The tremendous potential of deep-sea mud as a source of rare-earth elements - PubMed (original) (raw)

doi: 10.1038/s41598-018-23948-5.

Yutaro Takaya 1 2 3 4, Takehiro Kawasaki 5, Koichiro Fujinaga 3 4, Junichiro Ohta 3 4 6, Yoichi Usui 2 7, Kentaro Nakamura 5, Jun-Ichi Kimura 6, Qing Chang 6, Morihisa Hamada 6, Gjergj Dodbiba 5, Tatsuo Nozaki 2 3 4 8, Koichi Iijima 2, Tomohiro Morisawa 9, Takuma Kuwahara 10, Yasuyuki Ishida 11, Takao Ichimura 11, Masaki Kitazume 12, Toyohisa Fujita 5, Yasuhiro Kato 13 14 15

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The tremendous potential of deep-sea mud as a source of rare-earth elements

Yutaro Takaya et al. Sci Rep. 2018.

Abstract

Potential risks of supply shortages for critical metals including rare-earth elements and yttrium (REY) have spurred great interest in commercial mining of deep-sea mineral resources. Deep-sea mud containing over 5,000 ppm total REY content was discovered in the western North Pacific Ocean near Minamitorishima Island, Japan, in 2013. This REY-rich mud has great potential as a rare-earth metal resource because of the enormous amount available and its advantageous mineralogical features. Here, we estimated the resource amount in REY-rich mud with Geographical Information System software and established a mineral processing procedure to greatly enhance its economic value. The resource amount was estimated to be 1.2 Mt of rare-earth oxide for the most promising area (105 km2 × 0-10 mbsf), which accounts for 62, 47, 32, and 56 years of annual global demand for Y, Eu, Tb, and Dy, respectively. Moreover, using a hydrocyclone separator enabled us to recover selectively biogenic calcium phosphate grains, which have high REY content (up to 22,000 ppm) and constitute the coarser domain in the grain-size distribution. The enormous resource amount and the effectiveness of the mineral processing are strong indicators that this new REY resource could be exploited in the near future.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1

Figure 1

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. Bathymetric data were obtained from ETOPO1 (NOAA’s National Centers for Environmental Information;

https://www.ngdc.noaa.gov/mgg/global/global.html

). Those in right panel were obtained by each research cruises mentioned in the text. Both maps were created by using the Generic Mapping Tools (GMT) software (https://www/soest.hawaii.edu/gmt/), Version 4.5.8.

Figure 2

Figure 2

Concentration maps of average ΣREY of mud from the seafloor to 10 mbsf and of each 1-m depth interval. The target area (Fig. 1) 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.

Figure 3

Figure 3

ΣREY in BCP grains determined by EPMA and LA-ICP-MS. The vertical axis shows the total value [%] of the analysis (left axis) and the frequency of the samples (right axis). A moderate negative correlation (gray shaded area) can be observed between ΣREY in BCP and the total value.

Figure 4

Figure 4

ΣREY, weight distribution, and REY amount distribution [%] of each fraction obtained from the grain-size separation experiment with test sieves.

Figure 5

Figure 5

Concentration factor of ΣREY through the grain-size separation experiments with test sieves (ΣREY of the >20 µm component/ΣREY of the original sample) and the hydrocyclone separator (ΣREY of the under-flow component/ΣREY of the original slurry sample). Data of the original sample, under-flow component, and over-flow component are shown in gray, red, and blue, respectively. The pink shaded area shows the expected concentration factor of grain-size separation with respect to ΣREY of the original sample/slurry.

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