Bioabsorpsi Asam Jawa

8/13/2019 Bioabsorpsi Asam Jawa

1/8

Biosorption of aqueous chromium(VI) by Tamarindus indica seeds

G.S. Agarwal a , Hitendra Kumar Bhuptawat b , Sanjeev Chaudhari b, *a MP Public Health Engineering Department, Bhopal, MP, India

b Centre for Environmental Science and Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai 400 076, India

Received 28 January 2005; received in revised form 6 April 2005; accepted 8 April 2005Available online 16 June 2005

Abstract

The effectiveness of low cost agro-based materials namely, Tamarindus indica seed (TS), crushed coconut shell (CS), almond shell(AS), ground nut shell (GS) and walnut shell (WS) were evaluated for Cr(VI) removal. Batch test indicated that hexavalent chro-mium sorption capacity ( qe) followed the sequence qe(TS) > qe(WS) > qe(AS) > qe(GS) > qe(CS). Due to high sorptive capacity, tam-arind seed was selected for detailed sorption studies. Sorption kinetic data followed rst order reversible kinetic t model for all thesorbents. The equilibrium conditions were achieved within 150 min under the mixing conditions employed. Sorption equilibriaexhibited better t to Freundlich isotherms ( R > 0.92) than Langmuir isotherm ( R 0.87). Hexavalent chromium sorption byTS decreased with increase in pH, and slightly reduced with increase in ionic strength. Cr(VI) removal by TS seems to be mainlyby chemisorption. Desorption of Cr(VI) from Cr(VI) laden TS was quite less by distilled water and HCl. Whereas with NaOH, max-imum desorption achieved was about 15.3%. When TS was used in downow column mode, Cr(VI) removal was quite good buthead loss increased as the run progressed and was stopped after 200 h.

2005 Elsevier Ltd. All rights reserved.

Keywords: Chromium(VI); Adsorption; Tamarindus indica ; Low cost biosorbent

1. Introduction

Heavy metals such as chromium, copper, lead, cad-mium, etc., in wastewater are hazardous to the environ-ment. Because of their toxicity, their pollution effect onour ecosystem presents a possible human health risk(Nourbakhsh et al., 1994 ). In recent years, increasingawareness of water pollution and its far reaching effectshas prompted concerted efforts towards pollution abate-

ment. Among the different heavy metals, chromium is acommon and very toxic pollutant introduced into natu-ral waters from a variety of industrial wastewaters(Donmez and Aksu, 2002 ). The two major sources of contamination are electroplating, metal nishing indus-

tries (hexavalent chromium) and tanneries (trivalentchromium). Chromium occurs most frequently asCr(VI) or Cr(III) in aqueous solutions ( Dakiky et al.,2002 ). Both valences of chromium are potentially harm-ful but hexavalent chromium poses a greater risk due toits carcinogenic properties ( Dakiky et al., 2002 ). Hexa-valent chromium, which is primarily present in the formof chromate CrO 24 and dichromate Cr 2O

27 , poses

signicantly higher levels of toxicity than the other va-

lency states ( Sharma and Forster, 1995 ).Conventional methods for removing Cr(VI) ionsfrom industrial wastewater include reduction ( Kim etal., 2002 ), reduction followed by chemical precipitation(Ozer et al., 1997 ), adsorption on the activated carbon(Lot and Adhoum, 2002 ), solvent extraction ( Mauriet al., 2001 ) cementation, freeze separation, reverseosmosis ( Padilla and Tavani, 1999 ), ion-exchange(Rengaraj et al., 2003 ) and electrolytic methods ( Namas-ivayam and Yamuna, 1995 ). These methods have found

0960-8524/$ - see front matter 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.biortech.2005.04.030

* Corresponding author. Tel.: +91 22 25767855; fax: +91 2225723480.

E-mail address: [email protected] (S. Chaudhari).

Bioresource Technology 97 (2006) 949956
mailto:[email protected]:[email protected]


2/8

limited application because they often involve highcapital and operational costs. Adsorption is an effectiveand versatile method for removing chromium. Naturalmaterials that are available in large quantities, or certainwaste products from industrial or agricultural opera-tions, may have potential as inexpensive sorbents. Due

to their low cost, after these materials have been ex-pended, they can be disposed of without expensiveregeneration. Most of the low cost sorbents have thelimitation of low sorptive capacity and thereby for thesame degree of treatment, it generates more solid waste(pollutant laden sorbent after treatment), which posesdisposal problems. Therefore, there is need to explorelow cost sorbent having high contaminant sorptioncapacity.

