2860 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Coarse Particle Flotation
The leading technology of coarse particle beneficiation is
fluidised bed flotation. Fluidised bed flotation enables early
waste rejection, increases throughput to the plant, and
decreases the energy demand of the comminution processes.
One of the most successful examples of this technology is
Eriez’s HydroFloat ®, patented only at the beginning of this
century (Fosu, Awatey, Skinner et al., 2015 Kohmuench,
Mankosa, Thanasekaran et al., 2018 Zanin, Chan, &
Skinner, 2021).
The HydroFloat ® combines principles of flotation
and gravity separation, achieving outcomes that would be
impossible with either one of these methods used on their
own. In fluidised bed flotation, particles are suspended
within a low-shear fluidised bed environment. Air bubbles
are introduced to the cell and pass through the fluidised
bed, where bubble-particle aggregates are formed. Bubble-
particle aggregates have lower apparent density than the
particles alone, allowing them to be carried upwards by
the fluidisation water current, where they are discharged
to a product launder (Kohmuench, Luttrell, &Mankosa,
2001). The quiescent hydrodynamic environment of the
HydroFloat ® significantly reduces the probability of par-
ticle/bubble detachment, substantially increasing the recov-
ery of coarse particles with low levels of liberation (Awatey,
Thanasekaran, Kohmuench et al., 2013).
Role of Bubble Size in Flotation
Air bubbles are the primary particle transportation medium
in the flotation process. Therefore, their properties directly
influence the process performance. Bubble size in any flota-
tion cell is a function of two processes and their interaction:
the mechanism for bubble generation and the degree of
bubble coalescence (Nesset, Hernandez-Aguilar, Acuna et
al., 2006). Bubble coalescence is a phenomenon where two
or more gas bubbles in a liquid medium come into con-
tact and merge to create one large bubble (Chanson, 1996).
Similarly to the formation of particle-bubble aggregates,
coalescence involves several sub-processes. They include
bubble collision, drainage of the liquid film between these
bubbles, and later film rupture, forming a single larger bub-
ble (Liao &Dirk, 2010).
Like flotation, coalescence is a probability-based pro-
cess—not all bubble collisions result in bubble coales-
cence. Therefore, the concept of a “coalescence rate” was
introduced. It is determined by collision frequency and
coalescence efficiency (Liao &Dirk, 2010). The collision
frequency depends on the number of bubbles, bubble size
distributions, the flow structure, and whether the flow is
laminar or turbulent. In other words, collision frequency is
primarily a hydrodynamic parameter (Boshenyatov, 2012).
On the other hand, coalescence efficiency is a function
of all collisions between bubbles that result in a coales-
cence event (Boshenyatov, 2012) and is, therefore, strongly
related to the properties of the liquid film surrounding the
bubbles. Coalescence efficiency is consequently considered
to be strongly dependent on solution chemistry.
Influence of Frothers on Bubble Size
Frothers are used to prevent coalescence, control bubble
size, and provide higher froth stability in mineral flotation
(Finch, Nesset, &Acuña, 2008). In conventional flotation,
the smallest possible bubble size is desirable, resulting in the
largest available bubble surface area for flotation, a concept
known as bubble surface area flux (Sb) (Yoon &Luttrell,
1989 Gorain, Franzidis, &Manlapig, 1997). High Sb
maximises the efficiency of particle transport out of the flo-
tation cell, resulting in higher recoveries (Reis, Reis Filho,
Demuner et al., 2019).
Frother molecules function by adsorbing onto the sur-
faces of air bubbles, reducing their surface tension (Gupta
&Yan, 2006). This makes the bubble surface more elastic
and less susceptible to rupture. The rupture of two adjoin-
ing liquid films leads to a coalescence event between two
bubbles.
Frothers are commonly classified as alcohols and polyg-
lycols (Zhang, 2016). The difference in the molecular struc-
ture of different frother reagents leads to a difference in their
surface activity (i.e., their ability to affect the properties of
the gas/liquid interface). Alcohol-type frothers generally
have a weaker ability to decrease surface tension. However,
their frothing properties increase with increasing hydrocar-
bon chain length, where the maximum number of carbon
atoms varies between six and ten (Klimpel &Isherwood,
1991). This occurs because larger frother molecules retain
more water around the bubbles, making the adjoining films
harder to rupture. Methyl isobutyl carbinol (MIBC) is this
group’s most commonly used frother (Harris &Jia, 2000
Zhang, 2016)
The ability of frother molecules to affect the properties
of the gas/liquid interface is strongly dependent on their
concentration in solution. This led to the introduction of
the concept of critical coalescence concentration (CCC)
(Cho &Laskowski, 2002). This concept describes the
minimum frother concentration needed to prevent bubble
coalescence. It has been shown that frother molecular prop-
erties influence CCC, whereas lower CCC values character-
ise stronger frothers.
