Kinetic and Thermodynamic Studies for Methylene Blue Adsorption using Activated Carbon Prepared from Agricultural and Municipal Solid Wastes

Transcription

1 Asian Journal of Chmistry; Vol. 5, No. 15 (013), Kintic and Thrmodynamic Studis for Mthyln Blu Adsorption using Activatd Carbon Prpard from Agricultural and Municipal Solid Wasts ZEID ABDULLAH AL-OTHMAN 1, MOHAMED ABDELATY HABILA 1,*, RAHMAT ALI 1 and MOHAMED SALAH EL-DIN HASSOUNA 1 Advancd Matrials Rsarch Chair to Affliction, Dpartmnt of Chmistry, Collg of Scinc, King Saud Univrsity, P.O. Box 455, Riyadh 11451, Kingdom of Saudi Arabia Dpartmnt of Environmntal Studis, Institut of Graduat Studis and Rsarch, Alxandria Univrsity, 163 El-Horrya Avnu, P.O. Box 83, Alxandria, Egypt *Corrsponding author: Tl: ; mhabila@ksu.du.sa (Rcivd: 0 Octobr 01; Accptd: 19 August 013) AJC This study aimd to valuat and optimiz th rmoval of mthyln blu onto low cost starting matrial activatd carbon. Th ffcts of ph, contact tim, initial concntration on adsorption procss wr invstigatd. Rsults showd that ffctiv adsorption was occurrd in th ph rang of 5-1. Th maximum adsorption capacity ( mg/g) was obtaind at contact tim 480 min, at initial mthyln blu concntration of 150 ppm. Adsorption kintics of mthyln blu was analyzd by psudo first ordr, psudo scond ordr and intraparticl diffusion modls. Rsults showd that mthyln blu adsorption onto activatd carbon followd scond ordr kintics modls most appropriatly. Thrmodynamic paramtrs; Gº, Hº and Sº indicat that th sorption procss was spontanous and ndothrmic in natur. Th magnitud of Gº was -6.7 to -1 kj/mol, th standard nthalpy and th ntropy valus in th rang of 5-50 ºC wr obtaind as kj mol -1 and kj mol -1 K -1. Ky Words: Copyrolysis, Municipal solid wast, Chmical activation, Activatd carbon, Adsorption, Kintic modls. INTRODUCTION Th rmoval of dys from wast fflunts is considrd as an nvironmntal nd bcaus thy can b visibl and highly toxic vn at vry low concntration lvls 1. Dys contaminat nvironmnt from various industris, lik txtils, papr, cosmtics, printing and foods. Dys can dstroy auatic lif bcaus thy prvnt sunlight from rching watr bottom totally. Also dys may b mutagnic and/or carcinognic to human. Usually, mthyln blu is usd for cotton and wood. Mthyln blu can caus y damag for human and animals. On inhalation, it may lad to short priods of rapid or difficult brathing; ingstion may caus nausa and mthmoglobinmia 3. Many mthods ar usd to rmov colour from industrial fflunts such as biological biodgradation 4 and adsorption 5. Many prvious works studid th rmoval of mthyln blu using diffrnt adsorbnt such as coff husks 6, yllow passion fruit wast 7, ric husks 8, banana pl 9, cral chaff 10, spnt coff grounds 11, orang pl 9, what shlls 1, durian pl 13, tc. Th application of untratd agricultural or plant wast as adsorbnts, in addition to its low adsorption fficincy, may lad to additional organic load in th tratd fflunt in th form of chmical oxygn dmand (COD), biological oxygn dmand (BOD) and total organic carbon (TOC) du to rlas of solubl organic compounds containd in th plant wasts 14. Activatd carbon is mostly usd for commrcial systms 15,16, but limitdly usd bcaus of its high oprating costs 17,18. To rduc th production cost, th utilization of rnwabl and lss xpnsiv prcursors for th prparation of activatd carbon is attracting th intrst of