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Biosorption of copper (II) from aqueous solutions by wheat shell
DESALINATION Desalination
ELSEVIER
164 (2004) 135-140 www.dscvkr enmifocaie/dcsa(
Biosorption of copper (II) from aqueous solutions by wheat shell Nurgul Basci, Erdem Kocadagistan*, Beyhan Kocadagistan Department of Environmental Engineering, Atatiirk University, Erzurum 25240, Turkey Tel. +90 (442) 231-4808 ; Fax +90 (442) 233-6961 ; email : [email protected] .tr
Received 17 June 2003 ; accepted 22 September
2003
Abstract
The adsorption capacity of wheat shell for copper (II) was studied at various pH (2-7), agitation speeds (50250 rpm) and initial metal ion concentrations (Co, from 10 to 250 mg .L - ') . Maximumbiosorption of copper onto wheat shell occurred at 240 rpm agitation speed and at pH between 5 and 6 . The biosorption values of copper (II) were increased with increasing pH from 2 to 5 and decreased with increasing copper/wheat shell (x/m) ratios from 0 .83 to 10 .84 mgCu(II) .g ' wheat shell . The biosorption efficiencies at these x/m ratios were 99% and 52%, respectively, at the end of the 120 min contact time (t) . The equilibrium isotherms and kinetics were obtained from batch adsorption experiments at 298 K . It was observed that wheat shell was a suitable biosorbent for removing Cu(II) from aqueous solutions . Keywords :
Biosorption ; Copper (II) ; Wheat shell ; Heavy metal
1 . Introduction Copper is present in large quantities in nature as an element or in the other forms . It is an Environmental Protection Agency regulated heavy metal that is often used for anti-corrosion and as a decorative coating on metal alloys [I] . Treatment of wastewaters containing heavy metal could be achieved with settling as settleable metal hydroxides, activated carbon adsorption, ion exchange, reverse osmosis, electrochemical treatment, evaporation and biological methods . *Corresponding author . 0011-9164/04/$-
See front matter ©
P11 : SOO11-9164(04)00172-9
2004
But these methods are not economical and do not exhibit high treatment efficiency, especially at metal concentrations in the range of 0 .0100 .1 g .L - ' [2] . More economical and effective methods are currently being developed for removal of heavy metals from wastewaters [3,4] . There are many studies for removing copper from aqueous solutions by using biosorption . In these studies researchers used aquatic plants, microorganisms and some other similar living or nonliving biosorbents such as dried plant leaves, marine or freshwater algae, pine, rice husk, pine bark, and canola meal [5-10] .
Elsevier B .V . All rights reserved
1 36
N. Basci et al. /Desalination 164 (2004) 135-140
It has been reported that agitation speed, pH, temperature and initial metal and biosorbent concentrations have an important effect on the efficiency of the biosorption process [11] . The increasing biosorption efficiency with increasing total surface area of the biosorbent has also been reported in the literature [12] . Wheat is one of the cereals used for the preparation of bread and other bakery products, and wheat shell is the by-product of wheat bread production industries . Wheat shell is a rich source of dietary fibre and contains carbohydrates, proteins, starch, sugar and celluloses [13] . The aim of this work was to study the effect of several parameters as initial pH, agitation speed and metal concentration on the biosorption efficiency of Cu(II) ions from aqueous solutions . The biosorbent used was wheat shell, which is a very cheap and readily available materiel in most countries .
2 . Materials and methods 2.1 . Preparation of the biosorbent Wheat shell was used as a biosorbent for the biosorption of copper ions . Before the start of all experiments, the wheat shell was properly cleaned with deionised water, dried at a temperature of 353 K and finally blended in a mortar and sieved through a 0 .005 m sieve .
multiparameter device during all of the experiments . Concentrations of Cu(II) ranging from 10 to 250 mg.L - ' and dried wheat shell (10 to 250 mg .L -1 ) were added to Erlenmeyer flasks . These 0 .25 L flasks were stirred at a constant temperature (298 K) in a shaker (Rosi 1000) for 2 h . Samples were taken at the end of the process and immediately filtered with a vacuum filtration apparatus for removing the suspended wheat shell and analyzed for metal ions content . The Cu(II) concentration was determined by flame atomic absorption spectrophotometry using a Shimadzu AA-670 spectrophotometer. Zeta potentials were measured with a Zeta-Meter (Zeta-Meter 3 .0 + 542, USA) .
