Adsorptionofheavymetalionfromaqueoussinglemetalsolution
bychemicallymodifiedsugarcanebagasse
´sarPerindeMeloa,´lioCeOsvaldoKarnitzJr.a,LeandroViniciusAlvesGurgela,Ju
´rciaSacramentoMeloa,ˆniaMaVagnerRobertoBotaroa,Ta
´de´ricGila,*RossimiriamPereiradeFreitasGilb,LaurentFre
aˆnciasExataseBiolo´mica,InstitutodeCie´gicas,UniversidadeFederaldeOuroPreto,35400-000OuroPreto,DepartamentodeQuı
MinasGerais,Brazil
bˆnciasExatas,UniversidadeFederaldeMinasGerais,31270-901BeloHorizonte,´mica,InstitutodeCieDepartamentodeQuı
MinasGerais,Brazil
Received22November2005;receivedinrevisedform28April2006;accepted2May2006
Availableonline14July2006
Abstract
Thisworkdescribesthepreparationofnewchelatingmaterialsderivedfromsugarcanebagasseforadsorptionofheavymetalionsinaqueoussolution.Thefirstpartofthisreportdealswiththechemicalmodificationofsugarcanebagassewithsuccinicanhydride.Thecarboxylicacidfunctionsintroducedintothematerialwereusedtoanchorpolyamines,whichresultedintwoyetunpublishedmodifiedsugarcanebagassematerials.Theobtainedmaterialswerecharacterizedbyelementalanalysisandinfraredspectroscopy(IR).Thesec-ondpartofthisreportsfeaturesthecomparativeevaluationoftheadsorptioncapacityofthemodifiedsugarcanebagassematerialsforCu2+,Cd2+,andPb2+ionsinaqueoussinglemetalsolutionbyclassicaltitration.AdsorptionisothermswerestudiedbytheFreundlichandLangmuirmodels.
Ó2006ElsevierLtd.Allrightsreserved.
Keywords:Adsorption;Modifiedsugarcanebagasse;Polyamines;Isotherm;Heavymetals
1.Introduction
Waterpollutionisamajorenvironmentalproblemfacedbymodernsociety(Baird,1995)thatleadstoeco-logicaldisequilibriumandhealthhazards(Kelteretal.,1997).Heavymetalionssuchascopper,cadmium,lead,nickel,andchromium,oftenfoundinindustrialwaste-water,presentacutetoxicitytoaquaticandterrestriallife,includinghumans.Thus,thedischargeofeffluentsintotheenvironmentisachiefconcern.Themethodscommonlyusedtoremovetoxicheavymetalfrommunicipalandindustrialwastewaterarebasedontheadsorptionofionsontoinsolublecompoundsandtheseparationofthesed-imentsformed.Manyeffortshavebeenmaderecentlyto
*Correspondingauthor.Tel.:+553135591717;fax:+55315511707.E-mailaddress:laurent@iceb.ufop.br(L.F.Gil).
findcheaperpollutioncontrolmethodsandmaterials
˘lu(Pandayetal.,1985;AliandBishtawi,1997;Acemiog
andAlma,2001).
Thenewmaterialworldtrendspointtotheimportanceofusingindustrialandagriculturalresiduesasproductionstartingmaterials.Reusingandrecyclingtheseresiduescanminimizetheenvironmentalproblemsassociatedwiththeirbuild-upandreducetheuseofnoblestartingmateri-als.Thistrendhascontributedtothereconsiderationoftheuseoftraditionalbiomaterialssuchasnaturallignocellu-losicfiberstosubstitutesyntheticpolymers,forexample,sinceinmanycasestheyhaveabetterperformance.
