Effects of temperature on the sorption of Pb 2+ and Cd 2+ from aqueous solution by Caladium bicolor (Wild Cocoyam) biomass

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1 Elctronic Journal of Biotchnology ISSN: Vol.8 No.2, Issu of August 15, by Pontificia Univrsidad Católica d Valparaíso -- Chil Rcivd Novmbr 12, 2004 / Accptd March 15, 2005 RESEARCH ARTICLE Effcts of tmpratur on th sorption of Pb 2+ and Cd 2+ from aquous solution by Caladium bicolor (Wild Cocoyam) biomass Michal Horsfall Jnr* Dpartmnt of Pur and Industrial Chmistry Univrsity of Port Harcourt Uniport P.O.Box 402, Choba Port Harcourt, Nigria Tl: horsfalljnr@yahoo.com Aybami I. Spiff Dpartmnt of Pur and Industrial Chmistry Univrsity of Port Harcourt Uniport P.O.Box 402, Choba Port Harcourt, Nigria Tl: mispiff@yahoo.com Financial support: Th Intrnational Foundation Scinc, Swdn supportd this work through grant numbr W/ to Dr M. Horsfall Jnr. Kywords: biosorption, Cocoyam, havy mtals rmoval, tmpratur, thrmodynamics of sorption, wast managmnt. This rport is basd on th invstigation of th ffct of tmpratur on th rmoval of Pb 2+ and Cd 2+ in aquous fflunt using C. bicolor biomass in a batch sorption procss. Th rsult showd that th most suitabl sorption tmpratur was 40ºC with maximum sorption capacitis of mg/g and mg/g for Pb 2+ and Cd 2+ rspctivly. Various thrmodynamic paramtrs, such as G o, H o, S o and E a hav bn calculatd. Th data showd that th sorption procss is spontanous and xothrmic in natur and that lowr solution tmpraturs favours mtal ion rmoval by th biomass. Th findings of this invstigation suggst that physical sorption plays a rol in controlling th sorption rat. Th sticking probability modl was furthr mployd to assss th applicability of th C. bicolor biomass as an altrnativ adsorbnt for mtal ion contaminants in aquous systm. Tmpratur is a crucial paramtr in adsorption ractions. According to th adsorption thory, adsorption dcrass with incras in tmpratur and molculs adsorbd arlir on a surfac tnd to dsorb from th surfac at lvatd tmpraturs. But for activatd carbon, a diffrnt trnd is noticd whr dcrasing viscosity and incrasing molcular motion at highr tmpratur allows th uptak of molculs into th pors mor asily, causing adsorption to incras as tmpratur incrass. Howvr, tmpratur has not bn studid as rlvant variabl in biosorption xprimnts. Th tsts ar usually prformd at approximatly 25-30ºC. Howvr, Tszos and Volsky, (1987); Kuyucak and Volsky (1989) and Aksu and Kutsal (1991) rportd a slight incras in cation uptak by sawd in th rang of 4 to 55ºC. Havy mtals in th nvironmnt hav bcom a major thrat to plant, animal and human lif du to thir bioaccumulating tndncy and toxicity and thrfor must b rmovd from municipal and industrial fflunts bfor discharg. It is thrfor ncssary that thr ar tchnologis for controlling th concntrations of ths mtals in aquous dischargs/fflunts. Th convntional tchnologis, which hav bn usd, rangd from granular activatd carbon to rvrs osmosis (Garda-Torrsdy t al. 1998). Howvr, ths procsss ar not conomically fasibl for small-scal industris prvalnt in dvloping conomis du to hug capital invstmnt. It is thrfor ncssary to sarch for altrnativ adsorbnts, which ar low-cost, oftn naturally occurring biodgradabl products that hav good adsorbnt proprtis and low valu to th inhabitants. A rang of products has bn xamind. Ths includ pillard clay (Vinod and Anirudhan, 2001), sago wast (Quk t al. 1998), cassava wast (Abia t al. 2003), banana pith (Low t al. 1995), panut skins (Randall t al. 1974), Mdicago sativa (Alfalfa) (Garda-Torrsdy t al. 1998) and spagnum moss pat (Ho t al. 1995) just to mntion a fw. Th proximat composition and som surfac charactristics ssntial in assssing th ability of C. bicolor as an adsorbnt, and th ffct of ph on th sorption *Corrsponding author This papr is availabl on lin at

