Most desalination plants only concentrate the ocean salts a little.

The more you concentrate them, the more energy you need to put in to get any more water out. I think the only time this would make economic sense is if there are laws in place saying brine may not be returned to the ocean (for environmental reasons). In that case, it would make sense to concentrate it further with reverse osmosis, and then use multi-stage flash to further concentrate the brine.

After a few more steps, you could probably sell most of the resulting salts.