Brazilistheworldleadingproducerofsugarcaneforboththealcoholandthesugarindustries.Theseindustriesproducealargeamountofsugarcanebagasseandalthoughitisburnedtoproduceenergyforsugarmills,leftoversarestillsignificant.Thus,onaccountoftheimportanceof
0960-8524/$-seefrontmatterÓ2006ElsevierLtd.Allrightsreserved.doi:10.1016/j.biortech.2006.05.013
1292O.KarnitzJr.etal./BioresourceTechnology98(2007)1291–1297
bagassesugarasanindustrialwaste,thereisagreatinterestindevelopingchemicalmethodsforrecyclingit.Sugarcanebagassehasaround50%cellulose,27%polyoses,and23%lignin(Caraschietal.,1996).Thesethreebiologicalpoly-mershavemanyhydroxyland/orphenolicfunctionsthatcanbechemicallyreactedtoproducematerialswithnewproperties(Xiaoetal.,2001;Navarroetal.,1996).
Despitethemanystudiesofthechemicalmodificationofcellulosepublishedaroundtheworldinthisarea(Gurnanietal.,2003;GellerestedandGatenholm,1999),onlyafewhaveinvestigatedthemodificationofbagassesugar(Krish-nanandAnirudhan,2002;Orlandoetal.,2002).
Thisworkdescribesthepreparationandtheevaluationofnewchelatingmaterialsfromsugarcanebagassetoadsorbheavymetalionsinaqueoussolution.Inaprelimin-arystudy,ithasbeenchosentostudytheadsorptionofCu2+,Cd2+,andPb2+.Thefirstpartofthisworkdescribesthemodificationofsugarcanebagassewithsuccinican-hydridetointroducecarboxylicfunctionstosugarcanebagasseandthechemicalintroductionofcommerciallinearpolyamineviatheformationofamidefunctions.Itiswellknownthatpolyamineshavepowerfulchelatingproperties,mainlytowardsionssuchasCu2+,Zn2+,andPb2+(Bian-chietal.,1991;MartellandHancock,1996).
ThesecondpartofthisworkevaluatestheadsorptionofCu2+,Cd2+,andPb2+ontothreemodifiedsugarcanebag-asses(MSBs)fromaqueoussinglemetalionsolutionsbyclassicaltitration.TheresultswereanalyzedbytheLang-muirandFreundlichmodels(Hoetal.,2005).2.Methods2.1.Materials
Polyaminesethylenediamine3andtriethylenetetramine4wereusedinthiswork.Succinicanhydride,1,3-diiso-propylcarbodiimide(DIC),andtriethylenetetramine,fromAldrich,wereusedwithoutpurification.Ethylenediamineanddimethylformamideweredistilledbeforeuse.PyridinewasrefluxedwithNaOHanddistilled.2.2.Sugarcanebagassepreparation
Sugarcanebagassewasdriedat100°Cinanovenforapproximately24handnextfibersizewasreducedtopow-derbymillingwithtungstenring.Theresultingmaterialwassievedwitha4-sievesystem(10,30,45,and60mesh).Then,thematerialwaswashedwithdistilledwaterunderstirringat65°Cfor1handdriedat100°C.Finally,itwaswashedanewinasohxletsystemwithn-hexane/ethanol(1:1)assolventfor4h.2.3.SynthesisofMSBs1and2
Washedanddriedsugarcanebagasse(5.02g)wastrea-tedwithsuccinicanhydride(12.56g)underpyridinereflux(120mL)for18h.Thesolidmaterialwasfiltered,washed
insequencewith1MsolutionofaceticacidinCH2Cl2,0.1MsolutionofHCl,ethanol95%,distilledwater,andfinallywithethanol95%.Afterdryingat100°Cinanovenfor30minandinadesiccatorovernight,MSB1(7.699g)wasobtainedwithamassgainof53.4%.MSB2wasobtainedbytreatmentof1withsaturatedNaHCO3solu-tionfor30minandafterwardsbyfilteringusingsinteredfilterandwashingwithdistilledwaterandethanol.2.4.SynthesisofMSBs5and6
TheprocessusedtointroduceaminefunctionswasthesameasthatusedtoprepareMSB5and6.MSB1wastrea-tedwith5equivof1,3-diisopropylcarbodiimide(DIC)and6equivofpolyamineinanhydrousDMFatroomtempera-turefor22hunderstirring.Afterfiltration,thematerialswerewashedwithDMF,asaturatedsolutionofNaHCO3,distilledwater,andfinallywithethanol.Next,theyweredriedat80°Cinanovenfor30minandinadesiccatorovernight.2.5.KineticstudyofmetalionadsorptionofMSBs2,5,and6
Experimentswitheachmaterialandmetalionwereper-formedtodeterminetheadsorptionequilibriumtimefrom10to90minin10minintervals.Theamountof100mgMSBwasplacedina250-mLErlenmeyerwith100.0mLmetalionsolutionwithconcentrationof200mg/Lunderstirring.TheexperimentsweredoneatpHs5.8forCu2+,7.0forCd2+,and6.2forPb2+,optimalvaluestoobtainthebestadsorption.ToadjustpHvalues,wasaddedNaOHsolution(0.01mol/L)intometalsolutionswithMSB.Afterfiltration,metalionconcentrationwasdeter-minedbyEDTAtitration.
