Development of modelling equations for the removal of Nickel (II) from aqueous solutions

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1 Intrnational Journal of ChmTch Rsarch CODEN (USA): IJCRGG ISSN: Vol.8, No.11 pp , 2015 Dvlopmnt of modlling quations for th rmoval of Nickl (II) from aquous solutions G.Babu Rao 1, M. Krishna Prasad 1, Ch.V.R.Murthy 2 1 Dpartmnt of Chmical Enginring, GMR Institut of Tchnology,Rajam, Srikakulam District, Andhra Pradsh, India 2 Dpartmnt of Chmical Enginring, Univrsity Collg of Enginring, Andhra Univrsity, Visakhapatnam ,Andhra Pradsh, India. Abstract: This papr prsnts adsorption rsults concrning nickl (II) ions on th surfac of 5Å molcular sivs. Th paramtrs which tnd to favour th adsorption of aquous solution wr optimizd and th surfac morphology of th molcular sivs was dtrmind by mans of Scanning Elctron Microscopy (SEM) whil th vidnc of functional groups was highlightd by Fourir transform infrard spctroscopy (FTIR) masurmnts. Ths quilibrium & kintic studis wr compard by computr simulations to invstigat th dviations. FTIR analysis rvald that NH (bnding), C-H (Strtching), C=O (Strtching) and OH functional groups ar rsponsibl for Ni (II) adsorption. Th xprimntal paramtrs invstigatd includ initial solution ph, mtal concntration, adsorbnt dos and tmpratur. Kywords: 5Å molcular sivs, Adsorption, Nickl (II), Isothrm, Kintics, SEM, FTIR. Introduction Th contamination of wastwatr by toxic havy mtallic cations is a worldwid nvironmntal problm. A numbr of tchniqus such as filtration, rvrs osmosis; chmical prcipitation, ion xchang, lctro-dposition and adsorption hav bn usd to rmov th toxic mtals from aquatic nvironmnt with varying dgr of succss. All ths mthods hav inhrnt advantags and limitations 1. Natural zolits ar hydratd aluminosilicat minrals of a porous structur with valuabl physicochmical proprtis, such as cation xchang, molcular siving, catalysis and sorption. Th us of natural zolits for nvironmntal applications is gaining nw rsarch intrsts mainly du to thir proprtis and significant worldwid occurrnc. Application of natural zolits for watr and wastwatr tratmnt has bn ralisd and is still a promising tchniqu in nvironmntal claning procsss. In th past dcads, utilisation of natural zolits has bn focussd on ammonium and havy mtal rmoval du to th natur of ion xchang and som rviw paprs hav bn appard 2. Molcular sivs ar widly applid in catalysis, adsorption, and sparation, as ths procsss bnfit from thir highly ordrd channls and ion xchang abilitis. Molcular sivs ar usually prpard using hydrothrmal or solvothrmal synthsis mthods. Morovr, th challngs associatd with novl approachs for th synthsis of molcular sivs with xotic structurs and proprtis continu to b of grat importanc in th fild of molcular siv matrials 3.

