Junichiro Ohta

REY-Rich Mud: A Deep-Sea Mineral Resource for Rare Earths and Yttrium

Abstract This chapter focuses on newly discovered extensive deposits of deep-sea mud containing high concentrations of rare-earth elements and yttrium (REY). The deep-sea REY-rich muds are found in pelagic region of the Pacific Ocean and very recently also in the Indian Ocean. REY-rich muds are characterized by the following five advantages: (1) tremendous resource potential by virtue of their wide distribution, (2) high REY concentrations with significant heavy REE enrichment, (3) a stratiform distribution that allows relatively simple and cost-effective exploration, (4) very low concentrations of radioactive elements such as Th and U, and (5) ease of extraction of REY by acid leaching. These features demonstrate that the REY-rich mud could constitute a highly promising REY resource for the future. A system to mine REY-rich muds is also presented. This system can be developed based on a system developed and tested for sulfide-rich muds in the Red Sea and manganese nodules in the Pacific Ocean, although pressurized air-lift system will be needed to lift REY-rich muds from very deep water.

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

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.