Treatment of Wastewater Contaminated with Nickel Using Khulays Activated Bentonite

Transcription

1 Intrnational Journal of Enginring & Tchnology IJET-IJENS Vol:12 No:04 14 Tratmnt of Wastwatr Contaminatd with Nickl Using Khulays Activatd Bntonit S. S. Al-Shahrani Abstract-- This rsarch projct invstigats th application of Khulays activatd clay (bntonit) to rmov nickl from wastwatr. Th rmoval charactristics of nickl ions from wastwatr using Khulays activatd bntonit wr invstigatd undr various oprating variabls lik shaking tim, solution ph, clay dosag and initial mtal concntration. Th rsults showd that th sorption of nickl ions on Saudi activatd clay was rlativly fast and th quilibrium was rachd aftr 40 min. Thy also showd that incrasing th initial nickl concntration dcrasd nickl rmoval prcntag du to th saturation of clay with nickl ions. Furthrmor, th adsorption of nickl incrass from 70 to 100 % with an incras in solution ph from 2.0 to 9.0. Th adsorption isothrm data wr wll fittd with both th linarizd Langmuir and Frundlich modls. Nickl adsorption onto Saudi activatd bntonit was wll rprsntd by th psudo-scond-ordr kintic modl. Indx Trms-- Rmoval of nickl, Saudi bntonit, adsorption of nickl, havy mtals rmoval, adsorption isothrm, adsorption kintic. I. INTRODUCTION Efflunt wastwatrs from procsss such as lctroplating, mtal finishing, mtallurgical, chmical manufacturing and battry manufacturing industris contain toxic substancs, mtal acids, alkalis, and othr substancs. Rmoval of havy mtals such as nickl from aquous solutions is ncssary bcaus of th frqunt apparanc of ths mtals in wast strams. This problm has rcivd considrabl attntion in rcnt yars du primarily to concrn that thos havy mtals in th wast strams can b radily adsorbd by marin animals and dirctly ntr th human food chains, thus prsnting a high halth risk to consumrs [1, 2]. Nickl compounds ar important in modrn industry and ar usd in lctroplating, lctroforming, and for production of nickl cadmium battris and lctronic quipmnt. Nickl alloys, lik stainlss stl, ar usd in th production of tools, machinry, armamnts, and appliancs. Thy ar also usd to cast coins, and to produc jwllry and mdical prosthss. As th rsult of acclratd consumption of nickl-containing S. S. Al-Shahrani is srving in Dpartmnt of Chmical and Matrial Enginring, King Abdulaziz Univrsity, Saudi Arabia products nickl compounds ar rlasd to th nvironmnt at all stags of production and utilization. Thir accumulation in th nvironmnt may rprsnt a srious hazard to human halth. Among th known halth rlatd ffcts of nickl ar skin allrgis, lung fibrosis, variabl dgrs of kidny and cardiovascular systm poisoning and stimulation of noplastic transformation [3,4]. Adsorption of nickl ions by clay has bn th subjct of svral rcnt studis [5,6,7,8,9]. It was found that th adsorption of nickl from aquous solution dpnds on contact tim, amount of adsorbnt, solution ph and Nickl concntration. Th main objctiv of this study is to invstigat th fasibility of using Khulays activatd clay (bntonit) to rmov nickl from wastwatr. Th choic of this matrial is basd on its low cost, considring its abundanc in Khulays bntonit dposit, 95 km north of Jddah. II. MATERIALS AND METHODS A. Prparation of Saudi activatd bntonit Th clay usd in this study was collctd from Khulays bntonit dposit, 95 km north of Jddah. It was not activ in its natural stat. In ordr to modify its adsorptiv proprty, natural bntonit was activatd using sulfuric acid laching. Th xprimntal st up and chmical tratmnt mthod with H 2 SO 4 which was carrid out in this study ar similar to what hav bn dscribd prviously [10]. Tabl (1) shows th chmical composition of Saudi Activatd bntonit. TABLE I Chmical composition of and Saudi Activatd bntonit [10]. Compound Chmical composition (%) Sio Al 2 O F 2 O TiO2 1.5 MgO 0.73 CaO <0.05 K 2 O 0.48 Na 2 O 0.12 MnO 0.05 SO 3 <0.05 P 2 O 5 <0.05 L.O.I.(1000oC) 15.3

