 0.096 0.054 0.075 0.071 0.057
0.242 0.234 0.180 0.075 0.091 0.049 0.075 0.071 0.050
0.233 0.218 0.172 0.071 0.093 0.051 0.071 0.069 0.050
SSE L
NL
0.061 9.142 0.428 1.53 E−3 0.357 1.42 3.35 E−4 6.737 1.059
1.36 E−29 2.31 E−07 1.69 E−29 3.77 E−32 4.44 E−31 2.99 E−14 1.17 E−28 4.07 E−31 6.84 E−13
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Note: Adapted from.[26] Table 2. Metalion Cu(II) Ni(II) Zn(II)
EBCT and BUR for different bed heights.
(a)
Bed height (cm)
EBCT (min)
Q (mmol g−1 )
BUR (g L−1 )
100 160 100 160 100 160
15 24 15 24 15 24
0.217 0.264 0.092 0.111 0.069 0.075
18.97 13.63 55.8 53.1 53.9 46.15
Note: Adapted from.[26]
With the values of Kt and q0 for each metal, the total mass of biosorbent required to treat wastewater in a column can be obtained under the same conditions, requiring only knowledge of the feed concentration for each metal, the daily flow rate and the volume of solution to be treated. Applying the EBCT model and BUR (Equations (1) and (2), respectively) to the data obtained from the breakthrough curves for bed height study resulted in the data shown in Table 2 and Figure 2(a). It can be seen that the breakthrough volume for each metal and the adsorption capacity increased while the BUR decreased with the increase in bed height. The BUR is lower for copper due to the effect of competition between metal ions in solution and biosorbent sites. The lower the BUR is, the greater is the adsorption capacity. The literature reports that the greater the bed height is, the greater the service time of the column because the surface area of the biosorbent increases as the number of active sites available for metal–biosorbent interaction increases. The amount of biosorbent required to treat the same volume of solution at the same concentration therefore decreases.[19,29,30] The maximum HRT of 35 min [19] is not exceeded when the column length increases from 100 to 160 cm. Figure 2(b) presents the critical bed depths (the bed height when tb (breakthrough time) = 0) or the smaller bed depth to obtain an effluent concentration equals to Cb .
(b)
Figure 2. (a) BUR versus EBCT and (b) breakthrough times versus bed heights.
The critical bed depth depends on the choice of Cb and is obtained by extrapolating the curve of breakthrough time versus bed height to zero. The values of critical bed depths were 40, 4 and-60 cm for copper, zinc and nickel, respectively. The negative value found for nickel means that, in a bed height greater than zero, it is possible to obtain an effluent concentration Cb used in this work.[19] 3.3. Treatment influence on biosorbent The results obtained with non-treated (CS) and treated CS outside (CSWO, CSBO) and inside (CSWI, CSBI) the column are shown in Figure 3. According to the results shown
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(a)
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Figure 3. Comparison of the treatments outside and inside column for the three metal ions studied.
in Figure 3, the green CS treated with water (CSWO, CSWI) or NaOH (CSBO, CSBI) led to an increase in the adsorption capacity as well as the breakthrough and exhaustion volumes, when compared with raw material (CS). For the CSBO treatment, the adsorption capacity increased about 40% for each metal ion when compared with the non-treated material (CS). This occurs because when the lignocellulosic material is washed with NaOH solution (0.1 mol L−1 ), the cellulosic fibre expands, and increases the number of active sites available to improving the adsorption process.[8,9] The increase in adsorption capacity was 27% for copper and zinc, while for nickel it was 37% when CSWO and CSWI treatments were compared. On the other hand, according to the results obtained for both treatments, outside (CSBO) and in the column (CSBI), the use of green CS powder treated with NaOH (0.1 mol L−1 ) increased the removal percentage at 55.7% for copper, 58.9% for nickel and 73.7% for zinc from aqueous solution. However, the use of this material for the same purpose without treatment is also possible, with the potential for co-processing in other industrial sectors. 3.3.1. pH Monitoring The pH, among several factors, can be regarded as the most important parameter to influence the adsorption process. In acid, there is an electrostatic repulsion between metal ions and the biomass surface, enhancing the competition effect. In an alkaline medium, precipitation takes place with the formation of metal hydroxides. Moreover, depending on the concentration of metal ions in solution, complexes can be formed, and other mechanisms can occur. On the other hand, the hydroxyl group increases the number of adsorption sites on the fibre surface, with interaction with metal ions most likely occurring.[15–17] Figure 4(a) shows effluent solutions resulting from biosorbent treatment in the column. With CSWI treatment, the pH of the effluent solution changes very little, remaining at approximately neutral. At the beginning of treatment CSBI, the pH was acid even the feed solution has a basic character, indicating that the sodium hydroxide influent is
(b)
Figure 4. pH-Curve of collected aliquots at the outlet of the column filled with green CS powder (a) during treatments CSWI and CSBI and (b) from aliquots collected after percolating metallic solution through the column.
interacting with the biosorbent in the column by modifying its structure and morphology.[10,15,31,32] After 6–7 L of basic solution, the pH starts to increase, indicating that an excess of basic solution has percolated through the column. Then, 20 L of water was passed through the column to remove the excess basic solution, leaving the pH at approximately 13. The pH of metallic effluent solutions that has been passed in experiments carried out to estimate the effect of the treatment outside and inside the column was monitored (Figure 4(b)). The pH remained almost constant in all three studies (CS, CSWO, CSBO) performed after treatment outside the column, suffering little decrease. For CS and CSWO treatments, the pH was approximately 5, and for CSBO treatment, the pH was approximately 7. These decreases may be due to ionic exchange between the biosorbent surface and the solution, where the metal ion binds to the fibre and releases H+ and the slightly acid (approximately 4.5–6.0) character of the multi-component metallic solution. Treatment with NaOH (0.1 mol L−1 ) showed better results, due not only to adsorption but also most likely to the mechanisms of precipitation and complexation.[33] The use of hydroxides elevates the effluent pH to 7.0, leaving the effluent pH approximately neutral. In general, a low influence on effluent pH was observed when the biosorbent was treated outside the column.
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Figure 5.
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COD curves for aliquots of collected effluent for CSWI and CSBI treatments.
