18 EhpHSamples要点Word文档下载推荐.docx

18 EhpHSamples要点Word文档下载推荐.docx

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S

1.0000,1.0000

Numberoftemperatures

25.000,75.000'

ValuesofTemperaturesin°

C

N'

Showstabilityareasofions（Y/N）

-56.6781,-54.7567'

∆GvaluesofH2Oforalltemperatures

1.0000,1.0000'

DielectricConstant

0'

Ionstrenght

-2,2,0,14'

Limitsofthediagram

Cu,0.0000,0.0000'

Nameofaspeciesand∆Gvaluesforalltemperatures

CuH3,67.7313,68.0470

CuO,-30.6627,-29.5533

Cu2O,-35.3446,-34.4294

CuO*CuSO4,-189.3533,-183.9282

Cu（OH）2,-85.8077,-82.4437

CuS,-12.7800,-12.7952

Cu2S,-20.6662,-20.8844

CuSO4,-158.2417,-153.8574

Cu2SO4,-156.4294,-152.5214

CuSO4*3H2O,-334.5808,-323.1528

CuSO4*5H2O,-449.2635,-433.1954

H2SO4,-164.8848,-159.9397

H2SO4*3H2O,-345.1000,-334.0907

H2SO4*4H2O,-402.9123,-389.9613

S,0.0000,0.0000

S（M）,0.0190,0.0068

SO3（B）,-89.4025,-86.2283

SO3（G）,-89.7786,-86.7094

Cu（+2a）,15.6300,15.7317

Cu（+a）,11.9450,11.0901

Cu（OH）2（a）,-59.5596,-53.6263

CuSO4（a）,-162.3104,-155.5767

Cu2SO3（a）,-92.2243,-87.8581

H2S（a）,-6.5160,-6.1670

HS（-a）,2.9113,4.2276

H2SO3（a）,-128.5529,-125.6145

H2SO4（a）,-177.9474,-171.0575

HSO3（-a）,-126.1208,-122.2317

HSO3（-2a）,-121.3430,-116.7342

HSO4（-a）,-180.6580,-175.4083

HSO4（-2a）,-175.2501,-169.3171

HSO5（-a）,-152.3532,-147.0925

S（-2a）,20.5471,22.6438

S2（-2a）,19.0406,21.0895

S3（-2a）,17.6446,19.6504

SO2（a）,-71.8354,-71.1981

SO3（a）,-125.6315,-121.1608

SO3（-2a）,-116.2971,-110.0146

SO4（-2a）,-177.9474,-171.1338

S2O3（-2a）,-123.9775,-118.6055

S2O4（-2a）,-143.5482,-137.2786

S2O5（-2a）,-188.0263,-180.6896

S2O6（-2a）,-231.6077,-223.3179

S2O8（-2a）,-266.4866,-257.3452

S3O6（-2a）,-244.8178,-236.2948

EpHCase1:

MetalCorrosioninFe-H2O-system

Eh-pH-diagramsmaybeusedtoestimatecorrosionbehaviorofdifferentmetalsinaqueoussolutions.Themostcommoncorrosionphenomenonisrustformationontheironsurfaces.Thecorrosionratesandtypesdependonthechemicalconditionsintheaqueoussolution.TheEh-pH-diagramofanFe-H2O-systemmayeasilybecreatedasdescribedinChapter17.ThechemicalsystemspecificationisshowninFig.1andthecalculateddiagraminFig.2.

Thestabilityareasmaybedividedintothreegroups13:

1.Corrosionarea:

Formationofionsmeansthatmetaldissolvesintoanaqueoussolution.Forexample,Fe（+3a）,Fe（+2a）,FeO2（-a）andHFeO2（-a）-ionsinanFe-H2O-system.

2.Passivearea:

Formationofoxidesorsomeothercondensedcompoundsmaycreatetightfilm（impermeable）onthemetalsurfacewhichpassivatesthesurface,goodexamplesareAl2O3onaluminiumorTiO2ontitaniumsurfaces.Iftheoxidelayerisnottightenough（porous）topreventoxygendiffusionintothemetalsurface,corrosionmaycontinue.Thisisthecasewiththemostoftheironoxidesbuttheymayalsocausepassivationinfavourableconditions.

