Adsorption of Acid blue 25 dye on diatomite in aqueous solutions

Transcription

1 Indian Journal of Chmical Tchnology Vol.17, January 2010, pp Adsorption of Acid blu 25 dy on diatomit in aquous solutions Khashayar Badii 1*, Faramarz Doulati Ardjani 2, Masoud Aziz Sabri 2, Nargs Yousfi Lima 1 & Syd Zia--din Shafai 2 1 Dpartmnt of Environmntal Rsarchs, Institut for Colorants, Paints, and Coatings, Thran, , Iran 2 Faculty of Mining, Ptrolum and Gophysics, Shahrood Univrsity of Tchnology; Shahrood, P.O. Box: , Iran badii@icrc.ac.ir Rcivd 17 April 2009; rvisd 14 Octobr 2009 Th adsorption of Acid blu 25 (AB 25) dy from aquous mdium on diatomit was studid. Th ffcts of ph, contact tim, initial dy concntration, calcinations and sorbnt dosag on th adsorption procss wr xamind and optimum xprimntal conditions wr idntifid. Th maximum rmoval of dy was obtaind undr acidic conditions, in particular, at ph 2, but ph 8 was mor suitabl for industrial purposs. Th prcntag rmoval of dy dcrasd with an incras in initial concntration. Also, th rsults indicatd that an incras in tmpratur raisd th prcntag rmoval of dy. Th maximum prcntag rmoval of AB 25 dy from aquous solution using raw diatomit at ph 2, tmpratur 25±1 C, agitation spd of 200 rpm, initial dy concntration of 50 mg/l, and for a mixing tim priod of 300 min was 72.81% (64.22% at ph 8). Furthrmor, undr sam conditions, th maximum adsorption of dy on calcind diatomit was 54.5%. Th xprimntal data showd that th adsorption of dy on raw diatomit follows th Langmuir modl, but its adsorption on calcind diatomit followd th Frundlich modl. Th kintics ffct of th adsorbnt was psudo-scond-ordr. Kywords: Dy rmoval, Adsorption, Diatomit, Isothrms, Acid blu 25 Contamination of surfac and groundwatr with th txtil industry fflunts is a major concrn to public halth. Synthtic dys, suspndd solids and dissolvd organics ar th main hazardous matrials found in txtil fflunts 1. Ths matrials can affct th physical and chmical proprtis of frsh watr. In addition to th undsirabl colours of txtil fflunts, som dys may dgrad to produc carcinogns and toxic products 2. Furthrmor, th colourd fflunts rduc light pntration and potntially prvnt photosynthsis 3,4. Many tratmnt systms hav bn proposd for th rmoval of synthtic dys from aquous solutions. Coagulation 5, flocculation 6, photocatalytic dgradation 7-9, mmbran filtration 10, microbiological dcomposition 11, lctrochmical oxidation 12, fungus biosorbnt 13 and adsorption 2-5,14-18 ar th most commonly usd mthods for rmoving dys from wast fflunts systms. Adsorption is considrd to b particularly comptitiv, conomically cost ffctiv and fficint procss for th rmoval of dys, havy mtals and othr organic and inorganic hazardous impuritis from aquous solutions Bsids, th microbiological, photocatalytic and lctrochmical dcomposition procdurs ar not fficint bcaus many dys can not b asily dcomposd 12. Although activatd carbon is th most fficint and popular adsorbnt and has bn usd with grat succss, th high cost of activatd carbon somtims rstricts its applicability for dy rmoval 17,20,22. Thrfor, in rcnt yars, considrabl attntion has bn dvotd to th study of diffrnt typs of low-cost and fficint matrials as sorbnt for th rmoval of dys from aquous solutions, which includd wood and saw dust 23,24, fly ash 25, what straw 26, appl pomac 26, orang pl 27-29, banana pl 30, panut hull 3, laf 31, soy mal hull 32, gg shll mmbran 33 tc. AB 25 dy is usd in hug quantitis in Iran and producs many nvironmntal problms. So, to sarch for an appropriat and low-cost adsorbnt is an important considration for dsigning a suitabl tratmnt plant for minimising pollution load. Diatomit (SiO 2.nH 2 O) is a pal-colourd, soft, lightwight silicous sdimntary rock mad up principally from th skltons of aquatic plants calld diatoms. Diatomit contains a wid varity of shap and sizd diatoms, typically µm, in a structur including up to 80-90% por spacs 34. Diatomit s xtrmly porous structur, low dnsity and high surfac ara mak it suitabl as an adsorbnt for organic and inorganic chmicals. Diatomit is found in abundanc in Iran. Svral studis hav bn

