奧托昆普哈賈瓦爾塔精煉廠鎳電解工藝設(shè)計

./NickelelectrolysisprocessatOutokumpuHarjavaltaMetalsOy奧托昆普哈賈瓦爾塔金屬公司鎳電解工藝AbstractThispaperdealswiththeelectrolysisofnickelfromsulphatesolutionanditselectrochemicalprinciples.Asanexample,thenickelelectrolysisprocessatOutokumpuHarjavaltaMetalsOyisdiscussedinmoredetail.Theleachingofnickelmatteandthepurificationofthenickelsulphatesolutionpriortoelectrolysisisalsodiscussed.Inaddition,ashortreviewofotherhydrometallurgicalnickelmattetreatmentprocessesandnickelelectrolysistechnologiesisgiven.摘要：本論文主要研究了硫酸鎳溶液的電解過程及其電化學(xué)原理。作為例子,本論文主要在細(xì)節(jié)方面討論了奧托昆普哈賈瓦爾塔金屬公司的鎳電解過程。同時也討論了電解過程之前的鎳浸出及凈化過程。除此之外,其它鎳濕法冶金處理過程及電解技術(shù)也在文中涉及到。OutokumpuhasproducedelectrolyticnickelatHarjavaitaworkssince1960.Nickeliselectrowonfromanickelsulphatesolutionusingdiaphragmcellswhereadiaphragmclothisusedtopreventthecatholytesolutionandtheacidicanolytefrommixing.Nickelisdepositedonthinnickelstartersheetsandtheanodesareofunalloyedlead.Thecurrentdensityis200A/m2andthedepositiontimeissevendays.Thereadycathodesweighabout65kgandtheyareharvested,washedandcutintosquaresandstripsandfinallypackedfordelivery.Electrolyticnickelissuppliedtotheelectroplating,meltingandsuperalloyingindustry.早在1960年開始,奧托昆普便在哈賈瓦爾塔工廠開始生產(chǎn)電解鎳。電解鎳是從硫酸鎳溶液中用隔膜電解槽電解產(chǎn)出的,而隔膜布的作用是防止陰極液和陽極液混合。電鎳在很薄的始極片上沉積,而陽極是純鉛陽極。陰極電流密度為200A/m2,陰極周期為7天。達(dá)到生產(chǎn)周期的電解鎳約65kg,經(jīng)出槽、燙洗后剪切成方塊和條狀,最終包裝并發(fā)送至客戶廠家。電解鎳主要用在電鍍、熔煉和超耐熱合金等領(lǐng)域。Inadditiontonickelcathodes,Outokumpuhasalsobeenproducingnickelbriquettessincethelastexpansionin1995.Theexpansionofthenickelproductionhasalsobroughtaboutseveralprocesschangesinthesmelterandtherefinery.Thesmelternowproducestwotypesofnickelmattes,whicharetreatedinseparateleachingplants.Afterleaching,thenickelsolutionistreatedinanewsolventextractionsteptoproduceapurifiednickelsulphatesolutionforelectrolysisandhydrogenreduction.Theannualcapacityofthenickelplantis18,000tonsofcathodesand22,000tonsofbriquettes.除電解鎳之外,奧托昆普從1995年擴(kuò)建之后也開始生產(chǎn)鎳磚。這次擴(kuò)建對冶煉廠和精煉廠都帶來了很多的技術(shù)改革。冶煉廠現(xiàn)生產(chǎn)兩種類型的冰鎳,分別用不同的浸出裝置處理。浸出后,含鎳溶液在新的溶劑萃取工序處理,并產(chǎn)出純凈硫酸鎳溶液用來進(jìn)行電解和氫還原。鎳廠生產(chǎn)能力為18000t/a的電解鎳和22000t/a的鎳磚。1.IntroductionNickelisanimportantalloyingelementinthemetalindustry.Morethan70%ofthenickelisconsumedinstainlessandalloyingsteels/1/.Othermainusesofnickelarenon-ferrousalloys<11%>andcorrosionresistantanddecorativeplatedcoatings<8%>.Theworldprimarynickeldemandwas928000tonsin1996/2/.1、簡介鎳是金屬工業(yè)中一種非常重要的元素。超過70%的鎳消費(fèi)于不銹鋼行業(yè)和合金行業(yè)〔文獻(xiàn)1。鎳的其它用途有非鐵合金〔11%和防腐蝕以及裝飾性電鍍〔8%。在1996年,全球鎳需求量為92.8萬噸/年〔文獻(xiàn)2。Nickelisrefinedfromsulphideorlateriteores.About60%ofthenickelisminedfromsulphidedepositsand40%fromlateritedeposits/3/.Inlateriteoresnickelisboundinironoxideorsilicacompoundsfromwhichitisdifficulttoupgrade.Therefore,directsmeltingoforeisgenerallyusedtoproduceferronickelornickelmatte.Directleachingoflateritewithammoniaorsulphuricacidisalsoused.Studiesonthehydrometallurgicalprocessingoflateriteoreshavebeenverynumerousrecentlyandvariousnewleachingandrefiningprocesseshavebeenproposed.Also,severalminingprojectsonlateritesareunderway.