Rare-Earth Metal Recovery for Green Technologies: Methods and Applications

© Springer Nature Switzerland AG 2020

R. K. Jyothi (ed.)Rare-Earth Metal Recovery for Green Technologieshttps://doi.org/10.1007/978-3-030-38106-6_1

1. Introduction of Rare Earth Metal Recovery for Green and Clean Energy Technologies

Ana Belen Cueva Sola¹, Pankaj Kumar Parhi¹, ², Thriveni Thenepalli³ and Rajesh Kumar Jyothi¹  

(1)

Convergence Research Center for Development of Mineral Resources, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, South Korea

(2)

School of Chemical Technology and School of Biotechnology, Kalinga Institute of Industrial Technology (KIIT) Deemed to be University, Bhubaneswar, Odisha, India

(3)

Mineral Resources Division, Center for Carbon Mineralization, Korea Institute of Geosciences and Mineral Resources (KIGAM), Daejeon, South Korea

Rajesh Kumar Jyothi

Email: [email protected]

Keywords

Rare earthsRecoveryRecyclingGreen technology applications

The demand and supply of high-tech rare earth elements (REEs) accomplishing Nd, Tb, Eu, Y, Dy, Pr, La, and Ce, in global scenario, is one of the thrust area exclusively in extractive metallurgy domain. Rare earth metals play a critical role in the development of high-end smart materials for their extensive usages in electronic devices as well as several other sectors. Specifically, rare earths are widely used currently in various fields such as electric and electronics devices, chemical industry, computers, televisions, glass, alloys, various types of catalyst for petroleum-refining industry, phosphors for energy-efficient lighting, etc. (Working Group on Defining Critical Raw Materials 2010; Barteková and Kemp 2016; Rollat et al. 2016). During the last decades, the rare earth trade and commercialization have been led by China creating a monopoly in the supply chain and some risk and instability in terms of shortage and nonavailability of these precious resources (US Department of Energy 2010; Mancheri 2015; Tsamis and Coyne 2015; Weng et al. 2016). Rare earths are a group of 17 elements, which are abundant in the earth’s crust, but the mining sites contain very low concentration of them to be profitable for extraction (Jha et al. 2016). The most abundant rare earth elements in the crust are cerium, yttrium, lanthanum, and neodymium with abundances similar to commonly mined and used metals such as nickel and zinc; however, they are usually found in deposits with such low concentration that extraction becomes almost impossible (Dutta et al. 2016; Jha et al. 2016). The US Department of Energy (2010) has created a plot where they place the supply risk of rare earths against the importance for clean energy development; from this graph it is deducted that for clean energy development europium, yttrium, terbium neodymium, and dysprosium are critical materials, while the supply risk is very high due mostly to the monopoly of the market. In addition, at this time, there are no substitutes for the different applications of the REE materials; the development of technologies to substitute the usage of REEs will improve flexibility, while meeting the needs of clean energy (US Department of Energy 2010; Barteková and Kemp 2016; Dutta et al. 2016). Finally, recycling REE waste and scraps is a promising alternative to reduce the demand and the necessity of extraction from ores.

In consequences of time, there have been enormous efforts being put forward by scientists, academicians, and industrialist to develop the technologies for recovering of these REEs from both primary and secondary sources routed through physical, chemical, and bioprocessing approaches. As per the reports (Behera and Parhi 2016; Behera et al. 2019; Parhi et al. 2015), there is a limited reserve of REEs in natural sources besides the major deposit (more than 90% of total earth deposit) in countries like China which led to explore the technologies, while exploiting these REEs from the secondary sources. The key REE-bearing sources include CRT lamp phosphor, waste magnet, wind turbine, PCBs, LEDs, EVM, spent batteries, and fly ash. In the twenty-first century, the biggest challenge is how the recycling of REEs from the above secondary sources can be optimized on an economic and technological basis with product life cycles with an objective toward sustainable metal management. In contrast to the conventional approaches (energy intensive), the development of green technology for recycling of REEs from secondary sources could be promising for resolving the issues that pertain to socioeconomics as well as environment. In the near future, it is estimated that 26% of the demand of REEs will be to cover the permanent magnet market followed by metal alloys 19%, polishing 16.5%, catalysts 15%, glass/phosphors 6%, and ceramics/others 5.5% (Working Group on Defining Critical Raw Materials 2010; Weng et al. 2016). While it is clear that the demand for automobiles, single-life electronics, catalysts, and green lighting will increase in the following decade, the demand for REEs will also continue to increase especially in the permanent magnet and battery industries. In 2017 it was estimated that China possesses approximately 40% of the world mine reserves of REs with 22 million metric tons and produces around 80% (105 thousand metric tons annually) of the metals sold around the world (US Department of Energy 2010; Han et al. 2015; Barteková and Kemp 2016; Dutta et al. 2016; Klossek et al. 2016). Other countries with high RE reserves are Brazil, Russia, Vietnam, and India, but their production of the metals is insignificant compared to China and its biggest competitor Australia with 15% of the production (20 thousand metric tons annually) of these precious metals (International Resource Panel of United Nations Environment Programme 2013; Ali 2014).

