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Citation: Filho, W.L.; Kotter, R.;
Özuyar, P.G.; Abubakar, I.R.;
Eustachio, J.H.P.P.; Matandirotya,
N.R. Understanding Rare Earth
Elements as Critical Raw Materials.
Sustainability 2023,15, 1919. https://
doi.org/10.3390/su15031919
Academic Editor: Changhyun Roh
Received: 6 October 2022
Revised: 16 January 2023
Accepted: 17 January 2023
Published: 19 January 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
sustainability
Article
Understanding Rare Earth Elements as Critical Raw Materials
Walter Leal Filho 1,2,* , Richard Kotter 3, Pinar Gökçin Özuyar 4, Ismaila Rimi Abubakar 5,
João Henrique Paulino Pires Eustachio 1,6 and Newton R. Matandirotya 7,8
1Department of Natural Sciences, Manchester Metropolitan University, Manchester M15 6BH, UK
2European School of Sustainability Science and Research, Hamburg University of Applied Sciences,
Ulmenliet 20, D-21033 Hamburg, Germany
3Department of Geography and Environmental Sciences, Northumbria University,
Newcastle upon Tyne NE1 8ST, UK
4Department of Business Administration, Bahçe¸sehir University, 34349 Istanbul, Turkey
5College of Architecture and Planning, Imam Abdulrahman Bin Faisal University (Formerly, University of
Dammam), Dammam P.O. Box 1982, Saudi Arabia
6School of Economics, Business Administration and Accounting at Ribeirão Preto, University of São
Paulo (USP), Avenida dos Bandeirantes 3900, Ribeirão Preto 14040–905, São Paulo, Brazil
7Centre for Climate Change Adaptation and Resilience, Kgotso Development Trust,
Beitbridge P.O. Box 5, Zimbabwe
8
Department of Geosciences, Faculty of Science, Nelson Mandela University, Port Elizabeth 6000, South Africa
*Correspondence: w.leal@mmu.ac.uk
Abstract:
The boom in technological advances in recent decades has led to increased demand for rare
earth elements (REEs) (also known as rare earth metals) across various industries with wide-ranging
industrial applications, including in the clean energy sector, but with some environmental, economic,
and social footprint concerns. This paper reviews the complexities of the production, consumption,
and reuse or recovery of REEs, presenting current trends in terms of potentials and challenges
associated with this. This paper in particular focuses on the supply, demand, and (environmental
and economic) sustainability of REEs, as a subset of critical raw materials. It does so via a critical
stocktaking of key discussions and debates in the field over the past 15 years up until now, through
a thematic analysis of the published and gray (policy) literature with a grounded theory approach.
The paper finds that carefully balanced lifecycle sustainability assessments are needed for assessing
the respective dimensions of the extraction, processing, and reuse or recovery methods for different
types of REE sources and supplies to meet current and future demands. It furthermore diagnoses
the need for taking into account some shifts and substitutions among REEs also for reasons of cost
and locational supplies for the security of supply. Finally, the paper provides some overall policy
recommendations for addressing current problems, with a conceptual framing of the UN Sustainable
Development Goals.
Keywords:
rare earth elements; critical raw materials; supply; demand; lifecycle sustainability assess-
ment
1. Introduction: Rare Earth Elements (Rare Earth Metals) and Critical Raw Materials
1.1. Rare Earth Elements
Rare earth elements (REEs) [
1
], sometimes also referred to as rare earth metals
(REMs) [
2
] as the basis for rare earth materials [
3
], are critical to producing high technology
equipment [
4
] and for innovative technologies [
5
], often as alloys [
6
] or additives thereof [
7
],
to achieve advanced material performance characteristics [
8
]. However, although some
REEs, such as cerium, can be found relatively more often in the earth’s crust [
9
], REEs in
general are considered critical raw materials (CRMs) [
10
], alongside some other strategic
mineral resources, such as cobalt, lithium, tellurium, and nickel [
11
]. These can be listed
as follows: scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium
Sustainability 2023,15, 1919. https://doi.org/10.3390/su15031919 https://www.mdpi.com/journal/sustainability
Sustainability 2023,15, 1919 2 of 18
(Nd), promethium (Pm), samarium (Sm), europium (Eu), yttrium (Y), gadolinium (Gd),
terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), ytterbium (Yb), lutetium (Lu),
and thulium (Tm) [
12
]. From 2017 onwards, in an increasingly systematic fashion, the Eu-
ropean Commission [
13
,
14
], for instance, has been developing the availability, accessibility,
and criticality assessment of critical raw materials and has included REEs in that context.
There are 17 REEs that are grouped for their similar chemical and physical proper-
ties [
15
], 8 in the light REEs category, and 7 in the heavy REEs category [
8
]. These materials
consist of 15 lanthanides, plus scandium and yttrium. Source [
16
] notes that the Interna-
tional Union of Pure and Applied Chemistry (IUPAC) considers the elements from La to
Eu as light REEs and those from Gd to Lu and Y as heavy ones. In contrast, in Europe,
the elements from La to Sm are often grouped as light ones and Eu to Lu plus Y as heavy
ones; in China, Sm is considered a heavy REE. The classification of Gd varies between
the two groups, according to IUPAC and the United States Geological Survey (USGS) [
17
].
Furthermore, Sc is also often not described as an REE and is often treated separately as
an element [16].
1.2. Relative Geological Abundance of REEs
Notwithstanding the label, REEs are moderately abundant (except for Pm), often more
so than critical metals (e.g., copper). REEs are considered rare thanks to the comparatively
low quantities of them in locations that support economical mining [
17
]. REEs are frequently
also denominated as “rare earth oxides”, currently the predominant way they are traded.
Heavy REEs are less common and may be more valued and sought, though this also
depends on use forms, material intensity, and substitution cases.
REEs are neither particularly geologically rare or present only in limited deposits.
These range from bastnäsite to monozites in quite a few countries and continents, but also,
especially for heavy rare earths, apatites, cheralites, eudialytes, loparites, and phospho-
rites. The latter are sedimentary marine phosphate deposits, which are relatively easily
extractable by dissolving them in diluted sulfuric acid to obtain all the REEs in there. REEs
are also found in rare earth–bearing (ion-absorption) clays, where REEs can be relatively
easily extracted in a trivalent cationic state via surface/mountaintop mining, followed by
leaching [
18
] and then using ion exchangers, secondary monazite, spend uranium solution,
and xenotime. REEs typically do not geologically occur as individual elements but instead
in differing (and often low) concentrations in ore-accessory minerals. Igneous rocks (alka-
line ones and carbonatites) and metamorphic rocks are their classic sources, but there is an
increasing interest in sedimentary rocks. Residual deposits from pegmatites and iron oxide
copper-gold nickel laterites may also hold interesting concentrates in some cases [19].
1.3. Economically Relevant Geological Deposits of REEs and Accessing Them
Even though there are over 250 minerals that may contain REEs, in principle, eco-
nomically interesting concentrations for (at least official) profitable mining are found pre-
dominantly in carbonatites, alkaline igneous settings, ion-absorption clays, and monazite-
xenotime-bearing placer deposits as a result of deep weathering and fluvial processes.
REEs are found as solid minerals [
20
], frequently with radioactive traces of uranium and
thorium [
17
] with both potential yield interests here [
21
], but also with potentially more
challenging handling associated with them because of those traces [
22
]. Overall, these have
also been termed strategic minerals [11].
The primary extraction process of REEs (or primary resources, as opposed to secondary
ones from recycling) can vary from open or surface mining, underground mining, or
leaching on site, each of which has a different landscape and different environmental, cost,
and safety implications, and they will leave byproducts and mine tailings in different ways.
Currently, REEs predominantly come from open mining as a byproduct of other mining
operations. As REEs are not geologically found in their isolated element form, separation
and purification are required. This is typically performed on rare earth oxides through
extensive and resource-intensive processing involving mechanical, flotation, chemical, and
Sustainability 2023,15, 1919 3 of 18
thermal steps [
21
]. After mining REEs must undergo several water-, chemical-, and energy-
intensive steps for processing, from crushing, milling, cracking, and separation through
froth flotation into dissolved concentrates in the first phases. Then purification is necessary,
involving several complex chemical reactions to either produce rare earth oxides [
21
] or to
merge those with other elements to produce either metals [22] or alloys [19].
1.4. Notable Supply Chain Risks of REEs
REEs, along with other critical resource materials (CRMs), have high risks associated
with their supply chains [
23
] and have unique properties that are often difficult to replace
or duplicate by using modern technology [
24
] or conventional methods [
25
]. According
to the European Commission [
14
], CRMs are important for many industries across all
their supply chains thanks to their relevance to modern technology (e.g., electric motors,
intelligent household applications) and the quality of life based on that and for a clean
technology–based future: they are currently irreplaceable, for instance, in solar panels;
wind turbines; electric batteries and electric vehicles; automotive catalysts; energy-efficient
lighting; liquid-crystal displays for mobile phones, computers, and television sets; glass
additives and ceramics; metallurgy; phosphors; and polishing powders.
REEs can become commercially scarce or potentially problematic because of supply
restrictions (e.g., for economic production considerations or potential export restrictions
by producing countries for domestic national consumption priorities) [
26
], geopolitical
reasons, or substantially increased demand in regional markets [
9
]. Furthermore, some
of the REEs can also cause significant corporate social responsibility headaches for multi-
national companies because of, in some countries severe, conflict/human rights issues,
such as the forced displacement of (what can be indigenous) communities, unsafe labor
conditions, and the at times environmentally harmful features of mining/production as
well as not yet fully solved waste hierarchy (avoid, reuse, recycle) issues at the production
and consumptions ends [21].
