Processing Gold Ore
Once raw gold has been harvested, it must be separated from the stone which surrounds it. After larger pieces have been broken down to a manageable size, different techniques are used to extract the gold. The two most common methods are cyanide extraction, and mercury extraction. Both large scale and artisanal mining groups use these methods, which contribute to some of the worst environmental hazards in the world.Cyanide Extraction
Once the rock containing precious ore has been ground into fine pieces, it is mixed with a solution of sodium cyanide to remove the gold. It is then mixed with zinc to separate the metal from the cyanide, and sulfuric acid is used to remove the zinc.
Once the gold has been removed, the remaining solution is mixed with lime and dumped into a tailings pond. Over time, the chemicals naturally become less toxic, though exposure to the solution can cause serious harm to surrounding ecosystems. Accidental spills are of particular significance. Although incidents are rare, contamination from a single mine can kill fish and other organisms for several miles.
The Center for Disease Control defines cyanide as "a rapidly acting, potentially deadly chemical that can exist in various forms". Cyanide exposure prevents the cells of the body from using oxygen, causing the following symptoms: rapid breathing, restlessness, dizziness, weakness, headache, rapid heart rate, nausea and vomiting. Large amounts of cyanide can have even more serious effects on the body such as convulsions, lung injury and fatal respiratory failure. Prolonged exposure to cyanide has been known to cause brain damage and heart failure.
"One-third of all mercury pollution is caused by artisanal gold mining."Mercury Extraction
The process of removing gold from rock with mercury is fairly simple. Fine pieces of ore bearing rock are mixed with liquid mercury, which separates them. Once the gold has been collected, it is heated to burn off any residual mercury.
This technique is commonly used by small scale miners, and disposal of the chemicals is rarely ideal. Small milling operations often dump their used mercury directly into fresh water systems. The United Nations Industrial Development Organization estimates that one-third of all mercury pollution is caused by artisanal mining. Each gram of gold requires as much as five grams of mercury to process. To create a typical wedding ring can use anywhere from 56 to 140 grams (5 ounces) of mercury.
Mercury is a neurotoxin that can cause damage to the brain, nervous system, lungs and kidneys. Even in small quantities, it is most harmful to pregnant women and children. Because of the large amounts of mercury present in the world's water, many ecosystems experience lower birth rates, in addition to illness and death caused by mercury poisoning.
Some mining companies claim that their dumping methods have little impact on the environment, because they are able to pipe their trailings directly into ocean trenches, where little to no sea-life exists. Although it is unclear what effect pollution may have at such depths, any mercury that does find it's way into habited areas will ultimately effect the entire food chain.
Once mercury has been exposed to bacteria in the water, it is converted into methylmercury. This chemical is easily absorbed by surface contact, and accumulates in small animals such as plankton. Once lower organisms have been affected, a process called bioaccumulation begins. As larger animals consume the contaminated organisms, they are exposed to higher concentrations of methylmercury. This trend continues up the food chain, until higher predator species such as birds suffer serious health and development problems.
It is because of mercury poisoning that the Environmental Protection Agency suggests adults avoid eating more than one can of tuna per week, to avoid health problems. Similar guidelines are suggested for shark, swordfish and fresh or frozen tuna, since these predator fish have the highest levels of bioaccumulation.
