100 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
with the various sub-processes required for successful flo-
tation. For a particle to be recovered by flotation, it must
first collide with bubbles in the pulp (Pcollision), it must
attach to the bubble during collision (Pattachment) and then
must successfully remain attached to the bubble as it moves
upward through the pulp and froth phases (1 – Pdetachment).
It is common to represent the probability of flotation as a
function of the probabilities of these various sub-processes
(Trahar and Warren, 1976) (Equation 1).
Pflotation =PcollisionPattachment (1 – Pdetachment) (1)
Conventional flotation is a size-sensitive process and opti-
mum results are obtained for intermediate sized particles
(10 to 100 micron). Figure 1 shows the recovery as a func-
tion of size measured in nine different copper concentrators
published by Batterham and Moodie, 2005. It shows the
typically observed shape of the relationship between size
and flotation recovery.
The shape of this relationship is a consequence of
hydrodynamic effects adversely affecting the mechanisms of
flotation for the fine and coarse particle sizes. Fine particles
have low momentum and exhibit poor bubble-particle col-
lision efficiencies. They tend to follow the fluid streamlines
around the bubbles, rather than to collide and attach to the
bubble surface. Recoveries drop in the coarser sizes because
the turbulence created in the conventional flotation tank to
keep particles in suspension imparts a force that results in
the detachment of particles from bubbles. Coarse particles
have greater momentum, so they are more susceptible to
the detachment mechanism.
Coarse particles also exhibit poorer recovery during flo-
tation because they are usually poorly liberated, with the
valuable mineral in composite with the gangue. Flotation
recovery is strongly correlated with the degree of libera-
tion (Fosu et al, 2015). Liberated particles exhibit higher
flotation recoveries because they have a greater probability
of attaching to a bubble during collision, and there is an
improvement in the stability of the particle bubble bond,
making it less susceptible to detachment forces.
The presence of poorly liberated particles in a flota-
tion feed also adversely affects flotation because it results in
poor selectivity. The valuable mineral cannot be recovered
without also recovering large quantities of gangue, reduc-
ing flotation grades. Flotation circuits are not just operated
to maximize recovery. They also must produce a concen-
trate with an acceptable flotation grade to be economically
treated in downstream metal production processes. Poor
flotation selectivity can inadvertently result in poor recov-
ery because the operators cannot pull all the floatable valu-
able minerals into the concentrate without going below the
concentrate grade target.
Figure 1. Overall plant recovery as a function of particle size in nine different copper
concentrators (after Batterham, and Moodie, 2005)
with the various sub-processes required for successful flo-
tation. For a particle to be recovered by flotation, it must
first collide with bubbles in the pulp (Pcollision), it must
attach to the bubble during collision (Pattachment) and then
must successfully remain attached to the bubble as it moves
upward through the pulp and froth phases (1 – Pdetachment).
It is common to represent the probability of flotation as a
function of the probabilities of these various sub-processes
(Trahar and Warren, 1976) (Equation 1).
Pflotation =PcollisionPattachment (1 – Pdetachment) (1)
Conventional flotation is a size-sensitive process and opti-
mum results are obtained for intermediate sized particles
(10 to 100 micron). Figure 1 shows the recovery as a func-
tion of size measured in nine different copper concentrators
published by Batterham and Moodie, 2005. It shows the
typically observed shape of the relationship between size
and flotation recovery.
The shape of this relationship is a consequence of
hydrodynamic effects adversely affecting the mechanisms of
flotation for the fine and coarse particle sizes. Fine particles
have low momentum and exhibit poor bubble-particle col-
lision efficiencies. They tend to follow the fluid streamlines
around the bubbles, rather than to collide and attach to the
bubble surface. Recoveries drop in the coarser sizes because
the turbulence created in the conventional flotation tank to
keep particles in suspension imparts a force that results in
the detachment of particles from bubbles. Coarse particles
have greater momentum, so they are more susceptible to
the detachment mechanism.
Coarse particles also exhibit poorer recovery during flo-
tation because they are usually poorly liberated, with the
valuable mineral in composite with the gangue. Flotation
recovery is strongly correlated with the degree of libera-
tion (Fosu et al, 2015). Liberated particles exhibit higher
flotation recoveries because they have a greater probability
of attaching to a bubble during collision, and there is an
improvement in the stability of the particle bubble bond,
making it less susceptible to detachment forces.
The presence of poorly liberated particles in a flota-
tion feed also adversely affects flotation because it results in
poor selectivity. The valuable mineral cannot be recovered
without also recovering large quantities of gangue, reduc-
ing flotation grades. Flotation circuits are not just operated
to maximize recovery. They also must produce a concen-
trate with an acceptable flotation grade to be economically
treated in downstream metal production processes. Poor
flotation selectivity can inadvertently result in poor recov-
ery because the operators cannot pull all the floatable valu-
able minerals into the concentrate without going below the
concentrate grade target.
Figure 1. Overall plant recovery as a function of particle size in nine different copper
concentrators (after Batterham, and Moodie, 2005)