Adsorption of Cd(II) and Pb(II) onto Clarified Sludge - Kinetics, Thermodynamics and Desorption and Application Study

Transcription

1 T. K. Naiya t al. / GMSARN Intrnational Journal 3 (009) Adsorption of and onto Clarifid Sludg - Kintics, Thrmodynamics and Dsorption and Application Study T. K. Naiya, S. N. Mandal *, B. Singha, A. K. Bhattacharya and S. K. Das Abstract Clarifid sludg is a major wast obtaind from basic oxygn furnac during stl making procss. In th prsnt study clarifid sludg has bn charactrizd and usd for th rmoval of and from aquous solution. Th ffct of various physicochmical paramtrs such as ph, adsorbnt dosag, adsorbat concntration, contact tim and tmpratur on adsorption procss was studid in batch xprimnts. Kintics data for th adsorption of as wll as wr bst dscribd by psudo-scond ordr modl. Th ffctiv diffusion co-fficint of for and adsorption wr of th ordr of m /s and m /s rspctivly. Th maximum uptak wr 36.3 mg/g and 9.51 mg/g for adsorption of and rspctivly. Th adsorption data for both th mtal adsorption can b wll dscribd by Langmuir and Frundlich isothrm rspctivly. Th rsult of th quilibrium studis showd that th solution ph was th ky factor affcting th adsorption. Th optimum ph for both th adsorption was 5. Mass transfr analysis was also carrid out for th adsorption procss. Th valus of mass transfr cofficints (β) obtaind from th study indicat that th vlocity of th adsorbat transport from bulk to th solid phas was quit fast. Th thrmodynamic studis indicatd that th adsorption is spontanous and xothrmic for adsorption and ndothrmic for adsorption. Th sorption nrgy calculatd from Dubinin-Radushkvich isothrm modl indicatd that both th mtal adsorption procss wr chmical in natur. Dsorption studis wr carrid out using dilut minral acids to lucidat th mchanism of adsorption. Application studis wr carrid out considring th conomic viwpoint of wastwatr tratmnt plant oprations. Kywords Clarifid sludg, Adsorption, Psudo scond ordr, Frundlich adsorption isothrm, Mass transfr. 1. INTRODUCTION Rapid industrialization has lad to incrasd disposal of havy mtals into th nvironmnt. Environmntalists ar primarily concrnd with th prsnc of havy mtals du to thir toxicity and impact on human halth and nvironmnt. Th harmful ffcts of includ acut and chronic mtabolic disordrs, such as itai-itai disas, rnal damag, mphysma, hyprtnsion and tsticular atrophy tc. [1-]. Lad poisoning in human causs svr damag to kidny, nrvous systm, rproductiv systm, livr and brain. Svr xposur to lad has bn associatd with strility, abortion, stillbirths and no-natal daths tc. [3-4]. Cadmium is introducd into th watr from smlting, mtal plating, cadmium-nickl battris, phosphat frtilizrs, mining, pigmnts, pigmnts, stabilizrs, alloy industris and swag sludg. Whr as Procss industris, lik battry manufacturing, printing and pigmnt, mtal plating and finishing, ammunition, B. Singha, A. K. Bhattacharya and S. K. Das ar with th Chmical Enginring Dpartmnt, Calcutta Univrsity, 9, A. P. C. Road, Kolkata , India. Phon: Ext 47; Fax: ; drsudipkdas@vsnl.nt. T. K. Naiya is with Dpartmnt of Chmical Enginring, Durgapur Institut of Advancd Tchnology and Managmnt, Rajbandh, Durgapur-1, India. * S. N. Mandal (corrsponding author) is with National Institut of Tchnical Tachrs Training and Rsarch, Block-FC, Sctor- III, Salt