Received 28 May, 2018; Accepted 6 June, 2018.

Transcription

1 Vol. (8), pp. xxx-xxx, Augus 8 DOI:.5897/AJEST8.xxxx Aricl Numbr: xxxxx ISSN: Copyrigh 8 Auhor(s) rain h copyrigh of his aricl hp:// African Journal of Environmnal Scinc and Tchnology Full ngh Rsarch Papr Equilibrium, kinic and hrmodynamics sudis of biosorpion of zinc ions from indusrial waswar using drivd composi biosorbns from walnu shll Olafadhan, O. A. *, Akpo, O. Y., Enmuo, O., Amoo, K. O. and Abaan, O. G. Dparmn of Chmical and Prolum Enginring, Univrsiy of agos, Akoka-Yaba, agos, Nigria. Dparmn of Chmical Enginring, Covnan Univrsiy, Canaan and, Oa, Ogun Sa, Nigria. Rcivd 8 May, 8; Accpd 6 Jun, 8. Th biosorpion procss of Zn (II) ions in indusrial waswar was invsigad using drivd composi biosorbns from walnu and snail shlls. Composi adsorbns wr producd by acivaing walnu shll carbon (WSC) wih phosphoric acid o obain acid-rad walnu shll carbon (AWSC) and WSC and AWSC wr indpndnly imprgnad on chiosan o produc walnu shll carbon imprgnad on chiosan (WSCC) and acid-rad walnu shll carbon imprgnad on carbon (AWSCC) rspcivly. Th rmoval fficincis of Zn (II) ions from synhic waswar using h prpard adsorbns wr drmind. Th ffcs of opraional paramrs on Zn (II) ions adsorpion wr invsigad. Th adsorpion daa of Zn (II) ions wr analysd using angmuir, Frundlich and Tmkin isohrms. Th angmuir isohrm fid h adsorpion daa xcllnly for h drivd composi biosorbns, giving an indicaion of monolayr covrag on h drivd composi biosorbns and h drminaion cofficins wr clos o uniy. Also, h maximum adsorpion capaciis of 3.4, 3.85, and mg/g wr obaind for WSC, AWSC, WSCC and AWSCC a ph=5, g of adsorbn dosag, Zn (II) ions iniial concnraion of 3 mg/, conac im of h, agiaion spd of 5 rpm, paricl siz of 6 BSS and mpraur of 3 C. Th kinic modlling of Zn (II) ions adsorpion showd ha psudo scond-ordr kinic modl gav h bs fi amongs h invsigad kinic modls. Th adsorpion of Zn (II) ions on h prpard adsorbns was filmdiffusion conrolld. Th xprimnal rsuls of his sudy showd ha acid-rad walnu shll carbon imprgnad on chiosan has h ponial o b applid as alrnaiv fficin low-cos biosorbn in h rmdiaion of havy mal conaminaion in waswar. Th hrmodynamic paramrs indicad ha h adsorpion of Zn (II) ions on h drivd composi biosorbns was xohrmic, ndogonic, favourabl, non-sponanous wih changs in nhalpy ( H, ngaiv), nropy [ S, narly zro (hough ngaiv)], and Gibbs fr nrgy ( G, posiiv), for all h prpard adsorbns. Ky words: Adsorpion, biosorbns, chiosan, isohrm, kinic modls, film diffusion. INTRODUCTION War polluion is on of h major problms facd globally du o h random rlas of domsic and urban waswars, agriculural wass and indusrial ffluns ino war courss. Th main impac of such polluion is h normous amoun of havy mals (such as nickl, lad, coppr, zinc, cadmium, c) in ffluns rlasd by indusris lik lcroplaing, plasic and pain manufacuring, mining and mallurgical procsss, pulp and papr, prochmical and bary manufacuring indusris (Oboh al., 9). Ths mals ar oxic and

2 non-biodgradabl, and can caus nvironmnal polluion. Morovr, human halh can b advrsly affcd as hs mal ions ar highly solubl in war and can b absorbd ino h body. Hnc, rmoval of hs havy mals from waswar is ssnial for h purpos of procing h nvironmn and human halh. Trac concnraions of zinc ar imporan for h physiological funcions of living issu and rgulaion of many biochmical procsss. Howvr, lik ohr havy mals, whn zinc is dischargd ino naural wars a incrasd concnraions from indusris involvd in acid min drainag, galvanizing plans, naural ors and municipal waswar ramn plans, i can hav svr oxicological ffcs on humans and aquaic cosysms (Armu al., ). Zinc is nonbiodgradabl and i ravls hrough h food chain via bioaccumulaion. World Halh Organizaion rcommndd h maximum accpabl concnraion of zinc in drinking war as 5. mg/ (Hawari al., 9). Th orhodox ramn chniqus for h havy mals rmoval from indusrial waswar includ chmical prcipiaion, mmbran filraion, lcrolyic rducion, solvn xracion, ion xchang, lcrodialysis, ulra filraion and adsorpion on acivad carbon (Bhaacharyya al., 9; Amadi and Ukpaka, 5; Babarind al., 6; Babarind and Onyiaocha, 6; Iqbal, 6; Iqbal and Bhai, 5b; Iqbal and Khra, 5; Iqbal and Nisar, 5; Iqbal al., 7; Jamal al., 5; Nourn al., 7; Pal al., 7; Qurshi al., 5; Sayd, 5; Ukpaka and Izonowi, 7; Ukpaka and Igw, 7). Howvr, adsorpion has bn rcognisd as a viabl chniqu for rmoval of havy mal ions from waswar (Adsola al., 6; Babarind and Onyiaocha, 6; Iqbal and Bhai, 5a; Iqbal al., 6; Iqbal and Khra, 5; Mushaq al., 6; Rashid al., 6) owing o is simpliciy, cos ffcivnss and fasibiliy (Foo al., ). Acivad carbon is h mos imporan adsorbn usd indusrially for h sparaion and purificaion of producs and also for h ramn of liquid and gasous ffluns owing o is porous surfac ara, conrollabl por srucur, hrmo-sabiliy and low acid/bas raciviy (Mohan al., 7). Dspi is us in adsorpion procsss, h biggs barrir in is applicaion by indusris is is cosly naur and h diousnss of is manufacuring and rgnraion procsss. Consqunly, rlaivly low cos adsorbns from biomass, calld biosorbns, hav bn dvlopd. Exampls of som biological marials usd as biosorbns ar ric sraw, coconu shll, walnu shll, banana pih, bch lavs, orang pls, moss, r frn, soya cak, cacus lavs and carbonizd biomass producs (Bhaacharyya al., 4). Morovr, Kausr al. (7) compard bach and column adsorpion sudis for h uranium (VI) ions adsorpion ono ric husk was biomass (RHWB) and concludd ha RHWB had ponial for rmoving uranium (VI) ions wih bach adsorpion mor fficin han h column mod. Nam al. (7) carrid ou uranium adsorpion using modifid low cos Vigna radiaa biomass, wih maximum uranium rmoval of 3 mg/g obaind a h opimizd procss paramrs of ph=4, biosorbn dos of.5 g, conac im of 6 min and mpraur of 4 C using 4 mg/ uranium ions concnraion. Akram al. (7) showd h fficacy of h prpard biocomposi of mango (Mangifra indica) wih surfacans and comal ions (Na +, K +, Ca +, Cu +, Al 3+ and F 3+ ) for Cr (VI) ions rmoval from indusrial ffluns. Thy also obaind opimum lvls of procss variabls of ph, Cr(VI) ions iniial concnraion, adsorbn dosag, conac im and mpraur as 3,.5 g, 3 min, mg/ and 33 C, rspcivly for maximum Cr (VI) adsorpion ono h prpard biocomposi. Zarur al. (8) invsigad h us of agroindusrial was, corn husk biomass (Za mays) as adsorbn for h rmoval of Cr (VI) and Hg (II) ions, wih a viw o carrying ou hrmodynamic, kinic and quilibrium sudis of h procss. In hir work, Elovich kinic modl and Frundlich isohrm corrlad h xprimnal daa xcllnly, and h hrodynamic paramrs ( H, G and S ) suggsd a favourabl, sponanous, rvrsibl and ndohrmic rmoval procss. Biosorpion can b dfind as h passiv and nonmabolically simplifid procss of mal ion binding by dad biomass (Kumar al., 6). I is ffciv, flxibl and can rmov larg amouns of havy mal ions from indusrial fflun using a vry simpl and sraighforward mhod. Morovr, i is bnficial o h nvironmn as polluans from boh aquous and gasous srams can b ffcivly rmovd wih minimum sludg discharg. Furhrmor, biosorpion producs rad waswar of highr puriy as compard wih h convnional mal rmoval mhods (Kumar al., 6). Ohr advanags of biosorpion includ high vrsailiy, mal slciviy and ovrall prformanc wih no concnraion dpndnc, no nurin rquirmns, high olranc for organics and possibiliy of biosorbn rgnraion and rus (Volsky, 99). Biosorpion is also cos ffciv as raw marials can b obaind asily in larg quaniis, mosly from naural or was marials (Dash, ). Thrfor, biosorpion chnology has bcom an araciv *Corrsponding auhor. oolafadhan@unilag.du.ng. Tl: Auhor(s) agr ha his aricl rmain prmannly opn accss undr h rms of h Craiv Commons Aribuion icns 4. Inrnaional icns

