102 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
IMPROVING LIBERATION
The primary aim of the comminution and classification
process is to achieve sufficient liberation, which plays a cru-
cial role in the separation achieved in downstream units. It
is also important to avoid fine particle generation (generally
less than 10 µm) as fines can adversely affect the efficiency
of comminution and classification and are also poorly
recovered in downstream flotation.
The traditional comminution methods (e.g., tumbling
mills) are energy-intensive and produce excessive fines and
poor liberation in the coarser sizes. In recent years, innova-
tive technologies have emerged, aiming to improve both
energy efficiency and liberation and reduce fines produc-
tion (Klein et al., 2018). The novel comminution technolo-
gies apply the minimum comminution energy required to
fracture particles under primary breakage (Austin, 1971)
and liberate valuable minerals at coarser sizes suitable for
separation units (Gerold et al., 2012 Guldris Leon et al.,
2020 Bracey et al., 2016). Two such novel comminution
units which are enhancing energy efficiency and improv-
ing liberation efficiency are the Loesche Vertical Roller Mill
(VRM) and EDS Multishaft mills (Figure 3) (Altun et al.,
2017 Bracey et al. 2018).
High voltage pulse (HVP) is another emerging com-
minution technology which has been shown to improve
particle liberation with the electrical energy preferentially
passing and breaking through the mineralized particles
(Shi et al, 2018). An HVP electrode grizzly arrangement
has been developed which has the potential to be used to
pretreat an ore and improve liberation downstream (Andre
et al, 2023).
A key processing step in a comminution circuit is the
classification unit. The role of classification is to separate
particles by size, return the coarser particles to the com-
minution stage and pass finer particles to the downstream
separation unit. The unit’s classification efficiency is key in
ensuring particles are not misplaced in the wrong stream
(Runge et al., 2024). Hydrocyclones are the technology of
choice for classification as they can manage higher capaci-
ties and have low maintenance requirements. These devices,
however, have poor separation efficiencies and because they
use hydraulic forces for classification, there can be a mis-
placement of particles by density (Carpenter et al., 2019,
Jokovic et al, 2022, Sahoo et al., 2020, Lisso, 2024).
The density effect in classification can result in the recir-
culation of high-density fine particles containing valuable
minerals (e.g., gold, copper, lead) and the over-grinding of
those particles in the comminution stage. It can also result
in low-density poorly liberated coarse particles bypassing
grinding and diverting to downstream separation, causing
poor liberation in the coarser sizes. Frausto et al, 2017 in an
industrial case study showed that poor coarse particle lib-
eration and thus coarse particle recovery can be improved
by changing from cyclones, where classification is affected
by density, to screens which separate particles according to
size only (Figure 4). This improvement in coarse lead recov-
ery in this case study was shown to result in an average
improvement in overall lead recovery of 7% in downstream
flotation.
Improving classification efficiency is a key factor in
ensuring the overall performance of comminution and
flotation circuits (Rasyid et al., 2019, Jokovic et al., 2022,
Runge et al., 2024). Vibrating screens generally have a
higher classification efficiency with minimum misplaced
particles, but their capacity drops significantly as the parti-
cle size becomes finer (i.e., less than 500 µm). A promising
Figure 3. Loesche Vertical Roller Mill (Loesche, 2024) and EDS 10 Shaft Multishaft Mill (EDS, 2022)
IMPROVING LIBERATION
The primary aim of the comminution and classification
process is to achieve sufficient liberation, which plays a cru-
cial role in the separation achieved in downstream units. It
is also important to avoid fine particle generation (generally
less than 10 µm) as fines can adversely affect the efficiency
of comminution and classification and are also poorly
recovered in downstream flotation.
The traditional comminution methods (e.g., tumbling
mills) are energy-intensive and produce excessive fines and
poor liberation in the coarser sizes. In recent years, innova-
tive technologies have emerged, aiming to improve both
energy efficiency and liberation and reduce fines produc-
tion (Klein et al., 2018). The novel comminution technolo-
gies apply the minimum comminution energy required to
fracture particles under primary breakage (Austin, 1971)
and liberate valuable minerals at coarser sizes suitable for
separation units (Gerold et al., 2012 Guldris Leon et al.,
2020 Bracey et al., 2016). Two such novel comminution
units which are enhancing energy efficiency and improv-
ing liberation efficiency are the Loesche Vertical Roller Mill
(VRM) and EDS Multishaft mills (Figure 3) (Altun et al.,
2017 Bracey et al. 2018).
High voltage pulse (HVP) is another emerging com-
minution technology which has been shown to improve
particle liberation with the electrical energy preferentially
passing and breaking through the mineralized particles
(Shi et al, 2018). An HVP electrode grizzly arrangement
has been developed which has the potential to be used to
pretreat an ore and improve liberation downstream (Andre
et al, 2023).
A key processing step in a comminution circuit is the
classification unit. The role of classification is to separate
particles by size, return the coarser particles to the com-
minution stage and pass finer particles to the downstream
separation unit. The unit’s classification efficiency is key in
ensuring particles are not misplaced in the wrong stream
(Runge et al., 2024). Hydrocyclones are the technology of
choice for classification as they can manage higher capaci-
ties and have low maintenance requirements. These devices,
however, have poor separation efficiencies and because they
use hydraulic forces for classification, there can be a mis-
placement of particles by density (Carpenter et al., 2019,
Jokovic et al, 2022, Sahoo et al., 2020, Lisso, 2024).
The density effect in classification can result in the recir-
culation of high-density fine particles containing valuable
minerals (e.g., gold, copper, lead) and the over-grinding of
those particles in the comminution stage. It can also result
in low-density poorly liberated coarse particles bypassing
grinding and diverting to downstream separation, causing
poor liberation in the coarser sizes. Frausto et al, 2017 in an
industrial case study showed that poor coarse particle lib-
eration and thus coarse particle recovery can be improved
by changing from cyclones, where classification is affected
by density, to screens which separate particles according to
size only (Figure 4). This improvement in coarse lead recov-
ery in this case study was shown to result in an average
improvement in overall lead recovery of 7% in downstream
flotation.
Improving classification efficiency is a key factor in
ensuring the overall performance of comminution and
flotation circuits (Rasyid et al., 2019, Jokovic et al., 2022,
Runge et al., 2024). Vibrating screens generally have a
higher classification efficiency with minimum misplaced
particles, but their capacity drops significantly as the parti-
cle size becomes finer (i.e., less than 500 µm). A promising
Figure 3. Loesche Vertical Roller Mill (Loesche, 2024) and EDS 10 Shaft Multishaft Mill (EDS, 2022)