Globally, China is still the leading producer of REEs in the world [
14
], followed a long
way behind by the US, Myanmar, Australia, Madagascar, India [
27
], Russia, Thailand, Viet-
nam, and Brazil [
28
], but there are variations in terms of key countries depending on which
REEs and CRMs are focused on. There are some further possibilities of producing critical
raw materials, including rare earth elements, from primary resource sources in Europe [
29
].
1.5. Prominent Use Fields of REEs
REEs are used in the production of storage batteries, radar (and radiography) instru-
ments, portable electronics (such as smart phones), advanced television sets, different kinds
of electric vehicles (both light and heavy), energy systems, and permanent magnets, among
others. Table 1describes some of the ways they are used. As the problems of climate
change and the pressure on sustainability responses grow, REEs are expected to receive
more attention for the production of solar panels, electric motors, (hybrid, full battery,
and fuel cell) electric vehicles and their batteries, wind turbines and their systems, and
other energy systems [
7
], and they remain important as catalysts and ingredients in many
domains (including petroleum refining, specialty steel, the glass and lighting industries,
and the aerospace and defense industries) [17].
Table 1. REEs and their usages.
Name Usage Reference
Light REEs
Scandium (Sc)
As alloy additive in aluminum-based products
(such as Al-Mg alloys) for strength. In
“super-alloys”, such as in steel. Additionally, in
NiMH batteries.
[6,19]
Sustainability 2023,15, 1919 4 of 18
Table 1. Cont.
Name Usage Reference
Lanthanum (La)
In optics and lighting (e.g., lasers, LEDs, and
fluorescent lamps, though these are being phased
out), and more specifically in carbon lighting.
Capacitors, sensors, and semiconductors.
Additionally, in NiMH batteries, and super-alloys,
AL-Mg alloys, and steel. Flat display electronics.
X-ray imagining. Petroleum refining, automotive
catalysts, and diesel additives. Water treatments.
Fuel cells. Polishing colorants.
[19,30]
Cerium (Ce)
The catalyst for lighters. In carbon arc lighting. For
glass polishing. In NiMH batteries, super-alloys,
AL-Mg alloys, and steel. Flat display electronics.
X-ray imagining. In capacitors, sensors, and
semiconductors. Petroleum refining, automotive
catalysts (converters), and diesel additives. Water
treatments. Fuel cells. Polishing colorants.
[19,31]
Praseodymium (Pr)
In alloys for aircraft engines. In motors and
generators more widely. For NdFeB magnets in
lieu of Nd. In NiMH batteries, super-alloys,
AL-Mg alloys, and steel. Magnetic resonance
imaging (MRI) contrasting agents. In capacitors,
sensors, and semiconductors. In flat display
electronics. In addition, for X-ray and MRI
imagining. In HD drives, microphones, and
speakers. For petroleum refining, automotive
catalysts, and additives. For water treatments. In
fuel cells. For polishing colorants.
[19,26,32]
Neodymium (Nd)
Production of magnets incorporated into
electronics, such as computers and cell phones.
The basic element for the NdFeB magnets. It is
widely used in many vehicle components, such as
motors, brakes, speakers, doors, windows, and air
conditioners. In NiMH batteries, super-alloys,
AL-Mg alloys, and steel. Magnetic resonance
imaging (MRI) contrasting agents. Also in HD
drives, microphones, and speakers.
[19,26,33,34]
Promethium (Pm) To produce atomic batteries incorporated into
pacemakers and satellites. [35]
Samarium (Sm) In optical lasers. [36]
Europium (Eu)
The most reactive REM and not so widely used.
May be used in lasers. Flat display electronics.
X-ray imagining. Capacitors, sensors, and
semiconductors. In addition, in NiMH batteries,
super-alloys, AL-Mg alloys, and steel. Flat display
electronics. Petroleum refining, automotive
catalysts, and diesel additives. Water treatments.
Fuel cells. Polishing colorants. Fluorescent
powders are used in lighting equipment, though
this is being phased out by LED.
[19,26,37]
Sustainability 2023,15, 1919 5 of 18
Table 1. Cont.
Name Usage Reference
Heavy REEs
Yttrium (Y)
As additive alloys (mostly with aluminum and
magnesium) to increase the strength of materials.
Can be used to produce YVO
4
europium and Y
2
O
3
europium phosphors and gives the red color in
color television sets. Flat display electronics. X-ray
imagining. Fluorescent powders in lighting
equipment, though this is being phased out
by LED.
[19,26,38,39]
Gadolinium (Gd)
Not widely used but may be used in alloy
production. NiMH batteries, super-alloys, AL-Mg
alloys, and steel. Flat display electronics. In HD
drives, microphones, and speakers.
In capacitors, sensors, and semiconductors. For
X-ray and MRI imagine contrasting agents. For
petroleum refining, automotive catalysts, and
diesel additives. Water treatments. Fuel cells.
Polishing colorants.
[19,40]
Terbium (Te)
Calcium fluoride, calcium tungstate, and
strontium molybdate are all used in the making of
solid-state devices. Flat display electronics. X-ray
and MRI imagining contrasting agents. In HD
drives, microphones, and speakers.
[19,41]
Dysprosium (Dy)
The basic element in NdFeB magnets for a range of
vehicle components. May feature in nuclear
reactors. May be combined with other REEs in
laser material. For magnetic resonance imaging
(MRI) contrasting agents. In HD drives,
microphones, and speakers.
[19,26,42]
Holmium (Ho)
In laser production. In capacitors, sensors, and
semiconductors. In NiMH batteries, super-alloys,
AL-Mg alloys, and steel. Flat display electronics.
X-ray imagining. Petroleum refining, automotive
catalysts, diesel additives. Water treatments. Fuel
cells. Polishing colorants.
[19,43]
Erbium (Er) During optical fiber production. [44]
Ytterbium (Yb) May be used in memory devices and lasers.
Furthermore, as an industrial catalyst. [45]
Lutetium (Lu) As a catalyst for cracking hydrocarbons in oil
refineries and the petroleum industry. [46]
Thulium
(Tm)
The least abundant REM. May be used in X-ray
machines. Has the potential as an energy source. [47]
2. Methodology
For this paper, the authors used a systematic literature review [
48
], with a number
of critical key words (“rare earth elements”, “rare earth metals”, “critical raw resources”,
“renewable energy”, “supply”, “demand”, “sustainability”, “markets”, “trade”, “tech-
nology”) adopted in a bibliographic search on scientific indexes/web engines of studies
[Science Direct, Scopus, Google Scholar]. The abstracts of those papers were first scanned
for relevance, and if they appeared to be within the scope of the investigation, the full paper
was scrutinized. Because China acted as the then (and still) dominant market player in
producing and exporting REEs, in 2010 it imposed some export restrictions [
49
]. As per
the lead-in time of impacts, academic scrutiny, and academic publishing take about three
Sustainability 2023,15, 1919 6 of 18
years to be reflected in the peer-reviewed literature debate. Therefore, the authors chose
to favor papers from 2013 onwards; they also favored more-recently published papers
by authors who have published multiple works on the subject and favored very recently
published papers because trends, pressure points, and potential strategies and management
options are discussed in them and because of their state-of-the-art and contemporaneous
applicability. The framing here stretched from applied geology, resource economics, and
political economy to environmental sciences, and some directly pertained to policy fields.
The abstracts of papers and the summary descriptions of edited books or monographs were
preliminarily assessed for whether they met the inclusion criteria, namely covering REEs at
the center of a much wider set of metals, minerals, and critical resources.
In terms of data analysis, a grounded theory approach was employed so as to under-
stand and analyze the data collected from the published literature (articles, book chapters,
monographs, reports, and directly pertaining industry analysis media). Although it is a
flexible (and iterative) method, it is also a complex one and does not have a rigid framework;
it can thus be tailored to a particular research project. The following steps were involved
(see Figure 1): the sampling and thematically coding of the data; reviewing the emerging
patterns of discussions (agreement and disagreements); familiarization with deeper points
made by the respective authors; and clustering them to the point of saturation.
Sustainability 2023, 15, x FOR PEER REVIEW 6 of 19
years to be reflected in the peer-reviewed literature debate. Therefore, the authors chose
to favor papers from 2013 onwards; they also favored more-recently published papers by
authors who have published multiple works on the subject and favored very recently pub-
lished papers because trends, pressure points, and potential strategies and management
options are discussed in them and because of their state-of-the-art and contemporaneous
applicability. The framing here stretched from applied geology, resource economics, and
political economy to environmental sciences, and some directly pertained to policy fields.
The abstracts of papers and the summary descriptions of edited books or monographs
were preliminarily assessed for whether they met the inclusion criteria, namely covering
REEs at the center of a much wider set of metals, minerals, and critical resources.
In terms of data analysis, a grounded theory approach was employed so as to under-
stand and analyze the data collected from the published literature (articles, book chapters,
monographs, reports, and directly pertaining industry analysis media). Although it is a
flexible (and iterative) method, it is also a complex one and does not have a rigid frame-
work; it can thus be tailored to a particular research project. The following steps were
involved (see Figure 1): the sampling and thematically coding of the data; reviewing the
emerging patterns of discussions (agreement and disagreements); familiarization with
deeper points made by the respective authors; and clustering them to the point of satura-
tion.