3 alrnaiv for waswar ramn oday. Biomarials from agriculural opraions hav ponial o b usd as low-cos adsorbns sinc hy ar unusd, ar widly availabl and nvironmnally frindly rsourcs (Dans and Dixon, 99). Walnu shll (Tracarpidium conophorus) is a highly carbonacous and fibrous marial wih lil or no conomic valu, and is abundanc and low cos maks i a good sourc for h producion of acivad carbon. Is disposal is no only cosly bu also causs nvironmnal problms. Hnc, h producion of char from walnu shlls adds valu o h walnu shlls. I also hlps o rduc h cos of was disposal, and provids a ponially chap alrnaiv o h commrcial carbonacous adsorbns (ogan and Rosmari, ). Ahlam al. (), Firas and Aurlia (5), Ghasmi al. (5) and Mahboobh al. () hav rpord procssing of walnu shlls ino char for h ramn of indusrial and municipal waswars. Amongs h low cos adsorbns, chiosan posssss h highs sorpion capaciy for svral mal ions (Babl and Kurniawan, 4; Nomanbhay and Palanisamy, 5). Chiin, -acamido--doxy-β-dglucos-(n-acylglucan), is h scond mos abundan polymr in naur. I occurs in naur as ordrd crysallin micro fibrils forming srucural componns in h xosklon of anhropoids (Rinaudo, 6); is major sourc is from xosklon of sa foods (crab, shrimp, prawn, and lobsr shlls) ha ar usually disposd as was marial. Dpnding on is sourc, hr diffrn crysallin polymorphic forms of chiin hav bn idnifid: α-chiin (shrimp and crab shlls), β-chiin (squid pn), and γ-chiin (somach cuicls of cphalopoda) (Jang al., 4). Chiosan, -acamido--doxy-β-dglucos-(n-acylglucosamin), is a biopolymr wih fr amin groups ha ar suiabl for h adsorpion of havy mals. I is producd on an indusrial lvl by chmical dacylaion of chiin wih NaOH. Chiosan can also b producd by nzymaic dacylaion of chiin using lysozym, snailas, nural proas, and chiin dacylas (Cai al., 6). Chiosan is slighly solubl a low ph valus and poss problms for dvlopmn in commrcial applicaions. Th aciv binding sis of chiosan ar no radily availabl for sorpion. Th sis ar rpord o b sof and hav a ndncy o agglomra or form gl in aquous soluions. Transpor of mal conaminans o h binding sis plays a vry significan rol in procss dsign. Thrfor, i is impraiv o provid physical suppor and incras h accssibiliy of h mal binding sis for procss applicaions (Amuda al., 7; Nomanbhay and Palanisamy, 5). Som invsigaors (Bamgbos al., ; Karhikyan al., 4; Muzzarlli, 977; Schmuhl al., ; Vold al., 3; Wana al., ) hav rpord h us of chiosan as adsorbn for h ramn of indusrial and municipal waswars. Howvr, imprgnaion of ihr char obaind from carbonacous marials or of acivad carbon on chiosan (Amuda al., 7; Ding al., 6; Nomanbhay and Palanisamy, 5; Wu al., ) has rsuld in a divrsiy of adsorbns wih far suprior adsorpion capaciy. Th objcivs of his sudy wr o prpar char from walnu shll, prform surfac modificaions of h walnu shll carbon (WSC) via chmical acivaion using phosphoric acid o obain acid-rad walnu shll carbon (AWSC), and h rspciv imprgnaion of WSC and AWSC on chiosan o obain walnu shll carbon imprgnad on chiosan (WSCC) and acid-rad walnu shll carbon imprgnad on chiosan (AWSCC) wih a viw o invsigaing h rspciv rmoval fficincis of Zn (II) ions in aquous soluions using h prpard adsorbns. Th ffcs of soluion ph, adsorbn dosag, iniial mal ion concnraion, conac im, agiaion spd and mpraur on h prcnag rmoval of Zn (II) ions in indusrial waswar wr also invsigad. Thr adsorpion isohrms (angmuir, Frundlich and Tmkin) and fiv kinic modls wr usd o analys h quilibrium adsorpion daa and h kinic daa of Zn (II) ions rmoval rspcivly. Thrmodynamic sudis of h Zn (II) ions adsorpion on h prpard biosorbns wr carrid ou o drmin h sponaniy, xohrmic or ndohrmic naur of h procss, and is fasibiliy. MATERIAS AND METHODS All h chmicals usd wr of analyical grad, purchasd from Sigma Aldrich in Grmany and usd as rcivd. Ths includd zinc (II) raoxosulpha hpahydra (ZnSO 4.7H O) (99%) for h synhsis of h indusrial waswar, NaOH (98%) and hydrochloric acid (99%) for h prparaion of chiosan, and oxalic acid (99.9%) for h prparaion of chiosan gl. Prparaion of char from walnu shll (WSC) Th locally purchasd walnu shlls wr cland and washd svral ims wih disilld war o rmov surfac impuriis. Afr drying, h shlls wr crushd. To prvn a sicky ffc in scrning, h sampls wr drid in an ovn a 5 C ill consan mass for 4 h prior o scrning. Th drid shlls wr scrnd (sivd) ino diffrn paricl sizs of.8,.45,.5,. and.5 nm and sord in plasic air-igh conainrs. Th carbonizaion procss was carrid ou as prviously dscribd by Amuda and Ibrahim (6). Th quaion for carbonizaion procss is shown hus: Walnu shll o 6 C, h WSC + CO () Prparaion of acid-rad walnu shll carbon (AWSC) Th acivaion of h walnu shll carbon (WSC) using phosphoric acid was carrid ou by h mhod prviously dscribd by Idowu (5) wih a sligh modificaion. Exacly 3 g of h carbonizd walnu shll was wighd ino a crucibl and mixd wih M H 3PO 4. Th crucibl wih is conn was had a 75 C or a priod of 5

