ASTM D859-2005 水中二氧化硅的标准试验方法

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【英文标准名称】:StandardTestMethodforSilicainWater
【原文标准名称】:水中二氧化硅的标准试验方法
【标准号】:ASTMD859-2005
【标准状态】:现行
【国别】:
【发布日期】:2005
【实施或试行日期】:
【发布单位】:美国材料与试验协会(US-ASTM)
【起草单位】:D19.05
【标准类型】:(TestMethod)
【标准水平】:()
【中文主题词】:试验;含量测定;硅;水
【英文主题词】:colorimetric;silicawater
【摘要】:Siliconcomprisesabout28%ofthelithosphereandis,nexttooxygen,themostabundantelement.Itisfoundastheoxideincrystallineforms,asinquartz;combinedwithotheroxidesandmetalsinavarietyofsilicates;andinamorphousforms.Siliconisthemostabundantelementinigneousrocksandisthecharacteristicelementofallimportantrocksexceptthecarbonates.Itistheskeletalmaterialofdiatomsbutisnotknowntoplayasignificantroleinthestructureofprocessesofhigherlifeforms.Silicaisonlyslightlysolubleinwater.Thepresenceofmostsilicainnaturalwaterscomesfromthegradualdegradationofsilica-containingminerals.Thetypeandcompositionofthesilica-containingmineralsincontactwiththewaterandthepHofthewateraretheprimaryfactorscontrollingboththesolubilityandtheformofsilicaintheresultingsolution.Silicamayexistinsuspendedparticles,asacolloid,orinsolution.Itmaybemonomericorpolymeric.Insolutionitcanexistassilicicacidorsilicateion,dependinguponpH.Thesilicacontentofnaturalwatersiscommonlyinthe5to25mg/Lrange,althoughconcentrationsover100mg/Loccurinsomeareas.Silicaconcentrationisanimportantconsiderationinsomeindustrialinstallationssuchassteamgenerationandcoolingwatersystems.Undercertainconditions,silicaformstroublesomesilicaandsilicatescales,particularlyonhigh-pressuresteamturbineblades.Incoolingwatersystems,silicaformsdepositswhensolubilitylimitsareexceeded.Incontrast,silicamaybeaddedasatreatmentchemicalinsomesystems,forexample,incorrosioncontrol.Silicaremovaliscommonlyaccomplishedbyionexchange,distillation,reverseosmosis,orbyprecipitation,usuallywithmagnesiumcompoundsinahotorcoldlimesofteningprocess.1.1Thistestmethodcoversthedeterminationofsilicainwaterandwastewater;however,theanalystshouldrecognizethattheprecisionandaccuracystatementsforreagentwatersolutionsmaynotapplytowatersofdifferentmatrices.1.2Thistestmethodisacolorimetricmethodthatdeterminesmolybdate-reactivesilica.Itisapplicabletomostwaters,butsomewatersmayrequirefiltrationanddilutiontoremoveinterferencesfromcolorandturbidity.Thistestmethodisusefulforconcentrationsaslowas20[u]g/L.1.3Thistestmethodcoversthephotometricdeterminationofmolybdate-reactivesilicainwater.Duetothecomplexityofsilicachemistry,theformofsilicameasuredisdefinedbytheanalyticalmethodasmolybdate-reactivesilica.Thoseformsofsilicathataremolybdate-reactiveincludedissolvedsimplesilicates,monomericsilicaandsilicicacid,andanundeterminedfractionofpolymericsilica.1.4Theusefulrangeofthistestmethodisfrom20to1000[u]g/Latthehigherwavelength(815nm)and0.1to5mg/Latthelowerwavelength(640nm).Itisparticularlyapplicabletotreatedindustrialwaters.Itmaybeappliedtonaturalwatersandwastewatersfollowingfiltrationordilution,orboth.Forseawaterorbrines,thistestmethodisapplicableonlyifmatchedmatrixstandardsorstandardadditiontechniquesareemployed.1.5Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappropriatesafetyandhealthpracticesanddeterminetheapplicabilityofregulatorylimitationspriortouse.Note1--Formanynaturalwaters,ameasurementofmolybdate-reactivesilicabythistestmethodprovidesacloseapproximationoftotalsilica,and,inpractice,thecolorimetricmethodisfrequentlysubstitutedforothermoretime-consumingtechniques.Thisisacceptablewhen,asfrequentlyoccurs,themolybdate-reactivesilicaisinthe