2948 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Increased Sb indicates more bubble surface area, which will
increase increased kinetics in the cell. In this case the Sb is
a characterization of the aerator or cell, and if two cells are
operated in parallel on the same ore, the cell with higher Sb
will have the higher recovery.
PARTICLE SIZE EFFECTS
The significance of the mineral particle size in the flotation
process was recognized stage (Gaudin et al. 1942, Morris
1952, and Spedden and Hannan, 1948). For conventional
flotation circuits, typical feed size is less than 150 μm
(Jameson, 2010b). This size range provides the highest
recovery in conventional flotation circuits, for most of the
base metal sulfide minerals, as shown in Figures 3 and 4.
When the feed size increases to above 150 μm or drops
below 20 μm, a significant decrease in flotation recovery
occurs (Kohmuench et al. 2018 Lynch et al. 1981 Rahman
et al. 2014).
While the scales in Figures 3 and 4 are different—one
linear and one logarithmic—all of the data is in microns so
the figures can be interpreted consistently. Both figures are
shown to illustrate that in some 40 years, the performance
of flotation machines has changed very little.
In flotation, the recovery of particles requires the colli-
sion of particles with air bubbles, the attachment of hydro-
phobic particles to air bubbles, and the non-attachment or
detachment of hydrophobic particles. Because of the high
turbulence and inertia generated in conventional flotation
cells, coarse particles are more likely to detach from air
bubbles, which leads to a reduction in recovery. Theoretical
analysis of the upper limit of coarse particle flotation sug-
gests that a quiescent flow field is necessary to prevent the
particles from becoming detached from the bubbles. A bed
of fluidized air provides a suitable environment for particle-
bubble contact.
Coarse particles attach to the bubbles rising through
the bed and are lifted into the froth layer that is main-
tained on top of the cell. Effective use of fluidized bed
technology provides major advantages beyond the ability
to recover coarse particles currently lost in existing opera-
tions. Liberation of the values is the key limitation. Also,
a fluidized bed flotation cell can accept a feed with much
higher percent solids, leading to significant reductions in
water requirements.
Ultrafine particles are influenced more by viscous drag
than inertia, and tend to follow the fluid streamlines in flo-
tation. This results in a lower number of collisions between
ultrafine particles and air bubbles, resulting in a low flo-
tation recovery. A higher-energy flow regime will result in
the attachment of more fine particles. However, as noted
above, if that energy is too high, coarse particles are more
likely to detach. Ideally, the flow regime in a cell should be
managed to optimize overall grade and recovery. Of course,
this is not always possible.
FROTH MANAGEMENT
The froth phase plays an important role in flotation pro-
cessing by preventing the short circuiting of pulp to the
concentrate. It also contributes to increasing the concen-
trate grade by gravity drainage of entrained particles, back
into the pulp. The mean residence times of solids, liquid,
and gas in the froth are the key parameters effecting its per-
formance. The respective mean residence times depend on
the froth depth, gas flowrate, gas hold-up, and flow regime.
These in turn depend on froth stability and froth mobility.
Figure 3. Recovery vs. particle diameter (from data presented
by Lynch et al. 1981)
Figure 4. Recovery vs. particle diameter (Vollner et al., 2019)
Increased Sb indicates more bubble surface area, which will
increase increased kinetics in the cell. In this case the Sb is
a characterization of the aerator or cell, and if two cells are
operated in parallel on the same ore, the cell with higher Sb
will have the higher recovery.
PARTICLE SIZE EFFECTS
The significance of the mineral particle size in the flotation
process was recognized stage (Gaudin et al. 1942, Morris
1952, and Spedden and Hannan, 1948). For conventional
flotation circuits, typical feed size is less than 150 μm
(Jameson, 2010b). This size range provides the highest
recovery in conventional flotation circuits, for most of the
base metal sulfide minerals, as shown in Figures 3 and 4.
When the feed size increases to above 150 μm or drops
below 20 μm, a significant decrease in flotation recovery
occurs (Kohmuench et al. 2018 Lynch et al. 1981 Rahman
et al. 2014).
While the scales in Figures 3 and 4 are different—one
linear and one logarithmic—all of the data is in microns so
the figures can be interpreted consistently. Both figures are
shown to illustrate that in some 40 years, the performance
of flotation machines has changed very little.
In flotation, the recovery of particles requires the colli-
sion of particles with air bubbles, the attachment of hydro-
phobic particles to air bubbles, and the non-attachment or
detachment of hydrophobic particles. Because of the high
turbulence and inertia generated in conventional flotation
cells, coarse particles are more likely to detach from air
bubbles, which leads to a reduction in recovery. Theoretical
analysis of the upper limit of coarse particle flotation sug-
gests that a quiescent flow field is necessary to prevent the
particles from becoming detached from the bubbles. A bed
of fluidized air provides a suitable environment for particle-
bubble contact.
Coarse particles attach to the bubbles rising through
the bed and are lifted into the froth layer that is main-
tained on top of the cell. Effective use of fluidized bed
technology provides major advantages beyond the ability
to recover coarse particles currently lost in existing opera-
tions. Liberation of the values is the key limitation. Also,
a fluidized bed flotation cell can accept a feed with much
higher percent solids, leading to significant reductions in
water requirements.
Ultrafine particles are influenced more by viscous drag
than inertia, and tend to follow the fluid streamlines in flo-
tation. This results in a lower number of collisions between
ultrafine particles and air bubbles, resulting in a low flo-
tation recovery. A higher-energy flow regime will result in
the attachment of more fine particles. However, as noted
above, if that energy is too high, coarse particles are more
likely to detach. Ideally, the flow regime in a cell should be
managed to optimize overall grade and recovery. Of course,
this is not always possible.
FROTH MANAGEMENT
The froth phase plays an important role in flotation pro-
cessing by preventing the short circuiting of pulp to the
concentrate. It also contributes to increasing the concen-
trate grade by gravity drainage of entrained particles, back
into the pulp. The mean residence times of solids, liquid,
and gas in the froth are the key parameters effecting its per-
formance. The respective mean residence times depend on
the froth depth, gas flowrate, gas hold-up, and flow regime.
These in turn depend on froth stability and froth mobility.
Figure 3. Recovery vs. particle diameter (from data presented
by Lynch et al. 1981)
Figure 4. Recovery vs. particle diameter (Vollner et al., 2019)