2170 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
EXPERIMENTAL METHODS
Immersion Calorimetry
Samples were dried at 40°C and 150 mbar in a vacuum oven
until repeated weighing showed no change in sample mass.
This was usually achieved in about 4 days. Approximately
1 g of precisely weighed dry sample was transferred to a
silica ampoule and loaded into the reaction vessel, which
was filled with 100 mL of the solution of choice – usu-
ally water or hexanol. The entire device was then loaded
into the TA Instruments TAM III microcalorimeter SolCal
channel. Once thermal equilibrium was reached at 25°C,
the ampoule was broken to allow the dry powder to come
into contact with the liquid and the resulting increase
or decrease in temperature was measured over time. The
area under the heat change peak was integrated using TA
Instruments software to give the change in energy in joules,
which was then normalised by dividing by the mass or sur-
face area of the mineral. The system was calibrated using
an internal electronic calibration, as well as a KCl standard
technique as described in Wadso &Goldberg, 2001. In
addition, blank measurements were performed by measur-
ing the temperature change when an empty ampoule was
broken. The experimental method is explained in detail in
Magudu (2024) and Taguta el al (2018).
Isothermal Titration Calorimetry
Mineral slurry samples of known mass and surface area,
or PtCl42– samples of known concentration, were loaded
into the titration ampoule, sealed and placed into the TA
Instruments TAM III calorimeter titration channel and
allowed to reach thermal equilibrium at 25°C. Collector of
known concentration was loaded into the titration syringe
and known volumes were titrated at pre-determined time
intervals. The area under the resultant heat flow peaks
was integrated by the TA Instruments software. Likewise,
the software fitted a ligand binding model to the data to
determine the thermodynamic parameters discussed in
the results section. Calibrations were performed using an
internal electronic calibration as well as a standardized reac-
tion described by Wadso and Goldberg (2001). Full experi-
mental details can be found in McFadzean and O’Connor
(2014).
RESULTS
Isothermal Titration Calorimetry
Previous work published by the authors using isothermal
titration calorimetry (ITC) has focussed largely on the
interaction between pure minerals and flotation collectors
in an effort to, firstly, understand the interfacial interactions
occurring and, secondly, to relate these findings to flotation
performance (McFadzean et al., 2023 McFadzean et al.,
2022 Taguta et al., 2018 Taguta et al., 2017 McFadzean
et al., 2015 McFadzean and O’Connor, 2014). ITC has
been found to be a very useful technique for the former
objective, but not as suitable in terms of predicting flota-
tion performance. As is well known, a collector must first
interact with the mineral surface via adsorption in order for
flotation to occur, but this interaction is not sufficient to
ensure that flotation will occur or to predict which collector
will be better than another in promoting flotation. It was
shown by Taguta et al. (2017) that there was no consistent
correlation between the heat of adsorption and the flota-
tion response. In certain cases, notwithstanding large heats
of interaction being measured, these were accompanied by
relatively poor flotation recoveries. However, this may be
partly due to the difficulty of controlling the pH within the
microcalorimetry ampoule which is a drawback of the tech-
nique. This has been subsequently addressed by performing
scaled up experiments external to the calorimeter prior to
conducting the ITC experiments, to determine the amount
of acid or base required to adjust pH to the desired value.
One of the main applications for ITC for the purposes
of this paper is to test the interaction of novel reagents
with the mineral surface prior to, or in addition to, flota-
tion experiments. An ongoing challenge for novel reagent
design is how to achieve high throughput testing without
the need for time-consuming and costly experiments that
use large quantities of ore. An obvious first step is the use
of computational modelling and many of the studies by the
authors and colleagues have been reported (McFadzean et
al., 2023 McFadzean et al., 2022 Zhang et al., 2019).
However, there is sometimes another step required prior
to flotation experiments, particularly when the mineral of
interest is very scarce and costly as is the case with platinum
group minerals, for example. In this case it was found to be
of interest to study the interactions of dissolved metal salts
with collectors. This also avoids the complexities resulting
from variable mineral surface oxidation, impurities, min-
eral dissolution, variation of the system pH and other chal-
lenges when using pure minerals. Such an approach can be
considered reasonable since as is well known that all miner-
als undergo dissolution and that the dissolved species may
be present in the Stern layer which is first encountered by
the collector. Reactions with metal salts were first carried
out in a mineral processing context by Mellgren (1966)
who found that the heat of reaction of xanthate with oxi-
dised galena was the same as that occurring with the corre-
sponding lead salt. Robledo-Cabrera et al. (2015) also used
lead nitrate in reactions with xanthates of increasing carbon
EXPERIMENTAL METHODS
Immersion Calorimetry
Samples were dried at 40°C and 150 mbar in a vacuum oven
until repeated weighing showed no change in sample mass.
