奥托昆普哈加瓦尔塔镍加压浸出流程

NEWNICKELPROCESSINCREASINGPRODUCTIONATOUTOKUMPUHARJAVALTAMETALSOY,FINLANDTABLEOFCONTENTSTOC\o"1-5"\h\z1.0Introduction22.0NickelSmelter33.0Nicke!Refinery54.0Conclusions18PresentedatALTA1997Nickel/CobaltPressureLeaching&HydrometallurgyForum,May19-20,1997,PerthAusffalia1.0INTRODUCTIONOutokumpuOyhasproducednickelatHarjavaltaWorksinFinlandsince1960.Theproductionhasbeenbasedonflashsmeltingtechnologyandelectrowinningofnickel.Thecapacityoftheprocesshasbeenincreasedgraduallyto18000tpabyseveralsmallexpansionsandprocessimprovements.TheproductionreliedondomesticnickelconcentratesuntilthaAttheturnofthe1990sanewnickelstrategywasdevelopedandOutokumpustartednickelexplorationinAustraiiaandCanada.TheworksecuredlongtermdeliverycontractsofnickelconcentratesfromMt.KeithandstartingofminingoperationsatForrestaniaandSilverSwaninAustralia.AtthesametimeOutokumpustudieddifferentalterativestoexpandthenickelandcopperproduction.n1993,adecisionwasmadetoinvestintheexpansionandmodernisationofHarjavaltaoperations.Outokumpudecidedtoincreasenickelproductionfrom18000tpato32000tpaandblistercopperproductionfrom100000tpato160000tpa.ThecopperrefineryinPoriwasexpandedfrom72000tpato125000tpa.Inaddition,theexpansionincludedanewoxygenplant,twohydrogenplantsandanewsulphuricacidplant.Theconstructionstartadin1993andtheHarjavaltaprojectwascompletedin1996.Duringtheconstructionthenickelproductionwasdecidedtoincreasefurtherto40000tpa.TherealisedcapitalexpenditureofthewholeexpansionprojectofHarjavaltawasFIM1600million($US370million).Theexpansionofthenickelproductionhasmeantseveralprocesschangesinthanickelsmelterandrefinery.ThedecisiontoinvestinnickelwasprecededbyresearchanddevelopmentworkatOutokumpuHarjavaltaMatalsOyandatOutokumpuRasaarchOy.Theinvestigationprogramledtothefollowingimprovementsoftheprocess:DevelopmentofdirectOutokumpuNickelSmelting(DON)Process.LeachingprocessforhighironnickelmatteUtilizationofOutokumpu-developedanddesignedreactorsforatmosphericandpressureleaching.UtilizationofOutokumpu-developedsolventextractionprocessinthenickel/cobaltseparationUtilizationoftheSherrittprocessforhydrogenreductionofnickalandcobalt.SulphuroutletasammoniumsulphateTheprocessimprovementswereincorporatedintheexistingnickelflashsmelter,matterefineryandelectrowinningprocaiss.Thecapacityofthenickelrefineryis18000tpanickelcathodesand22000tpabriquettes.2.0NICKELSMELTERIntha1980sOutokumpustartedtodevelopaconverterlessdirectsmeltingprocesstopraduceahighgradenickelmatteforfurtherrefining.TheprocesswastestedonapilotscaleatOutokumpuResearchOyinPoriandfoundtobeviable.ThebenefitsofthisprocesswereinasimplifiedflowsheetandhighgradeS。？gasflowtotheacidplant.TheprocesswasnamedthedirectOutokumpuNickelSmeltingProcessorDONProcess/1-3/.Attumof1990sOutokumpucontinuedthedevelopmentworkontheDONProcessbasedonafeedwithhighnickelandmagnesiacontentandlowironcontent.AsaresultofthisworktheDONPrccesswasfurtherdevelopedtoproducetwomattes:Lowironmatteintheflashsmaltingfumace(FSF)tobeleachadintheexistingleachingcircuitofHarjavalta.Highironmatteintheelectricfurnace(EF)tobeleachedinanewEFmatteleachingcircuit.Byproducingtwomattesitwaspossibletoeliminatetheconverterswhichhasmeantasimpleprocesswithlowinvestment,maintenanceandoperatingcosts.Inaddition,itisnowpossiblatosmeltconcentrateswithahighmagnesiumcontent.TheferricresiduefromtheEFmatteleachingisaddedtothesmeltingchargetoincreasetheirontomagnesiumratioandtoreducesmeltingtemperatureoftheslag.Futher,thecobaltrecoveryoftheDONPracessishigherthanintheconventionalsmeltingprocess.InHarjavalta'scase,itwasessentialthattheprocesscouldusetheexistingflashfurnaceandelectricfurnaceaswellastheexistingleachingplant.FigurelshowstheflowsheetoftheDONProcessatHarjavaltanickelsmelter.Theprimaryfeedofthenickelsmelterisablendofvariousconcentrates.Alsonickelcontainingsecondarymaterialsareusedasafeed.Inadditiontothefluedustfromthewasteheatboilerandtheelectrostaticprecipitator,theironprecipitatefromtheEFmatteleachingiscirculatedbacktotheflashfurnace.Thismakesitpossibletoconvertleachresiduetodisposablefayaliteslag.Concentratesandsandaredriedinanoil-firedrotarydrum.Afterdrying,thefeedmixtureandoxygenenrichedairarefedthroughtheconcentrate'burnerintothereactionshartoftheflashsmeltingfumace.Duringtheoxidationprccesstheironcontentofthenickelmatteiscurrentlyreducedtofivepercent.Thenickeimatteisgranulateddirectlyintowaterdewateredandfedtotheleachingplant.Theslagfromtheflashfumaceistappedintotheelectricfumaceforcleaning.Inthepurificattonprocess,coalisusedasareductantanddrynickelconcentrateasasulphidizingagenttoproduceadesiredqualityofmatteandslag.ThematteisgranulatedbyasimilarprocassasusedfortheFSFmatteandisfedtothenewEFmatteleachingplant.TheslagfromtheEFfumaceisalsogranulatedandfinailystoredinslagdumps.Hotgasfromtheflashfurnaceiscooleddownto350Cinawasteheatboilerandbeforefeedingtotheacidplant,dustisremovedinanelectrostaticprecipitator.Tablelgivesatypicalcompositionofthefeedmixture,flashfurnacematte,andelectricfurnacematteandslags/4/.Thesmeltingcapacityofconcentratesis250000tpacorresponding40000tpaofnickelatthecurrentblendofconcentrates.TablelCompositionoffeedmixture,flashsmeltingfurnacematte,electricfurnacematteandslags.Ni%Cu%Fe%S%MgO%SiO2%Concentratemixture151303068FSFDust15335268FeResidue32505<0,1<0,1FSFMatte655421<0,1<0,1FSFSlag40,5400.2827EFMatte-506307<0,1<0,1EFSlagQ30,2420,39313.0NICKELREFINERYAnoyerallflowsheetofthenickelproductionprocessatHarjavaltaisshowninFigure2.ThegranulatedmattesfromtheFSFandtheEFarethestartingmaterialsforthenickelrefinery,where,aftergnnding,themattesareleachedinseparatecircuits.Theproductsolutionfromtheleachingplantisledtoasolventextraction(SX)processforcobaltseparation.TheSXplanthasreplacedtheformercobaltremovalprocess/5,6/,wherecobaltwasprecipitatedasacobaltichydroxide.Therearetwofinalproducts;cathodenickelproducedinanelectrowinningstepandnickelbriquettesproducedinahydrogenreductionstep.Therearealsofacilitiesforhydrogenreductionofcobalt.Thenickelrefinery,orinfacttheentireHarjavaltaplant,isautomatedusingtheVALMETDamaticXDprocesscontrolsystem.Inthenickelrefinery,OutokumpuMintecon-streamanalysersformanessentialpartoftheautomation,TheCourier30APanalysersmeasureliquidphaseconcentrationsofcopper,ironandarsenicusingX-rayfluorescencewhereasautomaticOTItitratorsareusedformeasuringsulphuricacidconcentration.LEACHINGPLANTTheleachingplantatHarjavaltaisespeciallydesignedfortreatmentofthetwomattesfromtheDONProcess.ThechemistryoftheIeachingprocessisdescribedpreinsection3.1.1,whereastheactualcircuitatHarjavaltaanditsparametersaresentedinsection3.1.2.OutokumpunickelmatteleachingprocessBasedonexperiencesfromtheHajavaltaleachingplantandresearchworkusingsmall-scaleequipment,OutokumpuhasdevelopeditsmethodforIeachingtwodifferentnickelmattes.AflowsheetoftheOutokumpunickelmatteIeachingprocessisshowninFigure3.AccordingtotheOutokumpunickelmatteleachingconcept,theFSFmatteisleachedinthreestepsconnectedincounter-currentandtheEFmatteisIeachedintwostepsinseries.Mainleachingagentsareoxygenandsulphuricacid.ThemainproductoftheIeachingplant,i.e.thesolutiongoingtocobaltandnickelseparation,isachievedfromthecopperremovalstep.ThecopperisobtainedascoppersulphideprecipitatefromthenickelIeachingautoclaveintheFSFpressureleachingstep.AnypreciousmetalsintheFSFmattearecollectedintotheresiduefromthetotalIeachingautoclave/7/.TheironisprecipitatedasgoethiteorhematiteintheEFIeachingcircuit.AtmosphericcopperremovalTheatmosphericcopperremovalintheFSFIeachingcircuitproducesaNi-andCo-sulphatesolutionwithimpuritiesatlevelslowenoughforsubsequentcobaltextractionandnickelreduction.ThemainmineralsinthematteareheazlewooditeNi3S2,coppersulphideCu2SandaNiCualloy.Theotherelementsoccurpartlyinseparatephasesbutalsomixedintothethreemainphases.ThemostreactivephaseisthemetallicalloyfollowedbyNi3S2andthenCu2S.Importantreactionsaretheprecipitationofcopperandthesimultaneousleachingofnickel.Mostimportantnetreactionsareshowninthefollowing:TOC\o"1-5"\h\zCuSO4+NiCu+0.5O2—Cu2O+NiSO4(1)2CuSO4+2Ni3S2+0.5O2—Cu2O+2NiSO4+4NiS(2)3CuSO4+2Ni3S2+O2+2H2O—Cu3SO4(OH)4+2NiSO4+4NiS(3)2CuSO4+NiCu+O2+2H2O—Cu3SO4(OH)4+NiSO4(4)lroninthesolutionsfedtothecopperremovalstepisvirtuallyasFe++,anditisoxidizedandprecipitatedasFeOOHaccordingtoFeSO4+Ni3S2+0.75O2+0.5H2O—FeOOH+NiSO4+2NiS(5)butsomeFe(OH)3isalsoformed.Arsenic,antimonyandbismutharemainlyprecipitatedtogetherwithironinpoorlysolubleferriccompoundssimilartoferricarsenate,FeAs04.Thus,theremovaloftheseelementsfromthesolutionisenhancedbyanincreasedironprecipitation.NickelatmosphericleachIntheatmosphericleach,themainobjectiveistoleachremainingNi3S2ascompletelyaspossibleleavingNiSasthesecondaryphase.OtherobjectivesaretocontrolCu,Fe,As,SbandBiinthesolutionsatlevelsthatcaneasilybehandledintheatmosphericcopperremoval.ThemainreactionisleachingofNi3S2,andforthesucceedingnickelpressureleach,itisimportantthatNi3S2isconvertedtoNiSascompletelyaspossible.TOC\o"1-5"\h\zNi3S2+H2SO4+0.5O2—NiSO4+2NiS+H2O(6)AlsoCu2Sreacts,butmoreslowlythanNi3S2.Apartofthecopperisleached,andtheremainingpartisconvertedintomoreoxidizedsulphidespecies.ThemostcommonspeciesfoundareCul.8SandCuS.Cu2S+0.2H2SO4+0.1O2—Cu18S+0.2CuSO4+0.2H2O(7)Cu18S+0.8H2SO4+0.4O2—CuS+0.8CuSO4+0.8H2O(8)NiSispartlyconvertedintoCuSthroughareactionpathprobablyinvolvinganoxidationandareductionmechanism.Asinthecopperremovalstep,mostoftheincomingFe,As,SbandBiisprecipitatedattheendoftheatmosphericleach.SincethepHislowerinthisstepthaninthecopperremoval,thesolubilityofNiandCuarsenateswillbemuchhigherandtheAsconcantrationinthesolutionismostlydeterminedbythemorestablecompoundsformedwithiron.lronischieflyprecipitatedasFeOOH.NickelpressureleachTheaimofthepressureleachistobringunleachedorprecipitatednickelandironintothesolutionandproduceanoutletforcopperintheformofcoppersulphide.Thestepconsistsofaselectivenickelleachingpart/6,8/wherenoorlittleoxygenjsusedandatotalleachingpartwithefficientoxidization.Intheselectivenickelleachingautoclave,NiSandeventuallyremainingNi3S2areconvertedintothecoppersulphide,digenite,Cu1.8S.Thereactionscanbewrittenas:TOC\o"1-5"\h\z6NiS+9CuSO4+4H2O-5Cu18S+6NiSO4+4H2SO4(9)8Ni3S2+27CuSO4+4H2O-15Cu18S+24NiSO4+4H2SO4(10)NiSreactsveryfast,whereastheleachingrateofNi3S2ismuchslower.AlsoCuSandCu++ionsarereactingformingCu18Sandsulphuricacid,accordingtothereaction:6CuSO4+3CuSO4+4H2O—5Cu1.8S+4H2SO4(11)Asthesolutionisacidic,Fe3+insolutionwillbereducedbythesulphideFe2(S04)3+l.2bCul.8S—2Fe3O4+1.25CuS+CuSO4(12)WhenFe3+isremovelfromtnesolution,adissolutionofFeOOH,FeAsO4aswellasSbandBicompoundswillproceedaslongasfreeacidandreducingsuiphideareavailable.Thus,dissolutionoftheironcompoundsisenhacedbykeepingahighconlcentrationofsulphuricacidinthereactor.Onthecontrary,SeisprecipitatedfromthesolutionIthisstep.Inthetotalpressureleach,anyremainingNi3S2isleachedaccordingtowhereasNiSandCuSareleachedaccordingtoMeS+2O2—MeSO4,Me=Ni,Cu(13)Thus,thesulphideofthematteareleachedalmostcompletely,andtheleachresiduefromthetotalleachingautoclaveismainlyanoutletforpreciousmetals.EFmatteleachTheobjectiveoftheEFleachingcircuitistoleachnickel,copperandcobaltofthematteandprecipitatetheironasgoethite-hematite.ThemaincomponentoftheEFmatteisametallicalloyNiFe.Alsocoppermaybemixedintotheailoy,Pentlandite((NiFe)9S8)isthemajorsulphidecomponentofthematte.TheEFmattecanreactveryvigorouslywithsulphuncacidandformhydrogenandhydrogensulphideifthemixingandthefeedofoxygenarenotadequate.Especiallyathightemperatures,theriskofhydrogenformationishigh.Therefore,theleachingcircuitconsistsofanatmosphericleachandapressureleach.Themetailicalloysareleachedintheatmosphericleachwhereasthesulphidesareleachedinthepressurestep.Thus,ahighrecoveryofnickel,cobaltandcopperisachievedwithashortresidencetimeandalsotheironprecipitationisoptimizedbythisprocessarrangement.TheEFmatteIeachingcanroughlybedescribedbythefollowingoverallreactions.Nickel,copperandironinthemetallicphaseareleachedaccordingtoTOC\o"1-5"\h\zMe+H2S04+1/2O2—MeS04+H2O,Me=Ni,Cu,Fe(14)Thepentlanditereactsaccordingto(NiFe)9S8+H2S04+16.502—9(Ni,Fe)S04+H20(15)HydrogencanbeproducedaccordingtoNiFe+2H2S04—NiS04+FeS04+2H2(16)Hydrogensulphidemaybeformedaccordingto(NiFe)9S8+4H2S04—5NiS+4FeS04+3H2S+H2(17)Theformationoftheseunwantedproductsispreventedbyproidingforanintensivemixingandanexcessofoxygeninthesolution.Ironismainlyprecipitatedasgoethiteintheatmosphericleach:2FeS04+3H20+0.502—2FeOOH+2H2S04(18)andashematiteinthepressureleach:(19)2FeSO4+2H2O+0.5O2—Fe2O3+2H2SO4IfthepHoftheatmosphericleachislowerthan2,ironcanbeprecipitatedasjarosite.So,withpHcontroltheironcanbeprecipitatedintoadesiredform.Atthesametime,acarefulpHmonitoringisneededtogetagoodrecoveryofnickelandcopper.(19)HarjavaltaleachingplantTheactualcircuitatHarjavaltadifferssomewhatfromtheflowsheetinFigure3.PriortotheexpansionprojectatHarjavalta,therewasnotanyindustrialscaleexperienceofleachinghighironmattes.Thus,certainsafetymeasuresweretakentoensuretheremovaloftheEFmatteiron.A1so,therewasnaturallyaneedtoutilizeexistingequipmentwhichledtosomespecialarrangementsinthecircuit.ThemaindifferencescomparedtotheflowsheetinFigure3are:TheautoclavesintheFSFpressureleachareconnectedinparallelwithrespecttothesolidmaterial,andtheleachresiduesarecombined.ThesolutionfromtheFSFnickelpressureleachisledtotheFSFatmosphericleach.Asolid/liquidseparationismadeaftertheEFatmosphericleach,andthesolutionisledtoanironremovalautoclavewithsubsequentliquid-solidseparation.ThesolutionfromtheironremovalautoclaveisledtothecopperremovalstepintheFSFcircuitwhereasthesolutionfromtheEFpressureleachingstepisrecycledtotheEFatmosphericIeachingstep.Theproductsolutionfromtheleachingplantisledtothesolventextractionplantforcobaltseparation.ThecoppersuiphideprecipitatefromtheFSFleachingcircuftisledtothecoppersmelterwhereastheironresiduefromtheEFleachingcircuitisrecycledtothefiashsmeltingfurnace.Feedandproductstreamsb)Thecompositionoftherawmaterialfortheleachingplant,theFSFandtheEFmattes,isspecifledinTablel.Sulphuricacidisfedinconcentratedformandintheformofanolyte,whichisarecyclestreamfromthenickelelectrowinningcircuitwith.100g/lNiand50g/lH2S04.Theproductsolution,goingtocobaltSX,isanickel-cobaitsulphatesolution.Thenickelconcentrationis130g/l.Themaintargetsfortheproductsolutionarelowconcentrationsofiron,copper,arsenic,andotherimpurities.AspecificationofitscompositionisgiveninTable3.ThesolidproductsoftheleachingplantarethecopperprecipitatefromtheFSFcircuitandtheironprecipitatefromtheEFcircuit.Thecopperprecipitate,whlchismainlycomposedofcoppersulphidesandironaswellasasmallamountunleachednickel,isledtothecoppersmelter.AnypreciousmetalsintheFSFmattearecontainedinthecopperprecipitate.Theironprecipitate,i.e.goethiteorhematitewithsmallamountsofcopperandnickel,isrecirculatedtothenickelflashsmeltingfurnace.Atypicalcompositionoftheironprecipitate(Feresidue)isgiveninTable1.b)EquipmentPriortoleaching,thetwomattesaregroundfromgranulatedsizedownto90%-53以m.Thewetgrindingisearnedoutinballmills.Theatmosphericcopperremovalstepconsistsoffivereactors,ailconnectedinseries.Allreactorsareagitatedvesselswithoxygeninletbelowthestirrer.ThereactorsareoftheOKTOP-typeshowninFigure4,providedwithveryefficientmixingdevices.Theagitationiscarriedoutbystirrersofgls-type,whichisamodificationoftheRushtonturbinestirrer.ThisOKTOPreactorhasreplacedtheformerreactortype,whereoxygenwasfedasairandtheaerationprovidedtheentireagitation.Theproductsolutionfromthecopperremovalisseparatedwithathickener,fromwhichtheoverflowisfurtherledthroughapressfilter.TheFSFatmosphericleachconsistsoffourreactors,ailconnectedinseries.Thereactortypesaresimilartothoseinthecopperremovalstep.Athickenerisusedforthesolid-liquidseparationafterthereactors.Theunderflowfromtheatmosphericleachingstepthickenerisdistributedbetweenthetotalleachingautoclaveandthenicke!leachingautoclave.Thetotalleachingautoclaveisa7-compartment,titaniumImedvesselwithoxygeninletatthebottomofeachcompartment.Thenickelleachingautoclaveisa5-compartment,brick-linedvessel.Thesolidmaterialis,afiereachautoclave,separatedwithpressfiltersandfurtherdriedwithaLaroxpressurefilter.IntheEFmatteleachingcircuit,theatmosphericstepconsistsoffiveOKTOP-reactors(seeFigure4)connectedinseries,afterwhichtheliquid/solidseparatiooriscarriedoutinaSupaflowthickener.Thethickenerunderflowisledtotheleachingautoclave,whichisa5-compartmentvesselwhereeachcompartmentisequippedwithadoublebladedagitatorandoxygeninletatthebottom.Thethickeneroverflowisledtoanironremovalautoclave,similartotheEFleachingautoclave.TheautoclavesareofthetypeshowninFigure5.TheironresidueisseparatedbySupaflowthickeners.TheunderflowfromboththickenersisfiiteredwithaLaroxpressurefilter,andthefiltercakeisfurtherledthroughadrierbeforeitistransportedtotheflashsmeltingfurnace.SOLVENTEXTRACTION3.2.1VSFtechnologyWithinOutokumpusolventextractionhashadastrongpositionasamethodtorecoverandpurifymetals.OutokumpuResearchinPorihasbeeninvolvedinallSXprocesseslistedinTable2.In1995twoprocesseswereputonstream;namelythecobaltremovalandrecoveryintheHarjavaltanickelrefIneryandthecopperrecoveryintheZaldivarmineinChile.1995年，AlltheotherolderprocesseshavebeentailoredtomatchtheneedofKokkolaChemicals,nowamemberoftheOMGroup,Inc/9-12/.Mixer-settlerdevelopmenthasbeenongoingsince1971andanadvancedliquid-liquidcontactingtechnique,the"VerticalSmoothFlow"(VSF)wasintroducedbothforcobaltandnickelin1991.Expressedasthesizeofthemixersofthemixer-settlersthemixervolumeis21m3inHarjavalta,and40m3inZaldivar.In1997,a50m3mixerisunderconstructionattheRadomiroprojectinChileo

GenerationTypicalfeaturesApplicationsYearFirst-pre-settlerKokkofain1977-81-lowshearturbineRecoveryofMo1977RecoveryofRe1981Removalofanions1987RemovalofCaandMn1994Second-pre-settlerKokkolain1983-84-verticalmixercirculationRemovalZn1984SeparationofCoandNi1984RecoveryofNi1986Third-pre-settierKokkolain1990-96-verticalmixercirculationRemovalofMg1991-helicalmixingRecoveryofRe1991-separatepumpingRecoveryofNi111991-emphasisonsettlingSeparationofCoandNi1994SFdesignincludesfollowingfeatureslowshear,axial:lowmixingZaldivarseparate,lowheadpumpingRecoveryofCu1995simpledispersionmodecontroltotalairexclusio1HarjavaltaRemovalofCo1995Table2MixersettlerdevelopmentatOutokumpuOyAgeneralviewofamixer-settler,designedaccordingtoVSFmixingandflowprinciplesforcobalt/nickelseparationisgiveninFigure6.Theunitconsistsofadispersionoverflowpump(DOP)locatedinthesettlerandtwomixerssurroundedbyapre-settler.Theconstructionofacoppermixer-settlerisdifferent,theretheDOPandthemixersarelocatedoutsideofthesettler.Theverticalflowconfigurationinthemixerisobtainedbyatubulardoublehelixstirrer(SPIROK)inaliftingoperationmode,bywhichthelowshearingcharacteristicsofthemixerareemphasized.ThepurposeistoachievelowshearingIiquid-Iiquidcontacting,resultingincleanphaseseparationsandcorrespondinglowentrainmentvaiuesinbothorganicandaqueousflows.TheprimarymixingregionofaSPIROKislarge.Thestirrerrotatesinavolume,whichcoversmorethan40%ofthetotalmixervolume.Inanoldtypeturbinemixer,themixercoversonlyaround4%ofthetotalmixervolume.Consequently,alowmixingenergyisrequired,onlyclosetohalfofwhatisnormallyusedinmoreconventionaldesign.ThemixingenergyintensitywithinaSPIROKvolumeisclosetotentimeslessthanwithinavolumeofarelativelylargeturbine.Thepipeconnectionbetweenthemixersisdrawntopromotetheflowofdispersionfromthefirsttothesecondmixer:Thedispersionoutletfromthesecondmixerislocatedclosetoawallmountedbetweenthemixers.Thedispersionisthusforcedtoflowawayfromthesettleranddividedintotwoequalstreamsaroundthemixers.Byguidingbafflesthestreamsareforcedintothefrontcornersofthepre-settler.Additionalbalesandapicketfenceoverthewholesettlerwidthimprovetheoverallphaseseparationoftheunit.Thepicketfenceisdesignedtogiveaproperpressuredropandthusthedispersioniskeptinadenseclosepackedconditiononthepre-settlerside.Thankstothepressuredrop,thedispersionandpartlyseparatedliquidsareevenlydistributedintotheactualsettler.ChemistryCobaltseparationfromnickelisperformedwithCyanex272/13/.Thesolventcompositionis10volumepercentCyanex272inShellsolK.SheilsolKisarefinedaliphaticdiluentwithafiashpointof720°C.ThephosphinicacidCyanex272hasprovedtobeareliableextractantforcobalt/nickeiseparation.Inadditiontocobalt,alsozinc,copper,manganeseandleadareseparatedfromthenickelintheSXstage.TheextractionofmetalsbyCyanex272fromsulphatesolutionsisshowninFigure7.Neutralizationintheextractionisdonewithammonia.Nickelwashingisperformedwithanacidiccobaltsulphatesolutionandcobaltstrippingwithsulphuricacid.Zincandironremovalfromthesolventisalsodonewithsulphuricacid.ProcessflowsheetandoperationTheflowsheetofthecobaltsolventextractionprocessisshowninFigure8.BeforetheSXprocess,thefllteredsolutionfromtheatmosphericcopperremovaliscooledinheatexchangers.Amaximumoperatingtemperatureof50Cisdesignedfortheprocess.ThevaluableCyanexsoiventisprotectedbyakerosenewashinonemixer-settler.InthiskerosenewashthenickelsolutionfromthelastleachingstepiscontactedwithShellsolK.Thiswashremovesundefinedorganicsandfinesolids,whichoccasionallymaypassthoroughthefiltration.Afterthecobaltextractionstagesthereisanotherkerosenewash,whichrecoverstheCyanexsolventleftinthenickelsolution.Thecobaitextractionisamodifiedcountercurrentcircuitwithfourstages.AmmonianeededasneutralisationagentisfedintotheorganicstreamjustbeforetheentranceintotheDOPdeviceofthethreelastextractionstages.Thecobaltandnickelloadedsolventiswashedcountercurrentlyinfivemixer-settlerswithanacidiccobaltsulphatesolution.Theamountofwashsolutionisonly1.5%ofthenickelsolutionfeed.Thestrippingofthecobaltloadedsolventisdoneinfourstagesinastraightforwardcountercurrentmodeinwhichwayacobaltsulphatesolutionfreeofzincandironisobtained.Afterthecobaltstrippingtheorganicstreamiswashedinonestage,namelythecobaltwashstage.Thelaststageinthesolventextractioncircuisdoneinonemixer-settler.ThestrippedCyanexsolventisthentransferredtoastoragetank.ThecontrolofthecontinuousoperationisbasedontheDamaticXDprocesscontrolsystemusingCourierX-rayapparatusforonlineanalysisofcobaltandnickeiofboththeaqueousandtheorganicstreams.Alsoon-linepHmeasurementisusedInthecontrolofthesolventextractionprocess.ResultsfromtheoperationTable3showstypicalanalysisofthefeedsolutionandtheproducednickelsulphateandcobaltsulphatesolution.Theseparationofcobaltandnickelisexcellentandthepurityofthenickelsulphateisoutstanding.Theonlydivalentmetalswhicharenotcompletelyremovedarecalciumandmagnesium.Table3.TypicalanalysisoftheSXfeed,raffinateandcobaltsulphatesolutionattheNickelrefineryinHarjavalta.Nig/iCog/iZnmg/lCumg/lPbmg/lMnmg/lMgmg/lCamg/lFemg/l料液1300,8-10,510,50,180400,1萃余液1300,01<0,05<0(1<0,5<0t18040<0,1硫酸钻0,02110<0,0530&I23320<0,1Theamountoforganicintheraffinatehasbeenverylow.TheentrainmentIevearound20ppm.Theraffinateisstilltreatedwithactivatedcarbonbeforeitpumpedtothenickelelectrowinningandthehydrogenreductionprocess.3.3ELEC'TROWINNINGIntheelectrowinningprocess,nickelisprecipitatedfromanlckelsulphatesolutiontometallicformwithelectriccurrent.ThecathodicreactionisreductionofnickelIonsonthecathodeandtheanodicreactionisoxidatfonofwateronthesurfaceoftheleadanode.Electrolysisreactionscanbedescribedbythefollowingoverallreactions:Ni2++2e=Ni0CathodereactionH20'=1/202+2H++2e-AnodereactionNi2++H20=Ni0+2H++1/202CellreactionBecausenickelislessnoblethanhydrogenintheelectrochemicalseries,diaphragmelectrolysismustbeused.Thecathodesstandinadiaphragmbagandcatholytehavinglowacidconcentrationisfedtothebag.Thecatholyteflowsthrougharotameterfromacatholytedistributionpipewhichislocatedatthesideofthecell.Thehydrostaticheaddifferencebetweenthecatholyteandanolyteandthepermeabilityofthediaphragmclothallowsthesolutionflowfromthecathodespacetoanodespace.Theheaddifferenceassureskeepingtheacidnickelsulphatesolutionoutsidethecathodespaceandthusavoidingthehydrogenevolution.Thecatholyteflowisabout12l/hintoonecatholytebagandthedecreaseofnickelionconcentrationordelta-Niis30g/l.Respectively,theacidconcentrationisincreasedby50g/lintheanodespace.Figure9showsaviewofthesectionoftheelectrowinningcell.Thepolishfilteredcatholytefromthesolventextractionprocessispumpedthroughtheheatexchangerstotheheadtankofthetankhouse.ThepHofthecatholyteisadjustedto3.5-3.8beforedistributiontothecells.Theanolyteoverflowofeachtankiscirculatedbacktotheleaching.Thetemperatureoftheelectrolyteis65C.Thetankhousehas126cellsofwhich108arecommercialcellsand18startersheetcells.Thetankhousehasbeenenlargedinseveralstages.Theolderparthas90cellswith48cathodesand49anodes.Thelastexpansionofthethetankhousewasin1982with36cellshaving52cathodesand53anodeseach.Thecellsarepolypropenelinedandeachcellisconnectedtoavoltageandtemperaturemonitoringsystem.Thespacingbetweenthecathodeandanodeis133mm.Theanodematerialisunalloyedlead.Electrolysiscellsareelectricallyconnectedinseries.Theelectrolysiscurrentisfedfroma15MWrectifier.NormalloadoftherecMeris17kAand470V.Theelectrolysiscurrentdensltyis180-200Am2andthecurrentefficiencyis93%.Thecapacityofthetankhouseis18000tpanickel.Sodiumlaurylsulphateisaddedtothecatholyteasafoamertosuppressthenickelsulphatemistfromtheelectrolysiscells.Inthestartersheetcells,thestartersheetsareprecipitatedontitaniummotherblanksfortwodaysafterwhichtheplatesarewashedandsrippedinanautomaticstrippingmachine.Thestartersheetsarefurtherpreparedinthestartersheetmachinewhichincludestheunitsforcuttingthesheetsinsizeof970mmx890mm,forstraighteningandrigidizingthesheets,forWeldingtheloopstothetopedgeofthesheet,andforattachingofthecathodehangerbar.Thedepositiontimeissevendaysinthecommercialcelts,andtheweightofonenickelcathodeis65kg.Intheharvesting,thecathodesarecranedtotheautomaticcathodemachinewherethecathodesarewashedfromtheelectrolyte.Thenthecathodehangerbarsareremovedandthecathodesarestackedandweighted.Thereadystacksaremovedforcuttingofcathodeswithaforklifttruck.Cathodesarecutandpackedautomaticallyonaproductionlinewhichconsistsoftwocuttingmachinesinseries.Thefirstonecutsintostripsandthesecondonetointosquares.Thesquaresarecontinuouslypackedintodrumswhichareweightedandtransferredtopallets.Thestandardsizesofthesquaresare25x25,50x50,100xl00mm.Also,stripswithnon-standardsizearecutwithtwoothercuttingmachines,EdgesandthehangingloopsofthecathodesarenormallysenttoOutokumpu'sTornioSteelWorksforstalnlesssteelproduction.Thecustomersforelectrolyticnickelareinelectroplating,meltingandsuperalloyingindustry.HYDROGENREDUCTIONPROCESSNickelbriquettesareanewproductofHarjavaltanickelrefinery.ThebriquetteproductionstartedinSeptember1995.In1996thebriquetteproductionwas14300tonsandin1997theproductionwillbe23000tons.TheproductionofcobaltpowderstartedinJune1996.ThehydrogenreductionisbasedontheSherrittprecipitationprocess.Theproductionofnickeliscarriedoutbydirecthydrogenreductionunderpressurefromammoniacalammoniumsulphatesolution,Thehydrogenreductionplantconsistsoffiveautoclaveshavingavolumeof40m3each.Afterthehydrogenreduction,thepowderfromtheautoclavesiswashed,dried,briquetted,sinteredandpackedfordelivery.Theplantishighiyautomatedstartingfromthepreparationoffeedsolutionandendingtoafullyautomatedproductstorage.Ammoniumsulphateiscrystallizedinfourvacuumcrystallizers.Abouthalfoftheammoniumsulphateiscirculatedtopreparationofthefeedsolutionforhydrogenreduction,andtherestiscentrifugalizedanddriedtoasaleableform.Ammoniumsulphateisthemainsulphuroutletoft