XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2431
where the collection zone is an independent unit in which
the particles and bubbles are contacted under a high energy
dissipation condition, before passing to the bubble disen-
gagement and separation zone. In addition, the comparison
with a self-aerated mechanical cell shows the time the pulp
spends in the surroundings of the impeller, assuming a con-
trol volume of five times the impeller volume.
SIMILITUDES BETWEEN THE
EFFECTIVE COLLECTION ZONES IN
CONVENTIONAL AND INTENSIFIED
FLOTATION CELLS
In conventional mechanical cells, the bubbles generation
occurs near the impeller discharge, where the tangential
velocities of the rotor are around 5–7 m/s, and the super-
ficial gas velocities are significantly higher, relative to the
rotor discharge cross-section. In a typical laboratory flota-
tion cell, e.g., LA-500 Agitair, the tangential velocities are
around 4–6 m/s at 900–1300 rpm. This means the condi-
tions for gas dispersion, bubbles formation, and bubble-
particle collision near the rotor are in the same range of
industrial operations, with similar bubble sizes. In an indus-
trial flotation cell of 130 m3, the bubbles residence time in
the pulp zone was around 42 s (Yianatos et al., 2010b),
which means it can reach more than 70 s in larger size cells.
However, in the laboratory cell, the bubbles residence time
is much smaller, around 2 seconds in the pulp zone, with
periodical froth removal.
For example, the superficial gas rate in the downcomer
of a Jameson cell can be around 10–12 cm/s with a high gas
holdup (30–50%) due to co-current flowrate of pulp and
air entrained downwards. In mechanical cells, these vari-
ables vary in a lower range (e.g., superficial gas rate, JG=
1–2 cm/s, and gas holdup in the pulp zone, εG=5–10%,
relative to the cross-sectional area of the cell. However, in
mechanical forced air and self-aerated cells assuming an
effective collection zone exists, mainly near the impeller
discharge area, where the bubble generation occurs and the
bubble swarm moves out from that region, the local condi-
tions become more closer to that observed in pneumatic
cells, with JG=5–10 cm/s and εG around 30%. Figure 2
illustrates an estimation of these conditions.
Effect of Mineral Feed Characteristics
The feed mineralogical characteristics affect the flotation
performance at same particle size distribution and feed
grades. Complex minerals association and altered gangue
minerals will strongly affect the overall flotation perfor-
mance. On the contrary, good minerals reach excellent
performance in terms of recovery and selectivity. A good
example was the conventional column flotation perfor-
mance at Minera Los Pelambres (Yianatos and Henríquez,
2007b), where a single cleaner circuit for columns with
a scavenger in mechanical cells reaches recoveries near
98–99%, with both copper and molybdenite recoveries in
flotation columns around 80%. On the other hand, single
cleaner stages with columns operating at normal cleaning
recoveries around 60–70%, with significant upgrade from
6–10% copper in feed to around 30–32% copper in con-
centrate has been reported from Salvador (Bergh et al.,
1999) and Andina (Cortes and Yianatos, 1995 Yianatos
et al., 1999), with column mean residence times around
10–12 min. At present, however, feed mineralogical charac-
teristics have changed which poses new challenges and the
opportunity for new technologies.
Here, it is relevant to notices that in all these examples
of cleaning stages the minerals are regrind at P80 around 45
microns and columns have not an intensive energy dissipa-
tion zone as the one provided by an impeller in mechanical
cells. This means that a smoother environment, in terms of
energy dissipation, is also favourable for collecting fine size
liberated particles and medium size liberated or less liber-
ated particles. These results justify the role of the quite zone
below the pulp-froth in mechanical cells, that allows for
collection and recollection of the lower floatability minerals
(coarser and/or low liberated) which are circulating or drop
back from the froth zone. As well, the quite zone favours
the presence of a distinctive pulp/froth interface and the
fine particles entrainment.
Table 1. Estimation of effective collection time in intensified flotation cells
Cell Scale
Type of
Contactor
Gas Holdup
in Contactor, %
%of Cell Volume
in Contactor
Contactor Residence
Time, s
Jameson Industrial downcomer 30–50 15–16 12–13
SFR Industrial PCU 35* 19–22 17–20
RFC Pilot downcomer 30–50 2–3 0.5–2.2
Mechanical self-aerated Industrial impeller 13* 3† 11
*Estimated
† Estimated as 5 times the volume of impeller
where the collection zone is an independent unit in which
the particles and bubbles are contacted under a high energy
dissipation condition, before passing to the bubble disen-
gagement and separation zone. In addition, the comparison
with a self-aerated mechanical cell shows the time the pulp
spends in the surroundings of the impeller, assuming a con-
trol volume of five times the impeller volume.
