Activated Carbon From Corn Cobs and Coconut Shell for Heavy Metal Ions Adsorption

8/3/2019 Activated Carbon From Corn Cobs and Coconut Shell for Heavy Metal Ions Adsorption

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ACTIVATED CARBON FROM CORN COBS AND COCONUT

SHELL FOR HEAVY METAL IONS ADSORPTION

Document by:Bharadwaj

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ABSTRACT

Heavy metal ions removal has received considerable attention due to their toxicological

affects on ecosystem, agriculture and human health. Commercial activated carbon is widely

used as an adsorbent for the removal of heavy metal ions from industrial wastes. Its highcost is, however, a restricting factor to its wider application. The present study explores the

effectiveness of activated carbon obtained from corn cob and coconut shell for the removal

of cadmium and chromium from aqueous wastes. Batch scale equilibrium adsorption

studies carried out for various pH values and a range of initial concentrations of cadmium

and chromium on the activated carbon prepared at different temperatures by pyrolysis

process. Higher iodine value for coconut shell compared to corn cob at 8000C indicates that

activated carbon obtained from coconut shell should be used preferably.

Keywords: Coconut shell; Corn cob; Carbonization temperature; Heavy metals

NOMENCLATURE

Qe,= Amount of metal ion adsorbed, mg/gmCe,= Equilibrium metal ion concentration in solution, mg/literCo,= Initial metal ion concentration in solution, mg/literm = Amount of adsorbent, gm

V= volume of solution, liter

Qo= Langmuir constant related to maximum sorption capacity, mg/gmb = Langmuir constants that relate energy of adsorption,l/mg.

k= Freundlich constant representing adsorption capacity (mg/g),

n= Freundlich constant representing intensity of adsorbent

INTRODUCTION

Industrial modernization has increased the production and discharge of heavy metal ions into the

environment. These metals are toxic in nature and generate various disastrous risks to humanhealth. For removal of hazards associated with water have played an important role in

development of various technologies for wastewater purification namely filtration, ion exchange,

precipitation and adsorption. Although these methods are effective for removing metals from

contaminated water but they are expensive or time consuming and their inherent limitations also

have proved to be less efficient than adsorption process based on low cost activated carbon

[1].Throughout the world non conventional agricultural by product such as Coconut shell[2],coconut jute carbon[3],Coconut tree saw dust carbon [4], Sawdust and used Tyres carbon [5],
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Rice husk carbon , Coconut fibre compost, Maize cob, Sugar beet pulp and Cane Bagasse,Hazelnut shell [6], Almond shell , Corncob, Stones of Apricot, Date, Peach, Olive and shell of

Walnut & Coconut[2], Peanut husk[7] , Hazelnut husk[8], Olive stones & Almond shell,Casurina equisetifolia Leaves[9], Bagasse[10], Rice hulls, Rice straw, Apricot Stone, peachstones andEucalyptus globulus chips and Rice husk[11] are some of the raw materials for

activated carbon production which has been reported to be an important adsorbents for theremoval of heavy metals and organics from municipal and industrial waste water. Coconut shell

is mostly used for preparing microporous activated carbon due to its excellent natural structure

and low ash content [12,13]. There are two methods for manufacture of activated carbon: physicaland chemical activation. In chemical activation the activating agent functions as a dehydrating

agent inhibiting the formation of tar [12]. However the product needs washing to remove residual

inorganic, which causes a serious pollution problem. Physical activation uses gaseous activation

agent [14] and does not produce waste water, therefore is considered to be an environmentally

benign technology. In the present study agricultural waste materials like coconut shell and

corncob are used for preparation of activated carbon followed by removal of cadmium and

chromium ions from synthetic waste water to establish equilibrium characteristics.

MATERIALS AND METHODSChemicals

All the chemicals used in this study are of AR grade obtained from CDH,India. Water used in this

study is double distilled water.

Activated carbon preparation

Coconut shell and corncob are used as raw materials to produce activated carbon are obtained

from Modinagar local vendor. The starting materials are cleaned and dried at 1100C for 48 hrs

and then broken into 2 to5 inches pieces with the help of hammer. The Characteristics of biomass

are given in Table 1. The broken biomass is pyrolysed at 350 0C for 1.5-2 hours followed by sizereduction to 1-3 mm size and Physical activation in a Microprocessor controlled Tube furnace.

The Physical activation is done at three different temperatures of 600 0C, 7000C and 8000C for

30min in each case with inert atmosphere of nitrogen.

