ISO/TR 19588:2017

TECHNICAL ISO/TR
REPORT 19588
First edition
2017-07
Background information and guidance
on environmental cyanide analysis
Informations et lignes directrices sur l’analyse environnementale
du cyanure
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Cyanide methods for soil, water, effluents and wastes considered for this document .2
5 Summary of cyanide species and degradation products . 3
5.1 Main cyanide species . 3
5.1.1 Free cyanide . 3
5.1.2 Simple (weakly complexed) cyanides . 3
5.1.3 Strongly complexed cyanides . 4
5.2 Cyanide degradation products . 4
5.2.1 Cyanogen halides . 4
5.2.2 Thiocyanate (SCN) . 4
5.2.3 Organic cyanides . 4
-
5.2.4 Cyanates (CNO ) . 4
5.2.5 Cyanide environmental fate and degradation potential . 5
6 Information on cyanide analysis parameters to determine various cyanide species
(see also Annex B) . 5
6.1 General . 5
6.2 Free cyanide. 6
6.3 Liberatable Cyanide . 6
6.3.1 General. 6
6.3.2 Easily liberatable cyanide (ELC) . 6
6.3.3 Free cyanide (or alternatively: easily liberatable cyanide) . 6
6.3.4 Weak acid dissociable (WAD) cyanide . 6
6.4 Total cyanide . 6
6.5 Cyanide amenable to chlorination . 7
7 Current ISO/CEN environmental cyanide standards (see also Annex C) .7
7.1 Water . 7
7.1.1 ISO 6703 . 7
7.1.2 ISO 17690 . 7
7.1.3 ISO 14403-1 . 8
7.1.4 ISO 14403-2 . 8
7.2 Soil . 9
7.2.1 ISO 11262 . 9
7.2.2 ISO 17380 . 9
7.3 Waste (Slurries) . 9
7.3.1 CEN/TS 16229 . 9
7.4 Concluding remark .10
8 Other national and international cyanide standards, methodologies and guides .10
8.1 General .10
8.2 USEPA Method Kelada-01: Kelada automated test methods for total cyanide, acid
dissociable cyanide, and thiocyanate, Revision 1.2 (2001) .10
8.3 USEPA Method 335.4 Determination of total cyanide by semi-automated
colorimetry, Revision 1.0 (August 1993) . .11
8.4 USEPA Method 9012b Total and amenable cyanide (Automated colorimetric, with
off-line distillation), Revision 2 (Nov 2004, Rev 2) .11
8.5 USEPA Method 9010C Total and amenable cyanide: Distillation (Nov 2004, Rev 3) .11
8.6 USGS I-2302/I-4302/I-6302 Cyanide, calorimetric, barbituric acid, automated-
segmented flow (1989) .11
8.7 EPA/OIA-1677-09 Available cyanide by flow injection, ligand exchange,
and amperometry .12
8.8 ASTM International methods .12
8.9 The Picric acid method for determining weak acid dissociable (WAD) cyanide .12
8.10 Standard methods for the examination of water and wastewater standard
-
methods 4500-CN cyanide (1999) .13
8.11 The determination of cyanide and thiocyanate in soils and similar matrices
(2011). Methods for the examination of waters and associated materials, standing
committee of analysts, 2011 (Method 235) .14
8.12 The determination of cyanide in waters and associated materials (2007) Methods
for the Examination of Waters and Associated Materials, Standing Committee of
Analysts, 2011 (Method 214) .15
8.13 The Direct Determination of Metal Cyanides by Ion Chromatography with UV
[23]-[28] 15
Absorbance Detection .