2 8 INDIAN J. CHEM. TECHNOL., JANUARY 2010 carrid out on th us of diatomit as an adsorbnt for rmoving som contaminants such as havy mtals 34, basic dy (Mthyln blu) 2, basic and ractiv dys (Mthyln blu, ractiv black, ractiv yllow) 4,35 and som txtil dys (Sif Blau BRF, Evrzol Brill Rd 3BS, Int Yllow 5GF) 36. Furthrmor, th uniqu proprtis of diatomit causd its applications as filtration mdia in a numbr of industris 34,36. Diatomit is approximatly 500 tims chapr than commrcial activatd carbon 36 and has th potntial of bing succssfully usd as a cost-ffctiv altrnativ to activatd carbon. In th prsnt papr, th possibility of utilization of th diatomit in th original or calcind form as an adsorbnt for rmoval of AB 25 dy from an aquous mdium has bn studid. Th quilibrium and kintic study ar invstigatd to obsrv th ffcts of various procss paramtrs such as ph, contact tim, initial dy concntration, tmpratur, calcinations and th sorbnt dosag on th adsorption procss. Equilibrium data ar attmptd by various adsorption isothrms including Langmuir, Frundlich and Brunaur- Emmtt-Tllr (BET) isothrms in ordr to slct an appropriat isothrm modl. Morovr, a kintics study of th adsorption procss is also considrd to dscrib th rat of sorption. Exprimntal Procdur Prparation of adsorbnt Diatomit sampl was obtaind from Tabriz, Iran. Th sampl was washd svral tims with distilld watr to rmov fins and othr adhrd impuritis and to achiv nutralization. Th sampl was finally filtrd, drid at 40 C and stord in closd containrs for furthr us. Th calcination procss was carrid out by placing diatomit sampl in th furnac at 980 C for 4 h. Th sampl was thn allowd to cool in a dsiccator. Th calcind sampl was usd to xamin th ffct of silanol groups and th rol of por siz distribution on th adsorption procss. Ragnts and solutions AB 25 dy was obtaind from Ciba Ltd. and was usd without furthr purification. Th chmical structur of this dy is shown in Fig. 1. Distilld watr was throughout mployd as solvnt. For adsorption xprimnts, various concntrations of dy solutions (50, 100 and 150 mg/l) wr prpard. Th ph masurmnts wr mad using Hach ph mtr. Th ph adjustmnts of th solution wr mad by adding a small amount of HCl or NaOH (1 M). Ths chmicals wr of analar grad and purchasd from Mrck, Grmany. Adsorption procdur Th adsorption xprimnts wr prformd by mixing various amounts of diatomit ( g) in jars containing 250 ml of dy solutions with varying concntrations (ranging from mg/l) and 5 g NaCl at various ph (2-12). Th ph studis wr carrid out to dtrmin th optimum ph at which maximum dy rmoval could b achivd with diatomit. Adsorption xprimnts wr conductd at various concntrations of dy solutions (50, 100 and 150 mg/l) using optimum amount of diatomit (0.9 g) at ph 2, an agitation spd of 200 rpm and tmpratur 25 ±1 C for 5 h to attain quilibrium conditions. An FC6S-VELP (Scintifica) jar tst was usd for agitating purpos. Th changs of absorbanc wr dtrmind at crtain tim intrvals (2, 4, 6, 8, 10, 20, 30, 60, 120, 180, 240, 300 and 1440 min) during th adsorption procss. Aftr adsorption xprimnts, th dy solutions wr cntrifugd for 12 min in a Httich EBA20 cntrifug at 4000 rpm in ordr to sparat th sorbnt from th solution and dy concntration was thn dtrmind. Analysis Th rsidual dy concntrations in aquous mdium wr dtrmind using a CECIL 2021 spctro-photomtr corrsponding to maximum wavlngth (λ max ) of AB 25 dy. Th XRD analysis was prformd on raw and calcind diatomit sampls using a Philips Xprt x-ray diffractomtr. Th sampls wr scannd from 10º to 70º. Scanning lctron microscopic (SEM) of both raw and calcind diatomit wr carrid out using LEO 1455VP scanning lctron microscop bfor and aftr adsorption procss. Fig. 1 Chmical structur of AB 25 dy.

