Int. J. Environ. Res., 6(1):297-308, Winter 2012ISSN: 1735-6865

Received 11 April 2011; Revised 25 July 2011; Accepted 14 Aug. 2011

*Corresponding author E-mail: dr.amitkeshav@gmail.com

297

Removal of Glycolic Acid From Aqueous Solution using Bagasse Flyash

Soni, A. B.1, Keshav, A.1*, Verma, V.1 and Suresh, S. 2

1 Department of Chemical Engineering, National Institute of Technology (NIT) Raipur,Chhattisgarh -492010, India

2 Department of Chemical Engineering, Maulana Azad National Institute of Technology (MANIT)Bhopal, Madhya Pradesh, India

ABSTRACT: Present study deals with the adsorption of glycolic acid (GA) from aqueous solutions by usingbagasse fly ash (BFA). BFA is a solid waste generated from bagasse fired boilers and can be used as anadsorbent. Batch adsorption studies were carried out to evaluate the effect of various parameters like adsorbentdose, contact time, initial concentration and temperature on the removal of GA from aqueous solutions. For theselected dosage, it was found that the adsorption increases with increase in BFA doses and decreases withincrease in acid concentration. The effect of contact time on removal shows that the adsorption of glycolic acidon BFA is very fast. The kinetics of the sorption of GA was well represented by Elovich model, first order,pseudo-second order and Weber and Morris intra-particle diffusion model. The adsorption isotherm analyseswere also carried out by using Langmuir and Freundlich isotherm equations. Freundlich equation was foundsatisfactory to represent the equilibrium data. Thermodynamic studies revealed that the adsorption of GA onBFA is exothermic in nature.

Key words: Glycolic acid, Adsorption, Bagasse fly ash, Equilibrium, Kinetics

INTRODUCTIONGlycolic acid (Alpha hydroxy acid, GA) also known

as hydroxyacetate acid, is the most frequently usedalpha-hydroxy acid in facial treatments or chemicalpeels. GA is a key ingredient in an increasing numberof skin care products that are available in the markettoday, including peels, creams, exfoliants, cleansers andtoners. It may reduce wrinkles, acne scarring,hyperpigmentation. It is also a useful intermediate fororganic synthesis in a range of reactions including:oxidation-reductions, esterification, long chainpolymerization, and is used as a monomer in thepreparation of polyglycolic acid. Among other usesthis compound finds employment in the textile industryas a dyeing and tanning agent, in food processing as aflavoring agent and as a preservative. GA is oftenincluded into emulsion polymers, solvents, andadditives for ink and paint in order to improve flowproperties and impart gloss. Natural sources of GAinclude sugar cane, sugar beets, pine apple, canteloupe,and unripe grapes. By synthetic means it can also beprepared, example by reaction of carbon monoxide withformaldehyde, preferably in the presence of water(Leupold et al., 1978).

Recovery of GA is essential from its varioussources of production. There are many technologiesfor the recovery of acids from dilute solution such asadsorption, extraction, electrodialysis, reverseosmosis etc. Among all these, adsorption is widelyused technology employed in waste water treatmentprocess for recovery of certain useful products forfurther processing. Adsorbents are classified into threedifferent types i) oxygen containing compounds e.g.silica gel and zeolite; ii) carbon based compounds e.g.activated carbon and graphite and iii) polymer basedcompounds e.g. porous polymer matrix. Althoughsynthetic polymeric and silica based adsorbents areused for waste water adsorption but since they arecostly, cheap adsorbents such as activated charcoal,bagasse fly ash (BFA), tea waste etc. are gainingattractiveness in advanced wastewater treatment.

