Mining with Cyanide
Cyanide compounds are widely used by the mining industry to assist in the extraction of both precious and non-precious metals from rock.
In gold mining, cyanide solution is sprayed on crushed ore that is placed in piles, commonly called heaps.
The cyanide attaches to small 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 discarded mine wastes.
How does cyanide affect living organisms?
Cyanide is highly toxic compound which can be lethal if ingested or inhaled by any living organism.
Most risks associated with cyanide use are related to discharges, spillages and transportation. In recent years, a string of cyanide related mining accidents has added to the environmental and community concerns.
As a result more questions have been raised about current operating and monitoring strategies being used in the country.
What happens to cyanid ewhen it enters the environment?
- Cyanide enters the environment from both natural processes and human industrial activities.
- In air cyanide is mainly found as gaseous hydrogen cyanides
- It takes about 1-3 years for half of the hydrogen cyanide to disappear from the air
- Most cyanide in surface water will form hydrogen cyanide and evaporate.
- Cyanide does not build up in the bodies of fish.
- At high concentrations, cyanide becomes toxic to soil micro-organisms.
How might I be exposed to cyanide?
- Breathing air, drinking water, touching soil, or eating foods containing cyanide
- Smoking cigarettes and breathing smoke-filled air during fires are major sources of cyanide exposure
- Breathing air near a hazardous waste site containing cyanide.
- Eating foods containing cyanide compounds, such as cassava roots, lima beans, and almonds
- Working in an industry where cyanide is used or produced, such as electroplating, metallurgy, metal cleaning, and photography
Regulations associated with hazardous substance usage in mining activities
One of EMA’s mandates is to ensure that every citizen has a right to a clean and safe environment that is not harmful to health.
To this effect the agency encourages all stakeholders who are either in the importation, transportation or selling of this toxic chemical substance to be effective when handling them.
The statutes that regulate this chemical are Statutory Instrument 5 0f 2011 which clearly states that it is an offence to carry hazardous substances from between 6pm and 6am.
It is also the responsibility of the owner to cater for all costs of re-mediation to the environment in the case of chemical spillages.
Using the polluter pays principles, any person who causes any spillages of hazardous substances into the environment may be ordered to take some remedial action to restore the environment to its original state S.I 77 of 2009).
EIA and Ecosystems Protection Regulations SI 7, 2007 takes a precautionary approach were it seeks to minimise leaching of such chemicals to the environment. It clearly states that prescribed projects such as mining should be commenced after an EIA.
An EIA is a planning tool used to identify, predict and assess potential impacts that may arise from planned projects such as extracting of gold.
This means, precautions should be taken to prevent cyanide solution from escaping into the environment by means of leach pads lined with a plastic membrane to prevent leaching. The cyanide should also be captured and recycled. In order to minimise the impact of cyanide that is not recycled, mining facilities should treat the cyanide waste through several processes.
This method allows it to degrade naturally in sunlight (photodegredation) and through hydrolysis and oxidation, among other natural processes. Mine managers can also enhance the natural degradation, as well as use other methods to accelerate cyanide breakdown.
The Environmental Management Act CAP 20:27 places great emphasis on evaluations of potential waste water discharges because once mining operations have been initiated, discharges cannot be stopped or reduced if the effluent does not meet the water quality standards outlined in the Statutory Instrument 6 0f 2007
The public should be aware that the agency responds to reports of spillages of hazardous substances and require re-mediation of such sites.
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