Several recent publications utilized locally availableadsorbents e.g. y ash, peat, microbial biomass ( Baiand Abraham, 2003; Nourbakhsh et al., 1994 ) and agri-cultural byproducts ( Bailey et al., 1999 ) for heavy metalremoval. However, the literature is still insufficient tocover this problem and more work and investigationsare needed to deal with other locally available and cheapadsorbents to eliminate Cr(VI) from industrial composi-tions and characteristics. Tamarind ( Tamarindus indica )is a common tree in tropical countries. It is grownmainly for its sour fruits pulp. Tamarind seed, a byproduct of the tamarind pulp industry, is an underuti-lized or waste material ( Bhattacharya et al., 1997 ). Liter-ature survey by the author in most of the peer reviewed journals indicated that adsorption study of Cr(VI) withTamarind seed as an adsorbent has not been investi-

gated and this is the rst such study undertaken by theauthors.

This study aims at comparative evaluation of agro-based materials, namely T. indica (tamarind) seed(TS), almond shell (AS), ground nut shell (GS), walnutshell (WS), and crushed coconut shell (CS) for removalof Cr(VI) from simulated industrial wastewater. Basedon their efficacy, tamarind seed was selected for furtherstudy. The effect of pH, contact time, adsorption equi-libria and temperature were investigated. Desorptionof Cr(VI) from Cr(VI) laden TS was also attempted.Further continuous wastewater treatment was done incolumn mode to assess the viability of TS for continuousoperation.

2. Methods

All the chemicals used were of analytical grade.Cr(VI) concentrations in aqueous phase were estimatedby diphenyl carbazide method as per standard methods(APHA, 1985 ). AIMIL colorimeter with green lter(540 nm) was used for colorimetric measurement. TheCr(VI) loadings on sorbents were computed based onmass balance through loss of metal from aqueous solu-

tion. The pH of solution was maintained using acetateand sodium tetra borate buffer. The initial Cr(VI) con-centration was maintained by adding stock solution of chromium.

2.1. Preparation of biosorbents

The sorbents used were crushed coconut shell, al-mond shell, ground nut shell, walnut shell and tamarindseed. All the materials were obtained from local market;materials were washed, dried and then pulverized in pul-verizer and air-dried in the sun for two days. After dry-ing, the materials were kept in air tight plastic bottles.All the materials were used as such and no pretreatmentwas given to the materials. The particle size was main-tained in the range of 212300 l m (geometric mean size:252.2 l m).

2.2. Screening of biosorbents

For the comparative evaluation of different sorbentsfor Cr(VI) removal capacity, the experiments were con-ducted in 150 ml double stoppered polyethene bottles at28 C on a rotary shaker at 70 rpm. Experiments wereconducted at pH 4, 6 and 9 and initial Cr(VI) concentra-tion of 10 mg/l was maintained. After 4 h of mixing, thesamples were ltered through Whattman No. 42 lterpaper, and ltrates were analysed for residual chromiumconcentration.

2.3. Sorption kinetics

Sorption studies were conducted in 150 ml polyethenebottles at 2728 C on a rotary shaker at 70 rpm. Thechromium concentration was maintained by addingappropriate quantity of stock solution of K 2Cr 2O7.The ionic strength of the aqueous phase was adjustedby adding appropriate quantity of KNO 3 . The samplebottles were taken out at different time intervals andsamples were ltered through Whattman No. 42 lterpaper. The ltrates were analysed for residual chromiumconcentration and pH. Sorption experiments were con-ducted for TS, GS, WS at pH of 4, 6 and 9 for initialchromium concentration of 10 mg/l.

2.4. Sorption equilibria

Batch sorption experiments were conducted in 150 mlpolyethene double stoppered bottles at 28 C on a rotaryshaker (70 rpm) for mixing. The pH values were ad- justed using acetate buffer or sodium tetra borate bufferbefore addition of biosorbent and were maintainedthroughout the experiments. The sorption equilibriaexperiments were performed for different pH conditionsand for different sorbents. The aqueous solution wasmixed till equilibrium time of 180 min. After equilibrium

950 G.S. Agarwal et al. / Bioresource Technology 97 (2006) 949956


3/8

time, the sample bottles were taken out for the analysisof residual chromium concentration in the solution.

