Surface charge properties of tropical soils and their influence on Cd and Pb sorption PDF
Preview Surface charge properties of tropical soils and their influence on Cd and Pb sorption
SURFACECHARGEPROPERTffiSOFTROPICALSOILS ANDTHEIRINFLUENCEONCdANDPbSORPTION 'CHRISTOPHER^STEWARTAPPEL ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 2001 Theexperimentsperformedinconjunctionwiththisdissertationcouldnothave beencompletedwithouttheassistanceofseveraltalentedindividualsintheSoiland WaterScienceDepartmentattheUniversityofFlorida. Idedicatethisworktothestaff membersofthisfinedepartment,namely,Dr.AbidAl-Agely,Mr.KeithHollien,Mrs. ElizabethKennelley,Mr.ThomasLuongo,Ms,MaryMcLeod,Ms.AnNguyen,Ms. IrenePoyer,Mr.BillReve,Mr.LarryShwandes,Mrs.JoyceTaylor,andMrs.Laura Studstill. Ithankyouforyoursupportofmeandmywork. ACKNOWLEDGEMENTS Firstandforemost,IthankandpraiseGodforthecomplexityofHiscreationand forallowingandprovidingmetheopportunitytopursueandcompletethisdegree. The prayers,encouragement,andsupportofmyfamilyandfriendsthroughoutthecourseof myworkattheUniversityofFloridawereahugeblessingandgreatlyappreciated. I especiallythankmystepmother,Mrs.PatriciaAppel,forhelpingbeginmydevelopment asascientist. IwillbeforeverindebtedtoPattiforspendingcountlesshourstutoringme inhighschoolchemistryandbiology. IamalsoverygratefultoDr.LenaQ.Ma,my advisor,forhersupportinprovidingmeeveryopportunitytodoexcellentworkaswellas developasascientist. Dr.R.DeanRhuedeservesmuchgratitudeforbeingpartofmycommitteeand forteachingmetothinkcritically,becreative,andforshowingmewhereandhowto catchbigRedFish. Ithankhiswife,Mrs.JaniceRhue,foradoptingmeandcookingme lotsofgoodmeals. IthankDr.WillieG.Harrisforbeingonmycommitteeandforhis genuineinterestinmeandthisproject. IhavelearnedalotfromDr.Harris,thegreatest ofwhicharethequalities-humilityandunselfishness. Dr.MichaelJ.Scott,fromthe ChemistryDepartment,deservesmythanksforservingonmycommitteeandalways beingwillingtohelp. IalsothankDr.GustavoMartinezforprovidingthesoilsamplesusedinthis research;Dr.GalinJonesforhisassistancewiththestatisticalmethodsusedinthis project;Dr.KevinPowers,Mr.GillBrubaker,andMr.WayneAcreefortheirassistance iii withsomeoftheinstrumentsIusedduringthisproject;andthanksgototheTraceMetal ChemistryLabgroup(includingNadineCo-JackKabengi)fortheirsuggestions regardingmyresearchandforhelpingprovideafunplacetowork. Lastly,IthankDr.RandallBrown,whoinitiallyencouragedmetoattendthe UniversityofFlorida,aswellasDr.BrianMcNealforprovidingmuchassistancetome duringthisdegree. IcanhonestlysaythatIcouldnotimaginehavingabettergraduate schoolexperienceanywhereelse. Ialsothankmyfriend.Dr.SarahGlover,forproofing andprovidingaplethoraofconstructivesuggestionsregardingthisdissertation. iv TABLEOFCONTENTS page ACKNOWLEDGEMENTS "i ABSTRACT viii CHAPTERS 1 INTRODUCTION 1 2 LITERATUREREVIEW 3 HeavyMetalContaminationinSoils 3 ToxicitiesofCdandPbtoHumans "7 Cadmium ^ Lead 8 SpeciationandBioavailabilityofCdandPbinSoils 9 Cadmium 1^ Lead 12 CdandPbContaminationintheTropics 13 ExtentoftheTropicsandTropicalSoils 15 SurfaceChargeOriginationinTropicalSoils 15 Summary 19 3 POINT OF ZERO CHARGE DETERMINATION IN SOILS AND MINERALS 20 Introduction 20 MaterialsandMethods 26 Materials 26 GeneralAnalyticalMethods 28 DeterminationofElectricCharge 29 Potentiometrictitration 29 Ionadsorption 30 Electrophoreticmobility 31 StatisticalMethods 34 ResultsandDiscussion 34 PotentiometricTitration 34 V IonAdsorption ^' ElectrophoreticMobility ComparisonoftheThreePointsofZeroCharge 45 Conclusions 4 CONCENTRATION, pH, AND SURFACE CHARGE EFFECTS ON Cd ANDPbSORPTIONINTHREETROPICALSOILS 48 Introduction 48 MaterialsandMethods 49 SoilSamples 49 DeterminationofCdandPbSorption 51 SorptionisothermsasafunctionofinitialCdandPbconcentration 51 SorptionofCdandPbasafianctionofpH 52 Surfacecharge 53 Statistics 53 ResultsandDiscussion 54 SorptionIsothermsasaFunctionofInitialCdandPbConcentration 54 SorptionofCdandPbasaFunctionofpH 57 SurfaceChargeandCdandPbSorption 60 Conclusions 64 5 SEQUENTIALSORPTIONOFPbANDCdINTHREETROPICALSOILS 67 Introduction 67 MaterialsandMethods '71 Materials ^1 DeterminationofCdandPbSorption 71 SequentialAdditionofMetals 72 StatisticalMethods "74 ResuhsandDiscussion 74 EffectofSequenceofMetalAddition 74 MechanismsofMetalSorption 77 PbandCdAffmityforSoilSurfaces 