REPROCESSING AND TAILINGS REDUCTION
combination with thickeners, hydrocyclones and
other equipment to create an integrated system able
to reprocess existing or legacy dams, to both generate
additional revenue and clean up the facilities.
Upping the flotation threshold
Eriez believes there is a different way to reduce
the production of wet tailings at the same time as
recovering more metals and minerals. That is
through re-engineering the flotation process.
As Eric Bain Wasmund, Global Managing
Director of Eriez Flotation, says, conventional
sulphide flotation technology is not effective at
floating particles greater than about 200 microns,
leading to this threshold being the practical end
point for grinding operations.
“Grinding energy increases dramatically as the
size decreases, and over-grinding creates
additional flotation efficiency challenges because
‘slimes’ do not float with high efficiency,”
Wasmund said.
“But the most serious consequence of current
grinding practise is that the entire volume of
mined ore is necessarily reduced to a slurry of fine
particles, predominantly less than 200 microns.”
The handling and long-term storage of this
cumulative volume is a major cost and long-term
risk management concern for mining companies
and other stakeholders.
This is where coarse particle flotation and the
HydroFloat ® comes in, Wasmund said. The
commercially available solution uses fluidisation
COUNT ON GIW
FOR RELIABLE
PERFORMANCE.
GIW® pumps deliver reliable performance in
the most aggressive slurries.
GIW Industries is built tough too. We are more committed than ever
to providing our partners with an uninterrupted supply of pumps and
parts. We will stop at nothing to ensure the success of your operation.
Learn more at www.giwminerals.com
16 International Mining | MAY 2020
to effectively float sulphide particles up to 700
microns, upping the flotation threshold.
The HydroFloat has already been used to
scavenge sulphide tails and allow operations like
Newcrest’s Cadia copper-gold mine in New South
Wales, Australia, to coarsen its grind size,
according to Eriez. It is also helping the miner
recover gold and copper from the concentrator
tailings stream.
Wasmund explained: “While this allows only a
marginal bump in the size distribution of their
tails, it does allow the reduction of grinding
energy and the recovery of payable metals in the
waste, as well as proving the long-term operability
of the HydroFloat as a technology platform for
coarse particle flotation.”
The next opportunity being developed for Eriez
Coarse Particle Flotation is to use the HydroFloat
to allow coarse gangue to bypass conventional
flotation, “acting analogously to an ore-sorting
application, and thereby generating a significant
fraction of the total volume of tailings in a primary
size range two-to-three-times coarser than the fine
tails produced by conventional flotation”,
Wasmund said.
The accompanying block diagram (opposite)
shows how the coarse gangue rejection
application works.
Wasmund said: “In a conventional mill circuit,
the product of secondary grinding in a ball mill is
fed to a sizing unit, typically a cyclone. The
cyclone is configured so that the overflow
produces the right size distribution for
conventional flotation, while the mainly coarse-
sized underflow, which also contains some
‘misplaced fines’, is returned directly to the mill.”
In this example, which illustrates the idea
behind coarse gangue rejection, the cyclone
underflow passes through a set of sizing unit
operations, here shown as a set of screens with
160-micron and 700-micron apertures for
illustration purposes.
Wasmund said: “The screens split the cyclone
underflow into three sizes classes: a fine stream
less than 160 micron, typically about 20% by
mass, which can be added back to the
conventional flotation feed; a coarse stream
greater than 700 micron, typically 20-30% by
mass which can be returned to the grinding mill;
and a mid-range stream between about 160 and
700 microns, typically 50-60% by mass, which can
be used to feed the HydroFloat.”
Because the HydroFloat has very high
recoveries in this size range comparable with
conventional flotation at conventional grind sizes,
it can perform as a pre-rougher flotation unit on
this mid-range material and generate a coarse
barren tail permanently removed from the flotation
circuit at an 80th percentile size typically between
500 and 600 microns, according to Wasmund.
“While fine grinding is still required for