Selective adsorption of Cu(II) from synthetic wastewater using melamine-formaldehyde- NTA resin

Transcription

1 Watr Pollution VIII: Modlling, Monitoring and Managmnt 519 Slctiv adsorption of Cu(II) from synthtic wastwatr using mlamin-formaldhyd- NTA rsin P. J. Hall, M. J. Hslop & A. Baraka Dpartmnt of Chmical and Procss Enginring, Univrsity of Strathclyd, Glasgow, UK Abstract A nw chlating rsin was prpard by anchoring th chlating agnt nitriloamintriactic acid (NTA) to mlamin via an amid covalnt bond during mlamin-formaldhyd condnsation raction in an acidic mdium. Th ffct of prparation conditions (tmpratur, acidity, and watr contnt) on rsin charactristics (watr rgain, rigidity, NTA functionality, and porosity) wr monitord to spcify th bst prparation conditions. A ph of 1.3, tmpratur of 150 C and watr contnt of 5 ml wr found as th bst conditions for rsin prparation with statd amounts of ractants. This nw rsin was chmically charactrizd via infrard spctroscopy (FT-IR), CHNO lmntal analysis, and morphologically charactrizd via nitrogn gas adsorption (BET) and fild mission-scanning lctron microscopy (FE-SEM). Th bst-producd rsin sampl has a surfac ara of 159 m 2 /g. Th contnt of NTA was about 1.24 mmol/g. Simultanous adsorption of Co(II), Cd(II), Zn(II), and Cu(II) from synthtic wastwatr solutions using a batch tchniqu was quantitativly analysd using atomic absorption. Slctiv adsorption of th Cu(II) ion amongst Co(II), Cd(II), and Zn(II) ions by this rsin was notd. It was found that Cu(II) adsorption is spontanous ( G ads <0), xothrmic ( H ads <0), and rvrsibl ( S ads <0). Kintically, it follows rvrsibl and psudo first-ordr. According to th Langmuir modl, th capacity for Cu(II) adsorption is 52.6 mg/g (0.83 mmol/g). EDTA solution can rgnrat th rsin by stripping adsorbd mtal ions. Aftr rgnration, it was obsrvd that th capacity dcrasd and this may b du to partial hydrolysis of NTA sits. Kywords: mlamin-formaldhyd-nta rsin, slctiv adsorption, havy mtals, kintics, isothrm, thrmodynamics. doi: /wp060511

2 520 Watr Pollution VIII: Modlling, Monitoring and Managmnt 1 Introduction Environmntal contamination by havy mtals sriously thratns human halth bcaus of its high toxicity. Mining, mtal plating, tannris, nuclar powr plants, industrial missions, agricultur and domstic activitis ar xampls of such contamination sourcs. Convntional tchniqus for th rmoval of havy mtals from wastwatr fflunts ar chmical prcipitation, ion xchang, lctrodialysis, mmbran sparation, solvnt xtraction and adsorption. Diffrnt typs of adsorbing matrials ar usd for rmoving havy mtals from wastwatr such as zolits, biosorbnts, activ carbon and polymric rsins. Th aim of this work is to produc a chlating rsin and invstigat its simultanous rmoval bhaviour against slctd havy mtals [Cu(II), Co(II), Cd(II) and Zn(II)]. Only a fw studis dscrib th simultanous mtal ions rmoval (Machida t al [3]). MF-NTA chlating rsin was synthsisd by anchoring NTA to th MF matrix whr carboxylic groups of NTA ract with primary amin groups of mlamin forming amid bonds [1, 2]. Th ffcts of diffrnt paramtrs (solution initial ph, tmpratur, mtal ions initial concntration and contact tim) on adsorption wr considrd. As Cu(II) showd slctiv adsorption, its xprimntal adsorption data was fittd to slctd adsorption kintics and isothrm modls. Th thrmodynamic paramtrs (adsorption fr nrgy, nthalpy and ntropy) wr also calculatd. 2 Thory 2.1 Rsin prparation (chmistry of raction) MF-NTA rsin was synthsisd undr acidic conditions. In th cours of rsin formation, mthylol groups (triazin NH CH 2 OH) ar formd from raction of formaldhyd with amin groups. Subsquntly, th mthylol groups condns to form mthyln and thr bridgs constructing th rsin matrix [4, 5]. During MF matrix formation, NTA molculs ar anchord to th matrix by forming amid covalnt bonds (Sharmin t al [6]). 2.2 Rsin charactrization Th watr amount hld intrinsically by th rsin rprsnts th watr rgain factor. To calculat this factor, qn (1) was mployd: W % = 100( W W (1) w Wd ) / w whr W w and W d ar wights (g) of th wt and drid rsin rspctivly. Charactrization using IR spctroscopy, CHNO lmntal analysis (MF-NTA and MF rsins), N 2 adsorption/dsorption analysis using BET mthod and SEM imaging (MF-NTA rsin only) wr carrid out.

