The Critical Raw Materials Issue between Scarcity, Supply Risk, and Unique Properties

This editorial reports on a thorough analysis of the abundance and scarcity distribution of chemical elements and the minerals they form in the Earth, Sun, and Universe in connection with their number of neutrons and binding energy per nucleon. On one hand, understanding the elements’ formation and their specific properties related to their electronic and nucleonic structure may lead to understanding whether future solutions to replace certain elements or materials for specific technical applications are realistic. On the other hand, finding solutions to the critical availability of some of these elements is an urgent need. Even the analysis of the availability of scarce minerals from European Union sources leads to the suggestion that a wide-ranging approach is essential. These two fundamental assumptions represent also the logical approach that led the European Commission to ask for a multi-disciplinary effort from the scientific community to tackle the challenge of Critical Raw Materials. This editorial is also the story of one of the first fulcrum around which a wide network of material scientists gathered thanks to the support of the funding organization for research and innovation networks, COST (European Cooperation in Science and Technology).


Introduction
The European Union (EU) has a long history of extracting, processing, and producing raw materials. Modern and optimized mining technologies and resource-efficient production are a reality at many European mining sites, and yet, the import dependency for many raw materials sourced outside the EU has dramatically increased over the last decades. With the Raw Materials Initiative, which was started in 2008 and consolidated in 2011 [1,2], the EU restarted actions to secure the global competitiveness of the manufacturing industries and to accelerate the transition to a resource-efficient and sustainable society. The Raw Materials Initiative has three pillars with the following aims: (i) ensure fair and sustainable supply of raw materials from global markets; (ii) foster sustainable supply of raw materials within the EU; and (iii) boost resource efficiency and supply of "secondary raw materials" through recycling.
Securing access to metals and minerals that are strategic for high-tech products is a global concern, and it is common also to other highly industrialized countries, such as Japan and the United States, whose high-tech products are strongly dependent on the import of raw materials. In 2011, the EU started also a trilateral initiative with Japan and US to promote cooperation in critical raw material issues. Despite the different domestic approaches to CRMs from the above-mentioned countries, since 2011, the EU, US, and Japan representatives meet every year in a one-day conference for discussing and updating about raw materials data, analysis of trade, and recycling and substitution issues. Securing access to metals and minerals that are strategic for high-tech products is a global concern, and it is common also to other highly industrialized countries, such as Japan and the United States, whose high-tech products are strongly dependent on the import of raw materials. In 2011, the EU started also a trilateral initiative with Japan and US to promote cooperation in critical raw material issues. Despite the different domestic approaches to CRMs from the above-mentioned countries, since 2011, the EU, US, and Japan representatives meet every year in a one-day conference for discussing and updating about raw materials data, analysis of trade, and recycling and substitution issues.
According to analyses that recognize increasing pressure on resources, roadmaps of several initiatives, networks, and EU-funded projects were established.
Among the initiatives, we mention the European Innovation Partnership (EIP) on Raw Materials, which is a platform that brings together representatives from industry, public services, academia, and non-governmental organizations (NGOs) with the aim of reinforcing the Raw Materials Initiative by mobilizing the stakeholder community to implement actions for reducing Europe's import dependency on critical raw materials strategic for the industrial sector, while focusing also on the societal benefit of research and innovation (R&I) activities. Its mission is to provide high-level guidance to the European Commission, EU countries, and private actors on innovative approaches to the challenges related to raw materials. To address the EIP's initiative, several EIP Commitments were established. Commitments are networks undertaken by several partners who commit themselves to activities aimed at achieving the EIP's objectives. The first call for EIP Commitment was in 2013 and in 2017, already 127 EIP Commitments were settled up [8]. The last call was in 2019.
The EIT (European Institute of Innovation and Technology) Raw Materials is the largest consortium in the raw materials sector worldwide, comprising more than 120 members. Its mission is to enable sustainable competitiveness of the European minerals, metals, and materials sector along the value chain by driving innovation, education, and entrepreneurship. It was initiated and funded by the EIT (European Institute of Innovation and Technology), which is a body of the European Union. The EIT boosts education and encourages new entrepreneurs and innovators to turn their innovative ideas into business opportunities, funding several projects on the whole raw materials value chain. The EIT is the largest consortium in the raw materials sector worldwide [9].
The European Battery Alliance (EBA) was launched in 2017 by the European Commission, EU countries, industry, and the scientific community. The European Battery Alliance aims to develop an innovative, competitive, and sustainable battery value chain in Europe. Securing access to raw materials for batteries is one of the six priority areas [10].
