Journal of Scientific & Industrial Research Vol.58, October 1999, pp 807-814

Adsorption Characteristics of Hg(II) on Humus-Kaolin Complex: Kinetics and Equilibrium

Beena T Abraham & T S Anirudhan* Department of Chemistry, University of Kerala, Trivandrum 695581, India

Revised received : 18 February 1999: accepted: 23 Apri l 1999

The kinetics and equilibri um of thc adsorpt ion of Hg( lI ) by humic acid coatee! kaolin (HA-kaolin), a syntheti c soil , are studied. The parameters studied arc: pH, ini tial metal ion concentrati on, particle size of the HA-kao lin and temperature. The uptake of Hg(l l) increases as the pH is increased and reaches a maximum of 82.8% for the in iti al concentrati on of 10 mg/L at pH 9.0. The applicability of external mass transfer and intrapanicle mass transfer diffusion mode ls has been investigated. The kineti c parameters such as mass transfer coefficient, diffusion ccefTicient and intraparti cle ra te constant as a func tion of initial metal concent ration , particle size of the sol id and tem perature have been calculated fo r predicting the nature of adsorpt ion. The intraparlicle diffusion of metal ions through pores in the HA-kaolin is found to be the main rate li miting step. Temperaturc dependence indicates the endothermi c nature of the process. Thc signi fi cance of the two linear relationships obtai ned by plott ing the data according to the conventional Langmuir equation is di scussed in terms of the binding energies of the two populati on sites involved whi ch have a widely differing affi nity for Hg(lI ) ions.

Introduction T he adso rption of trace metals by solid surfaces has

long been considered an important process, affect ing their transport and reguiating their free concentrations innatu­ral waters and bed sediments I. Clay mineral s, hydrous metal oxides and organic materia ls are the adsorbent species that are mostly present in sediments and sus­pended materials2. Sediments from different sources have varied adsorption c haracteristics. The importance of or­

ganic matter (humus) has been recogonised to be a ma­jor factor re lated to adsorption of heavy metals in soils or sediment/ water systems3. Therefore, it is difficult to compare experimental data from metal adsorpti on in so ils or sediments without controlling the cons istency of or­ganic coating on the solid surface. The density of metal adsorption is dependent on the humic coati ng on the sedi­ment or soi l. The adsorption of heavy metal s onto min­era i and metal ox ide surfaces has been th e subject of many studies over recent years4

-6 . However, little is known about the adso rption behaviour of c lay and ox ide sUlfaces modified by the adsorbed organic compounds 7,8

The functional groups of an adsorbed ligand may serve as new adsorption sites' for metal s at the surface. The artificial preparation of soi l as a substi tu te for severdl soils, has been accomplished by two methods, name ly coating method and evaporation method9. In thi s work,

* Aut hor for correspondence

an attempt has been made to use commercially available humic acid to prepare 'synthetic soil' with known com­position and to replace natural soil in the adsorption ex­periments. The ai m of this work was to identify the roie of adsorbed humic acid (li gand) in determining the over­all effect on Hg( IJ ) uptake by kaolin .

Experimental Procedure

Preparatiol! of Synthetic Humus-kaolin Complex The stock solution of 200 mg/L humic acid (HA) was

prepared by di ssolving humic acid (Fluka, Switzerland) in an alkali solution. The kaolin (Loba Chemie, Bombay) with average d iameter of 0 .096 mm was used. To coat the kaolin us ing 100 mL of 200 mg/L HA solut ion, acid was added by dropwise addition of 0. 1 M HCI until a pH of 3.0 was maintained and the so luti on was mixed continuos ly for about 6 h. The quantity of HA in the supernatant sol~ltion was determined using uv-vi s ible spectrophotometer (Bausch and Lomb spectronic 21-UVD) at 350 nm. The humic acid - coated kaolin (HA­kao li n) was washed with 0.0 1M NaCI04, followed by d isti lled water and was dried at 60°C for 24 h. and was fi nall y stored in a des iccator.

