Exhausted Tea Leaves a low cost bioadsorbent for the removal of Lead (II) and Zinc (II) ions from their aqueous solution

Transcription

1 J. Npal Chm. Soc., vol. 3, 1 Exhaustd Ta Lavs a low cost bioadsorbnt for th rmoval of Lad (II) and Zinc (II) ions from thir aquous solution Bindra Shrstha*, P.L. Homagai, M.R. Pokhrl, K.N. Ghimir Cntral Dpartmnt of Chmistry, Tribhuvan Univrsity, Kirtipur, Kathmandu, Npal. binraghu@yahoo.com Abstract An fficint and cost ffctiv bioadsorbnt has bn prpard from xhaustd ta lavs using hydrazin monohydrat. Th aminatd ta lavs (ATL) was charactrisd by lmntal and spctral analysis. Th batch adsorption study was prformd using ATL for th rmoval of ++ and ++ from thir aquous solution. Adsorption xprimnt was conductd as th function of solution ph, initial mtal concntration and contact tim. Th maximum adsorption capacity of th adsorbnt was found to b 1.8 mg/g for ++ and mg/g for ++. Ths rsults indicatd that th aminatd ta lavs hold grat potntial to rmov ++ and ++ from aquous solution. Ky words: Ta Lavs, bioadsorbnt, havy mtals, Langmuir-isothrm, amination Introduction Most of th havy mtals ar toxic and prsnt a thrat to human halth and th nvironmnt 1. To rmov ths mtal ions from thir aquous solution at trac concntration, adsorption has bn usd as an ffctiv mthod than othr convntional mthods, 3. Rcntly many rsarchrs ar focusd on th us of wast matrials as adsorbnt for rmoval of havy mtals from industrial wast watr, as thy ar co-frindly, cost ffctiv and mor fficint. Chitosan, chitin, sugarcan bagass, appl and orang juic rsidu, what straw, ric husk, ta wast hav bn invstigatd as biosorbnt for rmoval of havy mtals 4-1. Mtal binding capacity of biosorbnts is du to th functional groups such as hydroxyl, carboxylat, sulphat, amin, amid, phosphat groups prsnt in th biosorbnt. Th dnsity of ths groups which ar ffctiv for mtal binding is gnrally low in most of th biosorbnts. Surfac modification of such biosorbnts incrass such groups and significantly nhancs th sorption capacity. In particular th amino group onto an adsorbnt has bn found to b on of th most promising chlating groups for th adsorption of th havy mtal ions from thir aquous solution 11. In this study, wast ta lavs ar slctd as biosorbnt which vitally contains lignin, cllulos and hmiclluloss 1. Ths natural polymrs hav bn rportd having low mtal binding capacity. To nhanc th mtal binding capacity, th biosorbnt is chmically modifid to introduc amino group on th surfac of th biosorbnt. This aminatd biosorbnt is usd to rmov common mtallic pollutants lik lad and zinc. * Corrsponding author

2 J. Npal Chm. Soc., vol. 3, 1 Matrials and Exprimntal Chmicals Th stock solutions of 1 mg/l of ++ and ++ wr prpard by dissolving rquird amount of lad nitrat and zinc sulphat in.1 M HNO 3. Th stock solutions wr dilutd to rquird dilution of working solutions. In all th xprimntal works.1 M solution of -[4-(-hydroxymthyl)-1- piprazinyl] thansulfonic acid [HEPES] was usd as buffr. Th ph of th working solutions was maintaind using.1 M HNO 3 and.1 M NaOH solution. All th chmicals usd wr of AR grad and doubl distilld watr was usd for th xprimnt. During th xprimnt th concntration of mtal ions wr analyzd using Atomic Absorption Spctroscopy [Chmito AA, AAS]. Biosorbnt prparation 5 g of xhaustd ta lavs was washd with boiling watr till th filtrat bcam colorlss. It was drid in an ovn. Th drid adsorbnt was powdrd and sivd through 1µ siv. Th adsorbnt was charrd with concntratd H SO 4. Aftr charring th sampl was washd thoroughly with distilld watr to rmov fr acid and thn drid in an ovn. Th adsorbnt was chmically modifid by using hydrazin monohydrat. Th prpard adsorbnt is aminatd ta lavs [ATL]. Exprimntal Th biosorption of ++ and ++ onto ATL was invstigatd by batch quilibrium xprimnts. To study th ffct of initial concntration on adsorption, ml of mtal solution with diffrnt concntration wr mixd with 5 mg of th adsorbnt and shakn for 4 hrs. at 15 rpm at 5 C in a mchanical shakr. A sris of adsorption xprimnt wr carrid at 1 to 6 initial ph to study th ffct of ph. Th kintics of th adsorption was studid by shaking 5 mg adsorbnt with ml mtal solution for 5 to 4 min. Aftr adsorption th solutions wr filtrd and analyzd for th concntration of mtal ions. Th adsorption fficincy A% can b calculatd by using quation (1) A % Ci C Ci X 1 (1) Th amount of mtal adsorbd is th concntration of mtal ions on th adsorbnt and can b calculatd on th basis of mass balanc principl as givn in quation. Ci - C q W L X 1 () whr q is amount of mtal adsorbd pr unit mass of adsorbnt (mg/g) at quilibrium tim, V is th volum of mtal solution (ml), W is mass of adsorbnt (g), C i and C ar concntration of mtal ions at initial and at quilibrium tim rspctivly. Rsults and Discussion Charactrization Th morphological diffrnc of th surfac of th TL and ATL ar visually shown in Fig. 1. Th surfac of adsorbnt bcam much roughr aftr amination which confirmd th chmical modification of

