奥托昆普哈贾瓦尔塔精炼厂镍电解工艺设计

./NickelelectrolysisprocessatOutokumpuHarjavaltaMetalsOy奥托昆普哈贾瓦尔塔金属公司镍电解工艺AbstractThispaperdealswiththeelectrolysisofnickelfromsulphatesolutionanditselectrochemicalprinciples.Asanexample,thenickelelectrolysisprocessatOutokumpuHarjavaltaMetalsOyisdiscussedinmoredetail.Theleachingofnickelmatteandthepurificationofthenickelsulphatesolutionpriortoelectrolysisisalsodiscussed.Inaddition,ashortreviewofotherhydrometallurgicalnickelmattetreatmentprocessesandnickelelectrolysistechnologiesisgiven.摘要：本论文主要研究了硫酸镍溶液的电解过程及其电化学原理。作为例子,本论文主要在细节方面讨论了奥托昆普哈贾瓦尔塔金属公司的镍电解过程。同时也讨论了电解过程之前的镍浸出及净化过程。除此之外,其它镍湿法冶金处理过程及电解技术也在文中涉及到。OutokumpuhasproducedelectrolyticnickelatHarjavaitaworkssince1960.Nickeliselectrowonfromanickelsulphatesolutionusingdiaphragmcellswhereadiaphragmclothisusedtopreventthecatholytesolutionandtheacidicanolytefrommixing.Nickelisdepositedonthinnickelstartersheetsandtheanodesareofunalloyedlead.Thecurrentdensityis200A/m2andthedepositiontimeissevendays.Thereadycathodesweighabout65kgandtheyareharvested,washedandcutintosquaresandstripsandfinallypackedfordelivery.Electrolyticnickelissuppliedtotheelectroplating,meltingandsuperalloyingindustry.早在1960年开始,奥托昆普便在哈贾瓦尔塔工厂开始生产电解镍。电解镍是从硫酸镍溶液中用隔膜电解槽电解产出的,而隔膜布的作用是防止阴极液和阳极液混合。电镍在很薄的始极片上沉积,而阳极是纯铅阳极。阴极电流密度为200A/m2,阴极周期为7天。达到生产周期的电解镍约65kg,经出槽、烫洗后剪切成方块和条状,最终包装并发送至客户厂家。电解镍主要用在电镀、熔炼和超耐热合金等领域。Inadditiontonickelcathodes,Outokumpuhasalsobeenproducingnickelbriquettessincethelastexpansionin1995.Theexpansionofthenickelproductionhasalsobroughtaboutseveralprocesschangesinthesmelterandtherefinery.Thesmelternowproducestwotypesofnickelmattes,whicharetreatedinseparateleachingplants.Afterleaching,thenickelsolutionistreatedinanewsolventextractionsteptoproduceapurifiednickelsulphatesolutionforelectrolysisandhydrogenreduction.Theannualcapacityofthenickelplantis18,000tonsofcathodesand22,000tonsofbriquettes.除电解镍之外,奥托昆普从1995年扩建之后也开始生产镍砖。这次扩建对冶炼厂和精炼厂都带来了很多的技术改革。冶炼厂现生产两种类型的冰镍,分别用不同的浸出装置处理。浸出后,含镍溶液在新的溶剂萃取工序处理,并产出纯净硫酸镍溶液用来进行电解和氢还原。镍厂生产能力为18000t/a的电解镍和22000t/a的镍砖。1.IntroductionNickelisanimportantalloyingelementinthemetalindustry.Morethan70%ofthenickelisconsumedinstainlessandalloyingsteels/1/.Othermainusesofnickelarenon-ferrousalloys<11%>andcorrosionresistantanddecorativeplatedcoatings<8%>.Theworldprimarynickeldemandwas928000tonsin1996/2/.1、简介镍是金属工业中一种非常重要的元素。超过70%的镍消费于不锈钢行业和合金行业〔文献1。镍的其它用途有非铁合金〔11%和防腐蚀以及装饰性电镀〔8%。在1996年,全球镍需求量为92.8万吨/年〔文献2。Nickelisrefinedfromsulphideorlateriteores.About60%ofthenickelisminedfromsulphidedepositsand40%fromlateritedeposits/3/.Inlateriteoresnickelisboundinironoxideorsilicacompoundsfromwhichitisdifficulttoupgrade.Therefore,directsmeltingoforeisgenerallyusedtoproduceferronickelornickelmatte.Directleachingoflateritewithammoniaorsulphuricacidisalsoused.Studiesonthehydrometallurgicalprocessingoflateriteoreshavebeenverynumerousrecentlyandvariousnewleachingandrefiningprocesseshavebeenproposed.Also,severalminingprojectsonlateritesareunderway.镍主要从硫化矿或红土矿中提取。