2270 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
can be explained by a beneficial combination of two effects
observed in the single-mineral flotation [13]: BHA has very
slow adsorption kinetics on nonhydrated hematite at pH 4
(due to the absence of the Fe-OH surface groups), while its
adsorption on ceria is faster. As follows from the XPS study
(see below) and in agreement with Refs [29, 30], BHA
adsorbs on CeO2(red) through complexing of the CeIII-OH
surface groups, which results in their dissolution. The pres-
ence of CeIV ions on the ceria surface expands the BHA
adsorption to pH 4 through promoting the formation of
the CeIV-OH adsorption sites.
In contrast, the highest selectivity to hematite vs.
CeO2(red) is achieved by LSL at pH 4, where the hema-
tite grade and recovery is 85–95% (Figure 8a). This result
is unexpected as LSL renders CeO2(red) superhydrophobic
[13]. It is explained by the selective rejection of superhy-
drophobic CeO2(red) particles due to their selective hydro-
phobic agglomeration to a large non-floatable size [13].
LSL renders the hematite surface hydrophobic by the coor-
dination of the sophorose group to the surface, while the
adsorption starts with the adherence of the LSL colloids.
The selectivity of LSL to hematite is suppressed at high pH
(Figure 8b,c), which results from increasing the floatability
of CeO2(red).
The increased oxidation of ceria adversely affects its
separation from hematite with all three collectors, while
BHA remains the best collector [13].
The Interaction of ASL, LSL, and BHA with Ceria
To understand the effect of the oxidation state of ceria on its
flotation against hematite at pH 4, we measured adsorption
density, solubility, and XPS spectra. For comparison, we
included BHA in the study.
As seen from Table 3, the affinity of the metal oxides
to both biosurfactants decreases in the order of hematite
CeO2(red) CeO2(°x). LSL consistently has a higher surface
density than ASL, which can be explained by the adsorp-
tion of LSL through the surface deposition of its colloids
[10]. The solubility data (Table 4) indicate that at 110 µM
ASL slightly leaches CeO2(red). In contrast, LSL passivates
the CeO2(red) surface, preventing its dissolution.
The XPS Ce 3d and O 1s spectra show that CeO2(red)
has a higher percentage of CeIII and is more hydroxylated
compared to CeO2(°x) (Figure 9). After the BHA adsorp-
tion from a 100 µM solution at pH 4 for 2 h, the con-
centration of the surface CeIII and OH groups significantly
decreases (Figure 10a,b). The reduction of the ceria surface
is also observed for CeO2(°x) but is less pronounced than for
CeO2(red), which is consistent with the lower concentration
of CeIII-OH surface species [13]. This result agrees with
the established adsorption mechanism postulating that
hydroxamic acids can form water soluble complexes with
CeIII-OH species [29, 30].
65% of the NH groups of BHA are chemisorbed on
CeO2(red) in the deprotonated form as evidenced by the
appearance of a peak at 400.0 eV (Figure 10c). This peak
assignment is based on that proposed for hydroxamic acids
adsorbed on Cu oxides [33, 34]. The remaining 35% are due
to physisorbed BHA. Since the O 1s spectrum of adsorbed
BHA does not display the BHA peak at 533 eV (Figure
10b), the oxygen atoms of adsorbed BHA are strongly
coordinated to the cerium ions, which shifts the O 1s peak
Table 3. Adsorption density of ASL and LSL on –20 µm α-Fe2O3, CeO2(red) and CeO2(ox) and measured using total organic
carbon (TOC) after 2 h of equilibrating in 100 µM surfactant solutions at pH 4
α-Fe2O3 CeO2(°x) CeO2(red)
ASL LSL ASL LSL ASL LSL
Adsorption density, µM/m2 30.0 ± 0.5 44.0 ± 0.5 8.1 ± 0.6 12 ± 3 14 ± 3 16 ± 2
Formal Monolayer 0.8 1.2 0.21 0.34 0.37 0.45
Table 4. Effect of ASL and LSL on solubility of –20 µm CeO2(red) and CeO2(ox) after 2 h of equilibrating at pH 4
Samples at pH 4 ± 3
Surfactant concentration, µM
0 110 150 175
Cerium, µg/L
ASL
CeO
2 (°x) 14 ± 3 10 ± 2 14 ± 3 18 ± 3
CeO
2
(red) 11 ± 2 23 ± 4 14 ± 3 17 ± 3
LSL
CeO
2 (°x) 14 ± 3 3 1 14 ± 3
CeO
2
(red) ± 2 5 5 ± 2
can be explained by a beneficial combination of two effects
observed in the single-mineral flotation [13]: BHA has very
slow adsorption kinetics on nonhydrated hematite at pH 4
(due to the absence of the Fe-OH surface groups), while its
adsorption on ceria is faster. As follows from the XPS study
(see below) and in agreement with Refs [29, 30], BHA
adsorbs on CeO2(red) through complexing of the CeIII-OH
surface groups, which results in their dissolution. The pres-
ence of CeIV ions on the ceria surface expands the BHA
adsorption to pH 4 through promoting the formation of
the CeIV-OH adsorption sites.
