Underwater treasure

Materials World magazine
1 Jun 2018

A potentially game changing deposit of rare earth elements has been discovered in Japanese waters, but an efficient means of extraction is yet to be developed, as Ellis Davies reports. 

Rare earths are in heavy demand due to their favoured use in the production of a range of electrical products such as smartphones and electric vehicles. However, a recent study has revealed that an estimated 16 million tonnes of rare earths – labelled semi-infinite – has been found in the waters surrounding Minamitorishima Island, Japan. The deposit could last hundreds of years.

Following the discovery of the materials in sea sludge, researchers at Tokyo’s Waseda University, Japan, determined that the 2,500km2 region off the southern Japanese island could contain the treasure chest of rare earths. The team used geographical information system software to observe the distribution of elements in the seabed to evaluate the potential. 

Six research cruises were sent to the area to inspect the detailed distribution of the mud. The cruises were able to confirm a maximum of 8,000ppm of total rare earth content in the region from 573 samples. 

Although the discovery of such a vast resource is cause enough for excitement, the researchers also believe that it is possible to increase the economic value of the mud by selectively recovering the host mineral of the rare earths. They were able to recover selectively biogenic calcium phosphate grains, containing a high rare earth content, from the seabed by using a hydrocyclone separator (a device that separates particles from a liquid solution), which improves the ore grade, enhancing the deposit by 20 times in comparison to ore found in China, the team claims.

The researchers determined, using X-ray fluorescence analyses, that the host mineral in the deposit is a group of calcium phosphates. It has been previously thought that rare earths are absorbed by calcium phosphates, which has been confirmed for the area using electron probe microanalyser and laser ablation-inductively coupled plasma-mass spectrometry. This is an elemental analysis performed on solid samples using lasers and a plasma torch.

However, it could take up to 10 years or more to develop the infrastructure to be able to mine the deposit as there is currently no profitable way to extract the minerals, as they are more than three miles beneath the surface. Yutaro Takaya, Associate Professor at Waseda University and leading author of the study and his team hope to develop efficient means of extraction in the next five years, he told Materials World

The discovery, and the ability to up its value, could lead to lower operation costs and increased efficiency in Japan’s rare earth industry. New industries may be born as a result, and the country could finally edge out from China’s shadow.

Breaking away from China

Although Japan is currently the world’s second-largest consumer of rare earth elements, it largely relies on imports from China, which controls 90% of the market and extracted 150,000 tonnes of material in 2016. 

This supply has been troubled in the past, with China restricting supply amid political tensions, such as in 2010 when shipments of minerals were suspended for two months following the arrest of a Chinese fishing boat captain by the Japanese navy in the disputed East China Sea.

Researchers believe that the deposit near Minamitorishima Island will contribute to the resource security of Japan, as well as serving as a diplomatic card, or a safety net amongst inflating rare earth prices following the crackdown on illegal mining in China. 

Takaya stated, ‘Our findings may change the nation’s policies and strategies on natural resource management, for we could possibly become self-reliant in terms of rare-earth mineral resource and build a sustainable future.’