3. Results and discussion

3.1. Screening of biosorbents

Preliminary experiments were conducted with initialCr(VI) concentration of 10 mg/l and biosorbents doseof 2 g/l at different pH. The results are presented inFig. 1 . At pH 4, the Cr(VI) removal was 30%, 36%,35%, 40%, and 80% for CS, AS, GS, WS, and TS respec-tively, which at pH 6 decreased to 22%, 24%, 23%, 27%and 64%. It further decreased at pH 9. These prelimin-ary results indicated the higher Cr(VI) removal capacityof tamarind seeds in the pH range of 49, as comparedto other biosorbents. The sequence of Cr(VI) removalwas TS > WS > AS > GS > CS. Though percentage re-moval of Cr(VI) decreased with increase in pH, butthe sequence remained same.

3.2. Sorption kinetics

To evaluate sorption as a unit operation, it requiresconsideration of two important physico-chemical as-pects of the process, the kinetics and the equilibria of sorption. Kinetics of sorption describing the solute up-take rate, which in turn governs the contact time, isone of the important characteristics dening efficiencyof sorption. The study of the equilibrium established

in any liquidsolid system is important in determiningdistribution of the solute between the solid and liquidphases and determining feasibility and capacity of thesorbent for sorption.

The rate at which dissolved heavy metal ions are re-moved from dilute aqueous solution by solid sorbents

is a signicant factor for application in water qualitycontrol. The rate at which sorption proceeds is impor-tant in terms of the contact time to be provided betweenthe solution and the sorbent. The capacity of the sorbentfor the uptake of sorbate i.e., the position at which equi-librium is attained determines the useful life of sorbent

to a large extent.Fig. 2 shows the adsorption of Cr(VI) by tamarindseed, walnut shell, almond shell and groundnut shellbiosorbents as a function of time at pH of 4.04.25 forinitial Cr(VI) concentration of 10 mg/l. Tamarind doseof 2 g/l was used while 3 g/l dose of other sorbents wereused. Fig. 2 shows rapid adsorption in the initial 20 minfor all biosorbent. The initial high adsorption rate de-creased gradually as the equilibrium approached. Equi-librium time was approximately 60 min for groundnut,while for walnut and tamarind seed, it was 120 and150 min respectively. Cr(VI) removal was found to be90% at 60 min, 95% at 120 min and 98% at 180 minfor tamarind seed.

The effect of pH on the rate of Cr(VI) sorption wasinvestigated at different pH for tamarind seed as indi-cated in Fig. 3 . It is interesting to note that rate of sorp-tion is more at lower pH. This may be due to differencein the speciation of Cr(VI) and pore density (morphol-ogy) of sorbents at different pH. The likely effect of pH on Cr(VI) adsorption has been discussed under Sec-tion 3.4.

The rate constant for the sorption of Cr(VI) on tam-arind seed was evaluated using the Lagergen equation(Orhan and Buyukgungor, 1993; Selvaraj et al., 2003 )

ln1 U t K a t 1where U t qqe is called the fractional attainment of equilibrium. qe and q are the amount of Cr(VI) adsorbed(mg/g) at equilibrium and at time t, respectively, k a is therst order rate constant and t is the time (min). The plots

0

10

20

30

40

50

60

70

80

90

Sorbents

F r a c t

i o n

S o r b e d

( % )

pH = 4 pH = 6 pH = 9

CS AS GS WS TS

GMS = 252.2 ;Initial Cr(VI) conc. = 10 mg/l;Sorbent dose = 2 g/l;

Temp. = 26-27

C;contact time = 3 hrs

Fig. 1. Comparative evaluation of different biosorbents.

0

20

40

60

80

100

120

140

0 50 100 150 200 250 300 350 400

Time (min)

% o

f C r (

V I ) s o r b

e d

Walnut shell Groundnut shell Almond shell Tamarind seed

Fig. 2. Sorption kinetics of Cr(VI) for TS, AS, GS, and WS.

G.S. Agarwal et al. / Bioresource Technology 97 (2006) 949956 951


4/8

of ln( qe q) versus t were linear (not shown) for the bio-sorbents and indicated that the adsorption can beapproximated to rst order reversible kinetics. The rateconstants determined from the slopes of the plots wereobtained as TS: 0.0767 min 1 , GS: 0.0433 min 1 , WS:0.0142 min 1 , AS: 0.0135 min 1 .

3.3. Adsorption isotherms

The adsorption data were tted by least square meth-od to linearly transformed Freundlich and Langmuiradsorption isotherms. The linearised Freundlich equa-tion is mentioned below.

log qe log K f 1n

log C e 2

where qe is the amount of Cr(VI) adsorbed per unit massof biosorbent (mg/g), C e is the residual concentration of Cr(VI) in solution (mg/l), K f is a constant which is a

measure of adsorption capacity and (1/ n) is a measureof adsorption intensity.

