1696 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
extraction of metallic values (Agrawal and Dhawan, 2021a).
Red mud mainly contains iron, aluminum, silicon, tita-
nium, and calcium oxides that are naturally interlocked
and cannot be liberated easily. Additionally, it includes a
significant concentration of scandium, gallium, and rare-
earth elements (REEs). REEs present in the bauxite ore are
enriched in the red mud.
The red mud samples with varying compositions are
investigated to recover metallic values majorly through
established hydrometallurgical, pyrometallurgical, or a
combination of both techniques. The interlocked phases in
the red mud restrict the efficient liberation of metallic val-
ues, resulting in low purity and poor recovery of the prod-
ucts. Acid leaching using mineral and organic acids was
also investigated to dissolve metallic values from red mud
(Pepper et al., 2016 Borra et al., 2015). The leachate con-
taining different metallic values was treated using various
liquid-liquid separation techniques such as ion exchange,
solvent extraction (DEHPA, Cyanex 272, Cyanex 301,
Aliquat 336), and precipitation (oxalic acid) process to gen-
erate high-purity value-added products like Sc2O3, Fe3O4,
TiO2, and RE-oxide (Akcil et al., 2018).
The current work compares the techniques investigated
at the laboratory scale to recover metallic values from the
Indian red mud samples. The comparative analysis was per-
formed based on the efficiency of metal recovery, prelimi-
nary cost analysis, and electrical energy consumption. The
value of the red mud is estimated based on the quality and
nature of the product generated, which is beneficial for map-
ping the valuable elements in the red mud. The approach
in current work also helps in process selection based on the
red mud chemistry for the metal recovery process.
MATERIALS AND METHODOLOGY
The red mud samples were procured from the two distinct
alumina refineries in India, and the samples were named
HRM and NRM. The mineralogy of both samples was the
same and composed of major hematite, gibbsite, anatase,
quartz, cancrinite, and sodalite phases. The major distinc-
tion lies in the chemical composition, with the HRM sam-
ple containing exceptionally high values of anatase (15%)
and the NRM sample containing 50% of the hematite
phase in the feed.
The authors have developed various processes for recov-
ering valuable elements from Indian red mud. These pro-
cesses are classified as multi-stage–acid leaching (MS-AL),
acid baking–water leaching (AB-WL), alkali baking–acid
leaching (AB-AL), carbothermal reduction–acid leaching
(CR-AL), and hydrogen reduction–acid leaching (HR-AL).
Quantitative process flowsheets of the processes are shown
in Figures 1(a–e), and the reported values in the figures are
based on the optimal conditions (Agrawal and Dhawan,
2021a, 2022a, 2022b, 2023, 2023b). The Indian red mud
samples have different compositions and are used in the
work (Agrawal and Dhawan, 2021b).
METAL EXTRACTION EFFICIENCY
The hydrometallurgical processes such as acid leaching
(AL), acid baking–water leaching (AB-WL), and alkali bak-
ing–acid leaching (AB-AL) processes are optimized for the
recovery of titanium meanwhile, microwave carbothermal–
acid leaching (CR-AL) and hydrogen reduction–leaching
(HR-AL) processes were optimized for the recovery of iron
values. Nevertheless, the processes at optimal conditions are
investigated in both samples. The optimal conditions of the
process are reported in Table 1.
Iron, aluminium, titanium, and scandium are extracted
using different processes in Figure 2. In CR-AL and HR-AL
processes, titanium and other critical metals like scandium
and gallium are enriched in the residue. The Fe recovery
in these processes was determined by the iron content in
the form of magnetite or ferrite obtained after reduction
(in magnetic concentrate). Hematite and anatase phases,
which constitute the Fe and Ti values in both the red mud
samples, are known to be refractory. As expected, the direct
leaching and mechanical activation followed by the acid
leaching process were found inefficient for the dissolution.
However, multi-stage leaching using hydrochloric acid and
oxalic acid resulted in partial dissolution of Fe (~60%). The
advanced acid and alkali treatment methods investigated
in this work for the first time were found efficient for the
dissolution of Fe, Ti, and critical elements (Sc, Ga). The
microwave-assisted AB-WL process is a simplified two-step
process, leading to 73–74% Fe and Ti, 98% Al, and 88% Sc
dissolution in the HRM sample. The process is an improve-
ment over the conventional AB-WL process. The gibbsite,
cancrinite, sodalite, and other phases except hematite and
anatase are easily amenable in acidic conditions. Therefore,
Al dissolution is considerably significant in all the processes
except the CR-AL and HR-AL processes. These processes
involve reduction at high temperatures, decomposing
gibbsite to alumina, and reducing the overall Al extraction
during the subsequent leaching step.
In comparison, the AB-AL process, which involves
three steps: alkali baking, water leaching, and sulfuric acid
leaching, is the most efficient method for metal recovery
(%).Moreover, the process responses in both the HRM and
NRM samples were similar, suggesting the process can be
efficiently applied to the red mud samples that have var-
ied compositions. Nevertheless, the comprehensive analysis
extraction of metallic values (Agrawal and Dhawan, 2021a).
