Dry Stack Tailings - Concept, Pros and Cons. Environmental effect.

1. Dry Stack Tailings
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Prepared by:
Dragan Radojcic, CPEng, RPEQ
Principal Mechanical Engineer
Mobile: +61 404 433 842
Skype: dragan.radojcic
ABN 87 502 288 089
8 Rigg Place, McDowall QLD 4053
08 August 2016

2. Dry Stack Tailings
Dewatering tailings to below saturation prior to placement in a permanent
storage facility, referred to as “Dry Stacking”.
Filtered dry stacked tailings are becoming an increasingly common
consideration for tailings management at many mines.
There is a growing use of the practice of dewatering tailings using vacuum or pressure filters
so the tailings can then be stacked. More and more mines are choosing to filter press their
tailings and place the tailings in a stack. Dry Stacking is increasing because of the need to
reduce water consumption; the need to limit seepage from the tailings; and the imperative to
build a stable stack not subject to slope failure, breaching or collapse.

3. Figure 1: Dry Stack Tailings Process Flow Diagram

4. Advantages
• Lowest amount of water consumption. Water is recovered from filtration circuit and
re-used in processing.
• Risks of catastrophic tailings breaches as associated with conventional storage
facilities are eliminated.
• Concurrent reclamation. Progressive rehabilitation is possible, spreading the cost of
closure over a longer time period when compared to conventional storage facilities.
• Higher rates of rise can be achieved due to the high dense state of the placed tailings
when compared to conventionally deposited tailings. Amenable to stacking. Reduced
footprint of storage facility.
• For cold climates, dry stacking prevents pipe freezes and frosting problems (filtered /
dry cake is conveyed or trucked, not pumped).
• Groundwater contamination through seepage is virtually eliminated.
• Filtered tailings allow better recovery of dissolved metals (e.g. heap leach).
Disadvantages
• High capital and operating costs associated with modern filtration technology that
renders other tailings storage options more economic to develop.
• Only really suited to low throughput operations (currently around 20,000 tpd; for
proposed Rosemont Copper Mine daily throughput is 75,000 t) due to equipment
costs and operational management of a large filtration plant.
• Re-handling of tailings (dozing and/or compaction) to construct stackable geometries.
• Surface contour management required to prevent accumulation and easy removal of
surface water.
• May not be practical for some ore types - oxidation of sulphides in the tailings can
create high concentrations (but low volume) of seepage water. Detailed geochemical
testing is required.
• 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.
• Seasonal fluctuations are an important consideration in the design of a dry stack
facility. A dry stack installation in a high rainfall environment can create day to day
management problems for accessibility of haulage and compaction equipment.

5. Figure 2: Dry Stacking Illustration

6. Figure 3: Concept of Converting Slurry Tailing Facility to Dry Stack Tailings Facility