Study on Process Mineralogy of Cyanide Tailings

Cyanide tailings, generated after flotation and cyanidation of gold concentrates, exhibit complex mineralogy and chemistry, varying by ore type and processing route. Key characteristics include:

• Metal Minerals:
  • Primary sulfides: Pyrite (FeS₂) dominates, with minor chalcopyrite (CuFeS₂), galena (PbS), and sphalerite (ZnS).
• Gangue Minerals:
  • Quartz (SiO₂) is predominant, alongside chlorite, mica, feldspar, and kaolinite.
• Chemical Residue:
  • Contains residual cyanide (CN⁻) and processing reagents, often with fine-grained (<0.045mm) particles and high mud content.

Core Challenges in Tailings Recovery

Three critical factors complicate metal recovery from cyanide tailings:

1. Ultra-Fine Particle Size & Colloidal Behavior
   • Over 95% of particles may be -0.045mm, forming a colloidal dispersion that hinders flotation separation.
   • High specific surface area increases reagent adsorption, reducing selectivity.
2. Mineral Inhibition from Cyanidation
   • Cyanide forms stable complexes with metal surfaces (e.g., Cu-CN, Fe-CN), suppressing natural hydrophobicity.
   • Prolonged aeration during cyanidation further oxidizes mineral surfaces, diminishing floatability.
3. Pulp Chemistry Interference
   • Argillaceous silicates (e.g., kaolinite) consume collectors and depress valuable minerals.
   • Residual CN⁻ and dissolved metals (e.g., Cu²⁺, Fe³⁺) destabilize flotation froths and compete with collectors.

Targeted Recovery Strategies

1. Copper and Sulfur (Pyrite) Recovery

• Rationale: Chalcopyrite is the primary recoverable copper mineral, while pyrite can be recycled as a sulfur source or neutralizing agent.
• Process Steps:
  • Regrinding: Optimize to -0.038mm to liberate locked chalcopyrite from gangue.
  • Depression of Pyrite: Use lime (CaO) to raise pH to 10–11, suppressing pyrite while activating chalcopyrite with copper sulfate (CuSO₄).
  • Flotation: Employ xanthate-based collectors (e.g., sodium isobutyl xanthate) for copper sulfide flotation.
• Outcome: Achieve copper concentrates with 18–22% Cu grade at 70–80% recovery.

2. Mitigating Colloidal and Chemical Interferences

• Desliming Pre-Treatment:
  • Use hydrocyclones or centrifuges to remove <20μm slimes, reducing reagent consumption.
• Cyanide Degradation:
  • Apply in-line chlorination (e.g., Ca(ClO)₂) or peroxide (H₂O₂) to decompose CN⁻ before flotation.
• Pulp pH Control:
  • Adjust to neutral-to-alkaline pH (8–10) to minimize argillaceous mineral swelling.

Operational Considerations

Economic and Environmental Benefits

• Cost Efficiency: Recovering copper and sulfur offsets processing costs, with payback periods often <18 months for retrofitted circuits.
• Sustainability: Reduces cyanide discharge risks and minimizes tailings volume, aligning with circular economy goals.
• Regulatory Compliance: Pre-treating tailings for cyanide and metal removal ensures adherence to strict effluent standards.

Actionable Steps for Mine Operators

1. Tailings Characterization:
   • Conduct mineralogical analysis (e.g., SEM-EDS, XRD) and cyanide speciation testing to design tailored flowsheets.
2. Pilot Testing:
   • Evaluate flotation parameters (reagent dosages, pH, grind size) on representative tailings samples.
3. Technology Partnerships:
   • Collaborate with suppliers of advanced flotation reagents (e.g., cyanide-degrading agents) or fine-particle separation equipment.