SIMILITUDES BETWEEN THE
EFFECTIVE COLLECTION ZONES IN
CONVENTIONAL AND INTENSIFIED
FLOTATION CELLS
In conventional mechanical cells, the bubbles generation
occurs near the impeller discharge, where the tangential
velocities of the rotor are around 5–7 m/s, and the super-
ficial gas velocities are significantly higher, relative to the
rotor discharge cross-section. In a typical laboratory flota-
tion cell, e.g., LA-500 Agitair, the tangential velocities are
around 4–6 m/s at 900–1300 rpm. This means the condi-
tions for gas dispersion, bubbles formation, and bubble-
particle collision near the rotor are in the same range of
industrial operations, with similar bubble sizes. In an indus-
trial flotation cell of 130 m3, the bubbles residence time in
the pulp zone was around 42 s (Yianatos et al., 2010b),
which means it can reach more than 70 s in larger size cells.
However, in the laboratory cell, the bubbles residence time
is much smaller, around 2 seconds in the pulp zone, with
periodical froth removal.
For example, the superficial gas rate in the downcomer
of a Jameson cell can be around 10–12 cm/s with a high gas
holdup (30–50%) due to co-current flowrate of pulp and
air entrained downwards. In mechanical cells, these vari-
ables vary in a lower range (e.g., superficial gas rate, JG=
1–2 cm/s, and gas holdup in the pulp zone, εG=5–10%,
relative to the cross-sectional area of the cell. However, in
mechanical forced air and self-aerated cells assuming an
effective collection zone exists, mainly near the impeller
discharge area, where the bubble generation occurs and the
bubble swarm moves out from that region, the local condi-
tions become more closer to that observed in pneumatic
cells, with JG=5–10 cm/s and εG around 30%. Figure 2
illustrates an estimation of these conditions.
Effect of Mineral Feed Characteristics
The feed mineralogical characteristics affect the flotation
performance at same particle size distribution and feed
grades. Complex minerals association and altered gangue
minerals will strongly affect the overall flotation perfor-
mance. On the contrary, good minerals reach excellent
performance in terms of recovery and selectivity. A good
example was the conventional column flotation perfor-
mance at Minera Los Pelambres (Yianatos and Henríquez,
2007b), where a single cleaner circuit for columns with
a scavenger in mechanical cells reaches recoveries near
98–99%, with both copper and molybdenite recoveries in
flotation columns around 80%. On the other hand, single
cleaner stages with columns operating at normal cleaning
recoveries around 60–70%, with significant upgrade from
6–10% copper in feed to around 30–32% copper in con-
centrate has been reported from Salvador (Bergh et al.,
1999) and Andina (Cortes and Yianatos, 1995 Yianatos
et al., 1999), with column mean residence times around
10–12 min. At present, however, feed mineralogical charac-
teristics have changed which poses new challenges and the
opportunity for new technologies.
Here, it is relevant to notices that in all these examples
of cleaning stages the minerals are regrind at P80 around 45
microns and columns have not an intensive energy dissipa-
tion zone as the one provided by an impeller in mechanical
cells. This means that a smoother environment, in terms of
energy dissipation, is also favourable for collecting fine size
liberated particles and medium size liberated or less liber-
ated particles. These results justify the role of the quite zone
below the pulp-froth in mechanical cells, that allows for
collection and recollection of the lower floatability minerals
(coarser and/or low liberated) which are circulating or drop
back from the froth zone. As well, the quite zone favours
the presence of a distinctive pulp/froth interface and the
fine particles entrainment.
Table 1. Estimation of effective collection time in intensified flotation cells
Cell Scale
Type of
Contactor
Gas Holdup
in Contactor, %
%of Cell Volume
in Contactor
Contactor Residence
Time, s
Jameson Industrial downcomer 30–50 15–16 12–13
SFR Industrial PCU 35* 19–22 17–20
RFC Pilot downcomer 30–50 2–3 0.5–2.2
Mechanical self-aerated Industrial impeller 13* 3† 11
*Estimated
† Estimated as 5 times the volume of impeller