9 Sample preservation and interferences .16
9.1 Sample preservation .16
9.1.1 ISO 5667-3 .16
9.1.2 ISO 17690 .17
9.1.3 Other cyanide methods .17
9.2 Interferences .18
10 Conclusions .19
Annex A (informative) Summary of cyanide terms and definitions .20
Annex B (informative) Summary of cyanide analytical methods .23
Annex C (informative) Summary of the methodology scopes and performance
characteristics of the ISO/CEN cyanide standards .28
Annex D (informative) Summary of ASTM international cyanide methods .37
Annex E (informative) Summary of potential cyanide method interference effects .42
Bibliography .46
iv © ISO 2017 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3,
Chemical methods and soil characteristics, in cooperation with ISO/TC 147, Water quality.
Introduction
Cyanide is a useful industrial chemical and its key role in the mining industry is to extract gold from its
ores. Worldwide, mining uses approximately 13 % of the total production of manufactured hydrogen
cyanide while the remaining 87 % is used in many other industrial processes, apart from mining. In
manufacturing, cyanide is used to make paper, textiles, and plastics. It is present in the chemicals used
to develop photographs. Cyanide salts are used in metallurgy for electroplating, metal cleaning, and
removing gold from its ore. Cyanide gas (HCN) is used to exterminate pests and vermin in ships and
buildings.
There is a large number of “official national and international methods” for the analysis of various
cyanide parameters for waters, effluents, leachates, soils and wastes. This document attempts to
provide background information and guidance on environmental cyanide analysis.
Cyanide can exist in many chemical forms (cyanide species) with various toxicity levels for a given mass
-
of CN. Highest toxicity has free cyanide appearing as HCN or CN .
Hydrogen cyanide is a colourless, poisonous gas having an odour of bitter almonds (mp = −13,4 °C,
-
bp = 25,6 °C, pKa = 9,36). It is readily soluble in water existing as HCN or CN , or both, depending on
the pH conditions (Figure 1). At a pH of 7 or less in water, free cyanide is effectively present entirely as
-
HCN; at pH 11 or greater, free cyanide is effectively present entirely as CN .
Figure 1 — Dissociation degree (%) of hydrocyanic acid (HCN) with pH
Owing to its high toxicity at low concentrations (especially to fish), “free or bioavailable cyanide” is
[1]-[7]
regulated in environmental wastewater discharges and in drinking waters . Cyanide is regarded
as an acute rather than a chronic toxin as low levels can be metabolised. It does not bioaccumulate. The
sensitivity of aquatic life to available cyanide varies with the species present and the characteristics
of the water matrix. Fish and aquatic invertebrates are particularly sensitive to bioavailable cyanide
exposure.
[6]
It is worth noting that the WHO guideline limit for cyanide in drinking water is 70 µg/l. An allocation
of 20 % of the tolerable daily intake (TDI) to drinking water is made because exposure to cyanide from
other sources is normally small and because exposure from water is only intermittent. This results in
the guideline value of 70 µg/l which is considered to be protective for both acute and long-term human
exposure.
Hydrogen cyanide and many complexed cyanides are readily soluble in water. An overview of solubilities
in water is given in Table 1.
vi © ISO 2017 – All rights reserved

[32]
Table 1 — Solubility of cyanides in water
Solubility Temperature
Species
g/l °C
Alkaline cyanides
LiCN very high unknown
NaCN 583 20
KCN 716 25
RbCN very high unknown
CsCN very high unknown
Alkaline earth cyanides
Mg(CN) unstable
Ca(CN) unstable
Sr(CN) 4H O very high unknown
2 2
Ba(CN) very high unknown
Heavy metal cyanides
−5
AgCN 2,8 × 10 18
AuCN almost insoluble unknown
Pt(CN) almost insoluble unknown
Co(CN) 2H O almost insoluble unknown
2 2
−3
Zn(CN) 5,8 × 10 18
CuCN 0,014 20
Ni(CN) 4H O 0,0 592 18
2 2
Cd(CN) 17 15
Hg(CN) 93 14
Pb(CN) high unknown
Pd(CN) high unknown
Therefore, the majority of methods are on the analysis of soluble cyanides in water, mainly to protect
the environment from toxic effects.