Figure 1. Flowchart of selecting articles/chapters/books coming into the sample frame (source: au-
thors).
Figure 1.
Flowchart of selecting articles/chapters/books coming into the sample frame
(source: authors).
Sustainability 2023,15, 1919 7 of 18
3. Results and Discussion: The Problems in Supply and Demand
While there are considerable agreements among the sampled literature (English-
language only), there are at the same time diverging assessments and emphases. These
concern multiple themes, including market concentration; parts of the production and
value chains to be concerned about, as well as national or international perspectives, which
forms of and actions within public policy (on balance) ought to be pursued by a range of
concerned players (at sometimes local/regional levels but often mostly at the national level,
with room or development for the international levels of governance, though the EU level
is flagged up here within the external multinational/internal single common market), and
finally which different methodological or focused takes on (aspects of) sustainability. The
yield from the systematic review is summarized in Table 2.
Table 2. Themes emerging from the (sampled) literature (source: authors).
REEs are not geologically rare
but there are varied legislation/regulatory and
financial barriers to accessing them.
Different REEs can be mined/extracted in
various forms and by various processes
and these have different
environmental/pollution profiles and thus
different lifecycle sustainability ones too.
There are active assets and active reserves and
those that could be activated,
and there could be further reserves, based on
indications from geological
explorative indicators.
There is some differential geographical/spatial
concentration in REEs, but typically with
alternatives in several countries and continents.
The activation and use (domestically and or for
export to developing countries/world markets)
depends in part on national policy instruments
(which may change over time) as well as
insertion of REEs suppliers and processors into
downstream value chain activities.
The role of the state can be quite critical,
including as a (political or commercial) partner
for the private sectors (or in some cases
through state ownership), as a regulator, and as
an actor involved in encouraging
benchmarking to standards
but the role of both multinational and national
corporations in crucial in investment, processes,
technological innovations, and compliance to
(perhaps changing) regulations (including
environmental) or activities to ensure enhanced
corporate social responsibility/environmental,
social and governance perfor-
mance/reporting/accountability/brand image.
Sourcing from secondary sources, i.e., reuse
and recycling, can be seen as
increasingly promising
but also needs to be seen in the context of
efficiency and needs to be subjected to lifecycle
sustainability assessments.
The two sections below summarize in more detail the supply and demand prob-
lems of REEs.
3.1. Demand-Side Issues
REEs are increasingly needed in industrial ecosystems such as the automotive, renew-
able energy, high-capacity battery, defense, aerospace [
50
], and other industries that are
putting efforts into developing high-tech devices.
The boom in technological advances in recent decades has led to increased demand for
critical raw materials and rare earth elements across various industries, with wide-ranging
applications [
12
] from the high-tech industry [
17
], defense industry, chemical catalyst,
telecommunications (fiber optic cables, cell phones), electric car rechargeable batteries,
silicon chips, medical applications, wind turbines, and LED lights [
51
]. The manufacturing
industry’s need for REEs (with regard, for instance, to permanent magnets, polishing, and
alloy making) with the emergence of green energy is connected to an increase in demand
for solar panels [
12
], chips [
17
], and smart batteries for alternative energy vehicles [
52
].
Sustainability 2023,15, 1919 8 of 18
The fourth industrial revolution is also adding more pressure on the demand for REEs
as more supercomputers with higher processing capabilities, robots, and other artificial
intelligence accessories are needed. In 2019, estimates were that the global cell phone sales
stood at USD 400 billion [
51
], with projections estimating an upward trajectory in demand
being driven mostly by the diversification toward green energy and electric vehicles [
17
].
Furthermore, the REE market is also projected toward growth from USD 5.3 billion (2021)
to USD 9.6 billion by 2026 at an anticipated annual growth rate of 12.3% [
53
]. It is also
further projected that there will be significant demand growth for neodymium oxide, which
is key in the production of magnets placed in electric vehicles, wind turbines, computer
hard drives, and planes [
17
]. By 2020, the price per metric ton of neodymium oxide was
USD 49,763; in 2025, it is expected to reach USD 77,500 per metric ton [17].
The automotive sector will likely need more REEs, as the traditional gasoline- and
diesel-powered vehicle production will still require REEs (particularly Nd, Y, Ce, Eu, and
Te), while the production of electric vehicles will push the demand for these materials
(especially dysprosium and neodymium) because of the importance of neodymium magnets
used in electric batteries, especially in the form of the alloy NdFeB. With the addition of Dy,
NdFeB can also resist demagnetization at high temperatures. Many electric vehicle batteries
also contain Ce and La [
21
]. Source [
26
] diagnoses, on the basis of scenario studies for
the electrification (hybrid, plugin hybrid, battery and fuel cell electric vehicles) of China’s
automotive industry, that Nd, Dy, Ce, Pr, and La will increasingly be sought after (with,
e.g., Nd and Dy normally in all NdFeB magnets), with the stress of balancing supply and
demand for Dy and Pr intensifying. The intensity of this will depend on technological
pathways. For instance, La and Ce (the main raw materials of NiMh batteries) optimize
hydrogen storage. Source [
26
] also projects that in addition to the high demand for Ce in
hybrid electric vehicles for NiMh batteries, automobile exhaust catalytic converters will
increase the demand for it in hybrid and plugin hybrid electric vehicles. They also point
to studies by [
54
] for the increased demand for driving motors and the NiMh battery of
hybrid electric vehicles in Japan by 2030 (with significant recovery potentials), as well
as [
55
] in terms of an increased demand for REEs contained in magnets, batteries, and
fluorescent powders.
The growing importance of renewable technologies is also among the main factors that
are increasing the demand for REEs in the sector, because they are important elements for
the wind power industry for the production of turbines using Nd, Pr, and Dy and for the
production of solar panels (indium, selenium, and tellurium) [
51
]. Therefore, the recycling
of RE-containing products will have to be explored to ease some of the longer-term supply
issues of REEs.
The end form in which REEs are traded (as oxides, metal, and alloys or in powders)
depends on the industrial application and has shifted with changing industrial demand
over the recent decades, with REE magnets, phosphors, and polishing powders now
dominant [
21
]. For REE magnets, one of the most important application markets, alloys
of neodymium and dysprosium are frequently used so as to avoid demagnetization at
high temperatures, which is critical for devices such as laptops and tablets, TV screens,
mobile phones, portable DVD players, and disc drives, which generate heat. In medical
fields, devices such as X-ray and MRI equipment contain REEs, and in the military domain,
for instance, fighter jet engines, missile guidance, antimissile defense systems, and space-
based satellites and communication systems contain REEs. Steel, aluminum, and glass are
other industrial application domains to change their functional properties. The addition of
REEs to specialty glasses covers filters, lenses, light-sensitive and photochromic glasses,
coloring/decoloring agents, X-ray and gamma-ray absorption properties, luminescence
and fluorescence effects, and communication fibers. Innovations such as semiconductor
lasers have also been enabled by adding REEs to glasses. REEs are also used as catalysts
in many settings, such as La and Ce in the cracking of petroleum to produce gasoline [
21
].
Source [
56
] pointed out that permanent magnets with Nd, Sm, Gd, Dy, or Pr has enabled
the miniaturization of many electric/electronic components in a range of devices, and it
Sustainability 2023,15, 1919 9 of 18
noted that magnetic refrigeration enabled by REEs could become significant. Most wind
turbines contain Nd and Dy, but recycling these is only the beginning.
3.2. Supply-Side Issues
Source [
57
] argued that supply bottlenecks in countries processing and using REEs
are a result of market failures. End-user industries across the world were not in tune with
the criticality of REEs owing to the normally small share of production costs and did not
become involved in keeping mines going. Major mining companies outside China were
not focused on REEs as they have other high-volume ores to focus on. REE separation
is difficult and specialized and thus handled by smaller companies, which have more
difficulties in raising investment, and in any case, there is then a significant time lag. The
supply market failures arguably apply to both domestic consumption vs. supply and
international trade for REEs. Until 1995, the US was the biggest supplier in the world, and
China gained its near monopoly only around 2002 [
57
]. A Chinese state export-restriction
policy in 2010 from a dispute between China (domestically strengthening its technology-led
industry and investing in not just mining but also processing capabilities) and Japan (whose
advanced product exports often contain REEs) was subsequently settled when China lost a
World Trade Organization case brought against it, but it still contributed to a (short-term)
rare earths international supply crisis. Prices rose very significantly for many REEs in
2010/2011 more than ten-fold [
58
]. This in turn meant that a number of countries (Australia,
followed by the US, Canada, and, with some delay, Brazil [
59
], Malaysia, Russia, Thailand,
and Vietnam) saw the (re)opening [
60
] or expansion in established mines [
61
] and of known
and accessible reserves [
62
]. From the end of 2016, global REE prices significantly rose
again [
63
]. Sources [
16
,
64
] explain the “balance/balancing problem” between the economic
market demand (through supply chains) of REEs and their natural abundance: avoid the
over- or undersupply (production) of REEs because this would stabilize prices, reduce their
volatility, and provide more investor security. This would mean to either find new uses
for those REEs that are produced beyond current demands or substitute high-demand and
limited-supply REEs with another [
64
] or with a non-REE if at all feasible (achieving the
same or at least similar effectiveness) thanks to technological innovations [
56
]. REEs became
the key focus of innovation for geoscientists and process engineers in enterprises, R&D labs,
and universities after the price shocks of 2010/2011 to improve our understanding of the
sources and geological deposits of future reserves as well as to make primary production
and the recycling of secondary sources of REEs more efficient [
65
]. This was supplemented
by material scientists and industrial engineers working on reducing or substituting the
REE input in applications and products. Risk–value constructions matter in terms of efforts
undertaken to close loops of rare earth elements in global value chains and how this is
underpinned by (corporate as well as state) governance [66].