After the treatments inside the column (CSWI and CSBI) were performed, a great decrease is observed when the metallic solution is passed, especially for CSBI treatment (Figure 4(b)). This may be due the excess of OH− available at the medium that is leached by the metallic solution. The OH− ions available in the solution react with Cu(II), Zn(II) and Ni(II) ions to form Cu(OH)2 , Zn(OH)2 and Ni(OH)2 , respectively, although complexes such as Cu(OH)2 , CuOH+ , NiOH+ , Ni2 OH3+ , ZnOH+ , Zn2 OH3+ can be formed.[3] After this great decrease, the same behaviour for CSWO and CSBO is observed due to the same reasons explained before. 3.3.2. Chemical oxygen demand Figure 5 shows that a maximum COD (approximately 4900 mg L−1 ) was achieved when the biosorbent was treated with NaOH (CSBI). Natural fibres such as green CS powder contain high levels of lignin and cellulose. When these cellulosic materials are subjected to a basic treatment, soluble phenolic compounds in the fibre are removed, resulting in the destruction of the lignocellulosic complex, solubilizing hemicelluloses and expanding fibrous materials, as well as extracting organic matter such as tannins.[10,16,32,34] The high COD is the result of hydroxide action in the fibre, which removes large amounts of organic matter. After percolation of the treatment solutions through the column, the remaining COD was 60.3 mg L−1 for CSWI and 171.9 mg L−1 for CSBI.
3.4.
Column adsorption in single- and multi-component solutions The breakthrough curves of the three metal ions studied in single-component systems were prepared after optimization
Table 3. Comparison between adsorption capacities of green CS powder submitted to treatment CSBI in multi- and single-component systems, when C/C0 = 0.5 (Fm = 200 ml min−1 ; C0 = 200 mg L−1 ). Q (mmol g−1 ) Metal ion Cu(II) Ni(II) Zn(II)
CSBI multi-component
CSBI single-component
0.509 0.185 0.121
0.746 0.452 0.394
of the flow rate, bed height and biosorbent treatment. Table 3 shows the adsorption capacities of the biosorbent for treatment CSBI in multi-component and single-component solutions, and can be observed that the adsorption capacity of each metal increased when passed from a multicomponent to a single-component system, especially for zinc and nickel. This increase in adsorption capacity is due to the effect of competition between metal ions for the active sites of the biosorbent. The results show that copper ions are preferred by the sites over other ions studied because the increase in adsorption capacity of copper from a multicomponent to a single-component system was lower than the other two ions, zinc and nickel as seen in Table 3.
3.5.
Desorption of metal ions
In the desorption of metal ions, 20 L of HNO3 (0.5 mol L−1 ) was used to elute these metal ions after CSBI treatment and column saturation. After 20 L of acid solution percolated through the column, the residual concentrations of metal ions were 11 mg L−1 for copper, 4 mg L−1 for nickel and 4 mg L−1 for zinc. Almost all of the copper was desorbed (98.54%), whereas only 50% of the nickel and zinc have
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been desorbed, possibly due to desorption of nickel and zinc ions after saturation (C/C0 > 1) resulting from the competition effect with copper for active sites. Sousa et al.,[35] studied the removal of metal ions using the green CS powder treated with NaOH (0.1 mol L−1 ), verified that the biosorbent can be used in only one cycle of adsorption under these conditions because the efficiency of removal decreased after the second cycle. As the estimation of exhaustion volume for copper was about 120 L, a reduction of 84% in the volume is reached with desorption. 4. Conclusions The results indicated that the use of treated green CS powder is feasible for the removal of copper, nickel and zinc from aqueous solutions. With the increase in bed height, the adsorption capacity increases and a smaller amount of biosorbent is required per litre of solution to be treated. On the other hand, the increase in flow rate leads to a decrease in adsorption capacity. Among the treatments both outside and in the column, the one with NaOH (0.1 mol L−1 ) on the column had the best result, indicating an increase in pH and COD. Although the use of green CS without treatment is possible, with the potential for co-processing in other industrial sectors. The adsorption capacity for a single-component solution was higher than that for a multi-component solution due to the competition effect. Supplemental data Supplemental data for this article can be accessed http://dx.doi.org/10.1080/09593330.2014.880747. References [1] Baird C. Química ambiental. Porto Alegre: Editora Bookman;2002. [2] Sud D, Mahajan G, Kaur MP. Agricultural waste material as potential biosorbent for sequestering heavy metal ions from aqueous solutions – a review. Bioresour Technol. 2008;99:6017–6027. [3] Revathi M, Saravanan M, Chiya AB, Velan M. Removal of copper, nickel, and zinc ions from electroplating rinse water. Clean – Soil Air Water. 2012;40:66–79. [4] Tarley CRT, Arruda MAZ. Biosorption of heavy metals using rice milling by-products. Characterisation and application for removal of metals from aqueous effluents. Chemosphere. 2004;54:987–995. [5] Ayoob S, Gupta AK, Bhakat PB. Analysis of breakthrough developments and modeling of fixed bed adsorption system for As(V) removal from water by modified calcined bauxite (MCB). Sep Purif Technol. 2007;52:430–438. [6] Suksabye P, Thiravetyan P. Cr(VI) adsorption from electroplating plating wastewater by chemically modified coir pith. J Environ Manage. 2012;102:1–8. [7] Huisman JL, Schouten G, Schultz C. Biologically produced sulphide for purification of process streams, effluent treatment and recovery of metals in the metal and mining industry. Hydrometallurgy. 2006;83:106–113.