3 BADII t al.: ADSORPTION OF ACID BLUE 25 DYE ON DIATOMITE IN AQUEOUS SOLUTIONS 9 Rsults and Discussion Surfac charactrization In ordr to xplor th surfac charactristics of diatomit, an FTIR analysis was prformd in th rang of 450 to 4000 cm -1. Figur 2 shows th infrard spctra of raw and calcind diatomit sampls. In th first spctrum ( Raw curv in Figur 2), th pak positions showing major adsorption bands wr obsrvd at 3846, 3736, 3615, 3590, 3564, 3444, 2929, 2867, 1638, 1087, 794, 696, 523 and 470 cm -1. Th bands at 3846 and 3736 cm -1 illustrat th H atom that is attachd to htroatoms (Si-H). Th paks at 3615, 3590, 3564, 3444, 2929 and 2867 cm -1 ar du to th fr silanol group (Si-O-H), th band at 1638 cm -1 rprsnts H-O-H bnding vibration of watr, th band at 1087 cm -1 rflcts th siloxan (-Si-O-Si-) group strtching, th bands at 794 and 696 cm -1 corrspond to SiO-H vibration. Th pak positions of 523 and 470 cm -1 ar attributd to th Si- O-Si bnding vibration. Th pak positions of th major bands in th spctrum of calcind diatomit (mntiond as Calcind in Figur 2), is sn mor or lss at th sam position as in th spctrum of raw diatomit. In addition, thr is a small pak at 2364 cm -1. It can b a trac of ammonia ions bcaus of calcinations at high tmpratur and xistnc of nitrogn in air. Comparison of ths two spctra shows that thr is only slight diffrnc btwn th band positions of ths two adsorbnts, spcially at 2364 cm -1 position that it is not vry important on adsorption procss. Th most important diffrnc of ths spctra is in th intnsity of th fr silanol group. It mans that th amount of this group in raw diatomit is mor than th calcind on. This group is rsponsibl for th adsorption procss. Scanning lctron micrographs of raw and calcind diatomit ar shown in Figs. 3 and 4 rspctivly. As vidnt from Fig. 3, raw diatomit has considrabl numbrs of por spacs whr dys can b adsorbd into ths rlativly larg pors. An important chang in th surfac charactristics and th siz of th por spacs of th diatomit is sn aftr calcination procss at 980 C, as vidnt from Fig. 4, th thrmal tratmnt of th diatomit rducd th volum of th por spacs and dcrasd th surfac functional groups from th raw diatomit (FTIR spctra). Morovr, th solid structur of diatomit bcoms mor visibl. As a rsult, th adsorption of dy by calcind diatomit is dcrasd. Fig. 2 FT-IR of raw and calcind diatomit. Fig. 3 Scanning lctron micrographs of raw diatomit. Aadsorbnt dosag = 0.9 g, Tmpratur= 25 ± 1 C, quilibrium tim=5 h, agitation spd = 200 rpm. Fig. 4 Scanning lctron micrographs of calcind diatomit. Adsorbnt dosag = 0.9 g, Tmpratur= 25 ± 1 C, quilibrium tim=5 h, agitation spd = 200 rpm.

