Bioresource Technology 97 (2006) 2124–2130

Removal of lead from aqueous solutions by agriculturalwaste maize bran

K.K. Singh *, M. Talat, S.H. Hasan

Water Pollution Research Laboratory, Department of Applied Chemistry, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India

Received 16 August 2004; received in revised form 6 September 2005; accepted 6 September 2005Available online 4 November 2005

Abstract

Maize bran is a low cost biosorbent that has been used for the removal of lead(II) from an aqueous solution. The effects of variousparameters such as contact time, adsorbate concentration, pH of the medium and temperature were examined. Optimum removal at20 �C was found to be 98.4% at pH 6.5, with an initial Pb(II) concentration of 100 mg l�1. Dynamics of the sorption process and masstransfer of Pb(II) to maize bran were investigated and the values of rate constant of adsorption, rate constant of intraparticle diffusionand the mass transfer coefficients were calculated. Different thermodynamic parameters viz., changes in standard free energy, enthalpyand entropy were evaluated and it was found that the reaction was spontaneous and exothermic in nature. The adsorption data fitted theLangmuir isotherm. A generalized empirical model was proposed for the kinetics at different initial concentrations. The data were sub-jected to multiple regression analysis and a model was developed to predict the removal of Pb(II) from an aqueous solution.� 2005 Elsevier Ltd. All rights reserved.

Keywords: Adsorption; Monolayer; Lead(II); Maize bran; Exothermic; Multiple regressions; Isotherm

1. Introduction

The presence of metal ions in natural or industrialwastewater and their potential impact has been a subjectof research in environmental science for a long time. Metalions such as cadmium, chromium, copper, lead, zinc andiron are commonly detected in both natural and industrialeffluents. To minimize this problem, biosorption can bepart of the solution. Biosorption of heavy metals by bacte-rial fungal or algal biomass (viable or non-viable cells) andagricultural waste biomass (Feng and Aldrich, 2004; Bek-tas et al., 2004; Ho et al., 2004; Saed and Iqbal, 2003;Marin and Ayele, 2003; Reddad et al., 2003; Wong et al.,2003; Krishnan et al., 2003; Ho, 2003; Singh et al., 2003,2004, 2005; Naseem and Tahir, 2001; Ahuja et al., 2001;Mamman and Salewu, 2001; Ariff et al., 1999; Matheickaland Yu, 1999) has been recognized as a potential alterna-

0960-8524/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.biortech.2005.09.016

* Corresponding author. Tel.: +91 5443 221147.E-mail addresses: kks_envir@yahoo.co.in (K.K. Singh), hasanitbhu@

yahoo.co.in (S.H. Hasan).

tive to existing technologies such as precipitation, ionexchange, solvent extraction and liquid membrane for theremoval of heavy metals from industrial wastewaterbecause all these processes have the limitations of technicaland/or economical viability.

The literature reveals two distinct approaches to use ofliving organisms and the use of a non-viable biomass(Darnall et al., 1986; Khummongkol et al., 1982). Thereare significant practical limitations to systems, whichemploy living microorganisms. The most significant limita-tion is that microbial growth is inhibited when the concen-trations of metal ions are too high or when significantamount of metal ions are adsorbed by microorganisms(Darnall et al., 1986). Dead cells or agricultural wastesaccumulate heavy metal ions to the same or to a greaterextent than living cells (Darnall et al., 1986; Khummongkolet al., 1982). The reason for this is that the changes, whichoccur in the cell structure after the cells are dry-killed,affect adsorption in a positive manner (Nourbakhshet al., 1994). For metal removal applications, the use ofnon-viable biomass or agricultural waste may be preferable

Nomenclature

C0 (mg l�1) initial adsorbate concentrationCt (mg l�1) adsorbate concentration at time t (min)kad (min�1) rate constant of adsorptionkid (mg g�1, min�1/2) rate constant of intraparticle pore

diffusionq (mg g�1) amount adsorbed at time t (min)qe (mg g�1) amount adsorbed at equilibriumCe (mg l�1) equilibrium concentration of the adsorbateD (cm2 s�1) pore diffusion coefficientDG0 (kcal mol�1) change in standard free energyDH0 (kcal mol�1) change in standard enthalpyDS0 (cal mol�1 K�1) change in standard entropyDH (kcal mol�1) apparent heat of adsorption

