You can find the answers to the questions "What is Cyanide? Why is it used? How dangerous is it?" in this article. Remember, all chemicals used in industry are harmful to humans and nature. However, what matters here is how much exposure nature and humans have to these chemicals. I would also like to remind you that sometimes people can even experience water poisoning.
If you're ready, let's get started.
Cyanide is a chemical compound containing a carbon atom triple-bonded to a nitrogen atom, represented by the C≡N group. This group is also known as the cyano group. Cyanides, which exist in both organic and inorganic forms, are primarily produced for use in industry.
An example of an inorganic cyanide is the highly toxic potassium cyanide, while an example of an organic cyanide is the less toxic acetonitrile (methyl cyanide). Not all cyanides are highly toxic.
Where is Cyanide Used?
Cyanogenic compounds are commonly used in industry as toxic salts, such as sodium cyanide and potassium cyanide, mainly for transportation and storage safety reasons. These salts are widely used in various industries including iron and steel, and mining, while hydrogen cyanide gas (HCN) is preferred in applications such as acrylic fiber, plastic production, and synthetic rubber.
Various types of cyanides are used in different industries today. Among these, the most important area of use is the chemical production industry. It is also widely used in sectors such as nylon, polyamide, acrylic, and plastic production. In mining, it is used in the leaching processes of gold and silver.
As we can see, cyanide can be found as a chemical product used in almost every industry.
Use of Cyanide in Mining
To put it simply:
Preparation: The mining area is prepared, and the ore containing gold is crushed or ground to increase accessibility.
Leaching Ponds: The ground ore is placed in large leaching ponds. These ponds are usually made of steel or concrete and lined with a plastic membrane.
Cyanide Application: Water and sodium cyanide are added to the ponds to create a cyanide solution. This solution dissolves the gold particles.
Leakage Control: The ponds' leakproofness is regularly checked. This measure helps prevent cyanide leakage into the environment.
Activation: The gold in the cyanide solution reacts with carbon or zinc to form gold complexes. This step increases the solubility of gold.
Filtration: When the solution becomes saturated with complexes containing gold, it is filtered. This step helps separate other minerals from the solution.
Recovery: Carbon or zinc is added to the filtered solution to recover gold complexes. This step allows the separation of gold.
Gold Recovery: The recovered gold is usually purified by electrolysis or other methods and poured into gold bars or dore bars for sale.
Frequently Asked Questions about Cyanide
Can Cyanide Evaporate from the Leach Field or Waste Deposit?
The most reactive form of cyanide is known as free cyanide, which includes the cyanide anion and hydrogen cyanide. The term "free cyanide" is used because cyanide in this form is not bound to metals or other compounds. This free form of cyanide is highly reactive and thus forms the most toxic forms of cyanide.
Whether cyanide is in the gas phase or the water phase depends on the pH level of the solution. At low or neutral pH levels, the dominant form of cyanide is hydrogen cyanide (HCN). As the pH increases, the cyanide anion (CN-) becomes the dominant form. At pH levels above 11, 99% of the cyanide remains in the solution as CN-. At pH 7, 99% of the cyanide is in the form of HCN and evaporates into the gas phase. At pH 9.3-9.5, CN- and HCN are in equilibrium.
The pH level of the cyanide solution used in gold mining is typically kept at 11, which is an attempt to prevent evaporation. However, maintaining this pH level can be challenging, considering the open structure of waste ponds to environmental conditions. Due to climate change, increased levels of carbon dioxide in the atmosphere, and irregular rainfall, it can be difficult to maintain the pH level and liquid volume of the ponds.
Various scientific studies indicate that cyanide can evaporate within the mining area and convert to the form of HCN. Sayed Mohamed Zain and colleagues (2017) detected different concentrations of HCN in the atmosphere near a gold mine. Orloff et al. (2006) detected HCN concentrations ranging from 0.26 to 1.86 ppb in the air within a 457.2-meter radius of a gold heap leach pad. Tran et al. (2019) reported finding HCN levels of 1 ppm at a distance of 1 meter from the leach pad, and HCN levels in the air ranging from 0.3 to 0.6 ppm depending on the distance. Brüger et al. (2018) found levels up to 5 ppm in the air in some areas. Some of the levels reported in the literature exceed the permissible levels for occupational safety and health (NIOSH, 2024).
