Dry stacking is the most sustainable method used to store filtered tailings — the silty, sandy material that's left over once the metals are extracted. In the dry stack method, tailings are placed and compacted in a mound that is concurrently reclaimed with native soil and vegetation.
What are the problems with dry stack tailings?
Tailings.info ▫ Dry Stacking of tailings
Dust generation is a common problem in arid climates and can occur relatively quickly after tailings disposal due to the low moisture content of the placed material. A dry stack installation in a high rainfall environment can create day to day management problems for trafficability of haulage and compaction equipment.
On-Land Storage (“Dry-Stack”)
In “dry-stack” disposal, tailings stored in dry form, typically by burial in a covered and lined pit. In this regard, dry-stack storage is more similar to a modern, sealed landfill. This method takes up much less space, is less susceptible to earthquake hazards, and doesn’t require active water treatment. This makes it particularly relevant in locations where precipitation, earthquake risk are high, or space is limited.
However, dry-stack disposal has much higher up-front costs than wet storage. Dry-stack tailings must be dried, and the solid tailings must be transported by truck or conveyor instead of by slurry pipeline, which adds logistical complexity and cost.
Pits covers for dry-stack storage, like the damns around artifical lake impoundments, must be maintained in perpetuity. However, the long-term maintenance is much less than it is for large, wet tailings impoundment with dams.
In Alaska, Pogo Mine, Greens Creek Mine, and Nixon Fork Mine use dry-stacking for tailings disposal. In contrast, the Fort Knox and Red Dog mines use artifical wet impoundments with earthen dams, and Kensington Mine stores its tailings in a natural lake.
