XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2841
(Brito-Parada &Cilliers, 2012 Neethling et al., 2000). To
prevent these wall flows from easily reporting to the con-
centrate, a funnel design has been selected as a promising
retrofit design modification. Funnels consist of a conical-
shaped physical barrier inserted near the pulp-froth inter-
face to redirect the water flows away from the walls of the
tank, modifying the hydrodynamics of the interface and
froth. In this work, two variations of a funnel design con-
cept have been assessed using laboratory experiments and
computational fluid dynamics simulations.
Experimental work was carried out to understand the
impact of the different funnel designs on key flotation vari-
ables. Two sets of flotation experiments were used, the first
using a simplified single-species three-phase system, and
the second using a synthetic two-species ore. Changes in
froth stability were assessed by measuring air recovery, while
metallurgical impacts were studied in terms of changes in
concentrate grade and recovery, particle size distribution
and entrainment. Simulations were performed using the
in-house Smooth Particle Hydrodynamics (SPH) code pre-
sented in Neethling &Barker (2016) to predict the effects
of these retrofit design modifications on the fluid dynamics
of the system.
MATERIALS AND METHODS
Bench-Scale Flotation Tank
All the experiments were performed using the 4-litre con-
tinuously overflowing bench-scale flotation cell described
in Mesa et al. (2021), as shown in Figure 1. Air was injected
into an air reservoir under the flotation cell, which diffused
the air into the cell through a frit with a mesh hole size of
20 µm for the dispersion of small bubbles in the cell. The
overflowing concentrate was collected in the launder and
fed back into the tank in a closed circuit. This continuous
operation ensured that a steady state could be attained.
The tank was fitted with instrumentation includ-
ing a power transducer to control the impeller speed and
a manometer with an analogue flowmeter to control the
airflow rate. An optical level sensor (OLS) was installed to
measure froth height and a digital camera was fitted to mea-
sure the overflowing froth velocity. The 3D-printed rotor-
stator system described in Mesa et al. (2021) was used as
shown in Figure 2.
Funnels as Retrofit Design Modifications
Two different funnels were designed and 3D printed (see
Figure 3). The effect of these designs on froth stability and
metallurgical performance was assessed experimentally and
compared to the base case without a funnel, while their
effect on flotation fluid dynamics was assessed using CFD
simulations.
All the funnels consisted of a truncated conic barrier,
with an angle of 30°, and an inner hole of 60 mm diameter,
which allows the impeller shaft to be positioned, and the
froth to be formed. Funnel 1 has an external diameter of
160 mm, leaving 10 mm of clearance from the tank’s wall
to enable particle drop down from the froth. Funnel 2, on
the other hand, has an external diameter almost identical to
the tank, leaving no space for particle flow near the walls,
but it has a series of holes with a honey-comb mesh pattern
for particle motion, as those studied by Brito-Parada et al.,
2017, Mackay, 2019 and Cole et al., 2023.
Figure 1. Bench scale flotation cell schematic (left) and an annotated photograph specifying the
concentrate recirculation for continuous operation (right)
(Brito-Parada &Cilliers, 2012 Neethling et al., 2000). To
prevent these wall flows from easily reporting to the con-
centrate, a funnel design has been selected as a promising
retrofit design modification. Funnels consist of a conical-
shaped physical barrier inserted near the pulp-froth inter-
face to redirect the water flows away from the walls of the
tank, modifying the hydrodynamics of the interface and
froth. In this work, two variations of a funnel design con-
cept have been assessed using laboratory experiments and
computational fluid dynamics simulations.
Experimental work was carried out to understand the
impact of the different funnel designs on key flotation vari-
ables. Two sets of flotation experiments were used, the first
using a simplified single-species three-phase system, and
the second using a synthetic two-species ore. Changes in
froth stability were assessed by measuring air recovery, while
metallurgical impacts were studied in terms of changes in
concentrate grade and recovery, particle size distribution
and entrainment. Simulations were performed using the
in-house Smooth Particle Hydrodynamics (SPH) code pre-
sented in Neethling &Barker (2016) to predict the effects
of these retrofit design modifications on the fluid dynamics
of the system.
MATERIALS AND METHODS
Bench-Scale Flotation Tank
All the experiments were performed using the 4-litre con-
tinuously overflowing bench-scale flotation cell described
in Mesa et al. (2021), as shown in Figure 1. Air was injected
into an air reservoir under the flotation cell, which diffused
the air into the cell through a frit with a mesh hole size of
20 µm for the dispersion of small bubbles in the cell. The
overflowing concentrate was collected in the launder and
fed back into the tank in a closed circuit. This continuous
operation ensured that a steady state could be attained.
The tank was fitted with instrumentation includ-
ing a power transducer to control the impeller speed and
a manometer with an analogue flowmeter to control the
airflow rate. An optical level sensor (OLS) was installed to
measure froth height and a digital camera was fitted to mea-
sure the overflowing froth velocity. The 3D-printed rotor-
stator system described in Mesa et al. (2021) was used as
shown in Figure 2.
Funnels as Retrofit Design Modifications
Two different funnels were designed and 3D printed (see
Figure 3). The effect of these designs on froth stability and
metallurgical performance was assessed experimentally and
compared to the base case without a funnel, while their
effect on flotation fluid dynamics was assessed using CFD
simulations.
All the funnels consisted of a truncated conic barrier,
with an angle of 30°, and an inner hole of 60 mm diameter,
which allows the impeller shaft to be positioned, and the
froth to be formed. Funnel 1 has an external diameter of
160 mm, leaving 10 mm of clearance from the tank’s wall
to enable particle drop down from the froth. Funnel 2, on
the other hand, has an external diameter almost identical to
the tank, leaving no space for particle flow near the walls,
but it has a series of holes with a honey-comb mesh pattern
for particle motion, as those studied by Brito-Parada et al.,
2017, Mackay, 2019 and Cole et al., 2023.
Figure 1. Bench scale flotation cell schematic (left) and an annotated photograph specifying the
concentrate recirculation for continuous operation (right)