4 min. Th acivad sampl was allowd o cool o ambin mpraur; h sampls wr washd svral ims wih dionizd war unil ph 6-7, filrd wih Whaman No. filr papr (5 mm diamr, Ca No. 5) and drid a C for 4 h. Th chmical quaion for h acivaion procss is shown hus: WSC o 75 C, H 4, 5min 3 PO Prparaion of chiin from snail shll AWSC + CO () Snail shlls wr ground o a smallr paricl siz, pulvrizd and scrnd o a paricl siz of mm. Th mhod rpord by Mohanasrinivasan al. (4) was mployd for h prparaion of chiin wih sligh modificaion. 8 g of h powdr was mixd wih m of 4 w% NaOH. Th mixur was boild and sirrd a C for h in a war bah. I was hn filrd and washd wih disilld war. Rd limus was usd o chck if h bas was complly washd away. Afr washing, h mixur was filrd and h rsidu was drid a C for 3 h. Afr dproinaizaion, h wigh of h sampl was 6 g. 3 m of 5 w% M HCl was addd o h dproinizd sampl. Th mixur was boild and sirrd for 45 min a C in a war bah in ordr o rmov all minral marials (mainly CaCO 3). Subsqun washing was don wih disilld war followd by filraion. Th mixur was xamind wih blu limus o chck h acidiy of h mixur. Th rsidu (chiin) obaind was drid in h ovn a C for h. Prparaion of chiosan Dacylaion racion was usd o convr chiin o chiosan according o a rvisd procdur of Coughlin al. (99). Thn, a mhod dscribd by Nomanbhay and Palanisamy (5) was usd for h prparaion of chiosan gl. Th dgr of dacylaion of chiosan was drmind by applying h mhod usd by Guibal al. (994). Th molar mass of chiosan was drmind by using h quaion of Mark-Houwink-Sakurada for viscosiy masurmns a diffrn concnraions, givn by Paul and odg (7): km (3) Whr, and M ar h rspciv inrinsic viscosiy and molcular wigh of chiosan, k and ar h Mark-Houwink Sakurada consans for a givn polymr-solvn mpraur sysm. Surfac modificaion of WSC and AWSC wih chiosan Th surfac modificaion of WSC and AWSC wih chiosan gl was carrid ou using h mhod dscribd by Babl and Kurniawan (4). 5 g of h AWSC was slowly addd o ml of chiosan gl dilud wih 5 ml of war and had o 5 C and hn agiad a 5 rpm for 6 h. Th prpard AWSCC was washd wih dionizd war and drid a for h. Th sam procss was applid o WSC o obain walnu shll carbon imprgnad on chiosan (WSCC). Th AWSCC and WSCC wr hn soakd in.5% NaOH soluion ill any rsidual acid was rmovd. Boh adsorbns wr rinsd xnsivly wih dionizd war and drid in an ovn a C for h, coold a room mpraur and sord in dsiccaor. Characrizaion of diffrn prpard adsorbns Drminaion of surfac ara Th spcific surfac ara (S) of h acivad carbon was simad using Sar mhod (Alzaydian, 9) by agiaing.5 g of h adsorbn in ml of dilud hydrochloric acid a a ph of 3. Thn, 3 g of NaOH was addd whil sirring h suspnsion and h volum was mad up o 5 ml wih dionizd war. Th rsuling soluion was irad wih. N NaOH o rais h ph from 4 o 9 V and h volum, OH, of NaOH was rcordd. Th surfac ara, S, of h adsorbn was calculad hus: S 3V 5 (4) OH Drminaion of ash conn Th ash conn (AC) of h acivad carbon was drmind by h mhod of Jyakumar and Chandraskaran (4), and is givn by: M M X AC (5) Whr, M is h mass of sampl akn for s, M mass of ash, and X h % of moisur conn prsn in sampl akn for s. Drminaion of bulk dnsiy Th apparn or bulk dnsiy, b, of ach adsorbn was drmind using h apping procdur dscribd by Ahmda W al. (997), and is givn by: b M, whr W is h wigh of dry marial (g) and V M h volum of dry marial (m). Drminaion of ph Th procdur of Jyakumar and Chandraskaran (4) was usd o obain ph. g of h drid sampl was wighd and ransfrrd ino a brakr. 3 m of frshly boild war (adjusd o ph 7.) was addd. Afr digsing for min, h soluion was hn filrd whil ho, rjcing h firs m of h filra. Th rmaining filra was hn coold o room mpraur and h ph was drmind using a ph mr. Drminaion of iodin numbr Th iodin numbr, I, was drmind using h mhod prviously dscribd by ASTMD (6), and is givn by: EVB c w I (6) s Whr, E is h quivaln wigh of iodin (=7), V B and c h volum and normaliy of sodium hiosulpha usd rspcivly and w s h wigh of sampl usd in g. V

5 Fourir-ransform infrard (FTIR) analysis Th FTIR analysis of h adsorbns was drmind using Shimadzu FTIR-83 Spcromr. Th corrsponding spcra of h chiosan and h drivd composi biosorbns wr obaind showing h wavlnghs in h rang 4 o 4 cm - of h diffrn funcional groups in h sampls which wr idnifid by comparison wih hos in h library. K K V d () d m All h adsorpion xprimns wr duplicad o nsur accuracy, rliabiliy and rproducibiliy of h adsorpion daa. Rlaiv rror did no xcd ±.. Prparaion of synhic waswar Sock zinc soluion of concnraion mg/ was prpard by dissolving 3.93 g of ZnSO 4.7H O in m of disilld war. Th rang of iniial concnraion of h prpard mal soluions varid bwn and 8 mg/. Th sock soluions wr furhr dilud wih disilld war o dsird concnraions (s soluions). Th ph of h soluions was adjusd wih. N H SO 4 and NaOH. Blank xprimns wr conducd o nsur ha no adsorpion occurrd on h walls of h apparaus usd. Bach adsorpion xprimn Th bach adsorpion sudis wr carrid ou a ambin mpraur using h diffrn adsorbns prpard: WSC, AWSC, WSCC and AWSCC, for h rmoval of zinc (II) ions in simulad indusrial waswar a h opimum condiions of all facors ha influnc adsorpion: ph, adsorbn dos, iniial mal ion concnraion, paricl siz and agiaion im. 3 mg/l of ZnSO 4.7H O was prpard by diluing 3 ml of ml ZnSO 4 soluion wih disilld war in ml volumric flask. ml of his aquous soluion was masurd ino 5 ml Erlnmyr flasks conaining g of ach adsorbn. Th mixur was mchanically agiad wih a basic rciprocaing shakr a 5 rpm for h and lf undisurbd for 3 min o allow h sysm o quilibra. Th mixur was filrd, and h concnraion of h rsidual mal ion in h filra was drmind a 8 min using Aomic Absorpion Spcrophoomr (Prkins Elmr Modl 3). Th quilibrium mal upak, q (mg/g), adsorpion prcnag,, and adsorpion capaciy valus, q (mg/g) a im (min) wr calculad using Eqs (7)-(9) rspcivly: c c q V m c c c c c q V m (8) Th disribuion raio, K d, was drmind hus: amoun of Zn in adsorbn amoun of Zn in soluion K d () Erdm al. (4) corrlad h adsorpion prcnag,, and K d by h following quaion: (7) (9) RESUTS AND DISCUSSION Fourir Transform Infrard (FTIR) characrizaion of chiosan FTIR was prformd o confirm h formaion of chiosan. Th paks apparing in h FTIR spcrum wr assignd o various funcional groups according o hir rspciv wav numbrs as rpord in h liraur. Various absorpion bands wihin h 4-4 cm - rang wr rcordd in h FTIR spcra of chiosan, prpard from snail shll. Th adsorpion bands for h prpard chiosan and significan paks ar prsnd in Tabl. A characrisic band a and cm - could b assignd o h srching vibraions of NH, - OH, -NH and inrmolcular hydrogn bonds which ovrlap ach ohr. Th obsrvd pak a cm - was du o h prsnc of h mhyl group in NHCOCH 3. Th characrisic NH band of h prpard chiosan indicas h prsnc of a carbonyl group a h obsrvd band a cm -, which could b aribud o h incompl dacylaion of chiin o chiosan. Th obsrvd pak a 87.3cm - was assignd o CN srch of aliphaic amins. Th obsrvd band a 94.8 cm - was indicaiv of h prsnc of -glycolic linkag. Th obsrvd band a cm - was aribud o ring srching and ha obsrvd a 7.6 cm - is aribud o NH ou-of-plan bnding (Snha al., 4). Th characrisic absorpion bands of h prpard chiosan from snail shlls wr compard wih h sandard valus obaind from Sigma-Aldrich, as shown in Tabl. Exclln agrmns wr obaind wih AAD bing. %, hus confirming h producion of chiosan from snail shll usd in his sudy. Also, a sraigh lin was obaind whn h xprimnal daa wr plod agains h sandard daa, wih a vry high cofficin of corrlaion, R hrby burssing h arlir samn mad. Drminaion of dgr of dacylaion of chiosan Th dgr of dacylaion (DD) of chiosan is an imporan paramr o b nod as i affcs h solubiliy, chmical raciviy and biodgradabiliy of chiosan. DD may rang from 3% o 95% (Marino