3. Results and discussion 3 .1 . Effect ofpH According to the great importance of the pH on heavy metal biosorption [ 1,3,14,18], tests were undertaken with different initial pH values of the Cu(II) solution using a constant concentration of wheat shell (m =12 g .L - ' ) . At the initial pH below 6, there were not any perceptible pH changes while at pH of solutions adjusted above 6 at the 100 90 80 6 w
2.2. Preparation of stock solution An aqueous stock solution of CuSO 4.5H20 in a concentration of 1000 mg .L - ' of Cu(II) was used in all experimental runs .
70 60
0 'g 50 0 0 40 14 30 20 0
2.3 . Experimental run HCl and NaOH solutions (0 .1 N) were used for adjusting the initial pH of solutions after addition of the biosorbent . The pH measurements were achieved with a WTW Multi-340i model
1
2
3
4
5
6
7
pH
Fig . 1 . Effect of initial solution pH on Cu(II) biosorption efficiency by wheat shell . (Initial Cu(II) concentrations = 50 mg .L -1 ; temperature = 298 K, wheat shell concentration = 12 g .L- ', agitation speed = 250 rpm, contact time = 2 h .)
137
N. Basci et al. /Desalination 164 (2004) 135-140
beginning of the experiments, some slight decreases were observed along the process . The effect of pH on copper biosorption is given in Fig. I where it is seen that biosorption efficiencies increased from 33% at pH 2 to 95% at pH 5 . Further experimental runs were performed at a pH range between 5 and 6 because the highest biosorption efficiencies were achieved in these pH intervals . Similar results were reported using Sphaerotilus natans as the biosorbent at pH 5 .5-6 [15], Australian marine algae at pH 5 .5 [16], the fungus Pharerochaete chryssporium at pH 6 [17] and waste brewery biomass at pH 5-6 [14] .
15 10
5
-
5-
-15
2
3
4
5
6
7
8
9
pH
Fig . 2 . Effect of pH on zeta potential value . (Initial Cu(II) concentrations = 50 mg .L -1 , temperature = 298 K, wheat shell concentration = 12 g .L- ', agitation speed = 250 rpm, contact time = 2 h .)
3.2. Zeta potentials Zeta potential values of wheat shell biosorbent were determined at various pHs by using a Zeta-Meter (Fig . 2) . Wheat shell zeta potential values were measured as positive at pH 3 .65 and below . The isoelectric pH point of wheat shell was observed from the curve at pH 3 .65 (zP = 0 mV) . Above this point, values were negative and at pH 5 maximum the zeta potential value of wheat shell was obtained (- 10 .6 mV) . Under the isoelectric point, the overall surface charge of wheat shell became positive and biosorption decreased. As the pH increased up to 5 .5, the overall surface charge of wheat shell was negative and biosorption efficiencies increased . Thus, at pH values between 3 .5 and 5 .5, the interaction of the copper with wheat shell was primarily electrostatic in nature . As the pH rose above 5 .5, biosorption efficiencies were decreased slightly and above pH 7 biosorption efficiencies were not noticeable because copper was being precipitated as hydrous oxide above this pH value . As seen from Figs . 1 and 2, there is a relationship between initial solution pH, zeta potentials and biosorption efficiencies . The maximum biosorption efficiency (95%) and zeta potential values (-10 .6 mV) were obtained at the same pH of 5 .