鎳主要從硫化礦或紅土礦中提取。目前約60%的鎳是從硫化礦中提取,40%的鎳從紅土礦中提取〔文獻(xiàn)3。由于紅土礦中鎳表面被氧化鐵或氧化硅覆蓋而難以提煉,因此礦石被直接冶煉生產(chǎn)鎳鐵或冰鎳。也可從紅土礦中由氨或硫酸直接進(jìn)行鎳浸出。目前對于紅土礦濕法冶金過程有很多研究,并且提出了很多新的浸出和精煉過程。同時,很多公司正在開展紅土礦采礦工程。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.典型的含鎳硫化礦有鎳黃鐵礦<Ni,Fe>9S8、磁黃鐵礦Fe1-xS和針鎳硫礦NiS。硫化鎳礦可以通過浮選來濃縮并提升鎳含量,獲得含Ni約7～25%的鎳精礦。鎳精礦一般通過冶煉富集其中的鐵和氧化鎂,并將其轉(zhuǎn)化為硅酸鐵爐渣。鎳則成為含Ni35～70%的硫化冰鎳。冰鎳中主要含有六方硫鎳礦Ni3S2、輝銅礦Cu2S和Ni-Cu合金。冰鎳中含有的其它主要金屬有鈷、銅和鉑族金屬。Becauseofvaluablesidemetalsandalsobecauseofharmfulimpurityelements,nickelmattemustgothroughamulti-stagerefiningprocess.Generally,matteistreatedbyhydrometallurgyconsistingofoxidationofmatteinleachingorinelectrorefining,purificationofthenickelsolutionandrecoveryofhighgrademetallicnickelbyelectrolysisorhydrogenreduction.由于冰鎳中含有很多其它金屬,并且很多金屬為有害金屬,因此冰鎳必須經(jīng)過一個多級精煉過程。一般來說,冰鎳需經(jīng)過由冰鎳氧化浸出或電解、鎳溶液提純組成的濕法冶金流程,再通過電解或氫還原工藝得到高等級的金屬鎳。2.HydrometallurgicalmatterefiningprocessesHydrometallurgicalprocessestorefinenickelmattecanbespecifiedasfollows/4,5,6,7,8/:1>Matteelectrolysis.Castnickelmatteanodesaredissolvedinadiaphragmelectrolysiscellusingachloride/sulphateelectrolyte.Theelectrolytefromtheanodecompartmentiscirculatedthroughthesolutionpurificationbeforefeedingtothecathodebag.Alsotheanodesarebaggedtocollectthesulphur-containinganodeslimeoftheanode.TheprocessisinuseatInco'sThompsonrefineryinCanada/9/.2、冰鎳精煉濕法冶金過程以下是幾種冰鎳精煉濕法過程的詳細(xì)說明〔文獻(xiàn)4、5、6、7、8：1冰鎳電解。將冰鎳澆筑成陽極板并在隔膜電解槽中用氯化物-硫酸鹽溶液進(jìn)行電解。陽極液循環(huán)經(jīng)過溶液凈化過程后再進(jìn)入隔膜袋進(jìn)行電解。陽極同樣套袋以收集含有硫磺的陽極泥。加拿大Inco公司湯普森精煉廠便采用此流程。2>Chlorideleachprocessofmatteandelectrowinning.Matteisleachedinachloridesolutionusingchlorinegasasanoxidant.Thechlorinegasisgeneratedintheelectrowinningcells.Theprocessisinoperatione.g.atFalconbridge'srefineryinKristiansandinNorway,Sumitomo'sNiihamarefineryinJapanandatEramet'srefineryinSandouvilleinFrance/9,10,11,12,13/.2冰鎳氯化浸出-電解流程。冰鎳在氯化物溶液中使用氯氣作為氧化劑進(jìn)行浸出。氯氣是在電解過程中產(chǎn)出的副產(chǎn)物。挪威克里斯蒂安松鷹橋精煉廠、日本住友新居濱精煉廠和法國桑杜維爾埃赫曼精煉廠都采用這一流程。3>Atmosphericacidleachandelectrowinning.Matteisleachedinacidsulphatesolutioninoxygenorair-spargedleachvessels.Aftertheatmosphericleach,atwo-stagepressureleachfollowstodecreasethenickelcontentintheresidueandtooxidiseaportionofthecoppersulphidetocirculatethedissolvedcopperinatmosphericleaching.Thenickelsulphatesolutionispurifiedbysolventextractionorbycobaltichydroxideprecipitation.Thenickelisprecipitatedascathodesintheelectrowinningprocess.TheatmosphericacidleachandthesulphateelectrowinningprocesshavebeendevelopedbyOutokumpuOyandthesemethodsareusede.g.byBindura,EmpressandHartleyrefineriesinZimbabweandbyOutokumpuatHarjavaitaWorksinFinland/4,5,14/.3常壓酸浸-電解流程。冰鎳在氧氣或空氣噴射入浸出槽中,并用硫酸溶液進(jìn)行浸出。常壓浸出后,繼續(xù)進(jìn)行兩段加壓浸出,以降低浸出渣中鎳含量,同時將一部分硫化銅氧化,并將溶解的銅返回常壓浸出。硫酸鎳溶液通過溶劑萃取法或鈷的氫氧化物沉淀法凈化。經(jīng)凈化后的溶液在電解工序產(chǎn)出電解鎳。