rsarchrs all ovr th world. Th prcursors of intrst ar primarily industrial and agricultural byproducts and forst wasts, such as coconut shll 19, sugar bt bagass 0, ric straw 1, rubbr wood sawdust and coconut husk 3. Wast plastics and tirs, which ar organic matrials, can also b convrtd into activatd carbon. Svral xprimntal studis 4,5 hav rportd th production of char and activatd carbon from wast tirs. Th potntial of ths products as possibl adsorbnts of various pollutants has bn assssd and found to b vry grat. Also th disposd solid wast (SW) may b usd as prcursor in th production of a low cost adsorbnt to trat wastwatr contaminatd with havy mtals and rfractory compounds 6. Th convrsion of locally availabl solid wasts such as biomass, wast cartons, wast nws paprs, plastics and industrial byproducts into activatd carbon for wastwatr tratmnt would improv th conomic valu by providing an altrnativ to costly activatd carbon 7,8. Pyrolysis is on of th ways to tak advantag of th nrgtic and organic valu of ths wast matrials. Many authors hav

2 830 Al-Othman t al. Asian J. Chm. studid th pyrolysis of biomass and plastic wast and hav dmonstratd that it is a suitabl mthod of wast procssing 9,30. Th goals of this study wr to optimiz th adsorption factors affcting rmoval of mthyln blu from auous solutions. Our prviously prpard activatd carbon from mixd wasts (biomass, wast cartons and poly styrn) by chmical activation with ZnCl was usd as an adsorbnt 8. Th sorption procss was xamind in trms of kintics and thrmodynamics. Batch adsorption xprimnts wr conductd to valuat th sorption procss ovr a wid rang of opration conditions for sorbat concntration, ph, contact tim and sorbnt dos. Th adsorption capacity at th optimum condition was compard to othr adsorbnt from th litratur. EXPERIMENTAL Raw matrials and activatd carbon prparation: Th prcursors usd in this study wr trunks of palm trs, wast cartons and poly styrn collctd from a municipal solid wast station in Riyadh, Saudi Arabia. In this study, th thr-stag procss was usd for th prparation of activatd carbon from mixd wasts. In this procss, th prcursors ar carbonizd, imprgnatd with ZnCl and thn activatd for a spcific priod of tim as dscribd in our prvious work 8. Mthyln blu (MB), C 16 H 18 CIN 3 S 3H O (Fig. 1) supplid by Sigma Aldrich was usd as an adsorbat. Stock solution was prpard by dissolving 1 g of mthyln blu in L distilld watr. H 3 C N CH 3 N S N + CH 3 Fig. 1. Structur of mthyln blu CH 3 Batch adsorption studis: Th adsorption capacity of th activatd carbon was valuatd using mthyln blu as an adsorbat. Th adsorption was dtrmind using a batch mthod, which allows for th convnint valuation of paramtrs that influnc th adsorption procss. A stock solution of mthyln blu (1000 mg/l) was prpard in doubl-distilld watr and furthr dilutd to th dsird concntrations. Th batch adsorption xprimnts wr prformd in 50 ml conical flasks by mixing 80 ml of th mthyln blu solution with 0.03 g of activatd carbon and thn uilibratd in a thrmostat-cumshaking assmbly (modl MSW 75) at 30 ºC and 00 rpm. Aftr uilibrating, th concntration of rmaining mthyln blu in th solution was masurd using a UV-visibl spctrophotomtr (UV-30 LC, Thrmo Scintific, England) at λ max = 665. Th amount of mthyln blu pr unit wight of adsorbnt, (mg/g), was calculatd using th following uation: V(Co C ) = (1) W whr C o