Batch AdsOlptiol1 Experiments

The adsorption capacity of Hg(IJ) ions onto HA-ka­olin complex was assayed by batch experiments. For this,

808 J SCI IND RES VOL.58 OCTOBER 1999

50 mL of Hg(II) solution of required concentration was agitated with 0.1 g ofHA-kaolin at 120 rpm forpredeter­mined time intervals and at 30° C using a temperature controlled water bath shaker (Remi. model G-16) . The ionic strength was maintained with O.OIM NaCI. The pH of the solution was kept constant using 0 . 1 M HCI or 0.1 M NaOH. The adsorbate and adsorbent were sepa­rated by centrifugation. The residual Hg(Il) ions were analysed using a Perkin-Elmer Mercury Analyser (Model MAS - 50A). The amount of Hg(JI) ions adsorbed was calculated from the difference between the amount ini­tially taken and the amount remaining after attainment

of equilibrium.

Adsorption Kinetic Model The adsorption of metal ions onto sorbent is assumed

to occur by the three step model:

I. Mass-transfer of Hg(JI) ions from the bulk solution to the particle surface (film diffusion)

2. Adsorption of Hg(lI) ions onto sites; and 3. Internal diffusion of Hg(II) ions via either a pore

diffusion model or a homogeneous so lid phase dif­

fusion model.

Step (2) is considered to occur very fast and so the two res istances encountered are in steps (I) and (3).

External Mass-transfer Diffusion Model This model suggested by Mckay et af. 10 has been em­

ployed for the determination of the mass transfer coeffi­cient , BL for the adsorption of Hg(II) on HA - kaolin , i. e.

... ( I )

where C is the initial concentration of metal; C, , the (I

metal concentration after ti me t; 111 , the mass of the ad-sorbent per unit volume of particle-free meta l so luti on

(giL) ; kL' the Langmuir constant (ob tained by multiply­ing (I' and b) and S, is the ou ter surface of the adsorbent per unit vo lume of particle - free slurry (cm- I) . The value of S,. was calculated using the method described ea rlier lo.

[ntraparticLe Mass-transfer Dijf"usioll Model Intraparticle diffusion was extens ively stud ied, in this

work the chosen model was based on theories devel-

oped by Weber and Morris II. The fractional approach to equi librium varies according to a function of (Oi/,-2)05, where Oi is the diffusion coefficient in the solid and r is the particle radius. Hence, the initial rate of intraparticle diffusion is calculated by linearisation of the curve {f= f (to 5).

Urano and Tachikawa l 2 proposed another kind of intraparticle diffus ion model. In this mode l, the adsorp­tion rate is assumed to be independent of the stirring speed. The diffusion coeffic ient, Oi, in the solid can be calculated using Eq.(2).

f(q,)- [1'(1 (qr)21l_4TI2DJ qa - - og - qa )J - 2.303d 2 ••• (2)

where q, and q aare the metal concentrations' on the sol id at time t and at equilibrium respectively, and d is the particle diameter.

Results and Discussion

Adsorption Isotherm ofHA The adsorption isotherm of HA by kaolin was deter­

mined by agitating 0.1 g of solid with 100 mL HA so lu­tion of concentration ranging between 10 and 300 mg/L at 30°C for 6h (Figure I). According to a category of the liquid phase adsorption from aqueous solution by Gi les et al.13 the curve of the adsorpt ion isotherm belongs to C-type, in which the apparent saturated concentration of HA on the kaolin is 2 1.0 mg/g. The C-type isotherm in­dicates that the number of adsorption sites remains con­stant irrespective of the quantity of the sorbed substance. This happens when the molecules of dissolved substance are equally weli adsorbed on the surface of the sorbent itself as well as on earli er adsorbed layer of the di ssolved substances. Humic acid forms a second layer outside the first layer with the hydrophobic interact ion l 4 . Accord­ing to thi s adsorption isotherm, it was possible to design an operation condition for prepari ng synthetic humu s -kaol in complex.

