COMPARISON OF METHYLENE BLUE ADSORPTION FROM AQUEOUS SOLUTION USING SPENT TEA DUST AND RAW COIR PITH

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1 Global NEST Journal, Vol XX, No X, pp XX-XX, 214 Copyright 214 Global NEST Printd in Grc. All rights rsrvd COMPARISON OF METHYLENE BLUE ADSORPTION FROM AQUEOUS SOLUTION USING SPENT TEA DUST AND RAW COIR PITH RAMESH S.T. Dpartmnt of Civil Enginring GANDHIMATHI R.* National Institut of Tchnology ELAVARASI T.E. Tiruchirappalli ISAI THAMIZH R. Tamilnadu, India. SOWMYA K. NIDHEESH P.V. Rcivd: 2/1/213 Accptd: 3/12/213 *to whom all corrspondnc should b addrssd: -mail: rgmathii@nitt.du ABSTRACT Th purpos of th prsnt work is to tst th possibility of using th spnt ta dust and raw coir pith for th rmoval of mthyln blu (MB) from aquous solution. Th ffcts of th contact tim, adsorbnt dosag and solution ph wr studid in batch xprimnts at 27 C. Rsults showd that a ph of 7 is favourabl for th adsorption of dy. Th isothrmal data could b wll dscribd by th Langmuir quations. Kintic paramtrs of adsorption such as th Langrgn psudo-first-ordr, psudo-scond-ordr rat constant and th intraparticl diffusion rat constant wr dtrmind. Th adsorption capacitis of Spnt Ta Dust (STD) and Raw Coir Pith (RCP) wr found to b mg and mg g -1 of th adsorbnt rspctivly. Th rsults indicat that STD and RCP could b mployd as low-cost altrnativs to commrcial activatd carbon for th rmoval of dys from aquous solution. KEYWORDS: Adsorption; isothrm; Kintics; Mthyln blu; Spnt ta dust; Raw coir pith. 1. INTRODUCTION Many industris, such as dystuffs, txtil, papr and plastics, us dys in ordr to color thir products and also consum substantial volums of watr. As a rsult, thy gnrat a considrabl amount of colord wastwatr. It is rcognizd that public prcption of watr quality is gratly influncd by th color. Color is th first contaminant to b rcognizd in wastwatr (Banat t al., 1996). Th prsnc of vry small amounts of dys in watr (lss than 1 ppm for som dys) is highly visibl and undsirabl (Robinson t al., 21; Banat t al., 1996). Ovr 1, commrcially availabl dys xist and mor than 7 X 1 5 tonns pr yar ar producd annually (Parc t al., 23). Du to thir good solubility, synthtic dys ar common watr pollutants and thy may frquntly b found in trac quantitis in industrial wastwatr. An indication of th scal of th problm is givn by th fact that two prcnt of dys that ar producd ar dischargd dirctly in aquous fflunt (Robinson t al., 21; Parc t al., 23). Thr ar many structural varitis of dys, such as acidic, basic, disprs, azo, diazo, anthroquinon basd and mtal complx dys. Basic dys ar widly usd in acrylic, nylon, silk, and wool dying. Most of ths dys ar toxic, mutagnic and carcinognic (Ern and Acar, 26, Nidhsh t al., 213). Thrfor, thir rmoval from industrial fflunts bfor discharging into th nvironmnt is xtrmly important (O Nill t al., 1999; Hamd and El-Khaiary, 28). Many tratmnt mthods hav bn dvlopd to rmov dys from wastwatr. Ths tratmnt mthods can b dividd into physical, chmical and biological schms. Ths includ: adsorption (Nidhsh t al., 211, Gandhimathi t al., 212), coagulation (Ellouz t al., 211), photo-lctro-catalytic mthods (Khata and Zari, 211), lctrocogulation (Rajabi t al., 211), mmbran (Srivastava t al., 211) and photo catalysis (Lodha t al., 211). Although chmical and biological approachs ar ffctiv in rmoving dys, thy rquir spcial quipmnt and ar usually nrgy intnsiv; additionally, ths procsss oftn