Glycolic acid could also be obtained from seawater. Shah and Wright (1994) studied the adsorptionof glycolic acid by alumina from sea water (IpswichBay (Gulf of Maine, USA)), followed by extraction withsulphuric acid and then colorimetry. The overallefficiency of recovery of this method, which isstandardized internally, is approximately 67%, andabout 20-fold concentration of glycolic acid is

298

Soni, A. B. et al.

achieved. Method for improved quantification ofglycolic acid dissolved in seawater has been describedby Leboulanger et al. (1994). The extraction of glycolicacid was performed by an organic solvent and itsquantification by HPLC. With this method, the glycolicacid dissolved in seawater is extracted in a reproduciblemanner with a constant yield, and dosed with aprecision >±7.5%. Removal of glycolic acid by theweakly basic adsorbent Amberlite IRA-67 has beenstudied at three different temperatures by Uslu et al.(2010). The maximum adsorption efficiency has beenfound to be 86.29 % for glycolic acid. The Langmuirisotherm fitted the experimental data better than theFreundlich isotherm for both acids. Thermodynamicparameters ∆G, ∆H, and ∆S were also evaluated.

Another successful method for recovery ofglycolic acid has been using reactive extraction. Manysuccessful works have been presented in the literature.Datta and Kumar (2011) presented the removal ofglycolic acid from aqueous solution by two differentextractants (tri-n-butyl phosphate (TBP) and tri-n-octylamine (TOA)) at constant concentration of 0.573kmol/m3 dissolving in a wide range of diluents (n-hexane, decane-1-ol, n-hexane + decane-1-ol (1:1 v/v),4-methylpentan-2-one (MIBK), benzene, anddichloromethane (DCM)). Effects of various parameterssuch as acid concentration (0.10-0.57 kmol/m3),extractant type, and type of diluents have beenpresented. Extraction of glycolic acid was investigatedfrom aqueous solutions by different organic solutionscontaining Amberlite LA-2, a secondary amine mixture.1-octanol, cyclohexane, isooctane, toluene, 2-octanone, and methyl isobutyl ketone (MIBK) wereused as diluents (Selim and Inci, 2009). The effect ofsolvent type, amine concentration, and initial acidconcentration has been investigated. The maximumremoval of glycolic acid was 79.43 % with MIBK and0.93 mol/L initial concentration of Amberlite LA-2.Partitioning of glycolic acid from aqueous solutionsby TOMAC in mixtures of three individual dilutingsolvents (propanol, cyclohexane, isooctane, butanol,toluene, methyl isobutyl ketone, and ethyl acetate) waspresented by Inci and Uslu (2005). The distributioncoefficients, loading factors and extraction efficiencieswere derived. The maximum removal of glycolic acidwas 49% with propanol with a 1.76 mol/L initialconcentration of trioctyl methylammonium chloride.Inci (2002) presented novel distribution data of glycolicacid between water and different organic solutions oftrioctylamine and Alamine 336. Diluting solvents usedin this study were heptane, cyclohexane, toluene andmethyl isobutyl ketone (MIBK). The distributioncoefficients and loading factors are calculated andinterpreted from experimental results.

In the present study, BFA has been employed forthe recovery of GA from dilute aqueous solutions. BFA,a waste produced in sugar industries, could be aninexpensive and effective adsorbent for the removal ofcarboxylic acid from dilute solutions. Only a limitednumber of studies, however, have so far been focusedon the use of BFA and that for the removal of ions fromwastewater.

Gupta et al. (2000) studied the utilization of BFAfor the removal of copper and zinc from wastewater.Nassar et al. (2004) studied the kinetic andthermodynamic parameters during thermaldecomposition of dye when BFA was used asadsorbent. Equilibrium, kinetics and thermodynamicsof adsorption of phenol on BFA and activated carbon-commercial grade (ACC) and laboratory grade (ACL)were investigated by Srivastava et al. (2005). Karnitzet al. (2006) studied adsorption of heavy metal ion fromaqueous single metal solution by chemically modifiedBFA. The obtained materials were characterized byelemental analysis and infrared spectroscopy (IR). Thesecond part of this report features the comparativeevaluation of the adsorption capacity of the modifiedBFA for Cu2+, Cd2+, and Pb2+ ions.