Characterizatio/l oll-IA-kaolill Complex The IR spectra of kaolin and HA - kaolin were ob­

tained using a Bruker IFS 66V FfIR spectromete r. Ka­olin shows a peak at 1028 ern-I which is att ributab le to the vibrations of the Si - 0 or - 0 Si - 0 valence bonds ls The absorption of H-O-Al appears at 773 cn,-I. The band at 457 cm-I is due to the deformation

ABRAHAM & ANIRUDHAN: ADSORPTION OF Hg(lI) ON HlJMUS-KAOLlN COMPLEX 809

CI) --CI)

E

~

30

25

20 .

15

10

5

0 0 ' 50 100

Adsorbent dose : I giL Equilibrium time: 6 h Ionic strength : 0.01 M pH : 3.0

150 200 250 300

C.' mglL

Figure I - Adsorption isotherm of HA on kaolin

oscillation of Si-O and Si - 0 - A116. The IR spectrum of HA - kao lin shows a broad spectru m around 34 18

em-I representing the overlap of OH, C-H, N- H a nd

C-O stretchin g v ibrati o n . The peaks at 1596 a nd

2922 cm-I a re due to the N-H bonding and C - H

stretching from CH2 group, respective ly. The add i­

tional peaks at 1740 cm-I (v c.o) and 1425 cm-I (v c=o) indicate the presence of COOH groups in H A-ka­

o lin . Based on the results, it is assumed th at kao lin

surface is coated with humic acid.The ph ysica l and

surface properties of HA- kao lin a re: surface area,

56.60 m 2/g; appare nt density, 2.42 g/mL; poros ity,

0.49 mUg; cati on - exchange capacity, O.4 lmeq/g and pHzpc 3.5 .

Effect of pH on H g( II) Adsorption

The removal of Hg(II) by HA-kaolin from an aq ue­ous so luti on at va ri ous pH was examined by batch tech­nique (Figure 2). The percentage adsorption of Hg( lI ) increased as the pH was increased and reached a maxi­mum of 82.8% at pH 9.0. Precipitation of meta l hydrox­ide was not visual ly detected because the initial concen­tration of metal ions was ve ry low (10 mg/L). The effect of pH on metal ion adsorpt ion can be expla ined as due to the exchange behaviour of H+ ions from per ipheral -COOH groups from the adsorbed hum ic ac id. T he fi nal pH of the reaction mixture remai ned between 2.4 and 7.6 during the ex periments when the initial pH of the reaction mixtu re varied from 2.0 to 9.0. This indicates that as the metal ions are bound on the substrate, H+ ions

100

90

80

~ 70 0

«I 60 , 0 50 . e .,

0:: 40 .

30

20

10 .

O .

0 2

Init ial Hg(lI) concn : 10 mgIL Equilibrium time : 6 h Ionic strength : 0.01 M Adsorbent dose : 2.0 gIL

4 6

pH

8 10

Figure 2 - Effect of pH on the removal of Hg(I1) by HA-kaolin

are released into the solution. Other sites on the modi­fied kaolin can also contribute to the adsorpti on process .

Adsorption Dynamics Mercury adsorpti on kinetics using H A - kao lin was

studi ed re lative to initia l metal concentration, particle size of the sol id and temperature using three model s of s in g le diffusion desc ribed prev iously. The pl ots of

In ( cC I - I + I k ) versus t were found to be linear, sug-... {I 1" L

ges ting the va lidity of the Mckay et ai. equat ion fo r the present system (Figures 3-5) . The variat ion of BL va lues with initial concentrati on, parti c le s ize and temperature were determined fro m the slopes and intercepts of the plots and are gi ven in Table I. The BL values increased with increase in te mperature but decreased with increase in particle size and initial concentration. This is because, smaller particles have large ex tern al surface area ava il­able for adsorpt ion per un it mass of adso rbent than larger particles and could anticipate hi gher BL values.

