Indian Journal of Engineering & M aterials Sciences Vo l. Y. April 2002. pp. 128- 136

Treatment of phenol rich aqueous solutions using surface modified pillared clay

Y P Yinod & T S An irudhan*

DcpJrtment of Chemistry. Uni versit y of Kerala, Kariavattom, Tri vandrum 69558 1, India

Received 28 ll/lle 200 / ; accepted 2 l Oll l/wy 2002

The erri c;Jcy 0 ( humic acid trcated zirconium pillared clay (HA -PILC) in the removal of phcnol fro m aqueous so lution has been in vesti gated using batch adsorpti on techniquc at different sorbate concentrations, rate of agi tati on. pH and tem­pcrature. The maximum removal of 98.0. 84.0 and 73.2 % has been noted at p H 5.0 for an initial concentra tion of 25, 50 and 100 mg/L respcc ti ve ly. The maximum adsorp ti on capacity has been observed at p H 5.0. The process of uptake fol lows a fi rst-ordcr revcrsibic kineti c expression. The removal process has also been found to be diffusion controlled. The adsorption capac ity has been increJsed fro m 78.2 to 92.6 % with an increase in agitation speed from 100 to 400 rpm at an ini tial con­centration of 50 mg/L. The ad sorpti on isotherm for phenol removal may be classifi ed as L -type of the Giles classifi ca ti on, which suggests a favourahle ad sorption, and the adsorbcnt has a high affinity for phenol. The adsorpti on data points have been fitted to both Langmui r and Freundlich isotherm equJtions. The max imum adsorpt ion capac ity ( Qo) decreascs from

179.86 mg/g at 10°C to 126.69 mg/g at 40°c' Lower temperat ure has been found 10 be more effecti ve in the removal of

phenol. ThcnnodYIIJmic paramcters such as !'J.Co, !'J.lfl and 1'J.:f1 for the adsorption pmcess have been ca lculated 10 predict the nature of adsorption process . Cost o f the HA-PILC and its adsorption capacity w ith ot her adsorbent material s reportcd in the li tt: raturc, have also been presentcd.

Removal of phenolic compounds from aquatic env i­ronment and polluted waters got special attention due to their well known tox ic effects on fl ora and fauna and stringent water quality standards. The potential sources of phenols in industri al was tewaters include oil refineri es, paper and pulp, pesti cides, sy nthetic ru bber, steel plants, plastics and coke oven plants J.

The limit of phenol acceptable in drinking water is 0.00 I mg/L. Phenolics are strong sk in irritants and consumption of water containing these substances leads to severe pai ns. vo mi ti ng and capi lIary damage2

Among the various types of technologies fo r the re­mOVed of phenol from wastewater chemical oxidation , steam and gas stripp ing. solvent ex traction , ion ex­change, adsorpti on seems to be an att raeti ve method espec iall y when low cost material s can be used as ad­sorbents .1 . Due to its sludge free and clean operati on adsorption technique is still remains as a promi sing technique. Preparati on of ac ti vated carbon fro m a wide range of li gnocellulosic agricultural by-products for phenolic wastew;lter treatment has recently been rev iewed by Pollard ef o f. .j. Prev ious research has sugges ted that chemi a ll y mod ifi ed clay mineral s rep­resent a new and promising class of adsorbent mate ri ­als for removing phenolic compollnds from wastewa­lers5

. The use of organo clays for the removal of phe-

" Fur correspondence

nol from aq ueous solution has been reported in the literature!>. This study reports the results of the effect of concentration of sorbate, pH and temperature on the adsorption capaci ty along with isothermal studies of phenol adsorption on a newly prepared adsorbent material namely humic ac id. impregnated- zirconium pillared clay complex and poss ible mechani sm of ad­sorpti on is also presented .

Experimental pJ'ocedure

Preparation of adsorbent

Detai Is of the preparat ion and characteri zation of the zi rcony I pi lI ared clay (PI LC) using Jl1ontmori 110-nite was reported elsewhere7

.8

. Montmorillonite ob­tained from Flub, Switzerland, was L1 sed for the preparation of the PILe About 20 g of clay was re­fluxed with 500 mL of freshly prepared 0. 1 M zir­conyl chloride solution at 90°C for 4 h. The resultant slurry was filtered and washed free of chl oride with deioni zed water and tes ted with 0.1 M AgNOJ . The PILC was then dried at 105°C for 4 h.

