I'd have to say that

I'd have to say that repurposing the grain silos to salt or sand would be VERY unusual... Salt and sand are much denser and heavier than grain.

Now, if you want to turn it into a hotel...

https://www.quakersquareakron.com/

Many of them that aren’t demolished …

Many of them that aren’t demolished …due to fire risk and insurance costs, etc. get moved to private farms for grain storage.

A rice operation might work, or perhaps some kind of seed that isn’t dusty or heavy.  Maybe along side a flour mill or a seed cleaning/drying operation. 
 

If memory serves they are made of stacked and pinned wooden beams and were cross braced with the individual silos inside (typically 3x3 or 4x4, so stacked weight is a real factor as the pressure at the bottom of the silos is pretty intense.  I remeber the i sides of the one my Grandpa ran were very highly polished from all the grain flowing against the wood over many decades.

Here is a handy chart of densities of common substances. Lots of ideas in here. 

Frac sand

I can imagine the density and weight being a factor that would work against using grain silos for something else, but the prototype often comes through.

I have no idea what sort of structural preconditions or modifications were met, but during the heyday of the recent past when fracking ruled in the oil field, this decades old grain elevator in El Reno, Oklahoma was partially converted to handle frac sand. They could load straight to trucks or store in silos.

They are heavy duty concrete silos and were advertised by NORAG Energy as providing  "UP Rail access with 50 car siding,  40,000 tons of storage space, 15 acres".

None of that may be true any longer, I haven't checked lately.

Antique store

Up in Plains, MT there is an old grain elevator about 50ft off the tracks which got repurposed into an antique store. As Mike said, some get moved and used on private farms for grain storage.  Or, if you are a farmer in the rural midwest, you can often times just buy the elevator alongside half the vacant town.  There's a couple of ghost towns between Ft. Pierre and Rapid City that are just the grain elevators and a couple of old buildings.

As for salt, no I haven't seen that before.  The problem is silos aren't waterproof, at least no more so than a steel shed.  Grain's moisture content will fluctuate a bit inside the elevator and inside a silo grain gets turned into silage through fermentation, so needless to say there has to be some sort of moisture exchange otherwise the grain would either rot or dehydrate.  With old grain elevators, their exterior might be steel but the walls are just 2x6's or 2x8's stacked on top of each other Lincoln Log style.  If water gets under the steel, there's nothing stopping it from being absorbed by a 40 ft column of salt.

Now what you could do is pretend someone bought the old wooden elevator next to the tracks, repurposed the office and scale, then set up additional hoppers (the stationary kind) to store salt and sand.  The elevator itself can sorta just sit there boarded up and the track still gets used to offload sand and salt at the property.

Another option would be to repurpose a cement grain elevator kit and turn that into a salt distributor, but not an old wooden grain elevator.  Most of the time they just get torn down rather than re-used.  Up in Canada the old wooden elevators are becoming a rarity and in another 20-30 years it will be the same across the Dakotas and Montana.