Dry stack or filtered tailings provide several benefits over conventional slurry tailings. They are the most water conservative option as they experience minimal water losses. Seepage is limited in quantity and rate compared to other tailings types due to lower moisture content. The dry stacked tailings can be used as construction material and allow for concurrent reclamation with no long term water management issues after closure. The higher upfront costs of filtering are offset by reduced long term water treatment and liability.

1. Dry Stack Tailings Overview
John F. Lupo, Ph.D., P.E.
Principal Engineer

2. Introduction
n Types of tailings materials
n Filtered (Dry Stack) tailings
n Benefits

3. Tailings Materials Types

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. 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. Tailings Slurry

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. 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. Tailings Slurry Closure
Considerations
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. Thickened Tailings

11. Thickened Tailings
n 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 design
n Moisture content control – deposition angle
n Non-segregating (suspended fines)

12. Thickened Tailings Design
Considerations
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. Thickened 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)

14. Paste Tailings

15. Paste Tailings
n 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 design
n Moisture content control - slope
n Non-segregating (suspended fines)

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. 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. Filtered Tailings

19. What Are Filtered Tailings ?
Recovered Process Mill Crushing
Metal Circuit Circuit Circuit
Tailings
Thickener
Common to all tailings
Filter Press
OR Filtered/Dry Stack
Vacuum Belt/Plate

20. Filtered Tailings
n 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 design
n Moisture content and dust control critical to
facility operation
n One of the highest operating cost option

21. Filtered Tailings Design
Considerations
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. 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. Filtered Tailings Benefits

24. Filtered Tailings
n Limited seepage compared to other tailings.
q Rate
q Quantity
n Material can be used as construction material
q Compacted fill with high shear strength.
n Concurrent reclamation
n Surface water management
q No water pool to manage
q No chance of upset condition discharge

25. Filtered Tailings Seepage
n Seepage occurs as Saturated ~ 25 %
draindown from as- Moisture Content
placed to field
capacity moisture
content. As-Placed ~ 18 %
Moisture Content
n No water pool Draindown
providing constant moisture
recharge (like slurry
Field Capacity ~ 11
tailings) % Moisture Content
LIMITED VOLUME OF SEEPAGE WATER

26. Seepage Rates
n Slurry tailings: 6.4 gpm/ac
n Paste/Thickened tailings: 0.06 gpm/ac
n Filtered tailings: 0.007 gpm/ac

27. Construction

28. Dry Stack Example
Pogo - Alaska

29. Dry Stack Example
Pogo - Alaska

30. Dry Stack Example
La Coipa Mine – Chile

31. THANK YOU