6 Tabl. FTIR showing h diffrn bonds prsn in chiosan. Wav numbr (cm - ) Funcional groups Rfrnc O H srching of h hydroxyl group, N H srching Rumngan al. (4) C=O in NHCOCH 3 group (amid I band) Dilyana and Soyanka () Primary and scondary amid or C=O group NO srch of nirogn conaining compounds and CO srch of carbonyl compounds Rumngan al. (4) Dilyana and Soyanka () 87.3 CN srch of aliphaic amins Dilyana and Soyanka () β-glycolic linkags Ring srching NH ou-of-plan bnding Snha al. (4) Rumngan al. (4) Snha al. (4) Tabl. Characrisics absorpion bands in h FTIR spcra of sandard and xprimnally prpard chiosan. Sandard wavlngh (cm - ) Exprimnal wavlngh (cm - ) % rror ±.6 ±. ±.6 ±.3 ±. ±.6 Tabl 3. Proxima analyss of chiin and chiosan from snail shll. Marials Proxima analysis, % Moisur conn Ash conn Proin Fibr Chiin Chiosan al., 5), dpnding on h availabl sourc and procdur. % DD is vry scarcly obaind, wih commrcial chiosan wih various DD in h rang of 75-85%. IR chniqu was usd for drmining h dgr of dacylaion, DD, of chiosan, according o h mhods dscribd by Domszy and Robrs (985) and Hiral al. (99) using Equaion (): A657.7 DD () A Whr, A and A ar valus of absorbanc a h wavlnghs and cm - rspcivly. From h FTIR analysis of chiosan, h % ransmianc of h wavlngh and cm - was obaind as 95 and 78 rspcivly. This was hn convrd o absorbanc [=-log (% ransmianc)] o drmin h dgr of dacylaion of h prpard chiosan from snail shlls as 85.53%, using Equaion. This valu is in h rang givn by Marino al. (5). Proxima analysis of chiin and chiosan Th proxima analyss of chiin and chiosan prpard in his sudy ar prsnd in Tabl 3. I was found ha h moisur conn of chiin was highr han ha of chiosan owing o h fac ha war was rmovd from h chiin prior o h producion of chiosan. Th ash conn of chiin was lowr han ha of chiosan as a rsul of h prsnc of h acyl group in h chiin sampl. Proin conn of h chiin was high afr dproinizaion of h chiin and his could b aribud o h low dgr of acylaion of h chiin, which was found o b 4.47% (ha is -DD of chiosan). Th fibr conn of h chiosan was highr han ha of chiin owing o h fac ha h rmoval of mor mar from h chiin o obain chiosan could hav

7 Tabl 4. Ulima and proxima analyss of raw walnu shll. Ulima analysis (%) Proxima analysis (%) C H N S O Moisur conn Ash conn Volail mar Fixd carbon Tabl 5. Proxima analysis and physicochmical propris of h prpard adsorbns. Proxima analysis Adsorbns WSC AWSC WSCC AWSCC Moisur conn (%) Ash conn (%) Volail mar (%) Fixd carbon (%) Physicochmical propris Surfac ara (m /g) Bulk dnsiy (g/ml) ph Iodin valu (mg/g) ld o h prsnc of mor fibr in h chiosan han in chiin. Th rsuls of h proxima analysis of chiin and chiosan obaind in his sudy wr consisn wih hos obaind by Isa al. () in h xracion and characrizaion of chiin and chiosan from Nigrian shrimps. Th solubiliy of chiosan was chckd using four diffrn solvns: war, hanol, NaOH and hanoic acid. I was found ha h chiosan was solubl in acidic condiion bu insolubl in alkalin, hanol and nural soluion. Th ph valu of h chiosan also varid from 6.3 o 8., as rpord by Snha al. (4) in h xracion and purificaion of chiosan from chiin isolad from sa prawn. Ulima and proxima analyss of raw walnu shll Th rsuls of h ulima and proxima analyss of h walnu shll ar givn in Tabl 4. From h ulima analysis, h prcursor for h prparaion of diffrn adsorbns usd in his sudy has vry low nirogn and no sulphur and hus canno conribu o nvironmnal issus involving oxids of nirogn and sulphur. Also, h walnu shlls hav a high volail mar conn and low ash conn, which is ssnial for pyrolysis and gasificaion procsss. Th lignocllulosic composiion of h walnu shll was drmind according o h Robrson and Van Sos (98) mhod. Th % of cllulos, hmicllulos and lignin was found o b 4.4,. and 7.6 rspcivly. Thus, h lignin conn of h walnu shll usd in his sudy was las. Howvr, marials wih a low conn of h lignin fracion ar candidas for h producion of microporous acivad carbon (Daud and Ali, 4; Grgova al., 994). Characrisics of h prpard adsorbns Tabl 5 shows h characrisics of h prpard adsorbns. Th moisur conn of AWSCC was 4.78%, which was h lows amongs h prpard adsorbns. Hnc, AWSCC could b adjudgd h bs adsorbn amongs h prpard adsorbns, wih xclln adsorpion prformanc sinc lowr moisur conn incrass h adsorpion capaciy of carbon by concnraing h acion of acivad carbon. Th ash conn of AWSCC was found o b.6%, which was h lows amongs h invsigad adsorbns. Th lowr h ash conn, h br h saring marial for rmoval of havy mal ions from indusrial waswar (in and Wu, ). Hnc, AWSCC was found o b a br adsorbn han WSC, AWSC and WSCC. Morovr, h las ash conn valu for AWSCC was favourabl bcaus h ash conn can inrfr wih h adsorpion procss (Khan al., 9). AWSCC has h lows volail mar compard o WSC, AWSC and WSCC. This can b aribud o h fac ha during hrmal acivaion, mos of h noncarbon lmns such as hydrogn, oxygn, nirogn and sulphur migh hav bn liminad as volail gasous producs by h pyrolysis.

