Utilization of Sago Waste as an Adsorbent for the Removal ... · The adsorption kinetics of the Pb...

C.Karthika et. al. / International Journal of Engineering Science and Technology Vol. 2(6), 2010, 1867-1879

Utilization of Sago Waste as an Adsorbent

for the Removal of Pb(II) from Aqueous

Solution: Kinetic and Isotherm Studies C.KARTHIKAa , N.VENNILAMANI b, S.PATTABHI c , M. SEKAR a*

a Department of Chemistry , Sri Ramakrishna Mission Vidyalaya College of Arts And Science,

Coimbatore-641020, India.

b Department of Chemistry, P.S.G.R. Krishnammal College for Women, Coinbatore-641004, India.

c Department of Environmental Science, P.S.G. College of Arts And Science, Coimbatore-641014 , India.

Abstract The effectiveness of a carbononaceous sorbent prepared from sago waste for the removal of Pb (II) ions from aqueous solution and industrial effluent was studied as a function of agitation time, adsorbent dosage, particle size and pH. Through Scanning Electron Microscopy (SEM), X-ray Photo electron Spectroscopy (XPS) and Fourier Transform Infra-red (FTIR) spectroscopy analysis, the surface properties of the adsorbent were studied. The experimental isotherm data were analyzed using Langmuir, Freundlich, Redlich Peterson, Temkin and Dubinin-Radushkevich equations. The maximum adsorption capacity (Q0) was found to be 14.35 mg g-1 at an initial pH of 3.5. The Lagergren rate constant for adsorption was found to be constant for various initial concentrations of Pb (II) which implies that adsorption follows first order kinetics. Since the raw material used in the preparation of activated carbon is available abundantly, the resulting carbon is expected to be economically viable. Keywords: Sago waste carbon; Adsorption isotherms; Removal of Pb (II); Wastewater treatment; Desorption

1. Introduction

Heavy metals are known to be harmful to humans. They are important contaminants in the liquid wastes of a number of industries such as paint, dyes, glass operations, lead batteries, electroplating, mining and smelters1.The removal of lead from wastewaters has received considerable attention in recent years2, 3. Lead accumulates mainly in bones, brain, kidney and muscles and may cause many serious disorders like anemia, kidney disease, nervous disorders, sickness and even death4. Conventional methods for removing dissolved heavy metal ions include chemical precipitation, chemical oxidation or reduction, filtration, ion exchange, electrochemical treatment, application of membrane technology and evaporation recovery5, 6. However, these technology processes have considerable disadvantages including incomplete metal removal, requirements for expensive equipment and monitoring system, high reagent or energy requirements or generation of toxic sludge or other waste products that require disposal7, 8.

Adsorption is an efficient process which has a wide application in the removal of metal ions from wastewater. The most generally used sorbent is activated carbon. However, in view of the high cost and associated problems of regeneration, there is a constant search for alternate low-cost adsorbents. These low-cost sorbents include industrial or agricultural waste products such as lignin9, straw and nut shells10, sawdust and bark11. The present study deals with the use of activated carbon prepared from sago waste as an adsorbent for the removal of Pb (II) from aqueous solution.

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2. Materials and methods

2.1. Preparation of the adsorbent

The roots of Cassava (Manihot esculenta crantz) are used for the manufacture of sago. The material sago waste was collected from a sago industry at Salem district, Tamilnadu, India. It was dried in sunlight for three days and the impurities present were removed. The dried sago waste was allowed to chemical activation, by the addition of 50% sulfuric acid and ammonium persulphate (0.5%) with constant stirring (w/w). The charred material was kept in hot air oven at 25±5o C for 12 hours. This was washed with double distilled water (5 times). This material was soaked in 5% sodium bicarbonate solution and allowed to stand overnight to remove the residual acid from pores of the carbon. The material was washed with the distilled water, until the pH of the adsorbent reached 5±0.5. Then it was dried in a hot air oven at 105±5o C. The dried material was ground and sieved to get the particle size of 125-250 µm, which was used in this study12.

2.2. Preparation of the adsorbate

A stock solution of 1000 mg L-1 of Pb (II) was prepared by dissolving 1.599g of anhydrous lead nitrate in double distilled water acidified with 5 ml of concentrated nitric acid to prevent hydrolysis and made up to 1000 mL (1 mL = 1mg).