2 G.Babu Rao t al /Int.J. ChmTch Rs. 2015,8(11),pp Equilibrium Studis: Matrials Molcular Sivs 4 or zolits, Mrck Ltd., Worli, and Mumbai ar crystallin aluminum silicats of group IA and IIA lmnts usd for th sparation. Natural zolits ar good potntial matrial for watr and wastwatr tratmnt. Th potntial advantags for application of natural zolits in watr and wastwatr tratmnt ar promising. Firstly, a bnfit gaind by using natural zolits for watr and wastwatr tratmnt is thir ability to undrgo ion-xchang and adsorption. In addition, natural zolits can b tratd and modifid in ordr to trap contaminants in watr and wastwatr. Also, natural zolits xist abundantly low cost and only low tchnology systms ar rquird. An additional bnfit of using natural zolits is thir rgnrativ proprtis 5. Prparation of stock solution Nickl Sulphat solution was prpard by dissolving g Nickl Sulphat salt in 1000 ml standard volumtric flask with d-minralizd watr, which approximatly givs 2000 ppm of Ni 2+ in solution. From th stock solutions, xprimntal tst solutions wr prpard by diluting th primary stock solution with dminralizd watr. Th ph rang was adjustd by rational addition of spcifid minral acid. Mthods: Equilibrium studis Th xprimnts wr carrid out in 250 ml Erlnmyr conical flasks, at a constant agitation spd (160 rpm) with 100 ml solution and rquird amount of adsorbnt using orbital shakr (Kmi mak). Initially th ffct of contact tim (0 360 min) on th sorption capacity of 5Å Molcular sivs was valuatd. Th quilibrium tim was obtaind and th xprimnts wr conductd for th sam tim for all conditions. Batch xprimnts wr carrid out to invstigat th adsorption bhaviour of Ni 2+ on 5Å Molcular siv. Analysis of havy mtal ions Th concntrations of unadsorbd Ni 2+, in th sampl solutions wr dtrmind using an Atomic Absorption Spctrophotomtr (PrkinElmr modl AA 400). Th mtal uptak (q ) was calculatd using th gnral dfinition: q V ( CT - C ) = (1) M whr q is th mtal uptak of mg Ni 2+.g -1 adsorbnt, V is th volum of mtal containing solution in contact with th adsorbnt in L, C T and C ar th total and quilibrium (rsidual) concntration of mtal in th solution mg L -1, rspctivly, and M is th amount of addd adsorbnt in g. Mtal % of rmoval by 5Å Molcular sivs was dtrmind by Eq. (2) as follows: R (%) = (C T -C )/C T *100 (2) whr R is th prcntag of Ni(II) adsorbd by biomass, C T is th total concntration of mtal ions in mg L -1 and C is th concntration of mtal ions at tim t in mg L -1. Rsults and discussions 1. Effct of contact tim: Exprimnts wr conductd to stimat th tim rquird to rach th sorption quilibrium by taking an initial charg of 100 ml of aquous solution containing Ni (II) ions and rquird quantitis of biomass. Th mixtur was shakn in an orbital shakr; th sampls wr drawn at rgular tim intrvals, and th mtal concntration was stimatd using AAS. Th data of concntration of mtal ion Ct in solution with tim ar shown for diffrnt quantitis of biomass in fig1. Exprimntal rsults shows fastr uptak at initial stags of

3 G.Babu Rao t al /Int.J. ChmTch Rs. 2015,8(11),pp contact, and subsqunt slowing down as th quilibrium is approachd. In th initial stags of contact, larg numbrs of vacant sits ar availabl, and hnc th uptak is fastr. Th slowing down of mtal uptak latr is du to difficulty in occupying th rmaining vacant sits. Rpulsiv forcs btwn th adsorbd Pb (II) ions and aquous Pb (II) may also most probably contribut to th slowing down of uptak of mtal at quilibrium 6. It can b obsrvd from th graph th mtal ion concntration dcras with tim and rachs a platau aftr 5 hours for Ni 2+ using 5Å molcular sivs, indicating attainmnt of quilibrium for th prsnt study. No significant chang in th adsorption with furthr incras in contact tim was noticd. Fig.1. Variation of aquous mtal (Ni 2+ ) concntration with tim using 5Å molcular sivs as an adsorbnt at 25 C, 97.3 mg/l and ph 5. Effct of ph Th ph of th solution aftr contact with synthtic zolit MAP incrasd to rgardlss of th initial ph (3.2 for th synthtic solution, 7.1 for th storm watr). This is typical of synthtic zolits and is du to hydronium ion xchang rducing th concntration of protons in solution 7. Th ffct of ph on th adsorption of Ni 2+ mtal ion ovr 5Å molcular sivs wr studid in th ph rang 3 6.In cas of 5Å molcular sivs th prcnt rmoval of adsorption was incrasd from 53.36% to 59.12% (Fig.2) at a total mtal ion concntration of 95 mg/l as ph was incrasd from 3 to 5. Th maximum adsorption was found to b 60.85% at ph 5 thrfor all th subsqunt xprimnt runs wr conductd at ph 5 and ph byond 5, th adsorption yild for Ni 2+ ions showd a dclin. Fig2. Effct of ph on prcnt adsorption at various total mtal ion (Ni 2+ ) concntration and at a tmpratur of 25 C and 20g/L, using 5Å molcular sivs. Effct of mtal ion concntration An incras in total Ni 2+ concntration of mg/l to mg/l dcrasd th prcnt of rmoval to 49.09% (Fig C) at Sorbnt dos of 20g/L, tmpratur 25 0 C and ph 5 using 5Å molcular sivs shown in fig3.

