BIOSORPTION OF AN AZO DYE FROM AQUEOUS SOLUTIONS ONTO SPIROGYRA

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1 Journal of th Univrsity N. Sivarajaskar, of Chmical Tchnology R. Baskar, V. and Balakrishnan Mtallurgy, 44,, 9, BIOSORPTION OF AN AZO DYE FROM AQUEOUS SOLUTIONS ONTO SPIROGYRA N. Sivarajaskar, R. Baskar, V. Balakrishnan Dpartmnt of Chmical nginring, Kongu Enginring Collg, Erod, India , sivarajaskar@gmail.com Dpartmnt of Biotchnology, Rcivd 4 August 8 Accptd April 9 K.S.R. Collg of Tchnology, Tiruchngod, India ABSTRACT Th frsh watr alga Spirogyra was ffctivly invstigatd for th rmoval of Dirct Brown dy from aquous solutions. Th optimum paramtr for biosorption was studid. Th quilibrium btwn dy solution and biomass was attaind at min. Th adsorption was found to b highr at acidic ph rang. Th quantity uptak of biomass incrasd with incras of th tmpratur. Th biosorption data wr analyzd with thr typs of isothrms. Among thm Langmuir isothrm fits th data bttr than Frundlich and Tmkin isothrms. This numratd th fact that th mor homognous natur of th biomass powdr and adsorption of ach dy molcul has sam activation nrgy. Th kintic mchanism was studid using psudo-first ordr, psudo-scond ordr, and intraparticl diffusion modl. Psudo-scond ordr fits wll th data with th avrag rgrssion cofficint of.987. Intraparticl diffusion modl rvald that th procss was complx and followd both surfac adsorption and particl diffusion. Kywords: biosorption, Spirogyra, azo dy, isothrms, kintics. INTRODUCTION Numrous tchniqus hav bn proposd by various rsarchrs for th tratmnt of dy fflunts [, ]. Ths includ ion-xchang [3], chmical prcipitation [4], lctrochmical mthods [5] and mmbran tchnology [6]. Anothr mthod, which has gaind momntum in rcnt yars, is biosorption inhrnt advantags and applications of biosorption hav bn xtnsivly rviwd by svral invstigators [7 9]. Many adsorbnts lik chitosan [], gothit [], silica gl [], rd mud [3, 4], papr mill sludg [5], blast furnac sludg [4], and bituminous coal [6] wr invstigatd by diffrnt authors for dy rmoval. Rcntly, som agricultural and forstry products/wasts lik pongam sd coat [7], saw dust[8], ric husk [9], ric shlls, panut shlls, cotton sd shll [], cotton stalks [], Cornlian chrry, apricot ston, almond shll [] and oak wood wast, corn hulls, corn stovr [3] coir [4], banana pith [5] and jut [6] hav bn rcognizd as nw adsorbnts. In gnral, th cost of this biomatrial is ngligibl, compard to th cost of ion xchang and chmically prpard adsorbnts. Hnc in this papr, th rmoval of dirct brown dy by Spirogyra was prsntd. Th prsnt invstigation aims at studying th kintics and isothrms of th adsorption of dirct brown dy with an objct to xplor optimum conditions for sparation of th dy by adsorption mthods. EXPERIMENTAL Matrials and mthods Dirct Brown : [C.I.No.3; Atul Products, Atul] a dirct application class synthtic dy blonging to triazo chmicals class was usd in th xprimnts as 57

2 Journal of th Univrsity of Chmical Tchnology and Mtallurgy, 44,, 9 tst dy to valuat th biosorption potntial of non-viabl alga. Synthtic tst dy solution was prpard by dissolving accuratly wighd amount of dy (.5 g l - ) in distilld watr and subsquntly dilutd to rquird concntration. All othr chmicals usd wr of analytical grad and doubly distilld watr was usd for solution prparation. Bio- adsorbnt dvlopmnt Th bio-adsorbnt Spirogyra spcis was collctd from in and around Mttupalayam of Coimbator District, Tamilnadu. Th collctd algal biomass was dwatrd and washd with ultra pur watr and subjctd to drying undr diffusd sunlight for 7 days. Th drid biomass was crushd to particl siz of mm. Th biomass particls wr tratd with.n HCl for hours at room tmpratur and washd with ultra pur watr twic