In contrast, the highest selectivity to hematite vs.
CeO2(red) is achieved by LSL at pH 4, where the hema-
tite grade and recovery is 85–95% (Figure 8a). This result
is unexpected as LSL renders CeO2(red) superhydrophobic
[13]. It is explained by the selective rejection of superhy-
drophobic CeO2(red) particles due to their selective hydro-
phobic agglomeration to a large non-floatable size [13].
LSL renders the hematite surface hydrophobic by the coor-
dination of the sophorose group to the surface, while the
adsorption starts with the adherence of the LSL colloids.
The selectivity of LSL to hematite is suppressed at high pH
(Figure 8b,c), which results from increasing the floatability
of CeO2(red).
The increased oxidation of ceria adversely affects its
separation from hematite with all three collectors, while
BHA remains the best collector [13].
The Interaction of ASL, LSL, and BHA with Ceria
To understand the effect of the oxidation state of ceria on its
flotation against hematite at pH 4, we measured adsorption
density, solubility, and XPS spectra. For comparison, we
included BHA in the study.
As seen from Table 3, the affinity of the metal oxides
to both biosurfactants decreases in the order of hematite
CeO2(red) CeO2(°x). LSL consistently has a higher surface
density than ASL, which can be explained by the adsorp-
tion of LSL through the surface deposition of its colloids
[10]. The solubility data (Table 4) indicate that at 110 µM
ASL slightly leaches CeO2(red). In contrast, LSL passivates
the CeO2(red) surface, preventing its dissolution.
The XPS Ce 3d and O 1s spectra show that CeO2(red)
has a higher percentage of CeIII and is more hydroxylated
compared to CeO2(°x) (Figure 9). After the BHA adsorp-
tion from a 100 µM solution at pH 4 for 2 h, the con-
centration of the surface CeIII and OH groups significantly
decreases (Figure 10a,b). The reduction of the ceria surface
is also observed for CeO2(°x) but is less pronounced than for
CeO2(red), which is consistent with the lower concentration
of CeIII-OH surface species [13]. This result agrees with
the established adsorption mechanism postulating that
hydroxamic acids can form water soluble complexes with
CeIII-OH species [29, 30].
65% of the NH groups of BHA are chemisorbed on
CeO2(red) in the deprotonated form as evidenced by the
appearance of a peak at 400.0 eV (Figure 10c). This peak
assignment is based on that proposed for hydroxamic acids
adsorbed on Cu oxides [33, 34]. The remaining 35% are due
to physisorbed BHA. Since the O 1s spectrum of adsorbed
BHA does not display the BHA peak at 533 eV (Figure
10b), the oxygen atoms of adsorbed BHA are strongly
coordinated to the cerium ions, which shifts the O 1s peak
Table 3. Adsorption density of ASL and LSL on –20 µm α-Fe2O3, CeO2(red) and CeO2(ox) and measured using total organic
carbon (TOC) after 2 h of equilibrating in 100 µM surfactant solutions at pH 4
α-Fe2O3 CeO2(°x) CeO2(red)
ASL LSL ASL LSL ASL LSL
Adsorption density, µM/m2 30.0 ± 0.5 44.0 ± 0.5 8.1 ± 0.6 12 ± 3 14 ± 3 16 ± 2
Formal Monolayer 0.8 1.2 0.21 0.34 0.37 0.45
Table 4. Effect of ASL and LSL on solubility of –20 µm CeO2(red) and CeO2(ox) after 2 h of equilibrating at pH 4
Samples at pH 4 ± 3
Surfactant concentration, µM
0 110 150 175
Cerium, µg/L
ASL
CeO
2 (°x) 14 ± 3 10 ± 2 14 ± 3 18 ± 3
CeO
2
(red) 11 ± 2 23 ± 4 14 ± 3 17 ± 3
LSL
CeO
2 (°x) 14 ± 3 3 1 14 ± 3
CeO
2
(red) ± 2 5 5 ± 2