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[8] Bailey SE, Olin TJ, Bricka RM, Adrian D. A review of potentially lowcost sorbents for heavy metals. Water Res. 1998;33:2469–2479. [9] Gurgel LVA, Freitas RP, Gil LF. Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by sugarcane bagasse and mercerized sugarcane bagasse chemically modified with succinic anhydride. Carbohydr Polym. 2008;74:922–929. [10] Brígida AIS, Rosa MF. Determinação do Teor de Taninos na Casca de Coco Verde (Cocos nucifera). Proc Interamer Soc Trop Hort. 2003;47:25–27. [11] Johnson PD, Watson MA, Brown J, Jefcoat IA. Peanut hull pellets as a single use sorbent for the capture of Cu(II) from wastewater. Waste Manage. 2002;22:471–480. [12] Singh KK, Hasan SH, Rastogi RJ, Removal of cadmium from wastewater using agricultural waste rice polish. J Hazard Mater. 2005;A121:51–58. [13] Kim JW, Sohn MH, Kim DS, Sohn SM, Know YS. Production of granular activated carbon from waste walnut shell and its adsorption characteristics for Cu2+ ion. J Hazard Mater 2001;B85:301–315. [14] Moreira SA, Sousa FW, Oliveira AG, Nascimento RF, Brito ES. Remoção de Metais de Solução Aquosa Usando Bagaço de Caju. Quim Nova. 2009;32:1717–1722. [15] Gurgel LVA, Júnior OK, Gil RPF, Gil LF. Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by cellulose and mercerized cellulose chemically modified with succinic anhydride. Bioresour Technol. 2008;99:3077–3083. [16] Asadi F, Shariatmadari H, Mirghaffari N. Modification of rice hull and sawdust sorptive characteristics for remove heavy metals from synthetic solutions and wastewater. J Hazard Mater. 2007;154:451–458. [17] Muhamad H, Doan H, Lohi A. Batch and continuous fixedbed column biosorption of Cd2+ and Cu2+. Chem Eng J. 2010;158:369–377. [18] Sousa FW, Moreira SA, Oliveira AG, Cavalcante RM, Nascimento RF, Rosa MF. Uso da casaca de coco verde como biosorbente na remoção de metais tóxicos. Quim Nova. 2007;30:1153–1157. [19] Cooney DO. Adsorption design for wastewater treatment. Boca Raton, FL: Editora CRC Press; 1999. [20] Srivastava VC, Prasad B, Mishra IM, Mall ID, Swamy MM. Prediction of breakthrough curves for sorptive removal of phenol by bagasse fly ash packed bed. Ind Eng Chem Res. 2008;47:1603–1613. [21] Yan G, Viraraghavan T. Heavy metal removal in a biosorption column by immobilized M.rouxii biomass. Bioresour Technol. 2001;78:243–249. [22] Vijayaraghavan K, Thilakavathi M, Palanivelu K, Velan M. Continuous sorption of copper and cobalt by crab shell particles in a packed column. Environ Technol. 2005;26: 267–276. [23] Aksu Z, Gönen F. Biosorption of phenol by immobilized activated sludge in a continuous packed bed: prediction of breakthrough curves. Process Biochem. 2004;39: 599–613. [24] Rao M, Parwate AV, Bhole AG. Removal of Cr6+ and Ni2+ from aqueous solution using bagasse and fly ash. Waste Manage. 2002;22:821–830. [25] Rosa MF, Abreu FAP, Furtado AAL, Brígido AKL, Norões ERV. Processo agroindustrial: obtenção de pó de casca de coco verde. Fortaleza: Embrapa Agroindústria Tropical; 2001, 4 p (Comunicado Técnico, 61). [26] Sousa Neto VO, Raulino GSC, Freire PTC, Araújo-Silva MA, Nascimento RF. Equilibrium and kinetic studies in
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adsorption of toxic metal ions for wastewater treatment. In: Naushad Mu, Alothman Zeid A, editors. A book on ion exchange, adsorption and solvent extraction. 1 ed. Hauppauge, NY: Nova Science publishers Inc; 2013. p. 145–182. Gao Z, Bandosz TJ, Zhao Z, Han M, Qiu J. Investigation of factors affecting adsorption of transition metals on oxidized carbon nanotubes. J Hazard Mater. 2009;167:357–365. Shahbazi A, Younesi H, Badiei A. Functionalized SBA-15 mesoporous silica by melamine-based dendrimer amines for adsorptive characteristics of Pb(II), Cu(II) and Cd(II) heavy metal ions in batch and fixed bed column. Chem Eng J. 2011;168:505–518. Han R, Zou W, Li H, Li Y, Shi, J. Copper(II) and lead(II) removal from aqueous solution in fixed-bed columns by manganese oxide coated zeolite. J Hazard Mater. 2006;B137:934–942. Malkoc E, Nuhoglu Y. Fixed bed studies for the sorption of chormium (VI) onto tea factory waste. Chem Eng Sci. 2006;61:4363–4372.
[31] Gurgel LVA, Gil LF. Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by succinylated mercerized cellulose modified with triethylenetetramine. Carbohydr Polym. 2009;77:142–149. [32] Gu H. Tensile behaviours of the coir fibre and related composites after NaOH treatment. Mater Des 2009;30: 3931–3934. [33] Naja g, volesky b. Behavior of the mass transfer zone in a biosorption column. Environ Sci Technol. 2006;40: 3996–4003. [34] Filho JMP, Vieira EL, Silva AMA, Cezar MF, Amorim FU. Efeito do Tratamento com Hidróxido de Sódio sobre a Fração Fibrosa, Digestibilidade e Tanino do Feno de JuremaPreta (Mimosa tenuiflora. Wild). Rev Brasil Zootecnia. 2003;32:70–76. [35] Sousa FW, Oliveira AG, Ribeiro JP, Rosa FM, Keukeleire D, Nascimento RF. Green coconut shells applied as biosorbent for removal of toxic metal ions using fixedbed column technology. J Environ Manag. 2010;91: 1634–1640.
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Treatment influence on green coconut shells for removal of metal ions: pilot-scale fixed-bed column a
b
a
b
Giselle S. C. Raulino , Carla B. Vidal , Ari Clecius A. Lima , Diego Q. Melo , Juliene T. b
Oliveira & Ronaldo F. Nascimento
b
a
Department of Hydraulic and Environmental Engineering, Federal University of Ceará, Rua do Contorno, S/N Campus do Pici, Bl. 713 – CEP: 60451-970, Fortaleza, CE, Brazil b
Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Rua do Contorno, S/N Campus do Pici, Bl. 940 – CEP: 60451-970, Fortaleza, CE, Brazil Published online: 27 Feb 2014.
