3864 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
samples are dried before sieving, allowing for the calcula-
tion of moisture content based on the mass difference. The
mechanical power measurement is provided via mechanical
torque and rotational speed measurements of the milling
table. The torque is logged with a sensor made by Kistler
(Type: 4551A). The liberation degree is determined for the
fresh feed material and circuit product. Liberation is con-
sidered to be a decisive benchmark in milling concerning
the achievable concentrate quality.
Initial tests
Before running the first milling trials with the pilot plant,
several tests with the screening machine were performed
by Schröder et al. under the supervision of the authors
(Schröder et al., 2023). In the student thesis, the depen-
dence of the screening efficiency on the PSD, mill through-
put, and the amount of water per deck is investigated for
this type of screening machine. These parameters, are essen-
tial for further definition the boundary limits of the milling
tests. The screen bypass is used as an indicator of screen-
ing efficiency. The tests were carried out with granodiorite
in the fraction 0 up to 8 mm. The material throughput
was varied between 0.3 t/h and 5.0 t/h. Simultaneously,
tests were conducted in dry sieving and various wet siev-
ing modes with a calculated water-to-solid mass ratio of
150 %.The feed material of known PSD was dried and
homogenized before the tests. The screen was fed for
10 min with a constant mass flow. Coarse and fine materi-
als are discharged directly into a hopper after the screening
machine. The sampling of the fine and coarse materials is
performed at the end of each test. The results of this work
are summarized in the diagrams in Figure 5.
The various influencing variables are shown in the dia-
grams. Figure 5a shows the dependence of the screen effi-
ciency on the throughput at dry screening, while Figure 5b
shows the dependence on moisture at constant throughput
with 2.5 t/h. Figure 5a indicates that with a larger through-
put, the screening efficiency decreases, as reflected by a ris-
ing bypass. However, a large amount of water is required to
achieve the screening efficiency of dry screening.
EXPERIMENTAL PROCEDURE
Design of Experiments
The first milling tests were conducted to determine how
the processing plant reacts to different combinations of
milling parameters. Some simplifying assumptions were
adopted, to obtain knowledge about the boundaries. They
are described in the following section.
Granodiorite from the Kindisch quarry was used as the
test material. It was chosen because of its similarity to vari-
ous ore host rocks and abundant availability. Granodiorite
is characterized by mica, feldspar, and quartz. It has a Bond-
Work-Index of 16.3 kWh/t and a Point-Load-Index of
7.0 MPa (Reichert, 2016). Further information about the
test material can be found in (Popov et al., 2020). A size
fraction between 0 mm and 8 mm is used as in the screen-
ing tests presented in section 3.
The main milling parameters to be investigated in the
first tests are milling pressure, milling table speed, and
mill throughput. All these parameters can be controlled by
the PLC. A mill throughput of 1625 kg/h was set to start
the experiments. Table 1 shows the parameter combina-
tions investigated in the first tests. The added water flow
or moisture is another input parameter in the wet milling
operational mode. A feed moisture of approximately 15 %
is set for the initial wet milling test. This is derived from the
investigations by Ballentyne and Lane (Ballantyne and Lane,
2022). The wet milling test is only run in the coarse mode,
according to Figure 2 (red dashed line). This means that the
product will be classified at 200 µm for both dry and wet
milling to allow a better comparison. Therefore, a commi-
nution factor of 40 is assumed in a simplified manner.
Figure 4. Mill process room with (a) cylindrical and (b) conical rollers
samples are dried before sieving, allowing for the calcula-
tion of moisture content based on the mass difference. The
mechanical power measurement is provided via mechanical
torque and rotational speed measurements of the milling
table. The torque is logged with a sensor made by Kistler
(Type: 4551A). The liberation degree is determined for the
fresh feed material and circuit product. Liberation is con-
sidered to be a decisive benchmark in milling concerning
the achievable concentrate quality.
Initial tests
Before running the first milling trials with the pilot plant,
several tests with the screening machine were performed
by Schröder et al. under the supervision of the authors
(Schröder et al., 2023). In the student thesis, the depen-
dence of the screening efficiency on the PSD, mill through-
put, and the amount of water per deck is investigated for
this type of screening machine. These parameters, are essen-
tial for further definition the boundary limits of the milling
tests. The screen bypass is used as an indicator of screen-
ing efficiency. The tests were carried out with granodiorite
in the fraction 0 up to 8 mm. The material throughput
was varied between 0.3 t/h and 5.0 t/h. Simultaneously,
tests were conducted in dry sieving and various wet siev-
ing modes with a calculated water-to-solid mass ratio of
150 %.The feed material of known PSD was dried and
homogenized before the tests. The screen was fed for
10 min with a constant mass flow. Coarse and fine materi-
als are discharged directly into a hopper after the screening
machine. The sampling of the fine and coarse materials is
performed at the end of each test. The results of this work
are summarized in the diagrams in Figure 5.
The various influencing variables are shown in the dia-
grams. Figure 5a shows the dependence of the screen effi-
ciency on the throughput at dry screening, while Figure 5b
shows the dependence on moisture at constant throughput
with 2.5 t/h. Figure 5a indicates that with a larger through-
put, the screening efficiency decreases, as reflected by a ris-
ing bypass. However, a large amount of water is required to
achieve the screening efficiency of dry screening.
EXPERIMENTAL PROCEDURE
Design of Experiments
The first milling tests were conducted to determine how
the processing plant reacts to different combinations of
milling parameters. Some simplifying assumptions were
adopted, to obtain knowledge about the boundaries. They
are described in the following section.
Granodiorite from the Kindisch quarry was used as the
test material. It was chosen because of its similarity to vari-
ous ore host rocks and abundant availability. Granodiorite
is characterized by mica, feldspar, and quartz. It has a Bond-
Work-Index of 16.3 kWh/t and a Point-Load-Index of
7.0 MPa (Reichert, 2016). Further information about the
test material can be found in (Popov et al., 2020). A size
fraction between 0 mm and 8 mm is used as in the screen-
ing tests presented in section 3.
The main milling parameters to be investigated in the
first tests are milling pressure, milling table speed, and
mill throughput. All these parameters can be controlled by
the PLC. A mill throughput of 1625 kg/h was set to start
the experiments. Table 1 shows the parameter combina-
tions investigated in the first tests. The added water flow
or moisture is another input parameter in the wet milling
operational mode. A feed moisture of approximately 15 %
is set for the initial wet milling test. This is derived from the
investigations by Ballentyne and Lane (Ballantyne and Lane,
2022). The wet milling test is only run in the coarse mode,
according to Figure 2 (red dashed line). This means that the
product will be classified at 200 µm for both dry and wet
milling to allow a better comparison. Therefore, a commi-
nution factor of 40 is assumed in a simplified manner.
Figure 4. Mill process room with (a) cylindrical and (b) conical rollers