3 Watr Pollution VIII: Modlling, Monitoring and Managmnt Mtals adsorption Adsorption kintics, thrmodynamics and isothrm studis charactriz th adsorption bhaviour of a rsin towards havy mtal ions and giv an undrstanding about th adsorption mchanism. To rvals ths charactristics, ssntial paramtrs hav to b considrd such as th initial ph, tmpratur, tim of contact and initial concntration of th mtal ions. In this study, ph valus abov 6 wr avoidd bcaus of probabl mtal hydroxid formation which may giv spurious adsorption rsults [7-9]. Mtals undr study [Co(II), Cd(II), Zn(II), and Cu(II)] wr subjctd to comptitiv adsorption procss whr all ions wr prsnt in th batch solutions with th sam initial mass concntration. Sodium (I) ion, as sodium chlorid, was prsnt as wll in solution rprsnting salt matrix. For slctivly rmovd Cu(II), th adsorption kintics was studid using two convntional modls: rvrsibl first-ordr and psudo first-ordr [10, 11]. Th rvrsibl first-ordr has th following linar form, qn (2): ln( 1 U t ) = ln(1 x / X ) = kt (2) whr U t = x/x (x is th concntration of solut adsorbd on rsin at crtain tim and X is th concntration of solut adsorbd at quilibrium). Th ovrall adsorption rat constant (k) quals k 1 + k 2, whr k 1 and k 2 ar th forward (adsorption) and backward (dsorption) rat constants rspctivly. To calculat ths paramtrs, th auxiliary qn (3) was usd: K = /( = k (3) c X Ci X ) k1 / whr K c is th quilibrium constant and C i is th initial ion concntration. Th intgratd form of th psudo first-ordr quation is xprssd by qn (4): 2 log( q q ) = log q ( k / 2.303) t (4) t whr q and q t ar th solut amounts adsorbd by th rsin (mg/g) at quilibrium and tim t rspctivly and k ad is th adsorption rat constant (min 1 ). To calculat th thrmodynamic paramtr ( G ads ) (fr nrgy of th adsorption procss), qn (5) was mployd: ad Gads = RT ln K c (5) By plotting ln K c against 1/T, H ads and S ads (nthalpy and ntropy of adsorption) can b calculatd from th slop and intrcpt of qn (6): ln K c = ( S / R) ( H / RT ) (6) ads Two adsorption isothrm modls wr mployd in this study, th Frundlich and Langmuir. Th Frundlich modl is th on that is usually usd for aquous systms and assums a htrognous surfac whr th adsorption sits hav diffrnt nrgis (Faust and Aly [12]). It has th following linar form, qn (7): F ads log q = log K + (1/ n) logc (7)