目前约60%的镍是从硫化矿中提取,40%的镍从红土矿中提取〔文献3。由于红土矿中镍表面被氧化铁或氧化硅覆盖而难以提炼,因此矿石被直接冶炼生产镍铁或冰镍。也可从红土矿中由氨或硫酸直接进行镍浸出。目前对于红土矿湿法冶金过程有很多研究,并且提出了很多新的浸出和精炼过程。同时,很多公司正在开展红土矿采矿工程。Typicalnickel-containingsulphidemineralsarepentlandite<Ni,Fe>9S8,pyrrhotiteFe1-xSandmilleriteNiS.Nickel-bearingsulphideorescanbeconcentratede.g.byflotationtoupgradethenickelcontent.Nickelconcentrates,generallycontaining7-25%Ni,arerecovered.Thenickelconcentratesareusuallysmeltedtochargetheironandmagnesiumoxideoftheconcentrateintoanironsilicateslag.Thenickelisrecoveredintoasulphidemattecontaining35-70%Ni.ThemainmineralsofthematteareheazlewooditeNi3S2,chalcociteCu2SandaNi-Cualloy.Importantsidemetalsofthenickelmattesarecobalt,copperandplatinumgroupmetals.典型的含镍硫化矿有镍黄铁矿<Ni,Fe>9S8、磁黄铁矿Fe1-xS和针镍硫矿NiS。硫化镍矿可以通过浮选来浓缩并提升镍含量,获得含Ni约7～25%的镍精矿。镍精矿一般通过冶炼富集其中的铁和氧化镁,并将其转化为硅酸铁炉渣。镍则成为含Ni35～70%的硫化冰镍。冰镍中主要含有六方硫镍矿Ni3S2、辉铜矿Cu2S和Ni-Cu合金。冰镍中含有的其它主要金属有钴、铜和铂族金属。Becauseofvaluablesidemetalsandalsobecauseofharmfulimpurityelements,nickelmattemustgothroughamulti-stagerefiningprocess.Generally,matteistreatedbyhydrometallurgyconsistingofoxidationofmatteinleachingorinelectrorefining,purificationofthenickelsolutionandrecoveryofhighgrademetallicnickelbyelectrolysisorhydrogenreduction.由于冰镍中含有很多其它金属,并且很多金属为有害金属,因此冰镍必须经过一个多级精炼过程。一般来说,冰镍需经过由冰镍氧化浸出或电解、镍溶液提纯组成的湿法冶金流程,再通过电解或氢还原工艺得到高等级的金属镍。2.HydrometallurgicalmatterefiningprocessesHydrometallurgicalprocessestorefinenickelmattecanbespecifiedasfollows/4,5,6,7,8/:1>Matteelectrolysis.Castnickelmatteanodesaredissolvedinadiaphragmelectrolysiscellusingachloride/sulphateelectrolyte.Theelectrolytefromtheanodecompartmentiscirculatedthroughthesolutionpurificationbeforefeedingtothecathodebag.Alsotheanodesarebaggedtocollectthesulphur-containinganodeslimeoftheanode.TheprocessisinuseatInco'sThompsonrefineryinCanada/9/.2、冰镍精炼湿法冶金过程以下是几种冰镍精炼湿法过程的详细说明〔文献4、5、6、7、8：1冰镍电解。将冰镍浇筑成阳极板并在隔膜电解槽中用氯化物-硫酸盐溶液进行电解。阳极液循环经过溶液净化过程后再进入隔膜袋进行电解。阳极同样套袋以收集含有硫磺的阳极泥。加拿大Inco公司汤普森精炼厂便采用此流程。2>Chlorideleachprocessofmatteandelectrowinning.Matteisleachedinachloridesolutionusingchlorinegasasanoxidant.Thechlorinegasisgeneratedintheelectrowinningcells.Theprocessisinoperatione.g.atFalconbridge'srefineryinKristiansandinNorway,Sumitomo'sNiihamarefineryinJapanandatEramet'srefineryinSandouvilleinFrance/9,10,11,12,13/.2冰镍氯化浸出-电解流程。冰镍在氯化物溶液中使用氯气作为氧化剂进行浸出。氯气是在电解过程中产出的副产物。挪威克里斯蒂安松鹰桥精炼厂、日本住友新居滨精炼厂和法国桑杜维尔埃赫曼精炼厂都采用这一流程。3>Atmosphericacidleachandelectrowinning.Matteisleachedinacidsulphatesolutioninoxygenorair-spargedleachvessels.Aftertheatmosphericleach,atwo-stagepressureleachfollowstodecreasethenickelcontentintheresidueandtooxidiseaportionofthecoppersulphidetocirculatethedissolvedcopperinatmosphericleaching.Thenickelsulphatesolutionispurifiedbysolventextractionorbycobaltichydroxideprecipitation.Thenickelisprecipitatedascathodesintheelectrowinningprocess.TheatmosphericacidleachandthesulphateelectrowinningprocesshavebeendevelopedbyOutokumpuOyandthesemethodsareusede.g.byBindura,EmpressandHartleyrefineriesinZimbabweandbyOutokumpuatHarjavaitaWorksinFinland/4,5,14/.3常压酸浸-电解流程。