4 10 INDIAN J. CHEM. TECHNOL., JANUARY 2010 XRD analysis rsults of th raw and calcind diatomit ar shown in Fig. 5. It can b sn from Fig. 5 that th x-ray pattrn of th raw diatomit is diffrnt from th pattrn of th calcind diatomit, suggsting that a phas transformation probably occurrd during th calcinations procss. Th main composition of raw diatomit is quartz, anorthit and muscovit. It is vidnt that sanidin was appard; whil anorthit and muscovit wr compltly rmovd as th diatomit was calcind at 980 C. In fact, som paks in th diatomit disappard and som paks wr cratd by calcination procss. Similar bhaviour was prviously invstigatd by othr rsarchrs 4. Th surfac ara of th diatomit was dtrmind by BET mthod. In this invstigation, th valus and 7.5 m 2 /g wr calculatd for raw and calcind diatomit rspctivly. A particl siz analysis was carrid out to dtrmin th distribution of particls of th adsorbnt. Th maximum distribution of particls is varid from 10 to 40 µm. Effct of adsorbnt dosag Th adsorption of AB 25 dy on raw and calcind diatomit dosag was invstigatd at 25 ± 1 C by varying th adsorbnt amount from 0.2 to 1.1 g whil kping th volum of dy solution constant qual to 250 ml, with an initial dy concntration of 50 mg/l. Figur 6 shows th prcntag rmoval of AB 25 dy vrsus adsorbnt amount. As it is clar from th figur, th prcntag rmoval of dy incrasd with an incras in th adsorbnt amount. Th main rason for this fact is du to th gratr availability of th adsorption sits at highr concntrations of th adsorbnt 36. Basd on th rsults shown in Fig. 6, 0.9 g of th raw and calcind diatomit was usd for furthr xprimnts. Effct of initial dy concntration A chang in th initial dy concntration can considrably affct th adsorption procss. Figur 7 Fig. 5 XRD pattrns of (a) raw and (b) calcind diatomit. Q: Quartz, A: Anorthit, M: Muscovit and S: Sanidin.

5 BADII t al.: ADSORPTION OF ACID BLUE 25 DYE ON DIATOMITE IN AQUEOUS SOLUTIONS 11 Fig. 6 Effct of adsorbnt dosag on th prcntag rmoval of AB 25 dy by raw and calcind diatomit. Tmpratur = 25 ± 1 C, initial dy concntration = 50 mg/l, ph = 2, agitation spd = 200 rpm. Fig. 7 Effct of initial dy concntration on adsorption of AB 25 dy by raw diatomit. Contact tim = 300 min, Tmpratur= 25 ± 1 C, ph = 2, agitation spd = 200 rpm. dpicts th ffct of dy concntration on th prcntag rmoval of AB 25 dy by diatomit. As it is vidnt from th figur, whn th dy concntration was incrasd from 50 to 150 mg/l, th prcntag rmoval of AB 25 dy dcrasd from to 47.3%. As xpctd, whn th concntration of dy is incrasd, th limitd capacity of th adsorbnt chcks any furthr adsorption of dy and hnc th ovrall rmoval prcntag dcrass. Th quilibrium controls th maximum adsorption and dcrass th final rmoval prcntag du to incrasing amount of dy. Effct of contact tim Th adsorption of AB 25 dy onto diatomit was valuatd as a function of contact tim. Figur 8 shows th ffct of contact tim on th prcntag rmoval of AB 25 dy in th aquous phas by raw (Fig. 8a) and calcind diatomit (Fig. 8b). Th initial Fig. 8 Effct of contact tim on adsorption of AB 25 dy on (a) raw and (b) calcind diatomit. Tmpratur = 25 ± 1 C, ph = 2, agitation spd = 200 rpm, adsorbnt dosag = 0.9 g. dy concntration was varid from 50 to 150 mg/l. At