R (cal deg mol�1) gas constantT (K) absolute temperatureQ0 (mg g�1) Langmuir�s constants related to the capa-

city of adsorptionb (l mg�1) Langmuir�s constant related to the energy of

the adsorptionRL equilibrium parameter, it is dimensionlessb1 (cm min�1) it is the mass transfer coefficientSs (cm�1) it is the outer specific surface of the adsorbate

per unit volumem (g l�1) it is the mass of the biosorbent per unit volume

of particle free adsorbate solution

Table 1Physical and chemical properties of biosorbent maize bran

Surface area (m2 g�1) 437.00Bulk density (g cm�3) 0.2432Particle size (lm) <178Average particle diameter (cm) 1.75 · 10�2

Porosity 0.37

Proximate analysis (%)

Moisture 7.97Volatile matter 42.34Fixed carbon 31.28Ash (oxides of Al, Mn, Si, Fe, and others) 18.41

K.K. Singh et al. / Bioresource Technology 97 (2006) 2124–2130 2125

as large quantities are readily and economically availableas a byproduct of various industries (Tobin et al., 1993).Therefore, it was proposed to use maize bran for theremoval of Pb(II) from aqueous solution, because it is eco-nomical, easily available and mostly biodegradable.

2. Methods

2.1. Physico-chemical analysis of adsorbent

Maize bran was collected from M/s S.K. Industries(Flourmill), Narainpur, Mirzapur, UP, India. It was usedafter double washing to remove soluble lighter materials,drying at 70 �C in an oven, crushing and sieving to lessthan 178 lm size. The characterization of surface area ofthe adsorbent was determined by a three point N2 gasadsorption method using a Quantasorb Surface Area Ana-lyzer; model Q5-7, Quanta chrome Corporation, 1900 Cor-porate Drive, Boynton Beach, FL 33426 USA. The bulkdensity of the adsorbent was determined by densitometermodel D8 K, NGRI, Hyderabad, India. Sieve Analysisdetermined particle size of the adsorbent. Sieves were man-ufactured by Standard Appliances, Delhi, India. Porosityof the adsorbent was determined by a porositometer,model H: M7V, NGRI, Hyderabad, India. X-ray diffrac-tion of the adsorbent was obtained using X-ray diffracto-meter, model-ID-3000W, Rich Siefert and Company,Ahrensburg, Germany. Infrared spectra of the adsorbentwere recorded using an infrared spectrophotometer; modelFT/IR-5300, JASCO Corporation, Ishikawa-cho Hachioji,Tokyo, Japan in the range 4000–400 cm�1. Percentage ofvolatile matter, ash and moisture were determined as givenin the ‘‘Vogel�s Textbook of Quantitative Chemical Analy-sis’’, 5th Edition, Bath Press Ltd., UK.

Physical and chemical properties of the adsorbent aregiven in Table 1. Chemical analysis of the maize branshows the presence of various oxides. X-ray diffractionand IR studies of maize bran show that major constituentsare carbon while quartz, carbon hexagonal, Fe–O, Mn–O,

Si–C, Ca2SiO4, Ca–P and alumina were found to be18.41%.

2.2. Experimental procedure

In the present investigation batch mode of operationwas selected in order to measure the progress of adsorp-tion. Thus in a representative experiment 1.0 g of thedesired grade of maize bran was shaken with 50 ml of leadnitrate of desired concentration (100, 125 and 150 mg l�1)at different temperatures (20, 30 and 40 �C) and pH (3.2,4.0, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5 and 8.0) in different glass bot-tles in a shaking thermostat set at 20, 30 and 40 �C at aconstant speed of 125 rpm. The pH of the adsorbate solu-tion was adjusted by adding HCl or NaOH. The progressof the adsorption process was observed at different timeintervals till the attainment of saturation. At the comple-tion of predetermined time intervals, the adsorbate andadsorbent were separated by centrifugation at 15,000 rpmand the supernatant liquid was analysed by the OrionIon Selective Titrator plus System, model no. 960, madeby Thermo Orion, 500 Cummings Center, Beverly, MA01915-6199, USA to determine the residual concentrationof lead ion. Blank solutions were run without the adsorbentunder identical conditions of concentration, pH and tem-perature for all the cases to correct for any adsorption onthe internal surface of the bottles.