Lak City, Kolkata , India. drsailn@hotmail.com. soldring matrial, cramic and glass industris, iron and stl manufacturing units gnrat larg quantitis of lad. Du to toxicity, th rcommndd maximum tolranc intak of by IS for discharg in inland surfac watr and public swrs ar.0 and 1.0 mg/l rspctivly [5]. Th prmissibl lvl of in watr according to World Halth Organization is 0.05 mg/l [6] and in wastwatr as st by Environmnt Protction Agncy [7] is 0.05 mg/l. Whr as th tolranc limit of according to Burau of Indian Standards (BIS) is 0.1 mg/l [8]. Th saf and ffctiv disposal of mtal containing wastwatr is a challnging objctiv for industris bcaus cost-ffctiv tratmnts altrnativs ar not radily availabl. Convntional tchnologis for th rmoval of havy mtal ar chmical prcipitation, ion xchang, lctrochmical prcipitation, solvnt xtraction, mmbran sparation, concntration, vaporation, rvrs osmosis, mulsion pr traction and adsorption. Among ths tchnologis, adsorption is a cost-ffctiv and usr frindly tchniqu which can b usd only at th trtiary stag for th rmoval of havy mtal [9].. MATERIALS AND METHODS Th clarifid sludg was collctd from th sludg thicknr of Basic Oxygn Furnac of Rourkla Stl Plant, Rourkla, Orissa, India. Th sludg initially in th dust form in th basic oxygn furnac was arrstd by hydro jtting followd by passing through vntur scrubbrs and thn collctd from clarifir aftr sttling. 151

2 T. K. Naiya t al. / GMSARN Intrnational Journal 3 (009) Clarifid sludg, aftr collction it was ground, homognizd and drid at 105 ± 5 0 C for 3 hr and coold to ambint tmpratur in a dsiccators. All th ncssary chmicals usd in th study wr of analytical grad. Cadmium nitrat ttra hydrat [Cd(NO 3 ), 4H O] and Lad nitrat [Pb(NO 3 ) ] wr obtaind from E. Mrck Limitd, Mumbai, India. Stock solution of th abov havy mtals was mad by dissolving xact amount of rspctiv mtal salt. Diffrnt initial concntration of mtal solutions was prpard by propr dilution from stock 1000-ppm mtal standard. ph of th solution was monitord in a 5500 EUTECH ph Mtr using FET solid lctrod calibratd with standard buffr solutions. Ncssary amount of clarifid sludg was thn addd and contnts in th flask wr shakn for th dsird contact tim in an lctrically thrmo statd rciprocating stroks/min at 30 0 C. Th rmaining mtal concntration in th sampl was analyzd using Atomic Absorption Spctrophotomtr (VARIAN SPETRA AA 55, USA) as pr procdur laid down in APHA, AWWA standard mthods for xamination of watr and wastwatr, 1998 dition [10]. 3. RESULTS AND DISCUSSION 3.1 Effct of ph, contact tim, adsorbnt dosag In ordr to valuat th influnc ph on th adsorption, th xprimnts wr carrid out at diffrnt initial ph valus. Th ph rang was chosn as -7 in ordr to avoid mtal hydroxids. Th ffct of ph on adsorption fficincis ar shown in Figur 1. Th uptak of by clarifid sludg incrasd as th ph incrasd. Although a maximum uptak was notd at a ph of 8, as th ph of th solution incrasd to >7, startd to prcipitat out from th solution. Thrfor xprimnts wr not conductd ovr ph 7. Th incrasd capacity of adsorption at ph >7 may b a combination of both adsorption and prcipitation on th surfac of th adsorbnt. It is considrd that clarifid sludg had a maximum adsorption capacity at a ph = 5, if th prcipitatd amount is not considrd in th calculation. Th ph rang was