The European Raw Materials Alliance (ERMA)-launched 29 September 2020-aims to build resilience and strategic autonomy for Europe's rare earth and magnet value chains. The support of Europe's raw materials industry capability to extract, design, manufacture, and recycle materials is part of the actions. The ERMA is part of an Action Plan on Critical Raw Materials and the publication of the 2020 List of Critical Raw Materials [11].
We list below some of the EU and EIT-funded projects and EIP on CRM-related issues, which focus on technical solutions or on information on deposits, supply, and demand. The list is obviously non-exhaustive and reports only about some of the projects in which the authors of this manuscript were involved and/or linked:  [36].
The indisputable conclusion after about 10 years of finalized CRM projects research is that the most advanced technologies required for the green and digital transition will lead to a drastic increase demand for certain CRMs in Europe and elsewhere [37].
Each updated CRMs report at the moment of its publication is ironically outdated, since it is based on a picture covering the previous last five years of a varying geopolitical scenario, and that the SARS-CoV-2 pandemic has shown that countries are more interrelated than the concept of globalization had made us aware.
Even if the action plan on CRMs looks at the current and future challenges and proposes viable actions to reduce Europe's dependency on third countries, it would be interesting to examine more defined scenarios: (i) the natural abundance and scarcity of elements on Earth and the Universe and (ii) the availability from EU sources.

Abundance and Scarcity of Elements on Earth and Universe
Among the elements represented in Figure 1, which are presented as elements with important supply risk in the EU and of major importance for the economy, we have selected (in order of their atomic number Z) the following: Li, Be, B, P, Sc, Ti, V, Cr, Co, Ga, Ge, Se, Sr, Nb, In, Sb, Te, Ta, W, Bi, and rare earth elements. The main applications and main extraction and production countries of these elements are given in Table 1. Understanding the scarcity of certain materials necessarily involves the comprehension of the mechanisms of the formation of elements and their abundance on the scale of the Earth, the Sun, or the Universe. Hence, if we accept the nucleosynthesis hypothesis and taking into account that the most abundant element in the Universe is hydrogen, one can imagine that by consecutive fusion, nuclear reactions formed all the known elements up to now [38][39][40][41][42][43][44][45][46].
In this hypothesis, the formation of the first periodic table elements after hydrogen such as helium (Z = 2), lithium (Z = 3), Be (Z= 4), C (Z = 6), N (Z = 7) etc., pass through successive fusion reactions as they are depicted in Figures 2 and 3. This fusion scheme corresponds to the fusion nuclear reactions taking place in the Sun.  The nucleosynthesis of lithium, beryllium, and boron was, for a long time, difficult to explain due to the instability of these elements and their fragility at high temperature; this instability also being the cause of their very weak abundance in the "cosmic curve" of elements [47].
By analyzing the nuclear binding energy per nucleon ( Figure 4) as a function of the atomic mass number of elements (A), it could be remarked that this energy presents a maximum for iron (Z = 26, A = 56). Considering that the most stable elements are those for which the binding energy per nucleon is highest, we can conclude that the lighter the elements, the higher the tendency to turn into heavy elements through fusion reactions, and elements with higher atomic mass tend to turn into lower atomic mass elements through fission reactions. Hence, this observation can also explain in a simple way the life cycle of stars and the abundance and scarcity of elements in the Universe.  The nucleosynthesis of lithium, beryllium, and boron was, for a long time, difficult to explain due to the instability of these elements and their fragility at high temperature; this instability also being the cause of their very weak abundance in the "cosmic curve" of elements [47].
By analyzing the nuclear binding energy per nucleon ( Figure 4) as a function of the atomic mass number of elements (A), it could be remarked that this energy presents a maximum for iron (Z = 26, A = 56). Considering that the most stable elements are those for which the binding energy per nucleon is highest, we can conclude that the lighter the elements, the higher the tendency to turn into heavy elements through fusion reactions, and elements with higher atomic mass tend to turn into lower atomic mass elements through fission reactions. Hence, this observation can also explain in a simple way the life cycle of stars and the abundance and scarcity of elements in the Universe. The nucleosynthesis of lithium, beryllium, and boron was, for a long time, difficult to explain due to the instability of these elements and their fragility at high temperature; this instability also being the cause of their very weak abundance in the "cosmic curve" of elements [47].
