Figure 1: Dry stack facility at La Coipa Mine, Chile (Anglo American/Debswana)
Introduction
Dry stacking of tailings has been developed due to advancements in large capacity pressure and vacuum filters. The tailings are dried out to contain <20% water content (depending on the specific gravity) allowing them to be either trucked or by conveyor to the disposal site. The tailings are then spread out and compacted to increase the density of the stack. The deposit is much more stable than a paste disposal site.
Advantages:
- The high density of the tailings reduces the overall volume of the storage facility required (less land required).
- Surface stability is much safer than conventional wet deposition and allows for quick plantation.
- The dry stack can be raised to heights which would not be economical with conventional impoundments.
- Groundwater contamination is reduced.
- Useful in arid climates where water conservation is an issue.
- For cold climates dry stacking prevents pipe freezes and frosting problems with conventional impoundments.
- Binders (cement) can be used to increase the stability of the deposit.
- Low seepage levels from the stack
Disadvantages:
- Higher costs than conventional impoundment storage.
- Largely unproven technology and disposal method.
- Problems with dust and tailings becoming airborne.
The Mine
18,000t of tailings a day are dewatered by belt filters, conveyed to the stack area and deposited by a mobile radial stacker.
Vacuum filters
were used to dewater the tailings in the hope of retaining dissolved
gold from the process solution. The high rate of dewatering helps to
lower the saturation of the tailings stack which helps in water conservation
and stability in the high seismic area.
References
Martin, T. E.,
M. P. Davies, et al. (2002). "Stewardship of Tailings Facilities."
Engels, J. and D. Dixon-Hardy (2004). Tailings disposal - Today's storage
of high volumes of waste from mines. JKMRC Conference 2004, Brisbane,
Australia.
PlacerDome – Private communications, 2004
