XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3861
from the feed point in the center toward the dam ring by
centrifugal forces. During this process, it is stressed by the
rollers before the finer portion is finally lifted upward by
an air stream at the louvre ring. A cage classifier, in the
upper part of the VRM, separates the product (fines) from
the middling’s, which are returned to the milling table.
This configuration is a widely accepted standard for raw
meal milling and has widely replaced tumbling mills in
the cement industry. The VRM technology is also used
in many other fields, such as slag and phosphate milling
(Reichert, v2016).
There are different roller geometries available. For
example, the angle of conical rollers could be changed. This
allows selective adjustment of the shear stress via different
roll geometries depending on the feed material characteris-
tics and the comminution target. It also can be used as sup-
port rollers to precondition the confident bed. This already
have been described in (Meyer et al., 1992) to reduce the
vibration of the roller mill. Reichert reports on fundamen-
tal and promising investigations into ore milling on VRMs.
He pointed out that pneumatic transport in VRMs is par-
ticularly energy-intensive because of the high density of
many ores (Reichert, 2016).
LOESCHE developed a pilot VRM operating in over-
flow mode accompanied by external air sifting, as an alter-
native to the energy intensive internal classification. Using
this pilot mill, the comparison between internal and exter-
nal sifting was investigated. The results showed that airflow
and overflow modes were pretty close regarding size reduc-
tion ratio and specific energy while both used dynamic
classifiers. Furthermore, this study provides a comparison
between conventional rod and ball mill circuit grinding and
milling with VRM. According to these results, energy sav-
ings between 19.8 kWh/t to 24.2 kWh/t are possible (Altun
et al., 2015). The experiences gathered with this machine
were taken as the basis of the application in a copper-
gold ore project in Turkey (Harder, 2022). More recently,
OZ Minerals reported the exploitation of a copper-nickel
deposit at West Musgrave (Western Australia) by processing
comparably dry ore in a LOESCHE mill (Ogilvie, 2022).
Respective tests have already been conducted using VRMs
for ore liberation since 2020 (Gleeson, 2020).
In 2005 LOESCHE patented an external classification
in combination with a VRM operating in overflow mode
(Bätz et al., 2005). However, all these variants are suitable
for dry comminution of the material only. In the field of
wet grinding, there is no large-scale alternative for efficient
ore processing.
DRY- AND WET MILLING PLANT WITH
VERTICAL ROLLER MILL
The construction of a comminution circuit for dry and
wet milling of ores by a VRM was supported by pub-
lic research funding (Lieberwirth, 2023). An overview of
the plant is shown in Figure 1. The plant was built at the
Institute for Mineral Processing Machines and Recycling
Systems Technology (TU Bergakademie Freiberg, Saxony,
Germany). LOESCHE and the plant manufacturer AKW
were contracted to build the plant. It represents a closed
wet and dry milling circuit in its entire complexity from
controlled material feeding, considering the recirculated
load, to milling, multi-stage screening and dewatering by a
centrifuge on a pilot scale.
As shown in Figure 1, the plant extends over several
levels. Dry and wet milling tests can be performed. Two
different operating modes are available for the wet mill-
ing operation. The flow diagram of the plant is shown in
Figure 2.
As shown in the flow diagram, the core of the plant
is the milling-classifying circuit with external screen clas-
sification. This core circuit is used in all operating modes.
The two central elements are the new VRM (LM 3.6/3w)
developed by LOESCHE and a vibrating round screen
(VRS 1500/3) from Allgaier. The circuit design considers
a nominal throughput of up to 500 kg/h at a circuit load
of up to 5,000 kg/h. The separation occurs at 200 µm sup-
ported by several relieving decks in the screening machine.
The mill product classified as coarse material is recir-
culated with a tube chain conveyor onto a belt scale and is
then returned to the mill. The metered fresh feed material
is fed to the mill via a belt feeder equipped with a weighting
scale. The material feed is controlled as a function of the
recirculated material mass flow from the circuit and the tar-
get throughput. This allows to set the plant to a quite con-
stant mill throughput pre-selected by the plant operator.
The material routing of the fines (200 µm) classi-
fied by the screening machine is fundamentally different
in the various operating modes. As shown in the flow dia-
gram, the product is discharged directly after the screening
machine into a receiving hopper during dry operation. On
the other hand, the product is fed as a suspension into a
tank and pumped through tubes in wet milling. In this pro-
cess, the suspension in the “Coarse mode” is passed through
another tank to a hydro cyclone battery and a centrifuge
for separating the solids from the water, thus discharging
the final product with a particle size corresponding to the
finest screen cut. In the “Fine mode,” the slurry is directed
from the feed point in the center toward the dam ring by
centrifugal forces. During this process, it is stressed by the
rollers before the finer portion is finally lifted upward by
an air stream at the louvre ring. A cage classifier, in the
upper part of the VRM, separates the product (fines) from
the middling’s, which are returned to the milling table.
