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Biosorption of heavy metals and cyanide complexes on biomass
159 Studies in Surface Science and Catalysis, volume 159 Hyun-Ku Rhee, In-Sik Nam and Jong Moon Park (Editors) © 2006 Elsevier B.V. All rights reserved
141 141
Biosorption of heavy metals and cyanide complexes on biomass Seung Jai Kirn8'b, Jae Hoon Chung8, Tae Young Kim", and Sung Yong Cho" "Department of Environmental Engineering, bEnvironmental Research Institute, Chonnam National University, Gwangju, 500-757, Republic of Korea 1. INTRODUCTION Biosorption is a process that utilizes biological materials as adsorbents [Volesky, 1994], and this method has been studied by several researchers as an alternative technique to conventional methods for heavy metal removal from wastewater. In this work, the waste brewery yeast and Aspergillus niger were used for the adsorption of lead, copper and cadmium, and their cyanide complexes. Biosorption equilibrium was studied in a batch reactor with respect to pH, initial concentration of heavy metal and metal-cyanide complex. Biosorption equilibrium over the temperature range of 288K - 308K was investigated and the biosorption heat was evaluated. 2. EXPERIMENTAL Aspergillus niger was obtained from KCTC (Korean Collection for Type Cultures) and grown for five days at 23 °C in conical flasks which were kept in a rotary shaker agitated at 125rpm. The harvested biomass was pretreated and washed with generous amounts of deionized water. Waste yeast biomass obtained from a beer brewery was washed several times with deionized water and then dried in a vacuum drying oven at 80 °C for 48 h. The dried biomass was ground, sieved and stored in a sealed bottle with a silica gel to prevent resorption of moisture. Biosorption equilibria were studied for various pH and temperature. Heavy metal solutions were prepared by dissolving metal nitrates in deionized water. To study the effect of solution pH on heavy metal adsorption, the pH of the solution was adjusted between 2.5 and 6.0 with IN HNO3 or NaOH solution. The experiments were not conducted above pH 6.0 (5.0 for Pb) to avoid possible hydroxide precipitation. The effect of temperature on the adsorption equilibrium was studied at 288K, 298K, 303K and 308K. For heavy metal-cyanide complex experiments the molar concentration ratio of the cyanide to heavy metal in the solution was 4, and the initial pH of the solution was adjusted to 12. Samples were withdrawn at predetermined time intervals, filtered, and the heavy metal ion concentration was measured using ICP (Shimadzu ICPS7500). 3. RESULTS AND DISCUSSION
142 142
3.1. Adsorption equilibrium Langmuir and Freundlich equations were applied to represent equilibrium adsorption data of heavy metals and metal-cyanide complexes. To find parameters for each adsorption isotherm equation, a linear least-squares method and pattern search algorithm were used. Langmuir and Freundlich isotherm parameters are obtained and listed in Table 1. The equilibrium isotherms were favorable type and the Langmuir equation represents our experimental data very well. The biosorption capacity of heavy metal as metal-cyanide anion complexes for two biosorbents was decreased significantly compared to that of metal ion only. The biosorption capacity of Aspergillus niger for each heavy metal was much greater than that of brewery yeast as can be seen in Table 1. Table 1. Isotherm parameters and correlation coefficients. Langmuir
Biosorbent
Freundlich R2
0.054
0.99
10.42
2.759
0.92
44.93
0.060
0.98
5.622
2.522
0.89
12.03
0.029
0.98
1.383
2.714
0.90
Pb-CN (pH12)
21.76
0.012
0.98
3.030
1.339
0.84
Cu-CN (pH12)
14.36
0.021
0.98
0.776
2.219
0.79
Cd-CN (pH12)
9.442
0.022
0.99
0.613
1.650
0.82
Pb (pH5)
303.5
0.070
0.99
57.27
3.222
0.91