and C ar th initial and uilibrium concntrations of mthyln blu in solution (mg/l), V is th solution volum (L), W is th wight of th adsorbnt (g) and is th adsorption capacity (mg/g). Cl - Th ffct of th initial ph on th rmoval of mthyln blu was xamind ovr th ph rang of -1 using 80 ml solutions with a mthyln blu concntration of 50 mg/l. Th solution ph was adjustd to th dsird valu by th addition of 0.1 M HCl or NaOH. Th ffct of shaking tim on th adsorption of mthyln blu was xamind at thr diffrnt initial concntrations (40, 80, 10 mg/l) of mthyln blu at 30 ºC, 0.03 g of adsorbnt and th slctd ph. At prdtrmind tims; th solution of th spcifid flask was filtrd using Whatman No. 4 filtr papr and analyzd using a UV-visibl spctrophotomtr. Adsorption kintic modls Lagrgrn-first-ordr uation: Lagrgrn-first-ordr uation is th most popular kintics uation 31. Th form is d t = k1( t ) () dt whr and t ar th sorption capacitis at uilibrium and at tim t, rspctivly, (mg/g) and k 1 is th rat constant of psudo first-ordr sorption (min -1 ). Aftr intgration and applying initial conditions, t =0 to t = t at t = 0 to t = t, th intgratd form of n. bcoms: k1t log ( t ) = log (3).303 Th adsorption rat constant k 1, can b dtrmind xprimntally by plotting of ln ( - t ) vrsus t. Psudo-scond-ordr uation: Th psudo-scondordr chmisorption kintic rat uation is xprssd as 3 : d t = k ( t ) (4) dt whr and t ar th sorption capacitis at uilibrium and at tim t, rspctivly, (mg/g) and k is th rat constant of psudo-scond-ordr sorption (g/(mg min)). Aftr intgration and applying initial conditions, t = 0 to t = t at t = 0 to t = t, th intgratd form of n. 4 bcoms: t dt 1 1t = + K (5) whr t is th contact tim (min) and (mg/g) and (mg/g) ar th amount of th solut adsorbd at uilibrium. Intraparticl diffusion modl: Th intraparticl diffusion modl was tstd to idntify th diffusion mchanism 33, is xprssd as: 1/ t id + = k t C (6) whr k id is th intraparticl diffusion rat constant (mg/g min 1/ ), C is th intrcpt (mg/g). Th plot of t vrsus t 1/ gav straight lin and th valus of k id wr calculatd from th slops of th plots. Valus of C gav an ida about th thicknss of boundary layr, i.., th largr th intrcpt, gratr th contribution of th surfac sorption in th rat controlling stp. Effct of mthyln blu concntration and Dubinin- Radushkvich (D-R) modl: Th ffct of mthyln blu concntration on th adsorption capacity xamind at thr diffrnt initial concntrations (5, 10, 0, 30, 40, 50, 100, 150 mg/l) of mthyln blu at 30 ºC, 0.03 g of adsorbnt and th

3 Vol. 5, No. 15 (013) Kintic and Thrmodynamic Studis for Mthyln Blu Adsorption using Activatd Carbon 8303 slctd ph. Th adsorption data was also modld by D-R isothrm to dtrmin th adsorption typ (physical or chmical) 34,35. Th linar form of this modl is xprssd in n. 7 ln m = ln βε (7) whr is th amount of th mtal adsorbd onto pr unit dosag of th adsorbnt (mol/l); m, th monolayr adsorption capacity (mol/g); β, th activity cofficint rlatd to man sorption nrgy (mol /J ) and ε is th Polanyi potntial (ε = RT ln (1 + 1/C )) 34,35. Th man sorption nrgy E (kj/mol), can b calculatd using n. 8 E = 1 Thrmodynamic studis: Thrmodynamic paramtrs, such as chang in Gibbs fr nrgy ( Gº), nthalpy ( Hº) and ntropy ( Sº), wr valuatd using ns. 9 and 10: β (8) Sº Hº log K d = (9).303R.303RT Gº = RT ln K d (10) whr K d is th uilibrium partition constant calculatd