The Effectiveness of Low Cost Adsorbents (Onion and Garlic Skins) In The Removal of Cd(II) from Aqueous Solution

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1 Th Effctivnss of Low ost Adsorbnts (Onion and Garlic Skins) In Th Rmoval of d(ii) from Aquous Solution Evbuomwan, B.O and Oput, Dpartmnt of hmical Enginring, Univrsity of Port Harcourt, Port Harcourt, Nigria. Abstract: - In this study, th ffctivnss of onion and garlic skins for th rmoval of d(ii) from aquous solution was invstigatd. Th physical charactrization, quilibrium and batch studis wr undrtakn to xamin th kintic and thrmodynamic aspct of d(ii) adsorption by ths biosorbnts. Th rsults showd that ph, surfac ara, spcific gravity, spcific gravity, ash contnt and moistur contnts wr 7.2 and 6.87, 2.4m 2 /g and 874.2m 2 /g, 2.25% and.25%, 42.5% and 27% for onion and garlic rspctivly. Th macro lmnts containd in onion and garlic skins wr a, Mg, K, Na, P, and F. Th FTIR analysis showd that th major functional groups on th biosorbnt surfac took part in th mtal ion uptak procss.th Langmuir isothrm modl was found to b suitabl for th adsorption of d(ii) for both biosorbnts. Th kintic study of th adsorption procss follows th psudo scond-ordr. Th thrmodynamic procss was fasibl, spontanous and ndothrmic. In gnral, onion and garlic skins xhibit ffctiv sorption potntials for th rmoval of d(ii) from aquous solution. Kywords: Adsorption, Onion, Garlic, admium, Isothrm, Kintic, aquous solution I I. INTRODUTION n rcnt yars, th incrasing awarnss of th nvironmntal impact of havy mtals has promptd a dmand for th purification of industrial wast watr prior to discharg into watrs bodis by rgulating authoritis. Also, th potntial halth hazard posd by th influx of ths havy mtals in th nvironmnt has stimulatd rsarch into various mans of rmoving thm from th nvironmnt [] At prsnt, thr ar numbr of diffrnt convntional ways for th rmoval of ths havy mtal pollutants from wast watrs whn thy ar prsnt in high concntrations. Ths includ mthods lik prcipitation, ion xchang, ultrafiltration, vaporation, lctrodialysis and solvnt xtraction [2]. Howvr, ths tchnologis ar inffctiv for rmoving ths havy mtals prsnt in low concntrations and costly. Othr drawbacks ar incomplt rmoval of mtals, limitd tolranc to ph chang, modrat or no mtal slctivity, and production of toxic wast products that also nd disposal [2]. As a rsult of th abov challngs, of convntional mtal sparation mthods, thr has bn nd for rsarchrs to look into altrnativs for rmoving havy mtals from wast watrs, which ar cost ffctiv. As a rsult, by-products of agricultur ar rciving much attntion du to thir low cost, availability and nvironmntal frindlinss. Also, using agricultural wast for purifying watr, provids mans of rducing solid wast disposal. Onion and garlic ar bttr altrnativ for th tratmnt of fflunt pollutd with havy mtals. Th biosorbnt ar availabl locally and is cost ffctiv. Both adsorbnts will not pos any nvironmntal problm bcaus thy ar biodgradabl. Thrfor, instad of mploying importd chmicals and tchnologis which ar xpnsiv and somtims poss som nvironmntal challngs, onion and garlic ar bttr altrnativ. Th major cadmium compounds found in air ar cadmium oxid, chlorid, and sulfat.t.c, and ths compounds ar usually xpctd to undrgo transformation in th atmosphr. Th main sourc of cadmium in air is through transportation and dposition. admium can also travl through long distancs in th atmosphr and thn finally sttl (wt or dry) onto soil surfac and watr, which will vntually rsult in lvatd cadmium lvls vn in rmot locations. It can b shown from th 26 final rport of EPA s Urban Air Toxic Monitoring program that th avrag daily cadmium lvls of <. μg/m 3 at svral monitoring sits throughout th Unitd Stats [3[. Ths sits includ: Bountiful, Utah; Northbrook, Illinois; Austin, Txas; St. Louis, Missouri; Indianapolis,.t.c[3]. Atmosphric concntration of cadmium is gnrally highst in th nvironmnt of cadmium-mitting industris [4]. Du to th advancmnt in pollution control tchnologis, cadmium missions to air ar not xpctd to incras, vn though th industris mitting cadmium ar xpctd to grow [5]. Apart from thos who liv nar cadmium-mitting industris, inhalation of cadmium from th ambint air is not th main sourc of xposur. Howvr, immobilizd cadmium is availabl to plant lif and can asily b introducd into th food supply. admium in soil tnds to b mor availabl whn th soil ph is low (acidic) [6]. In this study, th ffctivnss of onion and garlic skins for rmoval of d(ii) from aquous solutions is studid. Th skin of th onion and garlic is th drid up outr parchmnt of bulbs and ar kitchn and agricultural wast products. Pag