Besides adsorpt ion at the outer surface of the adsor­bent, there is also a possibility of intraparticle diffussion of Hg(JI) ions from the bulk of the outer surface into the pores of the material of the adsorbent. T hi s possibility was tested usin g the two models deve loped by Weber and Morri s (W&M) and Urano and Thachikawa (U&T). The W &M model was tested by plotting q, amount of Hg(U) adso rbed per uni t weight of adsorbent versus time 1/2 The double nature (curved and linear) plot , were obta ined fo r the adsorpti on process at different concen­tration s, partic le size and temperature (Figures 3-5 ), in-

8 10 J SCI IND RES VOL.58 OCTOBER 1999

0 (A)

:t -1 S + - -2 '-' ---"'-U

-3 Initial Hg(1I) concn. : + 10 mgIL

u- -4 • 25 mgIL

'-' :s- A 50 mgIL

-5 x 75 mg/L

-6

0 100 200 300 400

t, min

1 • • (B) 0.9 .. 0.8

0.7

0.6

r:r 0.5

---0- 0.4

0.3 Initial Hg(IJ) concn. : + 10 mgIL

0.2 . 25 mgIL

0.1 . A 50 mgIL x 75 mgIL

0 0 100 200 300 400

t, min

20 Initial Hg(II) concn. : + 10 mgIL (C)

18 • 25 mg/L

16 A 50 mg/L

14 x 75 mg/L

D!I ~ 12

~ 5 ~

10

8

6

4 • • • • 2

0

0 5 10 15 20

t Yo, min'!, Figure 3 - Effect of initi al concentration on the kineti cs of Hg(lI )

sorption by HA-kaolin. (A) Ex ternal mass transfer diffu ­sion model , (8) Intrapa rti cle diffus ion model of Urano and Tachikawa, and (C) Intraparti cle diffusion model of Weber and Morris

dicating the existence of intraparticle diffusion in the adsorpti on process!? The initia l curved portion repre­senting the film diffusion and subsequent linear portion representing intraparticl e di ffusion . The values of

0

~ -1 ~

S -2 + -'-' -3 ---• ~ U -4 --. U '-' -5 :s-

-6 .

-7

0

Part icle size: + 50.8 x 10') em • 14.9 x 10') em A 10.6 x 10') cm x 7.4 x 10') em

(A)

100 200 300

t, min

t'!"min'h

400

Figure 4 - Effect of panicle size on the kinetics of Hg(l l) sorpti on by HA-kaolin . (A l External mass trans fer diffusion model, (8) Int raparticle di rfusion model of Urano and Tachi kawa, and (C) Illlrapanicle diffusion model of Weber and Morri s

intraparticle diffusion rate constant, k far different con-I'

centrat ians, particle s ize and temperature were calcu-lated from the linear portion af the respective plots and are given in Table I . The k values increased with in·

~ p

ABRAHAM & AN IRUDHAN : ADSORPTION OF Hg( lI ) ON HUMUS- KAOLIN COMPLEX 8 11

crease in the concentration, suggesting that the rate of adsorption is governed by the di ffusion of adsorbed ions within the pores of the adsorbent. The increase in metal concentrations in solution seems to reduce the diffusion of metal ions in boundary layer and to enhance the dif­fu sion in the solid .

The particle size had a marked effect on the adsorp­tion rate. The values of k increased with lowering the

f1 particle size of the sorbent. For larger particles, the di f-fusional resi stance to mass transport is higher and most of the internal surface of the particle may not be utili sed for adsorption and consequently, the amount of Hg(lT) adsorbed is small. Similar conclusions were obtained for the adsorption of heavy metal s on var ious so lid sur­faces 18-20. It is apparent from the tab le that the k" values observed in thi s experiment support the hypothysis that the intraparticle diffusion mechanism places a signifi ­cant role in the adsorption of Hg(IT) by HA-kaolin .