In view of the applications of BFA as adsorbent, ithas been decided to study the adsorptioncharacteristics of BFA for the removal of GA from dilutesolutions. Effect of BFA doses, in itial acidconcentration, contact time, thermodynamic wereinvestigated. Also the kinetics of adsorption waspresented and various models were fitted to the kineticdata such as Elovich model, first order, second ordermodel, Weber & Morris intra-particle diffusion model.

MATERIALS & METHODSBFA was obtained from Deoband sugar mill,

UP, India which was collected from the particulatecollection device that is attached to the flue gas line ofa bagasse fired boiler stack and it was used withoutany pre-treatment other than sieving. Glycolic acid(C2H4O3; molecular weight 76.05; density1.27 g/cm3)was obtained from the Luba Chemical India. Theaverage particle size of BFA used for the sorption ofBA is in the range of 180 to 1400 µm. The BET surfacearea of BFA was estimated by the standard adsorptionof N2 at 77.15 K (Brunauer et al., 1938). The Bulk densityof BFA was determined using MAC bulk density meter.SEM analysis of BFA was carried out before and afterthe adsorption of BA by using LEO 435 VP Scanningelectron microscope.

Different concentrations of GA were prepared (0.2,0.4, 0.6, 0.8, 1.0, 1.2 mol/L). 50ml each of these solutionswere taken in 100ml conical flasks and known weightof BFA was and added and the contents were shaken

Int. J. Environ. Res., 6(1):297-308, Winter 2012

299

for 4 hrs and made to settle for 2 h. The mixtures werefinally filtered to separate BFA. The left out solutionwas titrated with standard NaOH solution usingphenolphthalein as an indicator.

KineticsKinetics was studied in CSTR operating at 2000

rpm. The stirring duration was from 0-90 min. 10ml ofsolution was pipetted out every 10 minutes and settledfor 2 h and filtered with filter paper. 3 ml of this solutionwas taken and titrated against NaOH usingphenolphthalein as an indicator.

ThermodynamicsEffect of temperature on the adsorption was

studied for various concentrations of acid (0.2, 0.4,0.6, 0.8, 1.0, 1.2 mol/L) using BFA as absorbent.Temperature was varied from 303 – 323 K. Experimentsinvolved shaking equal volumes of aqueous phase atdifferent temperatures in water bath shaker. Settlingwas done at the same temperature and samples weretitrated using NaOH for determination of acidconcentration in the aqueous phase after theexperiment.

RESULTS & DISCUSSIONIt is observed that BFA has bulk density (121.04

kg/m3). The amount of carbon content is high in BFAwhen compared to other adsorbents like rick husk ash.The average particle size is 375.34 µm and BET surfacearea of pores is 230.07 m2/g. Physical characteristics ofBFA are follows: Moisture (14.39%), Volatile matter(9.80%), Ash (53.22%), Fixed carbon (23.59%). Themorphologies of blank and GA-loaded BFA, wasexamined by scanning electron microscopy (SEM).SEM micrograph of BFA is at 1000X magnification. Fig(1) shows the fibrous structure and strands of the fiber.

It can be inferred from these fig.s that the surfacetexture of the blank adsorbents changes after theadsorption of GA. The chemical structure of theadsorbents is very important in understanding thesorption process by using FTIR spectroscopyanalysis. The sorption capacity of BFA is stronglyinfluenced by the chemical structure of their surface.The carbon-oxygen functional groups are by far themost important structures in influencing the surfacecharacteristics and surface behavior of BFA.

BFA spectra is shown in (Fig. 2a). A broad bandbetween 3100 and 3800 cm-1 in the BFA is indicative ofthe presence of both free and hydrogen bonded OHgroups on the surface of BFA. This stretching is dueto both the silanol groups (SiOH) and adsorbed water(peak at 3800 cm-1) on the surface. C-O group stretchingfrom aldehydes and ketones can also be inferred frompeaks at ~1500 cm-1. The band around ~1400 cm-1 in allboth the adsorbents may be attributed to the carboxyl-carbonate structures. The functional groupssuggested most often are: (i) carboxyl groups, (ii)phenolic hydroxyl groups, (iii) carbonyl groups (e.g.quinone-type), and (iv) lactone groups (e.g.fluorescein-type). (Fig. 2b) shows the FTIR spectra ofthe blank and BFA loaded GA. Two clear peaks around1300 to 1800 cm-1 can be identified which seemed to beaffected due to GA-adsorption onto BFA. These peaksare normally attributed to adsorbed bound water ontothe sorbent surface. The peak around 1300 cm-1

corresponds to bound water coordinated to cations.This may also be attributed to single C-N bond (not tohydrogen).