2 Intrnational Journal of Enginring & Tchnology IJET-IJENS Vol:12 No:04 15 Th acid tratmnt was conductd using a batch ractor with boilr-rflux condnsr and a magntic stirrr/hot plat. Acid activation was don using th optimum oprating variabls such as, 15% by wight acid concntration, th tmpratur of boiling, 90 minuts raction tim, modrat mixing, grain siz of -200 msh (74 m) and watr to clay ratio of 5:1. B. Adsorption procss Adsorption tsts wr mad by batch tchniqu at room tmpratur (25 o C). Stock solution (1000 mg/l) of nickl is prpard by dissolving th appropriat amounts of analytical ragnt grad Ni(NO 3 ) 2.6H 2 O, in distilld watr. Th stock solutions wr dilutd as rquird to obtain standard solutions containing mg/l of a rquird havy mtal. A sampl of 50 ml of th dilutd nickl solution was addd to a group of 100 ml conical flasks. Saudi activatd bntonit sampl in th rang of g was addd to ach flask undr continus mixing using Horizontal Shakr (JULABO SW 22). ph adjustmnts was carrid out using 1N HCl and 1N NaOH. 200 rpm shaking was applid in th shakr. Aftrward, sampls wr takn out from th shakr at rgular contact tim intrvals and th clay was sparatd by filtring. Th filtrat was analyzd for nickl concntration by atomic absorption spctrophotomtr (AAS). Th ffcts of svral factors such as ph, concntration of solution, clay mass and contact tim on nickl rmoval fficincy wr invstigatd. III. RESULT AND DISCUSSIONS C. Effct of contact tim Nickl adsorption was studid by varying th contact tim btwn th adsorbat and adsorbnt in th rang 1-60 min. Adsorption of nickl at diffrnt contact tim was studid for initial nickl concntration ranging from 20 to 100 ppm, whil th dos of clay sampl was 0.5 g/50 ml and th solution ph was kpt unchangd at 3.2. Th data showd that th sorption of nickl ions on Saudi activatd bntonit was rlativly fast whr th quilibrium was rachd aftr 40 min (Figur 1). Th adsorption procss is fast at th bginning of th raction du to th adsorption of nickl on th surfac sits of clay. Th rsults show that shaking th mixtur of diffrnt initial concntration for 40 minuts was sufficint to rach quilibrium. Thy ar also show that incrasing th initial nickl concntration dcrasd nickl rmoval prcntag du to th saturation of clay with nickl ions. Saudi activatd bntonit rmoval fficincy nds to b incrasd by incrasing solution ph about 7 to avoid th nickl hydroxids prcipitation rgion which it is start at th ph of 8 [11] Fig. 1. Effct of shaking tim on th rmoval of nickl by Saudi Activatd bntonit. Initial mtal concntration varis btwn 20 and 100 mg/l, clay dosag: 0.5 g/ 50 ml, ph= 3.2. D. Effct of PH Solution ph is an important variabl which controls th adsorption of th havy mtal from wastwatr. Th ffct of ph on th rmoval of nickl ions by Saudi activatd bntonit was invstigatd. Th adsorption of nickl was studid in th ph rang 2 9 with a constant clay amount of 0.5 g/50 ml of nickl solution, shaking tim of 40 min and nickl concntration of 50 ppm. Th rsults prsntd in Figur (2) show that th adsorption of nickl incrass from 70 to 100 % with an incras in solution ph from 2.0 to 9.0. Th ffct of initial ph on nickl rmoval may b xplaind as mntion bfor [11], whr in th acidic conditions, both adsorbnt and adsorbat ar positivly chargd (M 2+ and H + ) and thrfor, th nt intraction is that of lctrostatic rpulsion. In addition, th H + ions prsnt in highr concntration in th aquous mdium compt with th positivly chargd Ni 2+ ions for th surfac adsorbing sits, rsulting in a dcras in th rmoval of nickl.