Humic ac id (HA) impregnated PILC (HA-PILC) was prepared fo ll owing the method desc ribed by Abraham and AnirudhanlJ. HA supplied by Flub, Switzerland was used in thi s work . Ahout 10.0 g PILC sieved between -80 and +230 mesh was im­mersed in 500 mL of aqueous so lution containing 1250 mg HA . The pH of the suspension was adju sted

)

VINOD & ANIRUDHAN: TREATM ENT OF PH ENOL RICH AQU EOUS SOLUTIONS 129

to 3.0 using HCI04. The medium was heated in a sea led reactor for 24 h at a shak ing speed of 300 rpm and at 60°e. The HA impregnated PILC (HA-PILC) was fi Itered and washed wi th 0.0 I M HCI04, foll owed by dei oni zed water. The adsorbent was dried in an air oven at 70°e. Clay particles were sieved to obtain -80 and +230 mesh size particles (average diameter 0.096 mm) using standard tes t sieves.

The amount of HA loaded was determined by the following procedure. The filtrate and washin gs were collected in 1000 mL flask and made up to the mark. The amount of unadsorbed HA was determined using UV-visible spectrophotometer at 350 nm . The amount of HA loaded in the PILC was then calcu lated and found to be 86.89 mg/g PTLe. In order to find out whether there is any leakage from HA-PILC during the adsorpti on and desorption processes, the super­natant so lutions were analysed for HA. It was ob­served that there was no leaking of HA from the ad­sorbent with pH range of 2-8. However, at hi gher pH range of 8.5- 12, a small amount of HA (8- 18.6%) was leached out from HA-PILe. Since phenol ri ch was te­waters are always acidic in nature and the optimum pH range fo r wastewater treatment is 4-5 (result s of the present study), the HA leaching at hi gher p H will not create any problem.

Adsorption experiments

Phenol adsorption fro m the aqueous so lution was investi gated in batch adsorption equilibrium experi­ments . The effect of pH on phenol adsorption on both PILC and HA-PILC was studi ed. A weighed quantity of the adsorbent (100 mg) was shaken together with 50 mL of an aq ueous phenol so lution in a stoppered bott le usi ng a water bath shaker mai ntai ned at 30°C about 4 h. From the preliminary ex periments eq uilib­rium was confi rmed to has been attained within thi s period of shaking for all cases. The adsorbent was separated from the medium at the end of each adsorp­ti on ex periment and quantity of phenol in the aqueous phase was measured using UV- visible spectropho­tometer at a wavelength of 270 nm. The amount of adsorbed phenol was calculated as

qt" == (Co - CII )V

. .. (I) II/

where, (je is the amount of phenol adsorbed onto unit adsorbent. C" and CII are the concentration of phenol in the initi al solutions and in the aqueous phase after time { respectively. V is the volume of the aqueous phase and 1/1 is the mass of the adsorbent.

Kinetic studies were carried out using initial phenol concentration of 25, 50 and 100 mg/L at different time intervals. The effect of temperature on the ex tent of adsorption kinetics was also in vestigated using an initial concentration of 50 mg/L phenol at 10, 20, 30 and 40°e. Adsorption isotherm was determined in 50 mL so lutions in which adsorbent was in contact with phenol solution of concentration range from 50 to 600 mg/L. The temperatures at which the studies con­ducted were 10, 20, 30 and 40°e.

Adsorbent characterization

The surface and physical properties corresponding to adsorben t particles having average diameter 0.096 mm were determined . A Rigaku Geigerflex X-ray diffractometer with Ni filtered CuKa radiation (40 kV 20 mA) was used for X-ray powder diffraction. The accuracy of the d (00 I) va lues is - 0.004 nm. The FTIR spectra (50-600 cm·1 and 500-4000 cm· l

) of PILC and HA-PILC were recorded on a Bruker IFS 66V FTfR spectrophotometer using KBr pellets. Sur­face area of the adsorbent was determined by methyl­ene blue (MB ) adsorption method as described by

I· k 10 11 Bid . h . ear ler wor ' ers ' . atc 1 a sorption tec nlque was performed to determine MB adsorption on clays. The tests were performed for a known amount of clay (100 mg) with 50 mL solution of MB ( lx IO's to 2.5x I0·4

M) for 6 h at 30°C using a temperature contro ll ed water bath shaker. After equilibration, adsorbent and adsorbate were separated by centri fugation and res id­ual concentration of M B was measured spectropho­tometrically at 660 nm.

The zero point charge (pHLp C) is defined as the p H of the suspension at which urface charge density Go

(C/cm" ) == O. The Go as a fun ction of pH was dete r­mined by using potentiometric titratio n method l 2 The porosity and the density of the ad orbents were de­tennined by a mercury intrus ion porosimeter (Mi­crometric model-93 I 0) and by a speci fi c gravity bot­tl e (nitrobenzene is used as di sp lacing liquid) respec­tively. The cation exchange capacity (CEC) of PILC and HA-PILC was measured by MgCI2 saturation and subsequent di splacement by CaCl2" .

