XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2405
Sessile Water Drop Contact Angle Measurements
Flat, polished substrates were prepared from hand-picked
specimens of chalcocite and pyrite. In addition, plates of
high purity (99%) Cu, Au, and Ag were used. All sub-
strates were polished with a slurry of 0.5 µm Al2O3 and
rinsed with MilliQ water prior to measurements.
Contact angle (CA) measurements were conducted
using a modified Ramé-Hart contact angle goniometer. 5
µL sessile droplets of MilliQ water were deposited at vari-
ous locations across the surface of each substrate. CA distri-
butions were generated by measuring a total of 120 contact
angles with and without conditioning (for 1 min) in 5 ×
10–5 M solution of BCBDTC.
Cyclic Voltammetry
Working electrodes of Cu, chalcocite, pyrite, Au, and Ag
encased in epoxy were used. Voltammograms were gener-
ated in borate-buffer (pH – 9.2) solution and at 5 × 10–5 M
BCBDTC concentration. Several voltammograms were
also generated at 5 × 10–5 M concentration of sodium di-
isobutyl dithiophosphinate (DIBDTPI) for comparison.
DIBDTPI is a well-known and widely used sulfide collec-
tor (Tercero et al., 2019) with a similar affinity for soft acids
like BCBDTC, but distinctly different in terms of its struc-
ture and specific interactions with minerals.
A conventional three-electrode circuit consisting of the
working electrode, an Ag/AgCl reference electrode, and a
platinum mesh counter electrode was used. Prior to all mea-
surements, the working electrode was polished with Al2O3
slurry and rinsed with nanopure water. Voltammograms
were generated at a 30 mV/s scan rate. The electrode poten-
tial was controlled using a Metrohm Autolab PGSTAT
128N Potentiostat.
Time-of-Flight Secondary Ion Mass Spectroscopy
High purity (99%) plates of Au, Ag, and Au-Ag (50:50
ratio) were also used. The plates were polished with Al2O3
slurry and rinsed prior to conditioning in 5 × 10–4 M solu-
tion of BCBDTC for 15 minutes. The plates were then
rinsed by brief immersion in nanopure water to remove
residual ligand solution before drying.
SIMS spectra were generated with a PHI nanoTOF
Mass Spectrometer using a 30 kV liquid metal ion gun
(LMIG) with Bi emitter and dual beam charge neutraliza-
tion. All materials were mounted on double-sided tape.
Ore Flotation
Laboratory batch flotation tests were conducted using
a variety of ore systems. The same commercial sample of
BCBDTC was used. Specific experimental conditions
were chosen with respect to each ore system and are only
described when necessary. The systems of study were: a) a
porphyry Cu ore containing chalcopyrite, secondary Cu
sulfides, and pyrite, b) an Au ore containing pyrite and free
Au species, c) a Pb-Zn-Ag ore containing galena, sphaler-
ite, pyrite, and free Ag species, d) a tailing from the same
Pb-Zn-Ag operation, and e) a PGM ore containing chalco-
pyrite, pentlandite, pyrrhotite, and PGMs.
RESULTS AND DISCUSSION
Sessile Water Drop Contact Angle Measurements
The CA distributions for chalcocite and pyrite are shown
in Figure 4. It is apparent that the adsorption of BCBDTC
on either chalcocite or pyrite shifts the distribution to a
higher CA range. In the case of chalcocite, the untreated
substrate exhibits a much wider distribution which dem-
onstrates significant surface heterogeneity. The distribution
becomes much narrower upon adsorption of BCBDTC,
demonstrating its ability to effectively hydrophobize such
heterogeneous surfaces. The adsorption of BCBDTC
onto chalcocite supports the concept that its soft S donor
interacts with Cu1+, a soft acid. On the other hand, it is
unusual that for pyrite (even at a low concentration), the
surface acquires a hydrophobic character. This behavior of
BCBDTC contrasts with its thionocarbamate and thiourea
analogues, which are both very selective against iron sul-
fides. However, it should be noted that a borderline acid
like Fe2+ can behave like a soft acid in the presence of soft S
donors. It is also important to recognize that pyrite is never
the only sulfide mineral present in many ores this implies
competitive adsorption of BCBDTC between pyrite and
other chalcophile mineral species. Thus, the observed
hydrophobicity that BCBDTC confers to pyrite in these
measurements does not necessarily translate to its behavior
in real ore systems.
CA distributions for pure Cu, Au and Ag are shown in
Figure 5. Au and Ag demonstrate a stronger degree of natu-
ral hydrophobicity (~50–60°) compared to the other sub-
strates, though this is simply a manifestation of not being
fully hydrated. It is important to recognize that in aquatic
ore pulps, floatability of the value species is hindered due
to hydration. Despite this, shifts of the distribution to a
higher range after conditioning with BCBDTC are still
apparent. The shifts are notably stronger in the following
order: Cu Ag Au while reasons for this are not yet fully
known, it indicates differences in packing of BCBDTC
between the three.
