ASIAN JOURNAL OF CHEMISTRY

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1 Asian Journal of Chmistry; Vol. 3, No. 4 (8), ASIAN JOURNAL OF CHEMISTRY Adsorption Study of Lad(II) Ions on Poly(mthyl mthacrylat) Wast Matrial CYPRIAN YAMESO ABASI, DONBEBE WANKASI 2 and EZEKIEL DIXON DIKIO,* Applid Chmistry and Nanoscinc Laboratory, Dpartmnt of Chmistry, Vaal Univrsity of Tchnology, P.O. Box X2, Vandrbijlpark, South Africa 2 Dpartmnt of Chmical Scincs, Nigr Dlta Univrsity, Wilbrforc Island, P.M.B. 7, Ynagoa Baylsa Stat, Nigria *Corrsponding author: zkild@vut.ac.za Rcivd: 3 Octobr 7; Accptd: 3 January 8; Publishd onlin: 28 Fbruary 8; AJC-88 Th sorption of Pb 2+ from solution by poly(mthyl mthacrylat) (PMMA) wast has bn invstigatd. Th morphological charactrization of th collctd PMMA polymr wr studid by scanning lctron microscopy. Equilibrium, kintics and thrmodynamic batch adsorption xprimnts of Pb 2+ on th PMMA wast sampls wr carrid out. This study nabld th dtrmination of th concntration, tim and tmpratur ffcts, rspctivly on th adsorption proprtis of th PMMA polymr. Th morphological imag of th PMMA polymr showd th prsnc of irrgular small siz particls that indicatd a high surfac which is thrfor possibl to facilitat sorption. Th raction kintics of th adsorption studis of Pb 2+ by th polymr followd a scond-ordr rat procss. Th rsults indicatd that th adsorbnt, PMMA, provd to b an ffctiv matrial for th tratmnt of lad contaminatd watr solution. Th thrmodynamic studis suggstd a raction that favourd a rlativly low tmpratur (low nrgy) sorption that is xothrmically controlld with a physisorption mchanism. Kywords: Sorption, Poly(mthyl mthacrylat) wast, Adsorbnt, Havy mtals, Polymr. INTRODUCTION It is known that chmical substancs spcially lad, if prsnt in crtain concntrations in watr, wastwatr and th nvironmnt constitut a dangr to human halth and othr organisms. Lad dischargd by svral industrial and commrcial activitis is found in th nvironmnt, such that its rmoval, from watr and wastwatr has bcom a challng to rsarchrs [,2]. Th most convntional and applid mthods of rmoval of havy mtals lik lad from wast watr which includ prcipitation, flocculation, filtration, ion xchang, rvrs osmosis, tc., ar vry much capital intnsiv. In th rcnt past, rnwabl matrials ar bing idntifid for th rmoval of mtals from fflunts which includ biomasss lik Nipa palm [3], Manihot sculnta Cranz. [4], sa wd [5] and Mdicago sativa [6]. A nw low-cost or lss capital intnsiv and mor ffctiv adsorbnts ar rquird for wastwatr tratmnts lading rsarchrs to ngag in th sarch for a low-cost and possibly, a locally availabl matrial that could b usd as adsorbnt providing maximum adsorption capacitis. Poly(mthyl mthacrylat) (PMMA) producd from th polymrization of mthyl mthacrylat is a transparnt thrmoplastic which is oftn usd as a light wight or shattr-rsistant altrnativ matrial. It has modrat proprtis, asy handling as wll as procssing and has a low cost. Th non-modifid PMMA is brittl undr an impact forc and mor pron to scratching. Howvr, th modifid PMMA achivs vry high scratch and impact rsistanc. It has good impact strngth highr than both glass and polystyrn. Poly(mthyl mthacrylat) is solubl in dichloromthan or trichloromthan. It has a maximum watr absorption ratio of (.3-.4) % by wight [7]. H CH 3 C C H C O O CH 3 Mthyl m hacrylat Fr radical vinyl polymrization CH 3 CH 2 C C O O CH n 3 Poly(mthyl mthacrylat) Poly(mthylmthacrylat) has numrous applications such as in rsidntial aquariums, submarins, lnss of xtrior lights of vhicls and othr mans of transport, windows of air crafts bcaus of this usag [8]. It is also usd for furnitur, pictur framing, CDs, DVDs, plastic optical fibr, intraocular lnss, contact lnss and in cosmtic surgry and dntal fillings [9]. Th low lvls of rcycling and biodgradation of poly(mthyl mthacrylat) has rsultd in much of it nding in landfills and as a pollutant in th outdoor nvironmnt, prdominantly