2 Sorption potntial of Caladium bicolor Tabl 1. Langmuir adsorption isothrm paramtrs. Pb 2+ Cd 2+ Tmp (ºC) X m (mg/g) K R 2 X m (mg/g) K R of Pb 2+ and Cd 2+ using C. bicolor (Wild Cocoyam) biomass has bn rportd lswhr (Horsfall and Spiff, 2004). Th data showd that C. bicolor is an xcllnt adsorbnt for mtal ions in aquous solutions. In this papr, w rport th ffct of tmpratur on th sorption of Pb 2+ and Cd 2+ from singl mtal ion solution using th biomass of C. bicolor (Wild Cocoyam) in a tmpratur rang of 30-80ºC. MATERIALS AND METHODS Biomass prparation Th plants wr harvstd and carfully prpard to obtain th biomass as prviously rportd in our work lswhr (Horsfall and Spiff, 2004a). A rcnt scrning (Horsfall and Spiff, 2004b) for chmical composition and surfac charactrization has shown that th major functional groups on C. bicolor biomass ar polar hydroxyl, aldhydic and carboxylic groups. Ths groups has mad C. bicolor to hav grat potntial as an adsorbnt for mtal ions in aquous solutions. Sorption study as a function of tmpratur A volum of 50 ml of mtal ion solution [Pb 2+ (from Pb(NO 3 ) 2 and Cd 2+ (from Cd(NO 3 ) 2.4H 2 O)] with varying initial mtal ion concntrations of mg/L was placd in a 125 ml conical flask in triplicats. An accuratly wighd Caladium bicolor biomass sampl (250 ± 0.01mg) with particl siz of 100 µm was thn addd to th solution to obtain a suspnsion. Th suspnsions wr adjustd to ph 5.0. A sris of such conical flasks was thn shakn at a constant spd 100 x g in a shaking watr bath at tmpraturs of 30, 40, 50, 60, 70, and 80ºC rspctivly. Aftr shaking th flasks for 2 hrs, th suspnsion was filtrd using Nº 45 Whatman filtr papr and thn cntrifug at 2800 x g for 5 min. Th suprnatants wr collctd in sparat clan tst tubs. Th mtal contnt at ach tmpratur rang was dtrmind using flam atomic absorption spctromtr modl A300. Thory and data valuation Th man mtal ion sorbd by th biomass at ach tmpratur was dtrmind using a mass balanc quation xprssd as q ( Co C )ν = [1] m whr q = mtal ion adsorption pr unit wight of biomass (mg/g biomass) at quilibrium, C = mtal ion concntration in solution (mg/l) at quilibrium, C o = initial mtal ion concntration in solution (mg/l), ν = volum of initial mtal ion solution usd (L), m = mass of biomass usd (g). Two modls wr usd to fit th xprimntal data: Langmuir modl and th Frundlich modl. Th Langmuir quation was chosn for th stimation of maximum adsorption capacity corrsponding to biomass surfac saturation. Th linalisd form of th abov quation aftr rarrangmnt is givn blow: Tabl 2. Thrmodynamic Paramtrs for th adsorption of Pb 2+ and Cd 2+ on to th biomass of Caladium bicolor. Tmp (ºC) G o KJ/gmol E a KJ/gmol Pb 2+ Cd 2+ S o H o *S G o E a S o J/ gmol K J/gmol x 10-4 KJ/gmol KJ/gmol J/ gmol K H o J/gmol *S x

