Baolu Zhou, Zhongxue Li, and Congcong Chen report that Rare earth elements (REE) are widely used in high technologies, medical devices, and military defense systems, and are especially indispensable in emerging clean energy. Along with the growing market of green energy in the next decades, global demand for REE will increase continuously, which will put great pressure on the current REE supply chain. The global REE production is currently mainly concentrated in China and Australia; they respectively contributed 85% and 10% in 2016. However, there are 178 deposits widely distributed in the world, and reported REE resources as of 2017 totaled 478 megaton (Mt) rare earth oxides (REO); 58% of these deposits contained exceed 0.1 Mt REO; 59 deposits have been technically assessed.
These resources could sustain the global REE production at the current pace for more than a hundred years. It is noted that REE demand from clean technologies will reach 51.9 thousand metric tons (kt) REO in 2030, Nd and Dy, respectively, comprising 75% and 9%, while these two elements comprise 15% and 0.52% of the global REE resources, respectively. This indicates that Nd and Dy will strongly influence the development of exploring new REE projects and clean technologies in the next decades.
Rare earth elements (REE) were first discovered in 1788. However, global annual REE production and consumption was less than 5000 metric tons of rare earth oxides (REO) before the 1950s and, until the 1960s, they were even rarely used in our daily life. Since the 1960s, rare earth applications gradually have expanded to everyday life, such as television screens, the petroleum industry, and computer systems; therefore, the global REE production and consumption have seen a significant increase in the following decades. REE are now widely used in auto and fluid catalysts, metallurgy, medical systems, high technology, clean energy, and military defense systems, and they are especially indispensable in emerging clean technologies, such as wind power turbines, electric vehicles, energy-efficient lighting, and catalytic converters.
The total value of worldwide products containing REE is at least $1.5–2 trillion US dollars (US$), which comprised nearly 5% of the global total gross national product in 2009. A significant shift from traditional energy sources towards clean energy, such as electric vehicles, is occurring; wind turbines are becoming recognized on a global scale. This transition will lead to a continuous increase in demand for REE in the coming decades, and such an increasing demand puts forward a higher request for global production of REE, and requires a steady supply chain in the long run. The International Union of Pure and Applied Chemistry defines REE as a group of 17 elements comprising the 15 elements in the lanthanide group, plus scandium and yttrium. Based on the structure of electron shell, REE are typically subdivided into light rare earth elements (LREE) and heavy rare earth elements (HREE). However, there is no unified classification on which element is LREE or HREE. According to U.S. Geological Survey (USGS), lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, and gadolinium are LREEs, while terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium constitute HREEs.
Due to similar properties, scandium and yttrium are generally considered as REE, while yttrium is classified as a HREE since it shares similar properties with other elements belonging to HREEs. Scandium does not belong to LREE or HREE because it is not extracted from the same deposits as other REEs, and Pm is rarely found in nature; therefore, they will not be further discussed in this paper. In addition, a third classification is sometimes added into LREEs and HREEs: middle rare earth elements (MREEs).
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