XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2271
to 531.5 eV. The N/Ce ratios for CeO2(red) and CeO2(°x)
are similar (Table 5), suggesting that the adsorption den-
sity of BHA is not affected by the oxidation state of ceria.
However, the percentage of chemisorbed BHA decreases to
55% for CeO2(°x). Hence, assuming that the chemisorbed
BHA is more hydrophobic, the drop in the floatability of
CeO2(°x) with BHA compared to that of CeO2(red) can be
explained by the suppression of BHA chemisorption.
The low intensity of the C-O(H) peak at 286.8 eV in
the C 1s spectrum (Figure 11c) indicates that LSL is coordi-
nated to the ceria surface through the sophorose group. The
small peak at ~289 eV in C 1s spectra of the ceria surface
corresponds to Ce 4s [35]. The extra O 1s peak at 533 eV
is due to the sophorose group (Figure 11b and Figure 5b).
The LSL adsorption is accompanied by the removal of CeIII
and OH from the CeO2(red) surface (Figure 11a,b). This
536 534 532 530 528
Binding Energy (eV)
925 920 915 910 905 900 895 890 885 880
Binding Energy (eV)
CeIII
OH
a
Ce 3d
b
O 1s
CeO2(red)
CeO2(ox)
Figure 9. XPS (a) Ce 3d and (b) O 1s spectra of initial (green) ultrafine CeO
2
(red) and CeO
2
(ox) red after conditioning in water
at pH 4 LSL for 2 h. Arrows show the CeIII and OH (associated with CeIII) features
result could suggest that, like BHA, LSL forms soluble
complexes with CeIII-OH, which, however, contradicts the
passivating effect of LSL (Table 4). Given the hydrolytic
instability of ester/lactone bonds in the presence of basic
OH groups and the catalytic activity of ceria, we tentatively
assign this result to a redox reaction between CeIII-OH (and
associated oxygen vacancy) and the di-acetylated sophorose
group. Further studies are required to delineate the electron
acceptor in this redox reaction in our system.
In contrast, as in the case of hematite, ASL transfers
electron density to the ceria surface. Figure 12a shows this
effect for CeO2(°x) as it is much more pronounced com-
pared to CeO2(red). The electron transfer can be linked to
the coordination of the carboxylic group of ASL to the sur-
face. This conclusion follows from the pronounced C-O(H)
peak at 286.8 eV in the C 1s spectrum (Figure 12c), which
930 920 910 900 890 880
Binding Energy (eV)
537 534 531 528
Binding Energy (eV)
408 404 400 396
Binding Energy (eV)
a Ce 3d b O 1s
BHA
ads BHA
ads BHA
CeO2(red)+BHA
c N 1s
ads BHA
BHA
CeIII
Figure 10. XPS (a) Ce 3d, (b) O 1s, (c) C 1s and (d) N 1s spectra of initial (green) CeO
2
(red) and (red) after conditioning in
100 mM BHA solution at pH 4 LSL for 2 h. The blue trace is the spectra of solid BHA
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to 531.5 eV. The N/Ce ratios for CeO2(red) and CeO2(°x)
are similar (Table 5), suggesting that the adsorption den-
sity of BHA is not affected by the oxidation state of ceria.
However, the percentage of chemisorbed BHA decreases to
55% for CeO2(°x). Hence, assuming that the chemisorbed
BHA is more hydrophobic, the drop in the floatability of
CeO2(°x) with BHA compared to that of CeO2(red) can be
explained by the suppression of BHA chemisorption.
The low intensity of the C-O(H) peak at 286.8 eV in
the C 1s spectrum (Figure 11c) indicates that LSL is coordi-
nated to the ceria surface through the sophorose group. The
small peak at ~289 eV in C 1s spectra of the ceria surface
corresponds to Ce 4s [35]. The extra O 1s peak at 533 eV
is due to the sophorose group (Figure 11b and Figure 5b).
The LSL adsorption is accompanied by the removal of CeIII
and OH from the CeO2(red) surface (Figure 11a,b). This
536 534 532 530 528
Binding Energy (eV)
925 920 915 910 905 900 895 890 885 880
Binding Energy (eV)
CeIII
OH
a
Ce 3d
b
O 1s
CeO2(red)
CeO2(ox)
Figure 9. XPS (a) Ce 3d and (b) O 1s spectra of initial (green) ultrafine CeO
2
(red) and CeO
2
(ox) red after conditioning in water
at pH 4 LSL for 2 h. Arrows show the CeIII and OH (associated with CeIII) features
result could suggest that, like BHA, LSL forms soluble
complexes with CeIII-OH, which, however, contradicts the
passivating effect of LSL (Table 4). Given the hydrolytic
instability of ester/lactone bonds in the presence of basic
OH groups and the catalytic activity of ceria, we tentatively
assign this result to a redox reaction between CeIII-OH (and
associated oxygen vacancy) and the di-acetylated sophorose
group. Further studies are required to delineate the electron
acceptor in this redox reaction in our system.
In contrast, as in the case of hematite, ASL transfers
electron density to the ceria surface. Figure 12a shows this
effect for CeO2(°x) as it is much more pronounced com-
pared to CeO2(red). The electron transfer can be linked to
the coordination of the carboxylic group of ASL to the sur-
face. This conclusion follows from the pronounced C-O(H)
peak at 286.8 eV in the C 1s spectrum (Figure 12c), which
930 920 910 900 890 880
Binding Energy (eV)
537 534 531 528
Binding Energy (eV)
408 404 400 396
Binding Energy (eV)
a Ce 3d b O 1s
BHA
ads BHA
ads BHA
CeO2(red)+BHA
c N 1s
ads BHA
BHA
CeIII
Figure 10. XPS (a) Ce 3d, (b) O 1s, (c) C 1s and (d) N 1s spectra of initial (green) CeO
2
(red) and (red) after conditioning in
100 mM BHA solution at pH 4 LSL for 2 h. The blue trace is the spectra of solid BHA
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