Why is zinc added to gold cyanide
http://www.mine-engineer.com/mining/minproc/cyanide_leach.htm
Zinc is added to gold cyanide solutions as a reducing agent in a process known as the Merrill-Crowe process. This process is used to recover gold from a cyanide solution by precipitation.
Now, let's understand why zinc is specifically used in this process:
1. Cyanide Complex: Gold cyanide exists as a complex compound, known as a cyanide complex. When gold ore is treated with a cyanide solution, it forms a soluble gold cyanide complex.
2. Precipitation: In order to recover gold from the cyanide solution, a precipitation step is needed. This step involves the reduction of gold ions (Au+) to elemental gold (Au) that separates and settles out from the solution. This is achieved by the addition of a reducing agent.
3. Reducing Agent: Zinc is used as a reducing agent in the Merrill-Crowe process. It has a higher affinity for cyanide ions than gold does. When zinc is added to the gold cyanide solution, it reacts with the cyanide complex, displacing gold from the complex. This reaction results in the precipitation of gold as metallic particles.
4. Adsorption: The zinc not only acts as a reducing agent, but it also undergoes a reaction where it gets oxidized and forms zinc hydroxide complexes. These complexes tend to adsorb gold particles, aiding in the separation and recovery of gold.
In summary, by adding zinc to gold cyanide solutions, the zinc functions as a reducing agent that displaces gold from the cyanide complex, resulting in the precipitation of gold as metallic particles. This process is an effective way to recover gold from cyanide solutions in mining operations.