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MRF
> Environment >
Technical Issues > Cyanide Facts
CYANIDE FACTS
Q & A
This section provides basic frequently asked questions
on cyanide and its use in mining.
 What
is cyanide?
Cyanide is a general term for a group of chemicals containing
carbon (C) and nitrogen (N). Cyanide compounds include both naturally
occurring and human-made chemicals. Naturally, cyanide can be produced
by certain bacteria, fungi, algae, and it is found in a number of
foods and plants. The principal human-made cyanide forms are hydrogen
cyanide (HCN), sodium cyanide (NaCN) and potassium cyanide (KCN).
Hydrogen cyanide is a colorless gas with a faint, bitter, almond-like
odor. Cyanide is acute toxic and is lethal if ingested or inhaled.
What
happens to cyanide when released to the environment?
Cyanides are not persistent in water or soil. Cyanides
may accumulate in bottom sediments, but residues are generally as
low as <1 mg/kg even near polluting sources. Majority of
an accidental release of cyanide is volatilised to the atmosphere
where it is quickly diluted and degraded by ultra violet. Other factors,
such as biological oxidation, precipitation and the effects of sunlight
also contribute to cyanide degradation. There is no evidence of bioaccumulation
in the food chain, and hence, secondary poisoning does not occur.
How
is it used?
Cyanide combines with many organic and inorganic compounds.
Because of its unique properties, cyanide is used in the manufacture
of metal parts and numerous common organic products. About 1.4 million
tonnes of hydrogen cyanide (HCN) are produced annually worldwide,
of which only about 20% is converted into sodium cyanide (NaCN) and
mainly used in the extraction of precious metals such as gold and
silver, and others (e.g. copper). The remaining 80 % of the hydrogen
cyanide (HCN) is used in electroplating, metallurgy, and in the production
of a wide range of chemicals, such as plastics, fire retardant, cosmetics,
dyes, nylon, paints, pharmaceuticals, Plexiglas, rocket propellant,
and road and table salts.
Figure: Industrial use of cyanide production.
Sources: Terry Mudder; The Management of Cyanide
in Gold Extraction (ICME)
Why
is cyanide dangerous?
Cyanide is a fast acting poison in the human body. It
affects our ability to breathe. Severe breathing difficulties develop
very rapidly when cyanide is swallowed, inhaled or absorbed through
the skin. Highly poisonous cyanide gas can be produced when cyanide
solids or liquids are mixed with moisture in air, or with steam, acid,
acid fumes or if air is bubbled through a cyanide solution. Cyanide
gas is highly flammable and reacts violently in some situations (e.g.,
a large amount of cyanide gas mixed with air may suddenly explode).
There is an extremely high risk of explosion if cyanides are exposed
to heat or flames.
How
is cyanide used in mining?
Cyanide is one of only a few chemical reagents that
dissolves gold in water. It is a common industrial chemical that is
readily available at a reasonably low cost. For both technical and
economic reason, cyanide is the chemical of choice for the recovery
of gold from ores. In gold mining, a dilute cyanide solution is sprayed
on crushed ore that is placed in piles, commonly called heaps, or
mixed with ore in enclosed vats. The cyanide attaches to minute particles
of gold to form a water-soluble, gold-cyanide compound from which
the gold can later be recovered. Cyanide is used in a similar manner
to extract silver from ores. In the extraction of non-precious metals,
such as copper, nickel, cobalt, and molybdenum, cyanide is used in
the milling and concentration processes to separate the desirable
metals from the wastes. Consequently, cyanide and related compounds
often are contained in mine tailings.
There are a number of recent reports of alternative
technologies for use in extracting gold from the waste rock, none
of which are in widespread use yet.
See the following sites for more details:
What
are the cyanide extraction processes?
The most common processes that use cyanide to extract
gold are Merrill-Crowe recovery which uses zinc powder to precipitate
the gold from solution, Carbon in Column (CIC), Carbon in Pulp (CIP),
Carbon in Leach (CIL) a variation of CIP, and Heap Leaching.
The CIP process is currently one of the most favoured in modern large
scale mines, a general description of which is provided below. A brief
overview of the various gold recovery processes available, and in
particular the processes using cyanide, can be found at the Denver
Mineral Engineers Inc. website. Further information on the CIP
process can be found on the Mintek
website.
