B6
REY-rich mud
discovery of a new marine mineral resource

Rare earth elements (REEs) are the set of fifteen lanthanide elements, with scandium and yttrium sometimes included in the set often referred to REY. Among the REEs, in order of atomic number, the first seven are termed light REEs and the last eight heavy REEs. REEs are extensively used in modern technology such as hydrogen-absorbing alloys for hard disks and nickel-metal hydride batteries, catalysis for automobile exhaust, satellite telecommunication systems, and refractory material for jet engines.

Ore deposits, which mainly comprise light REEs, are distributed throughout the world, mostly in China, the United States, and Australia. Their production is extremely difficult because light REEs contain Uranium and Thorium that generate harmful radio isotopes. Furthermore, their production can severely damage the environment. In addition, because the production of REE by China dominates 90% of the total worldwide production, a fundamental solution is strongly anticipated to avoid a potential short supply or a sudden rise in the REY price.

A research group of the School of Engineering, the University of Tokyo, led by Yasuhiro Kato, discovered large-scale, deep-sea REY-rich mud highly enriched in REY along the floor of the Pacific Ocean, at ocean depths greater than 4,000 m. Based on the whole-rock compositional analyses of more than 2,000 deep-sea mud samples, they discovered: a layer of mud with thickness ranging from 2 to 10 meters containing 1,000 to 1,500 ppm of REY in the southeastern Pacific near Tahiti, and a layer of mud with thickness reaching 70 meters containing 400 to 1,000 ppm of REY in the central Pacific around Hawaii. The displayed samples are examples of deep-sea mud containing abundant REEs. The estimated total amount of REY for both regions is 800 times that of the current estimated onland REE deposit. Developing REEs-enriched, deep-sea mud has the following three advantages over conventional onland REE production: (1) easier to explore, (2) easier to extract using diluted acid, and (3) overall less content of radio isotopes. Thus, deep-sea mud is considered to be a favorable source of REY offsetting the otherwise likely future short supply and price increase. (Ryodo Hemmi)