2 8 Abasi t al. Asian J. Chm. along shors, watrways and wast dumps, du to its varity of uss [7]. In this study, w prsnt th us of poly(mthyl mthacrylat), wast matrials obtaind from th nvironmnt in th Nigr Dlta rgion of Nigria as adsorbnt matrial for th sorption of lad ions in watr solution. Th poly(mthyl mthacrylat) polymr matrial is charactrizd by FTIR, XRD, SEM and EDS. EXPERIMENTAL Poly(mthyl mthacrylat) (PMMA) polymr matrials wr acquird from th discardd bins and thoroughly washd with th dionizd watr and drid in ovn at 3 C. Th dry sampls wr crushd, milld and passd through th - msh partitioning panls using a Wily mill. Ths particl sizs wr thn washd twic with. M HCl to liminat any mtal and othr hard thrash fragmnts that might b in th polymr prior to xprimntal mtal ion xposur. Th acid washd PMMA polymr sampls wr washd twic again with dionizd watr to rmov acid and thn ovn drid at 3 C to constant wight. Charactrization of polymr sampl: Th morphological dpictions of th polymr wr analyzd by diffrnt tchniqus such as FE-SEM, HR-TEM, EDS, XRD and FTIR. Th outward morphology and EDS masurmnts wr rcordd with a JEOL 75F Fild Emission scanning lction microscop. Th HR-TEM imags of th sampl wr obtaind by a CM lction microscop opratd at KV. Powdr X-ray diffraction configurations wr assmbld with a Brukr AXS D8 Advancd diffractomtr opratd at 45kV and ma with monochromatd coppr Kα radiation wavlngth (λ =.5598) and Kα2 radiation wavlngth (λ = ). Scan spd of s/stp and stp siz of.3. Th Fourir transform infrard spctra wr rcordd on a Prkin-Elmr spctrum FTIR/FT-NIR spctromtr in th rang - cm -. Batch adsorption xprimnt Concntration ffct:.2 g of th polymr sampl was wighd and placd in pr-cland tst tubs. Six Pb 2+ ion solutions with standard concntrations of 2.8, 48., 72.3, 97.7,.9 and 4.5 mg/l wr mad from spctroscopic grad standards of Pb 2+ [from Pb(NO 3 ) 2 ]. ml of ach lad ion solution wr addd to ach tub comprising th PMMA polymr sampl and quilibratd for h by shaking at 29 C. Th polymr particl colloidal suspnsions wr cntrifugd for 5 min at 25 rpm. Th suprnatants wr analyzd as statd in mtal analysis. Th amount of Pb 2+ rmovd from th systm was stimatd using qn.. Tim dpndnt studis:.2 g of th polymr sampl was wighd and placd in fiv pr-cland tst tubs. Th Pb 2+ ion solution with standard concntration of 72.3 mg/l was mad from spctroscopic grad standard of Pb 2+ [from Pb(NO 3 ) 2 ]. ml of th Pb 2+ ion solution was addd to ach tub containing th polymr sampl and quilibratd for ach tim intrvals of (5,,, and ) min, rspctivly by shaking at 29 C. Th polymr suspnsions wr cntrifugd for 5 min at 25 rpm. Th suprnatants wr analyzd as statd in mtal analysis sction. Th amount of lad mtal ion rmovd from th solution was procssd using qn.. Tmpratur ffct:.2 g of th polymr sampl was wighd and placd in four pr-cland tst tubs. Mtal ion solution with standard concntration of 72.3 mg/l was mad from spctroscopic grad standard of Pb 2+. ml of th mtal solution was addd to ach tub containing th polymr sampl and quilibratd for h by shaking at tmpraturs of (28,, and 8) C, rspctivly using a Compnstat Gallnhamp watr bath. Th polymr suspnsions wr cntrifugd for 5 min at 25 rpm. Th suprnatants wr valuatd as statd in th mtal analysis. Th amount of lad mtal ion rmovd from solution was calculatd using qn.. Mtal analysis: Th mtal analysis was prformd by AAS using a Buck Scintific Atomic Absorption/Emission spctrophotomtr A (AAES). Controls of on of th mtal solution wr run to dtct any possibl mtal prcipitation or contamination. Data analysis: Data intrprtation utilizing diffrnt quilibrium, kintic and thrmodynamic simulations wr mployd to intrprt th data and stablish th xtnt of adsorption. Th amount of mtal uptak was computd using th matrial balanc quation for batch dynamic studis qn. [5]. V q = (Co C ) () M whr q is mtal uptak capacity (mg/l) polymr at quilibrium, C is mtal ion concntration in solution (mg/l) at quilibrium, C o is th initial mtal ion concntration in solution (mg/l), V is th volum of solution in litrs and M is th dry wight of polymr usd in grams. Langmuir plots wr carrid out using qn. 2: qmklc q = + KLC (2) whr q is th amount of Pb 2+ adsorbd in mg/g of adsorbnt, C is th rsidual concntration of adsorbat in mg/l, K L is th Langmuir constant and q m is th maximum amount of adsorbat adsorbd in mg/g, obtaind from th slop and intrcpts of th plots, rspctivly. Th ssntial charactristics of th Langmuir isothrm wr xprssd in trms of a dimnsionlss sparation factor or quilibrium paramtr S f []. Sf = ( + K LC o) (3) whr C o is th initial concntration of Pb 2+ in solution. It has bn shown by mathmatical calculations that th magnitud of th paramtr S f provids a masur of th typ of adsorption isothrm []. If S f >., th isothrm is unfavourabl; S f =. (linar); < S f <. (favourabl) and S f = (irrvrsibl). Th adsorption intnsity of Pb 2+ was assssd from th Frundlich plots using th qn. 4: q /n KFC = (4) whr K F and n ar Frundlich constants and /n is approximatly qual to th adsorption intnsity.