Red mud mainly contains iron, aluminum, silicon, tita-
nium, and calcium oxides that are naturally interlocked
and cannot be liberated easily. Additionally, it includes a
significant concentration of scandium, gallium, and rare-
earth elements (REEs). REEs present in the bauxite ore are
enriched in the red mud.
The red mud samples with varying compositions are
investigated to recover metallic values majorly through
established hydrometallurgical, pyrometallurgical, or a
combination of both techniques. The interlocked phases in
the red mud restrict the efficient liberation of metallic val-
ues, resulting in low purity and poor recovery of the prod-
ucts. Acid leaching using mineral and organic acids was
also investigated to dissolve metallic values from red mud
(Pepper et al., 2016 Borra et al., 2015). The leachate con-
taining different metallic values was treated using various
liquid-liquid separation techniques such as ion exchange,
solvent extraction (DEHPA, Cyanex 272, Cyanex 301,
Aliquat 336), and precipitation (oxalic acid) process to gen-
erate high-purity value-added products like Sc2O3, Fe3O4,
TiO2, and RE-oxide (Akcil et al., 2018).
The current work compares the techniques investigated
at the laboratory scale to recover metallic values from the
Indian red mud samples. The comparative analysis was per-
formed based on the efficiency of metal recovery, prelimi-
nary cost analysis, and electrical energy consumption. The
value of the red mud is estimated based on the quality and
nature of the product generated, which is beneficial for map-
ping the valuable elements in the red mud. The approach
in current work also helps in process selection based on the
red mud chemistry for the metal recovery process.
MATERIALS AND METHODOLOGY
The red mud samples were procured from the two distinct
alumina refineries in India, and the samples were named
HRM and NRM. The mineralogy of both samples was the
same and composed of major hematite, gibbsite, anatase,
quartz, cancrinite, and sodalite phases. The major distinc-
tion lies in the chemical composition, with the HRM sam-
ple containing exceptionally high values of anatase (15%)
and the NRM sample containing 50% of the hematite
phase in the feed.
The authors have developed various processes for recov-
ering valuable elements from Indian red mud. These pro-
cesses are classified as multi-stage–acid leaching (MS-AL),
acid baking–water leaching (AB-WL), alkali baking–acid
leaching (AB-AL), carbothermal reduction–acid leaching
(CR-AL), and hydrogen reduction–acid leaching (HR-AL).
Quantitative process flowsheets of the processes are shown
in Figures 1(a–e), and the reported values in the figures are
based on the optimal conditions (Agrawal and Dhawan,
2021a, 2022a, 2022b, 2023, 2023b). The Indian red mud
samples have different compositions and are used in the
work (Agrawal and Dhawan, 2021b).
METAL EXTRACTION EFFICIENCY
The hydrometallurgical processes such as acid leaching
(AL), acid baking–water leaching (AB-WL), and alkali bak-
ing–acid leaching (AB-AL) processes are optimized for the
recovery of titanium meanwhile, microwave carbothermal–
acid leaching (CR-AL) and hydrogen reduction–leaching
(HR-AL) processes were optimized for the recovery of iron
values. Nevertheless, the processes at optimal conditions are
investigated in both samples. The optimal conditions of the
process are reported in Table 1.
Iron, aluminium, titanium, and scandium are extracted
using different processes in Figure 2. In CR-AL and HR-AL
processes, titanium and other critical metals like scandium
and gallium are enriched in the residue. The Fe recovery
in these processes was determined by the iron content in
the form of magnetite or ferrite obtained after reduction
(in magnetic concentrate). Hematite and anatase phases,
which constitute the Fe and Ti values in both the red mud
samples, are known to be refractory. As expected, the direct
leaching and mechanical activation followed by the acid
leaching process were found inefficient for the dissolution.
However, multi-stage leaching using hydrochloric acid and
oxalic acid resulted in partial dissolution of Fe (~60%). The
advanced acid and alkali treatment methods investigated
in this work for the first time were found efficient for the
dissolution of Fe, Ti, and critical elements (Sc, Ga). The
microwave-assisted AB-WL process is a simplified two-step
process, leading to 73–74% Fe and Ti, 98% Al, and 88% Sc
dissolution in the HRM sample. The process is an improve-
ment over the conventional AB-WL process. The gibbsite,
cancrinite, sodalite, and other phases except hematite and
anatase are easily amenable in acidic conditions. Therefore,
Al dissolution is considerably significant in all the processes
except the CR-AL and HR-AL processes. These processes
involve reduction at high temperatures, decomposing
gibbsite to alumina, and reducing the overall Al extraction
during the subsequent leaching step.
In comparison, the AB-AL process, which involves
three steps: alkali baking, water leaching, and sulfuric acid
leaching, is the most efficient method for metal recovery
(%).Moreover, the process responses in both the HRM and
NRM samples were similar, suggesting the process can be
efficiently applied to the red mud samples that have var-
ied compositions. Nevertheless, the comprehensive analysis