常壓酸浸-硫酸鎳電解流程是奧托昆普公司研發(fā)的,津巴布韋的Bindura、Empress和Hartley精煉廠以及芬蘭奧托昆普哈賈瓦爾塔廠均采用這一流程。4>Ammoniapressureleachandhydrogenreduction.Matteisleachedintoammoniacalammoniumsulphatesolutioninpressureautoclavesusingairasanoxidant.Afterthesulphideprecipitationofcopper,nickelsolutionisreducedwithhydrogeninthereductionautoclavestoproducemetallicnickelpowder.Theammoniumsulphateforminginthehydrogenreductionisrecoveredbycrystallisation.Afterthehydrogenreductiontherestofthedissolvednickelandallthecobaltareprecipitatedwithhydrogensulphide.ThisprocessisknownastheSherrittGordonProcess/15/anditisappliedatSherritt'sFortSaskatchewanplantinCanadaandatWMC'sKwinanarefineryinAustralia4加壓氨浸和氫還原。冰鎳在加壓浸出釜中以硫酸銨溶液并通入空氣作為氧化劑進(jìn)行浸出。經(jīng)過硫化物除銅,含鎳溶液在還原釜中用氫氣還原生成金屬鎳粉。氫還原過程中生成的硫酸銨通過結(jié)晶回收。經(jīng)過氫還原后,游離的鎳和所有的鈷用硫化氫氣體沉淀。這一過程便是謝里特戈登法,加拿大謝里特的福特薩斯喀徹溫廠和澳大利亞奎那那廠均使用這一方法。5Acidpressureleachandhydrogenreduction.Matteisleachedwithspentcopperelectrowinningelectrolyteusingpressureautoclavesandairasanoxidant.Aftertheleaching,copperandironareprecipitated.Thenthenickelsolutionisammoniatedforhydrogenreduction.TheprocesswasdevelopedbySherrittGordonandisoperatede.g.byImpalaPlatinuminSouthAfrica/8/.RustenburgPlatinuminSouthAfricaalsousestheacidpressureleachbutmetallicnickelisdepositedwiththeelectrowinningprocess/16,17/.5加壓酸浸和氫還原。冰鎳在加壓釜中用廢銅電解液并通入空氣作為氧化劑進(jìn)行浸出。浸出后,銅和鐵被沉淀,含鎳溶液被氨化以備氫還原。這一流程是由謝里特戈登研發(fā)出的。南非因帕拉鉑金廠便使用此法〔文獻(xiàn)8。南非里斯騰堡鉑金廠同樣應(yīng)用加壓酸浸法,但通過電解法生產(chǎn)電鎳〔文獻(xiàn)16,17。3.NickelelectrolysisprocessesAllelectrolyticnickelproductionprocessesuseadiaphragmcelloriginallydevelopedbyNorwegianchemistN.V.Hybinetteatthebeginningof1900's/18/.TheHybinettecellwasdevelopedforelectrolyticrefiningofcastmatteanodes.Inthecell,theanodeandcathodeareseparatedbyapermeablediaphragmcloth.Thematteanodedissolvesintheanodebagandtheelectrolytewiththedissolvedimpuritiesoftheanodeisfedtosolutionpurification.Thepurifiednickelsolutionisfedintothecathodecompartmentoftheelectrolysiscell.Thehydrostaticpressuredifferencebetweencathodeandanodesolutionspreventsthesolutionsfrommixing.TheHybinetteprocesswasfirstintroducedattheKristiansandrefinerywherematterefiningelectrolysiswasintroducedin1910.3、鎳電解流程所有的鎳電解流程都使用隔膜電解法,這一方法是挪威化學(xué)家N.Y.Hybinette在1900年左右首先提出的。Hybinette電解槽開始時是為冰鎳澆筑陽極〔可溶陽極而研發(fā)的。電解槽中,陽極和陰極用一個具有滲透性的隔膜布隔開。冰鎳陽極在陽極袋中溶解,含有各類雜質(zhì)的電解液進(jìn)入溶液凈化工序。經(jīng)過凈化后的電解液進(jìn)入電解槽的陰極室。溶液靜壓力的不同阻止了陰極液和陽極液混合。Hybinette電解流程于1910年首先在克里斯蒂安松精煉廠使用。3.1MatteelectrolysisMatteelectrolysisiscarriedoutinamixedchloride-sulphatesolution.Theprincipalanodicreactionisoxidationofheazlewoodite,asshowninreaction<1>.Onthesurfaceoftheanodeasulphur-containinganodelayerisformed.Thesulphurlayercausesanodicpolarisationastheanodedissolves.3.1冰鎳電解冰鎳電解是在氯化物-硫酸鹽混酸體系中進(jìn)行的。主要的陽極反應(yīng)是Ni3S2的氧化,如方程式〔1所示。隨著反應(yīng)進(jìn)行,陽極表面形成一層含硫?qū)印碴枠O泥。陽極泥層在陽極溶解過程中引起陽極極化。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公司湯普森精煉廠的陽極約重250kg〔文獻(xiàn)9。電流密度為240A/m2,槽電壓為3～6V,槽電壓取決于陽極泥厚度。