6km underwater sounds bad (and it is), but the main bottleneck is still separation and refining.
I would have given a Japanese source directly but anything remotely skeptical is hard-paywalled and the archive sites can’t get through. This article from China US Focus heavily cites a paywalled article from Mainichi Shimbun. The tone reads like a hit piece, but after digging around I think the picture is broadly accurate. Japan is many years away from having a commercially viable rare earths supply chain.
More links of interest:
It’s a mud layer off the coast of a small Japanese Pacific island.
Japanese survey estimates 16 million tons of heavy REEs and yttrium
General paper on formation and distribution of sea floor REE deposits
In Minamitorishima mud, REEs are concentrated in “fish bone debris”
Paper looks at REE-rich mud cores (from elsewhere) and plots contents
The environmental cost of deep sea mining could be significant
- https://earthjustice.org/article/deep-sea-mining-explained
- https://deep-sea-conservation.org/wp-content/uploads/2023/02/DSCC_FactSheet1_DSM_intro_4pp_OCT_23.pdf-2.pdf
- https://www.int-res.com/articles/feature/m712p001.pdf
Just to round out the perspective, these guys think Minamitorishima could be economical, but the paper focuses on the mining and leaching, which are early steps, and not the complex separation and refining infrastructure that China dominates. If even the mining and leaching steps are in question, I think that emphasizes what an uphill battle rare earth self-sufficiency would be for Japan.
This is what deep see mining will murder.