Mining in focus
Tailings dams form an important part of a mine’s infrastructure. In picture is the construction of
the tailings dam at Sepfluor’s Nokeng fluorspar mine in Gauteng, South Africa.
in a classifier. The coarse-grained
material is used to build the wall and
the finer material is discharged into
the interior of the dam. The slimes
materials will settle on the inside face
and penetrate a short distance, forming
an impervious layer that prevents
leakage. To raise the wall, the classifier
will be mounted on a temporary track
on the dam wall. The tailings material is
then pumped through the classifier and
the coarse material is discharged until
the secondary wall reaches the desired
height. The classifier is then moved a
distance to construct the next portion
of the wall on the same level.
Another method is to install
stationary classifiers at short intervals
along the dam wall, under the tailings
launder. The overflow is directed to the
inner edge of the existing embankment
by short lengths of launder, which
are shifted to construct a continuous
wall of the desired dimensions. The
embankments are constructed with the
steepest possible slopes to reduce cost.
Deposition
The design and operation of a tailings
storage facility depend on the mode
of deposition selected. This could
range from conventional deposition of
relatively low-density tailings, to paste
deposition of high-density tailings. In
both cases, however, metallurgical test
work needs to be conducted on the
slurry prior to deposition in the tailings
facility, notes Andrew Vietti, director of
Vietti Slurrytec.
This would entail, but not be limited
to, understanding the properties of
the slurry, notably the clay mineral
content and process water quality as
well as the dewatering and rheological
behaviour of the tailings. These test data
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provide the basic input on which the
geotechnial engineers are able to provide
secure construction and operational
designs. Vietti adds that Vietti Slurrytec
has developed ClariVie44, a process
water conditioning reagent for the
improvement of flocculation efficiency
and overflow clarity, particularly in
high-clay-containing slurries or any
other poor settling slurry environment
where thickening or dewatering of the
tailings is problematic.
Commenting on the re-processing
of old tailings dumps, Vietti notes that
the company has developed the KraVi
de-slimer washing device to remove fine
slimes, or fine, light particles from larger
or heavier particles in any metallurgical
slurry. In most instances, these fine
particles comprise the clay mineral or
fine silicate fraction. The KraVi finds
its application in any mineral slurry
stream where there is a need to remove
a problematic fine clay/silicate particle
fraction to improve the metallurgical
efficiency of a secondary upgrading or
recovery process. Vietti explains that
the main benefit of this product is that
it is highly efficient at separation, based
on size and density and a cost-effective
and high-throughput device. It offers
an alternative to ultra-fine screens and
de-sliming cyclones and to cyclone
classification for tailings dam wall
building.
Legislative requirements
South African legislation requires that
mine residue deposits (MRDs), tailings
storage facilities, tailings deposits, or
slimes dams be managed over their
entire life cycle by appropriately
qualified persons, so that it does not
pose an unreasonable risk to the public
and the environment. This includes the
controlled seepage from the tailings
facilities and containing hazardous
materials, such as cyanide, from entering
the water system. The issue of acid mine
drainage (AMD) has been a hot topic
over the years. The other environmental
and health concerns are related to the
fine dust blown from these tailings
dams and affecting the surrounding
communities. Groundwater monitoring
is also conducted from monitoring wells
surrounding the tailings dam for the
continued life of the installation.
Geotechnical perspectives
From a geotechnical perspective,
tailings facilities must be designed to
withstand the force of earthquakes, have
adequate drainage to remain stable,
and account for ground conditions. If
there is excess seepage, liners are often
used, particularly in gold mining where
cyanide is used to leach the metal from
the ore. There is no one-size-fits-all
approach that can be used in the
design of tailings dams. The design
of the tailings dam is dependent on a
number of factors; among others, the
quantity of tailings being produced and
the rate at which it is being produced.
The topographic setting needs to be
considered, along with climatic factors
and the hydrological characteristics.
Maintenance on tailings
In terms of maintenance, typical
work includes keeping tailings pipes
and water reclamation systems in
repair; monitoring water levels in the
embankment’s fill and foundation
to make sure it is meeting safety
requirements; and monitoring for
deformations within the structure itself.
Survey pins or instruments inside
the structure are used to detect any
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