3.Immunityarea:

Allmetalsarestableiftheelectrochemicalpotentialislowenough.Mostnoblemetalsarestableevenatzeropotential,butatleast–0.6voltsareneededatthecathodeforirontoprecipitate,seeFig.2.

ThestabilityareasofwaterareshownbydottedbluelinesinEh-pH-diagrams,seeFig.2,thecolorscannotbeseeninthisB&

Wcopy.Usuallyitisdifficulttoexceedtheselimitsduetotheformationofoxygenattheupperlimitandhydrogenatthelowerlimit.Insomesolutionstheselimitsmaybeexceededduethenecessaryoverpotentialofhydrogenandoxygenformation.OnthebasisofFig.2itseemsthathydrogenformationoccursoncathodebeforethemetallicironcomesstable.

TheEh-pH-diagramsmaybeusedinseveralways,forexample,

-tofindpH,potentialandtemperatureregionswhichpreventcorrosion.

-tofindoutwhichcompoundsarethecorrosionreactionproducts.

-tofindimmunematerialswhichcanbeusedasprotectivecoating.

-tofindoutametalwhichmaycorrodeinsteadoftheconstructivematerial.Forexample,thezinclayeronasteelsurface.

Fig.1.SpecificationofFe-H2O-systemforEpH-diagramat25°

C.

Fig.2.Eh-pHDiagramofFe-H2O-systemat25°

C.MolalityofFeis10-6M.

EpHCase2:

CorrosionInhibitorsinFe-Cr-H2O-system

Someelementsorcompoundsmaypreventcorrosionevenatverylowcontentinthechemicalsystem.Thesesubstancesarecalledcorrosioninhibitorsandtheycanbedividedintoanodicandcathodicinhibitors.Theanodicinhibitorsprimarilypreventtheanodicreactionandpassivatemetalsinthisway,thelatteronessuppressthecorrosionratebypreventingthecathodicreactionorbyreducingthecathodicarea13.

Chromateanddichromateionsarewellknownanodiccorrosioninhibitors.Smallamountsofchromateswillcreateatightcomplexoxidefilmonthesteelsurfacewhichpreventscorrosion.Theoxidefilmismainlyformedofmagnetite（Fe3O4）,hematite（Fe2O3）andchromicoxide（Cr2O3）.

TheinhibitorbehaviorofchromatesmaybeillustratedwithEh-pH-diagrams.TheFe-Cr-H2O-systemspecificationsareshowninFig.3.ThecalculationresultsforFe-H2OandFe-Cr-H2O-systemsareshowninFigs4and5.Asshowninthediagrams,alargeareainthecorrosionregionofironFe（+2a）,Fig.4,iscoveredbytheCr2O3andCr2FeO4stabilityareasandthusprotectedfromcorrosion,Fig.5.

ItiseasytocreateEh-pH-diagramswiththeEpHmodule.However,youshouldrememberthatthistypediagramgreatlysimplifiestherealsituation.Theydonottakeintoaccount,forexample,thekineticaspectsornon-idealityofrealsolutions.Smallerrorsinthebasicthermochemicaldatamayalsohaveavisibleeffectonthelocationofthestabilityareas.Inanycase,thesediagramsgivevaluablequalitativeinformationofthechemicalreactionsinaqueoussystemsinbriefandillustrativeform.

Fig.3.SpecificationofFe-H2O-systemforEpH-diagramat100and300°

Fig.4.Fe-H2O-systemat100°

C.Molality:

Fe10-2M,pressure1bar.

Fig.5.Fe-Cr-H2O-systemat100°

C.Molalities:

FeandCr10-2M,pressure1bar.