2 2 RAMESH S.T. t al. gnrat larg amounts of byproducts (Zary t al., 212). As synthtic dys in wastwatr cannot b fficintly dcolorizd by traditional mthods, th adsorption of synthtic dys on inxpnsiv and an fficint solid support was considrd as a simpl and conomical mthod for thir rmoval from watr and wastwatr (Forgacs t al., 23). MB is also an important basic dy widly usd for printing calico, dying, printing cotton and tannin and dying lathr. Although not strongly hazardous, MB can hav various harmful ffcts. Th dy can caus y burns, which may b rsponsibl for prmannt injury to th ys of human and animals, irritation to th gastrointstinal tract with symptoms of nausa, vomiting and diarrha and also caus mthmoglobinmia, cyanosis, convulsions, tachycardia, and dyspna. Contact of MB with skin causs irritation (Hamdaoui and Chiha, 27). Th studis on MB adsorption onto coir pith (Namasivayam t al., 21), activatd carbon (Shaobin t al., 25), ric husk (Vadivlan and Vasanth Kumar, 25), panut hull (Rnmin t al., 25) KOH-activatd and stam-activatd carbons (Wu t al., 25), pumic powdr (Fryal, 25), glass fibrs (Sampa and Binay, 25), coir pith carbon (Kavitha and Namasivayam, 27), Pumpkin sd hull (Hamd and El-Khaiary, 28), br brwry wast (Tsai t al., 28) hav bn rportd. Ta is basically th drid and procssd lavs of only on spcis of plant calld Camllia sinnsis (Mokgalaka t al., 24). It is consumd by th largst numbr of popl in th world and considrd th scond most popular bvrag in th world. Cannd or bottld ta drinks as wll as instant ta drinks ar producd on industrial scal by hot watr xtraction of ta lavs, and th producrs fac a problm in disposing of th spnt ta lavs aftr th xtraction. Agro wasts and wast matrials ar currntly rciving attntion as raw matrials for watr pollution control bcaus of thir availability and low-cost (Horsfall Jnr and Spiff, 25). In this contxt, w ar invstigating th potntial of STD and RCP an agricultural solid wast, as altrnativ low-cost adsorbnts for th rmoval of MB dy from aquous solutions. Vry fw studis wr rportd th comparativ rmoval of dys using ths agricultural wasts. Basd on th kintic and isothrm studis, adsorption capacitis of both low cost adsorbnt compard. 2. MATERIALS AND METHODS 2.1 Adsorbat MB obtaind from Mrck was usd for all xprimnts, without furthr purification. Th MB was chosn in this study bcaus of its known strong adsorption onto solids. Th maximum absorption wavlngth of this dy is 668 nm. Th structur of MB is shown in Fig. 1. Figur 1. Th Chmical Structur of MB 2.2 Adsorbnt STD was collctd from th Opal Hostl Mss, NIT, Trichy. It was rpatdly washd with watr until th filtrd watr was clar. It was thn ovn drid at 6 C for 48 hours. Th drid sampl was groundd and sivd to a particl siz of 3 to 6 microns. Wast coir pith was obtaind from a coir industry at Omalur, Salm district, India. It was drid in sunlight for 5 hours. It was thn powdrd and sivd to a siz of 6-3 microns. No othr chmical or physical tratmnts wr usd prior to th adsorption xprimnt. Th prpard STD and RCP is shown in Fig. 2.