chosn as 3-7 in ordr to avoid prcipitat in th form of lad chlorid and lad hydroxids, which has bn stimatd to occur at ph<.0 for PbCl and ph>6.5 for Pb(OH). Th ffct of ph on adsorption fficincis ar shown in Figur 1. Rmoval of incrass with incrasing solution ph and a maximum valu was rachd at an quilibrium ph of around 5. Th mtal ions in th aquous solution may undrgo solvation and hydrolysis. Th procss involvd for mtal adsorption is as follows [11], M + + nh O = M (H O) n + (1) M(H O) n + = [M(H O) n-1 (OH)] + + H + () M + + nh O K a = [M(H O) n-1(oh)] + + H + (3) Th pk a valu for and ar 10.1 and 7.7 rspctivly. Prusal of th litratur on mtal spciation shows that th dominant spcis is M(OH) at ph > 6.0 and M + and M(OH) + at ph < 6.0. Maximum rmoval of mtal was obsrvd at ph 5 for adsorption. On furthr incras of ph adsorption dcrass probably du to th formation of hydroxid of cadmium and lad bcaus of chmical prcipitation. Th optimum ph valu for adsorption was found to b 5. Th ffct of shaking tim on th adsorption of and ion ar shown in Figur. During th xprimnt contact tim was varid from 0 to 5 h for adsorption of and 0 to 3 h for adsorption of. Th ffct of contact tim variation in th Figur indicats that th adsorption procsss rach th quilibrium aftr h and 1 h rspctivly for adsorption of and. Th initial rapid adsorption givs away a vry slow approach to quilibrium. Prcntag rmoval of mtal ion, % Symbol Mtal ion Cd Pb Initial conc. 5 mg/l Adsorbnt dosag 7.5 g/l Contact tim h Initial ph Figur 1 Effct of ph on and rmoval Fig. 1. Effct of ph on and rmoval. Effct of adsorbnt dosag on th rmoval of and was studid using Clarifid sludg at concntration ranging from 1g/L to 30g/L. With an incras in adsorbnt dosag, th mtal ion rmoval incrasd to highr mtal ion uptak by th incrasd amount of adsorbnt. For highr adsorbnt dosag, th incrmntal mtal ion rmoval bcoms vry low as th surfac mtal ion concntration and th solution mtal ion concntration coms to quilibrium with ach othr. Th optimum adsorbnt dosag on th and rmoval wr found to b 7.5 g/l for both th cass. 3. Adsorption kintics modl Th study of adsorption kintics dscribs th solut rmoval rat and vidntly this rat controls th rsidnc tim of adsorbat rmoval at th solid - solution intrfac including th diffusion procss. Th mchanism of adsorption dpnds on th physical and chmical charactristics of th adsorbnt as wll as on th mass transfr procss. With th maximum shaking spd of 10 rpm, it was assumd to offr no mass transfr (both xtrnal and intrnal xtrnal) rsistanc to th ovrall adsorption procss. Thrfor kintic can b studid through th rsidual mtal ion concntration in th solution. Th rat kintics of mtal ion adsorption on clarifid sludg was analyzd using psudo first-ordr 15

3 T. K. Naiya t al. / GMSARN Intrnational Journal 3 (009) [1], psudo-scond ordr [13], and intraparticl diffusion modls [14]. Th conformity btwn xprimntal data and th modl prdictd valus was xprssd by corrlation cofficints, r and Chi-squar tst, χ. Prcntag rmoval of mtal ion, % Symbol Mtal ion Cd Pb Initial ph 5 Initial concntration 10 mg/l Adsorbnt dosag 7.5 g/l Contact tim, min Figur Effct of contact tim on and rmoval Fig.. Effct of contact tim on and rmoval Psudo first ordr modl Th psudo first ordr kintic modl was proposd by Lagrgrn [1]. Th intgral form of th modl gnrally