Fixed-bed Column Study of Textile Dye Direct Blue 86 by using A Composite Adsorbent

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1 Availabl onlin at Archivs of Applid Scinc Rsarch, 212, 4 (2): ( ISSN X ODEN (USA) AASR9 Fixd-bd olumn Study of Txtil Dy Dirct Blu 86 by using A omposit Adsorbnt Monal Dutta, Jayanta Kumar Basu*, Md Hassan Faraz, Nitin Gautam and Adarsh Kumar Indian Institut of Tchnology, Kharagpur, India ABSTRAT In th prsnt study, th adsorption of a txtil dy dirct blu 86 was studid through a fixd-bd column by using a carbon-alumina composit pllt. Th adsorbnt was dvlopd by using microwav assistd activatd carbon and commrcial alumina. In ordr to find out th batch adsorption charactristics various adsorption isothrms such as, Langmuir, Frundlich and Tmpkin wr invstigatd and th corrsponding monolayr capacity was found to b 5.16 mg/g. Th fixd bd column was usd to invstigat th dynamic adsorption charactristics whr th ffcts inlt dy concntration (5 2 mg/l), fd flow rat (5 15 ml/min) and activatd carbon bd hight ( cm) on th adsorption brakthrough wr also invstigatd. Th maximum rmoval capacity in th column study was found to b mg/l with an initial dy concntration and flowrat of 1 mg/l and 12 ml/min according to Bohart-Adams modl. Th brakthrough bhavior was also ffctivly dscribd by th Yoon-Nlson and lark modl. Kyword: Dirct blu; arbon alumina paltt; Euilibrium study; olumn study; Bohart-Amams modl; Yoon- Nlson modl; lark modl. INTRODUTION In th rcnt ra of tchnological and industrial advancmnt, th introduction of various colord compounds into diffrnt watr bodis caus svr imbalanc to auatic nvironmnt [1, 2]. Ths colord substancs ar mainly originatd from diffrnt txtil, lathr, papr, food and cosmtic industris. It has bn stimatd that ovr 7 x 1 5 tons of dys producd annually worldwid and narly 2% of ths dys ar dischargd dirctly into th watr bodis which may prov dtrimntal to auatic lif du to th prsnc of mtals and chlorids in thm [3]. Morovr dys may b mutagnic or carcinognic and if contactd, can caus svr damag to human bings such as malfunction of kidny, rproductiv systm, livr, brain and cntral nrvous systm. [4]. Among such dys Dirct Blu 86 (DB 86) is a wll known anionic dy usd for various purposs such as dying of cllulosic fibrs lik cotton, flax, viscos rayon, actat and jut. It is also applicabl for lathr and papr coloration. Wast watr containing dys cannot b tratd asily as thy ar chmically vry stabl. Hnc thy nd to b rmovd. Various rmoval tchnologis lik adsorption, photo-dgradation, coagulation, flocculation, chmical oxidation, lctro-chmical oxidation, biological procss tc. ar availabl for th rmoval of dy from th wastwatr [5, 6]. But adsorption by activatd carbon is worth mntioning amongst all bcaus of its as of procssing and ability to adsorp a larg varity of adsorbat [7]. ommrcial activatd carbon is widly usd to rmov various adsorbats but its high cost limits its widsprad us. Thrfor, sarch for an altrnativ low cost raw matrial for making activatd carbon has bcom vry important now a day. In th prsnt invstigation, an activatd carbon was dvlopd from th scrap 882