The amount of acid adsorbed (Qe) mg/g and theadsorption efficiency (AE %) can be calculatedaccording to the expressions:

Blank-BFA GA-BFA

Fig. 1. SEM of blank-BFA and GA-loaded BFA at 500X and 1000X

300

Removal of Glycolic Acid From Aqueous Solution

477.6

4530.

76

768.

451356

.19

1384

.39 15

89.9

8

1646

.31

2357

.32

3224

.90 3307

.58

3354

.14

3399

.18

3434

.51

3475

.87

3531

.08

3568

.49

3591

.50

3614

.31 3

652.7

0

3698

.67

3798

.11

3858

.89

3960

.35

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0Ab

sorb

ance

500 1000 1500 2000 2500 3000 3500 4000 Wavenumbers (cm-1)

(a). Blank-BFA

668.

31

773.

80

1353

.01

1459

.4215

23.3

215

99.8

716

51.0

216

96.1

517

74.84

2234

.17

2339

.69

3142

.88

3256

.40

3300

.18

3363

.50

3385

.68

3446

.40

3485

.26

3525

.333570

.9236

11.1

537

77.5

138

55.6

739

36.73

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

Abso

rban

ce

500 1000 1500 2000 2500 3000 3500 4000

Wavenumbers (cm-1)

(b). GA-loaded BFAFig. 2. FTIR spectra of blank-BFA and GA-loaded BFA. (a).Blank-BFA. (b). GA-loaded BFA

Vw

*[HA][HA]Qs

oe ×−= (1)

(2)

Where, Qe = amount of acid adsorbed g/mg, [HA]o and[HA]* are the initial and equilibrium concentrations(mol/L) of acid, V the volume of solution (l), ws theweight of adsorbents (g).

The effect of solute adsorption wasinvestigated by varying BFA doses (ws) from 0.1 to 10gm for 0.4 mol/L of glycolic acid at 303-323 K. For theselected dosage, it was found that the adsorptionincreases with increase in ws. The reason for this beingthat higher dosage provides higher surface area andhence more adsorption sites for removal of glycolicacid. The maximum adsorption was obtained to be27.21%, 22.18%, 20.67% for T = 303, 313 and 333 K,respectively (Fig. 3).

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Int. J. Environ. Res., 6(1):297-308, Winter 2012

To study the effect of initial acid concentration onadsorption for glycolic acid, its concentration wasvaried from 0.2 mol/L to 1.2 mol/L for a fixed BFA (1 g).It can be observed that increasing the initial acidconcentration from 0.2 mol/L to 1.2 mol/L percentageacid removed decreases from 11.50 to 4.53 %, 10.05 to4.43 % and 9.53 to 4.15 % (Fig. 4), on the other hand,glycolic acid uptake per unit mass of BFA increasesfrom 0.0017 to 0.0041, 0.0015 to 0.0040 and 0.0014 to0.0037 respectively for BFA at 303, 313, 323 K. Thusadsorption using BFA is effective when acid is presentin dilute solutions. At higher initial concentrations ofacid the ratio of initial moles of glycolic acid to theavailable surface area is high and hence the fractionaladsorption becomes dependent on the initial acidconcentration. Further, the decreases in percentageremoval efficiency can be explained on the view pointof the saturation of BFA surface. At fixed BFA dosage,the available sites become the limiting parameter andhence adsorb the same amount of sorbate. This resultsin the decrease of the percentage removal of adsorbatewith increase in initial acid concentration. Decreasemay be caused with the rate uptake of adsorbate isfound to increase non-linearly with increasingconcentration of solute.