2.3. Batch mode Adsorption Studies

Batch mode experiments were carried out by taking 50 mL of Pb (II) solution of desired concentration and a known amount of adsorbent in 100 mL conical flasks. The flasks were agitated at 120 rpm using a mechanical shaker at room temperature (27±2oC). The adsorbent and adsorbate solution were separated by centrifugation at 3000 rpm for 10 minutes. The factors influencing the rate and extent of Pb (II) uptake by the adsorbent such as agitation time, particle size, adsorbent dosage, pH and desorption were studied.

The effect of agitation time on the removal of Pb (II) from radiator industry wastewater was studied by adjusting the pH to 3.5±0.3 and using 100 mg of the adsorbent of particle size 125-250 µm and agitating with 50 mL of wastewater sample. The effect of adsorbent dosage on the removal of Pb (II) was carried out by taking 50 mL of wastewater (pH 3.5±0.2) and adding different amounts of carbon ranging from 50 to 400 mg and agitated for 180 minutes. After agitation, the samples were centrifuged and the supernatant was analyzed. By varying the pH of the wastewater from 2 to 9 and agitating it with 100 mg of the adsorbent of particle size 125-250 µm for 180 minutes, the effect of pH on the removal of Pb (II) from the wastewater was analyzed.

2.4. Desorption Studies

After adsorption experiments with 20 mg L-1 solution of Pb (II) and 100 mg of carbon, the Pb (II) laden carbon was separated out by filtration and the filtrate was discarded. The carbon was given a gentle wash with double distilled water to remove the unadsorbed metal ions. Desorption studies were carried out using several such carbon samples. They were agitated with 50 ml of HCl of various strengths (0.025 to 0.3 N).

3. Results and Discussion

3.1. Adsorbent characterization

Characteristics of carbon prepared from sago waste are presented in Table 1. The adsorbent exhibited considerable hardness, granular nature and low moisture adsorption capacity.

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Table 1. Characteristics of sago waste carbon Parameter Value pH of 1% solution 7.1 pH zpc 5.7 Moisture ( %) 4.33 Cation Exchange capacity (eq g-1) 0.75 Carbon (%) 65.0 Hydrogen (%) 2.0 Nitrogen (%) 3.0 Oxygen (%) 30.0 Yield (%) 78.0 Ash (%) 12.0 pparent Density (gm L-1) 0.75 Decolorizing power (mg g-1) 55.5 Matter Soluble in H2O (%) 5.5 Matter Soluble in 1M HCl (%) 8.0 Porosity (%) 80.0 Surface Area (m2 g-1) 625.00 Surface acid groups (meq g-1)

Carboxyl 1.20 Lactonic 1.80 Phenolic 0.90 Carbonyl 1.60

Total basic groups (meq g-1) 1.10 Pore Volume (mL g-1) 0.67

The waste water from radiator manufacturing industry, Coimbatore, India was collected and some of its characteristics are presented in Table 2.

Table 2. Characteristics of radiator manufacturing industry wastewater

Parameter Value pH 3.50 Total dissolved solids (mg L-1) 6020 Total suspended solids (mg L-1) 90.60 Turbidity (NTU) 65 Sodium (mg L-1) 350 Potassium (mg L-1) 15 Calcium (mg L-1) 340 Chloride (mg L-1) 312 Lead (mg L-1) 52 Sulphate (mg L-1) 40

Fig.1 (a) shows the surface morphology of the activated carbon. The measured BET surface area (625 m2 g-1) was higher than other low cost adsorbents namely, eichhornia13 (266 m2 g-1), cassava14 (270 m2 g-1) and silk cotton hull carbon15 (228 m2 g-1).

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Fig. 1 (a). Scanning Electron Microscopy photograph of sago waste carbon

Lactonic groups are present in high concentration in activated carbon, followed by carbonyl, carboxyl basic and phenolic groups. XPS analysis revealed a peak at 285 eV, which is the C (1S) peak. This shows the presence of graphitic structure of carbon, Fig.1 (b).

Fig. 1 (b). X-ray Photo electron Spectrum of sago waste carbon

The FTIR spectra of the sago waste activated carbon and the metal laden carbon are compared in Fig.1(c) and Fig.1 (d).

Fig.1(c). FTIR spectrum of sago waste carbon

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Fig. 1(d). FTIR spectrum of Pb (II) laden sago waste carbon.

The spectra displayed a number of adsorption peaks, indicating the complex nature of the material

examined. There is a remarkable change with the broad band around 3200-3600 cm-1 and it is narrowed in the spectrum of metal laden carbon. Many other bands, which appeared in the spectrum of carbon disappeared, weakened or shifted in the spectrum of metal laden carbon. Thus it can be considered that the metal adsorption is due to the formation of metal surface complexes between the metal ion and the surface functional groups of the activated carbon16.

