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Separation and Purification Technology 57 (2007) 11–16

Removal behavior of sericite for Cu(II) and Pb(II) fromaqueous solutions: Batch and column studies

Diwakar Tiwari a, Hyoung-Uk Kim b, Seung-Mok Lee b,∗a Department of Chemistry, School of Physical Sciences, Mizoram University, Aizawl 796 009, India

b Department of Environmental Engineering, Kwandong University, Gangnung, Gangwon-do 210-701, Republic of Korea

Received 11 October 2006; received in revised form 5 March 2007; accepted 7 March 2007

bstract

Applicability of naturally and abundantly available sericite was assessed for the removal of two important heavy metal toxic ions viz., Cu(II)nd Pb(II) from aqueous solutions. The present investigation is an attempt for cleaner/greener cost effective technologies in waste/effluent waterreatment. The batch type experiments showed, sericite was found to be useful sorbent for the removal of these two cations from aqueous solutions.t is to be observed that with the increase in sorptive concentration, the amount of metal uptake increased and the concentration dependence dataere fitted well for the Langmuir adsorption isotherm than Freundlich adsorption model. Langmuir monolayer adsorption capacity was found

o be 1.674 mg g−1 for Cu(II) and 4.697 mg g−1 for Pb(II). Kinetic studies enabled, a rapid equilibria was established between the soild/solution

nterface as within ca. 10 min for Cu(II) and ca. 90 min for Pb(II). Moreover, the removal behavior of sericite for these two metal ions was greatlynfluenced by the solution pH. Further, the column data were explained with the Thomas model hence to optimize the Thomas constants for thesewo ions, i.e., Cu(II) and Pb(II) for sericite. 2007 Elsevier B.V. All rights reserved.

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eywords: Sericite; Cu(II); Pb(II); Adsorption; Langmuir isotherm; Wastewate

. Introduction

The removal of heavy metal toxic ions from wastewatersas received an increased attention in recent decade for globalwareness of the underlying detriment of heavy metals in thenvironment. Applications of traditional treatment techniqueseed enormous cost and continuous input of chemicals, whichecome impracticable and unconventional and also caused forurther environmental concern. Moreover, beyond the certainimit the conventional methods viz., chemical precipitation,lectrode-deposition, membrane separations, evaporation, sol-ent extraction, etc., are technologically inapplicable. Hence, thenterest lies for more effective, economic and eco-friendly tech-iques to be developed for fine-tuning of effluent/wastewaterreatment [1–2]. In this regard ion-exchangers play a promi-

ent role for the removal/speciation of several cationic/anionicpecies in waste waters and if the adsorbent is chosen so care-ully and the solution chemistry adjusted accordingly, it can

∗ Corresponding author. Tel.: +82 33 649 7535; fax: +82 33 642 7635.E-mail address: leesm@kwandong.ac.kr (S.-M. Lee).

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383-5866/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.seppur.2007.03.005

tment

rovide an effective waste treatment even at wide range of solu-ion pH [3–6]. Interestingly, the adsorption process may alsoffer to remove effectively/efficiently inorganic- and organic-omplexed metals that would not be removed by conventionalreatment methods [7–9].

Applications of clay and minerals in waste water treatment,articularly the speciation/removal of heavy metals, has longeen assessed because of their high specific surface area, chem-cal and mechanical stability, variety of structural and surfaceroperties, higher values of cation exchange capacities, etc.10–20]. Presence of both Bronsted and Lewis acidity on clayurface further enhances its adsorption capacity [21]. Moreover,ince the clays are able to exchange their alkali metal cationsith protons, hence they can behave as a buffering medium in

ontrolling the pH of lakes undergoing acid rain [22]. Sericites a layered silicates mineral, generally recognized as white fineowders of muscovite in form, with nano-sized layer structure,nterlayer spacing of (0 0 2) plane is 10 A. It has been reported

hat it is widely used in the alkali flux [23] and cosmetics [24]owever; the application in wastewater treatment is yet to bexplored. Hence, in a quest for eco-friendly and cost effectiveleaner technologies we attempted to exploit the abundantly

12 D. Tiwari et al. / Separation and Purifica

Table 1Percentage composition of various metal oxides in sericite

Metal oxides % Composition

SiO2 70.12Al2O3 17.97Fe2O3 0.71CaO 0.27MgO 1.36KN

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2

2

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3

3

3

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3

tof sericite keeping the solution ionic strength (0.001 mol L−1

NaNO3) and pH ∼ 5.5 as constant and the initial sorptive con-centration 20 mg L−1. Results obtained are returned in Fig. 3,which clearly shows that a fast initial uptake slows down with the

2O 6.07a2O 0.14

vailable sericite for the removal of two important heavy metaloxic ions viz., Cu(II) and Pb(II) from aqueous solutions.