What happens to millions of tons of soil in cyanide gold mining?
Cyanide gold mining leads to the contamination of millions of tons of soil. There are several reasons for this: acid mine drainage, leaks from waste dams, overflows or dam accidents, erosion in heaps undergoing cyanide leaching, etc. Accidents related to cyanide in the EU in recent years (Stava, Italy, 1985; Los Frailes, Spain, 1998; Baia Borsa, Romania, 2000) should be carefully examined.
Acid Mine Drainage: After the stripping process (cutting down trees and stripping the fertile topsoil), blasts are made to reach the ore-bearing layer in the mine area (These blasts are a source of particulate pollution). The ore-rich soil is transported to the leaching area, while the ore-free rock and soil (gangue) are deposited elsewhere.
The rock piles or gangues in the mine area cause the formation of acid mine drainage (acidic and highly polluted leakage water). The reaction of iron sulfide minerals (such as pyrite) in these gangues and rock piles with oxygen and moisture/water in the atmosphere results in the formation of acidic water flows. These waters dissolve heavy metals they encounter, leading to the contamination of water and soil (Tabelin et al., 2020).
Considering that gold is typically found in very low concentrations (10 ppm) in ore, it is evident that tons of soil will be excavated and processed for every gram of gold. A large portion of this soil will contribute to acid mine drainage. There are many examples of acid mine drainage caused by both the mine area and the waste dams in the scientific literature after the mine is closed.
Naicker et al. (2003) analyzed surface waters, groundwater, and soils in a region of South Africa where gold mining is conducted. The results showed that the groundwater was acidic due to pyrite oxidation and contained very high levels of heavy metals. It was observed that the topsoil (at a depth of 20 cm) was heavily contaminated with heavy metals in places where the water table was close to the surface. It was stated that the cause of soil contamination was the capillary rise and evaporation of groundwater. The contaminated groundwater reached the river in the area, lowering the pH level of the river. Water pollution was observed to persist even 10 km away from the source.
Hidayati et al. (2009) investigated heavy metal pollution in aquatic environments (water and sediment) in two gold mining areas and reported high levels of heavy metal and cyanide pollution. The researchers noted that cyanide leaked from the waste dam. Additionally, Miserendino et al. (2013) reported problems related to gold mining, including leakage or overflow from waste dams, pollutant drainage resulting from improper closure of waste areas, and pollutant flow due to soil erosion caused by changes in land use.
Do Cyanide and Its Compounds Accumulate in Organisms?
Cyanide, while quickly reacting and decomposing, forms complexes and salts of varying stability (Flynn and Haslem, 1995). It can form hundreds of different compounds and is toxic to organisms even at very low concentrations (Flynn and Haslem, 1995). Although the compounds formed by cyanide are less toxic than the original cyanide, they can persist in environmental settings for long periods. It is known that some of these compounds can accumulate in plant tissues (Eisler, 1991). Similarly, many studies have shown this accumulation in organisms (Moran, 1999). However, existing laws do not require the investigation of these cyanide compounds. Cyanide used in mining areas rapidly breaks down to form potentially toxic compounds, which can persist for long periods (Moran, 2001).
Debates continue about how much cyanide evaporates. Most of the original cyanide in depleted ores is converted into other toxic forms (cyanide-metal complexes, cyanate, thiocyanate, etc.). Most metal cyanide complexes can remain stable for decades depending on climate and environmental conditions in depleted ores (Moran, 2001; Johnson, 2000).
What Is the European Union's View on Cyanide Mining?