The toxicity of a metal cyanide complex is associated with its stability constant because the more easily
dissociated cyanide species will release cyanide more readily into the environment. The more stable
metal cyanide complexes are less likely to release cyanide into the environment.
The stability constants of the various relevant cyanide species is given in Table 2. Any complex with
a log K > about 35 is regarded as a strong complex, with lower relative toxicity, and will generally
only be detected when using a total cyanide method, often without quantitative recovery of the strong
complexes. There are method recovery problems of strong complexes in most total cyanide methods.
Nickel and copper cyanide complexes are considered to be in the weak acid dissociable (WAD) category
due to greater relative toxicity.
Table 2 — Stability constants (log K at 25 °C) of relevant metal cyanide complexes
Metal cyanide
Stability constant Weak or strong complex Reference
complex
(log K at 25 °C) (Strong log K > 30)
10 10
2-
[Cd(CN) ] 17,9 Weak [10]
2-
[Zn(CN) ] 19,6 Weak [10]
–
[Ag(CN) ] 20,5 Weak [10]
3-
[Cu(CN) ] 23,1 Weak [10]
Table 2 (continued)
Metal cyanide
Stability constant Weak or strong complex Reference
complex
(log K at 25 °C) (Strong log K > 30)
10 10
2-
[Ni(CN) ] 30,2 Weak [10]
Hg(CN) 32,8 Weak and dissociable ASTM D 6696
4-
[Fe(CN) ] 35,4 Strong [10]
-
[Au(CN) ] , 37 (best estimate) Strong [10]
2-
[Pt(CN) ] 40,0 Strong [17]
2-
[Pd(CN) ] 42,4 Strong [10]
3-
[Fe(CN) ] 43,6 Strong [10]
3-
[Co(CN) ] 64 (best estimate) Strong [10]
It is sometimes difficult to determine any individual species without interference from other cyanide
species or interference species (thiocyanate) and some cyanide degradation products (ammonia, nitrite
and nitrate) that may be present.
Thus, cyanide method parameters are empirical, where the actual method protocol often determines
the result obtained. Hence, cyanide is a method defined analyte. This is especially true for samples with
complex matrices. Many methods will determine the sum of a number of species with some not being
quantitatively determined (i.e. incomplete breakdown). Thus, it is essential that any standard cyanide
method is drafted in an unambiguous manner and the method protocol shall be closely followed to
ensure consistent results are obtained within and between laboratories. Moreover, all values reported
shall be attributed to the specific method applied.
A comprehensive overview of cyanide management is given in Reference [1].
It is felt that any regulatory limit legislation should specify the actual method to be used especially
for “bioavailable” cyanide (e.g. free, weak and dissociable, available, weak acid dissociable or easily
liberated cyanide).
NOTE The terms easily liberated cyanide and easily liberatable are both widely used and refer to the same
parameter.
It is vitally important to understand how the numerous forms of cyanide are incorporated into water
quality regulations for the protection of human health and the environment. In many countries, the
regulatory agencies tasked with implementing regulations and the public who are ultimately affected
by those regulations do not fully understand the implications of choosing one form of analysis over
another upon which to base numerical water quality standards. Also the effect of matrix interferences
on the results is not fully appreciated.
Methods with options (e.g. distillation versus gas membrane diffusion); or cyanide ion detection
systems based upon colorimetry or amperometry may give different results owing to variation in
species detection efficiencies and/or interference effects.
4- - 2-
Even when determining “total cyanide” some species such as [Fe(CN) ] , [Au(CN) ] , [Pt(CN) ] ,
6 2 4
2- 3-
[Pd(CN) ] and [Co(CN) ] may not be fully broken down to cyanide (or hydrogen cyanide) and some
4 6
distillation methods may convert thiocyanate (SCN) to cyanide.
