2266 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
pH 6 and pH 10, respectively (Figure 3c,d). DDM does
not have collecting properties except for a weak (60%)
selectivity to malachite vs. quartz at pH 10.
Ultrafine particle size significantly improves the grade
of hematite in the NaOl and DDM flotation at pH 5 and
10, and in the DDM flotation at pH 5 (Figure 3a,b). In
the oleate flotation, the grade reaches 90%. However, the
ultrafine particle size has no significant effect on the mala-
chite grade in the oleate flotation, and on the grades of both
metal oxides in the LSL and ASL flotation (Figure 3). To
compare, hydroxamic acids lose their collecting efficiency
in the flotation of malachite against quartz as the particle
size decreases from (–150 +38 µm) to –38 µm [14]. Hence,
the tolerance to the ultrafine particle size makes LSL and
ASL promising as collectors of iron and copper oxides.
Further tests on ores are required to verify this preliminary
conclusion.
The correlation between the effect of ultrafine particle
size and the collector is currently poorly understood. The
improved hematite grades in the NaOl and DDM flota-
tion can be explained by the improved adsorption of the
surfactants on the surface defects of ultrafine particles, as
their adsorption on the smooth crystallographic planes of
hematite is expected to be weak [10]. In addition, NaOl
improves the floatability of ultrafine iron oxides through
their hydrophobic flocculation [15].
The Interaction of Sugar-Based Surfactants with
Hematite and Malachite
We gained insight into the interaction of the biosurfac-
tants with hematite and malachite using zeta-potential,
single-mineral flotation, and solubility [10]. In addition,
we measured ex situ XPS.
Zeta-potential shows that in a pH range from 2.5 to
10.5, all the four collectors are adsorbed in the anionic form
[10]. This result is expected for anionic oleate and ASL.
However, it is surprising for non-ionic LSL and DDM,
suggesting the dissociation of their acidic OH groups upon
adsorption. In addition, LSL is likely to adsorb at acidic pH
in the colloidal form and degrades at basic pH through the
hydrolytic cleavage of its weak ester bonds.
Single-mineral flotation was used to characterize the
hydrophobicity of the particles under flotation condi-
tions. In these tests, all the four surfactants achieve a maxi-
mum hematite recovery of 70%, though at different pH
(Figure 4a). In agreement with literature [15, 16], the
oleate flotation of hematite has a maximum at pH 6. The
decrease in the adsorption of fatty acids at basic pH is typi-
cally explained by their intrinsically weak (monodentate)
coordination to hematite, coupled with the electrostatic
repulsion from the increasingly more negatively charged
hematite surface [17, 18]. The hematite flotation with
non-ionic LSL and DDM also has a 70% maximum at pH
4–6 and 6–8, respectively. Their origin remains unclear.
In contrast, the flotation with anionic ASL monotonically
increases with pH, reaching 70% at pH 10. This increase
can be explained by the transition of adsorbed ASL from the
hydrophilic configuration with its carboxyl headgroup dan-
gling in the solution to the hydrophobic one in which both
the headgroups are coordinated to the metal cation. The
preferential coordination of ASL to hematite through the
sophorose group follows from the XPS study (see below).
c
Figure 4. Effect of pH on single-mineral flotation of –20 µm fraction of (a) hematite, (b) malachite, and (c) quartz with 50 µM
of () LSL, () ASL, () DDM, and () NaOl. The line “no collector” corresponds to flotation using 50 µM DowFroth 200
(a frothing agent)
pH 6 and pH 10, respectively (Figure 3c,d). DDM does
not have collecting properties except for a weak (60%)
selectivity to malachite vs. quartz at pH 10.
Ultrafine particle size significantly improves the grade
of hematite in the NaOl and DDM flotation at pH 5 and
10, and in the DDM flotation at pH 5 (Figure 3a,b). In
the oleate flotation, the grade reaches 90%. However, the
ultrafine particle size has no significant effect on the mala-
chite grade in the oleate flotation, and on the grades of both
metal oxides in the LSL and ASL flotation (Figure 3). To
compare, hydroxamic acids lose their collecting efficiency
in the flotation of malachite against quartz as the particle
size decreases from (–150 +38 µm) to –38 µm [14]. Hence,
the tolerance to the ultrafine particle size makes LSL and
ASL promising as collectors of iron and copper oxides.
Further tests on ores are required to verify this preliminary
conclusion.
The correlation between the effect of ultrafine particle
size and the collector is currently poorly understood. The
improved hematite grades in the NaOl and DDM flota-
tion can be explained by the improved adsorption of the
surfactants on the surface defects of ultrafine particles, as
their adsorption on the smooth crystallographic planes of
hematite is expected to be weak [10]. In addition, NaOl
improves the floatability of ultrafine iron oxides through
their hydrophobic flocculation [15].
The Interaction of Sugar-Based Surfactants with
Hematite and Malachite
We gained insight into the interaction of the biosurfac-
tants with hematite and malachite using zeta-potential,
single-mineral flotation, and solubility [10]. In addition,
we measured ex situ XPS.
Zeta-potential shows that in a pH range from 2.5 to
10.5, all the four collectors are adsorbed in the anionic form
[10]. This result is expected for anionic oleate and ASL.
However, it is surprising for non-ionic LSL and DDM,
suggesting the dissociation of their acidic OH groups upon
adsorption. In addition, LSL is likely to adsorb at acidic pH
in the colloidal form and degrades at basic pH through the
hydrolytic cleavage of its weak ester bonds.
Single-mineral flotation was used to characterize the
hydrophobicity of the particles under flotation condi-
tions. In these tests, all the four surfactants achieve a maxi-
mum hematite recovery of 70%, though at different pH
(Figure 4a). In agreement with literature [15, 16], the
oleate flotation of hematite has a maximum at pH 6. The
decrease in the adsorption of fatty acids at basic pH is typi-
cally explained by their intrinsically weak (monodentate)
coordination to hematite, coupled with the electrostatic
repulsion from the increasingly more negatively charged
hematite surface [17, 18]. The hematite flotation with
non-ionic LSL and DDM also has a 70% maximum at pH
4–6 and 6–8, respectively. Their origin remains unclear.
In contrast, the flotation with anionic ASL monotonically
increases with pH, reaching 70% at pH 10. This increase
can be explained by the transition of adsorbed ASL from the
hydrophilic configuration with its carboxyl headgroup dan-
gling in the solution to the hydrophobic one in which both
the headgroups are coordinated to the metal cation. The
preferential coordination of ASL to hematite through the
sophorose group follows from the XPS study (see below).
c
Figure 4. Effect of pH on single-mineral flotation of –20 µm fraction of (a) hematite, (b) malachite, and (c) quartz with 50 µM
of () LSL, () ASL, () DDM, and () NaOl. The line “no collector” corresponds to flotation using 50 µM DowFroth 200
(a frothing agent)