Table 1 :Characteristic of Biomass

Property Coconut shell Corn Cob

Calorific value ( kcal/kg) 5967.92 4153.79

Moisture content(%) 6.54 7.08

Volatiles matter(%) 65.05 71.2

Fixed carbon (%) 27.0 20.9

Ash content(%) 1.54% 1.85

Bulk density(kg/l) 1.025 0.39

Equilibrium experiments:

Batch adsorption experiments are carried out in 100 ml conical flask. 50 ml of metal ion solution

of known concentration (10-100 ppm) and adjusted pH by acetate buffer is poured into flask

containing accurately weighed amount of the adsorbents. The adsorbent weight ranged from

0.120-0.310gm per 50 ml of solutions. The flasks are shaken at 150-200rpm using an electric

shaker(DK-S1020 DAIKI) for about 24hrs to attain equilibrium. After 24 hours the content of


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flask are filtered thorough the filter paper. Clear filtrate are analyzed for metal ion concentration

(Ce) by AAS model-EC4141(make ECI). Amount adsorbed (Qe) in the adsorbent isdetermined by metal ion balance using following equation.

( )(1)-----

m

VCeCoQe

=

RESULT AND DISCUSSIONS

Characterization of activated carbon

The activated carbon are analyzed in terms of their iodine number bulk density, moisture contentand pH. The iodine number is determined according to ASTM procedure D4607-94 (ASTM

Directory, 1986)[15]. Greater iodine value of coconut shell activated carbon indicates that

coconut shell activated carbon have less ash content as shown in Table 2. Other characteristics are

given in Table3.

Table 2 : Iodine values of Activated carbon

Temp of activation Type of biomass

Corn cob Coconut shell

8000C 786.85 926.35

7000C 780 800.56

6000C 700 649

Table3: Characteristics of activated carbons

Property Coconut shell activated

carbon

Corn cob activated carbon

Bulk Density 0.5906kg/l 0.1863kg/l

Moisture 1.3% 2.58%

pH 7.26 5.89

Effect of pH

The mechanism of adsorption at the carbons surface reflects the nature of physicochemical

interaction of the metal ions in the solution and the active sites of the carbons. One of the most

important parameters that affect this mechanism is the pH of the solution. It is, therefore planned

to conduct adsorption experiments at different pH values of the solution. The pH is varied from 2-

10 for chromium and cadmium solution for both type of biomass at 250 C and 150 rpm. The effect

of pH on the removal of chromium ions found to be max at pH 3.0 for corn cob and at pH 4.5 for

coconut shell as shown in fig 1. The results indicate that the pH affects the Cr(VI) adsorption. An

acidic solution at a pH value about 3-5 is an optimal condition for the adsorption of Cr(VI) andthe reason may be due to the partial reduction of Cr(VI)-Cr(III) on the surface of the carbon and

electrostatic attraction of the highly protonated carbon surface to the major chromium

species(HCrO4-) in solution. The effect of pH on the removal of Cadmium ions found to be max

at pH range 5for corn cob carbon and 6.0 for coconut shell carbon as shown in fig 2 . The metal

adsorption found again max at pH >6.0 because of the formation of metal oxide precipitation.


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Effect of adsorption temperature

The effect of adsorption temperature on the uptake of chromium and cadmium, at the optimum

pH is examined. Fig 3 and Fig 4 shows the temperature influence on the adsorption of chromium

and cadmium simultaneously. The removal of metal ions increases with an increase in the

temperature. For both type of metal ions with both type of adsorbents there is a substantialincrease in the amount adsorbed when the temperature increases from 15oC-35o C. It can be easily

inferred that the removal of metal ions increases with increase in temperature.

Figure 1 :Effect of pH on Cr

adsorbed,t=24hrs, CO=100ppm,

m=0.120gm,

0

5

10

15

20

25

0 2 4 6 8 10 12

ph

metaladsorbed

(mg/gm)

coconut

corn cob

Figure 2: Effect of pH on cd adsorbed,

t=24 hrs,Co=100ppm,m=0.120gm

0

5

10

15

20

25

30

35

40

45

50

0 2 4 6 8 10 12

pH

metaladsorbed

(mg/gm)

coconut shell

corn cob

Figure3: Effect of temp for Cr,

t=24hrs,100ppm,0.120gm,150rpm

0

5

10

15

20

25

30

0 10 20 30 40

temp

metaladsorbed

(mg/gm)

shell ac

cob ac

Figure4: Effect of temp for Cd,

t=24 hrs,100ppm,0.120 gm,150rpm

0

1

2

3

4

5

6

7

0 10 20 30 40

temp

metaladsorbed

(mg/gm)

shell ac

cob ac

Effect of adsorbent dose

The effect of amount of adsorbent on the uptake of chromium and cadmium, at the optimum pHis examined. Amount if carbon dosage versus % removal of chromium and cadmium ions