Currently the research in energy and transportation is going toward more sustainable, green, and clean sources of energy. That is why the prediction of the utilization of rare earth metals, especially neodymium and dysprosium, is vital for the development and installation of wind turbines onshore and offshore as well as for all electric vehicles that are being developed and are starting to commercialize. In the case of electric and hybrid vehicles, the average weight of permanent magnets is 1 kg, from which 31% consists of neodymium and 4.5–6% consists of dysprosium, while in the case of wind turbines, the weight of permanent magnets per MW generated is 200 kg from which 31% is neodymium and 2–4% is dysprosium (US Department of Energy 2010; Working Group on Defining Critical Raw Materials 2010; Tsamis and Coyne 2015). The continuous supply of rare earths for green energy represents one of the biggest challenges for the current research and development fields. Though the investigations reported till date does not address extensively the development of complete clean energy technologies, there are several scopes out of these studies that rely on further exploration. Unlike regular pyrometallurgical and hydrometallurgical processes, presently the adoption of green technologies has dragged more attention. Even though the current monopoly supply and the low substitutability of the rare earth metal-based technologies build a scenario where supply can be at risk at any point for clean technology development, there is a resource that has not yet been exploited in its full capacity, and it has become a major topic for research in the recent years: the recycling and recovery of REEs from secondary resources and waste (Binnemans and Jones 2014; Binnemans et al. 2015; Gutiérrez-Gutiérrez et al. 2015; Jha et al. 2016).

To reduce the demand and the necessity of reliable supply of REEs from ores, recycling is one of the techniques that can support and alleviate this market necessity. Rare earth materials can be found in many end-of-life products such as phosphors where europium, terbium, yttrium, cerium, gadolinium, and lanthanum can be recycled and recovered (US Department of Energy 2010; Working Group on Defining Critical Raw Materials 2010; Tunsu et al. 2015). Used permanent magnets are one of the most important sources from where dysprosium, neodymium, terbium, and praseodymium can be recycled (Du and Graedel 2011; Dutta et al. 2016). Finally, from nickel metal hybrid batteries, it is possible to reprocess lanthanum, cerium, and neodymium. In addition, magnet swarfs and rejected magnets are an important source of REEs that can be used for recovery of the metals, while different industrial residues also possess REEs that could be reprocessed, not only alleviating the pressure in the production of REEs from ores but also reducing the landfill and disposal necessities for these wastes (Binnemans et al. 2015; Tsamis and Coyne 2015; Tunsu et al. 2015; Dutta et al. 2016; Jha et al. 2016). While recycling of REEs becomes a hot topic, the applications for green technologies also gain great attention and provide a big niche for rare earth metal utilization for effective and green energy production, while demand of these technologies is projected to grow significantly in the short and medium term (US Department of Energy 2010; Working Group on Defining Critical Raw Materials 2010; Rollat et al. 2016). Rare earths are utilized in various green and clean energy sectors (Fig. 1.1).

Fig. 1.1

Rare earth applications in green and clean energy technologies

The main clean energy technologies that depend deeply on rare earth metals are wind turbines, electric vehicles, and fluorescent lightings. In the case of wind turbines and electric vehicles, one key constituent is permanent magnets, which produce a stable magnetic field without the necessity of an external power source (Du and Graedel 2011; Tsamis and Coyne 2015; Tunsu et al. 2015). Permanent magnet generators are used in wind turbines to transform wind energy into electricity, and in the case of electric and hybrid vehicles, permanent magnet motors help convert the energy stored in the batteries into mechanical power (US Department of Energy 2010; Tsamis and Coyne 2015; Rollat et al. 2016). Another important application for rare earths in the electric vehicle field is in the case of batteries, where lanthanum, cerium, praseodymium, and neodymium play a key role in the production of lightweight and energy-efficient batteries (US Department of Energy 2010; Working Group on Defining Critical Raw Materials 2010; Tsamis and Coyne 2015). Fluorescent lighting using rare earth phosphors is one of the proposed solutions for the improvement in lighting efficiency, which will lead to a reduction in the demand of energy overall. The main rare earth elements used for phosphors in fluorescent lighting are lanthanum, cerium, europium, terbium, and dysprosium; therefore the continuous and stable supply of these elements is a key concern globally (Han et al. 2015; Mancheri 2015; Weng et al. 2016). In the transformation toward a greener, energy-efficient society, rare earth metals play a key role in the human life. Rare earths can be found from hybrid and electric vehicles to house lighting and many electric and electronic devices that are used in daily life (Gutiérrez-Gutiérrez et al. 2015; Tunsu et al. 2015; Dutta et al. 2016). Color displays in television screens, speakers, smartphones, optical glasses used in cameras and telescopes, computer displays, and hard drives are some of the examples of commonly used items that rely on a stable and continuous supply of rare earth metals. The necessity of a greater and broader research toward substitutability and recycling of rare earths from secondary sources is and should be one of the priorities of the current scientific world.

