Dry Stack Tailings Overview

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Presented to the Rosemont Technical Team by AMEC at a project meeting to discuss the merits and the overview of Dry Stack Tailings in general. This was part of the orientation for non-technical and technical staff.

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Dry Stack Tailings Overview

  1. 1. Dry Stack Tailings Overview John F. Lupo, Ph.D., P.E. Principal Engineer
  2. 2. Introductionn  Types of tailings materialsn  Filtered (Dry Stack) tailingsn  Benefits
  3. 3. Tailings Materials Types
  4. 4. Tailings Continuum Tailings Type Consistency Tailings Slurry Water w/ sand DECREASING WATER CONTENT PUMPABLE Thickened Tailings Thin milk shake Paste Tailings Sandy yoghurt Fully Saturated NON-PUMPABLE Unsaturated Wet Filtered Tailings Wet Sand Dry Filtered Tailings Moist Sand
  5. 5. Tailings Percent Water 67 % Tailings Slurry: 30% solids by wt 42 % Thickened Tailings: 60% solids by wt 27 % Paste Tailings: 75% solids by wt 19 % Filter Tailings: 18% moisture content
  6. 6. Tailings Slurry
  7. 7. Tailings Slurry n  Least water conservative. Losses to: q  Evaporation q  Seepage q  Lock-up (in tailings pore space) n  Seepage issues depending on water quality and impoundment design n  Water management (reclaim pool) critical to facility operation n  Most often lowest operating cost option
  8. 8. Tailings Slurry Design Considerations n  Containment dam: q  Usually High Hazard q  Impoundment of water pool q  Piping concerns through dam n  Seepage management: q  Underdrains q  Cut-off walls q  Pump back systems
  9. 9. Tailings Slurry ClosureConsiderations n  Closure challenges: q  Concurrent reclamation difficult q  Long-term consolidation settlements q  Water management (seepage, consolidation, etc) continue during post-closure q  Changing geochemical environment (saturated to unsaturated)
  10. 10. Thickened Tailings
  11. 11. Thickened Tailingsn  Dewatered material but still a slurry.n  Better water conservative than slurry. Losses to: q  Evaporation q  Seepage q  Lock-up (in tailings pore space)n  Seepage issues depending on water quality and impoundment designn  Moisture content control – deposition anglen  Non-segregating (suspended fines)
  12. 12. Thickened Tailings DesignConsiderations n  Containment dam: q  Low, Medium, High Hazard q  Containment of process water and tailings q  Tailings “stacked” (.5 to 1 % slope) q  Stability of tailings stack (seismic, high rainfall, etc) n  Seepage management: q  Underdrains q  Pump back systems
  13. 13. Thickened Tailings ClosureConsiderations n  Closure challenges: q  Concurrent reclamation difficult, but can be accomplished after surface drying q  Long-term consolidation settlements q  Water management (seepage, consolidation, etc) continue during post-closure q  Changing geochemical environment (saturated to unsaturated)
  14. 14. Paste Tailings
  15. 15. Paste Tailingsn  Dewatered, but still a slurry (100% saturated)n  Better water conservative than thickened. Losses to: q  Evaporation q  Seepage q  Lock-up (in tailings pore space)n  Seepage issues depending on water quality and impoundment designn  Moisture content control - slopen  Non-segregating (suspended fines)
  16. 16. Paste Tailings Design Considerations n  Containment dam: q  Low, Medium, High Hazard q  Containment of process water and tailings q  Tailings “stacked” (.5 to 3 % slope) q  Stability of tailings stack (seismic, high rainfall, etc) n  Seepage management: q  Underdrains q  Pump back systems
  17. 17. Paste Tailings Closure Considerations n  Closure challenges: q  Concurrent reclamation difficult, but can be accomplished after surface drying q  Long-term consolidation settlements q  Water management (seepage, consolidation, etc) continue during post-closure q  Changing geochemical environment (saturated to unsaturated)
  18. 18. Filtered Tailings
  19. 19. What Are Filtered Tailings ?Recovered Process Mill CrushingMetal Circuit Circuit Circuit Tailings Thickener Common to all tailings Filter Press OR Filtered/Dry Stack Vacuum Belt/Plate
  20. 20. Filtered Tailingsn  Most water conservative. Losses to: q  Evaporation q  Seepage q  Lock-up (in tailings pore space)n  Seepage issues depending on water quality and impoundment designn  Moisture content and dust control critical to facility operationn  One of the highest operating cost option
  21. 21. Filtered Tailings DesignConsiderations n  Containment dam: q  Low to Medium Hazard q  Tailings stacked (+10% slope). q  Tailings become construction material. q  Stability of tailings stack. No liquefaction n  Seepage management: q  Underdrains q  Pump back systems
  22. 22. Filtered Tailings Closure Considerations n  Closure challenges: q  Amenable to concurrent reclamation q  No long-term consolidation settlements q  Minimal water management during post-closure q  No changing geochemical environment
  23. 23. Filtered Tailings Benefits
  24. 24. Filtered Tailingsn  Limited seepage compared to other tailings. q  Rate q  Quantityn  Material can be used as construction material q  Compacted fill with high shear strength.n  Concurrent reclamationn  Surface water management q  No water pool to manage q  No chance of upset condition discharge
  25. 25. Filtered Tailings Seepagen  Seepage occurs as Saturated ~ 25 % draindown from as- Moisture Content placed to field capacity moisture content. As-Placed ~ 18 % Moisture Contentn  No water pool Draindown providing constant moisture recharge (like slurry Field Capacity ~ 11 tailings) % Moisture Content LIMITED VOLUME OF SEEPAGE WATER
  26. 26. Seepage Ratesn  Slurry tailings: 6.4 gpm/acn  Paste/Thickened tailings: 0.06 gpm/acn  Filtered tailings: 0.007 gpm/ac
  27. 27. Construction
  28. 28. Dry Stack ExamplePogo - Alaska
  29. 29. Dry Stack ExamplePogo - Alaska
  30. 30. Dry Stack ExampleLa Coipa Mine – Chile
  31. 31. THANK YOU

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