as th ratio btwn sorption capacity ( ) and uilibrium concntration (C ), R is th gas constant (8.314 J/mol/K) and T is th tmpratur in Klvin (K). From n. 9 a plot of log K d vrsus 1/T (Fig. 8) giv Hº and Sº. RESULTS AND DISCUSSION Effct of ph: Th ph of auous solution is on of th most important factors that influnc th adsorption of dys du to its impact on both th surfac binding-sits of th adsorbnt and th ionization procss of th dy molcul 36. Th adsorption of mthyln blu was studid as a function of ph ovr a ph rang of -1 onto th activatd carbon at initial concntration of 100 ppm, as shown in Fig.. It is clar that th adsorption capacity prsntd a slight incras with incrasing th ph, but thr is no significant chang in th prcntag rmoval of mthyln blu ovr th whol ph rang. Aftr 4 h, th adsorption capacity was 56.0 % at ph = and prsntd an avrag of % in th ph rang of 4-1. This may b du to th formation of mor functional groups on th surfac of activatd carbon which incras thir surfac complxation capability. Effct of contact tim: Th amount of mthyln blu adsorbd onto activatd carbon was studid as a function of th shaking tim at diffrnt initial concntrations at 30 ºC and dsird ph. Th ffct of contact tim for thr diffrnt concntrations (40, 80, 10 ppm) of mthyln blu adsorption by activatd carbon is givn in Fig. 3. It is vidnt from th figur that th amount of mthyln blu adsorbd incrass with incrasing contact tim. Furthr, th adsorption was rapid in th arly stags and thn gradually dcrasd to bcom constant aftr th uilibrium point. Th saturation point is almost rachd at 480 min. At this point, th amount of dy dsorbing from th activatd carbon is in a stat of dynamic uilibrium with th amount of th dy bing adsorbd on th activatd carbon. Th amount of dy adsorbd at th uilibrium tim rflcts th maximum adsorption capacity of th adsorbnt. Th rmoval of mthyln blu was found to b dpndnt upon th initial concntration. Th amount of mthyln blu adsorbd, (mg/g), incrasd with an incras in th initial concntration. In this study, th amount of mthyln blu adsorbd at uilibrium incrasd from mg/g with th incras in th initial dy concntration from ppm. Th mass transfr driving forc bcoms largr whn th initial concntration incrasd and hnc rsulting in highr adsorption of mthyln blu. At low concntrations, th ratio of availabl surfac to initial mthyln blu concntration is largr, so th rmoval bcoms indpndnt of th initial concntration. Howvr, in th cas of highr concntrations, this ratio is low and th prcntag rmoval dpnds upon th initial concntration. (mg/g) Fig. 3. Tim (min) Effct of contact tim on mthyln blu adsorption onto activatd carbon prpard from mixd wasts at low carbonization tmpratur of 00 ºC, followd by activation with M ZnCl solution Fig.. Effct of ph on mthyln blu adsorption onto activatd carbon prpard from mixd wasts at low carbonization tmpratur of 00 ºC, followd by activation with M ZnCl solution Batch kintic studis: Adsorption kintics provids valuabl information about th raction pathways and mchanism of th ractions. In ordr to xamin th controlling mchanism of th adsorption procss, th psudo first-ordr, psudo scondordr and intraparticl diffusion modls wr applid to analyz th xprimntal data of adsorption of mthyln blu on th prpard activatd carbon. Th conformity btwn xprimntal data and th modl prdictd valus was xprssd by th corrlation cofficints (R ).

