XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2165
base metal sulphides have been reported to also float due
to underpotential deposition (Buckley and Woods, 1994)
i.e., potentials less than the dixanthogen oxidation poten-
tial, the papers reviewed do not report notable presence
of chemisorbed thiols on the surface. Shackleton (2007)
reports floatability of pure synthetic PtS2 with recoveries
of up to 94% by micro-flotation at solution potentials that
are around 0.2 V and pH 9, and 95% recovery for PdS.
The results do suggest that some floatability can be achieved
at lower Eh values with reduced degree of hydrophobicity.
The lower limit of Eh is therefore yet to be defined.
Pt-Pd-Te
Telluride PGMs are reported to be slower floating than sul-
fide minerals. In contrast to sulfide minerals they have been
shown to be very readily oxidized on the mineral surface
indicating high anodic currents at oxidation (Shackleton
et al., 2007a Tadie et al., 2015 Vermaak et al., 2004).
The rapid oxidation of telluride minerals may be the deter-
rent towards faster flotation kinetics. High conductivity in
these minerals, however, also makes them a relatively good
catalyst for collector oxidation. Figure 4 shows empirically
determined hydrophobicity domains for PtTe2 and PdTe2
derived from electrochemical experiments and supported
in the region of pH 9 by flotation and surface speciation
tests. At pH regions below pH 9.2 and potentials above
the oxidation potential PtTe2 was shown to preferentially
adsorb ethyl xanthate in the form of the dithiolate. pH 9.2
is observed in this figure to have the widest potential range
for formation of hydrophobic xanthate species enabling the
formation of the metal thiolate species as well as dixantho-
gen. The same result is observed for PdTe2. Above pH 9.2
the metal thiolate is the preferred species on PtTe2. Figure 4
indicates that the widest control window for achieving
hydrophobicity is at the pH that most PGM concentrators
operate, which is around pH 9. Shackleton (2007) showed
that at Eh conditions amounting to above 0.2 V it was pos-
sible to obtain up to 99% recovery of both synthetic PdTe2
and PtTe2 at pH 9. Shackleton et al. (2007a) suggested that
the poor floatability of these minerals in real ores was not
attributed to the lack of collector adsorption but may be
attributed to particle size or liberation.
Pt-Pd-Bi-Te
The bismuth containing telluride mineral is common
in the Great Dyke and the Platreef ores as discussed and
is also considered to be slow floating, even more so than
the “pure” telluride minerals. Vermaak et al., (2004) have
shown that the order of decreasing rate of oxidation of the
elements within this mineral is Pt/Pd-Bi Pt/Pd-Bi-Te
Pd/Pt-Te. The rapid oxidation of these minerals is problem-
atic towards their achievement of sufficient hydrophobicity
for flotation. The empirically determined regions of hydro-
phobicity presented in Figure 5 are corroborated by contact
angle and floatability of pure PGMs. The work of Vermaak
et al., (2005) showed from both Raman spectroscopy and
contact angle measurements that at potentials greater than
0.10 V but lower than 0.15 V a contact angle of 50° was
observed on the surface of the mineral whilst above 0.15 V
the contact angle increased to 63° which corresponds to
the formation of dixanthogen on the mineral surface.. The
specific study demonstrated how hydrophobicity can be
achieved by a mixture of collector species to result in a nett
higher contact angle. Vermaak (2007) also floated the min-
eral at its rest potential (0.12 V) and achieved recoveries
of 60% via micro-flotation. Shackleton (2007) floated the
Figure 4. Eh and pH domains of hydrophobicity for PdTe
2 and PtTe
2 compiled from Tadie (2015) and (Shackleton et al., 2007b)
base metal sulphides have been reported to also float due
to underpotential deposition (Buckley and Woods, 1994)
i.e., potentials less than the dixanthogen oxidation poten-
tial, the papers reviewed do not report notable presence
of chemisorbed thiols on the surface. Shackleton (2007)
reports floatability of pure synthetic PtS2 with recoveries
of up to 94% by micro-flotation at solution potentials that
are around 0.2 V and pH 9, and 95% recovery for PdS.
The results do suggest that some floatability can be achieved
at lower Eh values with reduced degree of hydrophobicity.
The lower limit of Eh is therefore yet to be defined.
Pt-Pd-Te
Telluride PGMs are reported to be slower floating than sul-
fide minerals. In contrast to sulfide minerals they have been
shown to be very readily oxidized on the mineral surface
indicating high anodic currents at oxidation (Shackleton
et al., 2007a Tadie et al., 2015 Vermaak et al., 2004).
The rapid oxidation of telluride minerals may be the deter-
rent towards faster flotation kinetics. High conductivity in
these minerals, however, also makes them a relatively good
catalyst for collector oxidation. Figure 4 shows empirically
determined hydrophobicity domains for PtTe2 and PdTe2
derived from electrochemical experiments and supported
in the region of pH 9 by flotation and surface speciation
tests. At pH regions below pH 9.2 and potentials above
the oxidation potential PtTe2 was shown to preferentially
adsorb ethyl xanthate in the form of the dithiolate. pH 9.2
is observed in this figure to have the widest potential range
for formation of hydrophobic xanthate species enabling the
formation of the metal thiolate species as well as dixantho-
gen. The same result is observed for PdTe2. Above pH 9.2
the metal thiolate is the preferred species on PtTe2. Figure 4
indicates that the widest control window for achieving
hydrophobicity is at the pH that most PGM concentrators
operate, which is around pH 9. Shackleton (2007) showed
that at Eh conditions amounting to above 0.2 V it was pos-
sible to obtain up to 99% recovery of both synthetic PdTe2
and PtTe2 at pH 9. Shackleton et al. (2007a) suggested that
the poor floatability of these minerals in real ores was not
attributed to the lack of collector adsorption but may be
attributed to particle size or liberation.
Pt-Pd-Bi-Te
The bismuth containing telluride mineral is common
in the Great Dyke and the Platreef ores as discussed and
is also considered to be slow floating, even more so than
the “pure” telluride minerals. Vermaak et al., (2004) have
shown that the order of decreasing rate of oxidation of the
elements within this mineral is Pt/Pd-Bi Pt/Pd-Bi-Te
Pd/Pt-Te. The rapid oxidation of these minerals is problem-
atic towards their achievement of sufficient hydrophobicity
for flotation. The empirically determined regions of hydro-
phobicity presented in Figure 5 are corroborated by contact
angle and floatability of pure PGMs. The work of Vermaak
et al., (2005) showed from both Raman spectroscopy and
contact angle measurements that at potentials greater than
0.10 V but lower than 0.15 V a contact angle of 50° was
observed on the surface of the mineral whilst above 0.15 V
the contact angle increased to 63° which corresponds to
the formation of dixanthogen on the mineral surface.. The
specific study demonstrated how hydrophobicity can be
achieved by a mixture of collector species to result in a nett
higher contact angle. Vermaak (2007) also floated the min-
eral at its rest potential (0.12 V) and achieved recoveries
of 60% via micro-flotation. Shackleton (2007) floated the
Figure 4. Eh and pH domains of hydrophobicity for PdTe
2 and PtTe
2 compiled from Tadie (2015) and (Shackleton et al., 2007b)