Japanese scientists already have a method of gathering uranium from seawater that is close to being economically viable at $200 kg for UOX. no entropy problems there its a matter of ion exchange with a floating polymer that can be reused again and again they have already done limited production runs on the process. the same kind of ion exchange can be done with other heavy metals gold being one of them the issue is and always will be how expensive the recovery process is vs the commodity value of the metal the energy ROI is positive for uranium by a few.orders of magnitude due to the density of nuclear vs chemical Gibbs energies. The next metal coming out of seawater will be lithium and magnetism for high energy batteries may research universities are working on seawater lithium recovery.
At $200/kg, it’s still a lot higher than mined uranium, so the word “economically” is relative. UT published an article saying 4-10 times the cost of mined uranium. But, as they pointed out, it sets an upper limit to the cost of uranium.
In any case, I’m convinced that this is something to keep an eye on.