all initial dy concntrations invstigatd, th adsorption occurs vry fast initially. Aftr 2 min of adsorption procss, th amount of adsorption by raw diatomit rachs to 84, 89 and 73% of th ultimat adsorption of AB 25 dy for initial dy concntrations of 50, 100 and 150 mg/l rspctivly. As illustratd in Fig. 8b, th adsorption is also fast at arly stag of th adsorption procss for calcind diatomit. Typically about 95% of th ultimat adsorption of AB 25 dy with an initial concntration of 50 mg/l taks plac within th first 2 min of contact and it almost rmains constant thraftr. It mans that th most of mass transfr rsistanc is in bulk of fluid and high rat agitation would dcras this rsistant. In addition, ths rsults show that most of th dy molculs ar adsorbd on th outsid surfac of th adsorbnt, and transfrrd to th pors and intrnal surfacs layr. Mor xprimnts ar ncssary to b carrid out to prov this invstigation.

6 12 INDIAN J. CHEM. TECHNOL., JANUARY 2010 Adsorption isothrms Th distribution of dy btwn th adsorbnt and th dy solution at quilibrium is important in stablishing th capacity of th adsorbnt for dy rmoval from aquous systms. Th adsorption isothrms of AB 25 dy on both raw and calcind diatomit ar shown in Fig. 9. It is clarly sn from Fig. 9 that th amount of adsorbd AB 25 dy on calcind diatomit was much lowr than that of raw diatomit. Rsults of FTIR, SEM, XRD and BET show that th important functional groups, such as fr silanol, and siz of pors dcrasd and th structur of diatomit changd. Th BET tst illustratd that th surfac ara of diatomit dcrasd 17.3 tims aftr calcination procss. Thrfor, th amount of th xisting surfac ara is th most important diffrnc btwn raw and calcind diatomit. Th xprimntal data obtaind wr valuatd by various isothrm modls incorporating Langmuir, Frundlich 5,13,17 and Brunaur-Emmtt-Tllr (BET) 13,37 isothrms. Langmuir isothrm is applicabl for monolayr adsorption on a surfac containing a finit numbr of idntical adsorption sits 17. A linar xprssion for th Langmuir isothrm is as follows: 1 1/ q = ( 1/ C ) + 1/ Q0 K L Q (1) 0 whr C is th concntration of dy undr quilibrium condition (mg/l), q dnots th amount of dy adsorbd at quilibrium (mg/g), Q 0 indicats th maximum adsorption capacity and K L is th Langmuir isothrm constant (l/mg). Th valus of K L and Q 0 wr calculatd from th slop and intrcpt of th linar plot of 1/q vrsus 1/ C. Fig. 9 Adsorption isothrms of AB 25 dy onto raw and calcind diatomit. Frundlich quation was also applid for th adsorption of AB 25 dy on diatomit as givn blow: q F 1 n = K C (2) whr C is th quilibrium dy concntration in aquous systm (mg/l), q is th amount of dy adsorbd pr wight of th adsorbnt usd (mg/g), K F and n ar Frundlich isothrm constants incorporating all factors affcting th adsorption procss. Taking log 10 from both sids of th Eq. (2) yilds th following quation: 1 log 10 q = log10 K F + log10 C (3) n Although not shown hr, linar plot of log 10 q vrsus log 10 C givs th valus of K F and n. Brunaur-Emmtt-Tllr (BET) modl was also usd to fit th adsorption data according to th linar form of its rarrangd adsorption isothrm modl, which may b xprssd as: C 1 K b 1 C = + ( C ) s C q K b qm K b qm Cs (4) whr C is th concntration of dy in