By analyzing the nuclear binding energy per nucleon ( Figure 4) as a function of the atomic mass number of elements (A), it could be remarked that this energy presents a maximum for iron (Z = 26, A = 56). Considering that the most stable elements are those for which the binding energy per nucleon is highest, we can conclude that the lighter the elements, the higher the tendency to turn into heavy elements through fusion reactions, and elements with higher atomic mass tend to turn into lower atomic mass elements through fission reactions. Hence, this observation can also explain in a simple way the life cycle of stars and the abundance and scarcity of elements in the Universe. Based on astronomical, geological, and theoretical data [48][49][50][51][52][53], the abundance of elements at the Universe, Sun, or Earth scale was estimated for each element of the periodic table. Based on these data, we plot the graphs as a function of the even and odd A numbers of elements, but also by distinguishing for elements with odd A numbers, their odd or even number of neutrons (N). These graphs are given in the following: (a) Figure 5 for Universe-abundant elements, (b) Figure 6 for Sun-abundant elements, and (c) Figure 7 for Earth-abundant elements.
A series of similarities are shown in these three graphs. In all cases, the elements having an even A number are more abundant (blue points) than the elements having an odd A number but an even number of neutrons (red points). This rule is respected including the noble gases in the case of the abundance of elements at the Universe and Sun scale ( Figures  4 and 5), but not for Earth, for which in the case of noble gases, even if they have an even A number, they are less abundant than all the other elements ( Figure 6).  Based on astronomical, geological, and theoretical data [48][49][50][51][52][53], the abundance of elements at the Universe, Sun, or Earth scale was estimated for each element of the periodic table. Based on these data, we plot the graphs as a function of the even and odd A numbers of elements, but also by distinguishing for elements with odd A numbers, their odd or even number of neutrons (N). These graphs are given in the following: (a) Figure 5 for Universe-abundant elements, (b) Figure 6 for Sun-abundant elements, and (c) Figure 7 for Earth-abundant elements.
A series of similarities are shown in these three graphs. In all cases, the elements having an even A number are more abundant (blue points) than the elements having an odd A number but an even number of neutrons (red points). This rule is respected including the noble gases in the case of the abundance of elements at the Universe and Sun scale (Figures 4 and 5), but not for Earth, for which in the case of noble gases, even if they have an even A number, they are less abundant than all the other elements ( Figure 6).  Based on astronomical, geological, and theoretical data [48][49][50][51][52][53], the abundance of elements at the Universe, Sun, or Earth scale was estimated for each element of the periodic table. Based on these data, we plot the graphs as a function of the even and odd A numbers of elements, but also by distinguishing for elements with odd A numbers, their odd or even number of neutrons (N). These graphs are given in the following: (a) Figure 5 for Universe-abundant elements, (b) Figure 6 for Sun-abundant elements, and (c) Figure 7 for Earth-abundant elements.
A series of similarities are shown in these three graphs. In all cases, the elements having an even A number are more abundant (blue points) than the elements having an odd A number but an even number of neutrons (red points). This rule is respected including the noble gases in the case of the abundance of elements at the Universe and Sun scale ( Figures  4 and 5), but not for Earth, for which in the case of noble gases, even if they have an even A number, they are less abundant than all the other elements ( Figure 6).    The abundance of elements on Earth as a function of their atomic number is given in Figure 8. Noble gases are represented in green and the other scarce elements are represented in red. It is not surprising to see that the scarce elements Be, B, P, Sc, V, Cr, Co, Ga, Ge, Se, Nb, In, and Te are rare earth elements; Ta and Bi are the same as the elements that were represented in Figure 1, presenting a supply and an economical risk. Many of the above-mentioned elements are also those that are continuously monitored by EU, and they are included in all the CRMs lists released since 2011.  The abundance of elements on Earth as a function of their atomic number is given in Figure 8. Noble gases are represented in green and the other scarce elements are represented in red. It is not surprising to see that the scarce elements Be, B, P, Sc, V, Cr, Co, Ga, Ge, Se, Nb, In, and Te are rare earth elements; Ta and Bi are the same as the elements that were represented in Figure 1, presenting a supply and an economical risk. Many of the above-mentioned elements are also those that are continuously monitored by EU, and they are included in all the CRMs lists released since 2011. The abundance of elements on Earth as a function of their atomic number is given in Figure 8. Noble gases are represented in green and the other scarce elements are represented in red. It is not surprising to see that the scarce elements Be, B, P, Sc, V, Cr, Co, Ga, Ge, Se, Nb, In, and Te are rare earth elements; Ta and Bi are the same as the elements that were represented in Figure 1, presenting a supply and an economical risk. Many of the above-mentioned elements are also those that are continuously monitored by EU, and they are included in all the CRMs lists released since 2011. These graphs in connection with the intrinsic properties of these elements at the nuclear scale (number of protons and number of neutrons) lead us to the idea that the properties of these elements may be very unique, and hence, these elements might be difficult to be replaced.
