Tailings Disposal - Mining and the Environment: From Ore to Metal - page 716

Tailings Impoundment
Erosion

Burrowing Animals

Miscellaneous
Erosion

Wind Erosion Water Erosion

Human Intrusion
or Sabotage

Subsurface, Seepage
and Piping

FIGURE 18.5
Erosion Processes

Surface Erosion

Wind erosion is often the greatest
problem in arid areas and water
erosion in wetter areas.
Source:
Based on Schoenhardt 2004

Sheet and Rill
Erosion

Flood Erosion Gully Erosion

Most adverse environmental impacts of tailings are water related. As tailings consoli-
date, 'supernatant water' separates from the slurry, forming a pond on the surface, from
where it can be decanted for disposal or, more commonly, for re-use. In tropical regions
where precipitation exceeds evaporation, decant water from a TSF may carry signii cant
loads of tailings i nes that need to be managed. Once released to the environment, i ne
tailings will spread over long distances before eventually settling as soft sediments.
Sometimes associated with i ne particles are elevated concentrations of trace metals that
are potentially mobilized by natural chemical or biological processes.
Even when all tailings solids are contained, discharged water may remain harmful to
the environment. Commonly, large volumes of water associated with tailings placement
are expelled over time. Water enters a tailings impoundment as process water, runoff
from surrounding areas, seepage from abutments and precipitation. As with waste rock,
the potential for tailings to impact water quality depends on the minerals involved and
their geochemistry and the specii c conditions at the tailings disposal site. Water ini ltrat-
ing, emanating from and passing through tailings storages may become acid with elevated
concentrations of dissolved trace metals. Chemicals introduced in the benei ciation process
may remain in water that is ultimately released to the environment. Some reagents are
toxic. Notable examples are cyanide in cyanide-based gold leaching and mercury com-
monly used in artisanal gold and silver mining. Leakage through the embankments or the
TSF l oor as a result of ongoing consolidation can continue over many decades, enabling
the transport of contaminants into ground or surface water. In most cases however, natu-
ral attenuation processes will 'bind' potential contaminants, thereby limiting their travel.
If tailings solids are potentially acid-generating with the potential to cause acid or heavy
metal contamination of surface water or groundwater, tailings deposits present particular
challenges for rehabilitation as discussed in Chapter Twenty One on Mine Closure.
Other environmental concerns relate to the mortality of wildlife or livestock alighting
on or drinking from tailings ponds, or becoming bogged in unconsolidated tailings. In arid
and seasonally dry areas where surface water sources are few and far between, birds tend
to be attracted to tailings ponds. In such situations, bird deaths have been associated with
red mud ponds adjacent to alumina rei neries, or ponds containing cyanide solutions.

Most adverse environmental
impacts of tailings are water
related.