凈化后的電解液含有75g/LNi2+、51g/LCl-和120g/LS042-。電解液中加入硼酸作為pH值緩沖劑。陰極周期為10天,陽極周期為15天。陰極上沉積的鎳要比陽極溶解的鎳多。為保證溶液體系鎳平衡,在空氣攪拌槽中浸出一部分磨細(xì)的冰鎳。湯普森精煉廠年產(chǎn)電解鎳55000t。3.2ChlorideelectrowinningTheFalconbridgeChlorineLeachProcesswasinstalledatKristiansandrefineryattheendofthe1970'storeplacematteelectrolysis/10,11/.Theanodicreactionoftheelectrolysisistheevolutionofchlorinegas,whichisusedasanoxidantintheleachingofgroundmatte.Afterleaching,ironisprecipitated.Cobaltisrecoveredbysolventextractionandelectrowinning.Thenickelsolutionfromleachingcontains230g/Lnickelwhichisdilutedwiththedechlorinatedanolyteto85g/L.AfterthefinalpurificationthenickelchloridesolutionisfedtotheEWtanks.Anodesareseparatedfromthecathodecellcompartmentwithadiaphragm.Thechlorinegasvacuumintheanodesidekeepsthehydrostaticheadandthecatholyteflowstotheanodecompartment.TheanodesareDSAanodes<dimensionalstableanodes>.Thecapacityofthetankhouseis68,000tpaascathodesandcrowns.3.2氯化電積二十世紀(jì)七十年代末期,鷹橋氯化浸出工藝在克里斯蒂安松精煉廠應(yīng)用,并取代了冰鎳電解流程〔文獻(xiàn)10,11。電積過程的陽極反應(yīng)是氯氣的析出,氯氣回收后作為磨細(xì)冰鎳浸出的氧化劑。浸出后,鐵被沉淀。鈷被溶劑萃取回收并以電解方法產(chǎn)出。浸出液中含鎳為230g/L,用除氯后的陽極液稀釋至85g/L。在最終凈化后,氯化鎳溶液進(jìn)入電積槽陰極室。陽極和陰極用隔膜袋隔開。陽極產(chǎn)生的氯氣被抽出以保證陽極室內(nèi)靜壓頭較小,陰極液流入陽極室內(nèi)。陽極是DSA陽極〔固定尺寸陽極。電解產(chǎn)能為每年68000t的電積鎳和鎳冠。SumitomochangedfromthematteelectrolysisprocesstoMatteChlorineLeachandElectrowinning<MCLE>atitsNiihamarefineryin1993/12/.TheoutlineoftheprocessisinprincipalthesameasintheFalconbridgeprocess.Copperisremovedasaformofcopperpowderbyelectrowinning.CobaltandironareremovedashydroxideprecipitateusingCl2asanoxidantandbyneutralisingwithnickelcarbonate.1993年,日本住友公司新居濱精煉廠將其冰鎳電解流程改為冰鎳氯氣浸出-電積流程〔MCLE〔文獻(xiàn)12。其主要流程與鷹橋流程基本相同。銅雜質(zhì)是用電解法生產(chǎn)銅粉而除去。鈷和鐵雜質(zhì)是用Cl2作為氧化劑并通入碳酸鎳中和水解除去。TheMCLEcellsareequippedwithDSAanodesandeachcellhas53anodesand52cathodes/13/.Electrolyteisfedfromonesideofthecellandabout30%ofthefeedelectrolyteoverflowsfromtheotherside.Therestoftheelectrolytepassesthroughthediaphragmbagintotheanodecompartmentandiswithdrawnbyvacuumwithchlorinegasgeneratedattheanode.Theelectrolytecontains70g/LNi2+and85g/LCl-.About10g/LnickelisdepositedintheEWcircuit.Nickelisdepositedonthestartingsheetplatesthataredepositedonatitaniummotherblank.Thecurrentdensityisintherangeof230-250A/m2andthecellvoltageis3.1V.Thecathodelifeis7or8days,dependingonthecurrentdensity.Thetankhousehas168nickelelectrolysiscells.Theproductioncapacityis30,000tpa.冰鎳氯氣浸出-電積流程的電積槽中使用固定尺寸陽極,每個電積槽有53塊陽極和52塊陰極〔文獻(xiàn)13。電解液從陰極室的一側(cè)流入,約30%的陰極液會從另一側(cè)溢出流走。剩余的陰極液經(jīng)過隔膜袋進(jìn)入陽極室,并隨著陽極產(chǎn)生的氯氣被抽真空抽走。陰極液含有70g/LNi2+和85g/LCl-。約10g/L的Ni2+在陰極沉積。鎳是在用鈦種板產(chǎn)出的始極片上面沉積。電流密度為230～250A/m2,槽電壓為3.1V。陰極周期為7～Eramet'snickelrefineryinSandouville,Francealsousesachlorideelectrowinningprocess/9/.Therefinerywascommissionedin1978.Inleachingofmattethelixiviantisferricchlorideandironisreoxidisedusingchlorinegasfromtheanodecompartmentoftheelectrolysiscell.Ferricironisextractedfromthenickelchloridesolutionbysolventextraction,isstrippedandrecycledtoleach.Cobaltisalsorecoveredwithsolventextraction.Nickelisdepositedascathodeplatesusingthestarter法國桑杜維爾埃赫曼精煉廠同樣也采用氯氣電積流程〔文獻(xiàn)9,精煉廠于1978年投產(chǎn)。