This configuration is a widely accepted standard for raw
meal milling and has widely replaced tumbling mills in
the cement industry. The VRM technology is also used
in many other fields, such as slag and phosphate milling
(Reichert, v2016).
There are different roller geometries available. For
example, the angle of conical rollers could be changed. This
allows selective adjustment of the shear stress via different
roll geometries depending on the feed material characteris-
tics and the comminution target. It also can be used as sup-
port rollers to precondition the confident bed. This already
have been described in (Meyer et al., 1992) to reduce the
vibration of the roller mill. Reichert reports on fundamen-
tal and promising investigations into ore milling on VRMs.
He pointed out that pneumatic transport in VRMs is par-
ticularly energy-intensive because of the high density of
many ores (Reichert, 2016).
LOESCHE developed a pilot VRM operating in over-
flow mode accompanied by external air sifting, as an alter-
native to the energy intensive internal classification. Using
this pilot mill, the comparison between internal and exter-
nal sifting was investigated. The results showed that airflow
and overflow modes were pretty close regarding size reduc-
tion ratio and specific energy while both used dynamic
classifiers. Furthermore, this study provides a comparison
between conventional rod and ball mill circuit grinding and
milling with VRM. According to these results, energy sav-
ings between 19.8 kWh/t to 24.2 kWh/t are possible (Altun
et al., 2015). The experiences gathered with this machine
were taken as the basis of the application in a copper-
gold ore project in Turkey (Harder, 2022). More recently,
OZ Minerals reported the exploitation of a copper-nickel
deposit at West Musgrave (Western Australia) by processing
comparably dry ore in a LOESCHE mill (Ogilvie, 2022).
Respective tests have already been conducted using VRMs
for ore liberation since 2020 (Gleeson, 2020).
In 2005 LOESCHE patented an external classification
in combination with a VRM operating in overflow mode
(Bätz et al., 2005). However, all these variants are suitable
for dry comminution of the material only. In the field of
wet grinding, there is no large-scale alternative for efficient
ore processing.
DRY- AND WET MILLING PLANT WITH
VERTICAL ROLLER MILL
The construction of a comminution circuit for dry and
wet milling of ores by a VRM was supported by pub-
lic research funding (Lieberwirth, 2023). An overview of
the plant is shown in Figure 1. The plant was built at the
Institute for Mineral Processing Machines and Recycling
Systems Technology (TU Bergakademie Freiberg, Saxony,
Germany). LOESCHE and the plant manufacturer AKW
were contracted to build the plant. It represents a closed
wet and dry milling circuit in its entire complexity from
controlled material feeding, considering the recirculated
load, to milling, multi-stage screening and dewatering by a
centrifuge on a pilot scale.
As shown in Figure 1, the plant extends over several
levels. Dry and wet milling tests can be performed. Two
different operating modes are available for the wet mill-
ing operation. The flow diagram of the plant is shown in
Figure 2.
As shown in the flow diagram, the core of the plant
is the milling-classifying circuit with external screen clas-
sification. This core circuit is used in all operating modes.
The two central elements are the new VRM (LM 3.6/3w)
developed by LOESCHE and a vibrating round screen
(VRS 1500/3) from Allgaier. The circuit design considers
a nominal throughput of up to 500 kg/h at a circuit load
of up to 5,000 kg/h. The separation occurs at 200 µm sup-
ported by several relieving decks in the screening machine.
The mill product classified as coarse material is recir-
culated with a tube chain conveyor onto a belt scale and is
then returned to the mill. The metered fresh feed material
is fed to the mill via a belt feeder equipped with a weighting
scale. The material feed is controlled as a function of the
recirculated material mass flow from the circuit and the tar-
get throughput. This allows to set the plant to a quite con-
stant mill throughput pre-selected by the plant operator.
The material routing of the fines (200 µm) classi-
fied by the screening machine is fundamentally different
in the various operating modes. As shown in the flow dia-
gram, the product is discharged directly after the screening
machine into a receiving hopper during dry operation. On
the other hand, the product is fed as a suspension into a
tank and pumped through tubes in wet milling. In this pro-
cess, the suspension in the “Coarse mode” is passed through
another tank to a hydro cyclone battery and a centrifuge
for separating the solids from the water, thus discharging
the final product with a particle size corresponding to the
finest screen cut. In the “Fine mode,” the slurry is directed