Results and Discussion The results of the estimation of physical and sur­

face charac teristics of PILC and HA-PILC are listed in Table I. The res ults of X-ray ana lysis of PILC were reported in our earlier papers. The parent PILC had a d-spacing of 1.42 nm which increased to 1.53 nm upon impregnation with HA. The IR-spectra of ad-

130 I DIAN J. ENG. MATE R. SC I. , APRIL 2002

Table I- Physica l and surface properties of PILC and HA-PILC

Parameters

rI-spacing (nm ) Humic ac id co ntent (mg/g) Surface area (1ll 2/g)

Apparent density (g/IllLJ Purosity (mUg) Ca tion exchange capaci ly (meq/g) Zero point charge (p ll , pc! Parti cle size (nlln )

Magn itude PILC HA-PILC

1.42 1.53 86.89

203.9 555.7 1.32 1.33 0.52 0.55 0. 83 1.1 3 3.2 4.3

0.096 0.096

sorbents show the broad asymmetric absorption bands at 3370 and 3440 em-I for PILC and HA-PILC re­specti ve ly indicating the presence of exchangeabl e hydroxy l groups. The peaks at 1041 cm-I for PILC, and at 1035 cm-I for HA-PILC are caused by the vi­bration of the O- Si- O valence bond. H- O- AI bond­ing in both samples is confirmed by observing the peaks at 766 and 478 cm-I for PILC and 741 and 470 cm-I for HA-PfLC. The bands at 576 and 4 18 cm- I for PILC and 508 and 447 cm-I for HA-PILC are due to the deformation osc illati on of Si- O and Si- O- AI' 4. The new peaks at 17 14 and 1450 cm-I in HA-PILC indicate the presenc of - COOH groups from loaded HA. The C-H stretch ing from CH2 groups and - NH vibration from amide groups are also observed at 2940 and 1584 cm-I respectively for HA-PILC I4. These spectral data clearly indicate that the surface of the ori ginal PILC has been modifi ed by treatment with HA.

The specifi c surface area of PILC and HA-PfLC was determined using the fo llowing equation

. . . (2)

where, XIII is the amount of MB required to complete a monolayer on the solid surface, N is the Avogadro number and a is the cross-secti onal area of MB which was taken to be 130 A. The value of XIII was obtained from the intercept and slope of the BET isotherm equation .

. .. (3)

where Co is the initi nl concentration of M B, Ce is the equil ibrium concentration, X is the amuunt of MB ad­sorbed . The value of X IIl was calcu lated from the BET plot of C/x(C()-C) versus C/C) (Fi g. I) and substi­tuting in the above eq uation gave the va lue of the sur-

.-.. ell E

50

4 0

29 3 0

u~

r.:.f 20 ~ U~

10

•

0 .2

Sorbent dose : 2 giL Agitation rime : 6 Ilr Agitation speed : 200 rpm

. : PILC

. : HA - PILC

o 4 0 .0 0 .8

CJCo

Fig. I- BET isotherm plots for th e adsorpt ion of meth yl ne blue onto PILC and HA-PILC

15 0 30

• ---- : IIA-PILC ~. PILC 100 . 20

~- - • : 0.0 1M I'al\C\ . • : 0.00 I M NaNO, E 50 . I U ~ ~ u

~ • U =\.

~ 0 0 ~

0 0 b b

- 511 -1 0

• ·100 -2 0

6

pH Fig. 2- The potenti ometri c titrali on curves dep icting the surface charge as a fun cti on of so lut ion pH

face area of the clays. The increase in surface area after HA impregnati on indicates the easy access ibility of MB molecules to the surface sites of the adsorbent.

The variation of ao as a function of pH at an ionic strength of 0.01 and 0.00 1 M NaN03 was determined using potentiometric titration method 12 wi th the fol­lowing equation.

