7.8 Developing and implementing best practice for cyanide management
The discovery of the use of cyanide in the extraction of gold was hailed as a breakthrough at the end of the 19th century. Miners could recover lower concentrations of gold in ore that could not otherwise easily be extracted using the more conventional recovery methods of that time. This process involves a leaching step during which the gold is extracted from the host rock via an aqueous medium (cyanide), followed by the separation of the gold from the solution and recovery by precipitation or electro-deposition.
While its users respect the potential impact of cyanide on both people and the environment, high profile spillages and accidents have caused public concern during the last decade. Probably the most significant of these was the accidental spill in 2000 of cyanide to the Tisza River in Romania that, between the spill and corrective actions, resulted in significant fish deaths and the water pollution affecting downstream communities. In 2001 two cyanide-related incidents at AngloGold Ashanti's Ergo operation in South Africa, resulted in the death of an employee, while two others sustained serious injuries.
AngloGold Ashanti is acutely aware of the importance of the correct management of cyanide and was actively involved in the development of the adoption of the International Cyanide Management Code (Code) as the standard for cyanide management. This code is a voluntary industry initiative developed by a multi-stakeholder steering committee formed under the auspices of the United Nations Environment Programme (UNEP) and what is now the International Council on Mining and Metals (ICMM). The committee included participants from government, non-governmental organisations, cyanide producers, labour, financial institutions, and the gold mining industry. After an intense work programme, the committee finalised the technical aspects of the code in May 2002 and, in many cases, these technical aspects reach beyond the requirements of most governments and regulatory agencies. The code has two major elements:
- a principles section that commits signatories to manage cyanide in a responsible manner and covers the areas of production, transportation, handling and storage, operations, decommissioning of facilities, worker safety, emergency response training, and communications with the public.
- the second element establishes the practice that must be followed to implement each principle.
At the beginning of 2004, AngloGold Ashanti - along with several other mining companies and cyanide manufacturers - reconstituted the Industry Advisory Group (IAG) to give impetus to the global adoption and implementation of the code. The IAG met on numerous occasions during 2004 to assist in developing the administrative elements of the code. It also has engaged with the International Cyanide Management Institute (ICMI) - the entity that is the home for the code - on issues regarding future implementation of the code.
With regards to Code implementation, AngloGold Ashanti has taken a very structured approach during the past two years. Its various operations have been charged with it ensuring stricter measures are adhered to during the usage, maintenance, and transportation of cyanide. A corporate office team - headed by Bill Lethlean, head of metallurgy - is responsible for its oversight and ensuring that the company achieves compliance with the code by 2007. This process started with the regions and individual operations conducting gap analyses to determine compliance or deficiencies with the code. Then at the start of 2004, a group audit team was established to determine the level of each active mine's compliance with the Code.
Audit leader Drew Noble, coordinator, cyanide code audits, from AngloGold Ashanti Australia, heads the team, which effectively acts as an 'independent auditor' reporting its results to regional management and corporate centre. In an effort to transfer technology, the team composition changes from region to region, by including two or three different experienced personnel from other regions within the group.
"The auditing process is different from a straightforward audit in that the team takes with them the positive features that they have been identified at the various mines and shares these with the operations they visit," says Bill Lethlean. "This method also allows the team to identify common themes of compliance and non-compliance, and in so doing gives them a clear indication of areas where more work is required to attain the goals of the code."
For further information...
For more information on cyanide use in the mining industry and the effects of cyanide on people and the environment, see the electronic version of the Report to Society, or go to
www.cyanidecode.org. This website is the location of the 'International Cyanide Management Code For The Manufacture, Transport and Use of Cyanide In The Production of Gold' (Code) which is a voluntary industry code developed by a multi-stakeholder committee formed under the auspices of the United Nations Environment Programme (UNEP) and the International Council on Metals and the Environment (ICME) (now the ICMM). The site contains information about the International Cyanide Management Institute, which administers the Code and the administrative procedures used by the Institute as well as references and other information to assist in the responsible management of cyanide in gold mining. The site also includes information and application forms for potential signatories and certified operations and Code auditors.
Major Gold Producers and Suppliers Commit to the International Cyanide Management Code
(June 18, 2004 - Denver, Colorado) Six of the world's largest gold producers, together with three manufacturers of sodium cyanide, announced today their commitment to the International Cyanide Management Code (Code). The Code is a voluntary industry program for companies involved in the production of gold. Sodium cyanide is an essential chemical used in the production of gold.
The Code provides comprehensive guidance for best practice in the use and management of cyanide at gold mines around the world and reaches beyond the requirements of most governments and regulatory agencies. It covers nine key areas: production, transportation, handling and storage, operations, decommission of facilities, worker safety, emergency response, training, and communications with the public.