8 Thr is no much diffrnc on h fixd carbon conn of WSC, AWSC, WSCC and AWSCC, as h % rror bwn h highs and lows valus for WSCC and AWSC rspcivly was ±3.84<±5.. Hnc, all h prpard adsorbns in his sudy could b viabl opions for acivad carbon producion. Th surfac ara of an acivad carbon is dircly rlad o h porosiy of h carbon. From Tabl 5, h incrasing ordr of surfac aras of h prpard adsorbns was WSC < WSCC < AWSC < AWSCC. Thrfor, AWSCC could b adjudgd h bs and highly porous adsorbn. Howvr, h surfac aras of hs adsorbns conformd o h rang for plan adsorbns, which is bwn and 3 m /g. Th rsuls of bulk dnsiy of h prpard adsorbns rvald ha AWSCC had h highs bulk dnsiy, which is indicaiv of highr qualiy adsorbn han h ohr hr adsorbns. Thrfor, AWSCC could provid br conac wih h adsorba, lading o mor ffciv adsorpion procss. Th ph paramr is a facor affcing adsorpion capaciy of havy mals. I is wll known ha ph could affc h proonaion of funcional group on h aciv sis of h adsorbn, as wll as mal chmisry (Tszos and Bll, 989). Th ph valus of WSC, AWSC, WSCC and AWSCC wr drmind o b 9., 7.6, 9. and 5.5. Ths findings wr in agrmn Chrmisnoff and Ellrbusch (978) who confirmd ha h ph of ihr raw or carbonizd agriculural marials in war suspnsion can vary bwn 4 and. Iodin valu is a fundamnal paramr usd o characriz h prformanc of acivad carbons. I is ofn usd o drmin h micropor conn of h acivad carbon and is obaind by h adsorpion of iodin from soluion by h acivad carbon sampl (Jyakumar and Chandraskaran, 4). Highr valu of h iodin valu indicas highr dgr of acivaion. Th iodin valus of WSC, AWSC, WSCC and AWSCC ar givn in Tabl 5. Th WSCC had h highs iodin valu of mg/g, indicaing ha is por surfac and srucur wr h bs dvlopd in his sudy. Fourir Transform Infrard (FTIR) characrizaion of prpard adsorbns Th FTIR spcra of h prpard biosorbns wr sudid in h rang of 4 o 4 cm -. Th FTIR spcra of h WSC and AWSC obaind in his sudy did no xhibi significan diffrncs in h surfac chmisry of hs wo adsorbns. Howvr, sligh diffrncs on h innsiy of h bands wr dcd. Th following surfac funcional groups wr idnifid for WSC and AWSC (Gonzálz al., 9). Th wid bands a 34 cm - wr rlad o vibraions v(o H) in war molculs. Th wak band was found around 9 cm -, which was aribud o carboxylic acids or aliphaic groups. Th band a 35 cm - is gnrally associad wih vibraions in aliphaic bonds. Th bands wihin h rgion 4-8 cm - can b aribud o C=O bonds, which is rlad o h prsnc of carbonyl groups or aromaic rings. Finally, h wak band dcd around 3 cm - was rlad o v(c O) bonds in lacons, poxids and hr srucurs. For WSCC, h broad band posiiond bwn and cm - rvald h xisnc of OH srching of h hydroxyl group, inra molcular hydrogn groups and fr N H. Th obsrvd band a and 36.4 cm - was aribud o C H srching. Th obsrvd band a 93. and cm - was as a rsul C C (alkyn). Th obsrvd band a cm - could b aribud o primary and scondary amid or C=O group prsn in WSCC. Th obsrvd band a cm - was as a rsul of N H dforming. Th obsrvd band a cm - was aribud C C srch (in ring). Th obsrvd band a cm - was indicaiv of CH 3 in h NHCOCH 3 group. Th obsrvd band a and cm - was du o nira (NO ) symmric srching vibraion. Th obsrvd band a 9.5 cm - was as a rsul of h srching of h CO bond. Th obsrvd band a cm - was indicaiv of h srching of O-O bond and h obsrvd band a cm - was as a rsul of h srching of halognad compounds, C X, whr X rprsns halogns. For AWSCC, h broad band posiiond a 343 cm - rvald h xisnc of OH srching of h hydroxyl group. Th 65.8 cm - band was a bnd vibraion of N H (Argun and Dursun, 6). Th obsrvd band a 35.8 cm - was as a rsul of h nira (NO ) symmric srching vibraion and h obsrvd band a 56.6 cm - was aribud o h vibraion C=O=C and O H in polysaccharids. Th obsrvd band a cm - was du o h C=CH bnding and ha a and cm - could b aribud o h prsnc of h SO 3 group and C S srching rspcivly. Dynamics of Zn II ions adsorpion on prpard adsorbns Effc of ph on h rmoval of Zn (II) ions Whil opraional paramrs (adsorbn dos, agiaion im and iniial mal ion concnraion) wr kp consan and mpraur and agiaion spd kp a 3 C and 5 rpm rspcivly, h rsuls of h ffc of soluion ph ( ph 9) on h adsorpion of Zn (II) ions ono WSC, AWSC, WSCC and AWSCC ar shown in Figur. I was obsrvd ha h adsorpion capaciis of WSC, AWSC, WSCC and AWSCC for Zn (II) ions rmoval incrasd as ph incrasd unil opimum ph valu of 5, and hn dcrasd whn ph was incrasd furhr. This may b du o h formaion of solubl

9 % rmoval of Zn (II) ions WSC AWSC WSCC AWSCC ph Figur. Effc of ph on h rmoval fficincy of Zn (II) ions using WSC, AWSC, WSCC and AWSCC a c 3 mg/, dos of ach adsorbn=g, agiaion spd=5 rpm, conac im= min, paricl siz=6bss and mpraur of soluion=3 C. hydroxyl complxs. Th ons of mal hydrolysis and prcipiaion bgins a ph > 5 (Bas and Msmr, 976). Compiiv adsorpions bwn H + and Zn + ions rsul in low adsorpion fficincy of Zn + as H + concnraion incrass if ph is blow 3 (Amuda al., 7). A low ph, h amin group on h chiosan is proonad o a varying dgr (Nomanbhay and Palanisamy, 5). Th surfac acidiy was du o h inroducion of svral oxygn-conaining funcional groups (Faria al., 4). Acid acivaion of walnu shll carbon using phosphoric acid and subsqun imprgnaion on chiosan o produc AWSCC improvd h lcrosaic inracion bwn chiosan and AWSC. Hnc, mor aciv sis wr availabl for h adsorpion of Zn (II) ions on AWSCC hrby rsuling in h highs mal ion rmoval fficincy as shown in Figur. Thrfor, h incrasing ordr of Zn (II) ions rmoval fficincy a ph bwn and 9 is WSC<AWSC<WSCC<AWSCC. Effc of adsorbn dosag on h rmoval of Zn (II) ions Figur shows Zn (II) ions rmoval fficincy as funcion of adsorbns dosag. Th dos of ach adsorbn was varid bwn 5 and 5 g/, kping ohr opraional paramrs (ph, agiaion im, iniial ion concnraion and paricl siz) a h opimum and mpraur and agiaion spd wr kp a 3 and 5 rpm rspcivly. Owing o h availabiliy of mor binding sis, i was obsrvd ha incrasing h dos of h ach adsorbn incrasd h rmoval fficincy of Zn (II) ions. Howvr, incrasing h dos of h adsorbns abov 5 g/ for WSC, g/ for AWSC, 5 g/ for WSCC and g/ for AWSCC producd no apprciabl incras in h Zn (II) ions rmoval fficincy. Th highs Zn (II) rmoval fficincy for WSC and AWSC was and 7.67% rspcivly a 5 g/ dos of h adsorbn. As i can b sn from Figur, 5 g/ and g/ dos of WSCC and AWSCCC rspcivly xhibid and 83.8% Zn (II) ions rmoval fficincy rspcivly, indicaing ha surfac ara of h carbon has significan ffc on h rmoval of Zn (II) from synhic waswar. In Tabl 5, AWSCC had h highs surfac ara hrby h highs Zn (II) ions rmoval fficincy. Thrfor, h dcrasing ordr of h surfac ara and hus Zn (II) ions rmoval fficincy is AWSCC>WSCC>AWSC>WSC. From Figur, i can b sn ha afr a crain dos of adsorbn, no significan amoun of ions is bound o h adsorbn. Th amoun of fr ions rmains consan vn wih furhr addiion of h dos of adsorbn (Nomanbhay and Palanisamy, 5). Th diffrnc in h surfac

