Client Issue:
A gold mine in Africa using coconut shell activated carbon for CIP gold extraction experienced a drop in gold recovery rate from 92% to below 85%, with increased gold grade in tailings.
Initial Misdiagnosis:
The client suspected declining carbon quality and requested a supplier change.
Our Diagnosis:
Testing confirmed iodine value and hardness met standards. Further investigation revealed slurry pH was too low (around 9.5), affecting gold-cyanide complex stability. The carbon-to-slurry ratio was suboptimal, resulting in insufficient retention time. Some carbon surfaces were covered by ore slime, reducing effective adsorption area.
Solution:
- Adjusted slurry pH to 10.5–11.0;
- Optimized carbon-to-slurry ratio and extended retention time;
- Added a carbon washing stage to remove surface slime;
- Recommended 6×12 mesh gold recovery grade coconut shell AC.
Result:
Gold recovery rate restored to over 93%, tailings gold grade reduced to below 0.02 g/t, monthly gold output increased by approximately 8%.
Key Takeaway:
Declining gold recovery is not always a carbon issue. Optimization of process parameters (pH, carbon-to-slurry ratio, retention time) is equally critical.