冰镍在氧气或空气喷射入浸出槽中,并用硫酸溶液进行浸出。常压浸出后,继续进行两段加压浸出,以降低浸出渣中镍含量,同时将一部分硫化铜氧化,并将溶解的铜返回常压浸出。硫酸镍溶液通过溶剂萃取法或钴的氢氧化物沉淀法净化。经净化后的溶液在电解工序产出电解镍。常压酸浸-硫酸镍电解流程是奥托昆普公司研发的,津巴布韦的Bindura、Empress和Hartley精炼厂以及芬兰奥托昆普哈贾瓦尔塔厂均采用这一流程。4>Ammoniapressureleachandhydrogenreduction.Matteisleachedintoammoniacalammoniumsulphatesolutioninpressureautoclavesusingairasanoxidant.Afterthesulphideprecipitationofcopper,nickelsolutionisreducedwithhydrogeninthereductionautoclavestoproducemetallicnickelpowder.Theammoniumsulphateforminginthehydrogenreductionisrecoveredbycrystallisation.Afterthehydrogenreductiontherestofthedissolvednickelandallthecobaltareprecipitatedwithhydrogensulphide.ThisprocessisknownastheSherrittGordonProcess/15/anditisappliedatSherritt'sFortSaskatchewanplantinCanadaandatWMC'sKwinanarefineryinAustralia4加压氨浸和氢还原。冰镍在加压浸出釜中以硫酸铵溶液并通入空气作为氧化剂进行浸出。经过硫化物除铜,含镍溶液在还原釜中用氢气还原生成金属镍粉。氢还原过程中生成的硫酸铵通过结晶回收。经过氢还原后,游离的镍和所有的钴用硫化氢气体沉淀。这一过程便是谢里特戈登法,加拿大谢里特的福特萨斯喀彻温厂和澳大利亚奎那那厂均使用这一方法。5Acidpressureleachandhydrogenreduction.Matteisleachedwithspentcopperelectrowinningelectrolyteusingpressureautoclavesandairasanoxidant.Aftertheleaching,copperandironareprecipitated.Thenthenickelsolutionisammoniatedforhydrogenreduction.TheprocesswasdevelopedbySherrittGordonandisoperatede.g.byImpalaPlatinuminSouthAfrica/8/.RustenburgPlatinuminSouthAfricaalsousestheacidpressureleachbutmetallicnickelisdepositedwiththeelectrowinningprocess/16,17/.5加压酸浸和氢还原。冰镍在加压釜中用废铜电解液并通入空气作为氧化剂进行浸出。浸出后,铜和铁被沉淀,含镍溶液被氨化以备氢还原。这一流程是由谢里特戈登研发出的。南非因帕拉铂金厂便使用此法〔文献8。南非里斯腾堡铂金厂同样应用加压酸浸法,但通过电解法生产电镍〔文献16,17。3.NickelelectrolysisprocessesAllelectrolyticnickelproductionprocessesuseadiaphragmcelloriginallydevelopedbyNorwegianchemistN.V.Hybinetteatthebeginningof1900's/18/.TheHybinettecellwasdevelopedforelectrolyticrefiningofcastmatteanodes.Inthecell,theanodeandcathodeareseparatedbyapermeablediaphragmcloth.Thematteanodedissolvesintheanodebagandtheelectrolytewiththedissolvedimpuritiesoftheanodeisfedtosolutionpurification.Thepurifiednickelsolutionisfedintothecathodecompartmentoftheelectrolysiscell.Thehydrostaticpressuredifferencebetweencathodeandanodesolutionspreventsthesolutionsfrommixing.TheHybinetteprocesswasfirstintroducedattheKristiansandrefinerywherematterefiningelectrolysiswasintroducedin1910.3、镍电解流程所有的镍电解流程都使用隔膜电解法,这一方法是挪威化学家N.Y.Hybinette在1900年左右首先提出的。Hybinette电解槽开始时是为冰镍浇筑阳极〔可溶阳极而研发的。电解槽中,阳极和阴极用一个具有渗透性的隔膜布隔开。冰镍阳极在阳极袋中溶解,含有各类杂质的电解液进入溶液净化工序。经过净化后的电解液进入电解槽的阴极室。溶液静压力的不同阻止了阴极液和阳极液混合。Hybinette电解流程于1910年首先在克里斯蒂安松精炼厂使用。3.1MatteelectrolysisMatteelectrolysisiscarriedoutinamixedchloride-sulphatesolution.Theprincipalanodicreactionisoxidationofheazlewoodite,asshowninreaction<1>.Onthesurfaceoftheanodeasulphur-containinganodelayerisformed.Thesulphurlayercausesanodicpolarisationastheanodedissolves.3.1冰镍电解冰镍电解是在氯化物-硫酸盐混酸体系中进行的。主要的阳极反应是Ni3S2的氧化,如方程式〔1所示。随着反应进行,阳极表面形成一层含硫层〔阳极泥。阳极泥层在阳极溶解过程中引起阳极极化。