There is a general trend (Oddo–Harkins rule) that elements become geologically
scarcer with an increase in atomic number; furthermore, elements with an even atomic
number have more deposits than those with an odd atomic number [
56
]. Accordingly,
reserves of the light REEs, Ce or La, are much higher than those for the heavy REEs, Dy, Eu,
and Tb, though the heavy REE Y is also more abundant. This is also reflected in supplies
and prices. There can be innovation trends that help to address the REE balancing problem
and yield net environmental gains, such as using La and Ce as substitutes, where possible,
for Pr and Nd in NdFeB magnets. Similarly, rechargeable La-Ni-H are beginning to replace
Ni-Cd batteries in electronics and may perhaps eventually replace lead-acid batteries in the
(conventional) automotive sector.
The author of [
63
] is skeptical of how much China can influence, distort, or dictate
prices. China’s price advantage is argued to be predominantly from lower labor costs and
less-stringent (though increased in recent years) environmental standards; if it significantly
raised prices, this would stimulate (further) REE production in other countries. However, in
particular, the argued fragmentation of China’s producers, with many small and diversified
producers and exporters, results in disadvantages when negotiating prices with large
Sustainability 2023,15, 1919 10 of 18
international importers. The same source [
63
] points out that China is currently in a “low-
end locking dilemma” as far as international trade is concerned, with the majority of its
exports being primary materials rather than final products. Although China still has price
and regulatory competitive advantages in lower value-added processes, it is lagging behind
in the higher value-added processes. The latter is also reflected in industrial patents in
key materials (such as REE magnets). The authors of [
62
], on the other hand, comes to
different analytical results concerning the impact of China’s state policies. They see global
REE prices as largely dependent on China’s domestic policies and further consider that
international standards, Chinese imports of REEs, and global hoarding by countries and
their environmental standards negatively affect REE supply resilience.
Source [
49
] cautions that we do not know, from the outside, enough about recent
trends in consolidation into several large groups of domestic REE companies or enough
about the significant Chinese overseas investments into REEs. Furthermore, China, as in
the past, could develop different foci, e.g., extracting REEs from recycled materials from
products at the end of their lifespan and/or keeping more of this within China with rising
demand. By reviewing official Chinese policy documents, they distilled five sequentially
linked phases of Chinese REE policies that were shaped by markets and players therein,
the progression of the extractive industry, and the shape and state of the Chinese economy.
In their analysis, this started from the encouragement and development of upstream value-
adding activities in the mid1970s until the early 1990s. Following on from that, China
reoriented its focus more on the furthering of downstream processing and products, where
REEs are used in manufacturing intermediate and final commodities. From the 2000s
onward, China has put additional emphasis on addressing issues to do with environmental
impacts stemming from REE mining, processing, and production and on efforts to bring
more from all industrial production into the official and legally approved domain.
While China over the past recent decades has had a near monopoly on the production
of REEs overall [
67
], variously put at 85–95% in legal supplies (and hence ignoring the illicit
producing and smuggling of REEs), perhaps one-third of the legal production according
to [
63
], after 2010, the Chinese share declined to about 65% of oxide ores containing REEs
as REEs have been increasingly produced elsewhere. The majority of REE resources,
production, processing, and supply are currently located in Asia-Pacific [22].
Sources [
68
–
71
] argue that just now there is a new window of opportunity for non-
Chinese processors and productive industries needing REE input, because China’s domestic
demand exceeds its domestic supply. This means that China would also need to source some
REE supplies on global markets and therefore would find it less opportune to internationally
control supplies or try to keep prices very high if it can by at times strategically limiting
REE flows out of China (which they call “limit pricing”). Now would be the time for
more US, federal administration, and other Western governmental financial backers to
become more significant REE input producers via viable REE production and processing
supply chains. Furthermore, they recommend that efforts focused on long-term solutions
“should include stockpiling and recycling, increasing domestic production and refining,
and investing in joint ventures with trusted strategic partners. In order to succeed, these
ventures will require significant public investments and enduring public support”.
According to the United States Geological Survey [
6
], the worldwide production of
REEs was up between 2019 and 2020, including in the US but also Myanmar and Mada-
gascar. US import compounds and metals obtained from Estonia, Japan, and Malaysia
stemmed from concentrated minerals and chemical substances sourced from Australia,
China, etc., which points to the international supply chains. Source [
70
] showed that West-
ern green-tech companies sourcing REEs from Chinese suppliers experienced difficulties
related to environmental supply credentials with regard to both the structures of the chains
and environmental standards–related implementation issues, thus requiring the dynamic
capabilities of sensing, alignment, and resilience.
Source [
71
] considers the imbalance in REEs in terms of supply and demand as primar-
ily a self-imposed phenomenon in countries beyond China, primarily down to regulation
Sustainability 2023,15, 1919 11 of 18
barriers because thorium and uranium contain REE minerals accruing in conventional
mining in several Western countries. The same source [
71
] does see a need for additional
non-Chinese (or perhaps also Myanmar, etc.) REE resources with a corresponding em-
phasis on the further integration of REE product value chains. A recent panel regression
study [
72
] has found evidence of especially fierce international competition by advanced
economies/countries for REEs for their high-end value chains (Figure 2).
Sustainability 2023, 15, x FOR PEER REVIEW 11 of 19
stemmed from concentrated minerals and chemical substances sourced from Australia,
China, etc., which points to the international supply chains. Source [70] showed that West-
ern green-tech companies sourcing REEs from Chinese suppliers experienced difficulties
related to environmental supply credentials with regard to both the structures of the
chains and environmental standards–related implementation issues, thus requiring the
dynamic capabilities of sensing, alignment, and resilience.
Source [71] considers the imbalance in REEs in terms of supply and demand as pri-
marily a self-imposed phenomenon in countries beyond China, primarily down to regu-
lation barriers because thorium and uranium contain REE minerals accruing in conven-
tional mining in several Western countries. The same source [71] does see a need for ad-
ditional non-Chinese (or perhaps also Myanmar, etc.) REE resources with a corresponding
emphasis on the further integration of REE product value chains. A recent panel regres-
sion study [72] has found evidence of especially fierce international competition by ad-
vanced economies/countries for REEs for their high-end value chains (Figure 2).
Figure 2. Summary of demand and supply problems of REEs (source: authors).
3.3. Future Pathways
Expert-based scenario analyses for specific REEs may help to better understand the
modes and uses of specific REEs in supply chains, such as those performed for indium as
a critical metal by [73]. This is likely to be needed, for instance, for metals such as Nd.
Source [74] investigated the recycling potential of NdFeB permanent magnets, finding a
knowledge gap in the detailed amounts of Nd in wind turbines (depending on
type/model/generation, etc.), computer hard disks, and electric cars. Mobile phones are
being argued to be not viable for Nd recycling, owing to only minute concentrations in
them.
The methodological approach set out by [75] to assess the criticality of metals appears
applicable to REEs also across three broad dimensions: supply risk (geological reserves
and accessibility, active extraction, and direct and indirect factors influencing this process,
such as social, regulatory, geopolitical, technological, and economic indicators). In addi-
tion, vulnerability to supply restrictions (e.g., export and import barriers) and environ-
mental implications play roles in the process. A lifecycle sustainability assessment with a
multicriteria indicator of REEs can help in this respect, as [76] has set out, based on the
three broad dimensions of sustainable development. As the authors of [76] argue,
Figure 2. Summary of demand and supply problems of REEs (source: authors).
3.3. Future Pathways
Expert-based scenario analyses for specific REEs may help to better understand the
modes and uses of specific REEs in supply chains, such as those performed for indium
as a critical metal by [
73
]. This is likely to be needed, for instance, for metals such as
Nd. Source [
74
] investigated the recycling potential of NdFeB permanent magnets, find-
ing a knowledge gap in the detailed amounts of Nd in wind turbines (depending on
type/model/generation, etc.), computer hard disks, and electric cars. Mobile phones
are being argued to be not viable for Nd recycling, owing to only minute concentrations
in them.
The methodological approach set out by [
75
] to assess the criticality of metals appears
applicable to REEs also across three broad dimensions: supply risk (geological reserves
and accessibility, active extraction, and direct and indirect factors influencing this process,
such as social, regulatory, geopolitical, technological, and economic indicators). In addition,
vulnerability to supply restrictions (e.g., export and import barriers) and environmental
implications play roles in the process. A lifecycle sustainability assessment with a multicri-
teria indicator of REEs can help in this respect, as [
76
] has set out, based on the three broad
dimensions of sustainable development. As the authors of [
76
] argue, evaluation models
ought to be consistent across parameters and have short- vs. long-term stocks (reserves)
and backups (including substitutions and recycling/reuse) built in.
It is believed that the recycling of REEs and CRMs [
77
] can be more economical than
extraction from the source in the context of waste electrical and electronic equipment
(WEEE) [
56
] and other secondary resources [
78
]. This includes end-of-life motors [
79
] and
LED lights [
80
,
81
]. It is worth noting that the variety of final application and use forms of
REEs presents challenges for their recovery [
21
] and recycling [
82
]. However, several rare
materials have a high recycling potential, which is economically beneficial. For instance,
they can be recovered from wastewater, which has been observed in acid mine drainage
Sustainability 2023,15, 1919 12 of 18
that provides an alternative economical method to regular extraction [
83
]. There are also
possibilities from the coal-related material occurrences of REEs [72].