3 Vol. 3, No. 4 (8) Adsorption Study of Lad(II) Ions on Poly(mthyl mthacrylat) Wast Matrial 86 Th linarity of hat of adsorption with th surfac covrag of Pb 2+ on th adsorbnt was assssd from th Tmkin plot using qn. 5: RT q = ln(k C ) (5) T bt whr K T is th Tmkin isothrm constant (dm 3 g - ) and b T is th adsorption potntial of th adsorbnt (J mol - ). Th fraction of polymr surfac covrd by Pb 2+ was computd using qn. 6: C θ= C (6) o whr θ is th dgr of surfac covrag. Th prdominant form of adsorption was valuatd using Dubinin-Radushkvich quation (qn. 7). q = qdxp( B D[RTln(+ /C )] ) (7) Th man fr nrgy of sorption E, is rlatd to th constant B D by qn. 8: E = Th prvalnt sorption procss btwn monolayr and multilayr was assssd by th Rdlich-Ptrson and th Sip s isothrms as givn in qns. 9 and, rspctivly. q q 2B D RP g RP 2 (8) k C = (9) + a C n S S n S S QKC = () S + K C Th ffctivnss of adsorbnt (polymr) was assssd by th numbr of cycls of quilibrium sorption procss rquird to rduc th lvls of Pb 2+ in solution according to th valu of distribution (partition) cofficint (K d) in qn. []. K d Caq = () C whr C aq is th concntration of Pb 2+ in solution (mg/l); C ads is th concntration of Pb 2+ in adsorbnt in (mg/l). Th hat of adsorption (Q ads ) was obtaind using th following Suzuki quation [2]: ln KoCo Qads ln θ=.5 T + RT (2) whr T = solution tmpratur (K); K o = constant and R = gas constant (8.34 J/Kmol). Th linar form of th modifid Arrhnius xprssion was applid to th xprimntal data to valuat th activation nrgy (E a) and sticking probability S * as shown in qn. 3 [3]. * Ea ln( θ ) = S + (3) RT Th apparnt Gibbs fr nrgy of sorption G which is a fundamntal critrion for spontanity, was valuatd using th following quation: ads G = RTlnK o (4) whr K o is obtaind from th Suzuki quation (qn. 2). Th xprimntal data was furthr subjctd to thrmodynamic tratmnt in ordr to valuat th apparnt nthalpy ( H ) and ntropy ( S ) of sorption using qn. 5: S H lnko = (5) R RT To valuat th packing of Pb 2+ on th polymr surfac, thrmodynamic analysis of adsorption dnsity (ρ) was carrid out with th following quation: ( H /RT) ρ= ZrC (6) whr Z is th valncy of Pb 2+, ρ is th ffctiv radius of Pb 2+ in cm and C is th quilibrium concntration in mol/cm 3. Th rlationship btwn th numbr of hopping (n) and that of th surfac covrag (θ) as shown in qn. 7 was applid to th xprimntal data. n = (7) ( θ) θ Othr thrmodynamic paramtrs such as adsorption potntial (A) was tstd by applying qn. 8: Co A = RTln C (8) whr C o and C = initial and quilibrium concntrations, rspctivly in mol/cm 3, R = gas constant and T = solution tmpratur in K. Th kintic prformanc of th sorption procss was invstigatd by tsting th data using th first, scond, psudofirst and psudo-scond ordr kintic modls as prsntd in qns q t kt = q (9) o qo qt = + q kt () o 2 kt t = (2) q q ( ) 2 2 q kt qt = (22) + k q t 2 whr q t is th quantity of Pb 2+ on polymr (mg/g or mmol/g) at tim t, q o is th amount of Pb 2+ on polymr at tim t o, k and k 2 ar th first and scond ordr rat constant, rspctivly. RESULTS AND DISCUSSION Charactrization studis: Fourir transform infrard (FTIR) spctroscopy was xtnsivly usd to study th nvironmnt of chmical bonds of polymrs and th supramolcular intractions btwn molculs through th charactrization of thir vibrational typs [4-]. FTIR spctroscopic study of th polymr was conductd to ascrtain th activ functional groups on th polymr accountabl for attaching of Pb 2+ from solution. Fourir transform infrard spctrum of poly(mthyl mthacrylat) in th wavnumbr rang of - cm - is prsntd in Fig.. Th wak band obsrvd at 349 cm - is du to hydrogn bondd O H strtching vibration rsulting

