Part 3: Gold Leaching and Recovery
1. Gold Concentration in Precious Liquid
- Theoretical peak gold concentration in pregnant solution should be 5× the ore grade.
- Example: Ore grade = 3 g/t → Peak solution = 15 g/m³.
- In practice, aim for 2–3× the ore grade.
- In granulation heap leaching under optimal conditions:
- Peak concentration should occur between Day 1 to Day 3.
- Peak value: 6 g/m³ or more.
- Decline to <1 g/m³ signals nearing completion.
Signs of Poor Leaching
- No clear peak concentration.
- Delayed or prolonged peak period.
- Low leaching rate.
These issues may result from:
- Improper pH
- Low NaCN concentration
- Excessive spray intensity
- Poor granulation or stacking
2. Field vs. Laboratory Leaching Rate
- Lab column leaching rate (ideal conditions): ~70%.
- Field leaching rate: Expected 60–65%.
- If field results fall far below lab results:
- Investigate differences in conditions, such as spray rate, cyanide concentration, or pH.
Summary of Key Parameters
| Parameter | Recommended Value |
|---|---|
| Granule pH | 9.5 – 10.5 |
| Final pH (after NaCN addition) | ~11.5 |
| Sodium Cyanide Concentration | 0.1% → decrease to 0.02% during cycle |
| NaCN Dosage | 60 – 150 g/ton |
| Granule Moisture | 15% – 20% |
| Total Moisture (incl. ore) | ≤ 30% |
| Curing Time | ≥ 72 hours |
| Spray Intensity | 6 – 20 L/m²·h |
| Spray Duration (daily) | 7 – 8 hours max |
| Heap Height | 3 – 4 meters |
| Activated Carbon Capacity | 8 – 10 kg/t |
| Desired Pregnant Solution Peak | 2× – 5× ore grade 2× – 5× grade hours |
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