bfor drying. Th rsultant biomass was stord in airtight containrs and subsquntly usd in th adsorption xprimnts. Th tratd algal biomass containd (%) N 4.69, C 33.74, S. and H Th algal biomass had a spcific surfac ara of.9m /g and surfac wighd man diamtr of mm. SEM micrograph of alga biomass is shown in Fig.. a fixd agitation spd of 8 rpm. Th xprimnts wr carrid out for various biomass loading, diffrnt initial dy concntration, for diffrnt contact tims, tmpratur and ph. At th nd of prdtrmind tim intrval, sampls wr withdrawn from th shakr, cntrifugd and th suprnatant solution was analyzd for rsidual dy concntration. Th concntration of dy was dtrmind spctrophotomtrically at a wavlngth of 36 nm. RESULTS AND DISCUSSIONS Effct of agitation tim and biomass loading on prcntag dy rmoval Th influnc of contact tim on adsorptiv rmoval of dy from aquous phas with rspct to dy concntration was shown in Fig. a. It is vidnt from sorption profil that th rat of dy rmoval was rapid Rmoval % rmoval of dy, of dy % a) 5ppm ppm 5ppm 3 4 Contact tim (min) Fig.. SEM micrograph of alga biomass. Batch adsorption xprimnts Th stock solution containing dirct brown dy was prpard by dissolving th dy in doubl distilld watr. All adsorption xprimnts wr carrid out by agitating th powdrd biomass of rquird amount with ml of dirct brown solution of dsird concntration and at room tmpratur in a mchanical shakr at Rmoval of dy, % Biomass (g/lit) Fig.. Effct of contact tim and biomass loading on prcntag rmoval Dirct Brown dy: (a) Effct of contact tim; (b) Effct of biomass loading. b) 58

3 N. Sivarajaskar, R. Baskar, V. Balakrishnan initially and thn gradually slowd down until quilibrium was rachd. Byond which thr was no significant incras in th rat of dy rmoval. A larg fraction of th dy was rmovd within min of th contact tim in all th xprimntal variations studid. Th initial rapid dy sorption obsrvd may b prhaps du to participation of activ surfac sits/spcific functional groups on th biosorbnt surfac. Initially th plots wr stp indicats th instantanous chmisorpton of th dy on th biosorbnt. Thn from th plots it was infrrd that th dy sorption rat was dcrasd. This may b du to th utilization of activ sits on th biosorbnt surfac. Th initial high uptak of th dy at rlativly lss contact tim numratd th chmisorption natur of sorption. Th amount of dy adsorbd pr unit mass of alga showd incrasing trnd up to 5 mg l - of dy concntration [34]. Th influnc of biosorbnt mass on th sorption of dy was studid at 5 mg l - of sorbnt concntration. Highst prcntag of dy sorption was obsrvd at.5 g of biosorbnt mass (Fig. b). Rmoval % rmoval of of dy, dy % Rmoval of dy, % ph a) b) 4 6 Tmpratur (Dg C) Effct of ph on prcntag dy rmoval Sorption procss is dpndnt on th aquous phas ph and th functional groups on th algal cll walls and thir ionic stats (at particular ph) dtrmin th xtnt of biosorption [8, 6-3]. Th ionic form of dy in solution and th lctrical charg of th algal cll wall componnts dpnd on th solution ph. Batch sorption xprimnts wr prformd at various aquous phas ph by kping all othr xprimntal conditions constant. Th ffct of ph on th sorptiv rmoval of dy with th function of th contact tim is dpictd in Fig. 3a. Th xtnt of dy sorption on th algal-sorption systm showd a markd dcras as th ph of th aquous solution incrasd from. to. Th highst sorption valus wr obsrvd at acidic ph of.. This phnomnon of sorption charactristics could b attributd to th anionic sorption, which indicatd that th Fig. 3. Effct of ph and tmpratur on prcntag rmoval of Dirct Brown dy: (a) Effct of ph; (b) Effct of tmpratur. adsorbnt surfac is of H + (cationic)-typ [8, 3]. At lowr ph valus, th surfac of th biosorbnt turnd out to b positivly chargd and this facilitatd