吴王锁sorptionandprecipitationppt课件专题培训

Radionuclideadsorptionandprecipitation:models,dataandapplicationstoperformanceassessment（放射性核素旳吸附与沉淀：模型、数据及其在性能评价方面旳应用）WUWangsuo(吴王锁)RadiochemistryLaboratory,LanzhouUniversityObjectives-TableofcontentsScopeofthistalk:overviewonchemicalmodelsusedtoquantifyradionuclideretentionpresentafewselectedresultsrelevanttoPerformanceAssessment(PA)showhowdataareintegratedinPAmodelsTableofcontents:Definingradionuclideadsorptionand(co)precipitationAdsorption:concepts,modelsanddata(Co)precipitation:concepts,modelsanddataVerifyingtheuptakemechanismDataintegrationinPAandtheirinfluenceoncalculationsDefinitions

fromthepointofviewofradionuclides(RN’s)Adsorption:ElectrostaticorchemicalbindingofRN’stoastablemineralsurfaceUsuallyareversible,kineticallyfastprocesstherearedifferenttypesofadsorptionmechanismsPrecipitation:IncorporationofRN’sinthelatticeofagrowingmineralUsuallyirreversible,aslongasthesolidremainsstable“Precipitation”isagenericconceptwhichincludes: formationofpureRNphases(i.e.RNisamajorconstituentofprecipitate)formationofsolidsolutionsviacoprecipitationorrecrystallization(RNisaminorcomponentofprecipitate)AdsorptionModels(1)

Empiricalpartitioningmodels–thedistributioncoefficient

(Kd)

Thedistributioncoefficientisthesimplest(andmostinadequate)adsorptionmodel:A =SAEquilibriumsoluteconc.dependsonlyonsolid/liquidratioV/mInreality,Kdisaconditionalconstant:strongvariationsasf(pH,I,composition)AdsorptionModels(2)

Empiricalpartitioningmodels–Isotherms

A+=S =SAIsothermmodelsrelyonlawofmassactionequationsimilartoacomplexformationconstant...densityofoccupiedsitesdensityofunoccupiedsitesmolm-2...andonamassbalanceforavailablesites:(Langmuirisothermeq.)AdsorptionModels(3)

Empiricalpartitioningmodels–Langmuirisotherm

GT,tot.availablesitesLangmuirisothermaccountsforsaturationofavailablesitesAtlowadsorbateconcentrations,itisequivalenttoaKdmodelsisthespecificsurfaceinm2g-1(e.g.BET)AdsorptionModels(4)

Empiricalpartitioningmodels–failures

Poinssotetal.(1999)GCA,63,3217–3227ProblemswithKdandLangmuirisothermmodels:distributionratios(Rd)arestronglydependentonpHandsolutioncompositionisothermnonlinearitystartsmuchearlierthansitesaturationslope=1datapH6.9Why?realityismorecomplex:multiplesitesmanycompetingsurfacespeciesEuonCa-montmorillonitepH6.9pH6.0Csonillite

AdsorptionModels(5)

Empiricalpartitioningmodels–ConclusionsKdandKLareconditionalconstants.TheirvaluesmaygreatlyvarywithpH,Iandsolutioncomposition.Empiricalmodelsarethusinadequatetodescribeadsorptioninarealisticway.Nevertheless,KdandKLareacceptableparametersinPAcalculationsaslongastheyrefertothechemicalconditionsrelevanttothespecificrepositorysystem.ThismeansthatKdvaluesusedtocalculatenuclideretardationinPAmustrelyonaccurateandrealisticdeterminationoftherelevantporewatercompositions.Surfacecomplexationmodels(6)

basicassumptions-oxidesurfacesinwaterdevelopamphoteric(acidorbasic)surfacesites(=SOH2+,=SOH,=SO-)-solutespeciesbindtosuchfunctionalsitesaccordingtolawofmassactionequationssimilartocomplexationreactionsinsolution-suchsurfacesarecharged(+or-).ChargemaystronglydependonpHandthetype/amountofsurfacecomplexesformed-inturn,surfacechargedirectlyaffectstheformationofsurfacecomplexes>achargedependenttermisrequiredinlawofmassactionconstantsoxidemineralsurfaces,e.g.Al2O3,FeOOH,SiO2=SOH+H+ =SOH2+