3 Transmittanc (au) J. Npal Chm. Soc., vol. 3, 1 th sorbnt. Th surfac of aminatd biosorbnt is full of cavitis which ar xpctd to nhanc th mtal binding capacity of th adsorbnt. 1 a 1 b Figur 1: Scanning Elctron Microscopic imags of (a) TL and (b) ATL TL ATL Wavnumbr (Cm -1 ) Figur : Fourir Transform Infrard spctra of TL and ATL Th FTIR-spctra of TL and ATL ar shown in Fig.. In th spctrum of TL th broad and intns pak around 338 cm -1 corrsponds to th O-H strtching vibration. It indicats th fr OH-group of alcohols and polyphnols prsnt in cllulos and lignin. Th C-H strtching pak is obsrvd at 93 cm - 1 and th pak at 1647 cm -1 is du to C=O group. Aftr chmical modification th spctrum of ATL shows many significant changs. In th spctrum of ATL, th strong broad band ranging from about 385 cm -1 to 3653 cm -1 corrsponds to th combination of strtching vibration bands of OH and NH groups. Similarly th paks at 1433 cm -1 and 194 cm -1 corrspond to CH bnding and CN strtching vibration rspctivly 13. Th information obtaind from FTIR, indicats th introduction of amino group on th surfac of th adsorbnt

4 q t (mg/g) % A J. Npal Chm. Soc., vol. 3, 1 Effct of ph Th mtal adsorption is dpndnt on th ph of th solution, as it affcts th surfac charg of adsorbnt, th dgr of ionization and th spcis of adsorbat. Th adsorption incrass with incras of ph 1 ti ph 6 as shown in Fig. 3. At low ph mtal ions compt with H+ ions for binding sits. As ph incrass concntration of H+ ions dcras and positiv charg dnsity on th sorption sits also rducd which nhancs th adsorption of mtal ions to gt optimum valu. At still highr ph, prcipitation occurs ph Effct of contact tim Figur 3: Effct of ph on th adsorption of ++ and ++ onto ATL Adsorption xprimnts wr carrid out for diffrnt tims with a fixd concntration of mtal ions (5 mg/l) and adsorbnt dos of 5 mg at optimum ph. Th rsults ar prsntd in Fig. 4. Th quilibrium is rachd within minuts and rachd a saturation lvl. In th initial stat th adsorbd ions occupy slctivly on th activ sits on th adsorbnt. As th contact tim incrass th activ sits on th adsorbnt ar filld. Th rat of adsorption gradually bcom slowr and rachd a platau Tim (min). Figur 4: Adsorption kintics of ++ and ++ onto ATL

5 C /q (g/l) q (mg/g) J. Npal Chm. Soc., vol. 3, 1 Effct of initial concntration Th ffct of initial concntration in th rmoval of mtal ions was studid at various concntrations of 5-8 mg/l of mtal ions and 5 mg of adsorbnt at optimum ph. Th rsults shown in Fig. 5 indicat that th prcntag rmoval of mtal ions initially incrass and th furthr incras in concntration dcrass th prcntag rmoval, indicating that th mtal uptak is dpndnt on th initial concntration of mtal ions in solution. At low concntration of mtal ions, th ratio of numbr of mols of mtal ions to th availabl surfac ara is low. Hnc adsorption at low concntration of mtal ions is indpndnt of initial concntration of mtal ions. At highr concntration, th availabl sits for adsorption ar alrady saturatd and mtal rmoval is dpndnt on th initial concntration of mtal ions C (mg/l) Figur 5: Adsorption isothrms for th adsorption of Cu ++ and ++ onto ATL C (mg/l) Figur 6: Langmuir plot for adsorption of ++ and ++ onto ATL Th isothrm curv suggstd that th sorption is according to Langmuir adsorption modl. Th linar form of th Langmuir modl was usd as shown blow

