XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1371
as monazite, but with higher HREE (yttrium) content. The
overall REO content of xenotime is approximately 67%
(Gupta and Krishnamurthy 2005). However, there is no
published literature describing the recovery of REEs from
xenotime using scCO2 extraction to date.
Secondary Sources
Secondary sources refer to recycled or reused materials that
contain REEs. These sources can include electronic waste,
magnets, batteries, and industrial waste streams and have
become increasingly important sources of REEs, particu-
larly due to the limited accessibly and economic viability
of primary sources (Binnemans, Jones et al. 2013). Urban
mining of end-of-life products is advantageous to an envi-
ronmentally sustainable approach to sourcing REEs as it
reduces the scarcity of REE supply and diminishes the vol-
ume of landfill waste. Applying green scCO2 extraction
technology to the secondary sources mitigates environmen-
tal and health concerns regarding using traditional hazard-
ous solvents and producing toxic wastes.
Fluorescent lamp waste. The use of fluorescent light-
ing (FLs) has been dominating the market due to its energy
conservation advantage, with a 75% energy consumption
reduction compared to incandescent lights. These FLs
comparatively also have an increased life expectancy. The
increase in usage has resulted in growing waste stockpiles
of FLs. Rare earth elements are widely used as functional
material within these lamps, and currently, FLs are being
investigated as a secondary source of REEs, with up to
28% of the FL phosphors by weight being REEs in a more
concentrated abundance than primary ore sources (Zhang,
Anawati et al. 2022).
The investigation of FL lamps has previously been not
considered practical due to a lack of available processing
methods however, SFE technology has enabled the expan-
sion of extraction capacity for REEs. Experimental studies
such as Shimizu et al. and Zhang et al. have demonstrated
the use of SFE to achieve selective extraction of yttrium (Y)
and europium (Eu) from the FL phosphors containing a
mixture of various complex REE-containing compounds,
including red phosphors, green phosphors and blue phos-
phors. The literature also showed that SFE was less selective
to extract lanthanum (La), terbium (Tb) and cerium (Ce)
(Shimizu, Sawada et al. 2005, Zhang, Anawati et al. 2022).
Shimizu et al. reported that the REE content within the
FL was – Y – 29.6%, Eu – 2.3%, La – 10.6%, Ce 5.0%, Tb
2.6% while Zhang et al. also reported similar contents with
exception to the larger weight of Y to be 41.2% (Shimizu,
Sawada et al. 2005, Zhang, Anawati et al. 2022). From these
studies, it has been identified that this secondary feed is
more consistent with its feed of REE ratios hence this may
enable the extraction process conditions to be optimised
to suit most FL feed sources to produce reliable extraction
efficiency of REEs. This reflects that waste phosphors are a
potentially significant secondary feed source with relative
certainty of feed material characteristics (Shimizu, Sawada
et al. 2005).
Nickel-metal hydride battery. Spent nickel metal
hydride (NiMH) batteries are the most efficient recharge-
able batteries on the market and play a fundamental role in
hybrid electric cars. The use of hybrid cars is growing trac-
tion due to their environmental advantages, inadvertently
driving the production of NiMH batteries. Rare earth ele-
ments account for 33% of the weight of these batteries,
which is a viable REE source. Currently, Umicore, Japan
Metals &Chemicals Co, and Honda Motor Co. Ltd are
processing recycled spent NiMH batteries utilising conven-
tional hydrometallurgical methods resulting in alloy prod-
ucts containing base metals and REOs. The amenability of
this feed source to SFE has been experimentally explored
by Yao and co-authors, who reported recovery efficiencies
of La (86%), Ce (86%), Pr (88%), and Nd (90%) at 35 °C
and under 31.0 Mpa (Yao, Farac et al. 2018).
Neodymium-iron-boron magnets. Neodymium-
iron-boron magnets, also known as NdFeB magnets, are
the strongest permanent magnets currently available in the
market. They are made from a combination of neodymium,
iron, and boron, and are often coated in nickel or zinc to
prevent corrosion. NdFeB magnets are a crucial compo-
nent in modern technology with the use having a tie to the
increasing global focus on reducing greenhouse gas emis-
sions with their use in wind turbines and electronic cars.
Investing in these technologies that provide cleaner energy
production and consumption options, evidently increases
the use and production of NdFeB magnets.
Pyrometallurgy and hydrometallurgy are traditional
methods of recycling the materials in NdFeB magnets,
however scCO2 extraction has been investigated to recover
Nd as an alternative green technique recently. The magnets
contain approximately 22–33% by weight REEs which
is higher in concentration than primary sources, making
them a desirable source of REEs (Zhang, Anawati et al.
2018, Reisdörfer, Bertuol et al. 2020). In addition, NdFeB
magnets require pre-treatment to demagnetise, remove
external coating and reduce particle size prior to scCO2
extraction. The recovery of REEs from NdFeB magnets by
scCO2 extraction is summarised in Table 1.
as monazite, but with higher HREE (yttrium) content. The
overall REO content of xenotime is approximately 67%
(Gupta and Krishnamurthy 2005). However, there is no
published literature describing the recovery of REEs from
xenotime using scCO2 extraction to date.
