Speaker:	Kentaro Nakamura (UTokyo)
Title:	REE-rich mud as an important key for sustainable development of our society
Date (JST):	Wed, Jul 08, 2026, 15:30 - 17:00
Place:	Lecture Hall
Abstract:	Rare-earth elements (REE) are widely recognized as strategic materials (U.S. Department of the Interior, 2025; European Union, 2024), which are crucial for high-technology applications (e.g., laptop computers, cell phones, and flat screen televisions) and green energy technologies (e.g., electric/hybrid vehicles, wind power generators, and fuel cells). World demand for REE is increasing rapidly (e.g., IEA, 2025, 2026) and a stable supply of REE is a key to future development of technology and the global economy (Patel et al., 2023; Chen et al., 2024; IEA, 2026). However, several problems currently exist with rare-earth resources at present. For example, more than half of the world's production of REE is from China (USGS 2021). Moreover, China's overwhelming dominance is particularly evident in heavy rare-earth elements (HREE) that are critically important materials for high-technology products including electronic, clean energy, and military technological devices (Service, 2010; Goodenough et al., 2018). Indeed, known HREE reserves are almost all in ion-adsorption-type ore deposits in southern China (e.g., Longnan and Xinxiu ore deposits), even though light rare-earth elements (LREE) can be obtained from carbonatite/alkaline igneous complexes in many countries (Goodenough et al., 2018). Thus, diversification of sources and increased access to REE resources, especially HREE, are required to maintain stable supply of meeting the ever-rising demand for the elements. Another problem is that most onshore REE deposits have high concentrations of radioactive elements such as U and Th (Murakami and Ishihara, 2006; Sørensen et al., 2011; Yang et al., 2009; Goodenough et al., 2018) due to the behavior of these elements during magma genesis similar to that of LREE. Therefore, production of REE from onshore LREE deposits produces massive amounts of radioactive waste, resulting in a serious and persistent environmental problem in REE mining. In 2011, we discovered that deep-sea muds enriched in REE, here termed REE-rich mud, are distributed over large areas of the Pacific Ocean, including the high seas (Kato et al., 2011). Subsequently, extremely REE-rich mud was discovered in the Japanese Exclusive Economic Zone (EEZ) around Minamitorishima Island in the western North Pacific Ocean, where some mud layers exhibit remarkably high REE concentrations and strong HREE enrichment (Iijima et al., 2016; Fujinaga et al., 2016). This discovery is particularly significant because it demonstrates that REE-rich mud occurs not only in international waters but also within Japan’s EEZ. REE-rich mud has also been reported from the Indian Ocean (Yasukawa et al., 2014). Furthermore, a recent study has shown that REE-rich mud is also a promising resource for Sc, an important element for leading-edge technologies in the energy and environmental fields (Yasukawa et al., 2018). REE-rich mud has five notable advantages as a mineral resource: (1) tremendous resource potential due to its extensive distribution, (2) high REE concentrations with HREE enrichment, (3) ease of exploration, (4) very low concentrations of radioactive elements, and (5) high recovery rates of REE through simple acid leaching. Owing to these characteristics, REE-rich mud has recently attracted particular attention as a promising new resource that could help diversify the global REE supply and support the sustainable development of future society.

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