Nuclear power is basically a carbon-free energy source but, we have to admit, it has its own special problems.
The radioactive fuel that goes into nuclear power plants is typically mined the standard way, but there is a vast untapped reserve trapped in the world’s oceans. Water is the universal solvent, and seawater is much more complex than simply salt dissolved in water. Uranium ions are present in very low concentrations, just three parts per billion, so extracting them is difficult. On the other hand, the ocean is, well, huge, and could theoretically hold all the uranium we’d ever need in case traditional sources fail us.*
Current methods of extracting uranium from seawater involve the use of plastic absorbent, which is left in the ocean for a few weeks and then recovered. The plastic is then processed and can extract about 3mg uranium per gram of plastic. Because there are other ions that bind similar to uranium, this is about as efficient a the process gets.
A new material developed at Oak Ridge National Laboratory [ORNL], a metal-organic framework [MOF], can be tuned to have better affinity for uranium ions than others. In lab tests, the MOF was able to sequester over 200mg of uranium per gram of MOF. Of course, this was in lab conditions without other competing ions as there would be in seawater, so more testing is needed.
*Not sure, but my rudimentary math skills tell me there could be about 400 cubic kilometers of uranium in the oceans.