Cu (pH5)
134.2
0.107
0.95
37.03
4.250
0.80
Pb (pH5)
Brewery yeast
Aspergillus niger
Cu(pH5) Cd (pH5)
87.44
Cd (pH5)
81.40
0.064
0.98
24.97
3.997
0.88
Pb-CN (pH 12)
91.58
0.009
0.96
3.464
1.867
0.91
Cu-CN (pH12)
33.43
0.040
0.97
1.512
1.433
0.85
Cd-CN (pH12)
26.75
0.020
0.98
0.542
1.694
0.81
Langmuir eq. : q(mg f g) = fm
g
Biosorption capacity (mg metal /g biomass)
l + bCe
Freundlich eq.: q{mg I g) = KCl"
(1)
(2)
140
120 -g 120
4
S 100
I
§>
80 80 60 — -• — • — * — —O— D A
40 20 0
2
3
4
5
Pb on on Aspergillus Pb Aspergillus niger Cu on on Aspergillus niger Cu Cd on on Aspergillus niger Cd Pb on on brewery brewery yeast yeast Pb Cu on on brewery brewery yeast yeast Cu Cd brewery yeast yeast Cd on on brewery
6
pH
Figure 1. Effect of initial pH on the biosorption capacity (Co: 200mg/L, biomass cone: lg/L, 25 °C)
143 143
3.2. Effects of pH The effect of pH on metal biosorption was studied at 25 °C by varying the solution pH from 2.5 to 6.0 (for Pb 5.0). The plot of metal adsorption capacity (mg/g) versus pH was shown in Figure 1. From the figure it is observed that the adsorption on biomass was highly pH dependent. The biosorption capacity increased with increasing pH and the effect of pH was in the order of Pb > Cu > Cd. The effect of pH on the biosorption capacity can be interpreted by the competition of the hydronium ions and metal ions for binding sites. At low pH values, the ligands on the biomass are closely associated with the hydronium ions, but when the pH is increased, the hydronium ions are gradually dissociated and the positively charged metal ions are associated with the free binding sites on the biomass.
100
50
80
40
Biosorption capacity(mg/g)
Biosorption capacity(mg/g)
3.3. Effects of initial metal concentration The equilibrium time required for adsorption of metals on biomass was studied for various initial metal concentrations and the results were shown in Figure 2. The adsorption increases rapidly with time in the initial period of adsorption and approaches an equilibrium at about 120min for all the concentrations studied (10-100 mg/L). The slow but gradual increase of metal biosorption after 120min indicates that the adsorption occurs through a continuous formation of adsorption layer in the final period of adsorption.
60
40
20
30
20
10
0
0 0
50
100
150
200
250
300
0
50
Time (min) • • A — -O— D— A—
100
150
200
250
300
Time (mm Time (min)
._
10mg/Lwit Aspergillus niger niger 10mg/L with Aspergillus 50mg/L SOmg/L with wil Aspergillus Aspsrgillus niger 100mg/L with Aspergillus 100mg/L wil Aspergillus niger 10mg/Lwil 10mg/L with Brewery yeast SOmg/L with wil Brewery yeast 50mg/L 100mg/Lwit 100mg/L with Brewery yeast B»w.ryy..sl
(a) (a)
—o—
D— — -A —
10mg/L with with Aspergillus Aspergillus niger niger 10mg/L 50mg/L SOmg/L with with Aspergillus niger 100mg/L 100mg/L with vtth Aspergillus Aspergillus niger 10mg/L with with Brewery Brewery yeast 10mg/L SOmg/L with with Brewery Brewery yeast 50mg/L 100mg/L with vith Brewery Brewery yeast 100mg/L
(b) (b)
Figure 2. Biosorption capacities for different initial concentrations (pH 5.0, biomass cone: lg/L, 25°C),(a)Pb,and(b)Pb-CN. 3.4. Heat of adsorption The heat of adsorption can be evaluated from adsorption equilibrium data and Eq. (3). If b values are known for different temperatures, the biosorption heats can be calculated from the plot of In b versus 1/T [Ozer, 2003]. b = bn exp -
AH RT
(3)
Where bo is a constant, zlH (kcal-mol") is the heat of adsorption, R is a universal gas
144 144
