Removal of Cu 2+ from Aqueous Solution by Biosorption on Rice Straw - an Agricultural Waste Biomass

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1 Intrnational Journal of Environmntal Scinc and Dvlopmnt, Vol. 3, No. 1, Fbruary 2012 Rmoval of Cu 2+ from Auous Solution by Biosorption on Ric Straw - an Agricultural Wast Biomass Achanai Buasri, Nattawut Chaiyut, ssarin Tapang, Supparok Jaronsin, and Suthra Panphrom Abstract Th potntial of ric straw, agricultural wast, to rmov coppr (II) from auous solution was valuatd in a batch procss. Exprimnts wr carrid out as function of contact tim, initial concntration, ph and tmpratur. Adsorption isothrms wr modld with th Langmuir, Frundlich, Tmkin and Dubinin-Radushkvich isothrms. Th data fittd wll with th Frundlich isothrm. Th uilibrium biosorption isothrms showd that biosorbnt possss high affinity and sorption capacity for Cu(II) ions, with sorption capacitis of mg Cu 2+ pr 1 g biomass. Thrmodynamic paramtrs such as fr nrgy chang (ΔG ), nthalpy chang (ΔH ) and ntropy chang (ΔS ) hav bn calculatd on th basis of Langmuir constants. Th rsults indicatd that th ric straw could b an altrnativ for mor costly adsorbnts usd for havy mtal rmoval. Indx Trms Biosorption, ric straw, biosorbnt, wastwatr tratmnt, havy mtal I. INTRODUCTION Industrial wastwatr is oftn charactrizd by considrabl havy mtal contnt and, thrfor, tratmnt is ruird prior to disposal in ordr to avoid watr pollution. Havy mtal contamination xists in auous wast strams from divrs industris such as mtal plating, mining, painting, wir drawing, battris and printd circuit board manufacturing, as wll as agricultural sourcs whr frtilizrs and fungicidal sprays ar intnsivly usd. Havy mtals, such as Cu, Zn, Pb and Cd, ar prior toxic pollutants xistnt in industrial wastwatr, whil thy also constitut common groundwatr contaminants [1]-[2]. Coppr ions (Cu 2+ ) ar watr-solubl, whr thy function at low concntration as bactriostatic substancs, fungicids, and wood prsrvativs. In sufficint amounts, thy ar poisonous to highr organisms, at lowr concntrations it is an ssntial trac nutrint to all highr plant and animal lif. Th main aras whr coppr is found in animals ar tissus, livr, muscl and bon. A varity of suitabl mthods can b usd for th rmoval of mtal pollutants from such liuid wasts, including filtration, chmical prcipitation, coagulation, solvnt xtraction, lctrolysis, ion xchang, Manuscript rcivd Dcmbr 6, 2011; rvisd Dcmbr 28, Achanai Buasri and Nattawut Chaiyut ar with th Dpartmnt of Matrials Scinc and Enginring, Faculty of Enginring and Industrial Tchnology, Silpakorn Univrsity, Nakhon Pathom, Thailand and th National Cntr of Excllnc for Ptrolum, Ptrochmicals and Advancd Matrials, Chulalongkorn Univrsity, Bangkok, Thailand (-mail: achanai130@hotmail.com; nchaiyut@hotmail.com). ssarin Tapang, Supparok Jaronsin and Suthra Panphrom ar with th Dpartmnt of Matrials Scinc and Enginring, Faculty of Enginring and Industrial Tchnology, Silpakorn Univrsity, Nakhon Pathom, Thailand. mmbran procss and adsorption. Ion xchang and adsorption ar th most common and ffctiv procsss for th rmoval of havy mtal ions [3]-[4]. From last fw dcads, biosorption procss has mrgd as a cost ffctiv and fficint altrnativ for watr and wastwatr tratmnt utilizing naturally occurring and agricultural wast matrials as biosorbnts as ths ar chapr, rnwabl and abundantly availabl [5]-[8]. Agricultural by-products usually ar composd of lignin and cllulos as major constitunts and may also includ othr polar functional groups of lignin, which includs alcohols, aldhyds, ktons, carboxylic, phnolic and thr groups. Ths groups hav th ability to som xtnt to bind havy mtals by donation of an lctron pair from