Mining in focus
Tailings dams usually only hit the headlines when
they fail, resulting in the loss of life and catastrophic
environmental damage. As a result, the proper
design, management, construction, and monitoring
thereof are vital, writes Nicolaas C Steenkamp.
A
tailings dam exists because of the
processing of ore. When raw
ore is mined, it is processed
in several ways. In the majority of
precious and base metal operations, the
ore rock is crushed, and then milled
before being processed. Most of these
processes use a significant amount of
water. Once the processing is complete,
the waste material, referred to as tailings,
are pumped to mining residue storage
facilities, or what is generally better
known as tailings dams.
A tailings dam is the physical
structure that holds, or impounds, the
tailings pond, which serves the dual
role of containing the fine material
and recycling the water to be reused in
processing. The tailings are piped out in
slurry form to the pond, where solids
settle to the bottom and the water on
top is pumped via a reclamation barge
back into the mill. There are a number
of tailings facility construction methods,
which include valley impoundments,
ring-dyke impoundments, in-pit
impoundments, and special dug-pit
impoundments.
Need for tailings dams
Prior to the 19th century, most run-off
from mines were disposed of in water
systems. Tailings dams were also not
needed in most cases, as operations
were relatively small compared to
modern operations today. Due to the
development in processing methods and
mine equipment, operations are now able
to mine deposits well into lower-grade
material, resulting in an increase in
mining process fines. In the past century,
there has been a lot of advances in the
design of tailings facilities.
Tailings dam designs depend on
the topography of the ground and the
material available to build it. The tailings
facilities can be built by earth-filled
structures or built from the waste rock
generated during mining. The pond
is built by forming an embankment
of waste rock at the onset of mine
construction. Tailings are piped in and
deposited at the crest of the embankment
where they drain to form a beach. The
beach is an important buffer between
the dam’s embankment and water in the
pond area.
The general approach to building a
tailings dam is to separate the tailings
into coarse- and fine-grained material
www.miningmirror.co.za
JANUARY 2019 MINING MIRROR
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