3.2. Effect of agitation time and initial concentration on Pb (II) adsorption

The effect of agitation time on the removal of Pb (II) is shown in Fig.2. The removal increases with time and attains equilibrium within 180 minutes for all concentrations studied (5-20 mg L-1). The amount of metal uptake decreases with increase in metal ion concentration. The curves were single, smooth and continuous leading to saturation indicating monolayer adsorption of Pb (II) on the surface of the adsorbent.

0 50 100 150 200 2500

10

20

30

40

50

60

70

80

Per

centa

ge

rem

ova

l

Agitation time in min

Concentration of Pb(II)

5mg L-1

10mg L-1

15mg L-1

20mg L-1

Fig.2. Effect of agitation time on Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL;

particle size: 125-250 µm; pH: 3.5±0.2).

3.2. Adsorption Kinetics

The adsorption kinetics of the Pb (II) on sago waste carbon follows first order rate expression given by Lagergren17

Log10 (qe-q) = log10 qe-Kad t/2.303 (1) Where, q and qe are the amount of Pb (II) adsorbed (mg g-1 ) at time t (min) and at equilibrium time respectively. Kad is the rate constant of adsorption (1/min). The linear plots of log10 (qe-q) versus t at different initial Pb (II)

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concentrations (Fig.3(a)) confirm the applicability of the above equation for Pb (II) adsorption onto sago waste carbon. The values of Kad were calculated from the slope of these linear plots (Fig.3 (a)) and are presented in Table 3 for different Pb (II) concentrations.

0 20 40 60 80 100 120 140

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

log(q

e-q)

Agitation time in min


5mg L-1

10mg L-1

15mg L-1

20mg L-1

Fig.3(a). Lagergren plots for Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL; particle size: 125-250 µm; pH: 3.5±0.2: agitation time: 90 min).

In the case of micro porous adsorbents, the uptake of solute consists of the following four basic steps: 1. Bulk transport of the solute to the hydrodynamic boundary layer surrounding the carbon particle. 2. Diffusive film transport through the boundary layer referred to as external or film diffusion. 3. Diffusive transport through the internal pores of the carbon or along the pore-wall surface (intra-particle diffusion). 4. Adsorption or attachment of the solute particle at a suitable site on the carbon surface. One or more of the above steps may be the rate controlling factor. In order to find out the possibility of the metal ion being transported within the pores of sago waste carbon, the equation proposed by Weber18 is applied, which is as follows:

q = Kp t1/2 (2)

Where, q is the amount of the metal adsorbed (mg/g) at time t and Kp is the intra-particle diffusion rate constant. Table 3. Lagergren adsorption kinetic constants for Pb (II) adsorption

Pb (II) Concentration Kad (min-1) (mg L-1) qe(mg-1) 5 1.925 0.037 10 2.943 0.057 15 4.308 0.062 20 5.283 0.073

The plots of q versus t1/2 (Fig.3(b)) are not linear over the entire time range, indicating that more than one process is affecting the adsorption.

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0 2 4 6 8 10 12 14 160.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

q (m

g/g)

t1/2 (min)

Pb(II) concentration

5 mg g-1

10 mg g-1

15 mg g-1

20 mg g-1

Fig.3 (b). Plots for intra particle diffusion for Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL; particle size: 125-250 µm; pH: 3.5±0.2).

This type of non-linearity has been reported previously by various authors19, 20 and has been interpreted as showing that both boundary layer diffusion (the initial curved portion) and intra-particle diffusion (the final linear portion) are occurring. Kp values were obtained from the slope of the linear portion of the curves. Results show that increase in metal ion concentration increased the intra-particle diffusion rate constant.

4.1. Effect of carbon dosage on Pb(II) removal

Fig.4 shows the effect of carbon dosage on Pb (II) adsorption. The figure shows that the removal of Pb (II) increases with the increasing carbon concentration. This is due to the availability of more surface area with more functional groups at higher carbon dosages. The carbon dose required for the complete removal of Pb (II) from 50 mL of 10 and 20 mg L-1 was 250 and 400 mg respectively.

0 100 200 300 400 5000

20

40

60

80

100

Per

centa

ge

rem

ova

l

Adsorbent dosage (mg)


10mg L-1

20mg L-1

Fig.4. Effect of adsorption dosage on Pb (II) adsorption by sago waste carbon (particle size: 125-250 µm; pH: 3.5±0.2: agitation time: 180 min).