3 Intrnational Journal of Enginring & Tchnology IJET-IJENS Vol:12 No:04 16 Fig. 2. Effct of ph on th rmoval of nickl by Saudi Activatd Bntonit. Initial nickl concntrations 100 mg/l, clay dosag: 0.5g/50 ml, contact tim: 40 min. E. Effct of clay dosag Th ffct of th amount of Saudi activatd bntonit on nickl rmoval was invstigatd at a constant valu of initial mtal concntration (100 ppm), clay dosag ( g/50 ml), contact tim (40 min), ph = 7 and tmpratur (25 o C). As shown in figur (3), th rmoval of nickl incrasd gradually from 16% at 0.05 g/50 ml up to 94% at 1.25 g/50 ml. Howvr, this rsult was xpctd sinc as th dos of adsorbnt incrass, th numbr of adsorbnt sits incrass. Ths amounts attach mor ions to thir surfacs [12]. Similar rsults wr rportd whr many typs of matrials wr usd as adsorbnts [13]. F. Adsorption isothrm Th adsorption isothrm for nickl was studid using initial concntrations of mtal at 100 ppm, ph = 7, tmpratur at 25 o C and amount of clay dosag ( g/50 ml). Th data obtaind wr fittd to th Langmuir [14] and Frundlich [15] isothrms. Ths modls wr tstd to dtrmin th maximal capacity of nickl rmoval using Saudi activatd bntonit. Th quality of th isothrm fit to th Th Langmuir quation, in th linar form is writtn as: C 1 C q bq q max (1) whr C is th quilibrium concntration of mtal ions (mg/l), q is th amount of mtal ions adsorbd pr unit wight of adsorbnt (mg/g bntonit), q max is th maximum adsorption capacity (mg/g), and b is th adsorption quilibrium constant (l/mg). For th Frundlich quation th linar form is writtn as: 1 log q log K log C n (2) whr k and n ar th constant charactristics of th systm. Th bst stimatd valus of all th quation paramtrs ar summarizd in Tabl (2).Th adsorption isothrm data ar wll fittd with both th linarizd Langmuir and Frundlich quations and giv R 2 = as shown in figurs (4) and (5). Th maximum adsorption of Saudi activatd clay quals to mg/g. Isothrm paramtrs max TABLE II Th Langmuir and Frundlich quation paramtrs prdictd from adsorption isothrm data of nickl ions onto Saudi activatd bntonit at ph = 7, 25 o C and initial nickl concntration of 100 ppm. Valu Langmuir q max (mg/g) b (l/mg) 0.03 R Frundlich K (mg/g) N 1.73 R According to Tryball [16], it has bn shown using mathmatical calculations that n valus of btwn 1and 10 for th Frundlich isothrm indicat ffctiv adsorption. Fig. 3. Effct of clay dosag on th rmoval of nickl by Saudi activatd bntonit. Initial nickl concntrations 50 mg/l, ph = 7,contact tim: 40 minuts.

4 Intrnational Journal of Enginring & Tchnology IJET-IJENS Vol:12 No:04 17 Fig. 4. Langmuir plot for th adsorption of nickl on Saudi activatd bntonit. k1 (log q qt ) log q t (3) whr k 1 (min 1 ) is th first-ordr rat constant, q (mg /g) is th amount of adsorbd mtal ions on th Saudi bntonit at quilibrium and q t (mg /g) is th amount of nickl adsorbd at tim t (min). Th first-ordr constants can b obtaind by plotting log (q q t ) vrsus tim. Th xprimntal adsorption kintics data wr analyzd by applying th psudo-scond-ordr kintics modl, which is xprssd as: t 1 1 t (4) 2 q k q q t 2 whr k 2 (g/(mg/min)) is th psudo-scond-ordr kintics constant, q (mg /g) is th amount of adsorbd mtal ions on th Saudi bntonit at quilibrium and q t (mg /g) is th amount of nickl adsorbd at tim t (min). Th fit of this modl was chckd by ach linar plot of (t/q t ) vrsus t as shown in Figur (6). By comparing to th rgrssion cofficints for ach xprssion. A good agrmnt of th xprimntal data with th scond ordr kintic modl was obsrvd. Th corrlation cofficint for th scond ordr kintic modl is and th calculatd q valus agr vry wll with th xprimntal data. Thus, a plot of t/q t against t should giv a linar rlationship with a slop of 1/q. Ths rsults agr with sam rsults rportd bfor [18]. Fig. 5. Frundlich plot for th adsorption of nickl on Saudi activatd bntonit. G. Adsorption kintics Th modls of adsorption kintics corrlat th solut uptak rat. It is on of th important charactristics dfining th fficincy of sorption. Th kintic paramtrs for th adsorption procss wr studid on th batch adsorption at room tmpratur, initial nickl concntration of 50 ppm, clay dosag was 0.5 g and th initial solution ph was kpt unchangd at 3.2. Th data wr fittd to th first-ordr Lagrgrn quation [17], Fig. 6. Plot of scond ordr modl for nickl adsorption by Saudi activatd bntonit.

