Gold Ore Processing Guide: From Crushing to Cyanidation
Gold ore processing involves transforming raw ore into a useful product through various stages. The journey from ore to gold involves crushing, milling, concentration, and extraction. Here's a comprehensive guide to walk you through all the essential steps, with a particular focus on the cyanidation process.
1. Crushing and Grinding
A. Primary Crushing
Objective: Reduce the ore to a manageable size.
Crushing is the first mechanical step in the process of comminution. A primary crusher, often a jaw crusher, is used to reduce large rocks into smaller rock fragments. This stage is critical for preparing the ore for further processing.
B. Secondary Crushing
Objective: Achieve a finer texture suitable for grinding.
Secondary crushers, such as cone crushers, further reduce ore size. This fine crushing ensures the material is small enough to enter a grinding mill, subsequently reducing processing costs.
C. Grinding
Objective: Liberate gold particles from rock.
Grinding mills, such as ball or rod mills, further pulverize the crushed ore, releasing gold particles. This stage ensures that the subsequent processing methods will be effective.
2. Classification and Concentration
A. Classification
Objective: Separate fine particles from larger particles.
Hydrocyclones or spiral classifiers are used to classify the ground ore. Proper classification ensures that only the material small enough for the next step is processed further, improving efficiency.
B. Gravity Concentration
Objective: Separate gold particles based on gravity.
Methods like jigs, tables, and spirals use gravity to separate gold particles from other materials. This step is particularly effective for free-milling ores.
3. Leaching and Adsorption: The Cyanidation Process
A. Leaching
Objective: Dissolve gold into the solution.
- Cyanide Solution Preparation: Mix sodium cyanide with water to prepare a cyanide solution.
- Ore Slurry: Combine the classified, finely ground ore with the cyanide solution to create a slurry.
- Leaching Tanks: The slurry is agitated in tanks, allowing the cyanide to chemically react with the gold, dissolving it into the solution.
B. Adsorption
Objective: Extract gold from the cyanide solution.
Activated carbon is added to the slurry. The gold particles in the solution naturally adhere to the carbon.
- CIL (Carbon-in-Leach): Carbon is added during the leaching process.
- CIP (Carbon-in-Pulp): Carbon is added after the leaching process.
4. Gold Recovery and Refining
A. Desorption
Objective: Transfer gold from the carbon to the solution.
- Elution: The loaded carbon is treated with a hot, cyanide-stripping solution known as an eluant, reversing the gold adsorption process.
- Electrowinning: The gold-loaded eluate is passed through an electrowinning cell, where gold is deposited onto steel wool cathodes.
B. Refining
Objective: Purify the recovered gold.
The final step involves refining the gold to achieve the desired purity level:
- Melting: The gold is melted in a furnace to remove impurities.
- Casting: The molten gold is poured into molds to form ingots or other shapes for commercial use.
5. Environmental Considerations
A. Cyanide Management
Proper handling and disposal of cyanide are critical due to its toxic nature. Implementing a detoxification process for the spent slurry, such as the INCO SO2/air process, can neutralize cyanide and make it environmentally safe.
B. Tailings Management
Removing residual chemicals and securing tailings ponds prevent environmental contamination, ensuring the long-term sustainability of mining operations.
Gold ore processing, from crushing to cyanidation, involves a meticulous approach to ensure maximum gold recovery while minimizing environmental impact. Understanding each step allows miners to efficiently manage resources and achieve superior results. Implementing best practices and continuous monitoring can lead to a successful and sustainable gold extraction process.
By following this guide, those in the industry can ensure they are equipped with the knowledge to process gold ore effectively, responsibly, and profitably, tapping into the wealth that these precious metals offer.