3 Horsfall, M. and Spiff, A. Tabl 3. Th potntial sticking probability rlationship btwn sorbat and sorbnt. Valus of S* Potntial sticking probability C q 1 C = + [2] q K q max L max whr K L (dm 3 g -1 ) is a constant rlatd to th adsorption/dsorption nrgy, and q max is th maximum sorption upon complt saturation of th biomass surfac. Th xprimntal data wr fittd into quation [2] for C linarisation by plotting against C q. Th Frundlich modl was chosn to stimat th adsorption intnsity of th sorbnt towards th biomass and th linar form is rprsntd by quation 3: 1 ln q = ln KF + lnc [3] n S* > 1 Adsorbat unsticking to adsorbnt no sorption S* = 1 whr; q = th mtal ion uptak pr unit wight of biomass (mg of mtal ion adsorbd/g biomass); C = Conc. of mtal ion in solution at quilibrium (mg dm -3 ); K L and n ar th Frundlich constants. Th valu of n indicats th affinity of th sorbnt towards th biomass. A plot of ln C against Linar sticking rlationship btwn adsorbat and adsorbnt- possibl mixtur of physisorption and chmisorption mchanism S* = 0 Indfinit sticking of adsorbat to adsorbnt chmisorption mchanism prdominant 0 < S* < 1 Favourabl sticking of adsorbat to adsorbnt- physisorption mchanism prdominant S*: sticking probability. ln q in quation [3] yilding a straight lin indicats th confirmation of th Frundlich adsorption isothrm. Th constants 1 n and ln K L can b dtrmind from th slop and intrcpt rspctivly. In ths systms, th Gibbs fr nrgy chang is th driving forc and th fundamntal critrion of spontanity. Ractions occur spontanously at a givn tmpratur if G o is a ngativ quantity. Th fr nrgy of th sorption raction, considring th sorption quilibrium constant, K o, is givn by th following quation: o G = RT ln K o [4] Whr G o is standard fr nrgy of chang, J/gmol; R is univrsal gas constant, J/(gmol K); K o is th thrmodynamic quilibrium constant and T is absolut tmpratur, K. Valus of K o for th sorption procss may q b dtrmind by plotting ln against q at diffrnt C tmpraturs and xtrapolating to zro q according to th mthod of Khan and Singh (1987). Th othr thrmal paramtrs such as nthalpy chang ( H o ), and ntropy Figur 1. Effct of tmpratur on th adsorption on to Caladium bicolor biomass. (a) Pb 2+ ; (b) Cd

4 C = θ 1 [6] C o Sorption potntial of Caladium bicolor whr C o and C ar th initial and quilibrium mtal ion concntrations rspctivly. Statistical analyss wr prformd using Data Analysis Toolpak Microsoft Excl for Windows 2000 with lvl of significanc maintaind at 95% for all tsts. On-way analysis of varianc (ANOVA) without rplication was furthr usd to tst th null hypothsis of no significant diffrncs in th applicability of th C. bicolor biomass towards th sorption of Pb 2+ and Cd 2+. RESULTS AND DISCUSSION Effct of tmpratur Figur 2. Plots of Frundlich isothrm paramtrs as a function of tmpratur. chang ( S o ), may b dtrmind using th rlationships: So H o ln K o = [5] R RT Th surfac covrag (θ) for studying th sticking probability was calculatd from th rlation Th purpos of this rsarch is to ascrtain th ffct of tmpratur on th sorption of mtal ion by th non usful C. bicolor biomass plant. Th ffct of tmpratur on th rmoval of Pb 2+ and Cd 2+ in aquous solution by C. bicolor biomass was studid by varying th tmpratur btwn 30 and 80ºC. Th data prsntd in Figur 1a and 1b showd that adsorption of mtal ion by th C. bicolor biomass incrasd with incras in tmpratur, which is typical for th biosorption of most mtal ions from thir solution (Manju t al. 1998; McKay t al. 1999; Ho, 2003). Howvr, th magnitud of such incras continus to dclin as tmpraturs ar incrasd from 30 to 80ºC. This is bcaus with incrasing tmpratur, th attractiv forcs btwn biomass surfac and mtal ions ar waknd and th sorption dcrass. Carful xamination of th figurs rvald that most of th mtal ions wr rmovd btwn Figur 3. Langmuir isothrm plots for th adsorption onto Caladium bicolor biomass. (a) Pb 2+ ; (b) Cd