The linear form of the Langmuir adsorption isothermis represented as

C eqe

1Q0b

C eQ0

3

where C e is the equilibrium concentration (mg/l), and qeis the amount of Cr(VI) adsorbed per gram at equilib-rium (mg/g). Q0 (mg/l) and b (l/mg, i.e., l of adsorbentper mg of adsorbate) are Langmuir constants relatedto the adsorption capacity and energy of adsorption,respectively.

The data obtained from the adsorption experimentsconducted at 29 C were tted to Eqs. (2) and (3) , linearplot (not shown) were obtained for log( qe) versus log( C e)and C e/qe versus C e. The isotherm parameters for bothequation along with the values of coefficient of correla-tion ( R) and standard error of estimate ( r ) are presentedin Table 1 . Table shows that data better ts to Freund-lich equation than Langmuir equation, which is indi-cated from the higher values of R and lower values of r .

3.4. Effect of pH on sorption

Aqueous phase pH governs the speciation of metalsand also the dissociation of active functional sites onthe sorbent. Hence, metal sorption is critically linkedwith pH. Not only different metals show different pHoptima for their sorption but may also vary from onekind of biomass to the other ( Tiwari et al., 1995; Ucun

et al., 2002 ). Fig. 4 shows the sorption isotherms at dif-ferent pH. It can be observed from the gure that theuptake of Cr(VI) decreases with increase in pH. In gen-eral, the Cr(VI) adsorption by different biosorbents haveshown similar trend and the optimum pH 2 has been re-ported ( Donmez and Aksu, 2002; Dakiky et al., 2002;Selvaraj et al., 2003; Yu et al., 2003; Ucun et al., 2002;Hu et al., 2003; Gupta et al., 2001 ). The highest sorption

0

20

40

60

80

100

120

0 100 200 300 400

Time (min)

% o

f C r (

V I ) s o r b e

d

pH = 4 pH = 6 pH = 9

Sorbent dose = 2 g/l

Fig. 3. Sorption kinetics of Cr(VI) at different pH for tamarind seed.

Table 1Estimated Freundlich and Langmuir isotherm parameters and relevant statistical information for Cr(VI) sorbents system

Sorbent pH Ionic strength Initial soluteconcentrationC 0 (mg/l)

Sorbentdose (g/l)

Freundlich isotherm Langmuir isotherm

K f 1/n r R 1/Q0 1/bQ 0 r R

GS 4.0 0.01 10 3 0.3239 0.8730 0.0648 0.9759 0.170 2.852 0.1173 0.98794.0 0.01 10 5 0.1978 1.0541 0.0870 0.9639 0.06 5.100 0.1694 0.9915

WS 4.0 0.01 10 3 0.9866 0.4392 0.0667 0.9550 0.4384 0.341 0.1629 0.91684.0 0.01 10 5 1.0873 0.2924 0.0307 0.9790 0.05421 0.2137 0.1038 0.9214

AS 4.0 0.01 10 3 0.6134 0.6020 0.1025 0.9200 0.04536 0.8560 0.2509 0.87614.0 0.01 10 5 1.3326 0.3022 0.0387 0.9716 0.4152 0.2329 0.04382 0.9877

TS 2.0 0.01 50 0.53.5 4.9910 0.2403 0.02348 0.9905 0.0102 0.0079 0.00149 0.96834.0 0.01 50 0.53.5 2.5320 0.3830 0.0165 0.9964 0.0181 0.0177 0.00395 0.95236.0 0.01 50 0.53.5 2.0982 0.7591 0.02963 0.9782 0.0125 0.1175 0.00392 0.97688.0 0.01 50 0.53.5 3.0615 0.4419 0.01253 0.9821 0.04343 0.8563 0.0025 0.9785



5/8

capacity of TS for Cr(VI) was at pH 2 and the decreasein sorption capacity with increase in pH may be attrib-uted to the changes in metal speciation and the dissoci-ation of functional groups on the sorbent. Ucun et al.(2002) have reported that the pH dependence of metaluptake could be largely related to the various functionalgroups on the adsorbent surface along with metal solu-tion chemistry.

The pH of zero point charge (pHZPC) of tamarindseed was determined by fast alkalimetric titration method.In absence of specic chemical interaction between the

single electrolyte and the surface, the net titration curvesusually meet at a point that is dened as the pHZPC(pH of zero point charge). The net titration curves fortamarind seed were plotted to obtain pH of zero pointcharge. The value of pHZPC of tamarind seeds wasfound to be 6.00. The pH ZPC (zero point of charge) of tamarind seed is 6.0, i.e., below this pH, the surfacecharge of the adsorbent is positive and above pH 6,tamarind seed would have a net negative charge.

