XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3705
words, lower CO2 emissions per ton of produced copper
concentrate.
Mill Liners. The impact of different mill liners geom-
etry or materials on the grinding performance has been pre-
sented in several papers. The Constancia concentrator from
Hudbay Minerals in Peru has two parallel grinding lines in
a typical SAB circuit, with a potential addition of a pebble
circuit (SABC), followed by flotation (Tavchandjian, 2021)
the two SAG mills are dual pinion mills with gearboxes
and equipped with variable speed mill drives, as where the
two ball mills are dual pinion mills with gearboxes driven
by fixed speed motors. The installed power on each mill
is 2 × 8 MW, which later have been upgraded to 2 × 8.25
MW (Medina et al. 2023), perhaps by running the motors
slightly hotterSimulation of the Constancia ball mill showed
that the fixed speed ball mill could be running a little bit
too fast, resulting into overthrowing of some balls onto the
bare double-wave mill liners (Rajamani et al. 2017): “The
operating conditions imposed on the simulations include
mill diameter, length, mill speed at 11.27 rpm, 67 mm top
ball size, and mill filling of 32%.” “In other words, the ball
strike on the mill shell does not result in any grinding of the
mineral ore.,” meaning that the energy to lift these balls has
been wasted. “Hence, in the case of Constancia’s Ball mill
#4, one observes a number of ball strikes on the mill shell
between 7:00 and 8:00 on the clock-circle.” “Simulating
the change from the double-wave steel liners to lighter
rubber-steel liners showed that with the identical fixed mill
speed of 11.27 rpm all direct impact of balls to the mill shell
have been eliminated.” Refer to Figure 4 for the simulated
ball trajectories in the ball mill with steel liners on the left
and rubber liners on the right. Note that if the Constancia
ball mill would have been variable speed driven, then by
just reducing the speed slightly, an optimized ball trajectory
with the original double wave steel liners could have been
achieved conveniently. Still the change at the Constancia
fixed speed ball mills from the heavier double-wave steel
liners to the lighter rubber-steel liners resulted into some
energy savings, but only around 6% (Rajamani et al. 2017,
as cited in Torrealba-Vargas et al. 2019).
Source: Davis 1925
Figure 3. Relationship between circulating load and ball mill
circuit capacity
Source: Rajamani et al. 2017
Figure 4. Different ball trajectories in the Constancia ball mill at same speed depending upon liner technology
words, lower CO2 emissions per ton of produced copper
concentrate.
Mill Liners. The impact of different mill liners geom-
etry or materials on the grinding performance has been pre-
sented in several papers. The Constancia concentrator from
Hudbay Minerals in Peru has two parallel grinding lines in
a typical SAB circuit, with a potential addition of a pebble
circuit (SABC), followed by flotation (Tavchandjian, 2021)
the two SAG mills are dual pinion mills with gearboxes
and equipped with variable speed mill drives, as where the
two ball mills are dual pinion mills with gearboxes driven
by fixed speed motors. The installed power on each mill
is 2 × 8 MW, which later have been upgraded to 2 × 8.25
MW (Medina et al. 2023), perhaps by running the motors
slightly hotterSimulation of the Constancia ball mill showed
that the fixed speed ball mill could be running a little bit
too fast, resulting into overthrowing of some balls onto the
bare double-wave mill liners (Rajamani et al. 2017): “The
operating conditions imposed on the simulations include
mill diameter, length, mill speed at 11.27 rpm, 67 mm top
ball size, and mill filling of 32%.” “In other words, the ball
strike on the mill shell does not result in any grinding of the
mineral ore.,” meaning that the energy to lift these balls has
been wasted. “Hence, in the case of Constancia’s Ball mill
#4, one observes a number of ball strikes on the mill shell
between 7:00 and 8:00 on the clock-circle.” “Simulating
the change from the double-wave steel liners to lighter
rubber-steel liners showed that with the identical fixed mill
speed of 11.27 rpm all direct impact of balls to the mill shell
have been eliminated.” Refer to Figure 4 for the simulated
ball trajectories in the ball mill with steel liners on the left
and rubber liners on the right. Note that if the Constancia
ball mill would have been variable speed driven, then by
just reducing the speed slightly, an optimized ball trajectory
with the original double wave steel liners could have been
achieved conveniently. Still the change at the Constancia
fixed speed ball mills from the heavier double-wave steel
liners to the lighter rubber-steel liners resulted into some
energy savings, but only around 6% (Rajamani et al. 2017,
as cited in Torrealba-Vargas et al. 2019).
Source: Davis 1925
Figure 3. Relationship between circulating load and ball mill
circuit capacity
Source: Rajamani et al. 2017
Figure 4. Different ball trajectories in the Constancia ball mill at same speed depending upon liner technology