From this observation, the obvious conclusion is that although the substitution of CRMs represents an obvious solution (not at all easy to achieve), a more realistic option relates to a combination with rational use, enhanced recycling, sustainable mining, and reinvented products and processes.

From Solar Nebula to Planet Earth
Forming the chemical elements of our Universe was the first step. These clouds of gas and particles (solar nebula) accumulated and formed the proto-Earth about 4.54 Ga ago not showing significant order of the accumulated material, although the fractionation of refractory and volatile elements started [54]. Since then, the Earth passed several developing stages. Meteoroid impacts, radioactive decay, and further planetary compression led to enormous temperature melting the vast majority of the material. The melting point of Fe and Ni must have been reached to allow the metal-silicate fractionation that formed the Fe-Ni core [55], while the Earth's rotation speed was much higher than it is today.
This early Earth was predominantly of mafic composition [56]. With time, the Earth further cooled down, forming a solid rigid crust that floats on a viscoelastic mantle, since crystal-liquid fractionation is considered as being a dominating fractionation process [57]. What is known as the giant impact model (GI) [58] has been simulating the collision of the proto-Earth with another Mars-sized [59] body or Mercury-sized [60] about 4.5 Ga ago. The GI model suggests that parts of the proto-Earth have been ejected and mingled with the impacting body while rotating around the Earth, forming discs and finally the Moon that helps to slows the rotation down, changed the inclination of the Earth's axis, and keeps the Earth on a rather stable curve around the Sun and at today's suitable distance and conditions. Those processes together with the ongoing plate tectonics caused by mantle convection leads to further separation of the chemical elements due to their physical properties and characteristics.
The Earth is still a dynamic planet that reworks its crust by different geological processes with variation in the rates of crustal reworking [61] and shifting from a highly mafic to a felsic bulk composition [62] through time.
Understanding the processes that formed the Earth of today and the behavior of the different elements is essential to discover unknown mineral deposits and for the processing of mined and waste material. The geological processes in combination with parameters such These graphs in connection with the intrinsic properties of these elements at the nuclear scale (number of protons and number of neutrons) lead us to the idea that the properties of these elements may be very unique, and hence, these elements might be difficult to be replaced.
From this observation, the obvious conclusion is that although the substitution of CRMs represents an obvious solution (not at all easy to achieve), a more realistic option relates to a combination with rational use, enhanced recycling, sustainable mining, and reinvented products and processes.

From Solar Nebula to Planet Earth
Forming the chemical elements of our Universe was the first step. These clouds of gas and particles (solar nebula) accumulated and formed the proto-Earth about 4.54 Ga ago not showing significant order of the accumulated material, although the fractionation of refractory and volatile elements started [54]. Since then, the Earth passed several developing stages. Meteoroid impacts, radioactive decay, and further planetary compression led to enormous temperature melting the vast majority of the material. The melting point of Fe and Ni must have been reached to allow the metal-silicate fractionation that formed the Fe-Ni core [55], while the Earth's rotation speed was much higher than it is today.
This early Earth was predominantly of mafic composition [56]. With time, the Earth further cooled down, forming a solid rigid crust that floats on a viscoelastic mantle, since crystal-liquid fractionation is considered as being a dominating fractionation process [57]. What is known as the giant impact model (GI) [58] has been simulating the collision of the proto-Earth with another Mars-sized [59] body or Mercury-sized [60] about 4.5 Ga ago. The GI model suggests that parts of the proto-Earth have been ejected and mingled with the impacting body while rotating around the Earth, forming discs and finally the Moon that helps to slows the rotation down, changed the inclination of the Earth's axis, and keeps the Earth on a rather stable curve around the Sun and at today's suitable distance and conditions. Those processes together with the ongoing plate tectonics caused by mantle convection leads to further separation of the chemical elements due to their physical properties and characteristics.
The Earth is still a dynamic planet that reworks its crust by different geological processes with variation in the rates of crustal reworking [61] and shifting from a highly mafic to a felsic bulk composition [62] through time.
