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The Impact of Funnels as Pulp-Froth Interface Retrofit Design
Modifications on Froth Flotation
Diego Mesa, Stephen J. Neethling, Pablo R. Brito-Parada
Department of Earth Science and Engineering, Imperial College London
ABSTRACT: Retrofit design modifications offer great potential to improve the performance of existing flotation
cells at low capital costs. Common retrofits include novel rotor-stator systems to improve pulp hydrodynamics,
and launders/crowders to enhance froth transport. However, retrofit designs for the pulp-froth interface remain
largely understudied. We introduce a funnel design retrofitted near the pulp-froth interface that is shown to
enhance froth stability and reduce entrainment. Experimental results are complemented with Smooth Particle
Hydrodynamics simulations to understand the effect of the funnels on the fluid dynamics within the flotation
cell, which highlights their role in redirecting fast ascending flows near the walls.
INTRODUCTION
A general problem in froth flotation is the entrainment
of gangue, as it results in a reduction of the concentrate’s
grade. Entrainment occurs when particles are mechanically
reported to the concentrate through non-selective pro-
cesses, i.e., regardless of their hydrophobicity. Examples of
entrainment mechanisms include particles being carried by
ascending water flows, particles entrapped between clusters
of other hydrophobic particles, and particles pushed into
the froth by fast ascending bubble swarms (Cilek, 2009
Konopacka &Drzymala, 2010 Neethling &Cilliers,
2009 Trahar, 1981 Wills &Finch, 2016). Trahar (1981)
proposed that there is a linear relationship between water
recovery and gangue recovery. Although more recent pub-
lications have shown non-linear relationships at low water
recoveries (Zheng et al., 2006), it remains clear that there
is a strong proportionality between these two variables.
Moreover, there is a strong effect of particle size on the
magnitude of that proportionality. Most experimental and
theoretical work has shown that fine particles are more
prone to be entrained (Neethling &Cilliers, 2009 Trahar,
1981 Zheng et al., 2006), due to their low probability of
bubble-particle collision and low inertia, implying that fine
particles tend to follow water streamlines, avoiding bubbles
and being carried to the froth and overflowing regardless of
their hydrophobicity.
Many alternatives have been studied to decrease
entrainment, either by reducing water recovery, pseudo-
increasing particle size, or both. Examples include the use
of different frothers that exhibit different water-carrying
capacities (Kracht et al., 2016 Moyo et al., 2007), the
use of selective depressants and flocculants to increase the
apparent particle size of the fine gangue particles (Gong et
al., 2010), and the variation of operating conditions, such
as decreasing air flowrate and increasing froth depth, in
order to have a drier froth.
In this work, the use of retrofit design modifications
purposely built to decrease entrainment by reducing water
recovery has been studied. Previous work using computa-
tional fluid dynamics (CFD) simulations has shown the
presence of fast ascending water flows near the walls of the
tank that can result in non-selective overflow of particles
The Impact of Funnels as Pulp-Froth Interface Retrofit Design
Modifications on Froth Flotation
Diego Mesa, Stephen J. Neethling, Pablo R. Brito-Parada
Department of Earth Science and Engineering, Imperial College London
ABSTRACT: Retrofit design modifications offer great potential to improve the performance of existing flotation
cells at low capital costs. Common retrofits include novel rotor-stator systems to improve pulp hydrodynamics,
and launders/crowders to enhance froth transport. However, retrofit designs for the pulp-froth interface remain
largely understudied. We introduce a funnel design retrofitted near the pulp-froth interface that is shown to
enhance froth stability and reduce entrainment. Experimental results are complemented with Smooth Particle
Hydrodynamics simulations to understand the effect of the funnels on the fluid dynamics within the flotation
cell, which highlights their role in redirecting fast ascending flows near the walls.
INTRODUCTION
A general problem in froth flotation is the entrainment
of gangue, as it results in a reduction of the concentrate’s
grade. Entrainment occurs when particles are mechanically
reported to the concentrate through non-selective pro-
cesses, i.e., regardless of their hydrophobicity. Examples of
entrainment mechanisms include particles being carried by
ascending water flows, particles entrapped between clusters
of other hydrophobic particles, and particles pushed into
the froth by fast ascending bubble swarms (Cilek, 2009
Konopacka &Drzymala, 2010 Neethling &Cilliers,
2009 Trahar, 1981 Wills &Finch, 2016). Trahar (1981)
proposed that there is a linear relationship between water
recovery and gangue recovery. Although more recent pub-
lications have shown non-linear relationships at low water
recoveries (Zheng et al., 2006), it remains clear that there
is a strong proportionality between these two variables.
Moreover, there is a strong effect of particle size on the
magnitude of that proportionality. Most experimental and
theoretical work has shown that fine particles are more
prone to be entrained (Neethling &Cilliers, 2009 Trahar,
1981 Zheng et al., 2006), due to their low probability of
bubble-particle collision and low inertia, implying that fine
particles tend to follow water streamlines, avoiding bubbles
and being carried to the froth and overflowing regardless of
their hydrophobicity.
Many alternatives have been studied to decrease
entrainment, either by reducing water recovery, pseudo-
increasing particle size, or both. Examples include the use
of different frothers that exhibit different water-carrying
capacities (Kracht et al., 2016 Moyo et al., 2007), the
use of selective depressants and flocculants to increase the
apparent particle size of the fine gangue particles (Gong et
al., 2010), and the variation of operating conditions, such
as decreasing air flowrate and increasing froth depth, in
order to have a drier froth.
In this work, the use of retrofit design modifications
purposely built to decrease entrainment by reducing water
recovery has been studied. Previous work using computa-
tional fluid dynamics (CFD) simulations has shown the
presence of fast ascending water flows near the walls of the
tank that can result in non-selective overflow of particles