ASTM D6696-01

Standard Guide for Understanding Cyanide Species

SCOPE
1.1 This guide defines standard terminology used for the classification of the various chemical forms of cyanide. It is intended to provide a general understanding of the chemical nature of distinct cyanide species as related to chemical analysis and environmental fate and transport.

General Information

• Status: Historical
• Publication Date: 09-Jul-2001
• ICS: 01.040.79 - Wood technology (Vocabularies)
• ICS: 71.080.99 - Other organic chemicals
• Technical Committee: D19 - Water
• Drafting Committee: D19.06 - Methods for Analysis for Organic Substances in Water

Relations

• Replaced By: ASTM D6696-05 - Standard Guide for Understanding Cyanide Species
• Effective Date: 01-Jul-2005

Standards Content (Sample)

Designation: D 6696 – 01
Standard Guide for
1
Understanding Cyanide Species
This standard is issued under the fixed designation D 6696; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 5.1.2 Free Cyanide—The form of cyanide that is bioavail-
able and known for its toxic effect on organisms (1). Free
1.1 This guide defines standard terminology used for the
cyanide refers to either molecular hydrogen cyanide (HCN) or
classification of the various chemical forms of cyanide. It is
-
ionic cyanide (CN ). Hydrogen cyanide is a colorless, poison-
intended to provide a general understanding of the chemical
ous gas having an odor of bitter almonds (mp = -13.4°C,
nature of distinct cyanide species as related to chemical
bp = 25.6°C). It is readily soluble in water partitioning itself as
analysis and environmental fate and transport.
-
either HCN or CN depending on the pH conditions
2. Referenced Documents (pK = 9.36). At a pH of 7 or less in water, free cyanide is
a
present entirely as HCN; the opposite is true at pH 11 or
2.1 ASTM Standards:
2
greater. Because of its toxicity, free cyanide is regulated in
D 1129 Terminology Relating to Water
environmental wastewater discharges.
3. Terminology
5.1.3 Simple Cyanide—A neutral compound comprised of
an alkali metal, alkaline earth metal or ammonium cation
3.1 Definitions—For a definition of terms used in this guide,
bound to cyanide. Simple cyanides are so named because of
refer to Terminology D 1129.
their structural simplicity and their ability to completely
4. Significance and Use
dissociate in water to produce free cyanide and a cation
according to the following reaction:
4.1 This guide provides standard terminology for use in
identifying and describing the different chemical forms of 1 2
ACN → A 1 CN (1)
cyanide. The complex nature of cyanide chemistry, existence
of numerous distinct chemical forms as well as the various where:
A = alkali metal, alkaline earth metal or ammonium cation.
regulatory distinctions that may be made can lead to confusion
Examples of simple cyanides include sodium cyanide
in technical discussions on cyanide and in the selection of
(NaCN) and potassium cyanide (KCN).
appropriate methods for its analysis. This guide is intended to
5.1.4 Metal Cyanide Complex—A negatively charged ionic
provide clarification and a common framework of terms and
complex consisting of several cyanide ions bound to a single
definitions from which to discuss and reference different
transition metal cation. Also referred to as “metal-complexed
cyanide chemical species and groups of cyanide compounds.
cyanides,” “metal cyano-complexes” or “transition metal cya-
4.2 The use of such common terminology is particularly
nides,” these species have the general formula:
important from an environmental perspective because certain
forms of cyanide are considered to be toxic. Therefore, their x2
@M~CN! # (2)
b
release into the environment is regulated by federal and state
agencies. Thus a general understanding of cyanide chemistry where:
M = transition metal cation,
and species definitions is needed for proper wastewater man-
b = number of cyanide groups, and
agement and testing.
x = ionic charge of the transition metal complex.
5. Cyanide Species Terms and Definitions
Metal cyanide complexes are relatively stable and require
moderate to highly acidic conditions in order to dissociate and
5.1 Chemistry Related Terms and Definitions:
form free cyanide. The dissociation reaction occurs as follows:
5.1.1 Cyanide—The term used to describe a negatively
charged ion comprised of one carbon atom and one nitrogen x2 1 2
@M~CN! # → M 1 bCN (3)
b
-
atom triply bonded to each other (C[N ). The cyanide ion is
relatively reactive and readily forms neutral compounds or where:
M = transition metal cation,
anionic complexes with most metals.
b = number of cyanide groups, and
x = ionic charge of the transition metal complex.
1
This guide is under the jurisdiction of ASTM Committee D19 on Water and is
Based on their stability, metal cyanide complexes are di-
the direct responsibility of Subcommittee D19.06 on Organic Constituents in Water.
vided into two categories: 1) “weak metal cyanide complexes”
Current edition approved July 10, 2001. Published August 2001.
2
and 2) “strong metal cyanide complexes”.
Annual Book of ASTM Standards, Vol 11.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
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D 6696
TABLE 2 Selected Strong Metal Cyanide Complexes (2, 3)
5.1.4.1 Weak Metal Cyanide Complex—A cyanide complex
that dissociates under mildly acidic conditions (pH = 3-6) and Cyanide Complex Stability Constant (log K at 25°C)
4-
in dilute solutions, forming f
...