1686 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Many nations’ economic growth and national security
depend on the reliable supply and durability of these vital
resources[4]. Rare earth element availability is currently
less than demand [5], [6], with imports from China fre-
quently accounting for a large portion of the supply[7].
Today, many critical metals that are needed by the US and
other industrialized countries are sourced from outside [8].
China provides a significant portion of the rare earth (RE)
supply imported by the US [5]. The United States is seek-
ing to expand domestic production and recover rare earth
elements (REs) from various sources to reduce supply chain
vulnerability, given the significance of these minerals in
technological and economic advancement [4], [9].
Neodymium and samarium, two rare elements among
the REEs are the foundational elements for making power-
ful permanent magnets [10]. The most prevalent kind of
RE magnets are Nd-Fe-B magnets[11]. Since neodymium-
iron-boron (NdFeB) magnets primarily replaced SmCo
magnets after 1985 [12], the market share of SmCo mag-
nets is currently less than 2% in the permanent magnet
segment [12], [13]. Nonetheless, new applications in con-
sumer electronics, automotive and medical technology,
aerospace, and military equipment are driving growth in
the global market for SmCo magnets. Due to their greater
optimal operating temperature (250–350°C) than that of
NdFeB magnets (60, 220°C), SmCo magnets are still val-
ued for their capacity to operate at high temperatures and
are frequently utilized in the aviation industry [13], [14].
Samarium is utilized in the filter glass of Nd (Neodymium):
YAG (Yttrium–Aluminium–Garnet) solid-state lasers to
encircle the laser rod and increase efficiency by collecting
stray emissions due to its narrow spectral absorption band
[15]. At microwave frequencies, samarium can be used in
coatings and capacitors because it forms stable titanate
compounds with beneficial dielectric characteristics[15].
Cobalt and samarium can be obtained from End-of-life
SmCo magnets as valuable secondary sources [13].
It is challenging to mine REEs since they are fre-
quently found in very small concentrations [5]. Extraction
and separation of REEs from their complex ore are very
difficult due to their unique physical and chemical prop-
erties process, thereby making them scarce in the market
[1]. Currently, the recovery of REEs involves the traditional
pyro- or hydrometallurgical process [16]. The pyrometal-
lurgical method suffers from environmental concerns such
as gaseous emissions while the traditional hydrometallurgi-
cal process involves the use of dilute and strong acids to
dissolve REE evolve hydrogen gas [15], [17].
The overall process in the recovery and separation of
individual elements from complex REE systems suffers
from high energy demands as it requires complex energy-
consuming solutions with the use of many hazardous
chemicals that negatively impact the environment [5]. In
response to the scarcity of these REEs and their potential
supply risk recent research has focused on improving recov-
ery and separation techniques as well as developing recy-
cling approaches for secondary resources like mine tailings
and electronic waste as alternative sources to natural ores
[12], [13]. The evolution of recycling processes as a sec-
ondary source for REEs has seen the majority of rare-earth
magnet recycling research concentrated on NdFeB magnet
recycling [18], [19], [20] with little attention to SmCo
magnet recycling [7]. However, the recycling of SmCo
magnets will not only be a secondary source for samarium
but also cobalt a critical metal that is economically very
important for the steel industry [13], [21] due to its unique
resistance to oxidation and its usage in cathode materials
for lithium-ion batteries which is very crucial to the transi-
tion to electric vehicles [13].
With the growing trend toward a circular economy
aiming to balance sustainability, efficiency, and environ-
mental impacts, this research is focused on recycling SmCo
magnets using green (ionometallurgy), smart, and novel
extraction pathways. That is the use of Deep Eutectic
Solvents (DESs) for leaching and novel Resodyn Acoustic
Mixing (RAM) for intensification of the leaching process.
DESs are systems formed from eutectic mixtures of
Lewis or Brønsted acids and bases, which can contain a
variety of anionic and cationic species[22]. The eutectic
combinations have melting points lower than their compo-
nents, giving a room-temperature ionic liquid [23]. They
are liquid at temperatures lower than 150 °C, but most are
liquid between room temperatures and 70 °C [24]. The
advantages DESs have over conventional hydrometallur-
gical reagents are that they are environmentally benign or
have minimal risk and environmental impacts, are readily
available in larger quantities, are cost-efficient, and chemi-
cally stable to allow prolonged reuse, and are able to do
selective leaching. The major difference between hydro-
metallurgy and ionometallurgy is that the latter uses non-
aqueous solvents.
DES is typically created by combining a quaternary
ammonium salt with metal salts or a hydrogen bond donor
(HBD) that can form a complex with the quaternary
ammonium salt’s halide anion. DESs are defined using the
general formula Cat+X–zY where Cat+ is an ammonium,
phosphonium, or sulfonium cation, and X is a Lewis base,
a halide anion generally and Y is a Brønsted acid while z
refers to the number of Y molecules that interact with the
anion [22]. Although DESs differ slightly from traditional
Many nations’ economic growth and national security
depend on the reliable supply and durability of these vital
resources[4]. Rare earth element availability is currently
less than demand [5], [6], with imports from China fre-
quently accounting for a large portion of the supply[7].