2 Litratur survy has shown that thr has bn no prvious study for rmoval of cadmium ion using onion and garlic skins. II. MATERIALS AND METHODS Sampling and sampl prparation Onion and garlic bulbs bought from markt wr cut into small pics, drid, crushd, and washd thoroughly twic with distilld watr to rmov th adhring dirt. Thy wr finally drid in an air ovn at 2 o for 24hours. Aftr drying, th adsorbnt wr sivd. Prparation of mtal ion standard solution mg/l cadmium was prpard by dissolving g of cadmium nitrat in litr of distilld watr. Th ph of th solution was adjustd by using.n of Hl and NaOH. haractrization of biosorbnt Th moistur contnt was dtrmind by wighing xactly 2g of th sampl into th ptridish. Thn th ptridish and sampl wr put in th ovn and hatd at o for hour and th rsult notd. This was rpatd for anothr hour until a stady rsult is obtaind and th final wight notd. w w2 Moistur () w Whr w =Wight of ptridish and sampl bfor drying W 2 =Wight of ptridish and sampl aftr drying W 3 =Wight of sampl ph was masurd by lctromtric mthod using Laboratory ph mtr (ph mtr Hanna modl H993) [7].Th functional group prsnt in th adsorbnts (Onion and Garlic) wr dtrmind using th Fourir Transform Infra Rd Spctroscopy (FTIR). Th surfac ara was dtrmind by prparing.5g of th sampl in ml of dilut hydrochloric acid (Hl) at ph of 3. Thraftr, sodium chlorid (Nal) of mass 3g was addd to it and th volum mad up to 5ml using dionizd watr. Finally, th solution was titratd with.in NaOH until th ph is raisd to th rang of 4 to 9. Th volum V is rcordd. S = 32V 25 (2) Whr S is th spcific surfac ara V is th final volum of solution at ph 4 to 9. Adsorption xprimnt Four diffrnt sts of batch xprimnts wr carrid out to invstigat sparation of d(ii) using onion and garlic bulb. Th xprimnts wr rpatd at ph from 2-, concntration of mtal from ppm to 5ppm, tim intrvals of 2mins-mins, dos of adsorbnt ranging from.g 3.5g, tmpratur rang of 5 o to 9 o to invstigat th bstparamtrfor th rmoval of d(ii) from aquous solution. Th batch xprimnts wr don using a 25ml volumtric flask. For ph adjustmnts, concntratd hydrochloric acid or sodium hydroxid solutions wr addd to adjust th ph of th solution.at quilibrium, th mixturs wr filtrd using Whatman No 42 and analyzd for fr mtal concntrations using Atomic Adsorption Spctrophotomtry. Th prcntag of th mtals adsorbd at quilibrium, %M is givn in th quation blow. M (3) Th adsorption capacity of th adsorbnts. q t is givn as: q t V Whr o is th initial concntration of th mtal ions (mol), is th concntration of th mtal ions at quilibrium (mol), v is th volum of th mtal ions in contact with th adsorbnt and m is th mass of th adsorbnt in (g). Dtrmination of th ffct of agitation tim on biosorption of d(ii) by onion and garlic 2ml of watr with 6mg/l of th cadmium solution wr contactd with.4g of th adsorbnts at th room tmpratur and optimum ph to dtrmin th ffct of contact tim on th amount of d(ii) adsorbd by ths adsorbnts. Th sampls wr shakn with.4g of th adsorbnts (onion and garlic) at 2rpm for a duration of 2mins, 4mins, 6mins, 8mins,and mins rspctivly using a plastic tub and thn filtrd. Finally, th initial and final concntrations wr dtrmind using AAS. Dtrmination of th ffct of particl siz on biosorption of d (ii) by onion and garlic Th ffct of particl sizs on th amount of d(ii) ion adsorbd was invstigatd by contacting th sampl with varying sizs of th adsorbnt to dtrmin th adsorbnt siz for highst rmoval capacity. Aftr agitation, th solution was filtrd and th concntration of fr cadmium ion in th filtrat was dtrmind using AAS. Th prcntag of th mtals adsorbd at quilibrium, %M is givn in th quation blow. (4) M Dtrmination of th ffct of tmpratur on biosorption of d(ii) by onion and garlic (6) Pag 2

