DOC

Reaction Process of Chromium Slag Reduced Industrial Waste in Solid Phase

By Connie Ross,2014-01-25 08:53
8 views 0
Reaction Process of Chromium Slag Reduced Industrial Waste in Solid Phase

    Reaction Process of Chromium Slag Reduced Industrial Waste in Solid Phase Availableonlineatwww.sciencedirect.c,om

    ?::,scienceDirect

    JOLTRNM.OFIRONANDSTEElRESEARCH,INTERNATIONAL.2007,14(1):12-15 ReactionProcessofChromiumSlagReducedby

    IndustrialWasteinSolidPhase

    SHIYu-min,DUXinghong,MENGQing-jia,SONGShiwei.,SUIZhitong

    (1.SchoolofMaterialsandMetallurgy,NortheasternUniversity,Shenyang110006,Liaoning,China;

    2.BeijingSentchEnvironmentalTechnologyCoLtd,Beijing100089,China;3.BeijingZhongSheng

    TaiKeEnvironmentScienceandTechnologyDevelopmentCoLtd,Beijing100089,China) Abstract:M,aparticularindustrialwaste,wasselectedtodetoxifychromiumslagatahightemperature.Thecar

    bonremaininginMreducedCr(VI)ofNa2Cr04borneinthechromiumslagtoCr(1I)inthesolidphasereaction,

    anditsthermodynamicsandkineticswerestudied.ThereductionprocessofNa2Cr04bycarbonproducedCO,

    which'wasendothermic.

    Undertheexperimentalcondition,theapparentactivationenergywas4.41kJ?mol_., the'appaientorderofreactionforNa2CrO4wasequaltoone,andthepartialpressureofCOwasonly0.22Pa

    at1330?.

    Keywords:chromiumslag;industrialwaste;reductionreaction;solidphase;reactionprocess

    Considerableattentionhasbeenpaidtothe

    managementandapplicationofhazardousmaterials andwasteallovertheworld,inthepresentcrisisof population,resource,energy,andenvironment, whichurgentlyneedsprofessionaltreatmentanddis

    posaltechnologiestoreducethem,andmakethem innoxiousand'utilizable,specificallyforthehazard

    OUSwaste.Chromiumslag,aresidueofchromate andmetallicchromiumproduction,isoneofthe47 kindsofhazardouswastelistedbyChina,thoughit isanimportantmaterialandplaysagreatroleinin

    dustries.However,7tofchromiumslagwaspro

    ducedwhen1tofmetallicchromiumwasmanufac

    tured.and1.74.2tofchromiumslagwerepro

    ducedwhen1tofsodiumdichromatewasmanufac

    tured.Hundredthousandtonsofchromiumslagcan bereleasedinthecountrywideeveryyear,andmore than2.5Mtofchromiumslaghavebeenreleasedin thecountrysofar[?.Waterandacidsolublehexava

    lentchrome,recognizedasoneofthethreekindsof matter,whichcancausecancer,hascaudsevere hazardstotheenvironment,especiallytohumans andanimals.Itisanurgenttasktodetoxifyand treatchromiumslagforenvironmentalprotection. Therewerethreemethodsthatwerefollowedto treatchromiumslagaroundtheworld,i.e.,stabili

    zation,reduction,andcomplexation['.Stahiliza

    tionwasfavorableabroad[4--6],whichwasnotsuit

    ableforChinabecauseofthecostofagreatdealof cementandenergy.Morethantwentymethodshave beeninpracticeinChinasince1960.andthesolid

    phasereductionofchromiumslagwaspreferred[.8].In thisprocess,athightemperature,Cr(VI)wasreduced toCr(m)byreducer,suchascarbonpowder,saw

    dust,ricehull,gangue,andferrite,whichdetoxi

    fiedthechromiumslagcompletelyandstablyinthe formofaspinel,withlowcostandbyusingsimple techniques,anditsfina1slagcanbeusedasrawma

    terialsofcement,brick,andcaststone,whichrecy

    cledtheresourceandreducedoccupyingland.Some researchersarenowtryingtofindnewandefficient approachesforthetreatmentanddisposalofchromi

    umslagbyreductioninthesolidphase.Thetrend ofresourceutilitiesisthatindustrialslagwaschosen asareducerforitslowenergyconsumptionandlow cost[910]

    .