Another issue is that there are few reference materials for the various cyanide parameters other than
for total cyanide. This is mainly due to the unstable nature of most cyanide species in environmental
matrices. Thus, traceable calibration in most matrices can be very difficult to achieve.
There are also a number of significant interference effects from a range of species. Clause 9 gives
[7]-[21]
guidance. More useful information is also given elsewhere .
There is no universal agreement on the best technique to overcome (or minimize) these interference
effects. The recommended guidance given is often that the method user should demonstrate that the
viii © ISO 2017 – All rights reserved

method employed should be fit for purpose in relation to the samples analysed. This can be difficult
for contract laboratories which receive a wide range of unknown origin samples when using a method
for which the laboratory is accredited and the method may be inappropriate for some sample matrices.
It is important to appreciate that a single employed method may not be suitable for all the samples
received and site specific holding time analysis studies may be required to verify stability of samples
being transported to a laboratory.
A number of studies in soil samples have demonstrated that it is impossible to obtain reliable results for
easily liberatable cyanide (ELC) using a manual ELC cyanide extraction/reflux method. Consequently,
the current ISO 11262 standard does not include an ELC method.
Another key issue is the use of suitable interference and preservation treatments of the sample between
taking and analysing the sample. The presence of sulfide drastically reduces the maximum permitted
storage time from taking the sample to analysing it from 7 days to 24 hours (ISO 5667-3). See also
Reference [7].
It is considered important that regulators consider the typical measurement uncertainty when
setting very low regulatory cyanide limits; typical background levels of the parameter of interest and
finally how to ensure there is no significant sample degradation prior to analysis. See Annex C and
Reference [4].
The objective of this document is to provide a broad overview, background and guidance in the above
areas. It has attempted to review this very complex topic and highlight the various problems of carrying
out fit for purpose sampling and analysis for various cyanide species in a wide range of waters and
soils especially at low levels. It should also be helpful as a training aid for staff involved in the analysis
of cyanide. It should also be relevant to regulatory bodies involved in both setting cyanide species
regulatory limits and monitoring regulatory cyanide analysis results.
TECHNICAL REPORT ISO/TR 19588:2017(E)
Background information and guidance on environmental
cyanide analysis
1 Scope
This document provides background information on the various International (ISO), American (ASTM,
EPA), and European (CEN) cyanide methods for soils, waters, effluents and wastes. It gives guidance
on how to carry out fit for purpose analysis of various forms of cyanide in environmental samples, the
significance of the results, how to minimize interference effects and the preservation of samples. Some
information is also provided on other national and international cyanide methods.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
See Annex A.
NOTE It is important to note that there is limited international consensus about many of these terms. The
International Cyanide Management Code — under guidance of the United Nations Environmental Program
(UNEP) and the International Council on Metals and the Environment (ICME) are two examples.
The International Cyanide Management Institute (ICMI) was established for the purpose of administering the
“International Cyanide Management Code for the Manufacture, Transport and Use of Cyanide in the Production
of Gold”, and to develop and provide information on responsible cyanide management practices and other factors
related to cyanide use in the gold mining industry.
ICMI’s primary responsibilities are to administer the International Cyanide Management Code for gold mining,
promote the Cyanide Code’s adoption and implementation, evaluate its implementation, manage the certification
process and to make information on the safe management practices for cyanide widely available.
The “International Cyanide Management Code For the Manufacture, Transport, and Use of Cyanide In the
Production of Gold” (Code) was developed by a multi-stakeholder Steering Committee under the guidance
of the United Nations Environmental Program (UNEP) and the then- International Council on Metals and the
Environment (ICME).
The Code is an industry voluntary program for gold mining companies. It focuses exclusively on the safe
management of cyanide and cyanidation mill tailings and leach solutions. Companies that adopt the Code shall
have their mining site processing operations that use cyanide to recover gold audited by an independent third
party to determine the status of Code implementation. Those operations that meet the Code requirements can
be certified. A unique trademark symbol can then be utilized by the certified operation. Audit results are made
public to inform stakeholders of the status of cyanide management practices at the certified operation.
