XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2871
al., 1986). The froth layers in conventional flotation also
limits the maximum wash water flow that can be applied
due to the requirement of maintaining a froth stability (Tan
et al., 2020). By eliminating the froth layer in the RFC, the
gaps between the bubbles expand, and a better downward
drainage of entrained liquid and solid could be expected.
Eliminating the froth layer also allows the RFC to apply a
much higher downward wash water flow, which promotes
the displacement of liquid that contains entrained particles
to further reduce gangue entrainment (Chen et al., 2022).
The concept of eliminating the froth layer in the RFC’s
reverse fluidized bed by adding more downward wash water
in reducing gangue entrainment in coal flotation has been
studied previously. Dickinson and Galvin (2014) found
that by fluidizing the froth layer in the reverse fluidized
bed into bubbly flow, silica entrainment recovery can be
reduced from the maximum of 10% down to around 4%.
Cole et al. (2020) found that in coal flotation the product
ash could be reduced from 18% to around 7% by increas-
ing the wash water flux from 0.2 to 2.1 cm/s. The increased
wash water flux further fluidizes the froth layer and creates
a stronger downward bias flow that displaces and dilutes
the liquid containing unattached particles.
Compared to coal, minerals usually have a different
physical property. Taking chalcopyrite as an example, it has
a much higher particle density than coal (Castellon et al.,
2022). Hence, for the same particle size, chalcopyrite par-
ticle- bubble aggregates will have a higher relative density
than coal particle- bubble aggregates, leading to a lower
rising velocity and higher gas hold up in flotation pulp
as identified by Yan et al. (2021) and Yianatos and Levy
(1989). Since the uprising gas and its interaction with the
counter wash water influence the entrainment in the RFC’s
fluidized bed, it is expected that particle density will play a
significant role in entrainment in the RFC.
Therefore, the objective of this study was to investi-
gate the change in gangue entrainment in the RFC when
the light coal particles were replaced with heavy chalco-
pyrite particles. Chalcopyrite and coal flotation tests were
conducted first under the operating conditions optimized
for coal flotation to determine quartz entrainment. Then
the operating conditions were changed to reduce quartz
entrainment in chalcopyrite flotation. To understand the
effect of particle density on quartz entrainment in the
RFC, Computational Fluid Dynamic (CFD) modelling
was performed to simulate the gas-liquid interaction and
explain its role in gangue reduction. The findings from this
study will recommend the optimal conditions to minimize
gangue entrainment in base metal sulfide mineral flotation
in the RFC.
METHODOLOGY
Materials
A chalcopyrite sample sourced from GeoDiscoveries was
used in this study. Based on X-ray Fluorescence (XRF) and
Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
analysis, the purity of the chalcopyrite sample is above
95%. A quartz powder sample with 99.7% SiO2 was used
as the gangue mineral. 80% of the quartz powder is below
75 μm and 47% is below 30 μm. Sodium ethyl xanthate
(SEX) and 2-Octanol were used as collector and frother,
respectively, in flotation tests.
RFC Flotation
Continuous flotation tests were performed with a 15 L lab-
scale RFC with a dimension of 103 cm × 9.8 cm × 8.5 cm
for the vertical section. The inclined section has a height
of 72 cm and an inclined angle of 70°. The gap between
the inclined plates is 18 mm. The layout of the RFC set-
up is shown in Figure 2. For a continuous RFC test, the
feed was prepared and conditioned in a mixing tank first.
250 g/t SEX was added and conditioned for 10 min, fol-
lowed by the addition of 20 ppm 2-Octanol with 10 min
of conditioning. Then, the feed was pumped into the RFC
through the downcomer. Compressed air was fed into the
downcomer to mix with the feed slurry. Wash water was
Figure 1. Schematic diagram for Reflux Flotation Cell
(adapted from (Chen et al., 2022 Jiang et al., 2019))
al., 1986). The froth layers in conventional flotation also
limits the maximum wash water flow that can be applied
due to the requirement of maintaining a froth stability (Tan
et al., 2020). By eliminating the froth layer in the RFC, the
gaps between the bubbles expand, and a better downward
drainage of entrained liquid and solid could be expected.
Eliminating the froth layer also allows the RFC to apply a
much higher downward wash water flow, which promotes
the displacement of liquid that contains entrained particles
to further reduce gangue entrainment (Chen et al., 2022).
The concept of eliminating the froth layer in the RFC’s
reverse fluidized bed by adding more downward wash water
in reducing gangue entrainment in coal flotation has been
studied previously. Dickinson and Galvin (2014) found
that by fluidizing the froth layer in the reverse fluidized
bed into bubbly flow, silica entrainment recovery can be
reduced from the maximum of 10% down to around 4%.
Cole et al. (2020) found that in coal flotation the product
ash could be reduced from 18% to around 7% by increas-
ing the wash water flux from 0.2 to 2.1 cm/s. The increased
wash water flux further fluidizes the froth layer and creates
a stronger downward bias flow that displaces and dilutes
the liquid containing unattached particles.
Compared to coal, minerals usually have a different
physical property. Taking chalcopyrite as an example, it has
a much higher particle density than coal (Castellon et al.,
2022). Hence, for the same particle size, chalcopyrite par-
ticle- bubble aggregates will have a higher relative density
than coal particle- bubble aggregates, leading to a lower
rising velocity and higher gas hold up in flotation pulp
as identified by Yan et al. (2021) and Yianatos and Levy
(1989). Since the uprising gas and its interaction with the
counter wash water influence the entrainment in the RFC’s
fluidized bed, it is expected that particle density will play a
significant role in entrainment in the RFC.
Therefore, the objective of this study was to investi-
gate the change in gangue entrainment in the RFC when
the light coal particles were replaced with heavy chalco-
pyrite particles. Chalcopyrite and coal flotation tests were
conducted first under the operating conditions optimized
for coal flotation to determine quartz entrainment. Then
the operating conditions were changed to reduce quartz
entrainment in chalcopyrite flotation. To understand the
effect of particle density on quartz entrainment in the
RFC, Computational Fluid Dynamic (CFD) modelling
was performed to simulate the gas-liquid interaction and
explain its role in gangue reduction. The findings from this
study will recommend the optimal conditions to minimize
gangue entrainment in base metal sulfide mineral flotation
in the RFC.
METHODOLOGY
Materials
A chalcopyrite sample sourced from GeoDiscoveries was
used in this study. Based on X-ray Fluorescence (XRF) and
Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
analysis, the purity of the chalcopyrite sample is above
95%. A quartz powder sample with 99.7% SiO2 was used
as the gangue mineral. 80% of the quartz powder is below
75 μm and 47% is below 30 μm. Sodium ethyl xanthate
(SEX) and 2-Octanol were used as collector and frother,
respectively, in flotation tests.
RFC Flotation
Continuous flotation tests were performed with a 15 L lab-
scale RFC with a dimension of 103 cm × 9.8 cm × 8.5 cm
for the vertical section. The inclined section has a height
of 72 cm and an inclined angle of 70°. The gap between
the inclined plates is 18 mm. The layout of the RFC set-
up is shown in Figure 2. For a continuous RFC test, the
feed was prepared and conditioned in a mixing tank first.
250 g/t SEX was added and conditioned for 10 min, fol-
lowed by the addition of 20 ppm 2-Octanol with 10 min
of conditioning. Then, the feed was pumped into the RFC
through the downcomer. Compressed air was fed into the
downcomer to mix with the feed slurry. Wash water was
Figure 1. Schematic diagram for Reflux Flotation Cell
(adapted from (Chen et al., 2022 Jiang et al., 2019))