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shows(in Fig 5&6) that the removal of metal ions increases with an increase in the amount of

carbons. For chromium ions there is a substantial increase when the does of carbons increases

from 0.1-0.2gm but not more increases for 0.3 gm for corn cob but for coconut shell activated

carbons it found increase in good condition. So it can be easily inferred that the percent removal

or metal ions increases with increasing weight of carbons.

Figure 5: Effect of carbon dose-Cr,100ppm,150 rpm ,t=24hrs,pH-5

0

5

10

15

20

25

0 0.1 0.2 0.3 0.4

carbon dose (gm)

metaladsorbed

(mg/gm)

shell ac

cob ac

Figure6: Effect of carbon dose-cd,t=24 hrs,100ppm,150rpm,pH-6

0

2

4

6

8

10

12

0 0.1 0.2 0.3 0.4

carbon dose (gm)

metaladsorbed

(mg/gm)

shell ac

cob ac

Effect of initial metal ion concentration

The effect of initial ion concentration on the uptake of chromium and cadmium, at the optimum

pH is examined and results are shown in Figure7. The percentage removal of chromium and

cadmium ions increases with an increase in the initial ion concentration for fixed amount ofadsorbent dose. For both metal ions the rate of percentage removal fast at low concentration and

it becomes slow with increases in initial concentration which may be due to saturation of

adsorbent

Equilibrium Isotherms

The equilibrium study is carried out for removal of Chromium and Cadmium by activated carbon.

Equilibrium equation, commonly known as sorption isotherm, is basic requirement for the design

of adsorption system. The isotherm provides information on the capacity of the adsorbent forremoving a unit mass of pollutant under the operating conditions. Optimizing the design of

adsorption system to remove Chromium and Cadmium from effluent requires appropriate

correlation for the equilibrium data. Two isotherms have been tested in the present study, namely,

Langmuir and Freundlich. The Langmuir isotherm represents one of the first theoreticaltreatments of non-linear adsorption, and has been successfully applied to a wide range of data that

exhibit limiting or maximum adsorption capacities. It assumes uniform energies of adsorption

onto the surface and no transmigration of the adsorbate in the plane of the surface. The Langmuir

isotherm is represented by:

(2)---------1

ebC

CQQ eoe

+

=


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Figure 7: Effect of initial ion conc, t=24hrs, pH 6.0 for Cd,

pH 5.0 for Cr, m=0.220 gm

0

10

20

30

40

50

6070

80

90

100

0 20 40 60 80 100 120

conc(ppm)

%r

emovalofmetalion

Cr ion

Cd ion

Linear form of equation (1) is

(3)-----------111

eo oe Q

b

CQQ+

=

A plot of 1/Qe versus 1/Ce from the linear form of Eq. (2) can be used to determine the values of

Qoand b. The calculated parameters are presented in Table3. The equilibrium data is also fitted tothe Freundlich isotherm. Freundlich equation has the following linear form

-(4)-----------log1

kloglog Aee Cn

Q

+=

Where Qe is the amount of solute present in the adsorbent phase at equilibrium (mg/g), Ce is theequilibrium solute concentration in the solution phase (mg/l), and k and n are constant

representing adsorption capacity (mg/g), and intensity of adsorbent respectively. The values of k

and n obtained from the intercept ands slope of the plot between log Qe and log Ce are presented

in Table3.

Conclusions

In the present study, the waste coconut shell and corn cob are used as a low cost source material

for the preparation of activated carbons and the carbons activated at 8000

C gives the highestiodine value. Lower Iodine value in case of corn cob compared to that for coconut shellcarbon indicates that coconut shell activated carbon is better. The optimum pH for

cadmium adsorption is in the range 5-6 while that for chromium the range is 3-4. Metal

removal increases with increase in the amount of activated carbon. Freundlich isotherm

fits well in the equilibrium data for adsorption of chromium and cadmium on activatedcarbon.