The objective of the Code is to improve the management of cyanide used in gold mining and assist in the protection
of human health and the reduction of environmental impacts. ASTM International has produced a guide for
selection of their cyanide methods to use with the implementation of the cyanide code: ASTM D7728 Standard
Guide for Selection of ASTM Analytical Methods for Implementation of International Cyanide Management Code
Guidance. Ref: http:// www .cyanidecode .org/ about -icmi (accessed 03.11.2016).
Moreover, in some cases, different terms are used for the same species, and sometimes the same species are
named differently (see Clause 6 and Annex A).
As stated previously, cyanide analysis is empirical whereby the cyanide parameter method employed will define
the result obtained for a given sample. Hence, cyanide is a method defined analyte.
4 Cyanide methods for soil, water, effluents and wastes considered for this
document
Table 3 lists the analytical methods providing information on the determination of cyanide in
environmental samples from soils, waters, effluents and wastes which were considered during the
preparation of this document.
Table 3 — Analytical methods for the determination of cyanide in environmental samples from
soils, waters, effluents and wastes
Designation Title Refer to
ISO 6703-1 Water quality — Determination of cyanide — Part 1: 7.1.1
Determination of total cyanide
ISO 6703-2 Water quality — Determination of cyanide — Part 2: 7.1.1
Determination of easily liberatable cyanide
ISO 6703-3 Water quality — Determination of cyanide — Part 3: 7.1.1
Determination of cyanogen chloride
ISO 17690 Water quality — Determination of available free cyanide 7.1.2/Annex C
(pH 6) using flow injection analysis (FIA), gas-diffusion
and amperometric detection
ISO 14403-1 Water quality — Determination of total cyanide and free 7.1.3/Annex C
cyanide using flow analysis (FIA and CFA) — Part 1: Meth-
od using flow injection analysis (FIA)
ISO 14403-2 Water quality — Determination of total cyanide and free 7.1.4/Annex C
cyanide using flow analysis (FIA and CFA) — Part 2: Meth-
od using continuous flow analysis (CFA)
ISO 11262 Soil quality — Determination of total cyanid 7.2.1/Annex C
ISO 17380 Soil quality — Determination of total cyanide and easily 7.2.2/Annex C
liberatable cyanide — Continuous-flow analysis method
CEN/TS 16229 Characterization of waste — Sampling and analysis of 7.3.1
weak acid dissociable cyanide discharged into tailings
ponds
USEPA Method Kelada-01 Kelada automated test methods for total cyanide, acid 8.2
dissociable cyanide, and thiocyanate
USEPA Method 335.4 Determination of total cyanide by semi-automated col- 8.3
orimetry
USEPA Method 9012b Total and amenable cyanide (Automated colorimetric, 8.4
with off-line distillation)
USEPA Method 9010C Total and amenable cyanide: Distillation 8.5
USGS I-2302/I-4302/I-6302 Cyanide, calorimetric, barbituric acid, automated-seg- 8.6
mented flow
EPA/OIA-1677 09 Available cyanide by flow injection, ligand exchange, and 8.7
amperometry
ASTM D2036–09 Standard Test Methods for Cyanides in Water 8.8/D.1
2 © ISO 2017 – All rights reserved

Table 3 (continued)
Designation Title Refer to
ASTM D4282–02 Standard Test Method for Determination of Free Cyanide 8.8/D.2
in Water and Wastewater by Microdiffusion
ASTM D4374–06 Standard Test Methods for Cyanides in Water-Automated 8.8/D.3
Methods for Total Cyanide, Weak Acid Dissociable Cyanide,
and Thiocyanate
ASTM D6888–09 Standard Test Method for Available Cyanide with Ligand 8.8/D.4
