Leaching of Gold by Metal Cyanide

Gold leaching is the process of extracting gold from its ore using a chemical solvent. One commonly used method is the cyanide process, in which gold is dissolved in an aqueous solution of cyanide. The gold particles are then adsorbed onto activated carbon and subsequently recovered through electro-winning or precipitation.

Metal cyanide compounds, particularly sodium cyanide (NaCN), are the most commonly used solvents in gold leaching. These compounds have a high affinity for gold and can effectively dissolve it from the ore. Here is a detailed explanation of why metal cyanide is used for leaching gold:

1. Chemical Reaction:
- When sodium cyanide is added to the ore, it forms a complex with gold called a cyanide complex. This complex is highly stable and soluble in water.
- The chemical reaction can be represented as follows:
Au + 2NaCN + O2 + H2O → Na[Au(CN)2] + NaOH

2. Stability of Cyanide Complex:
- The cyanide complex formed with gold is stable, which means it does not readily decompose or react with other elements.
- This stability allows the complex to remain in solution, preventing the re-precipitation of gold.

3. Selective Dissolution:
- Cyanide selectively dissolves gold from the ore, leaving behind other impurities and unwanted minerals.
- This selectivity is due to the high affinity of cyanide for gold and its weak interaction with other elements.

4. Cyanide Availability:
- Sodium cyanide is readily available and relatively inexpensive compared to other solvents.
- Its availability and cost-effectiveness make it a preferred choice for large-scale gold mining operations.

5. Environmental Considerations:
- While the use of cyanide for gold leaching has some environmental concerns, proper management and control can minimize the potential risks.
- Strict regulations and protocols are in place to ensure the safe handling, storage, and disposal of cyanide solutions.

In conclusion, the leaching of gold is commonly done using metal cyanide, specifically sodium cyanide. Metal cyanide compounds have a high affinity for gold, form stable complexes, and selectively dissolve gold from the ore. The use of metal cyanide for gold leaching is a widely accepted and effective method in the mining industry.