XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 119
re-configuration, including full mine-process chain, com-
minution, classification and beneficiation
• Equipment modification/removal
• Use of current, alternative equipment
• Novel equipment (mechanical and non-mechanical)
• Measurement and control
– Measurement and sensing, including feed material
and stream characterization
– Process control.
• Flowsheet designs and configuration.
In terms of changes to current equipment, there is the usual
range from minor modifications through to major changes
that deliver far greater value. From the perspective of tum-
bling mills, Bouchard et al. (2017) showed that, on aver-
age, 79% of the supplied electrical energy converts to heat
absorbed by the slurry. Of the remainder, 8% is lost through
the drive system about 2% of the energy is transmitted to
ambient air, and just about 10% is used for the grinding
work. Such values suggest that the overall energy balance
for a circuit including tumbling mills could be improved, if
energy recovery can be effectively implemented.
In terms of the mechanical and operating aspects of
tumbling mills, the improvement opportunities have
remained unchanged, i.e., liner design, media charge (type,
size and distribution), mill speed, grate design, transfer size,
classification efficiency, pebble crushing etc. Obviously
there is a tremendous body of work and development that
has been applied to optimize tumbling mill performance,
but are we now at the end of the effort-benefit curve? Even
if we have a fully optimized tumbling mill application,
is this enough to significantly move the dial? Embodied
energy related to manufacture and consumption of media
is a factor that could be addressed via wider applications of
AG milling and this option was described and discussed by
Powell (2023). An example of a reduced media application
is exemplified by the Aitik flowsheet, with use of both AG
and Pebble mills, McElroy et al., (2019).
Away from tumbling mills there is a wide range of
equipment that uses more direct forms of breakage via
compression of particles or packed beds, i.e., crushers,
HPGR, Vertical Roller Mills etc., or other forms of media
based milling that are able to generate more intense com-
minution, i.e., stirred mills. The advantage of these devices
is that in terms of a direct transfer of input energy into
breakage, they demonstrate significant improvements over
tumbling mills.
Morrell (2022) examined HPGR circuits either in
combination with ball mills, or with subsequent stage of
HPGR. His findings were that in terms of CO2 emissions,
the use of a HPGR +Ball mill circuit would deliver sav-
ings of 16.3Mt/year compared to a AG/SAG +Ball Mill
circuit, with the reduction in CO2 improving further to
34.5Mt/year in a HPGR +HPGR circuit. For the base
direct reduction in electrical consumption for the circuits
studied, Morrell used values stated by previous workers. For
the HPGR +Ball Mill circuit this base line value explicitly
included ancillary HPGR circuit requirements (conveyors,
screens, pumps dust extraction etc.) pumps. For the HPGR
+HPGR, the base value assumes that ancillary electrical
consumption is the same as for the HPGR +Ball Mill
circuit.
Importantly, included in Morrell’s analysis of CO2
emissions was the energy impost for power generation and
the manufacture and consumption of steel grinding media.
Recognition of the wider energy context for comminution
is essential to obtain a proper comparison of compressive
based equipment versus tumbling mills.
In highly complementary developments in the world of
stirred milling, the design, configuration and deployment
has advanced considerably. Various vendors now position
their stirred mills as an energy efficient replacement for ball
mills. Typical application ranges for the Swiss Tower Mill
range is shown in Figure 7, with a recent paper (Zhmarin
et al., 2023) discussing the design of a 12.5MW Vertical
Regrind Mill (VRM – for fine, regrind duties), with a
75,000litre capacity. It is also noted that the upper bound
for the Vertical Power Mill (VPM) in Figure 7, appears to
be now push further upstream, with a feed size of 6mm
stated by Paz et al., (2023)
The breakage and transport mechanisms in vertical
stirred mills in combination with HPGR, also offer inter-
esting alternatives in flowsheet configuration and exploiting
the breakage characteristics of ore and gangue. In an exami-
nation of flowsheets-of-the-future, van de Vijfeijken et al.,
(2023) developed the circuit shown in Figure 8, whereby
the aim is to use the combination of vertical stirred mills
and Coarse Particle Flotation to prevent overgrinding and
loss of recovery.
Other features noted by van de Vijfeijken et al. (2023),
included the vertical stirred mill consuming 20–25% less
energy than an equivalent ball mill in a similar grinding
duty and the open circuit stirred mill producing fewer
slimes than a closed circuit ball mill – cyclone combination.
The discussion towards the finer, or ultrafine, area
of comminution has often centered on a comparison of
vertical and horizontal stirred mills. In a study compar-
ing the HIGMill versus the horizontal IsaMill, Can &
Altun, (2023), concluded, for the application studied, that
the IsaMill was more energy efficient at a grind size d80
re-configuration, including full mine-process chain, com-
minution, classification and beneficiation
• Equipment modification/removal
• Use of current, alternative equipment
• Novel equipment (mechanical and non-mechanical)
• Measurement and control
– Measurement and sensing, including feed material
and stream characterization
– Process control.