3.3 . Effect of initial Cu(II) concentration The biosorption of Cu(II) by wheat shell was studied at several different initial copper concentrations ranging from 10 to 250 mg .L - '. As seen from Table 1, biosorption efficiencies decreased with the increasing of initial metal concentrations due to the increase of x/m ratios even though there was an increase of Cu(II) ions adsorbed onto the wheat shell . For determining the adsorption constants and adsorption capacity of wheat shell for removal of Cu(II), Langmuir and Freundlich isothelnls were tested at various initial ion concentrations ranging from 10 to 250 mg .L -1 , while the wheat shell dry weight in each sample was constant at 12 g .L -1 . In this study, Langmuir was the best-fit isotherm for biosorption of Cu(II) on wheat shell (Fig. 3) . The Langmuir isotherm was given as q = x/m = (b. gmax .Ce) l ( I + b . Ce)
(1)
and the linear form of this equation can be given as 1/(x/m) = ( 1/b.gmax)(1/Ce) + (1/gmax)
(2)
where q is the adsorption capacity at the
N. Basci et al . /Desalination 164 (2004) 1 3 5-140
138
Table 1 Effect of initial Cu(II) concentration on biosorption
C, mg.L - '
C, mg .L - ' 0 .1 0 .62 1 .21 1 .98 7 .52 18 .21 46 .42 92 .81 119 .92
10 20 30 40 50 100 150 200 250
Copper adsorbed on wheat shell, mg .L - '
x/m, mg Cu(II) .g - '
wheat shell
Biosorption efficiency,
9 .90 19 .38 28 .79 38 .02 42 .48 81 .79 103 .58 107 .19 130 .08
0 .83 1 .62 2 .40 3 .17 3 .54 6 .82 8 .63 8 .93 10 .84
99 97 96 95 85 82 69 54 53
m =12 g .L - ', T = 298 K, rpm = 250, pH = 5, t = 2 h .
k
40 35 30 25 20 15 105 0 0
Table 2 Adsorption capacities for some adsorbents reported in the literature [18] y = 0.32x+ 7.62 RZ = 0.98
Adsorbent
qmax, mmol .g - '
Aspergillus oryzae
0 .07 0 .10 0 .13 0 .25 0 .30 0 .80 0 .96 1 .11 1 .20
Lignite Wheat shell (this study) 10
20
30 40
50
60
70
80
90 100
1/Ce Fig . 3 . Plot of linear form of Langmiur isotherm for the biosorption of Cu(II) onto wheat shell . (m =12 g .L -1 , T= 298 K, rpm = 250, pH = 5, t = 2 h .)
equilibrium solute concentration C e (mg of solute adsorbed per g of adsorbent or mol .g - ') ; Ce is the concentration of adsorbate in solution (mg.L - ' or mmol .L - ') ; gmax is the maximum adsorption capacity corresponding to complete monolayer coverage (mg of solute adsorbed per g of adsorbent or mmol .g - ') and b is a Langmuir constant related to the energy of adsorption (mg .L - ' or mmo1 .L- ') . The adsorption constants of the Langmuir isotherm gmax and b were estimated from the intercept and slope of 1/(x/m) vs, (1/C e), respectively, according to Eq . (2) and obtained as
R . arhizus Pseudomonas aeruginosa Padina sp . S. fluitans E. radiata L. japonica
8 .34 mg.g - ' (0 .13 mmol .g"') and 24 L .mmol - ', respectively . The adsorption capacity (gmax) of wheat shell and some other biosorbents reported in the literature are given in Table 2 . The correlation coefficient of the Langmuir isotherm (r) obtained from 1/(x/m) vs . 1/Ce plot was 0 .98 . 3.4 . Effect of biosorbent concentration on the equilibrium time The effect of agitation time of Cu(II) on wheat shell was studied at various biosorbent concen-
N. Basci et al. /Desalination 164 (2004) 1 3 5-140
139
range conditions ; the agitation time was continued at 120 min to achieve the equilibrium time . Biosorption efficiencies were increased by increasing agitation speed (Fig . 5) . Maximum efficiencies (horizontal slope) were observed at 240 rpm .