3 5ml of 5mg/l of th sampl solution was agitatd with.4g of th adsorbnts (onion and garlic) rspctivly at tmpraturs of 2, 4, 6, 8 and to invstigat th ffct tmpratur on th amount of cadmium ion rmovd.th agitatd solution was filtrd and th quilibrium concntration of th fr d(ii) ion in th sampl was dtrmind using AAS. Dtrmination of ash contnt of th biosorbnt Th sampl (2g) was wighd into a porclain crucibl. This was transfrrd into th muffl furnac st at 55 o c and lft for about 4 hours. About this tim it had turnd to whit ash. Th crucibl and its contnt wr cabld to about o c in air, thn room tmpratur in a dsiccator and wighd. Th prcntag ash was calculatd from: % ash contnt = wight of ash wight of dish x Original wight of sampl (7) FTIR spctra analysis III. RESULTS AND DISUSSION Fourir Transform Infrard Spctroscopy was usd to analyz th biosorbnt sampls loadd with admium mtal to idntify th compounds and its functional group availabl for th uptak of havy mtal. FTIR spctra for onion and garlic loadd with havy mtal (admium) ar shown in Figurs 4. and 4.2. From figur 4., th pak valu at cm - is assignd to -l strtch whil th pak valus at 2.937cm - and cm - ar assignd to -N strtch (mdium) and strtch of aliphatic and aromatic amins rspctivly. Furthrmor, FTIR spctra intrprtation of garlic loadd with cadmium can b sn in figur 4.2. Alkyl halids functional group was prsnt as indicatd with a pak valu of which can b assignd to -l strtch. Pak valus of 3.46cm - and corrsponds to -N strtch of Aliphatic and Aromatic Amins rspctivly. Fig. 4. FITR of onion loadd with cadmium Pag 3

4 Figur 4.2 FITR of garlic loadd with cadmium TABLE : Physical charactrization of Onion and Garlic omposition Onion Garlic ph Spcific Gravity Moistur contnt % Surfac Ara (m 2 /g) Ash contnt (%) TABLE2: Mtal ion concntration of Onion and Garlic Paramtrs ppm Onion Garlic alcium Magnsium Potassium..969 Sodium.249. Phosphorus Iron Pag 4

5 Th ph, spcific gravity, moistur contnt, bulk dnsity, surfac ara, ash contnt and mtal ion prsnt in th sampls was dtrmind as shown in tabls and 2. Th ph of onion and garlic skin wr found to b 7.2 and 6.87 rspctivly. Ths ph lvls rsult in mor ngativ chargs on th biosorbnt surfac that is likly to attract th positivly chargd d(ii) ions to bind to its surfac. Also, th surfac ara of onion and garlic skin ar 2.4m 2 /g and 874.2m 2 /g rspctivly. Th largr th surfac ara of an adsorbnt, th gratr its adsorptiv capacity[8]. Th spcific gravity of garlic is highr than that of onion. Th ash contnt of th biosorbnts wr also dtrmind. Th ash contnts of th biosorbnts wr found to b 2.25% for onion and.25% for garlic. Ash contnt is th portion of any organic matrial that rmains aftr it is burnd at vry high tmpratur. It rprsnts th total minral contnt in an organic matrial. Ash contnt plays an important rol from a physicochmical, tchnological and nutritional point of viw. Onionhas highr moistur contnt of 42.5% than garlic with moistur contnt of 27%. Finally, th macro lmnts containd in Onion and Garlic skin ar a, Mg, K, Na, P and F. TABLE 3: Effct of adsorbnt dosag on d (ii) % rmoval and adsorptiv capacity S/N Mass q t (Onion) mg/g % Rmoval (Onion) q t (Garlic) mg/g % Rmoval (Garlic) TABLE 4: Effct of contact tim on d (ii) rmoval (%) and amount adsorbd. S/N Tim (mins) q t (onion) (mg /g) % Rmoval (Onion) qt (Garlic) (mg /g) % Rmoval (Garlic) TABLE 5: Effct of tmpratur on d (ii) rmoval (%) and amount adsorbd. S/N Tmpratur ( o ) q t (Onion) (mg/g) % Rmovd (Onion) q t (Garlic) (mg/g) % Rmovd (Garlic) Effct of adsorbnt dosag Th ffct of adsorbnt dosag on th amount of cadmium adsorbd was carrid out at fixd tim, concntration, tmpratur and ph. Th biosorbnts adsorbd maximum cadmium at dosag lvl of.2g but dcras as th dosag is incras from.4g to.6g. This is as a rsult of mor comptition for availabl d(ii) ion. Howvr, th amount adsorbd incrasd slightly as dosag of th biosorbnts was incrasd from.8g to.g. Hnc, smallr mass of adsorbnt can ffctivly rmov d(ii) ion from aquous solution Effct of agitation tim Th uptak of cadmium mtal ions from aquous solution occurrd rapidly at a contact tim of 2mins furthr incras of agitation tim only rsult in slight changs in mtal ion concntration until th quilibrium tim of mins was achivd for garlic sampl and 8mins for onion sampl. From th figurs blow, it can b sn that th uptak of th mtal ions by th biosorbnt occurs in two stags: th initial rapid stag whr th adsorption procss is vry fast and th scond slowr stag whr th adsorption Pag 5

