XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 543
Southdown ore samples are abrasive and difficult to
grind in a ball mill. However, the large grain size makes
the ore relatively easy to break at crushing sizes. The ore is
more than one third magnetite as directly measured by the
Davis Tube Recovery (DTR) values, and this is the cause
of the high SG value. Conventional wet milling was tested
in 2010/2011 and again a few years later. The VRM pilot
work was conducted from 2020 to 2022. Despite the long
time between pilot programs, tests showed that little, if any,
degradation of the sample had occurred.
TEST WORK
Summary Results
Within the different feasibility stages of the Southdown
Magnetite project intensive metallurgical test work and
detailed comparisons of conventional and new comminu-
tion processes, including HPGR and VRM have been car-
ried out. The test programs and their analysis are described
in detail by Dean David et al (2023). Only the comparative
results will be discussed within this paper.
Loesche installed a continuously operable closed circuit
pilot plant in their test center in Neuss, Germany, able to
extract and process grits from the VRM, then return the
magnetic grits to the mill for further comminution. The
magnetic separation produced a coarse and dry grits waste
stream. The final P80 85 µm VRM baghouse product con-
tained the magnetite, as illustrated in Figure 6.
The pilot plant configuration is shown in Figure 6. This
is similar in all ways to Figure 4, except that the grits (14)
are magnetically separated, the barren waste (16) disposed
of and the magnetics (15) returned to VRM feed.
In grit extraction and processing mode the VRM
achieves a 41% reduction in power compared to the AG/
Ball mill circuit and reduces the mass to be processed and
ground in the final IMS stages of the flowsheet by 5.5%
whilst maintaining the same Magnetite recovery. The P80
85 µm IMS concentrate is subjected to flotation to remove
pyrrhotite, then ground to approximately P80 40 µm before
cleaner magnetic separation generates the final magnetite
concentrate.
The greater power benefits achieved when the VRM is
operated in grit extraction mode confirms the benefits seen
in the first comparison, confirms the promise offered by
the grit circuit and confirms that VRM technology has the
attributes to shift project economics in a positive direction.
DESIGN CONSIDERATIONS
Design Changes and Key Project Benefits
The change from AG/Ball grinding to VRM brings with it
many advantages, other than reduced power consumption,
for the Southdown project.
The power benefit of changing from AG/Ball to VRM
reduces the maximum and average amount of power that
needs to be supplied to the operation. It also means that
a given renewable energy installation will account for a
greater proportion of the total power.
The ability to reject 35% of the feed mass as dry non-
magnetic grits is estimated to reduce the water supply
requirements for the project by 24%. Not only is the dry
disposal of coarse tailings possible, but it is also possible
to mix thickened fine tailings with the coarse material to
produce conveyable and compactable tailings with mini-
mal water content (13% moisture). It may be necessary to
dispose of a small proportion of the fine tailings as slurry to
ensure that the remainder of the tailings is always convey-
able, but the amount of wet tailings disposal required with
VRM technology will be at least one order of magnitude
below that required with AG/Ball milling. It is also pos-
sible to filter minor excess fine tails without a major capital
investment in filters.
In the AG/Ball circuit the RMS tails with a top size
of 3 mm were cycloned to separate the coarse from fines.
Table 1. Comminution properties of Southdown iron ore
Test
Measurement
kWh/t g/cm3 %
DWI 5.80
CWI 12,00
RWI 13.10
BWI 18.20
AI 0.40
SG (g/cm3) 3,52
Davis Tube Test recovery (%)36.00
Sulfur content 0.40
Source: David et al., 2023
Southdown ore samples are abrasive and difficult to
grind in a ball mill. However, the large grain size makes
the ore relatively easy to break at crushing sizes. The ore is
more than one third magnetite as directly measured by the
Davis Tube Recovery (DTR) values, and this is the cause
of the high SG value. Conventional wet milling was tested
in 2010/2011 and again a few years later. The VRM pilot
work was conducted from 2020 to 2022. Despite the long
time between pilot programs, tests showed that little, if any,
degradation of the sample had occurred.
TEST WORK
Summary Results
Within the different feasibility stages of the Southdown
Magnetite project intensive metallurgical test work and
detailed comparisons of conventional and new comminu-
tion processes, including HPGR and VRM have been car-
ried out. The test programs and their analysis are described
in detail by Dean David et al (2023). Only the comparative
results will be discussed within this paper.
Loesche installed a continuously operable closed circuit
pilot plant in their test center in Neuss, Germany, able to
extract and process grits from the VRM, then return the
magnetic grits to the mill for further comminution. The
magnetic separation produced a coarse and dry grits waste
stream. The final P80 85 µm VRM baghouse product con-
tained the magnetite, as illustrated in Figure 6.
The pilot plant configuration is shown in Figure 6. This
is similar in all ways to Figure 4, except that the grits (14)
are magnetically separated, the barren waste (16) disposed
of and the magnetics (15) returned to VRM feed.
In grit extraction and processing mode the VRM
achieves a 41% reduction in power compared to the AG/
Ball mill circuit and reduces the mass to be processed and
ground in the final IMS stages of the flowsheet by 5.5%
whilst maintaining the same Magnetite recovery. The P80
85 µm IMS concentrate is subjected to flotation to remove
pyrrhotite, then ground to approximately P80 40 µm before
cleaner magnetic separation generates the final magnetite
concentrate.
The greater power benefits achieved when the VRM is
operated in grit extraction mode confirms the benefits seen
in the first comparison, confirms the promise offered by
the grit circuit and confirms that VRM technology has the
attributes to shift project economics in a positive direction.
DESIGN CONSIDERATIONS
Design Changes and Key Project Benefits
The change from AG/Ball grinding to VRM brings with it
many advantages, other than reduced power consumption,
for the Southdown project.
The power benefit of changing from AG/Ball to VRM
reduces the maximum and average amount of power that
needs to be supplied to the operation. It also means that
a given renewable energy installation will account for a
greater proportion of the total power.
The ability to reject 35% of the feed mass as dry non-
magnetic grits is estimated to reduce the water supply
requirements for the project by 24%. Not only is the dry
disposal of coarse tailings possible, but it is also possible
to mix thickened fine tailings with the coarse material to
produce conveyable and compactable tailings with mini-
mal water content (13% moisture). It may be necessary to
dispose of a small proportion of the fine tailings as slurry to
ensure that the remainder of the tailings is always convey-
able, but the amount of wet tailings disposal required with
VRM technology will be at least one order of magnitude
below that required with AG/Ball milling. It is also pos-
sible to filter minor excess fine tails without a major capital
investment in filters.
In the AG/Ball circuit the RMS tails with a top size
of 3 mm were cycloned to separate the coarse from fines.
Table 1. Comminution properties of Southdown iron ore
Test
Measurement
kWh/t g/cm3 %
DWI 5.80
CWI 12,00
RWI 13.10
BWI 18.20
AI 0.40
SG (g/cm3) 3,52
Davis Tube Test recovery (%)36.00
Sulfur content 0.40
Source: David et al., 2023