. . . (4)

where F is the Faraday constant, CII and C/J are the concentrations of ac id and alka li after each addition during titration _ [W] and [OW] are the equi li. brium concentration of H+ and OH- bound to the suspension surface (equ/cm2) . A is the surface area of suspension (cm2/g). A graph is plotted with ao versus p H (Fig. 2). The point of intersecti on of ao versus p H plot shows that the pH zpc of PILC and HA-PILC was found to occur at 3.2 and 4.3 respectively. The increase in pHzpc after HA treatment ind icates that the surface

VINOD & AN IRUDHAN: TREATMENT OF PH ENOL RI CH AQU EOUS SOLUTIONS 13 1

150 ,....------------------,

~ 100 ~

Sorbcnt dose Temperature Agit ali on time

Agit ali on speed

: 2 giL :30 °C : 4 hI'

: 200 rpm

. : HA-P ILC

. : PILC

o L-__ ~ __ ~ __ ~ ___ ~_~

o 2 4 6 8 10 pH

Fig. 3-The effect of p H on the adsorplion of phenol onlO PILC and HA-PILC

becomes more positive after impregnation of HA. The CEC of PI LC was increased by the impregnation of HA. The functional groups of the loaded HA (-COOH groups) prov ide new adsorption sites for cations at the surface. A variation in density and poro­sity was al so observed after HA impregnati on.

Effect of pH on phenol adsorption

The pH of the solution has a significant effect on adsorbent as \Nell as on the adsorbate. Both adsorbate and adsorbent may have functional groups which are affected by the concentration of H+ ions in the so lution and which are in vo lved in the adsorpti on process at the active sites of the adsorbent. A t low pH , HA behaves like an uncharged molecule that can penetrate interlamellar spaces and displace water molecules from between the sili cate layers of the montmorillonite. The functi onal groups of interchelated HA molecule in PILC may serve as " new adsorpti on sites". For HA-PILC, it was proposed to take these new adsorpti on sites as well as edge hydroxy l groups of the PILC for the phenol adsorption process. Fig. 3 shows the effect of pH on the extent of adsorpti on of phenol by PILC and HA­PILe. The percentage adsorpt ion increases first with increasing the pH and then reaches a maximum at about 4 for PILC and at pH 5 for HA-PILC and thereafter decreases with a further increase in pH . A similar behav iour has been observed by other researchers 15 fo r phenol adsorpti on on r eat, n y ash and bentonite. At an initial concentrati on of 25 mg/L , maximum adsorpti on of 42.5 and 92.7 % was observed for PILC and HA-PILC at an optimum pH of 4 and 5 respectively. A t low pH values the clay surface of both samples is protonated that res trict access to edge hydroxy l groups by protonated phenol molecules as a

60

50

40

30

<= g 20 E -«

15

Sorbent dose pH

: 2 gi L : 5.0

Temperature : 30"C Agilation speed: 200 rpm

10 .."k"-:: ____

Sorbent dose pH

: 2 gi l . : 5.0

Initial conen. : 5Umg/L Agit ati on speed : 200 rpm

• : 100lllg/L • : 50mg/L .. : 2S mg/L

( Il )

• : 10u( • : 200

(

.. : 30"( • : 40°C

u ~-~--~--~--~-~~-~ o 50 100 150 20C 250 300

Time (min)

Fig. 4- The effect of ag itati on time on the adsorpti on of phenol onto HA-PI LC at different (A) concen tr:lliOIlS and (B) tempera­tures

result of repulsive forces; ihis repulsion is stronger at lower pH. The mechanism of adsorption of phenol by HA-PILC involves H-bonding sites on HA and clay surfaces by acting as proton acceptors. The reduction in adsorption at higher p H is poss ible due to increased solubility of phenol and the abundance of OW ions thereby increasing hindrance to diffusion of phenolate ions.

Effect of initial conccntration and agitat ion timc

The percentage of phenol removal for di fferent agitation time as a functi on of initial concentration is depicted in Fig. 4. The uptake of phenol from water by HA-PILC increases w ith time and attain equi librium in 4 h at an agitation speed of 200 rpm for each concentrat ion showing its independent nature towards sorbate concentra ti on. The percentage adsorpti on W elS lower at higher initial concen tration and vice versa. The maximum removal of 12.25 mg/g (98%) was noted for an initial concentrati on of 25 mg/L, whi le low removal 36.6 mg/g (73.2%) was noted at hi gher concentration of 100 mg/L At low initi al concentration the rati o of initial number of moles of the sorbate to the available surface area is low, then fractional adsorpti on becomes independent

132 INDIAN J. ENG. MATER. SCI. , APR IL 2002

of initial concentration, however, at hi gher initi a l concentrati on the number of mo les of adsorbate become hi gher as compared to the surface area avai lab le for adsorption, and at hig her concentration the removal percentage depends on the initi a l concentration.