To cite this article: Giselle S. C. Raulino, Carla B. Vidal, Ari Clecius A. Lima, Diego Q. Melo, Juliene T. Oliveira & Ronaldo F. Nascimento (2014) Treatment influence on green coconut shells for removal of metal ions: pilot-scale fixed-bed column, Environmental Technology, 35:14, 1711-1720, DOI: 10.1080/09593330.2014.880747 To link to this article: http://dx.doi.org/10.1080/09593330.2014.880747
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Environmental Technology, 2014 Vol. 35, No. 14, 1711–1720, http://dx.doi.org/10.1080/09593330.2014.880747
Treatment influence on green coconut shells for removal of metal ions: pilot-scale fixed-bed column Giselle S. C. Raulinoa , Carla B. Vidala , Ari Clecius A. Limaa , Diego Q. Melob , Juliene T. Oliveirab and Ronaldo F. Nascimentob∗ a Department of Hydraulic and Environmental Engineering, Federal University of Ceará, Rua do Contorno, S/N Campus do Pici, Bl. 713 – CEP: 60451-970, Fortaleza, CE, Brazil; b Department of Analytical Chemistry and Physical-Chemistry, Federal University of Ceará, Rua do Contorno, S/N Campus do Pici, Bl. 940 – CEP: 60451-970, Fortaleza, CE, Brazil
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(Received 2 July 2013; accepted 3 January 2014 ) This work investigates copper, nickel and zinc ion biosorption in single- and multi-component systems in a fixed-bed column using green coconut shells (CS). Approximately 85% of biosorbents are in a particle size ranging from 0.25 to 2 mm. Operational parameters selected include a flow rate of 200 mL min−1 and a bed height of 100 cm, which were selected for a shorter execution time and good adsorption capacity. Empty-bed contact time and Thomas models were applied, showing a good fit with the experimental data. The column adsorption capacity increased after the green CS powder was treated in a column with NaOH at a concentration of 0.1 mol L−1 . The highest values of adsorption capacities founded were 0.69, 0.45 and 0.39 mmol L−1 for Cu(II), Ni(II) and Zn(II), respectively, using green CS treated inside a column with NaOH of 0.1 M. The pH and chemical oxygen demand were monitored in the treatment solution and indicated that the adjustment of these parameters is necessary before disposal of these solutions. A study of desorption using an acid solution was carried out for recovery of metal ions. Keywords: biosorption; green coconut shells; metal ions; wastewater; biosorbent treatment
1. Introduction Heavy metal ions are known to be toxic and carcinogenic to living organisms. They are not degradable and can accumulate in the environment where they manifest their toxicity. Because of its mobility, metal ions are very difficult to trace when they are introduced into the ecosystem, and the ultimate destination of these metal ion species is frequently unknown.[1–3] Among the processes for removing toxic metals from aqueous effluents are chemical precipitation, flocculation, carbon adsorption, ion exchange, reverse osmosis and electrodialysis.[3–7] These methods present disadvantages, including high cost or production of sludge with a high metal concentration which is difficult to dispose of.[8,9] Adsorption using low-cost materials is emerging as an economically attractive potential treatment for toxic metal removal and recovery.[2,8] Lignocellulosic materials are examples of low-cost materials with excellent mechanical properties that may originate from agricultural or industrial waste.[2,9] Due to the high organic matter content and the large volume of these agricultural or industrial wastes, the improper disposal of these materials can contaminate water bodies and soil.[8,10] Many of
∗ Corresponding
author. Email: [email protected]
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these agricultural or industrial waste materials have been investigated for potential use as a biosorbent, including carrot waste, peanut shells, rice, nuts and crushed sugar cane, among others.[2,8,11–14] One problem with the use of lignocellulose-containing materials for wastewater treatment is the high tannin content. These compounds add colour to water, an undesirable characteristic in the effluent.[8,10] Some studies of metal ion removal with lignocellulosic materials proposed treatments of these lignocellulosic materials to increase their adsorption capacity.[6,9,15–18] However, the quality of the final solutions resulting from these treatments is not monitored, and the solutions are not treated further. The aim of this work was to investigate the treatment influence on green coconut shells (CS) using a fixed-bed system for the removal of metal copper, nickel and zinc ions in aqueous solution. The adsorption capacity of the treated biosorbent was determined in singleand multi-component solutions and equilibrium modelling of Thomas and empty-bed contact time (EBCT) was applied. The treatment solutions were monitored for pH and COD.
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2. Materials and methods 2.1. Biosorbent The green CS (Cocos nucifera) was supplied by Embrapa Tropical-CE (EMBRAPA/CE – Brazil) in its powdered form with particle sizes less than 5 mm. To study the distribution of biosorbent particle sizes, a mass of 90.0017 g of biosorbent was weighed and placed at the top of a sieving tower composed of sieves for various particle sizes (5-2/2-0.84/0.84-0.25/0.25-0.15/0.15-0.106/0.1060.075/0.075-0.062/0.062-0.045/below 0.045 mm), overlapping in a descending manner. The tower was then stirred for 15 min. The fractions retained in the different sieves were weighed carefully.[19] 2.2. Chemicals and solutions For the adsorption study, the synthetic solutions of Cu(II), Ni(II) and Zn(II) (Carlo Erba, Italy) were prepared from the following salts: Cu(NO3 )2 · 3H2 O, Zn(NO3 )2 · 6H2 O and Ni(NO3 )2 · 6H2 O, analytical grade (VETEC, São Paulo, Brazil). The reagents sodium hydroxide (Merck, São Paulo, Brazil) and nitric acid (VETEC, São Paulo, Brazil) were used. Single- and multi-component solutions of metal ions (copper, zinc and nickel) were prepared in concentrations of approximately 200 mg L−1 of Cu(II), Ni(II) and Zn(II) from their respective salts in water (from Water Supply Company). The water was untreated to prepare a synthetic sample as similar to a real effluent as possible. A large volume of solution was used in each experiment (approximately 70 L). The characteristics of the water used in this work were measured and are described as follows: pH = 7.12; conductivity = 631 μS cm−1 ; calcium = 16.8 mg L−1 ; magnesium = 21.87 mg L−1 ; chloride = 137.55 mg L−1 ; hardness = 132 mg L−1 and total dissolved solids: 305 ppm. Solutions of NaOH (0.1 mol L−1 ) and HNO3 (0.1 mol L−1 ) were used in the treatment of the biosorbent, and a solution of HNO3 (0.5 mol L−1 ) was used as an eluent for metal ions adsorbed on the material. 2.3. Adsorption column The adsorption studies were performed in a fixed-bed system after treatment with different solutions (NaOH (0.1 mol L−1 ), HNO3 (0.1 mol L−1 ) or water). A peristaltic pump (model Watson-Marlow Sci-Q 323) was used to control the flow rate on the poly(vinyl chloride) (PVC) column (100 and 160 cm × 62 cm ID) filled with the biosorbent. The solution was pumped through the column in an upward flow. All experiments occurred at room temperature (27 ± 2◦ C). The apparent density (ρap ) of the bed was determined by American Society for Testing and Materials Method D2854, and the apparent volume (Vap ) for a given mass was calculated. The packing density (ρE ) (the ratio between the total mass of particles (ML ) and the volume of the empty
column (VL ) was used to calculate the porosity (ε) of the bed, according to Equation (1)): ε =1−
VL − Vap ρE = , ρap VL
(1)
where ρE is the packing density, ρap is the apparent density, VL is the total volume (internal) of the empty column and Vap is the total volume of the bed particles (apparent volume). The maximum adsorption capacity of the biosorbent is given by Equation (2) [19]: [(C0 /MM) × Fm ] t=x 1 − C Q= dt, (2) ms C0 t=0 where Q is the maximum adsorption capacity (mmol g−1 ), C0 is the initial concentration of the solution, MM is the molar mass, C is the concentration of adsorbate at a certain volume, ms is the mass of biosorbent (g), Fm is the volumetric flow (L min−1 ) and t is the time (min). 2.4.