2.6.pHstudyofmetalionadsorptionofMSBs2,5,and6Experimentswitheachmaterialandmetalionwereper-formedtodeterminetheeffectofpHonionadsorption.Anamountof100mgMSBwasplacedintoa250-mLErlen-meyerwith100.0mLofmetalionsolution200mg/Lunderstirring.pHwascalibratedwithHClorNaOHsolutions(0.1–1.0mol/L).Thereactiontimesusedwere30min(MSB2)or40min(MSB5and6)forCu2+andCd2+,and40min(MSB2)or50min(MSB5and6)forPb2+.MetalionconcentrationwasdeterminedafterfiltrationbyEDTAtitration.NosignificativevariationofpHwasobservedattheendofeachexperiment.2.7.AdsorptionisothermsofMSBs2,5,and6
Experimentswereperformedforeachmaterialandmetaliontodetermineadsorptionisotherms.Ineachexperiment,100mgofMSBwasplacedintoa250-mLErlenmeyerwith100.0mLofmetalionsolutioninspecificconcentrations(between200mg/Land400mg/L)understirring.EachexperimentwasperformedatthepHof
O.KarnitzJr.etal./BioresourceTechnology98(2007)1291–12971293
10 mol acid groups per mglargerionadsorptionduringthetimenecessaryforequilib-rium(Tables3and4).Afterfiltration,themetalioncon-centrationwasdeterminedbyEDTAtitration.2.8.CharacterizationofthenewobtainedmaterialsMSB1,2,5,and6werecharacterizedbyIRspectro-scopyinaNicoletImpact410equipmentwithKBr.ElementalanalyseswereaccomplishedinAnalyzer2400CHNS/OPerkinElemerSeriesII.3.Resultsanddiscussion
3.1.SynthesisofMSBs1,2,5,and6
ThesynthesisrouteusedtoprepareMSBs1,2,5,and6arepresentedinScheme1.Prewashedsugarcanebagassewassuccinylatedforvariousperiodsoftime.Thedegreeofsuccinylationofthebagassefiberswasdeterminedbymeasuringthequantityofacidfunction.TheresultsareshowninFig.1.Theconcentrationofcarboxylicfunctionspermgofbagassewasdeterminedbyretrotitration.Forthis,MSB1wasinitiallytreatedwithanexcesssolutionofNaOH(0.01mol/L)for30min.SoonafterwardsthematerialwasfilteredandtheobtainedsolutionwastitratedwithanHClsolution(0.01mol/L).Thehighestdegreeofsuccinylationwasreachedafter18-hreaction.Usingthisreactiontime,sugarcanebagassewassuccinylatedtopro-duceMSB1,whichpresentedaweightgainof54%andaconcentrationofcarboxylicacidfunctionpermgof3.83·10À6mol.Next,MSB1wastreatedwithasaturatedNaHCO3solutiontoproduceMSB2.