3 3 COMPARISON OF METHYLENE BLUE ADSORPTION FROM AQUEOUS SOLUTION (a) Spnt Ta Dust (b) Raw coir pith Figur 2. Adsorbnts usd in th prsnt study 2.3 Effct of contact tim Batch xprimnts wr carrid out by placing.35 g of STD and.1 g of RCP sparatly in 1 ml of aquous solution containing 25 mg l -1 of MB and thn agitating th mixturs at 13 rpm with varying contact tims from 2 min to 24 min in a systm ph of 7 at 27 C. Th adsorbnt and adsorbat wr sparatd by cntrifugation at 45 rpm for 1 min. Thn, th MB concntration rmaining in th suprnatant was masurd using a UV- visibl spctrophotomtr (Lambda 25, PrkinElmr, USA). Th amount of sorption at tim t, q (mg g -1 ), was calculatd by: (C C t )V qt W whr C and C t (mg l -1 ) ar th liquid-phas concntrations of dy at initial and any tim t, rspctivly. V is th volum of th solution (l) and W is th mass of dry sorbnt usd (g). 2.4 Effct of adsorbnt dosag Th ffct of th adsorbnt dosag on th adsorption of MB was studid by varying th STD dosag (.5 to.4 g) and RCP dosag (.2 to.24 g) in 1 ml of dy solution. Th mixturs wr agitatd in shakr at 13 rpm and 27 C for 18 min incas of STD and 6 min in cas of RCP until quilibrium was rachd. Aquous sampls wr takn from th solutions and th concntrations wr analyzd. At tim t = and at quilibrium, th dy concntrations wr masurd by UV/VIS spctrophotomtr at 668 nm. Th amount of quilibrium adsorption, q (mg g -1 ), was calculatd by q (C C W )V whr C and C (mg l -1 ) ar th liquid-phas concntrations of dy at initial and quilibrium, rspctivly. 2.5 Effct of systm ph Th ffct of th systm ph was studid, following th sam procdur as for th contact tim, ovr a systm ph rang from 2 to 1 adjustd with 1M NaOH or.1m H 2 SO 4 aftr th addition of STD (.35 g pr 1 ml) and RCP (.12 g pr 1 ml). Agitation was providd for quilibrium tim priod with a constant agitation spd of 13 rpm. Th ph was masurd by using a ph mtr (phtstr 3, Eutch, Singapor). (1) (2)

4 Rmoval fficincy(%) Rmoval Efficincy (%) 4 RAMESH S.T. t al. 3. RESULTS AND DISCUSSION 3.1 Effct of contact tim Initial batch studis conductd to assss th tim takn for th quilibrium to b attaind wr prformd for two diffrnt typs of adsorbnts (STD and RCP). Th influnc of contact tim on rmoval of MB by STD and RCP is shown in Fig. 3. It is vidnt that both th adsorbnts ar fficint to adsorb MB with diffrnt fficincis. It was obsrvd that dy uptak is rapid for th first 15 min and thraftr it procds at a slowr rat and finally attains saturation. This mayb xplaind by a rapid adsorption on th outr surfac, followd by slowr adsorption insid th pors. RCP posssss highr adsorption capacity (24.95 mg g -1 ) than STD (7.59 mg g -1 ) at quilibrium (Tabl 1). To attain quilibrium, it taks 6 min and 18 min for STD and RCP rspctivly. In th procss of dy colour adsorption, initially dy molcul has to first ncountr th boundary layr ffct and thn it has to diffus from boundary layr film onto adsorbnt surfac and thn finally it has to diffus into th porous structur of th adsorbnt. This phnomnon will tak rlativly long contact tim (Malik, 23) STD RCP Tim (min) Figur 3. Effct of Contact Tim on MB Adsorption by STD and RCP 3.2 Effct of adsorbnt dosag Fig. 4 shows th rmoval of MB at diffrnt adsorbnt dosags (.5 to.4 g of STD pr 1 ml and,.2 to.24 g of RCP pr 1 ml) at an agitation tim of 6 min for STD and 12 min, for RCP STD RCP,5 1 1,5 2 2,5 3 3,5 4 Dosag (g l -1 ) Figur 4. Effct of Dosag on MB Adsorption by STD and RCP