4 862 Abasi t al. Asian J. Chm Wavnumbr (cm ) Fig.. Fourir transform infrard (FTIR) spctrum of poly(mthyl-2- mthacrylat) sampl Transmittanc (%) from nvironmntal dilapidation of th polymr matrial. Th paks at 2925 and 2885 cm -, rspctivly manat from th prsnc of CH 2 asymmtric and symmtric strtching vibrations of th mthyln group. Th absorption band at 743 cm - is a CO strtching vibration of th poly(mthyl mthacrylat) [2]. Th absorption bands at 453, 374, 28, 29 and 98 cm - ar du to bnding dformation, CH 3 symmtric dformation, wagging dformation, twisting dfor-mation and wagging dformation vibrations. Th C O C symmtric strtching vibration and th O CH 3 dformation vibrations which ar th fingrprint vibrations of PMMA ar obsrvd at 98 and 374 cm -, rspctivly. Poly(mthyl mthacrylat) is a saturatd polymric str (-COOR) that yilds an intns pak at 743 cm - du to th symmtrical strtching vibration of th carbonyl group [22,23]. Th absorption bands obsrvd in cm - rgion du to th prsnc of bnding, ring out of plan or rocking dformation vibrations of poly(mthyl mthacrylat). Th prsnc of ths absorption bands indicats that no functional group hav playd a major rol in th sorption procss. X-ray diffraction outlins of th poly(mthylmthacrylat) usd in this study is prsntd in Fig. 2. X-ray powdr diffraction is mployd to show th crystallit siz, phas and th strss or strain of th polymr. Th crystallin morphology of th polymr spcis will hav a uniqu X-ray diffraction pattrn whn invstigatd. With a diffraction pattrn, an xaminr can idntify an unknown spcis or rval th atomic scal structur of an alrady rcognizd substanc. Fig. 2 givs th diffractogram of th poly(mthyl mthacrylat) polymr sampl. Poly(mthylmthacrylat) is catgorizd as a polymr matrial that compriss mainly of an amorphous and a crystallin rgion in diffrnt proportions. Th XRD pattrn show notabl high intnsity Bragg diffraction paks at 2θ = 9.6 and 9.2. Ths paks ar charactristic XRD paks of poly(mthyl mthacrylat) [6]. Th intns pak at 2θ = 9.2 indicats th crystallinity of th poly(mthylmthacrylat) polymr sampl whil th pak at 2θ = 9.6 indicats that th polymr is amorphous in natur. A 2θ valu of 8. has bn rportd for PMMA [2]. Th wak background hump around 2θ = 42 has bn obsrvd in othr works [2,22]. This 2θ valu is also indicativ of th amorphous natur of th matrial. Intnsity (a.u.) 8 Fig θ ( ) X-ray diffraction (XRD) pattrn of poly(mthyl mthacrylat) sampl Enrgy disprsiv X-ray (EDX) was ngagd for lmntal analysis of th polymr sampls. Th EDX spctrum prsntd in Fig. 3 confirmd sharp paks du to th following lmnts: C (93 %), Al (2 %) and O (5 %) in addition to hydrogn. Th occurrnc of ths lmnts will gnrat chargs on th surfac of th polymr and crat lctrostatic forcs of attraction btwn th sampl and Pb 2+ in solution. To dfin th morphology of th polymr, scanning lctron microscop (SEM) imag of th sampl was takn at magnifi- 8 (a) (b) Wight (%) kv C O Al Fig. 3. Enrgy disprsiv X-ray (EDX) of poly(mthyl mthacrylat) sampl (a) quantitativ rsult and (b) spctrum

5 Vol. 3, No. 4 (8) Adsorption Study of Lad(II) Ions on Poly(mthyl mthacrylat) Wast Matrial 863 cation x27. Th SEM imag shows that th surfac of th polymr sampl had irrgular small siz particls which indicatd a high surfac ara and porous natur (Fig. 4). Th prsnc of substantial surfac ara of any adsorbnt facilitats xtrm adsorption [2]. linar plots. Th linar plots stablishd th application of th Langmuir and Frundlich isothrm modls to th adsorption of Pb 2+ by th polymr (figurs not shown). Th gradints and intrcpts wr usd to comput th Langmuir constants and adsorption capacity. Th linar isothrm paramtrs of th adsorption ar givn in Tabl-. Fig. 4. Scanning lctron microscop (SEM) imag of poly(mthyl mthacrylat) sampl Sorption quilibrium studis: Th prcntag of sorption of Pb 2+ by PMMA at diffrnt concntrations of Pb 2+ is prsntd in Fig. 5. Th maximum adsorption of % took plac at quilibrium concntration of mg/l Pb 2+. This is bcaus at lowr concntration mor polymr por spacs wr availabl for Pb 2+, but as th concntration of Pb 2+ incrasd, th adsorption capacity of th polymr diminishd considrably du to rducd availability of fr por spacs. Th rsults indicatd that th sorption of Pb 2+ wr considrably dpndnt on th concntration of Pb 2+. Adsorbd (%) Concntration (mg/l) Fig. 5. Effct of initial concntration of Pb 2+ on th sorption by poly(mthyl mthacrylat) sampl Th xtnt of adsorption of lad ions onto th wast matrial can b compard by mans of an isothrm. Efforts wr mad to fit th data obtaind from th adsorption xprimnts into svral adsorption isothrms. Langmuir