Highly Efficient Removal of Chromium (VI) from Water by Mesoporous Alumina

Transcription

1 Highly Efficint Rmoval of Chromium (VI) from Watr by Msoporous Alumina V. N. Bhusari,,Rashmi Dahak 2, Sadhana Rayalu 2, Amit Bansiwal 2 G.H. Raisoni Collg of Enginring, 44006, Nagpur (M.S.), India 2 Environmntal Matrials Division 3,4 National Environmntal Enginring Rsarch Institut, CSIR (NEERI) ABSTRACT Msoporous Activatd alumina (MAA) was usd for rmoval of hxavalnt chromium from watr. Th activatd alumina was charactrizd for Powdr X-ray diffraction (XRD), Scanning Elctron Microscop (SEM).Th charactrizd adsorbnt was valuatd for th rmoval of chromium (VI) from watr. Th adsorption fficincy of activatd alumina was studid by batch adsorption study. MAA xhibit highly fficint rmoval with mor than 99% rmoval at initial concntration of 5 mg/l. Th xprimntal data was fittd to Langmuir and Frundlich adsorption modl and found that Langmuir modl fits wll confirming mchanism of monolayr adsorption on uniform surfac. Th adsorption kintic data was wll dscribd by psudo first ordr kintics. Th rsidual Cr(VI) concntrations aftr tratmnt with MAA wr blow th prscribd limits as pr WHO and Indian Drinking watr standards. Kyword : - Msoporous, Alumina, Adsorption, Chromium(VI). Introduction Chromium is on of th important industrial mtal usd in various products and procss. About 60% chromium is usd in lctroplating industry and othr stl fabrication, lathr tanning, rfractory product, fin chmicals tc.[]. Th contamination of havy mtal ion in surfac and ground watr has mattr of concrn du to incrasing th lvl of mtal ion lik Cr, As, Cd, Hg and Cu in watr and wastwatr. Chromium has wid toxicity ffct on nvironmnt and human halth.[2]. Chromium mainly occurs in watr and wastwatr in trivalnt and hxavalnt form of which hxavalnt form of chromium is mor hazardous as compard to trivalnt form as it has bn associatd with carcinognic and mutagnic ffcts on human.[3]. Cr (VI) is highly mobil and mutagnic pollutants, which not only damags plant and animal tissus but also givs ris to varitis of disass in humans vn in small quantitis. Thrfor, it is ncssary to rmov Cr (VI) from contaminatd watr[4].according to Burau of Indian Standard (BIS) th industrial fflunt prmissibl discharg lvl of total Cr and Cr(VI) into inland watr is 2 and 0.05 mg l,rspctivly. Th diffrnt mthods usd to rmov hxavalnt chromium from watr includ mmbran filtration, chmical prcipitation, solvnt xtraction, adsorption, tc. Among ths mthod, adsorption is considrd as an ffctiv procss for rmoving chromium from watr.[4] Various adsorbnts hav bn rportd for th rmoval of Cr(VI) from watr namly natural adsorbnts lik clay, dolomit, bntonit [5], bio matrials and agricultural wasts including tr barks[6], ric bran, what bran[7], coconut shll, lavs, alga, saw dust [8], activatd alumina[9], activatd carbon[0], modifid chitosan [2], hydrocalcit, zro valnt iron[], bimtal oxids [2] tc. Thr ar many disadvantags of xisting adsorbnts such as low fficincy, sludg gnration and rusability. Th highly porous activatd alumina has many advantags ovr ths limitations as it provids grains with diamtr of 0.3 to 0.6 mm having both macro and microspors and high surfac ara for sorption. Msoporous activatd alumina is commonly usd to rmov diffrnt havy mtals from watr. Thrfor th highly msoporous activatd alumina (MAA) hav bn studid for th rmoval of chromium (VI) from watr. Th adsorption capacity of MAA was dtrmind by computing th adsorption isothrm