Time for the attainment of equilibrium (t) wasdetermined when the glycolic acid and BFA werecontacted with each other in a mechanically agitatedcontactor (2000 rpm). Time was varied from 0-90 minfor the initial acid concentration 0.4 mol/L and 1 g BFAconcentration at 303 K (Fig. 5). A quasi stationary statewas obtained within 85 minutes of shaking and isindependent of BFA dose. Thus based on this study, itcan be suggested that 85 minutes is sufficient time forstudying the equilibrium characteristics of glycolic acidadsorption using various BFA. It was observed thatadsorbent rate is fast at the initial stages of the contact

0

5

10

15

20

25

30

0 5 10 15

AE

%

303

323K

313K

W s (gm)Fig. 3. Effect of the BFA dosage (0.1-10 gm) on the

adsorption of GA Using BFA

02468

101214

0 0.5 1 1.5

[HA]O(mol/ l)

AE

%

303K

313K

323K

period, and thereafter, it become slower near theequilibrium. This is obvious from the fact that a largenumber of vacant surface sites are available foradsorption during the initial stage and after a lapse oftime, the remaining vacant surface sites are difficult tobe occupied due to repulsive forces between the solutemolecules on the solid and bulk phases. Further it canbe seen that equilibrium could be achieved in 90minutes.

Fig. 4. Effect of acid concentration on the adsorptionof GA using BFA

02468

1012141618

0 20 4 0 60 80 100Contact time (min)

AE

%

Fig. 5. Effect of contact time on the adsorption of GAusing BFA

To study the effect of temperature on theadsorption of GA three different temperatures (303, 313and 323K) for different initial acid concentration (0.2-1.2 mol/L) and different BFA dosage of (1-10 g) wereemployed (Fig. 3-4). For a fixed BFA concentration (1g) it was found that adsorption decreases with increasein temperature for all acid concentrations (Fig. 4). Theaverage decrease in adsorption is 34%. However, forfixed acid concentration, as the amount of BFAincreases, the percentage adsorption increases but withthe increase in temperature adsorption decreases (Fig.

302

Soni, A. B. et al.

3). The percentage increase (I% = {AE% at 323 K-AE% at 303 K}/ AE% at 323 K) was higher at lowerBFA concentration and decrease as the amount of BFAis increased. I % decreases from 27.21 to 4.27 % asBFA concentration was increased from 0.1 g to 10g.The maximum ratio of [HA]*/Qe for glycolic acidadsorption using BFA was found to be 21248.78,21802.50, 23640.54. This value shows that theadsorption efficiency of the BFA decreases withincreasing temperature. Thus, it could be understoodthat the adsorption of GA is exothermic in nature, suchlike the most of adsorption reactions.Thethermodynamic parameters such as change in standardfree energy (∆Gº), enthalpy (∆Hº) and entropy (∆Sº)can be determined by using the following equations:

RT∆H

R∆SInK

oo

A −= (3)

S T∆∆H∆G −= (4)

Where, R (8.314 J/mol K) is the gas constant, T (K) theabsolute temperature and KA (mol/g) is the standardthermodynamic equilibrium constant. By plotting agraph of ln KA versus 1/T the values ∆Hæ% and ∆Sæ%can be estimated from the slopes and intercepts. Valuesof ∆Go, ∆Ho and ∆So are given in Table 1 and shown in(Fig. 6).

It is observed that the adsorption of GA decreaseswith increase in temperature. Favorable condition foradsorption of GA is at lower temperature. The decreasein adsorption with increase in temperature is partlydue to the weakening of the attractive force betweenthe GA and BFA surface, and partly due to theenhancement of thermal energies of the adsorbate, thusmaking the attractive force between BFA and GAinsufficient to retain the adsorbed molecules at thebinding sites. From Table 1, it can be seen that the freeenergy of the system increases with increase intemperature decreasing the spontaneity of the process.The value of enthalpy and entropy change suggeststhat, the process is exothermic in nature.