StartingfromMSB1,twopolyamineswereintroduced:ethylenediamine3andtriethylenetetramine4.Themethod-
43.532.52010203040-6Time (h)Fig.1.Quantityofacidfunctionasafunctionofsuccinicanhydridetreatmenttime.ologyusedtointroducethepolyamineswasthesameforthetwoMSBs5and6,asshowninScheme1.Concentra-tionsof2.4·10À6mol(5)and2.6·10À6mol(6)ofaminefunctionpermgofmaterialweredeterminedbybacktitra-tionwithexcessHClsolution.TheintroductionoftheaminefunctionswasalsoverifiedbyIRspectroscopy(Table1)andelementalanalysis(Table2).3.2.CharacterizationofMSBs1,5,and6
CharacterizationofcarboxylatedMSB1wasaccom-plishedbyIRspectroscopy.ThespectrumofunmodifiedsugarcanebagasseandMSB1arepresentedinFig.2.ThespectrumofMSB1displayedtwostrongbandsat1740and1726cmÀ1inrelationtothatofunmodifiedsug-arcanebagasse.Thisdemonstratedthepresenceoftwotypesofcarbonylfunctions,onerelativetocarboxylicacidandanotherrelativetotheester.TheacidandesterIRbandsindicatethatsuccinicanhydrideacylatedthe
OO_O Na+O_O Na+OHOHSugarcane bagasseOOOOOOMSB1OOOHH2NOHDICDMFNH2NaHCO3OOMSB2OOpyridine, ΔOOOOOOHNHNNHNHNH2nNH2n3HNNHMSB5 n=0MSB6 n=2H2N4NH2Scheme1.SynthesisrouteusedtoobtainMSBs1,2,5,and6.1294O.KarnitzJr.etal./BioresourceTechnology98(2007)1291–1297
Table1
MainIRspectrumbandsobservedinMSBs1,5,and6MSBMainbandsobserved(cmÀ1)
11740,1726
51745,1650,1635,1575,1423,1060
6
1738,1651,1635,1560,1400,1159,1060
Table2
ElementalanalysisofMSBs1,2,5,and6
C(%)
H(%)N(%)Sugarcanebagasse43.986.020.13MSB145.415.620.10MSB238.045.140.01MSB544.016.512.21MSB6
46.88
6.65
3.43
35 unmodified sugarcane bagasse MSB 130)%( e25cnattims20narT1517401726104000350030002500200015001000500Wavenumber (cm-1)Fig.2.IRspectrum(KBr)ofunmodifiedsugarcanebagasseandMSB1.hydroxygroupofbagassetogenerateanesterbondwithconsequentreleaseofacarboxylicacidfunctionalgroup.ThespectraofMSBs5and6(Figs.3and4,respectively)showedthreenewstrongbandsat1550–1650cmÀ1(seedatainTable1)correspondingtothepresenceofamideandaminefunctions,andonebandat1060cmÀ1correspondingtoC–Nstretch.Thebandsat1635and1650cmÀ1(Fig.3)correspondtotheaxialdeformationofthecarbonyloftheamidefunctionandtheangulardeformationoftheN–Hbondoftheaminefunction.Thebandat1575cmÀ1correspondstotheangulardeformationoftheN–Hbondoftheamidefunction.Thebandat1159cmÀ1(Fig.4)correspondstotheasymmetricstretchofC–N–Cbond.
ThemainbandsobservedinallMSBsarepresentedinTable1.
MSBelementalanalysisdatapresentedinTable2showamodificationinthecarbonandhydrogencompositionofMSB1andalargerproportionofnitrogenasthenumberofaminefunctionsintheusedpolyamineincreases.
60)%( ecnatti40msna1650rT16352017451423157510604000350030002500200015001000500Wavenumber (cm-1)Fig.3.IRspectrum(KBr)ofMSB5.60)%( ecnatti40msnarT1738140016351560115910602016514000350030002500200015001000500Wavenumber (cm-1)Fig.4.IRspectrum(KBr)ofMSB6.3.3.StudyofadsorptionofCu2+,Cd2+andPb2+onMSBs2,5,and6
ThestudyoftheMSBadsorptionpropertieswasaccom-plishedforeachmaterialandmetalion.AkineticstudyandanadsorptionstudyasafunctionofpHwerefirstcarriedout.