2 2. Exprimntal 2. Matrial and Mthod. All chmicals usd wr AR grad purchasd from E Mrck. Th msoporous activatd alumina bads of Sasol (Grmany) mak wr usd. Th alumina bads wr wash with DI watr and drid in ovn at 80 0 C tmpratur and was usd for valuation of chromium from watr. 2.2 Charactrisation of Activatd alumina Msoporous Activatd alumina (MAA) was charactrisd for th structural and morphological proprtis. X ray diffraction (Modl Rigaku: Miniflx) was usd to idntify structural phas and crystallin natur. Th PXRD pattrns for th adsorbnt wr rcordd at 2Ɵ rang from 0 0 to 80 0.Th AA was also charactrizd using Scanning lctron Microscopy (SEM) JEOL instrumnt. 2.3Batch Adsorption studis Chromium adsorption study was prformd to dtrmin th adsorption fficincy of MAA. Th batch adsorption study was conductd using to 5 gm/l dos of alumina bads in synthtic chromium(vi) watr. Chromium (VI) solution of 5 mg/l of initial concntration was prpard from 000 mg/l of chromium stock solution. Th dsird dos of adsorbnt was takn in 250ml polycarbonat flask and kpt for shaking in orbital shakr at 50 rpm on room tmpratur. Th ph of sampl was maintaind btwn using 0. M NaOH or 0. M HCl. Th sampls wr withdrawn from orbital shakr aftr 24 h. Th concntration of chromium (VI) in sampls was dtrmind by ICP- MS.Th xprimnts wr rpatd twic and it was obsrvd that th xprimntal rror was within ±2%. Th amount of Cr(VI) adsorbd (mg. g - ) at tim t was computd using following quation[2]: 3. Rsult and Discussion 3..Charactrization of Alumina Th PXRD pattrns of activatd alumina is prsntd in Fig. which shows that th broad paks obtaind at about and 66 confirms th prsnc of γ alumina phass. Also th pattrn of PXRD rvld th amorphous natur of alumina. Scanning lctron micrograph of activatd alumina is prsntd Fig.2 shows th highly porous structur of alumina may allow th diffusion in fin pors and crat intimat contact of mtal ion with th surfac of alumina. Fig.-PXRD of MAA

3 Fig.2- SEM of MAA 3.2 Adsorption studis Th prcntag adsorption of Cr(VI) with initial concntration on activatd alumina givn in Fig.3.Th maximum adsorption was 99% occur with 5mg/L initial Chromium(VI) solution using 0.5g/50 dos of alumina. Fig. 3- Dos study of MAA To study adsorption mchanism of activatd alumina, two adsorption modls wr usd Langmuir adsorption is basd on Langmuir thory in which molculs ar adsorbd at a fixd numbr of activ sits with homognous distribution ovr th surfac of th adsorbnt. Ths activ sits hav sam affinity for adsorption of a mono molcular layr and thr is no intraction btwn th adsorbd molculs. Th Langmuir isothrm plot is prsntd in Fig.4(a) basd on linar form of Langmuir quation which can b writtn as: q q m K C L q m [2] Frundlich isothrm modl intrprts th adsorption on htrognous surfacs with intractions btwn th adsorbd molculs and is not rstrictd to th formation of a monolayr. This modl assums that whn th adsorbat concntration incrass, th concntration of adsorbat on th adsorbnt surfac also incrass and corrspondingly, th sorption nrgy xponntially dcrass ovr th compltion of th sorption cntr of th adsorbnt[3].th linar form for Frundlich quation, it is writtn as:

4 log n q logk log C [3] whr q is th amount of adsorbat adsorbd pr unit wight of adsorbnt at quilibrium (mg g ), q m is th maximum adsorption capacity (mg g ), K L is th Langmuir constant, C is th quilibrium concntration of adsorbat in solution (mg l ), K f is th Frundlich constant, n is th Frundlich constant, which rflcts th adsorption intnsity. Th plot for Frundlich isothrm is givn in Fig.4(b). Fig.4(a)-Langmuir Adsorption Isothrm Fig.4(b)-Frundlich adsorption Isothrm It was obsrvd that th xprimntal data was wll fittd to Langmuir modl with corrlation cofficint (R 2) of and th adsorption capacity obtaind from Langmuir modl was 2.64 mg/g. 3.4 Adsorption kintics During adsorption th adsorbat migrat from bulk solution to th outr surfac of adsorbnt by diffusion. To study th raction kintics psudo-first-ordr and psudo-scond-ordr modls wr usd. A simpl psudo-first-ordr kintic modl known as Lagrgrn quation is givn as:[4] ln q q ln q k t t Whr q t is th amount of Chromium adsorbd at tim t (mg g ) and k ad is th quilibrium rat constant of psudofirst-ordr adsorption (min ). Th linarisd plots of log (q q t ) vrsus t will giv th rat constants. Th linar plots of (Eq. 5) ar prsntd in Fig.5 (a). ad [4] Fig. 5(a)-Psudo First ordr kintics Fig.5(b)-Psudo scond ordr kintics

5 Th psudo-scond-ordr modl is usd to prdict th kintic paramtrs th linar quation for which is rprsntd as[4] : t [5] Psudo scond-ordr (Eq. 6) modls for Cr(VI) ar prsntd in Fig.5(b). t q h t q And h = kq 2 [6] Whr q t is th amount of Chromium adsorbd at tim t (mg g ), q is th amount of Chromium adsorbd at quilibrium (mg g ), h is th initial sorption rat (mg g min ). Th valus of q (/slop), k (slop 2 /intrcpt) and h (/intrcpt) is obtaind from th plots of t/qt vrsus tis prsntd in Tabl. Tabl - Kintic paramtrs for chromium adsorption on Alumina Psudo first ordr Psudo scond ordr K ad (min - ) r 2 Kf (g mg - min - ) /n r It is clar from th valus of corrlation cofficints that th psudo-scond-ordr modl is bttr fittd as compard to psudo-first-ordr modl for Cr(VI). Th valus of corrlation cofficint (r 2 ) indicat psudo-scond ordr modl is fittd wll which confirms that th prvailing mchanism is chmisorption Effct of ph Svral litraturs hav rportd that th adsorption procss is highly dpndnt on ph. Th rmoval fficincy for Cr(VI) of MAA was valuatd at diffrnt ph rang from 3 to 0. It was obsrvd that adsorption capacity slightly vary with ph. Th Fig.6 shows th ffct of ph on adsorption of Cr(VI) on activatd alumina. Th rmoval of chromium (VI) in at ph 3 to 6 is highr than alkalin ph. Th maximum rmoval (>95%) was obtaind at ph 3 thraftr slight rduction in rmoval was obtaind. Fig.6- Effct of ph on Chromium (VI) adsorption