The composition of tamarind seeds powder as re-ported by Siddhuraju et al. (1995) is as: crude protein11.914.1%; crude lipid 67.74%; crude bre 12.7 15.3%; moisture 79.14%; and ash 3.454.7%. It ishydrophilic in nature. Tamarind seeds are a rich sourceof protein and amino acids ( Marathe et al., 2002; Sid-dhuraju et al., 1995 ). Some functional groups, such asamines, are positively charged when protonated andmay electrostatically bind with negatively charged metalcomplexes. The decrease in the adsorption with increaseof pH may be due to the decrease in electrostatic forceof attraction between the sorbent and sorbate ions. Atlower pH ranges, due to the high electrostatic force of attraction, the percentage of Cr(VI) removal is high.At very low pH value, the surface of sorbent would alsobe surrounded by the hydronium ions which enhance

the Cr(VI) interaction with binding sites of the bio-sorbents by greater attractive forces. A sharp decreasein adsorption above pH 4 may be due to occupationof the adsorption sites by anionic species likeHCrO 4 ; Cr 2O

27 ; CrO

24 , etc., which retards the ap-

proach of such ions further toward the sorbent surface

(Das et al., 2000; Donmez and Aksu, 2002 ). The de-crease in adsorption at high pH values may be due tothe competitiveness of the oxyanion of chromium andOH ions in the bulk. As the pH increased, the overallsurface charge on tamarind seed became negative andbiosorption decreased. Marathe et al. (2002) have re-ported that tamarind seed have excellent stability overacidic pH range.

3.5. Effect of ionic strength

Ionic strength, besides pH is also one of the impor-tant factors that inuence the equilibrium uptake. Effectof ionic strength on Cr(VI) sorption is shown in Fig. 5 .It is clear from the gure that Cr(VI) removal decreaseswith increasing ionic strength though the decrease isinsignicant at lower ionic strength. But, it is slightlysignicant at ionic strength greater than 0.5 M. In gen-eral, adsorption decreases with increasing ionic strengthof the aqueous solution ( Donmez and Aksu, 2002 ). Thisbehaviour may be due to the competition between an-ions of salt with chromate anions sorbed on the activecentre of tamarind seed. This may also be due to thelowering in chromate anions CrO 24 , a reduction incolumbic attraction, for chromate species on solid sur-

faces and/or to the presence of competing anions. Theresults indicate the possibility that adsorption of Cr(VI)on tamarind seed is mainly by chemisorption rather

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50

Equilibrium Concentration (mg/l)

m g o

f C r (

V I ) r e m o v a

l / s o r b e n

t w

t , q e ,

m g

/ g pH = 2 pH = 4 pH = 6pH = 7 pH = 8

Fig. 4. Effect of pH on Cr(VI) sorption by tamarind seed.

0

10

20

30

40

50

60

70

80

0 10 20 30

Equilibrium Concentration (mg/l)

m g o

f C r (

V I ) r e m o v a

l / s o r

b e n

t w

t , q e ,

m g

/ g

IS = 0.001 M IS = 0.1 MIS = 0.5 M IS = 1.0 M

Initial Cr(VI) conc. = 50 mg/lpH = 4, Temp. = 24-25

C

Fig. 5. Effect of ionic strength on Cr(VI) sorption by tamarind seed.



6/8

than physical sorption as effect of ionic strength is not sosignicant on the Cr(VI) removal capacity.

3.6. Effect of temperature

Temperature dependence of the adsorption process is

associated with several thermodynamic parameters. Fig.6 shows an increasing trend of Cr(VI) removal with therise in temperature from 12 to 58 C. The reason may bethat, at high temperature some polymers might have re-leased from the sorbent which assist in adsorption, be-cause the tamarind seed contains some free sugars.The increase in Cr(VI) uptake may also be due to crea-tion of some new sorption sites on the sorbent surface orthe increased rate of intraparticle diffusion of sorbateions into the pores of adsorbent at higher temperature,as diffusion is an endothermic process ( Das et al.,2000; Guo et al., 2002 ). Up to certain extent, enhance-ment of adsorption capacity of tamarind seed at highertemperatures may be attributed to enlargement of poresize and/ or activation of the adsorbent surface ( Namas-ivayam and Yamuna, 1995 ).

