赤泥蜂窝陶瓷文献.docx

赤泥蜂窝陶瓷文献.docx

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赤泥蜂窝陶瓷文献

Fabricationofredmudhoneycombporousceramicsusingdolomiteaspore-formingagent

ABSTRACT

Redmudfromaluminumindustrywasregardedasperniciousandpoisonousindustrywastearoundtheworld.Inordertoeffectivelyutilizetheintensealkalineslag,anovelredhoneycombceramicwasdevelopedsuccessfullybyextrusionmoldingusingbauxiteresiduesasrawmaterials,withbitsofdolomiteasporeformingagent.Theaimofthisresearchwastoinvestigatetheinfluencesofamountofdolomiteaswellasofthesinterpointonthemechanicalstrength,porosity,bulkdensity,crystallinephaseandmicrostructure.Theresearchshowsthattherelativelybestcomprehensiveperformancecanbeobtainedbyaddingapproximately12%dolomiteandusingsinteringtemperatureof1175℃，leadingtocomprehensivestrength,porosity,bulkdensity,medialporediameter,about14.5MPa,65%,0.94g/cm3,5.2μm,respectively,whichmeetrequirementofcommonhoneycombceramicaccordingtoChinesenationalstandard.

Introduction

Redmud（RM）,generatedbycommercialaluminamanufacturingproduces,isgraduallytriggeringseriousenvironmentissuesduetoitshighalkalinity（>11）[1-2].Generallyspeaking,nearlytwotonsofredmudslurrywillgeneratealongwiththeproductionofonetonaluminaandapproximatelythreebilliontonneswasteresidueshavesofarstackedaroundtheworld[3].Mostresiduesevacuatedanddisposedinhugelandfills,whichwilloccupyhugeareasoflandandcontaminatingundergroundwater[4].Siegfriedetal.investigatedthegenotoxiceffectsofvanadiumofredmudinhigherplants.TheresultsindicatethatredmudnotonlycausegenotoxiceffectinplantsbutdamageinhumanDNA.Andthebiggestenvironmentcatastrophe“Kolontardisaster”[5]allowpeopleincreasinglyawareofthatbauxiteresiduesrequiretreatmentbeforetheycouldreleasesafelyintotheenvironment.

Overtheyears,comprehensiveworkhasbeendonetodevelopvariousmeasuresforresourceutilizationandinnocuitytreatmentofbauxiteresiduesbytheboffinsinavarietyofareas.Luetal.[6]successfullysynthesizedanewfoamceramicsbyconventionalceramicsinteringprocedureusingredmudasmainrawmaterialswithaspotofsodiumsilicateastheporeformingagent.Excellentmechanicalstrength,microstructurewereobtainedbyaddingabout40-50%bauxiteresidues.Lvetal.[7]undertakentheresearchofdevelopingthecapacityofzirconiumhydroxide-modifiedbauxiteresiduesporousmaterialsforremovaloffluoridefromaqueoussolutions.Theporousmaterialswerepreparedbyanorganicfoamimpregnationprocesswithskyscrapingredmudcontentabout60%,whichhasamaximumadsorptionoffluorideatpHof3.0aswellasequilibriumwithin60min.Toconsumenumerousalkalinesolidwastes,Yangetal[8].hasdevelopedunsinteredconstructionmaterialsfromredmudwasteswiththepercentagecompositionabout20-40,curedatambientconditions.ResultsshowthatthebrickproductreachtheChinesecriterionofthe1st-classbrickandshowexcellentdurabilityinrigidclimateconditions.Asforutilizingredmudascatalystsupport,Yangetal[9].fabricatedmulti-functionalbauxiteresidueshoneycombceramicsbycompressionmoldingforming.Theredmudhoneycombproductsrevealoutstandingbendingstrength,wateradsorptionandporosityunderthesinteringtemperatureof1075℃,whichhasagoodadvantageofapplicationinenvironmentalprotectionsuchasantibiosis,waterfiltration.Inadditiontotheabove,thereareplentyofotherresearchworkaboutwatertreatment[10-15],metalrecovery[16],constructionmaterials[17-21]andglassceramic[22-24].However,lessresearchhasbeenreportedonpreparationofextrusionmoldingRMhoneycombceramics.

ThepresentpaperhammersatresearchingthefeasibilitytoreusebauxiteresiduesintheproductionofRMhoneycombceramics.Inthepresentstudy,theRMhoneycombceramicsarefabricatedbyvariouspilot-scalefacilitiessuchasvacuumkneader,vacuumpugmill,andextrusionmoldingmachine,whichareusedasstructuralsubstrateinapplicationssuchasdenitration, desulfurationandcatalyticcombustion.Mechanicalproperties,microstructure,andsurfaceperformanceoftheproductionshavebeenstudiedinthispaper.

Experimentaldetail

Materials

TheRMhoneycombceramicsweremanufacturedwithredmud,dolomite,andadditiveasmainrawmaterials.TheprimarycompositionofredmudanddolomitesuppliedbyQiXinCo.Ltd.islistedinTable1[25].Theadditivesincludediaspore（Aluminiumcorp.ofchinaLtd.）,fibrepower（Yubangindustrialceramicsco.Ltd.,Zibo）,CMC（Oubokaichemicalco.Ltd.,Tianjin）,PVA（Zhonghechemicalco.Ltd.,Tianjin）,glycerol（Fuyuchemicalco.Ltd.,Tianjin）.Intheprocessionofextrusionmolding,theadditiveagentsarecriticalforsuccessfulextrusionmolding.AsrevealedinTable2,5%PVAwereusedaslowtemperaturebinder,3%glycerolaslubricant,2%CMCasplasticizer,22%waterassolvent[26],fiberpowderanddiasporewereusedtoimprovebendingstrength[27,28].Andthensmooth,flatredmudhoneycombgreenbodycanbecontinuouslyextruded.