0
so
100
150
t (min) Fig . 4 . Effect of contact time on biosorption . (Initial Cu(II) concentrations = 50 mg .L - ', temperature = 298 K, agitation speed = 250 rpm, contact time = 2 h .)
87 0
°~. 86 U 85 U
w 84 w 0 83 0
82 8180 0
50
100
150
200
Agitation speed (rpm) Fig . 5 . Effect of agitation speed on biosorption . (Initial Cu(II) concentrations = 50 mg .L - ', temperature = 298 K, agitation speed = 250 rpm, contact time = 2 h .)
trations . During all of the experiments, equilibrium was reached within 2 h after a first fast initial step which lasted for 5-30 min and a second slower step that followed (Fig . 4) . There was a slight increase in biosorption efficiencies later than equilibrium time as shown in Fig . 4 .
4 . Conclusions The biosorption of Cu(II) onto wheat shell was investigated . Wheat shell that was sieved at 0.005 m at various concentrations was used for this purpose, and the following conclusions are drawn based on the experimental results . • pH has a significant role on biosorption efficiencies . The maximum efficiency was observed at 99% at pH 5 for a 12 g .L -1 wheat shell concentration in this study . • Above pH 7, copper was precipitated as hydrous oxides . • The biosorption performance of wheat shell was also affected by initial metal concentration, contact time and agitation speed of the process . Biosorption efficiencies were increased with increasing contact time and agitation speed and decreased with increasing Cu(II) concentration . Better results were obtained at a contact time of 120 min and 250 rpm agitation speed . • To optimize the performance of biosorption of Cu(II) using the wheat shell process, a pH 5 and below 1 mg .g - ' x/m concentrations should be used . References [1]
3.5 . Effect of agitation speed Experimental runs were carried out in a shaker for various biosorbent concentrations at 50 mg.L- ' initial Cu(II) ion concentrations, pH 5, room temperature, and 50-240 rpm agitation speed
P .A . Terry and W . Stone, Chemosphere, 47 (2002) 249-255 . [2] N . Goyal, S .C . Jain and U .C . Banerjee, Advances in Environmental Research, in press . [3] B . Volesky, Biosorption of Heavy Metals, CRC Press, Boca Raton, 1990. [4] F . Woodard, ed ., Industrial Waste Treatment Handbook, Butterworth-Heinemann, USA, 2001 .
140
N. Basci et al. /Desalination 164 (2004) 135-140
[5] D .W . Darnall, B . Greene, M . Hosea, R.A. McPher-
son, M . McPherson and M .D . Alexander, Recovery of heavy metals by immobilized algae, in : R . Thompson, ed.,Trace Metal Removal from Aqueous Solutions, Royal Society of Chemistry, London, 1986 . [6] H . Niu, X .S . Xu and B . Volesky, Biotechnol . Bioeng ., 42 (1993) 785-787 . [7] Z .R. Holan, B . Volesky and I . Prasetyo, 41 (1993) 819-825 . [8] R.P . Carvalho, K .H. Chong and B . Volesky, Biotechnol . Lett ., 16 (1994) 875-880 . [9] H . Ucun, Y .K. Bayhan, Y. Kaya, A . Cakici and O .F. Algur, Bioresearch Technol ., 85 (2002) 155-158 .
[10] N . Khalid, A . Rahman, S . Ahmad, S .N . Kiani and J . Ahmed, Plant and Soil, 197 (1998) 71-78 . [11] L .D . Benefield, J .R . Judkins and B .L. Weand,
eds ., Process Chemistry for Water and Wastewater Treatment, Englewood Cliffs, NJ, 1982, pp . 433435 . [12] J.R . Weber, ed., Physicochemical Processes for
Water Quality Control, Wiley- Interscience, USA, 1972 . [13] C .D . Nandini and P .V . Salimath, Food Chem ., 73 (2001) 197-203 . [14] P .A . Marques, H .M . Pinheiro, J.A. Teixeira and F .M . Rosa, Desalination, 124 (1999) 137-144 . [15] A . Episoto, F . Pagnanelli, A . Lodi, C . Solicio and F . Veglio, Hydrometallurgy, 60 (2001) 129-141 . [16] J .T . Matheickal and Q . Yu, Bioresource Technol ., 69 (1999) 223-229 . [17] R . Say, A . Denizli and M .Y . Arica, Bioresource Technol ., 76 (2000) 67-70 . [18] P . Kaewsarn, Chemosphere, 47 (2002) 1081-1085 .