ln KA= 2792.1/ T - 12.49

R2 = 0.99

-4.6

-4.3

-4

-3.7

-3.4

-3.1

0.0029 0.00295 0.003 0.00305 0.0031 0.00315 0.0032 0.00325 0.0033 0.00335

ln K

A

Fig. 6. Effect of ln KA vs. 1/T for estimation of thermodynamic parameters for adsorption of GA using BFA

1/T (K)

Table 1. Thermodynamic parameters for adsorption of GA using BFA

Adsorbent Temperature (K) Go (kJ/mol) S o (kJ/ Kmol) H o (kJ/mol)

303 7033589.69

313 7265724.79

Bag

asse

fly

ash

323 7497859.89

-23213.51 -103.84

∆ ∆ ∆

303

Int. J. Environ. Res., 6(1):297-308, Winter 2012

Langmuir derived a simple adsorption isotherm basedon theoretical consideration. The Langmuir equationis defined as:

*.[HA]K1*.[HA].QKQ

A

maxAe += (5)

Where Qmax denotes the maximum adsorbent and Qedenotes the experimental adsorbent uptake atequilibrium (g/mg). [HA]* is the equilibriumconcentration of solute in the solutions (g/L). KA is aLangmuir model coefficient and it is related to theaffinity between the BFA and GA. The value of KA andQmax could be determined by transforming Eq. (5) as(Hall et al., 1996).

maxAmaxe Q*[HA]

.KQ1

Q*[HA]

+= (6)

The values of KA & Qmax could be determined fromthe intercept and slope of the straight line in Eq. (6).Langmuir isotherm was fitted to the experimental datafor GA concentration (0.2-1.2 mol/L) and 1 g of BFAfor different temperatures (303-323 K). The calculatedmodel parameters determined by least square fit of theexperimental sorption data and their correspondingregression coefficients (R2) are presented in Table 2.The graphical comparison of the isotherm and theexperimental data is given in (Fig. 7). The essentialcharacteristics of Langmuir isotherm can be expressedin terms of dimensionless constant separation factoror equilibrium parameter (RL).

oLL [HA]K1

1R+

= (7)

R2 = 0.96

R2 = 0.95

R2 = 0.82

0

5000

10000

15000

20000

25000

30000

0 20 40 60 80 100[HA]* (mol/l)

[HA

]*/Q

e

303K

313K323K

Fig. 7. Fit of Langmuir isotherm for the adsorption of GA at different temperatures using BFA

Table 2. Isotherm parameters for adsorption of GA using BFA

Langmuir Isotherm Freundlich Isotherm

T (K) Qmax (g/ mg) KA (l/mg) R2 T (K) Kf n R 2

303 0.0048 0.035 0.9674 303 0.00069 2.62 0.9709

313 0.0049 0.026 0.9519 313 0.00051 2.30 0.9800

323 0.0058 0.014 0.8214 323 0.00031 1.93 0.8595

304

Removal of Glycolic Acid From Aqueous Solution

Kf is the Freundlich capacity factor, (mg absorbate/gadsorbent) and 1/n is the Freundlich intensityparameter. The value of Kf and 1/n at differentconcentrations were determined from the slope andintercept of the linear plots of log Qe and log [HA]*.Fig. (8), shows the plots of Freundlich equilibriumisotherms for GA adsorption at three differenttemperatures using BFA as adsorbent. Results ofFreundlich equation were presented in Table 2 andFig. (8). The plot of log Qe and log [HA]* is a straight

Where, KL is Langmuir constant and [HA]o, theinitial glycolic acid concentration (mg/L). RL indicatesthe type of isotherm that is favorable: RL >1 unfavorable; RL =1 linear; 0 < RL < 1 Favourable,RL = 0 Irreversible. Adsorption system is ‘favourable’or ‘unfavourable were predicted according to the effectof isotherm shape (Hall et al., 1966). RL was evaluatedusing Eq. (7) and was found to vary from 0.96-0.99 at T= 303K, 0.97-0.99 at T= 313 K and 0.98-0.99 at T= 323K.Thus in all cases it was found to be less than 1 andhence the adsorption is favorable.Derived empirically in 1912, Freundlich isotherm wasthe second method employed for studying theequilibrium characteristics (Azizian et al., 2009; Iftikharet al., 2009)