and Frundlich isothrm modls for th sorption of Pb 2+ by PMMA show th TABLE- LINEAR ISOTHERM PARAMETERS OF Pb 2+ SORPTION BY PMMA Isothrm Paramtr Valu Langmuir Frundlich Tmkin Dubinin- Radushkvich q max (mg/g) K (L/g) K F (mg/g) n B K T q D (mg/g) B D (mol 2 kj -2 ) E (kj/mol), Ths linar plots confirmd th application of th isothrm modls to th adsorption of Pb 2+ by th polymr. All th linar isothrm plots gav cofficints of dtrmination ( ) of. Th high linar corrlation cofficints of both isothrms imply that chmisorption and physisorption occurrd simultanously. Th valu of th Frundlich adsorption intnsity paramtr, n of.9997 also gav indication of a favourabl adsorption. Valus of n btwn or and hav bn shown to b bnficial adsorption [7-9]. Th n valu of this adsorption lis within rang and hnc it is favourabl. Non-linar forms of th applid isothrms wr also usd to show th closnss and hnc validity of th paramtrs obtaind in th linar modls. Th non-linar paramtrs ar shown in Tabl-2. Th valus of th non-linar isothrm paramtrs ar consistnt with thos of th linar paramtrs, for th Frundlich and Tmkin isothrms. Th non-linar plot of th Langmuir isothrm positions q max at mg/g of adsorbnt and this is not clos to that of th linar valu. To idntify th bst fit modl btwn th Langmuir and th Frundlich, as wll as show th validity of th paramtrs of th applid modls; two thr-paramtr non-linar isothrms, namly; Rdlich-Ptrson and Sip s wr applid to th adsorption data. Th rspctiv isothrm modls ar givn in qns. 9 and and th paramtrs ar shown in Tabl-2. Th rlationship with th non-linar modls of Langmuir, Frundlich and Tmkin ar shown in Fig. 6. Th Rdlich-Ptrson modl is on that incorporats th trms in th Langmuir and th Frundlich isothrms. It proposs that th quation rducs to th

6 864 Abasi t al. Asian J. Chm. TABLE-2 NON-LINEAR ISOTHERM PARAMETERS OF Pb 2+ SORPTION BY PMMA Isothrm Paramtr Valu Langmuir q max (mg/g) K L (L/g) Frundlich Tmkin Rdlich-Ptrson Sip s K F (mg/g) n B k T (J/mol) R2 K RP a RP g Q S k S n S th n S valu is slightly gratr than (n S =.269), k S valu is mor on th sid of zro than, it is obvious thn that th quation rducs to th Frundlich; in which cas, physisorption bcoms mor dominant. A furthr tst of bst-fit btwn Langmuir and Frundlich modls was th us of chi-squard ( ) tst as rcommndd by Tran t al. []. Th tst showd that th Frundlich modl to b closr to zro than th Langmuir, hnc th Frundlich modlld th sorption bttr than th Langmuir. Th chisquard ( ) valu of th Frundlich data was about th sam with thos of Rdlich-Ptrson and Sip s (Tabl-2). Though monolayr and multilayr adsorption occurrd simultanously, th multilayr procss smd to b prvalnt, basd on th prdictiv valus of th paramtrs and tsts masurmnts. It is worth noting hr that valu (Tabl-2) of Langmuir plot was also far highr than that of Frundlich. Th fraction of th polymr surfac nvlopd by Pb 2+ is givn as.592 (Tabl-3). This valu alluds to th fact that ovr 59 % of th por spacs of th polymr surfac wr maskd by Pb 2+, which mans modratly high dgr of adsorption. Surfac covrag (θ) TABLE-3 EQUILIBRIUM PARAMETERS Sparation factor (S f ) Sorption cofficint (K d ) Adsorption capacity (mg/g) EXPT TEMKIN LANG R-P FREUND SIP s C (mg/l) Fig. 6. Non-linar isothrm plots for th sorption of Pb 2+ by th polymr sampl Q (mg/g) Langmuir whn th paramtr g = and bcoms Frundlich with g = and th dnominator product a RP C >>. Th product a RP C is lss than for th first two valus of C whil th rst highr concntrations hav product valus gratr than. Th variation in ths valus could man that th sorption tnds mor to th Frundlich which approximats multilayr physisorption, as th rsidual adsorbat concntration incras with th quantity adsorbd. Th valu of th g trm of th quation, though slightly gratr than (.66) is closr and could nhanc th chmisorption procss, but with a highr numbr of th product a RP C gratr than, th physisorption procss could b assumd to prdominat. Th Sip s isothrm is anothr modl that incorporats th trms of both th Langmuir and Frundlich isothrms and it provids that th quation bcoms Langmuir, if th paramtr n S = and rducs to th Frundlich as