3.3.1.Effectofcontacttime
ThekineticstudyofMSB2withCu2+,Cd2+,andPb2+ionsinaqueoussolutionispresentedinFig.5.Adsorptionequilibriumwasreachedafter20minforCd2+ions.Atimeof30minwaschosenforallstudiesofMSB2withCd2+.TheadsorptionequilibriumtimeschosenforpHandcon-centrationdependentexperimentsarepresentedinTable3.SimilarstudieswereaccomplishedforMSBs5and6forCu2+,Cd2+,andPb2+.TheresultsarepresentedinTable3.3.3.2.pHEffect
TheremovalofmetalionsfromaqueoussolutionsbyadsorptionisdependentonsolutionpHasitaffectsadsor-
O.KarnitzJr.etal./BioresourceTechnology98(2007)1291–1297
1295
140130Cu2+Cd2+)1-120gPb2+ gm(110 debr100osd al90ateM8070600102030405060708090100Time (min)Fig.5.EffectofcontacttimeonMSB2metalionadsorption.Table3
AdsorptionequilibriumtimesofMSBs2,5and6MSBEquilibriumtime(min)Cu2+Cd2+Pb2+230304054040506
40
40
50
bentsurfacecharge,thedegreeofionization,andthespeciesofadsorbates.ThestudyofadsorptionofCd2+,Cd2+,andPb2+onMSB2asafunctionofpHwasaccom-plishedwiththereactiontimesgiveninTable3;theresultsarepresentedinFig.6.TheadsorptionofthethreemetalionsincreaseswiththeincreaseinpH.MaximumremovalofCd2+wasobservedabovepH6andinthecaseofPb2+andCu2,abovepH5and5.5.
SimilarstudieswereaccomplishedforMSBs5and6andCu2+,Cd2+andPb2+withsimilarresults,asshowninTable4.
160140)1-g120 gm( d100ebro80sda l60ateM40Cd2+Cu2+20Pb2+0012345678pHFig.6.AdsorptionofmetalionsonMSB2asafunctionofpH.Table4
pHoflargestadsorptionofMSBs2,5and6MSBpHoflargestadsorptionCu2+Cd2+Pb2+25.5–6.06.5–7.55.0–6.055.5–6.06.5–7.55.0–6.06
5.5–6.0
6.5–7.5
5.0–6.0
3.3.3.Adsorptionisotherms
TheLangmuir(Hoetal.,2005)(Eq.(1))andFreundlich(Eq.(2))isothermswereevaluatedbyadsorptionexperi-mentsasafunctionoftheinitialmetalionconcentrationsinaqueoussolutionunderequilibriumtimeandpHcondi-tionsgiveninTables3and4.TheresultsofeachmaterialandmetalionarepresentedinFig.7(Langmuir)andFig.8(Freundlich)andTable5.c1q¼Qbþ
cð1ÞmaxÂQmax
lnq¼lnkþ1
n
lnc
ð2Þ
1.81.6MSB 2 1.41.210.80.6Cu2+0.4Cd2+0.2Pb2+00501001502002503001.61.4MSB 51.2)1L/g( 0.8q/c0.6Cu2+0.4Cd2+0.2Pb2+00501001502002503003MSB 62.521.51Cu2+Cd2+0.5Pb2+0050100150200250300c (mg/L)Fig.7.TheLangmuirisothermsofMSBs2,5,and6.1296
O.KarnitzJr.etal./BioresourceTechnology98(2007)1291–1297
5.35.2MSB 25.154.94.8Cu2+4.7Cd2+4.6Pb2+4.511.522.533.544.555.55.3MSB 55.25.1qnl5Cu2+4.9Cd2+Pb2+4.833.544.555.565.7MSB 65.55.35.14.94.7Cu2+Cd2+4.5Pb2+4.322.533.544.555.56lncFig.8.TheFreundlichisothermsofMSBs2,5,and6.Table5
TheLangmuirandFreundlichparametersforCu2+,Cd2+andPb2+adsorptionMetalion
MSB
LangmuirFreundlichQmaxb
r2k
nr2(mg/g)
(L/mg)(mg/g)Cu2+21140.4311
91.623.90.919351390.1730.999898.315.80.906161330.0140.992722.83.640.9635Cd2+21960.1030.993459.44.160.977351640.0680.995762.85.490.983463130.0040.95285.151.630.9856Pb2+21890.1100.994566.04.660.757951890.1250.999914724.510.9816
313
0.121
0.9994
121
5.21
0.877
whereq(mg/g)istheconcentrationofadsorbedmetalionspergramofadsorbent,c(mg/L)istheconcentrationof
metalioninaqueoussolutionatequilibrium,QmaxandbaretheLangmuirequationparametersandkandnaretheFreundlichequationparameters.