2 Jayanta Kumar Basu t al Arch. Appl. Sci. Rs., 212, 4 (2): wood of Acacia Auriculiformis for th rmoval of txtil dy Dirct Blu 86 (DB 86). Gnrally, in th batch adsorption study th adsorbnt is usd in its powdrd form which has th grat disadvantag of sparation aftr bing usd. To ovrcom this difficulty, th carbon may b usd in its plltizd form. On th othr hand, a continuous flow procss using a packd bd is mor advantagous for th tratmnt of wast watr on a larg scal. A lot of litratur is alrady availabl on th batch adsorption study but non on fixd bd adsorption of a txtil dy using Acacia Auriculiformis as th prcursor matrial for activatd carbon. Thrfor, in th prsnt study, th adsorption charactristics of DB 86 wr invstigatd in a fixd bd column by using microwav assistd activatd carbon. Th ffcts of diffrnt procss paramtrs such as, dy flowrat, bd hight and inlt dy concntration on th brakthrough pattrn wr also invstigatd. Th adsorption brakthrough bhavior was analyzd by using Yoon-Nlson, lark and Bohart-Adams modl. MATERIALS AND METHODS 2.1. Raw matrials Th scrap wood of Acacia Auriculiformis slctd for this work, was collctd from local saw mill. Hydrochloric acid and ammonia wr procurd from Mrck Spcialitis Privat Limitd, Mumbai, India Prparation of activatd carbon Th char was prpard by carbonization of Acacia Auriculiformis scrap wood in an inrt atmosphr. Th wood scrap was first cut into small pics of 2 mm width and 4 mm of lngth, cland with distilld watr and was sun drid for 24 h prior to th carbonization. Th wood pics wr kpt on a cramic boat which was placd at th cntr of a 4-mm i.d tubular furnac. Th matrial was thn hatd from ambint tmpratur to th carbonization tmpratur of 75 at th rat of 4 /min in a continuous flow of N 2 (3 ml/min) and thn it was kpt at this tmpratur for 1h for subsunt activation. It was thn allowd to cool to ambint tmpratur in prsnc of N 2 flow. Th char (75N) was sivd to obtain th dsird siz fractions and stord in a dsiccator ovr silica gl. Th 75N was furthr activatd in a domstic microovn (IF2PG3S) for fiv minuts at a constant input powr of 8 W and a fruncy of 245 MHz. Aftr trating in th microovn 75N was trmd as A75NMW Prparation of th composit adsorbnt Microwav assistd activatd carbon (A75NMW5) and commrcial alumina powdr was mixd thoroughly with PVA in a wight ratio of 2:2:1.5. Thn, th slurry was prpard by adding a small uantity of watr which was thn hatd up to 9 for 3 min in a constant tmpratur watr bath and th hating procss was carrid out till a sticky mass was formd. Thn th sticky mass was shapd into sphrical pallts. Th pllts wr kpt ovrnight in an air ovn at 11 and placd in tubular furnac whr ths wr hatd up to 3 for 2 h in a flow of nitrogn (3 ml/ min). Th pllts wr kpt at to 3 for 1 h for subsunt activation. Th rsulting pllts wr thn coold to room tmpratur and stord in a dsiccator ovr silica gl. Th prpard pllts wr trmd as carbon-alumina composit pallts (AP) haractrization of activatd carbon Th surfac ara and th total por volum of th prpard char and th activatd carbon wr dtrmind by using N 2 adsorption-dsorption mthod by using Brunaur Emmtt Tllr (BET) apparatus (Autosorb-1, Quantacrom) Euilibrium and kintic study of DB-86 Th monolayr adsorption capacity of th prpard char for dirct blu-86 (DB-86) was dtrmind by th uilibrium study. Th uilibrium study was carrid out by adding.1 g of adsorbnt into a sris of 25 ml conical flask containing 1 ml solution of dirct blu 86 and was shakn for 36 h at room tmpratur. Aftr this th sampls wr cntrifugd and th concntrations wr analyzd in a UV-Vis spctrophotomtr. Th kintic study was carrid out by analyzing adsorptiv uptak of th dy from auous solution at diffrnt tim intrvals. Th adsorptiv capacity of diffrnt adsorbnts was compard through batch adsorption. Th uilibrium adsorption capacity was calculatd from th rlationship ( ) = V w (1) 883