冰鎳浸出過程中浸出劑是氯化鐵,鐵元素被電積槽陽極室內(nèi)生成的氯氣重新氧化。鐵離子在溶劑萃取過程中被萃取,反萃后再返回浸出過程。鈷也在萃取過程中被萃取。電積廠房有80個電積槽,年產(chǎn)量為13000t電積鎳。3.3SulphateelectrowinningOutokumpuwasthefirsttointroduce,onanindustrialscale,thesulphateelectrowinningprocessfornickelusinginsolubleleadanodesin1960.Outokumpuhaddevelopedamattetreatmentprocesswhichwasbasedonleachingofgroundmattetoasulphatesolution.Thismeantthatacompatibleelectrolysisprocesswithleachingalsohadtobedeveloped.ThenickelsmelterandrefinerywasbuiltatOutokumpu'sHarjavaltaworks,whereacoppersmelteralreadyexisted.3.3硫酸鹽電解奧托昆普公司于1960年首次使用不溶陽極并采用硫酸鹽電解流程生產(chǎn)電積鎳,并形成工業(yè)規(guī)模。奧托昆普公司將冰鎳磨細(xì)后進(jìn)行浸出并生成硫酸鎳溶液。這意味著電積過程和浸出過程要兼容。鎳熔煉廠和精煉廠均設(shè)在奧托昆普哈賈瓦爾塔廠,而此前這里已經(jīng)有銅熔煉廠存在。TheelectrochemicalprinciplesofelectrowinninginnickelsulphatesolutianandtherefineryoperationsatOutokumpuHarjavaltaMetalsOyarediscussedinmoredetailinthefollowingchapters.在后面章節(jié)中將詳細(xì)介紹奧托昆普哈賈瓦爾塔金屬公司的硫酸鹽溶液電積過程電化學(xué)原理和精煉操作流程。4.CharacteristicsofelectrowinninginnickelsulphatesolutionIntheelectrowinningprocess,nickelisprecipitatedfromanickelsulphatesolutionintometallicformbyelectriccurrent.Thecatholicreactionisthereductionofnickelionsonthecathodeandtheanodicreactionistheoxidationofwateronthesurfaceoftheleadanode.Electrolysisreactionscanbedescribedbythefollowingoverallreactions:4、硫酸鎳溶液電積過程的特點(diǎn)在電積過程中,硫酸鎳溶液中的鎳離子通過電流作用沉積為金屬鎳。陰極反應(yīng)是鎳離子在陰極上還原析出,陽極反應(yīng)是水在鉛陽極上氧化分解。電極反應(yīng)可用以下方程式表示：陰極反應(yīng)： Ni2++2e-===Ni0 <2>陽極反應(yīng)： H2O===2H++1/2O2+2e- <3>電極反應(yīng)： NiSO4+H2O===Ni0+H2SO4+1/2O2 <4>Becausenickelislessnoblethanhydrogenintheelectrochemicalseriesandthereductionoverpotentialfornickelishigherthanthatforhydrogen,hydrogenevolutionisapreferentialreactionandapartoftheelectriccurrentisconsumedinthehydrogenevolutionreaction:由于在電化學(xué)過程中鎳元素比氫元素的活性高,鎳的還原超電勢也要比氫的高,因此在電積過程中析氫反應(yīng)是首先發(fā)生的,一部分的電流消耗在析氫反應(yīng)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.為減小析氫反應(yīng),溶液的pH值必須足夠高以保證鎳沉積時的電流效率。圖1顯示了不同pH值下鎳還原的極化曲線。曲線表明,氫離子濃度越高,氫的還原峰越高,還原電勢位于－600～－650mV。還原峰表示了氫離子的活性。pH值在2.5或更高時,析氫反應(yīng)比較小,主要反應(yīng)是鎳離子的沉積。在不同pH值下電流效率的研究同樣證明了這一現(xiàn)象。在電流密度為200A/m2的條件下,當(dāng)pH值為3.0時,鎳沉積電流效率為97%,當(dāng)pH值為2.5時鎳沉積效率為94%。當(dāng)pH值小于2.0或者更低時,電流效率大幅度下降。Fig.1alsoshowsthatthepolarisationcurvesshifttomorepositivevalueswhenthepHdecreases.Theshiftis60mVperonepHunit,whichisameasureoftheactivityofhydrogenionsaccordingtotheNernstequation.WhenthepHvalueistoohigh,thereisadangerthatnickelhydroxidewillbedepositedwithnickel.Hydroxideprecipitationcausesdisturbancesinthecrystalstructureofnickelwhichcanbenoticedastension,brittlenessorhardeningofthedeposit.圖1同時顯示當(dāng)pH值減小時,極化曲線趨向于更正的值。移動值是每個pH值單位變化60mV,這也是根據(jù)能斯特方程計算出的氫離子的活度變化。當(dāng)pH值太高時,將會有形成氫氧化鎳的可能性。氫氧化鎳會影響鎳沉積物晶體結(jié)構(gòu)的張力、脆性和硬度。