Ni3S2===3Ni2++2S0+6e- <1>AtInco'sThompsonrefinerytheanodesweighabout250kg/9/.Thecurrentdensityis240A/m2andthevoltageis3-6V,dependingontheslimelayerthicknessofthematteanode.Thepurifiedelectrolytecontains75g/LNi2+,51g/LCl-and120g/LS042-.BoricacidisaddedtobufferthepHoftheelectrolyte.Thecathodecycleis10daysandtheanodecycleis15days.Morenickelisdepositedatthecathodethanisdissolvedattheanode.Tokeepthenickelbalanceinthesolution,aportionofgroundmatteisleachedintheair-agitatedreactors.ThecapacityoftheThompsonrefineryis55,000tpanickel.Inco公司汤普森精炼厂的阳极约重250kg〔文献9。电流密度为240A/m2,槽电压为3～6V,槽电压取决于阳极泥厚度。净化后的电解液含有75g/LNi2+、51g/LCl-和120g/LS042-。电解液中加入硼酸作为pH值缓冲剂。阴极周期为10天,阳极周期为15天。阴极上沉积的镍要比阳极溶解的镍多。为保证溶液体系镍平衡,在空气搅拌槽中浸出一部分磨细的冰镍。汤普森精炼厂年产电解镍55000t。3.2ChlorideelectrowinningTheFalconbridgeChlorineLeachProcesswasinstalledatKristiansandrefineryattheendofthe1970'storeplacematteelectrolysis/10,11/.Theanodicreactionoftheelectrolysisistheevolutionofchlorinegas,whichisusedasanoxidantintheleachingofgroundmatte.Afterleaching,ironisprecipitated.Cobaltisrecoveredbysolventextractionandelectrowinning.Thenickelsolutionfromleachingcontains230g/Lnickelwhichisdilutedwiththedechlorinatedanolyteto85g/L.AfterthefinalpurificationthenickelchloridesolutionisfedtotheEWtanks.Anodesareseparatedfromthecathodecellcompartmentwithadiaphragm.Thechlorinegasvacuumintheanodesidekeepsthehydrostaticheadandthecatholyteflowstotheanodecompartment.TheanodesareDSAanodes<dimensionalstableanodes>.Thecapacityofthetankhouseis68,000tpaascathodesandcrowns.3.2氯化电积二十世纪七十年代末期,鹰桥氯化浸出工艺在克里斯蒂安松精炼厂应用,并取代了冰镍电解流程〔文献10,11。电积过程的阳极反应是氯气的析出,氯气回收后作为磨细冰镍浸出的氧化剂。浸出后,铁被沉淀。钴被溶剂萃取回收并以电解方法产出。浸出液中含镍为230g/L,用除氯后的阳极液稀释至85g/L。在最终净化后,氯化镍溶液进入电积槽阴极室。阳极和阴极用隔膜袋隔开。阳极产生的氯气被抽出以保证阳极室内静压头较小,阴极液流入阳极室内。阳极是DSA阳极〔固定尺寸阳极。电解产能为每年68000t的电积镍和镍冠。SumitomochangedfromthematteelectrolysisprocesstoMatteChlorineLeachandElectrowinning<MCLE>atitsNiihamarefineryin1993/12/.TheoutlineoftheprocessisinprincipalthesameasintheFalconbridgeprocess.Copperisremovedasaformofcopperpowderbyelectrowinning.CobaltandironareremovedashydroxideprecipitateusingCl2asanoxidantandbyneutralisingwithnickelcarbonate.1993年,日本住友公司新居滨精炼厂将其冰镍电解流程改为冰镍氯气浸出-电积流程〔MCLE〔文献12。其主要流程与鹰桥流程基本相同。铜杂质是用电解法生产铜粉而除去。钴和铁杂质是用Cl2作为氧化剂并通入碳酸镍中和水解除去。TheMCLEcellsareequippedwithDSAanodesandeachcellhas53anodesand52cathodes/13/.Electrolyteisfedfromonesideofthecellandabout30%ofthefeedelectrolyteoverflowsfromtheotherside.Therestoftheelectrolytepassesthroughthediaphragmbagintotheanodecompartmentandiswithdrawnbyvacuumwithchlorinegasgeneratedattheanode.Theelectrolytecontains70g/LNi2+and85g/LCl-.About10g/LnickelisdepositedintheEWcircuit.Nickelisdepositedonthestartingsheetplatesthataredepositedonatitaniummotherblank.Thecurrentdensityisintherangeof230-250A/m2andthecellvoltageis3.1V.Thecathodelifeis7or8days,dependingonthecurrentdensity.Thetankhousehas168nickelelectrolysiscells.Theproductioncapacityis30,000tpa.冰镍氯气浸出-电积流程的电积槽中使用固定尺寸阳极,每个电积槽有53块阳极和52块阴极〔文献13。电解液从阴极室的一侧流入,约30%的阴极液会从另一侧溢出流走。剩余的阴极液经过隔膜袋进入阳极室,并随着阳极产生的氯气被抽真空抽走。阴极液含有70g/LNi2+和85g/LCl-。约10g/L的Ni2+在阴极沉积。镍是在用钛种板产出的始极片上面沉积。