电絮凝RemovalofCrVIfrommodelwastewatersbyel

SeparationandPurificationTechnologyVolume61,Issue1,6June2008,Pages15–21RemovalofCr(VI)frommodelwastewatersbyelectrocoagulationwithFeelectrodesIlonaHeidmann,,WolfgangCalmanoInstituteofEnvironmentalTechnologyandEnergyEconomics,TechnicalUniversityHamburg-Harburg,EissendorferStr.40,21073Hamburg,GermanyPermissions&ReprintsAbstractTheperformanceofanelectrocoagulationsystemwithironelectrodesforCr(VI)removalfrommodelwastewatersinlaboratoryscalewasstudiedsystematically.Severalparameters–suchasinitialmetalconcentration(10–50mg/lCr),chargeloading,andappliedcurrent–andtheirinfluenceontheelectrocoagulationprocesswereinvestigated.Crconcentrationdecreasedonlyslightlybycoagulationtimeathighcurrents(1.0–3.0A),whereasatlowcurrents(0.05–0.1A),10mg/lCrwasremovedcompletelyfromthesolutionafter45min.Initialconcentrationsfrom10to50mg/lCrdidnotinfluencetheremovalratesatlowcurrents,whereashigherinitialconcentrationscausedhigherremovalratesathighcurrents.Atallinvestigatedcurrents,theCr(VI)concentrationwasalwaysonlyalittlelowerthantheCrtotalconcentrationandtheFe2+concentrationinsolutionwasalwaysbelow0.1mg/l.ThestudygaveindicationsontwodifferentremovalmechanismsofCr(VI)withironelectrodesathighandlowcurrents.WeproposethatathighcurrentsCr(VI)wasreduceddirectlyatthecathodeandprecipitatedafterwardsasCr(OH)3.TheCrremovaldependedoninitialconcentrationandtheremovalrate(μmol/As)wasindependentfromtheinsertedcurrent.AtlowcurrentstheCr(VI)removalwasproposedtoworkbyreductionbyFe2+.Undertheseconditions,ironwasquantitativelydissolvedasFe2+fromtheelectrodesaccordingtoFaraday'slawandthedissolvedamountsweretwoordersofmagnitudehighercomparedtotheirondissolutionathighcurrents.TheremovalprocessatlowcurrentswasmuchmoreefficientandseemedtobeapplicablefortheremovalofCr(VI)fromindustrialwastewaters.KeywordsElectrocoagulation;Chromium;Ironelectrodes;WastewaterFig.1.SketchofthebatchcellandsomebasicprocessesFig.2.ConcentrationsofCr(closedsymbolsandsolidlines)andcorrespondingpHvalues(opensymbolsanddottedlines)againstcoagulationtime(min).InitialCrconcentrationswere50mg/l(●),20mg/l(■),and10mg/l(▴).Appliedcurrentswere1.0and0.05A,respectively.Fig.3.InfluenceofinitialconcentrationonremovalofCr(μmol/l)athigh(1.0A)andlow(0.05A)currentsagainstchargeloading(As/l).Initialconcentrationswere50mg/l(●),20mg/l(■),and10mg/l(▴).Appliedcurrentswere1.0and0.05A.Fig.4.ConcentrationsoftotalCr(closedsymbolsandsolidlines)andcorrespondingCr(VI)concentrations(opensymbolsanddottedlines)overcoagulationtime(min).Appliedcurrentswere1.0/2.0/3.0and0.05/0.07/0.1/0.2A,respectively.InitialCrconcentrationwas20mg/l.Fig.5.InfluenceofappliedcurrentonremovalofCr(μmol/l)athigh(1.0–3.0A)andlow(0.05–0.2A)currentsagainstchargeloading(As/l).Initialconcentrationswere20mg/lforCr.