铬铁矿氧化焙烧动力学

20920109Vol.20No.9TheChineseJournalofNonferrousMetalsSep.20101004-0609(2010)09-1822-07(410083)()99%68.7231.8kJ/molTF111AKineticsofchromiteoreinoxidationroastingprocessLIXiao-bin,QITian-gui,PENGZhi-hong,LIUGui-hua,ZHOUQiu-sheng(SchoolofMetallurgicalScienceandEngineering,CentralSouthUniversity,Changsha410083,China)Abstract:Thetraditionallime-freeroastingprocessusedformanufacturingchromatefromchromiteorehaslowoxidationratewhichimpactthechromateproductionefficiencyandchromiumrecoveryrateseriously.Tointensifytheoxidationroastingprocessofchromiteore,theoxidationkineticsanditsmechanismwerestudied.Theresultsshowthattherearetwostagesfortheoxidationroastingprocessofchromiteore.Theoxidationreactionisveryrapidintheinitialstagebutquiteslowinthelaterstage.Theoxidationrateofchromium()inchromiteorecanreachmorethan99%undertheoptimizedconditions.Thewholeoxidationprocessofchromiteorefollowstheshrinkingunreactedcoremodel,andthesurfacechemicalreactionisthecontrollingstep.Theapparentactivationenergiesoftheinitialandlaterstagesare68.7and231.8kJ/mol,respectively.Andthesodiumchromateisproducedbythereactionofchromitewithsodiumcarbonateandoxygenintheinitialstage,whereassodiumchromateisformedbythereactionofchromitewithsodiumferriteformedintheinitialstageandoxygeninthelatterstage.Keywords:chromiteore;sodiumchromate;oxidationroasting;kinetics[1−3][4−5]75%[6−7](2009FJ1009)[e-mail]2091823ANTONY[8][9,10]Cr3+VILAS[11]Na2CrO4-Na2CO3Na2CrO4-Na2CO3[12][13][14]11.1()(1)11Table1Chemicalcompositionofchromiteore(massfraction,%)Cr2O3Al2O3Fe2O3SiO2MgO41.4222.9522.294.248.631.21XRDFig.1XRDpatternofchromiteoreSX2−5−12SHY−14−13V−0.12/8STA409PC1.362um45um45~62µm2h4~6mm3001h10gEPD1700X22.1222010918242Fig.2Effectsofroastingtemperatureanddurationtimeonoxidationrateofchromium()inchromiteore(1223~1373K)0~20min1323K0~20min90.34%20~100min9.15%2.2−O2O2O2−xt(1)(2)(3)[15]1323K33x=kt(1)1+2(1−x)−3(1−x)2/3=kt(2)1−(1−x)1/3=kt(3)3(a)31323KFig.3Relationshipsbetweendifferentmodelfunctionsandoxidationtimeat1323K:(a)Wholeprocess;(b)Initialstage;(c)Laterstage.Curve1F(x)=x;Curve2F(x)=1+2(1−x)−3(1−x)2/3,Curve3F(x)=1−(1−x)1/3209182515~20min1323K(0~10min)(20~100min)3(b)(c)3(b)(c)F(x)=1−(1−x)1/3t1323KF(x)=1−(1−x)1/3F(x)t441−(1−x)1/3Fig.4Relationshipbetween1−(1−x)1/3andtimeatdifferentroastingtemperatures:(a)Initialstage;(b)Laterstage41223~1373K(3)k222kTable2ApparentreactionrateconstantofchromiumoxidationatdifferentroastingtemperaturesTemperature/KApparentreactionrateconstant,k/min−1InitialstageLaterstage12232.52×10−27.0×10−412733.47×10−21.4×10−313234.53×10−23.6×10−313735.22×10−28.1×10−3ARTEklnlna+−=(4)kEaJ/molRR=8.314J/molTKAlnk1/T568.7231.8kJ/mol2.3FeCr2O4+2Na2CO3+7/4O2=2Na2CrO4+1/2Fe2O3+2CO2(5)FeCr2O4+Na2CO3+1/4O2=Na2Cr2O4+1/2Fe2O3+CO2(6)201091826Fe2O3+Na2CO3=2NaFeO2+CO2(7)FeCr2O4+4NaFeO2+7/4O2=2Na2CrO4+5/2Fe2O3(8)MgO+Fe2O3=MgFe2O4(9)1323KXRD66Na2Cr2O4Na2CrO4(6)Na2Cr2O4(Na2Cr2O4)Na2CO320minNa2CO390%Na2CrO4MgFe2O4MgONaFeO2NaFeO2XRDNaFeO2Na2CrO4MgFe2O4MgONa2CO3Na2CO3Na2CrO4NaFeO2Na2CO3NaFeO2(5)Na2CrO4Na2CO3(7)NaFeO2Na2CrO4NaFeO2[11]NaFeO2(8)Na2CrO4Na2CO3NaFeO2Na2CO3Na2CrO4(5)(8)5Fig.5Relationshipbetweenapparentreactionrateconstantandtemperature:(a)Initialstage;(b)Laterstage61323KXRDFig.6XRDpatternsofsinterobtainedat1323Kfordifferentroastingtimes2091827NaFeO2NaFeO2NaFeO29.2%(Cr2O3)()MgOMgFe2O415K/minCoats-RedfernF(x)=1−(1−x)1/3(10)[16]RTEERTEARTxaaa23/1)]21(ln[]3/1)1(1ln[−−=×−−β(10)xTKARR=8.314J/molEaJ/molβK/min(5)Ea/(RT)1,(1−2RT/Ea)≈1ln[(1−(1−x)1/3)/(1/3T2)]1/T−Ea/R1273~1473K(10)1/T77NaFeO2237.3kJ/mol7ln[(1−(1−x)1/3)/(1/3T2)]1/TFig.7Relationshipbetweenln[(1−(1−x)1/3)/(1/3T2)]andreciprocaloftemperatureunderconstantheatingrateNaFeO2Na2CrO431)2)68.7231.8kJ/mol3)Na2CO3Na2CrO4Na2CO3NaFeO2NaFeO2Na2CrO4REFERENCES[1].[J].,2004,23(4):345−348.DINGYi.PresentstatusandprospectofchromateproductioninChina[J].ChemicalIndustryandEngineeringProgress,2004,23(4):345−348.[2]TATHAVADKARVD,ANTONYMP,JHAA.ThephysicalchemistryofthermaldecompositionofsouthAfricanchromiteminerals[J].MetallurgicalandMaterialsTransactionsB,2005,36B(1):75−84.[3]JOHNM,KUBICEKDL.Sodiumchromateandsodiumdichromateproductioncapacities[J].EncyclopediaofChemicalProcessandDesign,1979,8:303−323.[4]MOONDH,WAZNEM,DERMATASD.Long-termtreatmentissueswithchromiteoreprocessingresidue(COPR):Cr6+reductionandheave[J].JournalofHazardousMaterials,2007,143(3):629−635.[5]BEWLEYRJF.Calciumpolysulfideremediationofhexavelantchromiumcontaminationfromchromiteoreprocessing201091828residue[J].ScienceoftheTotalEnvironment,2006,364(1/3):32−44.[6]SUNGURS,BABAOGLUS.InvestigationoftheeffectsofsomeparametersintheproductionofchromatefromchromiteoresinIskenderunregion[J].SteelResearch,2006,77(7):492−494.[7]XUHong-bin,ZHANGYi,LIZuo-hu.Developmentofanewcleanerproductionprocessforproducingchromicoxidefromchromiteore[J].JournalofCleanerProduction,2006,14(2):211−219.[8]ANTONYMP,JHAA,TATHAVADKARVD.AlkaliroastingofIndianchromiteores:thermodynamicandkineticconsiderations[J].MineralProcessingandExtractiveMetallurgy,2006,115(2):