电流密度为230～250A/m2,槽电压为3.1V。阴极周期为7～Eramet'snickelrefineryinSandouville,Francealsousesachlorideelectrowinningprocess/9/.Therefinerywascommissionedin1978.Inleachingofmattethelixiviantisferricchlorideandironisreoxidisedusingchlorinegasfromtheanodecompartmentoftheelectrolysiscell.Ferricironisextractedfromthenickelchloridesolutionbysolventextraction,isstrippedandrecycledtoleach.Cobaltisalsorecoveredwithsolventextraction.Nickelisdepositedascathodeplatesusingthestarter法国桑杜维尔埃赫曼精炼厂同样也采用氯气电积流程〔文献9,精炼厂于1978年投产。冰镍浸出过程中浸出剂是氯化铁,铁元素被电积槽阳极室内生成的氯气重新氧化。铁离子在溶剂萃取过程中被萃取,反萃后再返回浸出过程。钴也在萃取过程中被萃取。电积厂房有80个电积槽,年产量为13000t电积镍。3.3SulphateelectrowinningOutokumpuwasthefirsttointroduce,onanindustrialscale,thesulphateelectrowinningprocessfornickelusinginsolubleleadanodesin1960.Outokumpuhaddevelopedamattetreatmentprocesswhichwasbasedonleachingofgroundmattetoasulphatesolution.Thismeantthatacompatibleelectrolysisprocesswithleachingalsohadtobedeveloped.ThenickelsmelterandrefinerywasbuiltatOutokumpu'sHarjavaltaworks,whereacoppersmelteralreadyexisted.3.3硫酸盐电解奥托昆普公司于1960年首次使用不溶阳极并采用硫酸盐电解流程生产电积镍,并形成工业规模。奥托昆普公司将冰镍磨细后进行浸出并生成硫酸镍溶液。这意味着电积过程和浸出过程要兼容。镍熔炼厂和精炼厂均设在奥托昆普哈贾瓦尔塔厂,而此前这里已经有铜熔炼厂存在。TheelectrochemicalprinciplesofelectrowinninginnickelsulphatesolutianandtherefineryoperationsatOutokumpuHarjavaltaMetalsOyarediscussedinmoredetailinthefollowingchapters.在后面章节中将详细介绍奥托昆普哈贾瓦尔塔金属公司的硫酸盐溶液电积过程电化学原理和精炼操作流程。4.CharacteristicsofelectrowinninginnickelsulphatesolutionIntheelectrowinningprocess,nickelisprecipitatedfromanickelsulphatesolutionintometallicformbyelectriccurrent.Thecatholicreactionisthereductionofnickelionsonthecathodeandtheanodicreactionistheoxidationofwateronthesurfaceoftheleadanode.Electrolysisreactionscanbedescribedbythefollowingoverallreactions:4、硫酸镍溶液电积过程的特点在电积过程中,硫酸镍溶液中的镍离子通过电流作用沉积为金属镍。阴极反应是镍离子在阴极上还原析出,阳极反应是水在铅阳极上氧化分解。电极反应可用以下方程式表示：阴极反应： Ni2++2e-===Ni0 <2>阳极反应： H2O===2H++1/2O2+2e- <3>电极反应： NiSO4+H2O===Ni0+H2SO4+1/2O2 <4>Becausenickelislessnoblethanhydrogenintheelectrochemicalseriesandthereductionoverpotentialfornickelishigherthanthatforhydrogen,hydrogenevolutionisapreferentialreactionandapartoftheelectriccurrentisconsumedinthehydrogenevolutionreaction:由于在电化学过程中镍元素比氢元素的活性高,镍的还原超电势也要比氢的高,因此在电积过程中析氢反应是首先发生的,一部分的电流消耗在析氢反应上：2H++2e-===H2 <5>Tominimisethehydrogenevolution,thepHofthesolutionshouldbesufficientlyhightohaveagoodcurrentefficiencyfornickelelectrodeposition.Fig.1showsthepolarisationcurvesfornickelreductionatdifferentpHvalues.Thecurvesshowthatthehigherthehydrogenionconcentration,thehigherthereductionpeakofhydrogeninthepotentialvaluesbetween-600and-650mVvs.SCE.Thereductionpeakdemonstratestheactivityofhydrogenions.AtpHvaluesof2.5orhigher,hydrogenevolutionislowandthemainreactionisdepositionofnickel.ThecurrentefficiencystudiesatdifferentpHvaluesconfirmthisphenomenon.AtpH3.0thecurrentefficiencyfornickelis97%and94%atpH2.5,whenthecurrentdensityis200A/m2.AtpH2.0orlessthecurrentefficiencydecreasesdrastically.为减小析氢反应,溶液的pH值必须足够高以保证镍沉积时的电流效率。图1显示了不同pH值下镍还原的极化曲线。