10 % rmoval of zinc (II) ions WSC AWSC WSCC AWSCC Adsorbn dosag (g) Figur. Effc of adsorbn dosag on h rmoval fficincy of Zn (II) ions using WSC, AWSC, WSCC and AWSCC a c 3 soluion=3 o C. mg/, ph=5, agiaion spd=5 rpm, conac im= min, paricl siz=6bss and mpraur of modificaion of h adsorbns confrrd on hm diffrn dgrs of rmoval fficincy. Th oxidaion of WSC wih minral acids has bn implicad o inroduc mor acidic C=O groups on h surfac of WSC. This would nhanc h lcrosaic inracion bwn chiosan and h mor ngaivly chargd AWSCC, hus, prvning agglomraion of chiosan (Amuda al., 7). Th formaion of mor acidic surfac oxids on AWSCC han WSC, AWSC and WSCC nhancd fficin coaing of chiosan, nhancd is hydrophilic characr and hnc improvd h hydrodynamic flow of mal ion o h acidic surfac oxids on h carbon surfac. This could b rsponsibl for h high adsorpion capaciy of AWSCC ovr WSC, AWSC and WSCC. Effc of iniial mal ion concnraion on h rmoval of Zn (II) ions Th prcnag rmoval of Zn (II) ions by h adsorbns iniially incrasd rapidly wih incrasing Zn (II) ions concnraion and sagnas whn Zn (II) concnraion rachd 3mg/, as can b sn in Figur 3. A lowr concnraions, Zn (II) ions in h soluion would inrac wih h binding sis and hus faciliad % adsorpion (Amuda al., 7). A highr concnraions, mor Zn (II) ions wr lf unadsorbd in soluion du o h sauraion of binding sis, which was indicaiv of h involvmn of nrgically lss favourabl sis wih incrasing mal ion concnraions in h aquous soluion. Th Zn (II) ion adsorpion could b aribud o diffrn mchanisms of ion xchang procsss as wll as o h adsorpion procss. During h ion xchang procss, Zn (II) ions had o mov hrough h pors of h adsorbn mass, as wll as hrough channls of h laic, hrby rplacing xchangabl caions. Diffusion was rapid hrough h pors and was rardd whn h ions movd hrough h smallr diamr channls. In his cas, h Zn (II) ions sorpion could mainly b aribud o ion-xchang racions in h micropors of h adsorbns (Amuda al., 7). Th maximum prcnag of Zn (II) ions rmoval of 5. and 55. was achivd whn 75 mg/ Zn (II) ion concnraions was adsorbd wih g/ m of WSC and AWSC whil h maximum prcnag of Zn (II) ions rmoval of 95.4 and 97.8 was achivd whn 5 mg/ Zn (II) ion concnraions was adsorbd wih g/ m of WSCC and AWSCC. Effc of conac im on h rmoval of Zn (II) ions Equilibrium im is anohr imporan opraional

11 % rmoval of Zn (II) ions WSC AWSC WSCC AWSCC Iniial mal ion concnraion (mg/l) Figur 3. Effc of iniial mal ion concnraion on h rmoval fficincy of Zn (II) ions using WSC, AWSC, WSCC and AWSCC a ph=5, dos of ach adsorbn= g, agiaion spd=5 rpm, conac im= min, paricl siz=6bss and mpraur of soluion=3 o C. paramr for an conomical waswar ramn procss. Figur 4 dpics Zn (II) ions rmoval fficincy as funcion of agiaion im kping ph and adsorbn dos a h opimum and mpraur and agiaion spd a 3 and 5 rpm, rspcivly. From h Figur, incras in agiaion im incrasd h rmoval fficincy of Zn (II) ions unil quilibrium adsorpion was sablishd. Equilibrium adsorpions wr sablishd wihin 8 min for WSC, AWSC, WSCC and AWSCC wih Zn (II) ions rmoval fficincis of 6.5%, 68%, 8.8% and 85.4% rspcivly. This was du o grar availabiliy of various funcional groups on h surfac of chiosan rquird for inracion wih anions and caions and hus significanly improvd h binding capaciy and h procss procdd rapidly for AWSCC and WSCC, compard o WSC and AWSC. Effc of agiaion spd on h rmoval of Zn (II) ions Figur 5 shows h ffc of agiaion spd on h prcnag rmoval of Zn (II) ions from indusrial waswar using WSC, AWSC, WSCC and AWSCC as adsorbns, whil ohr paramrs such as ph and adsorbns dos wr kp a h opimum and mpraur a 3 C. I can b sn ha h rmoval fficincy of Zn (II) ions using h four prpard adsorbns incrasd as h agiaion spd incrasd unil h opimum valu and hn dcrasd whn h agiaion spd furhr incrasd. This can b aribud o h fac ha an incras in h agiaion spd ld o improvmn in h mixing bwn mal ions in soluion and aciv binding sis of h adsorbns (WSC, AWSC, WSCC and AWSCC) hrby rsuling in an incrasd rmoval fficincy of Zn (II) ions. Whn h mixur of mal ion and h adsorbns (WSC, AWSC, WSCC and AWSCC) was s on a shakr in svral Erlnmyr flasks, h fin paricls of WSC, AWSC, WSCC and AWSCC movd rapidly in h mal soluion and his ld o incrasd concnraion of mal ions nar h surfac of h aciv sis. According o Kafia and Surchi (), h high shaking spd providd sufficin addiional nrgy o brak nwly formd wak bonds bwn h mal ions and binding sis of h adsorbn. Consqunly, high agiaion spd may lad o h adsorbd mal ions o dsorb from h adsorpion sis. From Figur 5, a h opimum agiaion spd of 5 rpm, h rspciv valu of h rmoval fficincy of Zn (II) ions was found o b 6.3, 64., 8 and 85.4% using WSC, AWSC, WSCC and AWSCC as adsorbns

12 % rmoval of Zn (II) ions % rmoval of Zn (II) ions WSC AWSC WSCC AWSCC Conac im (min) Figur 4. Effc of conac im on h rmoval fficincy of Zn (II) ions using WSC, AWSC, WSCC and AWSCC a c 5 mg/, ph=5, dos of ach adsorbn= g, agiaion spd=5 rpm, conac im= min, paricl siz=6bss and mpraur of soluion=3 o C WSC AWSC WSCC AWSCC Agiaion spd (rpm) Figur 5. c 5 Effc of agiaion spd on h rmoval fficincy of Zn (II) ions using WSC, AWSC, WSCC and AWSCC a mg/, dos of ach adsorbn=g, agiaion spd=5 rpm, conac im= min, paricl siz=6bss and mpraur of soluion=3 o C.

