2286 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
whether a particular type of mineral should be treated as
a main product, as a by-product or as an impurity, thus
determining the quantity of mineral to be sent to the treat-
ment plant. Of the three factors, the economic context is
the most important. Indeed, 75% of extraction projects
have been prematurely abandoned, often due to the col-
lapse of raw material prices, leaving part of those resources
unextracted (Laurence, D. 2011). Not to mention that, for
decades now, ores have been exhibiting lower grades and
finer texture and finer liberation sizes (Calvo et al., 2016),
along with a diversification of the gangue minerals. Since
the common concentration methods are losing their effi-
ciency due to the decreasing particle size (Wills and Finch,
2016), using effective separation techniques such as froth
flotation (Farrokhpay et al. 2020) becomes more and more
important. Of note, it has been demonstrated that flotation
constitutes the most effective and economical method to
reduce the environmental impacts caused by the presence
of heavy metals (Jing et al. 2023).
On the Limitations in Assessing Efficiency in Flotation
Flotation aims at the selective separation of valuable miner-
als from gangue minerals and takes place in an aqueous pulp
that consists of solid (mineral particles), liquid (water), and
gaseous (air). As depicted in Figure 1, the separation pro-
cess in the flotation tank is mainly four-fold and involves:
(1) a collision between the hydrophobic solid particles and
the air bubbles (2) the solid particle attaches to the air bub-
ble following the rupture of the intervening liquid film (3)
as a result of the solid–liquid–gas interface, a stable bubble-
aggregate is generated (4) eventually, this aggregate rises
and generates the froth phase, from where it is collected
(Karimi et al. 2014). Obtaining a stable system allows
recovery of the predominantly hydrophobic particles over-
flowing the cell and the hydrophilic particles underflowing
the cell. A particle must in fact go through stages of colli-
sion and attachment with an air bubble, then the stability
of the aggregate formed by the decoration of the interface
of the bubble by the hydrophobic particles must resist the
hydrodynamic forces of detachment, such as turbulence,
rupture, separation, shearing, involved in the flotation cell
(Tran et al. 2010). In the recovery of mineral particles in
flotation, it was determined that for a value greater than
a certain contact angle called the critical angle, a particle
will be more likely to be carried away by a bubble of air
towards the concentrate of the cell (Chipfunhu et al. 2011).
This parameter is a surface property which is directly linked
to the hydrophobic nature of a solid surface. Of note, the
experimental evaluation of this parameter is complex and
affected by measurement uncertainties. In some cases, con-
tact angle measurement by the sessile drop method is used
(Erbil 2014). However, this methodology is difficult to use
for industrial ores which are characterized by heterogeneity
dealing with their mineralogy as well as by surface defects.
Such surface modifications raise a problem, since the high
sensitivity of the method means that the slightest change
on the surface of a particle can cause great variability in the
results (Erbil 2014). A single contact angle measurement
cannot therefore be considered representative of a de facto
heterogeneous sample, since the apparent value of the mea-
sured angle is an overall average that can vary depending
on the exposed surfaces (Feng and Nguyen 2017). Finally,
although it is possible to obtain the different contact angle
values which constitute the contact angle hysteresis, the
Figure 1. Pictorial representation of the separation principle in flotation process (Lainé 2023)
whether a particular type of mineral should be treated as
a main product, as a by-product or as an impurity, thus
determining the quantity of mineral to be sent to the treat-
ment plant. Of the three factors, the economic context is
the most important. Indeed, 75% of extraction projects
have been prematurely abandoned, often due to the col-
lapse of raw material prices, leaving part of those resources
unextracted (Laurence, D. 2011). Not to mention that, for
decades now, ores have been exhibiting lower grades and
finer texture and finer liberation sizes (Calvo et al., 2016),
along with a diversification of the gangue minerals. Since
the common concentration methods are losing their effi-
ciency due to the decreasing particle size (Wills and Finch,
2016), using effective separation techniques such as froth
flotation (Farrokhpay et al. 2020) becomes more and more
important. Of note, it has been demonstrated that flotation
constitutes the most effective and economical method to
reduce the environmental impacts caused by the presence
of heavy metals (Jing et al. 2023).
On the Limitations in Assessing Efficiency in Flotation
Flotation aims at the selective separation of valuable miner-
als from gangue minerals and takes place in an aqueous pulp
that consists of solid (mineral particles), liquid (water), and
gaseous (air). As depicted in Figure 1, the separation pro-
cess in the flotation tank is mainly four-fold and involves:
(1) a collision between the hydrophobic solid particles and
the air bubbles (2) the solid particle attaches to the air bub-
ble following the rupture of the intervening liquid film (3)
as a result of the solid–liquid–gas interface, a stable bubble-
aggregate is generated (4) eventually, this aggregate rises
and generates the froth phase, from where it is collected
(Karimi et al. 2014). Obtaining a stable system allows
recovery of the predominantly hydrophobic particles over-
flowing the cell and the hydrophilic particles underflowing
the cell. A particle must in fact go through stages of colli-
sion and attachment with an air bubble, then the stability
of the aggregate formed by the decoration of the interface
of the bubble by the hydrophobic particles must resist the
hydrodynamic forces of detachment, such as turbulence,
rupture, separation, shearing, involved in the flotation cell
(Tran et al. 2010). In the recovery of mineral particles in
flotation, it was determined that for a value greater than
a certain contact angle called the critical angle, a particle
will be more likely to be carried away by a bubble of air
towards the concentrate of the cell (Chipfunhu et al. 2011).
This parameter is a surface property which is directly linked
to the hydrophobic nature of a solid surface. Of note, the
experimental evaluation of this parameter is complex and
affected by measurement uncertainties. In some cases, con-
tact angle measurement by the sessile drop method is used
(Erbil 2014). However, this methodology is difficult to use
for industrial ores which are characterized by heterogeneity
dealing with their mineralogy as well as by surface defects.
Such surface modifications raise a problem, since the high
sensitivity of the method means that the slightest change
on the surface of a particle can cause great variability in the
results (Erbil 2014). A single contact angle measurement
cannot therefore be considered representative of a de facto
heterogeneous sample, since the apparent value of the mea-
sured angle is an overall average that can vary depending
on the exposed surfaces (Feng and Nguyen 2017). Finally,
although it is possible to obtain the different contact angle
values which constitute the contact angle hysteresis, the
Figure 1. Pictorial representation of the separation principle in flotation process (Lainé 2023)