XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 3869
screening condition. Most of the added water leaves the
screening machine with the fines, but some of it remains
with the coarse material. During the drying of the taken
samples, the mass loss was measured. Thus, a moisture con-
tent of approximately 17 %was calculated for the recir-
culated material. Therefore, the weighted mass flow of the
recirculated material during the test is 1419.35 kg/h with
the included water mass.
Figure 10 shows the influence of the milling pressure
on the mean value and on the scatter of the feed material
throughput at two milling table circumferential speeds.
It is noticeable that with higher milling pressure the
feed material throughput rises. The higher milling table
speed results in a higher throughput, consequently more
fine material is produced. This could be explained by the
lower bed height, which leads to a different particle stress.
The mean particle size distributions for each parameter set-
ting of the milling product, as shown in Figure 13, supports
this thesis. However, the difference between the two table
speeds seems to be marginal. This effect may be attributed to
the fact that with a higher table speed also the material can
leave the table more easily. Therefore, the effect of higher
energy input through the higher speed is affected by shorter
residence time of the milling material. Remarkably, both
curve trends of the mean values are at a similar through-
put level at a milling pressure of 1408 kN/m2. However,
the maximum throughput of 500 kg/h, achievable with the
pilot circuit, has not yet been reached by far.
Reichert et al. reported a similar behavior for dry mill-
ing of iron ore, but the throughput rates rise remarkably
steeper in his test results compared to the results presented
here. This may be attributed to the larger mill with more
rollers (LM 4.5/4) used by him and the different feed mate-
rial (Reichert et al., 2015). His study also included mill-
ing pressures up to 5,000 kN/m2. They showed that the
throughput will reach a maximum at a certain grinding
pressure beyond this point, a higher grinding pressure has
no more influence on the throughput. The point at which
this maximum is reached is specific to the milled material.
The above-described observations could only be confirmed
by tests with higher grinding pressures, but these were not
part of the ongoing study.
The comparison between wet and dry milling shows,
that with the same milling parameter the dry process has
a mean throughput of about 278 kg/h while the wet pro-
cess only reaches 157 kg/h of feed material throughput.
This could be attributed to the missing online detection of
the moisture within the recirculating material. Thus, the
weighted scale belt conveyor also measures the contained
water of the bulk material. Consequently, although the
parameter settings are the same, a different solid material
mill throughput is fed. However, the difference between
dry and wet milling is remarkably high. This means that
not only the different throughput is responsible, but also
differences in the feed material, for example the particle size
distribution. The corresponding particle size distribution is
Figure 10. Variation of the feed throughput as a function of milling pressure and milling table speed
screening condition. Most of the added water leaves the
screening machine with the fines, but some of it remains
with the coarse material. During the drying of the taken
samples, the mass loss was measured. Thus, a moisture con-
tent of approximately 17 %was calculated for the recir-
culated material. Therefore, the weighted mass flow of the
recirculated material during the test is 1419.35 kg/h with
the included water mass.
Figure 10 shows the influence of the milling pressure
on the mean value and on the scatter of the feed material
throughput at two milling table circumferential speeds.
It is noticeable that with higher milling pressure the
feed material throughput rises. The higher milling table
speed results in a higher throughput, consequently more
fine material is produced. This could be explained by the
lower bed height, which leads to a different particle stress.
The mean particle size distributions for each parameter set-
ting of the milling product, as shown in Figure 13, supports
this thesis. However, the difference between the two table
speeds seems to be marginal. This effect may be attributed to
the fact that with a higher table speed also the material can
leave the table more easily. Therefore, the effect of higher
energy input through the higher speed is affected by shorter
residence time of the milling material. Remarkably, both
curve trends of the mean values are at a similar through-
put level at a milling pressure of 1408 kN/m2. However,
the maximum throughput of 500 kg/h, achievable with the
pilot circuit, has not yet been reached by far.
Reichert et al. reported a similar behavior for dry mill-
ing of iron ore, but the throughput rates rise remarkably
steeper in his test results compared to the results presented
here. This may be attributed to the larger mill with more
rollers (LM 4.5/4) used by him and the different feed mate-
rial (Reichert et al., 2015). His study also included mill-
ing pressures up to 5,000 kN/m2. They showed that the
throughput will reach a maximum at a certain grinding
pressure beyond this point, a higher grinding pressure has
no more influence on the throughput. The point at which
this maximum is reached is specific to the milled material.
The above-described observations could only be confirmed
by tests with higher grinding pressures, but these were not
part of the ongoing study.
The comparison between wet and dry milling shows,
that with the same milling parameter the dry process has
a mean throughput of about 278 kg/h while the wet pro-
cess only reaches 157 kg/h of feed material throughput.
This could be attributed to the missing online detection of
the moisture within the recirculating material. Thus, the
weighted scale belt conveyor also measures the contained
water of the bulk material. Consequently, although the
parameter settings are the same, a different solid material
mill throughput is fed. However, the difference between
dry and wet milling is remarkably high. This means that
not only the different throughput is responsible, but also
differences in the feed material, for example the particle size
distribution. The corresponding particle size distribution is
Figure 10. Variation of the feed throughput as a function of milling pressure and milling table speed