solution (mg/l), C s dnots th saturation concntration of dy (mg/l), q is th amount of dy adsorbd pr wight of th diatomit usd (mg/g), q m is th amount of dy adsorbd in forming a complt monolayr (mg/g), K b indicats a constant xplaining th nrgy of intraction with th surfac. Th valus of K b and q m wr calculatd from th slop and intrcpt of th C 1 C linar plot of CS C vrsus. q CS Th dtrmind constants and th corrlation cofficints of th Langmuir, Frundlich and BET isothrms ar includd in Tabl 1. Th ngativ valus of K b rlatd to th BET isothrm modl dscrib that th adsorption procss did not follow th BET isothrm modl. It is vidnt from Tabl 1 that th isothrm data for th adsorption of AB 25 dy by raw diatomit wr bst-fittd using Langmuir modl with a corrlation cofficint of Furthrmor, th Frundlich modl is most appropriat for th adsorption of AB 25 dy on calcind diatomit with a corrlation cofficint of In addition, it is clar from Tabl 1 that th adsorption capacity of raw

7 BADII t al.: ADSORPTION OF ACID BLUE 25 DYE ON DIATOMITE IN AQUEOUS SOLUTIONS 13 Tabl 1 Paramtrs of various isothrms for adsorption of AB 25 dy onto raw and calcind diatomit. Langmuir Frundlich BET Adsorbnt Q 0 K L R 2 K F 1/n R 2 K b q m R 2 Raw diatomit Calcind diatomit diatomit is mor than calcind diatomit. Th Langmuir isothrm (or quilibrium) constant (K F ) and th maximum adsorption capacity (Q 0 ) for raw diatomit ar 2.2 and 2.3 tims mor than calcind on, rspctivly. Adsorption kintics Th prdiction of th adsorption kintics of dy from aquous systm is important in ordr to dsign a suitabl tratmnt systm. Th kintics of adsorption of AB 25 dy on diatomit may b dscribd by th psudo-first-ordr Lagrgrn rat quation 3,13,17 and th psudo-scond-ordr rat xprssion dvlopd by Ho and McKay 38. Th Lagrgrn quation is: log K t (5) , ad ( q q ) = logq t whr q and q t ar th amounts of dy (mg/m) adsorbd at quilibrium and at tim t (min) and K 1,ad is th psudo-first-ordr rat constant ( 1 / min ). Th Ho and McKay quation is givn blow: t q 1 = 2 t K 2, ad q + t q (6) whr q and q t ar th amounts of dy (mg/m) adsorbd at quilibrium and at tim t (min) and K 2,ad is th rat constant of th psudo-scond-ordr modl (g/mg min). Linar plot of log 10 ( q q t ) against t givs th rat constant of K 1,ad. Morovr, th valu of K 2,ad is obtaind from th intrcpt of th linar plot of t/qt vrsus t. Adsorption kintics constants of th psudo-firstordr and psudo-scond-ordr modls at ph 2, tmpratur 25 ± 1 C, an agitation spd of 200 rpm, an initial concntration of 50 mg/l and for a tim priod of 300 min ar givn in Tabl 2. As Tabl 2 shows, th high valus of corrlation cofficints of th psudo-scond-ordr modl for both raw and calcind diatomit showd that th adsorption data conformd wll to th Ho and McKay kintics modl [Eq. (6)]. Effct of ph Th ph is th most important factor affcting th adsorption procss. Th ph studis wr conductd to dtrmin th optimum ph at which maximum colour rmoval could b achivd with diatomit for AB 25 dy. Th ffct of ph was obsrvd by studying th adsorption of dy ovr a broad ph rang of Th rsults ar shown in Fig. 10. As dpictd in figur, for both raw and calcind diatomit, th amount of AB 25 dy adsorbd was maximum at ph 2. Th dy rmoval dcrasd as th solution ph was