5 Horsfall, M. and Spiff, A. th tmpraturs of 30 to 50ºC. Th tmpratur incrass wr obsrvd to b in two phass for lowr tmpraturs and thr phass for highr tmpraturs. For lowr tmpraturs, quilibrium sorption occurs rapidly at lowr mtal ion concntrations in th first phas and bcoms rlativly constant at highr concntrations. Th quilibrium concntration was obtaind at 50 mg/l for Pb 2+ and 70 mg/l for Cd 2+. As tmpratur incrasd abov 50ºC, an initial slow sorption was obsrvd followd by a rapid sorption procss to rach quilibrium and a rlativly constant sorption procss in th third and final phas.th quilibrium concntrations for highr tmpraturs (60-80ºC) wr not significantly diffrnt for thos of lowr tmpraturs. This indicats that incrasing th initial mtal ion concntrations abov th quilibrium concntrations of mg/l may not hav any significant incras in th sorption of mtal ions by C. bicolor biomass. At high tmpratur, th thicknss of th boundary layr dcrass, du to th incrasd tndncy of th mtal ion to scap from th biomass surfac to th solution phas, which rsults in a dcras in adsorption as tmpratur incrass (Aksu and Kutsal, 1991). Th dcras in adsorption with incrasing tmpratur, suggst wak adsorption intraction btwn biomass surfac and th mtal ion, which supports physisorption. According to Gils classification as rportd by Vinod and Anirudhan (2001), th adsorption isothrms for all tmpraturs may b furthr classifid into svral subgroups of I, II, III, tc according to th shap of th curvs. Th sorption isothrms at 10-40ºC blong to th subgroup III of Gils classification. On th othr hand, th sorption isothrms at 50-60ºC blongs to subgroup II, whil abov 70ºC is subgroup I. In this invstigation tmpraturs of 30 and 45ºC in Figur 1 tnd to dfin a platau; thrfor it sms rasonabl to support th proposal that for th xprimntal conditions usd, th formation of a complt monolayr of mtal ion covring th biomass surfac blongs to subgroup III, maning that saturation of th biomass surfac sms to b rachd at 10 to 40ºC and th optimal tmpratur of adsorption for Pb 2+ and Cd 2+ could b obtaind within this rang. To facilitat th stimation of th adsorption capacitis at various tmpraturs, xprimntal data wr fittd into quilibrium adsorption isothrm modls of Frundlich and Langmuir. Sorption data wr fittd by Frundlich adsorption isothrm at all tmpraturs (r 2 wr gratr than 0.94). Th Frundlich adsorption isothrm paramtrs, 1/n and K F, wr thn plottd against tmpratur (Figur 2). Th valus of 1/n wr found to b mor than unity at all tmpraturs xcpt 30 and 40ºC, indicating that dsorption occurs at abov 40ºC. This implis that significant adsorption took plac at low tmpraturs, which bcoms lss significant at highr tmpraturs. Th ultimat adsorption capacity of th biomass at th diffrnt tmpraturs can b calculatd from th isothrmal data by substituting th rquird quilibrium concntration in th Frundlich quation. Th valu of K F, which is a masur of th dgr of adsorption, dcrass with incras in tmpratur (Figur 2). Th highr K F valus at lowr tmpraturs indicat that mor sorption would b xpctd at ths tmpraturs. Figur 4. Plot of lnk o against rciprocal tmpratur for Pb 2+ and Cd 2+ sorption on Caladium bicolor biomass. 166