6 /q /q(g/l) Effct of tmpratur on th adsorption of d(ii) Th ffct of tmpratur on th adsorption of cadmium onto onion and garlic skins was also dtrmind. It can b shown from th rsults that th amount of cadmium uptak incrasd stadily as th tmpratur riss with th maximum cadmium uptak at a tmpratur lvl of 8 which is du to th incras in th numbr of availabl sits as th tmpratur is incrasing. Fitting xprimntal data to adsorption modl Langmuir modl quation can b givn as: q KQ Q (8) Plotting slop: q Q against givs a straight lin graph with and intrcpt KQ Th Langmuir, Frundlich, Tmkin and D-R isothrms modls wr mployd to dscrib th uptak of d (II) ions by onion and garlic. Langmuir paramtr K L was calculatd from th intrcpt of th linar plot of /q against as shown in Figurs 4.3 and 4.4. This was usd to calculat th sparation paramtr R L which shows th natur of adsorption. Th valus of R L rangs from.3 to.43 for Onion and. to.38 for garlic which confirms that th adsorption procsss was favourabl (<R L <). Also, th valu of R 2 for both onion and garlic shows that Langmuir isothrm modl favours both adsorbnt [9] y =.487x R² = (mg/l) Fig. 4.3: Langmuir adsorption Isothrm for garlic y =.483x R² = Fig.4.4: Langmuir adsorption Isothrm For onion Pag 6

7 Furthr mor, frundlich quilibrium constant n obtaind for onion and garlic ar.825 and.935 rspctivly which mans that both adsorption is a physical procss. If n =, that adsorption is linar, if n <, th adsorption is a chmical procss and if n > l, thn adsorption is a physical procss [].Tmkin isothrm was also mployd whr q was plottd against In to dtrmin th isothrm constants K T and B I, whr K t is th quilibrium binding constant corrsponding to th maximum binding nrgy whil B, shows th hat of adsorption Th adsorption nrgy obtaind for both onion and garlic ar.5kj/mol and.9kj/mol rspctivly, which ar in th nrgy rang of physical adsorption raction ( kj/mol). Tabl 6: Isothrm constants for th adsorption of d(ii) onto onion and garlic. ISOTHERM MODEL Langmuir Frundlich Tmkin ONION GARLI PARAMETERS VALUES PARAMETERS VALUES q t (mg/g) 2.7 q t (mg/g) 2.5 K L (l/mg).3 K L (l/mg).6 R R K f (mg/g).32 K f (mg/g).36 n.825 N.935 R 2.74 R B (kg/mol).46 B (kj/mol).447 K T (l/mg).3 K T (l/mg).62 R R D-R β (mol 2 /kj 2 ) 6E 7 β (mol 2 /kj 2 ) 2E 6 R 2.87 R E (kj/mol).9kj/mol E (kj/mol).5kj/mol Kintic modls Lagrgrn psudo first ordr quation Th lagrgrn rat quation is givn as: ad q q logq t t K 2.33 log (9) Psudo Scond Ordr Th Psudo Scond Ordr quation is givn as: t q 2 t K 2q () t q [] TABLE 7: Kintic modl paramtrs KINETI MODEL PARAMETER ONION GARLI K ad.4.2 Lagrgrn psudo first ordr quation Nataraja and Khalas Psudo first ordr kintic q (xp) (mg/g) q (cal) (mg/g) R K ad (min - ) -.2 R K 2 (g/mg min - ).47.8 Psudo scond ordr kintic q (xp) (mg/g) q (cal) (mg/g) R Pag 7