3.7. Effect of particle size

Effect of particle size on Cr(VI) sorption capacity of tamarind seed, walnut shell and groundnut shell are

shown in Table 2 . It is evident from the table that par-ticle size of sorbents has a signicant effect on Cr(VI)sorption. The larger sorbent size showed lesser Cr(VI)removal as compared to the smaller sorbent size. Thereason may be that surface area available for adsorptiondecreases with the increase of particle size for the same

dose of sorbent, providing less active surface sites foradsorption of sorbate. The reduction in Cr(VI) removalcapacity with increase in sorbent size gives an idea aboutthe porosity of sorbent i.e., if the sorbent is highly por-ous then it would not have signicant effect on Cr(VI)removal at equilibrium. The results obtained are inaccordance with adsorption/ion-exchange processes,where smaller particles of sorbents/ion exchanger en-hance the rate of metal uptake.

3.8. Cyclic sorption (continuous loading)

Experiments were conducted with TS to observe thepossibility of removal of Cr(VI) by spent sorbent. It isobvious from the sorption equilibria plots that sorptioncapacity qe decreases with equilibrium concentration C e.The regulatory C e is quite low. Therefore, when the bio-sorbent is used in both batch mode or in a CSTR (con-tinuous ow stirred tank reactor) for removal of acontaminant, the qe is quite less and thereby if countercurrent system is designed then spent sorbent can be re-used. To assess the Cr(VI) removal capacity of the spentsorbent, cyclic sorption test was conducted. For the cyc-lic loading of Cr(VI), 500 mg of TS was contacted with

100 ml of Cr(VI) solution having concentration of 50 mg/l for 1 h. The cycle was repeated for 10 times atpH: 4 and temperature: 24 C. At the end of every cycle,metal solution was ltered and the metal concentrationdetermined. The total amount of Cr(VI) sorbed on TS(in mg/g of TS) was 16.0, 31.0, 41.0, 44.5, and 45.0 after2nd, 4th, 6th, 8th and 10th cycle, respectively. Thisobservation indicates that TS was able to adsorb Cr(VI)ions even up to the 9th cycle, though the extent of metalsorption has gradually decreased. The results of theabove experiments indicate the possible reusability of spent sorbent without regeneration. However, the tama-rind seed is a low cost material and can be used on useand throw basis. Moreover, regeneration of sorbentmight not be economical as the cost of regenerationchemical might be signicant. Thereby, if Cr(VI) sorp-

Table 2Effect of particle size on Cr(VI) removal

Particle sizerange ( l )

GMS ( l ) Tamarind seed (%) Walnut shell (%) Groundnut shell (%) Remarks

150212 178.0 96.75 82.5 50 Initial Cr(VI) = 10 mg/l, pH = 4,temperature = 2930 C, sorbent dose,TS = 2 g/l, WS = 3 g/l, and GS = 3 g/l

212300 252.2 90 50 45300425 357.0 56.5 40 23

0

20

40

60

80

100

0 5 10 15 20Equilibrium Concentration (mg/l)

m g o

f C r (

V I ) r e m o v a

l / s o r b e n

t w

t , q e , m g

/ g

T = 10 C T = 20 CT = 28 C T = 48 C

Initial Cr(VI) conc. = 50 mg/lpH = 4,

Ionic strength = 0.01 M

Fig. 6. Effect of temperature on Cr(VI) sorption by tamarind seed.



7/8

tion is maximized then it would be advantageous for thesystem operation.

3.9. Column experiments

Downow column studies were conducted to evalu-ate the sorption behaviour of TS for chromium removalin a continuous mode. The time to breakthrough as wellas nal effluent concentration at four different bedheights of TS viz. 20, 35, 50 and 65 cm were studiedand the breakthrough time were 12 h, 28 h, 42 h and60 h respectively. After 200 h of column operation, thehead loss across the sorbent bed was increased to quitehigh values and then the operation was stopped due tochoking of TS bed. The overall system was capable of treating 195 l of 10 mg/l of chromium solution beforeany choking at initial ow rate of 0.76 m 3/m 2/h. Thisindicates that the tamarind seed can be effectively used

for chromium(VI) removal in column operation also.

3.10. Desorption and regeneration

Sorption of solute on any sorbent can either be byphysical bonding, ion-exchange or combination of both.If the adsorption is by physical bonding then the looselybound solute can be easily desorbed with distilled waterin most of the cases. However, if the mode of sorption isby chemical bonding or ion-exchange or combination of the both, then the desorption can be effected by strongerdesorbents like acid or alkali solutions.