13 hrby giving jusificaion o sing agiaion spd o 5 rpm for all adsorpion sudid in his work. Corrlaion of quilibrium adsorpion daa Th sorpion quilibrium daa gahrd in his sudy wr confrond wih h adsorpion isohrms of angmuir, Frundlich and Tmkin. Ths isohrms ar givn as follows: qmax K c angmuir isohrm: q (3) K c Which can b linarizd o fiv diffrn linar forms: c, q K q c q q max max q max c K q q q q qmax, K q K qmax K c c K qmax K c q max, and Th imporan characrisics of angmiur isohrm was xplaind by a dimnsionlss consan, known as sparaion facor or quilibrium paramr, R, givn by Zhai al. (4): R (4) K c Using mahmaical compuaions, Zhai al. (4) showd ha R indicas h shap of h isohrm hus: for R, R, R and R, w hav irrvrsibl, favourabl, linar and unfavourabl isohrms rspcivly. Frundlich isohrm: q F n Whos linar form is xprssd hus: K c (5) In q In KF In c (6) n Whr, KF is a masur of adsorpion capaciy and n sands for h hrogniy. Tmkin isohrm: q InA c In A Inc RT RT (7) T T b b T In hs isohrms, ncssary linar plos wr mad, as T shown in Figurs 6 o 8, slop and inrcp wr drmind and h inhrn isohrm paramrs wr calculad as shown in Tabls 6 and 7. Th cofficin of corrlaion, R, was h cririon for fiing h xprimnal daa o hs isohrms. I should b srssd ha all h fiv linarizd forms of angmuir isohrm wr fid o h xprimnal daa, and hy all gav almos h sam rsuls. From h R valus, angmuir isohrm corrlad xcdingly wll h quilibrium adsorpion daa of Zn + ions rmoval using WSC, AWSC, WSCC and AWSCC as adsorbns. Th maximum upak capaciis for Zn + ions wr 7.7, 6.45, 3.8 and 3. mg/g for AWSCC, WSCC, AWSC and WSC rspcivly. Th angmuir paramrs wr also usd o prdic h affiniy of h adsorbns surfacs oward h Zn + ions by using dimnsionlss sparaion facor, R, as xprssd in Equaion. Th R valus obaind wr in h rang R for Zn + ions concnraion sudid in his work (<c O < mg/l). This is indicaiv of a favourabl isohrm shap for h adsorpion of Zn + ions ono WSC, AWSC, WSCC and AWSCC in h concnraion rang sudid. Though n> for h four adsorbns using Frundlich isohrm, h R valu for AWSC is no ha clos o uniy whil promising rsuls wr obaind for WSC, WSCC and AWSCC. Th n valu of Frundlich quaion givs an indicaion of h favourabiliy of sorpion. I is gnrally sad ha valus of n in h rang of o ar good, o as modraly difficul and lss han as poor sorpion characrisic (Chn al., ). Hnc, Frundlich isohrm can b usd o corrla h adsorpion daa of Zn + ions rmoval using WSC, WSCC and AWSCC as adsorbns, wih h bs fid adsorpion daa obaind for AWSCC. Th simad valus of Tmkin paramrs and ar prsnd in Tabl 7. From h R valus, which ar clos o uniy, Tmkin isohrm could also b a rprsnaiv for h Zn + ions adsorpion ono h four adsorbns sudid. In gnral, angmuir adsorpion isohrm had h bs fi for h four adsorbns sd in his sudy as a rsul of h highs corrlaion cofficin. Th suiabiliy and applicabiliy of angmuir isohrm o h adsorpion of Zn + ions on WSC, AWSC, WSCC, and AWSCC rval h formaion of monolayr covrag of h Zn + ions on h surfac of hs adsorbns. Kinic modlling of Zn (II) ions adsorpion Diffrn kinic modls givn in Equaions 8,, 3, 4 and 6 wr usd o s h kinic daa for h adsorpion of Zn + ions on WSC, AWSC, WSCC and AWSCC. Th fracional powr modl, which has h form of R

14 c /q (g/) c /q (g/) WSC AWSC WSCC AWSCC c (mg/) Figur 6. angmuir adsorpion isohrm fid o h bach quilibrium daa of Zn (II) ions adsorpion on WSC, AWSC, WSCC and AWSCC as adsorbns. 3.5 In q.5 WSC AWSC WSCC AWSCC In c Figur 7. Frundlich adsorpion isohrm fid o h bach quilibrium daa of Zn (II) ions adsorpion on WSC, AWSC, WSCC and AWSCC as adsorbns.

15 q (mg/g) WSC AWSC WSCC AWSCC In c Figur 8. Tmkin isohrm fid o h bach quilibrium daa of Zn (II) ions adsorpion on WSC, AWSC, WSCC and AWSCC as adsorbns. Tabl 6. angmuir and Frundlich isohrm paramrs for adsorpion of Zn + ions by diffrn adsorbns a 3 C. Adsorbn q max (mg/g) angmuir paramrs K (/mg) R R Frundlich paramrs K F (mg/g) n R WSC AWSC WSCC AWSCC Tabl 7. Tmkin isohrm paramrs for adsorpion of Zn + ions by diffrn adsorbns a 3 C. Adsorbn A T (/g) Tmkin paramrs b RT T b T R WSC AWSC WSCC AWSCC Frundlich quaion, indicas h mal upak incrass xponnially wih im, and is givn by: N q k F (8) Taking naural logarihms of Eq. (6) givs: In q In k N In (9) F Hnc, h paramrs inhrn in h modl can b simad by making appropria linar plo of agains In In q

16 Th Elovich kinic modl is givn by: Th ingrad form of quaion (6) is: dq d xp q () q k q (7) kq Whr, and ar consans during an xprimn. As q dq d,, hnc is rgardd as h iniial, q q, ra of adsorpion. Whn, q and h ingrad form of Equaion is: q In In Whr, q. If In In (), Eq. () simplifis o: () Hnc, a linar plo of q agains In can b mad o chck if for h cofficin of drminaion, R, should b grar han. Th inraparicl diffusion (IPD) (or Wbr and Morris) modl is usd o idnify h mchanism involvd in h adsorpion procss. IPD modl has h form: q k IPD (3) A linar plo of q agains can b usd o drmin k IPD, wih no inrcp on q axis. Th agrgrn psudo firs-ordr kinic modl is xprssd as: dq k q q (4) d Th ingrad form of Equaion (4) is: In q q In q k (5) Th spcific racion ra consan, k, for h agrgrn psudo firs-ordr kinics is usually obaind In q q agains, whrby h slop of k. by ploing h sraigh lin obaind is Th psudo scond-ordr kinic modl is givn by: dq k q q (6) d Which givs diffrn forms whn linarizd. On of such forms usd in his sudy is: q kq q Hnc, a plo of q o nabl h drminaion of (8) agains should yild a sraigh lin q and k from slop and inrcp rspcivly. Th goodnss of fi was jusifid basd on h fac ha h cofficins of drminaion wr clos o. Th modls, hir simad paramrs and R valus ar prsnd in Tabl 8. Though h valu of h xponn, N, of h fracional powr modl was lss han, which indicad h imdpndn of h adsorpion of Zn + ions on WSC, AWSC, WSCC and AWSCC as adsorbns, h fracional powr modl did no provid a good fi o h kinic daa of h adsorpion of Zn + ions as h cofficins of corrlaion, R, in all cass of h four adsorbns usd in his sudy, wr no clos o uniy, as prsnd in Tabl 8. Morovr, h xprimnal kinic daa did no show saisfacory fi o Elovich kinic modl sinc R valus for h four adsorbns usd wr no clos o uniy. Th kinic plos for h inraparicl diffusion modl obaind in his sudy for h four adsorbns sd wr no linar for all h lins did no pass hrough h origin as xpcd: hy all had inrcps, C, as shown in Tabl 8. This indicad ha h inraparicl diffusion was no h ra-conrolling sp in h adsorpion of Zn + ions on h prpard adsorbns, and hr was som dgr of boundary layr diffusion. This was burssd by h fac ha h corrlaion cofficins ar far lss han uniy. In fac, in all h kinic modls sudid, IPD shows h wors fi of h kinic daa. Also, Tabl 8 dpics h kinic paramrs and h R valus for h agrgrn s psudo firs-ordr kinic modl and h psudo scondordr kinic modl. Alhough h R valus wr somwha high for h formr, is horical valus of in Tabl 8 wr far lss han h corrsponding xprimnal valus prdicd by h lar. This suggsd a poor fi bwn h kinics daa and h agrgrn psudo-firs ordr kinic modl for h four adsorbns usd in his sudy. Ths rsuls wr in consonanc wih similar works in h liraur (odi al., 998; Ho and Mckay, ) wih svral naural adsorbns and h sam iniial concnraion valus. Exclln agrmns wr obaind bwn h q