4 8304 Al-Othman t al. Asian J. Chm. Psudo-first ordr kintic modl: Th linarizdintgral form of th psudo first-ordr modl 31, is gnrally xprssd as: k1t log( t ) = log (3).303 whr and t ar th amounts of adsorbd of mthyln blu (mg/g) at uilibrium and at tim t, rspctivly and k 1 is th rat constant of first ordr adsorption (min -1 ). Straight lins wr obtaind by plotting log ( - t) against t, as shown in Fig. 4. Th valus of th rat constant k 1 and at thr diffrnt initial concntrations wr obtaind from th slops and intrcpts of th plots, rspctivly and prsntd in Tabl-1. Rsults showd that thr ar diffrncs btwn th xprimntal (70.15, and 1.3 mg/g) and th calculatd (65.8, 5.5 and 59. mg/g) in cas of initial mthyln blu dy concntration of 40, 80 and 10 ppm, rspctivly. log (-t) Fig ppm 80 ppm 10ppm Tim (min) Lagrgrn first ordr plot for mthyln blu adsorption onto activatd carbon prpard from mixd wasts at low carbonization tmpratur of 00 ºC, followd by activation with M ZnCl solution Psudo scond-ordr kintic modl: Th paramtrs of psudo scond-ordr adsorption kintic modl can b dtrmind from n. 5 t 1 t = + t k (5) Th plots of t/ t vrsus t of n. 6 gav linar plots Fig. 5. Th valus of and k wr dtrmind from th slops and intrcpts of th plots, rspctivly and ar listd in Tabl-1. Good agrmnt ar obtaind btwn th xprimntal (70.15, and 1.3 mg/g) and th calculatd (71.4, and 15 mg/g) in cas of initial mthyln blu dy concntration of 40, 80 and 10 ppm rspctivly. Intraparticl diffusion modl: Th intraparticl diffusion modl was tstd to idntify th diffusion mchanism, is xprssd as in n. 6: t/t ppm 5 80 ppm 10 ppm Tim (min) Fig. 5. Psudo-scond ordr plot for mthyln blu adsorption onto activatd carbon prpard from mixd wasts at low carbonization tmpratur of 00 ºC, followd by activation with M ZnCl solution 1/ t id + = k t C (6) whr k id is th intraparticl diffusion rat constant (mg/g min 1/ ), C is th intrcpt (mg/g). Th plot of t vrsus t 1/ gav straight lin and th valus of k id wr calculatd from th slops of th plots. Valus of C gav an ida about th thicknss of boundary layr, i.., th largr th intrcpt, gratr th contribution of th surfac sorption in th rat controlling stp. Th data for mthyln blu adsorption onto activatd carbons applid to intraparticl diffusion modl is shown in Fig. 6 and th rsults ar givn in Tabl-1. (mg/g) Fig / 1/ t (min) Intraparticl diffusion modl plot for mthyln blu adsorption onto activatd carbon prpard from mixd wasts at low carbonization tmpratur of 00 ºC, followd by activation with M ZnCl solution It is clar from Tabl-1 that among ths thr modls, psudo-scond ordr kintic uations had high R valus and also th xprimntal is in accordanc with calculatd. Th low valus of R for psudo-first ordr and intra particl diffusion modls indicatd apparntly that ths modls did not fit th data wll. Furthrmor, for psudo-first ordr kintic TABLE-1 KINETIC CONSTANT PARAMETERS OBTAINED FOR MB ADSORPTION ON ACTIVATED CARBON PREPARED FROM MIXED WASTES AT LOW CARBONIZATION TEMPERATURE OF 00 ºC, FOLLOWED BY ACTIVATION WITH M ZnCl SOLUTION Psudo-first ordr Psudo-scond ordr Intraparticl diffusion modl C i (ppm),xp K 1 (10-3 ),cal (mg/g) (min -1 R ) (mg/g) k (10-4 ),cal h (mg/g R (g/mg min) (mg/g) min) k id C (mg/g.min) (mg/g) R