4.2. Adsorption isotherm

The Langmuir isotherm model was applied to analyze the adsorption equilibrium of Pb (II) onto sago carbon21 Ce/q e= 1/ (Qob) + Ce/Qo (3)

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Where, Ce is the the equilibrium concentration (mg L-1), qe is the amount of Pb (II) adsorbed (mg/g), and Qo and b are Langmuir constants related to adsorption capacity and rate of adsorption, respectively. The linear plot of Ce/qe versus Ce (Fig.5 (a)) shows that the adsorption follows Langmuir isotherm model for Pb (II) adsorption. The values of Qo and b were calculated from the slope and intercept of the plot and the values obtained were Qo = 14.35 mg g-1 and b = 0.0947 L mg-1, respectively (Table 4).

0.5 1.0 1.5 2.0 2.5 3.0

0

5

10

15

20

25

30

Ce/q

e (gL

-1)

Ce (mg L-1)

Fig. 5(a). Langmuir plot for Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL; particle size: 125-250 µm; pH: 3.5±0.2; agitation time: 180 min).

The Freundlich isotherm (Freundlich, 1906) is derived by assuming a heterogeneous surface with a non uniform distribution of the heat adsorption over the surface. It can linearly be expressed as follows:

Log qe = logKf + (1/n) logCe (4) Where Kf and n are the Freundlich constants; n gives an indication of how favorable the adsorption is; and Kf (mg g-

1 (Lmg-1) 1/n) is the adsorption capacity of the adsorbent. Linear plots of log qe versus log Ce show that the adsorption of Pb (II) onto the sago carbon follows the Freundlich isotherm model (Fig.5 (b)). The values of constants n and Kf were calculated from the slope and intercept of the plot, which were found to be n = 3.6088 and Kf = 2.8773 for 20 mg L-1 of Pb (II) concentration (Table 4). According to Trayball23 , n values between 1 and 10 represented beneficial adsorption.

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

log q

log Ce

Concentration of Pb(II) 10mg/L 20mg/L

Fig. 5(b). Freundlich plot for Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL; particle size: 125-250 µm; pH: 3.5±0.2; agitation time: 180 min).

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Heat of adsorption and the adsorbate-adsorbent interaction on adsorption isotherm were studied by Temkin and Pyzhev24 who suggested that because of these interactions, the energy of adsorption of all the molecules decreases linearly with coverage. The temkin isotherm has been used in the form,

qe= RT / b lnKT + RT/b lnCe (5)

Where, RT/b=B The adsorption data can be analyzed according to Eq.(5). The linear plots of qe versus ln Ce (Fig.5 (c)) enable to determine the constant KT and b (Table 4).

2 4 6 8 10 12

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

qe(m

g g-1

)

lnCe

Fig. 5(b). Temkin plot for Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL; particle size: 125-250 µm; pH: 3.5±0.2; agitation time: 180 min).

Redlich and Peterson25 incorporated the features of the Langmuir and Freundlich isotherms into a single equation and presented a general isotherm equation as followed:

Ce / qe = 1 / KR + aR / KR Ceβ (6)

Where, the exponent β lies between 0 (Henry’s law equation) and 1 (Langmuir form). A minimization procedure is adopted to solve the above equation by maximizing the correlation coefficient between the theoretical data for qe predicted from the above equation and the experimental data. The fitted value of β was found to be 0.9461, which shows that the absorption is well fitted with the Langmuir isotherm (Fig.5 (d)).

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0.5 1.0 1.5 2.0 2.5 3.0

0

5

10

15

20

25

Ce/q e(

gL-1

)

Ce

ß(mg L-1)

Fig. 5(c). Redlich and Peterson plot for Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL; particle size: 125-250 µm; pH: 3.5±0.2; agitation time: 180 min).

Dubinin and Radushkevich proposed an equation for the analysis of isotherm of a high degree of rectangularity, which is as follows:

ln qe = ln qD – BDε2 (7)

Where, ε = RT ln [1+1/ Ce] The constant BD gives the mean free energy E of sorption per molecule of the sorbate when it is transferred to the surface of the solid from infinity in the solution and can be computed using the relationship:

E = 1/ √2BD (8) Where, R is the gas constant (8.314 J mol-1 K) and T is the absolute temperature. From the plot of lnqe versus ε2, the values of qD and E (Table 4) can be calculated (Fig.5 (e)).

