Chamarthy_et_al-2001-Journal_of_Chemical_Technology_and_Biotechnology

Adsorptionofselectedtoxicmetalsbymodified

peanutshells

SrinathChamarthy,1ChungWSeo1*andWayneEMarshall21DepartmentofHumanEnvironmentandFamilySciences,FoodandNutritionLaboratory,NorthCarolinaA&TStateUniversity,1601EMarketStreet,Greensboro,NC27411,USA2UnitedStatesDepartmentofAgriculture,AgriculturalResearchService,SouthernRegionalResearchCenter,1100RobertELeeBlvd,POBox19687,NewOrleans,LA70179,USA

Abstract:Theobjectiveofthisstudywastomodifypeanutshellstoenhancetheiradsorptivepropertiestowardthemetalionscadmium(Cd2󰀁),copper(Cu2󰀁),nickel(Ni2󰀁),lead(Pb2󰀁)andzinc(Zn2󰀁).Milledpeanutshellswereinitiallywashedwithwateror0.1NNaOHorleftunwashed.Followingthesetreatmentsorlackoftreatment,theshellswereeitherleftunmodi®edormodi®edbyaheattreatmentinthepresenceofeither1.0Mphosphoricacidor0.6Mcitricacid.Modi®edpeanutshellswereevaluatedeitherforadsorptionef®ciencyorforadsorptioncapacityusingthe®vemetalionslistedabove.Adsorptionef®cienciesandcapacitieswerecomparedwithef®cienciesand/orcapacitiesforthecommercialchelatingorcationexchangeresinsAmberlite200,AmberliteIRC-718,DuoliteGT-73,andcarboxymethylcellulose.Fortheadsorptionef®cienciesofindividualmetalions,modi®edpeanutshellsmetorexceededtheadsorptionvaluesforcadmium,copper,nickelorzincionscomparedwiththecommercialresinsDuoliteGT-73andcarboxymethylcellulose.Inasolutioncontainingall®vemetalions,modi®edpeanutshellsmetorexceededtheadsorptionef®cienciesforcadmium,copperandleadionscomparedwithDuoliteGT-73,AmberliteIRC-718andcarboxymethylcellulose.Adsorptioncapacitiesofmodi®edpeanutshellsmetorexceededtheadsorptioncapacityofDuoliteGT-73forleadionsonly.Citricorphosphoricacid-modi®edpeanutshellsshowedapreferenceforCu2󰀁andPb2󰀁andappearpromisingaspotentiallyinexpensiveadsorbentsforselectedmetalions.#2001SocietyofChemicalIndustryKeywords:peanutshells;citricacid;phosphoricacid;metalions;adsorbents

1INTRODUCTIONPeanutshellsarelowdensity,highvolumeagriculturalwastewhich,inpart,areusedinanimalfeedformulationsorareburnedforenergy.Thesearelowvalueusesfortheshellsandadditionalproductoutletsneedtobeidenti®edtocreatehighervalueproducts.Inordertoaddvaluetopeanutshells,attentionhasfocusedontheutilizationofpeanutshellsasadsor-bents.Inthisregard,peanutshellshavebeenmodi®edbyheatorchemicaltreatmenttoimprovetheirabilitytoadsorbdifferentmetalionsororganiccompounds.Therehavebeenseveralreports1±7thathavedescribedpeanutshell(hull)activatedcarbonforadsorptionofvariousmetalionsandorganiccom-pounds.Inadditiontotheiruseasactivatedcarbons,peanutshellshavebeenusedasisorundergonedifferentmodi®cationstoenhancetheirabilitytosequestermetalionsfromsolution.Hendersonetal8reportedthatuntreatedpeanutshellsadsorbedsig-ni®cantamountsofHg2󰀁,Cu2󰀁,Ni2󰀁andZn2󰀁atlowconcentrationsofthemetals.A1hexposureoftheshellstothesemetalionsolutionssigni®cantlyincreasedtheiradsorptionbydecreasingthesizeofthepeanutshells.AzabandPeterson9andWartelleandMarshall10usedalkalitreatmenttoincreaseCd2󰀁andCu2󰀁uptake,respectively,bypeanutshells.Okieimenetal11notedthattreatmentofpeanutshellswiththechelatingagentEDTAimprovedsubsequentCd2󰀁andPb2󰀁sorption.Recently,Wafwoyoetal12reactedpeanutshellsinthepresenceofeitherphosphoricacidorcitricacidtogreatlyincreasethemetalionbindingabilityoftheshells.ThepresentstudyisacontinuationofresearchreportedbyWafwoyoetal.12TheobjectiveofthisstudywastoextendtheresultsreportedbyWafwoyoetal12including:(1)addinga®fthmetalion,namelyPb2󰀁,tosolutionscontainingthefourmetalions,Cd2󰀁,Cu2󰀁,Ni2󰀁andZn2󰀁,(2)addingthecommer-cialcationexchangeresin,carboxymethylcellulose,forcomparisonpurposesand(3)determiningadsorptioncapacitiesformodi®edpeanutshellsandcommercialresins.Phosphoricandcitricacidswereagainchosenasmodifyingagentsinthisstudybecauseofthepromis-ingmetalionadsorptionresultsachievedbyWafwoyoetal12usingthesemodi®cationstrategies.

