铝酸钠溶液中aloh

铝酸钠溶液中aloh

1alumicapo体制solid-solid-alumica研磨u2004supplysupply第3个二级alu按顺序商业监督管理局，即第4个二级监督管理局的产品和商业监督管理局。此外，它还没有从未见过的预算编制过程中排除可执行的产品。ThesupersaturatedBayerliquorsarequitedifferentfromtheordinaryinorganicsaltsolutionsandverydifficulttonucleatespontaneously.Foraluminaproduction,alargenumberofseedsmustbeaddedtoreducetheinductionperiodofnucleationsoastopromotetheprecipitationofAl(OH)3.Generally,theseededprecipitationprocessofsodiumaluminatesolutioninvolvesthefollowingsteps:1)withtheinductioneffectsofseeds,theevolutionofotheraluminatespeciestothefavorableprecipitateunitsinthealuminatesolution,2)formationofAl(III)-containingionclustersoffavorableprecipitateunit,and3)precipitationofAl(OH)3bysecondarynucleationorgrowth.Therefore,theseededprecipitationofsodiumaluminatesolutionbelongstothesolid-liquidbinaryphasesystemcontainingtheBayerliquorsandthechargedsolidparticles.Inordertoinvestigatetheprecipitationmechanismsoastointensifytheprecipitationprocess,manystudiesfocusontwoaspects1)thestructureofaluminateanionsandthephysicochemicalpropertiesofsodiumaluminatesolutionand2)thebehaviorofAl(OH)3particles.TheAl(OH)3precipitationprocessofaluminatesolutionheavilydependsontheinterfacialpropertiesbetweenthesolidandthesolution.Intermsofthermodynamicsandkinetics,theprecipitateefficiencytosomeextentreliesontheequilibriumconcentrationofAl(OH)3particlesinthelateperiod;moreover,thesolubilityisdeterminedbythesmallestparticlesinthecrystalpopulationdistributionsystem.Additionally,theparticlesizegreatlyaffectstheratioofagglomerationandgrowthandthusaffectstheparticlesizedistributionofproducts.Althoughtheindustrialprecipitationprocesswithagreatnumberofseedsisquitedifferentfromthehomogeneousprocessanditsphysicochemicalprocessesaremorecomplicated,thecommonfeatureisthatthefavorableprecipitateunitstransferfromliquidphasetosolidphase.Therefore,theinvestigationofthesizeofthesmallestparticlebeingcompatiblewithaluminatesolution,i.e.thecriticalnucleussize,isaveryimportantresearchproject.Ordinarily,thecriticalnucleussizeisdeterminedthroughmeasuringtheinductionperiodofthespontaneousprecipitationandthencalculatingbasedonthehomogeneousnucleationtheory.Forexample,ROSSITERetalmeasuredtheinductionperiodofhomogeneousnucleationintermsofthechangesofliquorturbiditybyamulti-anglelaserscanningequipment,thenobtainedainterfacialtensionof(45±6)mJ/m2andacriticalnucleussizeof(0.0012±0.0001)μmat333KbyusingthenucleationrateequationandtheOstwaldripeningformula,respectively.ZHANGetalmeasuredtheinductionperiodofaluminatesolutionwithdifferentsupersaturationswithanin-situconductivityanalyzer,andthendeterminedtheinterfacialenergyof34-35mJ/m2andthecriticalnucleussizeof1.5-2.0μmbythesamemethodemployedbyROSSITERetal.ButLIetalreportedtheinterfacialtensionsofapproximate106mJ/m2andthecriticalnucleussizeof1.1-1.8μmbytheGibbs-Kelvinformulaat323Kand333K.Thedifferencesofthesolid-liquidinterfacialtensionandthecriticalnucleussizereportedabovemaybeattributedto1)thediscrepancyofthemeasuredinductionperiodduetothefactthatanymethodfordeterminingtheinductionperiodcannotaccuratelyseparatenucleationandgrowth,andthemeasuredinductionperiodincludesthenucleationtimeandgrowthtime(fromnucleustothedetectablesize);2)withoutconsideringtheactivitycoefficientduetothefactthatgenerally,itisfeasibleforcoarseparticletosubstitutetheconcentrationfortheactivityasitssolubilityisclosetotheequilibriumconcentration,butforthefineparticle,thedifferenceofactivitycoefficientcannotbeneglectedasitssolubilityismuchlargerthantheequilibriumconcentration;3)neglectingthevariationofsolid-liquidinterfacialenergy.Theoretically,thesolid-liquidinterfacialenergyisaffectedbyboththeparticlesizeandtheliquidproperties.Theabovementionedstudiesarelimitedtosomespecialconditions,whicharenotenoughfortheprecipitationsystemwithagreatchangeincompositionandtemperature.Underthoseconsiderations,thisworkpresentsastudyoftherelationshipbetweenAl(OH)3solubilityandparticlesizeinsyntheticBayerliquorsbasedonthesolid-liquidinterfacialpropertiesunderdifferentconditions,attemptingtoprovideaguidanceforadjustingthebehaviorofAl(OH)3particlesinseededprecipitationprocess.2母乳喂养2.1外部国际社会主导地位的要求ARgradesodiumhydroxidepelletsandAl(OH)3powder(TianjinKermelChemicalReagentLtd.,China)weredissolvedindeionizedwaterundertheheatingandstirringcondition.AndthentheobtainedsolutionwasfilteredtwicetogetthesyntheticBayerliquorforexperiments.TheconcentrationofsodiumhydroxideasNa2OandtheconcentrationofaluminumspeciesasAl2O3weredeterminedbytitrationusingavariationoftheWatts-Utleymethod.Thecausticratioofliquors(αk)wasdefinedasthemolarratioofNa2OtoAl2O3.2.2pocisonofTherequiredamountofsodiumaluminatesolutionwaspouredintoa2Lstainlesssteelprecipitationvesselsimmersedinathermostatwaterbathwithtemperaturecontrolledprecisionof±1°C.Asthesolutionwaspreheatedtothepresettemperature,weighedindustriaAl(OH)3seed(fromCHALCO,w(Al2O3)>64.5%w(SiO2)<0.02%,w(Fe2O3)<0.02%)wasaddedtotheprecipitationvesselsandagitationwasstartedwith140r/min.Thecompositionofspentaluminatesolutionwasdeterminedbytitrationandtheprecipitationratio(η)wascalculatedbyη=(1-αk0/αk,t)×100%,whereαk0andαk,tdenotecausticratiosofliquorsattheinitialstageandatimet,respectively.2.3que确立成us.1)Liquidsurfacetensionanalysis.Thesurfacetensionapparatus(KRUSS-K100,GER)wasconnectedtoawaterbathwithtemperature-controlledprecisionof±0.5°C.Thesodiumaluminatesolutionwaspouredintothetestingcontainerandthenpreheatedfor30mintotherequiredtemperature.TheliquidsurfacetensionsweredeterminedbytheWilhelmy-Platemethod.2)Infraredspectroscopyanalysis.TheIRspectraofthinfilmsofsodiumaluminatesolutiononKBrplatewerecollectedonaspectrometerwith4cm-1resolution(FT-IR6700,NicoletCo.,USA).Thewholeprocesswasinanitrogenatmosphere.3)Contactangleanalysis.TheAl(OH)3powders(~5g)wascompressedintoathinplate(pressure~10MPa)byatabletpressingmachine(YP-2,ShanghaiShanyueTechnologyInstrumentLtd.,China),thenthecontacanglesoftestingliquorsonAl(OH)3plateweredeterminedwithacontactanglemeter(CL200BShanghaiSolonInformationTechnologyLtd.,China).4)SEManalysis.Themorphologyoftheproducwasobservedbyscanningelectronmicroscopy(JSM-6360LV,ElectronicLtd.,Japan).3影响的神圣迪迪斯运营3.1tensionThepossibilityofestimatingsolidsurfacetensionsfromcontactanglesreliesonarelationrecognizedbyYOUNGin1805.Thecontactangleofaliquiddroponasolidsurfaceisdefinedbythemechanicalequilibriumofthedropundertheactionofthreeinterfacialtensions:whereγslisthesolid-liquidinterfacialtension;γsvisthesolidsurfacefreeenergy;γlvistheliquidsurfacetension;θisthecontactanglebetweensolidphaseandliquidphase.Inordertodeterminethesolid-liquidinterfacialtension,thesolidsurfacefreeenergy,theliquidsurfacetensionandthecontactangleweremeasuredandcalculated.1)SolidsurfacefreeenergyAstheparticlesizedistributionofthepowdermayhaveanimpactonthecontactangle,theBayerindustrialAl(OH)3powderwasscreened.Figure1showstheparticlesizedistributioncurvesofscreenedAl(OH)3powdersamples.ThecontactanglesoftheliquidsglyceroldiiodomethaneontheAl(OH)3platespreparedfromdifferentsamplesweremeasured,andthenthesolidsurfacefreeenergywascalculatedaccordingtoEqs.(2)and(3),asshowninTable1.OWENSandWENTdevelopedatwoparametersystemtodescribetheinterforcesbetweenthemoleculesandanestimationmethodofsurfacefreeenergy,whichwasmainlyappliedtothespecialsolidsurfaceandtestingliquid:whereuf0671Distheliquiddispersionforce;uf0671Pistheliquidpolarforce;uf067sDisthesoliddispersionforce;uf067sPisthesolidpolarforce.Table1indicatesthatthevaluesofsurfacefreeenergyofindustrialAl(OH)3powderswithdifferentparticlesizedistribution(D=1.67-196.04μm)areabout48mJ/m2withthevariationof1mJ/m2,whichmeansthatthereisnocorrelationbetweenthesurfacefreeenergyandtheparticlesizedistributionofAl(OH)3powderinsodiumaluminatesolutionsystem,havingagreementwithresultinRef..So,itisreasonabletoemploytheindustrialAl(OH)3powderastheobjectformeasuringsurfacefreeenergyofAl(OH)3withanyparticlesize.2)LiquidsurfacetensionThesurfacetensionsofthesodiumaluminatesolutionwithdifferentcompositionsat298Kand333Kweremeasured,asshowninFig.2.TheliquidsurfacetensionincreaseslinearlywiththeriseofNa2Oconcentrationanddecreasesobviouslywiththeelevationofcausticratio.Thisismainlyattributedtothefactthattheliquidviscosityincreaseswiththeelevationofthesolutedissolvedinsodiumaluminatesolution,renderingtheincrementofcontractilityverticallyactingonthesurfaceofliquid.Meanwhile,theliquidsurfacetensiondecreaseswiththeincreaseoftemperaturebecauseattractiveforcesamongthemoleculesweakenasthedistancebetweenthemoleculesincreasesandthethermalmotionofthemoleculesintensifieswiththeincreaseoftemperature.Thestructureofaluminateanionsinsolutionwithdifferentcompositionswascharacterizedbyinfraredspectroscopy,inordertofurtherunderstandtheunderlyingreasonsofthechangesinliquidsurfacetension.Figure3showsthatthepeakshapeandintensityofIRspectraofsodiumaluminatesolutionchangeobviouslyfordifferenttestingsamples.Foragivencausticratioofsolution,thepeakintensityandpeakareaoftheAl-OHvibrationofthetetrahedral-4)Al(OHatabout720cm-1reduceandtheAl-O-Alvibrationofthedimer2-62)O(OHAlatabout550cm-1increaseswiththeriseofNa2Oconcentration.Thereasonisthatthetetrahedralaluminateionsdehydrateandpolymerizeintocomplexdimeraluminateions.Foragivenalkaliconcentration,thepeakintensityandpeakareaoftheAl-O-Alvibrationatabout550cm-1increaseandtheAl-OHvibrationofthepolymerizedtetrahedralaluminateionsatabout880cm-1decreaseswiththeelevationofcausticratio.Thismaybeduetothefactthatsomecomplexpolymerizedtetrahedralaluminateionsdehydrateandfurtherpolymerizeintodimer2-62)O(OHAlwhentheconcentrationofOH-isrelativelyhigh.Accordingtotheelectrochemicalpropertiesofsodiumaluminatesolution,thetransferencenumberof-4)Al(OHismuchgreaterthanthatofthe2-62)O(OHAl.Therefore