曲线表明,氢离子浓度越高,氢的还原峰越高,还原电势位于－600～－650mV。还原峰表示了氢离子的活性。pH值在2.5或更高时,析氢反应比较小,主要反应是镍离子的沉积。在不同pH值下电流效率的研究同样证明了这一现象。在电流密度为200A/m2的条件下,当pH值为3.0时,镍沉积电流效率为97%,当pH值为2.5时镍沉积效率为94%。当pH值小于2.0或者更低时,电流效率大幅度下降。Fig.1alsoshowsthatthepolarisationcurvesshifttomorepositivevalueswhenthepHdecreases.Theshiftis60mVperonepHunit,whichisameasureoftheactivityofhydrogenionsaccordingtotheNernstequation.WhenthepHvalueistoohigh,thereisadangerthatnickelhydroxidewillbedepositedwithnickel.Hydroxideprecipitationcausesdisturbancesinthecrystalstructureofnickelwhichcanbenoticedastension,brittlenessorhardeningofthedeposit.图1同时显示当pH值减小时,极化曲线趋向于更正的值。移动值是每个pH值单位变化60mV,这也是根据能斯特方程计算出的氢离子的活度变化。当pH值太高时,将会有形成氢氧化镍的可能性。氢氧化镍会影响镍沉积物晶体结构的张力、脆性和硬度。4.1StructureofthedepositIntheelectrolysisprocessthedesireddepositionstructureshouldbefinegrainedandwellorientatedtogetunstrainednickelplatesbothinstartersheetcellsandincommercialcells.Fig.2showsatypicaldepositionstructureofthenickelstartersheet.Thestartersheetsaredepositedonthetitaniummotherblanks.Atfirst,thedeposithasanunorientateddisturbancezonethathasformedagainstthetitaniumblank.Thenthestructurechangestoafieldorientatedstructurehavingasmoothgrowthoflong,thincrystals.4.1镍沉积物的结构在电解过程中,希望得到的沉积物结构应该具有很细的纹理和颗粒并且取向较好,才能获得不发生形变的镍始极片和镍板。图2是镍始极片典型的沉积物结构,镍始极片是在钛种板上面沉积生长的。一开始沉积物形成一个无规律和取向的区域,之后沉积结构变得有取向性并平滑的形成长而薄的晶体。BoththecurrentefficiencyandthecrystalstructureofthenickeldepositdefinetheoptimumpHrangeforelectrodepositionofnickel.Inaddition,thepurityoftheelectrolyteisessentialtogetagooddeposit.Theimpuritiescodepositmainlyunderdiffusioncontrol.Thecontroloftheirconcentrationsgivesanadequatepurityforthenickeldeposit.Impurityelementsnoblerthannickelshouldbeaslowaspossibletodecreasetheircodepositionwithnickel.Forexample,ifthecobaltconcentrationis10mg/Lintheelectrolyte,200ppmofcobaltisfoundinthenickeldeposit.电流效率和镍沉积物晶体结构两者共同限定了镍电解过程最合适的pH值范围。除此之外,为了获得较好的镍沉积物,电解液纯度也非常重要。在扩散控制的作用下,各种杂质会与镍共同沉积。控制杂质离子的浓度才能提高镍沉积物的纯度。活性比镍低的杂质元素含量应尽可能低以防止它们与镍共同沉积。比如,如果电解液中钴离子浓度为10mg/L,则镍沉积物中的钴含量会达到200ppm。Inadditiontometallicimpurities,solids,organicsornon-metalliccompoundslikeseleniumorsulphurcompoundsareharmfulinthenickelelectrolyte.Theyalsocodepositwithnickelortheychangethecrystalstructuresothatthenickelisstrained.Agoodexampleofstrainingisselenium,whichshouldbelessthan0.5mg/Lintheelectrolyteinordertohaveasmoothdeposit.Athigherconcentrationsthehardnessandtensionofthedepositincreasesothatthestartersheetsandcathodesaredifficulttohandle.除了金属杂质外,溶液中的固体颗粒、有机物、非金属杂质如硒或硫化物对电镍都有坏处。它们与镍会共同沉积,并且改变晶体结构,使得镍产生应变。一个会产生应变的离子便是硒元素,在溶液中浓度应低于0.5mg/L以获得平滑的镍沉积物。当浓度升高时,镍沉积物的硬度和张力增加,使得始极片和电镍都很难加工处理。Organicimpuritiestendtoabsorbonthesurface,hinderingthenickeldepositionandcausingpittingofthecathodes.Theabsorptionoforganicstendalsotopromotehydrogenevolutionintheabsorbedareas.Thesolidparticlesshouldalsobecontrolledwithproperfiltration.Otherwise,thesuspendedsolidsabsorbonthesurfacesofthecathode,causingdisturbanceinthenickeldepositionwhichcanbeobservedasdendritesornodulesonthesurfaceofthecathode.