The pore diffusion coefficient , Oi , for the adsorp­tion of Hg(lI) into HA-kaolin at various concentrations, particle size and t emperature were calculated from the slope of the U & T plots (Figures 3-5 ). The Oi value was hi gher at higher concentration and temperature (Table I ). However, the va lues of Oi calculated from the U&T plots for various particle sizes were found to be non-linear and non-proporti onal and the particles of 14.9 x 10-3 and 50.8 x 10-3 cm showed partial super position of kinetic data. A similar phenomena in Di values with lowering particle size for vanadium (IV) adsorption onto chitosan has been reported by Charrier el al. 2 1. Among the two intraparticle diffusion models, it seems that W&M model fits the experimental results better than the model ofU&T. According to the earlier workers22.n , for pore diffusion to be rate limiting, the pore diffusion coefficients should be in the range of 10-11 - 10-13 m2/

min . As per thi s, the rate limiting step appears to be pore diffusion for the present system . However, further ex­perimental work is in progress to clarify thi s aspect. The increase in k and D values with temperature may be ", . due to enhanced rate of intraparticle diffusion of metal ions, as diffusion is an endothermic process.

Adsorption Equilibria In general, the adsorption isotherm defines the di s­

tribution of a solute between the liquid and solid phases after the sorption reaction has reached an equilibrium state. As pointed out by earlier workers, a major advan­tage of the Langmuir isotherm equation is that it is pos-

o ___ -1 ~..J

E -2 + -::r -3 , ---S2: -4 U :=: -5

Temperature: + 25°C

• 30°C ... 35°C x 40°C

(A) -7~ ____ -4~ __ ~~ ____ ~~ ____ ~

o

0.8 -

0.7

0.6 -

100 200 300 400

t, min

r:f 0.5

---0" 0.4

0.3

0.2 I 0.1

Temperature : + 25°C

• 30°C ... 35°C x 40°C

0 __ ----~------~ ______ 4_ ____ ~

o 100 200 300 400

t, min

6 r----------------------------, (C)

5

4

2 Temperature: + 25°C

• 30°C ... 35°C x 40°C o __ ------~------~--__ ~~ ____ ~

o 5 10 15 20

Figure 5 - Effec t of temperatu re on the kinetics of Hg(lI ) sorptio n by HA-kaolin. (A) External mass transfer diffus ion model, (B) Intra part icle dilfusion mode l of Urano and Tachikawa, and (C) In traparli c le diffusion model of Weber and Morris

sible to calculate an adsorption max imum and a relati ve binding energy constant for metal adsorption. The con­ventional LangJi'lUir adsorption equation can be written as Eq.(3):

812 J SCI IND RES VOL.58 OCTOBER 1999

Table I - Kinetic parameters for the adsorption of Hg(lI) on HA -kao lin

Parameters External diffu sion Intraparticle diffusion

BL

, em/s W&M model, k . mg/g/m inY> r '.

U&T model Di, mllmin

Initi al Conen, mglL 10.0 25.0 50.0 75.0 Particle size, em 7.4x I 0" 10.6x 10-J 14.9xlO-' 50.8x 1 O-J Temperature, "C 25 30 35

40

C I C

1.602X I0-' 0.425X I 0-' 0.244X I 0-' 0.189X 10"

2.811 x 10-' 2.564 x 10-' 1.761 X 10-5

1.023 x 10-'

1.973 x I 0-' 2.602 x IO-' 3.046 x 10-'

3.547 x I 0-'

-' -" = -+ - " C/ ,. b8 " 8

... (3)

where q e is the amount of metal adsorbed per unit weight

of adsorbent at equilibrium, Ce is the equilibrium metal concent ration band e are the Lanbcrmuir constants re-, (I

lated to binding energy or stab ility constant and maxi­mum adsorpti on capacity, respectively. When the sorp­tion data were plotted according to the above equat ion ,

i.e. Cel qc versus Ce' linearity was obtained for equilib­rium Hg(l[) concentration (C) greater than 37.2 mg/L

(Figure 6). Below this equil ibrium concenrration, de­viation from the linear relationsh ip was obtained and it

is clear that the deviation also resu lted in another s trJ ig ht line. This indicates the existence of two types of adsorp­tion sites, which have widely differing affi nity for Hg

(II) . The adso rpti on capacities for these two types of sites

were determined using rearranged Langmuir equLltion24

[Eq .(4)] .

hIe' C bile II "C,.

q,. = I + b;'C:: + 1+ b" C,. ...(4)

where superscripts I and II refers to part I (straig ht line corresponding to lower C

e values) and II (straight line

correspondi ng to higher Ce values). Equilibri um concen­trations for which two straigh t lines representing part 1