Source [
56
] notes the difficulties of increasing the recycling efficiency of, e.g., REEs in
batteries owing to collection issues as well as techno-economic problems associated with the
fact that they are present only in (very) low concentrations in WEEE (thanks to technological
innovations in production) [
84
] and because they play only a small part in the material blend.
Recycling routes should thus address both efficiency and environmental impacts [56].
There is now an increased interest from researchers in sustainability issues related
to the mining and treatment of REEs. Researchers who work in this field are often con-
cerned with the impacts of REEs on environmental systems and are studying the lifecycle
assessment of REEs because they can be a source of contamination in several ecological
systems [85] and generate several human-health risks [86].
Another stream that researchers are currently tackling is connected to the circular
economy strategies by understanding, for example, how it is possible to adopt the recycling,
recovering, or reusing of these elements, generating a reduction in the commercial tensions
or the dependency on these elements and teaching how the industries could use the REEs
in a more sustainable manner [
83
,
87
–
90
]. This would include recovering REE resources
from the industrial production and disposal of waste where techno-economically feasible,
with ongoing innovations in this field [19].
In the view of source [
19
], options for strategies for the more sustainable resource
management of REEs include establishing stricter standards and regulations for the indus-
try, reducing administrative barriers for reforms to the system, and cutting out illegal REE
mining through more controls.
In addition, other measures to make the use of REEs more sustainable may include
developing integrated market pricing and distribution systems for REEs rather than in-
ternational “free” trade, encouraging investment into environmental improvements in
the REE industry footprint, encouraging the participation of countries with a high annual
demand in REEs to adopt more-sustainable practices, and promoting REE recycling from
enriched wastes, end-of-life products such as consumer electronic devices [
91
], and other
mostly neglected resources.
There are ongoing trends and (dis)agreements with regard to rare earth elements
(REEs) (or rare earth metals) as a significant subset of critical minerals and critical raw
materials. A more recent trend is a detailed focus on the possibilities and efficacy of the
recovery (from byproducts and waste products) of REEs, including by (re)processing and
recycling. Some possible substitutions of REEs, and perhaps less so replacement of REEs
with the same physical and material performance, with non-REEs can be detected. Likewise,
some emerging trends of a more efficient (i.e., volume reducing) use of REEs can be noted.
To this, one can add some potential for the synthetic creation of some REEs. However, none
of these take away the reality of tradeoff considerations at national or regional (economic
and/or security) blocs with regard to supply security and supply chain management with
regard to REEs, including supply chain disruptions and risks that may emerge (again) for
economic or geopolitical reasons. Some balance of supply and demand (with substitutions
trends) issues is likely to persist, and so, there may well have to be steers and signals that
go beyond pure trade and commodity pricing on short-term platforms.
If the key players, that is, regional blocs, governments, multinational companies,
and regulators (on environmental and public health grounds and accountability), are to
be seen as credible and in line with the key targets of the UN Sustainable Development
Goals, then a fully-fledged framework of lifecycle sustainability assessments for REEs
also needs to be developed and implemented. There is a range of studies on lifecycle
assessments (LCAs) for (specific) REEs (and from specific sources and locations) available
(see e.g., [
92
] for a recent systematic overview, and see [
93
,
94
]), but these are more narrowly
focused on an at times limited set of environmental aspects (and typically also exclude
human-health risks connected with toxicity), with differing underlying inventories and
thus similar yet different outcomes (even when there are the same process chains). What
Sustainability 2023,15, 1919 13 of 18
they do not deliver is a more rounded sustainability assessment, which includes other
corporate social responsibility (CSR) or now environmental, social, and governance (ESG)
dimensions (which include labor conditions and work safety, for instance), or an economic
one with a trend and regulatory context analysis with a view to over- or under-supply and
the investment interfaces. This is to be explored more fully in future research. Furthermore,
this is arguably not as yet deeply applied or embedded, though discussions and some
efforts have clearly started on circular economy models of some REEs [
88
], which is one
link to the United Nation’s Sustainable Development Goals (SDGs), though as yet with
uncertain economic models underpinning them.
While there has been the development of frameworks on critical raw materials, for
instance by the European Commission within and for the European Union, with updating
at reasonably regular intervals, what is still needed is a move beyond the notions of lists,
classifications, and (mostly industry-sponsored) “round tables” toward a fully-fledged
horizon-scanning method and tool that is integrated across the domains listed above,
beyond the purvey of (very) expensive applied consultancy market analysis tracking to
investors and (stock market share) traders. This is a matter for follow-up research.
Source [
21
] cautions that the current and forecasted prospective rate of the consump-
tion of REEs raises intergenerational ethical issues that need to be reflected on. Public
health and toxicity exposure for workers and nearby residents as well as ecosystems, from
potentially unsafe storage and disposal of some materials, including from mine tailings,
need to be addressed under a Sustainable Development Goals perspective as well [
21
].
The (renewable) energy transition clearly does have a material basis in terms of modern
technologies [
95
] as applied in an energy context [
96
]. Even though rare earth metals are
not necessarily very “rare”, they do have ecological, spatial, and economic [
97
] footprints to
work through and variable availabilities depending on the strategies and trajectories of min-
ing, production, and consumption [
11
,
98
]. This is especially so if we are to enter a post-oil
and post-gas phase, with considerable potential for destabilization along that route [99].
As to future trends, there is a need to further explore suitable strategies for making the
use of critical raw materials more sustainable [
100
,
101
]. The current war in Ukraine and
the economic sanctions now imposed on Russia mean that the world’s supply of rare earth
metals is likely to be reduced, with a cascading effect on various sectors, such as the car
industry and aviation, as well as across the electronic goods branch. This shows the need
for more environmentally sustainable approaches toward handling REEs [
102
]. We need to
be cognizant of some REEs’ toxicity for human health if handled incorrectly [
103
], and need
to develop tools and strategies to encourage more reuse and recycling for these important
materials. In the context of sustainable development on the ground for communities close
to the extraction processes, critical anthropological/sociological research on the burden
and benefits [
104
] and investigative journalism on research, business/investment, and
environmental practices [
105
] are also of major interest. Source [
106
], for instance, explores,
through a case study in the northeastern borderlands of Myanmar, how Global North “just
transition” to clean/decarbonized energy may create sacrifice zones in vulnerable and
conflict zones, but nonetheless with a potential for a different supportive local development
strategy there.
The issue of the potentials and efficacy of the recycling of REEs [
107
], as well as
secondary sources [
108
] and production waste [
109
], will remain on the agenda and will
need to be studied for different REEs in different contexts on an ongoing basis. This will
be a part of the ongoing attention to the net environmental footprint of REEs and “clean
energy” [
110
]. So will the ongoing development of the lifecycle analyses of REEs [
111
],
including in energy applications [112].
4. Conclusions and Policy Recommendations
This paper has reviewed the current situation regarding critical raw materials, and
REEs in particular. There are various concerns about the current use of these materials
and in respect of future trends. These straddle extraction, processing, production uses,
Sustainability 2023,15, 1919 14 of 18
reuse/recycling/disposal, and the environmental (including carbon, energy and water)
footprints of all of these, as well as the economic, geostrategic and security, social (including
intergenerational), and spatial aspects of REEs in their industrial and social contexts. The
paper points out the need for increased and sustained action in order to address problems
related to the reuse and recycling of REEs, so as to make their use as critical raw materials
more sustainable.
The results of this present study suggest some policy recommendations that the
authors believe they should be deployed to support these efforts. First, the authors believe
that legislative initiatives to reduce the quantity of rare earth contained in single-use
products should be adopted. Second, there are policy opportunities to provide financial
incentives to better improve recovery processes and the reuse of products containing REEs.
Finally, the authors believe that research funding programs, which may be used to find
suitable alternatives and substitutes for REEs, should be further explored [
22
]. This is
important because they provide an opportunity to explore other options, especially those
that may be more sustainable.
This paper has some limitations. First, it examined international trends on REEs
without focusing on specific case studies. Second, the study did not include detailed cost–
benefit assessments. In addition, the study did not examine future forecasts for exploitation
and environmental impacts. Furthermore, this study did not have access to or did not use
field explorations on site; nor did it directly process any trading data for REEs on the (legal)
international and national markets. No direct expert interviews or surveys were conducted
for this study; rather, published literature and grey literature were used. Despite these
limitations, the paper is a welcome addition to the literature because it sheds some light on
the ways REEs are perceived and are being internationally used.
Author Contributions:
Conceptualization, W.L.F., R.K., P.G.Ö. and I.R.A.; methodology, W.L.F.,
R.K.; formal analysis, W.L.F., R.K., P.G.Ö., I.R.A., N.R.M. and J.H.P.P.E.; investigation, W.L.F., R.K.,
P.G.Ö., I.R.A., N.R.M. and J.H.P.P.E.; resources, W.L.F., R.K., P.G.Ö., I.R.A., N.R.M. and J.H.P.P.E.;
writing—original draft preparation, W.L.F., R.K., P.G.Ö., I.R.A., N.R.M. and J.H.P.P.E.; writing—review
and editing, W.L.F., R.K., P.G.Ö., I.R.A., N.R.M. and J.H.P.P.E.; visualization, W.L.F., I.R.A., P.G.Ö.,
N.R.M. and R.K.; supervision, W.L.F.; project administration, W.L.F. and R.K. All authors have read
and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement:
There was no Ethical Approval necessary at institutional
level for this research, as it drew on secondary and non-sensitive resources only.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments:
This paper is part of the “100 papers to accelerate the implementation of the UN
Sustainable Development Goals” initiative.