ths groups to form complxs with th mtal ions in solution [9]-[10]. Th rmoval of havy mtal ions using low-cost abundantly availabl adsorbnts: agricultural wasts such as sawdusts, palm krnl husk, coconut husk, corncobs, appl wasts, ta lavs and diffrnt agricultural by-products wr usd and invstigatd [11]-[23]. Ric straw is on of th abundant lignocllulosic wast matrials in th world. In trms of total production, ric is th third most important grain crop in th world bhind what and corn. In trms of chmical composition, th straw prdominantly contains cllulos (32-47%), hmicllulos (19-27%) and lignin (5-24%) [24]. Th lignin is promptly availabl to intract with cations, by firstly xchanging with protons and subsuntly by chlating with th mtallic ion [25]. Ric straw has svral charactristics to prdict th functional groups on th surfac of th biomass that mak it a potntial adsorbnt with binding sits capabl to tack up mtals from auous solutions [26]. In this work, w attmpt to us ric straw, which ar discardd as wast matrial availabl on a farm, as an altrnativ low-cost biosorbnt in th rmoval of coppr (II) from auous solutions. Also th influnc of various paramtrs such as contact tim, initial concntration, ph and tmpratur on biosorption potntial of agricultural wast matrial was studid in dtail. II. EXPERIMENTAL METHODS A. Prparation of Biosorbnt Ric straw usd as th biosorbnt in this study was collctd from a cultivatd ara nar Nakhon Pathom city, Thailand. In a 500 ml, thr-nckd flask uippd with a nitrogn inlt, a condnsr, a thrmomtr, and a stirrr, 224 g ura was addd, hatd at 140 o C and flushd with nitrogn. 30 g ric straw and 168 ml phosphorous acid wr addd 10

2 Intrnational Journal of Environmntal Scinc and Dvlopmnt, Vol. 3, No. 1, Fbruary 2012 altrnativly portionwis to th moltn ura in ordr to rduc th foaming. Th raction was allowd to procd at 150 o C for 2 h. Th fibr was washd with distilld watr and acton. A sampl of fibr was tratd with 0.5 M hydrochloric acid for 24 h undr slow stirring. Th modifid cllulos was washd svral tims with dionizd watr to rmov xcss acid from biosorbnt. It was drid for 24 h at 60 o C in an ovn bfor starting th xprimnts. B. Stock Solution Prparation All chmicals usd wr analytical grad ragnts (Mrck, >99 %purity). Stock solutions of mtals wr prpard in a concntration of 2,000 ppm using nitrat salts dissolvd in dionizd watr with a rsistivity valu of 17 M. Th chmicals usd in th batch xprimnts was nitrat solutions of Cu(NO 3 ) 2. C. Batch Adsorption Exprimnt Th influnc of ric straw modification on Cu 2+ uptak was invstigatd undr th following xprimntal conditions; a volum of 100 ml of mtal solution with biosorbnt was placd in a bakr to start th xprimnts. Batch mod adsorption isothrm was carrid out at o C. Amount of 2.0 g modifid cllulos wr introducd into conical flasks with havy mtal solution. Th flasks wr placd in a thrmostatic shakr and agitatd for min at a fixd agitation spd of 700 rpm. Th influnc of ph on th coppr(ii) adsorption was studid, varying th ph of solution from Th ph of mtal solutions was appropriat adjustd by using HNO 3 or NaOH. Sampls wr takn priodically for masurmnt of auous phas of havy mtal concntrations. Adsorption isothrms wr prformd for initial havy mtal concntrations of 250-1,250 ppm. Th Cu 2+ concntration of th sampls wr dtrmind by using a Varian Librty 220 inductiv coupld plasma mission spctromtr (ICP-ES). Th influnc of a spcific procss paramtr was dtrmind by calculating Cu 2+ uptak by ric straw and changing that paramtr and kping othr paramtrs constant. Th prcnt of mtal ion rmoval was valuatd from th uation: %Rmoval = [(C i - C )/C i x 100] (1) whr C i and C ar th initial and final (uilibrium) concntrations of th mtal