Effect of temperature on phenol adsorption

T he e ffect of temperature o n th e adso rpti o n of phenol o n HA-P ILC was s tudi ed us ing 50 mg/L of pheno l soluti on at different temperatures of 10, 20,

30 and 40°C (Fig . 4). The ra te of adso rption de­c reased with increase in temperature. T he amount of adsorpti o n of phenol o n the adso rbe nt dec reases from 2 1.25 (85 %) to 17 .8 (7 1.2%) mg/g with the

increase o f temperature from 10 to 40°C. A n in­crease of adso rpt ion capac ity of phen o l with the de­crease of tempera ture suggests th at pheno l adso rp­tion o n thi s adso rben t is exothermi c. The ac tivatio n energy of an exoth ermic process is zero. Exother­micity of the adsorpti on process indi cates that the forces ho ld ing the pheno l o n the surface of the ad­sorbent are physicai in nature o r physisorpti o n. Thi s arises due to the Van der Waa ls forces between the non-reacting molecules. At lower temperature the mo lecul es are effectively bound together to the sur­face of the so lid adsorbent. At lower temperatures the stabilization or phenol mo lecul es is maximum. T he low solubility of phenol at lower te mperature consti tutes much to the enhancement of hi gher phe­no l uptake at lower temperature.

Adsorption dynamics

The rate at which phenol will be removed from di­lute aq ueous solu tio ns by the adsorbent is a sig nifi ­cant fac tor for ap li cat io ns of thi s process in the treatment o f phenol ic wastewaters . In o rder to quan­tify the ex tent of change in adsorpt ion kineti cs, the first-order reversible kinetic model described by B . I 16 d anelJee el a. was use .

In [I-~l=-k I X ad Ae

. .. (5)

where karl is the first-order rate constant. XII and XII" are the fraction of phenol adsorbed at time t and at equilibrium respecti vely. The va lues of karl were cal­culated from the slope of the linear pl o t of In( 1-XI/X;\e) versus I . The va lues of diffusion coeffic ient D;, were ca lcul ated for the adsorption of pheno l onto HA- PILC by assuming parti c le phase contro l gover-

by assuming particle phase contro l governed by Ficks second law. Ruthven l

? proposed the following kinetic model for particle diffusion.

X II 6 7[- D; I

[

J 1 I ---=~ exp ---2- ... (6) X Ae n r

where D j is the intraparticle diffusion coeffic ient , r is the particle size radius. The va lues of D j were calcu­lated from the slope o f the In ( I -XI/XAe) versus 1 plots ; the slope can be represented as

n 2 D k =--' ad 2

r ... (7)

T he straight line plots of In ( I-XA/XIIJ versus l at dif­fere nt concentrat ions and temperatures (F ig. 5) indi­cate th at the present system is the di ffu sio n contro ll ed firs t-order revers ible kineti cs . The va lues of k arl and D; are presented in Table 2 . For the initial concentrati o n ranges between 25 and 100 mg/L, the va lues of k ad

vary between 6.67x I 0.3 and 6.2x I 0-3 min-I. With the

decrease in temperature from 40 to 10"C the values of

~

<I ~ X x< '---------"

.=

O ....---"""T""---r-----r------,

-0.5

-1

-1 .5

-2

0

-0 .5

-I

-1.5

-2

(A)

•

Sorbent dose : 2 gi L pI-! : 5.0 Temperature : 30°C Agitation speed : 200 rpm

(B)

• : 25 mg/L • : 50 mg/L .. : 100 mg/L

. : 10°C • : 20°C .. : 30°C • : 40°C

Sorbent dose : 2 gi L ~ pI-! : 5.0 ~ Init ia l eonen. : 50 mg/L • Agitation speed : 200 rpm -2.5 L...:..:::.....::...;,.:......:.::... ___ ....:.... _____ ---.J

o 50 100

Time(min)

i 50 200

Fig. 5- First- order reversible kinetic plots 1'0 1' the adsorption of phenol onto HA-PILC at different (A) concen trations and (B) temperatures

+

VINOD & AN IR UDH AN: TR EATM ENT OF PH ENOL RI CH AQUEOUS SOLUTI ONS 133

Table 2-Kinetic parameters for the adsorpti on of phenol onto HA- PI LC

Vari able

Concentrati on (mg/L)

25 50 100

Temperatu re (0C)

10 20 30 40

k ml

(x IO' min-l)

6.67 6.32 6.20

8.32 7.49 6.32 5.47

OJ (x I 013 n//s)

3.26 3.09 3.03

4.07 3.66 3.09 2.67

k arl increases fro m 5.47x 10-' to 8.32x lO-3 min-I. The results clearl y indicate that sorption is enhanced at lower temperatures. The increase in D; values with increasing concentrati on and decreasing temperature support the contention that particle diffusion is the rate controlling mechani sm. D; va lues for the phenol adsorpti on are comparable to those reported in the li terature_ For example, the adsorpti on of phenol on acti vated carbon controll ed by intraparticle diffusion l 8

and in thi s case the va lues of D; were found to be in range of 1.2x 10-13

- l .4x 10-13 m2/s.

