544 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The fines feed thickening and the coarse bypasses thicken-
ing before mixed coarse and fines are pumped to a tailings
dam or to filtration. In the VRM circuit the lack of wet
coarse tailings means that cycloning is no longer required.
Instead, a simple drum mixer will be used to combine dry
grit tailings with thickener underflow before it is conveyed
and trucked to tails stacking or used elsewhere for construc-
tion purposes.
Test work also showed that flotation performance after
VRM is superior to that achieved in the AG/Ball pilot plant.
Very low sulfur levels were achieved in the magnetite con-
centrate after VRM grinding and pyrrhotite was removed
by flotation. The levels achieved were 0.02 to 0.03% S, well
below the target value set to minimize SO2 gas production
in pelletizing. In addition, the pyrrhotite flotation rate for
VRM product was very fast and this is likely to result in a
smaller flotation section.
The enclosed nature of the VRM means that even
though dry milling is employed, the process will not emit
dust. This is important given the siliceous nature of the
non-magnetic gangue at Southdown. Immediately after
VRM grinding the 85 µm material is slurried ahead of IMS
followed by flotation. Even the dry magnetic separation
section will be essentially dust free due to the lack of sub
38 µm in the grit stream.
A second crushing stage is typically needed ahead of
VRM compared to AG/Ball. However, as the VRM top-
size only needs to be less than 100 mm (specifically for
Southdown, coarser is allowed for softer ores) an open cir-
cuit secondary cone crusher is sufficient. This compares less
Table 2. VRM vs AG and ball mill grinding to P80 85 µm with integrated non-mag waste rejection
Type of Figure AG/Ball VRM
AG SE (100% of Feed) 9.84 kWh/t Comminution SE 4.5 kWh/t
Ball Mill SE 13.7 kWh/t Fan, classifier, etc. 6.8 kWh/t
Mass rejected as coarse non-mag waste 32% of feed Mass rejected as coarse non-mag waste 35% of feed
Classification and internal conveyors 5%
allowance
+1.7 kWh/t Internal conveyors and mag separation +1 kWh/t
Total Duty Power 20.8 kWh/t Total Duty Power 12.3 kWh/t
Mass Rejected by IMS 27.7% of feed Mass Rejected by IMS 27.1% of feed
Mass of IMS Concentrate for Regrinding 40.0% of feed Mass of IMS Concentrate for Regrinding 37.9% of feed
Figure 6. Continuous VRM and grit magnetic separation pilot plant flowsheet
The fines feed thickening and the coarse bypasses thicken-
ing before mixed coarse and fines are pumped to a tailings
dam or to filtration. In the VRM circuit the lack of wet
coarse tailings means that cycloning is no longer required.
Instead, a simple drum mixer will be used to combine dry
grit tailings with thickener underflow before it is conveyed
and trucked to tails stacking or used elsewhere for construc-
tion purposes.
Test work also showed that flotation performance after
VRM is superior to that achieved in the AG/Ball pilot plant.
Very low sulfur levels were achieved in the magnetite con-
centrate after VRM grinding and pyrrhotite was removed
by flotation. The levels achieved were 0.02 to 0.03% S, well
below the target value set to minimize SO2 gas production
in pelletizing. In addition, the pyrrhotite flotation rate for
VRM product was very fast and this is likely to result in a
smaller flotation section.
The enclosed nature of the VRM means that even
though dry milling is employed, the process will not emit
dust. This is important given the siliceous nature of the
non-magnetic gangue at Southdown. Immediately after
VRM grinding the 85 µm material is slurried ahead of IMS
followed by flotation. Even the dry magnetic separation
section will be essentially dust free due to the lack of sub
38 µm in the grit stream.
A second crushing stage is typically needed ahead of
VRM compared to AG/Ball. However, as the VRM top-
size only needs to be less than 100 mm (specifically for
Southdown, coarser is allowed for softer ores) an open cir-
cuit secondary cone crusher is sufficient. This compares less
Table 2. VRM vs AG and ball mill grinding to P80 85 µm with integrated non-mag waste rejection
Type of Figure AG/Ball VRM
AG SE (100% of Feed) 9.84 kWh/t Comminution SE 4.5 kWh/t
Ball Mill SE 13.7 kWh/t Fan, classifier, etc. 6.8 kWh/t
Mass rejected as coarse non-mag waste 32% of feed Mass rejected as coarse non-mag waste 35% of feed
Classification and internal conveyors 5%
allowance
+1.7 kWh/t Internal conveyors and mag separation +1 kWh/t
Total Duty Power 20.8 kWh/t Total Duty Power 12.3 kWh/t
Mass Rejected by IMS 27.7% of feed Mass Rejected by IMS 27.1% of feed
Mass of IMS Concentrate for Regrinding 40.0% of feed Mass of IMS Concentrate for Regrinding 37.9% of feed
Figure 6. Continuous VRM and grit magnetic separation pilot plant flowsheet