=SOH

=SO-+H+oxygenmetalSurfaceprotonation/deprotonationleadstoanon-permanentpH-dependentsurfacecharge(+or-)

Surfacecomplexationmodels(7)

theamphotericoxidesurface–amicroscopicviewSurfacecomplexationmodels(8)

theamphotericoxidesurface–DDLmodel=SOH+H+ =SOH2+

chargedependenttermfromprotonsreleasedatsurfaceprotonsinsolution=pHapparentconstant

Kappinthediffusedoublelayer(DDL)model,theelectricalpotentialdecaysasymptoticallyduetoacharacteristicdistributionofcounterions=SOH+H+ =SOH2+

=SOH

=SO-+H+Surfacecomplexationmodels(9)

theamphotericoxidesurface–effectofelectrostatictermDpH~1Thecharge-dependenttermdoesmatter,asshownbythisexample(titrationofmontmorillonitesuspension):theadsorptionofhydroxylionsisdampedbythenegativechargeonthesurfacedevelopedbytheexcessof=SO-complexesSurfacecomplexationmodels(10)

additionalsurfacecomplexesInadditionto=SO-,=SOH,=SOH2+,alargevarietyofsurfacecomplexesmayformdependingonthesolutespresentintheaqueoussolutionTwomaincategoriesofcomplexes:innerspherecomplexes:directlyboundtosurfacefunctionalgroups(strongchemicalbonds)outerspherecomplexes:hydratedionsattractedtothesurfacebypurelyelectrostaticorVanderWaalforces(weak)Outerspherecomplexes

purelyelectrostaticinteractions:lowpH>positivesurface>anionadsorptionhighpH>negativesurface>cationadsorptionInnerspherecomplexes

bidentatecationicmonodentatecationicmonodentateanionicsurfacecomplexationreactionscanbeconsideredassurfaceproton/hydroxylreplacementreactions(Me-O-Hbondsarebroken,eitherH+replacedbymetalorOH-replacedbyanion){=SOH}2+Cu2+ {(=SO)2Cu}+2H+

=SOH+Pb2+ =SOPb++H+

=SOH+F- =SF+OH-

Ionexchange(Clayminerals)

pyrophyllite,Al2[Si4O10](OH)2,hasneutral(uncharged)structuralunits>noexchangeableionsneutralneutralNote:theunchargedTOTpacketsareheldtogetherbyweakVanderWaalforcesIonexchange(Clayminerals)

Li+forMg2+,Mg2+forAl3+(octahedralcharge)Al3+forSi4+(tetrahedralcharge)negativelychargedTOTlayerexchangeableinterlayercationsionicsubstitutioninthetetrahedral/octahedralstructurallayerleadstoapermanentnegativecharge,whichiscompensatedthroughexchangeablecations,e.g.inmontmorillonite

Combinedadsorptionmechanisms

inexpandableclayminerals

innerspheresurfacecplx.exchangeableinterlayercationsinexpandableclaymineralslikemontmorillonite/illite,atleast3differentadsorptionmechanismsoperatesimultaneously!outerspheresurfacecplx.Classificationofadsorptionreactions

SurfacecomplexProcessForcesinvolvedouterspherephysiosorption(e.g.gasadsorption)VanderWaalsionexchangeadsorptionofhydratedionspurelyelectrostaticinnerspherechemisorption(surfacecomplexationsensustrictu)chemicalbond(ionicorcovalent)Example

EusorptionmeasurementsonCa-montmorillonite

Contributionsofsinglecomplexes:curve1:Exchanged-Eu3+

curve2:=SSO-Eu2+

curve3:=SSO-EuOH+

curve4:=SSOEu(OH)2o

curve5:=SW1O-Eu2+

curve6:totalsorptionfrom:Bradburyetal.(2023)GCA69,5403–5412Note:thedistributioncoeff.Rdvariesby5ordersofmagnitude!Precipitation