. Materials and methods

.1. Materials

Sericite was obtained from the Keumnam deposit, Gagok-yun, Samcheok City, Kangwon province, Korea. Sample was

rushed and sieved to obtain 14–16 mesh size by using mechan-cal sieve. No further treatment was made before applying it asn adsorbent for present investigation. The BET surface areaas found to be 2.416 m2 g−1 and the cation exchange capacityas obtained to be 3.16 mequiv./100 g of sericite. Sericite sam-le contains various metal oxides; quantitatively it was analyzednd returned in Table 1.

Copper (CuSO4·5H2O; GR Reagent, Duksan Pure Chem.,o. Ltd., Korea) and lead (Pb(NO3)2; GR Reagent, Shinyo Purehem. Co. Ltd., Japan) salts were used of GR grade. The stock

olutions (0.1 mol L−1) of the Cu(II) and Pb(II) were preparedy dissolving the exact quantity of respective salts in doubleistilled water. The stock solution was further diluted to theequired experimental concentration. The other chemicals usedere of AR or equivalent grades.

.2. Methodology

.2.1. Batch experimentsBatch experiments were performed to obtain the adsorption

ata with the variation of time, sorptive concentration, pH andonic strength. The adsorption of Cu(II) or Pb(II) was investi-ated by taking 0.20 g of sericite (14–16 mesh size) in 0.10 L oforptive solution at the desired concentration. Equilibrated theolution mixture for the desired length of time, i.e., 24 h (excepthe time variation experiments) in an automatic shaker at con-tant temperature, i.e., 25 ± 2 ◦C. After equilibration the sampleas taken out and was filtered with 0.2 �m syringe filters, and

he bulk metal concentration was measured by using Atomicbsorption Spectrometer (Varian Spectra AA-300). While doing

he pH dependence study the pH adjustment was made by addi-ion of drops of strong HNO3/NaOH.

.2.2. Column experimentsColumn studies were performed with using 1.0 cm diam-

ter glass column at room temperature. Column was packedFC

tion Technology 57 (2007) 11–16

ith 1.0 g of sericite (14–16 mesh) and the sorptive solutionsu(II)/or Pb(II) (20 mg/L) at constant pH (∼5.5) and ionic

trength (0.001 M NaNO3) was pumped upward through the bot-om of the column, using Acuflow Series II high-pressure liquidhromatograph, at a constant flow rate. Effluent samples werehen collected using Spectra/Chhrom CF-1 Fraction collectors.fter filtration of the samples through 0.2 �m syringe filters, the

otal bulk metal concentration was measured by AAS.

. Results and discussion

.1. Batch studies

.1.1. Speciation of Cu(II) and Pb(II)To evaluate Cu(II) and Pb(III) removal through the adsorption

rocess without precipitation, speciation of Cu(II) and Pb(II)as simulated with MINEQL, a geochemical simulation pro-ram, to find out what concentration of Cu(II) and Pb(II) andH can be applicable without their precipitation. Hence, var-ous species of Cu(II) and Pb(II) in solutions were analyzedt initial sorptive concentration of 20 mg L−1 (for Cu(II)) and0 mg L−1 for Pb(II) at constant ionic strength 0.001 mol L−1

aNO3 and at constant temperature 25 ◦C using this MINEQLimulation program. The simulation results obtained are shownn Figs. 1 and 2, which clearly indicate that at these concentra-ions up to pH ∼ 5.8 both copper and lead exists in its ionic form,.e., Cu2+ and Pb2+ and beyond that they form the tenorite or pre-ipitated. Hence, keeping it in view almost similar concentrationor Cu(II) and much lower concentration, i.e., ca. 20 mg L−1 forb(II) and constant pH ∼ 5.5 were chosen for studying most of

he parameters in the present investigation.

