Assessment of REY resource potential in deep-sea sediments with Fe-Mn (oxyhydr)oxides in the Pacific Ocean

초록

Deep-sea sediments with an abundance bioapatites and Fe-Mn (oxyhydr)oxides in the Pacific Ocean have been considered potential reservoirs of rare earth elements and yttrium (REY). However, comprehensive assessment of the resource potential of REY in deep-sea sediments with Fe-Mn (oxyhydr)oxides throughout the Pacific Ocean is limited due to difficulties in accurately predicting the distribution of extensive Fe-Mn (oxyhydr)oxides and the associated REY. In this study, we predicted the prospective area and resource potential of REY-rich sediments with Fe-Mn (oxyhydr)oxides by considering multiple factors that control REY enrichment based on data from International Ocean Discovery Program (IODP) samples and previous research. According to the distribution map inferred by comprehensively evaluating lithology (clay sediment), hydrothermal fluid influence (delta 3He), and water depth (bathymetry), deep-sea sediments with Fe-Mn (oxyhydr)oxides, which have higher than 1000 ppm REY concentration, are distributed in the vicinity of the East Pacific Ridge within a water depth range of 4000-4600 m, and their distribution area is estimated to be approximately 1.1 million km2. If the sedimentation rate (<1.5 m/Myr) is considered, which is a crucial factor influencing REY enrichment, we can achieve a more precise assessment of their distribution area. Assuming a recovery depth of only 1 m, the REY resource amount was estimated to be approximately >450 million tons of REY oxide. Even without accounting for REY resource amount associated with bioapatite, the minimum REY resource amount estimated in this study exceed the world's current land reserves. Furthermore, these sediments contain a significant abundance of industrially important heavy REY, accounting for 53 % of REY resources. This implies that the deep-sea sediments with Fe-Mn (oxyhydr)oxides in the Pacific Ocean are a promising resource of REY. Our findings will serve as essential information for the technological progress required in the exploration and development of REY resources in deep-sea sediments in the future.

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