Effect of flow rate and bed height
The biosorbent used was washed with water and dried at room temperature before its use in the column. The weight used is referred to the dry mass. Flow rates of 100, 200 and 300 mL min−1 with a bed height of 100 cm were studied. The column was filled with 480 g of biosorbent, and a multi-component synthetic solution was percolated through it. Two bed heights were studied: 100 and 160 cm, filled with 480 and 600 g of biosorbent, respectively. Multicomponent synthetic solution was percolated through the column at a flow rate of 200 mL min−1 . Aliquots of 50 mL of column effluent solution were collected every 10 min, and the residual concentrations of metal ions were analysed by atomic absorption spectrophotometry (AAS). 2.5. Treatment influence on biosorbent Two procedures were carried out: treatment of biosorbent outside the column and treatment of biosorbent inside the column. 2.5.1. Treatment outside the column In the first study, the coconut shells were used untreated (CS). A second study was conducted with the CS washed with water out of the column (CSWO). A mass of raw CS was placed in a container with water at a ratio of 1:3. This mixture was stirred for 1 h, filtered and then the biosorbent material was dried at room temperature. In the third study, the CS was washed with NaOH (0.1 mol L−1 ) out of the column (CSBO). A mass of biosorbent was placed in a container with a solution of NaOH (0.1 mol L−1 ) at a ratio of 1:3. This mixture was stirred for
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1 h, filtered, washed with water to remove the excess basic solution, filtered again and the material was then dried at room temperature. For the above-mentioned three studies, a multicomponent synthetic solution was percolated through the column under the following conditions: flow rate of 200 mL min−1 , initial concentration of metal ions 200 mg L−1 , 480 g of untreated or treated CS. Aliquots of 50 mL were collected every 10 min for obtaining the breakthrough curves. The concentrations of metal ions were determined for each aliquot collected.
2.5.2. Treatment in the column The column was filled with CS and washed: with water coconut shell washed with water inside the column (CSWI) and with NaOH (0.1 mol L−1 ) coconut shell washed with basic solution inside the column (CSBI). In the first study, 20 L of water was percolated through the column filled with 402 g of CS (CSWI). Fractions were collected every 10 min, and the pH and COD were determined to measure the residual organic matter. In the second study, 11 L of NaOH solution (0.1 mol L−1 ) was percolated through the column, filled with 402 g of CS powder (CSBI), at a flow of 150 mL min−1 . Then, water (20 L) was percolated through the column to remove the excess of basic species. Fractions were collected every 5 min, and the pH and COD were measured. For the above-mentioned two studies, a multicomponent synthetic solution at a concentration of 200 mg L−1 was percolated through the column (100 cm bed height) after treatments. Aliquots of 50 mL were collected every 10 min, and the pH and concentration of metal ions were determined. The per cent mass loss was calculated and was found to be 6% for treatment with water and 17% for treatment with NaOH. The adsorption capacities of materials treated inside the column were calculated considering the cited values of mass loss.
2.6. Breakthrough curves for single component Breakthrough curves for single-component solutions of metal ions (copper, nickel and zinc) were evaluated. First, the biosorbent was subjected to CSBI treatment. Then, the single-component synthetic solution of copper, nickel and zinc was percolated through the column. Aliquots of 50 mL were collected every 10 min and single-metal ion concentrations were determined.
2.7.
Column regeneration
After CSBI treatment and column saturation with multielement synthetic solution, the metal ion desorption was
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carried out with HNO3 solution (0.5 mol L−1 ). The concentration of metal ions was analysed by an AAS, model GBC 933 plus, in an air-acetylene flame. 2.8. Fixed-bed column modelling In this study, Thomas and EBCT models were used to predict the performance of the column. 2.8.1. Empty-bed contact time In some systems on a real scale where default behaviour is not observed, the breakthrough curve depends on the column length. This dependence can be determined by performing experiments on a pilot-scale column at the same flow rate, varying the lengths of the biosorbent bed. The breakthrough times are then determined from the rupture concentration. The EBCT is a measure of how much time a parcel of fluid spends in the column, on the basis that the column contains no solid packing.[19,20] The EBCT is represented by Equation (3). Another important parameter is the biosorbent usage rate (BUR), that is, the ratio between the weight of biosorbent in the column and the amount of liquid passed into the column at the time of breakthrough (Equation (4)).[19] EBCT (min) =
VL × Asec , H
(3)
where VL is the total volume of the empty column (mL), H is the hydraulic loading and Asec is the bed cross-sectional area. ML , (4) Biosorbent usage rate = Vb where ML is the total mass of biosorbent inside the column (g) and Vb is the volume of treated solution at the breakthrough point (L). 2.8.2. Thomas model This model assumes a behaviour of continuous flow and uses the Langmuir isotherm for equilibrium and the reversible second-order kinetics reaction. The Langmuir isotherm is applicable for favourable and unfavourable adsorption conditions. Traditionally, the Thomas model is used to determine the maximum adsorption capacity of biosorbent in continuous systems. The Thomas model is expressed by Equation (5).[20–23] C kt (q0 mc − C0 Ve ) 1 . (5) = C0 1 + exp Fm The adsorption capacity of the bed (q0 ) and the coefficient (Kt ) may be obtained from the intercept and slope, respectively, of a curve obtained by plotting ln(C/C0 − 1) as a function of t or Ve from the breakthrough point (Cb ) until the
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exhaustion point (Cx ). The linearized form of the Thomas model is given by Equation (6): ln[(C0 /C) − 1] =
K t q0 ms − Kt C0 t, Fm
(6)
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where C is the adsorbate concentration at a determinate volume (mg L−1 ); C0 is the initial solution concentration (mg L−1 ); Kt is the Thomas rate constant (mL mg−1 min−1 ); q0 is the maximum solid phase concentration (mg g−1 ), i.e. the maximum adsorption capacity; ms is the amount of biosorbent (g); Fm is the volumetric flow rate (L min−1 ); and Ve is the effluent volume (L). 3. Results and discussion 3.1. Characterization of the biosorbent bed The contact surface between the biosorbent and the liquid phase as well as the biosorbent particle size plays an important role in the phenomenon of adsorption.[4,24] Green CS powder was submitted to a particle size determination. Approximately 85% of the biosorbent was in a particle size ranging from 0.25 to 2 mm. Rosa et al.,[25] performing the same type of analysis, found a value of 78% at the same particle size range. Sousa et al.,[18] studying the removal of metal ions Cu(II), Ni(II), Zn(II), Pb(II) and Cd(II) by green CS powder, found no significant effect on removal efficiency for metals studied in the particle size ranging from 0.15 to 0.25 mm. The results of determination of some physical properties of the biosorbent bed are described below for the bed heights of 100 and 160 cm, respectively: apparent density, 0.188 g cm−3 for both; packing density, 0.159 and 0.124 g cm−3 ; particle volume of 2553 and 3191 cm3 ; and porosity of the bed of 0.154 and 0.338. 3.2.