This was usually achieved in about 4 days. Approximately
1 g of precisely weighed dry sample was transferred to a
silica ampoule and loaded into the reaction vessel, which
was filled with 100 mL of the solution of choice – usu-
ally water or hexanol. The entire device was then loaded
into the TA Instruments TAM III microcalorimeter SolCal
channel. Once thermal equilibrium was reached at 25°C,
the ampoule was broken to allow the dry powder to come
into contact with the liquid and the resulting increase
or decrease in temperature was measured over time. The
area under the heat change peak was integrated using TA
Instruments software to give the change in energy in joules,
which was then normalised by dividing by the mass or sur-
face area of the mineral. The system was calibrated using
an internal electronic calibration, as well as a KCl standard
technique as described in Wadso &Goldberg, 2001. In
addition, blank measurements were performed by measur-
ing the temperature change when an empty ampoule was
broken. The experimental method is explained in detail in
Magudu (2024) and Taguta el al (2018).
Isothermal Titration Calorimetry
Mineral slurry samples of known mass and surface area,
or PtCl42– samples of known concentration, were loaded
into the titration ampoule, sealed and placed into the TA
Instruments TAM III calorimeter titration channel and
allowed to reach thermal equilibrium at 25°C. Collector of
known concentration was loaded into the titration syringe
and known volumes were titrated at pre-determined time
intervals. The area under the resultant heat flow peaks
was integrated by the TA Instruments software. Likewise,
the software fitted a ligand binding model to the data to
determine the thermodynamic parameters discussed in
the results section. Calibrations were performed using an
internal electronic calibration as well as a standardized reac-
tion described by Wadso and Goldberg (2001). Full experi-
mental details can be found in McFadzean and O’Connor
(2014).
RESULTS
Isothermal Titration Calorimetry
Previous work published by the authors using isothermal
titration calorimetry (ITC) has focussed largely on the
interaction between pure minerals and flotation collectors
in an effort to, firstly, understand the interfacial interactions
occurring and, secondly, to relate these findings to flotation
performance (McFadzean et al., 2023 McFadzean et al.,
2022 Taguta et al., 2018 Taguta et al., 2017 McFadzean
et al., 2015 McFadzean and O’Connor, 2014). ITC has
been found to be a very useful technique for the former
objective, but not as suitable in terms of predicting flota-
tion performance. As is well known, a collector must first
interact with the mineral surface via adsorption in order for
flotation to occur, but this interaction is not sufficient to
ensure that flotation will occur or to predict which collector
will be better than another in promoting flotation. It was
shown by Taguta et al. (2017) that there was no consistent
correlation between the heat of adsorption and the flota-
tion response. In certain cases, notwithstanding large heats
of interaction being measured, these were accompanied by
relatively poor flotation recoveries. However, this may be
partly due to the difficulty of controlling the pH within the
microcalorimetry ampoule which is a drawback of the tech-
nique. This has been subsequently addressed by performing
scaled up experiments external to the calorimeter prior to
conducting the ITC experiments, to determine the amount
of acid or base required to adjust pH to the desired value.
One of the main applications for ITC for the purposes
of this paper is to test the interaction of novel reagents
with the mineral surface prior to, or in addition to, flota-
tion experiments. An ongoing challenge for novel reagent
design is how to achieve high throughput testing without
the need for time-consuming and costly experiments that
use large quantities of ore. An obvious first step is the use
of computational modelling and many of the studies by the
authors and colleagues have been reported (McFadzean et
al., 2023 McFadzean et al., 2022 Zhang et al., 2019).
However, there is sometimes another step required prior
to flotation experiments, particularly when the mineral of
interest is very scarce and costly as is the case with platinum
group minerals, for example. In this case it was found to be
of interest to study the interactions of dissolved metal salts
with collectors. This also avoids the complexities resulting
from variable mineral surface oxidation, impurities, min-
eral dissolution, variation of the system pH and other chal-
lenges when using pure minerals. Such an approach can be
considered reasonable since as is well known that all miner-
als undergo dissolution and that the dissolved species may
be present in the Stern layer which is first encountered by
the collector. Reactions with metal salts were first carried
out in a mineral processing context by Mellgren (1966)
who found that the heat of reaction of xanthate with oxi-
dised galena was the same as that occurring with the corre-
sponding lead salt. Robledo-Cabrera et al. (2015) also used
lead nitrate in reactions with xanthates of increasing carbon