It’s not going to be pure NaCl though; making Morton salt with it would make sense only if it wouldn’t cost more to process it (net of its resale value) than just disposing of it somewhere not particularly sensitive. I’d propose the Utah salt flats or indeed, kinda love the idea of just sticking them in a salt mine that is all tapped out. If it used to be chock full of salt it seems pretty environmentally fair to make it salty again.