In 2000, a spill of cyanide and heavy metal-containing waste into the Tisza River, which spread to the Danube and the Black Sea, resulted from the collapse of the waste dam at the Baia Mare Gold Mine in Romania. After the accident, the cyanide concentration in the water increased by 100 times the limit values, seriously affecting marine life. The drinking water of more than 2 million people was contaminated. This accident brought the issue of cyanide mining to the forefront in many European countries and the European Parliament. The Czech Republic banned cyanide mining in 2002, and Germany and Hungary banned it in 2009 (EU, 2011). These bans prevented mining activities in economically feasible low-grade reserve areas. These developments affected European countries, and in 2010 (on the 10th anniversary of the disaster), the European Parliament called on the European Commission to propose legislation to ban cyanide mining in EU territories (EU, 2011). However, to date, the Commission has not responded to the Parliament's request.
What Is the World Wildlife Fund's View on Cyanide Mining?
The WWF has social and environmental concerns about mining. Particularly, low efficiency based on ore grades, excessive waste production, toxic wastes (arsenic, cadmium, cyanide, mercury), acid rock drainage, and high energy requirements for smelting are the major environmental concerns.
Socially, issues such as displacement and impoverishment of local communities, human rights violations, domestic violence, violence against women, imbalance in welfare and conditions, dangers faced by mining workers, and health problems, as well as decreased quality of life and livelihoods due to environmental degradation, are concerns.
The WWF highlights some best practices for mining. These include determining areas that will not be opened to mining, waste and toxic waste management, safe transportation and logistics, appropriate rehabilitation and site closure, adequate financial guarantees, offsetting biological diversity (creating a net positive biodiversity gain), involving local communities, minimizing displacement and resettlement, ensuring fair distribution of benefits, and signing "good neighbor agreements" with local communities.
What Is the Current Situation of Cyanide Mining in the World?
According to the Chamber of Mines, cyanide is used in approximately 85% of the world's gold production. When looking at the largest companies in the world, it is evident that cyanide is widely used. However, there are various restrictions on cyanide use in some countries. In 2010, the European Parliament voted on a resolution urging the European Commission to take action to completely ban cyanide mining. However, the Commission rejected proposing legislation to implement such a ban. Cyanide use in gold processing is banned in Montana and Wisconsin, USA.
Some provinces in Argentina have also banned cyanide mining, but there is no federal ban. In 2002, the Czech Parliament banned cyanide in gold mining. Cyanide mining was also completely banned in Hungary in 2009.
What Past Accidents Have Occurred?
Unfortunately, accidents that negatively impact people and the environment are quite common in gold mining.
The mining accident in Romania in 2000, known as the Baia Mare cyanide spill, is recorded as one of the most devastating industrial accidents in Eastern Europe after Chernobyl.
The incident, in which toxic substances leaked into the river, caused a major environmental disaster.
The leakage, which also reached Hungary and Serbia, resulted in mass fish deaths in the Tisza River.
Other major accidents in recent history in gold mines include:
1971: In a mining accident in Romania's Certej gold mine, 300,000 cubic meters of toxic water flooded the town of Certeju de Sus after the dam holding the waste water collapsed. The incident resulted in the deaths of 89 people.
1984: Over 2 billion tons of untreated waste water was discharged into the area surrounding the Ok Tedi mine in Papua New Guinea. It is believed that the toxic waste affected at least 50,000 people in the region.
The same year, it was discovered that over 610,000 cubic meters of cyanide-laden waste water had accumulated at the Summitville gold mine in the United States, operated by Canadian company Galactic Resources. Following the company's bankruptcy, the U.S. government had to spend hundreds of millions of dollars to clean up the waste water.
1995: A major leak occurred at the Omai Gold Mines mine in Guyana
Kaynaklar: Bilgi Notu - Prof. Dr. Güray Salihoğlu - BUÜ Çevre Mühendisliği Bölümü
EU, 2011, C 81 E/74, Official Journal of the European Union 15.3.2011, https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:C:2011:081E:0074:0077:EN:PDF
NIOSH, 2024. NIOSH pocket guide to chemical hazards - hydrogen cyanide. https:// www.cdc.gov/niosh/npg/npgd0333.html/
댓글