constant (1.987 cal-mor'-K"1) and T is the absolute temperature (K). Heats of adsorption obtained are listed in Table 2. The values of biosorption heats for heavy metals show that the reaction is endothermic. The heat of physical adsorption is less than lkcal mol"1, and that of chemical adsorption is 20-50 kcal-mol"1 [Smith, 1981]. Since the heat of adsorption for heavy metals in this study are 3.30-5.35 kcal-mc kcal-mol"1, we believe that both physical and chemical adsorptions are involved in the biosorption. Table 2. Adsorption heat of heavy metal on the biosorbent. Biosorbent Heavy metal Brewery yeast
Aspergillus niger
Pb Cu Cd Pb Cu Cd
Biosorption heat (kcal-mol"1) 4.06 3.30 5.35 4.44 3.68 4.61
4. CONCLUSION In this study, biosorption of heavy metals and their cyanide complexes on Aspergillus niger and brewery yeast was investigated and the following conclusions are obtained. - The biosorption capacity of heavy metals increased with initial metal concentration and pH. - The biosorption capacity of Aspergillus niger was much greater than that of brewery yeast, and the biosorption capacity of metal-cyanide anion complexes was significantly lower than that of metal ion only. - The equilibrium isotherms were favorable type and the Langmuir equation represents our experimental data very well. - The biosorption reactions of heavy metals and metal-cyanide complexes were endothermic, and the heats of adsorption were in the range of 3.3-5.3 kcal-mol"1, which imply that both physical and chemical adsorptions are involved. ACKNOWLEDGEMENTS This study was financially supported by research fund of Chonnam National University in 2003.
REFERENCES [1] A. Ozer and D. Ozer, Comparative study of the biosorption Pb(II), Ni(II) and Cr(VI) ions onto S. cerevisiae: determination of biosorption heats, Journal of Hazardous Materials B100,219-229, (2003). [2] B. Volesky, Advances in biosorption of metals: Selection of biomass type. FEMS Microbiology reviews, 14, 291-301(1994). [3] Smith, J.M., Chemical Engineering Kinetic, 3rd Edition, McGraw Hill, New York (1981).
141 141
Biosorption of heavy metals and cyanide complexes on biomass Seung Jai Kirn8'b, Jae Hoon Chung8, Tae Young Kim", and Sung Yong Cho" "Department of Environmental Engineering, bEnvironmental Research Institute, Chonnam National University, Gwangju, 500-757, Republic of Korea 1. INTRODUCTION Biosorption is a process that utilizes biological materials as adsorbents [Volesky, 1994], and this method has been studied by several researchers as an alternative technique to conventional methods for heavy metal removal from wastewater. In this work, the waste brewery yeast and Aspergillus niger were used for the adsorption of lead, copper and cadmium, and their cyanide complexes. Biosorption equilibrium was studied in a batch reactor with respect to pH, initial concentration of heavy metal and metal-cyanide complex. Biosorption equilibrium over the temperature range of 288K - 308K was investigated and the biosorption heat was evaluated. 2. EXPERIMENTAL Aspergillus niger was obtained from KCTC (Korean Collection for Type Cultures) and grown for five days at 23 °C in conical flasks which were kept in a rotary shaker agitated at 125rpm. The harvested biomass was pretreated and washed with generous amounts of deionized water. Waste yeast biomass obtained from a beer brewery was washed several times with deionized water and then dried in a vacuum drying oven at 80 °C for 48 h. The dried biomass was ground, sieved and stored in a sealed bottle with a silica gel to prevent resorption of moisture. Biosorption equilibria were studied for various pH and temperature. Heavy metal solutions were prepared by dissolving metal nitrates in deionized water. To study the effect of solution pH on heavy metal adsorption, the pH of the solution was adjusted between 2.5 and 6.0 with IN HNO3 or NaOH solution. The experiments were not conducted above pH 6.0 (5.0 for Pb) to avoid possible hydroxide precipitation. The effect of temperature on the adsorption equilibrium was studied at 288K, 298K, 303K and 308K. For heavy metal-cyanide complex experiments the molar concentration ratio of the cyanide to heavy metal in the solution was 4, and the initial pH of the solution was adjusted to 12. Samples were withdrawn at predetermined time intervals, filtered, and the heavy metal ion concentration was measured using ICP (Shimadzu ICPS7500). 3. RESULTS AND DISCUSSION