ELSEVIER
164 (2004) 135-140 www.dscvkr enmifocaie/dcsa(
Biosorption of copper (II) from aqueous solutions by wheat shell Nurgul Basci, Erdem Kocadagistan*, Beyhan Kocadagistan Department of Environmental Engineering, Atatiirk University, Erzurum 25240, Turkey Tel. +90 (442) 231-4808 ; Fax +90 (442) 233-6961 ; email : [email protected] .tr
Received 17 June 2003 ; accepted 22 September
2003
Abstract
The adsorption capacity of wheat shell for copper (II) was studied at various pH (2-7), agitation speeds (50250 rpm) and initial metal ion concentrations (Co, from 10 to 250 mg .L - ') . Maximumbiosorption of copper onto wheat shell occurred at 240 rpm agitation speed and at pH between 5 and 6 . The biosorption values of copper (II) were increased with increasing pH from 2 to 5 and decreased with increasing copper/wheat shell (x/m) ratios from 0 .83 to 10 .84 mgCu(II) .g ' wheat shell . The biosorption efficiencies at these x/m ratios were 99% and 52%, respectively, at the end of the 120 min contact time (t) . The equilibrium isotherms and kinetics were obtained from batch adsorption experiments at 298 K . It was observed that wheat shell was a suitable biosorbent for removing Cu(II) from aqueous solutions . Keywords :
Biosorption ; Copper (II) ; Wheat shell ; Heavy metal
1 . Introduction Copper is present in large quantities in nature as an element or in the other forms . It is an Environmental Protection Agency regulated heavy metal that is often used for anti-corrosion and as a decorative coating on metal alloys [I] . Treatment of wastewaters containing heavy metal could be achieved with settling as settleable metal hydroxides, activated carbon adsorption, ion exchange, reverse osmosis, electrochemical treatment, evaporation and biological methods . *Corresponding author . 0011-9164/04/$-
See front matter ©
P11 : SOO11-9164(04)00172-9
2004
But these methods are not economical and do not exhibit high treatment efficiency, especially at metal concentrations in the range of 0 .0100 .1 g .L - ' [2] . More economical and effective methods are currently being developed for removal of heavy metals from wastewaters [3,4] . There are many studies for removing copper from aqueous solutions by using biosorption . In these studies researchers used aquatic plants, microorganisms and some other similar living or nonliving biosorbents such as dried plant leaves, marine or freshwater algae, pine, rice husk, pine bark, and canola meal [5-10] .
Elsevier B .V . All rights reserved
1 36
N. Basci et al. /Desalination 164 (2004) 135-140
It has been reported that agitation speed, pH, temperature and initial metal and biosorbent concentrations have an important effect on the efficiency of the biosorption process [11] . The increasing biosorption efficiency with increasing total surface area of the biosorbent has also been reported in the literature [12] . Wheat is one of the cereals used for the preparation of bread and other bakery products, and wheat shell is the by-product of wheat bread production industries . Wheat shell is a rich source of dietary fibre and contains carbohydrates, proteins, starch, sugar and celluloses [13] . The aim of this work was to study the effect of several parameters as initial pH, agitation speed and metal concentration on the biosorption efficiency of Cu(II) ions from aqueous solutions . The biosorbent used was wheat shell, which is a very cheap and readily available materiel in most countries .
