1654 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
tests were conducted over temperature-controlled hot plate
stirrers in beakers covered with a watch glass, placed in a
water bath, and stirred using Teflon-coated magnetic stir-
rers. Samples were then pressure-filtered through a 0.1 μm
Durapore ® hydroscopic membrane filter. The leachate resi-
due was dried overnight in a drying furnace at 80°C.
Elemental recovery (%)from ABWL or DL was deter-
mined using the following equation:
Recovery %=100 × C M
C V
s
1 Li Li
s
i
j
#
#
=
/^h
where, CLi =Concentration of element in leachate VLi =
Volume of leachate i =number of bakes or leaches J=1 for
single bake or leach, and J= 2 for the two-stage acid baking
CS =Concentration of element in RM, MS =Mass of RM
used for the experiment.
RESULTS AND DISCUSSION
Comparison of ABWL and DL for Sc Recovery
Tests were performed to recover Sc from RM using DL based
on the conditions used by Borra et al. [13]. This was used as
a baseline to compare ABWL with baking performed under
similar conditions, as noted in Table 2. A modified DL pro-
cess was used where the RM was initially calcined at 340°C
to convert Na into water-soluble species. These water-solu-
ble species were then leached during the WL step to expose
new surfaces for improved Sc recovery in the DL stage.
The results from the leaching tests are shown in Figure 2.
ABWL achieved the highest Sc recovery (i.e.,56%) com-
pared to DL and Calcination, followed by WL and DL.
The results also showed that calcination followed by WL
and DL had no significant effect on the recovery of Sc as
initially expected. A previous study by Uzun et al. showed
that there was no marked increase in the total dissolution of
RM until 600°C calcination temperature [40]. The authors
suggested that enhanced dissolution was due to the decom-
position of Gibbsite [Al(OH3)]and Goethite [FeO(OH)].
It is also reported in the literature that Gibbsite decomposes
by 550°C and Goethite by 300°C [41, 42]. This conversion
of the phases into their respective oxides makes it easier to
leach by DL [43]. Therefore, RM needs to be calcined at
higher temperatures to see any notable improvement in Sc
recovery by a subsequent DL step. The ABWL recoveries
were comparable to those obtained by Anawati et al. [22].
The limited recovery of Sc using ABWL prompted the
authors to consider the role of the sulfated product layer in
limiting further penetration of acid through the particle.
SEM-EDS was performed on a RM sample baked at 250°C
for two hours using 1 ml H2SO4/g solid to analyze the pen-
etration of the sulfated layer through the particles. Fe was
used as an indicator for Sc sulfation since the Sc concentra-
tion is too low to be detected by the EDS detector and due
to their close association within the crystal structure and
similar chemical behavior [17, 18]. Figure 3 shows acid-
baked particles where the yellow sulfated Fe layer surrounds
a core of blue unsulfated Fe. This may be because the unsul-
fated Fe at the core may be inaccessible to the acid during
the bake due to the blocked sulfated pores. Since a super-
stoichiometric amount of acid was used for baking while
the Fe conversion was incomplete, it may be concluded that
not all the acid was consumed to sulfate the RM during
ABWL, thereby leading to acid waste. Additional unsul-
fated surfaces can be exposed by washing the sulfated layer
with water. The Sc that is trapped in the unsulfated can
be recovered by another round of ABWL. The leaching of
the sulfated layer may also expose new pores and increase
the surface area of the particle, thereby aiding in further
Sc recovery during the second round of ABWL. Therefore,
it is hypothesized that by using a TABWL process on RM
Table 2. Conditions for various initial Sc leaching processes
Leaching Method
Acid/Base Amount/
Sample
Baking/Calcination
Temp., °C
Baking/Calcination
Time, h
Leaching
Temp., °C
S/L Ratio for
Leaching, w/w
Leaching
Time, h
DL 6M H2SO4 --75 1/20 2
Calcination +WL +DL 6M H2SO4 340 2 75 1/20 2
H
2 SO
4 ABWL 1.0 ml/g of sample 200 2 75 1/20 2
0
10
20
30
40
50
60
70
80
90
100
DL Calcination +WL +
DL
ABWL
Fe
Sc
Figure 2. Comparison of recoveries from various leaching
methodologies applied to RM
Recovery
(%)
tests were conducted over temperature-controlled hot plate
stirrers in beakers covered with a watch glass, placed in a
water bath, and stirred using Teflon-coated magnetic stir-
rers. Samples were then pressure-filtered through a 0.1 μm
Durapore ® hydroscopic membrane filter. The leachate resi-
due was dried overnight in a drying furnace at 80°C.
