Unlocking Gold's Potential: The Role and Efficiency of Cyanidation Plants in Modern Mining

Cyanidation has been the dominant gold extraction method for over a century, with modern cyanidation plants achieving recovery rates of 90-98%. This article examines the step-by-step gold processing in cyanidation plants and presents real-world case studies demonstrating their effectiveness.

The Cyanidation Process: Step by Step

1. Ore Preparation

Crushing & Grinding: Reduces ore to 75-150 microns to liberate gold particles

Pre-Treatment: Refractory ores may require roasting or bio-oxidation

2. Leaching

Cyanide Solution (0.02-0.05% NaCN) dissolves gold:

4Au + 8NaCN + O₂ + 2H₂O → 4Na[Au(CN)₂] + 4NaOH

pH maintained at 10.5-11.0 with lime to prevent HCN gas formation

Retention time: 24-72 hours in agitated tanks

3. Gold Recovery

Carbon Adsorption (CIP/CIL): Activated carbon captures gold-cyanide complexes

Zinc Precipitation (Merrill-Crowe): For high-grade solutions (>5 ppm Au)

4. Elution & Electrowinning

Loaded carbon treated with hot NaOH/NaCN solution

Gold electrowon onto steel wool cathodes

5. Smelting

Doré bars (typically 80-90% Au) produced at 1,100°C

6. Tailings Treatment

Cyanide destruction (SO₂/air or H₂O₂)

Modern plants achieve <0.2 ppm WAD cyanide in discharge

Case Studies: Cyanidation in Action

1. Muruntau Mine, Uzbekistan (World's Largest)

Process: CIL with 8-stage leaching

Scale: Processes 60 million tonnes ore/year

Recovery: 91% from 2.6 g/t ore

Innovation: Automated pH control system reduces cyanide consumption by 15%

2. Ahafo North Project, Newmont (Ghana)

Ore Type: Sulfide-refractory

Solution: BIOX® pretreatment + CIL

Results:

Recovery increased from 40% to 92.5%

Cyanide consumption lowered to 0.35 kg/t

3. Pogo Mine, Alaska (High-Efficiency Model)

Feature: Compact CIP plant in Arctic conditions

Performance:

96.2% recovery from 14 g/t ore

Zero-discharge water recycling system

Economic Impact: $0.48/tonne processing cost

Technological Advancements

Modern cyanidation plants incorporate:

Real-time cyanide monitoring (e.g., Mintek's Cyanisense)

Glycine-assisted leaching (reduces cyanide use by 30-50%)

Modular plant designs for remote locations

Environmental & Safety Considerations

While highly effective, cyanidation requires stringent controls:

ICMC Code Compliance: <50 ppm CN⁻ in tailings

Double-Lined Leach Pads: Prevent groundwater contamination

Emergency Response: HCN gas detectors with automatic shutdown

Conclusion

Cyanidation remains the gold standard (pun intended) for gold extraction, with modern plants combining high recoveries with improved environmental performance. As the case studies demonstrate:

Properly designed plants achieve >90% recovery even from complex ores

Continuous innovation is reducing cyanide consumption and environmental impact

Modular approaches make cyanidation viable for projects of all scales

For new projects, the key lies in customizing the cyanidation flow sheet to ore characteristics while incorporating the latest safety and efficiency technologies. The future of gold extraction isn't about replacing cyanidation, but about making it smarter and more sustainable.