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08.13
tailings
The tailings dam at the Finsch diamond mine in the Northern Cape. The mine has implemented a paste system.
rapid draining than the fines, which are placed on the
floor of the tailings dam.
“The deployment of these units allows us to meet
geotechnical requirements in terms of the steepness
of the dam slope, its stability and drainage capability.
As a result, the dam has a smaller footprint, the rate of
rise can be increased, and the slopes can be lowered
in order to improve rehabilitation,” Gotz says.
He mentions that in order to overcome the chal-
lenges of using multiple cyclones, Fraser Alexander
has developed a tracked, single deposition point cy-
clone machine operated by remote control for use on
large tonnage tailings dams. Apart from the geotech-
nical and logistical advantages, mega tailings dams
can be structured and maintained in such a manner
that concurrent rehabilitation can be undertaken in
line with the future closure of the tailings dam and
possible retreatment of the material.
Gotz says Fraser Alexander retains ownership
and operates the SDP units, saving mines the capi-
tal cost of the equipment. In addition, the use of the
units brings life to prospective new mining projects
which may have been hindered by the cost challenge
brought about by the need for large tailings facilities
and their high capital and operating costs.
Marais indicates that the design of tailings facili-
ties is going through a robust gate-keeping process
in terms of technology, locality, economic consider-
ations and environmental imperatives.
“The process is governed and influenced by three
dimensions. Firstly, investors won’t put money into
a project that has a low standard of tailings design;
secondly, there is the need to meet robust legisla-
tion and regulations in South Africa and elsewhere
in Africa; and lastly, one has to consider stake-
holders in the social environment whose influence
should not be under-estimated. An optimised tail-
ings design is required to satisfy all role-players in
the process. And the responsibility of all involved
goes beyond design and implementation – it perme-
ates the entire tailings operation.”
Mike Abbott, Tailings Engineer at Golder, warns
that mining houses should avoid “grade hunting”
when investigating reprocessing. “Proper planning is
a fundamental requirement when a re-mining project
is being investigated. More thought needs to be given
to the development of new tailings facilities.”
He says the availability of water is among the de-
terminants of the technology selected in the design,
operation and rehabilitation of a tailings dam. On the
West Rand, where re-mining of tailings is growing,
water supply is abundant and the short-term solution
is to use decant water to reprocess the tailings.
Marais adds that the scarcity of water, especially
in new mining areas where greenfields platinum and
other mines are planned, will result in changes to
the technology used in the operation of tailings dams
with mines in those areas “forced to look at dewater-
ing. Water scarcity will become the dominant factor
in South Africa,” he says.
“Various technologies come into play to deal with
the preparation of the tailings scheme which could
change the characteristics of the material. The selec-
tion of these technologies can be impacted by local
climatic and geotechnical conditions. These technol-
ogies include filtration, thickening, paste, and floccu-
lation with additional chemicals.
“In South America where mining is undertaken in
high risk seismic areas, filtration is the chosen meth-
od to ensure greater stability with dewatered tailings.
In semi-desert regions such as in Namibia and Aus-
tralia, a different approach is taken.”
Marais says the selection of technology is also im-
pacted by the tonnage of tailings material that needs
to be handled with South African gold mines averag-
ing about 200 000 tonnes but other mines going for
far higher volumes with tailings dams having large
footprints and the dams operated in compartments.
“In terms of deposition technologies, several al-
ternatives are available depending on a tailings dam
receiving wet or diluted tailings material,” he says.
“A cycloned system is considered best practice since