k S tnds to zro. Though Th favourability or othrwis of th adsorption was dtrmind by th dimnsionlss constant sparation factor trm S f (qn. 3). Th rsult (S f =.95) was lss than on and gratr than zro, which showd that sorption of Pb 2+ onto th polymr was favourabl. Th ffctivnss of th polymr as an adsorbnt for Pb 2+ from solution was appraisd through th sorption distribution or partition cofficint K d prsntd in Tabl-3. Th valu of K d (.689) suggsts that th polymr is a rlativly ffctiv adsorbnt and that an insufficint numbr of cycls of quilibrium sorption procss will b rquird to rduc th lvls of Pb 2+ in solution. Adsorption kintics and diffusion: Tim dpndncy studis of th polymr sampl show th aggrgat tim ndd for maximum adsorption to nsu. Th disparity in th prcntag rmoval of Pb 2+ ions in solution with tim is shown in Fig. 7. This indicats that a minimum of 59 % rmoval of Pb 2+ was obsrvd in 5 min and continud constant aftrwards. Th rlativly short contact tim rquird to attain quilibrium implis that a rapid uptak of Pb 2+ by th polymr occurrd to fill som of th unoccupid pors in th polymr and subsquntly, th rmaining spacs wr difficult to b occupid du to rpllnt forcs btwn Pb 2+ ions. Th kintic bhaviour of th Pb 2+ ions towards th adsorbnt was valuatd using th non-linar first, scond, psudofirst ordr rat and th psudo-scond modls which tak th form of qns. 9-22, rspctivly. Ths wr plottd with th xprimntal to s which corrlatd bst. Th non-linar kintic plots for th first, scond, psudo-first and psudoscond ordr kintic modls rat modls ar givn in Fig. 8. It can b sn from th plot that th first-ordr modl followd

7 t Vol. 3, No. 4 (8) Adsorption Study of Lad(II) Ions on Poly(mthyl mthacrylat) Wast Matrial 865 Adsorbd (%) Tim (min) Fig. 7. Effct of contact tim on th sorption of Pb 2+ by th poly(mthyl mthacrylat) sampl EXPT FO SO PFO PSO Tim (min) Fig. 8. Non-linar kintic plot for th sorption of Pb 2+ by th poly(mthyl mthacrylat) sampl q (mg/g) th xprimntal data mor than th othr kintic modls. Thus, th controlling kintic mchanism for this sorption was th first ordr. Th non-linar kintic paramtrs ar givn in Tabl- 4. Diffusion modls for adsorption wr applid to th data to dtrmin th rat limiting mchanism. Th sorption diffusion mchanism that bst fittd xprimntal data was stimatd using th intra-particl diffusion or por diffusion. This is givn by qn. 23 a id R= k t (23) TABLE-4 NON-LINEAR KINETIC AND DIFFUSION PARAMETERS OF Pb 2+ SORPTION BY PMMA Typ Paramtr Valu First ordr q o (mg/g) K Scond ordr Intraparticl diffusion (por) q o (mg/g) K 2 K id a whr R is th prcnt adsorbd, k id is th intraparticl diffusion constant, a is a constant and t is th tim in minuts. Th plot givn in Fig. 9 shows that th modl followd clos to th xprimntal data, hnc th controlling diffusion mchanism is th por diffusion. Th paramtrs ar also givn in Tabl-4. R (%) R(Expt) R(id) Tim (min) Fig. 9. Intraparticl diffusion (por diffusion) plot for th adsorption of Pb 2+ by polymr Adsorption thrmodynamics: Fig. prsnts th plot of prcntag adsorption of Pb 2+ by PMMA at varying tmpraturs with optimum sorption of 49 % occurring at 3 C. Th plot showd that additional incras in tmpratur rsultd in a minor dcras in adsorption. This is in harmony with th gnral principl that physical adsorption dclins with incras in tmpratur, i.. molculs adsorbd arlir on a surfac tnd to dsorb from it at lvatd tmpraturs [,24]. This bhaviour might b attributd to th dwindling of attractiv forcs btwn th polymr and Pb 2+, incrasd kintic nrgy of Pb 2+ and dcras in th stiffnss of th boundary layrs of polymr du to th highr tndncy of Pb 2+ to scap from th polymr. Adsorbd (%) Tmpratur ( C) Fig.. Effct of tmpratur on th sorption of Pb 2+ by poly(mthyl mthacrylat) sampl To stimat th hat of adsorption (Q ads ) for th sorption of Pb 2+ onto th polymr, qn. 2 was usd. Th valu of Q ads (-.34 KJ/Kmol) is ngativ as givn in Tabl-5, which indicats that th adsorption was xothrmic i.. low tmpraturs support th adsorption of Pb 2+ by th PMMA polymr and implida diffusion controlld scond ordr kintic procss. Tmpratur incras did not boost th sorption procss.