incrasd from 2 to 4. Th amount of dy sorbd incrasd slightly whn ph was raisd from 4 to 6. From ph 6 to 8, th dy rmoval incrasd again by raw diatomit and rachd to mg/g at ph 8. But, in this rang of ph (6-8), th amount of dy sorbd on calcind diatomit rmaind constant, qual to 2.65 mg/g. Th adsorption of AB 25 dy dcrasd from to 9.04 mg/g with incrasing ph of dy solution from 8 to 12 whn raw diatomit was usd as th adsorption mdium, whras, th quantity of dy sorbd incrasd from 2.63 to 7.08 mg/g in th ph rang of 8 to 12 using calcind diatomit as adsorbnt. Bcaus th maximum dy adsorption occurrd at a ph of 2 and th corrsponding sorption capacitis wr and 8.08 mg/g for raw and calcind diatomit rspctivly, so th ffctiv ph was 2 and it was usd in all adsorption xprimnts. Th Ho and McKay linar plots wr obtaind for various ph rangd from 2 to 12. Th rsults ar shown in Fig. 11 for raw diatomit. Th kintics constants of th psudo-first-ordr and psudo-scond-ordr modls at diffrnt ph of th dy solution ar givn in Tabl 3 for raw and calcind diatomit. Ths paramtrs wr achivd from th Lagrgrn and Ho and McKay plots. At any ph and for both raw and calcind diatomit, th high valus of corrlation cofficints man that th adsorption procss follows th psudo-scond-ordr kintic modl. Effct of tmpratur Th tmpratur has a significant ffct on th adsorption procss. Incrasing th tmpratur will chang th quilibrium capacity of th adsorbnt for a

8 14 INDIAN J. CHEM. TECHNOL., JANUARY 2010 Tabl 2 Kintic constants for AB 25 dy adsorption by raw and calcind diatomit. Psudo-first-ordr Psudo-scond-ordr Adsorbnt q (mg/g) K 1,ad (1/min) R 2 q (mg/g) K 2,ad (g/mg min) R 2 Raw diatomit Calcind diatomit Tabl 3 Kintics constants of AB 25 dy adsorption onto raw and calcind diatomit at diffrnt ph. Psudo-first-ordr kintic constants Psudo-scond-ordr kintic constants Adsorbnt ph K 1,ad q R 2 K 2,ad q R Raw diatomit Calcind diatomit Fig. 10 Effct of ph on th adsorption of AB 25 dy by raw and calcind diatomit. Agitation spd = 200 rpm, Tmpratur=25 ± 1 C, quilibrium tim = 300 min. particular adsorbat. Furthrmor, an incras in tmpratur can rais th rat of diffusion of th dy molculs in th intrnal pors of th adsorbnt 15. In this study, th rmoval of AB 25 dy from aquous solution using diatomit has bn invstigatd at four diffrnt tmpraturs rangd from 25 to 55 C. Th Ho and McKay linar plots ar shown in Fig. 12 for diffrnt tmpraturs and for raw diatomit. Th kintics paramtrs of adsorption at diffrnt tmpraturs ar also givn in Tabl 4 for raw and calcind diatomit. From Tabl 4, it can b obsrvd Fig. 11 Psudo-scond-ordr sorption kintics of AB 25 dy onto raw diatomit at various ph. Agitation spd = 200 rpm, initial dy concntration = 50 mg/l, Tmpratur=25 ± 1 C. that at any tmpratur and for both raw and calcind diatomit, th adsorption procss follows th psudoscond-ordr kintic modl. Howvr, th adsorption of AB 25 dy on calcind diatomit at tmpratur 55 C may follow th psudo-first-ordr kintics modl. It is also vidnt from Fig. 12 that adsorption incrass with th incras in tmpratur. At 55 C, th prcntag rmoval of AB 25 dy from aquous solution is 89.75% aftr a procss tim of 300 min, whras at 25 C this valu is 72.81%. Hnc, incras in tmpratur favours th adsorption procss.