Elemental recovery (%)from ABWL or DL was deter-
mined using the following equation:
Recovery %=100 × C M
C V
s
1 Li Li
s
i
j
#
#
=
/^h
where, CLi =Concentration of element in leachate VLi =
Volume of leachate i =number of bakes or leaches J=1 for
single bake or leach, and J= 2 for the two-stage acid baking
CS =Concentration of element in RM, MS =Mass of RM
used for the experiment.
RESULTS AND DISCUSSION
Comparison of ABWL and DL for Sc Recovery
Tests were performed to recover Sc from RM using DL based
on the conditions used by Borra et al. [13]. This was used as
a baseline to compare ABWL with baking performed under
similar conditions, as noted in Table 2. A modified DL pro-
cess was used where the RM was initially calcined at 340°C
to convert Na into water-soluble species. These water-solu-
ble species were then leached during the WL step to expose
new surfaces for improved Sc recovery in the DL stage.
The results from the leaching tests are shown in Figure 2.
ABWL achieved the highest Sc recovery (i.e.,56%) com-
pared to DL and Calcination, followed by WL and DL.
The results also showed that calcination followed by WL
and DL had no significant effect on the recovery of Sc as
initially expected. A previous study by Uzun et al. showed
that there was no marked increase in the total dissolution of
RM until 600°C calcination temperature [40]. The authors
suggested that enhanced dissolution was due to the decom-
position of Gibbsite [Al(OH3)]and Goethite [FeO(OH)].
It is also reported in the literature that Gibbsite decomposes
by 550°C and Goethite by 300°C [41, 42]. This conversion
of the phases into their respective oxides makes it easier to
leach by DL [43]. Therefore, RM needs to be calcined at
higher temperatures to see any notable improvement in Sc
recovery by a subsequent DL step. The ABWL recoveries
were comparable to those obtained by Anawati et al. [22].
The limited recovery of Sc using ABWL prompted the
authors to consider the role of the sulfated product layer in
limiting further penetration of acid through the particle.
SEM-EDS was performed on a RM sample baked at 250°C
for two hours using 1 ml H2SO4/g solid to analyze the pen-
etration of the sulfated layer through the particles. Fe was
used as an indicator for Sc sulfation since the Sc concentra-
tion is too low to be detected by the EDS detector and due
to their close association within the crystal structure and
similar chemical behavior [17, 18]. Figure 3 shows acid-
baked particles where the yellow sulfated Fe layer surrounds
a core of blue unsulfated Fe. This may be because the unsul-
fated Fe at the core may be inaccessible to the acid during
the bake due to the blocked sulfated pores. Since a super-
stoichiometric amount of acid was used for baking while
the Fe conversion was incomplete, it may be concluded that
not all the acid was consumed to sulfate the RM during
ABWL, thereby leading to acid waste. Additional unsul-
fated surfaces can be exposed by washing the sulfated layer
with water. The Sc that is trapped in the unsulfated can
be recovered by another round of ABWL. The leaching of
the sulfated layer may also expose new pores and increase
the surface area of the particle, thereby aiding in further
Sc recovery during the second round of ABWL. Therefore,
it is hypothesized that by using a TABWL process on RM
Table 2. Conditions for various initial Sc leaching processes
Leaching Method
Acid/Base Amount/
Sample
Baking/Calcination
Temp., °C
Baking/Calcination
Time, h
Leaching
Temp., °C
S/L Ratio for
Leaching, w/w
Leaching
Time, h
DL 6M H2SO4 --75 1/20 2
Calcination +WL +DL 6M H2SO4 340 2 75 1/20 2
H
2 SO
4 ABWL 1.0 ml/g of sample 200 2 75 1/20 2
0
10
20
30
40
50
60
70
80
90
100
DL Calcination +WL +
DL
ABWL
Fe
Sc
Figure 2. Comparison of recoveries from various leaching
methodologies applied to RM
Recovery
(%)