Conflicts of Interest: The authors declare no conflict of interest.
References
1. Golloch, A. Handbook of Rare Earth Elements: Analytics, 2nd ed.; De Gryuter: Berlin, Germany, 2022; ISBN 9783110696363.
2. Atwood, D.A. (Ed.) The Rare Earth Metals: Fundamentals and Applications; Wiley: Chichester, UK, 2012; ISBN 978-1-119-95097-4.
3. Jha, A.R. Rare Earth Materials: Properties and Applications; CRC Press: Boca Raton, FL, USA, 2014; ISBN 9781138033870.
4. Orjuela, J.E.A. (Ed.) Rare Earth Element; InTechOpen: London, UK, 2017; ISBN 978-953-51-3402-2.
5.
Borges De Lima, I.; Leal Filho, W. (Eds.) Rare Earth Industry: Technological, Economic, and Environmental Implications; Elsevier:
Amsterdam, The Netherlands, 2016; ISBN 9780128023280.
6.
Weiss, D. Developments in aluminum-scandium-ceramic and aluminum-scandium-cerium alloys. In Light Metals 2019; Chesonis,
C., Ed.; Springer Nature: Cham, Switzerland, 2019; pp. 1439–1443. ISBN 978-3-030-05864-7.
7.
Zepf, V. An Overview of the Usefulness and Strategic Value of Rare Earth Metals. In Rare Earth Industry: Technological, Economic
and Environmental Implications; Borges De Lima, I., Leal Filho, W., Eds.; Elsevier: Amsterdam, The Netherlands, 2016; pp. 3–17.
[CrossRef]
8.
Voncken, J.H.L. The Rare Earth Elements—An Introduction; Springer International: Chem, Switzerland, 2016; ISBN 978-3-319-26809-5.
Sustainability 2023,15, 1919 15 of 18
9. De Boer, M.A.; Lammertsma, K. Scarcity of rare earth elements. ChemSusChem 2013,6, 2045–2055. [CrossRef] [PubMed]
10.
Massari, S.; Ruberti, M. Rare earth elements as critical raw materials: Focus on international markets and future strategies. Resour.
Policy 2013,38, 36–43. [CrossRef]
11.
Calvo, G.; Valero, A. Strategic mineral resources: Availability and future estimations for the renewable energy sector. Environ.
Dev. 2021,41, 100640. [CrossRef]
12.
Balaram, V. Rare earth elements—A review of applications, occurrence, exploration, analysis, recycling, and environmental
impact. Geosci. Front. 2019,10, 1285–1303. [CrossRef]
13.
European Commission, Directorate-General for Internal Market, Industry, Entrepreneurship and SMEs; Pennington, D.; Tzimas,
E.; Baranzelli, C.; Dewulf, J.; Manfredi, S. Methodology for Establishing the EU List of Critical Raw Materials: Guidelines; EU
Publications Office: Luxembourg, 2017. Available online: https://op.europa.eu/en/publication-detail/-/publication/2d43b7e2
-66ac-11e7-b2f2-01aa75ed71a1 (accessed on 4 January 2023).
14.
European Commission. Critical Raw Materials; European Commission: Brussels, Belgium, 2020. Available online: https:
//ec.europa.eu/growth/sectors/raw-materials/specific-interest/critical_en (accessed on 4 January 2023).
15.
British Geological Survey (BGS); Natural Environmental Research Council (NERC); Minerals UK—Centre for Sustainable Mineral
Development. Rare Earth Elements; Nottingham, Swindon, UK. 2021. Available online: https://www2.bgs.ac.uk/mineralsuk/
download/mineralProfiles/rare_earth_elements_profile.pdf (accessed on 4 January 2023).
16.
Binnemans, K.; Jones, T.M.; Müller, T.; Yurramendi, L. Rare Earths and the Balance Problem: How to Deal with Changing Markets?
J. Sustain. Metall. 2018,4, 126–146. [CrossRef]
17. Drobniak, A.; Mastalerz, M. Rare Earth Elements—A brief overview. Indiana J. Earth Sci. 2022,4, 33628. [CrossRef]
18.
Han, K.N. Editorial for Special Issue on ‘Leaching of Rare Earth Elements from Various Sources’. Minerals
2021
,11, 164. [CrossRef]
19.
Dutta, T.; Kim, K.H.; Uchimiya, M.; Kwon, E.E.; Jeon, B.-H.; Deep, A.; Yun, S.T. Global demand for rare earth resources and global
strategies for green mining. Environ. Res. 2016,150, 182–190. [CrossRef]
20.
Aide, M.; Nakajima, T. Rare Earth Elements and Their Minerals; InTech Open: London, UK, 2022; ISBN 978-1-78984-741-3. Available
online: https://www.intechopen.com/books/7787 (accessed on 4 January 2023).
21.
Martin, A.; Iles, A. On Ethics of Rare Earth Elements Over Time and Space. HYLE—Int. J. Philos. Chem.
2020
,26, 5–30. Available
online: http://www.hyle.org/journal/issues/26-1/martin.pdf (accessed on 4 January 2023).
22.
Dushyanta, N.; Batapola, N.; Illankoon, I.M.S.K.; Rohitha, S.; Premasiri, R.; Abeysinghe, B.; Ratnakake, N.; Dissanayake, K.
The story of rare earth elements (REEs): Occurrences, global distribution, genesis, geology, mineralogy, and global production.
Ore Geol. Rev. 2020,122, 103551. [CrossRef]
23.
Sanseverino, E.R.; Luu, L.Q. Critical Raw Materials and Supply Chain Disruptions in the Energy Transition. Energies
2022
,
15, 5992. [CrossRef]
24.
Girtan, M.; Wittenberg, A.; Grilli, M.L.; de Oliveira, D.P.; Giosuè, C.; Ruello, M.L. The Critical Raw Materials Issue between
Scarcity, Supply Risk, and Unique Properties. Materials 2021,14, 1826. [CrossRef] [PubMed]
25.
Domaracka, L.; Matuskova, S.; Tausova, M.; Senova, A.; Kowal, B. Efficient Use of Critical Raw Materials for Optimal Resource
Management in EU Countries. Sustainability 2022,14, 6554. [CrossRef]
26.
Li, X.Y.; Ge, J.P.; Quiang, W.; Wang, P. Scenarios of rare earth elements demand driven by automotive electrification in China:
2018–2030. Resour. Conserv. Recycl. 2019,145, 322–331. [CrossRef]
27. Singh, V. Rare Earth Element Resources: Indian Context; Springer: Cham, Switzerland, 2020; ISBN 978-3-030-41353-8.
28.
Pistilli, M. What Are the Uses of Rare Earths? 2021. Available online: https://investingnews.com/daily/resource-investing/
critical-metals-investing/rare-earth-metals-uses/ (accessed on 4 January 2023).
29.
Lewicka, E.; Guzik, K.; Galos, K. On the Possibilities of Critical Raw Materials Production from the EU’s Primary Sources.
Resources 2021,10, 50. [CrossRef]
30.
PubChem. Lanthanum. 2022. Available online: https://pubchem.ncbi.nlm.nih.gov/element/Lanthanum (accessed on 4 January 2023).
31.
PubChem. PubChem Element Summary for Atomic Number 58, Cerium. 2022. Available online: https://pubchem.ncbi.nlm.nih.
gov/element/Cerium (accessed on 4 January 2023).
32.
Ahmad, R.; Sheggaf, Z.; Asmael, M.; Hamzah, M. Effect of praseodymium addition on microstructure and hardness of cast ZRE1
magnesium alloy. ARPN J. Eng. Appl. Sci.
2016
,11, 6485–6489. Available online: http://www.arpnjournals.org/jeas/research_
papers/rp_2016/jeas_0616_4499.pdf (accessed on 4 January 2023).
33.
Reisdörfer, G.; Bertuol, D.; Tanabe, E.H. Recovery of neodymium from the magnets of hard disk drives using organic acids. Miner.
Eng. 2019,143, 105938. [CrossRef]
34.
Bian, Y.; Guo, S.; Jiang, L.; Liu, J.; Tang, K.; Ding, W. Recovery of rare earth elements from NdFeB magnets by VIM-HMS method.
ACS Sustain. Chem. Eng. 2016,4, 810–818. [CrossRef]
35. Elkina, V.; Kurushkin, M. Promethium: To strive, to seek, to find, and not to yield. Front. Chem. 2020,8, 588. [CrossRef]
36.
PubChem. PubChem Element Summary for Atomic Number 62, Samarium. 2022. Available online: https://pubchem.ncbi.nlm.
nih.gov/element/Samarium (accessed on 4 January 2023).
37.
PubChem. PubChem Element Summary for Atomic Number 63, Europium. 2022. Available online: https://pubchem.ncbi.nlm.
nih.gov/element/Europium (accessed on 4 January 2023).
38.
PubChem. PubChem Element Summary for Atomic Number 39, Yttrium. 2022. Available online: https://pubchem.ncbi.nlm.nih.
gov/element/Yttrium (accessed on 4 January 2023).
Sustainability 2023,15, 1919 16 of 18
39.
Favot, M.; Massarutto, A. Rare-earth elements in the circular economy: The case of yttrium. J. Environ. Manag.