EpHCase3:

SelectionofLeachingConditions

Thefirststepinahydrometallurgicalprocessisusuallyleachingordissolutionoftherawmaterialsinaqueoussolution.Theaimistoselectthemostsuitableleachingconditionssothatthevaluablemetalsdissolveandtherestremaininthesolidresidue.TheleachingconditionsmayeasilybeestimatedwithEh-pH-diagrams.Infavorableleachingconditionsthevaluablemetalsmustprevailinsolutionasaqueousspeciesandtheothersinsolidstate.

Roastedzinccalcineisthemostcommonrawmaterialforthehydrometallurgicalzincprocess.Itcontainsmainlyzincoxide.AnexampleofEh-pH-diagramsapplicationinzincoxideleachingisshowninFig.7,seeFig.6forchemicalsystemspecifications.ItcanbeseenfromthediagramthatacidorcausticconditionsareneededtodissolvetheZnOintosolution19.

InacidconditionsthepHofthesolutionmustbeloweredbelowavalueof5.5.InpracticalprocessesthepHmustbeevenlowerbecausetherelativeamountofzincinthesolutionincreasesifthepHisadjustedfartherfromtheequilibriumlinebetweentheZnOandZn（+2a）areas.ThedissolutionoftheZnOconsumeshydrogenionsascanbeseenfromreaction

（1）.Thereforeacidmustcontinuouslybeaddedtothesolutioninordertomaintainfavorableleachingconditions.

ZnO+2H（+a）=Zn（+2a）+H2O[1]

IncausticconditionszincmaybeobtainedinsolutionbytheformationoftheanioncomplexZnO2（-2a）.Theleachingreactionmaybedescribedbyequation

（2）.

ZnO+H2O=ZnO2（-2a）+2H（+a）[2]

Theleachingconditionschange,forexample,ifsulfurisincludedinthechemicalsystem.TheeffectofsulfurcanbeseeninFig.10.MuchsmallerpHvaluesareneedtodissolveZnSwhichhaswidestabilityarea.Thiswillleadtotheformationofhydrogensulfidegasandionsaccordingtoreaction（3）.

ZnS+2H（+a）=Zn（+2a）+H2S（g）[3]

Inoxidizingconditionsanumberofdifferentaqueousspeciesmayresultfromtheleachingreactionssuchas（4）,（5）and（6）,seeFig.6.Inthesereactionsitisimportanttonotethattheconsumptionofreagentsaswellasgenerationofreactionproductscontinuouslychangethesolutionconditions.Theseconditionsmustberegulatedbyfeedingmoreacidand/orremovingreactionproductsinordertothemaintainoptimumconditions.

ZnS=Zn（+2a）+S+2e-[4]

ZnS+4H2O=Zn（+2a）+HSO4（-a）+7H（+a）+8e-[5]

ZnS+4H2O=Zn（+2a）+SO4（-2a）+8H（+a）+8e-[6]

TheHSCdatabasecontainsalotofspecieswhichmayhavealongformationtime.Normallyitiswisetoselectonlysuchspecieswhichareidentifiedinrealsolutionsforchemicalsystemspecifications.AsystemspecificationwithonlycommonspeciesincludedisshowninFig.8andanotheronewithallthespeciesinFig.9.TheselectedspeciesmayhaveavisibleeffectonthediagramsascanbeseenbycomparingFigs.10and12aswellasFigs.11and13.Insomecases,diagramswithallthespeciesselectedintothecalculationsystemmaygivealsovaluableinformation,Figs.12and13.

Fig.6.Zn-H2O-systemspecifications.

Fig.7.Zn-H2O-systemat25°

C.DiagramisbasedonspecificationsinFig.6.

Fig.8.Zn-S-H2O-systemspecifications,onlyidentifiedspeciesincluded

Fig.9.Zn-S-H2O-systemspecifications,allspeciesincluded.

Fig.10.Zn-S-H2O-systemat25°

CbasedonspecificationsinFig.8.

Fig.11.S-Zn-H2O-systemat25°

Fig.12.Zn-S-H2O-systemat25°

Cbasedonspecificationsi