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Selective separation of copper and cadmium from zinc solutions by low current density electrolysis

By Cindy Marshall,2014-01-11 16:16
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Selective separation of copper and cadmium from zinc solutions by low current density electrolysis

    Selective separation of copper and cadmium from zinc solutions by low current density

    electrolysis

ELSEVIERPress

    Availableonlineat,?,^n^,.sciencedirect.com

    Direct

    Trans.NonferrousMet.Soc.China20(2010)533536

    Transactionsof

    NonferrousMetals

    SocietyofChina

    l|I}|,sc.cn

    Selectiveseparationofcopperandcadmiumfromzincsolutionsby

    lowcurrentdensityelectrolysis

    YANGBo(杨卜),WANGChengyan(~K成彦),LIDun.fang(李敦钫),

    YINFei(Yr),CHENYong.qiang(陈永强),WANGNianwei(~)

    GeneralResearchInstituteofMiningandMetallurgy,Beijing100044,China Received6July2009;accepted10January2010

    Abstract:Copperandcadmiumionswereselectivelyseparatedfromzincsulphateaqueoussolutionorzincammonia/ammonium

    sulphateaqueoussolutionby1owcurrentdensityelectrolysis.Itwasshownthattheconcentrationofcadmiumioninzincsulphate

    solutiondecreasedfrom4.56g/Lto0.18g/Linanelectrolysistimeof8.5h,whilstitdecreasedfrom5.16g/Ltolowerthan0.005

    g/Linzincammonia/ammoniumsulphateaqueoussolution.Ontheotherhand.thedepositionrateofcopperwassolowthatitwas

difficulttoseparatecopperandcadmiumionsfromthezincammonia/ammoniumsulphateaq

    ueoussolutionduringelectrolysis.But

    copperioncouldbedecreasedto0.002g/Linthissolutionthroughsolventextractionbyusing

    kerosenedilutedLIX984Nas

    extractant.Therefore.itisfavorabletorecovercadmiumionfromthezincammonia/ammoni

    umsulphatesolutionbyelectrolyrsis

    aftersolventextractionofcopper.

    Keywords:copper:cadmium;zincsolution;electrolysis 1Introduction

    Cadmiumisusedinpaint,alloy,electroplatingand battery.Itisextractedfromtheby.productsofzinc metallurgyamongwhichcoppercadmiumslag,

    cadmium..richdustandspentNi..Cdbatteriesarethe mainrawmaterials16].Purecadmiumcanbe

    recoveredthroughsolventextraction,electrolysis refiningorvacuumdistillation[7l51.Themetal

    elementsincopper-cadmiumslagarezinc.cadmium, copperandtheiroxideswithalittleamountofAs,Sb,Fe CoandNi.Intheindustrialtreatmentprocessof coppercadmiumslag,sulphuricacidisusuallyusedas leachingagentandMnO,isaddedtooxidizeiron.The iron.arsenicandantimonyionsinthesulphuricacid leachingsolutionareprecipitatedthroughneutralization oflimewater.Spongecadmiumisproducedby

    displacementofzincpowderafteradjustingthepHvalue to3-4.Finally,purecadmiummeta1isdepositedby electrolysis.Theprocessforcadmiumextractionis complicatedandalsoneedsalargequantityofzinc powder.Somestudieshaveshownthatcopperand cadmiumcouldbeseparatedfromzincinsulphate

    solutionbyelectrOdepositiOnusingspecial equipment[1617].Uptonow,thereislessresearch

    reportontheseparationofcopper,cadmiumandzincin ammoniasolution.