Coarse Particle Flotation
The leading technology of coarse particle beneficiation is
fluidised bed flotation. Fluidised bed flotation enables early
waste rejection, increases throughput to the plant, and
decreases the energy demand of the comminution processes.
One of the most successful examples of this technology is
Eriez’s HydroFloat ®, patented only at the beginning of this
century (Fosu, Awatey, Skinner et al., 2015 Kohmuench,
Mankosa, Thanasekaran et al., 2018 Zanin, Chan, &
Skinner, 2021).
The HydroFloat ® combines principles of flotation
and gravity separation, achieving outcomes that would be
impossible with either one of these methods used on their
own. In fluidised bed flotation, particles are suspended
within a low-shear fluidised bed environment. Air bubbles
are introduced to the cell and pass through the fluidised
bed, where bubble-particle aggregates are formed. Bubble-
particle aggregates have lower apparent density than the
particles alone, allowing them to be carried upwards by
the fluidisation water current, where they are discharged
to a product launder (Kohmuench, Luttrell, &Mankosa,
2001). The quiescent hydrodynamic environment of the
HydroFloat ® significantly reduces the probability of par-
ticle/bubble detachment, substantially increasing the recov-
ery of coarse particles with low levels of liberation (Awatey,
Thanasekaran, Kohmuench et al., 2013).
Role of Bubble Size in Flotation
Air bubbles are the primary particle transportation medium
in the flotation process. Therefore, their properties directly
influence the process performance. Bubble size in any flota-
tion cell is a function of two processes and their interaction:
the mechanism for bubble generation and the degree of
bubble coalescence (Nesset, Hernandez-Aguilar, Acuna et
al., 2006). Bubble coalescence is a phenomenon where two
or more gas bubbles in a liquid medium come into con-
tact and merge to create one large bubble (Chanson, 1996).
Similarly to the formation of particle-bubble aggregates,
coalescence involves several sub-processes. They include
bubble collision, drainage of the liquid film between these
bubbles, and later film rupture, forming a single larger bub-
ble (Liao &Dirk, 2010).
Like flotation, coalescence is a probability-based pro-
cess—not all bubble collisions result in bubble coales-
cence. Therefore, the concept of a “coalescence rate” was
introduced. It is determined by collision frequency and
coalescence efficiency (Liao &Dirk, 2010). The collision
frequency depends on the number of bubbles, bubble size
distributions, the flow structure, and whether the flow is
laminar or turbulent. In other words, collision frequency is
primarily a hydrodynamic parameter (Boshenyatov, 2012).
On the other hand, coalescence efficiency is a function
of all collisions between bubbles that result in a coales-
cence event (Boshenyatov, 2012) and is, therefore, strongly
related to the properties of the liquid film surrounding the
bubbles. Coalescence efficiency is consequently considered
to be strongly dependent on solution chemistry.
Influence of Frothers on Bubble Size
Frothers are used to prevent coalescence, control bubble
size, and provide higher froth stability in mineral flotation
(Finch, Nesset, &Acuña, 2008). In conventional flotation,
the smallest possible bubble size is desirable, resulting in the
largest available bubble surface area for flotation, a concept
known as bubble surface area flux (Sb) (Yoon &Luttrell,
1989 Gorain, Franzidis, &Manlapig, 1997). High Sb
maximises the efficiency of particle transport out of the flo-
tation cell, resulting in higher recoveries (Reis, Reis Filho,
Demuner et al., 2019).
Frother molecules function by adsorbing onto the sur-
faces of air bubbles, reducing their surface tension (Gupta
&Yan, 2006). This makes the bubble surface more elastic
and less susceptible to rupture. The rupture of two adjoin-
ing liquid films leads to a coalescence event between two
bubbles.
Frothers are commonly classified as alcohols and polyg-
lycols (Zhang, 2016). The difference in the molecular struc-
ture of different frother reagents leads to a difference in their
surface activity (i.e., their ability to affect the properties of
the gas/liquid interface). Alcohol-type frothers generally
have a weaker ability to decrease surface tension. However,
their frothing properties increase with increasing hydrocar-
bon chain length, where the maximum number of carbon
atoms varies between six and ten (Klimpel &Isherwood,
1991). This occurs because larger frother molecules retain
more water around the bubbles, making the adjoining films
harder to rupture. Methyl isobutyl carbinol (MIBC) is this
group’s most commonly used frother (Harris &Jia, 2000
Zhang, 2016)
The ability of frother molecules to affect the properties
of the gas/liquid interface is strongly dependent on their
concentration in solution. This led to the introduction of
the concept of critical coalescence concentration (CCC)
(Cho &Laskowski, 2002). This concept describes the
minimum frother concentration needed to prevent bubble
coalescence. It has been shown that frother molecular prop-
erties influence CCC, whereas lower CCC values character-
ise stronger frothers.