.1.2. Time variation of adsorptionStudy has been carried out with the variation of contact

ime for the adsorption of Cu(II) and Pb(II) on the surface

ig. 1. Percentage distribution of various species of Cu(II) as a function of pH.u(II) concentration: 20 mg L−1.

D. Tiwari et al. / Separation and Purification Technology 57 (2007) 11–16 13

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wo(tu(tFmodel and it infers that the interactions of metal ions to sericitesurface are chemical in nature. The reciprocal of the slopes wereobtained to find out the maximum adsorption capacity (mono-

ig. 2. Percentage distribution of various species of Pb(II) as a function of pH.b(II) concentration: 40 mg L−1.

apse of time and an apparent equilibria is to be achieved withina. 10 min (for Cu(II)) and ca. 90 min (for Pb(II)) between theolid/solution interface. No further adsorption could take places was checked even after 24 h of contact. This clearly suggestshat the adsorption of metal cations on the surface of sericiteould take place in a single step and not with any complexity25]. Nevertheless it is possible that during the initial stage of therocess, the surface coverage is low and adsorptive ions occupyctive surface sites rapidly in a random manner as a result of thishe rate of uptake is higher. As time lapses the surface coverages increased, the rate of uptake becomes slower in latter stagesnd ultimately almost a plateau region is attained when surfaceecome saturated [26,27].

.1.3. Sorptive concentration dependence studyConcentration dependence study has been carried out by

hanging the sorptive concentration from 1 to 14 mg L−1

for Cu(II)) and 1 to 40 mg L−1 (for Pb(II)) at constantonic strength (0.001 mol L−1 NaNO3) and temperature 25 ◦C.esults obtained for these two cations are plotted between themounts adsorbed (q; mg g−1) versus the equilibrium bulk con-

−1

entration (Ce; mg L ) and are shown in Fig. 4. It is to beoted that with the increase in sorptive concentration the amountdsorbed increases and almost a constant value achieved atigher concentration, this may be explicable as the adsorbent

ig. 3. Percentage adsorption of Cu(II) and Pb(II) on the surface of sericites a function of contact time. Initial sorptive concentration: 20 mg L−1; ionictrength: 0.001 mol L−1; pH ∼ 5.5.

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ig. 4. Amount of Cu(II) and Pb(II) adsorbed on the surface of sericite with theulk sorptive concentration. Ionic strength: 0.001 mol L−1 NaNO3; pH ∼ 5.5.

ites eventually become saturated with adsorbed ions and at thistage further addition of sorptive ions would not be expected toncrease the amount adsorbed significantly [28,29].

.1.4. Adsorption isothermThe Langmuir adsorption model with its usual form has been

dopted for the estimation of maximum metal uptake (q0) atifferent initial metal concentrations:

1

q= 1

q0bCe+ 1

q0(1)

here q is the amount of solute adsorbed per unit weightf adsorbent (mg g−1); Ce the equilibrium bulk concentrationmg L−1); q0 the Langmuir monolayer adsorption capacity, i.e.,he amount of solute required to occupy all the available sites innit mass of sericite (mg g−1) and b is the Langmuir constantL g−1). Fairly good straight lines were obtained while plot-ing the lines between Ce/q versus Ce (i.e., the reciprocal plot cf.ig. 5) clearly suggests the applicability of Langmuir adsorption

ayer adsorption capacity) for these two ions and these are found

ig. 5. Langmuir adsorption isotherm for Cu(II) and Pb(II) at various sorptiveoncentrations. Ionic strength: 0.001 mol L−1; pH ∼ 5.5.

14 D. Tiwari et al. / Separation and Purification Technology 57 (2007) 11–16

Table 2Comparison of Langmuir adsorption capacity of sericite for Cu(II) and Pb(II)with other adsorbents

Adsorbent Adsorption capacity(mg g−1)

Ref.

