ORE SORTING
TOMRA XRT ore sorting machines have
proven very useful in the recovery of
valuable diamonds (photo: the XRT
installation at Lucara Diamond Corp’s
Karowe mine in Botswana)
Preceding processing
In their time of need, mining companies are looking to
pre-concentration and ore sorting solutions to upgrade
their product feed. Dan Gleeson examines just what the
industry has to offer
he world of ore sorting has become a lot
more interesting in the past decade as
mining companies have started to re-
examine old concepts to stem the sector-wide
grade decline and improve profitability.
Photometric, electromagnetic, radiometric
and X-ray sensor technologies are, in some
instances, enabling miners to cut the amount of
waste material going into processing plants, or,
conversely, boost the amount of ore fed into the
comminution circuit.
When positioned correctly in a process
flowsheet, a pre-concentration stage or sensor-
based ore sorting mechanism can reduce
material transport costs, meaning less waste is
conveyed or hauled to the next part of the
mining process.
All of this can, potentially, lead to reduced
energy consumption, a smaller environmental
footprint and increased profitability; goals the
industry has been looking to achieve.
T
Mineralogy & heterogeneity
“It’s mostly driven by the mineralogy,” Cronimet
Mining Processing SA Operations Director, Ruan
Kroukamp, said in reference to how wide the
applications were for sensor-based ore sorting
in mining. While Kroukamp’s experience is
International Mining | MARCH 2019
mostly related to the application of X-ray
transmission (XRT) technology, the statement
rings true for most sensor-based ore sorting
solutions.
TOMRA Sorting Solutions’ Business
Development Manager, Christopher Robben,
added to this: “The value (of ore sorting) is
more dependent on the mineralisation of the
deposit and liberation characteristics of the ore
in combination with the value chain of the
operation.”
Robben raises an important point here – the
placement of the ore sorter in a mining
operation has a massive impact on just how
successful it is.
Place the ore sorter in the wrong place and
the separation efficiency is nowhere near as
high as it could be.
Metso explained: “Most mining deposits are
naturally heterogeneous and lend themselves
well to bulk ore sorting, but it should be
implemented as early in the process as possible
before excessive mixing occurs. Material
presented to the sorter needs to have sufficient
grade variability occurring in large enough
batches of material for effective separation.
“But every time the ore is re-handled,
transferred, crushed or blended, the degree of
mixing increases; reducing the variability and
thus the potential for effective separation of
batches of barren gangue from ore.”
In terms of the bulk ore sorting process (more
on this later in the Bulking up section), either
in-pit or plant feed conveyors provide the best
opportunities for sorting, according to Metso,
adding that this enables the sorter to exploit
the natural heterogeneity of the deposit.
And, the pre-concentration stage can be as
varied as the sensors used to separate ore and
waste.
Malcolm Guthrie, Lead Process Engineer for
Minerals & Metals at Ausenco, explained: “It is
a broad area of processing that to some degree
is an extension of grade control and
incorporates any technique that removes waste
based on identifiable/detectable characteristics,
including particle size, colour, detectable
minerals or elements and atomic density.”
Coal operations use a mixture of dense media
separation (DMS) and magnetic sensors in their
operations to remove the tramp metal, increase
the value of their product and protect the
screens, crushers and conveyors that process
the material later in the flowsheet.
Radiometric sensors have been used in
uranium operations to upgrade concentrate
before it is processed into yellowcake, while
research has shown photometric sensors could
have their uses in the gold mining industry, in
addition to other commodities.
And, of course, XRT sensor solutions have