2 . Materials and methods 2.1 . Preparation of the biosorbent Wheat shell was used as a biosorbent for the biosorption of copper ions . Before the start of all experiments, the wheat shell was properly cleaned with deionised water, dried at a temperature of 353 K and finally blended in a mortar and sieved through a 0 .005 m sieve .
multiparameter device during all of the experiments . Concentrations of Cu(II) ranging from 10 to 250 mg.L - ' and dried wheat shell (10 to 250 mg .L -1 ) were added to Erlenmeyer flasks . These 0 .25 L flasks were stirred at a constant temperature (298 K) in a shaker (Rosi 1000) for 2 h . Samples were taken at the end of the process and immediately filtered with a vacuum filtration apparatus for removing the suspended wheat shell and analyzed for metal ions content . The Cu(II) concentration was determined by flame atomic absorption spectrophotometry using a Shimadzu AA-670 spectrophotometer. Zeta potentials were measured with a Zeta-Meter (Zeta-Meter 3 .0 + 542, USA) .
3. Results and discussion 3 .1 . Effect ofpH According to the great importance of the pH on heavy metal biosorption [ 1,3,14,18], tests were undertaken with different initial pH values of the Cu(II) solution using a constant concentration of wheat shell (m =12 g .L - ' ) . At the initial pH below 6, there were not any perceptible pH changes while at pH of solutions adjusted above 6 at the 100 90 80 6 w
2.2. Preparation of stock solution An aqueous stock solution of CuSO 4.5H20 in a concentration of 1000 mg .L - ' of Cu(II) was used in all experimental runs .
70 60
0 'g 50 0 0 40 14 30 20 0
2.3 . Experimental run HCl and NaOH solutions (0 .1 N) were used for adjusting the initial pH of solutions after addition of the biosorbent . The pH measurements were achieved with a WTW Multi-340i model
1
2
3
4
5
6
7
pH
Fig . 1 . Effect of initial solution pH on Cu(II) biosorption efficiency by wheat shell . (Initial Cu(II) concentrations = 50 mg .L -1 ; temperature = 298 K, wheat shell concentration = 12 g .L- ', agitation speed = 250 rpm, contact time = 2 h .)
137
N. Basci et al. /Desalination 164 (2004) 135-140
beginning of the experiments, some slight decreases were observed along the process . The effect of pH on copper biosorption is given in Fig. I where it is seen that biosorption efficiencies increased from 33% at pH 2 to 95% at pH 5 . Further experimental runs were performed at a pH range between 5 and 6 because the highest biosorption efficiencies were achieved in these pH intervals . Similar results were reported using Sphaerotilus natans as the biosorbent at pH 5 .5-6 [15], Australian marine algae at pH 5 .5 [16], the fungus Pharerochaete chryssporium at pH 6 [17] and waste brewery biomass at pH 5-6 [14] .
15 10
5
-
5-
-15
2
3
4
5
6
7
8
9
pH
Fig . 2 . Effect of pH on zeta potential value . (Initial Cu(II) concentrations = 50 mg .L -1 , temperature = 298 K, wheat shell concentration = 12 g .L- ', agitation speed = 250 rpm, contact time = 2 h .)
3.2. Zeta potentials Zeta potential values of wheat shell biosorbent were determined at various pHs by using a Zeta-Meter (Fig . 2) . Wheat shell zeta potential values were measured as positive at pH 3 .65 and below . The isoelectric pH point of wheat shell was observed from the curve at pH 3 .65 (zP = 0 mV) . Above this point, values were negative and at pH 5 maximum the zeta potential value of wheat shell was obtained (- 10 .6 mV) . Under the isoelectric point, the overall surface charge of wheat shell became positive and biosorption decreased. As the pH increased up to 5 .5, the overall surface charge of wheat shell was negative and biosorption efficiencies increased . Thus, at pH values between 3 .5 and 5 .5, the interaction of the copper with wheat shell was primarily electrostatic in nature . As the pH rose above 5 .5, biosorption efficiencies were decreased slightly and above pH 7 biosorption efficiencies were not noticeable because copper was being precipitated as hydrous oxide above this pH value . As seen from Figs . 1 and 2, there is a relationship between initial solution pH, zeta potentials and biosorption efficiencies . The maximum biosorption efficiency (95%) and zeta potential values (-10 .6 mV) were obtained at the same pH of 5 .