Effect of agitation

Effect of agitation speed on the adsorption of phe­nol on HA-PILC was stud ied. The percentage adsorp­tion increases with increasing speed. With an initial concentrati on of SO mglL , the percentage removal of phenol was found to be 78.2, 84.5, 89.9 and 92.6% at 100, 200, 300 and 400 rpm respectively. The results indicate that external adsorption of phenol onto sorb­ent is controlled by the degree of ag itati on. The in­crease in ag itati on decreases the boundary layer re­sistance to mass transfer in the bulk and increase the driving force of phenol ions. The process would be influenced by the concentration gradient between those two points and the thickness of the diffusion layer, which is a functi on of the agitation process 19.

Another reason may be due to the kinetic energy gain by the sorbate species during the agitati on. With the increase in agitation speed, the phenol molecules get activated due to gain in kinetic energy and easily cross the potential barrier.

Adsorption isotherm

The adsorption isotherm has been of immense im­portance for environmentalists dealing with research

250 Sorbent dose : 2 giL • : 10 °C pH : 5.0 + : 20 °C 200 Agitat ion time : 4 h

• : 30 °C ,,-., Agitati on speed : 200 rpm

• : 40 °C e.II t50 -... e.II e '-' . 100 0"

50

5UU

Ce

(mg/L)

Fig. 6- The adsorpti on isotherms of phenol onto HA-PILC

work on wastewater treatment by adsorption tech­nique because it provides approx imate esti mation of adsorpti on capacity. The adsorpti on isotherms are regular, pos iti ve and concave to the concentrati on ax is (Fig .6). Initi ally the adsorption is quite rapid , which is foll owed by a slow approach to equili brium :1t

hi gher sorbate concentrati ons. According to Giles cl ass ifi cati on2U

, the isotherms are of the L- class, which suggests that initi ally more sites on the adsorb­ent are occupied by phenol molecules. With increased concentration vacant sites decreased, so that adsorp­tion tends to be limited. Several adsorption isotherm models have been extensively used for the in terpreta­tion of adsorpti on data. Because of the simplicity and reproducibility of results, Langmuir and Freund lich adsorption isotherms are most commonly used. The adsorption isotherms are characterized according to the Langmuir and Freundlich models described by the following equations

Ce 1 Ce -=--+ -qe Q"b Q"

I log qe =Iog KF + - logCe n

... (8)

. .. (9)

where Ce and qe are the equilibrium phenol concen­trations in liquid phase and solid phase respec ti vely. QO and b are Langmuir constants related to adsorption capacity and energy of adsorption respecti vely. KF and lin are Freundlich constants related to adsorption capacity and intensity of adsorpti on respecti vely. The plots of C/qe versus Ce were found to be linear at all temperatures (Fig. 7) . The parameters QO and b have been calculated using regressional analys is. The QO and b values decreased from 179_86 mg /g and 0_0 130

134 INDIAN 1. ENG. MATER. SCI., APRIL 2002

8 .---------------------------____ ~

6

2

Sorbent dose pH

: 2 giL : 5.0

Agitation time : 4 hr Agitation speed : 200 rpm

• : IODC

• : 20uC & : 30°C • : 40°C

o ~----~----~------~----~----~ o 100 300 400 500

Fig .7-The Langmuir plots for the adsorption of phenol onto HA-PILC

3 .-----.-----------------------------~

2

0

0

Sorbent dose pH

: 2 giL : 5.0

Agitation time : 4 hI' Agitation speed : 200 rpm

0.5 1.5

log Cc

• : IODC

• : 20DC & : 30°C • : 40°C

2 2.5 3

Fig .8- The Freu ndlich plots for the adsorpti oll of phenol onto HA-PILC

Table 3- Langmuir and Freundlich constants and standard free energy change for the adsorption of phenol onto HA-PILC

Temperature Langmuir constants

(0C) QO(mg/g) b ?

