Well if electricity is so cheap/free. Then brine left behind is not a problem as you can get a lot of chemicals out of it by processing it. Doing that though needs a lot of energy so it's not viable currently but would be with cheap/free electricity

You cannot just process salt out of salt water. Eventually you're left with a lot of salt.

yes you can https://www.nature.com/articles/s41929-018-0218-y the brine left behind is just not salt but many other minerals like lithium which require a lot of energy to separate out. But when you have free energy/electricity a lot of other things become viable.

Most people so far don't comprehend the kind of huge change free/extremely cheap electricity would bring to the world. We have the tech to do a lot of stuff but it is not cost effective cheap electricity will change that.

Well, money is, in essence, an exchange for energy, so if energy is free we'll see a significant change in our economy system and my guess it's gonna be a wild ride

Yes, and that free energy will be seeking an equilibrium (where excess energy converts back into liquid capital) through clever uses and previously non-economical activities like separating lithium from brine. The great news is that each niche is a business opportunity. We, the clever ones, can spot those opportunities, build the tech to make them possible and build the companies that live in those new energy niches.

I'm not a chemist nor have access to the paper. Can you summarize what happens to the seawater salt if that's applied? Surely it will still need to be deposited somewhere.

Apparently seawater has 3.5% salinity. So desalinating enough to water crops/supply cities leaves you with a lot of salt.

A lot of this is possible already but not economical as most of the process to extract minerals from sea water require a lot of energy/electricity where as it is extremely cheap comparable to mine them directly. But free energy electricity would change that.

Metals that can be extracted from seawater include:

Sodium (Na): One of the most common metals found in seawater, sodium can be extracted through solar evaporation or electrolysis.

Magnesium (Mg): A metal that can be extracted from seawater.

Calcium (Ca): A metal that can be extracted from seawater.

Potassium (K): A metal that can be extracted from seawater.

Lithium: A metal that may become more important in the future as demand for lithium batteries and fusion energy increases.

Copper: A high-value metal that is often present in seawater.

Nickel: A high-value metal that is often present in seawater.

Cobalt: A high-value metal that is often present in seawater.

Mix the brine with the treated sewage you are discharging. You're probably discharging a little less than you take out, but that gets you closer to the original salinity.

Dumping salt water into salt water doesn't immediately strike me as an environmental disaster.

Dramatically increasing the saltiness of salt water can have some negative effects. If you’ve ever kept an aquarium you’ll know that sudden changes in water composition kill your pets pretty quickly. A solvable problem, but a problem that requires a bit of careful consideration.

I wonder if the salt extracted during desalination could be dumped on top of underwater salt domes? Salt domes are one of the sources of the salt in the ocean [1].

The idea is that our salt would cover part of the salt dome, preventing that part of the salt dome from providing salt to the water. Instead, the salt that would have come from that part of the dome comes from our salt.

[1] https://oceanservice.noaa.gov/facts/whysalty.html