4 G.Babu Rao t al /Int.J. ChmTch Rs. 2015,8(11),pp Fig.3.Variation of % rmoval of Ni 2+ with various total concntration of Ni 2+ at tmpratur of 25 C, 20 g/l of 5Å molcular sivs. Effct Of Adsorbnt Dosag In cas of 5Å molcular sivs, th % obtaind incrasd from to 59.63% (Fig.4) at total Ni 2+ Concntration of 145mg/L and th uptak capacity showd a dcras from to 4.37 mg/g. Fig.4.Variation of % Ni 2+ adsorption with various adsorbnt wights at various total mtal ion concntration, at tmp of 25 C and ph 5 using 5Å molcular sivs. Effct of Tmpratur Th xprimnts with Ni 2+ wr conductd in th tmpratur rang of C. Th adsorption capacity of Ni 2+ incrasd from to % with an incras in tmpratur in th rang C (s at a total concntration of 24 mg/l in Fig.5 using 5Å molcular sivs. Fig.5.Variation of prcnt adsorption of Ni 2+ mtal ion with tmpratur using 5Å molcular sivs as adsorbnt at diffrnt total mtal ion concntrations and at ph of 5.

5 G.Babu Rao t al /Int.J. ChmTch Rs. 2015,8(11),pp Adsorption isothrm modls Th Langmuir and Frundlich quations ar commonly usd for dscribing adsorption quilibrium of adsorbat onto th adsorbnt. Th Langmuir isothrm is applicabl to monolayr chmisorptions whil Frundlich isothrm is usd to dscrib adsorption on surfac having htrognous nrgy distribution: Langmuir isothrm A basic assumption of th Langmuir thory 8 is that sorption taks plac at spcific homognous sits within th sorbnt. This modl can b writtn in non-linar form and is rprsntd by th quation: C q C = 1 + qmb q (3) m whr q m is th maximum amount of th mtal ion pr unit wight of adsorbnt to form a complt monolayr on th surfac bound at high C (mg.g -1 ), and b is a constant which accounts for th affinity of th binding sits (L mg - 1). From th plots btwn (C /q ) and C th slop (1/q m ) and th intrcpt (1/b q m ) can b calculatd. Th linar Langmuir adsorption isothrms of Ni 2+ for th adsorbnt obtaind at diffrnt tmpraturs ar givn in Fig.6.constant valus at diffrnt mtal ion concntrations was calculatd and th valus wr shown in Tabl 1. Fig.6. Langmuir plot for adsorption of Ni 2+ ovr 5Å molcular sivs as adsorbnt at various tmpraturs for adsorbnt wight 20g/L and at ph 5. Frundlich isothrm Frundlich isothrm[9] is th arlist known rlationship dscribing th adsorption quation and is oftn xprssd as: q f n f = K C (4) Taking logarithm on both sids: 1 logq = logk f + log C (5) n f 1 Whr q is quilibrium adsorption capacity (mg/g), C is th quilibrium concntration of th adsorbat in solution, K f and nf ar constants rlatd to th adsorption procss such as adsorption capacity and intnsity rspctivly. Th plots in Fig.8 shows linar that th isothrm drawn for adsorption of Ni 2+ onto 5Å Molcular sivs and fittd wll at various tmpraturs shown in fig7.