8 K d (mg/g min - / 2).8.2 Intra particl diffusion I R K o.59.7 Bangham s kintic modl Α R Tabl 8: Thrmodynamic paramtrs for th adsorption of d(ii) ontoonion and garlic Onion T (K) G o (KJ/mol) H o (KJ/mol) S o (KJ/mol) G o (KJ/mol) Garlic H o (KJ/mol) S o (KJ/mol) Equation 9 shows th Lagrgrn first ordr rat quation which isa plot of Log(q -q t ) against tim t. Th linar corrlation cofficintvalus obtaind for th adsorion of cd(ii) onto Onion and Garlic Skins arfound to b.47 and.4 (Tabl 7) which indicats that Lagrgrn first ordr ratquation is not suitabl for prdicting adsorption kintic modl. Bsid, th adsorption capacitis calculatd(q ) valus for both adsorptionis far lss that thos obtaind from th xprimnt. Similar rsult was obtaind by [2]. Th linar rgrssion corrlation cofficint valus obtain for both adsorption of d(ii) onto onion and garlic skins was found to b.35 and.99 which is an indication that Natarjan and Khalaf ratquation is not suitabl for th prdiction of adsorption kintic modl. Tabl 7 shows th Psudo-scond ordr rat plot. This is Plot of t/qvrsus tim,t. Th linar rgrssion corrlation cofficint obtaind for th adsorption of d(ii) onto onion and garlic skins wr found to b.999 and.85 rspctivly which indicats that this modlfit th adsorption kintic modl. Also, th adsorptiv capacitiscalculatd for both adsorptions was found to b vry clos whn compard with thos obtaind from th xprimnt which is a confirmation of th suitability of Psudo-scond ordr rat quation.similar to this rsult ar thos obtaind by [3]. Furthrmor, th thrmodynamic paramtrs of th adsorption procsss wr also calculatd such as Gibbs fr nrgy ( G ), Enthalpy chang ( H ) and th standard Entropy chang ( S ). Th nthalpy chang for th adsorption of cadmium onto Onion and Garlic wr both positiv (2.92kJ/mol and 4575kJ/mol rspctivly) which indicats that both adsorption procsss ar ndothrmic procss. Howvr, th valus of Gibbs fr nrgy at all tmpratur for both adsorbnt wr all ngativ which indicats that both adsorption procss ar fasibl and spontanous procss []. IV. ONLUSION Th rsults obtaind from this study showd that: Onion and garlic ar ffctiv adsorbnt for th rmoval of d (II) from aquous solution. Th valu of th sparation paramtr (R L ) obtaind for onion and garlic ar both in th rang of - which indicat favourabl adsorption. From Langmuir isothrm modl, th adsorptiv capacity of onion and garlic ar 2.7mg/g and 2.5mg/g rspctivly. Langmuir isothrm favourd th biosorption of d (II) onto onion and garlic on th basis of corrlation factor R 2. Adsorption of d (II) onto onion and garlic dpnds on ph, initial mtal concntration, adsorbnt dosag, agitation tim and tmpratur of adsorption. Th valu on n obtaind from Frundlich isothrm modl for th biosorbnt ar both gratr than, which indicats that th adsorption of d (II) onto onion and garlic is a physical procss. Among all th kintic modls usd, th psudoscond ordr kintic modl was provd as th bst fit for th adsorption of d(ii) onto onion and garlic skin. From th thrmodynamic studis, it can b shown that th adsorption procsss was ndothrmic, spontanous and incrasd dgr of randomnss. REFERENES []. Dvndra Yadav(27):. Adsorptiv Rmoval of Havy Mtals From Urban Storm Watr Run-off [2]. Antuns. W.M. Luna, S.A.(23). An Evaluation of oppr biosorption by a Brown Sa wd undr Optimizd conditions. Elctronic Journals of Biotchnology 6(3): [3]. EPA. Aquatic Lif Ambint Watr Quality ritria(985) [4]. Pirron and Othrs (996). Mrcury Fat and Transport in th global atmosphr. Pag 8

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