FLOTATION
Each Fresnillo flotation cell was equipped with
a control cabinet which houses the CPX-MPA
valves used to activate the actuators DFPI,
together with a Festo programmable controller
CPX-FEC and a front-end display FED which
displays the degree of opening of the dart
valves (Photo: Festo AG & Co. KG)
must be stopped for re-calibration to be carried
out. “People in the mining industry have put up
with these interruptions for many years,” says
Ing Juan Rucobo, Head of Instrumentation and
Control of the Fresnillo silver mine.
“Festo project engineers developed an
automation solution in which the linear actuators
no longer need to be re-calibrated and also no
longer break down because of external sensors
which cannot withstand the harsh environmental
conditions,” explains Juan Carlo Celaya, Process
Automation Manager with Festo Mexico.
Fresnillo was one of the first mines in the
world to use the new Festo linear actuator DFPI
with its dart valves instead of simple linear
actuators. The DFPI regulates the dart valves and
thus the level of the foam.
The advantages of the DFPI are obvious: it
combines the function of a linear actuator, a
position controller and a displacement encoder.
All the components are securely and compactly
enclosed by the cylinder barrel. In comparison
with modular systems, the actuator offers
impressive robustness for outdoor applications
and explosion protection for Zone 2.
At all stages, from engineering through to
purchasing, commissioning and operation, the
Festo solution made it possible to implement
automation right along the entire value chain.
The system can be configured and commissioned
quickly. Reliability is ensured by the technical
support provided by local Festo sales engineers
and the supply of spare parts by Festo Mexico.
However, this automation solution would not
be a complete solution if Festo had supplied only
actuators for the dart valves. Each flotation cell
30 International Mining | NOVEMBER 2017
was also equipped with a control cabinet which
houses the CPX/MPA valves used to activate the
actuators DFPI, together with a Festo
programmable controller CPX-FEC and a front-end
display FED which displays the degree of opening
of the dart valves.
Magotteaux’s Pulp Chemistry Monitor (PCM ® )
is attracting a lot of interest. It is an instrument
that measures key pulp chemical parameters (pH,
Eh, dissolved oxygen, temperature and oxygen
demand) on-line and in real time. These data
when combined with other measurements taken
in a flotation plant can be used to improve the
control of reagent additions which should make it
possible to achieve better stability in the plant.
With better stability and better reagent utilisation
the metallurgical performance should improve.
Magotteaux worked with Manta Controls to
develop the PCM, which measures the pulp
chemistry of critical process streams in real time,
introducing a new level of process optimised for
improved metallurgical performance. PCM
capabilities arise from a combination of a fully
integrated communication and high-level control
functions designed by Manta Controls utilising
Rockwell Automation Integrated Architecture
platform, and classical metallurgical knowhow
provided by Magotteaux.
The effect grinding media has on the pulp
chemistry and subsequent separation process
can be dramatic. A number of case studies for a
range of sulphide minerals have been published.
For example, at Perilya Broken Hill mine in
western New South Wales, Australia (Greet,
Myllynen and MacKay, 2009, Improving zinc
recovery at Perilya Broken Hill Concentrator by
changing the grinding chemistry, Proceedings of
the VI International Mineral Processing Seminar,
pp 243-256) the laboratory test work indicated
that a shift from forged steel to a Duromax ® alloy
would result in an increase in Eh of 160 mV and a
reduction in EDTA extractable iron by two thirds.
There was also a notable change in the
appearance of the froth in the laboratory tests
(see figure), and these changes in pulp chemistry
saw the zinc recovery increase by 1.3%.
The indications provided by the laboratory
study were realised in the industrial trial where
the Eh increased by 175 mV and the EDTA
extractable iron was decreased by about half. The
metallurgical results were slightly better than
expected with the zinc recovery increasing by
1.8% and the final zinc concentrate up by 0.8%.
“The work showed that carefully executed
laboratory studies can produce reliable results
that provide the decision maker with a sound
basis for process improvement.”
VEGA Americas unveiled its density-
compensated level measurement system at
MINExpo 2016. A reliable, repeatable means of
controlling froth thickness in flotation cells,
density-compensated level is attracting interest.
For flotation cells to operate efficiently,
thickness of the froth needs to remain consistent.
Zinc concentrate images for laboratory flotation tests ground with forged steel and high chrome
grinding media