4.1StructureofthedepositIntheelectrolysisprocessthedesireddepositionstructureshouldbefinegrainedandwellorientatedtogetunstrainednickelplatesbothinstartersheetcellsandincommercialcells.Fig.2showsatypicaldepositionstructureofthenickelstartersheet.Thestartersheetsaredepositedonthetitaniummotherblanks.Atfirst,thedeposithasanunorientateddisturbancezonethathasformedagainstthetitaniumblank.Thenthestructurechangestoafieldorientatedstructurehavingasmoothgrowthoflong,thincrystals.4.1鎳沉積物的結(jié)構(gòu)在電解過程中,希望得到的沉積物結(jié)構(gòu)應(yīng)該具有很細(xì)的紋理和顆粒并且取向較好,才能獲得不發(fā)生形變的鎳始極片和鎳板。圖2是鎳始極片典型的沉積物結(jié)構(gòu),鎳始極片是在鈦種板上面沉積生長的。一開始沉積物形成一個無規(guī)律和取向的區(qū)域,之后沉積結(jié)構(gòu)變得有取向性并平滑的形成長而薄的晶體。BoththecurrentefficiencyandthecrystalstructureofthenickeldepositdefinetheoptimumpHrangeforelectrodepositionofnickel.Inaddition,thepurityoftheelectrolyteisessentialtogetagooddeposit.Theimpuritiescodepositmainlyunderdiffusioncontrol.Thecontroloftheirconcentrationsgivesanadequatepurityforthenickeldeposit.Impurityelementsnoblerthannickelshouldbeaslowaspossibletodecreasetheircodepositionwithnickel.Forexample,ifthecobaltconcentrationis10mg/Lintheelectrolyte,200ppmofcobaltisfoundinthenickeldeposit.電流效率和鎳沉積物晶體結(jié)構(gòu)兩者共同限定了鎳電解過程最合適的pH值范圍。除此之外,為了獲得較好的鎳沉積物,電解液純度也非常重要。在擴(kuò)散控制的作用下,各種雜質(zhì)會與鎳共同沉積?？刂齐s質(zhì)離子的濃度才能提高鎳沉積物的純度?；钚员孺嚨偷碾s質(zhì)元素含量應(yīng)盡可能低以防止它們與鎳共同沉積。比如,如果電解液中鈷離子濃度為10mg/L,則鎳沉積物中的鈷含量會達(dá)到200ppm。Inadditiontometallicimpurities,solids,organicsornon-metalliccompoundslikeseleniumorsulphurcompoundsareharmfulinthenickelelectrolyte.Theyalsocodepositwithnickelortheychangethecrystalstructuresothatthenickelisstrained.Agoodexampleofstrainingisselenium,whichshouldbelessthan0.5mg/Lintheelectrolyteinordertohaveasmoothdeposit.Athigherconcentrationsthehardnessandtensionofthedepositincreasesothatthestartersheetsandcathodesaredifficulttohandle.除了金屬雜質(zhì)外,溶液中的固體顆粒、有機(jī)物、非金屬雜質(zhì)如硒或硫化物對電鎳都有壞處。它們與鎳會共同沉積,并且改變晶體結(jié)構(gòu),使得鎳產(chǎn)生應(yīng)變。一個會產(chǎn)生應(yīng)變的離子便是硒元素,在溶液中濃度應(yīng)低于0.5mg/L以獲得平滑的鎳沉積物。當(dāng)濃度升高時,鎳沉積物的硬度和張力增加,使得始極片和電鎳都很難加工處理。Organicimpuritiestendtoabsorbonthesurface,hinderingthenickeldepositionandcausingpittingofthecathodes.Theabsorptionoforganicstendalsotopromotehydrogenevolutionintheabsorbedareas.Thesolidparticlesshouldalsobecontrolledwithproperfiltration.Otherwise,thesuspendedsolidsabsorbonthesurfacesofthecathode,causingdisturbanceinthenickeldepositionwhichcanbeobservedasdendritesornodulesonthesurfaceofthecathode.有機(jī)物雜質(zhì)會在鎳板表面吸附,阻礙鎳離子的沉積,并且在鎳板表面形成凹痕。有機(jī)物的吸附同時會在吸附區(qū)域促進(jìn)析氫反應(yīng)發(fā)生。固體顆粒也應(yīng)該用合適的過濾設(shè)備過濾干凈,否則,固體顆粒吸附在鎳板表面,會干擾鎳的沉積,鎳板上會形成結(jié)粒。4.2ConstructionoftheelectrolysiscellDuringelectrolysistheanodicreactionproduceshydrogenionsintheelectrolyteandincreasestheacidconcentrationasthenickelisreducedatthecathode.Tokeepalowacidconcentrationinthevicinityofthecathodeandtoavoidhydrogenevolutionatthecathode,diaphragmelectrolysismustheused.Thediaphragmpreventstheanolyteandcatholytefrommixing.4.2電解槽結(jié)構(gòu)在電解過程中,陽極反應(yīng)產(chǎn)生氫離子,溶液中酸濃度增加,鎳離子在陰極上還原析出。