,thepolymerizationdegreeofaluminateionsincreaseswiththeriseofalkaliconcentration,resultinginradiusincrementandthusslowmovementofaluminateions.3)Solid-liquidinterfacialtensionThroughtrialcalculation,itisfoundthattheclassicYoung’equationwasnotsuitableforcalculatingtheinterfacialtensionbetweenAl(OH)3andBayerliquorsZHUetaldesignedamethodforcharacterizingthewettingpropertyofthesolid-liquidinterfaceanddeducedanexpressionformulaasfollows:Theliquidsurfacetensionsγlvwasobtainedasmentionedpreviously,andaccordingtotheaboveformula,solid-liquidinterfacialtensionscouldbecalculatedinthecaseofthevaluesofcontactanglebetweentheindustrialAl(OH)3andthesyntheticBayerliquorsavailable.ThemeasuredcontactanglesandthecalculatedresultsarelistedinTable2andTable3respectively.ItcanbeseenfromTable3thatthevariationtrendofsolid-liquidinterfacetensionmatchesthatoftheliquidsurfacetension.HERRMANNandSTIPETICreportedtheinterfacialtensionof1250MJ/m2,butthemethodthattheyusedwasnotpresentedandtheresultswerenotduplicatedbysubsequentstudies.vanSTRATENanddeBRUYNreportedtheinterfacialtensionof(67±20)mJ/m2forbayeriteandof~25mJ/m2forpseudo-boehmite,whileROSSITERetalreportedtheinterfacialtensionof(45±6)mJ/m2forgibbsiteat333K.ItshouldbenotedthattheliquorusedbyHERRMANNandSTIPETICwas10-3mol/LNaOHandthatbyROSSITERetalwas~4mol/LNaOH,and1.96-3.14mol/LAl(OH)3.Whiletheliquorsusedinthisworkwere4.58-6.48mol/LNaOHand3.18-4.5mol/LAl(OH)3.Therefore,thedeterminedinterfacialtensionsinthisworkarereasonablereferringtoRef.,inwhichthevaluesofinterfacialtensionsvaryintherangeof0-100mJ/m2forothermolecules.AstheprecipitationprocessofBayerliquorsisremarkablyinfluencedbythesolubilityofAl(OH)3correspondingtoitsparticlesize,itisnecessarytostudytherelationshipbetweenAl(OH)3solubilityandparticlesizeinthesyntheticBayerliquors.3.2solid-solu深刻信息Therelationshipbetweensolubilityandparticlesize,originallyderivedforvaporpressuresinliquid-vaporsystemsbyTHOMSONin1871,utilizedlaterbyGIBBS,andappliedtosolid-liquidsystemsbyOSTWALD(1900)andFREUNDLICH(1926),maybeexpressedasfollows:whereCisthesolubilityofparticlesofsize(radius)r;C*isthenormalequilibriumsolubilityofthesubstanceR=8.3J/(mol·K);Tisthethermodynamictemperature;ρisthedensityofthesolid;Misthemolarmassofthesolidinsolution;γslistheinterfacialtensionofthesolidincontactwiththesolution;υrepresentsthenumberofmolesofionsformedfromonemoleofelectrolyteObviously,foranequilibriumstateofsolid-liquidsystemunderaspecificcondition,iftheradiusofsolidparticlesislessthanr,thecorrespondingsolubilityisgreaterthanthesolubility,andthusthefineparticleswillbedissolved.Thatis,rinEq.(5)canbetakenasthecriticalnucleussize(rc).Forcoarseparticles,itisfeasiblethattheactivitycoefficientisnottakenintocalculationbecausetheactualconcentrationnearlyequalsnormalequilibriumsolubility.However,thedifferencesofactivitycoefficientcannotbeneglectedduetothesolubilitycorrespondingtofineparticlesmuchlargerthannormalequilibriumsolubility.SoCandC*inEq.(5)shouldbereplacedbytheiractivities:wheref*andfaretheactivitycoefficientsofthesodiumaluminatesolutionsatdissolutionequilibriumforcoarseAl(OH)3particleandfineparticlewithradiusrrespectively.Foragiventemperatureandcausticconcentrationf*andC*areavailablefromRef..Thecalculationprocessisasfollows:1)rcwasfirstdesignatedavalue2)γslandfwerethengiveninitialvalues,respectively3)anewvalueofCwasobtainedbasedonEq.