有机物杂质会在镍板表面吸附,阻碍镍离子的沉积,并且在镍板表面形成凹痕。有机物的吸附同时会在吸附区域促进析氢反应发生。固体颗粒也应该用合适的过滤设备过滤干净,否则,固体颗粒吸附在镍板表面,会干扰镍的沉积,镍板上会形成结粒。4.2ConstructionoftheelectrolysiscellDuringelectrolysistheanodicreactionproduceshydrogenionsintheelectrolyteandincreasestheacidconcentrationasthenickelisreducedatthecathode.Tokeepalowacidconcentrationinthevicinityofthecathodeandtoavoidhydrogenevolutionatthecathode,diaphragmelectrolysismustheused.Thediaphragmpreventstheanolyteandcatholytefrommixing.4.2电解槽结构在电解过程中,阳极反应产生氢离子,溶液中酸浓度增加,镍离子在阴极上还原析出。为保持阴极周围的酸度较小,避免阴极上发生析氢反应,必须采用隔膜电解工艺。隔膜袋阻止阳极液和阴极液混合。Thecathodesstandinadiaphragmbagandthecatholyte,havingalowacidconcentration,isfedintothebag.Thecatholyteflowsthrougharotameterfromacatholytedistributionpipewhichislocatedatthesideofthecell.Themixingofcatholyteandanalyteisalsopreventedwiththehydrostaticheaddifference;thepermeabilityofthediaphragmclothallowsthesolutionflowfromcathodespacetoanodespace.Thehydrostaticheaddifferenceassureskeepingtheacidnickelsulphatesolutionoutsidethecathodespaceandthusavoidstheevolutionofhydrogen.阴极放置于隔膜袋内,含酸浓度较低的阴极液流入阴极室。阴极液从电解槽旁边的上液总管流经一个转子流量计。利用阴极液和阳极液的静压头不同而阻止它们相混合；隔膜袋的渗透性允许溶液从阴极室流入阳极室。静压头的不同保证阴极室外的酸性硫酸镍溶液不进入阴极室而避免析氢反应发生。AtHarjavaltarefinery,thecatholyteflowisabout12L/hintoonecathodebagandthedecreaseofnickelionconcentrationordelta-Niis30g/L.Respectively,theacidconcentrationisincreasedby在哈贾瓦尔塔精炼厂,进入每个隔膜袋的阴极液流量为12L/h,镍离子降低的量或者说镍差为30g/L。相应的,阳极室内酸浓度增加量为50g/L。图3显示了哈贾瓦尔塔精炼厂电解槽的截面结构。5.DescriptionofthenickelprocessatHarjavaltaworksAnoverallflowsheetofthenickelproductionprocessatHarjavaltaisshowninFig.4.Theprocessconsistsofanickelsmelterandtherefinery.Thenickelconcentrateismeltedintheflashsmeltingfurnacewhichproducesahighgradenickelmatte.Theslagfromtheflashfurnaceiscleanedintheelectricfurnacewhichproducesiron-containingnickelmatte.5、哈贾瓦尔塔精炼厂镍生产流程描述图4是哈贾瓦尔塔精炼厂总体的镍生产流程。流程主要由镍熔炼和精炼组成。镍精矿在闪速炉进行熔炼并产出高冰镍。闪速炉产出的炉渣在电炉进行净化并产出含铁冰镍。Thegranulatedmattesfromtheflashfurnaceandtheelectricfurnacearethestartingmaterialsforthenickelrefinerywhereaftergrinding,themattesareleachedintheseparatecircuits.Theproductsolutionfromtheleachingplantisledtoasolventextraction<SX>processforcobaltseparation.TheSXplanthasreplacedtheformercobaltremovalprocess/19,20/wherethecobaltwasprecipitatedascobaltichydroxide.Therearetwofinalproducts:cathodenickelproducedintheelectrowinningstepandnickelbriquettesproducedinthehydrogenreductionstep.Therearealsofacilitiesforhydrogenreductionofcobalt.从闪速炉和电炉产出的颗粒状的冰镍是镍精炼的初始原料,经过磨矿后分别进入不同的生产流程进行浸出。浸出液进入溶剂萃取工序〔SX进行镍钴分离。现在的溶剂萃取设备已经取代了原有的除钴方法即中和水解除钴。最终有两种产品：电解法生产的电积镍和氢还原法生产的镍砖。精炼厂同样有氢还原生产钴的设备。5.1SmeltingTheprimaryfeedtothenickelsmelterisamixtureofdifferentnickelconcentrates.Afterdrying,thefeedmixtureandoxygen-enrichedairarefedintothereactionshaftofthenickelflashsmeltingfurnace<FSF>.ThemeltingproducesahighgradeFSFmatteandslag.TheFSFmatteisgranulateddirectlyinwater,dewatered,screenedandfedtotheleachingplant.Theslagfromtheflashsmeltingfurnaceistappedintotheelectricfurnace<EF>forcleaning.ThefurnaceproducesahighironEFmatteandslag.TheEFmatteisalsogranulatedandthegranulatedmatteisleachedintheEFmatteleachingplant.TheslagoftheEFfurnaceisalsogranulatedandfinallystoredinslagdumps.Table1givesthecompositionofthetypicalconcentratefeed,FSFmatte,EFmatteandslaps.5.1熔炼进入镍熔炼炉的主要原料是不同的镍精矿。