4 522 Watr Pollution VIII: Modlling, Monitoring and Managmnt whr q (mg/g) is th adsorbd amount at quilibrium, C (mg/l)is th concntration at quilibrium. Th trms K F and n ar Frundlich paramtrs which ar rlatd to adsorption capacity and adsorption intnsity rspctivly. Th Langmuir modl was arlist to dscrib adsorption phnomna. Th basic assumptions for this modl may b applicabl to MF-NTA rsin (dfinit sits, monolayr accommodation of soluts and sits hav th sam adsorption nrgy) Faust and Aly [12]. Th Langmuir modl linar quation has th following form, qn (8): 1/ q = 1/ Q + 1 bq C (8) ο / whr, q and C hav th sam maning as for th Frundlich modl. Th trms Q o (mg/g) and b (l/mg) ar Langmuir modl paramtrs. Q o rprsnts th adsorption capacity and b is rlatd to nrgy of adsorption and rflcts th affinity of th mtal ion towards binding sits. Th dimnsionlss factor, R L, indicats whthr th adsorption is favourabl or not (Adsorption is favourabl if 0<R L <1). It is dfind by qn (9): 2.4 Rsin rgnration ο R = /(1 + bc ) (9) L 1 i EDTA solution can rgnrat xhaustd MF-NTA rsin by stripping th chlatd mtal ions into aquous solution forming stabl solubl M(II)-EDTA complxs. 3 Exprimntal 3.1 Prparation of rsin (condition optimization) Analytical grad of mlamin (99%) (Aldrich), formaldhyd (38%) (BDH), NTA (Sigma) wr usd for MF-NTA and MF rsin prparation. For all prparations, dionisd watr was usd. Twlv MF-NTA rsin sampls wr prpard. All had th sam ractant amounts: 0.01 mol mlamin (1.26 g), formaldhyd (2 ml), and mol NTA (0.64 g). For ach sampl, th following procdur was carrid out. Mlamin was addd to NTA in a vial containing crtain amount of acidifid watr (5 ml or 10 ml). Th watr acidity (ph 1.5 or 1.3) was pr-adjustd using concntratd HCl. Finally formaldhyd was addd and th ractants wr mixd by an lctronic agitator to nsur formation of homognous slurry. Th tightly closd vial thn was put in a prhatd ovn at a spcifid tmpratur (90, 120 or 150 C). Th formd solid rsin was lft for an xtra 30 minuts at th sam prparation tmpratur for mor curing. Th vial was thn rmovd and lft on a bnch ovr night. Th sampl was thn ground and sivd. Th grains in th rang of 355 to 710 µm wr washd in 100 ml dionisd watr for 30 minuts fiv tims at ambint tmpratur using a shakr at 150 rpm to rmov acidity and any othr xcss ractant (mlamin, NTA, and Formaldhyd). Th washd sampl was stord in