3 Jayanta Kumar Basu t al Arch. Appl. Sci. Rs., 212, 4 (2): Whr, (mg/g) is th uilibrium adsorption capacity, is th dy concntration at uilibrium (mg/l/), V is th volum of solution (l) and w is th wight of adsorbnt (g) Exprimntal st-up Th fixd-bd column was mad of Pyrx glass tub of 1.3cm innr diamtr and 17 cm hight. Th column was packd with AP followd by a layr of glass bads on both th sid to provid uniform flow of solution. To avoid ntrapping of air bubbls insid th A pllts, th particls wr soakd in appropriat amount of watr and agitatd until no air bubbls wr dtctd in th solution. A known uantity of th prpard adsorbnt was packd in th column to yild th dsird bd hight of 2.54, 7.62 and 1.16 cm. Dy solution of known concntrations (5, 1 and 2 mg/l) at ph 1.5 was allowd to flow through th column at a dsird flow rat of 5, 1 and 15 ml/min. Th aliuot of th DB-86 solution was collctd at th outlt of th column at rgular tim intrvals and th rsidual dy concntration was masurd using a doubl bam UV visibl spctrophotomtr (Spctra scan UV 26, hmito, India).at 619 nm. All xprimnts wr carrid out at tmpratur of 28± Analysis of fixd-bd column data Th dynamic adsorption charactristics in a fixd-bd column wr studid through analyzing th shap of th xprimntal brakthrough curvs. Th xprimntal brakthrough curvs show th loading bhavior of th adsorbat on a fixd-bd column. Thy ar gnrally xprssd in trms of normalizd dy concntration, dfind as th ratio of instantanous or outlt adsorbat concntration to th initial adsorbat concntration ( t / ) as a function of tim for a givn bd hight or adsorbat flowrat [8]. Th fflunt volum (V ff ) can b calculatd as V ff = Qt total (2) Whr, t total and Q ar th total tim takn for th flow of adsorbnt (min) and volumtric flow rat (ml/min). Th total amount of dy adsorbd total (mg) for a givn bd hight, fd concntration and flow rat is can b dtrmind as: total Q = 1 t= tt otal t= ad dt (3) Bsids, th uilibrium uptak (mg/g) or maximum capacity of th column can b calculatd as [9]: total = (4) w Whr, total and w ar th th total amount of dy adsorbd ( total ) and amount of adsorbnt (mg) Data analysis Th xprimntal data wr analyzd using Origin Pro (vrsion 8) computr softwar. Th goodnss of fit was masurd through th rgrssion cofficint (R 2 ). RESULTS AND DISUSSION 3.1. haractrization of th prpard adsorbnts Th BET surfac ara (S BET ), total por volum (V tot ) and avrag por siz of 75N and A75NMW5 wr dtrmind from th physical adsorption data of N 2 at 77 K and th valus ar shown in Tabl 1. It can b sn from Tabl 1 that A75NMW5 has th highst surfac ara and total por volum. Insid th microovn a high tmpratur could b rachd in comparativly shortr priod of tim rsulting dissipation of hug amount of nrgy at a molcular lvl. onsuntly, th roughnss of th por walls may also b incrasd du to rapid hating with th formation of additional activ sits [1]. Bsids, rapid hating could acclrat th rlas of tar or volatil mattr from th por intrior which rsults into highr por volum [11]. 884