142 142
3.1. Adsorption equilibrium Langmuir and Freundlich equations were applied to represent equilibrium adsorption data of heavy metals and metal-cyanide complexes. To find parameters for each adsorption isotherm equation, a linear least-squares method and pattern search algorithm were used. Langmuir and Freundlich isotherm parameters are obtained and listed in Table 1. The equilibrium isotherms were favorable type and the Langmuir equation represents our experimental data very well. The biosorption capacity of heavy metal as metal-cyanide anion complexes for two biosorbents was decreased significantly compared to that of metal ion only. The biosorption capacity of Aspergillus niger for each heavy metal was much greater than that of brewery yeast as can be seen in Table 1. Table 1. Isotherm parameters and correlation coefficients. Langmuir
Biosorbent
Freundlich R2
0.054
0.99
10.42
2.759
0.92
44.93
0.060
0.98
5.622
2.522
0.89
12.03
0.029
0.98
1.383
2.714
0.90
Pb-CN (pH12)
21.76
0.012
0.98
3.030
1.339
0.84
Cu-CN (pH12)
14.36
0.021
0.98
0.776
2.219
0.79
Cd-CN (pH12)
9.442
0.022
0.99
0.613
1.650
0.82
Pb (pH5)
303.5
0.070
0.99
57.27
3.222
0.91
Cu (pH5)
134.2
0.107
0.95
37.03
4.250
0.80
Pb (pH5)
Brewery yeast
Aspergillus niger
Cu(pH5) Cd (pH5)
87.44
Cd (pH5)
81.40
0.064
0.98
24.97
3.997
0.88
Pb-CN (pH 12)
91.58
0.009
0.96
3.464
1.867
0.91
Cu-CN (pH12)
33.43
0.040
0.97
1.512
1.433
0.85
Cd-CN (pH12)
26.75
0.020
0.98
0.542
1.694
0.81
Langmuir eq. : q(mg f g) = fm
g
Biosorption capacity (mg metal /g biomass)
l + bCe
Freundlich eq.: q{mg I g) = KCl"
(1)
(2)
140
120 -g 120
4
S 100
I
§>
80 80 60 — -• — • — * — —O— D A
40 20 0
2
3
4
5
Pb on on Aspergillus Pb Aspergillus niger Cu on on Aspergillus niger Cu Cd on on Aspergillus niger Cd Pb on on brewery brewery yeast yeast Pb Cu on on brewery brewery yeast yeast Cu Cd brewery yeast yeast Cd on on brewery
6
pH
Figure 1. Effect of initial pH on the biosorption capacity (Co: 200mg/L, biomass cone: lg/L, 25 °C)
143 143
3.2. Effects of pH The effect of pH on metal biosorption was studied at 25 °C by varying the solution pH from 2.5 to 6.0 (for Pb 5.0). The plot of metal adsorption capacity (mg/g) versus pH was shown in Figure 1. From the figure it is observed that the adsorption on biomass was highly pH dependent. The biosorption capacity increased with increasing pH and the effect of pH was in the order of Pb > Cu > Cd. The effect of pH on the biosorption capacity can be interpreted by the competition of the hydronium ions and metal ions for binding sites. At low pH values, the ligands on the biomass are closely associated with the hydronium ions, but when the pH is increased, the hydronium ions are gradually dissociated and the positively charged metal ions are associated with the free binding sites on the biomass.
100
50
80
40
Biosorption capacity(mg/g)
Biosorption capacity(mg/g)
3.3. Effects of initial metal concentration The equilibrium time required for adsorption of metals on biomass was studied for various initial metal concentrations and the results were shown in Figure 2. The adsorption increases rapidly with time in the initial period of adsorption and approaches an equilibrium at about 120min for all the concentrations studied (10-100 mg/L). The slow but gradual increase of metal biosorption after 120min indicates that the adsorption occurs through a continuous formation of adsorption layer in the final period of adsorption.
