Heap Leaching: Key Technical Points – Part 2

Part 2: Spraying and Cyanide Management

1. Spraying Principles

• Do not wash agglomerated granules to adjust pH—do this during granulation.
• Pre-spraying the ore is not recommended; it can cause sludging and destroy granulation.

2. Sodium Cyanide Concentration During Spraying

• Initial spraying concentration (in cold weather or complex ore): 0.1% to 0.08%.
• Once gold concentration increases:
  • Adjust to 0.08% to 0.06%, then later to 0.04% to 0.02%.
• Avoid overuse of NaCN to minimize cost and environmental impact.

3. Spraying Cycle

• Recommended spraying duration: 7–8 hours per day, maximum 10 hours.
• Suggested cycles:
  • Daytime (warmer): Spray 1 hour, stop 1 hour.
  • Nighttime (cooler): Spray 30 minutes, stop 1 hour or more; avoid spraying if freezing.
• Avoid continuous spraying to allow oxygen absorption by the ore heap.

4. Spraying Intensity

• Recommended spray intensity: 6–20 L/m²·h.
• High spray intensity:
  • Increases solution volume.
  • Dilutes gold concentration.
  • Reduces activated carbon adsorption efficiency.
• Excessive spraying increases:
  • Desorption workload.
  • Electrolysis cost.
  • Precious liquid pool volume.

Note: Activated carbon typically adsorbs 8–10 kg of gold per ton. Over-spraying reduces this efficiency.

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