Attempts were made to desorb Cr(VI) from previ-ously Cr(VI) loaded tamarind seed using double distilledwater (pH 6.6). Cr(VI) recovery was not observed.Hence, experiments were conducted with acid and alkalisolutions to desorb Cr(VI) ions. The results obtained(not shown) indicate that the desorption of Cr(VI) ionswith acid was not achieved even when 0.1 N HCl and0.2 N HCl were used. However, there was very littledesorption with alkali solutions. It was found thatCr(VI) desorption was 2.7%, 4.5% and 6.7% with0.1 N NaOH at 1 h, 4 h and 24 h contact time respec-tively, whereas with 0.2 N NaOH, the percentagedesorption of chromium(VI) was 4.5%, 11% and 15.3%respectively at 1 h, 4 h and 24 h contact period.

From the results of desorption studies, the followinginference may be made. The negligible desorption of Cr(VI) with double distilled water indicates the predom-inance of chemical bonding between tamarind seed andCr(VI). This implies that physical adsorption is notplaying signicant role in Cr(VI) removal by TS. The re-sults of alkali desorption of metal suggest either chemi-sorption or ion-exchange as the possible mechanism of metal solution (0.2 N NaOH), about 84.7% of Cr(VI)still remained on sorbent, which indicates that most of the Cr(VI) ions are able to form strong bonds with TS.

3.11. Comparison with other sorbents

In the present study, TS has been compared withother sorbents based on their maximum sorptive capac-ity for Cr(VI). From Fig. 6 , it can be observed thatCr(VI) sorption capacity for tamarind seed is 90 mg/g

at equilibrium Cr(VI) concentration of 2.5 mg/l at pH2. Hu et al. (2003) reported Cr(VI) sorptive capacity inthe range of 3040 mg/g for three different commercialactivated carbon at equilibrium Cr(VI) concentrationof 310 mg/l at pH 3. Granulated activated carbonand brous activated carbon have approximately10 mg/g of Cr(VI) at equilibrium Cr(VI) concentrationof 35 mg/l ( Aggarwal et al., 1999 ). Lot and Adhoum(2002) have reported a Cr(VI) removal capacity of 6.84 mg/g for modied activated carbon (sodium diethyldithiocarbamate immobilized at the surface), which wasalmost two times that of plain activated carbon. Themaximum adsorption capacities of Cr(VI) removal re-ported by Bailey et al. (1999) are 16.05 mg/g for saw-dust, and 0.65 mg/g for zeolite. Donmez and Aksu(2002) have reported a maximum Cr(VI) removal capac-ity of 17.7 mg/g for hazelnut shell biomass at pH 2.0.Accordingly, it can be stated that TS has high sorptivecapacity in comparison to other available sorbents.

4. Conclusions

Following conclusions are made based on the resultsof present study and scientic information derived fromliterature:

1. The biosorbents evaluated viz. CS, AS, GS, WS andTS can remove hexavalent chromium from aqueousphase. Tamarind seed has high Cr(VI) removalcapacity than the other sorbent and can reduce aque-ous phase Cr(VI) concentration up to non-detectablelevel.

2. The removal of Cr(VI) ions by tamarind seed signi-cantly decreased with increase in pH, slightlydecreased with increase in ionic strength and increasedwith increase in temperature. The Cr(VI) removalappears to be mainly by chemisorption.

3. Desorption of Cr(VI) from TS was partially achievedunder alkaline conditions.

4. The use of tamarind seed as an adsorbent seems to bean economical and worthwhile alternative over con-ventional methods.

References

Aggarwal, D., Goyal, M., Bansal, R.C., 1999. Adsorption of chromium by activated carbon from aqueous solution. Carbon37 (12), 19891997.



8/8

APHA, 1985. Standard Methods for the Examination of Waste andWastewater, 16th ed., American Public Health Association,Washington, DC.

Bai, R.S., Abraham, E., 2003. Studies on chromium(VI) adsorption desorption using immobilized fungal biomass. Bioresource Tech-nology 87 (1), 1726.

Bailey, S.E., Olin, T.J., Bricka, R.M., Adrian, D., 1999. A review of potentially low-cost sorbents for heavy metals. Water Research 33(11), 24692479.

Bhattacharya, S., Bal, S., Mukherjee, R.K., Bhattacharya, S., 1997.Kinetics of tamarind seed hydration. Journal of Food Engineering33 (12), 129138.

Dakiky, M., Khami, A., Manassra, A., Mer eb, M., 2002. Selectiveadsorption of chromium(VI) in industrial wastewater using low-cost abundantly available adsorbents. Advances in EnvironmentalResearch 6 (4), 533540.