ions in th solution (ppm) Th amount of adsorbd Cu 2+ ions (mg mtal ions/g biomass) wr calculatd from th dcras in th concntration of mtal ions in th mdium by considring th adsorption volum and usd amount of th biosorbnt: ( C i C ) V m whr is th amount of mtal ions adsorbd into unit mass of th biosorbnt (mg/g) at uilibrium, V is th volum of mtal solution (L) and m is th amount of biosorbnt usd (g). D. Adsorption Isothrm Modls (2) Adsorption isothrms for coppr ions rmoval by ric straw in trms of Langmuir, Frundlich, Tmkin and Dubinin- Radushkvich modls wr xprssd mathmatically. Th obtaind xprimntal data hr ar xpctdly wll fittd with th linarizd form of four two-paramtr isothrm modls. Th Langmuir modl assums a monolayr adsorption of soluts onto a surfac comprisd of a finit numbr of idntical sits with homognous adsorption nrgy. This modl [27]-[28] is xprssd as follows: LaLC alc 1 (3) whr L and a L ar th Langmuir constants rlatd to th adsorption capacity (mg/g) and nrgy of adsorption (L/mg), rspctivly. Th thortical maximum monolayr adsorption capacity, m (mg/g), is givn by L /a L. Th Frundlich isothrm is an mpirical xprssion that taks into account th htrognity of th surfac and multilayr adsorption to th binding sits locatd on th surfac of th sorbnt. Th Frundlich modl [29] is xprssd as follows: F C 1/ n whr F and n ar indicativ isothrm paramtrs of adsorption capacity (mg/g) and intnsity, rspctivly. Tmkin isothrm assums that dcras in th hat of adsorption is linar and th adsorption is charactrizd by a uniform distribution of binding nrgis. Tmkin isothrm [30] is xprssd by th following uation: RT b ln ( T C) whr T is uilibrium binding constant (L/g), b is rlatd to hat of adsorption (J/mol), R is th gas constant (8.314 x 10-3 kj/ mol) and T is th absolut tmpratur (). Dubinin-Radushkvich isothrm is applid to find out th adsorption mchanism basd on th potntial thory assuming htrognous surfac. Dubinin-Radushkvich isothrm [31]-[34] is xprssd as follows: xp m 2 whr m is th maximum adsorption capacity (mg/g), is a constant rlatd to th man fr nrgy of adsorption and ε is th Polanyi potntial. E. Adsorption Thrmodynamics intic uations for th first ordr rvrsibl and first and scond ordr irrvrsibl ractions ar th uations most oftn usd to dscrib th rmoval of havy mtal ions from pollutd watr by us of natural matrial [35]-[36]. To calculat valus of th thrmodynamic paramtrs dscribing th Cu 2+ uptak by ric straw th following uations wr usd: (4) (5) (6) 11

3 Intrnational Journal of Environmntal Scinc and Dvlopmnt, Vol. 3, No. 1, Fbruary 2012 G o = -RT ln (7) H o = [RT 1 T 2 /(T 2 - T 1 )] ln ( 2 / 1 ) (8) S o = (H o - G o )/T (9) whr R is th gas constant,, 1 and 2 ar th uilibrium constants at th tmpratur T, T 1 and T 2, rspctivly. Th uilibrium constant was calculatd from: concntration and thn it bgins to a slight incras with incrasing mtal concntration in auous solutions in th lngth btwn 500 and 1,250 ppm. Ths rsults indicat that nrgtically lss favorabl sits bcom involvd with incrasing mtal concntrations in th auous solution. Th mtal uptak can b attributd to diffrnt mchanisms of ion xchang and adsorption procsss as it was concrnd in much prvious work [38]-[39]. = C,s /C,l (10) whr C,s and C,l wr th uilibrium concntrations of Cu 2+ on th sorbnt and in solution corrspondingly. III. RESULTS AND DISCUSSION A. Effct of Contact Tim Exprimnts conductd with diffrnt contact tims show that th amounts of Cu 2+ ions adsorbd pr unit mass of ric straw incras with th contact tim of mtal ions (Fig. 1). It was obsrvd that th biosorption of Cu(II) by ric straw was highly influncd by contact tim. Th kintics of mtal rmoval by biosorbnt was rlativly fast within 30 min and during th first hour was