(Received26October2000;revisedversionreceived4January2001;accepted13February2001

)*Correspondenceto:ChungWSeo,DepartmentofHumanEnvironmentandFamilySciences,FoodandNutritionLaboratory,NorthCarolinaA&TStateUniversity,1601EMarketStreet,Greensboro,NC27411,USAContract/grantsponsor:USDA-CSREESCapacityBuildingProgram;contract/grantnumber:95-38814-1729

#2001SocietyofChemicalIndustry.JChemTechnolBiotechnol0268±2575/2001/$30.00

593JournalofChemicalTechnologyandBiotechnologyJChemTechnolBiotechnol76:593±597(2001)DOI:10.1002/jctb.4182MATERIALSANDMETHODS2.1PeanutshellsPeanutshellswereagiftfromtheCarolina±VirginiaPeanutGrowersAssociation(Suffolk,VA).Theyhaveabulkdensityof0.22gcmÀ3foraparticlesizerangeof0.85to2.00mmandconsistpredominantlyofcellulose(45.3%).10Othermajorcomponentsincludelignin(32.8%),hemicellulose(8.1%),protein(4.9%)andash(2.3%).10Sodiumhydroxide,cupricsulfate,thenitratesofcadmium,lead,nickelandzinc,citricacidmonohy-drate,aceticacid(glacial),sodiumacetate(mono-basic),85%phosphoricacid,andnitricacid(tracemetalgrade)werepurchasedfromFischerScienti®c(FairLawn,NJ).Plasmaemissionstandardsforthe®vemetalionswereobtainedfromSolutionsPlusInc(Fenton,MO).ThecommercialresinsAmberliteIRC-718,Amberlite200,DuoliteGT-73,andcar-boxymethylcellulosewerepurchasedfromSupelco(Bellefonte,PA).AmberliteIRC-718andDuoliteGT-73arechelatingresinsdesignedtobeselectiveforcertainmetalions,includingCu2󰀁,Pb2󰀁,Cd2󰀁,andZn2󰀁,whileAmberlite200andcarboxymethylcellu-losearegeneral-purposecationexchangeresins.

2.2PreparationofpeanutshellsThepreparationofmilledpeanutshellsandtreat-mentsforunwashed,base-washedandwater-washedpeanutshellswerecarriedoutasdescribedbyWafwoyoetal.12Peanutshellmodi®cationswith0.6Mcitricacidor1.0MphosphoricacidwerealsocarriedoutaccordingtothemethodsofWafwoyoetal.12

2.3MetalionsolutionsThemetalionschosenforthestudywereCu2󰀁,Pb2󰀁,Cd2󰀁,Zn2󰀁,andNi2󰀁.Allsinglemetalionandmultiplemetalionsolutionsweremadetoaconcen-trationof20mMin0.07Msodiumacetate±0.03Maceticacidbuffer,pH4.8.Themultiplemetalionscontainedall®vemetalions,eachat20mM.Toproduceadsorptionisotherms,singlemetalionsolu-tionsofall®vemetalsweremadetoconcentrationsof5,10,15,20,25,30,35,40,45,and50mMinthesodiumacetate±aceticacidbuffer,pH4.8.

