XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2269
while the other surfactants have C18 tails, the adsorption
density decreases in the order of DDM≈NaOlLSLASL,
which is consistent with the single-mineral flotation results
at pH 6 (Figure 4a).
On malachite, the biosurfactants are adsorbed as on
hematite through their sophorose groups. This conclusion
follows from the hardly resolved C-O(H) component at
286.8 eV in the C 1s spectrum of ASL and SLS on mala-
chite (Figure 7a). In contrast, DDM is apparently adsorbed
exposing its headgroup to solution as evidenced by the
enhanced C-O(H) component (Figure 7a). The difference
with hematite can be explained by the stronger interaction
of the maltose group with malachite, resulting in bilayer
formation. The reason is that the OH groups of malachite
on average are more basic than those on hematite, as follows
from their iso-electric points (IEP) of 9.5 and 6.0, respec-
tively [10]. It has been proposed earlier that the maltose
headgroup is slightly acidic and hydrogen bonded to the
basic OH groups on the surface of the TiO2 particles [22].
Since the bilayer adsorption renders malachite hydrophilic,
this result implies that the dosage is an important control
of the hydrophobizing effect of sugar-based surfactants.
This effect is not necessarily proportional to the surface
coverage of the surfactants due to the strong contribution
of the non-covalent (hydrophobic and hydrogen bonding)
interactions.
As in the case of hematite, the highest surface density
on malachite is achieved by DDM, while the XPS-derived
adsorption densities of ASL, LSL, and NaOl are similar
(Table 2). In contrast, there is no significant difference
in the effect of the surfactants on the Cu(II) 2p spectrum
(Figure 7b), suggesting that there is no redox reactions
upon the surfactant adsorption.
Flotation of Ultrafine Hematite and Ceria with ASL,
LSL, and BHA
In this part, we study how the oxidation state of Ce in
CeO2 affects the separation of ultrafine ceria from hema-
tite. Cerium is the most abundant representative of redox
active REE. The main REM are bastnäsite (REE)CO3F,
monazite (REE)PO4, and (REE,Y)PO4 xenotime, as well
as lateritic ion-adsorption clays, which contain 45–50% of
Ce [23, 24]. Even though Ce is mostly in the trivalent state
in REM, it can be oxidized to CeIV during ore storage [25].
Cerianite (CeO2) has been found in lateritic soils. Cerium
in red mud also occurs predominantly as CeIV [26].
The collecting properties of ASL and LSL are com-
pared to those of benzohydroxamic acid (BHA). There is
consensus that hydroxamic acids at low concentrations are
adsorbed on bastnäsite through chemisorption [27–30].
At higher concentrations and extended reaction times, the
adsorption mechanism is surface precipitation. It includes
the natural dissolution of the mineral and the precipita-
tion of hydroxamate complexes with hydroxy cations
CeIII(OH)2+ and CeIII(OH)2+ [29, 30]. The chemisorp-
tion on FeIII-OH surface groups and surface precipitation
of FeIII-ligand complexes have also been proposed for the
adsorption of a hydroxamic acid on hematite [31, 32].
The highest selectivity to CeO2(red) vs. hematite at pH
4, 7 and 10 is achieved by BHA (Figure 8). The average
grade of CeO2(red) in the BHA flotation is 85–95% at a
recovery of 75%. The best figures are observed at pH 4,
where BHA floats 74% ceria at a 90% grade. This result
Figure 8. Recovery and grade of –20 µm CeO
2
(red) and hematite ultrafine particles floated by ASL, LSL, and BHA from their
binary mixtures at (a) pH 4, (b) pH 7, and (c) 10. A froth agent DowFroth200™ 50 µM concentration was used with BHA. The
reported grade and recovery are average from duplicates with an error of no more than 10%
while the other surfactants have C18 tails, the adsorption
density decreases in the order of DDM≈NaOlLSLASL,
which is consistent with the single-mineral flotation results
at pH 6 (Figure 4a).
On malachite, the biosurfactants are adsorbed as on
hematite through their sophorose groups. This conclusion
follows from the hardly resolved C-O(H) component at
286.8 eV in the C 1s spectrum of ASL and SLS on mala-
chite (Figure 7a). In contrast, DDM is apparently adsorbed
exposing its headgroup to solution as evidenced by the
enhanced C-O(H) component (Figure 7a). The difference
with hematite can be explained by the stronger interaction
of the maltose group with malachite, resulting in bilayer
formation. The reason is that the OH groups of malachite
on average are more basic than those on hematite, as follows
from their iso-electric points (IEP) of 9.5 and 6.0, respec-
tively [10]. It has been proposed earlier that the maltose
headgroup is slightly acidic and hydrogen bonded to the
basic OH groups on the surface of the TiO2 particles [22].
Since the bilayer adsorption renders malachite hydrophilic,
this result implies that the dosage is an important control
of the hydrophobizing effect of sugar-based surfactants.
This effect is not necessarily proportional to the surface
coverage of the surfactants due to the strong contribution
of the non-covalent (hydrophobic and hydrogen bonding)
interactions.
As in the case of hematite, the highest surface density
on malachite is achieved by DDM, while the XPS-derived
adsorption densities of ASL, LSL, and NaOl are similar
(Table 2). In contrast, there is no significant difference
in the effect of the surfactants on the Cu(II) 2p spectrum
(Figure 7b), suggesting that there is no redox reactions
upon the surfactant adsorption.
Flotation of Ultrafine Hematite and Ceria with ASL,
LSL, and BHA
In this part, we study how the oxidation state of Ce in
CeO2 affects the separation of ultrafine ceria from hema-
tite. Cerium is the most abundant representative of redox
active REE. The main REM are bastnäsite (REE)CO3F,
monazite (REE)PO4, and (REE,Y)PO4 xenotime, as well
as lateritic ion-adsorption clays, which contain 45–50% of
Ce [23, 24]. Even though Ce is mostly in the trivalent state
in REM, it can be oxidized to CeIV during ore storage [25].
Cerianite (CeO2) has been found in lateritic soils. Cerium
in red mud also occurs predominantly as CeIV [26].
The collecting properties of ASL and LSL are com-
pared to those of benzohydroxamic acid (BHA). There is
consensus that hydroxamic acids at low concentrations are
adsorbed on bastnäsite through chemisorption [27–30].
At higher concentrations and extended reaction times, the
adsorption mechanism is surface precipitation. It includes
the natural dissolution of the mineral and the precipita-
tion of hydroxamate complexes with hydroxy cations
CeIII(OH)2+ and CeIII(OH)2+ [29, 30]. The chemisorp-
tion on FeIII-OH surface groups and surface precipitation
of FeIII-ligand complexes have also been proposed for the
adsorption of a hydroxamic acid on hematite [31, 32].
The highest selectivity to CeO2(red) vs. hematite at pH
4, 7 and 10 is achieved by BHA (Figure 8). The average
grade of CeO2(red) in the BHA flotation is 85–95% at a
recovery of 75%. The best figures are observed at pH 4,
where BHA floats 74% ceria at a 90% grade. This result
Figure 8. Recovery and grade of –20 µm CeO
2
(red) and hematite ultrafine particles floated by ASL, LSL, and BHA from their
binary mixtures at (a) pH 4, (b) pH 7, and (c) 10. A froth agent DowFroth200™ 50 µM concentration was used with BHA. The
reported grade and recovery are average from duplicates with an error of no more than 10%