(6)4)fwascalculatedaccordingRef.andγslwascalculatedfromTable3bythesplineinterpolationmethod;5)repeatsteps(3)and(4),whenthevaluedifferenceofCbetweentwoadjacentcalculationswaswithin1.0×10-4mole,thelastcalculatedCwasoutputastheresultandthecalculationended.Meanwhile,thecalculationshouldmeettwoconditions:1)thevalueofthecausticratioisnotlessthan1.0;2)thedesignatedvalueofthecriticalnucleussizeislargerthanthatoftheunitcellof4.66Å(calculatedassphericalparticle).Thesolubilitywasplottedasafunctionofparticlesizeatdifferenttemperaturesandconcentrationsofsodiumaluminatesolution,asshowninFig.4.Clearlythesolubilitydeclinessharplyforextremelyfineparticles(<0.1μm)andthenslightlyforrelativelycoarseparticleswiththeincreaseofparticlesize,namely,thesolubilityoffineparticlesishigherthanthatofcoarseparticles.Infact,thisisthereasonforthepropertyofsupersaturationofBayerliquor.DuetothelargersolubilityoffineparticlesinBayerliquors,thepresenceoffineparticlesisanimportantfactortolimitthedepthofprecipitation.Furthermore,thesolubilityofAl(OH)3particlesincreasesobviouslywiththeriseofNa2Oconcentrationandtemperature,inaccordancewiththatinRef..Becausethefineparticleswillbedissolvediftheradiusislessthanrc,thecriticalnucleussizercincreaseswiththeriseofNa2Oconcentrationandtemperature.3.3cricacitiphunthiectinvi供给4.3.3.3.3—VerificationofcalculationresultsAsforthecriticalnucleussizerc,althoughthereweremanystudiesinliteratures,noagreementhasbeenreached.HALFONandKALIAGUINEdesignatedthecriticalradiusof0.01μmintheirstudyofkinetics,butitwasmuchlargerthanthevalueobservedfromthemicrograph.ZHANGetalandLIetalcalculatedthecriticalnucleussizercof1.1-2.0μmwhichwasalsomuchlargerthantheobservedone.WhileLOHcalculatedthecriticalnucleussizercof0.11μmusingthevalueofγslpublishedbyHERRMANNandSTIPETIC,andROSSITERetalpredictedthecriticalnucleussizercof(0.0012±0.0001)μmat333K.Inthiswork,thevaluesofrcwerecalculatedtobe0.002μmand0.05μmwithNa2Oconcentrationsof142g/Land182g/L,respectively,whentemperaturewas333Kandthecausticratiowas3.0.Itshouldbenotedthatthecalculationrepresentstheprimarynucleationwhichisdifferentfromthesecondarynucleationinseededprecipitation.Infact,itisverydifficulttomeasurethecriticalnucleussizercinseededprecipitationprocessbecausetheactualprocessinvolveslotsofinterrelatedphysicochemicalchangessuchasnucleation,agglomeration,growthandabrasion.Generally,micrographsoftheproductwereemployedtodeducethercvaluebyobservingthesmallestseparateparticleatnearequilibriumstate.Therefore,industrialAl(OH)3seedswereaddedintotheprecipitationvesseltogetherwiththesyntheticBayerliquorandtreatedfor70hundertheconditionsforourcalculationofrc.TheSEMmicrographsofthetreatedproductareshowninFig.5.InFig.5(a),therearemanyfineAl(OH)3particlesandpartofthemattachtocoarseAl(OH)3particles.Thevalueofthesmallestisolatedparticlesizeoncoarseoneismeasuredas0.002-0.004μmbyscaleplateinimageprocessing,whichisclosetothatcalculated.WhileinFig.5(b)fineparticlestremendouslyreduceandthesmallestisolatedparticlesizeismeasuredtobeabout0.05μmwhichalmostequalsthatcalculated.Additionally,theprimarycrystallineinFig.5(a)isapparentlysmallertha