2486 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Experimental Methods
Isothermal Titration Calorimetry and Microflotation
Isothermal titration calorimetry tests were carried out to
measure the adsorption enthalpies at 25°C using the TAM
III isothermal titration microcalorimeter. This technique
measures the heat consumed or released during a reaction
of the minerals with a given ligand. The synthetic sperrylite
sample of mass 0.2 ± 0.0005 g was weighed into an ampoule
and 0.7 ml of distilled water was added into each ampoule
and sonicated for 3 minutes to disperse the slurry. It was
not possible to control and adjust the pH of the slurry after
loading the ampoules into the titration channel, hence all
the tests were carried out at the natural pH of the slurry,
which was around 7. The ampoules were loaded into the
calorimeter and the titration syringe was loaded with the
collector solution. Time was given for the machine to sta-
bilise and full calibration of the machine against a known
power input was carried out before each run. The machine
was then programmed to run and to add 2 µL of the collec-
tor every hour once the selected conditions were met. The
2 µL collector solution was precalculated based on the BET
results of the –38 µm sperrylite sample to cover approxi-
mately 0.25 pseudo-monolayers of the mineral surface. Ten
titrations that amounted to 2.5 pseudo-monolayers collec-
tor coverage were carried out for each run.
The area under the peaks that result from the mineral-
collector interactions was integrated to obtain the specific
enthalpies of adsorption per injection. Heats of dilution
per injection of a collector were also carried out for each
collector and subtracted from the mineral-collector heats
of adsorption. In this study, data from four titrations that
amount to 1 pseudo-monolayer collector coverage heats of
adsorption were calculated and reported. This methodology
was developed in order to mimic as closely as possible the
computational modelling conditions. Further details of the
microcalorimetry technique can be found from McFadzean
et al. (2014).
The 2,6-dithio-4-butylamino-1,3,5-triazine (DTBAT)
collector was synthesised in BGRIMM Technology Group
lab as described by Mkhonto et al. (2023). The normal
butyl xanthate (NBX) and normal butyl dithiocarbamate
(NBDTC) collectors were purchased commerciallys as a
pure powder. PtAs2 mineral was synthesised by the method
of Shackleton et al. (2007). Microflotation experiments on
sperrylite were carried out as shown on the flow chart in
Figure 1. The interaction of the hydroxide ions was taken
into account when processing the calorimetry data and was
a reference value which was subtracted from the collector-
mineral interaction value. A 40 mL plexiglass cell on the
XFG5-35 flotation machine for the microflotation tests of
sperrylite mineral was used, with agitation speed which was
set at 1752 r·min–1. The flotation was conducted and lasted
for 4 min and then the concentrates and tailings were col-
lected under acidic (pH =4) and alkaline (pH =9) with
dilute HCl and NaOH solutions, respectively. The methyl
isobutyl carbinol (MIBC) frother dosage was 20 mg·L–1.
The collector dosage was varied to determine the effect
on mineral recovery as the dosage is increased, which was
maintained at 100% monolayer coverage. The synthetic
plant water (2SPW) was used for the flotation tests, which
was recommended to mimic the industrial application. The
mineral recovery was measured by ratio of the concentrates
to the feed minerals according to equation 4 (Mkhonto et
al., 2021).
Recoveries %h Mass of mineral in feed
Mass of mineral in concentrate 100% #=^
RESULTS AND DISCUSSION
Bulk and Surface Models
The study adopted the bulk model of sperrylite (PtAs2)
with space group symmetry of Pa-3 (#205) and platarsite
(PtAsS) which possesses a P213 (#198) space group and
the structures contained 12 atoms as shown in Figure 2a
and 2c, respectively. The PtAs2 and PtAsS models possesses
rock-salt type structure with Pt4+ cations at the face-centred
of the cubic cell and As22– and S22– dimers centred about
the anion positions (Cabri, Laflamme and Stewart, 1977).
The relaxed calculated structural lattice parameter for sper-
rylite and platarsite were a =5.989 Å and a =5.954 Å with
the experimental value of 5.968 Å (Szymański, 1979) for
PtAs2 and 5.790 Å (Cabri, Laflamme and Stewart, 1977)
for PtAsS structure. It was found that the computational
calculated lattice parameters were slightly larger but in
agreement with experimental data.