HighcorrelationcoefficientsoflinearizedLangmuirandFreundlichequationsindicatethatthesemodelscanexplainmetalionadsorptionbythematerialssatisfactorily.Therefore,bothmodelsexplainedmetalionadsorptionbyMSBs2,5,and6ascanbeobservedinTable5,withtheexceptionoftheFreundlichmodelforPb2+adsorptionbyMSB2.
TheLangmuirisothermparameterQmaxindicatesthemaximumadsorptioncapacityofthematerial,inotherwords,theadsorptionofmetalionsathighconcentrations.ItcanbeobservedinTable5thatMSB5presentsthelarg-estCu2+adsorptioncapacitywhileMSB6adsorbsCd2+andPb2+thebest.Langmuirparameterbindicatesthebondenergyofthecomplexationreactionofthematerialwiththemetalion.ItcanbeobservedthatMSB2presentsthelargestbondenergyforCu2+andCd2+,whilethreematerialsdonotdiffersignificantlyforPb2.
TheFreundlichisothermparameterkindicatestheadsorptioncapacitywhentheconcentrationofthemetalioninequilibriumisunitary,inourcase1mg/L.Thisparameterisusefulintheevaluationoftheadsorptioncapacityofmetalionsindilutesolutions,acaseclosertothecharacteristicsofindustrialeffluents.ThevaluesofkofMSB2and5aremuchsimilarforCu2+andCd2+andmuchhigherthanthatforMSB6.Thisshowsthesuperiorityofbothmaterialsintheadsorptionofthesemetalionsinlowconcentrations.MSB5hasahigherkvalueforPb2+whencomparedtothoseoftheothermaterials.
TheseresultswerecomparedwiththoseofVaughanetal.(2001)foracommercialmacroreticularchelatingresinwiththiolfunctionalgroups,DuoliteGT-73.TheQmaxofDuoliteGT-73forCu2+,Cd2+,andPb2+were62mg/g,106mg/g,and122mg/g,respectively.DuoliteGT-73exhibitedQmaxlowerthanthoseofMSBs(Table5).4.Conclusions
Throughafast,effective,andcheapmethodology,itwaspossibletodeviseastrategytointroducechelatingfunc-tions(carboxylicacidandamine)tosugarcanebagasse.ModifiedsugarcanebagassespresentedagoodadsorptioncapacityforCu2+,Cd2+,andPb2+ionswithmaximumadsorptioncapacityobservedforMSB6.Ithasbeendem-onstratedthatmetalionadsorptionefficiencyispropor-tionaltothenumberofaminefunctionsintroducedintothematerial.MSB2,whichcontainedonlycarboxylatefunctions,showedanefficiencysimilartothatofMSB5,amaterialofmuchmorecomplexsynthesis.Acknowledgements
WethankFAPEMIGforfinancialsupport,CAPESandUFOP.
O.KarnitzJr.etal./BioresourceTechnology98(2007)1291–12971297
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