2.4MetalionadsorptionofmodifiedpeanutshellsandcommercialresinsMetalionadsorptionwascarriedoutaccordingtotheprocedureusedbyWafwoyoetal.12ThepHofthesolutionswasmeasuredatthebeginningandendofthemetalionadsorptionexperimentsandvariedbetween4.6and5.0foranygivenexperiment.

2.5ICPandstatisticalanalysisICPanalyseswereperformedonthe®ltratesasdescribedbyWafwoyoetal.12Themetalionsremaininginsolutionafteradsorp-tion(equilibriumconcentration)andtheamountadsorbed(mmol)pergofsampleweredeterminedonadryweightbasisofadsorbent.AdsorptioncapacitywascalculatedusingtheLangmuirmodel,whichinitsnon-linearformisgivenas:X󰀃󰀄XmÂKÂCe󰀆=󰀄󰀇1󰀁K󰀈ÂCe󰀆󰀇1󰀈Where:X=amountofsoluteadsorbedperunitweightofadsorbent;Ce=equilibriumconcentrationofsolute;Xm=maximumadsorptioncapacityofadsorbentforsoluteandK=adsorptionequilibriumconstant.Solvingeqn(1)bynon-linear,leastsquaresregres-sionanalysisdeterminesvaluesforXm.ThesevalueswereobtainedbyusingaregressionanalysisprograminSigmaPlotv4.0(SPSSInc,Chicago,IL).Inallcases,regressionvalues(r2)weresuchthattheLangmuirmodelpredictedthedatasetatp<0.05.Theadsorptiondataobtainedwereanalyzedbyatwo-wayANOVAfollowedbyFischer'sleastsigni®-cantdifference(LSD)usingtheSASsystemANOVAprocedureata=0.05(v6.12fromSASInstituteInc,Cary,NC).

2.6MoisturedeterminationThemoisturecontentofthepeanutshellsandcommercialresinsweredeterminedaslossofweightondryingaccordingtoAAOCmethod24.003(a).13Moisturevaluesvariedfrom1.4to7.2%foracid-modi®edshellsand7.7to59%forcommercialresins.

3RESULTSANDDISCUSSIONWafwoyoetal12clearlydemonstratedthatlittle,ifany,metalionadsorptionoccurredintheabsenceofphosphoricacidorcitricacidmodi®cationofpeanutshells.Shellsexposedtonowashing,waterwashingorbasewashingaloneadsorbedlessthan0.2mmolgÀ1eachofthe®vemetalions.Forsomeofthesamples,nometalionadsorptionwasobserved.Wafwoyoetal12alsoobservedlittleornometalionadsorptionwhennon-modi®edshellswereplacedincontactwithamixtureofmetalionsCd2󰀁,Cu2󰀁,Ni2󰀁andZn2󰀁.Leadionswerenotincluded.Onthebasisofthesepublishedresults,onlyacid-modi®edshellswereevaluatedinthepresentstudy.

3.1AdsorptionofindividualmetalionsPhosphoricacidmodi®cationofunwashed,water-washedandbase-washedshellsgaveproductsthatshowedlittledifferenceintheirabilitytosequesterindividualmetalions(Table1).Therefore,pre-treatmentofshellswithwaterorbasemaynotbenecessaryforphosphoricacidmodi®cationtobeeffective.However,citicacidmodi®cationappearstobemosteffectivewithbase-washedshells.Thereason(s)forthisobservationisnotknown.Exposuretobaseremovesmorecoloredmaterialfromtheshellthanwaterwashing.Theremovalofcoloredcom-poundsandtheconcomitantchangesthatoccurintheshellapparentlyenhancecitricacidbutnotphosphoricacidmodi®cation.Additionally,treatmentwithNaOHmaysaponifyandremovesurfacelipidsfromthe

594JChemTechnolBiotechnol76:593±597(2001)SChamarthy,CWSeo,WEMarshall