XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2875
flux, the rising of bubbles was more significantly impeded
by the downward wash water, reducing the rising velocity
of bubbles. As mentioned before, lowering the rising veloc-
ity of bubbles increases the air fraction in flotation cells
(Yianatos and Levy, 1989), but this was not strictly reflected
at the equilibrium stage in Figure 3. However, Figure 3
showed that the reduction of air fraction did not respond
to the reduction of air flux proportionally. For example,
from test 1 to test 2, air flux was reduced by 50%, but the
air fraction was only reduced by 19.5%. This indicated that
some bubbles accumulated in the reverse fluidized bed at
the equilibrium stage, counteracting the reduction in air
fraction. The accumulation of bubbles had a negative effect
on entrainment reduction as they hindered the drainage of
the entrained particles.
To understand the effect of gas flux on liquid motion,
in addition to air fraction, in the reverse fluidized bed, vec-
tor plots for the liquid phase near the downcomer outlet
and wash water inlet in the RFC were generated for the
baseline condition (test 1), the condition with gas flux
reduced by 50% (test 2) and the condition with gas flux
increased by 20% (test 3) as shown in Figure 4. The arrows
in the plots show the moving directions of the liquid phase.
For better illustration, the large red arrows were drawn
based on the vector directions to show the movements of
major streams. In the reverse fluidized bed, the strongest
interactions between liquid and gas phases occurred at the
region near the downcomer outlet and the wash water inlet,
and hence, the vector plots were generated to focus on the
liquid phase at these two regions.
From Figure 4, it can be found that test 2 at the lowest
gas flux showed a different liquid motion behavior com-
pared to test 1 and test 3. For test 2, small eddy flows were
present in the reverse fluidized bed from the region near
the downcomer outlet to the region near the wash water
inlet as indicated by circulated red arrows. These eddy flows
were likely formed due to the encounter between the down-
ward wash water and the rising liquid lifted by bubbles. The
formation of these eddy flows could assist gangue entrain-
ment reduction initially as the wash water mixed with and
diluted the entrained liquid through these eddy flows.
However, when the bubbles accumulated in the reverse flu-
idized bed as discussed before, the bubbles would start to
push the entrained liquid and solid upward, diminishing
the effect of wash water on gangue entrainment reduction.
In this scenario, these small eddy flows would exacerbate
gangue entrainment by inhibiting the fast drainage of
entrained liquid and solids. The significantly accumulated
bubbles and small eddy flows in test 2 explained well the
poor entrainment reduction in this test.
Different to test 2, tests 1 and 3 at higher gas fluxes
presented less eddy flows and a more laminar flow behav-
ior. The uprising flow in tests 1 and 3 was stronger due
to the higher gas fluxes, indicated by the clear uprising
flow appearing on both sides of the downcomer from the
downcomer outlet to the top of the reverse fluidized bed.
Near the wash water inlet, this uprising flow flowed from
0
10
20
30
40
50
60
0 10 20 30 40 50
Simulation time (s)
Baseline (test 1)
Gas -50% (test 2)
Gas +20% (test 3)
Figure 3. Air fraction at the concentrate outlet versus simulation time for baseline
condition (test 1), the condition with gas flux decreased by 50% (test 2) and the
condition with gas increased by 20% (test 3)
Air
Fraction
(%)
flux, the rising of bubbles was more significantly impeded
by the downward wash water, reducing the rising velocity
of bubbles. As mentioned before, lowering the rising veloc-
ity of bubbles increases the air fraction in flotation cells
(Yianatos and Levy, 1989), but this was not strictly reflected
at the equilibrium stage in Figure 3. However, Figure 3
showed that the reduction of air fraction did not respond
to the reduction of air flux proportionally. For example,
from test 1 to test 2, air flux was reduced by 50%, but the
air fraction was only reduced by 19.5%. This indicated that
some bubbles accumulated in the reverse fluidized bed at
the equilibrium stage, counteracting the reduction in air
fraction. The accumulation of bubbles had a negative effect
on entrainment reduction as they hindered the drainage of
the entrained particles.
To understand the effect of gas flux on liquid motion,
in addition to air fraction, in the reverse fluidized bed, vec-
tor plots for the liquid phase near the downcomer outlet
and wash water inlet in the RFC were generated for the
baseline condition (test 1), the condition with gas flux
reduced by 50% (test 2) and the condition with gas flux
increased by 20% (test 3) as shown in Figure 4. The arrows
in the plots show the moving directions of the liquid phase.
For better illustration, the large red arrows were drawn
based on the vector directions to show the movements of
major streams. In the reverse fluidized bed, the strongest
interactions between liquid and gas phases occurred at the
region near the downcomer outlet and the wash water inlet,
and hence, the vector plots were generated to focus on the
liquid phase at these two regions.
From Figure 4, it can be found that test 2 at the lowest
gas flux showed a different liquid motion behavior com-
pared to test 1 and test 3. For test 2, small eddy flows were
present in the reverse fluidized bed from the region near
the downcomer outlet to the region near the wash water
inlet as indicated by circulated red arrows. These eddy flows
were likely formed due to the encounter between the down-
ward wash water and the rising liquid lifted by bubbles. The
formation of these eddy flows could assist gangue entrain-
ment reduction initially as the wash water mixed with and
diluted the entrained liquid through these eddy flows.
However, when the bubbles accumulated in the reverse flu-
idized bed as discussed before, the bubbles would start to
push the entrained liquid and solid upward, diminishing
the effect of wash water on gangue entrainment reduction.
In this scenario, these small eddy flows would exacerbate
gangue entrainment by inhibiting the fast drainage of
entrained liquid and solids. The significantly accumulated
bubbles and small eddy flows in test 2 explained well the
poor entrainment reduction in this test.
Different to test 2, tests 1 and 3 at higher gas fluxes
presented less eddy flows and a more laminar flow behav-
ior. The uprising flow in tests 1 and 3 was stronger due
to the higher gas fluxes, indicated by the clear uprising
flow appearing on both sides of the downcomer from the
downcomer outlet to the top of the reverse fluidized bed.
Near the wash water inlet, this uprising flow flowed from
0
10
20
30
40
50
60
0 10 20 30 40 50
Simulation time (s)
Baseline (test 1)
Gas -50% (test 2)
Gas +20% (test 3)
Figure 3. Air fraction at the concentrate outlet versus simulation time for baseline
condition (test 1), the condition with gas flux decreased by 50% (test 2) and the
condition with gas increased by 20% (test 3)
Air
Fraction
(%)