    Theobviousadvantageofammonialcaching

    technologyforzincextractionisthatthelowgradezinc oreswithhighimpuritiescanbetreated[18-19].Zincis dissolvedintotheammonialeachingsolutionwhilethe impurities,suchasarsenic,antimonyandironremainin theleachedresidue.Copper,cadmium,cobalt,nickeland silverarealsodissolved[20].Asaresult,alargeamount ofzincpowderisconsumedtoremovethecopperand cadmiumionsfromtheammonialeachingsolutionwhen theammonialeachingprocedureisusedtotreat copper-cadmiumslag.Therefore,newtreatmentmethod f0rthecopperandcadmiumcontainingmaterialsshould bedeveloped.Thepresentstudyrevealstheresultsof selectiveseparationofcopperandcadmiumfromzinc solutionsby1owcurrentdensityelectrolysis. 2Experimental

    2.1Solutionpreparation

    Allchemicalreagents,i.e.zincsulfate,cadmium Foundationitem:Projects(50774014,50734005)supposedbytheNationalNaturalScience

    FoundationofChina;Prcct(2O08AAO3z5l4)supportedby theNationalHigh-techResearchandDevelopmentProgramofChina Correspondingauthor:WANGChengyan;Tel:+86-10-88399551;Fax:+8610

    88377374;Email:wchy3207@sinacom

    DOI:101016/S10036326(09)60174-6

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    一孝雾

    韶萋

    

    534YANGBo.etal/Trans.NonferrousMet.Soc.China20(2010)533536

    oxide,coppersulfate,ammoniumsulfate,sulphuricacid andammoniawereusedinanalyticalpurity.Fourkinds ofsolutionswithdifferentconcentrationsofzinc,copper andcadmiumionswereprepared,twoofwhich conminedonlyzincandcadmiumionsinaqueous sulphatesolutionorammoniaammoniumsulphate

    solutionwhiletheothertwohadzinc,cadmiumand copperionsinthedifferentsolutions.respectively. Cadmiumoxidewasdissolvedinwaterbyadding concentratedsulphuricaciddropwiselyandthenzinc sulphatewasputintotoforinzinccadmiumsulphate

    solution.Coppersullc}hatewasfurtherdissolvedto preparethezinccoppercadmiumsulphatesolution.

    Ammonia,ammoniumsulphateandzincsulphatewere firstdissolvedinwatertoformulatetheammonia

    solutionintowhichcadmiumoxidewasaddedat ambienttemperaturebystirring.Thezinccadmium

    ammoniasolutionwasthenfiltered.Inthesameway,the zinc--copper?-cadmiumammoniasolutionwasmadeby dissolvingcoppersulphate.Theconcentrationsofzinc,

    copperandcadmiumionsinthesolutionswere30-55 g/L,6.06.3g/Land3.57.2g/L,respectively.ThepH

    valueinthesulphatesaltsolutionwasadiustedto6.5by using80g/LNaPHsolution.Theconcentrationsof ammoniaandammoniumsulphateintheammonia solutionwere15g/Land150g/L,respectively. 2.2Experimentalset-upandprocedure

    Twoleadsilveralloyanodeplateswithanefncient areaof68cm2wereusedastheanodebetweenwhicha aluminiumcathodeof46.1cmwasinsertedwitha interoolardistanceof35Iniil.Abeakerwith2000mL volumeasanelectrolyticcel1wasputonamagnetic stirrer(IKARETbasicC,inwhichtheelectrolytic solutionwasagitated.Thecathodecurrentdensitywas 50A/cmandaDCregulatedpowersupplyrwYK3010)

    wasemployedforcurrentsupply.Experimentalsamples of20mLweretakenforanalysiseachtimeatintervals. Efficiencyofelectrolyticseparationwascalculatedfrom theconcentrationsofthemetalionsintheelectrolyte solutions.

    35%(volumefraction)LIX984Ndilutedby

    sulfonatedkerosenewasusedasanextractanttoseparate copperionfromcadmiumionintheammoniasolutionin a250mLseparatoryfunne1.100mLammoniasolution and50mLorganicphaseweremixedeachtimeat2:1 (A/O)phaseratio.Theammoniasolutionandtheorganic phaseweremixedonanelectricoscillatorwitll5minof contacttimeand3minofstandingtime.Theorganic phasewasseparatedandsubsequentlymixedwithwater for3min.Thephaseratioofthewashingwatertothe

    organicwas1:2fA/O).Thewashedorganicwasthen strippedusing25mLof200g/Lsulphuricacidina separatoryfunnelonanelectricoscillatorfor8minand demixedafterstandingfor5min.

