3704 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The VFD drives allowed the operation to take full advantage
of the reduced power consumption, which ultimately resulted
in the need to utilise one less generator than planned during
the first year of operation.” It is obvious that in this case the
variable speed drive on the ball mill paid off not only eco-
nomically, but also from an energy efficiency and carbon
footprint viewpoint.
First Majestic Silver operates the Santa Elena plant in
Mexico and stated (Mezquita et al. 2022): “Operating a
fixed speed ball mill at lower throughputs than originally
designed while trying to maintain optimum and/or energy
efficient grinding operation was challenging for the opera-
tional team. A secondary objective was therefore adopted
which is to optimize or reduce energy consumption during
the first stage of the project. This could only be accomplished
by adding a VSD to the existing ball mill..”
A ball mill does not necessarily always have to be oper-
ated flat out at maximum speed and maximum power draw
(and maximum CO2 emissions) in case of lower fresh feed
rate or softer ore, the same ball mill circuit P80 product size
can also be achieved with a lower ball mill speed and lower
power draw, but with less overgrinding due to maintain-
ing a high circulating load. As shown in Figure 3, a high
recirculating load leads to an increased grinding through-
put capacity (Davis 1925) the cyclone classifies the ball
mill product in the closed circuit and a higher recirculating
load results into smaller size reduction steps on each pass
through the mill, which gives the cyclone the opportunity
to remove the finished particles earlier and the ball mill
consequently uses its energy rather on coarser particles than
on overgrinding already finished product.
At lower circuit feed rates or softer ore, the circulating
load can be maintained at a high level when the mill speed
is slowed down, resulting in a lower mill power draw and
lower amount of fines, thus a substantial increase of the
grinding efficiency. In other words, lower CO2 emissions
per ton of ground ore. In addition, a higher circulating load
does not only minimize overgrinding and reduce produc-
tion of slimes, it also positively affects the flotation kinetics,
resulting in higher recoveries (Pural et al. 2022) in other
Source: ABB’s remote monitoring platform
Figure 2. Speed histograms of four variable speed ball mills
The VFD drives allowed the operation to take full advantage
of the reduced power consumption, which ultimately resulted
in the need to utilise one less generator than planned during
the first year of operation.” It is obvious that in this case the
variable speed drive on the ball mill paid off not only eco-
nomically, but also from an energy efficiency and carbon
footprint viewpoint.
First Majestic Silver operates the Santa Elena plant in
Mexico and stated (Mezquita et al. 2022): “Operating a
fixed speed ball mill at lower throughputs than originally
designed while trying to maintain optimum and/or energy
efficient grinding operation was challenging for the opera-
tional team. A secondary objective was therefore adopted
which is to optimize or reduce energy consumption during
the first stage of the project. This could only be accomplished
by adding a VSD to the existing ball mill..”
A ball mill does not necessarily always have to be oper-
ated flat out at maximum speed and maximum power draw
(and maximum CO2 emissions) in case of lower fresh feed
rate or softer ore, the same ball mill circuit P80 product size
can also be achieved with a lower ball mill speed and lower
power draw, but with less overgrinding due to maintain-
ing a high circulating load. As shown in Figure 3, a high
recirculating load leads to an increased grinding through-
put capacity (Davis 1925) the cyclone classifies the ball
mill product in the closed circuit and a higher recirculating
load results into smaller size reduction steps on each pass
through the mill, which gives the cyclone the opportunity
to remove the finished particles earlier and the ball mill
consequently uses its energy rather on coarser particles than
on overgrinding already finished product.
At lower circuit feed rates or softer ore, the circulating
load can be maintained at a high level when the mill speed
is slowed down, resulting in a lower mill power draw and
lower amount of fines, thus a substantial increase of the
grinding efficiency. In other words, lower CO2 emissions
per ton of ground ore. In addition, a higher circulating load
does not only minimize overgrinding and reduce produc-
tion of slimes, it also positively affects the flotation kinetics,
resulting in higher recoveries (Pural et al. 2022) in other
Source: ABB’s remote monitoring platform
Figure 2. Speed histograms of four variable speed ball mills