2019
,240, 504–510.
[CrossRef]
40.
PubChem. PubChem Compound Summary for CID 23982, Gadolinium. 2022. Available online: https://pubchem.ncbi.nlm.nih.
gov/compound/23982#section=Use-and-Manufacturing (accessed on 4 January 2023).
41.
RSC. Terbium; Royal Society of Chemistry: London, UK, 2022. Available online: https://www.rsc.org/periodic-table/element/65
/terbium#:~{}:text=Terbium%20is%20used%20to%20dope,a%20much%20shorter%20exposure%20time (accessed on 4 January 2023).
42.
PubChem. PubChem Element Summary for Atomic Number 66, Dysprosium. 2022. Available online: https://pubchem.ncbi.nlm.
nih.gov/element/Dysprosium (accessed on 4 January 2023).
43.
Sari, S.; Çakici, M.Ç.; Kartal, I.G.; Selmï, V.; Özdemïr, H.; Ozok, H.U.; Karakoyunlu, A.N.; Yildiz, S.; Hepsen, E.; Ozbal, S.
Comparison of the efficiency, safety, and pain scores of holmium laser devices working with 20 watts and 30 watts using in
retrograde intrarenal surgery: One center prospective study. Arch. Ital. Urol. Androl. 2020,92, 149. [CrossRef] [PubMed]
44.
Lavrinovica, I.; Supe, A.; Porins, J. Experimental Measurement of Erbium-Doped Optical Fibre Characteristics for Edfa Perfor-
mance Optimization. Latv. J. Phys. Tech. Sci. 2019,56, 33–41. [CrossRef]
45.
RSC. Ytterbium; Royal Society of Chemistry: London, UK, 2022. Available online: https://www.rsc.org/periodic-table/element/
70/ytterbium (accessed on 4 January 2023).
46.
RSC. Lutetium; Royal Society of Chemistry: London, UK, 2022. Available online: https://www.rsc.org/periodic-table/element/
71/lutetium (accessed on 4 January 2023).
47.
PubChem. PubChem Element Summary for Atomic Number 69, Thulium. 2022. Available online: https://pubchem.ncbi.nlm.nih.
gov/element/Thulium#section=Uses (accessed on 4 January 2023).
48. Xiao, Y.; Watson, M. Guidance on Conducting a Systematic Literature Review. J. Plan. Educ. Res. 2017,39, 93–112. [CrossRef]
49.
Shen, Y.; Moomy, R.; Eggert, R.G. China’s public policies towards rare earths, 1975–2018. Miner. Econ.
2020
,33, 127–151.
[CrossRef]
50.
Grilli, M.L.; Valerini, D.; Slobozeanu, A.E.; Postolnyi, B.O.; Balos, S.; Rizzo, A.; Piticescu, R.R. Critical Raw Materials Savings
by Protective Coatings under Extreme Conditions: A Review of Last Trends in Alloys and Coatings for Aerospace Engine
Applications. Materials 2021,14, 1656. [CrossRef]
51.
Daigle, B.; DeCarlo, S. Rare Earths and the U.S. Electronics Sector: Supply Chain Developments and Trends. 2021. Available
online: https://www.usitc.gov/publications/332/working_papers/rare_earths_and_the_electronics_sector_final_070921_2
-compliant.pdf (accessed on 4 January 2023).
52.
Fishman, T.; Myers, R.J.; Rios, O.; Graedel, T.E. Implications of emerging vehicle technologies on rare earth supply and demand
in the United States. Resources 2018,7, 9. [CrossRef]
53.
Market Analysis Report. Rare-Earth Metals Market by Metal (Lanthanum, Cerium, Neodymium, Praseodymium, Smarium,
Europium, & Other), and Application (Permanent Magnets, Metal Alloys, Polishing, Additives, Catalyst, Phosphors), Region-
Global Forecast to 2026. 2021. Available online: https://www.marketsandmarkets.com/Market-Reports/rare-earth-metals-
market-121495310.html (accessed on 4 January 2023).
54.
Yano, Y.; Muroi, T.; Sakai, S. Rare earth element recovery potentials from end-of-life hybrid electric vehicle components in
2010–2030. J. Mater. Cycles Waste Manag. 2016,18, 655–664. [CrossRef]
55.
Rollat, A.; Gyonnet, D.; Planchon, M.; Tudori, J. Prospective analysis of the flows of certain rare earths in Europe at the 2020
horizon. Waste Manag. 2016,49, 427–436. [CrossRef]
56.
Zhang, S.; Ding, Y.; Liu, B.; Chang, C. Supply and demand of some critical metals and present status of their recycling in WEEE.
Waste Manag. 2017,65, 113–127. [CrossRef]
57.
Tukker, A. Rare earth elements supply restrictions: Market failures, not scarcity, hamper their current use in high-tech applications.
Environ. Sci. Technol. 2014,48, 9973–9974. [CrossRef]
58.
Sprecher, B.; Daigo, S.; Murakami, S.; Kleijn, R.; Vos, M.; Kramer, G.J. Framework for resilience in material supply chains, with a
case study from the 2010 rare earth crisis. Environ. Sci. Technol. 2015,49, 6740–6750. [CrossRef] [PubMed]
59.
Takehara, L.; Silveira-Robertoy, V.; Santos, V. Potentiality of Rare Earth Elements in Brazil. In Rare Earth Industry: Technological,
Economic and Environmental Implications; Borges de Lima, I., Leal Filho, W., Eds.; Elsevier: Amsterdam, The Netherlands, 2016;
pp. 57–72.
60.
Kiggins, R.D. The Political Economy of Rare Earth Elements: Rising Powers and Technological Change; Palgrave Macmillan: London,
UK, 2015; ISBN 978-1-137-36424-1.
61.
Mancheri, N.A. Word trade in rare earths, Chinese export restrictions, and implications. Resour. Policy
2015
,46, 262–271.
[CrossRef]
62.
Mancheri, N.A.; Sprecher, B.; Bailey, G.; Ge, J.; Tukker, A. Effect of Chinese policies on rare earth supply chain resilience. Resour.
Conserv. Recycl. 2019,142, 101–112. [CrossRef]
63.
Chen, J.; Zhu, X.; Liu, G.; Chen, W.; Yang, D. China’s rare earth dominance: The myths and the truths from an industrial ecology
perspective. Resour. Conversat. Recycl. 2018,132, 139–140. [CrossRef]
64. Binnemans, K.; Jones, P.T. Rare earth and the balance problem. J. Sustain. Metall. 2015,1, 29–38. [CrossRef]
65.
Eggert, R.; Wadia, C.; Anderson, C.; Bauer, D.; Fields, F.; Meinert, L.; Taylor, P. Rare Earths: Market Disruption, Innovation, and
Global Supply Chains. Annu. Rev. Environ. Resour. 2016,41, 199–222. [CrossRef]
Sustainability 2023,15, 1919 17 of 18
66.
Machacek, E.; Luth Richter, J.; Lane, R. Governance and Risk-Value Constructions in Closing Loops of Rare Earth Elements in
Global Value Chains. Resources 2017,6, 59. [CrossRef]
67.
Howanietz, R. China’s Virtual Monopoly of Rare Earth Elements: Economic, Technological and Strategic Implications; Routledge: London,
UK, 2018; ISBN 9780367590130.
68. Ferreira, G.; Critelli, J. China’s Global Monopoly on Rare-Earth Elements. Parameters 2020,52, 57–72. [CrossRef]
69.
USGS. Rare Earths Statistics and Information. National Minerals Information Centre. United States Geological Service. 2022.
Available online: https://www.usgs.gov/centers/national-minerals-information-center/rare-earths-statistics-and-information
(accessed on 4 January 2023).
70.
Rauer, J.; Kaufmann, L. Mitigating External Barriers to Implementing Green Supply Chain Management: A Grounded Theory
Investigation of Green-Tech Companies’ Rare Earth Metals Supply Chains. J. Supply Chain Manag. 2015,51, 65–88. [CrossRef]
71.
Kennedy, J.C. Rare Earth Production, Regulatory USA/International Constraints and Chinese Dominance: The Economic Viability
is Bounded by Geochemistry and Value Chain Integration. In Rare Earths Industry: Technological, Economic, and Environmental
Implications; Lima de Borges, I., Leal Filho, W., Eds.; Elsevier: Amsterdam, The Netherlands, 2016; pp. 37–55.
72. Zhang, H.; Wang, X.; Tang, J.; Guo, Y. The impact of international rare earth trade competition on global value chain upgrading
from the industrial chain perspective. Ecol. Econ. 2022,198, 107472. [CrossRef]
73.
Weiser, A.; Land, D.L.; Schomerus, T.; Stamp, A. Understanding the modes or use and availability of critical metals—An
expert-based scenario analysis for the case of indium. J. Clean. Prod. 2015,94, 376–393. [CrossRef]
74.
Zepf, V. Neodymium Use and Recycling Potential. In Rare Earth Industry: Technological, Economic and Environmental Implications;
Borges De Lima, I., Leal Filho, W., Eds.; Elsevier: Amsterdam, The Netherlands, 2016; pp. 305–318.
75.
Graedel, T.E.; Barr, R.; Chandler, C.; Chase, T.; Choi, J.; Christoffersen, L.; Friedlander, E.; Henly, C.; Jun, C.; Nassar, N.T.; et al.
Methodology of metal criticality determination. Environ. Sci. Technol. 2012,46, 1063. [CrossRef] [PubMed]
76.