2126 K.K. Singh et al. / Bioresource Technology 97 (2006) 2124–2130

3. Results and discussion

3.1. Effect of pH

Experiments were performed at different pH values (3.2,4.0, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5 and 8.0). The percentageremoval increased from 23.6% to 96.8% with an increaseof pH from 3.2 to 6.5 and thereafter removal decreasedfrom 96.8% to 31.2% with an increase of pH from 6.5 to8.0, at 30 �C and Pb(II) concentration of 100 mg l�1. Theoptimum pH for the removal of Pb(II) on maize branwas found to be 6.5 (Fig. 1). Furthermore, the adsorptionprocess can be explained on the basis of the nature ofadsorbent used which contained several metal oxides.These oxides when mixed up with adsorbate solutionundergo surface hydroxylation and form hydroxyl com-pounds on the surface which gives positively or negativelycharged surface as a result of subsequent acid base dissoci-ation (Pandey et al., 1984). It can be seen from Fig. 1 thatadsorption increased in the pH range 3.0–6.5 and above pH6.5, it began to decrease. It is obvious from Fig. 8 (Jean andBancroft, 1986) that up to pH 6.5 the presence of Pb(II) ionwas predominant which was responsible for maximumadsorption and above this pH, several hydroxide speciesof Pb(II) causes decrease in the adsorption.

3.2. Effect of contact time and concentration

A series of experiments were performed at differentadsorbate concentration viz., 100, 125 and 150 mg l�1

and time interval. The removal of Pb(II) was found to be96.8%, 92.0% and 85.73%, respectively, at 30 �C and pH6.5. The extent of adsorption increased rapidly in the initialstages and became slower at later stages until the attain-ment of equilibrium. Equilibrium time for the adsorptionof Pb(II) on maize bran at various adsorbate concentra-

pH2 3 4 5 6 7 8 9

Am

ount

Ads

orbe

d(m

g g-1

)

0

1

2

3

4

5

6

Fig. 1. Effect of pH on the removal of lead by maize bran. Conditions—temperature: 30 �C; pH: 3.2, 4.0, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5 and 8.0.Concentration: 100 mg l�1; particle size: <178 lm.

tions was found to be 100 min, which showed that equilib-rium time was independent of the initial adsorbateconcentration. The following correlation had been devel-oped between percentage removal and initial adsorbateconcentration (C0) to predict the percentage removal ofPb(II) by maize bran at any initial concentration.

Percentage removal of Pb(II) was considered equal to33:4C0:64

0 .

3.3. Adsorption dynamics

The rate constant kad (min�1) for lead(II) adsorption onmaize bran was determined by using the first order ratekinetic equation (Lagergren, 1898)

logðqe � qÞ ¼ log qe �kad

2:303� t ð1Þ

where q (mg g�1) and qe (mg g�1) are the amounts of adsor-bate at time t (min) and at equilibrium, respectively. Thelinear plots of log (qe � q) versus t (Fig. 2) suggest the firstorder kinetics of the uptake of Pb(II). The values of kad

(min�1) at different temperatures were calculated fromthe slopes of these plots and are presented in Table 2.

The data was also tested for pore diffusion using thefollowing equation (Weber and Morris, 1963):

q ¼ kidt1=2 ð2Þwhere kid (mg g�1, min�1/2) is rate constant for intraparti-cle diffusion. It was evident from Fig. 3 that the plot q

(mg g�1) versus t1/2 (min1/2) was linear to a certain extentbut did not pass through the origin. Therefore pore diffu-sion was not the only rate controlling step (Weber andMorris, 1963; Huang and Oliver, 1989; Bhattacharya andVenkobachar, 1984) in the removal of lead. The values ofkid at different temperatures were calculated from theslopes of later portion of these plots and are presented in

0 20 40 60 80 100

log

(qe-

q)

-2

-1

0

1

Time (min.)