rmarkably changd with tim. At th uilibrium tim th mtal ion uptak of 82% for Cu(II) was achivd. Th uilibrium tim was takn as 120 min for furthr xprimntal masurmnts. Euilibrium tim is a crucial paramtr for an optimal rmoval of mtal ions in th wast watr. Th incrasd uptak of mtal ions with contact tim can b du to th dcrasd mass transfr cofficint of th diffusion controlld raction btwn th adsorbnt and th mtal ion [26],[37]. Fig. 1. Effct of contact tim on th rmoval of Cu 2+ ions onto ric straw (initial concntration = 500 ppm, ph = 5.38 and tmpratur = 30 o C). B. Effct of Initial Concntration Fig. 2 illustrats th biosorption of Cu 2+ ions by ric straw as a function of initial mtal ion concntration. This incras continus up to 500 ppm and byond this valu, thr is not a significant chang at th amount of adsorbd mtal ions. This platau rprsnts saturation of th activ sits availabl on th biosorbnt sampls for intraction with mtal ions. It can b concludd that th amount of mtal ions adsorbd into unit mass of th biosorbnt at uilibrium (th adsorption capacity) rapidly incrass at th low initial mtal ions Fig. 2. Effct of initial concntration on th rmoval of Cu 2+ ions onto ric straw (contact tim = 120 min, ph = 5.38 and tmpratur = 30 o C). C. Effct of ph Th ph dpndnc of Cu 2+ biosorption onto ric straw is shown in Fig. 3. As it is sn in figur, is low at low ph valus. Th valu of is incrasd by incrasing th ph valu and rachs a platau at a ph valu of 7.0 for coppr(ii). It is apparnt that using solutions at ph valus btwn 9.0 and 11.0 givs th highst valus du to th prcipitation occurs during ion xchang xprimnts by NaOH. So, this mtal ion adsorption procss cloud not carrid out only at a crtain ph valu, but also in a wid rang of ph valus. Ths rsults ar in agrmnt with svral prvious invstigations on mtal rmoval by a varity of matrials [40]-[41]. It rvald that th adsorption capacity is low at ph valus blow 5.0 bcaus of th comptition btwn th protons (H + ) and mtal ions (Cu 2+ ) for th xchang sits on th biosorbnt. So, incrasd xtrnal H + concntration (du to lowrd ph) may hav ffctd mtal ion rmoval via ion xchang by dirct comptition ffcts btwn th protons and mtal ions for th xchang sits on th ric straw. D. Effct of Tmpratur Th ffct of th solution tmpratur on th adsorption capacity was invstigatd for Cu(II) ions solutions at initial concntration 500 ppm and amount of biosorbnt 2.0 g. Fiv diffrnt tmpraturs of 30, 40, 50, 60 and 70 ºC wr considrd. From Fig. 4, th amounts of adsorbd coppr onto th ric straw incras with an incras in th tmpratur of havy mtal solution. Raising th tmpratur from 30 to 70 o C rducs th amounts of mtal ions in solution 78.84%. Th maximum adsorption capacity was calculatd as mg Cu 2+ /g biomass. Ths rsults indicat that adsorbnt was suitabl for havy mtals rmoval from auous mdia and th adsorption of Cu(II) ions is ndothrmic in natur [37]-[38]. 12

4 Intrnational Journal of Environmntal Scinc and Dvlopmnt, Vol. 3, No. 1, Fbruary 2012 Fig. 3. Effct of ph on th rmoval of Cu 2+ ions onto ric straw (initial concntration = 500 ppm, contact tim = 120 min and tmpratur = 30 o C). TABLE I: ISOTHERM CONSTANTS FOR THE BIOSORPTION OF COPPER(II) IONS ON RICE STRAW. Isothrm constants Langmuir modl L (mg/g) a L (L/mg) Frundlich modl F (mg/g) n Tmkin modl T (L/g) b Dubinin-Radushkvich modl m (mg/g) TABLE II: THERMODYNAMIC PARAMETERS FOR THE BIOSORPTION OF COPPER(II) IONS ON RICE STRAW. Tmpratur () Biosorption Efficincy (%) (-) G (J/mol) -13,661-14,403-15,331-16,323-17,004 H (J/mol) 2,708 2,722 2,807 2,953 - S (J/mol.) Fig. 4. Effct of tmpratur on th rmoval of Cu 2+ ions onto ric straw (initial concntration = 500 ppm, contact tim = 120 min and ph = 5.38). E. Isothrm of Biosorption