XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1653
weight was mixed with the RM in a separate XRD anal-
ysis to determine the amorphous content in the sample,
which was later defined as an internal standard during the
data analysis in MDI-Jade ®. The acid-baked RM was set
in epoxy, and the cross-section was polished with water-
free 0.05μm colloidal silica suspension (after polishing with
coarser grit sizes). SEM-EDS was performed on the cross-
sectioned samples using Thermo Scientific Apreo SEM to
visualize the depth of sulfation of the acid-baked RM. N2
adsorption surface area and porosity were measured for
the raw and acid-baked water-leached RM solids using a
Micrometric ASAPTM 2020 analyzer.
The elemental analysis of the RM is shown in Table 1.
The red-mud sample used in this study is composed of Fe
(i.e., 43% Fe2O3), followed by Al, Ca, Si, Ti, and Na, and
minor amounts of Mg, Mn, and P. Fe, Ti, and Ca con-
tents are similar to the Red Muds reported in the literature.
However, the Si, Na, Al, Mg, and P contents are lower than
most other RM [12–14, 16–20, 26–39]. The RM sample
contained the highest Total Rare Earth Element (TREE)
content (4,672 ppm) and Sc content (167 ppm), higher
than most of the RM in the reviewed literature [12–14,
17–20, 26–37]. RM XRD analysis (Figure 1) showed that
Hematite, Goethite, Gibbsite, Calcite, Hatrurite, and
Cancrinite phases are present in this sample, consistent
with the previously reported phases [17–19].
Determination of Stoichiometric Amount of Acid
The calculated stoichiometric amount of acid required for
acid baking of RM to convert the elements to their respec-
tive sulfates was used to define the different acid-to-RM
ratios used in the experiments. For this calculation, it was
assumed that all the major components of RM (except Si)
were fully sulfated during H2SO4 baking. It was deter-
mined that 0.9 ml of acid was required per g of RM for
complete sulfation of the species.
Acid Baking and Direct Acid Leaching
H2SO4 (96% w/w ACS grade) was used for acid baking as
well as DL. A temperature-controlled muffle furnace placed
in a fume hood was used for acid baking or calcination
experiments. The acid was mixed with 2g of RM in a 5 ml
alumina crucible and placed in a preheated furnace for bak-
ing. After baking, the crucibles were cooled to room tem-
perature. S/L was defined based on the weight of the RM
for DL or the weight of the solid after ABWL. Leaching
Table 1. Elemental composition of RM
Major Elements, Wt% Rare Earth Elements, ppm
Na2O 3.9 MgO 0.2 Y 1243 Sm 114 Er 70
SiO2 6.8 MnO2 0.9 Sc 167 Eu 25 Tm 9
Fe
2 O
3 43.2 P
2 O
5 0.9 La 865 Gd 134 Yb 52
Al
2 O
3 15.3 Ce 1084 Tb 20 Lu 8
CaO 10.6 Pr 156 Dy 115 TREE 4672
TiO2 5.7 Nd 586 Ho 24
Figure 1. XRD pattern of RM
weight was mixed with the RM in a separate XRD anal-
ysis to determine the amorphous content in the sample,
which was later defined as an internal standard during the
data analysis in MDI-Jade ®. The acid-baked RM was set
in epoxy, and the cross-section was polished with water-
free 0.05μm colloidal silica suspension (after polishing with
coarser grit sizes). SEM-EDS was performed on the cross-
sectioned samples using Thermo Scientific Apreo SEM to
visualize the depth of sulfation of the acid-baked RM. N2
adsorption surface area and porosity were measured for
the raw and acid-baked water-leached RM solids using a
Micrometric ASAPTM 2020 analyzer.
The elemental analysis of the RM is shown in Table 1.
The red-mud sample used in this study is composed of Fe
(i.e., 43% Fe2O3), followed by Al, Ca, Si, Ti, and Na, and
minor amounts of Mg, Mn, and P. Fe, Ti, and Ca con-
tents are similar to the Red Muds reported in the literature.
However, the Si, Na, Al, Mg, and P contents are lower than
most other RM [12–14, 16–20, 26–39]. The RM sample
contained the highest Total Rare Earth Element (TREE)
content (4,672 ppm) and Sc content (167 ppm), higher
than most of the RM in the reviewed literature [12–14,
17–20, 26–37]. RM XRD analysis (Figure 1) showed that
Hematite, Goethite, Gibbsite, Calcite, Hatrurite, and
Cancrinite phases are present in this sample, consistent
with the previously reported phases [17–19].
Determination of Stoichiometric Amount of Acid
The calculated stoichiometric amount of acid required for
acid baking of RM to convert the elements to their respec-
tive sulfates was used to define the different acid-to-RM
ratios used in the experiments. For this calculation, it was
assumed that all the major components of RM (except Si)
were fully sulfated during H2SO4 baking. It was deter-
mined that 0.9 ml of acid was required per g of RM for
complete sulfation of the species.
Acid Baking and Direct Acid Leaching
H2SO4 (96% w/w ACS grade) was used for acid baking as
well as DL. A temperature-controlled muffle furnace placed
in a fume hood was used for acid baking or calcination
experiments. The acid was mixed with 2g of RM in a 5 ml
alumina crucible and placed in a preheated furnace for bak-
ing. After baking, the crucibles were cooled to room tem-
perature. S/L was defined based on the weight of the RM
for DL or the weight of the solid after ABWL. Leaching
Table 1. Elemental composition of RM
Major Elements, Wt% Rare Earth Elements, ppm
Na2O 3.9 MgO 0.2 Y 1243 Sm 114 Er 70
SiO2 6.8 MnO2 0.9 Sc 167 Eu 25 Tm 9
Fe
2 O
3 43.2 P
2 O
5 0.9 La 865 Gd 134 Yb 52
Al
2 O
3 15.3 Ce 1084 Tb 20 Lu 8
CaO 10.6 Pr 156 Dy 115 TREE 4672
TiO2 5.7 Nd 586 Ho 24
Figure 1. XRD pattern of RM