干燥后,镍精矿和富氧进入镍闪速炉。闪速炉产出等级很高的闪速炉镍锍和炉渣。闪速炉镍锍立即投入水中制成颗粒,脱水后再进行筛分并进入浸出设备。闪速炉产出的炉渣进入电炉进行净化。电炉产出高铁电炉镍锍和炉渣。电炉镍锍同样被颗粒化并进入电炉镍锍浸出设备进行浸出。电炉产出的炉渣被颗粒化后最终在炉渣场堆存。表1给出了镍精矿、闪速炉镍锍、电炉镍锍和炉渣的典型成分。表1镍精矿、闪速炉镍锍、电炉镍锍和炉渣的成分Ni%Cu%Fe%S%MgO%SiO2%混合精矿151303068闪速炉镍锍655421＜0.1＜0.1闪速炉熔渣40.5400.2827电炉镍锍506307＜0.1＜0.1电炉熔渣0.30.2420.3931ThesmeltingprocessisknownastheDirectOutokumpuNickelSmeltingProcessorDONProcesswhichstartedoperationin1995/21,22,23,24/.ThebenefitsoftheprocessareinasimplifiedflowsheetandahighgradeSO2flowtotheacidplant.NoconvertersareneededandtherawmaterialswithhighMgOcontentcanbetreated.Also,thecobaltrecoveryoftheDONprocessishigh.镍熔炼过程便是奥托昆普直接镍熔炼流程〔DON流程,这一流程从1995年开始运行〔文献21,22,23,24。此流程的优点是工艺简单,进入制酸系统的SO2浓度高,不需要使用转炉,含MgO高的粗料也可以处理。同时,DON流程中钴的回收率高。5.2LeachingThegranulatedmattesfromtheflashsmeltingfurnace<FSF>andtheelectricfurnace<EF>haveadifferentmineralogyandironcontent.Therefore,themattesareleachedinseparateleachingcircuits.TheFSFmattecontains5%ironandthemainmineralsofthematteareheazlewooditeNi3S2,chalcociteCu2Sandametallicnickel-copperalloy.TheEFmattecontains30%ironandthemainmineralofthematteismetallicnickel-ironalloy.Coppermayalsobepresentinthealloy.Pentlandite<Ni,Fe>9S8isthemajorsulphidecomponentoftheEFmatte.5.2浸出从闪速炉和电炉产出的颗粒状的镍锍〔冰镍有着不同的矿物和铁杂质的组成。因此,冰镍用不同的过程进行浸出。闪速炉冰镍含铁约5%,主要组分是Ni3S2、Cu2S和镍-铜合金相。电炉冰镍含铁约30%,主要组分是镍-铁合金相。铜也进入合金相。电炉冰镍中的硫化物主要是镍黄铁矿<Ni,Fe>9S8。TheflowsheetoftheleachingprocessisshowninFig.5/25/.TheFSFmatteiswetgroundinballmilts.Thefinegroundmatteisthenfedintoatwo-stagecounter-currentleachingprocess.Thefeedisstronglyagitatedinthereactorsandoxygenisusedasaleachingagent.70%oftheincomingnickelisleachedintheatmosphericleach.Therestofthenickelisleachedinthetwostagepressureleach.Thefirstautoclaveworksinnon-oxidisingconditionswherenickeldissolvesandcopperstaysinsolidformassulphide/26/.Inthesecondautoclave,aportionofthecoppersulphideisleachedinstrongoxidationconditionstomaintainthecopperlevelintheleachingcircuit.Therestofthecoppersulphideprecipitateisfedtothecoppersmelter.图5是浸出工艺的流程图〔文献25。闪速炉冰镍在球磨机中湿磨,湿磨完全的冰镍进入一个两级逆流浸出工序。浸出过程中原料反应剧烈,并通入氧气作为氧化剂。常压浸出过程可以将原料中70%的镍浸出。剩余的镍在两级加压浸出工序中浸出。第一级加压釜中不通氧,镍进行溶解,铜以硫化物形式进入固相〔文献26。在第二级加压釜中,一部分硫化铜在强氧化性条件下浸出到溶液中以保证浸出液中的铜离子浓度。剩余的硫化铜沉淀返回铜熔炼。ThegroundEFmatteisleachedinthestrongoxidisingconditionsintheatmosphericleach.Agreatdealofthenickel,cobaltandironisleached,whileironismostlyprecipitatedasasolid.Theleachingprocessiscontinuedinautoclaveswherethenickel,cobaltandcopperareleachedtotally.TheironprecipitateoftheEFmatteleach,goethiteorhematiteisrecirculatedtothenickelflashsmeltingfurnaceandmixedwiththeprimaryconcentratefeed.颗粒状的电炉冰镍在强氧化性条件下进行常压浸出。大部分的镍、钴和铁被浸出,但大部分的铁又形成了铁渣沉淀。固相继续在加压釜中浸出,镍、钴和铜被完全浸出