How
can cyanide affect human health?
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In large amounts, cyanide is very harmful to people.
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Exposure to high levels of
cyanide in the air for a short time may result in:
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Exposure to lower levels
of cyanide for a long time may result in:
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People who eat large amounts
of cyanide may have symptoms including:
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deep breathing and shortness of breath,
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convulsions,
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loss of consciousness, and may die.
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Skin contact with cyanide
can produce irritation and sores.
Rescue
and first aid - Take action immediately!
Rescuers must protect themselves
- wear self-contained breathing apparatus if cyanide gas or dust is
present. If the patient's skin or clothes are contaminated
handle with care - place clothes in a bin or plastic bag until they
can be decontaminated.
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Look for firm evidence that cyanide poisoning has actually occurred
(i.e. cyanide splash or spill, breath 2
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smell of bitter almonds, several people affected, etc.),
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If cyanide poisoning is suspected or if any evidence of cyanide
poisoning is found, take the patient out of the contaminated area
into fresh air.
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Remove contaminated clothing. Wash any parts of the body that have
been splashed with cyanide or covered with cyanide dust. Inform
ambulance drivers or staff at the emergency treatment canter. Keep
patient warm with a clean sheet or blanket.
Cyanide
and skin rashes - Q&A
Q: Can cyanide or any of its compounds cause skin
rashes? Immediately or after a period of 3-6 weeks? If yes, under
what conditions, and with what concentrations can this occur?
A: Cyanide can affect the body if it comes in contact
with skin, inhaled or swallowed. It may be absorbed through the skin,
especially if there are cuts to cause even fatal poisoning. The dust
of cyanide salts is irritating to the eyes. In the presence of tears,
it may cause the symptoms of poisoning such as weakness, headache,
confusion, nausea and vomiting. Also the dust of cyanide salts may
produce irritation of the nose and skin. Strong solutions of cyanide
salts are corrosive and may produce ulcers. So yes, contact with cyanide
can cause skin irritation/rashes. The dust is probably more of a rash
problem than a liquid, since the liquid would be more toxic.
Q: Given that cyanide accidents are often mitigated
with sodium hypochlorite, which has more lasting negative effects
on the environment than the original cyanide, could this be a cause
of dermatological conditions?
Sodium hypochlorite is common household bleach. It is
certainly corrosive in strong concentrations, but progressively less
so when diluted. So I would say that you may see some skin irritation
among people exposed to cyanide salt dusts, but it would unlikely
among those exposed to CN- and/or ClO- liquids.
Q: However, in some of the recent cyanide spills
at mine sites, and most of these are into free flowing water, (and
there are too, many of those), people are reporting some 2-6 weeks
after of people with skin rashes on arms and legs - and there are
no other symptoms. Any ideas?
A: It doesn't seem like it should be CN-, but maybe
it could be a cyanide salt. Of course, there could be many other possible
causes unrelated to cyanide.
Answer by Mr. Jim Willis, Head of the Chemicals Branch,
UNEP Division of Technology, Industry and Economics
For more information, view
ATSDR ToxFAQs for Cyanide, and
MSDS, Hazardous according to criteria of Worksafe of Australia
What
are cyanide regulation levels?
Drinking Water:
Occupational exposure limits:
Key Links on Cyanide
FAQs
in cyanide:
Technical
guides on the use of cyanide and remediation
Although the routine handling of cyanide at gold mines
around the world has generally been carried out with a high level
of safety, some accidents have nevertheless occurred in recent years,
affecting wildlife and river systems in the vicinity of the mine.
Cyanide
and the environment: The Issue Papers
Other
MRF sites and UNEP Publications
Other
Information
Cyantists.com (www.cyantists.com)
- The Cyantists, those who have devoted entire careers to the scientific
understanding of cyanide and its interaction with society, and this
new website are dedicated to the generation, collection and dissemination
of reliable environmental information about the natural and manmade
sources of cyanide.
The Mining Journal Books Ltd. - Cyanide
Compendium presents the fundamentals and the approaches used in
the development of the most efficient, economical and environmentally
acceptable water management system possible for a particular mining
operation utilising the cyanidation process.
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