Table1

Chemicalcompositionofredmudanddolomite,wt.%.

Rawmaterials

SiO2

Al2O3

Fe2O3

CaO

TiO2

Na2O

K2O

MgO

CO2

LOI

Redmud

26.43

17.89

34.89

2.68

0.72

12.18

0.37

0.10

-

11.70

dolomite

-

-

0.21

30.4

-

-

-

21.7

47.9

44.5

*LOI（lossonignition）

Table2

SampledesignationandprimarycompositionsofRMhoneycombceramics.

sample

Redmud/wt.%

Dolomite/wt.%

Additives

wt.%

PVA

glycerol

water

cmc

Fiberpower

diaspore

RM1

76

4

5

3

22

2

10

8

RM2

72

8

5

3

22

2

10

8

RM3

68

12

5

3

22

2

10

8

RM4

64

16

5

3

22

2

10

8

Preparation.

AsillustratedinFig.1,thebauxiteresiduesshouldbepreprocessedfirst（about160mesh）,andmixedwithdryadditivesbyball-millingforabout1h,thenkneadedbyvacuumpuggingmechinewiththewetassistantsfor30mins.Thepastematerialsneedwrappedwithclingfilmandbanalizedforapproximately24h,andnextextrusionmoldedtoachievegreen-pressingofredmudhoneycomb（Ø32mm）.Afterdryingintheshadefor48handdesiccationat100℃for1h,thegreenbodywassinteredinmufflefurnace.Thesinteringprocedurewasperformedasthefollowingprocedure[9,29]:

thegreenbodyneedheatedfromambienttemperatureto500℃ataheatingrateof10℃/min,heldfor1h,afterwardsheatedto1000℃attherateof5℃/min,thenceaselesslyheatedtotargettemperatureattherateof2℃/min,maintainedfor1h.

Redmudandadditiveagentskneadingpugging

RMhoneycombExtrusionmoldingAgingforhoursRMpaste

Fig.1PreparationflowchartforRMhoneycombceramics.

AsshowninFig.2,cellchannelsandchannelswallsconsistthestructureofthisredhoneycombceramic,whichwasmanufacturedbyafixedextrudingmachineundernormalbarreltemperatureandahoneycomb-shapediewhichhasasquarecellchannelshapedinapproximately120cellspersquareinchandawallthicknessofabout800μmaswellasouterwallthicknessof1mm.Andhighferricoxidecontentissufficienttogivethehoneycombgreenbodyasuitablyredcolorandbrightappearance.

Fig.2PhysicalphotographsofRMhoneycombceramics.

Characterization

Thecomprehensivestrengthofcylindricalhoneycombsampleswereconductedbyelectroniccompressivestrengthtestingmachine（SGY-II,Testerkingtestinstrumentsco.Ltd,Jinan）withaloadingrateof5mm/min.Themeasurementofporosity,waterabsorptioncapacity,bulkdensityofsinteredhoneycombsamplesrefertoChinesenationalstandardGB/T25994-2010[30].

ThephasecompositionofsinteredhoneycombsamplewasperformedbyPowderX-raydiffraction（BRUKERAXSGMBHD8Focus）at40kVand40mA.TheXRDgraphconduct2θfrom10°~80°atastepsizeof0.02°.Themicrostructureoffracturesurfaceofsinteredsampleswereobservedbysolid-imagelightmicroscope（BVM-300V,Batuoinstrumentco.Ltd,Shanghai）togetanoverviewaboutshapeandsizeexistingpores.Theporesizewasmeasuredonafractureofsamplesusinganimageimage-proplus.

Resultsanddiscussion

MechanicalpropertyofRMhoneycombceramic

Fig.3Effectsofsinteringtemperatureanddolomitecontentonbendingstrength.

Fig.3illustratesthecompressivestrengthofRMhoneycombceramicsamplescontainingdifferentdolomitecontentsbetween1100and1225℃.Asexhibitedinthediagram,thecompressivestrengthofsamplesrisesbeforetheyarereducedalongwiththefluctuationoftemperaturerunderthesamedolomitecontentandbycomparisonofthefourcurves,thetemperatureneededformaximumcrushingstrengthofthefourfiredbodiesriseswiththeincreasecontentofdolomite（sampleRM4hasmaximumcompressivestrengthon1275℃）.ThisismayprimarilyattributedtothejustificationthatthefreeCaOandMgOcontentofthefiredsamplesincreasescontinuouslywithincreaseofdolomitecontent,whiletheconpressivestrengthdecreasesgradually[31].Theincreasecontentofalkalimetalsrestrainsgenerationofdiopsidephase,promotesgenerationthehedenbergitephase,afterwardsenlargesthesinteringtemperature.

Fig.4Effectsofsinteringtemperatureanddolomitecontentonsampleporosity.

TheporosityoftheRMhoneycombceramicsatdifferentporeformingagentsbetween1100and1225℃areshowninFig.4.Onthetransversedirection,theporosityofthesinteredproductionsgravitatestowardstopresentdecliningtrendswiththeriseofsinteringtemperatureunderthesamecontent,whichismainlybecausesomeoftheglassymeltsflowintothegapaccumulatedbycrystalparticlesormicroporeformedbyCO2,theseglassyphasehassuccessfullybl