xprssd as follows: log K adt = log q (4).303 ( q q) 3.. Psudo scond ordr modl Th kintics of adsorption procss may also b dscribd psudo scond ordr rat quation [13]. Th linralizd form of quation is xprssd as t 1 1 = + t (5) q K q q Th adsorbat transport from th solution phas to th surfac of th adsorbnt particls occurs in svral stps. Th ovrall adsorption procss may b controlld ithr by on or mor stps,.g. film or xtrnal diffusion, por diffusion, surfac diffusion and th adsorption on th por surfac, or a combination of mor than on stps. Gnrally, a procss is diffusion controlld if its rat dpndnt upon th rat at which componnts diffus towards on anothr. Th intraparticl diffusion modl is basd on th thory proposd by Wbr and Moris [14]. According to this thory q = K idt (6) Th valus of rat constants and corrlation cofficints for ach modl ar shown in Tabl 1. In addition, th Chi-squar tst was also don to support th bst fit adsorption modl. Th quation for valuating th bst fit modl is to b writtn as ( q q ) t tm χ = (7) q tm It has bn found that χ valus ar much lss in psudo scond ordr modl (Figur 3) than that of psudo first ordr and intraparticl diffusion modl (Tabl1). Thus basd on th high corrlation cofficint and low χ valu, it can b said that adsorption of t and onto clarifid sludg follow psudo scond ordr modl Mass transfr analysis Mass transfr analysis for th rmoval of and from aquous solutions by clarifid sludg wr carrid out using th following quation as proposd by McKay t al.[15]. C 1 MK bq 1+ MK t bq ln = ln βs st Co 1 MK bq 1 MK bq MK + + bq (8) t/q, min/(mg/g) Symbol Mtal ion Initial ph 5 Initial concntration 10 mg/l Adsorbnt dosag 7.5 g/l C /q Symbol Mtal ion Tim, min Figur 3 Psudo scond ordr modl for and rmoval Fig. 3. Psudo scond ordr modl for and rmoval Intraparticl diffusion modl C Figur Fig Langumir plot plot for for adsorption of of and and rmoval rmoval. 153

4 T. K. Naiya t al. / GMSARN Intrnational Journal 3 (009) Tabl 1. Rat Kintics for adsorption of and by clarifid sludg Mtal Lagrgrn 1 st Ordr Psudo nd Ordr Wbr and Moris K ad x10 - min -1 r χ K g.mg -1.min -1 r χ K id x10 - r mg.g -1.min -1/ Tabl. Langmuir and Frundlich adsorption isothrm constants for and rmoval χ Langmuir Constants Frundlich Constants Mtal q max (mg g -1 ) B (L mg -1 ) r χ K f n r χ Tabl 3. Thrmodynamic paramtrs for th adsorption of and on clarifid sludg Mtal T (K) - G 0 (kj/mol) H 0 (kj/mol) S 0 (kj/mol) r Th valus of mass transfr cofficints (β) wr.514x10-5 cm s -1 and 4.873x10-5 cm s -1 with a high valu of co-rlation co-fficint for th rmoval of and rspctivly. Mass transfr cofficints (β) obtaind from th study indicat that th vlocity of th adsorbat transport from bulk to th solid phas was quit fast Dtrminatin of diffusivity Kintic data could b tratd by th modls givn by Boyd t al.[16] which is valid for th xprimntal conditions usd. Diffusion found to b rat controlling in th adsorption of and onto th particls of sphrical shap. For th rang 0 F(t) 1 in th solution of divalnt xchangabl ions, Boyd quation can b simplifid as [17-19] 1 π ln 1 = D t (9) F ( t) Ra Th valu of diffusion co-fficints as calculatd from th quation (9) wr found to b and m /s for th adsorption of and onto clarifid sludg rspctivly. For th prsnt systm, th valu of D, fall within th valus rportd in litratur, spcially for chmisorptions systm (10-9 to m /s) [0]. 