MicrostructuralanalysesofphosphogypsumgeneratedbyB

MicrostructuralanalysesofphosphogypsumgeneratedbyBrazilianfertilizerindustriesMarianaMoreiraCavalcantiCanuta,VanusaMariaFelicianoJacominob,⁎,KariBråtveita,AbdiasMagalhãesGomesa,MariaIreneYoshidacaEngineeringDepartment,FederalUniversityofMinasGerais,BeloHorizonte,BrazilbDevelopmentCenterofNuclearTechnology,BeloHorizonte,BrazilcChemicalDepartment,FederalUniversityofMinasGerais,BeloHorizonte,BrazilARTICLEDATAABSTRACTArticlehistory:Received30November2006Receivedinrevisedform8February2007Accepted9February2007Thispaperinvestigatesandcontraststhematerialpropertiesofphosphogypsum–awastebyproductoffertilizerproductiongeneratedinlargeamountsworldwideandgypsum–amineralthatoccursinnatureintheformofcalciumsulphatedihydrate.Thestudyisbasedontestsofcharacterizationthatenablephysicalandchemicalanalysesofbothmaterials.Alltestswereconductedinordertoevaluatewhetherornotphosphogypsumisaviablesubstituteforgypsumincivilconstruction.Byutilizingphosphogypsum(PG),naturaldepositsofgypsummightbeconservedandhighamountsofthewastebyproductusedinitsplacebythecivilconstructionindustry.Theresultsshowthatphosphogypsumcanbeaviablesubstituteforgypsumaftercertainbeneficiationprocesses.©2007ElsevierInc.Allrightsreserved.Keywords:PhosphogypsumMicrostructureanalysisWastemanagement1.IntroductionPhosphogypsumisabyproductofthechemicalreactioncalledthe“wetprocess”[1],wherebysulfuricacidisreactedwithphosphaterocktoproducethephosphoricacid(P2O5)neededforfertilizerproduction.Foreverytonofphosphoricacidmade,some4–5tonsofphosphogypsumarecreated.TheBrazilianproductionofthismaterialisaround4.5millionsoftonsperyear[2].Therearecurrentlythreepermittedoptionsformanagingphosphogypsum[3]:(i)stacking;(ii)disposalordumping;and(iii)touseitin,forexample,agriculture,constructionorlandfill.Insomejurisdictionstheseoptionsareconstrained.ForexampleintheUnitedStates,option2,stackingisthestandardprocedure,withlimitedexceptionsforcertaintypesofphosphogypsum,foruse,forexample,inpeanutfarming[4].Inotherjurisdictions,dumpingispermitted,mostlyintoopenwaterssuchastheAtlanticOcean[5].Inmanyjurisdictionswhereamixtureofuseanddisposaliscommonpractice,changingenvironmentallegislationiscausinganewemphasisonstackingintheshorttermandonpotentialbeneficialusesinthelongerterm.Globaldemandhasspurredinterestinfindingprocessesthatgenerategreatamountsofbothphosphoricacidandchemicalfertilizers.However,thereareseveralimportantenvironmentalconcernsunderlyingthedisposalofthiswastebyproduct,phosphogypsum,thatremainunaddressed.Thedisposalproblemsexistmainlybecausethismaterialcontainstoxicelementsasheavymetalsandradionuclides[6,7].Theseimpuritiescanpercolatethroughthepileandcontaminategroundwater,whicheventuallycancausedamagestohumanhealth[8].Researchesaccomplishedinseveralcountriesaroundtheworldhavedemonstratedthepotentialuseofthisproductasanagriculturalsourceofcalciumandsulfur;asaconditionerforsoilsthatcontainhighlevelsofsodiumintheconstructionMATERIALSCHARACTERIZATION59(2008)365–373⁎Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](V.M.F.Jacomino).1044-5803/$–seefrontmatter©2007ElsevierInc.Allrightsreserved.doi:10.1016/j.matchar.2007.02.001ofhighways;andasasubstituteforthetraditionalgypsumusedinPortlandcementandprefabricatedpanels[9].Thechronicshortageoflow-costhomesinBrazilasawholewouldjustifytheproductionofconstructionmaterialsbasedonphosphogypsumasasubstituteofgypsum.Theseconstructionmaterialsinclude,amongothers,blocks,liningforroofsandprefabricatedpanels.Takingintoaccountthepresenceofnaturalradionuclidesinthismaterial,whichwillresultintheinternalandexternalexpositionofindividuals,anyjustificationforitsuseshouldbemadestartingfromacost–benefitanalysis.Thecost–benefitanalysismusttakeintoconsiderationfactorsincludingtheincrementofdoseinpublicindividuals,theriskassociatedtotheintroductionofthispractice,costofalternativematerialsandimprovementoftheconditionsoflifeofthepopulationandoftheenvironmentandpsychoso-cialfactors,amongothers[10].WiththeintentionofwiselyregulatingphosphogypsumasasubstituteforgypsumincommercialbuildingsandcivilconstructioninBrazil,aresearchprojecthasbeenconductedbyapartnershipoftheDevelopmentCenterofNuclearTechnology(CDTN)andtheMaterialsandCivilConstructionEngineeringDepartmentoftheFederalUniversityinMinasGeraisStateinordertoperformmicrostructuralcharacteriza-tionsofphosphogypsumandgypsum,aswellastoevaluateandcontrasttheirphysicalproperties.Density,porosityandsizedistributionwerethefocusofthesestudies,aswellasthedeterminationofnaturalradionuclideconcentrationsinbothmaterials.Themainobjectiveofthispaperistopresentanddiscussthepreliminaryresultsofthisresearch.Wewouldliketoemphasizethatresultsobtainedinthisstudycanbecitedtoproposetechnologicalalternatives.Thesealternativescancontributenotonlytothepreservationofnaturalgypsumresources,butalsocontributetothevaluationofphospho-gypsum—abyproductsolidformerlylookeduponmerelyaswaste.2.Experimental2.1.MaterialsTheworkmethodologyiselaboratedbasedintheneedsforacharacterizationofPG.Alltheanalyseswerecarriedou