Today, many critical metals that are needed by the US and
other industrialized countries are sourced from outside [8].
China provides a significant portion of the rare earth (RE)
supply imported by the US [5]. The United States is seek-
ing to expand domestic production and recover rare earth
elements (REs) from various sources to reduce supply chain
vulnerability, given the significance of these minerals in
technological and economic advancement [4], [9].
Neodymium and samarium, two rare elements among
the REEs are the foundational elements for making power-
ful permanent magnets [10]. The most prevalent kind of
RE magnets are Nd-Fe-B magnets[11]. Since neodymium-
iron-boron (NdFeB) magnets primarily replaced SmCo
magnets after 1985 [12], the market share of SmCo mag-
nets is currently less than 2% in the permanent magnet
segment [12], [13]. Nonetheless, new applications in con-
sumer electronics, automotive and medical technology,
aerospace, and military equipment are driving growth in
the global market for SmCo magnets. Due to their greater
optimal operating temperature (250–350°C) than that of
NdFeB magnets (60, 220°C), SmCo magnets are still val-
ued for their capacity to operate at high temperatures and
are frequently utilized in the aviation industry [13], [14].
Samarium is utilized in the filter glass of Nd (Neodymium):
YAG (Yttrium–Aluminium–Garnet) solid-state lasers to
encircle the laser rod and increase efficiency by collecting
stray emissions due to its narrow spectral absorption band
[15]. At microwave frequencies, samarium can be used in
coatings and capacitors because it forms stable titanate
compounds with beneficial dielectric characteristics[15].
Cobalt and samarium can be obtained from End-of-life
SmCo magnets as valuable secondary sources [13].
It is challenging to mine REEs since they are fre-
quently found in very small concentrations [5]. Extraction
and separation of REEs from their complex ore are very
difficult due to their unique physical and chemical prop-
erties process, thereby making them scarce in the market
[1]. Currently, the recovery of REEs involves the traditional
pyro- or hydrometallurgical process [16]. The pyrometal-
lurgical method suffers from environmental concerns such
as gaseous emissions while the traditional hydrometallurgi-
cal process involves the use of dilute and strong acids to
dissolve REE evolve hydrogen gas [15], [17].
The overall process in the recovery and separation of
individual elements from complex REE systems suffers
from high energy demands as it requires complex energy-
consuming solutions with the use of many hazardous
chemicals that negatively impact the environment [5]. In
response to the scarcity of these REEs and their potential
supply risk recent research has focused on improving recov-
ery and separation techniques as well as developing recy-
cling approaches for secondary resources like mine tailings
and electronic waste as alternative sources to natural ores
[12], [13]. The evolution of recycling processes as a sec-
ondary source for REEs has seen the majority of rare-earth
magnet recycling research concentrated on NdFeB magnet
recycling [18], [19], [20] with little attention to SmCo
magnet recycling [7]. However, the recycling of SmCo
magnets will not only be a secondary source for samarium
but also cobalt a critical metal that is economically very
important for the steel industry [13], [21] due to its unique
resistance to oxidation and its usage in cathode materials
for lithium-ion batteries which is very crucial to the transi-
tion to electric vehicles [13].
With the growing trend toward a circular economy
aiming to balance sustainability, efficiency, and environ-
mental impacts, this research is focused on recycling SmCo
magnets using green (ionometallurgy), smart, and novel
extraction pathways. That is the use of Deep Eutectic
Solvents (DESs) for leaching and novel Resodyn Acoustic
Mixing (RAM) for intensification of the leaching process.
DESs are systems formed from eutectic mixtures of
Lewis or Brønsted acids and bases, which can contain a
variety of anionic and cationic species[22]. The eutectic
combinations have melting points lower than their compo-
nents, giving a room-temperature ionic liquid [23]. They
are liquid at temperatures lower than 150 °C, but most are
liquid between room temperatures and 70 °C [24]. The
advantages DESs have over conventional hydrometallur-
gical reagents are that they are environmentally benign or
have minimal risk and environmental impacts, are readily
available in larger quantities, are cost-efficient, and chemi-
cally stable to allow prolonged reuse, and are able to do
selective leaching. The major difference between hydro-
metallurgy and ionometallurgy is that the latter uses non-
aqueous solvents.
DES is typically created by combining a quaternary
ammonium salt with metal salts or a hydrogen bond donor
(HBD) that can form a complex with the quaternary
ammonium salt’s halide anion. DESs are defined using the
general formula Cat+X–zY where Cat+ is an ammonium,
phosphonium, or sulfonium cation, and X is a Lewis base,
a halide anion generally and Y is a Brønsted acid while z
refers to the number of Y molecules that interact with the
anion [22]. Although DESs differ slightly from traditional