9 BADII t al.: ADSORPTION OF ACID BLUE 25 DYE ON DIATOMITE IN AQUEOUS SOLUTIONS 15 Tabl 4 Kintic constants of AB 25 dy adsorption onto raw and calcind diatomit at diffrnt tmpraturs. Psudo-first-ordr kintic constants Psudo-scond-ordr kintic constants Adsorbnt T( C) K 1,ad q R 2 K 2,ad q R Raw diatomit Calcind diatomit Fig. 12 Psudo-scond-ordr sorption kintics of AB 25 dy onto raw diatomit at diffrnt tmpraturs. Agitation spd = 200 rpm, initial dy concntration = 50 mg/l, ph = 2. Conclusions Diatomit has bn studid for rmoval of AB 25 dy from aquous solution. Thrmal tratmnt of th adsorbnt at 980 C advrsly affcts its adsorption capacity du to th rduction of th volum of th por spacs and rmoval of th surfac functional groups from th raw diatomit. Th adsorption procss was also influncd by solution ph and tmpratur. Th maximum sorption capacity occurrd at ph 2, but thr is no big diffrnc btwn ph 2 ( q = mg / g at 25 C) and 8 ( q = mg / g at 25 C). Th adsorption of AB 25 dy by diatomit incrasd with an incras in tmpratur. Equilibrium data for th adsorption of AB 25 dy by raw diatomit fit wll to th Langmuir isothrm modl. Furthrmor, th Frundlich modl is most appropriat for th adsorption of AB 25 dy on calcind diatomit. In addition, th rat of adsorption procss obys th psudo-scond-ordr kintics modl. It was found that in ordr to obtain th highst possibl rmoval of AB 25 dy, th xprimnts can b carrid out at ph 2, tmpratur 25 C, an agitation spd of 200 rpm, an initial dy concntration of 50 mg/l, a cntrifugal rat of 4000 rpm and a procss tim of 300 min. Undr ths conditions, a maximum prcntag rmoval of (with a mass AB 25 dy rmovd/mass diatomit of mg/g) and 54.5% (with a mass AB 25 dy rmovd/mass diatomit of 8.08 mg/g) can thrfor b obtaind for AB 25 dy from aquous solution using raw and calcind diatomit rspctivly; but th high acidic solution (ph 2) would caus a high corrosion ffcts and it is suggstd that th pilot and industrial cass would b carrid out at ph 8, tmpratur 25 C, an agitation spd of 200 rpm, an initial dy concntration of 50 mg/l, a cntrifugal rat of 4000 rpm and a procss tim of 300 min by raw diatomit. In such cas, th rmoval prcntag is Th rsults prsntd hr can hlp to dsign an appropriat rmdiation plan to minimis th unfavourabl impacts causd by industrial fflunts containing AB 25 dy. Acknowldgmnt Th authors ar thankful to Institut for Colorants, Paints & Coatings (ICPC) for providing th financial hlp and to Shahrood Univrsity of Tchnology, for supporting this rsarch. Rfrncs 1 Bnkli Y E, Can M F, Turan M & Çlik M S, Watr Rs, 39 (2005) Shawabkh R A & Tutunji M F, Appl Clay Sci, 24 (2003) Gong R, Ding Y, Li M, Yang C, Liu H & Sun Y, Dys Pigm, 64, (2005) Khraishh M A M, Al-Ghouti M A, Alln S J & Ahmad M N, Watr Rs, 39 (2005) Vnkata Mohan S, Sailaja P, Srimurali M & Karthikyan J, Environ Eng Pol, 1 (1999) Panswd J & Wongchaisuwan S, Watr Sci Tchnol, 18 (1986) Chun H & Yizhong W, Chmosphr, 39 (1999) Hachm C, Bocquillon F, Zahraa O & Bouchy M, Dys Pigm, 49 (2001) 117.

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