0 200 400 600 800

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

lnq

e

RTln(1+1/Ce)

Fig. 5(e). Dubinin and Radushkevich plot for Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL; particle size: 125-250 µm;

pH: 3.5±0.2; agitation time: 180 min).

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Table 4. Isotherm model constants of five isotherm models for Pb (II) adsorption onto sago waste

Isotherm models Constants Value Langmuir Q0 (mg g-1) 14.35 b (L mg-1) 0.0947 R2 0.9904 Freundlich Pb (II) concentration 10 (mg L-1) 20 (mg L-1) KF (mg g-1) 1.9178 2.8773 n 1.8426 3.6088 R2 0.9923 0.9778 Temkin KT (L mg-1) -1.0656 B 3.0124 R2 0.9401 Redlich-Peterson KR (L g-1) 1.4393 aR (L mg-1) 0.1217 R2 0.9998 Dubinin-Radushkevich E (KJ mol-1) 28.9017 qD (mg g-1) 8.9406 BD (mol2 KJ-2) 0.0006 R2 0.8779

3.5. Effect of pH on Pb (II) removal

Fig.6 (a) shows the effect of pH on Pb (II) removal by adsorption. When the pH was increased from 2 to 9, the percent removal also increased from21.00% to 87.34% for 10 mg L-1 Pb (II) concentration and from 18.33% to 78.77% for 20 mg L-1 Pb (II) concentration. The percentage removal is less at lower pH levels and is quantitative above pH 7. Gardea et al. reported the same trend using hope stems and leaves for the removal of lead27. In the present study, above pH 4, turbidity was noted and the intensity of turbidity increased with the increase in pH of the solution. The turbidity may be due to the formation of Pb (OH) 2. The conventional methods for the removal of heavy metals are by precipitation as hydroxides or sulphides. This method has limitation in that; metals cannot be removed completely from solution owing to the solubility product of metal hydroxides or sulphides. Pb (II) removal by activated carbon increases with increase in pH and is due to the competition between H+ and Pb2+ ions for adsorption at the ion exchangeable sites28. The pH dependent trend implies that the mechanism of Pb (II) binding by sago waste carbon is through the deprotonation of carbon surface, more similar to the carboxyl resin and the recovery of bound lead may be achieved through reduction of pH. At pH above 5, precipitation of Pb (OH) 2 takes place. Hence, it was decided to maintain the pH at 3.5 for all other studies. The uptake of metal ions can be explained as an H+-Pb2+ exchange reaction. Similar findings of pH effect were reported for the adsorption of Pb (II) onto commercial peanut hull carbon29.

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1 2 3 4 5 6 7 8 9 1010

20

30

40

50

60

70

80

90

Per

centa

ge

rem

ova

l

Initial pH


10mg L-1

20mg L-1

Fig. 6(a). Effect of pH on Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL; particle size: 125-250 µm; agitation time: 180 min).

4.3. Desorption Studies

Regeneration of the adsorbent may make the treatment more economical. Fig.6 (b) shows the effect of HCl on desorption of Pb (II). The percentage desorption increases with decrease in pH and reaches a maximum of 63.96% for Pb (II) concentration of 20 mg L-1. This is due to the fact that, in acidic conditions, H+ ions protonate the adsorbent surface by replacing the metal ions on the adsorbent surface, leading to desorption of the positively charged metal ion species.

0.00 0.05 0.10 0.15 0.20 0.25

25

30

35

40

45

50

55

60

65

Per

cen

tag

e d

eso

rpti

on

Normality of HCl

20mg/L of Pb(II)

Fig. 6(b). Desorption plot for Pb (II) adsorption by sago waste carbon (carbon dose: 100 mg/50 mL; particle size: 125-250 µm; agitation time: 180 min; concentration of Pb (II): 20 mg L-1).

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4. Conclusion

Based on the results obtained, it is concluded that sago waste carbon can be used effectively for the removal of Pb (II) from aqueous solution and industrial effluent. In batch mode adsorption studies, increase of agitation time, adsorbent dosage and decrease of Pb (II) ion concentration and particle size increased the percent adsorption of Pb (II) ion. Adsorption followed Langmuir, Freundlich, Redlich Peterson, Temkin and Dubinin-Radushkevich isotherms. Considering its low-cost and technical feasibility, it is suggested that sago waste activated carbon is preferable for Pb (II) ion removal.

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Utilization of Sago Waste as an Adsorbent for the Removal ... · The adsorption kinetics of the Pb...

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Transcript of Utilization of Sago Waste as an Adsorbent for the Removal ... · The adsorption kinetics of the Pb...