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Journal of Hazardous Materials A121 (2005) 5158

Removal of cadmium from waagricultural waste rice

.H.lied Chi-22100aras H

ber 2002005

Abstract

A novel b l of cadcadmium(II) of 125parameters s nd temprocess were studied and the values of rate constant of adsorption, rate constant of intraparticle diffusion and mass transfer coefficient werecalculated. Different thermodynamic parameters, viz., changes in standard free energy, enthalpy and entropy have also been evaluated and it hasbeen found that the reaction was spontaneous and exothermic in nature. The applicability of Langmuir isotherm showed monolayer coverageof the adsorbate on the surface of adsorbents. A generalised empirical model was proposed for the kinetics at different initial concentrations.The data were subjected to multiple regression analysis and a model was developed to predict the removal of Cd(II) from wastewater. 2004 Else

Keywords: A

1. Introdu

Minimizresulting frBiosorptionheavy metadead cells)recognizedsuch as preliquid memwastewatereconomica

Corresponmobile: +91 9

E-mail adhasanitbhu@y

0304-3894/$doi:10.1016/jvier B.V. All rights reserved.

dsorption; Rice polish; Cadmium; Exothermic; Monolayer

ction

ing water pollution by toxic heavy metalsom human technological activities is challenging.

can be part of the solution. Biosorption ofls by bacterial fungal or algal biomass (live orand agricultural waste biomass [110] has beenas a potential alternative to existing technologiescipitation, ion exchange, solvent extraction andbrane for removal of heavy metals from industrialbecause these processes have technical and/or

l constraints.

ding author. Tel.: +91 542 2575758;415388484.dresses: kks [email protected] (K.K. Singh),ahoo.co.in (S.H. Hasan).

The literature reveals two distinct approaches to the use ofliving organisms and the use of a non-viable biomass [1113].There are significant practical limitations to the method,which employ living systems. Perhaps the most significantlimitation is that microbial growth is inhibited when the con-centrations of metal ions are too high or when significantamount of metal ions are adsorbed by microorganisms [11].Dead cells or agricultural wastes accumulate heavy metal ionsto the same or to a greater extent than living cells [1113].The reason for this is that the changes, which occur in thecell structure after the cells are dry-killed, affect adsorptionin a positive manner [14]. For metal removal applications,the use of dead biomass or agricultural waste may be prefer-able as large quantities are readily and cheaply available asa byproduct of various industries [15]. Therefore we havechosen rice polish (rice bran) for the removal of Cd(II) fromwastewater; because rice bran is cheap, easily available andmostly biodegradable.

see front matter 2004 Elsevier B.V. All rights reserved..jhazmat.2004.11.002K.K. Singh a, R. Rastogi b, Sa Water Pollution Research Laboratory, Department of App

Banaras Hindu University, Varanasb Department of Ceramic Engineering, Institute of Technology, Ban

Received 21 June 2004; received in revised form 31 OctoAvailable online 13 April

iosorbent rice polish has been successfully utilized for the removawas found to be 9.72 mg g1 at pH 8.6, initial Cd(II) concentrationuch as contact time, adsorbate concentration, pH of the medium astewater usingpolishHasan a,

emistry, Institute of Technology,5, Indiaindu University, Varanasi-221005, India

4; accepted 6 November 2004

mium(II) from wastewater. The maximum removal ofmg l1 and temperature of 20 C. The effect of differentperature were investigated. Dynamics of the sorption

52 K.K. Singh et al. / Journal of Hazardous Materials A121 (2005) 5158

2. Materials and methods

2.1. Physico-chemical analysis of the adsorbent

Rice polish is a byproduct of a rice milling plant. Ricepolish is biodegradable. Our sample were collected fromM/s Manoj Industries (rice mill), Chunar, Mirzapur (UP),and was used in experiments with double washing with dou-ble distilled water to remove soluble lighter materials anddrying at 60 C in an oven and crushing and sieving to

K.K. Singh et al. / Journal of Hazardous Materials A121 (2005) 5158 53

Fig. 1. Time variation plot for adsorption of Cd(II) on rice polish at initial concentration 100, 125 and 150 mg l1. Conditions: particle size,


Fig. 3. Intrap 0 C. CpH, 8.6; agita

where r (cmand t1/2 (mto the Mic1011 cm2rate determ(Table 2) omore thanthe intrapastep [22].intraparticlprocess.

3.3. Mass

The mamium(II) i30 and 40

ln(Ct

C0

= ln(

1 +where C0 ibate conceper unit voand b (Lancient, andunit volum

The val30 and 40ln(Ct/C0 of mass tra

to usedmium

Effect

perim20, 3

ed fro40 C5). Eqminenden

xothersorptiarticle diffusion plot for adsorption of Cd(II) on rice polish at 20, 30 and 4tion rate, 125 rpm.

) is the average radius of the adsorbent particlein) the time for half of the adsorption. Accordinghelsen et al. [22] a D value of the order ofs1 is indicative of intraparticle diffusion asining step. In this investigation, the values of Dbtained was in order of 109 cm2 s1 which wastwo orders of magnitude higher, indicated that

rticle diffusion was not the only rate controllingIt was concluded that both boundary layer ande diffusion might be involved in this removal

transfer analysis

[24]in ca

3.4.