6 G.Babu Rao t al /Int.J. ChmTch Rs. 2015,8(11),pp Fig.7.Frundlich plot for adsorption of Ni 2+ adsorbnt wight 20g/L and at ph 5. ovr 5Å molcular sivs at diffrnt tmpraturs for Tabl 1. Langmuir & Frundlich isothrm modl paramtrs and R L valus at diffrnt initial mtal ion concntrations for Ni 2+ adsorption by 5Å Molcular sivs Tmp. (K) Langmuir constants Frundlich constants Sparation factor q m (mg/g) b(l/mg) R 2 k f n f R 2 C T (mg/l) R L Adsorption kintic modls: Psudo-first-ordr/Lagrgrn kintic modl Th psudo-first-ordr or Lagrgrn kintic rat quation for th adsorption of liquid solid systm was drivd basd on solid adsorption capacity. It is on of th most widly usd adsorption rat quations for adsorption of a solut from a liquid solution. Th psudo first ordr kintic quation can b xprssd as: dq dt = k 1 (q - qt) (6) Aftr intgration and applying th boundary conditions, for q t = 0 at t= 0 and q t = q t at t= t, th intgratd form of Eq. (6) bcoms: log( q - q ) = logq - k1t t (7) In th prsnt study Psudo first ordr and Psudo scond ordr kintic modls hav bn attmptd. Th plots btwn log(q q t ) and tim, t of Eq.7 show that th Lagrgrn psudo-first ordr kintic modl dos not fit wll for th adsorption of mtal ions in th prsnt study, as thy do not follow a straight lin shown in Fig.8. Psudo-scond-ordr kintic modl In viw of th abov th fitnss of th sorption data was tstd using psudo-scond-ordr raction modl. Th psudo-scond-ordr raction modl could b xprssd by th rat xprssion as :

7 G.Babu Rao t al /Int.J. ChmTch Rs. 2015,8(11),pp dq = k ( q - q ) 2 dt 2 t (8) On intgration for boundary conditions whn t = 0 to t > 0 and qt = 0 to qt > 0 and furthr simplifications, Eq. (8) bcoms: t = t q k q 2 q t 2 (9) Th plot (Fig.10) of t/q t vs. t of Eq. (9) gav a linar rlationship from which th q and k 2 valus wr dtrmind. Th rat constants and th corrlation cofficints for psudo-scond-ordr kintic modl wr calculatd and summarizd in Tabl 2. Ths valus showd that th psudo-scond ordr kintic plots fit wll th adsorption data of cadmium mtal for th adsorbnt. Fig.8.First ordr kintic plot for adsorption of mtal ion (Ni 2+ ) at 25 C, C 0 50 mg/l and ph 5, using 5Å molcular sivs. Fig.9.Scond ordr kintic plot for adsorption of mtal ion (Ni 2+ ) at 25 C, C 0 50 mg/l and ph 5, using 5Å molcular sivs. Thrmodynamic paramtrs and thir dtrmination Thrmodynamic paramtrs Gibbs fr nrgy ΔG is th basic critrion for dciding whthr th chmical procss dos occur/procd or not. Th spontanity of th raction can also b judgd by th sign and magnitud of ΔG. A ngativ sign for ΔG is an indicativ of th spontanity of any chmical procss.

