Traditional lithium rock ore mining is a dirty, polluting process that also uses huge amounts of fresh water. But that’s not all necessarily inherent. There are several projects around the Salton Sea in California that promise not only to extract lithium cleanly, but also to generate a lot of GHG-free electricity along the way, because the ore is hot salty corrosive water extracted from deep underground. optimistic podcast episode 1 podcast 2 website article

Water Cycle 101: The oceans are salty because rain water has been flushing salt downstream for billions of years. Salt also collects in endorheic basins such as the Great Salt Lake and Mono Lake, for the same reason. Rain clouds form primarily from evaporation of ocean water, which leaves behind slightly increased salinity, although its effect is widely geographically distributed.

There’s a difference between that distributed evaporation and the concentrated salinity increase of effluent from a reverse osmosis desalination plant or a hypothetical hydrogen plant, but the basic answer is yes, leave the salt in the ocean. It will be fine.

Good thing people have been able to use untreated ocean water as the feedstock. It looks like it needs to be scaled up, but the economic advantage should help incentivize that (seawater is free; treated water is expensive!).