Effect of flow rate and bed height
The experimental and theoretical breakthrough curves obtained for flow rates (100, 200 and 300 mL L−1 ) are shown in Figure 1.[26] The breakthrough and exhaustion volume (chosen, respectively, as 5% and 90% of initial concentration for all three metal ions) observed are larger for copper than for zinc and nickel, due to higher affinity of Cu(II) by biosorbent surface, and a larger time period is required to reach the exhaustion volume, in contrast for Ni(II) and Zn(II). Gao et al. [27] found a similar behaviour in Cu(II), Ni(II), Cd(II) and Zn(II) removal by oxidized carbon nanotubes. According to them, the removal process is related to such factors as the surface chemistry of the adsorbent, the initial concentration of ions, the components in the adsorption system and the ratio of the metal ion species in solution and the redox reactions on the carbon surface involving metals might affect negatively the amount adsorbed.[27]
The results shown in Table 1 revealed that with increase in flow rate (100–300 mL min−1 ), the adsorption capacity decreased for Cu, Ni and Zn ions. Higher adsorption capacity values of 0.23 mmol g−1 for Cu(II), 0.07 mmol g−1 for Ni(II) and 0.07 mmol g−1 for Zn(II) were obtained for a flow rate of 100 ml min−1 . On the other hand, when flow velocity increased three times, the percentage removal decreases at 26.0%, 28.5% and 29.5%, respectively, for each metal ion. A similar trend was observed by Shahbazi et al. [28] in Pb(II), Cu(II) and Cd(II) removal by functionalized mesoporous silica. According to them, this is because metal ions leave the column before the equilibrium stage can be achieved by reducing the performance of the column. In contrast, Revathi et al. [3] observed that by increasing the flow rate, the adsorption capacity and Thomas constant were increased using the Ceralite IR 120 ion exchange resin for the removal of Ni(II),Cu(II) and Zn(II) ions from synthetic electroplating rinse water solutions. It is known that the increase in the flow rate implies a reduction in the hydraulic retention time (HRT) of metal ions inside the column. According to Cooney,[19] HRT is a typical parameter of design and operation of bed fixed columns, and the usual residence times on column range from 15 to 30 min. Larger residence times can lead to a decrease in the solute removal, while shorter times do not allow an effective contact interaction to occur between the sorbent and sorbate.[5,19] It is important that HRT be higher than equilibrium time that is determined in batch experiments, allowing a time of contact large enough between the adsorbent and adsorbate. In this study, the HRT decreased from 30 to 10 min when the flow rate increased from 100 to 300 mL min−1 . According to results obtained by the breakthrough curves, the flow rate of 200 mL min−1 was chosen for the following studies because it provided high adsorption capacity and the HRT. The Thomas model was applied to the experimental data (continuous line, nonlinear (NL) model and dashed line, linear model, in Figure 1). A linear plot of ln[(C0 /C) − 1] versus Ve to data located in the range 0.05 < /C0 < 0.90 allowed a previous determination of the kinetic coefficient, Kt , and the adsorption capacity of the bed, q0 , according to Equation (6). NL regression analysis was performed using Equation (5). The sum of the squares of the errors (SSE) was examined for every experimental data set, and the parameters of Kt and q0 were determined for the lowest error values in each case by adjusting and optimizing the functions themselves using the solver add-in for Microsoft Excel® . The values of Kt and q0 obtained for the lowest error values are given in Table 1. Except for copper, the Thomas model represented the flow rate data well. In general, the theoretical and experimental maximum adsorption capacities were closed. The increase in the flow rate resulted in an increase in the Thomas rate constant and a decrease in the maximum
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Figure 1. Comparison of experimental and theoretical breakthrough curves for metal ions at varied flow rates of (a) 100 mL min−1 , (b) 200 mL min−1 and (c) 300 mL min−1 (NL, nonlinear; L, linear). Adapted from.[26]
adsorption capacity for metals studied with an initial metal concentration of 200 mg L−1 . According to Shahbazi et al.,[28] this occurs due to difference of metal ion radius size as it passes through the column.
The NL regression analyses better represented the data than linear (L) regression analyses. From Table 1, it can be seen that the errors for NL were lower than L, showing a better fit.
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Table 1. Parameters by linear (L) and NL regression analysis with Thomas model for metal ions Cu(II), Ni(II) and Zn(II) for the three flow rates (CSWO treatment). Kt (mL min−1 mg−1 ) Metalion
Flow rate (mL min−1 )
L
NL
100 200 300 100 200 300 100 200 300
0.102 0.091 0.292 0.462 1.008 3.478 0.412 1.203 2.716
0.113 0.270 0.299 0.460 1.141 3.464 0.410 1.119 1.991
Cu(II) Ni(II) Zn(II)
q0 (mmol g−1 ) Theoretical L NL Experimental 0.242 0.258 0.191 0.075 0.096 0.054 0.075 0.071 0.057
0.242 0.234 0.180 0.075 0.091 0.049 0.075 0.071 0.050
0.233 0.218 0.172 0.071 0.093 0.051 0.071 0.069 0.050
SSE L
NL
0.061 9.142 0.428 1.53 E−3 0.357 1.42 3.35 E−4 6.737 1.059
1.36 E−29 2.31 E−07 1.69 E−29 3.77 E−32 4.44 E−31 2.99 E−14 1.17 E−28 4.07 E−31 6.84 E−13
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Note: Adapted from.[26] Table 2. Metalion Cu(II) Ni(II) Zn(II)
EBCT and BUR for different bed heights.
(a)
Bed height (cm)
EBCT (min)
Q (mmol g−1 )
BUR (g L−1 )
100 160 100 160 100 160
15 24 15 24 15 24
0.217 0.264 0.092 0.111 0.069 0.075
18.97 13.63 55.8 53.1 53.9 46.15
Note: Adapted from.[26]
With the values of Kt and q0 for each metal, the total mass of biosorbent required to treat wastewater in a column can be obtained under the same conditions, requiring only knowledge of the feed concentration for each metal, the daily flow rate and the volume of solution to be treated. Applying the EBCT model and BUR (Equations (1) and (2), respectively) to the data obtained from the breakthrough curves for bed height study resulted in the data shown in Table 2 and Figure 2(a). It can be seen that the breakthrough volume for each metal and the adsorption capacity increased while the BUR decreased with the increase in bed height. The BUR is lower for copper due to the effect of competition between metal ions in solution and biosorbent sites. The lower the BUR is, the greater is the adsorption capacity. The literature reports that the greater the bed height is, the greater the service time of the column because the surface area of the biosorbent increases as the number of active sites available for metal–biosorbent interaction increases. The amount of biosorbent required to treat the same volume of solution at the same concentration therefore decreases.[19,29,30] The maximum HRT of 35 min [19] is not exceeded when the column length increases from 100 to 160 cm. Figure 2(b) presents the critical bed depths (the bed height when tb (breakthrough time) = 0) or the smaller bed depth to obtain an effluent concentration equals to Cb .