5 Rmoval fficincy (%) 5 COMPARISON OF METHYLENE BLUE ADSORPTION FROM AQUEOUS SOLUTION Th adsorption fficincy gnrally improvd with incrasing adsorbnt dosag up to a crtain valu and thn rmaind constant. Th incras in STD dosag from.5 to 4. g l 1 rsultd in an incras from 66.9 to 97.49% in adsorption of MB. Th incras in th adsorption prcntag with incrasing adsorbnt dosag is du to th incras in th numbr of adsorbnt sits (charging sits) (Slvaraj t al., 23). Th optimum dosag for MB adsorption by STD was 3.5 g l -1 at 97.49% of MB adsorption. MB showd a maximum rmoval of 98.23% at a coir pith dos of 1.2 g l -1. Ths rsults indicat that th RCP hav potntial adsorbnt whn compard to STD for MB adsorption from aquous solution. 3.3 Effct of systm ph Effct of ph on th rmoval of MB is shown in Fig. 5. Th prcnt rmoval was mor than 9% in th ph rang 4 1 by STD and RCP rspctivly. Lowr adsorption (35%) of MB at ph 2 by STD is du to th prsnc of xcss H + ions compting with th dy cation for th adsorption sits. As th ph of th systm incrass, th numbr of positivly chargd sits dcrass and th numbr of ngativly chargd sits incrass (Kavitha and Namasivayam, 27). At ph 2, though positivly chargd surfac sits on th adsorbnt do not favor th adsorption of dy cations du to th lctrostatic rpulsion, dy rmoval by RCP was still high (mor than 8%). As th ph incrasd, th rmoval incrasd slightly. Svral invstigations hav rportd that MB adsorption usually incrass as th ph is incrasd (Gupta t al., 24; Singh t al., 23; Janos, 23). Basically, MB and othr cationic dys produc an intns molcular cation (C + ) and rducd ions (CH + ). At high ph, OH - on th surfac of adsorbnt will favor th adsorption of cationic dy molculs (Kavitha and Namasivayam, 27) STD RCP ph Figur 5. Effct of Systm ph on MB Adsorption by STD and RCP 3.4 Adsorption kintics Th kintics of MB sorption onto STD and RCP wr invstigatd using th psudo-first ordr and psudo-scond ordr kintics modls. Th Lagrgrn quation (Langrgrn, 1898) is th most widly usd rat quation in liquid phas sorption. Th linarizd form of th psudo first-ordr quation is xprssd as k1 log( q qt ) log(q ) (t) (3) 2.33 whr, q, q t = th adsorption capacity at quilibrium and at tim t, rspctivly (mg g -1 ) and k 1 = th rat constant of psudo first-ordr adsorption, (min -1 ). Th valus of log (q - q t ) wr linarly corrlatd with t, and th plot of log (q - q t ) vs t would rsult in a linar rlationship from which k 1 and q could b dtrmind from th slop and intrcpt of th plot, rspctivly. Th psudo scond-ordr adsorption kintic rat quation is givn blow (Ho and McKay, 1999);