Displacement and Flow Injection Analysis (FIA) Utilizing
Gas Diffusion Separation and Amperometric Detection
ASTM D6994–10 Standard Test Method for Determination of Metal Cyanide 8.8/D.5
Complexes in Wastewater, Surface Water, Groundwater
and Drinking Water Using Anion Exchange Chromatogra-
phy with UV Detection
ASTM D7237–10 Standard Test Method for Free Cyanide with Flow Injec- 8.8/D.6
tion Analysis (FIA) Utilizing Gas Diffusion Separation and
Amperometric Detection
ASTM D7284–08 Standard Test Method for Total Cyanide in Water by Micro 8.8/D.7
Distillation followed by Flow Injection Analysis with Gas
Diffusion Separation and Amperometric Detection
ASTM D7511–12 Standard Test Method for Total Cyanide by Segmented 8.8/D.8
Flow Injection Analysis, In-Line Ultraviolet Digestion and
Amperometric Detection
The Picric acid method for determining weak acid disso- 8.9
ciable (WAD) cyanide
Standard methods for the examina- CN- cyanide
tion of water and wastewater, Stand-
ard methods 4500
Methods for the examination of The determination of cyanide and thiocyanate in soils and
waters and associated materials, similar matrices
standing committee of analysts
(Method 235)
Methods for the Examination of The determination of cyanide in waters and associated
Waters and Associated Materials, materials
Standing Committee of Analysts
(Method 214)
various Direct determination of metal cyanides by ion chromatog-
raphy with UV absorbance detection
5 Summary of cyanide species and degradation products
5.1 Main cyanide species
5.1.1 Free cyanide
-
HCN(aq) and CN . This also includes simple fully ionised alkali and alkaline earth cyanide salts [e.g.
NaCN, KCN and Ca(CN) ] and a portion of the metal cyanide complexes dissociated under the testing
conditions.
5.1.2 Simple (weakly complexed) cyanides
- 2- - 2-
These include AgCN, Hg(CN) , Zn(CN) , CuCN, Cu(CN) , Cu(CN) , Cd(CN) , Ni(CN) , [Cd(CN) ] ,
2 2 2 3 3 2 4
2- - 3- 2- 2-
[Zn(CN) ] , [Ag(CN) ] , [Cu(CN) ] , [Hg(CN) ] , [Ni(CN) ] .
4 2 4 4 4
5.1.3 Strongly complexed cyanides
4- - 2- 2- 3- 3-
These are [Fe(CN) ] , [Au(CN) ] , [Pt(CN) ] , [Pd(CN) ] , [Fe(CN) ] , [Co(CN) ] .
6 2 4 4 6 6
NOTE The above cyanide complexes are in increasing stability constant order (see Table 2).
5.2 Cyanide degradation products
5.2.1 Cyanogen halides
These are CNCl and CNBr. These two species are rapidly hydrolysed in alkaline solution to cyanate.
The methods outlined in this document will not detect cyanogen halides if the samples are preserved
or extracted into sodium hydroxide. Cyanogen chloride hydrolyzes to cyanate at the pH used for
sample preservation (pH ≥ 12) and thus will not be detected. ISO 6703-3 can be used to determine this
parameter (see also 7.1, 8.9 J and 8.10 “CA”).
5.2.2 Thiocyanate (SCN)
Thiocyanate is not considered to be part of the free or total cyanide. The environmental impact
of thiocyanate is small compared with free (bioavailable) cyanides, and thiocyanate is normally
biologically oxidized into cyanate, carbonate, sulfate and ammonia. Thiocyanate should be determined
by a separate determination (see 8.9 “M”, 8.10 “CA” and ASTM D4374, Annex B). However, it should be
noted that upon oxidation thiocyanate can generate hydrogen cyanide under some conditions (this
includes chlorination).
NOTE Some methods for total cyanide include SCN. SCN is produced during the gold leaching process for
sulfidic ores and it finds its way in the tailings storage facilities (TSF) where accumulation over time can occur.