The recycling technology of RREs follows two major stages of operations: (i) upstream and (ii) downstream. In the upstream stage of hydro-processing approach, leaching is an integral part for extracting the RE metal values from solid to aqueous phase. Presently, the usages of green organic reagents are more preferred over the mineral acids or alkalis (Behera and Parhi 2016). Nevertheless, the incorporation of ultrasound assistance and microwave assistance is certainly becoming significant over conventional leaching process (Behera et al. 2019). In this way the exploration of technology with adoption of above reagents/processes ascertains a potential futuristic scope in REE recycling technologies. On the other hand in downstream operation, selective separation and purifications of REEs are carried out by either of these methods: solvent extraction, liquid membrane, ion exchange, and adsorption processes. The SX method is more often chosen owing to its larger prospective of commercialization scale and in which several functionalized organic solvents are used for separating out either of the REEs (Das et al. 2018). Over the past decades, it was realized to use green ionic liquids (ILs) other than the commercial organic reagents for extraction and separation of REEs from numerous secondary-based leached liquors (Parhi et al. 2019). Subsequently pure form of rare earth oxides/metal as such is obtained by precipitation process where major process is followed through green processing approach to end up on yielding a very high pure RE metal product(s). The major advantages of the green technology include low-energy consumption, less toxic emission, environment-friendly approach, and development of clean REE products.

The recycling subject becomes significant in Korea as well as all over the world due to three major issues: (1) protection of the environment from waste (at the time of manufacturing used wastes), (2) landfill problem issues, and (3) limited natural resources. Five major factors are influencing the recycling subject: (1) metal stocks in society, (2) recycling rates of the metals, (3) environmental risks and challenges, (4) future demand scenarios, and (5) critical metal policy options (Metal Recycling Opportunities, UNEP Book).

Why recycling needed for especially critical rare earths is population densities, it will causes to increase of demand as well as landfill problem issues arises due to wastes generation. Two major land countries such as Canada and USA and two highly populated countries such as China and India were compared with Korea (South) having less population densities (Fig. 1.2).

Fig. 1.2

Population densities of countries such as Korea, Canada, the USA, China, and India (data adopted from https://​data.​worldbank.​org/​indicator/​EN.​POP.​DNST?​locations=​CA-US-KR-JP-TH-CN-IN-RU-BR-OE)

Recycling policy implementation in Korea started from year 1986 (Waste Management Act) and year 1992 Act on the Promotion of Saving and Recycling of Resources, followed by Waste Disposal Facilities Assistance Act of 1995. In new millennium (twenty-first century), two acts were implemented such as construction waste recycling (2003) and resource recycling of waste electrical and electronic equipment (WEEE) as well as automobile vehicles (http://​eng.​me.​go.​kr/​eng/​web/​index.​do?​menuId=​50). Overall Korea’s strategy on resource recycling policy was represented in Fig. 1.3.

Fig. 1.3

Korea’s strategy on resources recycling policy and implementation of the R³ model

Hydrometallurgy, the aqueous processing of metals, is the oldest technique in metallurgy. Prof. Michel L. Free (Free 2013) discussed in his book on hydrometallurgy about historical events in chemical processing of the metals in aqueous media from year 1556 separation of silver from gold leaf with chemical methodology. The established twenty-first-century innovative technology in hydrometallurgical processing was pressure oxidation of copper concentrate (Free 2013). Hydrometallurgy research and development subject deals the primary step in the leaching process of the solid samples (primary ores/minerals and secondary solid wastes). In the leaching process, various techniques can be applied such as oxidation and roasting, acid or alkaline leaching, pressure, bacterial leaching, etc. Leach liquor preparation by leaching process further was followed by solution purification by various chemical methodologies such as precipitation, liquid-liquid extraction, adsorption, ion exchange, membrane process, cementation, crystallization, etc. The final part is the metal recovery by electrochemical methods such as electrowinning and electrorefining. Hydrometallurgy subject was interlinked with various accepts such as whole flow sheet development, engineering, and environmental issues. Process modeling is the key procedure involved in thermodynamics, kinetics, and heat transfer subjects. Hydrometallurgy had a major disadvantage which is waste water generation; it needs dewatering and water balancing to minimize the water usage and recycle the water and effluent treatment (Mooniman et al. 2005).

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