Cu(II) Pb(II)

Sericite 1.674 4.697 Presentwork

Granular activated carbon (coconut shell) 3.558 10.774 [30]Kaolinite 4.4 [10]montmorillonite 28.8Granular activated carbon (GAC) 10.77 [31]OXI-GAC (oxidized activated carbon) 49.728ZnO-GAC (zinc oxide loaded GAC) 331.52Coal fly ash prepared zeolite 50.45 [32]Commercial zeolite 53.45

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Table 3Freundlich coefficients for the adsorption of Cu(II) and Pb(II) on sericite

Cu(II) Pb(II)

Kf (mg g−1)0.868 2.056

1/n0.291 0.339

r2

0

I

wuecStcsIwpfwFfpff

S2–OH + M2+ → S2–O–M+ + H+

Moreover, on further increase in pH (i.e., beyond 7)there might be a mixed effect of adsorption and co-

Natural zeolite 8.968 [33]Clay (kaolinite based) 1.589 [15]

o be the 1.674 and 4.697 mg g−1, respectively for Cu(II) andb(II) onto the surface of sericite. While making comparisonith other commonly used adsorbents, it seems that sericiteas relatively lower adsorption capacity (cf. Table 2), howeverhe efficiency can be achieved by using cascade arrangementsn real wastewater treatment. Similarly, the Langmuir constantb’ was also estimated and these are found to be 1.289 and.626 L mg−1, respectively for Cu(II) and Pb(III). The Lang-uir constant ‘b’ can serve as an indicator of an isotherm rise

n the region of lower metal concentrations, which reflects thetrength and affinity of the adsorbent for the solute [34]. Alsot relates to the equilibrium constant of the process: Cu(II)/orb(II) + Sericite = Cu(II)/or Pb(II) . . . Sericite (surface adsorp-

ion complex). Relatively higher value of ‘b’ for Pb(II) againonfirms its higher affinity towards the sericite surface.

Further, the results on the steady-state values of sorption ofhese two cations on sericite surface at various sorptive con-entrations were also analyzed using the Freundlich adsorptionsotherm to its usual logarithmic form (Eq. (2)):

og q = 1

nlog Ce + log Kf (2)

here q and Ce are the amount adsorbed (mg g−1) and bulk con-entration (mg L−1) at equilibrium, respectively. Kf and 1/n thereundlich constants, respectively referred to “adsorption capac-

ty” and “adsorption intensity”. While plotting the lines betweenog q versus log Ce an almost non-linearity has been observed ashe r2 values lies between 0.887 and 0.687 (cf. Table 3) whichlearly suggest the non-applicability of Freundlich model. How-ver, the Freundlich constants were optimized with these linesnd these coefficients are returned in Table 3.

.1.5. pH dependence studyIn order to obtain the mechanistic aspects involved at solid

olution interface, study has been planned to obtain the pHependence data at constant sorptive concentration (20 mg L−1)nd, constant ionic strength (0.001 mol L−1 NaNO3). Resultsbtained are shown graphically in Fig. 6, which enables that

Fs0

.887 0.687

onic strength: 0.001 mol L−1 NaNO3; pH ∼ 5.5.

ith increasing the solution pH caused for increase in metalptake. The surface behavior of sericite is supposed to be differ-nt as to the usual metal oxide surface for the adsorption of metalations. It is to be noted that sericite mainly contains silanol (viaiO2 ca. 70%) and aluminol (via Al2O3 ca. 18%) groups and

hey are likely to play important role in adsorption/uptake pro-ess. Hence, the surface of sericite may behave as two differenturface-active groups, which is responsible for adsorption [15].t may be arbitrarily assigned as S1–OH site, mainly constituteith the silanol group and is become negatively charged at lowerH range (pH ca. 2–3; near to the pZPC value of silanol), whichacilitate the sorption of metal cations in this pH region. Hence,e observed relatively a higher uptake even at low pH ranges.urther, the second active centre, i.e., S2–OH represents mainlyor aluminol group, which becomes negatively charged at aroundH ∼ 6, further facilitate for the uptake of metal ions on the sur-ace of sericite. Schematically, we represent the surface behavioror metals cations (M2+) as given below:

S1–OH + M2+ → S1–O–M+ + H+

ig. 6. Effect of pH on the removal of Cu(II) and Pb(II) on the surface ofericite. Initial Cu(II) and Pb(II) concentration: 20 mg L−1; ionic Strength:.001 mol L−1 NaNO3.

D. Tiwari et al. / Separation and Purification Technology 57 (2007) 11–16 15

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perhaps be desorbed by the use of acid wash as an attemptof pre-concentration of metal ions or regeneration of thecolumn.

ig. 7. Variation of percentage adsorption of Cu(II) and Pb(II) on the surface ofericite as a function of ionic strength. Initial sorptive concentration: 20 mg L−1;H ∼ 5.5.

recipitation of metals ions on the surface. Hence, causedor apparently very high uptake of metal ions in this pHegion.

