Processing-plant tailings have traditionally been deposited as low-density slurry behind tailings dams. Failures such as Brumadinho in Brazil (2019) and Mount Polley in Canada (2014) drew global attention to the risks of these structures and led to the Global Industry Standard on Tailings Management (GISTM) in 2020.
The range of dewatering methods
- Conventional and high-rate thickeners: higher underflow density and partial water recovery.
- High-density and paste thickeners: high-viscosity tailings.
- Filtration: a low-moisture cake transported by conveyor or truck, placed in layers and compacted.
Filtration technology
Plate-and-frame pressure filters (filter presses) and vacuum belt filters are the most common equipment. Selection depends on tailings size distribution, clay content, required throughput and target cake moisture. Filterability tests (filtration rate, cake moisture and cycle time) are the basis for sizing and numbering filters.
- Target cake moisture is usually set close to the optimum moisture for compaction, so that the stack can be compacted and remain stable.
- Water recovery can reach about 85–90% of the water contained in the tailings.
Dry-stack design
Stack design covers bench height and slope, layer-by-layer compaction, drainage and run-off control, and static and seismic stability analysis. Progressive cover and rehabilitation are planned from the outset as part of mine closure.
Economics
Capital and operating costs of filtration (equipment, energy, filter cloth and cake haulage) are usually higher than for conventional deposition. However, lower fresh-water demand, a smaller footprint, no retaining embankment and reduced risk and closure costs often offset the difference — especially in arid regions.
Company experience
AriaHangard designed tailings dewatering and filtration units for the Gol-e-Gohar concentrate lines at 600 and 1,060 t/h of dry solids, and designed filtration-based dewatering of 7 Mt/y of tailings at the Chah-Firouzeh copper concentrator.