Exturescreas

20 to(Fig.be 90indepthe ein adss transfer analysis for the adsorption of cad-on was determined at various temperatures (20,C) using the following equation [23]:

11 +mK

)

mK

mK

)(

1 +mKmK

)1Sst (4)

s the initial adsorbate concentration, Ct the adsor-ntration after time t, m the mass of the biosorbentlume, K the constant obtained by multiplying Q0gmuirs constants), 1 the mass transfer coeffi-Ss the outer specific surface of the adsorbate pere.ues of 1 (Table 2) at different temperatures (20,C) calculated from the slopes and the plots of1/1 +mK) versus t (Fig. 4) suggest that the ratensfer of Cd(II) on to rice polish was rapid enough

weakeningthe adsorbeadjacent m

The varto temperathermodynenergy (Gwere calcu

(i) G

(ii) H

(iii) S

where R isscale andtemperaturparametersonditions: concentration, 125 mg l1; particle size,


Fig. 4. Massagitation rate,

Fig. 5. Timeagitation rate,

obvious froof free enenature of thdard enthalshowed thethe negativintervals su

Table 3Thermodynam

Temperature (203040transfer plot for adsorption of Cd(II) on rice polish at 20, 30 and 40 C. Condition125 rpm.

variation plot for adsorption of Cd(II) on rice polish at 20, 30 and 40 C. Condition125 rpm.

m this table that the negative and small valuesrgy change (G) is an indication of spontaneouse adsorption process. The negative values of stan-py change (H) for the intervals of temperaturesexothermic nature of the adsorption process and

e values ofS for the corresponding temperatureggested the probability of favorable adsorption.

3.5. Adsor

In theto fit theLangmuircoverage osaturated m

ic parameters for adsorption of Cd(II) on rice polish at different temperaturesC) G (kcal mol1) H

2.048 18.5891.4841.141 11.853s: concentration, 125 mg l1; particle size,


Fig. 6. Langm C. Coparticle size

[28]:Ce

qe= 1Q0b

where Ce iqe the amoand b the Lenergy ofplots Ce/qeLangmuirdeterminedplots anddecreased w

Heat ofdetermined

ln b = ln b

where b (menergy ofgas constan(7.075 kcof the proc

The eqRL = 1/(1 +adsorptionlibrium par

Table 4Values of Lan

Temperature (203040

wn infavora

Effect

perimnd 10.an incased f.0, atptimu

Fig. 7)nt use

when muir isotherm plot for adsorption of Cd(II) on rice polish at 20, 30 and 40


Fig. 7. Effect oncentagitation rate,

3.7. Empir

In orderwastewatermatical moand initialmg l1) oflog(t + 1)where K adifferent C

ForC0 = 1log(t +

ForC0 = 1log(t +

ForC0 = 1log(t +

The valuesintercept o

of logested te logg the

0.086

lot ofg rela

0.859

pplicamount

Multip

Table 5Percentage re

Initial adsorba

100125150of pH on the removal of Cd(II) by adsorption on rice polish. Conditions: c125 rpm.

ical model

to find out the rate of removal of Cd(II) fromby rice polish, the following empirical mathe-del was developed between contact time (min)and remaining concentration C0 and Ct (both inCd(II), respectively:= K(C0 Ct)A (10)nd A are constants. The following relations for0, was developed:

00 mg l1 :

1) = 0.4725(C0 Ct)0.7846 (11)

plotssugg

Thhavin

K =The plowin

A =The athe a

3.8.25 mg l1 :

1) = 0.5561(C0 Ct)0.7633 (12)

50 mg l1 :

1) = 0.6072(C0 Ct)0.7469 (13)of A and K were determined from the slope and

f the plot log[log(t+ 1)] versus log(C0 Ct). The

We havecontact timremoval byindependenfollowing r

Y = 2.243+0.37

where Y isconcentrati

moval at different conditions on experimental and predicted values at equilibrium t

te concentration (mg l1) Percentage removal TExp. value Predicted value

96.80 98.54 2092.16 90.59 3085.87 85.29 40ration, 125 mg l1; particle size, 178m; temperature, 30 C;

(t+ 1) versus (C0 Ct)A was linear in each casehe applicability of the above model.log plot of K and C0 produces a straight linefollowing relationship:

5C0.76890 (14)A and C0 also gives straight line having the fol-

tionship:

1 0.0008C0 (15)bility of the proposed model is helpful to calculateof Cd(II) adsorbed.

le regression analysisseen the effect of initial adsorbate concentration,e, temperature and pH of the system on Cd(II)rice polish. The cumulative effect of all these

t variables (cadmium removal) are given by theelation:

6 + 0.5880a1 + 0.4646a2 0.6023a372a4 + 0.0841a5 (16)the predicted value of Cd(II) removal; a1 the

on of adsorbate; a2 the contact time; a3 the

ime, pH 8.6 and agitation rate 125 rpmemperature (C) Percentage removal

Exp. value Predicted value

96.48 95.4092.16 90.5986.60 85.78


temperature; a4 the pH; a5 the agitation rate of the system.The model values calculated with the help of Eq. (16) andthe experimental values are given in Table 5. It may be seenthat predicted values are pretty close to the experimentalvalues. From these results it is concluded that all independentvariables have cumulative effect on the cadmium removalby rice polish.

4. Conclusion

Rice polish has been found to be a very effective biosor-bent for the removal of Cd(II) from wastewater. The maxi-mum removal of cadmium(II) was found to be 9.72 mg g1 atpH 8.6, initial Cd(II) concentration of 125 mg l1 and temper-ature of 20 C. The removal of cadmium was rapid in initialstages and became slower afterwards; it was also confirmedby mass transfer studies. The double nature of the curves wereattributed to the fact that the adsorption in the initial stageswas due tostages adsomodynamiand exotheisotherm co

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Removal of cadmium from wastewater using agricultural waste 'rice polish'IntroductionMaterials and methodsPhysico-chemical analysis of the adsorbentExperimental procedure

Results and discussionEffect of contact time and concentrationAdsorption dynamicsMass transfer analysisEffect of temperatureAdsorption isothermEffect of pHEmpirical modelMultiple regression analysis

ConclusionReferences

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