Mining companies committing to the Code are: AngloGold Ashanti Ltd., Barrick Gold Corp., Kinross Gold Corp., Newmont Mining Corp., Placer Dome Inc., and Rio Tinto. These companies are responsible for approximately 30 percent of annual mined gold production worldwide. Cyanide producers committing to the Code are Cyanco, CyPlus and DuPont.
The Code was developed by a steering committee of multi-stakeholders under the auspices of the United Nations Environment Programme and the International Council on Metals & the Environment. The committee was comprised of participants selected from government, non-governmental organizations, cyanide producers, labor, financial institutions, and the gold mining industry.
Today's announcement of commitment pertains to the technical aspects of the Code including the Principles, Standards and Guidance. An industry advisory group is providing support for the completion of administrative elements required to implement the certification aspects of the Code, including signatory procedures, auditor qualifications, and audit procedures.
The Code is administered by the International Cyanide Management Institute (ICMI), a non-profit organization. The full text of the Code and related information can be found at ICMI's web site: www.cyanidecode.org.
Press Release issued by the IAG
Cyanide use in the mining industry
Gold typically occurs at very low concentrations in ores and at these concentrations the use of aqueous chemical (hydrometallurgical) extraction processes is the only economically viable method of extracting the gold from the ore. Typical hydrometallurgical gold recovery involves a leaching step during which the gold is dissolved in an aqueous medium, followed by the separation of the gold bearing solution from the residues, or adsorption of the gold onto activated carbon. After elution from the activated carbon the gold is further concentrated by precipitation or electro-deposition.
Gold is one of the noble metals and as such it is not soluble in water. A complexant, such as cyanide, which stabilizes the gold in solution, and an oxidant such as oxygen are required to dissolve gold. Although alternative complexing agents for gold, such as chloride, bromide, thiourea, and thiosulfate are available, they form less stable complexes and thus require more aggressive conditions and oxidants to dissolve the gold. These reagents present risks to health and the environment, and are more expensive.
Approximately 1.4 metric tons of hydrogen cyanide are produced annually worldwide, with approximately 13% used to produce cyanide reagents for gold processing. The remaining 87% is used in industrial applications including production of plastics, adhesives, fire retardants, cosmetics, pharmaceuticals, food processing and as an anti-caking additive for table and road salts.
Cyanide is manufactured and distributed for use in gold mining industries in a variety of physical and chemical forms, including solid briquettes, flake cyanide and liquid cyanide. The form of cyanide reagent chosen for use is typically dictated by availability, means of transport, distance from source and cost. Large operations close to manufacturing facilities typically prefer liquid cyanide, but due to the risk of transporting liquids over long distances and the associated cost, smaller and more remote operations use solid forms.
Information drawn from www.cyanidecode.org
The effects of cyanide on people and the environment
Cyanide is acutely toxic to humans. Liquid or gaseous hydrogen cyanide and alkali salts of cyanide can enter the body through inhalation, ingestion or absorption through the eyes and skin. The rate of skin absorption is enhanced when the skin is cut, abraded or moist; inhaled salts of cyanide are readily dissolved and absorbed upon contact with moist mucous membranes.
The toxicity of hydrogen cyanide to humans is dependent on the nature of the exposure. Once in the bloodstream, cyanide forms a stable complex with a form of cytochrome oxidase, an enzyme that promotes the transfer of electrons in the mitochondria of cells during the synthesis of ATP. Without proper cytochrome oxidase function, cells cannot utilize the oxygen present in the bloodstream, resulting in cytotoxic hypoxia or cellular asphyxiation. The lack of available oxygen causes a shift from aerobic to anaerobic metabolism, leading to the accumulation of lactate in the blood. The combined effect of the hypoxia and lactate acidosis is depression of the central nervous system that can result in respiratory arrest and death. At higher lethal concentrations, cyanide poisoning also affects other organs and systems in the body, including the heart.
The body has several mechanisms to effectively detoxify cyanide. Some of the available antidotes to cyanide poisoning take advantage of these natural detoxifying mechanisms. Cyanide does not accumulate or biomagnify, so chronic exposure to sublethal concentrations of cyanide does not appear to result in acute toxicity. However, chronic cyanide poisoning has been observed in individuals whose diet includes significant amounts of cyanogenic plants such as cassava. There is no evidence that chronic cyanide exposure has teratogenic, mutagenic or carcinogenic effects.
Once released in the environment, the reactivity of cyanide provides numerous pathways for its degradation and attenuation including complexation, precipitation, adsorption, oxidation to cyanate and thicyanate, volatilization, biodegradation and hydrolysis. More information can be found at www.cyanidecode.org.
Although cyanide reacts readily in the environment and degrades or forms complexes and salts of varying stabilities, it is toxic to many living organisms at very low concentrations.
Information drawn from www.cyanidecode.org.
Press Release issued by the IAG