6 Sorption potntial of Caladium bicolor Th most probabl tmpratur of adsorption was furthr valuatd by th Langmuir isothrm. Th Langmuir maximum adsorption, X m, for a monomolcular surfac covrag and th adsorption quilibrium constants, K F, at th tmpraturs invstigatd wr obtaind from th plot (Figur 3) for th prdiction of th probabl tmpratur of adsorption. Rlvant paramtrs valus as shown in Tabl 1 indicat that optimal tmpratur of adsorption in utilizing Caladium bicolor biomass for th rmoval of mtals in aquous solutions is about 40ºC. Th Langmuir fits at all tmpraturs show slight curvaturs (Figur 3), which suggst that th surfac adsorption is not a singl monolayr with singl sits. Two or mor sits with diffrnt affinitis and maximum may b involvd in mtal ion sorption. Aftr 40ºC, th valus of X m and K dcrasd with incras in tmpratur, showing that adsorption capacity and intnsity of adsorption ar nhancd at lowr tmpraturs. Furthrmor, th cofficints of dtrmination, R 2, from th Langmuir modl was subjctd to th on-way analysis of varianc (ANOVA) at α = 0.05 to tst th null hypothsis (h o ) of no significant diffrnc in th applicability of C. bicolor to rmov Pb 2+ and Cd 2+ from aquous solution. Th statistical data obtaind showd that F cal (0.47) << F crit, (4.39), hnc, w accpt th h o, which indicats that th C. bicolor had similar sorption potntial for th rmoval of Pb 2+ and Cd 2+ from aquous fflunt. Thrmodynamic tratmnt of th sorption procss Th thrmodynamic tratmnt of th sorption data indicats that G o valus wr ngativ at all th tmpraturs invstigatd. Th ngativ valus of G o (Tabl 2) indicat th spontanous natur of adsorption of mtal ion by th biomass. It is of not that G o up to 20 KJ gmol -1 ar consistnt with lctrostatic intraction btwn sorption sits and th mtal ion (physical adsorption) whil G o valus mor ngativ than 40 KJ gmol -1 involv charg sharing or transfr from th biomass surfac to th mtal ion to form a coordinat bond (chmical adsorption). Th G o valus obtaind in this study for both mtal ions ar < - 10 KJ gmol -1, indicativ that physical adsorption is th prdominant mchanism in th sorption procss. Th valus of ( H o ) and ( S o ) wr obtaind from th slop and intrcpt of plots of ln K o vs 1/T (Figur 4) and ar shown in Tabl 2. Th ngativ valus of ( H o ) for Pb 2+ and Cd 2+ on to th biomass furthr confirm th xothrmic natur of th adsorption procss. Th positiv valus of S o (Tabl 2) show that th frdom of mtal ions is not too rstrictd in th biomass confirming a physical adsorption, which is furthr confirmd by th rlativly low valus of G o. Figur 5. Th rlationship btwn tmpratur and sticking probability for Pb 2+ and Cd 2+ sorption on Caladium bicolor biomass. 167

7 Horsfall, M. and Spiff, A. In ordr to furthr support th assrtion that physical adsorption is th prdominant mchanism, th valus of activation nrgy (E a ) and sticking probability (S*) wr stimatd from th xprimntal data. Thy wr calculatd using a modifid Arrhnius typ quation rlatd to surfac covrag as xprssd in quation 7: Ea S* = ( 1 θ ) xp [7] RT Th sticking probability, S*, is a function of th adsorbat/adsorbnt systm undr considration but must li in th rang 0 < S* < 1 and is dpndnt on th tmpratur of th systm. Th paramtr S* indicats th masur of th potntial of an adsorbat to rmain on th adsorbnt indfinitly. It can b xprssd as in Tabl 3. Th ffct of tmpratur on th sticking probability was valuatd throughout th tmpratur rang from 30 to 80ºC by calculating th surfac covrag at th various tmpraturs. Th plot of ln( 1 θ ) against 1/T gav linar E plots with intrcpt of and slop of a R as shown in Figur 5. Th apparnt activation nrgy (E a ) and th sticking probability (S*) ar stimatd from th plot with rasonabl good fit for th two mtal ions on th biomass (r 2 > 0.97). Th E a valus calculatd from th slop of th plot wr found to b KJ gmol -1 and 7.92 KJ gmol -1 for Pb 2+ and Cd 2+ rspctivly. Th ngativ valus of E a indicat that lowr solution tmpraturs favours mtal ion rmoval by adsorption onto th Caladium bicolor biomass and th adsorption