20 °C30 °C40 °C

Fig. 2. Rate constant plot for adsorption of Pb(II) on maize bran atdifferent temperatures. Conditions—concentration: 100 mg l�1; pH: 6.5;temperature: 20, 30 and 40 �C; particle size: <178 lm.

Table 2Adsorption rate constants for adsorption of Pb(II) on maize bran at different temperatures

Temperature (�C) kad (min�1) kid (mg g�1, min�1/2) D (cm2 s�1) b1 (cm min�1)

20 5.711 · 10�2 3.690 · 10�2 8.235 · 10�9 5.625 · 10�5

30 5.297 · 10�2 3.423 · 10�2 7.532 · 10�9 5.118 · 10�5

40 4.813 · 10�2 3.177 · 10�2 5.986 · 10�9 4.546 · 10�5

K.K. Singh et al. / Bioresource Technology 97 (2006) 2124–2130 2127

Table 2. This was further supported by calculating theintraparticle diffusion coefficient D (cm2 s�1) using the fol-lowing equation (Bhattacharya and Venkobachar, 1984):

D ¼ 0:03r2=t1=2 ð3Þ

where r (cm) is the average radius of the adsorbent particleand t1/2 (min) is the time for half of the adsorption.According to Michelsen et al. (1975) a D (cm2 s�1) valueof the order of 10�11 is indicative of intraparticle diffusionas the rate determining step. In this investigation, thevalues of D (Table 4) obtained was in order of 10�9 whichwas more than two order of magnitude higher, indicatedthat the intraparticle diffusion was not the only rate con-trolling step (Michelsen et al., 1975). It may be concludedthat both boundary layer and intraparticle diffusion wereinvolved in this removal process.

3.4. Mass transfer analysis

The mass transfer analysis for the adsorption of lead(II)ion was determined at various temperatures (20, 30 and40 �C) using the following equation (Mckay et al., 1981):

lnCt

C0

� 1

1þ mK

� �¼ ln

mK1þ mK

� �� 1þ mK

mK

� �21 � Ss � t

ð4Þwhere C0 (mg g�1) is the initial adsorbate concentration, Ct

(mg g�1) is the adsorbate concentration after time t (min),m (g l�1) is the mass of the biosorbent per unit volume of

Time (min.1/2)

0 2 4 6 8 10 12

Am

ount

Ads

orbe

d (m

g g-1

)

0

1

2

3

4

5

6

Fig. 3. Intraparticle diffusion plot for adsorption of Pb(II) on maize branat different temperatures. Conditions—concentration: 100 mg l�1; pH: 6.5;temperature: 20, 30 and 40 �C; particle size: <178 lm.

particle free adsorbate solution, K (l g�1) is the Langmuir�sconstant obtained by multiplying Q0 (mg g�1) and b

(l mg�1), b1 (cm min�1) is the mass transfer coefficient, Ss

(cm�1) is the outer specific surface of the adsorbent per unitvolume of particle-free slurry. The values of b1 (Table 2) atdifferent temperatures (20, 30 and 40 �C) calculated fromthe slopes and the plots of ln(Ct/C0 � 1/1 + mK) versus t

(Fig. 4) showed that the velocity of mass transfer of Pb(II)on to maize bran was rapid enough (Singh et al., 1998) toconsider this adsorbent for the removal of Pb(II).

3.5. Effect of temperature

Experiments were performed at different temperature(20, 30 and 40 �C), keeping the other conditions the same.The percentage of adsorption decreased from 98.4 to 91.0with the increase of temperature from 20 to 40 �C at con-centration 100 mg l�1 and pH 6.5. Equilibrium time for20, 30 and 40 �C was also found to be 100 min; it indicated(Fig. 5) that the equilibrium time was independent of tem-perature. These results also showed the exothermic natureof adsorption (Singh et al., 2003; Sharma et al., 1991).The decrease in adsorption with the rise of temperaturemay be due to weakening of adsorptive forces betweenthe active sites of the adsorbent and adsorbate speciesand also between the adjacent molecules of the adsorbedphase (Pandey et al., 1986).

