Alex;

here's a quote from Ron Shimek's forum on the topic of reusing sand that smells like rotten eggs:

someone posted:

Hi,

I am taking down my fuge to replace it with a bigger one. The sand in the fuge smells bad (rotten Eggs). Do I need to replace it, let it cycle or what? Please advise

Shimek replied:

I woujld replace it. The rotten egg smell is due to a small amount of hydrogen sulfide and this occurs when there is an excess of non-utilized organic material in the sediments. While it is normal, it indicates that the sand bed has not been maintained with an adequate number and variety of sediment organisms, and probably has accumulated a lot of organics in it.

It probably would be best to start anew, and inoculate it well with detritivores and other beneficial sand-dwelling animals.