Bioavailabilityandmobilityoftracemetalsinphosphogy

BioavailabilityandmobilityoftracemetalsinphosphogypsumfromAqabaandEshidiya,JordanM.S.Al-Hwaitia,n,J.F.Ranvilleb,P.E.Rossc,1aEnvironmentalEngineeringDepartment,Al-HusseinBinTalalUniversity,P.O.Box(20),Ma’an,JordanbDepartmentofChemistryandGeochemistry,ColoradoSchoolofMines,Golden,CO80401,USAcEnvironmentalScienceandEngineeringDivision,ColoradoSchoolofMines,Golden,CO80401,USAarticleinfoArticlehistory:Received9August2009Accepted29March2010Keywords:ToxicmetalsPhosphogypsumBioavailabilityMobilityabstractAs,Cd,Cr,Cu,U,andZninAqabaandEshidiyaphosphogypsumshowedrelativeuniformityinparticlesizepresentedbycoarse(40.212mm);medium(0.212–0.053mm);andfine(o0.053mm)inthestacksbyageofdeposition.JordanphosphogypsumcontainslowconcentrationsofAs,Cd,Cr,Cu,U,andZncomparedtothosereportedworldwide.Thebioavailabilityandmobilityoftracemetalswereestimatedusingaquaregialeachingexperiments.Leachingresultshaveshownthataround3%oftheAs,1%oftheCd,5%oftheCr,9%oftheCu,4%oftheU,and3%oftheZnaretransferredtothesurroundingaquaticenvironmentand/orsoils.Mobilityoftracemetalsinphosphogypsumwasclassifiedintothreedegrees:elementswithhighmobilitywereCuandU;thosewithmoderatemobilitywereAsandZn;andthosewithlowmobilitywereCdandCr.ItcanbeconcludedthatAs,Cd,Cr,Cu,U,andZnwerenotonlyuniformlydistributedinthestack,buttheyarenotleachedfromthephosphogypsumstacksinanysignificantamount,andthentheyarenoteasilytransferredtothesurroundingaquaticenvironmentand/orsoils.&2010ElsevierGmbH.Allrightsreserved.1.IntroductionPhosphogypsum(PG)isaby-productfromthephosphatefertilizerindustries.PGisproducedduringthemanufactureofphosphoricacidbyreactingrockphosphate(rawmaterial)withsulfuricacidaccordingtothefollowingchemicalreaction:Ca10(PO4)6F2+10H2SO4+20H2O-6H3PO4+10CaSO42H2O+2HF(1)PGisknowntocontainnaturalradionuclides,mainly226Raanditsdecayproducts.PGalsocontainsfluoride,certaintoxicmetals,particularlyCd,andisacidicwheninitiallystored,duetoresidualsulfuricacidthatisusedintheacidicwaterprocess(Rutherfordetal.,1994;ElinderandJarup,1996;VanKauwenberg,1997).AsPGisdewateredandweatheredinstoragepiles,theaciditydecreases.InsomecasesPGiswashedtoremoveitsacidicporewaterandhasneutralpH.TheworldwideproductionofPGisontheorderof50milliontonnesperyear(Burnettetal.,1995).PGisstockpiledinlargestacks,whicharegenerallyuncoveredandcanoftenallowPGdischargeintoaquaticenvironments.Insomecasesispurposelydischargeddirectlyintoaquaticenvironments(WissaandFuleihan,1984;Fergusson,1990).Thenatureandextentofradionuclidesandotherimpuritiesinphosphogypsumdifferwiththetypeofrawmaterialandthemethodofchemicalprocessing.Theelevatedconcentrationsofradionuclides,tracemetals,F-andacidicporewatershavebeenidentifiedasapotentialhazardduetothelargevolumesproducedandavarietyofhighvolumeapplicationsofPG(Altschular,1980;MayandSweeney,1984;Becker,1985;SENESConsultantsLimited,1987;Berish,1990;PaulandPillai,1990;Conkline,1992;Rutherfordetal.,1994;Burnettetal.,1999;Al-Masrietal.,2004).PGcurrentlyhashadseveralcommercialapplicationsintheUnitedStates(Conkline,1992;Papastefanouetal.,2006),including(a)asafertilizerandconditioner(remediationagent)forsoils;(b)asaback-fillandroad-basematerialinroadwayandparkinglotconstructions;(c)asanadditivetoconcreteandconcreteblocks;(d)inminereclamation;and(e)intherecoveryofsulfur,althoughcurrentuseisrestrictedbylaw.ThecommercialuseinJordaniscurrentlylimitedtotheproductionofcement,asasoilamendmentandasfillerinthepaperindustry(Al-Hwaitietal.2005a).However,suchapplicationsarerestrictedduetothecontentofharmfulminorelementsinPGandtopotentialleachingprocesseswhichmaycausereleaseoftheseelementstothesurroundingaquaticenvironmentorsoils,andsubsequenttransfertothefoodchain(CarterandScheiner,1992;Rutherfordetal.,1994;Al-Masrietal.,1999;Al-Oudatetal.,1998;Al-Oudat,1999).AdirectmethodofevaluatingtracemetalsandleachingprocessesinphosphogypsumwasdevelopedbyRutherfordetal.(1994),whoshowedthatdistributionoftraceContentslistsavailableatScienceDirectjournalhomepage::10.1016/j.chemer.2010.03.001nCorrespondingauthor.Tel.:[phone]x7565;fax:[phone]E-mailaddresses:[e-mail],[e-mail](M.S.Al-Hwaiti).1Deceased.ChemiederErde70(2010)283–291metalswasfoundtodependupontheircontentinthephosphaterocks,phosphoricacidproductionprocesses,andtheconditionsandquantityoforganiccompoundsinthesourcerock.ThephosphateindustryinJordanhasproducedandexportedphosphoricacidandphosphatefertilizerformanydecades.TheAqabaindustrialcomplexdatesfrom1982andislocatedalongtheshoresoftheRedSea,15kmsouthoftheportofAqabaandapproximately25kmsouthofthecityofAqaba(Fig.1).ThecomplexreceivesphosphaterockfeedstockfromtheAl-AbiedandAl-Hasamines(Fig.1)andannuallyproducesapproximately3105tonnesofphosphoricacid.PGisproducedbythewetacid,dihydrateprocess.CurrentestimatedstockpilesofPGareapproxi-mately40106tonnes.TheIndo-JordanChemicalsCompanydatesfrom1992andislocatedadjacenttotheEshidiyamineinsouth-centralJordanapproximately120kmnortheastofAqab