    Inthisstudy,asolidreductionmethodwas

    presented,inwhichcarbonremainedinM.akindof FoundationItem:ItemSponsoredbyNationalNaturalScienceFoundationofChina(502340

    40)

    Biography~SHIYumin(1968),Female,Doctor,SeniorEngineer;E-mail:shiym2005(~hotmail.tom;RevisedDate:Sep

    tember9,2005

No.1ReactionProcessofChromiumSlagReducedbyIndustrialWasteinSolidPhase

    industrialwaste,wasselectedasthereducertode

    toxifychromiumslagatahightemperaturewithlow cost.Thefinalslagmaybeusedasrawmaterialsfor building.whichalsomeetstheneedsofinnoxious

    nessandutilityforhazardouswasteinindustries,an

    importantpartofpollutionpreventionforwaste treatmentanddisposaltechnologies.Considering thefewtheoreticalresearchesonchromiumslagre

    ducedbycarboninsolidphase,itsthermodynamics andkineticsofreactionprocesswerestudied,and thereactiontemperature,thepartialpressureof CO,theapparentorderofreaction,andtheappar- entactivationenergyundertheexperimentalcondi- tionweredetermined.

    1Experimental

    l-1Materialsandequipment

    Thesamplesofchromiumslagwasobtained fromXinyuanChemicalsPlantofShenyang,andthe concentrationofwatersolubleCr(?)was0.5.

    Thetypicalchemicalcompositionofchromiumslag inmasspercent()wasMgO2830,CaO26

    28,Fe20310,Al20368,Si02810,Cr2O34.5,

    andNa2CrO^0.5.M,aparticularCheapwasteofin

    dustries,wasselectedasthereducer.inwhichthe remainedcarbonreducedCr(?.)toCr(?).

    Theequipmentusedfortheexperimentisas follows:ahightemperaturefurnacewithheatingel

    ementsofMoSi2,aPTC-?temperatureautocon

    troller(precision:3K),aTU1800PCUv-visible

    spectrophotometer,ahorizontalvibrator(11010

    timespermin),aSSX550Shimadzuelectronmicro

    scope,andaPW-1700PhilipX-rayelectrondiffrac

    tionspectroscope.

    1.2'I,estmethod

    TheindustrialwasteMandchromiumslagwere

crushedtolessthan1mm,thenmixed,homoge

    nizedinsomeproportions,afterthat,putintothe hightemperaturefurnace.Thesampleswereheated to13001450?,keptforhours,andthennatu

    rallycooled.

    Thefinalslagwascrushedtolessthan5mm9 andleachtestswereperformedaccordingtotheap

    pendixBofGB/T15555.11995.Theconcentrationof Cr(?)wasdeterminedaccordingtoGB/T15555.4

    19951,5Dipheny1carbonydrazidespectrophotomet- ricmethod.

    2ResultsandDiscussion

    2.1Solidphasereductionreactionofchromiumslag byM

    ThemostimportantcompoundsofCr(VI)re- mainedinthechromiumslagareNa2Cr04['3. The

    reactionsofsolidphasereductionofthechromium slagbyMare

    3C(s)+2Na2CrO4(s)2Na2O(s)+

    Cr203(s)+3CO(g)(1)

    3CO(g)+2Na2CrO4(s)2Na2O(s)+

    CrzO3(s)+3CO2(g)(2)

    3C(s)+4Na2CrO4(s)=4Na2O(s)+

    2CrzO3(s)+3CO2(g)(3)

    Theconditionsofreactionsaredeterminedby theGibbsHolmholtzequation.

    ]一一(4)IaT1PT

    whereAGisGibbsfreeenergyofreaction;?His

    heatcapacityofreaction;Tistemperature;Pis

pressure.

    Thereactionoccursas?G?0.

    Theequationcanbetransformedinto AG/T一一fdT+I(5)

    whereIisintegralconstant. AccordingtoGRKirchhofflaw, AH=?H0+lAcPdT(6)

    where?H0isintegralconstant;cPisafunctionof

    temperature,andcanbeexpressedby cP一口+bT+ctT

    n,b,andcareempiricalconstants.anddetermined

    bytheirsubstancecharacters. AcPAa+AbT+AcT

    and

    AH=?H0+AaT+1/2Ab7.2一?cT(7)

    SubstitutingEqn.(7)intoEqn.(5)andtrans

    posing

    AGAH0一?皿nnT+JT1/2~b1/2~cT

    (8)

    Basedonthermodynamicdata[.,.thecon

    stantsinstandardconditionswerecalculated.aslis

    tedinTable1.

    ThreeequationsofAGcanbeconsequentlyex-

    pressedasfollows:

    ?G3461305.3×104/T+290.43T

    62.03TlnTo.023T2}orReaction(1); b,tj'??qi.1_Ilj

JournalofIronandSteelResearch,InternationalVoL14

    Table1Thennod~naami~eomtants

?G一一186198+2.40×10./T+908.40T

    75.53TlnT+0.041T2forReaction(2);

    ?G=153620+2.35×10./T+1247.38T

    137.56TlnT0.055TforReaction(3).

    Therelationshipbetween?GandTofthreere-

    actionsat1OOO1800?isshowninFig.1.Reac-

    tion(1)isanendothermicreaction.ItoccursatT?