8 G.Babu Rao t al /Int.J. ChmTch Rs. 2015,8(11),pp Th thrmodynamic paramtrs such as changs in standard fr nrgy chang ΔG, nthalpy ΔH, ntropy ΔS for any givn adsorption procss could b dtrmind from th Equation: DG = -RTlnK C (10) whr ΔG,is th fr nrgy chang, xprssd as J mol -1. b is th Langmuir quilibrium constant for th procss. Th valus of b (Tabl 1) at diffrnt tmpraturs wr procssd according to th following Van t Hoff quation. Cad DH DS log = - + C 2.303RT 2.303R (11) whr b is in L mg -1, R is univrsal gas constant (8.314 J/mol.K) Th nthalpy changs ( H ) and ntropy changs (ΔS ) for th adsorption procss of Ni 2+ using 5Å Molcular sivs wr obtaind from th plot of Cad log drawn against 1/T (Fig.11)and wr compild in Tabl 3. C Fig.10.Vant Hoff plot for adsorption of Ni 2+ ovr 5Å molcular sivs as adsorbnt Plottd log Cad/C vs 1/T at diffrnt total mtal ion concntration using 20g/L adsorbnt at ph 5. Tabl 2. Kintic paramtrs for Ni 2+ adsorption on 5Å Molcular sivs. W(g L -1 ) K 2 (gmg -1 min -1 ) q (th) mg.g -1 q (xp) mg.g -1 R Tabl3. Thrmodynamic paramtrs for Ni 2+ adsorption 5Å Molcular sivs C 0 (mg L -1 ) H 0 (kj mol -1 ) S 0 (J mol -1 K) G 0 (kj mol -1 ) Tmp. (K)

9 G.Babu Rao t al /Int.J. ChmTch Rs. 2015,8(11),pp Biomass charactrization Fourir transform infra rd spctroscopy analysis. Th FTIR spctrum of 5Å molcular sivs bfor and aftr adsorption was shown in Fig.11&12. Th broad band at cm -1 is du to corrsponding to th OH-strtching vibration 10.Th band at cm -1 indicatd CºC strtch, alkyns. Th band at cm -1 indicatd that th prsnc of combinational functional groups of aromatic aryl rings. Fig.11.FT-IR Spctrum of unloadd 5Å molcular sivs Fig.12.FTIR Spctrum of Ni 2+ loadd 5Å molcular sivs Charactrization of 5Å Molcular sivs using SEM Studis Th SEM imags wr takn by applying 10 kv voltag with diffrnt magnification tims for th clarification of surfac. Th SEM micrographs of 5Å molcular sivs powdr bfor and aftr adsorption wr studid and ar dpictd in Fig.13&14. SEM imags of pur 5Å molcular sivs (Fig.13) show that numbr of pors with diffrnt diamtrs and diffrnt por aras. Furthr, pors facilitat th good possibility for mtal ions to b adsorbd 11. Th SEM obsrvation rvald its complx and porous surfac txtur. Pors and intrnal surfac ar rquisit for fficint adsorption.

10 G.Babu Rao t al /Int.J. ChmTch Rs. 2015,8(11),pp Fig.13.SEM of powdr 5Å molcular sivs without mtal ions Fig.14. SEM of powdr 5Å molcular sivs loadd with Ni 2+ ions. Rgrssion analysis Rgrssion analysis also carrid out to calculat th standard dviation and avrag dviation of th quilibrium data by Forc 2.0 softwar. Th standard and avrag dviations hav rprsntd in th blow dvlopd quation. Th valus of diffrnt constants obtaind by both graphical analysis and rgrssion analysis ar in good agrmnt.th blow quation prdicts th mtal uptak vry wll with an avrag dviation of 15-20%. Th FORTRAN program usd for rgrssion analysis. Th quilibrium mtal uptak capacity (q ) is givn by q = f (C, C H, L/S, T) (12) q= 0.374*10-4 (C ) (C H ) (L/S) (T) (13) Avrag Dviation=10%,Standard Dviation=13%. Conclusions Th tim rquird to rach quilibrium for 5Å molcular sivs was found to b 5 hours for Ni 2+.An incras in aquous mtal concntration incrasd mtal adsorption for all conditions of th study.dcrass in ph of aquous phas dcrasd mtal adsorption du to th prfrntial adsorption of H + ion compard to mtal ions. ph 5 was to b found to favor mtal adsorption of all mtal ions. Incras in wight of molcular sivs lads to slightly incrass prcnt adsorption and th quilibrium mtal uptak dcrass in all th conditions of prsnt study. Incrasing tmpratur incrass mtal adsorption from 288K to 313K in th rmoval of mtal ions in th prsnt study, indicating that ndothrmic in natur.

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