4 Jayanta Kumar Basu t al Arch. Appl. Sci. Rs., 212, 4 (2): Tabl-1: omparison of surfac proprtis of 75N and A75NMW5 Adsorbnt Surfac ara Total por volum (m 2 /g) (cc/g) Avrag por diamtr (Å) 75N A75NMW Euilibrium studis of DB-86 using A75NMW5 In ordr to invstigat th adsorption charactristics th xprimntal data wr fittd to Frundlich, Langmuir, Tmpkin and Harkins-Jura isothrms and th corrsponding uilibrium plot is shown in Fig (mg/g) Exprimntal data points Langmuir isothrm Frundlich isothrm Tmkin isothrm (mg/l) Fig. 1. Euilibrium isothrm for Db 86 Th Langmuir isothrm rprsnts th uni-molcular adsorption of th adsorbat molcul on th adsorbnt surfac [12]. Th modl can b xprssd as: = + (5) K lq Q Whr, is th uilibrium adsorption capacity, is th uilibrium dy concntration, K l is th Langmuir constant rlatd to th nrgy of adsorption (l /mg) and Q is th maximum amount of adsorption corrsponding to complt th monolayr covrag on surfac (mg/g). Th xprimntal data fittd to Langmuir modl and th corrsponding monolayr adsorption capacity was 5.16 mg/g. Similarly, th Frundlich isothrm can b usd for non-idal sorption that involvs htrognous surfac nrgy systms [13] and is xprssd by th following uation: log = log K + F 1 log n Whr, K F is a rough indicator of th adsorption capacity and 1/n is th adsorption intnsity. In gnral, with th incras of th adsorption capacity K F valu incrass. Th Tmpkin isothrm dscribs th hat of adsorption and intraction btwn adsorbnt-adsorbat molculs [14]. Th Tmpkin isothrm can b xprssd as: = B 1 ln kt + B1 ln (7) Whr, k T and B 1 ar Tmpkin isothrm constant. Th paramtrs valus of diffrnt isothrms ar shown in Tabl 2. (6) 885

5 Jayanta Kumar Basu t al Arch. Appl. Sci. Rs., 212, 4 (2): Tabl 2 Euilibrium modl paramtrs Isothrm modl Kintic paramtrs Frundlich K F = 38.36; n = 2.6; R 2 =.93; χ 2 = = K F 1/ n Langmuir K l =.3; Q = 5.16; R 2 =.98; χ 2 = 295. K lm = 1+ K l Tmpkin Km =.32; B = 12.59; R 2 =.96; χ 2 = = K log( h ) m Fig. 2. Brakthrough curvs for DB 86 adsorption at diffrnt inlt concntrations (bd hight = 7.62 cm, flow rat = 12mL/min, tmpratur = 28±1 ) Th fixd-bd study Effct of initial dy concntration Th ffct of initial dy concntrations was studid by varying th dy concntration from 5 2 mg/l with an adsorbnt bd hight of 7.62 cm whras th flowrat was kpt constant at 12 ml/min. Th ffct of initial concntration is shown in Fig. 2 by th adsorption brakthrough curv. It was sn from Fig. 2 that th valu of t/o incrasd from.66 to.73 with an incras in inlt concntration from 5 to 1 and 2 mg/l. It was furthr obsrvd that th brakthrough tim slightly dcrasd with incrasing inlt dy concntration. This may b 886

