1656 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
optimal for the formation of (H3O)Fe(SO4)2 accounting
for the consumption of the excess acid [22]. The lower acid
concentration in the first stage of TABWL may be forming
Fe2(SO4)3, thereby accounting for the more efficient use
of the acid. This phenomenon is being investigated in the
ongoing work.
Effect of the TABWL On Pore Area
The pore area of RM and its residue after completion of
TABWL were compared and superimposed with the Sc
recovery for that sample to establish whether the TABWL
is creating a new surface area. The samples here had been
baked at 250°C for two hours with 1 ml H2SO4/g RM
followed by water leach at 75°C for two hours with S/L =
1/20. Figure 5 shows a significant increase in micro, miso,
and macro pores after the first leach. Further improve-
ment in surface area is observed after the second stage
leach. Proportionally, Sc recovery also increased with the
improvement in the pore area. It must be noted here that
the recovery of Sc at stage one leach is associated with the
surface area of the head sample.
In contrast, stage two leach is associated with a sur-
face area of tailings recovered after leach 1. The correlation
between the improved surface area and enhanced recov-
ery supports the study’s hypothesis. A detailed analysis is
underway to compare the surface area of an acid-baked
sample with the surface area of the first–stage acid bake
from the TABWL sample and see if the surface area of the
baked samples is similar, even though less acid is used in
one of the cases.
Effect of RM Particle Size
RM is a fine residue from the Bayer process, which readily
agglomerates but breaks down quickly when brought into
contact with water. When it is dried, it agglomerates, and
the agglomerates need to be broken. It should be noted that
the term ‘particle’ here refers to the size of the agglomerates
of RM. The effect of particle size of RM was analyzed for
two size fractions, –35 mesh and +35 mesh. This mesh size
was chosen since 35 Mesh size was identified as the largest
particle size of RM in the literature. The chemical composi-
tion of the two size fractions was analyzed and presented
in Table 4. The composition of the different size fractions
was similar to that of the head sample of RM. The smaller
size fraction has 10% less Sc. These results agree with the
observations by Fofona et al., who found that RM has a
very homogenous composition. Particle size will impact the
comminution process, which is very energy-intensive [44].
RM fractions were TABWL at 200°C for two hours
using 1 ml H2SO4/g RM and leached at 75°C with S/L of
1/20 for two hours. Tests were also performed for a six-hour
baking time (arbitrarily chosen) to examine the influence of
mass transfer and chemical kinetics under conditions simi-
lar to the two-hour bake test. Figure 6 shows no statistically
Table 4. Chemical composition of different size fractions
of RM
Sample Sc (ppm) Fe (%)Al(%)
RM 167 30 8%
RM +35 164 30 7.9%
RM –35 150 27 7.5%
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
30
Red Mud TABWL Stage 1 TABWL Stage 2
Micro (2 nm)
Meso (2-50 nm)
Macro (50-300 nm)
Sc %
Figure 5. The pore area for RM and the residue after each leaching cycle vs. the
recoveries of Sc for baked RM
Recovery
(%)
Pore
area
(m2/g)
optimal for the formation of (H3O)Fe(SO4)2 accounting
for the consumption of the excess acid [22]. The lower acid
concentration in the first stage of TABWL may be forming
Fe2(SO4)3, thereby accounting for the more efficient use
of the acid. This phenomenon is being investigated in the
ongoing work.
Effect of the TABWL On Pore Area
The pore area of RM and its residue after completion of
TABWL were compared and superimposed with the Sc
recovery for that sample to establish whether the TABWL
is creating a new surface area. The samples here had been
baked at 250°C for two hours with 1 ml H2SO4/g RM
followed by water leach at 75°C for two hours with S/L =
1/20. Figure 5 shows a significant increase in micro, miso,
and macro pores after the first leach. Further improve-
ment in surface area is observed after the second stage
leach. Proportionally, Sc recovery also increased with the
improvement in the pore area. It must be noted here that
the recovery of Sc at stage one leach is associated with the
surface area of the head sample.
In contrast, stage two leach is associated with a sur-
face area of tailings recovered after leach 1. The correlation
between the improved surface area and enhanced recov-
ery supports the study’s hypothesis. A detailed analysis is
underway to compare the surface area of an acid-baked
sample with the surface area of the first–stage acid bake
from the TABWL sample and see if the surface area of the
baked samples is similar, even though less acid is used in
one of the cases.
Effect of RM Particle Size
RM is a fine residue from the Bayer process, which readily
agglomerates but breaks down quickly when brought into
contact with water. When it is dried, it agglomerates, and
the agglomerates need to be broken. It should be noted that
the term ‘particle’ here refers to the size of the agglomerates
of RM. The effect of particle size of RM was analyzed for
two size fractions, –35 mesh and +35 mesh. This mesh size
was chosen since 35 Mesh size was identified as the largest
particle size of RM in the literature. The chemical composi-
tion of the two size fractions was analyzed and presented
in Table 4. The composition of the different size fractions
was similar to that of the head sample of RM. The smaller
size fraction has 10% less Sc. These results agree with the
observations by Fofona et al., who found that RM has a
very homogenous composition. Particle size will impact the
comminution process, which is very energy-intensive [44].
RM fractions were TABWL at 200°C for two hours
using 1 ml H2SO4/g RM and leached at 75°C with S/L of
1/20 for two hours. Tests were also performed for a six-hour
baking time (arbitrarily chosen) to examine the influence of
mass transfer and chemical kinetics under conditions simi-
lar to the two-hour bake test. Figure 6 shows no statistically
Table 4. Chemical composition of different size fractions
of RM
Sample Sc (ppm) Fe (%)Al(%)
RM 167 30 8%
RM +35 164 30 7.9%
RM –35 150 27 7.5%
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
30
Red Mud TABWL Stage 1 TABWL Stage 2
Micro (2 nm)
Meso (2-50 nm)
Macro (50-300 nm)
Sc %
Figure 5. The pore area for RM and the residue after each leaching cycle vs. the
recoveries of Sc for baked RM
Recovery
(%)
Pore
area
(m2/g)