(b)
Figure 2. (a) BUR versus EBCT and (b) breakthrough times versus bed heights.
The critical bed depth depends on the choice of Cb and is obtained by extrapolating the curve of breakthrough time versus bed height to zero. The values of critical bed depths were 40, 4 and-60 cm for copper, zinc and nickel, respectively. The negative value found for nickel means that, in a bed height greater than zero, it is possible to obtain an effluent concentration Cb used in this work.[19] 3.3. Treatment influence on biosorbent The results obtained with non-treated (CS) and treated CS outside (CSWO, CSBO) and inside (CSWI, CSBI) the column are shown in Figure 3. According to the results shown
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(a)
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Figure 3. Comparison of the treatments outside and inside column for the three metal ions studied.
in Figure 3, the green CS treated with water (CSWO, CSWI) or NaOH (CSBO, CSBI) led to an increase in the adsorption capacity as well as the breakthrough and exhaustion volumes, when compared with raw material (CS). For the CSBO treatment, the adsorption capacity increased about 40% for each metal ion when compared with the non-treated material (CS). This occurs because when the lignocellulosic material is washed with NaOH solution (0.1 mol L−1 ), the cellulosic fibre expands, and increases the number of active sites available to improving the adsorption process.[8,9] The increase in adsorption capacity was 27% for copper and zinc, while for nickel it was 37% when CSWO and CSWI treatments were compared. On the other hand, according to the results obtained for both treatments, outside (CSBO) and in the column (CSBI), the use of green CS powder treated with NaOH (0.1 mol L−1 ) increased the removal percentage at 55.7% for copper, 58.9% for nickel and 73.7% for zinc from aqueous solution. However, the use of this material for the same purpose without treatment is also possible, with the potential for co-processing in other industrial sectors. 3.3.1. pH Monitoring The pH, among several factors, can be regarded as the most important parameter to influence the adsorption process. In acid, there is an electrostatic repulsion between metal ions and the biomass surface, enhancing the competition effect. In an alkaline medium, precipitation takes place with the formation of metal hydroxides. Moreover, depending on the concentration of metal ions in solution, complexes can be formed, and other mechanisms can occur. On the other hand, the hydroxyl group increases the number of adsorption sites on the fibre surface, with interaction with metal ions most likely occurring.[15–17] Figure 4(a) shows effluent solutions resulting from biosorbent treatment in the column. With CSWI treatment, the pH of the effluent solution changes very little, remaining at approximately neutral. At the beginning of treatment CSBI, the pH was acid even the feed solution has a basic character, indicating that the sodium hydroxide influent is
(b)
Figure 4. pH-Curve of collected aliquots at the outlet of the column filled with green CS powder (a) during treatments CSWI and CSBI and (b) from aliquots collected after percolating metallic solution through the column.
interacting with the biosorbent in the column by modifying its structure and morphology.[10,15,31,32] After 6–7 L of basic solution, the pH starts to increase, indicating that an excess of basic solution has percolated through the column. Then, 20 L of water was passed through the column to remove the excess basic solution, leaving the pH at approximately 13. The pH of metallic effluent solutions that has been passed in experiments carried out to estimate the effect of the treatment outside and inside the column was monitored (Figure 4(b)). The pH remained almost constant in all three studies (CS, CSWO, CSBO) performed after treatment outside the column, suffering little decrease. For CS and CSWO treatments, the pH was approximately 5, and for CSBO treatment, the pH was approximately 7. These decreases may be due to ionic exchange between the biosorbent surface and the solution, where the metal ion binds to the fibre and releases H+ and the slightly acid (approximately 4.5–6.0) character of the multi-component metallic solution. Treatment with NaOH (0.1 mol L−1 ) showed better results, due not only to adsorption but also most likely to the mechanisms of precipitation and complexation.[33] The use of hydroxides elevates the effluent pH to 7.0, leaving the effluent pH approximately neutral. In general, a low influence on effluent pH was observed when the biosorbent was treated outside the column.
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Figure 5.
G.S.C. Raulino et al.
COD curves for aliquots of collected effluent for CSWI and CSBI treatments.
After the treatments inside the column (CSWI and CSBI) were performed, a great decrease is observed when the metallic solution is passed, especially for CSBI treatment (Figure 4(b)). This may be due the excess of OH− available at the medium that is leached by the metallic solution. The OH− ions available in the solution react with Cu(II), Zn(II) and Ni(II) ions to form Cu(OH)2 , Zn(OH)2 and Ni(OH)2 , respectively, although complexes such as Cu(OH)2 , CuOH+ , NiOH+ , Ni2 OH3+ , ZnOH+ , Zn2 OH3+ can be formed.[3] After this great decrease, the same behaviour for CSWO and CSBO is observed due to the same reasons explained before. 3.3.2. Chemical oxygen demand Figure 5 shows that a maximum COD (approximately 4900 mg L−1 ) was achieved when the biosorbent was treated with NaOH (CSBI). Natural fibres such as green CS powder contain high levels of lignin and cellulose. When these cellulosic materials are subjected to a basic treatment, soluble phenolic compounds in the fibre are removed, resulting in the destruction of the lignocellulosic complex, solubilizing hemicelluloses and expanding fibrous materials, as well as extracting organic matter such as tannins.[10,16,32,34] The high COD is the result of hydroxide action in the fibre, which removes large amounts of organic matter. After percolation of the treatment solutions through the column, the remaining COD was 60.3 mg L−1 for CSWI and 171.9 mg L−1 for CSBI.
3.4.
Column adsorption in single- and multi-component solutions The breakthrough curves of the three metal ions studied in single-component systems were prepared after optimization
Table 3. Comparison between adsorption capacities of green CS powder submitted to treatment CSBI in multi- and single-component systems, when C/C0 = 0.5 (Fm = 200 ml min−1 ; C0 = 200 mg L−1 ). Q (mmol g−1 ) Metal ion Cu(II) Ni(II) Zn(II)
CSBI multi-component
CSBI single-component
0.509 0.185 0.121
0.746 0.452 0.394
of the flow rate, bed height and biosorbent treatment. Table 3 shows the adsorption capacities of the biosorbent for treatment CSBI in multi-component and single-component solutions, and can be observed that the adsorption capacity of each metal increased when passed from a multicomponent to a single-component system, especially for zinc and nickel. This increase in adsorption capacity is due to the effect of competition between metal ions for the active sites of the biosorbent. The results show that copper ions are preferred by the sites over other ions studied because the increase in adsorption capacity of copper from a multicomponent to a single-component system was lower than the other two ions, zinc and nickel as seen in Table 3.
3.5.