0. 164 0.365 0.598 0.632

0.215 0. 160 0.156 0. 130

0. 169 0.17 1 0.174

0. 197

1.014X10-12 1. 1I3X 10-12

1.1 57X IO-12 1.175X I 0-12

0.536 X 10.12

11.331 X 10-1) 22.782 x 10-12

18.132 x 10-12

0.979 x I 0-12

1.006 x 10-12

1.017 xiO-11

1.081 XIO-11

and II are inidicated by arrows in Figure 6. The values

of 8 1 and bl for part I were calculated by regress ional

analysis. The values of 8 1i and b" for part II were calcu­lated by subtract ing the 8 1

0 value for part I from each of

the qc values for the data points in part II . Thus, a new

regressional equat ion for C/qe versus Ce for part II was used to compute 8 i1 and b" for part II . The values of 8 1

and b' for part I and 8" and b" for part II were found to be 20 .37 mg/g and 768x 10-2 Llmg and 24 .29 mg/g and 1.61 x I 0-2 Llmg, respect ive ly. The to ta l adsorption

capapcity (8 ' + 8") was found to be 44.66 mg/g. The

adsorption maxima for part I (810

) was 45 .6% of the to­tal adsorption maxima (81

0+ 8 11

0), whereas the pemsal of

b l values reveals that the adsorption sites in part I (b l )

( b' l

have much greater affinity 47.7 times , i. c. /)" ) for the ad-

sorption of Hg(II) than those in part II (b ll ) .

Fried and Broeshart25 have modified the Lang muir equation as Eq. (5).

r. =e -~ 7,. " l C 7 ,.

... (5)

For a g iven site or uniform population si tes, a plot of qe versus q/Ce g ives a stra ight line frem which 8

0 can be

calcu lated directly from the intercept and b from inverse

o f slope. When the sorpt ion data were plotted accordi ng to thi s modified equation. a curved relationsh ip was ob­ta ined (Figure 7), indicating the presence of more than one population sites. This curve can be resoived into

ABR AHAM & AN IRUDHAN: ADSORPTION OF Hg(lI ) ON HUMUS-KAOLIN COMPLEX 813

8

7

6

~ 5

-.4 ~ U 3

2

Adsorbent dose : 2gIL pH : 6.0 Equilibrium time : 6 h

o+-______ +-______ +-______ ~------~

o 50 100 150 200

C.' mg/L

Figure 6 -Isotherm for the adsorption of Hg(lI ) by HA-kaoli n using the conventional Langmuir equation

two straight line components using graphical method . As a consequence, equation may be rewritten as fo ll ows for two population sites [Eq.(6)] :

, " , q ,. " q ,. q,. =8 ,, - -,- +8 " - -,,- ... (6)

b C, h C,.

where superscripts I and II referto reg ion I and II corre­sponding to lower and hi ghe r C,. va lues, respect ive ly. The values of eo and b for two populations were ob­tained by resolving the curve in Figure 7 into two straight lines. The total adsorpti on max ima fo r part I and n. (Y­intercepts of the curve, Figure 7) were fo und to be 14.2 1 and 29.64 mg/g, respecti vely; which, are in good agree-

ment w ith the va lues obta ined ( 8 ' 1/ +8"0 = 44.66 mg/g)

using regression analys is and the conventional Langmuir equation . A plot of the sorpti on data according to a rear­ranged form of the Langmuir equati on [Eq. (6)] gave a curve which could be resolved sati sfactoril y in to two straight line components, indicating the ex istence of two populations of sites .

Conclusions The adsorption behav iour of humic ac id on kao lin

can be described by C-type isotherm (multil ayer adsorp­tion). The adsorpti on of Hg(II) has been fo und to be pH dependent and increases with increase in pH up to 9.0. The kinetic data could be descri bed through ex ternal and internal mass-transfer di ffusion mode ls. T he kinetic pa­rameters as a function of ini tial concentrati on, part ic le size of the solid and te mperature have been determined .

