sonochemical-destruction-of-free-and-metal-binding-EDTA

WaterResearch37(2003)3155–3163Sonochemicaldestructionoffreeandmetal-bindingethylenediaminetetraaceticacidJ.AaronFrima,b,JamesF.Rathmanc,LindaK.Weaversa,*aDepartmentofCivilandEnvironmentalEngineeringandGeodeticScience,TheOhioStateUniversity,470HitchcockHall2070NeilAve.,Columbus,OH43210,USAbDepartmentofGeologicalSciences,TheOhioStateUniversity,Columbus,OH43210,USAcDepartmentofChemicalEngineering,TheOhioStateUniversity,Columbus,OH43210,USAReceived4June2002;accepted20March2003AbstractThisstudyfocusedonthesonochemicaldegradationofethylenediaminetetraaceticacid(EDTA)andchromium-EDTAcomplexes.Degradationofthecopper(II)-EDTAcomplexwasalsoinvestigatedasacomparisonmetalcomplex.A90%degradationofa150-mMEDTAsolutionwithcontinuousO2-bubblingwasshownforthe20-kHzsysteminapproximately3h(kpseudo-firstorder=1.22�10�2min�1)andlessthan1hforthe354-kHzsystem(kpseudo-firstorder=5.42�10�2min�1).TheseresultsareconsistentwiththehigherconcentrationsofhydrogenperoxidefoundinthehigherfrequencysystemandanexpectedoxidationofEDTAinbulksolution.Thepresenceofachelatedmetaldecreasedtherateofdegradationatbothfrequencies.Cr(III)-EDTAdegradedtheslowest,supportingthetheorythattheextremelyslowligandexchangerateofchromiumisthedeterminingfactorinhowfastdegradationbyhydroxylradicalcanoccur.The354-kHzsystemshoweda17%decreaseintheoriginal150-mMCr(III)-EDTAcomplexafter3hofsonication.AllofthechromiumfromthedegradedEDTAcomplexexistedasacombinationofoxidizedCr(VI)andpossiblysmallamountsofanewCr(III)-organiccomplex(Cr(III)-Y).The20-kHzsystemshowedasimilarextentofdegradation(16%)after3hofsonication,despitelowerhydroxylradicalproduction.FiftypercentofthechromiumfromthedegradedEDTAcomplexwasfoundasfreeCr3+ion,withtheremaining50%existingasbothCr(III)-YandCr(VI).Varyingdegreesofbulkoxidation,near-bubblethermolysis,andperhapsdifferentdegradationpathwaysatthetwofrequenciesareresponsibleforthesedifferences.r2003ElsevierScienceLtd.Allrightsreserved.Keywords:EDTA;Sonolysis;Degradation;Chromium;Complexation1.IntroductionThetre