Heap Leaching: Key Technical Points-Part1

Granulation and Stacking

1. Granulation Process

Proper granulation is essential for efficient gold leaching. The following parameters must be controlled:

pH Adjustment with Lime

• The pH of the ore-lime mixture must be between 9.5 and 10.5.
• To determine the correct lime dosage:
  1. Prepare samples in beakers using 1000 grams of ore.
  2. Add 2g, 4g, and 6g of lime to separate samples.
  3. Add water to form aggregates.
  4. Let the samples sit for 24 hours, then measure the pH.
  5. Select the mixture with a stable pH in the desired range.

Cement Testing (Aggregate Stability)

• Mix ore, lime, and a small amount of cement.
• After 24 hours in water, aggregates should not turn into mud.
• If aggregates remain intact, the lime dosage is sufficient.

Sodium Cyanide (NaCN) Dosage

• NaCN concentration: 0.1% to 0.5%.
• Dosage: 60 to 150 grams per ton of ore, depending on ore impurities and moisture.
• Final pH of granules: Around 11.5.

Moisture Content

• Granule moisture: 15% to 20%.
• Ore moisture: Approximately 10%.
• Total moisture must not exceed 30%, or granules may soften and break down.

Curing Time and Weather Considerations

• Curing time: At least 72 hours.
• If it rains during granulation:
  • Cover the ore to prevent gold loss.
  • Alternatively, use side-building and side-spraying to protect against weather during granulation.

2. Ore Stacking

Stacking affects permeability and leaching efficiency.

• Avoid excessive compaction; rolling the heap repeatedly can crush particles into dense “cakes.”
• Use conveyor belts when possible for even distribution.
• Recommended heap height: 3 to 4 meters.
• Proper stacking improves leaching rates over time.

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