40

35 -

25 blI

~ 20

r:r- 15

10

5

Adsorbent dose : 2gIL pH : 6.0 Equilibrium time : 6 h

o+, ____ ~------~----~----_+----~ O· 4 5

Figure 7 - Isotherm for the adsorption of Hg(ll ) by HA-kaolin obtained using the rearranged Langmuir equation ; curves resolved into two straight lines, parts I and II

T he adsorption isotherms have been determined and data have been analysed according to the rearranged Langmuir model for two populati on sites. It has been found that the sites in part I corresponding to lower equil ibrium concentrat ion have much hi gher (47 .7 times) bi nd ing energy constant than th ose in part II. correspond ing to higher equilibrium concentration.

Acknowledgement The authors are thankful to the Head, Department

of C hemi stry, Unive rs ity of Kerala, fo r provid ing the laboratory fac ilities.

References I Balistrieri L S & Murray J W, Ceochil1l Coslllochilll

Acta, 46 ( 1982) 43 1. 2 Elli ot H A, Liberati M R & Huang C P, Wa ter Air Soil

Poilu, 27 ( 1986) 279. 3 Sposito G, The Chemistry of Soils (Oxford University

Press, London) 1989. 4 Harvey D T & Linton R W, Colloid Surf, 11 (1989) 8 1 5 Bruemmer G W, Gerth J & Tiller K G, J Soil Sci, 39

(1 988) 37. 6

7

R 9

10

Davis J A & Kert D B, Mil/eral - Water Interface Chelll­istl)" edi ted by M F Hochel la and A F Whi te (Minera l So il , Ameri ca) 1990. Ki shi H, COl/taminated Soil, edited by K Wolf, W J Brink and F J Colon (Klu wer Academic, Gellnany) 1988 Rashid M A , Chelll C eol, 13 ( 1974) 115. Huang C & Yang Y, Water Res. 29 (1995) 2455. Mckay G, Olterburn M S & Sweeny A G, Water Res, 15 ( 198 1) 327.

8 14

II

12

13

14

15

16

17

J SCI IND RES VOL.58 OCTOBER 1999

Weber W J & Morri s J C, Ad va nces in water pollution research : Removal of biologically res istant po llutants from wastewaters by adsorpti on, in Proc, lilt COli! 011

Water Pollution (Pregemon Press, Oxford ) 1962.

Vrano K & Tachikawa H, Ind Ellg Che/ll Res, 3() (199 1)

1897.

Giles C H , Smith D & Huitson A, J Colloid Illte/face Sci, 4 (1974) 755 .

Murphy EM, Zachara J M & Smith S C, Ellviwll. Sci

Technol, 24 ( 1990) 8 14.

Nakanishi K & Solamon PH, IlIjiwed AbsOIptioll Spec­troscopy (Holden Day. ln c, San Francisco, USA) 1977

Szymanski H A & Alpert N C , TheO/)' Gild Practice of Infra red Spectroscopy (Plenum Press , New York) 1964.

Mckay G, Olterburn M S & Sweeny A G, W at Res,

(1980) 15 .

18

19

20

21

22

23

24

25

Saucedo I, Guibal E, Roulph C & Le Chloirec P, Ell viron Technol, 13 (1992) 1101.

Guibal E, Saucedo I, Roussy J, Roulph C & Le Chloirec P, Water S A, 19( 1993) 11 9.

Raji C, Shubha K P & Anirudhan T S, Ind iall J Ell viron Hlth , 39 ( 1997) 230.

Charrier M J, G ui bal E, Roussy J, De langhe B & Le Chloirec P, Wat Res, 30 ( 1996) 465.

Streat M, Patrick J W & Perez M J C. Wat Res, 29 ( 1995) 467.

Singh R D & Rawat N S , IlI.diall J Environ Hlth, 35 (1993) 262.

Syers J K, Browman M G, Smillie G W & Covey R B, Soil Sci 50'c A/ll er Pmc, 37 ( 1973) 358

Fried M & Broeshart H , Th e Soil-Plant System ill Rela­tioll to Ill organic NlltritiOIl (Academic Press, New York)

1967.