6 log (q-qt) 6 RAMESH S.T. t al. t q t 1 k2q 2 1 q (t) whr k 2 (g mg -1 min -1 ) is th rat constant of psudo-scond ordr adsorption raction. Th plot of t and t of Eq. 4 would rsult in a linar rlationship from which q and k 2 could b dtrmind from q t th slop and intrcpt of th plot, rspctivly. In ordr to distinguish th film diffusion or intraparticl diffusion procss, th Wbr Morris (1963) quation was tstd in th following form: a id (t) R K (5) A linarizd form of this quation is givn by logr whr logk alog(t) (6) id R = th prcnt MB adsorbd t = th contact tim, min a = th gradint of linar plots K id = th intraparticl diffusion rat constant, min -1 K id may b takn as a rat factor, i.., prcnt MB adsorbd pr unit tim. Th plot of log (R) and log (t) of Eq. 6 would rsult in a linar rlationship from which a and K id could b dtrmind from th slop and intrcpt of th plot, rspctivly. Figs. 6 8 show th plot of th first-ordr, scond-ordr and intraparticl diffusion modls for adsorption of MB by th STD and RCP rspctivly. (4) 1,5 1 STD RCP,5 -, y = -,369x + 1,2176 R² =,9927 y = -,123x +,46 R² =,8982-1,5-2 Tim (min) Figur 6. Psudo First ordr kintics plot for th rmoval of mthyln blu

7 Log (R) t/qt 7 COMPARISON OF METHYLENE BLUE ADSORPTION FROM AQUEOUS SOLUTION STD RCP y =,138x +,7467 R² =, y =,382x +,1329 R² =, Tim (min) Figur 7. Psudo Scond-ordr kintics plot for th rmoval of mthyln blu Exprimntal and thortically calculatd q valus and cofficints rlatd to kintic plots ar listd in Tabl 1. Th thortical q valus for th adsorbnts wr vry clos and significantly diffrnt to th xprimntal q valus in th cas of scond and first-ordr kintic modls, rspctivly (Tabl 1). Thrfor th scond-ordr kintics bst dscrib th data wll than that of psudo first ordr modl. Highr valus of th intraparticl diffusion rat constant K id illustrat an nhancmnt in th rat of adsorption, whras largr valus of th gradint of linar plots (α) illustrat a bttr adsorption mchanism (Kobya, 24). Th valus of α for MB by STD and RCP wr.196 and.199 rspctivly. Th valu of α bing lss than.5 indicats that th intraparticl diffusion is not a rat dtrmining stp (Kobya, 24). STD RCP 2,5 2 y =,1985x + 1,6258 R² =,9265 1,5 1 y =,1956x + 1,5756 R² =,768,5,5 1 1,5 2 2,5 Log (t) Figur 8: Intraparticl diffusion plot for th rmoval of MB by STD and RCP

8 1/q 8 RAMESH S.T. t al. PSEUDO-FIRST ORDER PSEUDO-SECOND ORDER INTRAPARTICLE DIFFUSION MODEL Tabl 1. Adsorption Kintic Modl Rat Constants ADSORBENT STD RCP q (xp) (mg g -1 ) q (cal) (mg g -1 ) Rat constant k 1 (min -1 ) R q (cal) (mg g -1 ) Rat constant k 2 (g mg -1 min -1 ) R K id Prcnt min α R Equilibrium isothrms Two isothrms wr tstd for thir ability to dscrib th xprimntal rsults, namly th Langmuir isothrm and th Frundlich isothrm. Th thrmodynamic assumptions of th bst fitting isothrm provid insight into both th surfac proprtis and th mchanism of adsorption. Th drivation of th Langmuir isothrm is basd on th assumption of idal monolayr adsorption on a homognous surfac. It is xprssd by: q qmbc 1 bc whr C is th quilibrium concntration (mg l -1 ), q th amount of dy adsorbd at quilibrium (mg g -1 ), q m is q for complt monolayr adsorption capacity (mg g -1 ), and b is th quilibrium adsorption constant (l mg -1 ). (7),14 STD RCP,12,1 y =,1427x +,116 R² =,9663,8,6 y =,187x +,7 R² =,9916,4,2,5 1 1,5 2 2,5 1/C Figur 9. Langmuir isothrm for th adsorption of MB on STD and RCP Th Frundlich isothrm is usd for non-idal adsorption on htrognous surfacs. Th htrognity is causd by th prsnc of diffrnt functional groups on th surfac, and also by