8 866 Abasi t al. Asian J. Chm. Hat of adsorption (Q ads ) (KJ/Kmol) Sticking probability (S * ) Activation nrgy (E a ) (J/Kmol) TABLE-5 RESULTS OF THERMODYNAMIC PARAMETERS Gibbs fr nrgy of adsorption ( G ) (KJ/mol) Apparnt ntropy ( S ) (J/Kmol) Apparnt nthalpy ( H ) (J/mol) Adsorption dnsity (ρ) (mol/cm 2 ) Hopping numbr (n) Adsorption potntial (A) (KJ/mol) x Th plot of ln (-θ) vrsus /T using qn. 3 showd a linar lin (Fig. ). Th activation nrgy (E a) and th sticking probability (S * ) wr assssd from th slop and intrcpt corrspondingly. Th valu of E a and S * wr shown in Tabl-5 as J/Kmol and.654, rspctivly. Th rlativly small and ngativ E a valu indicats that low tmpratur or nrgy supports th sorption. Th adsorption procss is thrfor xothrmic. Rlativly low valu of E a also implis that th sorption procss is diffusion controlld. Th sticking probability (S * ) indicats th masur of th potntial of an adsorbat to rmain on th adsorbnt. It is oftn intrprtd as S * > (no sorption), S * = (mixtur of physisorption and chmisorption), S * = (indfinit sticking chmisorption), < S * < (favourabl sticking physisorption). Th significanc of S * obtaind for th sorption of Pb 2+ by polymr was btwn zro and on, which indicats that adsorption was favourabl and obyd a physisorption mchanism. ln (- θ ) Fig.. Plot of ln (-θ) vrsus /T for th sorption of Pb 2+ by th poly(mthyl mthacrylat) sampl Tabl-5 also prsnts th Gibbs fr nrgy ( G ) for th sorption of Pb 2+ by th polymr which was calculatd from qn. 4. Gibbs fr nrgy is th fundamntal critrion of spontanity. Th G valu of KJ/mol was ngativ indicating that th sorption procss was spontanous. Th valu obtaind for G was also lss than - KJ/mol suggsting a spontanous procss in which thr was lctrostatic intraction btwn Pb 2+ and th polymr to support a physisorption mchanism. Th plot of ln K o vrsus /T from qn. 5 producd a straight-lin graph (Fig. 2), with th slop and intrcpt qual to - H /R and S /R, rspctivly. Th valu of th nthalpy chang ( H ) calculatd from th slop was -6. J/mol. Angativ H suggsts that sorption procdd favourably at a lowr tmpratur and th sorption mchanism was xothrmic. Th valu of th ntropy chang computd from th intrcpt was 4.99 J/Kmol and prsntd in Tabl-5. A positiv /T ln K o /T Fig. 2. Plot of ln K o vrsus /T for th sorption of Pb 2+ by th poly(mthyl mthacrylat) sampl S suggsts that frdom of th adsorbd Pb 2+ was not rstrictd in th polymr, indicating that physisorption mchanism prdominats. Th packing of Pb 2+ in th polymr was assssd using qn. 6 and rsults prsntd in Tabl-5. Th adsorption dnsity (ρ) obtaind was mol/cm 2. Th chang in th chmical potntial that occurrd as Pb 2+ movd from th solution to th surfac of th polymr was calculatd using qn. 8. Tabl-5 givs th adsorption potntial as.5 KJ/ mol. Th possibility of Pb 2+ finding unoccupid sit on PMMA polymr xtrior throughout th sorption procss was corrlatd by th numbr of hopping (n) don by Pb 2+. Th hopping numbr was found to b 4. Th lssr th hopping numbrs th quickr th adsorption [23,24]. Th small valu of n obtaind suggsts that th adsorption of Pb 2+ on polymr was vry fast and fficint. Conclusion Th quilibrium, kintic and thrmodynamic studis rcordd a comparativly rapid uptak of Pb 2+ by th polymr poly- (mthyl mthacrylat) which was a diffusion controlld in a first-ordr procss. Th adsorption was supportd by low tmpratur and nrgy which was xothrmic with a physisorption mchanism. Th rsult of this study has shown that th polymr PMMA, is an fficint adsorbnt for th rmoval of Pb 2+ from watr solution. Th calculations obtaind from this study will b constructiv in th production or formulation of a novl filtration tchnology matrial, which is ffctiv and nvironmnt rsponsiv for th rmoval and rcovry of toxic mtals such as lad from watr solution. Th high adsorption capacity of th polymr indicats that it can rplac som of th most convntional rlativly xpnsiv watr tratmnt tchniqus prsntly in us, which is not rasonably viabl for small scal industris du to normous capital invstmnt.