(L/g)

10 179.86 0.0130 0.9800

20 159.44 0.0100 0.9864

30 147.56 0.0063 0.9918 40 126.69 0.0032 0.9719

Table 4-Equilibrium parameter (RL) values for the adsorption of phenol onto HA-PILC

Concentration TemEerature (0C)

(mg/L) 10 20 30 40

50 0.6059 0.6675 0.7599 0.8613 75 0.5062 0.5724 0.6784 0.8054 100 0.4346 0.5010 0.6 127 0.7563 150 0.3388 0.4009 0.5 133 0.6742 200 0.2776 0.3342 0.4417 0.6081 300 0.2040 0.2507 0.3453 0.5085 500 0.133 0.1672 0.2404 0.3830 600 0.1136 0.1433 0.2087 0.3409

Llmg at 10°C to 126.69 mg/g and 0.0032 Llmg at 40°C (Table 3). Further, the essential characteristics of Langmuir isotherms can be described by a separa­tion factor RL which is defined b/ I

I RL =---

1 +hC" ... (10)

where C, is the initial concentration (mg/L) and h is the Langmuir constan t. The RL values between 0 and I at different concentrations and temperatures (Table 4)

Freundlich constants 1'1 GO KF 1111 ? (kllmo l)

8.3 1 0.5116 0.9917 -10.216 5.59 0.5472 0.9868 -1 1.227

3.12 0.6060 0.9865 -12.757 1.02 0.7236 0.9672 -14.931

indicate favourable adsorption of phenol onto HA­PILe.

The Freundlich adsorption isotherm was also ap­plied for the adsorption of phenol by HA-PILe. Lin­ear plot of log qe versus log C shows that the adsorp­tion of phenol onto HA-PILC also follows Freundlich isotherm model (Fig. 8). The values of KF and lin were calculated from the intercept and the slope of the plots and are depicted in Table 3. Table 3 shows a greater correlation coefficient with the Freundlich model than the Langmuir model. Freundl ich model is characterized by lin, the heterogeneity factor, hence it is applicable to adsorption on heterogenous surfaces, i.e., surfaces with non-energetically equivalent sites. For the Langmuir model , hypothesis predicts a ho­mogenous distribution of energies. The values of lin between 0.1 < lin < 1.0 represent good adsorption of phenol onto HA-PILe. The ultimate adsorption ca­pacity of the adsorbent can be calculated from the isothermal data. Thus, for an equilibrium concentra­tion of 1 mg/L each gram of HA-PILC can remove 8.3 1 mg of phenol at 10°C which is decreased up to 1.02 mg at 40°e. Reported adsorption capacities of organo cla/, coal f1yash22 and activated carbon22 for

+

VI NOD & ANIRUDHAN: TREATMENT OF PHENOL RICH AQUEOUS SOLUTIONS 135

phenol at an aqueous equilibrium concentration of I mg/L are 0 .50, 0.31 and 0.22 mglg respectively . The efficiency of HA-PILC for the removal of phenol from aqueous solutions is very much greater than the adsorbents reported in the literature.

The thermodynamic parameters such as !!"Co, Moot' and !!"SO for the adsorption of phenol onto HA-PILC were computed. The !!"Co values were calculated using the equation

!!"C (} =-RTlnb .. . (11)

Here b is chosen as Langmuir constant. !!,.F-f' and !!"SO values were obtained from the following equation

!!"S " !;Jf " Inb=---­

R RT . . . (12)

The values of In b were plotted against liT and using the linear regression analysis the values of !!,.F-f' (-33 .96 kJ/mol) and!!"sO (-155.19 J/mollK) were cal­culated from the slope and intercept. The negative values of !!"Co indicate that the overall process of ad­sorption is spontaneous and exothermic in nature. The negative values of !!"Co increases with increase in temperature suggesting that spontaneous nature of adsorption is inversely proportional to the tempera­ture. Exothermic nature of adsorption has also been reported by Sankaran and Anirudhan 18 for phenol ad­sorption on activated carbon. The enhancement of adsorption capacity of HA-PlLC at lower tempera­tures may be attributed to the increase of attractive forces at lower temperatures. The negative value of !!"SO indicates greater order of reaction during adsorp­tion of phenol on HA-PILe.

Cost estimation

The removal of phenol by porous polymeric ad­sorbents based on styrene matrix has been reported23

.

The porous strongly bas ic anionic exchangers based on cross-linked products of styrene and divinylben­zene (DYB), macroporous AY-17-2P anion exchanger based on styrene-DYB matrix in cr and OH- forms have also been used for the treatment of phenol rich aqueous solutions24

.25

. All these polymeric adsorbent materials are very expensive and are available for Rs . 60001-85001 per kg of resin . The cost of the adsorbent material, HA-PlLC used in the present study was cal­culated and was found to be approximately Rs . 50001 per kg. The overall cost of treatment with HA-PILC is cheaper than commercially available polymeric resins. The adsorption capacity of HA-PILC was also found to be higher than polymeric resins. The Freundlich constants, KF (related to adsorption capacity) for the

adsorption of phenol onto HA-PILC was 8.3 1 and it was very high much higher than (7 times) the value reported for strongly basic anion exchanger based on styrene-DYB matrix25 (1 .20). HA-PILC may also be used for the removal of heavy metals from aqueous solutions as the functional groups (-COOH and - OH groups) of the loaded HA provide new adsorption sites for metal ions and expected to bring down the cost factor. Studies have already been reported9

.26 on

the use of HA-clay for the removal of heavy metals from aqueous solutions. Further work is now under way to determine the effectiveness of HA-PILC at removing other phenols and heavy metals from aque­ous solutions.

