Acomparativestudyoftwomethodsforthesynthesisofflya

Acomparativestudyoftwomethodsforthesynthesisofflyash-basedsodiumandpotassiumtypezeolitesCarlosA.RíosR.a,b,*,CraigD.Williamsb,CliveL.RobertsbaEscueladeGeología,UniversidadIndustrialdeSantander,A.A678,Bucaramanga,ColombiabSchoolofAppliedSciences,TheUniversityofWolverhampton,WulfrunaStreet,CityCampus–South,WolverhamptonWV11LY,UKarticleinfoArticlehistory:Received17April2008Receivedinrevisedform4November2008Accepted10February2009Availableonline4March2009Keywords:FlyashSynthesisZeoliticmaterialsHydrothermalFusionabstractFlyash(FA)fromtheRugeleyPowerStation,WestMidlands(England)wasusedinastudyonsynthesisatlaboratoryscaleofzeoliticmaterialsundervariousconditionsbytwodifferentroutes.ZeoliticmaterialsweresynthesizedfromFAbyhydrothermaltreatmentinNaOH(Na-phillipsite,hydroxysodalite,hydroxycancrinite,tobermorite,analcimeandherschelite)andKOH(hydroxysodalite,zeoliteBarrer-KF,K-chabaziteandzeoliteLindeTypeF)solutions.ByfusionwithNaOHfollowedbyhydrothermalreac-tion,FAwasconvertedintofaujasiteandhydroxysodalite.NozeoliticmaterialswereobtainedbythismethodusingKOHasalkaliactivator.Theprocessofsynthesiswasoptimisedbyapplyingawiderangeofexperimentalconditionswithawiderangeofreactiontemperature,time,alkalihydroxideconcentra-tionandsolid/solutionratio.TheefficiencyFA-basedzeolites(FAZs)forheavymetalandammoniumuptakefromsyntheticsolutionsatlaboratoryscalehavebeeninvestigatedbytheauthors,revealingthattheseFAZsmayreachappropriatecationexchangecapacitiesfortheirapplicationinindustrialwastewa-tertreatment.2009ElsevierLtd.Allrightsreserved.1.IntroductionGlobally,over500milliontonnesofFAaregeneratedeveryyearfromcoalcombustionbythermalpower-plantsanditsdisposalaslandfillposesmajorchallengesandseriouseconomicandenviron-mentalproblems.Theburningofcoalfortheproductionofelec-tricitysuppliesaround40%oftheUKelectricity,andthereforeFAisanabundantmaterial.Furthermore,theamountofdischargedmaterialisexpectedtoincreasedramaticallyinthefuture.Duetoincreasinglandfillcosts,stricterenvironmentalregulationandcurrentinterestinsustainabledevelopment,theeffectiverecyclingofFAfortheproductionofproductsofgreatervaluetomitigatethedepletionofresourcesandenvironmentalimpacthasbecomeanincreasingconcerninrecentyears.ThemajorapplicationofFAisforconcretemanufacturing,whereitcanprovidebothtechnologi-calandeconomicbenefits.However,thisapplicationislimitedwithinthedemandofconstructionmaterials.Therefore,zeolitesynthesisfromFAbyseveralmethodshasbeenreceivingalotofattention.SincethepioneeringworkofHöllerandBarth-Wirsching[1]whowerethefirstresearchersthatsynthesizedzeolitesfromFA,alotofinvestigationshavebeenconductedtoconvertFAtozeolites.TheconversionofFAintozeolitesisconventionallydevel-opedbyhydrothermalcrystallizationunderalkalineconditions,whichhasbeenreportedbyseveralpatentsandscientificarticles[1–26].TheFAZscoverawiderangeofknownzeoliteframeworksandhavebeenreviewed[20].Recently,theconventionalalkalineconversionofFAhasbeenimprovedbyusingmoresophisticatedtreatments,whichincludeanalkalinefusionstepfollowedbyhydrothermaltreatment[17,19,27–31]facilitatedtheformationofhighlyactivealuminosilicatesaltsreadilysolubleinwaterandpromotedzeoliteformation,theapplicationofmicrowave-assistedzeolitesynthesis[32]resultedinadrasticreductionofthereactiontime,andamethodforsynthesizingzeoliteundermoltencondi-tionswithoutanyadditionofwater[33,34],althoughcompletezeolitizationofFAhasnotbeenobtained.Atwo-stepsynthesisprocess[35,36]hasbeendevelopedconsistingofaninitialSi-extractionfromFAbyusingalightalkalinetreatmentofFAfollowedbyasynthesisofpurezeolitesbyaddinganAl-bearingresiduesolutionobtainedfromAl-anodizingindustry.Apartfromtheformationofzeolites,thehydrothermalconversionofFAcanalsoproduceamorphousformaluminosilicate,referredtogeopoly-mers[37].ThesynthesisofFAZsinformssuitableforindustrialapplicationsisofgreatimportance,mainlyasionexchangers,molecularsieves,adsorbentsandcatalysts.TheresultantFAZshavehighpotentialtobedevelopedasahighefficientlowcostadsor-bentswithapplicationinenvironmentalproblems,particularlyinwastewatertreatment.ThepotentialuseofFAZsinwaterdecon-taminationhasbeenevaluatedbyanumberofresearchgroups0016-2361/$-seefrontmatter2009ElsevierLtd.Allrightsreserved.doi:10.1016/j.fuel.2009.02.012*Correspondingauthor.Address:SchoolofAppliedSciences,TheUniversityofWolverhampton,WulfrunaStreet,CityCampus–South,WolverhamptonWV11LY,UK.Tel.:[phone];fax:[phone].E-mailaddresses:[e-mail],[e-mail](C.A.RíosR.).Fuel88(2009)1403–1416ContentslistsavailableatScienceDirectFueljournalhomepage:[18,38–48],andturnswastematerialsintousefulones.Zeoliticmaterialsarehighlyselectivescavengersofavarietyofheavymetalsthatcanberemovedfromliquidefflu-entsthroughtheprocessofionexchange.Inthispaper,weinves-tigatethesynthesisofzeolitesfromFAatlaboratoryscalevia(1)hydrothermaltreatmentinalkalinesolutionsand(2)dissolutionofalkalifusedaluminosilicatesaltsinwaterfollowedbyhyd