XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3751
EFFECT OF FEED ORE HETEROGENEITY
IN LOCKED-CYCLE MODE AND
ACOUSTICS
To understand the sensitivity and the fluctuations caused
by feed ore heterogeneity (hardness and size distribution)
in steady-state industrial AG/SAG operations, locked-cycle
procedures in a laboratory AG/SAG mill coupled with
acoustic sensing were performed (Owusu et al., 2023b).
Model quartz of size range –12.7 +2 mm was used as
the initial feed and the grinding cycle was repeated until
near equilibrium was reached. Following near equilibrium
(within six grinding cycles for separate experiments), fresh
feed of quartz (–26.5+16 mm) and iron ore (–12.7+2 mm)
were introduced in the respective tests for an additional two
cycles. Notably, as the mass of the product size of less than
150 µm was reduced, the mill acoustic also appreciated until
the fourth cycle when a pseudo-steady state was achieved.
At the point where the mass of the product size reached
equilibrium (4–6 cycles), the average acoustic intensities
(RMS analysis) also reached equilibrium. By monitoring
acoustic emission as well as the mass of the product size,
the mill steady state was completely distorted after the 6th
and 7th cycles when the coarser fresh feed and another ore
type (different hardness) were introduced. The coarser fresh
feed aided the production of finer particles (–150 µm) but
a lower breakage rate of the top size particles was observed.
Regarding the blend of model quartz and iron ore, the mass
of the particles less than 150 µm was relatively lower com-
pared with when the coarser feed size was added. However,
the overall breakage rate improved. The study confirms the
report in the literature that the sudden change in feed ore
heterogeneity in the SAG mill as first stage grinding mill
has the potential to fluctuate and affect the stability of the
mill (Morrell, 2003 Morrell and Valery, 2001).
Comparatively, the batch and locked cycle modes of
grinding the same samples (model quartz and iron ore)
showed that the mill’s acoustic response was sensitive to
changes in the hardness and size distribution. The real-time
monitoring of the AG/SAG mill acoustics was observed to
be a good indicator of the state of the mill, by tracking the
stability and fluctuation caused by feed ore heterogeneity.
Accordingly, the technique can support plant operators to
take proactive action to solve the mill disturbances.
CONCLUSIONS
Real-time measurements of the internal conditions of
industrial tumbling mills (e.g., AG/SAG/ball mills) have
remained virtually impossible over the years due to the
hostile and aggressive environment of such mills. Taking
advantage of the inevitable noise emission during the
grinding process, acoustic sensing and analyses, reported in
this paper the possibility of determining the state of AG/
SAG mill operation in real-time. The results presented have
revealed substantial fundamental knowledge of the unique
sensitivity of operating laboratory AG/SAG mills under
different conditions.
The study findings have shown that excessive noise
emission may suggest a direct interaction of the grinding
media (steel balls) and liner/lifters interaction, which may
be related to issues regarding the mill speed, pulp den-
sity, and mill underloading. This can inform mill opera-
tors in time for proactive actions to be taken towards the
Figure 7. An illustration of acoustic responses to sudden changes in feed ore size distribution (increasing order) in a laboratory
AG/SAG mill
EFFECT OF FEED ORE HETEROGENEITY
IN LOCKED-CYCLE MODE AND
ACOUSTICS
To understand the sensitivity and the fluctuations caused
by feed ore heterogeneity (hardness and size distribution)
in steady-state industrial AG/SAG operations, locked-cycle
procedures in a laboratory AG/SAG mill coupled with
acoustic sensing were performed (Owusu et al., 2023b).
Model quartz of size range –12.7 +2 mm was used as
the initial feed and the grinding cycle was repeated until
near equilibrium was reached. Following near equilibrium
(within six grinding cycles for separate experiments), fresh
feed of quartz (–26.5+16 mm) and iron ore (–12.7+2 mm)
were introduced in the respective tests for an additional two
cycles. Notably, as the mass of the product size of less than
150 µm was reduced, the mill acoustic also appreciated until
the fourth cycle when a pseudo-steady state was achieved.
At the point where the mass of the product size reached
equilibrium (4–6 cycles), the average acoustic intensities
(RMS analysis) also reached equilibrium. By monitoring
acoustic emission as well as the mass of the product size,
the mill steady state was completely distorted after the 6th
and 7th cycles when the coarser fresh feed and another ore
type (different hardness) were introduced. The coarser fresh
feed aided the production of finer particles (–150 µm) but
a lower breakage rate of the top size particles was observed.
Regarding the blend of model quartz and iron ore, the mass
of the particles less than 150 µm was relatively lower com-
pared with when the coarser feed size was added. However,
the overall breakage rate improved. The study confirms the
report in the literature that the sudden change in feed ore
heterogeneity in the SAG mill as first stage grinding mill
has the potential to fluctuate and affect the stability of the
mill (Morrell, 2003 Morrell and Valery, 2001).
Comparatively, the batch and locked cycle modes of
grinding the same samples (model quartz and iron ore)
showed that the mill’s acoustic response was sensitive to
changes in the hardness and size distribution. The real-time
monitoring of the AG/SAG mill acoustics was observed to
be a good indicator of the state of the mill, by tracking the
stability and fluctuation caused by feed ore heterogeneity.
Accordingly, the technique can support plant operators to
take proactive action to solve the mill disturbances.
CONCLUSIONS
Real-time measurements of the internal conditions of
industrial tumbling mills (e.g., AG/SAG/ball mills) have
remained virtually impossible over the years due to the
hostile and aggressive environment of such mills. Taking
advantage of the inevitable noise emission during the
grinding process, acoustic sensing and analyses, reported in
this paper the possibility of determining the state of AG/
SAG mill operation in real-time. The results presented have
revealed substantial fundamental knowledge of the unique
sensitivity of operating laboratory AG/SAG mills under
different conditions.
The study findings have shown that excessive noise
emission may suggest a direct interaction of the grinding
media (steel balls) and liner/lifters interaction, which may
be related to issues regarding the mill speed, pulp den-
sity, and mill underloading. This can inform mill opera-
tors in time for proactive actions to be taken towards the
Figure 7. An illustration of acoustic responses to sudden changes in feed ore size distribution (increasing order) in a laboratory
AG/SAG mill