5 Vol. 5, No. 15 (013) Kintic and Thrmodynamic Studis for Mthyln Blu Adsorption using Activatd Carbon 8305 modl th xprimntal ar not in good agrmnt with calculatd. In th viw of ths rsults, it can b said that th psudo scond ordr kintic modl providd a good corrlation for th dscription of th mchanism of sorption of mthyln blu in contrast to th othr modls. Effct of initial mthyln blu concntration and D-R modl: Rsults prsntd in Tabl- shows th ffct of initial mthyln blu concntration on th adsorption capacity by mixd wast activatd carbon. Th adsorption capacity incrass from 10 to mg/g with incrasing initial mthyln blu concntration from ppm, at 30 ºC, contact tim 480 min. Th incras in th adsorption capacity may b du to nhancd driving forc, i.., th concntration gradint. Ths rsults ar in agrmnt with that rportd by Olivira t al. 6. TABLE- SHOWS THE EFFECT OF INITIAL METHYLENE BLUE CONCENTRATION ON THE ADSORPTION CAPACITY Initial mthyln blu conc. (ppm) Adsorption capacity (mg/g) Initial mthyln blu conc. (ppm) Adsorption capacity (mg/g) Th adsorption data wr also applid to th D-R isothrm modl basd on th htrognous surfac of th adsorbat to diffrntiat btwn physical and chmical adsorption. Fig. 7 shows th D-R isothrm plot for th adsorption of mthyln blu onto mixd wast activatd carbon. Th corrlation cofficint R is Th β constant and m wr calculatd from th slops and intrcpt of th plot. Th β constant and th m valu wr found to b mol /kj and mol/g, rspctivly. Th man fr nrgy of adsorption E givs information about adsorption mchanism as chmical ion-xchang or physical adsorption. If E valu is btwn 8 and 16 kj/mol, th adsorption procss follows by chmical ion xchang and if E < 8 kj mol, th adsorption is physical in natur 34,35. From n. 8, th numrical valu of E was calculatd as 5.33 kj/mol indicating th adsorption procss may b carrid out via physical intraction including van dr waals forcs. ln Fig. 7. ε J /mol Shows th D-R isothrm plot for th adsorption of mthyln blu onto mixd wast activatd carbon Thrmodynamic studis: Thrmodynamic paramtrs, such as chang in Gibbs fr nrgy ( Gº), nthalpy ( Hº) and ntropy ( Sº), wr valuatd using ns. 8 and 9: Sº Hº log K d = (9).303R.303RT Gº = RT ln K d (10) whr K d is th uilibrium partition constant calculatd as th ratio btwn sorption capacity ( ) and uilibrium concntration (C ), R is th gas constant (8.314 J/mol/K) and T is th tmpratur in Klvin (K). From n. 8 a plot of log K d vrsus 1/T (Fig. 8) giv Hº and Sº, th calculatd thrmodynamic paramtrs ar givn in Tabl-3. ln K Fig /T (K 1 ) Thrmodynamic study of adsorption of mthyln blu onto mixd wast activatd carbon TABLE-3 THERMODYNAMIC PARAMETERS OF ADSORPTION OF MB ONTO MIXED WASTE ACTIVATED CARBON Tmpratur T Thrmodynamic paramtrs (K) Gº (kj/mol) Sº (J/mol/K) Hº (kj/mol) y = -3049x R = Th ngativ valu of Gº indicats th spontanous natur of adsorption of mthyln blu onto mixd wast activatd carbon. Gnrally, a valu of Gº in btwn 0 and -0 kj/mol is consistnt with lctrostatic intraction btwn adsorption sits and th adsorbing ion (physical adsorption) whil a mor ngativ Gº valu ranging from -80 to -400 kj/ mol indicats that th adsorption involvs charg sharing or transfrring from th adsorbnt surfac to th adsorbing ion to form a coordinat bond (chmisorption) As shown, th magnitud of Gº (-6.7 to -1 kj/mol) which indicat a typical physical procss. According to th van't Hoff uation, th standard nthalpy and th ntropy valus in th rang of 5-50 ºC wr obtaind as kj mol -1 and kj mol -1 K -1 at initial ph 5 and initial mthyln blu concntration 50 ppm, rspctivly. As can b dducd from Fig. 8, th positiv valu of Hº suggsts th ndothrmic natur of adsorption whil th positiv valus of Sº indicats an incras in th dgr of frdom (or disordr) of th adsorbd spcis. In gnral, th thrmodynamic paramtrs indicat that th adsorption is spontanous and ndothrmic. Comparison of adsorption capacity of varous modifid adsorbant for mthyln blu: It is clar from Tabl-4 that by comparing maximum adsorption capacitis ( max ) of mixd wast activatd carbon and othr adsorbnts from litratur, mixd wast activatd carbon hav a larg capacity in th rmoval of mthyln blu from auous solutions.