Das, D.D., Mahapatra, R., Pradhan, J., Das, S.N., Thakur, R.S.,2000. Removal of Cr(VI) from aqueous solution using activatedcow dung carbon. Journal of Colloids and Interface Science 232(2), 235240.

Donmez, D., Aksu, Z., 2002. Removal of chromium(VI) from salinewastewaters by Dunaliella species. Process Biochemistry 38 (5),751762.

Guo, Y., Qi, J., Yang, S., Yu, K., Wang, Z., Xu, H., 2002. Adsorptionof Cr(VI) on micro and mesoporous rice husk-based active carbon.Materials Chemistry and Physics 78 (1), 132137.

Gupta, V.K., Shrivastava, A.K., Jain, N., 2001. Biosorption of chromium(VI) from aqueous solution by green algae Spirogyraspecies. Water Research 35 (17), 40794085.

Hu, Z., Lei, L., Li, Y., Ni, Y., 2003. Chromium adsorption on high-performance activated carbons from aqueous solution. Separationand Purication Technology 31 (1), 1318.

Kim, S.D., Park, K.S., Gu, M.B., 2002. Toxicity of hexavalentchromium to Daphnia magna : inuence of reduction reactionby ferrous iron. Journal of Hazardous Materials 93 (2), 155 164.

Lot, M., Adhoum, N., 2002. Modied activated carbon for the

removal of copper, zinc, chromium and cyanide from wastewa-ter. Separation and Purication Technology 26 (23), 137 146.

Marathe, R.M., Annapure, U.S., Singhal, R.S., Kulkarni, P.R., 2002.Gelling behaviour of polyose from tamarind seed kernel polysac-charide. Food Hydrolysis 16 (5), 423426.

Mauri, R., Shinnar, R., Amore, M.D., Giordano, P., Volpe, A., 2001.Solvent extraction of chromium and cadmium from contaminatedsoils. American Institute of Chemical Engineers Journal (AIChE)47 (2), 509512.

Namasivayam, C., Yamuna, R.T., 1995. Adsorption of chromium(VI)by a low-cost adsorbent: biogas residual slurry. Chemosphere 30(3), 561578.

Nourbakhsh, M., Sag, Y., Ozar, D., Aksu, Z., Kutsal, Caglar, 1994. Acomparative study of various biosorbents for removal of chro-mium(VI) ions from industrial waste waters. Process Biochemistry29 (1), 15.

Orhan, Y., Buyukgungor, H., 1993. The removal of heavy metals byusing agricultural wastes. Water Science and Technology 28 (2),247255.

Ozer, A., Altundogan, H.S., Erdem, M., Tumen, F., 1997. A study onthe Cr(VI) removal from aqueous solutions by steel wool.Environmental Pollution 97 (12), 107112.

Padilla, A.P., Tavani, E.L., 1999. Treatment of an industrial effluentby reverse osmosis. Desalination 129 (13), 219226.

Rengaraj, S., Joo, C.K., Kim, Y., Yi, J., 2003. Kinetics of removal of chromium from water and electronic process wastewater by ionexchange resins: 1200H, 1500H and IRN97H. Journal of Hazard-ous Materials 102 (23), 257275.

Selvaraj, K., Manonmani, S., Pattabhi, S., 2003. Removal of hexava-lent chromium using distillery sludge. Bioresource Technology 89(2), 207211.

Sharma, D.C., Forster, C.F., 1995. Column studies into the adsorptionof chromium(VI) using sphagnum moss peat. Bioresource Tech-nology 52 (3), 261267.

Siddhuraju, P., Vijayakumari, K., Janardhanan, K., 1995. Nutritionaland antinutritional properties of the underexploited legumes Cassialaevigata willd. and Tamarindus indica . Journal of Food Compo-sition and Analysis 8 (4), 351362.

Tiwari, D.P., Singh, D.K., Saksena, D.N., 1995. Hg (II) adsorptionfrom aqueous solutions using rice-husk ash. Journal of Environ-mental Engineering 121, 479481.

Ucun, H., Bayhan, Y.K., Kaya, Y., Cakici, A., Algur, O.F., 2002.

Biosorption of chromium(VI) from aqueous solution by conebiomass of Pinus sylvestris . Bioresource Technology 85 (2), 155 158.

Yu, L.J., Shukla, S.S., Dorris, K.L., Shukla, A., Margrave, J.L., 2003.Adsorption of chromium from aqueous solutions by maplesawdust. Journal of Hazardous Materials B 100, 5363.


Documents

Bioabsorpsi Asam Jawa