sorption of dy, probably by th anionic xchang sorption. At acidic ph du to th protonatd ffct of surfac functional groups such as amino, carboxyl, thiol, tc., imparts positiv charg on th surfac [3, 34]. Rlativly lss dy sorption obsrvd at basic ph rang might b attributd to th incras of hydroxyl ion thrby rtarding th sorption [33]. Howvr, th dy sorption fficincy at aquous phas ph 7. was found to b 64 %, which cannot b avoidd for all practical rasons with rspct to th up scaling of th tchnology. Tabl. Isothrms constants for biosorption of Dirct Brown dy onto Spirogyra. Frundlich Langmuir Tmkin a f (mg g - ) b f R q m (mg g - ) K L (l g - ) a L (l mg - ) R b R

4 Journal of th Univrsity of Chmical Tchnology and Mtallurgy, 44,, 9 Effct of tmpratur on prcntag dy rmoval Th ffct of aquous phas tmpratur on th biosorption of dy was invstigatd at thr diffrnt tmpraturs kping all othr xprimntal conditions constant. Incrasing in oprating tmpratur from to 5 o C showd a markd improvmnt in dy sorption capacity (Fig. 3b). Th incras of th dy uptak with incras in tmpratur suggsts that th dy-algal-sorption procss may b attributd to ndothrmic natur [8, 34]. Isothrm studis Th salint faturs of isothrms ar ndd bfor th kintics of th adsorption procss is intrprtd. Th dynamic adsorptiv sparation of solut from solution onto an adsorbnt dpnds upon a good dscription of th quilibrium sparation btwn th two phass. Many modls hav bn proposd to xplain adsorption quilibria, but th most important factor is to hav applicability ovr th ntir rang of procss conditions. Th most widly usd isothrm modls for solid-liquid adsorption ar th Langmuir, Frundlich and Tmkin isothrms. Frundlich isothrm Th xprimntal data wr analyzd according to th linar form of th Frundlich isothrm and ar shown in Fig. 4 a. Frundlich isothrm givs th rlationship btwn quilibrium liquid and solid phas capacity basd on th multilayr adsorption (htrognous surfac). This isothrm is drivd from th assumption that th adsorption sits ar distributd xponntially with rspct to th hat of adsorption and is givn by f b f q = a C () and linarizd as Ln q = ln a f + b f ln C () ln (q ).5.5 C/q q y =.989x +.75 R = ln (C) y =.896x +.49 R = C 5 y =.786x R = ln(c) Fig. 4. Isothrm plots for biosorption of Dirct Brown dy onto Spirogyra: (a) Frundlich plot; (b) Langmuir plot; (c) Tmkin plot. all sits) on th activ sits of th adsorbnt. It is givn by a) b) c) whr a f [mg g - ] and b f rlat th multilayr adsorption capacity and th intnsity of adsorption. Langmuir isothrm Th xprimntal data wr analyzd according to th linar form of th Langmuir isothrm and ar shown in Fig. 4b. Th Langmuir isothrm is basd on monolayr adsorption (constant hat of adsorption for q K lc = + alc (3) Th linar form of th Langmuir isothrm is givn by C alc = + (4) q K K L L 6

5 N. Sivarajaskar, R. Baskar, V. Balakrishnan whr K L [l g - ] and a L [ l mg - ] rprsnt th Langmuir constants. Th thortical maximum monolayr adsorption capacity q max [ mg g - ] is givn by K L /a L. Th maximum adsorption capacity q max was mg g - for Dirct Brown dy onto Spirogyra. Th Langmuir quation gav an accurat dscription of th xprimntal data, which was confirmd by th high valus of corrlation cofficint (.9853). Th applicability of th Langmuir isothrm suggstd th monolayr covrag of th dirct brown dy on th surfac of th biomass and adsorption of ach molcul has qual activation nrgy. Tmkin isothrm Tmkin isothrm, which considrs th ffcts of th hat of adsorption that dcrass linarly with covrag of th adsorbat and adsorbnt intractions, is givn as [37] RT q = ln AC b (5) and linarizd as RT RT q = ln A + ln C (6) b b whr A [l g - ] and b ar th Tmkin constants. Th Tmkin isothrm plot btwn ln C and q is shown Fig. 4c. Th xprimntal