6 Jayanta Kumar Basu t al Arch. Appl. Sci. Rs., 212, 4 (2): attributd to th fact that at lowr inlt concntrations, brakthrough occurrd slowly but with incras in inlt concntration th brakthrough tim dcrasd. Th driving forc for mass transfr was also incrasd with incras in inlt dy concntration which in turn incrasd th adsorption capacity. onvrsly, th rat of mass transfr got rducd at lowr inlt concntration rsulting into slowr transport. Thrfor it can b concludd that th adsorption procss is concntration dpndnt [15]. Similar rsults wr obtaind for biosorption of ractiv black by bamboo wast basd activatd carbon [16] and for th rmoval of acid dy using pristin and acid-activatd clays [17] Effct of th solution flow rat Th adsorbat flowrat had a significant ffct on DB-86 adsorption in th fixd bd column. Th ffct of flowrat was shown in Fig. 3 with th hlp of xprimntal brakthrough curv. Th flow rat was varid from ml/min with a constant bd hight and initial concntration of 7.62 cm and 1 mg/l rspctivly. It was sn from Fig. 3 that brakthrough occurrd at comparativly fastr rat at highr adsorbat flowrat and lss tim was takn to rach th saturation brakthrough. Th possibl rason may b at highr adsorbat flowrat DB-86 had lss tim to contact with th activatd carbon bd which rsultd into stpr brakthrough curv. This phnomnon can also b xplaind in th vicinity of mass transfr fundamntals. Th rat of mass transfr gts incrasd at highr flowrat lading to fastr saturation [18]. onvrsly, th adsorption capacity is dcrasd with incras in flowrat du to shortr rsidnc tim of th adsorbat molcul in th fixd bd column. Thrfor, th surfac of th activatd carbon nvr gts saturatd with th adsorbat molculs and as a rsult th uilibrium nvr rachd. Th rsults obtaind in th prsnt invstigation ar in wll agrmnt with th rsults obtaind by Zulfadhly t al. [19] whr macro fungus Pycnoporus sanguinus was usd to adsorb havy mtals (Pb, u and d) from auous solution in fixd-bd column at various flow rats. Fig.3. Brakthrough curvs for DB 86 adsorption at diffrnt flow rats (inlt Db 86 concntration = 1 mg/l, bd hight = 7.62 cm, tmpratur = 28±1 ) Effct of activatd carbon bd hight Th ffct of bd hight is shown in Fig.4. Th ffct of bd hight was studid at an initial dy concntration of 1 mg/l and a flowrat of 12 ml/min rspctivly. Th Bd hight was varid from cm. It was sn from th brakthrough curv that th slop of brakthrough curv dcrasd with incrasing bd hight. It may b bcaus of th rason that with th incras in bd hight th adsorbat has mor tim to contact with th activatd carbon which in turn rsults into highr rmoval capacity and lowr solut concntration in th fflunt. Bsids, at highr bd hight th availability of th ffctiv surfac ara of adsorbnt is mor which offrs mor activ sits to adsorption and it also broadns th mass transfr zon lngth [2]. 887

7 Jayanta Kumar Basu t al Arch. Appl. Sci. Rs., 212, 4 (2): Fig. 4. Brakthrough curvs for DB 86 adsorption on prpard BGA at diffrnt bd hights (inlt DB 86 concntration = 1 mg/l, flow rat = 12 ml/min, tmpratur = 28±1 ) Th Bohart-Adams Modl Th Bohart-Adams modl is widly usd for dsigning fixd bd column. Th modl is basd on surfac raction thory [21] and according to this modl th rat of adsorption is proportional to fraction of adsorption capacity that still rmains on th surfac of th adsorbnt [22]. Th Bohart and Adams modl dscribs a fundamntal rlationship btwn th normalizd concntration ( b / ) and th bd hight (Z) and th rlationship can b dscribd by th following uation: t b = N Z v k AB ln( 1 b 1) (7) whr, and b ar th initial and brakthrough concntration in mg/l rspctivly, k AB is th Bohart Adams, modl constant (l/mg-min), N is th adsorption capacity of th adsorbnt in mg/l, Z is th bd dpth in cm, v is th linar vlocity in cm/min and t b is th brakthrough tim (min). Th abov uation can b writtn in a linar form as t b = az + b (8) whr, N a = v b = ln ( ) 1 1 b k AB (9) (1) 888