9 log (q) 9 COMPARISON OF METHYLENE BLUE ADSORPTION FROM AQUEOUS SOLUTION various mchanisms of adsorbnt adsorbat intractions. Th Frundlich isothrm is rprsntd by th following mpirical quation: F 1/n q K C (8) whr K F is th Frundlich adsorption constant and n -1 is a masur of th adsorption intnsity. Fig. 9 and 1 shows th fittd quilibrium data to Langmuir and Frundlich, xprssions. Th fitting rsults, i.. isothrm paramtrs and th cofficints of dtrmination, R 2, ar shown in Tabl 2. It can b sn in Fig. 9 that th Langmuir plot is a bttr fit of th xprimntal data compard to Frundlich plot (Fig.1) for both th adsorbnts. Th MB adsorption capacity on RCP was mg g -1 at 27 C, whras that of STD was only 86.21mg g -1 adsorbnt undr th sam conditions. Th magnitud of th xponnt n givs an indication of th favourability and K F th capacity of th adsorbnt / adsorbat systm. Th n valus (1.17 for STD and 1.57 for RCP) btwn 1 and 1 indicat bnficial adsorption (Asfour t al., 1985). 2,5 STD RCP 2 y =,5599x + 1,5599 R² =,951 1,5 1 y =,7538x +,8495 R² =,976,5 -,6 -,4 -,2,2,4,6,8 1 log (C) Figur 1. Frundlich isothrm for th adsorption of MB on STD and RCP Tabl 2. Isothrm Paramtrs for Rmoval of MB by STD and raw coir pith Adsorbnt Langmuir Isothrm Constants Frundlich Isothrm Constants q m (mg g -1 ) b (L mg -1 ) R 2 R L K F (mg g -1 ) n R 2 STD RCP Th ssntial charactristics of Langmuir isothrm can b xprssd by a dimnsionlss constant calld quilibrium paramtr R L, dfind by Wbr and Chakkravorti (1974): R L 1 (9) 1 bc whr b is th Langmuir constant and C is th initial dy concntration (mg l -1 ), R L valus indicat th typ of isothrm. Tabl 2 shows R L valus btwn zro and on, which indicat favorabl adsorption (Kavitha and Namasivayam, 27). Th adsorption capacitis various adsorbnts usd for MB rmoval wr compard with prsnt study and givn in Tabl 3. From th Tabl 3, it is vry clar that th capacitis of adsorbnts for

10 1 RAMESH S.T. t al. adsorbing MB ar in a wid rang. It is vary from to mg g -1. Th adsorption capacitis of RCP and STD ar vry lss compard to straw carbon, ric husk carbon, what straw, ric husk tc. But th MB adsorption capacity of RCP is comparabl with groundnut shll carbon, hair, garlic pl and bamboo dust carbon. Similarly th adsorption capacity of STD is vry similar to that of raw dat pits and hazlnut shll. Tabl 3. Adsorption capacitis of various adsorbnts for th rmoval of MB No Adsorbnt q m (mg g -1 ) Rfrnc 1 Straw carbon Kannan and Sundaram, (21) 2 Ric husk carbon Kannan and Sundaram, (21) 3 What straw Gong t al., (28) 4 Ric husk 312. McKay t al., (1999) 5 Spnt ta lavs 3.52 Hamd, (29 a) 6 Jack fruit pl Hamd, (29 b) 7 Coconut shll carbon Kannan and Sundaram, (21) 8 Cotton wast 27. McKay t al., (1999) 9 Coal 25. McKay t al., (1999) 1 Coconut tr sawdust carbon Kadirvlu t al., (23) 11 Diatomit 198 Al-Ghouti t al., (23) 12 Groundnut shll carbon Kannan and Sundaram, (21) 13 Hair 158. McKay t al., (1999) 14 Bamboo dust carbon Kannan and Sundaram, (21) 15 RCP Prsnt Study 16 Garlic pl Hamd and Ahmad, (29) 17 Silk cotton carbon 12. Kadirvlu t al., (23) 18 STD Prsnt Study 19 Raw dat pits 8.29 Banat t al., (23) 2 Hazlnut shll 76.9 Frrro, (27) 