Conclusions A novel adsorbent material for the treatment of

phenol-containing wastewater is proposed in the pres­ent study. The data obtained in the present paper show that humic acid treated pillared clay (HA-PILC) is an effective sorbent for phenol. Removal of >98% has been achieved under optimum conditions using HA­PILe. Increase in agitation rate and decrease in tem­perature enhance the removal process. The uptake follows a first-order reversible kinetics and the proc­ess involves pore diffusion. Sorption of phenol is pH dependent and the best results are obtained at p H 5. The equilibrium data could be described well by the Langmuir and Freundlich isotherm equations.

Acknowledgments The authors are thankful to the Head, Department

of Chemistry, University of Kerala, Trivandrum for providing laboratory facilities .

References I Perrich J R, Adsorption for Wastewater Treatment (CRC

Press, Boca Raton, FL), 1981 . 2 Crosby D G, Pure Appl Chem. 53 (1981) 1051 . 3 Reddy K A, Anand P S & Dasare B D, Indian 1 Environ

Helth, 31 (1989) 197. 4 Po ll ard S J T , Thompson F C & McConn3chie G C. Water

Res, 29 (1995) 337. 5 Cadena F, J Environ Eng, 115 (1989) 756. 6 Dentel S K, Boltero J Y, Khatib K, Demougeot H, Duguet J

P & Anselme C, Water Res, 29 (1995) 1273. 7 Dyer A, Gallardo T & Roberts C W, in : Zeolites: Facts. Fig­

ures and Future, edited by Jacob P A & Van Santen R A (Elsevier Sciences Amsterdam), 1989.

8 Vinod V P & Anirudhan T S, 1 Chern Technol Biotechnol. 77 (2001) 92.

9 Abraham B T & Anirudhan T S, 1 Sci Ind Res, 58 (1 999) 807.

10 Vil adkar S, Agarwal R & Kamaluddin K, Bull Chem Soc lpn, 69 (1996) 95.

136 INDI AN 1. ENG. MATER. SCI., APRIL 2002

II Das S K & Chatteljee M K, Bull Marer Sci, 16 ( 1993) 205. 12 Schwarz J A, Dri sc II C T & Bhanot A K, J Colloid l/IIer­

fac e Sci, 97 ( 1984) 55. 13 Dentel S K, Jamrah A I & Sparks 0 L, Warer Res, 32 (1998)

3689. 14 Olphen H V & Fri piat J J, Dala H(lIIdbookfor Clay Mil/ erals

alld oIli er NOI/ -Melllllic Mmerials, (Perga mon Press, Lon­don), 1979.

15 Virarag hava n T & Alfaro F M, J Hazard Maler. 57 ( 1998)

59. 16 Banerjee K. Cheremisinoff P N, & Lwe Cheng S, Waler Res,

3 1 ( 1999) 249. 17 Ruth ven 0 M, Pril/ciple of Adsorpliol/ al/d Adsorplioll Proc­

esses (John Wil ey & Sons, New York), 1984. 18 Sankaran N 13 & Anirudha n T S, Il/di(1II J EI/g Maler Sci. 6

( \999) 229.

19 Mckay G, Otterburn M S & Sweeney A G, Ware r Res, 14 ( 1980) 15.

20 Giles C H, McEwan T H, Nakhwa S N & Smith 0 , J Chelll Soc. 4 ( 1960) 1973.

2 1 Hall K R, Eag leton L C, Aeri vos A & Vermeul en T, Ilid EI/g CiJelll FIII/d, 5 ( 1996) 2 12.

22 Mahadeva Swamy M, Mall I 0 , Prasad B & Mishra I M, POIIIII Res, j 6 ( 1987) 170.

23 Anand P S & Dasare B 0, II/dial/ J Techl/ol, 22 ( 1984) 15 1.

24 Kovenm an Y I & Alymova A T. Kollodin Zh, 4 1 ( 1979) 563 .

25 Reddy K A, Anand P S & Dasare B 0 , II/dial/ .I Chelll Tech-1/01,2 (1995) 270.

26 Huang C &Yang Y, Waler Res, 29 ( 1995) 2455.