    3Resultsanddiscussion

    3.1Concentrationvariationofcopperandcadmium Alltestswereconductedatroomtemperaturewith thefourtypesofelectrolytesolutions.Theresults showedthatthedepositedcadmiumwasuniformand compactintheZn.CdsulphatesolutionwhilethepH valueofthesolutiondecreasedto1.5.IntheZn-Cu-Cd sulphatesolution,therosycopperwasfirstdepositedon thesurfaceofaluminiumplateandthenthedeposited productbecamegreyafteraperiodofelectrolysis.The bluecolourofcoppersulphatebecamelightgradually untiltransparentatthefinalelectrolysisstage,indicating thatalmostallthecopperionswereremovedfromthe solution.IntheZn.Cdammonia.ammoniumsulphate solution,aloosespongypowderproductwithblack colourwasobtained,andcanbeeasilydetachedfromthe aluminiumcathodeduringelectrolysis.Incontrast, althoughrosycopperappearedfirstintheZn-?Cu?-Cd ammonia.ammoniumsulphatesolution,theelectrolyte solutionwasstillindarkbluecolourattheendof8.5h ofelectrolysis.Whatismore,theelectrolyticproduct wascombinedcloselywiththealuminiumcathode. resultingingreatdifficultyinseparatingthedeposited product.

    TheconcentrationvariationsofZn,CuandCdions beforeandafterelectrolysisinthefourelectrolyte

    solutionsarepresentedinTable1.Itcanbeseenthatzinc ionconcentrationsshowedalmostnochangeafter8.5h ofelectrolysisindifferentsolutions.InZnandCd containingsolutions.theCdionconcenationdecreased

    toa1owleve1.Especially,itwasonlyabout0.005g/L afterelectrolysisinZn..Cdammonia..ammoniumsulphate solution.Thedepositingratesofcopperandcadmium werealllowfromtheZn..Cu..Cdammonia..ammonium sulphatesolution.About53.7%copperwasdeposited Table1Concentrationsofzinc,copperandcadmiumionsbeforeandafterelectrolysis

    YANGBo,etal/Trans.NonferrousMet.Soc.China20(2O10)533536

    preferentiallyfromtheZnCu.Cdsulphatesolution.

    Asthestandardelectrodepotentialsofcopper6 (0.337V)andcadmium(0.44V)aremorepositivethan

    thatofzinc(0.76V)andhydrogenovervoltageonf5

    cadmiumishigh.cadmiumcouldbedepositedfrom ZnCdsulphatesolution.Cadmiumcanalsobe.

    codepositedwhenthecopperionconcentrationislow

    enough,whiletheconcentrationofzincionkeeps

    unchangedinthesolutionsafterelectrolysis.Inammoniag2 solution,Zn.CuandCdionswillformcomplexeswith.9 NH1orOHanions.andthefreeionconcentrationsof1 Zn,CuandCdwillthenbereduced,decreasingtheir electrodepotentials:

    (PM2+/M=,+

    RTl

    n[M2(1)

    Thereisagreatdifferenceamongthestandard electrodepotentialsofZn,CuandCd.So,thepriority orderforelectrOdepOsitionofthemetalswillnotchange.