Secondary Sources
Secondary sources refer to recycled or reused materials that
contain REEs. These sources can include electronic waste,
magnets, batteries, and industrial waste streams and have
become increasingly important sources of REEs, particu-
larly due to the limited accessibly and economic viability
of primary sources (Binnemans, Jones et al. 2013). Urban
mining of end-of-life products is advantageous to an envi-
ronmentally sustainable approach to sourcing REEs as it
reduces the scarcity of REE supply and diminishes the vol-
ume of landfill waste. Applying green scCO2 extraction
technology to the secondary sources mitigates environmen-
tal and health concerns regarding using traditional hazard-
ous solvents and producing toxic wastes.
Fluorescent lamp waste. The use of fluorescent light-
ing (FLs) has been dominating the market due to its energy
conservation advantage, with a 75% energy consumption
reduction compared to incandescent lights. These FLs
comparatively also have an increased life expectancy. The
increase in usage has resulted in growing waste stockpiles
of FLs. Rare earth elements are widely used as functional
material within these lamps, and currently, FLs are being
investigated as a secondary source of REEs, with up to
28% of the FL phosphors by weight being REEs in a more
concentrated abundance than primary ore sources (Zhang,
Anawati et al. 2022).
The investigation of FL lamps has previously been not
considered practical due to a lack of available processing
methods however, SFE technology has enabled the expan-
sion of extraction capacity for REEs. Experimental studies
such as Shimizu et al. and Zhang et al. have demonstrated
the use of SFE to achieve selective extraction of yttrium (Y)
and europium (Eu) from the FL phosphors containing a
mixture of various complex REE-containing compounds,
including red phosphors, green phosphors and blue phos-
phors. The literature also showed that SFE was less selective
to extract lanthanum (La), terbium (Tb) and cerium (Ce)
(Shimizu, Sawada et al. 2005, Zhang, Anawati et al. 2022).
Shimizu et al. reported that the REE content within the
FL was – Y – 29.6%, Eu – 2.3%, La – 10.6%, Ce 5.0%, Tb
2.6% while Zhang et al. also reported similar contents with
exception to the larger weight of Y to be 41.2% (Shimizu,
Sawada et al. 2005, Zhang, Anawati et al. 2022). From these
studies, it has been identified that this secondary feed is
more consistent with its feed of REE ratios hence this may
enable the extraction process conditions to be optimised
to suit most FL feed sources to produce reliable extraction
efficiency of REEs. This reflects that waste phosphors are a
potentially significant secondary feed source with relative
certainty of feed material characteristics (Shimizu, Sawada
et al. 2005).
Nickel-metal hydride battery. Spent nickel metal
hydride (NiMH) batteries are the most efficient recharge-
able batteries on the market and play a fundamental role in
hybrid electric cars. The use of hybrid cars is growing trac-
tion due to their environmental advantages, inadvertently
driving the production of NiMH batteries. Rare earth ele-
ments account for 33% of the weight of these batteries,
which is a viable REE source. Currently, Umicore, Japan
Metals &Chemicals Co, and Honda Motor Co. Ltd are
processing recycled spent NiMH batteries utilising conven-
tional hydrometallurgical methods resulting in alloy prod-
ucts containing base metals and REOs. The amenability of
this feed source to SFE has been experimentally explored
by Yao and co-authors, who reported recovery efficiencies
of La (86%), Ce (86%), Pr (88%), and Nd (90%) at 35 °C
and under 31.0 Mpa (Yao, Farac et al. 2018).
Neodymium-iron-boron magnets. Neodymium-
iron-boron magnets, also known as NdFeB magnets, are
the strongest permanent magnets currently available in the
market. They are made from a combination of neodymium,
iron, and boron, and are often coated in nickel or zinc to
prevent corrosion. NdFeB magnets are a crucial compo-
nent in modern technology with the use having a tie to the
increasing global focus on reducing greenhouse gas emis-
sions with their use in wind turbines and electronic cars.
Investing in these technologies that provide cleaner energy
production and consumption options, evidently increases
the use and production of NdFeB magnets.
Pyrometallurgy and hydrometallurgy are traditional
methods of recycling the materials in NdFeB magnets,
however scCO2 extraction has been investigated to recover
Nd as an alternative green technique recently. The magnets
contain approximately 22–33% by weight REEs which
is higher in concentration than primary sources, making
them a desirable source of REEs (Zhang, Anawati et al.
2018, Reisdörfer, Bertuol et al. 2020). In addition, NdFeB
magnets require pre-treatment to demagnetise, remove
external coating and reduce particle size prior to scCO2
extraction. The recovery of REEs from NdFeB magnets by
scCO2 extraction is summarised in Table 1.