3528 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
remaining valuable elements, such as scandium and tita-
nium, for downstream processing.
The present work proposes a hydrometallurgical
process for comprehensive recycling of bauxite residue.
Multistage leaching and precipitation are reported for the
selective recovery of major elements while upgrading the
trace metals to generate a concentrated feed. The present
work is one of the few studies focused on recovering dif-
ferent metallic oxides of high purity from bauxite residue
using a hydrometallurgy-based process, which results in the
simultaneous recovery of scandium values. The hydromet-
allurgical process is compared with the pyrometallurgical
method to highlight the outcomes of the two approaches
and provide guidelines for process development for large-
scale applications.
MATERIALS AND METHODS
Sample Information
The bauxite residue sample utilized in this work was pro-
cured from an alumina refinery in Quebec, Canada. The
bulk sample was collected from the dried section of the
storage pond and subsequently subjected to a 24-hour dry-
ing process in a laboratory oven at 95 °C to eliminate any
remaining moisture. The sample was further grounded with
a mortar and pestle to disintegrate agglomerated particles.
All the chemicals utilized in the experimental work were of
analytical grade.
Experimental Methods
Raw bauxite residue was leached with HCl in the first stage
of treatment. The leaching trials were conducted using a
1000 mL Pyrex reactor with three ports and a magnetic
stirrer. The reaction flask was placed in a silicone oil bath to
regulate temperature and ensure uniform heating. A con-
denser was attached to one port, while the remaining two
were employed to monitor the slurry temperature and pH.
Subsequently, the reacted slurry was filtered using a vacuum
filter to yield a solid residue and leach solution. These prod-
ucts were then analyzed to assess leaching efficiency. In the
case of multistage leaching, the solid residue was collected,
dried in a laboratory oven, and used in the next leaching
stage. Liquid solutions were collected for precipitation and
recovery of dissolved metallic values.
The leach residue from first stage HCl leaching was
further leached with oxalic acid solution in the next stage
of treatment. The leach liquor obtained after oxalic acid
leaching was subjected to photochemical reduction using a
100W UV lamp placed over the solution. The solid precipi-
tate recovered after photochemical reduction was subjected
to thermal decomposition in a low oxygen atmosphere to
generate magnetite product. The residue collected after
oxalic acid leaching was processed through sulfation bak-
ing and leaching process to recover Ti and RE values. The
detailed experimental procedure is described in our previ-
ous work (Tanvar and Mishra, 2021).
Characterization Techniques
The chemical composition of the samples was analyzed
using Inductively Coupled Plasma – Optical Emission
Spectroscopy (ICP – OES, Horiba Ultima 2). Solid samples
underwent thermal fusion with borate flux at 1000 °C for
1 hour, followed by dissolution in a 25% nitric acid solu-
tion, dilution, and subsequent analysis using ICP – OES.
Conversely, liquid samples were analyzed after dilution
with a 2% nitric acid solution. Mineral phase identification
in the solid samples at different stages was conducted using
an X-ray diffractometer (XRD, PANalytical Empyrean).
The diffraction data were collected with Cr – Kα radiation
in the 2 – theta range of 10 to 80°, employing a scanning
rate of 2 °/min and a step size of 0.02°. A Scanning Electron
Microscope (SEM Scios 2 Dual beam) equipped with
Energy-dispersive X-ray spectroscopy (EDS) was employed
to examine the morphology of the powder samples.
RESULTS AND DISCUSSION
Feed Characterization
Table 1 represents the bulk chemical analysis of the
feed sample used in this study, showing the presence of
21.4% iron, 10.2% aluminum, 7.0% sodium, 3.7%
titanium, 5.0% silicon, and 2.3% calcium as major ele-
ments, along with 0.0037% scandium. The major
phases determined from XRD analysis included hema-
tite (Fe2O3), gibbsite (Al(OH)3), boehmite (Al(OOH)),
calcium carbonate (CaCO3), quartz (SiO2), sodalite
(Na8Al6Si6O24(OH)2(H2O)2), and rutile (TiO2). Figure 2
shows the SEM analysis and elemental mapping of dif-
ferent elements from EDS. The SEM micrograph shows
micron-sized particles with variable geometry and elements
homogenously distributed throughout the matrix.
Table 1. Chemical analysis of bauxite residue
Element Ca Si Ti Na Fe Al Sc Y La Ce
Wt.% 2.31 5.01 3.67 6.98 21.44 10.21 0.0037 0.0062 0.0034 0.0179
remaining valuable elements, such as scandium and tita-
nium, for downstream processing.