8 Jayanta Kumar Basu t al Arch. Appl. Sci. Rs., 212, 4 (2): Th iso-rmoval lins ar constructd by plotting diffrnt bd hights (5.8, 7.62 and 1.16 cm) against brakthrough tims at constant flowrat (12 ml/min) and initial dy concntration (1 mg/l) as shown in Fig. 5. Th adsorption capacity (N ) and th rat constant of adsorption (k AB ) wr calculatd from th slop and intrcpt of th isothrmal lins. Fig. 5. Bohart-Adams plot at diffrnt adsorption brakthrough Th valus of N and k AB which can b furthr usd in column dsign ar shown in Tabl 3. Thrfor, by using th rspctiv linar uation, th brakthrough tim for a particular bd hight for nw fd concntration or flowrat can b prdictd asily [23]. Tabl 3 Th Bohart-Adams modl constants for th fixd bd column study Iso-rmoval a i b i N k AB R 2 Prcntag (min/cm) (min) (mg/l) (l/minmg) Th modifid slop (a f ) for a nw fd concntration was calculatd dirctly by multiplying th original slop (a i ) by th ratio btwn th original ( ) and nw fd concntration ( f ). a f = ai f (11) Th modifid intrcpt was also calculatd by th following uation ln( 1) f b f = bi f ln( 1) (12) whr, b i and b f ar th original and modifid intrcpt for a nw fd concntration. Similarly th modifid slop constant for a nw flowrat was calculatd as 889

9 Jayanta Kumar Basu t al Arch. Appl. Sci. Rs., 212, 4 (2): V a f = ai V f (13) whr, V and V f ar th original and nw flow rat. Th prdictd brakthrough tim calculatd from th abov uations was compard with obsrvd brakthrough tim and th corrsponding valus ar shown in Tabl 4 and 5. Tabl 4 Prdictd brakthrough tim form Bohart-Adams constant for a nw fd concntration Brak point (%) Brak point (%) a i b i f / f a f b f Z t Prd t Obs A high valu of rgrssion cofficint was obtaind whn ths prdictd valus of brakthrough tim wr plottd against th obsrvd valus of brakthrough tim. Thrfor, modl dvlopd can b furthr utilizd for modling of a contntious column undr diffrnt xprimntal conditions such as varying flow rats and fd concntrations Yoon-Nlson and lark Modl This modl is basd on th assumption that th rat of dcras in th probability of adsorption for ach adsorbat molcul is proportional to th probability of adsorbat adsorption and th probability of adsorbat brakthrough on th adsorbnt [24]. Th Yoon-Nlson modl is lss complicatd than othr modls. Th linarizd form of th Yoon- Nlson modl for a singl componnt systm is xprssd as: t ln t = k YN t τk YN whr, k YN is th rat constant (min 1 ) and τ (min) is th tim ruird for 5% adsorbat brakthrough. Th valus of k YN, τ, χ 2 and R 2 ar shown in Tabl 6 wr dtrmind from th from th slop and intrcpt of th linar plot of ln [ t /( t )] and t according to E. (13). Th 5% brakthrough tim (τ) was incrasd with incrasing fd concntration ( ) and bd hight (Z). Bsids, th rat constant (k YN ) was incrasd with dcrasing fd concntration and incrasing bd hight. Th rsults obtaind wr in a good agrmnt with th xprimntal rsults of Ahmad t.al. (14) Tabl 6 Paramtrs for Yoon-Nlson undr diffrnt xprimntal conditions oncntration (mg/l) bd hight (cm) Flowrat (ml/min) k YN (1/min) Τ (min) R 2 χ lark Modl Th lark modl introducs a nw procdur to simulat th brakthrough curvs by using th Frundlich isothrm constant [26]. Th linarizd form of th modl can b rprsntd as, ln ( ) t n 1 1 = rt + ln A whr, r (min -1 ) and A ar th lark modl paramtrs. (15) 89

