Changesinmobilityoftoxicelementsduringtheproductio

JournalofHazardousMaterials148(2007)745–750ShortcommunicationChangesinmobilityoftoxicelementsduringtheproductionofphosphoricacidinthefertilizerindustryofHuelva(SWSpain)andenvironmentalimpactofphosphogypsumwastesRafaelP´erez-L´opez∗,AntonioM.´Alvarez-Valero,Jos´eMiguelNietoDepartmentofGeology,UniversityofHuelva,Campus‘ElCarmen’,E-21071Huelva,SpainReceived27March2007;receivedinrevisedform19June2007;accepted20June2007Availableonline24June2007AbstractPresently,about3milliontonnesofphosphogypsumarebeinggeneratedannuallyinSpainasby-productfromphosphoricacidinafertilizerfactorylocatedinHuelva(southwesternIberianPeninsula).PhosphaterockfromMoroccoisusedasrawmaterialinthisprocess.Phosphogypsumwastesarestoredinastackcontaining100Mt(approximately1200haofsurface)oversaltmarshesofanestuaryformedbytheconfluenceoftheTintoandOdielrivers,lessthan1kmawayfromthecitycentre.AverylowproportionofthiswasteisusedtoimprovefertilityofagriculturalsoilsintheareaoftheGuadalquivirrivervalley(Seville,SWSpain).Thechemicalspeciationofpotentiallytoxicelements(Ba,Cd,Cu,Ni,Sr,UandZn)inphosphogypsumandphosphaterockwasperformedusingthemodifiedBCR-sequentialextractionprocedure,asdescribedbytheEuropeanCommunityBureauofReference(1999).Thisstudyhasbeendonewiththemainof:(1)evaluatechangesinthemobilityofmetalsduringtheproductionofphosphoricacid;(2)estimatetheamountofmobilemetalsthatcanaffecttheenvironmentalsurrounding;and(3)verifytheenvironmentallysafeuseofphosphogypsumasanamendmenttoagriculturalsoils.ThemainenvironmentalconcernassociatedtophosphoricacidproductionisthatUranium,aradiotoxicelement,istransferredfromthenon-mobilefractioninthephosphaterocktothebioavailablefractioninphosphogypsuminarateof23%.Around21%ofBa,6%ofCuandSr,5%ofCdandNi,and2%ofZnarealsocontainedinthewater-solublephaseofthefinalwaste.Consideringthetotalmassofphosphogypsum,theamountofmetalseasilysolubleinwaterisapproximately6178,3089,1931,579,232,193and77tforSr,U,Ba,Zn,Ni,CuandCd,respectively.Thisgivesanideaofthepollutionpotentialofthiswaste.©2007ElsevierB.V.Allrightsreserved.Keywords:Phosphogypsum;Phosphaterockprocessingplants;Elementtransferfactor;Uranium;Estuarypollution1.IntroductionPhosphatefertilizerforagricultureisobtainedbyphosphaterockwetchemicaltreatmentwithsulphuricacid.Inthisprocess,notonlythecommercialphosphoricacidisproducedbutalsoaninsolubleresidualcalciumsulphatecalledphosphogypsum(Eq.(1)).Phosphogypsumisaby-productcomposedmainlybyagypsummatrix(CaSO4·2H2O)withhighcontentsofimpuritiessuchasP2O5,F,organicsubstances,potentiallytoxicmetalsandradioactiveelements[1].Ca10(PO4)6F2+10H2SO4+20H2O→6H3PO4+10CaSO4·2H2O+2HF(1)∗Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](R.P´erez-L´opez).About5tofphosphogypsumaregeneratedforeverytonneofphosphoricacidmanufactured.Atpresent,worldwidepro-ductionofphosphogypsumisover100–280Mt/year[2].Thislow-costwasteisusuallyusedasafertilizerinagriculture,asabuildingmaterialandasamendmentforsoilstabiliza-tion[3–5].Nevertheless,suchpracticesarelimitedbythehighcontentoftoxicimpuritiesforhumanhealth,andonly15%oftheworldwideproductionisrecycled.Theremaining85%requiresbigdisposalsurfacesandcauseshugeenvironmentalproblems[6].InSpain,theproductionofphosphoricacid,andhenceofphosphogypsum,isrestrictedtoafertilizerindustrialsiteinthetownofHuelva(SWIberianPeninsula).ThislargecomplexislocatedattheconfluenceoftheTintoandOdielrivers,anestu-arinezoneofsaltmarsheswithhighecologicalvalue(Fig.1).Over3Mtofphosphogypsumwastesareproducedeachyearanddepositedinastackoccupyingalargepartofthesaltmarshes0304-3894/$–seefrontmatter©2007ElsevierB.V.Allrightsreserved.doi:10.1016/j.jhazmat.2007.06.068746R.P´erez-L´opezetal./JournalofHazardousMaterials148(2007)745–750Fig.1.LocationmapofthephosphogypsumpilenexttoHuelvatown(SWSpain).TheAtlanticOceanisapproximately10kmtothesouthofconfluencebetweenOdielandTintorivers.(*)Regeneratedzone:asoilcoverof30cmandavegetalcoveragewereaddedabovethenakedphosphogypsumsurface.ImagefromGoogleEarth©software.associatedtotherightmarginoftheTintoriver,locatedlessthan1kmawayfromthecitycentre.Until1998,around20%ofthewasteproducedwasalsopoureddirectlyintotheOdielriver.Thisdump(1200haofsurfaceand5mofaverageheight)containsabout100Mtofphosphogypsum,whichhavecausedanimportantenvironmentalandecologicaldeteriorationofthezone.However,similarsaltmarshesbutintheOdielrivermar-ginweredeclaredasaBiosphereReservebyUNESCOin1983,famousforitshighornithologicaldiversityandforthepresenceofhalophyticvegetation.TheradioactiveimpactoriginatedbytheradionuclidesoftheU-seriescontainedinthephosphogypsumsofHuelvaiswidelydescribedintheliterature[7,8].Thephosphogypsumstack,locatedinthetidalprismoftheestuary(Fig.1),isnottotallywatertight.Effluentscomingfromtheleachingofthiswasteaffectthewaterandsedimentsofthenearbyfluvialsys-temsbyradioactivity[9]andevenextendtosomeremotezonesoftheriversasaresultofthetidalaction[10].Probably,someUinthiswasteisassociatedtotheeasilymobilefractionbuttheexactratehasnotbeenestimatedyet.Therearealsonoworksestablishing