FLOTATION TECHNOLOGY
There is also an increasing acceptance of the
place for column flotation in the industry.
Previously mainly offered by Metso and other
groups like Eriez, both Outotec and FLSmidth
now offer their own column flotation option.
Thierry Monredon, Global Manager, Flotation at
Metso told IM: “Historically customers mainly
used mechanical cells with column cells offered
by specialist companies for certain applications.
Metso was the first to merge the technologies as
a package, and particularly successful has been
the use of mechanical cells for rougher/
scavenger and first cleaner stages with columns
for final cleaning.” In India, a major zinc miner is
planning a third flotation plant at one of its
operations, where it will use this set up from
Metso. Having a final column stage Monredon
says can mean a 1% grade increase, meaning
users can use more lower grade ore. In Chile
today most of the big copper/moly operations
are using columns, as an example.
However, back to the very large cells and
several in the industry believe that this 600 to
680 m 3 range really now represents the ceiling in
flotation cells, largely due to high initial cost and
the fact that only a relatively small number of
operations would consider using cells of this
size, mainly low grade, high volume copper,
though they have been used in certain industrial
minerals operations sch as for barytes flotation.
The flotation market currently is also dominated
by projects that are now going ahead that were
on hold in the downturn, and few of these
factored in these huge cells. For now the 300
m 3 cell seems to be the preferred option when
larger cells are being considered. Metso has a
recent order from a copper miner in Chile for
example for five of its RCS 300 cells which will be
amongst its largest orders for high capacity cells
to date.
The point has also been made by some that
the mining industry remains somewhat tied to
increasing capacity in flotation despite lower
recovery as this maximises throughput and
therefore short term profit. However, this means
far more material going to tailings, which could
be avoided with higher recovery and lower
capacity flotation.
There is no doubt, however, that there is a
greater focus on optimisation in flotation. Frank
Cappuccitti, President of flotation reagents and
technology company Flottec told IM: “The
industry is now making more progress on the
implementation of new technology and
sustainable optimisation of flotation (and other
unit operations) by incorporating a holistic
approach. This has been difficult because it
requires a full understanding of the complete
flowsheet and how each unit operation affects
the downstream process. As an example, when
the grinding circuit problems are not well
28 International Mining | NOVEMBER 2019
understood and are the root cause of flotation
problems, fixing flotation is the wrong priority.
Simply changing a reagent or adding a piece of
equipment without understanding the effects
of these changes on the rest of the circuit
usually doesn’t lead to long term, overall
improvement, and can miss opportunities for
even bigger gains. In order to truly optimise a
plant, a thorough understanding of the
chemistry, physics, geometallurgy, operating
strategy, circuit configuration and equipment
as well as operation training and education is
required to achieve true sustainable
improvement.”
One new technology that Cappuccitti says is
gaining acceptance is the use of new sensors
that can measure variables that before were
unable to be measured. One example is the use
of gas hold up as a key measurement for the
control of flotation is being proven in many
locations. Using gas hold up to control frother
dosage and air rates as well as cell levels is
showing improvements in recovery and grade
control. Flottec is working on the development of
robust sensors for use in the mills that will allow
this innovation to be utilised in mills.
“Measuring hydrodynamic parameters that
include bubble size, surface bubble flux, gas
hold up and superficial gas velocity is also
continuing to show that a good understanding of
these parameters and how they affect the circuit
can lead to new process control strategies that
provide optimal performance. In many
operations, it has been demonstrated that a
paradigm shift is required in the current
operating philosophy for mass recovery profiles
down the bank in rougher and cleaner circuits.
Using a strategy where mass recovery down the
bank is kept flat rather than the high initial
recoveries now common can lead to higher
grades at same recovery. We are also seeing
many newer innovative flotation circuit
configurations that include pre-flotation or first
cell bypass in the roughers that results in circuits
with very high grade in the first cells that are
controlled using hydrodynamic parameters. At
the same time, it has been shown that choosing
the right frothers is critical in using
hydrodynamic profiles. Poor choice of reagents
will not allow profiling to provide optimal results.
This new approach is gaining acceptance in the
industry as a method of increasing asset
utilisation by increasing tonnages with minimal
investment. New types of cells such as the use of
SFR and DFR technology are being implemented
now in full plant circuits. These cells perform
outside the norm of conventionally used
technology. Flottec is working with these cells to
better understand the hydrodynamic conditions
required for optimum operation. It is likely that
these cells operate outside the normal
benchmarks for operating cells. A knowledge of
the differences will assist in developing
operating procedures and reagent schemes that
will maximise their performance and increase
their adoption.”
Anglo looks to perfect coarse particle
flotation
Part of its FutureSmart Mining™ approach to
innovation and sustainability, coarse particle
flotation (CPF) technology Anglo American says
allows it to coarsen grind size while maintaining
recoveries – thereby reducing the energy
required to grind ore, as well as reducing water
intensity by more than 20%. Where CPF is
combined with dry-disposal technology, the
company is targeting a reduction in water
intensity of more than 50%. CPF is currently
being tested at several of Anglo’s mining sites
around the world. A 500 t/h unit, the biggest of
its kind, is currently under construction at El
Soldado copper mine in Chile and is due to come
online in the second half of 2019. The coarse
particle flotation process is already being used at
Las Tórtolas, part of the Los Bronces copper
mine, also in Chile.
CPF is part of a wider Anglo strategy called
Coarse Particle Recovery (CPR), designed to
follow advanced fragmentation and gangue
rejection technologies. It combines CPF and dry
stacking technologies. “Essentially, it allows us
to float particles at sizes two to three times
larger than normal. This has two main benefits.
Firstly we use less energy and can therefore
increase our production rates; and secondly, we
are able to easily extract water from the process
leaving a waste stream that is dry and
stackable.”
The upper size limit of coarse particle flotation
has been a long-standing challenge in the
industry, as the value of metal and minerals lost
to tailings is often in particles too coarse to float
(coarse particles are generally larger than 250
microns or 0.25mm, where, for example, 4% of
Cu recovery can be lost). “But regardless of how
coarse one is able to process particles there has
been, and always will be, a portion of ultra-fine
particles that require processing. We have
partnered with major chemical companies and
are experimenting with new techniques to
recover this previously unrecoverable metal.”
DRA Global has been awarded the contract for
the Feasibility Study for the Anglo American PLC
Coarse Particle Recovery (CPR) plant on the
Quellaveco project, currently in construction in
the Moquegua region of Peru.
Quellaveco is the first mine operation for
Anglo American in Peru and will be one of the
largest greenfield projects in the region. This
project also benefits from its location in Peru’s
most established copper producing region.