Environmental Engineering Reference
In-Depth Information
FIGURE 18.4
Typical Tailings Storage System
Tailings
Discharge
System
Decant
System
Decant Pool
The solids content of the slurry, as
discharged, infl uences the settling
characteristics and properties.
Beach
Water
Seepage
Collection
Ditch
Dam Wall
Tailings
Native Soil
Groundwater
Potential Impacts and Risks of Tailings Disposal
In the majority of cases, tailings are discharged into retention ponds known as tailings
impoundments or tailings storage facilities, where the solids settle out, leaving a pond of
supernatant water which may be recovered through a decant system and re-used. A typi-
cal tailings storage system is shown in Figure 18.4 .
The properties of the settled tailings solids including strength, permeability, consolida-
tion, moisture retention and potential for liquefaction under earthquake loading depend
on: (1) particle size distribution; (2) mineralogy, which affects the density and cohesive
properties; (3) extent of l occulation; and (3) moisture content and extent of consolidation,
including that resulting from desiccation on exposure.
The solids content of the slurry, as discharged, also inl uences the settling characteristics
and properties. Thick or viscous slurries, with high solids content, generally deposit homo-
geneously and form relatively steep beach slopes. Slurries with low solids contents form
l at beach angles and generally exhibit particle segregation with coarser particles settling
rapidly and successively i ner particles settling at increasing distance from the discharge
location.
Most tailings disposal operations are managed so as to maximize the extent of beach
development; i.e. the area of tailings exposed to the atmosphere. This means that the size
of the pool of supernatant water is minimized. The reason for this is to promote solar
drying, which enables relatively high densities to be achieved relatively rapidly, thereby
increasing the capacity of the storage. In some situations, the exposure of beaches is consid-
ered undesirable; for example if this would result in acid generation. In such cases, a pond
is maintained over the entire TSF surface, and the tailings slurry is discharged below pond
surface.
Potential Impacts
On land, tailings storage facilities are basically large landi lls in structure, similar to water
impoundment dams in design. By their sheer existence they have a physical impact. They
permanently alter the topography of the area where they are constructed. Tailings storages
are intended to exist for many centuries. Accordingly, they need to resist the same natural
forces that erode and level the surrounding landscape ( Figure 18.5 ). Adverse impacts may
result from exposure or removal of tailings due to these natural forces. Wind erosion is
often the greatest problem in arid areas and water erosion in wetter areas.
On land, tailings storage facilities
are basically large landfi lls in
structure, similar to water
impoundment dams in design.
Tailings storages are intended to
exist for many centuries.
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