6 8306 Al-Othman t al. Asian J. Chm. TABLE-4 COMPARISON OF ADSORPTION CAPACITY OF VAROUS MODIFIED ADSORBANT FOR METHYLENE BLUE Adsorbnt max (mg/g) (tmpratur ºC) Rfrnc Activatd carbon from mixd wasts (30) This study Coff husks 90.1 (30) 6 Yllow passion fruit wast 44.7 (5) 7 Ric husks 40.6 (3) 8 Banana pl 0.8 (30) 9 Cral chaff 0.3 (5) 10 Spnt coff grounds 18.7 (5) 11 Orang pl 18.6 (30) 9 What shlls 16.6 (30) 1 Posidonia ocanica (L.) fibrs 5.6 (30) 13 Conclusion Activatd carbon which is prpard by th copyrolysis of mixd solid wasts (biomass, cartons and polystyrn) and by chmical activation with ZnCl at low carbonization tmpratur showd high fficincy in rmoval of mthyln blu from auous solutions. By optimizing th adsorption procss, rsults showd that ph had no considrabl ffct on th adsorption of mthyln blu. Effctiv adsorption was occurrd in th ph rang of 5-1. Th kintics of mthyln blu adsorption followd psudo-scond ordr rat xprssions. Th adsorption of mthyln blu was found to b dpndnt on th initial concntration. Th amount mthyln blu adsorbd at uilibrium incrasd from mg/g with th incras in th initial dy concntration from ppm. Thrmodynamic paramtrs; Gº, Hº and Sº showd that th sorption procss was spontanous and ndothrmic in natur. Also D-R modl confirm th physical adsorption of mthyln blu onto mixd wast activatd carbon. ACKNOWLEDGEMENTS This work was supportd by NPST program by King Saud Univrsity projct numbr 09-nv REFERENCES 1. M.S. Chiou, P.Y. Ho and H.Y. Li, J. Dys Pigmnts, 60, 69 (004).. D. Shn, J. Fan, W. Zhou, B. Gao, Q. Yu and Q. Kang, J. Hazard. Matr., 17, 99 (009). 3. D. Ghosh and K.G. Bhattacharyya, Appl. Clay Sci., 0, 95 (00). 4. M. Gladchnko, E. Starostina, S. Shchrbakov, B. Vrsprill and S. Kalyuzhnyi, Watr Sci. Tchnol., 50, 67 (004). 5. A.Z. Aroguz, J. Guln and R.H. Evrs, Biorsour. Tchnol., 99, 1503 (008). 6. L.S. Olivira, A.S. Franca, T.M. Alvs and S.D.F. Rocha, J. Hazard. Matr., 155, 507 (008). 7. F.A. Pavan, E.C. Lima, S.L.P. Dias and A.C. Mazzocato, J. Hazard. Matr., 150, 703 (008). 8. V. Vadivlan and K.V. Kumar, J. Colloid Intrf. Sci., 86, 90 (005). 9. G. Annadurai, R.S. Juang and D.J. L, J. Hazard. Matr., 9, 63 (00). 10. R. Han, Y. Wang, P. Han, J. Shi, J. Yang and Y. Lu, J. Hazard. Matr., 137, 550 (006). 11. A.S. Franca, L.S. Olivira and M.E. Frrira, Dsalination, 49, 67 (009). 1. Y. Bulut and H. Aydin, Dsalination, 194, 59 (006). 