Gold processing involves several techniques to extract and refine gold from its ores. The choice of method depends on the type of ore, gold grade, and economic considerations. Here are the primary gold processing techniques:
1. Comminution (Crushing & Grinding)
– Purpose: Reduce ore size to liberate gold particles.
– Methods:
– Jaw Crushers & Cone Crushers: Break large rocks into smaller pieces.
– Ball Mills & SAG Mills: Further grind ore into fine powder for better gold recovery.
2. Gravity Separation
– Purpose: Separate gold from lighter gangue minerals based on density differences.
– Methods:
– Slucing Boxes & Gold Pans: Traditional methods for placer gold.
– Shaking Tables & Spirals: Used in hard rock mining.
– Centrifugal Concentrators (e.g., Knelson, Falcon): High-efficiency recovery of fine gold.
3. Flotation
– Purpose: Separate sulfide-associated gold from other minerals using chemicals.
– Process:
– Ore is mixed with water and frothing agents (e.g., xanthates).
– Air bubbles carry gold-bearing minerals to the surface for collection.
4. Cyanidation (Most Common Method)
– Purpose: Dissolve gold using cyanide solution (NaCN or KCN).
– Processes:
– Heap Leaching: Low-grade ores are stacked and sprayed with cyanide.
– Tank Leaching (CIL/CIP): Higher-grade ores are processed in agitated tanks.
– CIL (Carbon-in-Leach): Activated carbon adsorbs dissolved gold.
– CIP (Carbon-in-Pulp): Similar but with separate adsorption stages.
– Gold is later recovered from carbon via elution and electrowinning.
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5. Non-Cyanide Leaching Alternatives
(Due to environmental concerns)
– Thiosulfate Leaching: Less toxic, used for refractory ores.
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& Halide Leaching: Alternative lixiviants under research.
6. Refractory Gold Processing
(For ores where gold is locked in sulfides or not easily leachable)
– Roasting: Heat ore to oxidize sulfides and release gold.
– Pressure Oxidation (