項目七：硅酸鹽分析任務三：硅酸鹽質量分析硅酸鹽中氧化鋁含量測定課程：工業(yè)分析中文Scenario7:SilicateAnalysisTask3:QualityanalysisofsilicatesDeterminationofaluminacontentinsilicatesCourse:IndustrialAnalysisEglish水泥及其原料系統(tǒng)分析中，Al2O3的測定通常采用EDTA直接滴定法和CuSO4返滴定法，而且一般是在滴定Fe3＋之后的溶液中連續(xù)滴定鋁。本方法已列入水泥化學分析方法國家標準。直接滴定法為基準法，適用于MnO含量

0.5%的試樣；返滴定法為代用法，適用于MnO含量

0.5%的試樣。中文Intheanalysisofcementanditsrawmaterialsystems,thedeterminationofAl2O3isusuallycarriedoutusingEDTAdirecttitrationmethodandCuSO4backtitrationmethod,andaluminumisgenerallycontinuouslytitratedinthesolutionaftertitrationwithFe3+.Thismethodhasbeenincludedinthenationalstandardforchemicalanalysismethodsofcement.Thedirecttitrationmethodisthereferencemethod,suitableforsampleswithMnOcontent>0.5%;Thebacktitrationmethodisasubstitutemethod,suitableforsampleswithMnOcontent<0.5%.Eglish一、直接滴定法在pH=3的溶液中，加熱，使TiO2+水解為TiO（OH)2沉淀，以PAN和CuY為指示劑，用EDTA標液直接滴定溶液中的

Al3+。反應如下：1、方法原理中文一、DirecttitrationmethodInasolutionwithpH=3,heattohydrolyzeTiO2+intoTiO2(OH)2precipitate,andusePANandCuYasindicatorstodirectlytitrateAl3+inthesolutionwithEDTAstandardsolution.Thereactionisasfollows:1、MethodprincipleAttheendpoint,thesolutioncolour

changesfromredtoyellowred(yellow)Eglish2、測定步驟在滴定完鐵的溶液中加入1~2滴溴酚藍指示劑（2g/L），滴加氨水（1+2）至溶液出現藍紫色，再滴加鹽酸（1+2）至黃色，加入15mL醋酸-醋酸鈉緩沖溶液（pH=3），加熱至微沸，加入10滴CuY和2~3滴PAN指示劑，用EDTA標準溶液滴定至溶液變?yōu)榱咙S色。中文2、MeasurementstepsAdd1-2dropsofbromophenolblueindicator(2g/L)tothesolutionaftertitrationofiron,addammoniawater(1+2)dropwiseuntilthesolutionturnsbluepurple,thenaddhydrochloricacid(1+2)dropwiseuntilitturnsyellow,add15mLofaceticacidsodiumacetatebuffersolution(pH=3),heatuntilslightlyboiling,add10dropsofCuYand2-3dropsofPANindicator,andtitratewithEDTAstandardsolutionuntilthesolutionturnsbrightyellow.Eglish3、結果計算中文3、ResultcalculationAl2O3%c--ConcentrationofEDTAstandardsolution,mol/LV--VolumeofEDTAstandardsolution,mLM--MolarmassofAl2O3,g/molm--Massofthesample,gEglish4、注意事項（1）最適宜pH2.5~3.5<2.5Al3+

與EDTA絡合不完全；>3.5Al3+

水解傾向增大→偏低（2）指示劑用量PAN適量（2-3d）多→色深→不好觀色（3）終點控制（如何控制終點？）由于Al3+與EDTA反應較慢，故經反復煮沸，反復滴定，一般3次即可出現穩(wěn)定的黃色，其準確度滿足生產要求。中文4、Note(1)ThemostsuitablepHis2.5~3.5pH<2.5:incompletecomplexationofAl3+withEDTA;pH>3.5:Al3+hydrolysistendencyincreases→measurementresultislow(2)Indicatordosage

AppropriateamountofPAN(2-3drops),excessive→solutioncolordark→difficulttoobservechangesinsolutioncolor(3)Endpointcontrol(howtocontroltheendpoint?)

DuetotheslowreactionbetweenAl3+andEDTA,itisnecessarytorepeatedlyboilandtitrate.Generally,astableyellowcolorcanappearafter3repetitions,anditsaccuracymeetsproductionrequirements.Eglish二、返滴定法1、方法原理中文二、Backtitrationmethod1、MethodprincipleSolutionaftertitrationofFe3+AddexcessEDTAheat,TransformingmostofAlintoAlYboilbrightpurpleAlltransformedintoAlYEglish2、反應中文2、Chemicalreactionsinvolved:(colourless)(residual)(blue-green)(yellow)(red)Excessive1dropThepurplishredcoloristheendpointEglish3、注意事項（1）終點顏色紫紅色（好）終點顏色與過剩的EDTA量和所加PAN指示劑量有關中文3、Note(1)Colorofsolutionatendpoint:purplishredThecoloroftheendpointisrelatedtotheexcessamountofEDTAandtheindicateddosageofPANaddedToomuchEDTAortoolittlePANToolittleEDTAortoomuchPANEDTAexcessmoderateendpointBluepurpleorblueredPurplishredGenerallyEDTAexcess(i.e.reactionresidue)10-15mLEglish（2）pH調節(jié)時間加入過量EDTA，加熱至70~80?C，再調pH3.8~4.0Al3+與EDTA反應慢，過量EDTA及加熱均提高反應速度

過量后并不直接調至pH3.8~4.0，目的是讓大部分Al3+、TiO2+與EDTA絡合，以防pH提高至3.8~4.0水解。中文(2)TimeforpHadjustmentAddexcessEDTAandheatto70-80℃,thenadjustthepHto3.8~4.0ThereactionbetweenAl3+andEDTAisslow,andexcessiveEDTAandheatingbothincreasethereactionrateAfteraddingexcessiveEDTA,thesolutionpHisnotdirectlyadjustedto3.8-4.0.ThepurposeistoallowmostAl3+andTiO2+tochelatewithEDTAtopreventhydrolysiswhenthepHisincreasedto3.8-4.0.Eglish（3）PAN使用PAN與Cu-PAN都不易溶于水，為增大其溶解度，配成PAN的酒精溶液，滴定時在熱的條件下進行滴定，一般80-90?C。（4）滴定的體積：保持在200mL以上，以降低Ca、Mn對測定的干擾。本法測得的是Al、Ti合量，要求高時，用光度法測出Ti量，扣除得準確鋁量。中文(3)TheuseofPANPANandCuPANarenoteasilysolubleinwater.Toincreasetheirsolubility,analcoholsolutionofPANispreparedandtitratedunderhotconditions,typically80-90℃.(4)Volumeoftitration

Keepthesolutionvolumeabove200mLtoreducetheinterferenceofCaandMn