XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3745
In recent years, the application of acoustic sensing has
emerged for monitoring AG/SAG mill performance, yield-
ing promising results (Pax and Thornton, 2019). However,
there is limited knowledge of the feed heterogeneity (feed
size distributions and hardness) introduced into the mill.
The transition of feed inside the mill before discharge to
downstream processes is not well understood.
From our previous papers, ore heterogeneity (feed
hardness and size distribution), as well as critical process
variables and their acoustic emission responses in a labo-
ratory AG/SAG mill and ball mill have been investigated
(Owusu et al., 2021a Owusu et al., 2021e Owusu et al.,
2022b Owusu et al., 2023a Owusu et al., 2021h). This is
a valuable consideration offering the potential for energy
reductions and improvement in AG/SAG mill and ball mill
performance (providing consisting operations) through
near real-time measurements.
In this paper, the holistic insights gained from acoustic
emission during laboratory AG/SAG milling experiments
are discussed. The paper, therefore, aims to:
1. Synthesise and provide comprehensive discussions
of all the key findings from previous studies.
2. Provide the link between varied feed ores (hardness
and size distribution) and acoustics in a laboratory
AG/SAG/ball mill.
3. Discuss the potential implications of the key
research findings in addressing industrial chal-
lenges related to the real-time monitoring of feed
ore heterogeneity.
EXPERIMENTAL STUDY
Rock Samples
The different rock samples (model quartz, model calcite
and iron ore) used for the study are shown in Figure 1. The
mean surface hardness for model quartz, model calcite, and
iron ore was determined through multiple indentations,
yielding values of 13.15±1.02 GPa, 1.59±0.32 GPa, and
3.48±1.53 GPa, respectively. The elemental and chemical
composition of the rock samples can be found in the article
(Owusu et al., 2022b).
Purpose-Built Laboratory AG/SAG Mill and Test
Methodology
For in-depth research involving multiple variable manip-
ulations, a purpose-built laboratory-scale AG/SAG mill
of diameter 30 cm, length of 15 cm and critical speed of
77.5 rpm, equipped with six replaceable lifter bars was used
(Owusu et al., 2021b). The pictorial and schematic repre-
sentations of the AG/SAG mill are shown in Figure 2.
The mill size diameter of 30 cm was motivated by the
standard Starkey mill used for characterising ore hardness
and energy consumption suitable for an AG/SAG mill
operation (Amelunxen, 2002 Amelunxen et al., 2014).
Owing to the size of the mill, it offers several advantages
such as a smaller sample size, lower experimental cost, and
repeatability of tests. Methodology for optimal operation of
the laboratory AG/SAG mill has been developed using crit-
ical variables such as mill speed, pulp density (solid load-
ing), steel ball size distribution, and height of lifter bars and
Figure 1. Different rock samples (A) model calcite (B) model quartz, and (C) iron ore
In recent years, the application of acoustic sensing has
emerged for monitoring AG/SAG mill performance, yield-
ing promising results (Pax and Thornton, 2019). However,
there is limited knowledge of the feed heterogeneity (feed
size distributions and hardness) introduced into the mill.
The transition of feed inside the mill before discharge to
downstream processes is not well understood.
From our previous papers, ore heterogeneity (feed
hardness and size distribution), as well as critical process
variables and their acoustic emission responses in a labo-
ratory AG/SAG mill and ball mill have been investigated
(Owusu et al., 2021a Owusu et al., 2021e Owusu et al.,
2022b Owusu et al., 2023a Owusu et al., 2021h). This is
a valuable consideration offering the potential for energy
reductions and improvement in AG/SAG mill and ball mill
performance (providing consisting operations) through
near real-time measurements.
In this paper, the holistic insights gained from acoustic
emission during laboratory AG/SAG milling experiments
are discussed. The paper, therefore, aims to:
1. Synthesise and provide comprehensive discussions
of all the key findings from previous studies.
2. Provide the link between varied feed ores (hardness
and size distribution) and acoustics in a laboratory
AG/SAG/ball mill.
3. Discuss the potential implications of the key
research findings in addressing industrial chal-
lenges related to the real-time monitoring of feed
ore heterogeneity.
EXPERIMENTAL STUDY
Rock Samples
The different rock samples (model quartz, model calcite
and iron ore) used for the study are shown in Figure 1. The
mean surface hardness for model quartz, model calcite, and
iron ore was determined through multiple indentations,
yielding values of 13.15±1.02 GPa, 1.59±0.32 GPa, and
3.48±1.53 GPa, respectively. The elemental and chemical
composition of the rock samples can be found in the article
(Owusu et al., 2022b).
Purpose-Built Laboratory AG/SAG Mill and Test
Methodology
For in-depth research involving multiple variable manip-
ulations, a purpose-built laboratory-scale AG/SAG mill
of diameter 30 cm, length of 15 cm and critical speed of
77.5 rpm, equipped with six replaceable lifter bars was used
(Owusu et al., 2021b). The pictorial and schematic repre-
sentations of the AG/SAG mill are shown in Figure 2.
The mill size diameter of 30 cm was motivated by the
standard Starkey mill used for characterising ore hardness
and energy consumption suitable for an AG/SAG mill
operation (Amelunxen, 2002 Amelunxen et al., 2014).
Owing to the size of the mill, it offers several advantages
such as a smaller sample size, lower experimental cost, and
repeatability of tests. Methodology for optimal operation of
the laboratory AG/SAG mill has been developed using crit-
ical variables such as mill speed, pulp density (solid load-
ing), steel ball size distribution, and height of lifter bars and
Figure 1. Different rock samples (A) model calcite (B) model quartz, and (C) iron ore