adsorption capacity and th adsorption capacity prdictd by th thr isothrms ar compard and th corrsponding Langmuir, Frundlich, and Tmkin isothrm paramtrs, along with th rgrssion cofficints, ar listd in Tabl. Th Langmuir modl rducs to Hnry s law at low concntration; i.., as C bcoms lowr, th a L C tnds to a valu lss than unity and follows Hnry s law, whras th Frundlich modl dos not rduc to th linar isothrm at low surfac covrag. Howvr, th Langmuir modl was found to fit th data significantly bttr than ithr th Tmkin or Frundlich modl which shows th mor homognous natur of th biomass powdr. Frundlich valus of b f ( < bf < ) shows th favorability of adsorption of dirct brown onto Spirogyra. Kintic studis Th kintics of adsorption dscribs th rat of Dirct Brown dy uptak on biomass and this rat controls th quilibrium tim. Th kintics of adsorbat uptak is rquird for slcting optimum oprating conditions for th full-scal batch procss. Th kintic paramtr which is hlpful for th prdiction of adsorption rat, givs important information for dsigning and modling th procsss. Thus, th ffcts of initial concntration, contact tim and adsorbnt dosag wr analyzd from th kintic point of viw. Prliminary studis on th adsorption rat show that th amount adsorbd incrasd with incrasd Dirct Brown dy concntration. Th maximum amount of Dirct Brown dy was adsorbd within min and thraftr th adsorption procds at a slowr rat until quilibrium was rachd. Th quilibrium tim was found to b at 3 min for th initial dy concntration rang studid. Th rat of uptak incrasd as th adsorbnt dosag incrasd bcaus it lads to mor surfac ara for adsorption. Howvr, thr is no significant chang in adsorption abov ppm Tabl. Kintic and rgrssion cofficint valus. Psudo-first ordr modl Psudo-scond ordr modl Intraparticl diffusion modl K I R K II R (min - ) (g.mg - min - ) (mg g - min -/ ) Avrag 3 K R 6

6 Journal of th Univrsity of Chmical Tchnology and Mtallurgy, 44,, 9.3 g for th initial concntration rang studid. Hnc, this amount was fixd and assumd for all th adsorption studis. Th kintics of th sorption data was analyzd using diffrnt kintics modls such as psudo-first ordr psudo-scond ordr modl and intraparticl diffusion modls. Psudo-first ordr modl Th possibility of sorption data following Lagrgrn psudo-first ordr kintics is givn by: dq t /dt = K [q q t ] (7) log (q-qt) 5ppm.5 ppm 5ppm R =.9844 R =.98 R = Tim (min) a) b) Intgrating Eq. [3] with rspct to intgration conditions q = q to q = q at t = to t = t, th kintic rat xprssion bcoms: 8 R =.989 R =.985 ln [q q t ] = ln q K I t (8) Th first ordr rat constant K I can b obtaind from th slop of plot btwn log(q q t ) vrsus tim t. Fig. 5a shows th Lagrgrn psudo-first ordr kintic plot for th sorption of Dirct Brown onto Spirogyra. Th calculatd K I valus and thir corrsponding linar rgrssion corrlation cofficint valus ar shown in Tabl. Th linar rgrssion corrlation cofficint valus found in th rang of with an avrag valu of.9789, which shows that this modl can not b applid to prdict th sorption kintics. Psudo-scond ordr modl A psudo-scond ordr modl proposd by Ho and McKay [35] can b usd to xplain th sorption kintics. This modl is basd on th assumption that th biosorption follows scond ordr chmisorption. Th psudo-scond ordr modl can b xprssd as: dq t /dt = K II [q q t ] (9) t/qt qt R =.983 5ppm ppm 5ppm 3 4 tim t (min) 5ppm ppm 5ppm R =.97 R =.933 R = t^.5 Fig. 5. Kintic plots for biosorption of Dirct Brown dy onto Spirogyra: (a) Psudo First ordr kintic plot; (b) Psudo scond ordr kintic plot; (c). Intra-particl diffusion modl plot. c) Sparating th variabls in Eq. [3] givs: dq/[q -q] = K II dt () Intgrating Eq. () for th boundary conditions q = to q = q at t = to t = t, Eq. () simplifis to: t/q t = /[K II q ] + t/q () whr t is th contact tim [min], q [mg g - ] and q [mg g - ] ar th amount of dy adsorbd at quilibrium and at any tim, t. A plot btwn t/q t vrsus t givs th valu of th constants K II [g mg - h - ] and also q [mg g - ] can b calculatd. Fig. 5b shows th psudo-scond ordr plot for Dirct Brown onto biomass. Th psudo-scond ordr 6