10 Jayanta Kumar Basu t al Arch. Appl. Sci. Rs., 212, 4 (2): Th prdictd modl paramtrs calculatd using a Frundlich constant of n = 2.6 ar shown in Tabl 7. It was sn from Tabl 7 that valus of r incrasd with dcras in bd hight. Bsids, th valu of A also incrasd with incras in bd hight. Tabl 7 lark modl undr diffrnt xprimntal conditions Initial concntration (mg/l) Bd hight (cm) Flow rat (ml/min) r (l/min) A R 2 Χ 2 (1 4 ) ONLUSION Th adsorption of a typical txtil dy dirct blu 86 was studid through a fixd bd column. A carbon-alumina composit adsorbnt was dvlopd for this purpos. Th activatd carbon was dvlopd by microwav activation. Th monolayr adsorption capacity according to Langmuir isothrm was found to b 5.16 mg/g. Th dynamic adsorption charactristics for DB 86 adsorption wr invstigatd by using a ixd bd column. Th ffcts of various paramtrs such as initial dy concntration, adsorbat flow rat and adsorbnt bd hight on th brakthrough wr also invstigatd. Th maximum bd capacity was found to b mg/l. Th xprimntal brakthrough data wr fittd to Bohart Adams, Yoon-Nlson and lark modl. It was sn from Bohart Adams modl that with an incras in prcntag brakthrough th valus of N incrasd from mg/l rspctivly. REFERENES [1] D. harumathi, N. Das, Dsalination, 211, 285, 5-9. [2] Y. Yao, F. Xu, M. hn, Z. Xu, Z. Zhu, Biorsour Tchnol., 21, 11, 34. [3] D. Xu, S. Hin, S.L. Loo, K. Wang, Ind. Eng. hm. Rs., 28, 47, [4] K. Kadirvlu,. Karthika, N. Vnnilamani, S. Pattabhi, hmosphr, 25, 6, [5] A. Adak, M. Bandyopadhyay, A. Pal, Dys Pigm., 26, 69, [6] V. Ponnusami, R. Madhuram, V. Krithika, S.N. Srivastava, hm. Eng. J., 28, [7] M. Rafatullah, O. Sulaiman, R. Hashim, A. Ahmad, J. Hazard. Matr., 21, 177, 7. [8] J. Guo, A.. Lua, Matr. hm. Phys. 8 (23) [9] Z. Aksu, F. Gonn, Procss Biochm. 24; 39: [1] L. Huang, Y. Sun, W. Wang, Q. Yu, T. Yanga, hm. Eng. J., 211, 171(3), [11] Q.S. Liu, T. Zhng, P. Wang, L. Guo, Ind. rops Prod., 21, 31, [12] J. Song, W. Zou, Y. Bian, F. Su, R. Han, Dsalination, 21, 265(1-3), [13] N. Ozturk, D. Kavak, J. Hazard. Matr., 25, B127, [14] A. Ergn, K. Ada, S. Tan, H. Katırcıoğlu, Dsalination, 29, 249(3), [15] J. Gol, K. Kadirvlu,. Rajagopal, V.K. Garg, J. Hazard. Matr. B., 25, 125, [16] A.A. Ahmad, B.H. Hamd, J. Hazard. Matr., 21, 175, [17] S.H. Lina, R.S. Juangb, Y.H. Wang, J. Hazard. Matr., 24, B113, [18] K. D..K. Portr JF, G. McKay, hm. Eng. Sci., 2, 55, [19] Z. Zulfadhly, M.D. Mashitah, S. Bhatia, Environ. Pollut., 21, 112, [2] K. Vijayaraghavan, J. Jgan, K. Palanivlu, M. Vlan, J. Hazard. Matr., 24, 113B (1 3), [21] B. Kiran, A. Kaushik, hm. Eng. J., 28, 144(3), [22] M. Lhmann, A.I. Zouboulis, K.A. Matis, Environ. Pollut., 21, 113(2), [23] Y.H. Yoon, J. H. Nlson, Am. Ind. Hyg. Assoc. J., 1984, 45, [24] S. Singh, V.. Srivastava, I.D. Mall, oll. Surf. A: Physicochm. Eng. Asp., 29, 332(1), [25] A.A. Ahmad, B.H. Hamd, J. Hazard. Matr., 21, 175(1-3), [26] F.A. Batzias, D.K. Sidiras, Biorsour. Tchnol., 27, 98(6),