1/nfe *.[HA]KQ = (8)

Qe and [HA]* were the same as describe earlier inLangmuir’s isotherm. A logarithmic plot linearizes theequation enabling the exponent n and the constant Kfto be determined,

*[HA] (1/n)loglogKlogQ fe += (9)

line with slope 1/n and intercept log Kf. presenting theFreundlich capacity factor and Freundlich intensityparameter determined by least square fit and theircorresponding regression coefficients (R2). Further, Kfand n was found to decreases with increasingtemperature.

R2, the magnitude of regression coefficient hasbeen used to assess the fit of the isotherms. Langmuirisotherm fitted to experimental results for GA, providesR2 values of 0.96, 0.95, 0.82 and Freundlich isothermprovides R2 values of 0.97, 0.98, 0.86 for differenttemperatures, 303, 313 and 313 K, respectively.Comparing R2 values it could be seen that at alltemperatures of study, Freundlich found to bestrepresent the data for GA adsorption using BFA.

Kinetics in a time-dependent process and studyof kinetics is very important in order to know the rateof adsorption for designing and evaluating theadsorbent in removing the acids from aqueous streams.In order to determine the kinetics of adsorption ofglycolic acid onto bagasse fly waste, first order, pseudo-second order, Weber-Morris intraparticle diffusionmodel and Elovich model were applied. In the cases ofliquid phase adsorption systems, surface diffusion isan important phenomenon that describes theintraparticle diffusion. A number of studies on surfacediffusion have been carried out to elucidate themechanism of surface diffusion, and to develop anestimation procedure of surface-diffusion coefficient.A complete understanding of the mechanism is essentialto elucidate the diffusion coefficient. However,because of great influence of adsorbates, adsorbents,and solvents, estimation of diffusion coefficient is verydifficult. The dependence of this coefficient, on

R2 = 0.98

R2 = 0.97

R2 = 0.86

-2.9

-2.8

-2.7

-2.6

-2.5

-2.4

-2.3

-2.2

-2.1

-2

1 1.2 1.4 1.6 1.8 2log [HA]*

log

Qe

303K

313K

323K

Fig. 8. Fit of Freundlich isotherm for the adsorption of GA at different temperatures using BFA

305

Int. J. Environ. Res., 6(1):297-308, Winter 2012

temperature and the amount adsorbed, can beinvestigated as characteristic features of surfacediffusion. For the estimation of surface-diffusioncoefficient, numerous diffusion models are developedin literature.The Elovich model equation is generally expressed as(Low, 1960):

Where α is the initial adsorption rate (mg/g.min) and βis the desorption constant (g/mg). To simplify theElovich equation, αβt>> t is assumed and by applyingthe boundary conditions Q = 0 at t = 0 and Q = Q at t =t equation becomes:

A plot of qt versus ln(t) should yield a linear relationship(Fig. 9). The constants are listed in Table 3. The Elovichequation, which has been shown to be useful indescribing chemisorption on highly heterogeneousadsorbents, give a good account of adsorption ofglycolic acid with R2 = 0.98 for BFA.First order model:The Langmuir rate equation may have been the firstrate equation for the sorption of solid- liquid systems.

)Q(Qkdt

dQte1

t −= (12)

β.ln(t)β.ln(α.β)Qt += (11)

Table 3. Kinetic parameters for the removal of GA using BFA

Elovich model

α(mg/g.min) β(g/mg) R2

-6*10-4 5000 0.9554

W-M Intra pa rticle diffusion model

kid (mg/(g.min^0.5)) I (mg/g) R2

0.00003 -0.00046 0.9864

Pseudo First order

Qe k1(min-1 ) R2

0.950 0.798 0.9201

Pseudo second order

Qe k2(mg/g.min) R2

0.0242 3.8*10-4 0.9810

After the integration of Eq. (12), the equation can belinearized as (Lagergren, 1898)