9 Vol. 3, No. 4 (8) Adsorption Study of Lad(II) Ions on Poly(mthyl mthacrylat) Wast Matrial 867 ACKNOWLEDGEMENTS This work was supportd by a rsarch grant from th Rsarch Dirctorat of Vaal Univrsity of Tchnology, Vandrbijlpark, South Africa. REFERENCES. G.M. Anthony, Polym. Dgrad. Stab., 64, 353 (999); 2. E.M. Abdlrazk, A.M. Hzma, A. El-khodary and A.M. Elzayat, Egypt. J. Basic Appl. Sci., 3, (6); 3. D. Wankasi, Ph.D. Thsis, Kintics of Phytosorption of Havy Mtals using Unmodifid and Modifid Biomass Nipa palm (Nypa fruticans wurmb), Univrsity of Port Harcourt: Port Harcourt, Nigria (4). 4. M. Horsfall, A.I. Spiff and A.A. Abia, Bull. Koran Chm. Soc., 25, 969 (4); 5. K.H. Chu and M.A. Hashim, Acta Biotchnol., 2, 295 (); ABIO295>3..CO;2-F. 6. J.L. Garda-Torrsdy, J.H. Gonzalz, K.J. Timann, O. Rodriguz and G. Gamz, J. Hazard. Matr., 57, 29 (998); 7. O.A. Tasi, Basic Plastic Matrials and Tchnology, Owrri, Adyudo Prss, Nigria (). 8. M. Kutz, Handbook of Matrial Slction, John Wily & Sons, p. 34 (2). 9. T.J. Kaufmann, M.E. Jnsn, G. Ford, L.L. Gill, W.F. Marx and D.F. Kallms, Am. J. Nuroradiol., 23, (2).. V.J.P. Poots, G. McKay and J.J. Haly, J. Watr Pollut. Control Fd., 5, 926 (978).. D. Wankasi, M. Horsfall and A.I. Spiff, Chm. Tch. J., 4, 54 (6). 2. M. Suzuki, Adsorption Enginring, Elsvir, Amstrdam (998). 3. D. Wankasi, Adsorption: A Guid to Exprimntal Data Analysis, Ano Publication Company, Nigria (3). 4. M. Djbara, J.P. Stoqurt, M. Abdsslam, D. Mullr and A.C. Chami, Nucl. Instrum. Mthods B., 274, 7 (2); 5. Y. Dwivdi, A.K. Singh, R. Prakash and S.B. Rai, J. Lumin., 3, 245 (); 6. R. Kumar, S.A. Ali, P. Singh, U. D, H.S. Virk and R. Prasad, Instrum. Mthods B, 269, 755 (); 7. K. Kadirvlu, C. Faur-Brasqut and P.L. Cloirc, Langmuir, 6, 84 (); 8. K. Kadirvlu and C. Namasivayam, Environ. Tchnol., 2, 9 (); 9. K.V. Kumar, J. Hazard. Matr., 37, 638 (6); H. Tran, S.-J. You, A. Hossini-Bandgharai and H.-P. Chao, Watr Rs.,, 88 (7); 2. M.S. Gaur, P.K. Singh, A.P. Indolia, P.K. Yadav, A.A. Rogachv and A.V. Rogachv, Frrolctrics, 5, 56 (7); M. Khairy, N.H. Amin and R. Kamal, J. Thrm. Anal. Calorim., 28, 8 (7); S. Ramsh, K.H. Ln, K. Kumutha and A.K. Arof, Spctrochim. Acta A, 66, 237 (7); D. Wankasi, M. Horsfall Jnr. and A.I. Spiff, Afr. J. Biotchnol., 4, 923 (5).