Precipitationistheseparationofsolutespeciesasanewsolidphase,occurringwhenthethermodynamicsolubilityproductisexceeded:Inthisexample,apureRNphaseprecipitatesfollowingaccumulationofdissolvedRa2+andSO42-insolutionCoprecipitationAsarule,eveninHLWrepositoryenvironments,RN’sarepresentintraceamountscomparedtomajorelements.Inmostcases,RNaccumulationinsolutionfollowingreleasefromthewastewillnotbesufficienttoreachthesolubilityproductofapureRNsolid.Solidsofmajorelements(e.g.calcite)willprecipitate,carryingwiththemtheRN’s:IfNi2+(traceion)replacesCa2+sitesinthecalcitelattice,themixtureisthermodynamicallyatruesolidsolution（固体溶液，或混晶）.

ThehomogeneouspartitioncoefficientDdescribespartitioningofatraceelementbetweenliquidandsolid(analogoustoKd)(Trace:Carrier)concentrationratioinsolid(Trace:Carrier)totalelementconcentrationratioinaqueoussolutionpartitioncoefficientPartitioncoefficients(1)

Heterogeneouspartitionlaw

describespartitioningbetweenliquidandaninhomogeneous

solid:Applieswhentheprecipitatedsolidfailstoequilibrateinternally>zonedcrystals,frequentatlowTPartitioncoefficients(2)

Nofullthermodynamicequilibriuminthiscase!Partitioncoefficients(3)

The2modelsappliedtoRa-baritecoprecipitationdata(Germann,1921;DoernerandHoskins,1925)allowus:todistinguishbetweenhomogeneousorheterogeneousRaincorporationtodeterminethepartitioncoefficientSolidsolutionthermodynamics(1)

Foreverypureorimpuresolidthecorrectthermodynamicsolubilityproducthastheform:ionactivityproductactivityofend-memberinthesolidsolution(forpurephasesa

=1)Simplestcase,idealsolidsolutionForaconstantionicstrengthsolutionwithbufferedsulfateactivity:

Solidsolutionthermodynamics(2)xRaSO401mRa2+solubilityofpureRaSO4

solubilityofdilute(Ba,Ra)SO4

solidsolutionThebeneficialeffectofsolidsolutionsinanutshell:ThesolubilitylimitofadiluteSSisordersofmagnitudesmallerthanforthepuresolid!ordersofmagnitude

Solidsolutionthermodynamics(3)-Onlythermodynamicquantitiesappearontheright-side!-Forchemicallysimilarcations:CombiningthedefinitionsofK0sp

andD

leadsto:activitycoeff.ofsolidsol.end-members

fractionofdissolvedmetalasfreeion(1meansNOcomplexation)

ratioofthermodynamicsolubilityproductsactivitiesoffreeionsinaqueoussolutionHowdoempiricalpartitioncoefficientsrelatetothermodynamics?ConsiderabinarymixtureofBL(s)andCL(s),withacommonanionL

Correlationoftracemetalpartitioncoefficientsincalcitewithsolubilityproductsofpurecarbonates(Fajan’srule)EquilibriumactivityofthefreemetalMz+ineq.withpure

Mx(CO3)y

ata(CO32-)=10-5a(Mz+)=[Kosp/a(CO32-)1/y

]1/xalkalialkalineearthstransitionmetalsREE(III)Partitioncoefficients(4)

Publishedpartitioncoefficientsoftracemetalsincalcitewerecompiledasafunctionthepurephasesolubilityproduct:themoreinsolublethepuremetalcarbonate,thehigherthepartitioncoefficient

ThecorrelationbetweenDandKspworkswellandcanbeusedtoestimateunknownpartitioncoefficientsforradionuclides:Summaryofestimatedandmeasuredpartitioncoefficientsfortraceradionuclidesincalcite(Curti,1997)

Chem.AnalogonRadionuclides

DBasedon...REE(III)Cm,Am,Pu(III)100-5000Fajan’sruleCo(Zn,Mn,Fe)Ni1-10Fajan’srule-Sr0.03–0.2directmeasurementsBaRa0.01–0.1Fajan’sruleLi,NaCs<0.01Fajan’srule-U(VI)<0.2directmeasurements-Se(VI)~10-5directmeasurementsPartitioncoefficients(5)

TernaryidealSS:EuO(OH)EuH(CO3)2CaCO3

G*(kJ/mol)=-955-1775-1129cEupH=8pH=6pH=13WiththeGibbsEnergyMinimization(GEM)technique,itwaspossibletomodeldataonEuincorporationincalcite.