This was again confirmed by thermodynamic para-meters such as free energy (DG0, kcal mol�1), enthalpy

0 20 40 60 80 100 120-4

-3

-2

-1

0

ln(C

t/C0-

1/1+

mK

)

Time (min.)

20 °C30 °C40 °C

Fig. 4. Mass transfer plot for the adsorption of Pb(II) on maize bran atdifferent temperature. Conditions—concentration: 100 mg l�1; tempera-ture: 20, 30 and 40 �C; pH: 6.5; particle size: <178 lm.

Time (min.)

0 50 100 150 200 250

Am

ount

Ads

orbe

d (m

g l-1

)

1

2

3

4

5

6

20 °C30 °C40 °C

Fig. 5. Time variation plot for adsorption of Pb(II) on maize bran atdifferent temperatures. Conditions—concentration: 100 mg l�1; tempera-ture: 20, 30 and 40 �C; particle size: <178 lm; pH: 6.5.

Ce (mg l-1)

0 5 10 15 20 25 30 35

Ce/q

e (g

l-1)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

20 °C30 °C40 °C

Fig. 6. Langmuir isotherm plot for the adsorption of Pb(II) on maize branat different temperatures. Conditions—temperature: 20, 30, 40 �C; pH:6.5; concentration: 100, 110, 125, 140 and 150 mg l�1; particle size:<178 lm.

2128 K.K. Singh et al. / Bioresource Technology 97 (2006) 2124–2130

(DH0, kcal mol�1) and entropy (DS0, cal mol�1 K�1)changes during the process. These parameters (Table 3)were calculated by the method described by Singh et al.(1988) at 20, 30 and 40 �C temperatures. The negativeand small values of free energy change (DG0) were an indi-cation of the spontaneous nature of the adsorption process.The negative values of standard enthalpy change (DH0) forthe intervals of temperatures was indicative of the exother-mic nature of the adsorption process and the negative val-ues of DS0 for the corresponding temperature intervalssuggested the probability of favourable adsorption.

3.6. Adsorption isotherm

The experimental data was found to fit the Langmuirisotherm. The basic assumption of Langmuir adsorptionisotherm is based on monolayer coverage of the adsorbateon the surface of adsorbent. The saturated monolayer isrepresented by the following equation:

Ce

qe

¼ 1

Q0bþ Ce

Q0ð5Þ

where Ce (mg l�1) is the equilibrium concentration of theadsorbate, qe (mg g�1) is the amount of adsorbate adsorbedat equilibrium, Q0 (mg g�1) and b (l mg�1) is the Langmuirconstants related to the capacity and energy of the adsorp-tion, respectively. The linearity of the plots Ce/qe versus Ce

Table 3Values of thermodynamic parameters, Langmuir constants and RL values of P

Temperature (�C) �DG0 (kcal mol�1) �DH0 (kcal mol�1) �20 1.470

13.297 4030 1.067

18.344 5740 0.497

(Fig. 6) showed the applicability of the Langmuir isothermfor the present system. Q0 and b were determined from theslopes and intercepts of the respective plots. The decreasein their values (Table 3) with temperature increase also sup-ported that removal of Pb(II) on maize bran was exother-mic in nature (Sharma et al., 1991; Singh et al., 1998, 2003).High Q0 values (Table 3) also showed that the adsorbenthad a high capacity to remove Pb(II).

Heat of adsorption (DH, kcal mol�1) of the Pb(II) onmaize bran was determined using the following equation:

ln b ¼ ln b0 � DH=RT ð6Þwhere b (l mg�1) is the Langmuir constant related to the en-ergy of adsorption, b 0 is the constant and R (cal deg mol�1)and T (K) are gas constant and temperature, respectively.A negative value (�8.534 kcal mol�1) of DH confirmedthe exothermic nature of the process.

