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Recovery of Rare Earth Elements by Supercritical CO
2 :
A Mini Review
Chau Chun Beh, Jordan Evans, Jacques Eksteen
Curtin University, Western Australia School of Mines: Minerals, Energy and Chemical Engineering
ABSTRACT: Rare earth elements (REEs) are essential in renewable energy and defence sectors, particularly
for the manufacture of high-strength magnets using praseodymium, neodymium, dysprosium, and terbium.
Conventional extraction methods of REEs exhibit limitations such as using large amounts of acids and organics
that are harmful to the environment and health, and high post-processing costs to subsequently remove the
harmful solvents. Supercritical carbon dioxide (scCO2) extraction is a potential green alternative to conventional
extraction techniques. The study will review and discuss the effects on the extraction efficiency of REEs by
varying the scCO2 operating conditions including pressure, temperature, the addition of chelating agents, and
the pre-treatment of the samples.
INTRODUCTION
Rare earth elements (REEs) are a group of 15 lanthanides,
scandium, and yttrium. Rare earth elements are often char-
acterised into sub-groups of light REEs and heavy REEs.
REEs are not rare, but abundant on the Earth’s crust.
However, the supply of REE is vulnerable due to the dif-
ficulty of extraction and reliance on sources in China.
Rare earth elements have useful applications such as
the growing renewable energy field, and the defence field
(Dushyantha, Batapola et al. 2020). One of the major
fields that they are being used in is the magnet industry,
with the elements Praseodymium (Pr), Neodymium (Nd)
and Dysprosium (Dy) being used for the construction of
Nd2Fe14B permanent magnets, which are used in wind tur-
bines, electric motors and computers, as well as larger fields
such as the automotive, appliance, automation and medi-
cal fields (Brown, Ma et al. 2002, Dushyantha, Batapola
et al. 2020). They are also used for a variety of applica-
tions such as nickel-metal hydride batteries, glass additives,
lamp phosphors, lasers, alloys and radiation shielding
(Dushyantha, Batapola et al. 2020).
The lack of efficient and environmentally friendly
extraction and processing techniques is one of the major
risks to REE supply. There is a significant push for sus-
tainable technologies that are environmentally friendly to
extract REEs. Current REEs recovery techniques are either
pyrometallurgy or hydrometallurgy. Pyrometallurgical
extraction has high energy requirements while conven-
tional hydrometallurgy typically involves large amounts of
acids and organic solvents, which generate hazardous resi-
dues and require post-processing purification steps.
The hydrometallurgical recovery processes have a sig-
nificant environmental impact, as they involve toxic chem-
icals, leading to pollution of the environment. Providing
a green alternative scCO2 extraction technology helps to
address the environmental challenges for REE processing,
which inherently helps to reduce the overall environmen-
tal footprint. The aim of the current study is to provide a
mini review on the use of scCO2 to recover REEs. Various
Recovery of Rare Earth Elements by Supercritical CO
2 :
A Mini Review
Chau Chun Beh, Jordan Evans, Jacques Eksteen
Curtin University, Western Australia School of Mines: Minerals, Energy and Chemical Engineering
ABSTRACT: Rare earth elements (REEs) are essential in renewable energy and defence sectors, particularly
for the manufacture of high-strength magnets using praseodymium, neodymium, dysprosium, and terbium.
Conventional extraction methods of REEs exhibit limitations such as using large amounts of acids and organics
that are harmful to the environment and health, and high post-processing costs to subsequently remove the
harmful solvents. Supercritical carbon dioxide (scCO2) extraction is a potential green alternative to conventional
extraction techniques. The study will review and discuss the effects on the extraction efficiency of REEs by
varying the scCO2 operating conditions including pressure, temperature, the addition of chelating agents, and
the pre-treatment of the samples.
INTRODUCTION
Rare earth elements (REEs) are a group of 15 lanthanides,
scandium, and yttrium. Rare earth elements are often char-
acterised into sub-groups of light REEs and heavy REEs.
REEs are not rare, but abundant on the Earth’s crust.
However, the supply of REE is vulnerable due to the dif-
ficulty of extraction and reliance on sources in China.
Rare earth elements have useful applications such as
the growing renewable energy field, and the defence field
(Dushyantha, Batapola et al. 2020). One of the major
fields that they are being used in is the magnet industry,
with the elements Praseodymium (Pr), Neodymium (Nd)
and Dysprosium (Dy) being used for the construction of
Nd2Fe14B permanent magnets, which are used in wind tur-
bines, electric motors and computers, as well as larger fields
such as the automotive, appliance, automation and medi-
cal fields (Brown, Ma et al. 2002, Dushyantha, Batapola
et al. 2020). They are also used for a variety of applica-
tions such as nickel-metal hydride batteries, glass additives,
lamp phosphors, lasers, alloys and radiation shielding
(Dushyantha, Batapola et al. 2020).
The lack of efficient and environmentally friendly
extraction and processing techniques is one of the major
risks to REE supply. There is a significant push for sus-
tainable technologies that are environmentally friendly to
extract REEs. Current REEs recovery techniques are either
pyrometallurgy or hydrometallurgy. Pyrometallurgical
extraction has high energy requirements while conven-
tional hydrometallurgy typically involves large amounts of
acids and organic solvents, which generate hazardous resi-
dues and require post-processing purification steps.
The hydrometallurgical recovery processes have a sig-
nificant environmental impact, as they involve toxic chem-
icals, leading to pollution of the environment. Providing
a green alternative scCO2 extraction technology helps to
address the environmental challenges for REE processing,
which inherently helps to reduce the overall environmen-
tal footprint. The aim of the current study is to provide a
mini review on the use of scCO2 to recover REEs. Various