The reactions that take place during the dissolution of gold in cyanide solutions under normal conditions have been fairly definitely established. Most agree that the overall cyanide equation for leaching and cyanidation of gold is as follows: 4 Au + 8 NaCN + O2 + 2 H20 = 4 NaAu2 + 4 NaOH
The cyanide solution strength is also important in leaching gold, with the typical range of solution being in the 0.02% 0.05% NaCN. The gold particle size has a tremendous effect on the time required for dissolution in a cyanide solution. Generally, the finer the gold, the quicker it will dissolve.
Sodium cyanide is the most commonly used leaching chemical in gold extraction process. According to theoretical calculation, leaching 1 gram of gold only requires 0.5 grams of sodium cyanide. However, in most gold cyanidation plants, the consumption of cyanide is high, which is 50 100 times higher than the theoretical calculation.
In the process of leaching, a dilute form of sodium cyanide is added into the ore containing the gold. Since gold is soluble after the leaching process, it is free to move through the membrane while the rest of ore cannot pass through the membrane.
Leaching gold with a cyanide solution remains the most widely used hydrometallurgical process for the extraction of gold from ores and concentrates. Despite the difficulties and hazards of working with cyanide, no other process has yet been proven to be an economic viable alternative.
Cyanidation is a method used in the extraction of gold from its ore. This extraction is done by converting the gold to a water soluble form. The cyanidation process of gold extraction or the use of cyanide is the most common leaching process, used in the extraction of gold from its ores.
Heap leaching: In the open, cyanide solution is sprayed over huge heaps of crushed ore spread atop giant collection pads. The cyanide dissolves the gold from the ore into the solution as it trickles through the heap. The pad collects the now metal impregnated solution which is stripped of gold and resprayed on the heap until the ore is depleted.