為保持陰極周圍的酸度較小,避免陰極上發(fā)生析氫反應(yīng),必須采用隔膜電解工藝。隔膜袋阻止陽極液和陰極液混合。Thecathodesstandinadiaphragmbagandthecatholyte,havingalowacidconcentration,isfedintothebag.Thecatholyteflowsthrougharotameterfromacatholytedistributionpipewhichislocatedatthesideofthecell.Themixingofcatholyteandanalyteisalsopreventedwiththehydrostaticheaddifference;thepermeabilityofthediaphragmclothallowsthesolutionflowfromcathodespacetoanodespace.Thehydrostaticheaddifferenceassureskeepingtheacidnickelsulphatesolutionoutsidethecathodespaceandthusavoidstheevolutionofhydrogen.陰極放置于隔膜袋內(nèi),含酸濃度較低的陰極液流入陰極室。陰極液從電解槽旁邊的上液總管流經(jīng)一個轉(zhuǎn)子流量計。利用陰極液和陽極液的靜壓頭不同而阻止它們相混合；隔膜袋的滲透性允許溶液從陰極室流入陽極室。靜壓頭的不同保證陰極室外的酸性硫酸鎳溶液不進(jìn)入陰極室而避免析氫反應(yīng)發(fā)生。AtHarjavaltarefinery,thecatholyteflowisabout12L/hintoonecathodebagandthedecreaseofnickelionconcentrationordelta-Niis30g/L.Respectively,theacidconcentrationisincreasedby在哈賈瓦爾塔精煉廠,進(jìn)入每個隔膜袋的陰極液流量為12L/h,鎳離子降低的量或者說鎳差為30g/L。相應(yīng)的,陽極室內(nèi)酸濃度增加量為50g/L。圖3顯示了哈賈瓦爾塔精煉廠電解槽的截面結(jié)構(gòu)。5.DescriptionofthenickelprocessatHarjavaltaworksAnoverallflowsheetofthenickelproductionprocessatHarjavaltaisshowninFig.4.Theprocessconsistsofanickelsmelterandtherefinery.Thenickelconcentrateismeltedintheflashsmeltingfurnacewhichproducesahighgradenickelmatte.Theslagfromtheflashfurnaceiscleanedintheelectricfurnacewhichproducesiron-containingnickelmatte.5、哈賈瓦爾塔精煉廠鎳生產(chǎn)流程描述圖4是哈賈瓦爾塔精煉廠總體的鎳生產(chǎn)流程。流程主要由鎳熔煉和精煉組成。鎳精礦在閃速爐進(jìn)行熔煉并產(chǎn)出高冰鎳。閃速爐產(chǎn)出的爐渣在電爐進(jìn)行凈化并產(chǎn)出含鐵冰鎳。Thegranulatedmattesfromtheflashfurnaceandtheelectricfurnacearethestartingmaterialsforthenickelrefinerywhereaftergrinding,themattesareleachedintheseparatecircuits.Theproductsolutionfromtheleachingplantisledtoasolventextraction<SX>processforcobaltseparation.TheSXplanthasreplacedtheformercobaltremovalprocess/19,20/wherethecobaltwasprecipitatedascobaltichydroxide.Therearetwofinalproducts:cathodenickelproducedintheelectrowinningstepandnickelbriquettesproducedinthehydrogenreductionstep.Therearealsofacilitiesforhydrogenreductionofcobalt.從閃速爐和電爐產(chǎn)出的顆粒狀的冰鎳是鎳精煉的初始原料,經(jīng)過磨礦后分別進(jìn)入不同的生產(chǎn)流程進(jìn)行浸出。浸出液進(jìn)入溶劑萃取工序〔SX進(jìn)行鎳鈷分離?，F(xiàn)在的溶劑萃取設(shè)備已經(jīng)取代了原有的除鈷方法即中和水解除鈷。最終有兩種產(chǎn)品：電解法生產(chǎn)的電積鎳和氫還原法生產(chǎn)的鎳磚。精煉廠同樣有氫還原生產(chǎn)鈷的設(shè)備。5.1SmeltingTheprimaryfeedtothenickelsmelterisamixtureofdifferentnickelconcentrates.Afterdrying,thefeedmixtureandoxygen-enrichedairarefedintothereactionshaftofthenickelflashsmeltingfurnace<FSF>.ThemeltingproducesahighgradeFSFmatteandslag.TheFSFmatteisgranulateddirectlyinwater,dewatered,screenedandfedtotheleachingplant.Theslagfromtheflashsmeltingfurnaceistappedintotheelectricfurnace<EF>forcleaning.ThefurnaceproducesahighironEFmatteandslag.TheEFmatteisalsogranulatedandthegranulatedmatteisleachedintheEFmatteleachingplant.TheslagoftheEFfurnaceisalsogranulatedandfinallystoredinslagdumps.Table1givesthecompositionofthetypicalconcentratefeed,FSFmatte,EFmatteandslaps.5.1熔煉進(jìn)入鎳熔煉爐的主要原料是不同的鎳精礦。