21 Banana pl 37.7 Annadurai t al., (22) 22 Sugarcan bagass 34.2 Filho t al., (27) 23 Banana pith 2.8 Annadurai t al., (22) 24 Orang pl 18.6 Annadurai t al., (22) 25 Sugarcan dust Khattri and Singh, (1999) 3.6 Fourir transform infrard (FTIR) analysis Th functional groups on th surfac of th STD and RCP bfor and aftr adsorption of MB wr analyzd by a FTIR spctrophotomtr (FTIR-2, Prkin Elmr) whr th spctra wr rcordd from 4 to 5 cm 1 (Fig. 11). From th figur, it was found that both adsorbnts hav paks at 3417, 2923, 1634, 1518, 1451, 1383, 1239, 1148 and 149 cm -1. Th broad pak at 3417 cm 1 attributd to th O H strtching on th adsorbnt surfac (Ramsh t al., 211). Th strtching vibration of C-H group was obsrvd at 2923 cm 1 (Nidhsh t al., 212). Th prsnc of COO, N H and C O groups on th adsorbnt surfac was indicatd by th paks at 1634, 1518 and 1451 cm 1 rspctivly (Kumar and Ahmad, 211). Th paks of mthoxy groups (O CH 3, 1451 cm 1 ), O H dformation originating from th phnolic group (1383 cm 1 ), C OH strtching in primary alcohol (149 cm 1 ) and scondary alcohol (1148 cm 1 ) wr also obsrvd for both th adsorbnts (Ramsh t al., 211). Aftr th sorption of

11 11 COMPARISON OF METHYLENE BLUE ADSORPTION FROM AQUEOUS SOLUTION MB, th transmittanc of th paks at 3417 and 1451 cm 1 rducd. This indicats that mthoxy and hydroxyl groups wr involvd in th sorption of MB on both sorbnts. In addition to this, th transmittanc at 149 cm 1 dcrasd in th cas of RCP. Figur 11. FTIR spctra of STD and RCP bfor and aftr sorption of MB 4. CONCLUSIONS Th rsults of prsnt invstigation show that th low cost adsorbnt matrials, STD and RCP hav suitabl adsorption capacity with rgard to th rmoval of MB from its aquous solution. RCP has bttr adsorption capacity than spnt ta dust. Th adsorption is highly dpndnt on contact tim, adsorbnt dos and ph. Equilibrium adsorption was achivd in about 18 min with STD and 6 min with RCP. Kintics data tndd to fit wll in scond-ordr kintics, confirming th chmisorption of MB onto STD and RCP particls. Scond ordr kintics modl agrd wll with th q xprimntal valus, supporting th chmisorption. Th Langmuir isothrms bst rprsnt th quilibrium adsorption data. Th optimal ph for favorabl adsorption of MB is 7 by both th adsorbnts. It is fasibl to utiliz STD as a low-cost adsorbnt for rmoving MB dy from th industrial dying wastwatr. As th raw matrial, th coir pith is discardd as wast in coir industris; th tratmnt mthod using RCP is xpctd to b conomical. Th cost and adsorption charactristics favor RCP to b usd as an ffctiv adsorbnt for th rmoval of MB from wastwatr. REFERENCES Al-Ghouti M.A., Khraishh M.A.M., Alln S.J. and Ahmad M.N. (23), Th rmoval of dys from txtil wastwatr: A study of th physical charactristics and adsorption mchanisms of diatomacous arth, Journal of Environmntal Managmnt, 69, Annadurai G., Juang R.S. and L D.J. (22), Us of cllulos basd wasts for adsorption of dys from aquous solutions, Journal of Hazardous Matrials, 92, Asfour H.M., Fadali O.A., Nassar M.M. and El-Gundi M.S. (1985), Equilibrium Studis on Adsorption of Basic Dys on Hard Wood, J. Chm. Tch. Biotchnol., 35A,

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