Aternarysolidsolutionmodel,withEuO(OH)andEuH(CO3)2asend-memberstoichiometriesforEu,successfullyreproducesdataobtainedatwidelydifferentpH-pCO2conditionsSolidsolutionthermodynamics(4)from:Curtietal.(2023),GCA69,1721-1737ThermodynamicSSmodels:anexampleimportantissues

Howcanwedecide:whetheradsorptionorprecipitationwillbetherelevantuptakemechanismwhichsolidswillbetherelevantRNhostphasesintherepositoryProblemsforapplicationofadsorption/precipitationreactionstoPA:

metastability:thermodynamicssometimes“fails”(e.g.dolomiteproblem)

kineticsofprecipitationreactionsmaybetooslowforlaboratoryscale

multitudeofhostphaseswithcomplexchemistry(pickouttherightones)

stabilityofthesorbentsurface(recrystallization,phasetransformations)>>LaboratoryexperimentsandnaturalanaloguestudiesshouldbecombinedtoresolvetheseissuesVerifyingtheRNuptakemechanism(1)

42100mmm100

mmSwissnuclearwastereferenceglassMWcorrodedduring13y

NiistrappedinMg-richsecondaryclays(greeninXRFmap)

EXAFSconsistentwithincorporationasdiluteSSinhectorite(Mg-Li-clay)butadsorptioncannotberuledout(lowCNforNi-Mg)m-XRFNa,Mgmap

VerifyingtheRNuptakemechanism(2)Uptakeof45CaduringEu3+-calciteinteractionincementporewaterindicatesthat-afterinitialadsorption–Eu3+isincorporatedintorecrystallizedcalcite.Twostepskineticsstillunexplainedmmol45CaexchangedDataintegrationinPA(1)

Howaredataonradionuclideadsorptionand(co)precipitationintegratedinsafetyassessmentcalculation?Dplexityofcalculationslimitedprocessunderstandingincompletethermodynamicdata...RNuptakeisimplementedinPAmodelsthroughsimpleparametersthatcanbeeasilyintegratedintothetransporteqs.adsorption > distributioncoefficients(Kd)(co)precipitation > elementalsolubilitylimits(Cs)

DataintegrationinPA(2)Distributioncoefficients(Kd)plottedasafunctionofhalf-lifeforcationicRN’s,usedinPAcalculationsof“ProjectOpalinusClay”fromNagra(2023),NTB02-05RetardationissufficientformostRN’stodecayalmostcompletelywithinthebarriersystem(near-field+geosphere)MagentapointsindicateReferenceCasevaluesofthesorptioncoefficient(Kd).Greenpointscorrespondtopessimisticvalues.BluepointsareusedwheretheReferenceCaseandpessimisticvaluesarethesame.

DataintegrationinPA(3)Distributioncoefficients(Kd)plottedasafunctionofhalf-lifeforanionicRN’susedinPAcalculationsof“ProjectOpalinusClay”fromNagra(2023),NTB02-05Duetoweaksorption,aconsiderablefractionoflong-livedanionicradionuclides(129I,79Se,36Cl)willnotdecaywithinthebarriersystem

lowerlimitreferencecasehigherlimitNi1x10-53x10-58x10-5Se2x10-115x10-91x10-5Sr3x10-62x10-51x10-4Zr3x10-112x10-92x10-9IhighhighhighCshighhighhighRa4x10-122x10-115x10-8Pu3x10-95x10-81x10-6Am5x10-81x10-63x10-5Nearfieldsolubilitylimitsfor“projectOpalinusClay”safetyassessmentcalculationsfromNagra(2023),NTB02-05applicationofsolidsolutiontheory(Ra,Ba)SO4pureRaSO4solubilityDataintegrationinPA(4)solubilitylimitseffectofadsorptiononbentoniteeffectofRaincorporationinbariteInthe“OpalinusClayproj