• Flowsheet designs and configuration.
In terms of changes to current equipment, there is the usual
range from minor modifications through to major changes
that deliver far greater value. From the perspective of tum-
bling mills, Bouchard et al. (2017) showed that, on aver-
age, 79% of the supplied electrical energy converts to heat
absorbed by the slurry. Of the remainder, 8% is lost through
the drive system about 2% of the energy is transmitted to
ambient air, and just about 10% is used for the grinding
work. Such values suggest that the overall energy balance
for a circuit including tumbling mills could be improved, if
energy recovery can be effectively implemented.
In terms of the mechanical and operating aspects of
tumbling mills, the improvement opportunities have
remained unchanged, i.e., liner design, media charge (type,
size and distribution), mill speed, grate design, transfer size,
classification efficiency, pebble crushing etc. Obviously
there is a tremendous body of work and development that
has been applied to optimize tumbling mill performance,
but are we now at the end of the effort-benefit curve? Even
if we have a fully optimized tumbling mill application,
is this enough to significantly move the dial? Embodied
energy related to manufacture and consumption of media
is a factor that could be addressed via wider applications of
AG milling and this option was described and discussed by
Powell (2023). An example of a reduced media application
is exemplified by the Aitik flowsheet, with use of both AG
and Pebble mills, McElroy et al., (2019).
Away from tumbling mills there is a wide range of
equipment that uses more direct forms of breakage via
compression of particles or packed beds, i.e., crushers,
HPGR, Vertical Roller Mills etc., or other forms of media
based milling that are able to generate more intense com-
minution, i.e., stirred mills. The advantage of these devices
is that in terms of a direct transfer of input energy into
breakage, they demonstrate significant improvements over
tumbling mills.
Morrell (2022) examined HPGR circuits either in
combination with ball mills, or with subsequent stage of
HPGR. His findings were that in terms of CO2 emissions,
the use of a HPGR +Ball mill circuit would deliver sav-
ings of 16.3Mt/year compared to a AG/SAG +Ball Mill
circuit, with the reduction in CO2 improving further to
34.5Mt/year in a HPGR +HPGR circuit. For the base
direct reduction in electrical consumption for the circuits
studied, Morrell used values stated by previous workers. For
the HPGR +Ball Mill circuit this base line value explicitly
included ancillary HPGR circuit requirements (conveyors,
screens, pumps dust extraction etc.) pumps. For the HPGR
+HPGR, the base value assumes that ancillary electrical
consumption is the same as for the HPGR +Ball Mill
circuit.
Importantly, included in Morrell’s analysis of CO2
emissions was the energy impost for power generation and
the manufacture and consumption of steel grinding media.
Recognition of the wider energy context for comminution
is essential to obtain a proper comparison of compressive
based equipment versus tumbling mills.
In highly complementary developments in the world of
stirred milling, the design, configuration and deployment
has advanced considerably. Various vendors now position
their stirred mills as an energy efficient replacement for ball
mills. Typical application ranges for the Swiss Tower Mill
range is shown in Figure 7, with a recent paper (Zhmarin
et al., 2023) discussing the design of a 12.5MW Vertical
Regrind Mill (VRM – for fine, regrind duties), with a
75,000litre capacity. It is also noted that the upper bound
for the Vertical Power Mill (VPM) in Figure 7, appears to
be now push further upstream, with a feed size of 6mm
stated by Paz et al., (2023)
The breakage and transport mechanisms in vertical
stirred mills in combination with HPGR, also offer inter-
esting alternatives in flowsheet configuration and exploiting
the breakage characteristics of ore and gangue. In an exami-
nation of flowsheets-of-the-future, van de Vijfeijken et al.,
(2023) developed the circuit shown in Figure 8, whereby
the aim is to use the combination of vertical stirred mills
and Coarse Particle Flotation to prevent overgrinding and
loss of recovery.
Other features noted by van de Vijfeijken et al. (2023),
included the vertical stirred mill consuming 20–25% less
energy than an equivalent ball mill in a similar grinding
duty and the open circuit stirred mill producing fewer
slimes than a closed circuit ball mill – cyclone combination.
The discussion towards the finer, or ultrafine, area
of comminution has often centered on a comparison of
vertical and horizontal stirred mills. In a study compar-
ing the HIGMill versus the horizontal IsaMill, Can &
Altun, (2023), concluded, for the application studied, that
the IsaMill was more energy efficient at a grind size d80