5 Watr Pollution VIII: Modlling, Monitoring and Managmnt 523 clan tightly-closd vial until charactrization tsts. From ths twlv sampls, th on with highst surfac ara and good mchanical strngth was usd for a sris of mtal adsorption xprimnts. 3.2 Rsin charactrization For watr rgain dtrmination, rsin sampls wr cntrifugd for thr hours at 1000 rpm to rmov xcss watr and thn wighd (W w ). Ths sampls wr thn drid at C until complt drynss thn wighd again (W d ). Eqn (1) was thn usd to dtrmin watr rgain factor. Frz drid sampl was rquird for BET analysis and SEM imaging and this was carrid out by frzing th sampl at 80 C thn vaporating th watr undr low prssur (0.06 atm.). IR analysis was carrid out (KBr discs) in th rang 400 to 4000 cm -1 using a Prkin-Elmr FT-IR spctromtr. Drid sampls wr usd for CHNO lmntal analysis using Prkin-Elmr Sris II CHNS/O Analysr modl Th Micromritics ASAP 2405N adsorption analyzr was usd for masuring nitrogn adsorption/dsorption isothrms at 77.4 K to dtrmin porosity charactristics of th frz drid sampls. Fild Emission-Scanning Elctron Microscop (FE-SEM) was mployd for imaging th outr surfac of a frz drid grain of a slctd rsin sampl to lucidat th morphology and porosity. 3.3 Mtal ions adsorption Analytical grad of CuCl 2.2H 2 O (May & Bakr LTD), CoCl 2.6H 2 O (BDH), ZnCl 2.2H 2 O (Fishr Scintific), CdCl 2.2.5H 2 O (Sigma-Aldrich) wr usd for th prparation of standard stock solutions (1000 ppm and 1% HCl) for ach lmnt using dionisd watr. Standard dilunts wr frshly prpard from ths stock solutions for adsorption xprimnts. Standard dilunts wr phadjustd using concntratd and dilutd HCl and NaOH. Th batch adsorption tchniqu was conductd for xamining th adsorption bhaviour and th ssntial factors considrd for study wr ph (3, 4, 5 and 6), tmpratur (15, 20, 25, 30 and 35 C), contact tim (10, 20, 30, 40, 50, and 60 minuts) and mtal-ions initial concntrations (20, 30, 40, 50, 60 and 70 ppm). It is important to stat that initial concntrations of ths mtals ar diffrnt on a molar basis. Othr paramtrs wr st constant, shaking spd (200 rpm), grain siz ( µm), solution volum (50 ml) and wt rsin dos (0.3 g). Also, in all xprimnts xcpt isothrm on, 20 ppm of Na (I) ion was prsnt rprsnting th salt matrix ffct. Th adsorption was tstd by masuring th ion concntrations aftr th adsorption procss using th Prkin-Elmr atomic absorption spctromtr 3100 with multi-lmnt hollow cathod lamps and an air-actyln burnr was usd for dtrmining th rsidual mtal ion concntrations. Th wav-lngths (nm) applid wr thos rcommndd by th manufacturr and wr as follows: Co(II) 240.7, Cu(II) 324.8, Cd(II) 228.8, and Zn(II) Th ffct of initial ph was invstigatd by carrying out th adsorption procss at diffrnt fiv tmpraturs (15, 20, 25, 30 and 35 C). For ach tmpratur, four flasks (ach flask at crtain initial ph valu: 3, 4, 5 and 6) with

6 524 Watr Pollution VIII: Modlling, Monitoring and Managmnt mtal-ion initial concntrations of 20 mg/l wr shakn for 120 minuts. From ach flask, 5 ml was withdrawn and rsidual mtal-ion concntrations wr masurd. An adsorption isothrm study was carrid out by shaking six flasks with diffrnt initial concntrations (20, 30, 40, 50, 60 and 70 mg/l) at 20 C and an initial ph of 5. From ach flask, 5 ml was withdrawn to masur th rsidual mtal-ion concntrations. Th kintics of adsorption (60 minuts duration) was studid at 20 C for diffrnt ph valus (3, 4, 5, and 6). From ach flask, 3 ml was withdrawn ach 10 minuts and rsidual mtal-ion concntrations wr masurd. 3.4 Rgnration of MF-NTA rsin 50 ml of EDTA solution (0.1 M) was usd to rgnrat 0.3 g of xhaustd MF- NTA rsin by shaking th rsin dos for 30 minuts at 200 rpm and at room tmpratur. Th rsin dos was thn washd fiv tims ach with 50 ml of dionisd watr to rmov any rsidual of EDTA. Th rgnratd rsin mass was thn usd for a scond adsorption xprimnt. Tabl 1: Glling tim, Watr rgain, lmntal composition and rigidity of MF-NTA rsin sampls. Tmp. Watr ( ph G.T. a W R b Exprimntal No. C) contnt % C : H : N : O A 34.5:5.19:41.35: A 34.9:5.19:40.73: C D A 34.8:4.68:40.85: B 34.87:4.87:41.58: D C A 34.74:4.92:40.45: A 35.1:4.84:40.03: C D MF :5.6:41.4: rsin G.T. (Glling Tim), b Rigidity typ: A(vry hard), B (hard), C (fair hard), D (soft) 4 Rsults and discussion 4.1 Rsin charactrization Glling tim, Watr rgain, rigidity, and lmntal analysis of th rsin Th sampls showd glling tim rangs from 10 to 110 minuts (Tabl 1). Sampls with watr contnt of 10 ml had th highr glling tim. Th highr watr contnt incras spacing btwn ractants and this givs mor tim for matrix formation. Watr rgain ( 77%) shows th hydrophilicity of this rsin