7 N. Sivarajaskar, R. Baskar, V. Balakrishnan rat constant K II, th calculatd q valu and th corrsponding linar rgrssion corrlation cofficint valus ar givn in Tabl. At all initial dy concntrations, th linar rgrssion corrlation cofficint valus wr highr and rangd from.983 to.985. Th highr rgrssion valus confirm that th sorption data ar wll rprsntd by psudo-scond ordr kintics and th supports th assumption bhind th modl that th sorption is du to chmisorption. Th possibl raction mchanism can b gnralizd as Ho and McKay [35]: ( Dy) + + ( Biomass) = [Dy] [Biomass] () Avrag Rgrssion valu of.987, which was vn bttr than that of Rvrsibl first ordr rgrssion valus mad clar that th sorption data tnd to follow psudo-scond ordr kintic modl. Intraparticl diffusion modl Wbr and Morris [38] concludd that th uptak is proportional to th squar root of contact tim during th cours of adsorption. Accordingly: q t = k p t -/ (3) whr k p (mg g - min -/ ) is th rat constant of intraparticl transport. Th intraparticl diffusion plot may prsnt a multilinarity, indicating that two or mor stps tak plac [39]. Th gnral faturs of th plot wr initial curvd portion followd by linar portion and a platau. Th slop of th linar portion has bn dfind as a rat paramtr (k p ) and charactristic of th rat of adsorption in this rgion whr intraparticl diffusion is rat limiting. From Fig. 5c, it may b obsrvd that th straight lin did not pass through th origin and this furthr indicats that th intraparticl diffusion is not only th rat controlling stp. That adsorption data indicatd that th rmoval of dirct brown dy from aquous solution was rathr complx procss involving both boundary layr diffusion and intraparticl diffusion. CONCLUSIONS Spirogyra, a forstry wast, was invstigatd for th rmoval of Dirct Brown from aquous solutions. Paramtrs such as quilibrium tim, ffct of initial dy concntration, ffct of ph and tmpratur on th rmoval of dy wr studid. Th kintic mchanism was studid using psudo-first ordr, psudo-scond ordr, and intraparticl diffusion modl. Psudo-scond ordr fits wll with th avrag rgrssion cofficint of.987. Adsorption mchanism studis rvald that th procss was complx and followd both surfac adsorption and particl diffusion. Isothrm studis show that th Langmuir isothrm fits th xprimntal data significantly bttr than th Langmuir and Tmkin isothrms. REFERENCES. J.A.S. Tnorio, D.C.R. Espinosa, Wast Manag.,,, M.M. Matlock, B.S. Howrton, D.A. Atwood, Watr Rs., 36,, L. Kon, L.J.J. Janssn, Elctrochm. Acta, 47,, Y. Bnito, M.L. Ruiz, Dsalination, 4,, B. Volsky, Z.R. Holan, Biotchnol. Prog.,, 995, A. Kapoor, T. Viraraghavan, Biorsourc Tchnol. 53, 995, F. Vglio, F. Bolchini, Hydromtallurgy, 44, 997, T.A. Davis, B. Volsky, A. Mucci, Watr Rs., 37, 3, N. Kuyucak, B. Volsky, Biotchnol. Biong., 33, 989, R.A.A. Muzzarlli, R. Rocchtti, 986. Mtal adsorption by modifid chitins. In: Thompson, R. (Ed.), Trac mtal rmoval from aquous solution. Th Royal Socity of Chmistry, B.B. Johonson, Environ. Sci. Tchnol., 4, 99, N.L.D. Filho, Y. Gushikn, W.L. Polito, J.C. Moriza, Talanta, 4, 995, R. Apak, E. Tutan, M. Hugul, J. Hizal, Watr Rs., 3, 998, E. Lopz, B. Soto, M. Arias, A. Nunz, A. Rubinos, M. Barnal, Watr Rs., 3, 998, N. Calac, E. Nardi, B.M. Ptronio, G. Pitroltti, Tosti, Chmosphr, 5, 997, Singh, D., Rawat, N.s., Indian J. Chm. Tchnol., 63

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