The environmental impact of SCN, especially as it accumulates in the TSF and heap leach spoils is not yet clearly
understood and needs to be evaluated on a site-specific basis.
5.2.3 Organic cyanides
These include substances such as cyanohydrins, cyanogenic glucosides. These are organic compounds
containing a cyanide functional group. Examples of naturally occurring organic cyanides are the
cyanogenic glycosides. Organic cyanides also include nitriles, which are substituted hydrocarbons
such as acetonitrile (CH CN) or cyanobenzene (C H CN). The chemical bond to the cyanide functional
3 6 5
-
group in organic cyanides is very stable. Thus, free cyanide (CN ion) is generally not released from
organic cyanides in aqueous solution under normal ambient conditions. These are rarely encountered
at significant concentrations in the vast majority of environmental samples and are not considered any
[10]
further in this document. More information is given elsewhere .
-
5.2.4 Cyanates (CNO )
This virtually non-toxic cyanide degradation product is not determined by any cyanide method listed
under Clause 4. It is not discussed any further in this document as cyanate cannot readily revert to
cyanide. It is formed when cyanide is oxidized (i.e. by alkaline hypochlorite) and then hydrolyses as
outlined below:
−− −−
22CN +=CIOC22NO + CI
−− −−2 −
22CNOO++HC32lO =+NCOC++3 lH O
23 2
NOTE CNO is produced during the gold leaching process and it finds its way into the tailings storage facilities
where accumulation over time can occur. CNO analysis usually forms part of “cyanide speciation” studies to
[28]
determine how cyanide is consumed in the leaching process. S. Black and R.S. Schulz have published an ion
chromatographic method for cyanate.
4 © ISO 2017 – All rights reserved

5.2.5 Cyanide environmental fate and degradation potential
Table 4 derived from Reference [3] attempts to summarize Environmental Fate and Degradation
Potential Pathways. Formation of cyanate occurs when cyanide is in the presence of oxidising
compounds such as oxygen, ozone, hydrogen peroxide, Caro’s acid and hypochlorite. In soils and waters,
the ultimate degradation products are likely to be mainly thiocyanate, cyanate, ammonia, formate,
carbon dioxide, nitrite and nitrate.
Table 4 — Cyanide environmental fate and degradation potential
Mechanism Pathway
Volatilisation Free cyanide volatilisation to the atmosphere (i.e. as HCN gas) increases as the
pH decreases. Thus, the proportion of HCN increases. Also, aeration increases
the HCN volatilization rate: -
- -
CN + H O → HCN↑ + OH
Complexation Cyanide can potentially form complexes with a wide range of metallic
elements
Adsorption Adsorption of free and complexed cyanide forms on to solid phases
Precipitation Cyanide complexes forming metallocyanide precipitates
Formation of thiocyanate Reaction of cyanide with various forms of sulfur (e.g. sulfidic ores, poly-
sulfides and thiosulfate):
2- - 2- -
Sx + CN → [S ] - + SCN and
(x-1)
2- - 2- -
S O + CN → SO + SCN
2 3 3
Oxidation Oxidation to various reaction products, such as cyanate and/or cyanogens,
ammonia, nitrite, nitrate and water:
2HCN + O → 2HOCN (hydrogen cyanate);
-
2CN + O + catalyst → 2OCN (cyanate ion);
2+ - +
2Cu + 2CN → 2Cu + (CN) (cyanogen)
HCN + 0,5O + H O → CO + NH
2 2 2 3
- - -
(CN) + 2OH → OCN + CN + H O
2 2
Formation of cyanate occurs when cyanide is in the presence of strong oxi-
disers (e.g. ozone, hydrogen peroxide, Caro’s acid and hypochlorite)
Hydrolysis HCN + 2H O → NH COOH (ammonium formate), or
2 4
HCN + 2H O → NH + HCOOH (formic acid)
2 3
Hydrolysis of cyanate:
+ +
HOCN + H O → NH + CO
3 4 2
- 4+
OCN + NH = (NH ) CO
2 2
- - - -
Aerobic degradation CN + HCO + NH → NO + NO
3 3 2 3
2HCN + O + enzyme → 2HOCN (hydrogen cyanate)
- +
Anaerobic degradation CN + 2H S(aq) → HCNS + H
- +
HCN + HS → HCNS + H
6 Information on cyanide analysis parameters to determine various cyanide
species (see also Annex B)
6.1 General
As already mentioned in Clause 3, there is limited international consensus about many of these terms.
