The primary chemical used in the extraction of gold from its ore is sodium cyanide. This chemical is central to a process known as Cyanidation, also referred to as cyanide leaching, which has been the dominant gold extraction technology globally since the 1970s.
The Role of Sodium Cyanide in Gold Recovery
Sodium cyanide works by selectively dissolving gold from the crushed ore, allowing it to be separated from other minerals.
- Mechanism: When gold ore is mixed with a dilute solution of sodium cyanide, the gold reacts with the cyanide to form a soluble gold-cyanide complex. This chemical reaction allows the gold to go into solution, leaving behind the insoluble rock material.
- Concentration: The process typically uses a dilute solution of sodium cyanide, ranging from 100 parts per million (ppm) to 500 ppm, which translates to 0.01% to 0.05% cyanide by weight. This specific concentration is effective in dissolving gold while minimizing the consumption of the chemical.
- Selectivity: A key advantage of sodium cyanide is its ability to selectively target and dissolve gold, making it an efficient method for extracting the precious metal even from low-grade ores.
Understanding the Cyanidation Process
Cyanidation is a sophisticated metallurgical process involving several stages to ensure efficient gold recovery.
- Ore Preparation: Gold-bearing ore is first crushed and ground into a fine powder to expose the gold particles.
- Leaching: The finely ground ore is then mixed with a dilute sodium cyanide solution in large tanks. Agitation and aeration are often employed to facilitate the dissolution of gold.
- Gold Recovery: Once the gold is dissolved into the cyanide solution, it is typically recovered using methods like activated carbon adsorption (Carbon-in-Pulp or Carbon-in-Leach) or Merrill-Crowe process (zinc precipitation).
- Refining: The recovered gold concentrate undergoes further refining processes to achieve high purity.
Key Aspects of Sodium Cyanide in Gold Extraction
| Aspect | Description |
|---|---|
| Chemical Name | Sodium Cyanide |
| Process Name | Cyanidation (or Cyanide Leaching) |
| Primary Function | Selectively dissolves gold from ore |
| Solution Strength | 100 ppm to 500 ppm (0.01% to 0.05% cyanide) |
| Dominance | Dominant gold extraction technology since the 1970s |
| Environmental Note | While highly effective, cyanide is toxic and its use requires stringent environmental management and safety protocols to prevent contamination. |
Safety and Environmental Considerations
Given the inherent toxicity of cyanide, its use in gold extraction is subject to strict regulatory controls and environmental management practices. Responsible mining operations implement measures to neutralize cyanide in tailings and wastewater before discharge, ensuring minimal environmental impact. Research into alternative, less toxic reagents is ongoing, but sodium cyanide remains the most industrially viable and cost-effective method for large-scale gold extraction.