The equilibrium parameter RL which is defined asRL = 1/(1 + bC0) in the range 0 < RL < 1 reflects a favour-able adsorption process (Manju et al., 1999) where b

(l mg�1) is the Langmuir�s constant and C0 (mg l�1) is ini-tial adsorbate concentration. In the present investigationthe equilibrium parameter (Table 3) was found to be inthe range 0 < RL < 1 indicating that the adsorption processwas favourable and the Langmuir isotherm was applicable(Manju et al., 1999).

b(II) adsorption on wheat bran at different temperatures

DS0 (cal mol�1 K�1) Q0 (mg g�1) b (l mg�1) RL

0.959 0.0103142.86

.365140.85 0.542 0.0181

.019136.98 0.204 0.0467

K.K. Singh et al. / Bioresource Technology 97 (2006) 2124–2130 2129

3.7. Empirical model

In order to find out the rate of removal of Pb(II) froman aqueous solution by maize bran, the following empiricalmathematical model was developed using contact time forthe adsorption of Pb(II), t (min) and its initial and remain-ing concentration C0 and Ct (both in mg l�1), respectively:

logðt þ 1Þ ¼ KðC0 � CtÞA ð7Þwhere K and A are constants. The following relations fordifferent C0 have been found:

For C0 ¼ 100 mg l�1; logðt þ 1Þ ¼ 2:3692ðC0 � CtÞ1:1053

ð8ÞFor C0 ¼ 125 mg l�1; logðt þ 1Þ ¼ 2:9628ðC0 � CtÞ0:9833

ð9ÞFor C0 ¼ 150 mg l�1; logðt þ 1Þ ¼ 3:5180ðC0 � CtÞ0:9291

ð10Þ

The values of A and K were determined from the slopeand intercept of the plot log [log(t + 1)) versuslog (C0 � Ct). The plots of log (t + 1) versus (C0 � Ct)

A

(Fig. 7) were linear in each case showing the applicabilityof this model.

The log–log plot of K and C0 showed a straight line withthe following relationship:

K ¼ �1:5777C0:97650 ð11Þ

0 1 2 30

1

2

3

4

5

6

7

log(t+1)

(C0

-Ct)

A

100 mg l-1

125 mg l-1

150 mg l-1

Fig. 7. Empirical model plot for the adsorption of Pb(II) on maize branat different concentrations. Conditions—concentration: 100, 125 and150 mg l�1; pH: 6.5; particle size: <178 lm; temperature: 30 �C.

Table 4Percentage removal at different conditions (experimental and predicted values

Initial adsorbate concentration (mg l�1) Percentage removal

Experimental value Predicted v

100 96.6 97.9125 92.0 91.0150 85.7 86.5

The plot of A and C0 also showed a straight line with thefollowing relationship:

A ¼ 1:4464� 0:0035C0 ð12Þ

3.8. Multiple regression analysis

The effect of initial adsorbate concentration, contacttime, temperature and pH of the system on Pb(II) removalby maize bran had been examined. The cumulative effect ofall these independent variables (lead removal) are given bythe following relation:

Y ¼ 6:5594þ 0:6384a1 þ 0:5169a2 � 0:4680a3

þ 0:2834a4 � 0:0960a5 ð13Þ

where Y is the predicted value of Pb(II) removal; a1, con-centration of adsorbate; a2, contact time; a3, temperature;a4, pH; a5, agitation rate of the system. The model valuescalculated with the help of Eq. (13) and the experimentalvalues are given in Table 4. It may be seen that predictedvalues were pretty close to the experimental values.From these results it is concluded that all independent vari-ables have cumulative effect on lead removal by maizebran.

Fig. 8. Species distribution for the Pb(NO3)2 solution in the presence of0.1 M NaNO3.

at equilibrium time, pH 6.5 and agitation rate 125 rpm)

Temperature (�C) Percentage removal

alue Experimental value Predicted value

20 98.4 99.830 96.6 97.940 91.0 93.2

2130 K.K. Singh et al. / Bioresource Technology 97 (2006) 2124–2130

4. Conclusions

Maize bran was found to be an effective biosorbent forthe removal of Pb(II) from an aqueous solution. The studyshowed that the temperature and pH of the solutionstrongly influenced the adsorption process. Adsorption inthe initial stages was due to the boundary layer diffusionwhereas in the later stages adsorption was due to intrapar-ticle diffusion. Thermodynamic studies confirmed that theprocess was spontaneous and exothermic. The fit of theadsorption data into the Langmuir isotherm confirmedmonolayer adsorption.

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