ASTM_D_859_-_16.pdf

Designation:D85916Standard Test Method forSilica in Water1This standard is issued under the fixed designation D859;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope*1.1 This test method covers the determination of silica inwater and waste water;however,the analyst should recognizethat the precision and accuracy statements for reagent watersolutions may not apply to waters of different matrices.1.2 This test method is a colorimetric method that deter-mines molybdate-reactive silica.It is applicable to most waters,but some waters may require filtration and dilution to removeinterferences from color and turbidity.This test method isuseful for concentrations as low as 20 g/L.1.3 This test method covers the photometric determinationof molybdate-reactive silica in water.Due to the complexity ofsilica chemistry,the form of silica measured is defined by theanalytical method as molybdate-reactive silica.Those forms ofsilica that are molybdate-reactive include dissolved simplesilicates,monomeric silica and silicic acid,and an undeter-mined fraction of polymeric silica.1.4 The useful range of this test method is from 20 to 1000g/L at the higher wavelength(815 nm)and 0.1 to 5 mg/L atthe lower wavelength(640 nm).It is particularly applicable totreated industrial waters.It may be applied to natural watersand wastewaters following filtration or dilution,or both.Forseawater or brines,this test method is applicable only ifmatched matrix standards or standard addition techniques areemployed.1.5 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE1For many natural waters,a measurement of molybdate-reactive silica by this test method provides a close approximation of totalsilica,and,in practice,the colorimetric method is frequently substitutedfor other more time-consuming techniques.This is acceptable when,asfrequently occurs,the molybdate-reactive silica is in the milligram perlitre concentration range while the nonmolybdate-reactive silica,if presentat all,is in the microgram per litre concentration range.1.7 Former Test Method A(GravimetricTotal Silica)wasdiscontinued.Refer to Appendix X1 for historical information.2.Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD4841 Practice for Estimation of Holding Time for WaterSamples Containing Organic and Inorganic ConstituentsD5810 Guide for Spiking into Aqueous SamplesD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisE60 Practice for Analysis of Metals,Ores,and RelatedMaterials by SpectrophotometryE275 Practice for Describing and Measuring Performance ofUltraviolet and Visible Spectrophotometers3.Terminology3.1 Definitions:3.1.1 For definitions of terms used in this standard,refer toTerminology D1129.4.Summary of Test Method4.1 This test method is based on the reaction of the solublesilica with molybdate ion to form a greenish-yellow complex,which in turn is converted to a blue complex by reduction with1-amino-2-naphthol-1-sulfonic acid.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved June 15,2016.Published June 2016.Originallyapproved in 1945.Last previous edition approved in 2010 as D859 10.DOI:10.1520/D0859-16.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.Significance and Use5.1 Silicon comprises about 28%of the lithosphere and is,next to oxygen,the most abundant element.It is found as theoxide in crystalline forms,as in quartz;combined with otheroxides and metals in a variety of silicates;and in amorphousforms.Silicon is the most abundant element in igneous rocksand is the characteristic element of al