6 4.Conclusions Modifid Activatd Alumina(MAA) has bn usd for th rmoval of Chromium (VI) which showd adsorption fficincy 99% with 5 mg/l of initial chromium(vi) concntration. Th ffct of ph shows that th rmoval capacity is maximum at ph 3 and slightly rducd with incras in ph but th rmoval was almost sam from ph 3 to 6, hnc th alumina is considrd as fficint adsorbnt at wid rang of ph. Adsorption isothrm data wr wll fittd to Langmuir modl and th adsorption capacity was found to b 2.64 mg/g. Th kintic studis confirms th applicability of scond ordr kintic modl which is basd on chmisorption as prvailing mchanism 5. REFERENCES [] S. K. Sharma, B. Ptrusvski, and G. Amy, Rviw Papr Chromium rmoval from watr : a rviw, [2] V. Kumari, M. Sasidharan, and A. Bhaumik, Msoporous BaTiO drivd via solid stat raction and its xcllnt adsorption fficincy for th rmoval of hxavalnt chromium from watr, Dalt. Trans., vol. 44, no. 4, pp , 205. [3] N. K. Lazaridis, D. N. Bakoyannakis, and E. a Dliyanni, Chromium(VI) sorptiv rmoval from aquous solutions by nanocrystallin akaganèit., Chmosphr, vol. 58, no., pp , Jan [4 L. Xiao, W. Ma, M. Han, and Z. Chng, Th influnc of frric iron in calcind nano-mg/al hydrotalcit on adsorption of Cr (VI) from aquous solution., J. Hazard. Matr., vol. 86, no., pp , Fb. 20. [5] D. Krishna and R. Sr Padma, Rmoval of Chromium from Aquous Solution by Custard Appl ( Annona Squamosa ) Pl Powdr as Adsorbnt, Int. J. Appl. Sci. Eng., vol., no. Novmbr 202, pp. 7 94, 203. [6] A. R. Ntzahuatl-muñoz, F. D. M. Guillén-jiménz, B. Chávz-gómz, and T. L. Villgas-garrido, Kintic Study of th Effct of ph on Hxavalnt and Trivalnt Chromium Rmoval from Aquous Solution by Cuprssus lusitanica Bark, pp , 202. [7] M. U. Dakiky, M. Khamis, A. Manassra, and M. Mr, Slctiv adsorption of chromium ž VI / in industrial wastwatr using low-cost abundantly availabl adsorbnts, pp , [8] S. S. Baral, S. N. Das, and P. Rath, Hxavalnt chromium rmoval from aquous solution by adsorption on tratd sawdust, Biochm. Eng. J., vol. 3, no. 3, pp , [9] N. S. Rajurkar, A. N. Gokarn, and K. Dimya, Adsorption of Chromium(III), Nickl(II), and Coppr(II) from Aquous Solution by Activatd Alumina, CLEAN - Soil, Air, Watr, vol. 39, no. 8, pp , Aug. 20. [0] M. Gholipour, H. Hashmipour, and M. Mollashahi, HEXAVALENT CHROMIUM REMOVAL FROM AQUEOUS SOLUTION VIA ADSORPTION ON GRANULAR ACTIVATED CARBON : ADSORPTION, DESORPTION, MODELING AND, Ntwork, vol. 6, no. 9, pp. 0 8, 20. [] T. Liu, L. Zhao, D. Sun, and X. Tan, Entrapmnt of nanoscal zro-valnt iron in chitosan bads for hxavalnt chromium rmoval from wastwatr., J. Hazard. Matr., vol. 84, no. 3, pp , Dc [2] K. Xu, C. Li, J. Liu, and W. Png, Study on Chromium ( VI ) Rmoval from Aquous Solution Using F Mn Bimtal Oxid, Education, no. 2008, pp , 20. [3] U. Tknologi and M. Prlis, Adsorption Procss of Havy Mtals by Low-Cost Adsorbnt : A Rviw Dpartmnt of Chmical and Environmntal Enginring, Faculty of Enginring, Dpartmnt of Chmistry, Faculty of Applis Scinc, vol. 28, no., pp , 203. [4] S. Rngaraj, C. K. Joo, Y. Kim, and J. Yi, Kintics of rmoval of chromium from watr and lctronic procss wastwatr by ion xchang rsins : 200H, 500H and IRN97H, vol. 02, pp ,

7 Author Vivk Bhusari Associat Profssor,G.H.Raisoni Collg of Enginring, Nagpur Author 2 Ms.Rashmi Dahak Rsarch Fllow,(CSIR) NEERI,Nagpur Author 3 Dr.Sadhana Rayalu Principl Scintist & Had Environmntal Matrial Division CSIR, NEERI, Nagpur Author 4 Dr.Amit Bansiwal Sr. Scintist Environmntal Matrial Division CSIR, NEERI, Nagpur