PASTE FiTTON CONSULTANTS_proof 25/05/2016 09:33 Page 1
Paste Supplement
More tailings, less thickening
Tim Fitton, Principal Engineer, Fitton Tailings Consultants,
discusses a truncated variation of Central Thickened
Discharge which can allow mines to accommodate more
tailings with less thickening
Sunrise Dam CTD in 2004 (image from Google
Earth)
ome 50 years ago a Canadian professor
named Eli Robinsky invented the concept
of Central Thickened Discharge (CTD), in
which he envisaged a conical stack of tailings
being formed by the discharge of thickened
tailings slurry from a single point above a flat
plane. The first CTD was built some seven years
later at Kidd Creek in Canada, and since then,
about 50 such storage facilities have been
successfully installed around the world, with the
Sunrise Dam CTD (see title pic) being one of the
more circular CTDs in existence. One of the
major advantages of the CTD over conventional
tailings storages is the reduced risk to the
surrounding area by elimination of potentially
hazardous dams.
In more recent years it has been found that
steeper beach slopes can be achieved by
splitting the flow, which enables more tailings to
be stored on the same footprint. However, if
these smaller streams should merge on the
beach, the steepening benefit is lost. Some
operators have tried to manage this by regularly
opening and closing valves at individual
discharge points, but this requires regular care
(and cost). It is therefore desirable to configure
the discharge points in such a way that the
streams do not merge, but until now, there has
been no published method for configuring the
discharge points on a CTD to achieve this end.
Fitton Tailings Consultants has recently
developed a method for predicting the amount
of separation of the discharge points that is
required to minimise the merging of streams on
a CTD. Exploitation of this method has led to the
conception of the Truncated CTD, which enables
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P6 International Mining | JUNE 2016 Supplement
more tailings to be accommodated on a smaller
footprint with less thickening of the slurry,
whilst achieving the same low geotechnical risk
as a regular CTD.
A comparison between a regular CTD and the
new Truncated CTD is presented in Figure 1,
based on the example of a gold tai lings being
produced at a rate of 10 million dry tonnes per
annum for 20 years with a deposited dry density
of 1.6 t/m3.
The comparison in Figure 1 shows that a
Truncated CTD with 50 spigots, each with a 10%
chance of merging (effectively resulting in an
average of 45 streams), will occupy a land area
of 831 ha, compared to 2,163 ha for the pointy
CTD. Not only is the footprint reduced by two
thirds, but also the amount of required
thickening is reduced dramatically from 65% to
55% w/w. In situations where water recovery is
a major priority, higher concentration slurry
could be discharged, yielding steeper beach
slopes and an even smaller footprint with the
same 50 spigot split. The Truncated CTD concept
could be applied in a number of ways:
n It could be applied to an existing CTD, with
the installation of a small cartwheel at the
stack apex, maybe 5 m in diameter with five
or six spigots radiating outwards from it.
There will be some merging of streams
initially, but over the following weeks, once
the beach builds up at each spigot, each of
the spigot pipes would be lengthened
horizontally, to extend further outwards upon
the tailings. This lengthening of the spokes of
the cartwheel is effectively increasing the
diameter of the cartwheel. Later on,
additional intermediate spigots could be
added, thereby splitting the flow further and
steepening the beach further. The desired
hub diameter and beach slope would be
achieved over time.
n For a new CTD, a ramp and hub would need
to be constructed, but like the previous retrofit solution, the cartwheel could start out
small, thereby minimising the amount of upfront capital cost, and be gradually enlarged
over time, with the spigot pipes propped up
above the tailings. In the early stages, flatter
beach slopes would be achieved, but these
would eventually be buried under more
steeply beaching tailings later on.
n An alternative approach for a new CTD could
be to construct a flat topped circular platform
for the thickeners, with the cartwheel running
around them, as shown in Figure 2. This
avoids the need to pump the thickener
Figure 1: A comparison of a CTD with a Truncated CTD containing the same volume. Note the smaller
footprint, despite the lower concentration slurry discharge