1651
Enhanced Scandium Recovery from Red Mud Using Two-stage
Acid Baking and Water Leaching Process
Hari S. Jammulamadaka, Mohammad Rezaee, Sarma V. Pisupati
Penn State
Dan Mcfarland
Lawrence Livermore National Laboratory
ABSTRACT: Red Mud, a byproduct of bauxite processing via the Bayer process, has emerged as a potential
secondary source of the critical rare earth element (REE) Scandium. Previous research using direct acid leaching
or acid baking and water leaching processes achieved limited Scandium recoveries of up to 60%. Improved
recovery has been reported when using high-temperature pretreatments or extended leaching time with
associated energy costs. This study aims to develop a more efficient H2SO4 acid baking and water leaching
process to achieve higher Scandium recovery without using high temperatures or excess acid. Scanning Electron
Microscopy – Energy Dispersive Spectroscopy analysis to visualize the depth of sulfation of the baked sample
showed that Scandium recovery was limited by the mass diffusion of acid through the sulfated layer formed
during baking. An efficient two-stage acid baking and water-leaching process was developed to reduce mass
transfer limitations, achieving Scandium recovery exceeding 75%. Baking with H2SO4 at 200°C for two
hours and water leaching at 75°C for two hours at each stage offered a 20% improvement in recovery while
employing the same acid concentration as in the single-stage process. The improved recovery is attributed to the
enhanced Scandium accessibility due to improved porosity and surface area as measured by N2 adsorption in the
two-stage process.
INTRODUCTION
Scandium (Sc) is a vital element used in various industries,
including aerospace and automotive, where it strengthens
aluminum welds. It is also used as a tracer in oil refining,
contributes to solid oxide fuel cells, and fuels laser technol-
ogy[1–3]. Sc concentration in the upper continental crust
is typically around 14 ppm (parts per million). While min-
erals like Euxenite, Gadolinite, Kolbeckite, and Thortveitite
contain higher Sc concentrations, they are present in
such limited quantities that commercial mining remains
impractical [4–6]. Sc is primarily recovered from secondary
sources, including tungsten residue, titanium white waste
fluid, nickel laterite ore tailings, mine tailings from REE-
rich iron ore, and uranium processing tailings [2, 7–11].
Red Mud (RM), a Bayer Process residue rich in iron
(Fe), is also a source of valuable REEs. Resources with a
minimum Sc concentration between 20–50 ppm have been
proposed as viable sources for Sc recovery [7]. RM often
contains Sc levels, frequently surpassing 100 ppm, thus
emerging as a promising Sc source [12–14]. At an annual
RM production of approximately 150 million tons/year
[15] and a cumulative production of over 4 × 109 tons until
2015, primarily stockpiled in landfills worldwide [16],
extracting Sc from this resource could potentially supply
Enhanced Scandium Recovery from Red Mud Using Two-stage
Acid Baking and Water Leaching Process
Hari S. Jammulamadaka, Mohammad Rezaee, Sarma V. Pisupati
Penn State
Dan Mcfarland
Lawrence Livermore National Laboratory
ABSTRACT: Red Mud, a byproduct of bauxite processing via the Bayer process, has emerged as a potential
secondary source of the critical rare earth element (REE) Scandium. Previous research using direct acid leaching
or acid baking and water leaching processes achieved limited Scandium recoveries of up to 60%. Improved
recovery has been reported when using high-temperature pretreatments or extended leaching time with
associated energy costs. This study aims to develop a more efficient H2SO4 acid baking and water leaching
process to achieve higher Scandium recovery without using high temperatures or excess acid. Scanning Electron
Microscopy – Energy Dispersive Spectroscopy analysis to visualize the depth of sulfation of the baked sample
showed that Scandium recovery was limited by the mass diffusion of acid through the sulfated layer formed
during baking. An efficient two-stage acid baking and water-leaching process was developed to reduce mass
transfer limitations, achieving Scandium recovery exceeding 75%. Baking with H2SO4 at 200°C for two
hours and water leaching at 75°C for two hours at each stage offered a 20% improvement in recovery while
employing the same acid concentration as in the single-stage process. The improved recovery is attributed to the
enhanced Scandium accessibility due to improved porosity and surface area as measured by N2 adsorption in the
two-stage process.
INTRODUCTION
Scandium (Sc) is a vital element used in various industries,
including aerospace and automotive, where it strengthens
aluminum welds. It is also used as a tracer in oil refining,
contributes to solid oxide fuel cells, and fuels laser technol-
ogy[1–3]. Sc concentration in the upper continental crust
is typically around 14 ppm (parts per million). While min-
erals like Euxenite, Gadolinite, Kolbeckite, and Thortveitite
contain higher Sc concentrations, they are present in
such limited quantities that commercial mining remains
impractical [4–6]. Sc is primarily recovered from secondary
sources, including tungsten residue, titanium white waste
fluid, nickel laterite ore tailings, mine tailings from REE-
rich iron ore, and uranium processing tailings [2, 7–11].
Red Mud (RM), a Bayer Process residue rich in iron
(Fe), is also a source of valuable REEs. Resources with a
minimum Sc concentration between 20–50 ppm have been
proposed as viable sources for Sc recovery [7]. RM often
contains Sc levels, frequently surpassing 100 ppm, thus
emerging as a promising Sc source [12–14]. At an annual
RM production of approximately 150 million tons/year
[15] and a cumulative production of over 4 × 109 tons until
2015, primarily stockpiled in landfills worldwide [16],
extracting Sc from this resource could potentially supply