)β.Qα.exp(dt

dQt

t −= (10)

Where, k1 is the first order rate coefficient (1/min). Inthis model the limiting phenomenon is intra-particlemass transfer resistance.The equation for the pseudo-second order model isshown below,

Where, k2 is the pseudo second-order rate coefficient(mg/g.min). If Eq. (14) is integrated, a linear equation isobtained (Ho and McKay, 1998). This equation is

The initial sorption rate, (mg/g min) at t → 0 isdefined as;

The values of k2 and calculated Qe are obtainedfrom the slope of the plot t/Qt versus t. and k2 areobtained from the intercept. In this model, the limitingphenomenon is the adsorption mechanism, not thetransfer of mass resistance. The first order and thepseudo-second-order model parameters are shown inTable 3 and plot of both models can be seen from (Fig.10-11).First order and pseudo-second-order models wereinvestigated for GA, calculated from linear regression

t2.303

kQ log)Qlog(Q 1ete −=− (13)

2te2

t )Q(Qkdt

dQ−= (14)

tQ1

Qk1

Qt

e2

e2t

+= (15)

2esQkΓ = (16)

Γ

Γ

306

Soni, A. B. et al.

R2 = 0.98

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

2 2.5 3 3.5 4 4.5 5ln (t)

Qt

y = -0.022x - 2.8843R2 = 0.92

-5

-4.8-4.6

-4.4

-4.2

-4

-3.8

-3.6

-3.4

-3.2

-3

0 20 40 60 80 100

t (min)

Log

(Qe-

Qt)

y = 1700.7x + 108238

R2 = 0.981

100000

120000

140000

160000

180000

200000

220000

240000

260000

280000

300000

0 20 40 60 80 100

t (min)

t/Qt

Fig. 11. Pseudo second order equation fit for kinetic adsorption of the GA (0.4 mol/l) using BFA

Fig. 10. First order equation fit for kinetic adsorption of the GA (0.4 mol/l) using BFA

Fig. 9. Elovich equation fit for the adsorption of GA (0.4 mol/l) using GA using BFA

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Int. J. Environ. Res., 6(1):297-308, Winter 2012

y = 8E-05x - 0.0003R2 = 0.98

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

4 5 6 7 8 9 10t1/2

Qt

Fig. 12. Weber and Morris intra particle diffusion equation fit for adsorption of GA (0.4 mol/l) using BFA

and regression coefficient for first order is R2 0.92 andfor second order 0.98 for BFA shown in (Fig. 10-11).The values stated above that each of the sorptionprocess can be described using the second order kineticmodel with fairly high correlation coefficients.Weber and Morris intra-particle diffusion model:Intra-particle diffusion can be estimated by using theWeber-Morris intra particle diffusion model (Rajoriyaet al., 2007)

ItkQ 1/2idt += (17)

CONCLUSIONEquilibrium and kinetic adsorption of glycolic acid

recovery from dilute solution were investigated. Forthe selected dosage, it was found that the adsorptionincreases with increase in BFA doses when dosagewas varied from 0.1-10 g and decreases with increasein acid concentration when acid concentration wasvaried from 0.2 mol/L to 1.2 mol/L. A quasi stationarystate was obtained within 85 minutes of shaking in aCSTR used for kinetic study and is independent ofBFA dose. Adsorption decreases with increase intemperature for all acid concentrations. Equilibriumisotherms: Langmuir and freundlich isotherms providesR2 values of 0.96, 0.95, 0.82 and 0.97, 0.98, 0.86,respectively for different temperatures, 303, 313 and313 K, respectively. Freundlich found to best representthe data for GA adsorption using BFA. Kinetic modelsuch as the Elovich equation, give a good account ofadsorption of glycolic acid with R2 = 0.98 for BFA.First order and pseudo-second-order models wereinvestigated for GA adsorption and regressioncoefficient for first order were found to be R2 0.92 andfor second order 0.98 for BFA. Intra-particle diffusion

can be estimated by using the Weber-Morris intraparticle diffusion model

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