What is cyanide?
Cyanide is a chemical compound that contains a carbon and nitrogen (C≡N) functional group. Cyanide is a rapidly acting and potentially deadly compound if exposed to larger quantities and if not seeking immediate help.
Cyanide exists in various forms, in nature, usually in low concentrations it can be found in more than 1000 plants such as leaves (laurel), roots (potato, cassava), vegetables (broccoli, cauliflower), beans (lima), pits (apricots, plums) algae (blue-green algae), seeds (apple, flaxseeds) fungi, grain (corn, millet) and bacteria.
It can be a colourless gas, hydrogen cyanide or in crystal forms such as sodium cyanide or potassium cyanide.
Cigarette smoke is the most common source of cyanide exposure for people who don’t work in cyanide-related industries.
How can cyanide be used?
Cyanide is a critical raw material for various industries, some of them are metal processing, production of certain chemicals, plastics, insecticides, jewellery-making, and photographic applications.
The mining industry uses cyanide to process ore for around 150 years. The mining industry uses around 15% of produced cyanide, another 85% is used by other industries.
Why did we start using cyanide for the mining industry and gold extraction?
Contrary to popular belief, most of the gold is not found in nuggets anymore. Instances where people would find nuggets of gold in the river are quite rare now.
Nowadays, our demand for gold has increased a lot, and mining companies must meet those requirements. That is why it has become harder and harder to extract gold from ore. Just to give you an idea of how hard it is, it takes Barrick (one of the biggest gold producers in the world) anywhere from 2 tons to 91 tons of rock to produce just 1 ounce of gold.
This means we need an industrial extraction process to separate the gold from other materials. This is where cyanide comes to play, because of its ability to bond well with gold and other metals.
How do we use cyanide in modern-day mining?
Cyanide is one of the main substances used for gold extraction in a process called “Cyanide Leaching” (cyanidation).
Starting in the 1970s, cyanide in a form of diluted sodium cyanide solution was used to dissolve and extract gold from ore. The process was first introduced by large-scale commercial mining, having the additional benefit that it was safer than mercury amalgamation, which was the predominant method prior to cyanide use. Today, it is also used by Artisanal and Small-Scale Gold Miners, although they are still in the transition process from mercury usage.
Generic scheme of cyanidation flowsheet
Mining (ore extraction) – Ore characterization – Ore preparation – Cyanide Leaching – Recovery of gold – Gold is smelted into dore
The first step for the mines is to characterize correctly their ore: free milling ore, refractory ore, or complex ore.
After they have detected which type of ore they are processing they have to properly prepare ore for cyanidation. What kind of preparation and pre-treatments are needed depends on the ore characterization.
Then the next step is cyanide leaching. There are different leaching methods:
- Heap leaching
- Vat leaching
- Agitated leaching
- Intensive cyanidation
Leaching methods are decided by ore characterization and by economical possibilities, as well as staff knowledge about different cyanidation methods.
In this step, it is vital for all cyanide operators to properly equip their workers and technicians and properly train them to measure cyanide levels and pH levels and to understand the importance of it.
Therefore, when doing cyanide leaching, it is crucial to properly monitor the process and the amount of cyanide used in the process.
Experts estimate that more than 30 billion USD worth of gold are lost to tailing every year due to a lack of reliable process monitoring and optimization technology.
There are various methods for cyanide monitoring, one of the most traditional methods is colorimetry using titration with silver nitrate solution.
CyanoGuard has developed a new and innovative and currently best-on-the-market cyanide monitoring solution.
Our chemical test changes colour from red to purple when the cyanide sample is flushed through the cartridge, and the device detects the colour change and reads the amount of cyanide, which is automatically updated on our online platform.
The process is simple, fast, safe, and more reliable, as it is less prone to interferences when measuring cyanide levels for complex ore and refractory ore.
Recovery of gold is mostly done by the usage of activated carbon, usage of zinc, elution and electrowinning, acid digest and smelting of gold dore.
How do we manage cyanide in order to keep workers, environment, and wildlife safe?
The best practices in cyanide usage are regulated by “The International Cyanide Management Code”. The mining industry has voluntarily created the “Cyanide Code”. The goal being to protect the environment and ensure people and wildlife safety.
There are nine principles of the “Cyanide Code” which should be followed:
Manufacturing and Sourcing, Transport, Handling and Storage, Operations, Waste Disposal, Mine Decommissioning.
For the mine to comply with the Cyanide Code, it must comply with regulations and laws of the applicable national and regional legal frameworks.
The principles are:
Cyanide production
Encourage responsible cyanide production by sourcing materials from manufacturers who operate safely, socially, and environmentally responsible.
Transport
Protect communities and the environment during its transport by hiring certified and trained transportation companies.
Handling and storage
Protect workers and the environment during cyanide handling and storage.
Operations
Manage responsible cyanide process solutions and waste streams to protect human health and the environment.
Mine decommissioning
Protect the communities and the environment from cyanide by developing and implementing decommissioning plans for cyanide facilities.
Worker safety
Protect workers’ health and safety from exposure to cyanide.
Training
Train workers and emergency response personnel to manage cyanide in a safe and environmentally protective manner.
Dialogue
Protect communities and the environment through the development of emergency response strategies and capabilities.
Conclusion
Cyanide is a toxic substance, and it is not one to be used lightly or abused. But to fulfil our market demand for precious materials, we need cyanide for metal extraction.
That is why proper cyanide management and monitoring are crucial, not only it will make your operations more economical and reduce the cost of cyanide consumption and detox reagents, but it will also have a lesser impact on the environment.
References:
Planet GOLD, Report: Best Management Practices for Cyanide Use in the Small-Scale Gold Mining Sector (December 2021)
https://en.wikipedia.org/wiki/Cyanide
https://www.911metallurgist.com/blog/cyanide-in-nature
https://www.health.ny.gov/environmental/emergency/chemical_terrorism/cyanide_general.htm
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