    TheconcentrationsofCuandCdionsasafunction ofelectrolysistimeareshowninFigs.14.Asseenin

    Fig.1andFig.2,cadmiumorcoppercouldberemoved easilyfromzincsulphatesolution.Fig.3showsthatthe Electrolysistime/h

    Fig.1ConcentrationofCdioninZnCdsulphatesolution

    versuselectrolysistime

    8

    6

    4

    2

    0

    Electrolysistime/h

    Fig.2ConcentrationofCuandCdionsinZnCuCdsulphate

    solutionversuselectrolysistime

    Electrolysistime/h

    535

    Fig.3ConcentrationofCdioninZnCdammoniaammonium

    sulphatesolutionversuselectrolysistime Electrolysistime/h

    Fig.4ConcentrationofCuandCdionsinZnCuCd

    ammoniaammoniumsulphatesolutionversuselectrolysistime concentrationofCdiondecreasedlinearlywithin4.5h ofelectrolysisinZn.Cdammonia.ammoniumsullaIhate solutionandthenitschangebecamegentle.Compared withthee1ectrodeDOsitiOnratesinzincsulphatesolutions, Fig.4demonstratesthatitwasunfavourableforcopperor cadmiumtobeseparatedeffectivelyfromthezinc containingammoniasolution.Thatistosay,copperand cadmiumcouldnotberemovedsimultaneouslyby

    electrolysisfromtheammoniasolution.Thecopperion mustberemovedbeforeCdelectrodeDosition.So,other methodsshouldbedevelopedforcopperseparationfrom cadmiumfromzinccontainingammoniasolution.' 3.2Solventextractionofcopperinammoniasolution Fromtheaboveexperimenta1results.itcanbeseen thattheseparationofZn,CuandCdwasdifficultowing tothelowdepositionratesofCuandCdinZn.Cu.Cd ammoniaammoniumsulphatesolution.Incontrary,the depositionrateofCdionfromZn-Cd

    ammonia.ammoniumsulphatesolutionwasveryhigh. Thus,theseparationofZnandCdwouldbefavoredby 1.rI./u0g000u

    .

    J0一苗扫;0I100L10一口ul-,1./u0l】詈1u00u

    536YANGBo,etal/Trans.NonferrousMet.Soc.China20(2010)533536

    preferentialremovalofCufromtheZn--Cu--Cd ammonia-ammoniumsulphatesolution.

    35%LIX984N(volumefraction)wasusedto

    [5]

    extractcopperfromthewasteZn'Cu-Cd[6]

    ammonia.ammoniumsulphatesolutionwith1.022/L Cuand5.18g/tCdafterelectrolysis.Itwasshown thatthecopperionconcentrationintheextraction ranatewasonly0.002g/Lafterone.stageextraction whilethecadmiumionconcentrationwas5.10g/L. Namely,theextractionratesofcopperandcadmium were99.8%and1.54%.respectively.Thecopper-loaded organicphasewasstrippedforonetimewith200g/L sulphuricacid.Thestrippingrateofcopperwas99.5%

    andthecadmiumionconcentrationwas0.025g/Linthe strippingsolution.Theresultsindicatethatcoppercould effectivelybeseparatedthroughsolventextractionfrom theZn..Cu..Cdammonia..ammoniumsulphatesolution withhighzincandcadmiumionconcentrations. Subsequently,cadmiumwasthendepositedby electrolysisfromthecopper.freeammoniasolution, producingaimpurity-removedzincammoniasolution.If necessary,onlyasmallamountofzincpowderis consumedforfurtherpurificationofthezincammonia solution.

    4Conclusions

    [7]

    [8

    [9

    [1O

    [12]

    [13

    1)TheseparationofZn,Cu,andCdinsolutions wasfeasiblebylowcurrentdensityelectrolysis combinedwithsolventextraction.[14]

    2,TheelectrodepositionrateofcadmiuminZnCd

    sulphatesolutionwashigherthaninZn.Cd

    ammoniaammoniumsulphatesolution.

    3)Coppershouldberemovedbysolventextraction beforeCde1ecodeposition,andazinc

    ammoniaammoniumsulphatesolutionwaspossibly producedwithlessthan0.002g/LCuand0.005g/L Cdforzincrecovery.

    References

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