Gold mining has long been a dirty process, but the environmental costs have been rising. As gold deposits become depleted and demand for gold increases, more and more gold is being mined using environmentally destructive practices. Open-pit mining, cyanide heap leaching, and amalgamation are dirty gold mining practices found throughout the world.
Two-thirds of newly mined gold is recovered using an environmentally harmful practice known as open-pit mining. In open-pit mining, mining companies reach the gold-laden rock (known as ore) by digging or blasting from the ground level, creating vast craters. In the past, it was more common for mining companies to obtain ore by digging targeted underground tunnels. But with rich gold deposits becoming harder to find, companies increasingly rely on open-pit mining because it is a cheap way of recovering trace amounts of gold.
Unfortunately, open-pit mining destroys the landscape, opening up holes in the ground so large that they can be a mile wide and visible from outer space. The other problem with open-pit mining is waste. After the ore is brought to the surface, it must be processed to extract the gold. Only 0.000001 percent of the ore obtained through open-pit mining consists of gold. The rest must be discarded. It is estimated that open-pit mining creates at least 20 tons of toxic waste for every 0.333 ounce gold ring.Open-pit mining,
No Dirty Gold
A technique called “heap leaching” is commonly used to extract gold from ore. In heap leaching, the ore is crushed into fine particles. It is then heaped into large piles and sprayed with cyanide, which trickles down through the ore and bonds with the gold. The resulting gold-cyanide solution is collected at the bottom of the heap and pumped to a mill, where chemicals are used to separate the gold from the cyanide. One round of heap leaching usually takes a few months.
Heap leaching leaves behind large amounts of toxic waste laden with cyanide and heavy metals. To dispose of this waste, mines often construct a dam and place the waste inside. These dams, however, are not always structurally unsound. They can leak or even fail. And because they are not dismantled after mine closure, remaining behind permanently, each new dam creates a long-term environmental hazard.
No Dirty Gold
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Amalgamation is the gold extraction method most often used in artisanal, or small-scale, gold mining. Although amalgamation is a simple and effective way to isolate gold, it results in the release of mercury, a toxic substance, into the environment.
In amalgamation, miners bring crushed ore into contact with mercury. The gold in the ore binds with the mercury, forming an alloy called amalgam. The mercury is then removed from the amalgam by dissolving it in nitric acid or evaporating it with heat. The gold remains behind.
The technique is becoming increasingly common as gold prices rise and more people in developing countries turn to gold mining. The vapor released by burning mercury, however, is extremely harmful to the environment and to the health of miners. Regular exposure to mercury can cause neurological damage and harm to the kidneys, liver, heart, lungs, colon, and immune system. When pregnant women are exposed to mercury, it can affect the neurological development of unborn children.
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