7 Watr Pollution VIII: Modlling, Monitoring and Managmnt 525 which is du to th prsnc of carboxyl functional groups in th rsin and this prcntag suggsts that th rsin is rich in NTA. Th lmntal analysis of all sampls gav almost th sam C:H:N:O ratio indicating sam chmical structur. This ratio is diffrnt from that of MF control rsin du to modification by NTA. From calculation, NTA constituts 24% of th rsin mass (1.24 mmol pr gram dry rsin). It was notd that sampls with th highr watr contnt ar lss rigid du to incras of spacing in th matrix. Sampls classifid as A and B (for rigidity) in Tabl 1 wr chosn for porosity charactrization by th BET mthod IR spctra IR spctra of all twlv MF-NTA sampls (not shown) ar vry similar which indicats that all sampls hav th sam chmical structur. Comparing on of ths spctra against th MF rsin spctrum, as shown in Figur 1, shows som important diffrncs du to anchoring NTA. For MF-NTA spctrum, th amid (and/or carboxylic) carbonyl (C=O) strtch appard at 1636 cm 1 and th carboxylic O H in plan bnd appard at 1390 cm Porosity (BET charactrization) Th basic porosity charactristics of MF-NTA rsin sampls ar givn in Tabl 2. All sampls hav insignificant porosity in th micropor rang compard to BET surfac ara which is dsirabl from th mtal-ion adsorption point of viw. Nitrogn adsorption/dsorption hystrsis loop of sampl No. 6 (Figur 2) indicats an opn por structur (Do [13]). Th dark spots sn in FE-SEM imag of MF-NTA rsin (Figur 3) rprsnt th por opnings and cavitis. This opn structur nhancs adsorption kintics. Sampl No. 6 shows th highst surfac ara (159 m 2 /g) and th adsorption xprimnts wr conductd using it. T% MF %T MF-NTA cm cm cm 1 cm 1 Figur 1: IR spctra of MF and MF-NTA rsins.

8 526 Watr Pollution VIII: Modlling, Monitoring and Managmnt No. Tabl 2: Porosity paramtrs for six slctd sampls (No. 1-6). BET surfac ara, m 2 /g Micropor ara, m 2 /g BJH Adsorption Cumulativ Por Volum, cm 3 /g Avrag por diamtr, Å Volum adsorbd cm 3 /g Figur 2: Rlativ prssur (P/P o ) Dsorption Adsorption Th adsorption/dsorption loop of MF-NTA, sampl No.6. Figur 3: FE-SEM surfac imag of MF-NTA, sampl No Adsorption procss Effct of ph and tmpratur (thrmodynamics) Th xprimnts at diffrnt initial ph valus (3, 4, 5 and 6) and various tmpraturs (15, 25 and 35 C) indicatd that adsorption of Cd(II) and Zn(II) is ngligibl undr ths conditions whras Cu(II) and Co(II) show adsorption.