.1.6. Effect of ionic strengthThe change of ionic strength (from 0.001 to 0.1 mol L−1

aNO3) is assessed for the adsorption of Cu(II) and Pb(II) on theurface of sericite at constant sorptive concentration: 20 mg L−1

nd pH ∼ 5.5. Results obtained are returned in Fig. 7, whichlearly shows that while increasing the ionic strength the uptakef metal cations slightly suppressed. Quantitatively, the increasen ionic strength from 0.001 to 0.1 mol L−1 NaNO3 (i.e., 100imes) the uptake of metal ions decreases only ca. 11% foru(II) and ca. 26% for Pb(II). Traditionally, the ionic strengthependence of metal ions removal from solution by soil min-rals is used to distinguish between non-specific and specificdsorption. Outer sphere complexes involve only electrostaticnteraction and are strongly affected by the ionic strength ofhe aqueous phase, while inner sphere complexes involve muchtronger covalent or ionic binding and are only weakly affectedy the ionic strength [35]. Hence, we conclude that the uptake ofetal cations by sericite mainly proceeds through inner-sphere-

omplexation as it is not greatly affected by the 100-fold increasen ionic strength.

.2. Column studies

Further, in order to assess the applicability of sericite inynamic conditions, it has been used for the column experimentsor the removal of Cu(II) and Pb(II) from aqueous solutions. Theolumn data obtained are shown graphically in Figs. 8 and 9. Thereakthrough curves are analyzed by employing the Thomasquation [36] in its standard form:

Ce = 1(K (q m−C V ))/Q (3)

C0 1 + e T 0 0

here Ce is the Cu(II)/or Pb(II) concentration in the efflu-nt (mg L−1), C0 the Cu(II)/or Pb(II) concentration in theeed (mg L−1), KT the Thomas rate constant (L min−1 mg−1),

FT

ig. 8. Breakthrough curve for the ion exchange of Cu(II) on sericite fitted forhomas model. C0: 20.495 mg L−1; m: 1.0 g; Q: 4.5 × 10−4 L min−1.

0 the maximum amount of Cu(II)/or Pb(II) can be loadedmg g−1) under the specified conditions, m the mass of thedsorbent loaded (g), V the throughput volume (L), and Q ishe flow rate (L min−1), non-linear regression of the break-hrough data using Thomas equation, shown in Figs. 8 and 9,espectively for Cu(II) and Pb(II). The fitting constants KTnd q0 for the removal of Cu(II) and Pb(II) by sericitender the specified conditions are found to be respectively.32 × 10−3 L min−1 mg−1 and 0.607 mg g−1 (for Cu(II)) and.73 × 10−4 L min−1 mg−1 and 3.854 mg g−1 (for Pb(II)). Theifference observed between the static and dynamic experimentsor the removal capacity can be explained on the basis thathe insufficient time of contact given for the ion exchange of

etal ions on the sericite surface under the dynamic conditions37].

Further, the adsorbed species, i.e., Cu(II) and Pb(II) may

ig. 9. Breakthrough curve for the ion exchange of Pb(II) on sericite fitted forhomas model. C0: 19.874 mg L−1; m: 1.0 g; Q: 9.0 × 10−4 L min−1.

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6 D. Tiwari et al. / Separation and Pu

. Conclusions

The possible implication of sericite in wastewater treatmentas been assessed as it successfully applied for the removal ofwo important heavy metal toxic ions, i.e., Cu(II) and Pb(II)rom aqueous solutions. Batch type experiments revealed thatericite could be used as an alternative sorptive material forhe removal of these two heavy metal toxic ions from aqueousolutions. Adsorption data obtained for these two cations werexplained well for Langmuir adsorption model rather than Fre-ndlich model and the adsorption capacity obtained were foundo be 1.674 and 4.697 mg g−1, respectively for Cu(II) and Pb(II).he inner-sphere adsorption of Cu(II) and Pb(II) on sericite was

ound to be increased with solution pH and sorptive concen-ration. Further, the breakthrough curves obtained by columnxperiments were well explained with Thomas equation.

cknowledgement

This work was supported by grant No. RTI-05-01-02 obtainedrom the Regional Technology Innovation Program of the Min-stry of Commerce, Industry and Energy (MOCIE), Korea.

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[

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