Understanding the processes that formed the Earth of today and the behavior of the different elements is essential to discover unknown mineral deposits and for the processing of mined and waste material. The geological processes in combination with parameters such as pressure, temperature, time, fluid flow, and fugacity's trigger the enrichment processes that might lead to significant enrichment that is technically and economically feasible. Analyses of natural rocks, experimental studies, and calculations are compiled and provide reference for bulk compositions, of which the bulk composition of the upper continual crust [63] is of upmost interest in the given context. In his research, Lehmann (2020) provides examples of the fractionation pattern during Earth's history of which some are CRMs [57], indicating that exceptional processes needed to get significant anomalies. Geologists are looking for those outstanding features that might provide mineable future resources. The principle settings and European regions that host ore bodies enriched in siderophile (e.g., Fe, Ni, Pd) or chalcophile (e.g., Cu, In, Zn) elements have been described in projects such as FOREGS [64,65], also indicating the regions potential enriched in lithophile elements (e.g., Li, REE).

Principles on the Availability from EU Sources
The roughly 10.5 million km 2 of Europe's landmass is very diverse in terms of geology [66]. Regarding the remaining fragments of former continents, the different stages of reworked crust provide huge varieties in petrology of a differentiated crust that is composed of very unevenly distributed chemical elements [67]. These heterogeneities in the upper continental crustal composition range from about 3.8 to 3.9 Ga [68] and include old rocks of Greenland's Greenstone Belt as remains of the North Atlantic Craton [69,70] and the correlated Lewisian complex in northwest Scotland [71], the Greenstone Belt and Tonalite-Trondhjemite-Granodiorites (TTG) fragments that remained in the Baltic Shield (part of Fennoscandia) and Ukraine Shield (part of Sarmatia) of the East European Craton (EEC) [72], and the regions of active volcanism. Tectonic settings play a key role when oceanic crust is merged with continental crust, in particular when oceans close and might expose volcanogenic massive sulfide (VMS) deposits [73]. The different setting contain a huge variety of deposit types close to Europe's surface that have often been mined for centuries; among them are world-class producers of some economically important elements or even critical raw materials, including Pt, Sc, and Cr [57,[74][75][76]. Yet, many minor-metal concentrations (by-products) were mostly not beneficiated at that time also due to inefficient technology and a lack of demand. The complex tectonic settings of the Balkan region and Greece add to the technological challenges for mining the ophiolite-related deposits.
From a geological perspective, Europe has an elevated raw materials potential even for many of the CRMs. For 13 out of 30 raw materials on the current EU list, part of the EU supply is provided by European countries (primary and secondary sources), among those Sr, for which Spain is one of the world-class producers. Yet, the risk for a disruptive value chain is even higher when the bottleneck in the value chain is already placed at the very beginning at the mining stage, as it is the case for Be, B, Co, Ta, and Sb listed also in Table 1 [4].
With the increasing attention to ensure robust raw material supply chains, more European deposits have been studied for their CRM supply potential, from Finland [77] to Greece [78,79], in central Europe [80,81], and from Poland [82] to Portugal [83,84]. With the right technology, the political and social agreement deposits can become mining sites, if economically feasible. A promising example that there might be more to mine is lithium, where the discovery of a new CRM-forming mineral (LiNaSiB 3 O 7 (OH) Jadarite) within a world-class deposit might be the stimulus to develop other deposits further [85].
Since geology does not follow or stop at political boarders, there is a need for transnational efforts to identify this potential. The EU has built up a couple of actions to strengthen the raw materials value chain for Europe, including basic research and technological developments, trade agreements, and the promotion of investments and financial schemes.
Among these actions are the activities of the Regional and National Geological Survey Organizations (GSOs) of the European States. General information on geotectonic and geochemical background facts on Europe are compiled. Principles for interactive GIS (geographic information system) tools and 3D/4D models of deposits and mineralized belts are developed by projects such as FOREGS, ProMINE, and Minerals4EU [65,86] as a one-off. However, the periodical update of Europe's CRM list and other developments including land-use issues and the mining status in Europe calls for continues updating of validated, comparable, and timely updated information and the related maps provided through a publicly accessible and coordinated database. GeoERA Raw Materials takes advantage of the optimized network established by the GSOs, Europe's long tradition in mining and quarrying, and new exploration methods, models, and data to unlock domestic resource potential. It comprises four projects ranging from dimension stone (EuroLithos) to seabed (MINDeSEA) and land-based (FRAME) minerals supported by a data management project (Mintell4EU). Based on the respective national databases on sites and commodities, GeoERA Raw Materials compiles and further unifies the geoscientific knowledge of Europe. Currently, 30 data providers from 29 European countries add to the established harvesting routine that collects, validates, and stores data in a central database on Europe's resource potential, and more are about to join in 2021. The common and harmonized Minerals Inventory of known mineral resources, mining sites, and their status are visualized and publicly accessible.