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Table 3 : Isotherms Parameters

Isotherms Biomass Metal ion Experimental

conditions

Parameters R 2

Langmuir coconut

shell

Cadmium pH=6.0

Ads.Temp.=250C

Act.Temp.=8000C

Qo=1.045,

b=0.015942

0.9464

Freundlich coconut

shell

Cadmium pH=6.0

Ads.Temp.=250C

Act.Temp.=8000C

k = 6.931,

n =0.2978

0.9759

Langmuir Corn

cob

Cadmium pH=6.0

Ads.Temp.=250C

Act.Temp.=8000C

Qo=6.11,b=0.019511

0.9226

Freundlich Corn

cob

Cadmium pH=6.0

Ads.Temp.=250CAct.Temp.=8000C

k = 8.0634,

n=0.24200

0.9601

Langmuir coconut

shell

Chromium pH=5.0


Qo= 1.078,

b= 0.0375

0.7423

Freundlich coconut

shell

Chromium pH=5.0

Ads.Temp.=250C

Act.Temp.=8000C

k= 0.7374,

n=3.16656

0.9679

Langmuir Corn

cob

Chromium pH=5.0

Ads.Temp.=250C

Act.Temp.=8000C

Qo=5.175,

b= 0.09045

0.5612

Freundlich Corn

cob

Chromium pH=5.0


k= 1.8614,

n=1.8148

0.9842

References

1. O.S. Amuda, A.A. Giwa, I.A. Bello., Removal of heavy metal from industrial

Wastewater using modified activated coconut shell carbon, Biochem. Engg.Journal,36 pp.174181(2007).

2. Abdelrahman B. Fadhil and Mohammed M. Deyab , Conversion Of Some Fruit

Stones and Shells Into Activated Carbons,The Arabian Journal for Sci.and Engg.,

Vol. 33, Number 2A pp.175-184(2008).

3. Chand S, Agarwal VK and Pavankumar C., Removal of hexavalent chromiumfrom wastewater by adsorption.Ind. J. Environ. Health 36pp.151 - 158(1994).

4. Selvi K, Pattabhi S and Kadirvelu K., Removal of Cr(VI) from aqueous solution

by adsorption onto activated carbon.Bioresour. Technol. 80pp.7-89 (2001).

5. Hamadi NK, Chen XD, Farid MM and Lu Mgq.,Adsorption kinetics for the

removal of chromium (VI) from aqueous solution by adsorbents derived fromused tyres and sawdust.J.Chem.Eng. 84pp.95-105 (2001).


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6. Kobya M Adsorption, kinetic and equilibrium studies of Cr(VI) by hazelnut shell

activated carbon,Adsorp. Sci. Technol. 22pp.51-64(2004).

7. Ricordel S. A, Taha S. A, I. Cisse B, Dorange G. Heavy metals removal byadsorption onto peanut husk carbon: characterization, kinetic study and

modeling, Separation and Purification Tech. 24 pp.389401(2001).8. Mustafa Imamoglu, Oktay Tekir, Removal of copper (II) and lead (II) ions from

aqueous solutions by adsorption on activated carbon from a new precursorhazelnut husks, Desalination 228pp.108113 (2008).

9. William David OConnell A,C, Colin Birkinshaw B C,Francis Thomas ODwyer

A,C, Heavy metal adsorbents prepared from the modification of cellulose: Areview, Biores. Tech. 99 pp.67096724(2008).

10. Dinesh Mohan, Singh Kunwar P. Single- and multi-component adsorption of

cadmium and zinc using activated carbon derived from bagasse an agriculturalwaste, Water Res.36 (2002) pp.23042318.

11. Basso, M. C., Cerrella, E. G. and Cukierman, A. L., Activated carbons

developed from a rapidly renewable biosource for removal of cadmium (II) andnickel (II) ions from dilute aqueous solutions, Industrial & Engineering

Chemistry Research, vol. 41., pp.180-189. (2002).

12. Wei Su, Li Zhou, Yaping Zhou., Preparation of microporous activated carbon

from coconut shells without activating agents,carbon Journal.,41, pp.861-863.(2003).

13. W.T. Tan, S.T. Ooi, C.K. Lee., Removal of chromium (VI) from solution by

coconut husk and palm pressed fibers, Environ. Technol. 14 pp. 277282 (1993).14. Kadirvelu, K., Kavipriya, M., Karthika, C., Radhika, M., Vennilamani, V. and

Pattabhi, S., Utilization of various agricultural wastes for activated carbon

preparation and application for the removal of dyes and metal ions from aqueous

solutions, Biores. Tech., 87, pp 129-132. (2003).15. Standard Test Method for Determination of Iodine Number of Activated Carbon,

ASTM Designation: D4607-94.

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Activated Carbon From Corn Cobs and Coconut Shell for Heavy Metal Ions Adsorption