XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2907
pronounced at higher air flow rates compared to lower air
flow rates.
Dankwah et al. (2022) observed that increasing the air
flow rate in a batch fluidised bed reduced the bed height.
They attributed this behaviour to segregation of the par-
ticles within the bed, with the coarser particles settling and
packing at the bottom. Consequently, they conclude that
the packed bed reduces the effective velocity of the rising
fluidisation water, decreasing the upward forces on the
bubble-particle aggregates, thereby reducing recovery. This
is another possible reason for the drop in recovery at high
air flow rates.
The phenomenon where recovery does not continu-
ally increase with increasing air rates has also been found
in conventional flotation. Previous work by Barbian et al.
(2006) and Hadler et al. (2010) investigated the effect of
air flow rate on flotation in conventional cells. They found
that there was an optimum air flow rate at which flotation
recovery increases towards a maximum, followed by a sub-
sequent decrease. They attributed this finding to the prop-
erties of the flotation froth, corresponding to an optimum
balance between froth stability and froth residence time.
However, this mechanism is not applicable to these
tests, as the small-scale fluidised bed device has no froth
layer. These results, therefore, show that the mechanism by
which high air flow rates poorly affect copper recovery is
related to changes in the pulp (free-settling zone /fluidised
bed zone) or detachment at the pulp air interface. Further
work is required to fully understand the competing mecha-
nisms that cause poor recovery at high air flow rates in flui-
dised bed flotation.
Effect of Water Rate on Copper Recovery
The results of the effect of water flow rate on copper recovery
when the air flow rate was varied are presented in Figure 8.
Unlike the air flow rate, water flow rate has a linear rela-
tionship with copper recovery. The same relationship was
observed by Demir et al. (2022) when they varied the water
flow rate in a pilot-scale HydroFloat ® work. Recovery was
lowest at the lowest air flow rate tested, ranging from 62%
to 72% when the water flow rate was varied from 0.33 cm/s
to 0.99 cm/s. Copper recovery was significantly higher
when the cell was operated at Jg of 0.1 cm/s (71% to 85%).
Above Jg of 0.1 cm/s, no further increase in recovery was
observed with increasing water flow rate. Increasing the
water flow rate increases the upward forces on the bubble-
particle aggregates, thereby promoting recovery. This was
observed at both low and high air flow rates.
Other researchers have reported bed expansion with
increasing water flow rate (Zanin et al., 2021, Dankwah
et al., 2022, Verster et al., 2023). Increasing the water flow
rate expands the fluidised bed, which increases the bed
level, thereby shortening the travel distance (the distance
between the top of the bed and the overflow lip) for bub-
ble–particle aggregate. The longer the travel distance, the
higher the probability of the coarse bubble-particle aggre-
gates falling back and settling in the bottom of the bed,
especially at low water flow rates. However, it is important
to note that excessive water flow rates result in unselec-
tive elutriation of finer particles into the concentrate. In
contrast, an insufficient water flow rate will not allow the
fluidised bed to have sufficient porosity for particle-bubble
aggregates to travel through the bed.
50
60
70
80
90
100
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
Jg, cm/s
SWV 0.33 cm/s
SWV 0.66 cm/s
SWV 0.99 cm/s
Figure 7. Effect of air flow rate on the recovery of copper at varying fluidisation water flow rate
Cu
Recovery,
%
pronounced at higher air flow rates compared to lower air
flow rates.
Dankwah et al. (2022) observed that increasing the air
flow rate in a batch fluidised bed reduced the bed height.
They attributed this behaviour to segregation of the par-
ticles within the bed, with the coarser particles settling and
packing at the bottom. Consequently, they conclude that
the packed bed reduces the effective velocity of the rising
fluidisation water, decreasing the upward forces on the
bubble-particle aggregates, thereby reducing recovery. This
is another possible reason for the drop in recovery at high
air flow rates.
The phenomenon where recovery does not continu-
ally increase with increasing air rates has also been found
in conventional flotation. Previous work by Barbian et al.
(2006) and Hadler et al. (2010) investigated the effect of
air flow rate on flotation in conventional cells. They found
that there was an optimum air flow rate at which flotation
recovery increases towards a maximum, followed by a sub-
sequent decrease. They attributed this finding to the prop-
erties of the flotation froth, corresponding to an optimum
balance between froth stability and froth residence time.
However, this mechanism is not applicable to these
tests, as the small-scale fluidised bed device has no froth
layer. These results, therefore, show that the mechanism by
which high air flow rates poorly affect copper recovery is
related to changes in the pulp (free-settling zone /fluidised
bed zone) or detachment at the pulp air interface. Further
work is required to fully understand the competing mecha-
nisms that cause poor recovery at high air flow rates in flui-
dised bed flotation.
Effect of Water Rate on Copper Recovery
The results of the effect of water flow rate on copper recovery
when the air flow rate was varied are presented in Figure 8.
Unlike the air flow rate, water flow rate has a linear rela-
tionship with copper recovery. The same relationship was
observed by Demir et al. (2022) when they varied the water
flow rate in a pilot-scale HydroFloat ® work. Recovery was
lowest at the lowest air flow rate tested, ranging from 62%
to 72% when the water flow rate was varied from 0.33 cm/s
to 0.99 cm/s. Copper recovery was significantly higher
when the cell was operated at Jg of 0.1 cm/s (71% to 85%).
Above Jg of 0.1 cm/s, no further increase in recovery was
observed with increasing water flow rate. Increasing the
water flow rate increases the upward forces on the bubble-
particle aggregates, thereby promoting recovery. This was
observed at both low and high air flow rates.
Other researchers have reported bed expansion with
increasing water flow rate (Zanin et al., 2021, Dankwah
et al., 2022, Verster et al., 2023). Increasing the water flow
rate expands the fluidised bed, which increases the bed
level, thereby shortening the travel distance (the distance
between the top of the bed and the overflow lip) for bub-
ble–particle aggregate. The longer the travel distance, the
higher the probability of the coarse bubble-particle aggre-
gates falling back and settling in the bottom of the bed,
especially at low water flow rates. However, it is important
to note that excessive water flow rates result in unselec-
tive elutriation of finer particles into the concentrate. In
contrast, an insufficient water flow rate will not allow the
fluidised bed to have sufficient porosity for particle-bubble
aggregates to travel through the bed.
50
60
70
80
90
100
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
Jg, cm/s
SWV 0.33 cm/s
SWV 0.66 cm/s
SWV 0.99 cm/s
Figure 7. Effect of air flow rate on the recovery of copper at varying fluidisation water flow rate
Cu
Recovery,
%