ASTM_D_6696_-_16.pdf

Designation:D669616Standard Guide forUnderstanding Cyanide Species1This standard is issued under the fixed designation D6696;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.1.Scope*1.1 This guide defines guidance based on a consensus ofviewpoints for interpretation of test results to identify variouschemical forms of cyanide.It is intended to provide a generalunderstanding of the chemical nature of distinct cyanidespecies as related to chemical analysis and environmental fateand transport.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.2.Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1426 Test Methods for Ammonia Nitrogen In WaterD3590 Test Methods for Total Kjeldahl Nitrogen in WaterD6888 Test Method for Available Cyanide with LigandDisplacement and Flow InjectionAnalysis(FIA)UtilizingGas Diffusion Separation and Amperometric DetectionD7237 Test Method for Free Cyanide and Aquatic FreeCyanide with Flow InjectionAnalysis(FIA)Utilizing GasDiffusion Separation and Amperometric Detection3.Terminology3.1 DefinitionsFor a definition of terms used in this guide,refer to Terminology D1129.4.Significance and Use4.1 This guide provides standard terminology for use inidentifying and describing the different chemical forms ofcyanide.The complex nature of cyanide chemistry,existenceof numerous distinct chemical forms as well as the variousregulatory distinctions that may be made can lead to confusionin technical discussions on cyanide and in the selection ofappropriate methods for its analysis.This guide is intended toprovide clarification and a common framework of terms anddefinitions to facilitate discussions and referencing differentcyanide chemical species and groups of cyanide compounds.4.2 The use of such common terminology is particularlyimportant from an environmental perspective because certainforms of cyanide are considered to be toxic.Therefore,theirrelease into the environment is regulated by federal and stateagencies.Thus a general understanding of cyanide chemistryand species definitions is needed for proper wastewater man-agement and testing.5.Cyanide Species Terms and Definitions5.1 Chemistry Related Terms and Definitions:5.1.1 Cyanide IonThe term used to describe a negativelycharged ion comprised of one carbon atom and one nitrogenatom triply bonded to each other(CN-).The cyanide ion isreactive and readily forms neutral compounds or anioniccomplexes with most metals.5.1.2 Free CyanideThe form of cyanide that is bioavail-able and known for its toxic effect on organisms(1).3Freecyanide refers to the sum of molecular hydrogen cyanide(HCN)and cyanide ion(CN-).Hydrogen cyanide is a colorless,poisonous gas having an odor of bitter almonds(mp=-13.4C,bp=25.6C).It is readily soluble in water existing as HCN orCN-,or both,depending on the pH conditions(pKa=9.36).Ata pH of 7 or less in water,free cyanide is present entirely asHCN;the opposite is true at pH 11 or greater.Because of itstoxicity,free cyanide is regulated in environmental wastewaterdischarges.5.1.2.1 In Test Method D7237,sum of the free cyanide(HCN and CN-)and cyanide bound in the metal-cyanidecomplexes that are easily dissociated into free cyanide underthe test conditions described in Test Method D7237 at pH 6 androom temperature.5.1.3 Aquatic Free CyanideIn Test Method D7237,freecyanide measured when the buffer or temperature is adjusted tomimic the receiving water environment.5.1.4 Simple CyanideA neutral compound comprised ofan alkali metal,alkaline earth metal or ammonium cation1This guide is under the jurisdiction of ASTM Committee D19 on Water and isthe direct responsibility of Subcommittee D19.06 on Methods for Analysis forOrganic Substances in Water.Current edition approved April 1,2016.Published April 2016.Originallyapproved in 2001.Last previous edition approved in 2014 as D6696 14.DOI:10.1520/D6696-16.2For 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.3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.*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 bound to cyanide.Simple cyanides are so named because oftheir structural simplicity and their ability to completelydissolve and dissociate in water to produce free cyanide and acation according to the following reaction:ACNA11CN2(1)where:A=alkali metal,alkaline earth metal or ammonium cation.Examples of si