Moreover, in some cases, different terms are used for the same species, and sometimes the same species
are named differently. Extreme care needs to be taken when comparing results obtained by different
standards.
6.2 Free cyanide
Theoretically, only hydrogen cyanide and the cyanide ion in solution should be classified as free cyanide.
Methods used to detect free cyanide should not alter the stability of weakly complexed cyanides as they
-
may otherwise be included in the free cyanide result. Free cyanide includes HCN (aq) and CN .
6.3 Liberatable Cyanide
6.3.1 General
In practical terms, liberatable cyanide can be considered to be the forms of cyanide that are bioavailable
(including free and weakly complexed) and are responsible for its acute toxic effect on organisms. Most
methods for assessing acute toxicity of cyanide are based upon this parameter.
-
Cyanide is liberated by treatment with a weak acid and determined as CN . Among the standards
described in this document, three terms are used: easily liberatable cyanide (ELC), weak acid
dissociable (WAD) cyanide, and free cyanide.
All three terms are effectively equivalent and are actually defined by the method employed. WAD
should include weak acid dissociable for the distillation methods and weak and dissociable for the
ligand addition/gas diffusion methods.
6.3.2 Easily liberatable cyanide (ELC)
According to ISO 6703-2 (water analysis), easily liberatable cyanide is:
cyanide from substances with cyanide groups and a measurable hydrocyanic acid vapour pressure at
pH = 4 and room temperature.
Such substances include all cyanides which will undergo chlorination, especially hydrocyanic acid,
alkali- and alkaline earth metal cyanides, and complex cyanides of zinc, cadmium, silver, copper and
nickel. Complex cyanides of iron and cobalt, nitriles, cyanates, thiocyanates and cyanogen chloride are
not included.
6.3.3 Free cyanide (or alternatively: easily liberatable cyanide)
According to ISO 14403-1 (water analysis), free cyanide (or alternatively: easily liberatable cyanide) is:
Sum of HCN, cyanide ions and the cyanide bound in simple metal cyanides as determined in accordance
with ISO 14403-1.
CAUTION — Free cyanide in this context is not equivalent to free cyanide as defined in 6.2.
6.3.4 Weak acid dissociable (WAD) cyanide
There are many definitions given for WAD cyanide in various methods. Typically, WAD cyanide includes
those cyanide species liberated at pH 4,0; or 4,5; or 4,5 to 6,0; or 3,0 to 6,0 (see Annex B); or by strong
acid and ligand exchange reagents through a gas permeable membrane. WAD cyanides includes:
-
HCN(aq), CN , the metal bound cyanide complexes (Zn, Cd, Cu, Hg, Ni and Ag) and others with similar
dissociation constants.
6.4 Total cyanide
This measurement of cyanide includes all free cyanides, all dissociable cyanides and all strong metal
cyanides. Only thiocyanate is excluded from the definition of total cyanide. Total cyanide includes:
- -4 -3
- HCN(aq), CN , metal bound cyanide complexes including [Fe(CN) ] , [Fe(CN) ] , a fraction of
6 6
6 © ISO 2017 – All rights reserved

-3
[Co(CN) ] , Au, Pd and Pt complex cyanides present. Most total cyanide methods do not quantitatively
recover these latter four species.
6.5 Cyanide ame
...