Figure 1. Flow chart for microflotation experiments
Experimental Methods
Isothermal Titration Calorimetry and Microflotation
Isothermal titration calorimetry tests were carried out to
measure the adsorption enthalpies at 25°C using the TAM
III isothermal titration microcalorimeter. This technique
measures the heat consumed or released during a reaction
of the minerals with a given ligand. The synthetic sperrylite
sample of mass 0.2 ± 0.0005 g was weighed into an ampoule
and 0.7 ml of distilled water was added into each ampoule
and sonicated for 3 minutes to disperse the slurry. It was
not possible to control and adjust the pH of the slurry after
loading the ampoules into the titration channel, hence all
the tests were carried out at the natural pH of the slurry,
which was around 7. The ampoules were loaded into the
calorimeter and the titration syringe was loaded with the
collector solution. Time was given for the machine to sta-
bilise and full calibration of the machine against a known
power input was carried out before each run. The machine
was then programmed to run and to add 2 µL of the collec-
tor every hour once the selected conditions were met. The
2 µL collector solution was precalculated based on the BET
results of the –38 µm sperrylite sample to cover approxi-
mately 0.25 pseudo-monolayers of the mineral surface. Ten
titrations that amounted to 2.5 pseudo-monolayers collec-
tor coverage were carried out for each run.
The area under the peaks that result from the mineral-
collector interactions was integrated to obtain the specific
enthalpies of adsorption per injection. Heats of dilution
per injection of a collector were also carried out for each
collector and subtracted from the mineral-collector heats
of adsorption. In this study, data from four titrations that
amount to 1 pseudo-monolayer collector coverage heats of
adsorption were calculated and reported. This methodology
was developed in order to mimic as closely as possible the
computational modelling conditions. Further details of the
microcalorimetry technique can be found from McFadzean
et al. (2014).
The 2,6-dithio-4-butylamino-1,3,5-triazine (DTBAT)
collector was synthesised in BGRIMM Technology Group
lab as described by Mkhonto et al. (2023). The normal
butyl xanthate (NBX) and normal butyl dithiocarbamate
(NBDTC) collectors were purchased commerciallys as a
pure powder. PtAs2 mineral was synthesised by the method
of Shackleton et al. (2007). Microflotation experiments on
sperrylite were carried out as shown on the flow chart in
Figure 1. The interaction of the hydroxide ions was taken
into account when processing the calorimetry data and was
a reference value which was subtracted from the collector-
mineral interaction value. A 40 mL plexiglass cell on the
XFG5-35 flotation machine for the microflotation tests of
sperrylite mineral was used, with agitation speed which was
set at 1752 r·min–1. The flotation was conducted and lasted
for 4 min and then the concentrates and tailings were col-
lected under acidic (pH =4) and alkaline (pH =9) with
dilute HCl and NaOH solutions, respectively. The methyl
isobutyl carbinol (MIBC) frother dosage was 20 mg·L–1.
The collector dosage was varied to determine the effect
on mineral recovery as the dosage is increased, which was
maintained at 100% monolayer coverage. The synthetic
plant water (2SPW) was used for the flotation tests, which
was recommended to mimic the industrial application. The
mineral recovery was measured by ratio of the concentrates
to the feed minerals according to equation 4 (Mkhonto et
al., 2021).
Recoveries %h Mass of mineral in feed
Mass of mineral in concentrate 100% #=^
RESULTS AND DISCUSSION
Bulk and Surface Models
The study adopted the bulk model of sperrylite (PtAs2)
with space group symmetry of Pa-3 (#205) and platarsite
(PtAsS) which possesses a P213 (#198) space group and
the structures contained 12 atoms as shown in Figure 2a
and 2c, respectively. The PtAs2 and PtAsS models possesses
rock-salt type structure with Pt4+ cations at the face-centred
of the cubic cell and As22– and S22– dimers centred about
the anion positions (Cabri, Laflamme and Stewart, 1977).
The relaxed calculated structural lattice parameter for sper-
rylite and platarsite were a =5.989 Å and a =5.954 Å with
the experimental value of 5.968 Å (Szymański, 1979) for
PtAs2 and 5.790 Å (Cabri, Laflamme and Stewart, 1977)
for PtAsS structure. It was found that the computational
calculated lattice parameters were slightly larger but in
agreement with experimental data.
Figure 1. Flow chart for microflotation experiments