17 Tabl 8. Kinic modl paramr valus and cofficin of corrlaion valus. Kinic modl Fracional powr law Paramr valus k F N R Adsorbns WSC AWSC WSCC AWSCC Elovich modl (mg/g min) (g/mg) R IPD modl k IPD (mg/g min ½ ) C (mg/g) R agrgrn s psudo firs-ordr modl q (mg/g) k (min - ) R Psudo scond-ordr modl q (mg/g) k (g/mg min) R xprimnal and horical valus of q using h R psudo scond-ordr kinic modl. Morovr, h valus in all cass sudid wr narly uniy and vn uniy for AWSCC, which was indicaiv ha h kinics daa fid xcdingly wll h psudo scond-ordr modl for all adsorbns invsigad. Th psudo scond-ordr modl can b considrd as h ralimiing (or drmining) sp and probably a chmical adsorpion (chmisorpion) involving valanc forcs hrough ion xchang bwn ach mal ion and h aciv binding sis xisd in WSC, AWSC, WSCC and AWSCC. Th psudo-scond ordr kinic modl was also rpord o fi wll h kinic daa of h adsorpion of Zn + ions ono pomlo pl (Saikaw al., 9), adsorpion of Cu + ions ono Tcona grandis lavs (Kumar al., 6), adsorpion of Pb + ions ono pumpkin sd shll acivad carbon (Okoy al., ), adsorpion of Ni + ions ono poao pl (Prasad and Abdullah, 9), and adsorpion of Cr (VI) ions ono cookd a dus (Dhanakumar al., 7). Th kinic daa wr furhr analysd using h Boyd kinics in ordr o drmin h acual ra-conrolling sp involvd in h Zn + ions adsorpion procss on WSC, AWSC, WSCC and AWSCC owing o h wo mass ransfr of solu (boh film and por diffusion). Th Boyd kinics (Boyd al., 947) is givn by: 6 F xp B F (9) B In (3) F q q is h fracion of solu adsorbd a Whr, im,. Th valu of B was compud according o Eq. (8) for ach valu of F for ach of h adsorbns usd in his sudy, and hn plod agains im o consruc h Boyd plos (Ho al., ) for h sysm undr invsigaion, as dpicd in Figur 9. Th linariy of hs plos was usd o disinguish bwn xrnal ranspor (film diffusion) and inraparicl ranspor conrolld ras of adsorpion (Wang al., 6). A sraigh lin passing hrough h origin is indicaiv of adsorpion procss govrnd by inraparicl diffusion; ohrwis i is govrnd by film diffusion (Mohan and Singh, ). From Figur 9, h plos for h four adsorbns sudid wr nihr linar nor passd hrough h origin, which indicas ha in all h adsorbns sudid, film diffusion is h ra-drmining adsorpion procss for Zn (II) ions on WSC, AWSC, WSCC and AWSCC as adsorbns. This is in conformiy wih h arlir rsul prsnd in Tabl 8 ha a poor fi of h kinic daa was obaind for h IPD kinic modl.

18 B (min - ) WSC AWSC WSCC AWSCC (min) Figur 9. Boyd plos of h kinic daa for Zn (II) ions adsorpion on WSC, AWSC, WSCC and AWSCC as adsorbns. Thrmodynamic sudis of Zn (II) ions adsorpion Bfor invsigaing h hrmodynamics of Zn (II) ions adsorpion on h drivd composi biosorbns from walnu shll, h ffc of mpraur on h % rmoval of Zn (II) ions from synhic waswar using WSC, AWSC, WSCC and AWSCC as adsorbns was sudid. This is an imporan procss for rmoval of havy mals from indusrial waswar as ffluns ar producd a varying mpraurs in indusrial pracic. Tabl 9 shows h ffc of mpraur on h % rmoval of Zn (II) ions, whr h % rmoval of Zn (II) ions and quilibrium biosorpion capaciy dcrasd wih incrasing mpraur. Hnc, Zn (II) ions adsorpion was xohrmic in naur. I was found ha low mpraur favours h rmoval of Zn (II) ions from waswar for all h prpard biosorbns, wih maximum % rmoval bing 83.8, 78.8, 64.6 and for WSC, AWSC, WSCC and AWSCC rspcivly a 33 K for ph=5, g of adsorbn dosag, Zn (II) ions iniial concnraion of mg/, conac im of h, agiaion spd of 5 rpm and paricl siz of 6 BSS. Th quilibrium adsorpion capaciy dcrasd a mpraur blow 33 K, which suggsd h xohrmic adsorpion naur of Zn (II) ions ono h prpard composi biosorbns (Aksu and Tzr, 5). Thorically, % rmoval of Zn (II) ion on h prpard biosorbns dcrass wih incrasing mpraur owing o adsorpion of alrady adsorbd ions (Zubair al., 8). Th low % rmoval a highr mpraurs may b du o h dsrucion of aciv binding sis (Wik-Krowiak, ). Having sablishd h mpraur dpndnc of h Zn (II) ions rmoval, hrmodynamics sudis wr carrid ou o comprhnd wholly h naur of h adsorpion procss by compuing changs in nhalpy, H, nropy, S and Gibbs fr nrgy, G. This is wih a viw of confirming h xohrmiciy of h Zn (II) ions adsorpion on h prpard composi biosorbns, non-sponaniy and fasibiliy of h adsorpion procss undr invsigaion. Th hrmodynamic quilibrium consan, K, was drmind using h rlaion: c c q K c (3) and h chang in Gibb s fr nrgy was hus calculad by using:

19 Tabl 9. Effc of mpraur on % rmoval of Zn (II) ions and quilibrium biosorpion capaciy. T(K) WSC AWSC WSCC AWSCC q (mg/g) q (mg/g) q (mg/g) q (mg/g) Tabl. Valus of hrmodynamic paramrs for Zn (II) ions adsorpion on prpard composi biosorbns. T/K WSC AWSC WSCC AWSCC G (kj/mol) H S (kj/mol) (kj/(mol K)) G RT In K c (3) Howvr, so G H TS S H In K c R RT Sing and a H RT In K c (33) R Y In K c, X T a S R,,, quaion (33) bcoms: Y ao a X (34) Th rgrssion cofficins, a and a wr drmind using linar rgrssion analysis for ach of h prpard composi biosorbns, and h rsuls obaind ar as follows: For WSC, In K c 64.6 T.68, R. 979 For AWSC, In K c 455.T R. 993 For WSCC, In K c T , R For AWSCC, In K c 5.4 T 8.96, R.999 H and S Thus, valus of wr compud for h Zn (II) ions adsorpion on WSC, AWSC, WSCC and AWSCC as adsorbns, and h rsuls prsnd in Tabl. Th G valus wr posiiv a all mpraurs invsigad, which was an indicaion of h nonsponaniy of h adsorpion of Zn (II) ions on WSC, AWSC, WSCC and AWSCC. Hnc, h Zn (II) ions adsorpion procss was ndogonic. Th ngaiv valus of H for all h prpard composi biosorbns was a confirmaion of h xohrmiciy of h Zn (II) ions adsorpion procss. Th ngaiv valus of S for WSC, AWSC, WSCC and AWSCC usd for Zn (II) ions adsorpion suggsd ha randomnss a h solid/soluion inrfac dcrasd as a rsul of Zn (II) ions adsorpion ono hs adsorbns. Howvr, S valus for all h prpard adsorbns wr narly zro, implying quilibrium condiions wr sablishd during h adsorpion xprimn, and h limiing valu of zro bing rachd only by a rvrsibl procss. Conclusion Composi biosorbns wr drivd from walnu and snail shlls for h adsorpion of Zn (II) ions from h synhic indusrial waswar. Chmical acivaion using phosphoric acid improvd h spcific surfac ara of