13. S.-T. Ong, P.-S. Kng, M.-S. Voon and S.-L. L, Asian J. Chm., 3, 898 (011). 14. Gaballah, D. Goy, E. Allain, G. Kilbrtus and J. Thauront, Mt. Mtall. Trans. B, 8, 13 (1997). 15. A. Hubbard, Encyclopdia of Surfac and Colloid Scinc, Dkkr, Nw York (003). 16. J. Fbrianto, A.N. Kosasih, J. Sunarso, Y.H. Ju, N. Indraswati and S. Ismadji, J. Hazard. Matr., 16, 616 (009). 17. C. Sourja, D. Sirshndu, D. Sunando and K.B. Jayanta, Chmosphr, 58, 1079 (005). 18. B.H. Hamd, J. Hazard. Matr., 161, 753 (009). 19. M. Radhika and K. Palanivlu, J. Hazard. Matr., 138(B), 116 (006). 0. Y. Onal, C. Akmil-Basar, C. Sarici-Ozdmir and S. Erdogan, J. Hazard. Matr., 14, 138 (007). 1. S.L. Wang, Y.M. Tzou, Y.H. Lu and G. Shng, J. Hazard. Matr., 147, 313 (007).. B.G. Prakash Kumar, K. Shivakamy, L.R. Miranda and M.Vlan, J. Hazard. Matr., 136B, 9 (006). 3. I.A.W. Tan, B.H. Hamd and A.L. Ahmad, Chm. Eng. J., 137, 46 (008). 4. C.M.B. Lhmann, M. Rostam-Abadi, M.J. Rood and J. Sun, Enrgy Fuls, 1, 1095 (1998). 5. A.M. Cunliff and P.T. Williams, Enrgy Fuls, 13, 166 (1999). 6. S. Babl and T.A. Kurniawan, J. Hazard. Matr., B97, 19 (003). 7. T.A. Kurniawan, G.Y.S. Chan, W.H. Lo and S. Babl, Chm. Eng. J., 118, 83 (006). 8. Z.A. Al-Othman, M.A. Habila and R. Ali, In Procdings of 011 Intrnational Confrnc on Biology, Environmnt and Chmistry (ICBEC), Dubai, UAE, Dcmbr 8-30 (011). 9. W. Kaminsky, J.-S. Kim and B. Schlsslmann, J. Anal. Appl. Pyrol., 40-41, 365 (1997). 30. K.W. L and D.H. Shin, Wast Manag., 7, 168 (007). 31. V.K. Singh and P.N. Tiwari, J. Chm. Tchnol. Biotchnol., 69, 376 (1997). 3. Y.S. Ho, G. Mckay, D.A.J. Was and C.F. Fostr, Adsorp. Sci. Tchnol., 18, 639 (000). 33. S.K. Srivastava, R. Tyagi and N. Pant, Watr Rs., 3, 1161 (1989). 34. R.J. Gonzalz, J.R. Vida, E. Rodriguz, S.L. Ramirz and J.L. Torrsdy, J. Chm. Thrmodyn., 37, 343 (005). 35. K. Saltali, A. Sari and M. Aydin, J. Hazard. Matr., 141(B), 58 (007). 36. S.F. Adriana, S.O. Landro and E.F. Mauro, Dsalination, 49, 67 (009). 37. M. Horsfall, A.I. Spiff and A.A. Abia, Bull. Koran Chm. Soc., 5, 969 (004). 38. Z.A. AlOthman, A. Hashm and M.A. Habila, Molculs, 16, (011). 39. J.M. Smith and H.C. Van Nss, Introduction to Chmical Enginring Thrmodynamics, McGraw-Hill, Singapor, dn. 4 (1987). 40. E. Malkoc and Y. Nuhoglu, Chm. Eng. Procss, 46, 100 (007). 41. D. Sigh, Adsorp. Sci. Tchnol., 18, 741 (000).