Synthesisofgranularzeoliticmaterialswithhighcation

SynthesisofgranularzeoliticmaterialswithhighcationexchangecapacityfromagglomeratedcoalflyashRobertoJuan*,SusanaHerna´ndez,Jose´ManuelAndre´s,CarmenRuizInstitutodeCarboquı´mica(CSIC),MiguelLuesma,4,50018Zaragoza,SpainReceived21August2006;receivedinrevisedform9January2007;accepted9January2007Availableonline7February2007AbstractFlyashfromcoalcombustionisapotentialsourceofpollutionandthereiscontinuousinterestinitsrecyclingbyconvertingitintoproductssuchaszeoliticmaterialsforuseinretainingpollutants.Inthispaper,productionofgranularzeoliticmaterialfromacommer-cially-unusablefine-fractionofalightweightaggregate(LA)buildingmaterialmadefromcoalflyashagglomeratedwithlime,bycon-ventionalalkalineactivationisdescribed.NaP1zeolite,K-Fzeolite,K-PhillipsiteandK-Chabaziteweresynthesised.Theprocesswasoptimisedbycombiningfourreactionparameters(temperature,alkaliconcentration,solution/flyashratioandreactiontime).Zeoliticmaterialswiththehighestzeoliteyieldsandcationexchangecapacitieswereselectedforfutureapplicationinenvironmentalprocesses.End-productzeoliticmaterialsmaintainitsgranularformandthiscouldfavourtheiruseinsomeparticularapplicationsforenviron-mentalwastetreatment(e.g.ionicexchangeincolumn)withoutanyfurthertransformationstages.2007ElsevierLtd.Allrightsreserved.Keywords:Coalflyash;Zeolitesynthesis;Cationexchange1.IntroductionAlargeamountofflyash(43,476ktintheEuropeanUnion15in2004and71,100ktinUSAin2005)[1,2]aregeneratedannuallyfromcoalcombustioninThermalPowerPlantsbutonlyapart(50%inEU15and41%inUSA)isused,mainlybythebuildingandroadsectors.Themajoruseisasrawmaterialforcementandconcretemanufacture(36%inEU15and25%inUSA).Environ-mentally–friendlydisposalofflyashisagreatproblemowingtomeasuresrequiredforthepreventionofenviron-mentalpollution.Zeolitesynthesisfromflyashisaminorapplicationalthoughwithincreasinginterestgivenitspromisingenvironmentaluse.Zeolitesmaybeobtainedfromnaturaldepositsorthroughchemicalsynthesis.SyntheticzeolitesareobtainedonanindustrialscalefrompureSi–Alsolutions,combinedwiththeappropriatecation(Na,K,Ca,Mg,andBa).Overthelastfewdecades,intensiveresearchhasbeenunder-takeninthesearchforanotherstartingmaterialforzeolitesynthesis,suchascoalflyash[3].Currently,theproductionofzeolitesfromcoalflyashbymeansofdifferenthydro-thermalactivationmethodsisawellknownprocess.Thechemical,mineralogicalandtexturalfeaturesofflyashshowittobeaverysuitablestartingmaterialforzeolitesynthesis.Inmoststudies,classicalkalineconversionofflyashiscarriedoutindigestionbombsorautoclaves.Upto13dif-ferentzeolitesfromthesameflyashhavebeensynthesisedbyvaryingtheactivationagent,mainlyNaOH[4]andKOH[5]anditsconcentrationatatmosphericandautoge-nouswatervapourpressures,conversiontimefrom3to48h,temperaturefrom80to200C,anddifferentsolu-tion/flyashratios.Laboratoryconditionshavebeenextrapolatedtopilotplantscaletoproducelargeramountsofzeoliticmaterialsforapplicationinfieldtests[4].Ontheotherhand,adrasticreductionofthereactiontimehasbeenachievedbyapplyingpowerthroughmicrowavestoconventionalsynthesisparameters[6,7].0016-2361/$-seefrontmatter2007ElsevierLtd.Allrightsreserved.doi:10.1016/j.fuel.2007.01.011*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](R.Juan).(2007)1811–1821Theconventionalprocessusedinotherstudieshasbeenmodifiedbyintroducinganalkalinefusionstagebeforezeolitesynthesis,leadingtotheproductionofveryinterest-ingzeolitessuchasFaujasite[8,9].PureAandXzeolitescanbeobtainedthroughatwo-stepprocesswherealkalineextractfromflyashisusedasasilicatesource,whichisthenmixedwithapure,externalsourceofaluminatetosynthesizepurezeolite[8,10,11].Mostzeoliticmaterialspreparedfromflyasharedevotedtoenvironmentalapplications,utilizingtheiruptakepropertiesofmetalionsthroughcationexchangeprocesses[8,12].However,themajordrawbackinalltheseprocessesisthatzeolitesobtainedbyconventionalmethodshaveasmallparticlesize(powder0.0mm).Thispre-cludestheiruseinfutureapplicationssuchaspackedbedincolumnsforwastewatertreatments.Inthisrespect,somesolutionshavebeenproposedincludingpreparationofzeo-litebriquettesusingconformedashesasrawmaterial[13].Inordertoovercomethesizeproblem,thepresentworkdealswithgranularzeolitesynthesisthroughthehydro-thermaltreatmentofflyashpellets,obtainedfromagglom-erationofcoalflyashwithlime,andthecharacterizationoftheresultingzeoliticmaterialsfortheircationexchangecapacity(CEC).2.Experimental2.1.MaterialsThestartingmaterialforthisstudywasobtainedfromcommercially-unusablefine-fractionmaterialremainingafterthemanufactureofalightweightaggregate(LA)buildingmaterial.LAismadefroma95:5mixtureofcoalflyashfromtheTeruelPowerStation(Spain)andlime,withtheadditionofwateruntilaplasticmixture(about13%w/w)isformed.Pelletsobtainedbyagglomerationarehardenedandcuredat75Cduring12htoobtainthefinalproductforuseinthebuildingsector.Inthiswork,ourchoiceofthe0.8mmPBP0.2mmfractionwasbasedonpreviousexperience[14].Thissizerangeforzeoliticmaterialshasbeenproventobesuitableforworkinlaboratoryasbedloadinionexchangecolumns.Chemicalcharacterisationofthera