    1380?forAG40.0bviously,Reaction(2)isexo

    thermic.ItsverydifficulttooccurevenatT>1000 ?forAG>0.Reaction(3)isanendothermicreac- tion,similartoReaction(1),butatT>1700?,

    ?Gisstillaverylargepositivequantity,sothereac

    tioncannotoccur.Asaresult,onlyReaction(1)is promising.

    2.2口口I,睇岫nand00p盯幽_prcmn~forl~metion(1)

    Experimentsshowedthatthisreactioncanoccur at1330?underverylowCOpartialpressure.The theoreticalcalculationofCOpartialpressureisas follows:

    UsingVantHoffsconstanttemperatureequa

    tion

    ?G一一RTInK.+RTlnQ.(9)

    whereRisgasconstant;K.isreactionequilibrium constant;Q.isreactionactivationquotient.

    G<O,reactioncanoccur; AsQ.<K.,and?

    AsQ.>K.,andAG>O,reactioncannotoccur; AsQK.,andAG=0,reactionisinequilibrium. SubstitutingAG=RTlnK.intoEqn.(9):

    ?G一?G.+RTlnQ.

    ForReaction(1)

Q.

    P?aCr20a

    ?.

    口毛?

    wherePcoisCOpartial

    componenti.

    WithaknownAG.,

    canbecalculatedand

    (10)

    pressure;afisactivityof atsometemperature,Pco PcoO.22Pa,atT1330?;

    Pco5.3Pa,atT1380?.

    2.3KineticsOfReaction(1) Thekineticequationforthereactionisgenerally

    asfollows:

    r一一dc/dt=kc

    whererisspotvelocity;kisvelocityconstantofre

    action;cisinitialmassfractionofreactants;tisre

    actiontime;and,lisorderofreaction.

    ForReaction(1)

    r一一dc/dt=kc~CrO'4

    Logarithmofthisequationis logr=log(--dc/dt)1ogk+nlogc(11) FromthedatainTable2,log(dc/dt)-os IogcN.2C~O,canbeplotted,asshowninFig.2.Thus,

    ,l?1.02and忌?1.99hat1330?;,l?O.93and忌? 2.01hat1380?;andingeneral,,l?1,k?2

    h_..

    AccordingtoArrheniusformulae

dlnkE

    dTRT

    and

    k2

    

    E~

    f1_(12)whereEisreactionactivationenergy;kisreaction

    rate.

    EcanbecalculatedusingEqn.(12),andE

    4.41kJ?mol?.

    Table2LeachedCr(?)concentrationinms

    fractionsfor0.5hofreactiontime

    1330

    1380

    Z.52

    0.24

    2.96

    0.26

    3.45

    0.38

    4.08

    0.58

    ^,.Io.

N0.1RcactionProcessofChromiumSlagReducedbyIndustrialWasteinSolidPhase

    Fig.2Relationshipbetweenlog(--dc/dt)andlogcN%0o4 SO,apparentorderofreactionforreductionof chromiumslagbyMtoobtainNa2CrO4is1,and theapparentactivationenergyofthisreactionis

4.41kJ?mol.

    3Conclusions

    ThereductionofCr(?)inchromiumslagto

    Cr(?)fordetoxificationbyindustrialwasteM, wasconfirmedbythermodynamiccalculation.Kinet- icconstantsofthereactionwerecalculatedunderex- perimentalconditions.Thereactionisoffirstorder with4.41kJ?molofapparentactivationenergy,

    andtheequilibriumCOpartialpressureat1330?

    is0.22Pa.

    1"13LANSiguo,YINHuirain,DIYian,eta1.Detoxification TechniquesforChromiumSlagFJ].ResearchofEnvironmental Sciences,1998,11(3):5356(inChinese).

    r2]DINGYi.ViewsonTreatmenttoChromiumSlagFJ].Chemi

    calsIndustryandEnvironmentalProtection.1994,14(4):210

    215(inChinese).

    [3]RENQingyu.ComprehensiveUtilizationandTreatmentfor ChromiumSlag[J].EnvironmentEngineering,1989,7(3): 5O55(inChinese).

    r4]MollahMYA,TsaiYN,HessTR,eta1.AnFTIR,SEM andEDSInvestigationofSOlidificati0n/Stabilizati0nofChromi

    umUsingPortlandCementTypeVandTypeIPFJ].JHazard Mater,1992,30(3):273283.

    Fs]KindnessA,MaciasA,GlasserFP.ImmobilizationofChromi

    uminCementMatricesFJ].WasteManagement,1994,14(1): 311.

    F6]AllanML,KukackaLE.BlastFurnaceSlag-ModifiedGrouts f0rinSituStabilizationofChromiumContaminatedSoilFJ].

    WasteManagement,1995,15(3):193202.

Report this document

For any questions or suggestions please email
cust-service@docsford.com