3.3 Adsorption isothrms modl Th adsorption isothrm for th rmoval of mtal ion was studid using initial concntration of btwn 10 and 300 mg/l at an adsorbnt dosag lvl of 7.5 g/l for and at 30 o C Langmuir isothrm modl Th Langmuir quation is basd on th assumption of a structurally homognous adsorbnt whr all sorption sits ar idntical and nrgtically quivalnt. Th Langmuir adsorption isothrm [1] applid to quilibrium adsorption assuming mono-layr adsorption onto a surfac with a finit numbr of idntical sits and is rprsntd as follows, C q 1 C = + (10) q b q max max Linar plots of C /q vs. C (Figur 4) wr mployd to dtrmin th valu of q max (mg/g) and b (L/mg) Fruindlich isothrm modl Th Frundlich adsorption isothrm [] is an mpirical quation mployd to dscrib htrognous systms, in which it is charactrizd by th htrognity factor, n. Th linar form of Frundlich adsorption isothrm taks 154

5 T. K. Naiya t al. / GMSARN Intrnational Journal 3 (009) th following form 1 log q = log K f + log C (11) n Th Frundlich isothrm constants K f and n wr calculatd from Equation (11) and Frundlich plots (Figur 5) Symbol Mtal ion ln C abs log q Symbol Mtal ion log C Figur 5 Frundlich plot for and rmoval Fig. 5. Frundlich plot for and rmoval. From th Tabl, it was sn that for adsorption, χ valu of Langmuir is lowr than th Frundlich adsorption isothrm modl. Thrfor uptak of prfrably follows th Langnuir adsorption modl but it is rvrs for th adsorption on clarifid sludg Dubinin-Radushkvich (D-R) isothrm modl D-R isothrm rlats th htrognity of nrgis clos to th adsorbnt surfac. If a vry small sub-rgion of th sorption surfac is chosn and assumd to b approximatly by th Langmuir isothrm, th quantity, λ can b rlatd to th man sorption nrgy, E, which is th fr nrgy for th transfr of 1 mol of mtal ions from th infinity to th surfac of th adsorbnt. Th D-R isothrm [3] was mployd in th following linar form: ln C X λε abs = ln m (1) Th Polanyi potntial, ε, can b xprssd as, 1 ε = RT ln(1 + ) (13) C A plot of C abs vs ε is shown in Figur 6. Using th calculatd valu of λ, it is possibl to valuat th man sorption nrgy, E, from 1 E = (14) λ Th stimatd valu of E wr11.03 kj/mol and 9.90 kj/mol for and adsorption rspctivly which indicats th procss ar chmisorptions in natur Figur 6 D-R isothrm for and rmoval Fig. Fig Frundlich D-R isothrm plot for for and and rmoval. rmoval. ln K c ε Symbol Mtal ion /T Figur Fig Dtrmination Dtrmination of of thrmodynamic thrmodynamic paramtr paramtr. 3.4 Thrmodynamic study Th variation in th xtnt of adsorption with rspct to tmpratur has bn xplaind on th basis of thrmodynamic paramtrs viz. changs in Gibbs fr nrgy, nthalpy and ntropy. Th dpndnc on tmpratur of adsorption of and on th clarifid sludg wr valuatd using th following quations : 0 0 H S ln K C = + (15) RT R = (16) 0 G RT ln K C From th slop and intrcpt of th plot (Figur7), th valus of H 0 and S 0 had bn computd, whil G 0 wr calculatd using quation (16). Th valus of ths paramtrs thus calculatd ar rcordd in Tabl