3.3 . Effect of initial Cu(II) concentration The biosorption of Cu(II) by wheat shell was studied at several different initial copper concentrations ranging from 10 to 250 mg .L - '. As seen from Table 1, biosorption efficiencies decreased with the increasing of initial metal concentrations due to the increase of x/m ratios even though there was an increase of Cu(II) ions adsorbed onto the wheat shell . For determining the adsorption constants and adsorption capacity of wheat shell for removal of Cu(II), Langmuir and Freundlich isothelnls were tested at various initial ion concentrations ranging from 10 to 250 mg .L -1 , while the wheat shell dry weight in each sample was constant at 12 g .L -1 . In this study, Langmuir was the best-fit isotherm for biosorption of Cu(II) on wheat shell (Fig. 3) . The Langmuir isotherm was given as q = x/m = (b. gmax .Ce) l ( I + b . Ce)
(1)
and the linear form of this equation can be given as 1/(x/m) = ( 1/b.gmax)(1/Ce) + (1/gmax)
(2)
where q is the adsorption capacity at the
N. Basci et al . /Desalination 164 (2004) 1 3 5-140
138
Table 1 Effect of initial Cu(II) concentration on biosorption
C, mg.L - '
C, mg .L - ' 0 .1 0 .62 1 .21 1 .98 7 .52 18 .21 46 .42 92 .81 119 .92
10 20 30 40 50 100 150 200 250
Copper adsorbed on wheat shell, mg .L - '
x/m, mg Cu(II) .g - '
wheat shell
Biosorption efficiency,
9 .90 19 .38 28 .79 38 .02 42 .48 81 .79 103 .58 107 .19 130 .08
0 .83 1 .62 2 .40 3 .17 3 .54 6 .82 8 .63 8 .93 10 .84
99 97 96 95 85 82 69 54 53
m =12 g .L - ', T = 298 K, rpm = 250, pH = 5, t = 2 h .
k
40 35 30 25 20 15 105 0 0
Table 2 Adsorption capacities for some adsorbents reported in the literature [18] y = 0.32x+ 7.62 RZ = 0.98
Adsorbent
qmax, mmol .g - '
Aspergillus oryzae
0 .07 0 .10 0 .13 0 .25 0 .30 0 .80 0 .96 1 .11 1 .20
Lignite Wheat shell (this study) 10
20
30 40
50
60
70
80
90 100
1/Ce Fig . 3 . Plot of linear form of Langmiur isotherm for the biosorption of Cu(II) onto wheat shell . (m =12 g .L -1 , T= 298 K, rpm = 250, pH = 5, t = 2 h .)
equilibrium solute concentration C e (mg of solute adsorbed per g of adsorbent or mol .g - ') ; Ce is the concentration of adsorbate in solution (mg.L - ' or mmol .L - ') ; gmax is the maximum adsorption capacity corresponding to complete monolayer coverage (mg of solute adsorbed per g of adsorbent or mmol .g - ') and b is a Langmuir constant related to the energy of adsorption (mg .L - ' or mmo1 .L- ') . The adsorption constants of the Langmuir isotherm gmax and b were estimated from the intercept and slope of 1/(x/m) vs, (1/C e), respectively, according to Eq . (2) and obtained as
R . arhizus Pseudomonas aeruginosa Padina sp . S. fluitans E. radiata L. japonica
8 .34 mg.g - ' (0 .13 mmol .g"') and 24 L .mmol - ', respectively . The adsorption capacity (gmax) of wheat shell and some other biosorbents reported in the literature are given in Table 2 . The correlation coefficient of the Langmuir isotherm (r) obtained from 1/(x/m) vs . 1/Ce plot was 0 .98 . 3.4 . Effect of biosorbent concentration on the equilibrium time The effect of agitation time of Cu(II) on wheat shell was studied at various biosorbent concen-
N. Basci et al. /Desalination 164 (2004) 1 3 5-140
139
range conditions ; the agitation time was continued at 120 min to achieve the equilibrium time . Biosorption efficiencies were increased by increasing agitation speed (Fig . 5) . Maximum efficiencies (horizontal slope) were observed at 240 rpm .
