电化学法去除焦化废水中氨的动力学研究英文梁镇海

CATALYSIS,KINETICSANDREACTORSChineseJournalofChemicalEngineering,19(4)570—574(2011)TheKineticsforElectrochemicalRemovalofAmmoniainCokingWastewater*LIANGZhenhai(梁镇海)**,LISu(李素),GUOWenqian(郭文倩)andFANCaimei(樊彩梅)CollegeofChemistryandChemicalEngineering,TaiyuanUniversityofTechnology,Taiyuan030024,ChinaAbstractElectrochemicalremovalofammoniaisanewandeffectivemethodincokingwastewater.Thereactionmechanismofammoniaremovalwasprovedbystablepolarizationcurveinthispaper.First,thesupposingofreac-tionstepsoftheelectrodewereproposed.AndthenreactionparameteroftheelectrodewasmeasuredbyTafelcurve.Finally,thereactionmechanismwasdeterminedbyquasi-equilibriumapproach.TheresultsshowedthatCl2+H2O⎯⎯→HOCl+H++Cl−wastherate-determiningstep,thecalculatedapparenttransfercoefficientwasuniformtotheexperimentalvalue.Keywordsremovalofammonia,electrochemistry,cokingwastewater,quasi-equilibriumapproach,rate-determiningstep1INTRODUCTIONCokingplantisoneoftheindustriescausingen-vironmentalpollutioninChina.Sofarmanymethodsareusedtotreatwastewatersuchasmembrane-lessmicrobialfuelcell(ML-MFC)wasdesignedforwaste-watertreatmentandsoon[1].Thecompositionofwastewateriscomplicatedanditalwayscontainshighconcentrationofammonia,phenols,cyanideandotheraromaticorganicswhichhaveseriouseffecttoenvi-ronment[2].Mostofthesubstancesarebio-toxicalandthetraditionalactivatedsludgedegradationproc-essfailstoeliminatechemicaloxygendemand(COD)[3],ammoniaandcolor[4].Forexample,ammoniacancausepromotionofeutrophicationwhichisfataltoaquaticlives,hinderdisinfectionofwatersupplies,andhaveanoffensivesmellandcarcinogenesis[5].Theelectrochemicaloxidationprocesseshaveat-tractedgreatinterestsrecently.Theelectrochemicalmethodhasbeensuccessfullyemployedtodestroyavarietyofpollutantssuchasammonia,nitrite[6],chlorophenols[7],dyes[8]andsoon.ButtherewerefewreportsabouttheelectrochemicalremovalofammoniaincokingwastewaterexceptforChiangetal.[9],whofoundthatthistechniqueisfeasiblefortreat-ingcokingplantwastewater,andshowedtheremovalofthepollutantsinelectrochemicaloxidationprocessismainlyattributedtotheindirectoxidationofchiorine/hypochlorite.Inthispaper,wefocustheeffortsonthederivationofthereactionmechanismforelectro-chemicalremovalofammoniaincokingwastewateranditsconfirmationbyexperiments.2EXPERIMENTAL2.1InstrumentsandreagentsVMP3-Multipotentiostatelectrochemicalstation(PrincetonAppliedResearchInstruments,USA)wasusedtogetcyclicvoltammograms(CV).Allreagentswereanalyticalgrade.Thesolutionswerepreparedwithfreshdouble-distilledanddeionizedwater.2.2ElectrochemicalexperimentsThedetailofthepreparationmethodofthean-odescanbefoundinRef[10].AnX-raydiffractometerD/Max-IIIA(RigakuCo.Japan)usingCuKα1(λ=0.154056nm)asradiationsourcewasusedforidenti-ficationofthephases[11].Three-electrodesystemisusedintheCVex-periment.Ti/SnO2+Sb2O4/PbO2electrode(1.0cm×1.0cm)wasusedastheworkingelectrode,andaPtcounterelectrode(1.0cm×1.0cm)andanSCE(Saturatedcalomelelectrode)referenceelectrodewereemployedfortheexperiments.Theanolytewas0.1mol·L−1NaClsolutioncontaining0.1mol·L−1(NH4)2SO4.ThepHwasadjustedbyNaOHandH2SO4.Theeffectofscanningrateisdiscussed.Alltheexperimentswerecarriedoutatroomtemperature.3RESULTSANDDISCUSSION3.1Electrooxidationofammonia3.1.1EffectofsweeprateAccordingtotheelementarypotentialoftheba-sicreactions.0.23V1.275V2254NNHNH−++⎯⎯⎯⎯→⎯⎯⎯⎯→intheacidicsolution(ammoniumsulfatesolutionwasweaklyacidic),()[]24N/NH20.2331.275/50.673Vϕ+=×−+×=TheinfluenceofthesweeprateonthecyclicvoltammetryReceived2010-10-11,accepted2011-05-20.*SupportedbytheNationalNaturalScienceFoundationofChina(20771080,20876104).**Towhomcorrespondenceshouldbeaddressed.E-mail:[e-mail].,Vol.19,No.4,August2011571behavioroftheTi/SnO2+Sb2O4/PbO2electrodeinthesameconcentrationofammoniaisshowninFig.1.Asthesweeprateincreases,theanodicpeakpotentialsshifttomorepositivewhenthesweepratefrom5mV·s−1to100mV·s−1,whichshowedthatammoniaelectro-oxidationreactionontheTi/SnO2+Sb2O4/PbO2electrodeisirreversibleprocess.Theoxygenabsorp-tionpeakappearedwhenthesweeprateis5mV·s−1.However,withthesweeprateincreasetheoxygenabsorptionpeakbecomeslessobvious,whichmeansthatthescanratesofastthatitdoesn’tmatchwiththecurrentresponse.ThereactionofO2evolutionbeginstooccurwhenthesweeprateincreasesfurther.ThedepositionpotentialofO2issimilarwithCl2(=1.229V,=1.35827V),sothattheoxidationpeaksofthemwilloverlap.FromFig.1wealsocanseethattheinitialanodicpeakpotentialofnitrogenisslightlylargerthan24N/NHϕ+inthetheoryduetotheoverpotentialexists.SoalltheresultsshowedgoodagreementwithKim’s[5]reportthatammoniawasoxidizedtonitrogenfinally.(a)125mg·L−1(b)250mg·L−1(c)500mg·L−1(d)1000mg·L−1Figure2ThecyclicvoltammetrycurvesindifferentconcentrationofammoniapH=5,electrolytecontaining0.10mol·L−1NaClanddifferentconcentrationof(NH4)2SO4Figure1Thecyclicvoltammetrycurvesatdifferentsweepratea—5mV·s−1;b—50mV·s−1;c—100mV·s−1,pH=5,electro-lytecontaining0.10mol·L−1NaCland250mg·L−1(NH4)2SO4Chin.J.Chem.Eng.,Vol.19,No.4,August20115723.1.2EffectofammoniaconcentrationInordertofurtherclarifythemech