While the cases above demonstrate the adsorption
of BCBDTC and its conferred hydrophobicity onto the
selected substrates, it must be noted that CA measurements
Sessile Water Drop Contact Angle Measurements
Flat, polished substrates were prepared from hand-picked
specimens of chalcocite and pyrite. In addition, plates of
high purity (99%) Cu, Au, and Ag were used. All sub-
strates were polished with a slurry of 0.5 µm Al2O3 and
rinsed with MilliQ water prior to measurements.
Contact angle (CA) measurements were conducted
using a modified Ramé-Hart contact angle goniometer. 5
µL sessile droplets of MilliQ water were deposited at vari-
ous locations across the surface of each substrate. CA distri-
butions were generated by measuring a total of 120 contact
angles with and without conditioning (for 1 min) in 5 ×
10–5 M solution of BCBDTC.
Cyclic Voltammetry
Working electrodes of Cu, chalcocite, pyrite, Au, and Ag
encased in epoxy were used. Voltammograms were gener-
ated in borate-buffer (pH – 9.2) solution and at 5 × 10–5 M
BCBDTC concentration. Several voltammograms were
also generated at 5 × 10–5 M concentration of sodium di-
isobutyl dithiophosphinate (DIBDTPI) for comparison.
DIBDTPI is a well-known and widely used sulfide collec-
tor (Tercero et al., 2019) with a similar affinity for soft acids
like BCBDTC, but distinctly different in terms of its struc-
ture and specific interactions with minerals.
A conventional three-electrode circuit consisting of the
working electrode, an Ag/AgCl reference electrode, and a
platinum mesh counter electrode was used. Prior to all mea-
surements, the working electrode was polished with Al2O3
slurry and rinsed with nanopure water. Voltammograms
were generated at a 30 mV/s scan rate. The electrode poten-
tial was controlled using a Metrohm Autolab PGSTAT
128N Potentiostat.
Time-of-Flight Secondary Ion Mass Spectroscopy
High purity (99%) plates of Au, Ag, and Au-Ag (50:50
ratio) were also used. The plates were polished with Al2O3
slurry and rinsed prior to conditioning in 5 × 10–4 M solu-
tion of BCBDTC for 15 minutes. The plates were then
rinsed by brief immersion in nanopure water to remove
residual ligand solution before drying.
SIMS spectra were generated with a PHI nanoTOF
Mass Spectrometer using a 30 kV liquid metal ion gun
(LMIG) with Bi emitter and dual beam charge neutraliza-
tion. All materials were mounted on double-sided tape.
Ore Flotation
Laboratory batch flotation tests were conducted using
a variety of ore systems. The same commercial sample of
BCBDTC was used. Specific experimental conditions
were chosen with respect to each ore system and are only
described when necessary. The systems of study were: a) a
porphyry Cu ore containing chalcopyrite, secondary Cu
sulfides, and pyrite, b) an Au ore containing pyrite and free
Au species, c) a Pb-Zn-Ag ore containing galena, sphaler-
ite, pyrite, and free Ag species, d) a tailing from the same
Pb-Zn-Ag operation, and e) a PGM ore containing chalco-
pyrite, pentlandite, pyrrhotite, and PGMs.
RESULTS AND DISCUSSION
Sessile Water Drop Contact Angle Measurements
The CA distributions for chalcocite and pyrite are shown
in Figure 4. It is apparent that the adsorption of BCBDTC
on either chalcocite or pyrite shifts the distribution to a
higher CA range. In the case of chalcocite, the untreated
substrate exhibits a much wider distribution which dem-
onstrates significant surface heterogeneity. The distribution
becomes much narrower upon adsorption of BCBDTC,
demonstrating its ability to effectively hydrophobize such
heterogeneous surfaces. The adsorption of BCBDTC
onto chalcocite supports the concept that its soft S donor
interacts with Cu1+, a soft acid. On the other hand, it is
unusual that for pyrite (even at a low concentration), the
surface acquires a hydrophobic character. This behavior of
BCBDTC contrasts with its thionocarbamate and thiourea
analogues, which are both very selective against iron sul-
fides. However, it should be noted that a borderline acid
like Fe2+ can behave like a soft acid in the presence of soft S
donors. It is also important to recognize that pyrite is never
the only sulfide mineral present in many ores this implies
competitive adsorption of BCBDTC between pyrite and
other chalcophile mineral species. Thus, the observed
hydrophobicity that BCBDTC confers to pyrite in these
measurements does not necessarily translate to its behavior
in real ore systems.
CA distributions for pure Cu, Au and Ag are shown in
Figure 5. Au and Ag demonstrate a stronger degree of natu-
ral hydrophobicity (~50–60°) compared to the other sub-
strates, though this is simply a manifestation of not being
fully hydrated. It is important to recognize that in aquatic
ore pulps, floatability of the value species is hindered due
to hydration. Despite this, shifts of the distribution to a
higher range after conditioning with BCBDTC are still
apparent. The shifts are notably stronger in the following
order: Cu Ag Au while reasons for this are not yet fully
known, it indicates differences in packing of BCBDTC
between the three.
While the cases above demonstrate the adsorption
of BCBDTC and its conferred hydrophobicity onto the
selected substrates, it must be noted that CA measurements