0
so
100
150
t (min) Fig . 4 . Effect of contact time on biosorption . (Initial Cu(II) concentrations = 50 mg .L - ', temperature = 298 K, agitation speed = 250 rpm, contact time = 2 h .)
87 0
°~. 86 U 85 U
w 84 w 0 83 0
82 8180 0
50
100
150
200
Agitation speed (rpm) Fig . 5 . Effect of agitation speed on biosorption . (Initial Cu(II) concentrations = 50 mg .L - ', temperature = 298 K, agitation speed = 250 rpm, contact time = 2 h .)
trations . During all of the experiments, equilibrium was reached within 2 h after a first fast initial step which lasted for 5-30 min and a second slower step that followed (Fig . 4) . There was a slight increase in biosorption efficiencies later than equilibrium time as shown in Fig . 4 .
4 . Conclusions The biosorption of Cu(II) onto wheat shell was investigated . Wheat shell that was sieved at 0.005 m at various concentrations was used for this purpose, and the following conclusions are drawn based on the experimental results . • pH has a significant role on biosorption efficiencies . The maximum efficiency was observed at 99% at pH 5 for a 12 g .L -1 wheat shell concentration in this study . • Above pH 7, copper was precipitated as hydrous oxides . • The biosorption performance of wheat shell was also affected by initial metal concentration, contact time and agitation speed of the process . Biosorption efficiencies were increased with increasing contact time and agitation speed and decreased with increasing Cu(II) concentration . Better results were obtained at a contact time of 120 min and 250 rpm agitation speed . • To optimize the performance of biosorption of Cu(II) using the wheat shell process, a pH 5 and below 1 mg .g - ' x/m concentrations should be used . References [1]
3.5 . Effect of agitation speed Experimental runs were carried out in a shaker for various biosorbent concentrations at 50 mg.L- ' initial Cu(II) ion concentrations, pH 5, room temperature, and 50-240 rpm agitation speed
P .A . Terry and W . Stone, Chemosphere, 47 (2002) 249-255 . [2] N . Goyal, S .C . Jain and U .C . Banerjee, Advances in Environmental Research, in press . [3] B . Volesky, Biosorption of Heavy Metals, CRC Press, Boca Raton, 1990. [4] F . Woodard, ed ., Industrial Waste Treatment Handbook, Butterworth-Heinemann, USA, 2001 .
140
N. Basci et al. /Desalination 164 (2004) 135-140
[5] D .W . Darnall, B . Greene, M . Hosea, R.A. McPher-
son, M . McPherson and M .D . Alexander, Recovery of heavy metals by immobilized algae, in : R . Thompson, ed.,Trace Metal Removal from Aqueous Solutions, Royal Society of Chemistry, London, 1986 . [6] H . Niu, X .S . Xu and B . Volesky, Biotechnol . Bioeng ., 42 (1993) 785-787 . [7] Z .R. Holan, B . Volesky and I . Prasetyo, 41 (1993) 819-825 . [8] R.P . Carvalho, K .H. Chong and B . Volesky, Biotechnol . Lett ., 16 (1994) 875-880 . [9] H . Ucun, Y .K. Bayhan, Y. Kaya, A . Cakici and O .F. Algur, Bioresearch Technol ., 85 (2002) 155-158 .
[10] N . Khalid, A . Rahman, S . Ahmad, S .N . Kiani and J . Ahmed, Plant and Soil, 197 (1998) 71-78 . [11] L .D . Benefield, J .R . Judkins and B .L. Weand,
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