The identification and mapping of principal metallogenic areas that define models for different types of mineralization use modern and newly developed methods and technologies. Critical mineral potential mapping and quantitative mineral assessments on land and on the European seabed include the revisiting of residuals in EU historical mining sites. Based on a compilation of 509 Co-bearing deposits and occurrences identified in 25 European countries, a wide distribution for Co across Europe can be assumed that might be a viable future source [87]. The first Pan-European Map of Submarine Energy Critical Elements was compiled in 2018 [88] and has been improved periodically since 2020 [89]. Due to the societal needs, the first attempt put focus on the CRMs required for the energy transition ( Figure 9). Together with the assessment of the European seabed, new potential sources of supply are identified. As part of the European Marine Observatory and Data Network (EMODnet), MINDeSEA adds to the comprehensive information of Europe's maritime issues [90].
These new data and information merged with information on resource statistics (Minerals Yearbook), on demands, and others allow for strategic investments to develop Europe's domestic resources that abide to the high ethical, social, and ecological standards that are further recurring recommendations of the European Commission.
The scientific research in these projects solidifies and innovates on existing premises, models, and strategies for mineral deposit and CRM exploration and establishes the first stepping stones to secure a reliable and responsible sourcing of mineral raw materials from domestic sources as viable future sources. These new data and information merged with information on resource statistics (Minerals Yearbook), on demands, and others allow for strategic investments to develop Europe's domestic resources that abide to the high ethical, social, and ecological standards that are further recurring recommendations of the European Commission.
The scientific research in these projects solidifies and innovates on existing premises, models, and strategies for mineral deposit and CRM exploration and establishes the first stepping stones to secure a reliable and responsible sourcing of mineral raw materials from domestic sources as viable future sources.

Conclusions: Which Solutions for Critical Raw Materials under Extreme Conditions?
In March 2020, the European Commission proposed to the European Parliament "A New Industrial Strategy for Europe" [91] to strengthen Europe's open strategic autonomy by warning that with the transition of the European industry toward climate neutrality, current dependence on fossil fuels could be replaced by a dependence on raw materials. The communication says that the EU's open strategic autonomy in these sectors will need to continue to be anchored in diversified and undistorted access to global commodity markets, but at the same time, it asserts that in order to reduce external dependencies and environmental pressures, it is necessary to address the underlying problem of rapidly increasing demand for global resources by reducing and reusing materials before recycling them.
Since the relevance of CRMs for industrial ecosystems is specific, and within the same industrial sector, their relevance in relation to the specific application is specific as well, if

Conclusions: Which Solutions for Critical Raw Materials under Extreme Conditions?
In March 2020, the European Commission proposed to the European Parliament "A New Industrial Strategy for Europe" [91] to strengthen Europe's open strategic autonomy by warning that with the transition of the European industry toward climate neutrality, current dependence on fossil fuels could be replaced by a dependence on raw materials. The communication says that the EU's open strategic autonomy in these sectors will need to continue to be anchored in diversified and undistorted access to global commodity markets, but at the same time, it asserts that in order to reduce external dependencies and environmental pressures, it is necessary to address the underlying problem of rapidly increasing demand for global resources by reducing and reusing materials before recycling them.
Since the relevance of CRMs for industrial ecosystems is specific, and within the same industrial sector, their relevance in relation to the specific application is specific as well, if the aim is substitution, reduction, and recycling, it will be necessary to focus on a few specific raw materials.
This strategic assumption was the basis of the researcher's consortium joined around the COST Action CA 15,102 CRM-EXTREME "Solutions for Critical Raw Materials Under Extreme Conditions".
Practically, the researchers involved in the network were coordinated into four working groups that took on the issue with different approaches: (a) the first group studied why a particular element is so fundamental for the performances of a material; (b) the second group, on the basis of the knowledge of the first one, designed alternative materials; once they found an alternative material, (c) the third group developed the industrial process, and finally, (d) the fourth group dealt with the environmental and economic sustainability, including recycling issues, with a circular economy approach. This project strategy was demonstrated to be successful. This Special Issue collects the final project dissemination articles, and the advancement of the state of the art and solutions achieved by the partners of the CRM-ETREME Network can directly be appreciated.

Data Availability Statement:
The data presented in this study are available on request from the authors.