Adibi, N.; Lafhaj, Z.; Gemechu, E.D.; Sonnemann, G.; Payet, J. Introducing a multi-criteria indicator to better evaluator impacts of
rare earth materials of rare earth materials production and consumption in life-cycle assessment. J. Rare Earths
2014
,34, 288–292.
[CrossRef]
77.
Jowitt, S.M. Introduction to a Special Issue on the ‘Criticality of the rare earth elements—Current and future sources and recycling’.
Resources 2018,7, 35. [CrossRef]
78.
Swain, N.; Sujata, M. A review on the recovery and separation of rare earths and transition metals from secondary resources.
J. Clean. Prod. 2019,220, 884–898. [CrossRef]
79.
Bandara, H.D.; Field, K.D.; Emmert, M.H. Rare earth recovery from end-of-life motors employing green chemistry design
principles. Green Chem. 2016,18, 753–759. [CrossRef]
80.
Nikulski, J.S.; Ritthoff, M.; von Gries, N. The Potential and Limitations of Critical Raw Materials Recycling: The Case of LED
Lamps. Resources 2021,10, 37. [CrossRef]
81.
De Oliveira, R.P.; Benvenuti, J.; Espinosa, D.C.R. A review of the current progress in recycling technologies for gallium and rare
earth elements from light emitting diodes. Renew. Sustain. Energy Rev. 2021,145, 111090. [CrossRef]
82.
Akcil, A.A. Critical and Rare Earth Elements: Recovery from Secondary Resources; CRC Press: Boca Raton, FL, USA, 2019;
ISBN 9780367086473.
83.
Royer-Lavallée, A.; Neculita, C.; Coudert, L. Removal and potential recovery of rare earth elements from mine water. J. Ind. Eng.
Chem. 2020,89, 47–57. [CrossRef]
84.
Amankwah-Amoah, J. Global business and emerging economies: Towards a new perspective on the effects of e-waste. Technol.
Forecast. Soc. Chang. 2016,105, 20–26. [CrossRef]
85.
Akram, R.; Shah Fahad, N.; Hashmi, M.Z.; Wahid, A.; Adnan, M.; Mubeen, M.; Khan, N.; Rehmani, M.I.A.; Awais, M.; Abbas, M.;
et al. Trends of electronic waste pollution and its impact on the global environment and ecosystem. Environ. Sci. Pollut. Res.
2019
,
26, 16923–16938. [CrossRef] [PubMed]
86.
Gwenzi, W.; Mangori, L.; Danha, C.; Chaukura, N.L.; Dunjana, N.; Sanganyado, E. Sources, behaviour, and environmental and
human health risks of high-technology rare earth elements as emerging contaminants. Sci. Total Environ.
2018
,636, 299–313.
[CrossRef] [PubMed]
87.
Ahn, N.-K.; Shim, H.-W.; Kim, D.-W.; Swain, B. Valorization of waste NiMH battery through recovery of critical rare earth metal:
A simple recycling process for the circular economy. Waste Manag. 2020,104, 254–261. [CrossRef]
88.
Bonfante, M.C.; Raspini, J.P.; Fernandes, I.B.; Fernandes, S.; Campos, L.M.S.; Alarcon, O.E. Achieving Sustainable Development
Goals in rare earth magnets production: A review on state of the art and SWOT analysis. Renew. Sustain. Energy Rev.
2021
,
137, 110616. [CrossRef]
89.
Choubey, P.K.; Singh, N.; Panda, R.; Jyothi, R.K.; Yoo, K.; Park, I.; Jha, M.K. Development of Hydrometallurgical Process for
Recovery of Rare Earth Metals (Nd, Pr, and Dy) from Nd-Fe-B Magnets. Metals 2021,11, 1987. [CrossRef]
90.
Thompson, V.S.; Gupta, M.; Jin, H.; Vahidi, E.; Yim, M.; Jindra, M.A.; Nguyen, V.; Fujita, Y.; Sutherland, J.W.; Jiao, Y.; et al.
Techno-economic and Life Cycle Analysis for Bioleaching Rare-Earth Elements from Waste Materials. ACS Sustain. Chem. Eng.
2018,6, 1602–1609. [CrossRef]
91.
Buechler, D.T.; Zyakyina, N.N.; Spencer, C.A.; Lawson, E.; Ploss, N.M.; Hua, I. Comprehensive element analysis of consumer
electronic devices: Rare earth, precious and critical elements. Waste Manag. 2020,103, 67–75. [CrossRef]
Sustainability 2023,15, 1919 18 of 18
92.
Schreiber, A.; Marx, J.; Zapp, P. Life Cycle Assessment studies of rare earths production. Findings from a systematic review. Sci.
Total Environ. 2021,791, 148257. [CrossRef]
93.
Browning, C.; Northey, S.; Haque, N.; Bruckard, W.; Cooksey, M. Life Cycle Assessment of Rare Earth Production from Monazite.
In REWAS 2016: Towards Materials Resource Sustainability; Kirchain, R.E., Blanpain, B., Eds.; Springer: Cham, Switzerland, 2016.
[CrossRef]
94.
Bieda, B.; Grzesik, R.; Kozakiewicz, R.; Kossakowska, K. Life cycle environmental assessment of the production of rare earth
elements from gold processing. In Proceedings of the 2017 International Conference on Energy and Environment (CIEM),
Bucharest, Romania, 19–20 October 2017; IEEE: New York, NY, USA, 2017; pp. 134–137. [CrossRef]
95.
Yunxiong Li, G.; Ascani, A.; Iammarino, S. The Material Basis of Modern Technologies; Working Papers 59; Birkbeck Centre
for Innovation Management: London, UK; Birkbeck, University of London: London, UK, 2022. Available online: https:
//eprints.bbk.ac.uk/id/eprint/47608/ (accessed on 4 January 2023).
96.
Bleicher, A.; Pehlken, A. (Eds.) The Material Basis of Energy Transitions; Elsevier: Amsterdam, The Netherlands, 2020;
ISBN 978-0-12-819534-5.
97. Ayres, R.U. Editorial: The business case for conserving rare metals. Technol. Forecast. Soc. Chang. 2019,143, 307–315. [CrossRef]
98. Giese, E.C. Strategic mineral Global challenges post-COVID-19. Extr. Ind. Soc. 2022,12, 10113. [CrossRef]
99.
Korotayev, A.; Bilyuga, S.; Belalov, I.; Goldstone, J. Oil prices, socio-political destabilization risks, and future energy technologies.
Technol. Forecast. Soc. Chang. 2018,128, 304–310. [CrossRef]
100.
Martins, F.; Castro, H. Significance ranking method applied to some EU critical raw materials in a circular economy—Priorities
for achieving sustainability. Procedia CIRP 2019,84, 1059–1062. [CrossRef]
101.
Golroudbary, S.R.; Makarava, I.; Kraslawski, A.; Repo, E. Global environmental costs of using rare earth elements in green energy
technologies. Sci. Total Environ. 2022,832, 155022. [CrossRef] [PubMed]
102.
Sinharoy, A.; Lens, P. Environmental Technologies to Treat Rare Earth Element Pollution; IWA Publishing: London, UK, 2022. [CrossRef]
103.
Pagano, G. Rare Earth Elements in Human and Environmental Health: At the Crossroads between Toxicity and Safety; Jenny Stanford
Publishing: Singapore, 2016; ISBN 9789814745000.
104.
Klinger, J.M. Rare Earth Frontiers. From Terrestrial Subsoils to Lunar Landscapes; Cornell University Press: Ithaca, NY, USA, 2018;
ISBN 1501714597.
105.
Sanderson, H. Volt Rush: The Winners and Losers in the Race to Go Green; Oneworld Publications: London, UK, 2022; ISBN
978-0861543755.
106.
Sadan, M.; Smyer Yü, D.; Seng Lawn, D.; Brown, D.; Zhou, R. Rare Earth Elements, Global Inequalities and the ‘Just Transition’; The
British Academy: London, UK, 2022. Available online: https://www.thebritishacademy.ac.uk/documents/4203/Just-transitions-
rare-elements-global-inequalities.pdf (accessed on 4 January 2023).
107.
Binnemans, K.; Jones, P.T.; Blanpart, B.; Van Gerven, T.; Yang, Y.; Walton, A.; Buchert, M. Recycling of rare earths: A critical review.
J. Clean. Prod. 2013,51, 1–22. [CrossRef]
108.
Sprecher, B.; Kleijn, R.; Kramer, G.J. Recycling Potential of Neodymium: The Case of Computer hard Disk Drives. Environ. Sci.
Tecnol. 2014,48, 9506–9513. [CrossRef]
109.
Echeverry-Vargas, L.; Ocampo-Carmora, L.M. Recovery of Rare Earth Elements from Mine Tailings: A Case Study for Generating
Wealth from Waste. Minerals 2022,12, 948. [CrossRef]
110.
Arshi, P.S.; Vahidi, E.; Zhao, F. Behind the Scenes of Clean Energy: The Environmental Footprint of Rare Earth Products. ACS
Sustain. Chem. Eng. 2018,6, 3311–3320. [CrossRef]
111.
Vahidi, E.; Navarro, J.; Zhao, F. An initial life cycle assessment of rare earth oxides production from ion-adsorption clays. Resour.
Concervation Recycl. 2016,113, 1–11. [CrossRef]
112.
Navarro, J.; Zhao, F. Life-cycle assessment of the production of rare-earth elements for energy applications: A review. Front.
Energy Res. 2014,2, 45. [CrossRef]
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