Cyanide in mining

Cyanide-leaching allows mining companies to develop new mines and expand old mines what were previously considered economically unfeasible. There are two methods (heap leaching and vat leaching) which involve:
• Digging enormous pits (often miles wide); crushing and piling the extracted ore into heaps that would cover many football fields and are several hundred feet high (heap-leaching); or placing the crushed ore in large vats (vat-leaching)
• Spraying a cyanide solution over the heaps (or into the vats) so that the cyanide trickles down through the ore, bonding with gold (5), including particles of gold that are too small to be seen by the naked eye
• Collecting the cyanide-gold solution in ponds; then piping it to the processing plant where the gold is removed and the cyanide solution is recirculated
• Transporting the gold to a smelter/refinery to remove further impurities.
• Cyanide releases may occur in a number of ways, such as: process pond overflows, faulty liners, pipeline breaks, transportation accidents, and tailings impoundment or heap leach failures• As little as 2g of gold is extracted from one tone of low grade ore