Looks like there's three ways to mine Lithium:

1. Hard Rock mining (as mentioned in the article)
2. Natural Brine sources
3. De-salinated water brine

https://cen.acs.org/materials/inorganic-chemistry/Can-seawater-give-us-lithium-to-meet-our-battery-needs/99/i36

Maine has been burned in the past by previous mining operations closing up and leaving the state to clean up the remaining mess (also in the OP article). Definitely a tough situation all around.

Regarding how much Lithium can be recovered from desalination waste:

https://medium.com/prime-movers-lab/does-the-u-s-have-enough-lithium-to-support-the-growing-ev-market-d73a44a969e5

The US currently has one operating desalination plant, Carlsbad, that processes 50 million gallons of seawater per day. If it recovered 100% of the lithium in that water, it would produce… about 16 tonnes of lithium per year.

VS the amount needed/used per year:

https://www.statista.com/statistics/606481/estimated-lithium-consumption-in-the-united-states/

In 2022 the United States consumed an estimated 3000 metric tons of lithium.

https://www.neefusa.org/story/water/home-water-use-united-states

Each day in the United States, about 27.4 billion gallons of water are withdrawn and delivered from surface water and groundwater sources for residential use

So if we supplemented 10% of our needs from Desalinated water (2.74 Billion gallons a day) and recovered the same max amount of Lithium as the example a day (50 million gallons a day for 16T of Lithium a year) then we get:

(2.74B/50M)16T= 54.816T= 877T of Lithium a year