9 Watr Pollution VIII: Modlling, Monitoring and Managmnt 527 For ach tmpratur, th adsorption incrass slightly with initial ph and for ach initial ph valu, thr is a notabl dcras in adsorption with tmpratur for Cu(II) and Co(II). Cu(II) showd highr adsorption ovr Co(II) for all conditions. Th highst masurd adsorption for Cu(II) is about 67% of initial concntration (about 30% for Co(II)) and ths modrat prcntags may b du to using small amount of rsin (0.3 g of wt rsin corrsponds to a solid fraction of g). Tabl 3 givs adsorption fr nrgis for Cu(II) for diffrnt conditions. Ths ar ngativ which rflcts th spontanous procss and it is noticd that as tmpratur dcrass, th fr nrgy bcoms mor ngativ. This mans that adsorption is favourabl at lowr tmpratur. Plots of lnk c against 1/T for Cu(II) at ph 3, 4, 5, and 6 wr gnratd from which adsorption thrmodynamic paramtrs H ads and S ads wr calculatd. Tabl 4 shows ths paramtrs. Th ngativ nthalpy corrsponds to xothrmic procss and chlation adsorption is likly to b th main mchanism. Th ngativ valu of ntropy mans a dcras in randomnss which can b attributd to formation of mtal ion chlats (rstriction of mtal ions) accompanid by th accommodation of rlasd watr molculs (upon chlat formation) on rsin hydrophilic surfac. It also rflcts th rvrsibility of th procss. Tabl 3: Adsorption fr nrgy, G ads (kj mol 1 ). Tmp. ( C) ph 3 ph 4 ph 5 ph Tabl 4: Adsorption thrmodynamic paramtrs H ads and S ads. ph H ads (kj mol 1 ) S ads (J mol 1 K 1 ) Adsorption kintics Adsorption tim profils at tmpratur 20 C for Cu(II) (ovr a tim rang of 60 minuts) for diffrnt ph valus wr dtrmind and indicats that rmoval rat is high (th half load tim, t 1/2 [Cu(II)]=12, 10.7, 11.4 and 10.3 minuts for ph 3, 4, 5 and 6 rspctivly). Psudo first-ordr and rvrsibl first-ordr plots wr gnratd from which th constants wr calculatd (Tabl 5). Th valus of k ad ar vry similar to th corrsponding valus of k. k 1 /k 2 >1 for Cu(II) which mans that procss shifts to adsorption dirction. Both modls ar abl to rprsnt th adsorption of Cu(II) as th valus of corrlation factor (R 2 ) indicat.

10 528 Watr Pollution VIII: Modlling, Monitoring and Managmnt Tabl 5: Rat constants (min 1 ) of psudo and rvrsibl first ordr kintics. ph Psudo first-ordr rvrsibl first ordr k ad (R 2 ) k (R 2 ) k 1 k (0.9875) (0.9912) (0.9794) (0.9820) (0.9892) (0.9885) (0.9839) (0.9852) Adsorption isothrm Th adsorption isothrm for Cu(II) at 20 C and ph 5 shows that q incrass significantly with C. Plots of this adsorption isothrm data according to th Langmuir and Frundlich modls wr gnratd and constants wr calculatd (Tabl 6). Th valu of th Frundlich paramtr, 1/n, corrsponds to favourabl adsorption. Th othr Frundlich paramtr, K F, indicats high capacity [7, 8, 11]. Th Langmuir paramtr, Q, was found to b 52.6 mg/g (0.83 mmol/g). R L is in th rang of favourabl adsorption. Th Langmuir corrlation factor (R 2 ) is slightly highr than that for Frundlich modl which may man mor homognity of th surfac. Tabl 6: Adsorption isothrm constants of Frundlich and Langmuir for Cu(II). Frundlich Langmuir K F 1/n R 2 Q b R L R Rgnration and rcycling of MF-NTA rsin Th rgnration procss succdd in rnwing th rsin to about 91% of its original capacity. Th rlas of NTA into tratd wastwatr or during rgnration du to partial hydrolysis may b th rason of dcras in capacity [1]. Aftr complt xhaustion (svral rgnration cycls), th rsin can b incinratd to form porous carbon matrial which in turn can b usd for a varity of applications. 5 Conclusions Th optimum conditions for th prparation of mlamin-formaldhyd-nta (MF-NTA) rsin ar a ph of 1.3, tmpratur of 150 C, and watr contnt of 5 ml with th statd amounts of ractants. IR, lmntal analysis provd th succss of anchoring NTA to th MF matrix via amid bonds. Th producd rsin has high hydrophilicity (watr rgain 77 %) with a surfac ara of 159 m 2 /g. Calculations show that 1.24 mmol of NTA is prsnt pr gram of solid rsin. Th rmoval of Cd(II) and Zn(II) was ngligibl at all conditions but

