1. Ore Preparation
Crushing:
Primary crushing: Jaw crusher reduces ore to <150 mm.
Secondary crushing: Cone crusher further reduces ore to <25 mm.
Screening:
Vibrating screens separate crushed ore into size fractions (e.g., +2 mm, -2 mm).
2. Pre-Concentration (Optional)
Hand Sorting or Sensor-Based Sorting:
Manual removal of waste rocks or automated XRT/XRF sorting to discard low-grade material.
Coarse Gold Recovery:
Use Knelson Concentrators or Falcon Concentrators for free gold recovery from coarse fractions.
3. Grinding & Classification
Grinding:
Ball mill or rod mill grinds ore to ~0.5–1.0 mm to liberate gold particles.
Hydrocyclone Classification:
Cyclones separate slurry into fine and coarse fractions; undersize feeds gravity separation.
4. Gravity Concentration
Key equipment for gold recovery:
Jigging Machines (e.g., Pan American Jig):
Separates heavy minerals (gold) from lighter gangue via pulsating water flow.
Shaking Tables:
Finer particles (<2 mm) are stratified, with gold concentrated in grooves.
Spiral Concentrators:
For processing finer fractions (<0.5 mm); gold accumulates in inner spirals.
Centrifugal Concentrators:
Knelson or Hy-G Concentrators enhance recovery of ultrafine gold.
5. Concentrate Treatment
Cleaning:
Multi-stage gravity separation (e.g., shaking tables) to upgrade concentrate grade.
Gold Extraction:
Direct smelting of high-grade concentrates.
For complex ores: Combine with cyanidation or flotation for residual gold recovery.
6. Tailings Management
Tailings Dewatering:
Thickeners or filter presses remove water for dry stacking.
Environmental Control:
Neutralization of sulfide-bearing tailings (if present).
Key Advantages of Gravity Concentration
Low operating cost, minimal chemical use.
Ideal for coarse/free gold recovery.
Environmentally friendly compared to cyanidation.
Limitations
Lower recovery for fine or encapsulated gold.
Often combined with other methods (e.g., flotation, leaching) for optimal yield.
