COMMINUTION & CRUSHING
A pilot project to verify the Iron Bridge design
involved processing 1 Mt of ore through a full-
scale Enduron HPGR and air classifier over a
12-month period to produce a 67% Fe, low
impurity concentrate product
found in arid locations with minimal infrastructure
or access to process water. This requires moving
away from conventional grinding circuits as water
is becoming scarce, Dierx says.
“Combining with the HPGR, a complete fine
micron-size grinding system can be deployed
without consuming a single drop of water,” he
said. Such systems can help miners obtain
environmental approvals quicker, according to
Dierx.
While there is certainly more interest in dry
processing to reduce or eliminate water
consumption, Outotec’s Nielsen said most of the
best-practice beneficiation technologies still
require water, so the practical range of commodities
that can be processed in this way is limited.
“However, there has been interesting research
in dry processing in base metals recently and, I
think, eventually we will see some semi- or even
fully-dry plants installed in geographical locations
where water is scarce, or there are significant
social licence requirements around water use,” he
said.
One piece of research came from Metso’s
Boylston, Newmont’s VP Global Innovation,
Process & Metallurgy, Simon Hille, and the gold
miner’s Director Metallurgy and Global Projects,
Peter Lind, at the most recent SAG Conference, in
Vancouver, Canada.
In the paper, ‘Reducing Energy and Water
Consumption Through Alternative Comminution
Circuits’, the three presented back in September, a
dry processing route for a 100,000 t/d copper
plant was explored. This design involved HPGR
and a “quasi open-circuit” ball mill air
classification route, according to Boylston.
“The idea there was we were trying to maximise
savings on energy and water,” he said.
“If you’re talking about a copper ore, you are
eventually going to have to get it wet to float it,
but if you are going to make a separation on your
dry materials with the air classification, which we
showed with this paper, then you can take the
22 International Mining | APRIL 2020
coarse fraction through a coarse flotation step and
then have a final grind in a Vertimill on the rest of
the material. That way, the coarse flotation is
going to dewater much better than your fully
ground material, which saves a little bit of water
there even if there is likely to be a penalty on
metal recovery as you are not grinding all the way.”
While the design was very much “forward
looking”, leveraging all of the levers that would
allow such a circuit to be designed (regardless of
economics), Boylston said it showed you can
really reduce both energy and water consumption
if these aspects are prioritised.
A new coarse
Eric Wasmund, Global Managing Director, Eriez
Flotation, explained: “CPF is an enabling
technology for optimising traditional mineral
processing flowsheets because conventional
stirred tank cells are the primary unit operation
used in more than 90% of mineral processing
flotation operations worldwide and they are
inherently inefficient for floating coarse particles.
“Over the last 10 years there has been
increased interest and product development in the
area of CPF for sulphide minerals using liquid
fluidised beds to host the flotation process, as
practised in the Eriez HydroFloat.”
A number of these applications have been
commercialised, according to Eriez, most notably
the HydroFloat as a tail scavenger at Newcrest’s
Cadia copper/gold concentrator in New South
Wales, Australia. In such an application of CPF, the
cost to build a standalone coarse particle flotation
plant on the back end of the concentrator is
justified by increasing the overall recovery of
payable metals, Eriez says.
Rio Tinto also sees potential for this technology,
reporting back in 2017 that 70% of coarse copper
and 90% of coarse molybdenum in its plant tails
at the Kennecott copper operation in the US could
be recovered using CPF technology.
Eriez said: “This is the most obvious and
natural first generation of HydroFloat installations,
where a modest investment of capital for a
standalone CPF plant can allow the capture of 70-
90% of payable metals contained in coarse mine
tails.”
The need to reduce the size of ore from boulders
to a size range where it can practically be floated
using conventional technology – about 200
microns or less for many sulphide ores – is the
main reason the crushing and grinding process is
so energy intensive.
At the same time, most
The HydroFloat as a tail
scavenger at Newcrest’s
of the water used in
Cadia copper/gold
mining is required to carry
concentrator in New South
and convey these fine ore
Wales, Australia, is one of
the standout coarse
particles through the
particle flotation
process and to keep the
applications in mining,
fine tails stabilised in a
Eriez says
permanent impoundment.
If ore could be
practically floated at a
much coarser size, the
consumption of energy
and water could both be
greatly reduced, according
to Eriez. Enter coarse
particle flotation (CPF), an
innovative new process
technology based on
Eriez’s HydroFloat ®
technology.
This technology enables
semi-liberated ore to be
floated at much coarser
sizes, typically up to 600
microns for many copper
sulphide ores, according
to the company.