Desorption of metal ions
In the desorption of metal ions, 20 L of HNO3 (0.5 mol L−1 ) was used to elute these metal ions after CSBI treatment and column saturation. After 20 L of acid solution percolated through the column, the residual concentrations of metal ions were 11 mg L−1 for copper, 4 mg L−1 for nickel and 4 mg L−1 for zinc. Almost all of the copper was desorbed (98.54%), whereas only 50% of the nickel and zinc have
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been desorbed, possibly due to desorption of nickel and zinc ions after saturation (C/C0 > 1) resulting from the competition effect with copper for active sites. Sousa et al.,[35] studied the removal of metal ions using the green CS powder treated with NaOH (0.1 mol L−1 ), verified that the biosorbent can be used in only one cycle of adsorption under these conditions because the efficiency of removal decreased after the second cycle. As the estimation of exhaustion volume for copper was about 120 L, a reduction of 84% in the volume is reached with desorption. 4. Conclusions The results indicated that the use of treated green CS powder is feasible for the removal of copper, nickel and zinc from aqueous solutions. With the increase in bed height, the adsorption capacity increases and a smaller amount of biosorbent is required per litre of solution to be treated. On the other hand, the increase in flow rate leads to a decrease in adsorption capacity. Among the treatments both outside and in the column, the one with NaOH (0.1 mol L−1 ) on the column had the best result, indicating an increase in pH and COD. Although the use of green CS without treatment is possible, with the potential for co-processing in other industrial sectors. The adsorption capacity for a single-component solution was higher than that for a multi-component solution due to the competition effect. Supplemental data Supplemental data for this article can be accessed http://dx.doi.org/10.1080/09593330.2014.880747. References [1] Baird C. Química ambiental. Porto Alegre: Editora Bookman;2002. [2] Sud D, Mahajan G, Kaur MP. Agricultural waste material as potential biosorbent for sequestering heavy metal ions from aqueous solutions – a review. Bioresour Technol. 2008;99:6017–6027. [3] Revathi M, Saravanan M, Chiya AB, Velan M. Removal of copper, nickel, and zinc ions from electroplating rinse water. Clean – Soil Air Water. 2012;40:66–79. [4] Tarley CRT, Arruda MAZ. Biosorption of heavy metals using rice milling by-products. Characterisation and application for removal of metals from aqueous effluents. Chemosphere. 2004;54:987–995. [5] Ayoob S, Gupta AK, Bhakat PB. Analysis of breakthrough developments and modeling of fixed bed adsorption system for As(V) removal from water by modified calcined bauxite (MCB). Sep Purif Technol. 2007;52:430–438. [6] Suksabye P, Thiravetyan P. Cr(VI) adsorption from electroplating plating wastewater by chemically modified coir pith. J Environ Manage. 2012;102:1–8. [7] Huisman JL, Schouten G, Schultz C. Biologically produced sulphide for purification of process streams, effluent treatment and recovery of metals in the metal and mining industry. Hydrometallurgy. 2006;83:106–113.
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[8] Bailey SE, Olin TJ, Bricka RM, Adrian D. A review of potentially lowcost sorbents for heavy metals. Water Res. 1998;33:2469–2479. [9] Gurgel LVA, Freitas RP, Gil LF. Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by sugarcane bagasse and mercerized sugarcane bagasse chemically modified with succinic anhydride. Carbohydr Polym. 2008;74:922–929. [10] Brígida AIS, Rosa MF. Determinação do Teor de Taninos na Casca de Coco Verde (Cocos nucifera). Proc Interamer Soc Trop Hort. 2003;47:25–27. [11] Johnson PD, Watson MA, Brown J, Jefcoat IA. Peanut hull pellets as a single use sorbent for the capture of Cu(II) from wastewater. Waste Manage. 2002;22:471–480. [12] Singh KK, Hasan SH, Rastogi RJ, Removal of cadmium from wastewater using agricultural waste rice polish. J Hazard Mater. 2005;A121:51–58. [13] Kim JW, Sohn MH, Kim DS, Sohn SM, Know YS. Production of granular activated carbon from waste walnut shell and its adsorption characteristics for Cu2+ ion. J Hazard Mater 2001;B85:301–315. [14] Moreira SA, Sousa FW, Oliveira AG, Nascimento RF, Brito ES. Remoção de Metais de Solução Aquosa Usando Bagaço de Caju. Quim Nova. 2009;32:1717–1722. [15] Gurgel LVA, Júnior OK, Gil RPF, Gil LF. Adsorption of Cu(II), Cd(II), and Pb(II) from aqueous single metal solutions by cellulose and mercerized cellulose chemically modified with succinic anhydride. Bioresour Technol. 2008;99:3077–3083. [16] Asadi F, Shariatmadari H, Mirghaffari N. Modification of rice hull and sawdust sorptive characteristics for remove heavy metals from synthetic solutions and wastewater. J Hazard Mater. 2007;154:451–458. [17] Muhamad H, Doan H, Lohi A. Batch and continuous fixedbed column biosorption of Cd2+ and Cu2+. Chem Eng J. 2010;158:369–377. [18] Sousa FW, Moreira SA, Oliveira AG, Cavalcante RM, Nascimento RF, Rosa MF. Uso da casaca de coco verde como biosorbente na remoção de metais tóxicos. Quim Nova. 2007;30:1153–1157. [19] Cooney DO. Adsorption design for wastewater treatment. Boca Raton, FL: Editora CRC Press; 1999. [20] Srivastava VC, Prasad B, Mishra IM, Mall ID, Swamy MM. Prediction of breakthrough curves for sorptive removal of phenol by bagasse fly ash packed bed. Ind Eng Chem Res. 2008;47:1603–1613. [21] Yan G, Viraraghavan T. Heavy metal removal in a biosorption column by immobilized M.rouxii biomass. Bioresour Technol. 2001;78:243–249. [22] Vijayaraghavan K, Thilakavathi M, Palanivelu K, Velan M. Continuous sorption of copper and cobalt by crab shell particles in a packed column. Environ Technol. 2005;26: 267–276. [23] Aksu Z, Gönen F. Biosorption of phenol by immobilized activated sludge in a continuous packed bed: prediction of breakthrough curves. Process Biochem. 2004;39: 599–613. [24] Rao M, Parwate AV, Bhole AG. Removal of Cr6+ and Ni2+ from aqueous solution using bagasse and fly ash. Waste Manage. 2002;22:821–830. [25] Rosa MF, Abreu FAP, Furtado AAL, Brígido AKL, Norões ERV. Processo agroindustrial: obtenção de pó de casca de coco verde. Fortaleza: Embrapa Agroindústria Tropical; 2001, 4 p (Comunicado Técnico, 61). [26] Sousa Neto VO, Raulino GSC, Freire PTC, Araújo-Silva MA, Nascimento RF. Equilibrium and kinetic studies in
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