60
40
20
30
20
10
0
0 0
50
100
150
200
250
300
0
50
Time (min) • • A — -O— D— A—
100
150
200
250
300
Time (mm Time (min)
._
10mg/Lwit Aspergillus niger niger 10mg/L with Aspergillus 50mg/L SOmg/L with wil Aspergillus Aspsrgillus niger 100mg/L with Aspergillus 100mg/L wil Aspergillus niger 10mg/Lwil 10mg/L with Brewery yeast SOmg/L with wil Brewery yeast 50mg/L 100mg/Lwit 100mg/L with Brewery yeast B»w.ryy..sl
(a) (a)
—o—
D— — -A —
10mg/L with with Aspergillus Aspergillus niger niger 10mg/L 50mg/L SOmg/L with with Aspergillus niger 100mg/L 100mg/L with vtth Aspergillus Aspergillus niger 10mg/L with with Brewery Brewery yeast 10mg/L SOmg/L with with Brewery Brewery yeast 50mg/L 100mg/L with vith Brewery Brewery yeast 100mg/L
(b) (b)
Figure 2. Biosorption capacities for different initial concentrations (pH 5.0, biomass cone: lg/L, 25°C),(a)Pb,and(b)Pb-CN. 3.4. Heat of adsorption The heat of adsorption can be evaluated from adsorption equilibrium data and Eq. (3). If b values are known for different temperatures, the biosorption heats can be calculated from the plot of In b versus 1/T [Ozer, 2003]. b = bn exp -
AH RT
(3)
Where bo is a constant, zlH (kcal-mol") is the heat of adsorption, R is a universal gas
144 144
constant (1.987 cal-mor'-K"1) and T is the absolute temperature (K). Heats of adsorption obtained are listed in Table 2. The values of biosorption heats for heavy metals show that the reaction is endothermic. The heat of physical adsorption is less than lkcal mol"1, and that of chemical adsorption is 20-50 kcal-mol"1 [Smith, 1981]. Since the heat of adsorption for heavy metals in this study are 3.30-5.35 kcal-mc kcal-mol"1, we believe that both physical and chemical adsorptions are involved in the biosorption. Table 2. Adsorption heat of heavy metal on the biosorbent. Biosorbent Heavy metal Brewery yeast
Aspergillus niger
Pb Cu Cd Pb Cu Cd
Biosorption heat (kcal-mol"1) 4.06 3.30 5.35 4.44 3.68 4.61
4. CONCLUSION In this study, biosorption of heavy metals and their cyanide complexes on Aspergillus niger and brewery yeast was investigated and the following conclusions are obtained. - The biosorption capacity of heavy metals increased with initial metal concentration and pH. - The biosorption capacity of Aspergillus niger was much greater than that of brewery yeast, and the biosorption capacity of metal-cyanide anion complexes was significantly lower than that of metal ion only. - The equilibrium isotherms were favorable type and the Langmuir equation represents our experimental data very well. - The biosorption reactions of heavy metals and metal-cyanide complexes were endothermic, and the heats of adsorption were in the range of 3.3-5.3 kcal-mol"1, which imply that both physical and chemical adsorptions are involved. ACKNOWLEDGEMENTS This study was financially supported by research fund of Chonnam National University in 2003.
REFERENCES [1] A. Ozer and D. Ozer, Comparative study of the biosorption Pb(II), Ni(II) and Cr(VI) ions onto S. cerevisiae: determination of biosorption heats, Journal of Hazardous Materials B100,219-229, (2003). [2] B. Volesky, Advances in biosorption of metals: Selection of biomass type. FEMS Microbiology reviews, 14, 291-301(1994). [3] Smith, J.M., Chemical Engineering Kinetic, 3rd Edition, McGraw Hill, New York (1981).