A team of Japanese researchers from multiple institutions has calculated that an area of deep-sea mud in the western North Pacific Ocean near Minami-Torishima Island, Japan, contains more than 16 million tons of rare-earth elements and yttrium (REY). In an open-access paper published in Scientific Reports, they estimate that this research area could supply yttrium (Y), europium (Eu), terbium (Tb), and dysprosium (Dy) for 780, 620, 420, and 730 years, respectively, and has the potential to supply these metals on a “semi-infinite” basis to the world.

In 2013, Professor Yasuhiro Kato from the University of Tokyo and his research team conducted a research cruise to collect deep-sea mud in the Exclusive Economic Zone (EEZ) around Minami-Torishima, 1,900 km southeast of Tokyo, in collaboration with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). They obtained seven deep-sea mud core samples from the seafloor of 5,600 to 5,800 meters below sea level, and carried out chemical analysis of the mud to investigate the distribution of REY near the seafloor.

Locality and bathymetric maps of the research area. Star symbols show the piston coring sites, and the color-coding corresponds to each research cruise as noted in the legend. The white rectangle shown in the detailed map is the target area where the resource amount estimation was conducted. Takaya et al. Click to enlarge.

They found highly to extremely REY-rich mud (deep-sea sediments containing 2,000 ppm to more than 5,000 ppm REY) located only a few meters below the seafloor. Moreover, they found that critical information on depth distribution and thickness of REY-rich mud can be easily obtained by sub-bottom profiler (SBP) on shipboard.

REY-rich mud has several advantages, such as high rare earth element content (especially the heavy rare-earth elements [HREE], from Eu to Lu), huge amounts, a paucity of radioactive elements (U and Th), and easy extraction and recovery. Therefore, the mud is expected to be viewed as a highly promising new mineral resource. Because of the “extremely high grade” of the REY-rich mud found within the Japanese Minamitorishima EEZ, research on a development system and economic evaluations are ongoing through collaborations among members of industry, academia, and the government of Japan.

—Takaya et al. (2018)

In the new study, also led by Professor Kato, the team estimated the resource potential of REY-rich mud in detail using Geographical Information System (GIS) software. The team also proposed new dep-sea mineral processing techniques (e.g., the use of a hydrocyclone separator) that could enhance the economic value.

Additional research cruises revealed the detailed distribution of highly to extremely REY-rich mud in the southern part of the Minamitorishima EEZ, and confirmed REY-rich mud having a maximum of almost 8,000 ppm of total REY content (ΣREY).

The researchers divided the area in 24 grid squares and calculated the ΣREY values and resource potential of each grid.

Concentration maps of average ΣREY of mud from the seafloor to 10 mbsf and of each 1-m depth interval. The target area is divided into 24 areas (A1–D6). The maps were generated by ArcGIS and are shown with 2,400 grids (60 × 40). Coring sites are shown as white circles. Takaya et al. (2018) Click to enlarge.

The researchers found a more than 400 km₂ (154 square mile) area high in REY in the northwest part of the target area; that richer concentration continues loosely to the southeast.

The grid square with the highest REY potential (B1) holds an estimated resource amount of 1.2 Mt-REO—which would account for 62, 47, 32, and 56 years of annual global demand for Y, Eu, Tb, and Dy, respectively.

… our results demonstrate the enormous resource amount of REY-rich in the western North Pacific Ocean. In addition, a hydrocyclone separator can greatly enhance the economic value of REY-rich mud by taking the advantage of mineralogical features of the mud, which could stimulate future exploitation of this new deep-sea mineral resource. Given the huge resource amount, its high grade (notably Y and HREEs), and the effectiveness of simple grain-size separation with a hydrocyclone, we believe that the REY-rich mud has great potential as ore deposits for some of the most critically important elements in the modern society.

—Takaya et al.

Resources

• Yutaro Takaya, Kazutaka Yasukawa, Takehiro Kawasaki, Koichiro Fujinaga, Junichiro Ohta, Yoichi Usui, Kentaro Nakamura, Jun-Ichi Kimura, Qing Chang, Morihisa Hamada, Gjergj Dodbiba, Tatsuo Nozaki, Koichi Iijima, Tomohiro Morisawa, Takuma Kuwahara, Yasuyuki Ishida, Takao Ichimura, Masaki Kitazume, Toyohisa Fujita & Yasuhiro Kato (2018) “The tremendous potential of deep-sea mud as a source of rare-earth elements” Scientific Reports 8, Article number: 5763 doi: 10.1038/s41598-018-23948-5