In addition to th xprimntal data, th linarizd forms of Langmuir, Frundlich, Tmkin and Dubinin-Radushkvich isothrms using Es. (3), (4), (5) and (6), ar compard. Th isothrm constants and corrsponding corrlation cofficints for th biosorption of Cu 2+ is prsntd in Tabl I. Th corrlation cofficints dmonstrat that Langmuir, Frundlich and Tmkin modls aduatly fittd th data for Cu(II) adsorption. Howvr, th cofficint of dtrmination ( ) valus is highr in th Frundlich modl for coppr adsorption whn compard to othr modls [34],[42]. Th xprimntal data for havy mtal ions fit wll with th linarizd Langmuir, Frundlich, Tmkin and Dubinin-Radushkvich isothrms. valus rangd from to for adsorption of Cu 2+. Ths rsults indicatd that th uilibrium biosorption data of coppr conformd rasonably wll to th four two-paramtr isothrm modls uations. F. Thrmodynamic of Biosorption Thrmodynamic paramtrs for th procss of Cu 2+ uptak by ric straw ar prsntd in Tabl II. Valus found for G, H and S ar indicativ of th spontanous natur of th uptak procss. Th incras of th uilibrium constant with incrasing tmpratur and positiv valus obtaind for H show th ndothrmic natur of Cu 2+ uptak. Rsults obtaind in our xprimnts gnrally agr with th rsults prviously found for th uptak of havy mtal ions by natural matrials [38]. IV. CONCLUSION Ric straw is an nvironmntally frindly potntial biosorbnt for havy mtals. This work xamind th fficincy of this sorbnt in rmoval of Cu 2+ ions from auous nvironmnt. Th rsults indicatd that svral factors such as contact tim, initial concntration, ph and tmpratur affct th biosorption procss. Th physicochmical charactristics of wastwatrs from varying sourcs can b much mor complx compard to th auous mtal solution usd in this study. Bcaus of this, th ffcts of othr componnts of wastwatrs on commrcial mtal adsorption procss should b dtrmind. Howvr, this work can b considrd a prliminary study to conclud that ric straw is suitabl and fficint matrial for th adsorption of Cu 2+ from auous solution. Th xprimntal rsults wr a good fit with th adsorption isothrm modls. ACNOWLEDGMENT Th authors acknowldg sincrly th Dpartmnt of Matrials Scinc and Enginring (MSE), Faculty of Enginring and Industrial Tchnology, Silpakorn Univrsity (SU) and National Cntr of Excllnc for Ptrolum, Ptrochmicals, and Advancd Matrials (PPAM), Chulalongkorn Univrsity (CU) for supporting and ncouraging this invstigation. REFERENCES [1] J. Pric, M. Trgo, N. V. Mdvidovic, Rmoval of zinc, coppr and lad by natural zolit a comparison of adsorption isothrms, Watr Rs., 38, , [2] M. A. Stylianou, M.P. Hadjiconstantinou, V.J. Inglzakis,.G. Moustakas, M.D. Loizidou, Us of natural clinoptilolit for th 13

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Matr., 193, 27 36, Achanai Buasri rcivd his bachlor s dgr in ptrochmicals and polymric matrials from Silpakorn Univrsity, Thailand in 2002 and mastr s dgr in chmical nginring from Chulalongkorn Univrsity, Thailand in H is prsntly working as Assistant Profssor in Dpartmnt of Matrials Scinc and Enginring, Faculty of Enginring and Industrial Tchnology, Silpakorn Univrsity, Thailand and joind Institut in His main rsarch intrsts ar composit matrials, rnwabl nrgy and wastwatr tratmnt. Nattawut Chaiyut rcivd his bachlor s dgr in ptrochmicals and polymric matrials from Silpakorn Univrsity, Thailand in 1999 and doctor of philosophy (Ph.D.) dgr in polymr scinc and tchnology from Mahidol Univrsity, Thailand in H is prsntly working as Lcturr in Dpartmnt of Matrials Scinc and Enginring, Faculty of Enginring and Industrial Tchnology, Silpakorn Univrsity, Nakhon Pathom, Thailand and joind Institut in His main rsarch intrsts ar biopolymrs, polymr nanocomposits and polymr physics. 14