6 T. K. Naiya t al. / GMSARN Intrnational Journal 3 (009) Strngth of HCl (M) Tabl 4. Dsorption of and from loadd Clarifid sludg % Dsorption of Strngth of HNO 3 (M) % Dsorption of Tst Paramtr Untratd fflunt Tabl 5. Application studis using clarifid sludg Tratd Efflunt Untratd fflunt Tratd Efflunt Rmarks PH PH.7 -- Conductivity (µmhos/cm) Conductivity (µmhos/cm) (mg/l) (mg/l).84 Succssfully mt th IS [6] norms of and F (mg/l) F (mg/l) Ca (mg/l) Ca (mg/l) Mg (mg/l) Mg (mg/l) Chlorid (mg/l) 8 4 Chlorid (mg/l) TSS (mg/l) 3 7 TSS (mg/l) Dsorption studis for and clarifid sludg systm Batch dsorption xprimnts wr carrid out to furthr lucidat th mchanism of adsorption. Attmpts wr mad to dsorb and from clarifid sludg using diffrnt concntration of HCl or HNO 3 solution having good potntial to dissolv mtal ions undr study by batch dsorption tchniqu maintaining th sam conditions similar to batch adsorption studis. Th xprimnts conductd for h and 1 h for and dsorption rspctivly. Th rsults of dsorption xprimnts with various concntrations of HCl or HNO 3 ar shown in Tabl Application studis using industrial fflunts Industrial fflunt containing and wr collctd from lctroplating unit and battry manufacturing unit locatd nar Kolkata, India. Th charactristics of fflunt sampls wr shown in Tabl 5. Batch adsorption studis wr carrid out with th collctd industrial fflunt sampls using clarifid sludg as mtal adsorbnt at undr undr optimum condition as obtaind from batch adsorption studis. Th final concntration of and fall within th limit of th IS norms. 4. CONCLUSIONS In this study, batch adsorption xprimnts for th rmoval of and from aquous solutions hav bn carrid out using clarifid sludg (1) Maximum adsorption of and occurrd at ph 5 () Th xprimntal data wr bttr dscribd by psudo nd ordr modl as vidnt from corrlation cofficint (r ) and χ valus for both th mtal ions. (3) Th ffctiv diffusion co-fficint of and adsoption procss wr m /s and m /s rspctivly. (4) Langmuir adsorption isothrm modl was bttr fittd than Frundlich adsorption isothrm modl for but it was rvrs for adsorption. Th monolayr adsorption capacity wr obtaind 36.3 mg/g and 9.51 mg/g for and adsorption rspctivly. (5) Sorption nrgy for th and wr kj/mol and 9.90 kj/mol rspctivly which indicatd that adsorption procss wr chmical adsorption in natur. (6) Thrmodynamic paramtrs studis showd that both and adsorption wr spontanous in 156

7 T. K. Naiya t al. / GMSARN Intrnational Journal 3 (009) natur. Th nthalpy chang of th adsorption indicatd that procss wr xothrmic for and ndothrmic for rmoval. NOMENCLATURE B = Langmuir constant (Lmg -1 ) C abs = Conc. of mtal ion on adsorbnt at quilibrium, (mgl -1 ) C = Conc. of mtal ion in solution at quilibrium, (mgl -1 ) C 0 = Initial conc. of mtal ion in solution, (mgl -1 ) C t = Conc. of mtal ion in solution at tim t, (mgl -1 ) K = Psudo-scond-ordr rat constant of adsorption [(mg/g) min] K ad = Lagrgrn rat constant, (min -1 ) K c = Thrmodynamic quilibrium constant K f = Masur of adsorption capacity, (mg/g) K id = Intra-particl rat constant, [(mg/g) min 1/ ] K bq = Constant obtaind by multiplying q max and b M = Mtal ion in Equation (9) n = Frundlich constants, intnsity of adsorption q = Amount adsorbd pr gm of th adsorbnt, (mg/g) q = Amount adsorbd pr g of adsorbnt at quilibrium, (mg/g) q max = Maximum adsorption capacity, (mg/g) q t = Amount adsorbd pr g of adsorbnt at tim t r = Corrlation cofficint S s = Extrnal surfac ara of adsorbnt pr unit volum, (m -1 ) D = Diffusion cofficint (m /s) t = Tim, (min.) F(t) = Amount adsorbd pr g of adsorbnt at tim/amount