The present work proposes a hydrometallurgical
process for comprehensive recycling of bauxite residue.
Multistage leaching and precipitation are reported for the
selective recovery of major elements while upgrading the
trace metals to generate a concentrated feed. The present
work is one of the few studies focused on recovering dif-
ferent metallic oxides of high purity from bauxite residue
using a hydrometallurgy-based process, which results in the
simultaneous recovery of scandium values. The hydromet-
allurgical process is compared with the pyrometallurgical
method to highlight the outcomes of the two approaches
and provide guidelines for process development for large-
scale applications.
MATERIALS AND METHODS
Sample Information
The bauxite residue sample utilized in this work was pro-
cured from an alumina refinery in Quebec, Canada. The
bulk sample was collected from the dried section of the
storage pond and subsequently subjected to a 24-hour dry-
ing process in a laboratory oven at 95 °C to eliminate any
remaining moisture. The sample was further grounded with
a mortar and pestle to disintegrate agglomerated particles.
All the chemicals utilized in the experimental work were of
analytical grade.
Experimental Methods
Raw bauxite residue was leached with HCl in the first stage
of treatment. The leaching trials were conducted using a
1000 mL Pyrex reactor with three ports and a magnetic
stirrer. The reaction flask was placed in a silicone oil bath to
regulate temperature and ensure uniform heating. A con-
denser was attached to one port, while the remaining two
were employed to monitor the slurry temperature and pH.
Subsequently, the reacted slurry was filtered using a vacuum
filter to yield a solid residue and leach solution. These prod-
ucts were then analyzed to assess leaching efficiency. In the
case of multistage leaching, the solid residue was collected,
dried in a laboratory oven, and used in the next leaching
stage. Liquid solutions were collected for precipitation and
recovery of dissolved metallic values.
The leach residue from first stage HCl leaching was
further leached with oxalic acid solution in the next stage
of treatment. The leach liquor obtained after oxalic acid
leaching was subjected to photochemical reduction using a
100W UV lamp placed over the solution. The solid precipi-
tate recovered after photochemical reduction was subjected
to thermal decomposition in a low oxygen atmosphere to
generate magnetite product. The residue collected after
oxalic acid leaching was processed through sulfation bak-
ing and leaching process to recover Ti and RE values. The
detailed experimental procedure is described in our previ-
ous work (Tanvar and Mishra, 2021).
Characterization Techniques
The chemical composition of the samples was analyzed
using Inductively Coupled Plasma – Optical Emission
Spectroscopy (ICP – OES, Horiba Ultima 2). Solid samples
underwent thermal fusion with borate flux at 1000 °C for
1 hour, followed by dissolution in a 25% nitric acid solu-
tion, dilution, and subsequent analysis using ICP – OES.
Conversely, liquid samples were analyzed after dilution
with a 2% nitric acid solution. Mineral phase identification
in the solid samples at different stages was conducted using
an X-ray diffractometer (XRD, PANalytical Empyrean).
The diffraction data were collected with Cr – Kα radiation
in the 2 – theta range of 10 to 80°, employing a scanning
rate of 2 °/min and a step size of 0.02°. A Scanning Electron
Microscope (SEM Scios 2 Dual beam) equipped with
Energy-dispersive X-ray spectroscopy (EDS) was employed
to examine the morphology of the powder samples.
RESULTS AND DISCUSSION
Feed Characterization
Table 1 represents the bulk chemical analysis of the
feed sample used in this study, showing the presence of
21.4% iron, 10.2% aluminum, 7.0% sodium, 3.7%
titanium, 5.0% silicon, and 2.3% calcium as major ele-
ments, along with 0.0037% scandium. The major
phases determined from XRD analysis included hema-
tite (Fe2O3), gibbsite (Al(OH)3), boehmite (Al(OOH)),
calcium carbonate (CaCO3), quartz (SiO2), sodalite
(Na8Al6Si6O24(OH)2(H2O)2), and rutile (TiO2). Figure 2
shows the SEM analysis and elemental mapping of dif-
ferent elements from EDS. The SEM micrograph shows
micron-sized particles with variable geometry and elements
homogenously distributed throughout the matrix.
Table 1. Chemical analysis of bauxite residue
Element Ca Si Ti Na Fe Al Sc Y La Ce
Wt.% 2.31 5.01 3.67 6.98 21.44 10.21 0.0037 0.0062 0.0034 0.0179