6 t/q t (min/mg/g) J. Npal Chm. Soc., vol. 3, 1 C q 1 C q b q m m (3) whr, C (mg/g) is th concntration of mtal ions aftr adsorption, q (mg/g) is th amount of mtal ions adsorbd, q m (mg/g) is th maximum adsorption capacity and b (L/mg) is th binding constant. Th linar plot of C /q vs. C (Fig. 6) indicatd th applicability of adsorption isothrm. Th valu of q max (mg/g) and b (L/mg) wr calculatd using th linar plot. Th paramtrs of Langmuir isothrm for adsorption of ++ and ++ ar shown in Tabl 1. Th q max for th adsorption of ++ and ++ onto ATL ar 1.8 (mg/g) and (mg/g) rspctivly. Tabl 1: Langmuir adsorption isothrm modl paramtrs and xprimntal q max Mtal ions q max (mg/g) q max (mg/g) b (L/mg) R Langmuir modl Exprimntal Adsorption Kintics Th kintic data of adsorption of ++ and ++ onto ATL wr analysd using linar form of psudoscond ordr kintic modl 15. Th intgratd form of th modl is givn in quation (4) t 1 t q K q q t (5) whr q t (mg/g) is th amount of mtal ions adsorbd at tim t (min), K (g/ mg/ min) is th rat constant of psudo-scond ordr kintic modl 15. Fig. 7 shows th kintic plot for psudo-scond ordr raction rat Tim (min) Figur 7: Psudo- scond ordr kintic modl for adsorption of ++ and ++ onto ATL

7 J. Npal Chm. Soc., vol. 3, 1 Th valus of rat constant and corrlation cofficints ar givn in Tabl, which indicats th applicability of psudo-scond ordr kintics for adsorption of ++ and ++ onto ATL. Tabl : Psudo scond ordr kintics for ++ and ++ onto ATL Mtal ions K (g/mg/min) R Conclusion In this study xhaustd ta lavs has bn valuatd as an fficint bioadsorbnt for rmoval of ++ and ++ from thir aquous solutions. Th adsorbnt was aminatd with hydrazin monohydrat and that aminatd ta lavs was charactrizd by lmntal analysis, SEM, FTIR. Th adsorption capacity of th adsorbnt was found to b incrasd with incrasing ph upto optimum ph for mtal ions. Th quilibrium data fittd Langmuir isothrm with high cofficints which suggst that th adsorption procss followd monolayr sorption. Th kintic study of th sorption procss rsponds to psudoscond ordr rat. Hnc th aminatd ta lavs can b usd as an fficint and cost ffctiv biosorbnt for tratmnt of fflunts containing th mtal ions. Rfrncs 1. R. Ayyappan, A.C. Sophia, K. Swaminathan, S. Sandhya, Procss Biochm., 5, 4, 193. B. Volsky, Z.R. Holan, Biotchnol. Prog., 1995, 11, P. Mirtzky, C. Munoz, A.C. Chavz, Biorsourc Tchnol., 8, 99, V.M. Nurchi, I. Villascusa, Coodination Chmistry Rviws, 8, 5, S. Babl, T.A. Kurniawan, J. Hazardous Matrials, 3, B97, K.N. Ghimir, K. Inou, K. Ohto, T. Hayasida, Biors. Tchnol., 8, 99, 3 7. M.C. Basso, E.G. Crrlla, A.L. CuKirman, Ind. Eng. Chm. Rs.,, 41, P.L. Homagai, K.N. Ghimir, K. Inou, Sparation Scinc and Tchnol., 11, 46, 1 9. S. Chn, Q. Yu, B. Gao, X. Xu, J. Colloid and Intrfac Scinc, 1, 349, B.K. Biswas, K. Inou, K.N. Ghimir, H. Harada, Biorsourc Tchnol., 8, 99, S. Dng, Y.P. Ting, Langmuir, 5, 1, A.H. Mahvi, D. Naghipour, F. Vazi, S. Nazmara, Amrican J. Applid Scincs, 5, (1), R.L. Shrinr, C.K.F. Hrmann, T.C. Morill, D.Y. Curtin, R.C. Fuson, Th Systmatic Idntification of Organic compounds, Svnth d. Wily, Nw York, K.N. Ghimir, K. Inou, K. Makino, T. Miyajima, Sp. Sci. Tchnol.,1 (), 37, Y.S. Ho, G. McKay, Procss Biochmistry, 1999, 34,