干燥后,鎳精礦和富氧進(jìn)入鎳閃速爐。閃速爐產(chǎn)出等級很高的閃速爐鎳锍和爐渣。閃速爐鎳锍立即投入水中制成顆粒,脫水后再進(jìn)行篩分并進(jìn)入浸出設(shè)備。閃速爐產(chǎn)出的爐渣進(jìn)入電爐進(jìn)行凈化。電爐產(chǎn)出高鐵電爐鎳锍和爐渣。電爐鎳锍同樣被顆粒化并進(jìn)入電爐鎳锍浸出設(shè)備進(jìn)行浸出。電爐產(chǎn)出的爐渣被顆粒化后最終在爐渣場堆存。表1給出了鎳精礦、閃速爐鎳锍、電爐鎳锍和爐渣的典型成分。表1鎳精礦、閃速爐鎳锍、電爐鎳锍和爐渣的成分Ni%Cu%Fe%S%MgO%SiO2%混合精礦151303068閃速爐鎳锍655421＜0.1＜0.1閃速爐熔渣40.5400.2827電爐鎳锍506307＜0.1＜0.1電爐熔渣0.30.2420.3931ThesmeltingprocessisknownastheDirectOutokumpuNickelSmeltingProcessorDONProcesswhichstartedoperationin1995/21,22,23,24/.ThebenefitsoftheprocessareinasimplifiedflowsheetandahighgradeSO2flowtotheacidplant.NoconvertersareneededandtherawmaterialswithhighMgOcontentcanbetreated.Also,thecobaltrecoveryoftheDONprocessishigh.鎳熔煉過程便是奧托昆普直接鎳熔煉流程〔DON流程,這一流程從1995年開始運(yùn)行〔文獻(xiàn)21,22,23,24。此流程的優(yōu)點(diǎn)是工藝簡單,進(jìn)入制酸系統(tǒng)的SO2濃度高,不需要使用轉(zhuǎn)爐,含MgO高的粗料也可以處理。同時,DON流程中鈷的回收率高。5.2LeachingThegranulatedmattesfromtheflashsmeltingfurnace<FSF>andtheelectricfurnace<EF>haveadifferentmineralogyandironcontent.Therefore,themattesareleachedinseparateleachingcircuits.TheFSFmattecontains5%ironandthemainmineralsofthematteareheazlewooditeNi3S2,chalcociteCu2Sandametallicnickel-copperalloy.TheEFmattecontains30%ironandthemainmineralofthematteismetallicnickel-ironalloy.Coppermayalsobepresentinthealloy.Pentlandite<Ni,Fe>9S8isthemajorsulphidecomponentoftheEFmatte.5.2浸出從閃速爐和電爐產(chǎn)出的顆粒狀的鎳锍〔冰鎳有著不同的礦物和鐵雜質(zhì)的組成。因此,冰鎳用不同的過程進(jìn)行浸出。閃速爐冰鎳含鐵約5%,主要組分是Ni3S2、Cu2S和鎳-銅合金相。電爐冰鎳含鐵約30%,主要組分是鎳-鐵合金相。銅也進(jìn)入合金相。電爐冰鎳中的硫化物主要是鎳黃鐵礦<Ni,Fe>9S8。TheflowsheetoftheleachingprocessisshowninFig.5/25/.TheFSFmatteiswetgroundinballmilts.Thefinegroundmatteisthenfedintoatwo-stagecounter-currentleachingprocess.Thefeedisstronglyagitatedinthereactorsandoxygenisusedasaleachingagent.70%oftheincomingnickelisleachedintheatmosphericleach.Therestofthenickelisleachedinthetwostagepressureleach.Thefirstautoclaveworksinnon-oxidisingconditionswherenickeldissolvesandcopperstaysinsolidformassulphide/26/.Inthesecondautoclave,aportionofthecoppersulphideisleachedinstrongoxidationconditionstomaintainthecopperlevelintheleachingcircuit.Therestofthecoppersulphideprecipitateisfedtothecoppersmelter.圖5是浸出工藝的流程圖〔文獻(xiàn)25。閃速爐冰鎳在球磨機(jī)中濕磨,濕磨完全的冰鎳進(jìn)入一個兩級逆流浸出工序。浸出過程中原料反應(yīng)劇烈,并通入氧氣作為氧化劑。常壓浸出過程可以將原料中70%的鎳浸出。剩余的鎳在兩級加壓浸出工序中浸出。第一級加壓釜中不通氧,鎳進(jìn)行溶解,銅以硫化物形式進(jìn)入固相〔文獻(xiàn)26。在第二級加壓釜中,一部分硫化銅在強(qiáng)氧化性條件下浸出到溶液中以保證浸出液中的銅離子濃度。剩余的硫化銅沉淀返回銅熔煉。ThegroundEFmatteisleachedinthestrongoxidisingconditionsintheatmosphericleach.Agreatdealofthenickel,cobaltandironisleached,whileironismostlyprecipitatedasasolid.Theleachingprocessiscontinuedinautoclaveswherethenickel,cobaltandcopperareleachedtotally.TheironprecipitateoftheEFmatteleach,goethiteorhematiteisrecirculatedtothenickelflashsmeltingfurnaceandmixedwiththeprimaryconcentratefeed.顆粒狀的電爐冰鎳在強(qiáng)氧化性條件下進(jìn)行常壓浸出。大部分的鎳、鈷和鐵被浸出,但大部分的鐵又形成了鐵渣沉淀。固相繼續(xù)在加壓釜中浸出,鎳、鈷和銅被完全浸出