Answer:

In the extraction of gold and silver, the metals are leached into an aqueous solution using cyanide ions. This process is known as cyanidation or the cyanide process.

Cyanide Ion:

Cyanide ions (CN-) are highly effective in leaching gold and silver from their ores due to their ability to form stable complexes with these metals. The cyanide ions react with the metal atoms on the surface of the ore particles, forming soluble complexes that can be easily separated from the rest of the ore.

The Cyanidation Process:

The cyanidation process involves several steps:

1. Grinding: The ore is crushed into fine particles to increase its surface area, allowing for better contact between the cyanide solution and the metal particles.

2. Leaching: The crushed ore is then mixed with a dilute cyanide solution (usually sodium cyanide, NaCN) and oxygen (O2) in large tanks or vats. The cyanide ions react with the metal particles, forming soluble complexes.

3. Adsorption: The gold and silver complexes are adsorbed onto activated carbon particles, which act as a medium to separate the metal complexes from the rest of the solution. This process is known as carbon-in-pulp (CIP) or carbon-in-leach (CIL) adsorption.

4. Desorption: The loaded carbon particles are then transferred to another vessel where they are desorbed, or stripped, of the gold and silver complexes. This is usually done by passing a concentrated cyanide solution through the carbon bed.

5. Electrolysis: The desorbed gold and silver complexes are then recovered from the cyanide solution by electrolysis. The metal ions are reduced at the cathode, forming solid metal deposits, while the cyanide ions are oxidized at the anode.

6. Smelting: The solid metal deposits obtained from electrolysis are further processed through smelting to obtain pure gold and silver.

Advantages of Cyanidation:

- Cyanidation is a highly efficient process for extracting gold and silver from their ores.
- It is relatively simple and cost-effective compared to other methods.
- Cyanide is readily available and can be easily transported and stored.
- The cyanide complexes formed are stable and can be easily separated from the rest of the ore.
- The process can be easily scaled up for large-scale industrial production.

Disadvantages of Cyanidation:

- Cyanide is highly toxic and poses environmental risks if not handled properly.
- The storage and transportation of cyanide require strict safety measures.
- The process can release hazardous gases and chemicals if not properly controlled.
- Cyanidation can result in the contamination of soil, water, and air if not properly managed.

Overall, despite its disadvantages, cyanidation remains one of the most widely used methods for the extraction of gold and silver due to its efficiency and cost-effectiveness.