adsorbd pr g of adsorbnt at quilibrium X m = Maximum adsorption capacity, (mmol/g) E = Man sorption nrgy, (kj /mol) G 0 = Gibbs fr nrgy, (kjmol -1 ) H 0 = Hat of adsorption, (kjmol -1 ) S 0 = Entropy of adsorption, (kjk -1 mol -1 ) Grk lttr β = mass transfr cofficint, (m/s) λ = constant rlatd to nrgy (mol /kj ) ε = Polanyi potntial (kj / mol ) REFERENCES [1] Zhou, X., Kornaga, T., Takahashi, T., Moriwak, T. and Shinoda S A procss monitoring/ controlling systm for th tratmnt of wastwatr containing chromium (VI), Watr Rs. 7, [] [] Chakravarti, A. K., Chwodhury, S. B., Chakraborty, S., Chakraborty, T. and Mukhrj, D.C Liquid mmbran multipl mulsion procss of chromium (VI) sparation from wastwatrs. Colloids Surfac A: Physicochm. Eng. Aspcts 103, [3] Amuda, O. S., Giwa, A. A. and Bllo, I A. Rmoval of havy mtal from industrial wastwatr using modifid activatd coconut shll carbon, Biochm. Eng. J. 36, [4] Manahan, S., Environmntal chmistry, Brooks / Coli, CA, USA, [5] IS Drinking watr spcification (Raffirmd 1993), availabl at accssd dat [6] Guidlins for drinking watr quality, World Halth Organization: Gnva, Switzrland, 1984; Vol. 1 &. [7] EPA (Environmntal Protction Agncy, Environmntal Pollution Control Altrnativs EPA/65/5-90/05, EPA/65/4-89/03, Cincinnati, US. [8] Tolranc limits for industrial fflunts prscribd by Burau of Indian Standards, IS 490 (Part I); Burau of Indian Standards: Nw Dlhi, India, 1998 [9] [9] Bhattacharya, A.K., Mandal, S. N. and Das, S. K Adsorption of Zn(II) from aquous solution by using diffrnt adsorbnts, Chm. Eng. J. 13, [10] Standard mthods for xamination of watr and wastwatr, th dition, APHA, AWWA. Washington D.C., Nw York. [11] Wulfsbrg, G Principls of dscriptiv chmistry, Brooks/Col Publishing Montry CA, p- 5 [1] Lagrgrn, S Zur thori dr sognanntn adsorption glostr stoff. Kungliga Svnska Vtnskapasakadmins, Handlingar 4, [13] Ho, Y. S., Mckay, G., Was, D. J.and Fostr, C. F Study of th sorption of divalnt mtal ions on to pat, Ads. Sci. Tch. 18, [14] Wbr, W. J. and Morris, J. C Kintics of adsorption on carbon from solution. J. Sanit. Eng. Div. Am. Soc. Civ. Eng. 89, [15] McKay, G., Otrburn, M. S and Swny, A. C Surfac mass transfr procsss during colour rmoval from fflunt using silica, Watr Rs. 15, [16] Boyd, G. E., Adamson, A. W. and Mayrs, L. S Th xchang adsorption of ions from aquous solutions on organic Zolits. Kintic II, J. Am. Chm. Soc. 69, [17] Hlffrich, F Ion Exchang, Dovr publications Inc., Nw York [18] Inglzakis, V. J., Diamandis, N.A. Loizidou, M.D and Grigoropoulou, H.P Effct of por clogging on kintics of lad uptak by clinoptilolit, J. Colloid Intrfac Sci. 15, [19] Inglzakis, V. J. and Grigoropoulou, H. P Applicability of simplifid modls for th stimation of ion xchang diffusion cofficints in zolit, J. Colloid Intrfac Sci. 34, [0] Srivastava,V. C., Mall, I. D. and Mishra, I. M Adsorption of toxic mtal ions onto activatd carbon Study of adsorption bhavior through charactrization and kintics, Chm. Eng. Proc.47,

8 T. K. Naiya t al. / GMSARN Intrnational Journal 3 (009) [1] Langmuir, I. (1918) Th adsorption of gass on plan surfacs of glass, mica, and platinum, J. Am. Chm. Soc. 40, [] Frundlich, H Adsorption in solution, Phy. Chm. Soc. 40, [3] Dubilin, M. M. and Radushkvich, L.V. (1947) Proc. Acad. Sci. USSR, Phys. Chm. Sc. 55,