ASTM D6696-05e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´1
Designation:D6696–05
Standard Guide for
1
Understanding Cyanide Species
This standard is issued under the fixed designation D6696; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1
´ NOTE—Table 2 was corrected editorially in January 2006.
1. Scope 5. Cyanide Species Terms and Definitions
1.1 This guide defines standard terminology used for the 5.1 Chemistry Related Terms and Definitions:
classification of the various chemical forms of cyanide. It is 5.1.1 Cyanide Ion—The term used to describe a negatively
intended to provide a general understanding of the chemical charged ion comprised of one carbon atom and one nitrogen
-
nature of distinct cyanide species as related to chemical atom triply bonded to each other (C[N ). The cyanide ion is
analysis and environmental fate and transport. reactive and readily forms neutral compounds or anionic
complexes with most metals.
2. Referenced Documents
5.1.2 Free Cyanide—The form of cyanide that is bioavail-
2
2.1 ASTM Standards:
able and known for its toxic effect on organisms (1). Free
D1129 Terminology Relating to Water cyanide refers to the sum of molecular hydrogen cyanide
-
(HCN)andcyanideion(CN ).Hydrogencyanideisacolorless,
3. Terminology
poisonous gas having an odor of bitter almonds (mp = -13.4°C,
3.1 Definitions—Foradefinitionoftermsusedinthisguide,
bp = 25.6°C). It is readily soluble in water partitioning itself as
-
refer to Terminology D1129.
HCN or CN , or both, depending on the pH conditions
(pK = 9.36). At a pH of 7 or less in water, free cyanide is
a
4. Significance and Use
present entirely as HCN; the opposite is true at pH 11 or
4.1 This guide provides standard terminology for use in
greater. Because of its toxicity, free cyanide is regulated in
identifying and describing the different chemical forms of
environmental wastewater discharges.
cyanide. The complex nature of cyanide chemistry, existence
5.1.3 Simple Cyanide—A neutral compound comprised of
of numerous distinct chemical forms as well as the various
an alkali metal, alkaline earth metal or ammonium cation
regulatory distinctions that may be made can lead to confusion
bound to cyanide. Simple cyanides are so named because of
in technical discussions on cyanide and in the selection of
their structural simplicity and their ability to completely
appropriate methods for its analysis. This guide is intended to
dissolve and dissociate in water to produce free cyanide and a
provide clarification and a common framework of terms and
cation according to the following reaction:
definitions from which to discuss and reference different
1 2
ACN→ A 1 CN (1)
cyanide chemical species and groups of cyanide compounds.
4.2 The use of such common terminology is particularly
where:
important from an environmental perspective because certain
A = alkali metal, alkaline earth metal or ammonium cation.
forms of cyanide are considered to be toxic. Therefore, their
Examples of simple cyanides include sodium cyanide
release into the environment is regulated by federal and state
(NaCN) and potassium cyanide (KCN).
agencies. Thus a general understanding of cyanide chemistry
5.1.4 Metal Cyanide Complex—A negatively charged ionic
and species definitions is needed for proper wastewater man-
complex consisting of several cyanide ions bound to a single
agement and testing.
transition metal cation. Also referred to as “metal-complexed
cyanides,” “metal cyano-complexes” or “transition metal cya-
1
nides,” these species have the general formula:
This guide is under the jurisdiction of ASTM Committee D19 on Water and is
the direct responsibility of Subcommittee D19.06 on Organic Constituents inWater.
x2
@M~CN! # (2)
b
Current edition approved July 1, 2005. Published July 2005. Originally approved
in 2001. Last previous edition approved in 2001 as D6696 – 01. DOI: 10.1520/
where:
D6696-05E01.
2
M = transition metal cation,
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM b = number of cyanide groups, and
Standards volume information, refer to the standard’s Document Summary page on
x = ionic charge of the transition metal complex.
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1

---------------------- Page: 1 ----------------------
´1
D6696–05
TABLE 2 Selected Strong Metal Cyanide Complexes (2, 3)
Metal cyanide complexes are represented by the following
equilibrium in aqueous solution: Cyanide Complex Stability Constant (log K at 25°C)
A,B
x2
...