Even More On the Pacific Rare Earth Find

at the Register, via Ritholtz:

However, the part that doesn't make sense, at least not to me, is how to then make this silt a worthwhile source of extraction. They're certainly correct that if you dredge it up then wash it in dilute acids then you'll get a nice concentrate of the mixed rare earths. Easy enough to cut the salts out of that and dump your old acid over the side along with the 99.9 per cent of the silt you don't want any more (hey, we're in mid-ocean here!).
However, a concentration of 1,000 to 2,000 ppm isn't actually anything all that much to write home about. That red mud which went splat over Hungary has about the same sort of concentration. As does the other 40 to 80 million tonnes a year produced, including the 2 billion tonnes lying around in ponds. We've known for decades that we can extract the rare earths from this stuff: wash it in acid and get a nice solution of the metals. However – and here's the problem – you have to use so much acid that you can't make a profit doing this.
I say this not just on the Friedmanite basis that hundred dollar bills don't appear on pavements: for if they did someone would already have picked them up. It isn't that no one does this as yet, which would prove that it can't be done. It is that people have tried to do this (at least I have, in Greece, a couple of years back) and have found that the cost of getting the materials out is more than people will pay you for the materials you've got out. And this is a nice fine silt lying in ponds at ground level, silt which people will pay you to take away, not silt you've got to lift through 5,000 metres of salt water.

Makes sense.  I would probably try to mine the rare earth metals in groud-level sludge ponds before trying to mine them from the ocean floor.  Even extremely richly concentrated mines, such as the Mountain Pass mine, are expensive and environmentally problematic to operate:

In 1998, chemical processing at the mine was stopped after a series of wastewater leaks. Hundreds of thousands of gallons of water carrying radioactive waste spilled into and around Ivanpah Dry Lake.
In the 1980s, the company began piping wastewater as far as 14 miles to evaporation ponds on or near Ivanpah Dry Lake, east of Interstate 15 near Nevada. This pipeline repeatedly ruptured during cleaning operations to remove mineral deposits called scale. The scale is radioactive because of the presence of thorium and radium, which occur naturally in the rare earth ore. A federal investigation later found that some 60 spills—some unreported—occurred between 1984 and 1998, when the pipeline was shut down. In all, about 600,000 gallons of radioactive and other hazardous waste flowed onto the desert floor, according to federal authorities. By the end of the 1990s, Unocal was served with a cleanup order and a San Bernardino County district attorney's lawsuit. The company paid more than $1.4 million in fines and settlements. After preparing a cleanup plan and completing an extensive environmental study, Unocal in 2004 won approval of a county permit that allowed the mine to operate for another 30 years. The mine also passed a key county inspection in 2007.

I would guess that seabed mining isn't feasible until prices are incredibly high, making the deposits worthless and the news release wishful thinking.