Deep-Sea Mud in the Pacific Ocean as a Potential Resource for Rare-Earth Elements - 2011

Mining & Minerals - Evaluations / Deep Sea Mining

Kato, and 8 co-authors, reported in 2011 that world demand for rare-earth elements and the metal yttrium—which are crucial for novel electronic equipment and green energy technologies—is increasing rapidly Several types of seafloor sediment harbor high concentrations of these elements. However, seafloor sediments have not been regarded as a rare-earth element and yttrium resource, because data on the spatial distribution of these deposits are insufficient.

The authors report here the measurements of the elemental composition of over 2,000 seafloor sediments, sampled at depth intervals of around one meter, at 78 sites that cover a large part of the Pacific Ocean. We show that deep-sea mud contains high concentrations of rare-earth elements and yttrium at numerous sites throughout the eastern South and central North Pacific. We estimate that an area of just one square kilometer, surrounding one of the sampling sites, could provide one-fifth of the current annual world consumption of these elements.

Uptake of rare-earth elements and yttrium by mineral phases such as hydrothermal iron-oxyhydroxides and phillipsite seems to be responsible for their high concentration. The authors show that rare-earth elements and yttrium are readily recovered from the mud by simple acid leaching, and suggest that deep-sea mud constitutes a highly promising huge resource for these elements.

The authors concluded that their experiments using dilute acids (0:2 mol l^-1 H₂SO₄ or 0:5 mol l^-1 HCl) reveal that almost all of the REY, except Ce, are readily leached from the mud in 1 to 3 hours. In addition, pulverization and beneficiation are not needed before metal leaching. These features enhance the potential of the REY-rich mud as a REY resource. Unless the great water depths (mostly 4,000 to 5,000 m) have a significant impact on the technological and economic viability of mining REY on seafloor, the REY-rich mud in the Pacific Ocean may constitute a highly promising REY resource for the future, not withstanding comprehensive assessment of the environmental impact sea-floor operations.