3740 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
100% slurry filling load. A test with no slurry was also run
for power draw measurement. Note that 200% to 300%
loading probably represents close to typical operating over-
flow ball mill slurry levels, according to liquid tracer tests
conducted in plant ball mills (Austin et al, 1984).
Starting with high (typical overflow mill) slurry level,
the power draw was minimum with maximum slurry
loading. Power first increased with decreasing slurry load-
ing, reached an inflection point around 125%, and then
decreased with decreasing mill loading as shown in Figure 2.
Since the mill feed was the same ore for every test,
the “Cumulative Mill Grinding Rates” represent “Mill
Grinding Efficiencies” at each of the mesh sizes. Figure 3
shows, at 100 mesh (a 147 micron screen opening, in this
case), again starting with the highest loading, the grinding
rates were essentially constant from 300% down to 100%
slurry loading. There was a small increase at 75% loading,
and then a much higher grinding rate (0.94 t/kWh), 15 to
20% above the average (0.80 t/kWh) of all the others at the
lowest mill loading of 37.5%.
The conclusion regarding grinding efficiency in the
torque mill is that the lowest slurry level tested provided
the highest grinding efficiency. We note that test repeat-
ability is not exactly defined at this moment (perhaps it will
Table 2. Summary Table of Plant Grate versus Overflow Ball
Mill Efficiencies
Location (reported by)
and Mill Size
Relative Efficiency
Factor
Marcy (Mine and Smelter)
AZ 10.5×11 1.09
Mexico 8×6
AZ 8×6
CO 9.5×7
CO 6.5×6
ID 6.5×4.5
Canada 6.5×15.5
Canada 6.5×12.5
Gold Hunter (del Mar)
Tough-Oakes (del Mar)
Hollinger 6.5×14
Sylvanite 5×16
Lake Shore 5×16
Lake Shore 6×16
Int Nickel
Jindal Saw
1.09
1.17
1.04
1.29
1.07
1.06
1.13
1.15
1.28
1.0
1.18
1.10
1.19
1.0
1.34
Average of 16 plant comparisons:
Range:
1.14
1.0–1.34
Figure 1. Metcom torque mill
Figure 2. Effect of slurry filling level on power
Figure 3. Cumulative grinding rate as a function of slurry
level
100% slurry filling load. A test with no slurry was also run
for power draw measurement. Note that 200% to 300%
loading probably represents close to typical operating over-
flow ball mill slurry levels, according to liquid tracer tests
conducted in plant ball mills (Austin et al, 1984).
Starting with high (typical overflow mill) slurry level,
the power draw was minimum with maximum slurry
loading. Power first increased with decreasing slurry load-
ing, reached an inflection point around 125%, and then
decreased with decreasing mill loading as shown in Figure 2.
Since the mill feed was the same ore for every test,
the “Cumulative Mill Grinding Rates” represent “Mill
Grinding Efficiencies” at each of the mesh sizes. Figure 3
shows, at 100 mesh (a 147 micron screen opening, in this
case), again starting with the highest loading, the grinding
rates were essentially constant from 300% down to 100%
slurry loading. There was a small increase at 75% loading,
and then a much higher grinding rate (0.94 t/kWh), 15 to
20% above the average (0.80 t/kWh) of all the others at the
lowest mill loading of 37.5%.
The conclusion regarding grinding efficiency in the
torque mill is that the lowest slurry level tested provided
the highest grinding efficiency. We note that test repeat-
ability is not exactly defined at this moment (perhaps it will
Table 2. Summary Table of Plant Grate versus Overflow Ball
Mill Efficiencies
Location (reported by)
and Mill Size
Relative Efficiency
Factor
Marcy (Mine and Smelter)
AZ 10.5×11 1.09
Mexico 8×6
AZ 8×6
CO 9.5×7
CO 6.5×6
ID 6.5×4.5
Canada 6.5×15.5
Canada 6.5×12.5
Gold Hunter (del Mar)
Tough-Oakes (del Mar)
Hollinger 6.5×14
Sylvanite 5×16
Lake Shore 5×16
Lake Shore 6×16
Int Nickel
Jindal Saw
1.09
1.17
1.04
1.29
1.07
1.06
1.13
1.15
1.28
1.0
1.18
1.10
1.19
1.0
1.34
Average of 16 plant comparisons:
Range:
1.14
1.0–1.34
Figure 1. Metcom torque mill
Figure 2. Effect of slurry filling level on power
Figure 3. Cumulative grinding rate as a function of slurry
level