81 Non-ExchangeablePb:CdRatios 83 SitesofPbandCdRetention 84 Pb,Cd,andCaInteractions 86 Conclusions 89 6 DETERMINATION OF THE SELECTIVITIES AND ENTHALPIES OF K/Ca AND K/Pb EXCHANGE AND SURFACE HETEROGENEITY IN TWOTROPICALSOILSUSINGFLOWCALORIMETRY 92 vi Introduction MaterialsandMethods SoilSamples DeterminationofExchangeableCations 95 DeterminationofEquilibriumSelectivityCoefficients 97 CalorimetricMeasurements 99 DeterminationofSurfaceHeterogeneity 100 ResultsandDiscussion 101 CECDifferencesUnderCa^^Pb^^and Saturation 101 DeterminationofCaandPbSelectivity 102 EnthalpiesofCa/KandPb/KExchange(AHex)UsingFlowCalorimetry 106 NonexchangeablePb 112 SurfaceHeterogeneity 11^ Conclusions 7 CONCLUSIONS 121 LISTOFREFERENCES 125 BIOGRAPHICALSKETCH 141 vii AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy SURFACECHARGEPROPERTIESOFTROPICALSOILS ANDTHEIRINFLUENCEONCdANDPbSORPTION By ChristopherStewartAppel December,2001 Chairman: Dr.LenaQ.Ma MajorDepartment: SoilandWaterScience Reactionsofheavymetalswithsoilareimportantindeterminingmetalfatesin theenvironment. ImportantfactorsaffectingheavymetalretentionbysoilsarepH,ionic strength(/),andsurfacecharge,aswellaschemicalcharacteristicsofheavymetals. The objectivesofthisstudywereto(1)measurethesurfacechargeandpointsofzerocharge ofsurfacehorizonsfromtwohighlyweatheredsoilsfromPuertoRico,anOxisoland Ultisol,aswellasmineralstandardkaoliniteandsyntheticgoethiteusingthreemethods- a)potentiometrictitration,b)ionadsorption,andc)electroacousticmobility;(2) determinesorptioncharacteristicsofCdandPbintheOxisol,Ultisol,andaMollisol (alsofromPuertoRico)asafunctionofvaryingmetalconcentration,pH,/,andsurface charge;(3)evaluatetheabilityofthethreesoilstoretainCdandPbwhenthemetals wereaddedtothesesoilsinasequentialreactionscheme;andto(4)measurecation selectivityandsurfaceheterogeneityofK/CaandK/PbsystemsintheOxisolandUltisol usingcalculatedGaines-Thomasselectivitycoefficients(Kgt)coupledwithenthalpy Vlll change(AH)dataobtainedusingaflowcalorimeter. Thepointsofzerocharge determinedinthisstudyforkaoliniteandgoethitewerecomparablewiththosereported intheliterature. ThepointsofzerochargeobtainedfortheOxisolandUhisolwere consistentwiththesesoils'chemicalandmineralogicalproperties. AllsoilssorbedPbm preferencetoCdregardlessofinitialmetalconcentration,pH,/,surfacecharge,or sequenceofmetaladdition. Sorptionappearedtobemoredependentonmetaltypethan soilcompositionandPbwasmuchlessexchangeablethanCd. TheKgtandsurface heterogeneitydatademonstratedtheimportanceofsoilcomponentsintheexchange reactionsinvolvingK/CaandK/PbsystemsintheOxisolandUltisol. TheOxisolwas composedofhomogeneousadsorptionsiteswhiletheUltisolwasmadeupofsites exhibitingsurfaceheterogeneity. Therefore,retentionofCdandPbbytropicalsoilsis dependentonbothmetaltypeandsoilcomposition. Leadposeslessofathreatto groundwatersystemsthanCdduetoPb'slowermobilityandbioavailability. ix CHAPTER 1 INTRODUCTION Thestudyofheavymetalcontaminationinsoilshasreceivedmuchattentionin thelastseveraldecadesduetothepotentialdeleteriouseffectsoftheseelementstoplants andanimals. Asaresuh,regulatorsaroundtheworldhaveimplementedmuchlegislation aimedatcurbingthebuild-upofheavymetalsintheenvironment(Manahan,1990). Cadmium(Cd)andlead(Pb)aretwoheavymetalswhichhavebeenextensively researchedinthedeveloped,generallytemperateandsub-tropical,regionsoftheglobe duetotheirharmfuleffectsonhumansandwidespreaduseinindustry,agriculture,and urbanactivities(Adriano,1986;Forstner,1995;Nriagu,1998). Inthetropics,however,relativelyfewstudieshavebeenconductedonCdandPb contaminationinsoils. Thisispartlyduetothefactthatamajorityofcountriesinthe tropicsmaybeconsidereddevelopingnations. Thus,resourceallocationto environmentalcontaminationbyheavymetalsintheseareasismuchlowerthaninmost oftheirtemperateregioncounterparts. Furthermore,legislationtoprotectagainstbuild- upofpotentialenvironmentaltoxinssuchasCdandPbisgenerallyweakwithnolegal accountability(Moreira,1996). Thecharacteristicsofmanytropicalsoilsmayfurtheraggravatetheproblemof heavymetalcontaminationintheseregions. Unlikemosttemperateregionsoils,highly weatheredtropicalsoilshaveverylownegativesurfacechargeorretentioncapacityof cationicnutrientsorcontaminants. Undercertaincondition,theymayexhibitanet 1
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