I actually had a friend that asked me to smoke some salt for me so I did a bit of research on this.
You want to keep the temperature extremely low. I mean like smoking cheese low. Apparently, if the temp gets above 200, it will burn off the smoke resin, on the salt and you have to start over again.
I lit one briquette at a time, with a piece of wood on top, and tried to keep things around 100 degrees (that's fehrenheight).
I smoked it for about 4 hours, and it gave the salt a nice smokey aroma, I think that longer will give the salt a nice dark look, which is what people are looking for.
But I can't figure out what I would do with this.
I have also seen smoked salt going for $160 per kg, so I think that getting it right might be worth the effort. Personaly, I have yet to figure out what smoked salt would be used for. If I want a nice smokey flavour, I will cook it with my WSM or my Weber one touch Gold.
I hope this is helpful, if anyone has a good use for the end result, i would be very interested to know.
Chris
WSM
Weber One Touch Gold
Weber Smokey Joe Platinum (in the process of being modded)