11 Watr Pollution VIII: Modlling, Monitoring and Managmnt 529 Cu(II) and Co(II) showd considrabl rmoval and this may b du to limitd sits prsnt in rsin dos with rspct to total havy mtal ions concntration. Th priority of Cu(II) and Co(II) for adsorption ovr Cd(II) and Zn(II) may b attributd to thir chlat formation constants. Th rmoval is 67% for Cu(II) and 30% for Co(II). For Cu(II), adsorption procss is spontanous ( G ads <0), xothrmic ( H ads <0), and rvrsibl ( S ads <0). Th xothrmic adsorption suggsts chlation of ions to NTA sits prsnt in th rsin to b th mchanism of adsorption. Th rat of adsorption is considrably high (t 1/2 is within minuts). Th adsorption obys both rvrsibl and psudo first-ordr modls. According to th Langmuir modl, th capacity, (Q ) for Cu(II) is 52.6 mg/g (0.83 mmol/g). Th Langmuir modl gav a bttr fit to th xprimntal data suggsting mor homognity of th surfac. Th Cu(II) ion was slctivly rmovd from aquous solution of th mixd four ions [Cu(II), Co(II), Cd(II) and Zn(II)] by MF-NTA rsin. Similar rsins can b prpard using diffrnt polyaminpolycarboxylic acids (.g. DTPA and CDTA) and can prsnt diffrnt adsorption bhaviour towards havy mtals. Rfrncs [1] Solomons, T.W., Organic Chmistry, sixth dition, John Wily & Sons, INC., pp , [2] Brnkop-Schnürch, Andras & Krajick, Martina E., Mucoadhsiv polymrs as platforms for proral pptid dlivry and absorption: synthsis and valuation of diffrnt chitosan-edta conjugats. Journal of Controlld Rlas, 50, pp , [3] Machida, Motoi, Aikawa, Masami & Tatsumoto, Hidki, Prdiction of simultanous adsorption of Cu(II) and Pb(II) noto activatd carbon by convntional Langmuir typ quations. Journal of Hazardous Matrials, B120, pp , [4] Minopoulou, E., Dssipri, E., Chryssikos, G.D., Gionis, V., Paiptis, A. & Panayiotou, C., Us of NIR for structural charactrization of uraformaldhyd rsins. Intrnational Journal of Adhsion & Adhsivs, 23, pp , [5] Mquanint, K. & Sandrson, R., Nano-structur phosphorus-containing polyurthan disprsions: synthsis and crosslinking with mlamin formaldhyd rsin. Polymr, 44, pp , [6] Sharmin, Eram, Imo, L., Ashraf, S.M. & Ahmad, Shrif, Acrylicmlamin modifid DGEBA-poxy coatings and thir anticorrosiv bhaviour. Progrss in Organic Coatings, 50, pp , [7] Sad, Asma, Akhtr, M. Wahd & Iqbal, Muhammad, rmoval and rcovry of havy mtals from aquous solution using papaya wood as a nw biosorbnt. Sparation and Purification Tchnology, 45, pp , [8] Mna, Ajay Kumar, Mishra, G.K., Rai, P.K., Rajagopal, Chitra & Nagar, P.N., Rmoval of havy mtal ions from aquous solutions using carbon

12 530 Watr Pollution VIII: Modlling, Monitoring and Managmnt arogl as an adsorbnt. Journal of Hazardous Matrials, B122, pp , [9] Donat, R., Akdogan, A., Erdm, E. & Ctisli, H., Thrmodynamics of Pb 2+ and Ni 2+ adsorption onto natural bntonit from aquous solutions. Journal of Colloid and Intrfac Scinc, 286, pp , [10] Rngaraj, S. & Moon, Sung-Hyon, Kintics of adsorption of Co(II) rmoval from watr and wastwatr by ion xchang rsins. Watr Rsarch, 36, pp , 2002 [11] Singh, K.K., Rastogi, R. & Hasan, S.H., Rmoval of Cr(VI) from wastwatr using ric bran. Journal of Colloid and Intrfac Scinc, 290, pp , [12] Faust, Samul D. & Aly, Osman M., Adsorption Procsss for Watr Tratmnt, Buttrworths, [13] Do, Duong D., Adsorption Analysis: Equilibria and Kintics, Vol. 2, Imprial Collg Prss, London, 1998.