Not sure about this. I do know that at the Dead Sea it is not just the salt, it is a combination of many other minerals along with the climatic conditions created by being the lowest point on earth.
If you do try it, be careful because it could sting like mad, the derms at the Dead Sea generally dont let you in the sea for the first week, and keep a BIG bottle of moistureiser handy and apply immediatley this will dry your skin out real bad.
As for how much salt............

Good luck, Paul