5 Intrnational Journal of Enginring & Tchnology IJET-IJENS Vol:12 No:04 18 IV. CONCLUSIONS 1. Saudi natural bntonit sampls, which wr obtaind from khulays dposits, wr grindd and sivd to grain siz of -200 msh (75 m). Ths sampls wr activatd using sulphuric acid to modify thr adsorptiv proprty. 2. Acid activation was conductd using th optimum oprating variabls such as, 15% by wight acid concntration, th tmpratur of boiling, 90 minuts raction tim, modrat mixing and watr to clay ratio of 5:1. 3. Th sorption of nickl ions on Saudi activatd clay was rlativly fast and th quilibrium was rachd aftr 40 min. Th rsults show that shaking th mixtur of diffrnt initial concntration for 40 minuts was sufficint to rach quilibrium. Thy ar also show that incrasing th initial nickl concntration dcrasd nickl rmoval prcntag du to th saturation of clay with nickl ions. 4. Rmoval of nickl ions by Saudi activatd bntonit is ffctd by mixtur ph. Th adsorption of nickl incrass from 70 to 100 % with an incras in solution ph from 2.0 to Nickl rmoval dcrass with incrasing nickl concntration whn nickl concntration incrass from 20 to 100 ppm. 6. Th rmoval of nickl incrass as th dos of Saudi activatd bntonit incrass. This is du to incras in th numbr of adsorbnt sits. 7. Th adsorption isothrm data wr wll fittd with both th linarizd Langmuir and Frundlich. 8. A batch adsorption kintic xprimnt rvald that nickl adsorption onto Saudi activatd bntonit was wll rprsntd by th psudo-scond-ordr kintic modl. It can b concludd that film diffusion and intraparticl diffusion ar simultanously oprating in th whol adsorption procss. 9. Saudi activatd bntonit can b considrd as a promising adsorbnt for th rmoval of nickl from wastwatr. 10. Furthr rsarch can b don in th futur using Saudi activatd bntonit to rmov othr havy mtals such as cobalt, chromium, cadmium from wastwatr. V. ACKNOWLEDGMENT Th author would lik to thank th Danship of Scintific Rsarch, King Abdulaziz Univrsity, for thir financial support to accomplish this rsarch. Th invstigator would lik to thank Dpartmnt of Chmical Enginring staff, King Abdulaziz Univrsity, for thir continual support and invaluabl suggstion during this rsarch. VI. REFERENCES [1] S.H. Lin, S.L Lai, H.G. Lu, Rmoval of havy mtals from aquous solution by chlating rsin in a multistag adsorption procss. Journal of Hazardous Matrials B76, 2000, pp [2] Tonni Agustiono Kurniawan, Y.S. Gilbrt, Chana,Wai-Hung Loa, Sandhya Babl. Physico chmical tratmnt tchniqus for wastwatr ladn with havy mtals. Chmical Enginring Journal 118, 2006, pp [3] E. Dnkhaus, K. Salnikow. Nickl ssntiality, toxicity, and carcinognicity. Critical Rviws in Oncology/Hmatology 42, 2002, pp [4] RG. Garrtt, Natural sourcs of mtals to th nvironmnt. In: Cntno JA, Collry P, Frnt G, Finklman RB, Gibb H, Etinn J- C, ditors. Mtal ions in biology and mdicin, vol. 6. 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