procss is xothrmic in natur. Rlativly low valus of E a suggsts that mtal ion adsorption is a diffusion controlld procss. Th rsults as shown in Tabl 2 indicat that th probability of mtal ion sticking to th C. bicolor biomass surfac is vry high as S* << 1 for both mtals (Tabl 2). Ths valus confirm that, th sorption procss is physisorption. CONCLUDING REMARKS In conclusion, th rsults clarly stablish that th sorption of Pb 2+ and Cd 2+ onto C. bicolor is favourd at lowr solution tmpraturs. Th rang of tmpraturs which favours th adsorption procss was 10-45ºC with optimal tmpratur at 40ºC. This tmpratur rang is favourabl for solubility of chmicals in wastwatr tratmnt systms and will also nhanc th raction rats. Th activation nrgy furthr supports lowr solution tmpraturs and an xcllnt sticking of mtal ions on to C. bicolor biomass. Th sorption procss is spontanous and xothrmic and th mchanism is physisorption. Th quilibrium data agrs with th Langmuir isothrm. Th sorption capacity of Cd 2+ is highr than Pb 2+ bcaus of th ionic sizs of th ions; howvr, thr is no significant diffrnc in th sorption potntial of th biomass towards th two mtal ions in aquous solution. Caladium bicolor is a non-usful plant growing in th wild. Its us as an adsorbnt may vntually ncourag cultivation of th plant and nhanc th conomis of local farmrs and gnrat mploymnt. Th biomass from C. bicolor may b rcycld and th rcovrd biomass is biodgradabl and thrfor nvironmnt frindly. Hnc, not only is C. bicolor wast inxpnsiv and radily availabl, it also has th potntial for mtal rmoval and rcovry of mtal ions from contaminatd watrs. This procss will b nvironmnt frindly and rduc th hug amount of indiscriminat fflunt dischargs all around th small industry concrns in Nigria. It may also provid an affordabl tchnology for small and mdium-scal industry in Nigria. REFERENCES ABIA, A.A.; HORSFALL, M. Jnr and DIDI, O. Th us of chmically modifid and unmodifid cassava wast for th rmoval of Cd, Cu and Zn ions from aquous solution. Biorsourc Tchnology, 2003, vol. 90, no. 3, p AKSU, Z. and KUTSAL, T.A. A biosparation procss for rmoving Pb(II) ions from wastwatr by using C. vulgaris. Journal Chmical Tchnology and Biotchnology, 1991, vol. 52, no. 1 p GARDEA-TORRESDEY, J.L.; GONZALEZ, J.H.; TIEMANN, K.J.; RODRIGUEZ, O and GAMEZ, G. Phytofiltration of hazardous cadmium, chromium, lad and zinc ions by biomass of Mdicago sativa (Alfalfa). Journal of Hazardous Matrials, 1998, vol. 57, no. 1-3, p HO, Y.S. Rmoval of coppr ions from aquous solution by tr frn. Watr Rsarch, 2003, vol. 37, no. 10, p HO, Y.S.; JOHN WASE, D.A. and FORSTER, C. F. Batch nickl rmoval from aquous solution by spagnum moss pat. Watr Rsarch, 1995, vol. 29, no. 5, p HORSFALL, M. Jnr and SPIFF, A.I. Adsorption of mtal Ions from mixd mtal solutions on Caladium Bicolor (wild cocoyam) biomass surfac. Journal of Corrosion Scinc and Tchnology, 2004a, vol. 2, p HORSFALL, M. Jnr and SPIFF, A.I. Studis on th ffct of ph on th sorption of Pb 2+ and Cd 2+ ions from aquous solutions by Caladium bicolor (wild cocoyam) biomass. Elctronic Journal of Biotchnology [onlin]. 15 Dcmbr 2004b, vol. 7, no. 3. Availabl from Intrnt: indx.html. ISSN KHAN, A.A and SINGH, R.P. Adsorption thrmodynamics of carbofuran on Sn(IV) arsnosilicat in H +, Na + and Ca 2+ forms. Journal of Colloid Scinc, 1987, vol. 24, no. 1, p LOW, K.S.; LEE, C.K. and LEO, A.C. Rmoval of mtals from lctroplating wasts using banana pith. Biorsourc Tchnology,1995, vol. 51, no. 2-3, p

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